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The continuous sedimentary cores recovered at the International Ocean Discovery Program (IODP) Site U1505, Expedition 368, provide an opportunity for paleoceanography and paleoclimate reconstruction in the continental margin of the northern South China Sea (SCS). In this study, we conducted detailed rock‐ and paleomagnetic studies on 420 discrete samples from the top ∼200 m of the synthetic records of Holes U1505C and U1505D. Rock magnetic analyses indicate that low‐coercivity pseudosingle domain magnetite dominates as the primary ferromagnetic mineral of Site U1505. The magnetostratigraphic age model was constructed by correlating the interpreted polarity sequence with the Geomagnetic Polarity Time Scale 2020 with the constraints of the biostratigraphic data and the distribution probability of the age of each polarity zone provided by a Dynamic Time Warping algorithm. The Milankovitch cycles of the short eccentricity, obliquity, and precession cycles were identified in the magnetic susceptibility (MS) and natural gamma radiation (NGR) series based on paleomagnetic results. We established an ∼9 Myr high‐resolution astronomical time scale by tuning the MS and NGR records to the global oxygen isotope curves, the obliquity, and the eccentricity curves of the La2004 astronomical solution. Our new age model reveals detailed sedimentation rate variations and a ∼500 kyr hiatus across the Brunhes‐Matuyama boundary related to local tectonic activity. These results lay the foundation for understanding the paleoceanography and paleoclimate evolution of the SCS. Plain Language Summary: A high‐resolution time framework is essential for achieving the scientific objectives of the International Ocean Discovery Program Expedition 368 in the northern South China Sea. Here we conducted detailed magnetostratigraphic and cyclostratigraphic analyses on cores of Site U1505, providing a robust age constraint of the upper ∼200 m of the cores. Our results provide an almost continuous succession since ∼9 Ma with a ∼500 kyr hiatus at ∼30.517 m. Significant Milankovitch cycles corresponding to the short eccentricity, obliquity, and precession cycles were identified in the geophysical data, indicating an orbital forcing on the monsoon climate and terrigenous input variations over the northern South China Sea. The new magneto‐cyclostratigraphic age model will contribute to further paleoceanographic, paleoclimatic, and correlation studies. Key Points: Rock magnetic studies indicate that magnetic remanence is dominated by low‐coercivity magnetite in International Ocean Discovery Program Site U1505The fluctuation of the content of terrigenous materials over the northern South China Sea is driven and modulated by Milankovitch cyclesA new magneto‐cyclostratigraphic age model since ∼9 Ma is established, highlighting a ∼500 kyr hiatus across the Bruhnes/Matuyama boundary [ABSTRACT FROM AUTHOR]

Abstract 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 CO 2 level, a specific sequence of astronomical variations during the Middle Ordovician was responsible for the time when the critical threshold was crossed. Highlights • Onset and termination of a cooling event in the Middle Ordovician were dated. • Obliquity forcing dominated this cooling event. • 1.2 Myr obliquity modulation cycles controlled the third-order eustatic sequences. • Onset and termination of cooling event were controlled by astronomical forcing. [ABSTRACT FROM AUTHOR]

Termination of the late Paleozoic icehouse (LPI) serves as the Earth's first icehouse-to-greenhouse transition when the continents were covered by extensive vegetation. However, low-latitude climatic and biological responses to this climate transition remain unclear. In this study, we conducted a cyclostratigraphic analysis of a shallow marine succession of the Tieqiao section in South China. Variations in gamma rays that reflect continental weathering strength in the source regions are paced by Milankovitch cycles, including 405-kyr long eccentricity, 31.7-kyr obliquity, and ∼ 20-kyr (20.1 kyr and 18.7 kyr) precession. Based on the 405-kyr-scale cyclostratigraphic correlation between the Tieqiao section and the deep marine succession of Naqing, a floating astronomical time scale for the late Early Permian was constructed, and the base of the Kungurian stage was estimated as 284.83 ± 0.40 Ma. Climatic and astronomical variations were synchronized to this refined timescale and further compared with a geochronologically independent marine invertebrate biodiversity time series to interpret the dynamics of marine biological evolution during the late Paleozoic icehouse-to-greenhouse transition. The impacts of low-frequency obliquity forcing (with a period of ∼1.35 Myr) on climatic and biotic systems have differentiated in the changing climate backgrounds. When Gondwana land was minimally glaciated during the Artinskian, increased marine speciation was associated with elevated climatic humidity, nutrient inputs, linkage to glacial building at low-amplitude obliquity oscillation intervals (obliquity nodes). This cause-and-effect relationship gradually changed from ∼285.1 Ma, along with the termination of Gondwanan glaciation and tropical aridification over the long term. In an arid greenhouse, continental aridity and marine transgression at obliquity nodes led to a low nutrient level that the suppressed marine biodiversity. Our results show differential dynamics involving the Earth's astronomical parameters, climate change, and marine invertebrate biodiversity between icehouse and greenhouse conditions in the late Paleozoic Era. • The constructed astronomical time scale yields an age for the basal Kungurian stage of 284.83 ± 0.40 Ma. • Obliquity nodes led to climate humidity and marine speciation during the partially glaciated period. • Obliquity nodes led to aridity, marine transgression and reduced biodiversity in an ice-free world. [ABSTRACT FROM AUTHOR]

Organic matter (OM) sequestration acts as a significant sink of the CO 2 in Earth's carbon cycle and is tightly associated with the climate and depositional environments. However, the dominant factors controlling OM burial in different depositional settings and the orbitally forced variations in the lacustrine OM accumulation remain poorly constrained. Here, we investigate the depositional environment of the Lucaogou Formation in southern Junggar Basin, northwestern China and further decipher the astronomically forced OM accumulation in different depositional environments. Sedimentological and cyclostratigraphic studies show that both shallow lake and semi-deep to deep lake deposits recorded significant Milankovitch signals among of which ∼405 kyr, ∼91 kyr, 34.5–37.4 kyr, and 17.3–22.8 kyr are interpreted to be long eccentricity, short eccentricity, obliquity, and precession cycles, respectively. A linkage among the lithofacies, natural gamma ray (NGR), and total organic carbon (TOC) content suggests that the depositional environment and OM accumulation were in pace with the hydrological cycle and lake-level changes, in response to the astronomically forced changes in the ice volume and monsoonal intensity. In the semi-deep to deep lake, TOC content tightly tracks the lithofacies and shows an in-phase relationship with NGR. However, this phase relationship has changed with sedimentary facies. The gypsiferous shale deposited in the restricted environment during lowstand intervals has higher TOC content than highstand dolomitic mudstone, demonstrating an anti-phase relationship with NGR data. Our study indicates that the OM sequestration is a dynamically cumulative process of supply and degradation. The different responses of the OM sequestration to the climate change in different environments suggest that detailed sedimentological studies are essential for the cyclostratigraphic analysis. • A deep-time example for the OM burial in the continental basins was provided. • OM accumulation was orbitally forced in the Lucaogou Formation. • Dynamics of insolation-induced OM accumulation changes with sedimentary environments. [ABSTRACT FROM AUTHOR]

Abstract: The first complete Early Turonian–Early Campanian lacustrine succession has been recovered from the SK-I south (SK-Is) borehole in the Songliao Basin (SLB), northeastern China. We conducted a detailed cyclostratigraphic study of natural gamma-ray (GR) log, thorium (Th) log, and magnetic susceptibility (MS) data from this core. Spectral analysis of the upper Quantou Formation (K2q3+4), Qingshankou Formation (K2qn), Yaojia Formation (K2y), and lower Nenjiang Formation (K2n1+2) reveals a hierarchy of meter- to decameter-scale cycling in the data. The wavelength ratios of the cycles in these stratigraphic units are ~20:5:2:1, corresponding with those of Milankovitch cycle periods of 405kyr (long eccentricity):100kyr (short eccentricity):37kyr (obliquity):20kyr (precession), indicating astronomical control on sedimentation. An astronomical time scale (ATS) was established by tuning interpreted 405kyr cycles to a 405kyr orbital eccentricity target curve, and to four SIMS U–Pb zircon radioisotope ages. This ‘absolute’ ATS provides precise numerical ages for stratigraphic boundaries, biozones, geological and geophysical events, and serves as a basis for correlation of strata and events between marine and terrestrial systems. The ages of the C33r/C34n geomagnetic polarity boundary in K2n2 and three short reversal events in K2y are estimated as 83.633Ma, 84.819–84.862Ma, 84.982–85.092Ma and 85.240–85.629Ma, respectively. Long-period amplitude modulations in the obliquity and eccentricity bands of the 405-kyr-tuned GR-Th series provide strong evidence that long-period orbital forcing influenced climate change and depositional processes in the SLB. The extracted amplitude modulations provide evidence that the orbits of Earth and Mars were not in secular resonance, and were undergoing chaotic interactions during this time, although the modulations do not match those of recent astronomical models. [Copyright &y& Elsevier]

Pliocene diachronism and mismatches between planktic foraminifera and nannofossil bioevents are clearly observed in the Mediterranean Sea. Hence, astronomical tuning combined with calcareous nannofossils and plankton foraminiferal biozones constitutes one of the important tools for regional correlation between different paleolatitudes. Consecutive and high-resolution well logs from the Sapphire-Dd borehole in the Mediterranean contributed a vital role in exploring the astronomically forced sedimentation in Pliocene strata. A detailed cyclostratigraphic analysis is applied to the natural gamma-ray spectrum logging data that is used as a paleoenvironmental and paleoclimatic proxy to construct a floating astronomical time scale (ATS) for the first time in Egypt. The results show that the hierarchy of sedimentary cycles with a ratio of ~20 : 5 : 2 : 1 in the Kafr EI Sheikh Formation can be interpreted as Milankovitch cycles of eccentricity, obliquity, and precession cycles, respectively. The ATS is established by tuning the Gamma Ray log to the target curves of the insolation of the La2004 solution based on the biozones time framework of the Sapphire-Dd core, which indicates the highest occurrence (HO) of calcareous nannofossils Sphenolithus verensis at 4.03 Ma, the HO of Triquetrorhabdulus rugosus at 5.24 Ma, the highest common occurrence at 4.093 Ma; and the lowest common occurrence of planktic foraminifera Globorotalia margaritae at 5.1 Ma, respectively. The new time scale yields more reliable age constraints on the evolution of paleoclimate and paleoenvironment in southeastern Mediterranean area since the Pliocene. • Astronomical tuning combined with calcareous nannofossils and plankton foraminiferal biozones. • Pliocene calcareous nannofossil and planktic foraminiferal biozones. • Diachronous in the stratigraphic positions of marine microfossils between different palaeolatitudes are noted. [ABSTRACT FROM AUTHOR]