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Glacial–interglacial cycles are global climatic changes which have characterized the last 3 million years. The eight latest glacial–interglacial cycles represent changes in sea level over 100 m, and their average duration was around 100,000 years. There is a long tradition of modelling glacial–interglacialcycles with low-order dynamical systems. In some of these models, the cyclic phenomenon is caused by non-linear interactions between components of the climate system, which generate a limit cycle. Other models incorporate the established Milankovitch theory according to which changes in Earth’s orbit and obliquity force variations in ice volume and ice sheet extent along with, either directly or indirectly, variations in other variables of the climate system. One then distinguishes the strong interpretation, in which the astronomical forcing is necessary to generate glacial–interglacial cycles, from the weak interpretation, in which the astronomical forcing synchronizes a limit cycle. The purpose of the present contribution is to consider specifically the effects of stochastic forcings. Indeed, the trajectories obtained in presence of stochastic fluctuations are not necessarily noised-up versions of the deterministic trajectories. They may follow pathways which have no analogue in the deterministic version of the model. Our purpose is to demonstrate the mechanisms by which stochastic excitation may generate such large-scale oscillations, sometimes with an intermittent character. To this end, we consider a series of models previously introduced in the literature, starting with autonomous models with two variables, and then three variables. The properties of stochastic trajectories are understood by reference to the bifurcation diagrams, the vector field, and a method called stochastic sensitivity analysis. We then introduce models accounting for the Milankovitch forcing, and distinguish forced and synchronized ice-age scenarios. We show again how noise may generate trajectories which have no immediate analogue in the deterministic model. We conclude on a general reflection on the interest of this research and its potential applications on a wide range of climatic phenomena.

Biozones are routinely used for chronological purposes, but their nature is seldomly questioned. Here, we attempt to find the evolutionary-ecological basis for Iberian rodent biozones for the interval 8.5–2 Ma based on currently available paleontological, stratigraphic and paleoclimatic information. Our comparison of biozone boundary age uncertainty intervals to records of marine SST, δ18O and δ13C, terrestrial hydrological proxies and astronomical parameters suggests an orbitally forced climatic origin for the majority of biozones. Zone boundary ages during the late Miocene are mostly associated with humidity changes during 1.2-Myr obliquity nodes and 405-kyr eccentricity minima. Tectonics and strong regional cooling may additionally explain faunal change during the Messinian (7–5 Ma). A partly reversed pattern characterizes most Pliocene zone boundaries, which are mostly associated with wetter conditions during obliquity nodes and 405-kyr eccentricity maxima. A third configuration culminates in the early Pleistocene and consists of the combination of strong obliquity amplitude maxima and 2.4-Myr eccentricity minima. It is suggested that larger-scale, European Neogene mammal (MN) units have an astronomical basis as well, with an important role of 2.4-Myr eccentricity cycle and the 1.2-Myr obliquity cycle, with the latter becoming especially important after the mid-Miocene cooling (∼14 Ma). Whereas rodent events on the Iberian Peninsula during the late Miocene are shaped by replacements within resident communities dominated by dry-adapted clades of true mice (Murinae) and hamsters (Cricetinae), transitions during the cooler Pliocene involve invasions of newly emerging Eurasian clades of ‘microtoid hamsters’ and voles (Arvicolinae) preferring wetter and cooler environments. A new model of stepwise clade displacement is proposed in which the combination of long-period Milankovitch cycles and gradual long-term climatic change allows for the periodic functioning of migration corridors, along which increasingly pervasive dispersal events by members of new clades cause the gradual extinction of old clades.

It was 100 years ago (on August 7, 1920), that the comprehensive mathematical foundations of climate change research, written by a Serbian researcher, Milutin Milankovitch, were published. A later interpreter and developer of his results, Georg (in Hungarian: Gyorgy) Bacsak (Pozsony/Pressburg/Bratislava, June 5, 1870 - Fonyod, March 4, 1970) was born 150 years ago and died at the age of one hundred, half a century ago. In this commemorative paper we look back to special circumstances in revealing the secrets of ice ages that had puzzled scientists for at least several centuries. Recently, after 100 years, the Milankovitch theory, including related short-term forcings (ranging from interannual, multidecadal to millennial timescales) has not only been confirmed, but its climate forcing mechanism has also been identified and proposed. Owing to the uniqueness of the problem, the science of the orbital forcing of climate change can be proclaimed to be essentially settled.

The upper Silurian, and especially Pridoli epoch is a critical interval for the understanding the evolution of Earth’s biota, since it witnessed series of powerful extinction events, global reorganizations of paleocommunities, and expansion of new clades, which assumed dominance in the subsequent Devonian period. The stratigraphic record of the eastern part of the Silurian Baltic Basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics. Therefore we presenting here stratigraphic record of the Milaiciai-103 core (south western Lithuania) of conodonts, brachiopods,δ13Ccarb, δ 18Ocarb and a series of various geochemical and geophysical proxies, most of which were sampled at a very high resolution (~ 11 Ka), spanning uppermost Ludlow, Pridoli, and the lowermost Devonian. The analysis revealed that the Pridoli was characterized by four distinct long-term dynamic states here named: i) Normal Pridoli I, ii) Silalė negative carbon isotopic excursion and extinction event, iii) Normal Pridoli II, and iv) Klonk positive stable carbon isotopic event and excursion. The most significant change in most variables is detected approximately in the middle of the Pridoli, at the beginning of the Delotaxis detorta Zone, at the recovery after Silalė event of conodonts, and at the onset of collapse of brachiopod communities. The analysis of dynamic complexity revealed the strong evidence for the presence of ~ 405 Ka metronome Milankovitch cycles in the record of δ13Ccarb, which constrains the duration of the Pridoli epoch to 4.3 ± 0.2 Ma. The recurrence plot analyses revealed deterministic coordination between δ13Ccarband conodont paleocommunity dynamics at all scales. Finally lead-lag analysis, using conditional joint recurrence, revealed that conodont dynamics, as a rule, were driven by perturbations in the carbon cycle, although Silalė event interval shown opposite pattern, thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event.

High resolution (939 samples) total organic carbon content (TOC) analyses were conducted on the Shuanghe Section of ∼152.6 ​m in the Changning area, Sichuan Basin. The sampling section was divided into two units considering the distinct-different deposit environment and sediments accumulation rate. The lower part (Unit 1) and the peer part (Unit 2) with high resolution sample spacing (0.08–0.4 ​m) enables the identification of the precession cycle in two sedimentary sequences with distinct different sedimentary accumulation rate. MTM Power spectral analyses on untuned TOC series reveals significant peaks exceeding above the 95% confidence level and shows that both Unit 1 and Unit 2 have recorded Milankovitch cycles of 405 kyr long eccentricity, short eccentricity, obliquity and precession. The floating astronomical time scale (ATS) was constructed on the Shuanghe Section in the Early Silurian (∼439.673–444.681 ​Ma), and which was calibrated by 405 kyr long eccentricity cycles. The total duration of the Wufeng and Longmaxi shales is 5.01 Myr. The floating ATS used for estimating the duration of the graptolite zones and each stage in the study interval. Finally, we postulated two models that could verify the linkage between orbital cycle and organic accumulation. To make sure whether productivity or preservation is the main factor that under long eccentricity control, the phase correlation between the obtained filtered signal and the theoretical orbital solution should be made clear in the further research. Keywords: Cyclostratigraphy, Floating astronomical time scale, Early Silurian, Organic matter accumulation

In this paper, a singly-averaged, semi-analytical orbital dynamic model in terms of Milankovitch elements is given for geostationary transfer orbits (GTOs), which includes the Earth's oblateness, luni-solar perturbations, atmospheric drag and solar radiation pressure (SRP). The orbital dynamic model is verified through a numerical simulation compared with the Semi-analytic Tool for End of Life Analysis software (STELA) by CNES. We find that if the area-to-mass ratio of the object is relatively large, the SRP will have a significant impact on the long-term evolution of GTOs. Then, the long-term dynamical evolution and orbital resonances of rocket upper stages in inclined geostationary transfer orbits (IGTOs) are studied. It has been found that the luni-solar secular resonances, which are inclination-dependent-only, play a leading role in the long-term evolution of IGTOs. By comparing and analyzing long-term dynamical evolution of orbits with different initial inclinations, the effects of luni-solar secular resonances are studied in details. Finally, a mitigation method for IGTO objects by utilizing luni-solar secular resonances is proposed, in which the eccentricity growth caused by the resonances is used for an early atmospheric re-entry.

A major challenge in sequence stratigraphy is objectively identifying stratigraphic surfaces and sequences across multiple scales of observation. Identification is commonly dependent on the resolution of the data used (i.e., seismic vs. well data), its dimension (i.e., 1D vs. 2D vs. 3D) or the criteria chosen to select sequence boundaries. Through shelf-edge trajectory analysis, the clinothem (i.e., highest order seismic sequence identified on seismic data) can constitute the elementary building block of an observation-based and data-driven quantitative workflow to develop sequence stratigraphic frameworks across different orders and ranks of hierarchy. Here, we use high-quality 3D seismic data to interpret a Late Tithonian–Early Cretaceous shelf margin, the Lower Barrow Group (LBG), developed in the Northern Carnarvon Basin on the North West Shelf of Australia. Based on full-volume seismic interpretation techniques that integrate the 3D variability of the data when identifying seismic unconformities, a high-resolution seismic stratigraphic framework was built (73 interpreted clinothems with an average time duration of ~63,000 yrs). The computation of high-frequency shelf-edge trajectory angle (Tse) curves on selected seismic cross-sections is used to objectively pick sequence stratigraphic surfaces based on the accommodation succession method, thereby highlighting small changes in trajectory and proposing a method reproducible by interpreters based on the same quantitative data. Within the D. lobispinosum interval (142.3–140.9 Ma), the definition of stratigraphic sequences and composite stratigraphic sequences through this workflow is used to discriminate the controls at high and low temporal frequency on the vertical and lateral variability (which is here quantified) of this shelf-slope-basin system. The results show that the high-frequency interplay between short-term glacio-eustasy (i.e., Milankovitch eccentricity cycles of ~100,000 yrs) and sediment supply (locus of fluvial input along the margin) impacted the three-dimensional stratigraphic architecture of the LBG. In contrast, tectonic subsidence had a significant impact on the stratigraphic architecture of the LBG within the main depocentre at lower temporal frequency by overprinting the eustatic signal and accelerating/decelerating the rates of accommodation creation. However, identification of long-term glacio-eustatic Milankovitch cycles (~400,000 yrs) outside the main depocentre, where the rates of accommodation creation due to rift-related subsidence are moderate, also suggests low-frequency eustatic control. Therefore, the vertical and lateral variability of the LBG results from variations in sediment supply and subsidence regime under local (i.e., process regime, currents), regional (i.e., tectonics) and global (i.e., eustasy, climate) forcing parameters interplaying across timescales. In contrast to standard sequence stratigraphic workflows that are based on model-dependent choices to select sequence boundaries, quantitative 3D seismic stratigraphy constitutes an improved method to interpret 3D seismic data in shelf-margin depositional systems within a sequence stratigraphic framework, which provides an observation-based and model-independent tool allowing the definition of stratigraphic sequences with results that are reproducible across multiple stratigraphers. This work highlights the need for developing new sequence stratigraphic tools and methods that integrate the 4D variability of depositional systems and moves beyond the two-dimensionality inherent to current sequence stratigraphic methods. Quantitative 3D seismic stratigraphy represents a first step towards the creation of 3D sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships (source, reservoir, seal distribution) across shelf margins.

Astronomically forced variations of climate are well documented in lacustrine and marine settings. However, few studies have examined astronomical forced cycles within Quaternary fluvial-fan successions. To explore whether Milankovitch cyclicity might also be present in fluvial-fan successions, we carried out high-resolution gamma-ray (GR) from downhole logging, magnetic susceptibility (MS), Rb/Sr and total organic carbon (TOC) analysis of a core from an 800-m borehole (KT11) from the Kashgar region in the western Tarim Basin, China. Spectral analyses of the GR, MS and Rb/Sr data reveal cycles with ~70 m, ~30 m and ~14 m wavelengths. These pertain to relative variations in grain size. Electron spin resonance (ESR) dating and magnetostratigraphy imply that the cored interval spans the past 1.1 Myr. This age-span constraint, coupled with the comparison of the ratios of these cycle wavelengths to expected ratios of Milankovitch frequencies, suggests that these cycles represent ~100-kyr short-eccentricity, ~40-kyr obliquity and ~20-kyr precession frequencies, respectively. We constructed an astronomical time scale (ATS) spanning the past 1.13 Myr using the ~100-kyr short-eccentricity period. The average accumulation rate is about 70 cm/kyr for this 800-m core succession, and the evolutive spectrum emphasizes that long-term sedimentation rates were stable. We also applied correlation coefficient (COCO) analysis to identify the astronomical forcing. Thus, we conclude that orbitally forced climate change was the main driver of stratigraphic alternations between sand- and clay-rich intervals in the Kashgar region. During maxima of the 100-kyr short-eccentricity cycles, which correspond to interglacial intervals, more chemical weathering and increased seasonal runoff delivered a larger amount of relatively coarser-grained sediments to the fluvial fan in the Kashgar region, and vice versa. The Mid-Pleistocene Transition (MPT) at ca. 0.9 to 0.65 Ma is also well recorded in our GR and Rb/Sr data, and is characterized by a shift in dominant cycle period from 41 kyr obliquity to 100 kyr eccentricity. After 0.65 Ma, the average TOC content decreases whilst Rb/Sr values increase, which suggests that there was an increase in regional aridity of the Kashgar region in the western Tarim Basin following the MPT. This regional change is synchronous with the trend toward aridification observed throughout central Asia.

The mechanisms involved in the formation of 1- to 2-Myr-long third-order stratigraphic sequences through the Phanerozoic have been extensively debated, but the main underlying forcings remain uncertain. In this study, we investigated third-order sequences of Paleocene-Eocene age in the East China Sea Shelf Basin, identifying a prominent ∼1.2-Myr periodicity in the 405-kyr-tuned gamma ray profile of the WP-1 borehole. We infer that this ∼1.2-Myr cycle, which corresponds to long-period amplitude modulation of obliquity, was the main driver of third-order sea-level changes and sequence development. This modulation entails variation in the range of obliquity amplitude between a maximum of 2.4° (i.e. 24.5°–22.1°) and a minimum of 0.3° (i.e. 23.3°–23.0°) as a result of interactions among the three primary parameters of Earth's orbit (i.e., eccentricity, obliquity, and precession). We anchored our floating astronomical time scale (ATS) to the T42 seismic horizon, a major sequence boundary between the Lin Feng and Mingyuefeng formations that corresponds to the top of Nannofossil Zone NP8 (reported age of 57.7 Ma). This yields a fixed ATS for the late Paleocene-to-middle Eocene interval spanning 60.84 to 48.71 Ma. Finally, we evaluated our findings relative to the third-order sequence stratigraphy of the East China Sea Shelf Basin and to records of early Cenozoic eustasy and global events.

The tenet of the Milankovitch theory is that Northern Hemisphere solar insolation, controlled by Earth's orbital is responsible for cyclic climate variations. Eccentricity in this context is responsible for cyclic variability of 100 ka and may drive periodicity in climate change during the middle and late Pleistocene. Although abundant evidence exists for 100 ka cyclic climatic fluctuations driving glacial-interglacial cycles, our knowledge about the record of cyclic climatic changes preserved in terrestrial landscapes remains limited, especially over multi-millennial (several glacial-interglacial) timescales. The intermontane Yanqi Basin in the southeastern Tian Shan, Central Asia, preserves at least seven generations of alluvial surfaces spanning multiple glacial cycles and yields insights into the record of climatic fluctuations that lead to aggradation and incision of river systems. We complement existing chronologic data with two new cosmogenic 10Be depth profiles and four surface exposure ages of alluvial surface abandonment in the south Tian Shan piedmont within the Yanqi Basin. New surface-exposure dating reveals the successive abandonment of these surfaces with a 100 ka cyclicity between 5.1 ± 0.9 and ~550 ka and indicates that there were multiple aggradation-incision cycles. The superimposed 100 ka cycles of aggradation-incision are best explained by eccentricity-driven climate change. Within these cycles, sediment is produced during glaciations by glacial and periglacial erosion. However, due to the dry and cold conditions of the glacial periods in central Asia, there is little discharge available to transport and evacuate the sediment from the valleys to the piedmont. Later, during the glacial to interglacial transition, higher precipitation and high discharge due to glacial melt water resulted in higher transport capacity of the river beyond a threshold to evacuate sediment. Subsequent rapid incision occurs after the upstream sediment reservoir is depleted and its timing corresponds to the glacial to interglacial transition period in our study area. Compared with the aggradation and incision of the northern piedmont of the Tian Shan governed by the Westerlies, the sedimentary systems of the South Tian Shan piedmont within the Yanqi Basin are mainly controlled by eccentricity-driven glacial-interglacial cycles.

A high-resolution astronomical-tuned magnetostratigraphy was obtained from a continuous 333-m succession recovered at International Ocean Discovery Program (IODP) Hole U1499A in the north margin of the South China Sea (SCS) during joint Legs 367 & 368. A total of 12 magnetic reversals are identified through the Pliocene and Pleistocene. The cycle analysis of natural gamma ray (NGR) data shows an average suite of ca. 33 m and 8 m wavelengths with lesser 1.5-m cycles, which are consistent with the ratios of Milankovitch orbital-climate oscillations caused by long eccentricity (405 kyr), short eccentricity (~100 kyr), and precession (~20 kyr). The astronomical-tuned magnetostratigraphy correlates with nearly all features of the Pliocene-Pleistocene geomagnetic polarity time scale. There was a significant shift to ~100-kyr-dominated cyclicity at ca. 1.3 Ma, which marks the onset of the Mid-Pleistocene Transition, during which the influx of the clay component decreased. A general enrichment in silt-sand influx during the past 0.4 Myr was punctuated by surges in coarser-grained components (lowest NGR) during or at the end of each major global glacial event. Comparison to a high-resolution sediment record spanning the Pliocene-Pleistocene on the southern margin of the SCS (ODP Site 1143) indicates common intervals of changing rates of sediment accumulation. In both regions, there are relatively lower rates of sediment accumulation during the late Zanclean (mid-Pliocene; ca. 4.1 to 3.6 Ma), early Gelasian (ca. 2.5 to 2.0 Ma), early Calabrian (ca. 1.6 to 1.4 Ma) and the earliest Middle Pleistocene (ca. 0.6 Ma). The merger of magnetostratigraphy, cyclostratigraphy and the NGR record to produce a high-resolution profile of bulk sediment accumulation rates and relative clay to sand-silt components is a powerful tool and climate proxy to reconstruct the general history of sediment input into the SCS and its relationships to East Asia monsoon and tectonic evolution.

Expansions of coastal upwelling spots along the Brazilian coast were previously reported for Marine Isotope Stage (MIS) 5, but open questions remain regarding the climatic mechanisms and the periodicity of such changes. Based on two marine sediment cores, we provide evidence for multiple intensifications of the upwelling regime off the Southeast Brazilian margin (SBM) during several interglacials and highlight the major role of eccentricity as the responsible forcing. In addition, we show a two-step change in the upwelling regime across the Mid-Brunhes Event (MBE) and an increase in the amplitude of upwelling variability after this climatic transition. Our findings point to substantial modifications of the upwelling regions during several glacial-interglacial transitions that probably altered the regional marine productivity regime and the carbon budget.

Successions of Mesozoic and Paleozoic radiolarian-bedded cherts display a “binary” cyclic hierarchy of cm-scale chert and mudstone couplets. Some of these couplet successions contain an apparent imprint of Milankovitch cycles, in which the couplets may reflect changes in silica deposition related to Milankovitch forcing, for example, high insolation for chert deposition, and low insolation for mudstone. The challenge has been how to represent such binary lithologic series in a format that is suitable for signal processing to search for Milankovitch cycles. Here we present an analysis of chert-mudstone binary series by considering, in lieu of a “boxcar” linear interpolation, a “midpoint-triangle” linear interpolation. The procedure is demonstrated first on synthetic data, then on the binary chert-mudstone stratigraphic series of the Permian (Guadalupian: Roadian-lower Capitanian) Gufeng Formation, Chaohu, Lower Yangtze, South China. We assign −1 to the midpoint of each mudstone bed and 1 to the midpoint of each chert bed, then linearly interpolate from midpoint to midpoint along the succession. Time-frequency analysis of the midpoint-triangle series highlights a previously unnoticed stratigraphic alternation of obliquity and precession band power. Finally, we present a revised astrochronology for the Gufeng succession that is anchored at 270 Ma at the base of the Jinogondolella nankingensis conodont zone (base of Roadian stage) and ending at 264.6 Ma in the undifferentiated Follicucullus scholasticus-Ruzhencivisponus uralicas radiolarian zone (mid-Capitanian Stage), for a duration of 5.4 Myr.

South China provides exceptional and unique sedimentary archives of Earth's fundamental changes in Ediacaran time. However, the lack of robust geochronological constraints renders a poorly-defined chronostratigraphic framework for Ediacaran-aged strata in South China, thus making it difficult to understand Earth's critical changes during this time interval. Magnetostratigraphy and rock magnetic cyclostratigraphy turn out to be a few reliable methods in chronostratigraphic studies, especially in the Precambrian. Here, we present a detailed paleomagnetic and rock magnetic study of the Ediacaran Doushantuo Formation in the Huanglianba section, Guizhou Province, South China. The section consists of ~75 m thick carbonate succession and has a record of one of the largest carbon isotope excursions in the Earth history, known as the Shuram excursion. Stepwise thermal demagnetization of Doushantuo carbonates reveals single-component magnetizations that yield a paleomagnetic pole consistent with the Late Triassic segment of the apparent polar wander path of South China. The secondary origin of Doushantuo carbonates' magnetization is supported by their magnetic mineralogy based on various rock magnetic experiments and scanning electron microscopic analyses. We interpret that the secondary magnetization resides mainly in authigenic pyrrhotite that likely precipitated from the reducing fluids during the late stage of Indosinian orogeny in the Triassic. Interestingly, the companion high-resolution cyclostratigraphic study of a 4-m thick succession at the upper layers of the Doushantuo Formation in the Huanglianba section indicates that the Milankovitch cycles were encoded in the variation of magnetic susceptibility, immune from the influence of remagnetization. Variation of magnetic susceptibility is attributed to changes in the abundance of paramagnetic minerals which, by implication, means that the amount of terrestrial materials transported from the continent was regulated by Milankovitch cycles during the deposition of Doushantuo carbonates. Therefore, our results suggest that even though carbonates are prone to remagnetization, astronomical modulation of deposition could be encoded in rock magnetics of the remagnetized carbonates. As a result, rock magnetic cyclostratigraphy has potential in remagnetized carbonates for providing a floating astronomical timescale that can be applied to constrain sediment accumulation rates, estimate the duration of geological events, and construct high-resolution chronostratigraphies.

The Dales Gorge Member (DGM) of the Brockman Iron Formation (Hamersley Basin, Western Australia) is a classic banded iron formation (BIF) that was deposited during the Archean-Proterozoic transition just prior to the Great Oxidation Event. The goal of this study is to apply modern cyclostratigraphic principles to investigate the possible origins of the characteristic stratigraphic banding in this BIF, which indicates the influence of quasi-regular cyclic processes in the deposition of iron-rich and chert-rich lithologies. A grayscale scan series of the DGM ‘type section’ 47A* drillcore photographs from three cores drilled in the Wittenoon Gorge vicinity is examined using well established methods of time series analysis. Complex banding patterns suggest that Milankovitch forcing may have taken place with orbital-rotational parameters that were significantly modified from the present-day due to continuous planetary tidal dissipation over the past 2.5 billion years. The banding patterns change systematically and dramatically within the member in response to slowly varying environmental conditions, which are interpreted to be related to low-frequency sea level changes and/or tectonic evolution of the Hamersley Basin.

Oceanic Anoxic Event 2 (OAE2; c. 94.5–93.9 Ma) offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration. It has been studied extensively, but the vast majority of data come from marine records, thus providing an incomplete view of past climate dynamics. Here we integrate new high-resolution data and published records on depositional environments, the carbon-isotope composition of bulk organic carbon (δ13Corg) and plant cuticles (δ13Ccut), and stomatal-index values, a proxy for pCO2, in well-preserved terrestrial through marginal-marine archives of the initial phase of OAE2. The study area is located on the western margin of the Western Interior Seaway (southwestern Utah). Age constraints are based on a new U-Pb bentonite age and correlation to an orbitally calibrated interval of the Bridge Creek Limestone. n-Alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples. Despite similarities between carbon-isotope variations and transgressive-regressive shoreline movements, it is argued that δ13Corg and δ13Ccut are not strongly affected by local variables. A series of negative, ~2‰ carbon-isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric CO2 reservoir. The temporal spacing of these anomalies (80–120 kyr) is consistent with changes in insolation modulated by orbital eccentricity. A systematic, phase-shifted relationship between the negative carbon-isotope excursions and transgressive increments further suggests a link between carbon-cycle perturbations and meter-scale sea-level change on the 100-kyr time scale. A conceptual model involving insolation-controlled aquifer charge/discharge and biomass burial/degradation in the monsoonal belt is proposed. The framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during OAE2.

Recognition and interpretation of paleoclimate signals in sedimentary proxy datasets are time consuming and subjective. Acycle is a comprehensive and easy-to-use software package for time series analysis in paleoclimate research and education. It is designed to speed paleoclimate time series analysis, especially cyclostratigraphy, and to provide objective methods for estimating astrochronology. Acycle provides for detrending with multiple options to track and remove secular trends. A selection of power spectral analysis methodologies is offered for the detection of periodic signals. Many of the functions are specific to cyclostratigraphy and astrochronology that are not found in standard statistical packages. A specialized function is provided to assess the astronomical (Milankovitch) forcing of paleoclimate series and search for the most likely sedimentation rate by evaluating the correlation coefficient between power spectra of an astronomical solution and sedimentary proxy data. Sedimentary noise modeling (for past sea-level changes) is also provided in Acycle . As an example, Acycle is applied to a sedimentary proxy series from the cyclostratigraphy of the Paleocene-Eocene thermal maximum (PETM) in Core BH9/05 from the Paleogene Central Basin, Svalbard. Acycle detects significant astronomical forcing in the proxy series and relatively stable sedimentation rates during and after the PETM. Acycle runs in the MATLAB environment or as stand-alone software on Windows and Macintosh OS X, and is open-source software.

Detailed sedimentological and stratigraphical studies were performed in the Pilmatue Member of the Agrio Formation at Loma La Torre area, to recognize orbital signals in the Valanginian–Hauterivian of the Neuquen Basin. Facies analysis allowed us to recognize 4 facies associations, interpreted as a mixed siliciclastic-carbonate ramp setting. A sequence stratigraphic analysis was performed allowing to recognize two composite sequences and five high-frequency sequences. This eurybathic/eustatic trend was subtracted from time series constructed by lithological rhythms (limestone/marlstone couplets) to stabilize its variance. Cyclostratigraphic analysis shows that the rhythmic late Valanginian – early Hauterivian succession presents a cyclical stratigraphic pattern composed by elementary cycles (limestone/marlstone couplets), bundles (4–5 elementary cycles) and superbundles (4–5 bundles) suggesting a climatic Milankovitch control. The found periodicities correspond to the precession cycle (∼20 ky), which is modulated by the eccentricity cycle (∼90 and ∼400 ky). Some statically low-significant periodicities of ∼42 ky and ∼33 ky can be assigned to the obliquity signal. That periodicities fit well with the so-called precession-eccentricity syndrome (PES) characteristic of mid and low latitudes, where obliquity is erratically identified. Our results indicate that the early Hauterivian has a minimum duration of ∼3 myr, considerably longer than the durations proposed in the GTS.

Astronomically-forced insolation cycles (“Milankovitch cycles”) serve as a primary control on climate, and when preserved in the stratigraphic record, they provide a high-resolution in situ chronometer. These celestial rhythms derive from the fundamental frequencies of the Solar System, and Earth's precession constant. The fundamental frequencies of Earth and Mars presently define a secular resonance of 2:1 (2.4 Myr to 1.2 Myr), and are hypothesized to have undergone a transition between 50–100 Ma, due to the chaotic behavior of the Solar System. In this study, a 15-Myr long cyclostratigraphic record from the mid-latitude Western Interior Seaway (WIS; spanning 82–97 Ma) is assembled to quantify eccentricity amplitude modulation (AM) and obliquity AM, which could reveal the 2:1 resonance when present. Ten high-precision radioisotopic dates from the study interval permit a rigorous anchoring of the floating astrochronologies for comparison with theoretical astronomical models. The analysis is complimented by the construction of an astronomically tuned δ 13 C org composite for the early Cenomanian-early Campanian, which allows a new assessment of linkages between million-year scale astronomical forcing and perturbations of the Late Cretaceous carbon cycle. Evaluation of the La2004 model reveals a switch of eccentricity modulation from 2.4-Myr cycles to a 1.2-Myr cycle from 90 to 86.5 Ma, followed by a return to a 2.4 Myr cycle in younger strata, compatible with observations from the WIS composite. These two resonance transitions are absent in the La2010d and La2011 models. Among 11 solutions calculated by Zeebe (2017) , some show resonance transitions during this period, but none of them match the geological record with respect to the observed long eccentricity modulation. The results of this study also suggest that positive carbon isotope excursions are closely related to obliquity power minima, but this interpretation will require further analysis for full confirmation.

During the Late Ordovician, large explosive volcanic eruptions deposited worldwide K-bentonites, including the Millbrig and Deicke K-bentonites in North America and the Kinnekulle K-bentonite in Scandinavia. We have studied a classical locality in Oslo containing one of the most complete sections of K-bentonites in Europe. In a 53 m section of Sandbian age, we discovered 33 individual K-bentonite beds, the most notable beds being the Kinnekulle and the upper Grimstorp K-bentonite. Magnetic susceptibility (MS) measurements on two intervals show significant periodicity peaks interpreted as Milankovitch cycles and thus astronomically forced changes in sediment supply and composition. These cycles fit remarkably well with both the expected Milankovitch periodicities for the Ordovician as well as the radiometric ages presented in this study and may represent one of the most convincing demonstrations of Milankovitch cycles from the lower Paleozoic so far. Five of the K-bentonites have been dated by high-precision chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) U-Pb zircon geochronology, where the Kinnekulle K-bentonite gives an age of 454.06 ± 0.43 Ma. We have integrated the new data and calculated an age model showing the sedimentation rates through the section and thereby the ages of each of the 33 K-bentonites. Using the age model, we further present a new age for the Sandbian-Katian stage boundary. The section in Oslo provides the highest resolution window into the Upper Ordovician K-bentonite succession so far and helps shed more light on the chronology of one of the most intense volcanic periods of the Paleozoic and the relationship with the global carbon cycle changes that followed.

When Milankovitch cycles are preserved in the geologic record they provide a direct link between chronometer and climate change, and thus a remarkable opportunity to constrain the evolution of the surficial Earth System. The identification of such cycles has allowed exploration of the geologic record with unprecedented temporal resolution, and has spurred the development of a rich theoretical framework for climatic change. Accompanying these successes, however, has been a persistent skepticism: how does one reliably test for astronomical forcing/pacing in stratigraphic and paleoclimate data, especially when time is poorly constrained? From this perspective, it would seem that the merits and promise of astrochronology – a Phanerozoic time scale measured in 20,000 to 400,000 year increments – also serves as its Achilles heel, if the confirmation of such geologically short temporal rhythms defies rigorous hypothesis testing. The implications are substantial, since much of our understanding of paleoclimate change throughout the Cenozoic (and beyond) is firmly rooted in astrochronologic interpretation. In this study, a conceptual framework for assessing Earth System response to astronomical-insolation changes, and the propagation of that signal into the geologic record, is used as a guide to understand the nature of the problem of astrochronologic testing. This framework emphasizes three challenges – contamination, stratigraphic distortion, and temporal calibration. A statistical optimization method (TimeOpt; Meyers, 2015) is formulated as a solution to these three challenges, providing an approach for astrochronologic testing that objectively evaluates time scale uncertainty while simultaneously identifying an optimal model for climate and depositional system response to astronomical forcing. New extensions to the technique are presented, allowing explicit reconstruction of distortions to the primary forcing that are known to be omnipresent in the stratigraphic record. To illustrate the utility of this approach, it is applied to five well-studied stratigraphic series throughout the Phanerozoic, supporting their astronomical origin, and yielding constraints on the evolution of the Earth System and the astronomical solutions themselves. Future directions that build on this foundation are discussed, including the utility of process-based null models, approaches for Earth System transfer function reconstruction, and mapping out ancient Solar System behavior and Earth-Moon history using the geologic archive of Milankovitch cycles. The TimeOpt approach recognizes astronomy, geochronology, paleoclimatology and depositional system reconstruction as a unified geoscientific inverse problem.

Sedimentary deposits of the Lower Cretaceous Xiagou Formation form the most significant potential hydrocarbon reservoirs in the Qingxi Sag, Jiuquan Basin (NW China). Zircon U-Pb ages of the dated basalts at the top of the Xiagou Formation give an isochron age of 115.6 Ma, and the sedimentation interval of the Xiagou Formation was speculated to range from about 125/124 Ma to 115 Ma based on paleontological research and stratigraphic correlation analysis. Here we use GR logging data as a palaeoenvironmental and palaeoclimatic proxy to conduct a detailed cyclostratigraphic study of five selected wells. Power spectra, evolutionary fast Fourier transformation and wavelet analysis all reveal significant sedimentary cycles in the Xiagou Formation. The ratios of cycle wavelengths in these stratigraphic units are 33.82 m : 7.91 m : 3.06 m : 1.79 m, which is similar to the ratio of orbital targets of 20 : 5 : 2 : 1. The ratio of 20 : 5 : 2 : 1 is interpreted as Milankovitch cycles of 405 kyr long eccentricity, 100 kyr short eccentricity, 37 kyr obliquity, and 22 kyr precession cycles respectively. A high-resolution astronomical time scale is constructed by tuning the stratigraphy into target curves of orbital cycles respectively. Based on the astronomical time scale, the absolute ages of 55 samples were estimated, which are used for subsequent stable carbon and oxygen isotope stratigraphy analysis. The analysis results of the five studied wells in the Qingxi Sag indicate: (1) a negative trend of δ 13 C values upwards in the Xiagou Formation, and (2) negative δ 18 O values with a positive trend upwards. Both relatively heavy values and pronounced covariances of δ 13 C values and δ 18 O values indicate an arid-evaporation-controlled climate during the sedimentary period of the Lower Cretaceous Xiagou Formation, Qingxi Sag, Jiuquan Basin. Moreover, positive covariances of SQK 1 g 2+3 indicate extremely high temperature, and negative covariances of SQK 1 g 1 indicate a relatively low temperature.

Using topographic maps and terrestrial cosmogenic nuclide (TCN) 10Be exposure dating methods, we reconstructed a chronology with robust age constraints based on four alluvial terrace abandonment features in two study sites along the SW piedmont of Kepingtage Mountain in SW Tian Shan. Agreement between alluvial terrace abandonment ages and Guliya ice-core δ18O, LR04 stack of benthic δ18O, EPICA Dome C CH4, and solar insolation records suggests that alluvial terraces with 10Be age sequences at 63.7 ± 5.9 ka, 40.9 ± 3.84 ka, 36.2 ± 3.4 ka, and 22.1+5.1–4.7 ka correspond to three wetter climate intervals, possibly triggered by intensified South Asian summer monsoons since the Late Pleistocene. Given that the active thrust Kepingtage Fault experienced sustained uplift during this period, we suggest that the abandonment of alluvial terraces that formed since 22.1+5.1–4.7 ka may be related to sudden tectonic uplift. The occurrence of these four younger well-preserved alluvial terraces may also be related to the fact that the transient climatic incision has been no higher than the temporary tectonic uplift since 22.1+5.1–4.7 ka.

As one of the rare terrestrial archive with continuous sedimentation back to almost 1 Ma in Anatolia, the Eskisehir Graben was investigated in outcrops and cores by multi-proxy analysis regarding chronology and paleoclimatology. The present study comprises significant implications for both the impact of climate changes on fluvial systems in the timescales of the Milankovitch band and the controversial age and rate of the crustal extension in western Anatolia. Our findings indicate that LOI950 and delta O-18(carb), which are indicators for the amount of soil carbonate and paleo-temperature respectively are collectively capable of distinguishing between glacial and interglacial periods in the predominantly floodplain deposits of the graben infill. Secondarily, LOI550 and delta C-13(carb) values further help this discrimination via primary production and composition of vegetation cover respectively. Pollen data, albeit highly discontinuous due to poor preservation under subaerial conditions, point out a steppe-like vegetation cover where the forest components expand particularly in the wet interglacial periods. In the other hand, the chronological frame provided by astronomical calibration of certain proxy-records strongly suggest that the Eskisehir Fault Zone initiated as a boundary fault of a half-graben some 900 ka. The rate of vertical movement on its southern branch since the last 70 ka is unexpectedly high (2.3 mm a), a phenomenon that requires urgent risk assessment analysis in the vicinity of the Eskisehir city, UGC-DAE Consortium for Scientific Research, University Grants Commission: 2013/15009, The authors are grateful to the geologist Engin Başaran for his assistance with the preparation of samples for isotope measurements. Prof. M. Cihat Alçiçek (Pamukkale University) and two anonymous reviewers raised important comments that finally helped the amelioration of the manuscript. The Commission for Scientific Research at the Eskişehir Osmangazi University (Turkey) financially supported this study (Grant no. 2013/15009 ). Appendix A

The astronomical theory of Milankovitch supports the waxing and waning of ice sheets and polar glaciers by orbital forcing, excluding the fact that small changes in solar radiation flux are difficult to reconcile with the amplitude of glacial cycles. The numerical model explaining the 100 kyr problem has now revealed that the phase locking mechanism of orbital forcing has started to modulate the climatic transitions since ∼1.2 Myr back and remained locked till present climatic state (Rial et al., 2013). However, the true evidence to confirm it is not present. The present study is an attempt to comprehend the concept of synchronization of summer insolation modulation and internal climate forcing, responsible for glacial/interglacial termination present in and around the Himalaya-Tibet and worldwide. We present geographical evidences of glaciations from the Himalayan-Tibet region pointing out that responses (i.e. 18–24 kyr and 60–70 kyr BP glaciation events) are similar to the progression in climatic data and glaciations cycles for the last 100 kyr. The compelling evidence presents a possible explanation towards synchronized modulation of 100 kyr orbital cycles with 41 kyr obliquity cycles, coincidently resulting in unprecedentedly large glaciation around the last glacial cycle (60–70 kyr BP) and the Last Glacial Maxima (18–24 kys BP). By considering the influence of internal and external factors on glacier mechanism, we underline the most probable cause of 41 kyr cycle (obliquity) as the foremost driver of glaciations in the Himalaya and Tibet on longer timescales. We provide several lines of evidence to establish the possible connection of glaciation events and orbital cycles with the help of geographical and geological records consistent with the fact that resonance might be faded through time but the effect of frequency modulation still persists in the system.

A cooling trend during the Middle Ordovician may have resulted in significant biotic, atmospheric and hydrologic changes, but the exact timing and forcing of this climate event still remain largely ambiguous. Here, we present astronomically calibrated magnetic susceptibility (MS) and gamma ray (GR) data from the shale and carbonate successions of the Kalpin area in the Tarim Basin, NW China to study the Middle Ordovician climate. The spectral analyses of the 405-kyr calibrated MS and GR time series reveal periodicities close to 405 (calibrated), 100, 31 and 19 kyr, supporting a Milankovitch forcing for the sedimentary cyclicity. The eccentricity and obliquity amplitude modulation cycles show main periodicities of ~2.4 and ~1.2 Myr, respectively. A cooling event along with the middle Darriwilian isotope carbon excursion (MDICE) appears to have been initiated by the alignment of the eccentricity and obliquity amplitude minima at 4.07 Myr prior to the Darriwilian/Sandbian (D/S) boundary. This climate event was in pace with high-amplitude obliquity oscillations during a period when the 1.2 Myr obliquity amplitude modulation cycles controlled the global third-order eustatic sequences. The termination of this cooling event corresponding to a global third-order highstand was initiated by an eccentricity oscillation maximum at 0.63 Myr prior to the D/S boundary. Subsequent climate alleviation was dominated by eccentricity forcing until the earliest Sandbian. We suggest that although the climate changes have been primarily associated with the CO2 level, a specific sequence of astronomical variations during the Middle Ordovician was responsible for the time when the critical threshold was crossed.

The mechanisms governing the development of deep-sea fans is a matter of debate and their understanding at Milankovitch and millenial time-scales is challenged by complex architectures and the lack of material suitable for establishing reliable chronostratigraphies. Based on a detailed investigation of the emplacement of channel-levee-lobe systems and their successive bifurcations and seaward-landward migrations (Picot et al., 2016), we present for the last 210 ka a detailed chronostratigraphic framework of the migration pattern based mainly on radiocarcarbon dating of channels and lobes abandonment or initiation. The comparison of architectural cycles to proxies of external factors (sea-level and climate) suggest that sea-level changes have minor impacts on the architectural evolution of the Congo Fan. In contrast, comparison with climate and environmental proxies (West African monsoon, pollen grain assemblages, Kaolinite/Smectite) evidences a major impact on the timing of the development of the architectural pattern, at least for the last 38 kyr. A general scheme of the growth pattern of the Congo Fan in link with climate evolution is proposed: the stacking pattern of the Congo Fan responds to humidity/aridity cycles that generate successive progradation and retrogradation of avulsion points. These climate changes are under the control of the West African monsoon which, by controlling the rainfall and vegetation on the watershed, ultimately impacts the composition and volume of the sediment source and the transport capacity of gravity flow generated in the canyon and flowing in the turbiditic channels.

The shelf-margin prism of the Upper Pliocene to Pleistocene in the northeastern South China Sea has recorded significant signatures of glacio-eustatic cycles and paleo-climatic conditions. Integrated analysis of 3D seismic, well-logging, and borehole dating data in the study area provided a detailed depiction of the high-resolution sequence architecture and depositional evolution as they responded to the glacio-eustatic cycles and climate changes. The shelf-margin section of the Upper Pliocene to Pleistocene is comprised of a composite sequence bounded by a regional unconformity, which can be further divided into five sequences confined by subordinate unconformities. The two lower sequences (S1-S2) with similar and simple internal structures, are displayed as having roughly equal thicknesses (ca. 50 m) and gently seaward-dipping foresets. In contrast, the upper three sequences (S3-S5) are characterized by the development of high (200–600 m) and steep (2–5°) shelf-margin clinoforms, which can be further divided into fifteen clinothems. The sequences generally embody four systems tracts, showing different stratal stacking patterns, and the linking contemporaneous depositional systems including fluvial channels, deltaic and slope fan systems are documented. Based on the chronostratigraphic framework, comparisons have been made between the sequence cycles and the global oxygen isotopic records. The results suggest that the formation of different order sequences may have been in response to the glacio-eustatic cycles paced by the Milankovitch orbital cyclicity. The abrupt changes in the sequence and depositional architectures between S1-S2 and S3-S5 are assumed to be related to the significant increases in the amplitudes and durations of the glacio-eustatic fluctuations across the mid-Pleistocene climate transition (MPT). Intensively variable climatic conditions with strengthened monsoons during and after the MPT could have potentially led to an abundant sediment supply, which may have enhanced the development of shelf to shelf-edge delta systems with the large-scale prograding clinoforms.

Cyclostratigraphy has revealed the quasi-periodic nature that globally distributed sedimentary successions present through the Phanerozoic. This is mainly the case of the strong eccentricity-related greenhouse climate of the Cretaceous period, a time interval in which the long-eccentricity 405-kyr cycle has been routinely used to constrain high-resolution astronomical time scales. Despite the importance of the South Atlantic opening to the evolution of the Cretaceous climate and carbon cycle, few investigations have applied the modern cyclostratigraphic analysis to explore the eventual orbital pacing of the Cretaceous South Atlantic successions. We use geophysical and geochemical data analysis from the Petrobras well ES-1 (offshore Espirito Santo Basin to develop a floating and anchored astronomical time scale (ATS) and infer the relation between sedimentation rate and TOC accumulation. Additionally, we estimate the net primary productivity (NPP) during intervals of high TOC accumulation. Our results show a pervasive orbitally-driven forcing imprint according to the Milankovitch spectral peak ratio as predicted to Cretaceous times, with a prominent occurrence of a 405-kyr long-eccentricity cycle, being used to constrain the elapsed time. An abrupt shift in the GR data likely associated with the Cretaceous – Paleogene boundary was used to anchor our floating ATS. The evolutionary Average Spectral Misfit (eASM) and Correlation Coefficient (COCO/eCOCO) tests demonstrate that the sedimentation rate can have contrasting effects over the organic matter burial, which is likely related to the large-scale paleogeographic configuration. Our study exemplifies that orbitally-driven sedimentation can be used to build high-resolution chronology for Brazilian marginal basins.

Establishing a high-precision numerical geological time scale for the Paleozoic Era remains a considerable challenge. In this study, we conducted detailed cyclostratigraphic analysis on the Middle Ordovician of the Huangnitang section and the core Changjin 3 (CJ-3), Zhejiang Province, South China. Magnetic susceptibility (MS) series were obtained from a total of 3909 discrete samples and are used as a paleoclimate proxy indicative of variations in detrital input of magnetic minerals. Power spectral analyses show that both the section and core have recorded an excellent hierarchy of Milankovitch cycles of 405 kyr, 101–135 kyr, 31–34 kyr, and 15.8–21.3 kyr. An integrated floating astronomical time scale (ATS) for the section and core was established according to the extracted stable 405-kyr eccentricity cycles. This new floating ATS suggests that the durations of the Darriwilian and Dapingian stages were 8.38 ± 0.4 Myr and 1.97 ± 0.7 Myr, and the durations of complete graptolite zones of the Middle Ordovician were precisely estimated. The ratios of band (obliquity or short eccentricity) power to total power reveal periodicities of ~1.2 Myr for the s4–s3 term and ~1.9 Myr for the g4–g3 term, and ~1.2-Myr obliquity cycles may have controlled global third-order eustatic sequences during the late Darriwilian.

The Jurassic succession in Saudi Arabia represents the most prolific succession in the world. However, a detailed microfacies and paleoenvironmental model description, high-frequency cycles (HFC) analysis, and paleoenvironmental reconstruction of the main source rock interval for the Jurassic reservoirs, the Callovian Tuwaiq Mountain Formation (TMF) are poorly documented. This article reports on a study of the TMF, and discusses the succession of the microfacies, paleoenvironments, HFC, and depositional sequences, and paleoenvironmental constrains. On the basis of detailed field and lab work, 8 microfacies were recognized and interpreted to be deposited in four facies belts representing the inner part of a rimmed carbonate platform including: deep lagoon, shallow lagoon, shoal and peritidal and tidal flat. Within the deep and shallow lagoonal settings, massive platy and domal coral colonies form patch reefs. These patch reefs increase in size from deep to shallow lagoon settings under response to changing in environmental conditions; grater water clarity and harder substrate promoted larger patch reef size in shallow lagoon. Patch reefs decrease in size and disappear in shoal settings. The siliciclastic input was minute and could have been derived from tidal channels and/or windblown dust from the Arabian Shield. The stacking pattern of the microfacies revealed that the TMF represents a regressive cycle (3rd order depositional sequence), which is formed by repeated aggrading to prograding medium and small scale cycles. The HFC analysis gave an estimated duration of a small cycle about 45 Kyr, and an average rate of carbonate accumulation of 0.0455 m/Kyr. Therefore, medium and small scale cycles possibly represent 4th and 5th order depositional cycles, respectively, which are orbitally driven by high frequency eustatic fluctuations (Milankovitch cycles “obliquity”). The paleoenvironmental reconstruction revealed that the deposition occurred under the influence of occasional storm events with normal marine euhaline salinity and becomes more restricted towards the proximal part (lagoon to tidal flat).

A cyclostratigraphic and paleomagnetic study was carried out in the lower part of the Vaca Muerta Formation, Los Catutos Member (Lower to lowermost Upper Tithonian) at the southern region of the Sierra de la Vaca Muerta, Neuquén Basin, west-central Argentina. The Vaca Muerta Formation is known for its unconventional resource potential and its exceptional behaviour as a world-class source rock. The studied section is c. 90 m thick and is characterized by decimetre-scale rhythmic alternations of marls, mudstones and limestones, showing a well-ordered hierarchy of cycles. Elementary cycles, bundles and superbundles were recognized with frequencies within the Milankovitch spectrum band. A total of 280 standard specimens collected from 35 paleomagnetic sampling horizons, dated with ammonites, were analyzed. The quality and primary origin of the characteristic magnetization was proved through the corresponding reversal test. A magnetostratigraphic scale was thus constructed that comprises 5 reverse and 4 normal polarity intervals, spanning the Andean Virgatosphinctes andesensis (ex mendozanus) (Lower Tithonian) to Windhauseniceras internispinosum (lowermost Upper Tithonian) ammonite Zones. Polarities were correlated with the GPTS 2016 using the equivalences between the Andean and Standard ammonite zones which, allowed to interpret that Los Catutos section was deposited between M22r to M20n Subchrons. By means of the correlation between the cyclostratigraphic and magnetostratigraphic scales, it was possible to date the Tithonian succession with unprecedented precision. Rock magnetic studies indicate that the remanence is carried by titanomagnetite. Fil: Kohan Martinez, Melisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Kietzmann, Diego Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Iglesia Llanos, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Leanza, Hector Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Luppo, Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina

During the Albian and Cenomanian, the Earth underwent profound climatic and oceanographic changes that were recorded in sedimentary successions on a global scale. Carbon isotope records spanning this time interval have been established in the western Tethys, eastern Pacific and North Atlantic Oceans, but not yet in the eastern Tethys Ocean. In this paper, we present biostratigraphic, chemostratigraphic and cyclostratigraphic characteristics of the uppermost Albian–lowermost Cenomanian in an eastern Tethyan section (Youxia, southern Tibet). Based on calcareous nannofossil biozones and the bulk rock δ13C curve, the Albian-Cenomanian boundary interval (ACBI) was identified and correlated to the western Tethys and Atlantic Oceans. In the Youxia section, δ13C values range from approximately 0‰ to +1.3‰ (−0.03‰ to +1.31‰). Four subevents (a, b, c and d) were distinguished in the ACBI carbon isotope curve via correlation with other sections. Based on a spectral analysis of the carbonate content, we recognized Milankovitch short eccentricity (~100 kyr) and precession (22.2 kyr) cycles, suggesting that orbital variations modulated depositional processes. The duration of the ACBI was estimated at ~311 kyr, while OAE 1d lasted for ~233 kyr in the eastern Tethys Ocean, consistent with the duration calculated from Atlantic Ocean records.

Environmental changes within erosional catchments of sediment routing systems are predicted to modulate sediment transfer dynamics. However, empirical and numerical models that predict such phenomena are difficult to test in natural systems over multi-millennial timescales. Tectonic boundary conditions and climate history in the Panamint Range, California, are relatively well-constrained by existing low-temperature thermochronology and regional multi-proxy paleoclimate studies, respectively. Catchment–fan systems present there minimize sediment storage and recycling, offering an excellent natural laboratory to test models of climate-sedimentary dynamics. We used stratigraphic characterization and cosmogenic radionuclides (CRNs; 26Al and 10Be) in the Pleasant Canyon complex (PCC), a linked catchment–fan system, to examine the effects of Pleistocene high-magnitude, high-frequency climate change on CRN-derived denudation rates and sediment flux in a high-relief, unglaciated catchment–fan system. Calculated 26Al/10Be burial ages from 13 samples collected in an ∼180 m thick outcropping stratigraphic succession range from ca. 1.55 ± 0.22 Ma in basal strata, to ca. 0.36 ± 0.18–0.52 ± 0.20 Ma within the uppermost part of the succession. The mean long-term CRN-derived paleodenudation rate, 36 ± 8 mm/kyr (1σ), is higher than the modern rate of 24 ± 0.6 mm/kyr from Pleasant Canyon, and paleodenudation rates during the middle Pleistocene display some high-frequency variability in the high end (up to 54 ± 10 mm/kyr). The highest CRN-derived denudation rates are associated with stratigraphic evidence for increased precipitation during glacial–pluvial events after the middle Pleistocene transition (post ca. 0.75 Ma), suggesting 100 kyr Milankovitch periodicity could drive the observed variability. We investigated the potential for non-equilibrium sedimentary processes, i.e. increased landslides or sediment storage/recycling, to influence apparent paleodenudation rates; end-member mixing models suggest that a mixture of >50% low-CRN-concentration sediment from landslides is required to produce the largest observed increase in paleodenudation rate. The overall pattern of CRN-derived burial ages, paleodenudation rates, and stratigraphic facies suggests Milankovitch timescale climate transitions drive variability in catchment denudation rates and sediment flux, or alternatively that climate transitions affect sedimentary process regimes that result in measurable variability of CRN concentrations in unglaciated catchment–fan systems.

This high-resolution study (210 samples/44 m) of the uppermost Campanian–lower Maastrichtian chalk at Kronsmoor (northern Germany) intends to define the inorganic depositional setting of Late Cretaceous chalk deposition as well as to reconstruct contemporaneous sea-level fluctuations and palaeoenvironmental changes. A latest Campanian event associated with significantly decreased carbonate contents and palaeotemperatures is reflected in most geochemical palaeoproductivity proxies and indicates reduced marine fertility across the Campanian–Maastrichtian boundary. Sr/Ca and δ13C remain low afterwards while other productivity proxies show a significant rebound, indicating recovery and a potential qualitative change in marine productivity during the early Maastrichtian. Redox-sensitive proxies indicate overall well oxygenated conditions. The %terrigenous proxy tracks an argillaceous chalk depositional event related to an inferred glacio-eustatic latest Campanian sea-level fall followed by a low sea-level stand until the earliest Maastrichtian. It decreases and stays low up-section, reflecting an early Maastrichtian sea-level rise and highstand, parallelled by increasing and consistently high carbonate contents. However, the concomitant conspicuous variability and increase in other terrigenous input proxies indicate more strongly fluctuating and higher aeolian supply. Time-series analysis of selected geochemical proxies demonstrates the presence of the obliquity (∼40 kyr) the long-eccentricity (∼400 kyr) cycles of the Milankovitch Band. The covariance of productivity proxies and indicators of aeolian input suggests that obliquity forcing of dust input exerted control on (surface) water productivity, CaCO3 flux and the end-Cretaceous carbon cycle.

At the end of the Late Paleozoic Ice Age (LPIA) from late Early Permian to early Late Permian, the global climate was impacted by a prevailing megamonsoon and Gondwanan deglaciation. To better understand the abiotic and biotic responses to Milankovitch-forced climate changes during this time period, multi-element X-ray fluorescence (XRF) geochemistry analyses were conducted on 948 samples from the late Early−late Middle Permian Maokou Formation at Shangsi, South China. The Fe/Ti, S/Ti, Ba/Ti and Ca time series, which were calibrated with an existing “floating” astronomical time scale (ATS), show the entire suite of Milankovitch rhythms including 405 kyr long eccentricity, 128 and 95 kyr short eccentricity, 33 kyr obliquity and 20 kyr precession. Spectral coherency and cross-phase analysis reveals that chemical weathering (monitored by Fe/Ti) and upwelling (captured by S/Ti and Ba/Ti) are nearly antiphase in the precession band, which suggests a contrast between summer and winter monsoon intensities. Strong obliquity signal in the Ba/Ti series is proposed to derive from changes in thermohaline circulation intensity from glaciation dynamics in southern Gondwana. The abundance of foraminifer, brachiopod and ostracod faunas within the Maokou Formation were mainly controlled by the ~1.1 Myr obliquity modulation cycle. The obliquity-forced high-nutrient and oxygen-depleted conditions generally produced a benthic foraminifer bloom, but threatened the brachiopod and ostracod faunas.

The Late Devonian biosphere was affected by two of the most severe biodiversity crises in Earth's history, the Kellwasser and Hangenberg events near the Frasnian–Famennian (F–F) and the Devonian–Carboniferous (D–C) boundaries, respectively. Current hypotheses for the causes of the Late Devonian extinctions are focused on climate changes and associated ocean anoxia. Testing these hypotheses has been impeded by a lack of sufficient temporal resolution in paleobiological, tectonic and climate proxy records. While there have been recent advances in astronomical calibration that have improved the accuracy of the Frasnian time scale and part of the Famennian, the time duration of the entire Famennian Stage remains poorly constrained. During the Late Devonian, a complete Late Frasnian–Early Carboniferous succession of deep-shelf deposits accumulated in the epieric sea in Illinois Basin of the central North-American mid-continent. A record of this sequence is captured in three overlapping cores (H-30, Sullivan and H-32). The H-30 core section spans the F–F boundary; the Sullivan section spans almost all of the Famennian and the H-32 section sampled spans the interval of the Upper Famennian and the D–C boundary. To have the best chance of capturing Milankovitch cycles, 2000 rock samples were collected at minimum 5-cm-interval across the entire sequence. Magnetic susceptibility (MS) was measured on each sample and the preservation of climatic information into the MS signal was verified through geochemical analyses and low-temperature magnetic susceptibility acquisition. To estimate the duration of the Famennian Stage, we applied multiple spectral techniques and tuned the MS signal using the highly stable 405 kyr cycle for Sullivan and the obliquity cycle for the H-30 and H-32 cores. Based on the correlation between the cores we constructed a Famennian floating astronomical time scale, which indicates a duration of 13.5 ± 0.5 myr. An uncertainty of 0.5 myr was estimated for the uncertainties arising from the errors in the stratigraphic position of the F–F and D–C boundaries, and the 405 kyr cycle counting. Interpolated from the high-resolution U–Pb radiometric ages available for the Devonian–Carboniferous boundary we recalibrated the Frasnian–Famennian boundary numerical age to 372.4 ± 0.9 Ma.

Over the past century, numerous discoveries throughout East Africa have advanced our understanding of hominin evolution and provided substantive evidence that climatic and environmental variability played a critical role in evolutionary developments. Stratigraphic records with high temporal resolution aid in testing evolutionary hypotheses that invoke changes in climate and environment at various timescales as drivers of hominin evolution. Olduvai Gorge, Tanzania has a rich history of hominin fossil discoveries from its ~2.0 Ma sedimentary sequence, which includes multiple deep lake intervals. In 2014, the Olduvai Gorge Coring Project (OGCP) recovered a sequence of sediment cores that provide an extensive record of the Pleistocene sedimentary history, including paleolacustrine systems in this area. With >94% core recovery, these cores are ideally suited for high-resolution analyses of organic geochemical proxies and provide an exceptional opportunity to build on previously published outcrop-based paleoenvironmental data from Olduvai. The OGCP core 2A section between 76.6 and 86.9 m depth is considered as a time-stratigraphic equivalent of strata that host the hominin fossils OH24 and OH56 at the Olduvai DK archaeological site. This depositional interval age-bracketed between ~1.88 Ma (Bed I Basalt) and ~1.85 Ma (Tuff IB) was sampled for organic geochemical analyses. The carbon isotopic composition of organic matter (δ13CTOC) from this section varies between values representative of more forested and open grassland ecosystems over ~21 kyr. This observation is consistent with the Milankovitch precession cycle driving the availability of water, which was previously observed in lower resolution studies of outcrop samples. Complementary organic geochemical proxies provide further evidence of these shifts in environmental conditions and record sub-Milankovitch scale changes superimposed on the precession cycle. This suggests the occurrence of short-term fluctuations in the environments inhabited by hominins, which opens new lines of investigation on how environmental scenarios may affect particular evolutionary mechanisms that drove various evolutionary responses.

The identification of Milankovitch cycles and the establishment of a high-resolution astronomical time scale for the Palaeozoic represent a research frontier in cyclostratigraphy and astrochronology. A continuous core drilled through the Telychian Stage (Llandovery, Silurian) of the Paslek Formation in the Baltic Basin (Poland) is characterized by repetitive centimetre-scale alternations of homogeneous greenish-grey mudstones and faintly laminated dark-grey-to-black mudstones. Such lithological rhythmicity reflects a cyclical variation in redox conditions at the sediment-water interface, and therefore was used to construct a floating astronomical time scale (ATS) for the Telychian Stage. The cyclostratigraphic analysis was performed on a 5 mm resolution greyscale scan based upon photographs of the slabbed core, with lower values associated with greenish-grey mudstones and higher values related to dark-grey-to-black mudstone facies. Spectral density estimation by means of the multitaper method (MTM) reveals significant peaks rising above the 95% red noise confidence level that we interpret as the 405-kyr long-eccentricity, short-eccentricity, obliquity and precession components. The MTM evolutive power spectral analysis (EPSA) shows a gradual increase in the velocity of sedimentation from 5.03 m/Myr in the lowermost interval to 5.48 m/Myr towards the uppermost part of the studied sequence. We postulate that the observed cycles reflect orbitally-driven climatic variations from stable wet conditions to monsoon-like high seasonal contrasts that affected weathering intensity, runoff and nutrient supply. These cyclical variations led to rhythmic variations in organic matter fluxes and benthic anoxic conditions. In the analysed record, orbital precession influenced the deposition of the greenish-grey mudstone and dark-grey-to-black mudstone couplets, occurring on average every 10 cm. Furthermore, long-eccentricity modulation of precession controlled the relative depositional predominance of one facies over the other. Observed periodicities resemble those of Cenozoic and Mesozoic orbitally controlled records, thus suggesting that during the Silurian the orbital eccentricity forcing on the carbon flux acted in the same way as in the Cenozoic and Mesozoic. The orbital tuning of the studied interval, calibrated by means of accurate acritarch biostratigraphy, allowed for the estimation of an astronomically calibrated duration for the Telychian Stage of about 5.46 Myr.

Constructing an accurate timeline is critical for reconstructing the Earth systems through critical transitions in climate, geochemistry, and life. Existing dates constrain synchronous initiation (ca. 717 Ma) and termination (ca. 660 Ma) of the Sturtian glaciation from multiple continents. The termination of the younger Marinoan glaciation is also well dated at ca. 635 Ma, but the onset of this glaciation is only roughly constrained as ≤ ca. 654 Ma (South China) and ≥ ca. 639 Ma (Namibia). To test if the Marinoan glaciation started close to ca. 654 Ma or ca. 639 Ma, we have conducted a cyclostratigraphic study on the Cryogenian non-glacial Datangpo Formation that conformably overlies and underlies Sturtian and Marinoan glacial diamictites, respectively, in a deep-water basin section in South China. A total of 28,765 magnetic susceptibility (MS) measurements from a drillcore of the 292-m-thick, muddy siltstone- and shale-dominated Datangpo Formation are used for cyclostratigraphic analysis. The results reveal significant decameter- to meter-scale sedimentary cycles of 16–12 m, 3.6–3.0 m, 1.0–0.8 m, and 0.6–0.4 m. The ratios of these cycle wavelengths match well with those of the Milankovitch cycles calibrated for the Cryogenian Period. The established astrochronologic time scale suggests that the duration of the Datangpo Formation is about 9.8 million years. Together with the radiometric age of ca. 660 Ma for the termination of the Sturtian glaciation, the cyclostratigraphic data suggest that the Nantuo (Marinoan) glaciation in South China initiated at ca. 650 Ma, which is slightly younger than but consistent with the ca. 654 Ma U–Pb age from the top of the Datangpo Formation in shelf sections. This age, however, is significantly older than the ages obtained from Marinoan-age glacial diamictites in South China (ca. 636 Ma) and Namibia (ca. 639 Ma). Given that most of the shelf sections may have suffered from glacial erosion, obtaining the onset age of the Marinoan glaciation should focus on relatively complete, deep-water successions.

By the Early Cretaceous, the Araripe Basin (Northeastern Brazil) is interpreted as having gone through a phase of tectonic quiescence, during which rates of sediment accumulation were mostly modulated by climatic variations. The Crato Member (Santana Formation, upper Aptian of Araripe Basin) consists of gray calciferous mudstone and parallel-stratified micritic limestone deposited in a lacustrine environment. The present study applied the principles of cyclostratigraphic analysis in the uppermost carbonate unit of the Crato Member, which comprises laminated limestone displaying a characteristic cyclic alternation of pale to dark laminae, in order to estimate sediment accumulation rates by relating the depositional record with astronomical cycles of known periodicity. An 8.5 m thick limestone succession was analyzed in order to build a time series by using two distinct data sources, namely spectral gamma ray readings and color variation chart. Additionally, petrographic and organic composition analyses were performed to investigate if environmental changes have affected those parameters. Results indicate that darker laminae reflect periods with concentration of sulfite related to relatively anoxic water conditions. The time series analysis allowed for an identification of two different astronomical cycles: (1) Milankovitch cycles, ranging from 18.6 ky to 39.4 ky, resulting in an estimated depositional rate of 3.25 cm/ky, with a total of 261 ky for the deposition of the whole studied interval; (2) Suess solar cycles, ranging 180–200 years, with an estimated depositional rate of 3.3 cm/ky, and a total of 257 ky for the deposition of the same interval. Therefore, this multidisciplinary approach led to the identification of Milankovitch and Suess high frequency solar cycles, based on which it was possible to determine the rate of deposition as well as the time span involved in it.

Millennial-to-interannual events play important roles in driving climate change on Earth. However, most studies focus on Quaternary records, and few focus on pre-Quaternary periods due to preservation condition and stratigraphic resolution limitations. Favorable conditions for the preservation of annual laminae are recorded during the Eocene in the Shahejie Formation in the Bohai Bay Basin (BBB), which is an ideal place for studying solar activity cycles. Here, the sedimentary petrology and cyclostratigraphy of 202-m-thick lacustrine fine-grained sedimentary rocks during the Eocene from Well Niuye-1 were analyzed. Power spectrum analysis and evolutive harmonic analysis (EHA) of the gray values reveal prominent periodicities of 11.7–19.6 mm, 3.7–4.95 mm and 1.69–2.21 mm, interpreted as Gleissberg cycles, solar Hale cycles and Schwabe sunspot cycles, respectively. Laminar couplets of light and dark laminae have an average thickness of 189 μm, and their annual origin has been interpreted on meter, centimeter and millimeter scales. The light laminae, composed of pure calcite, likely precipitated during summer. The dark laminae, which are mixtures of clay minerals, quartz debris and organic matter, likely precipitated during winter. The dark laminae are thin, contributing little to the overall thicknesses of the annual laminae except for the abruptly thicker laminae deposited every 10–11 years. The coherent periods at different scales match the solar activity cycles well. The obvious solar activity cycles during the Eocene of the Shahejie Formation in the BBB suggest that solar activity did not significantly change during the transitional period from a greenhouse to an icehouse climate.

Cyclostratigraphy is a powerful tool in chronostratigraphic studies, and has shown its potential in Precambrian time. The Cryogenian Period is one of the most dynamic and intriguing intervals in Earth history and it is a witness to the most extreme climate changes on the planet, known as two Snowball Earth events. However, a robust chronostratigraphic framework is still lacking especially for the younger Marinoan Snowball Earth event, hampering the stratigraphic correlation and comparison among geographically separated records, as well as the understanding of the initiation and termination of this global-scale glaciation. The Cryogenian Fiq Formation in Oman is thought to be Marinoan-equivalent. The duration of the nonglacial units in the Fiq Formation could provide a conservative age constraint on the previously not well-determined onset age of the Marinoan glaciation. In this work, a cyclostratigraphic study has been conducted on three drill cores of the Fiq Formation. The multi-taper method (MTM) spectral analysis, the correlation coefficient (COCO), and the evolutionary correlation coefficient (eCOCO) analyses were performed on the high-resolution gamma-ray (GR) data from the three cores. A hierarchy of Milankovitch cycles (eccentricities, obliquities, and precessions) has been identified, which was used to estimate the optimal sedimentary accumulate rates and the duration of the Fiq Formation in each core. Based on the cyclostratigraphic results, the time scale of the Fiq Formation is at least ~6 Myr. Integrating the radiometric ages and the cyclostratigraphic data from other continents, the onset age of the Marinoan glaciation is suggested to be 650–641 Ma. This new result helps improve the chronostratigraphic framework for the Cryogenian Period and also provides critical temporal constraints for the geological and numerical models that explore the possible mechanisms for the Snowball Earth events.

Carbon and oxygen isotopes of both well-preserved articulate brachiopod Paucicrura rogata and cement in mid-Cincinnatian samples (Maysvillian to early Richmondian) on the eastern North American passive margin shelf in SW Ontario show no simple relationships. The δ13C trends of the brachiopods, organic matter and cements are little altered and vary little up section. The brachiopod δ13Cbrach pattern is very close to the American mid-continent whole rock δ13CWRcarb pattern across the Fairview excursions. The δ18Obrach variations, if primary, indicate fluctuating but generally slightly cooling temperatures upwards, though the actual temperatures depend on inferred salinities of the seawater. The temperature/ salinity relationships variations are compatible with the warm deep saline water hypothesis. The paleoceanography shows a change from a warm open passive carbonate margin to a fluctuating warmer/cooler enclosed clastic marginal basin with freshwater input, heralding the cold conditions of the Hirnantian ice age. The Milankovitch cyclicity determined from δ13Ccarb patterns, is practically identical to that from determined from magnetic intensities on the contemporary Yangtse Shelf.

This paper presents a multidisciplinary study of a new basinal section of Tithonian-Berriasian the Vaca Muerta Formation at Las Tapaderas area, including detailed, biostratigraphic, sedimentologic, sequence stratigraphic and cyclostratigraphic analysis. Biostratigraphy based on ammonite, calpionellids and calcareous dinoflagellate cysts indicate that Las Tapaderas section spans through the Lower Tithonian - lowermost Upper Berriasian, however, its upper part is covered through an erosive unconformity by Pleistocene volcaniclastic deposits, and therefore Las Tapaderas section could reach the Lower Valanginian. Two facies associations were identified, corresponding to basinal and distal outer ramp subenvironments. Recognition of flooding surfaces allowed the identification of three composite depositional sequences and eight high-frequency depositional sequences, which can be correlated with other sections throughout the basin. Cyclostratigraphic analysis based on the recognition of marlstone/limestone couples (elementary cycles) allowed to build a time series based on bed thickness. Fourier analysis indicates the characteristic mid latitude precession-eccentricity syndrome, with 220 precessional cycles (~20.4 and ~23 kyr), 53 low frequency eccentricity cycles (~79, ~90 and ~140 kyr) and 11 high frequency eccentricity cycles (~400 kyr). Spectral analysis also allowed to recognize the presence of the obliquity cycle (38.5 kyr), which has been erratically recorded in the Vaca Muerta Formation. Our data allowed the construction of an orbital scale, calibrated by cosmopolitan markers (calpionellids and calcareous dinoflagellate cysts), for this section. The precise bio- and cyclostratigraphic location of the Jurassic-Cretaceous boundary was established for this section. The sedimentation rate was studied at the scale of the precession cycle, showing values between 0.6 and 3 cm/kyr, while at the low-frequency eccentricity scale it shows values between 1 and 2 cm/kyr.

Upper Cretaceous marine sequences in the Gulf Coastal Plain (USA) span the Cretaceous–Paleogene (K–Pg) transition, allowing for detailed studies of one of the most severe extinction events of the Phanerozoic. To improve the temporal resolution of the stratigraphic record that represents environmental change leading up to the K–Pg boundary, we constructed a high-resolution chemostratigraphy and cyclostratigraphy of upper Maastrichtian shallow marine deposits located in the state of Mississippi (USA). Upper Maastrichtian strata in this area consist of alternating decimeter scale chalk and marl rhythmites deposited in a hemipelagic setting. New geochemical proxy records were used to test whether rhythmic sedimentation was driven by Milankovitch cycles. Stable isotopes (δ13Ccarb, δ18Ocarb), carbonate content (wt% CaCO3), and elemental concentrations (Ti, K, Fe) integrated with microfossil and ammonite biostratigraphy reveal astronomical forcing in the studied record. Spectral estimation suggests that rhythmic bedding was associated with climate change driven by precession (~20 kyr). Obliquity signals are also apparent in our analysis, and short eccentricity (~100 kyr) is inferred from amplitude modulation of precession. Studied sections were correlated at the precession scale with the recently tuned K–Pg succession near Morello, Italy which is stratigraphically equivalent to the well-characterized K–Pg sites in Gubbio, Italy (Bottaccione, Contessa Highway). Additionally, carbon isotope records from the study area exhibit large scale trends throughout the latest Maastrichtian, similar to those observed in the Morello and Bottaccione sections. Thus, we show that Milankovitch-scale climatic signals and low-amplitude carbon isotope shifts (

Milankovitch cycles during the Phanerozoic affected paleoclimate, the onset/termination of glacial/interglacial periods, sea-level changes, and thus the distribution of different facies in sedimentary basins. The effects of astronomical forcing have been recorded as astronomical frequency signals in sedimentary sequences through geological history. In this research, for the first time, the signal of Milankovitch cycles and orbital obliquity modulation cycles from the Oligocene–Early Miocene Asmari Formation at one of the oil fields in the Dezful Embayment of the Zagros Basin, Iran, have been identified, through wireline logs. Based on that, ten ~1.2 orbital obliquity modulation cycles have been recognized and correlated with global third-order sequences and δ18O events. The number of cycles during the Oligocene–Early Miocene in the Asmari Formation is equivalent to obliquity of the La2004 orbital solution. Additionally, the optimal sediment accumulation rates, depositional duration of this formation, and foraminiferal biozone durations have been calculated. The result of this study shows that sediment accumulation rates varied in the range 2.9 to 3.2 cm/kyr. The foraminiferal biozones are diachronous in this area. Based on the identified 405 kyr long-eccentricity cycles in the three studied wells, three astronomical time spans of 11.5 Myr, 9.42 Myr, and 9.02 Myr were obtained for the Asmari Formation in Wells A, B, and C, respectively.

This article is concerned with the internal dynamics of a conceptual model proposed by Maasch and Saltzman [J. Geophys. Res., 95, D2 (1990) 1955-1963] to explain central features of the glacial cycles observed in the climate record of the Pleistocene Epoch. It is shown that, in most parameter regimes, the long-term system dynamics occur on certain intrinsic two-dimensional invariant manifolds in the three-dimensional state space. These invariant manifolds are slow manifolds when the characteristic time scales for the total global ice mass and the volume of North Atlantic Deep Water are well- separated, and they are center manifolds when the characteristic time scales for the total global ice mass and the volume of North Atlantic Deep Water are comparable. In both cases, the reduced dynamics on these manifolds are governed by Bogdanov-Takens singularities, and the bifurcation curves associated to these singularities organize the parameter regions in which the model exhibits glacial cycles. This work was submitted March 30, 2017., 34 pages, 21 figures

The time scale of the Late Triassic Epoch has a divergence of age models, especially for the durations of competing definitions for its Rhaetian Stage (uppermost Triassic). The astrochronology derived from relative depth of lacustrine-bearing clastic successions and astronomically tuned geomagnetic polarity time scale (APTS) of the Newark Supergroup of eastern North America provides a basis for the Late Triassic time scale. However, the Newark APTS has been challenged regarding its age scale and completeness; therefore an independent astronomical-tuned magnetic polarity zonation is required to verify the upper Newark APTS reference scale. We compiled a 6.5 million year (myr) APTS with magnetic stratigraphy from four sections of the lacustrine-fluvial, dinosaur-track-bearing Xujiahe Formation in the Sichuan Basin of South China that also has dating from detrital zircons and regional biostratigraphy. Variations in natural gamma-ray and magnetic susceptibility that reflect variable continental weathering in the source regions of the Xujiahe Formation are paced by Milankovitch cycles, especially the 100-kyr short eccentricity and 405-kyr long eccentricity. The cycle-tuned magnetostratigraphy of the Xujiahe Formation is compared directly via the magnetic-polarity zones to the depth ranks of the Newark Supergroup that are indicative of relative depths of lacustrine facies. The Sichuan APTS indicates that there is no significant hiatus between the sedimentary succession and the basalt flows at the top of the Newark Supergroup. The Sichuan APTS is compatible with the magnetostratigraphy from the candidate Global Boundary Stratotype Section and Point (GSSP) for the Norian–Rhaetian boundary interval at the Pignola–Abriola of South Italy, but does not extend downward to the proposed GSSP in Austria associated with the longer Rhaetian option. The earliest dinosaur tracks in China are from the middle of this Xujiahe Formation, therefore are implied to be middle Rhaetian in age. This Sichuan APTS helps to resolve the controversy about the completeness and reliability of the Newark-APTS, and can be used in the future to verify if isotopic excursions in organic carbon recorded in the Italian sections that are proposed as possible secondary markers for a base-Rhaetian definition are global in nature.

In this study, we report a tuned astronomical time scale for a sedimentary formation in Early Cretaceous – the lower Linze Section located in the Zhangye Basin of the central Hexi Corridor, northwestern China. Based on detailed field investigations, we identified this sediment as the Xiagou Formation, which is widely distributed in the region. A thick, prominent limestone layer crops out in the middle portion of the Linze Section, and can be correlated to a similar limestone layer in the Liupanshan Group, which has been dated via high-resolution magnetostratigraphy. This correlation places an age constraint of around 114 Ma for the top of the underlying strata. A total of 1245 samples were collected from the 474-m-thick lower Linze Section, for magnetic susceptibility measurements and cyclostratigraphic analysis. Spectral and continuous wavelet analyses were applied to the low-frequency magnetic susceptibility series and the percentage frequency-dependent magnetic susceptibility series, as well as to specific subsections exhibiting visible rhythmic bedding. A hierarchy of sedimentary cycles was identified, with wavelengths of 21.5–37.0 m, 7.5–9.5 m, 2.1–4.4 m, and 1.4–1.7 m. The ratios between these lengths correspond well to the ratios between the durations of Earth's orbital long-eccentricity, short-eccentricity, obliquity, and precession cycles. We interpret these sedimentary cycles to reflect the effects of orbital forcing on sedimentary processes. Using band-pass filtering to specifically extract eccentricity cycles, we established a tuned astronomical time scale for the Xiagou Formation in the lower Linze Section, with a total duration of about 6.1 Myr (114.1 Ma to 120.2 Ma). Based on this timescale, the sedimentation rate of the Xiagou Formation is estimated to be in the range of 62–105 m/Myr, with most intervals yielding rates in the 70–80 m/Myr range.