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© 2020 Elsevier Ltd and INQUA Eurasian loess-paleosol sequences provide continuous records of global change in mid-latitude Northern Eurasia. The loess-paleosol sequence of West Siberia located in the central part of the mid-latitude Eurasian loess belt extending from West Europe to Yakutia is an outstanding paleoclimate archive in Northern Asia. The stratigraphy has been best documented on the left bank of the Ob River, in the so-called Ob Loess Plateau. This study focuses on the stratigraphy of the most complete Middle-Late Pleistocene loess-paleosol sequence at the Belovo section. The suggested high-resolution model of the Belovo Late Pleistocene stratigraphy is based on magnetic and sedimentological proxies and is correlated with other Eurasian loess records and with the global marine δ18O stratigraphy. The enviromagnetic signal at Belovo Loess-paleosol sequences shows a transitional pattern comparable with both typical Eurasian loess magnetic records. Detailed paleopedological interpretations of the magnetic and sedimentological data from the Belovo section have important implications for appropriate linking different Late Pleistocene climates and environments of other the well-known Eurasian loess provinces.

One of the most important occurrences of banded iron formation (BIF) worldwide is situated in the Carajas Mineral Province, southeastern Amazonian Craton. The BIFs are jaspilites and are hosted in the Neoarchean (∼2.74 Ga) volcano-sedimentary sequence of the Grao-Para Group. They are mostly composed of cm-thick intercalations of hematite, jasper, and chert. Their primary textures and structures are still preserved, which make them an ideal archive to evaluate the paleomarine environment. Low abundance of Al2O3 (

Multidisciplinary research suggests that Marine Isotope Stage 5 (~130–74 ka) was an important evolutionary stage in African deep history. Population expansion and growth spurred changes in material culture as well as the exploration of previously unoccupied regions and ecosystems. The archaeological sequence at Melikane Rockshelter (1860 masl) in the Maloti-Drakensberg Mountains of highland Lesotho, southern Africa, stretches from the late Holocene back to sub-stage 5a, ~80 ka. The site's earliest strata represent one of the earliest known examples of a sustained human presence in high mountain systems worldwide. This paper deals with the lithic assemblages from those levels, which are currently the oldest radiometrically dated archaeology in Lesotho and one of the few stratified assemblages of Last Interglacial age in the southern African interior. The results of a typo-technological analysis of the assemblages are presented. They suggest that the afromontane foragers who resided at Melikane employed both blade-focussed and bipolar flaking systems, curated a maintainable toolkit suited to frequent residential moves, and used a hybrid provisioning system adapted to their immediate environment. Comparisons with other late Last Interglacial assemblages across the subcontinent suggest that highland populations at this time were largely disconnected from their lowland counterparts. This implies that as Last Interglacial populations in southern Africa expanded into new environments, they also fragmented, adapting to local conditions rather than adhering to a universal technological system.

Objectives To investigate the arm–leg coordination from different perspectives of motor control during the underwater start sequence to understand whether differences exist between the three competitive breaststroke swimming events. Design Cross-sectional study. Methods Forty-one breaststroke races (with race times relative to the world record): 50-meter (n = 14, 87.6%), 100-meter (n = 14, 88.5%) and 200-meter (n = 13, 85.4%) were recorded. A race analysis system tracked the two-dimensional displacement of the head. Key points from the underwater start sequence were obtained from notational analysis in order to compute seven time-gaps and four phases to assess the arm–leg coordination and timing of the dolphin kick. A one-way ANOVA with Bonferroni post-hoc correction was used to assess differences between the time gaps and phases for the three events. Results Differences between the three events were found for total underwater glide, and the first (T0) and second (T1) major glide phase. No differences between the events were found in relative duration and distance for the time gaps related to arm–leg coordination (T1–3, T4, T6) and timing of the dolphin kick (T4–5) during the underwater start sequence. Conclusions The arm–leg coordination and timing of the dolphin kick showed no difference between the events, but the total underwater glide duration was longer in both the 100- and 200-meter compared with the 50-meter start. This shows that swimmers did not change the complex inter-limb coordination between the competitive events, but only modified the least complex movement, gliding, to adapt to the swimming speed of the respective events.

The Yinchuan Basin, one of the most important basins in the area adjacent to the northeastern Tibetan Plateau, contains a continuous sequence of fluvio-lacustrine deposits, which makes it an ideal area to study the interactions between the Tibetan Plateau uplift, climate change, and geomorphological evolution. Here, a 1200-m-deep drill core (YNZK01) is described with an average recovery rate of 96% in the depo-center of the Yinchuan Basin to establish a high-resolution palaeoenvironmental and tectonic reconstruction. Stepwise alternating-field demagnetization results showed a stable and high-qualified remanent magnetization of the samples. The polarity sequences consisted of 8 normal and 8 reverse zones that correlate well with the geomagnetic polarity timescale. Magnetostratigraphic results date the entire YNZK01 core from 3.927 Ma to the present. The B/M boundary (0.781 Ma) is at a depth of 246.4 m while the M/G boundary (2.581 Ma) is at a depth of 863.4 m. The G/Gi boundary (3.596 Ma) is identified at 1117.8 m and the bottom of the core was extrapolated to 3.927 Ma (1201 m) with an average sedimentation rate of 863.4–1117.8 m. This high-resolution magnetostratigraphy record provides a baseline chronological framework for further research and publications on the tectonic, paleoclimatic, and paleoenvironmental proxy data of the YNZK01 core in the Yinchuan Basin, NE Tibetan Plateau.

An integrated interpretation of processed 3D seismic data, a suite of well logs, biostratigraphic data and core photographs of AMO Field, deep offshore Niger Delta is carried out for the sequence stratigraphic analysis of strata penetrated by wells. Lithologic and key stratigraphic surfaces, that is the maximum flooding surfaces (MFSs) and sequence boundaries (SBs), are identified based on bioevents and log motifs. Biostratigraphic data help the delineation of MFSs and SBs, as well as dating, determination of depositional environment and paleobathymetry. The sequence stratigraphic study reveals seven MFSs (of 13.0 Ma, 11.0 Ma, 9.5 Ma, 7.4 Ma, 5.8 Ma, 5.0 Ma and 2.7 Ma) and six SBs (of 12.1 Ma, 10.3 Ma, 8.5 Ma, 6.3 Ma, 5.5 Ma and 4.2 Ma). The key stratigraphic surfaces identified involve three depositional sequences characterized by lowstand, transgressive and highstand system tracts respectively. The studied section is deposited in a deepwater environment ranging from Lower to Upper Bathyal and can be dated back to the Middle Miocene - Middle Pliocene in age. Seven faults and two horizons (corresponding to reservoir units) are identified and mapped across the seismic data volume to establish a continuity of the reservoir to areas lacking well control. The established sequence stratigraphic framework displays successions of sediments (system tracts) where the reservoir sand units of the lowstand and highstand system tracts are of hydrocarbon prospective units in the field.

A sub-bottom acoustic profile survey encountered a mass transport deposit (MTD) bed, 5–7 m thick, interbedded within glaciolacustrine deposits of glacial Lake Ojibway at Frederick House Lake, Ontario, Canada. Analysis of the thickness patterns of rhythmic couplets in recovered core samples revealed that the Connaught sequence, the youngest of the Timiskaming varve series, immediately underlie and overlie the MTD. Comparison to regional published varve series reveals two possible interpretations for the varve numbering: varve (v) 2066 to v2115, which requires the inference of a 55 varve year (vyr) disconformity just below the Connaught sequence, while the alternative numbering, v2011a to v2060a (a = alternative), extends continuously from older varves. Circumstantial evidence supporting the alternative numbering is as follows: (i) the uncertainty of applying a common 55 vyr disconformity to three varve series located up to 23 km apart and which otherwise exhibit closely matching thickness plots; (ii) the lack of evidence of an erosive unconformity in the sub-bottom acoustic profiles from Frederick House Lake; and (iii) the uncertain varve count within a key part of the Matagami series, located about 300 km away and from which the 55 vyr disconformity is extrapolated. At Frederick House Lake, the alternative numbering indicates that the maximum position of the Cochrane ice advance and the Connaught varves may be, in effect, contemporary in age. More broadly, the alternative numbering indicates that the youngest known varve that formed before the terminal drainage of glacial Lake Ojibway is v2074a rather than v2129 in the original numbering.

For seismic stratigraphy, a key issue is distinguishing the characteristics of seismic reflections generated by geologic events with different scales, which in turn assists in sequence stratigraphic interpretation. Data-driven signal decomposition approaches, such as variational-mode decomposition (VMD) and multichannel VMD (MVMD), can use waveform similarity to decompose seismic data into several intrinsic mode functions (IMFs). Unfortunately, it is a hard task to define the number of IMFs. To overcome the shortcoming of previous works, we have constructed an enhanced MVMD and then developed a workflow to decompose seismic data. We first determined the relationship between the IMFs and structures with different scales. Then, we developed a method to set the number of IMFs using contraction operator mapping and scale-space representation. Finally, we developed a workflow and applied it to synthetic and field data to identify seismic sequence stratigraphy boundaries. Synthetic and field data examples indicate that our workflow preserves lateral continuity and precisely extracts IMFs caused by depositional sequences with different geologic scales, facilitating the interpretation of subtle depositional patterns.

Abundant hybrid sediments composed of clastic rocks and carbonate rocks were deposited in the Devonian Yangmaba Formation in the northwestern of Sichuan Basin. Based on the measurement of the Ganxi section in detail, combined with the observation of the 30 slices, the hybrid facies, and hybrid sequence, the hybrid deposit mechanism and its controlling factors of the Yangmaba Formation were analyzed. It shows that the hybrid facies consists of the hybrid shore at the lower and clastic hybrid shelf and carbonate hybrid shelf deposits at the middle-upper of the Yangmaba Formation. The hybrid sequence, which can be divided into four sedimentary system tracts: the shelf-margin systems tract (SMST), the transgressive system tract (TST), the early highstand systems tract (EHST), and the late highstand systems tract (LHST), was developed in the Yangmaba Formation. There are three hybrid mechanisms including punctuated mixing, facies mixing, and in situ mixing, and the first two are the main types in the Yangmaba Formation. The punctuated mixing and in situ mixing are the main hybrid mechanisms of hybrid shore and clastic hybrid shelf deposits, and the facies mixing is the main hybrid mechanism of clastic hybrid shelf and carbonate hybrid shelf deposits. The hybrid mechanisms are different among the system tracts: the punctuated mixing is the main mixing manner in the SMST and LHST and the facies mixing developed in the TST and EHST. Storm action is the most important controlling factor of punctuated mixing of the Yangmaba Formation. Relative sea level change, carbonate productivity or the rate of terrestrial clastic supply, and climate change are factors that control and affect hybrid deposits. SMST and HST are mainly related to changes in the relative sea level, while TST is controlled by sedimentary source recharge, and climate change affects the hybrid action of system tracts to varying degrees.

In this study, our attempt is to integrate sedimentological and petrophysical data for reservoir evaluation in the sequence stratigraphic framework. Petrographic analysis of the Late Jurassic–Early Cretaceous Fahliyan Formation reservoirs of two oilfields in the northwest of the Persian Gulf led to recognition of twelve microfacies. They can be classified into four facies associations, including open marine, shoal, lagoon and tidal flat, which are deposited in a homoclinal ramp carbonate. Sequence stratigraphy of the studied successions led to the recognition of three third-order depositional sequences based on vertical changes in microfacies and gamma ray analysis. Except for the upper boundary of the third sequence, the other sequence boundaries are type I (SBT.1). Dissolution is the most important diagenetic feature that affected the lower depositional sequence which is caused by the development of subaerial exposure after the deposition of the Fahliyan Formation, whereas cementation is the main diagenetic feature affecting the second- and third depositional sequences, causing their lower reservoir quality. In order to identify the flow units, the flow zone index methods, porosity throat radius (R35) and modified Lorenz based on stratigraphy were applied. The key wells studied in this area have shown good correlation throughout the studied oilfields which may potentially be used for hydrocarbon exploration and field development in the Late Jurassic–Early Cretaceous deposits of the Persian Gulf. This study integrates geological and petrophysical data (rock typing) toward sequence stratigraphic framework.

The Crocker Formation, Late Eocene to Middle Miocene in age, was deposited in a deep-marine environment by a turbidity current. Most of the facies identified in the field are related to the sedimentary bed-form structures belonging to Bouma sequences. These prominently include unit divisions such as Ta referring to grading sand, Tb for parallel laminae, Tc for cross laminae, Td for mud laminae, and Te referring to hemipelagic mud. Five facies have adequately been identified using Bouma sequence implications, namely Facies 1 (F1: Ta-Tb layers), Facies 2 (F2: Ta-Te layers), Facies 3 (F3: Tb-Te layers), Facies 4 (F4: Tb / Tc-Te layers), and Facies 5 (F5: Td-Te layers). Based on the Crocker Formation facies analysis, three distinct groups of facies associations were recognised: Deep-Marine Channel-Lobe Association (Type A1), Deep-Marine Channel-Levee Association (Type A2), and Distal Lobe Association. These facies associations precisely revealed that the Crocker Formation's depositional environments were likely deposited in the middle-fan with associated outer-fan settings.

From 1985–2014, the Leon Levy Expedition to Ashkelon excavated a trench on the north side of Ashkelon’s central mound (Grid 38) exposing a Bronze and Iron Age sequence over an area of some 450 m2. ...

Palynofacies is based on the different types of the dispersed/sedimentary organic matter (DOM/SOM) and has been used as a proficient proxy for the palaeoclimatic reconstructions in sedimentary deposits of various time spans. It has also been acknowledged as an effective tool in the different domains like sequence biostratigraphy, palyno-biostratigraphy, palaeodepositional history, identification for depositional processes, oxic–anoxic environment, and variations in the water depth. It has been emerged as an analytical tool in palaeoclimatic reconstruction, which could complement geophysical and geochemical datasets. Since long palynofacies analysis has been exclusively applied in the marine sediments, it has recently dragged the attention of many researchers as a significant parameter for palaeoclimatic interpretation in continental deposits. In the last few decades, more consideration was focused on palynofacies that have become an essential proxy in the biostratigraphic and other non-biostratigraphic fields due to its requirement in the petroleum industries. The present study provides a basic idea of dispersed organic matter characterization, methodology, interpretations, and its application with special emphasis on the Gondwana deposits. The study also includes the summary of the worldwide distribution of the Gondwana sediments, especially for palaeodepositional settings through palynofacies along with other parameters.

In the article according to the geological and geophysical data of the well-exposed areas of development of Archean rocks of the Ukrainian Shield, two alternative approaches to establishing the structure and stratigraphy of the oldest granulite complexes are discuss. The outcrops of the enderbite-gneiss complex up to 3.6—3.8 billion years old are located along the Southern Bug River between the Gaivoron town and the Zavallia village. The first, «stratigenic-metamorphogenic» approach assumes that the main features of the composition and structure of the Lower Archean complexes are inherited from the original stratotypic strata. These strata are transformed in the conditions of quasi-isochemical metamorphism with preservation of the sequence of formation in section and the primary constitution in the form of stratification, rhythmicity, direction of change of their composition vertically and laterally. On the structural-formation map and geological section of the Gaivoron—Zavallia section, the Archean granulite complex is shown in the form of a synclinorium composed of four adjacent formations, which are equated to the world of metamorphosed volcanic-sedimentary rocks. The second, «deformation-metamorphogenic» approach, which is supported by the authors of this article, is based on the idea that the granulite complex of Pobuzhzhіa is a subvertically layered medium formed by tangential tectonic forces. The latter lead to shear deformations and displacement of matter at the atomic-molecular (with mineral transformation of rocks) and rock masses at the regional level. This creates structural and textural elements that are superimposed on the primary structure of rocks and often erase it. Field structural-tectonophysical, tectonofacial and magnetometric studies, its results are presented in the article. It was performed specifically to compare these two concepts. Magnetometric studies have shown that the enderbite-gneiss complex of the district by its magnetic characteristics belongs to the middle and lower crust of the Ukrainian Shield.

—The paper concerns the sediment sequence, which is widespread in the Yenisei valley and in the Tuva and Minusa depressions and also present in the valleys of the southern Chulym plain. The sediments of this sequence were previously described as “Neogene mud-shedding”, as well as moraines, alluvial fan deposits, alluvium of Middle Pleistocene high terraces, and lacustrine sediments. The giant ripple marks on the Upper Yenisei terraces was commonly interpreted as ribbed moraines; however, in recent studies, these ridges have been repeatedly referred to as marks of giant current ripples. Besides, some recently published papers provide description of geology of this sequence fragments suggesting its deposition by cataclysmic floods. Geomorphological analysis of the area shows Pleistocene glaciers to have been localized within the medium–high mountainous areas. The glaciers did not reach the Tuva and Minusa depressions and occupied large areas only in the Todzha basin and on the periphery of the Darkhat basin, forming a glacial dam at its outlet, which resulted in glacial-dammed lakes filling the basin completely. These lakes outburst, and the resultant flooding led to the deposition of megaflood sediments, which we refer to here as the Upper Yenisei sediment sequence. A detailed analysis of its facies architecture revealed similarity of these sediments to those of the Sal’dzhar and Inya sequences in Gorny Altai. Most of the Upper Yenisei megaflood sediments are localized in topographic lows of the Tuva and Minusa depressions. Beyond the Altai–Sayan mountainous area, the megaflood sediments of the Upper Yenisei sequence compose high terraces of the Yenisei, Chulym, Chet’, and Kiya rivers in the southern Chulym plain. The formation of Upper Yenisei sequence dates to the first half of the Late Pleistocene, inasmuch as it contains inset alluvial sediments of the second terrace of the Yenisei River. The available data allow suggesting that the Upper Yenisei sequence formed in the first Late Pleistocene regional glaciation. The Sal’dzhar sequence in Gorny Altai and the fourth terrace of the Ob’ River on the Fore-Altai plain are stratigraphic analogs of the Upper Yenisei sequence. The Upper Yenisei and Sal’dzhar sequences can thus be considered future regional markers serving as a link for the local stratigraphic schemes of the Altai–Sayan mountainous area and adjacent West Siberian plains. The results obtained call for verification by geochronological dating, first of all, by modern luminescence dating methods covering a wider chronological interval than radiocarbon dating.

From 1980s, electromagnetic prospecting is an integral component of geophysical techniques for oil and gas exploration in many regions of the Russian Federation. Electromagnetic methods are used at all stages of geological exploration, including reconnaissance, discovery, prospecting and appraisal, and economic mining. In oil and gas exploration, the most commonly used technique is the near-field transient electromagnetic sounding (TEM). On the other hand, for each of these stages, specific tasks of electromagnetic prospecting have not been clearly defined yet. Furthermore, there are no standard requirements to the volume of a priori geological and geophysical information, which is sufficient for solving a geological problem. If such information is lacking or insufficient, a geological problem may be incorrectly stated and/or improperly correlated with the current stage of works. Our study aims to define which geological problems should be addressed by electromagnetic survey at the different stages of geological exploration, and to specify the requirements to the availability of a priori geological and geophysical information. We have analyzed the electromagnetic data from the regions of East and West Siberia, which have different geological settings. The main geological problems that can be solved by the seismic and electromagnetic techniques are determined. We propose a set of geophysical survey operations, which is optimal for oil and gas exploration. An effective sequence of electromagnetic prospecting stages is determined, and preliminary and accompanying surveys are specified. The requirements to the availability of a priori information are proposed, and its volume is defined. Geological problems are defined with respect to the corresponding stages of geological exploration. Special attention is given to approaches to the mineral resource estimation and calculation of hydrocarbon reserves, taking into account electromagnetic survey results. It is proposed to use the electromagnetic data at the stage of prospecting and appraisal, which aims to assess the resources of categories D l and D 0 , as well as at the exploration stage for estimating the reserves of category C 2 in new and explored fields. Approaches to the economic assessment of using electromagnetic surveys as part of the geological exploration are discussed. Our study shows that a correct sequence of electromagnetic prospecting operations at each stage can ensure obtaining an original geological dataset of the given stage and thus providing a proper basis for the next stage of oil-gas field investigation.

Authigenic albites occur widely in clastic reservoirs with important implications for diagenesis and reservoir formation. The middle Permian Lucaogou Formation in the Jimusaer Sag (Junggar Basin, NW China), where major exploration breakthroughs in shale oil have been achieved, reveals a new phenomenon that authigenic albites are abundant in unique mixed carbonate–volcanic–clastic sequences. This has not been reported in the literatures. To fill the knowledge gap, the origin of these authigenic albites and their relationship with dissolution pores (i.e. diagenesis implications) were investigated. Results show that two types (I and II) of authigenic albite were identified within the shale oil reservoirs. Euhedral Type I authigenic albites with 3–10 μm only occur in dolarenite intraclasts and are symbiotic with amorphous dolomite minerals with a pure chemical composition of >99% albite-end-member content. Larger Type II authigenic albites with 10–50 μm are widely distributed in reservoirs, primarily in dissolution pores, and coexist with authigenic dolomite minerals or dolomite overgrowths. Their chemical composition is less pure with anorthite-end-member contents that range from undetectable to 9.77%, with an average of 1.34%. A symbiotic relationship, pure chemical composition, size, and euhedral morphology indicate that Type I authigenic albites precipitated during syngenetic hydrothermal action. However, the morphology of dissolution pores, residual symbiotic “orthoclase”, impure chemical composition and carbon–oxygen isotope indicate that Type II were the products of the dissolution and reprecipitation of “perthite” crystal pyroclasts influenced by acid organic fluids in latter diagenesis. The differential dissolution of “orthoclase” and “albite” components in “perthite” crystal pyroclasts formed enormous intergranular secondary pores in the presence of dolomite minerals in the shale oil reservoirs.

Morlet wavelet analysis is a method of studying the periodic spectrum of non-stationary physical signals and is applied to the Himalayan Tectonic Belt to explore whether there is any seismic periodicity, and to explore the possibility of harmony or commonality of properties among the seismic activities of different zones. The earthquake sequence during 1951–2016 with magnitudes M ≥ 6.0 is analysed. Wavelet non-periodicity for the Centre zone suggests a non-uniform spatial–temporal distribution of earthquake movement between plates which may relate with the rare great earthquakes, while the periodicities for the west and east zones may suggest the concurrence with the adjustment of the tectonic movement of the east- and west-end regions of the Himalayan Tectonic Belt relative to its central core. These three zones collectively form the Himalayan Tectonic Belt. This contains a periodicity of about five years of seismic activity that tests successfully with a 95% confidence statistic. Borrowing from the concept of musical harmony, this is the significant seismic harmonic which reflects the Belt’s pervasive tectonic stress and an overall harmony of continent–continent plate convergence. Morlet wavelet analysis also reveals the Himalayan Tectonic Belt and the Pamir–Hindu Kush Tectonic Zone to be engaged as a big new family: the Himalayan Tectonic Belt Plus. It is demonstrated that this new whole also has seismic harmony with the common property again being the 5-year periodicity. This indicates a unified structure of pervading active stress and seismic harmony permeating the overall seismicity.

An integrated approach using a three-dimensional (3-D) seismic survey over the Chevron-operated Bibiyana field in Bangladesh along with petrophysical well data and cores provides new insights into the stratigraphic development of the Miocene–early Pliocene Ganges Delta. From this, a sequence stratigraphic model was constructed for the Bibiyana field that more accurately depicts the internal architecture of the reservoir units of the field. As of 2019, Bibiyana field was producing approximately 1.3 billion SCF/day of gas and accounted for more than 45% of Bangladesh’s daily gas supply. The 3-D seismic volumes covering the field area were stratigraphically flattened using multihorizon seismic flattening techniques. The well-log data were also flattened to enable the wells to be tied and visualized within the flattened domain. Core data from the field were examined, interpreted, and integrated into the stratigraphic model. Reservoirs at Bibiyana are divided into a series of sequence stratigraphic units, each recognized by a seismically defined sequence boundary at both the base and the top of the units. Two types of major reservoir sandstones were observed: (1) erosional remnants of shallow-marine, tidal sandstones below sequence boundaries and (2) channel sandstones at the base of incised canyons above sequence boundaries. The focus of this investigation was on the architecture of the main reservoir known as the BB60 series (Miocene Bokabil Formation), containing approximately 50% of the field reserves. The BB60 series reservoir is an erosional remnant below a major sequence boundary (SB60) sealed by the thick canyon-fill prodelta shale of the BB55 interval. Channelized sandstones and associated mass transport deposits are present locally at the base of the canyon and have reservoir properties that contrast with the underlying and adjacent shallow-water, tidal-dominated deltaic sandstones of the BB60 reservoir. Multihorizon flattening of the seismic and well data in concert with 3-D visualization reveals the complexly eroded canyon system, incised into the underlying tidal deltaic deposits of the BB60 series. Similar erosional patterns are present in the underlying BH series reservoirs (Miocene Bhuban Formation), and the conceptual model developed for the BB60 reservoir can be applied and aide the understanding of the deeper reservoirs that are less well imaged by the existing seismic data. The recognition that unconformities with overlying canyon-fill shales seal many of the reservoirs at Bibiyana is critical in understanding and modeling the reservoir architecture and performance over time.

The results of stratigraphic studies carried out in the process of international deep-sea drilling in the last fifty years are presented. They make a great contribution to development and improvement of the methods for detailed stratigraphic studies and dating of marine sedimentary sequences as well as reconstructions of past oceanological and climatic events. The results obtained are of great methodological importance for stratigraphic investigations of the whole Phanerozoic. The distinguished Cenozoic biostratigraphic zones can really be traced across the whole tropical and subtropical area. The study data on planktonic microorganism (calcareous and siliceous) assemblages which were an integral part of Mesozoic and Cenozoic marine ecosystems made a considerable contribution to these works. These assemblages developed over time against the background of variable oceanic circulation and sedimentation conditions, changes in deep and surface water productivity, water temperature, etc. In general, the evolution trend of biotic communities reflects the development and reorganization stages of the past ecosystems. All these data make it possible to reveal the real sequence of not only biotic but also abiotic events (climatic, oceanographic, and eustatic) in the World Ocean for the last 70–75 million years.

The estimation of seismic reservoir properties faces difficulties such as delineating deceptive fluid contacts, over-estimating reserves and drilling dry holes. To overcome these problems, sequence stratigraphic and rock physics analyses that were constrained by the compaction trend were implemented in the Sigma Field. Sigma field is located in the Coastal Swamp depobelt, in the distal part. Seismic data from the field and a total of three wells, Sigma-30, 26, and 25 were provided for the analyses. Biostratigraphic data was also given for the field and dated to shale marker Cassidulina-7. The stratigraphic sequence analysis of the wells in field indicate they were deposited in a regressive, transgressive and aggradational episodes, whereas the entire depositional history shows predominantly regressive episode. Three field reservoirs, SM-14 (LST), SM-04 (TST), and SM-02 (HST) were delineated. Depositional analysis of the landscape from sequence stratigraphic analyses of the field indicates that Sigma field reservoirs were deposited in a front region of the delta. Trend to compaction has been generated for the well. Sigma wells showed a normal trend toward compaction. Rock physics analysis of the reservoirs of interest reveals that LST and TST reservoirs have been difficult to distinguish against HST reservoirs which are easy to classify regardless of their depth for fluids in a Vp/Vs crossplot versus acoustic impedance. In the analysis, a pattern is suggested for TST reservoirs. Therefore, this research work shows that fluid discrimination becomes simpler as we go basin ward as the sorting of the reservoir rocks increases with finer grain sand sizes.

Elucidating the cultural transition of the Middle and Upper Palaeolithic in northern China (Northeast and North China) is extremely important in considering the emergence and diffusion of Anatomically Modern Humans in East Asia. This article discusses 25 assemblages from 11 sites before and after ca. 42–40 cal ka in northern China. Each assemblage was given the techno-cultural category of “industry” (Industries D, DQ, DP, DL, PF, B, TB, UP, M, MO) based on the scheme of PaleoAsia modes. The PaleoAsia modes are an expanded version of J. J. Shea's modes, which describe and categorize flaking and lithic tool-production technologies. Following the chronological dating of assemblages, this study proposes that an industrial transition took place from the Middle Palaeolithic (MP) to Upper Palaeolithic (UP) in northern China. Characteristic technical elements were noted for each assemblage, including the Levallois technique, polished bone tool, personal ornament, blade technique, and UP tools. The following four stages were established for the abovementioned industrial transition in northern China: MP (before 41.5–40.0 cal ka), IUP (41.5–40.0 cal ka), EUP (40.0–28.0 cal ka), and MUP/LUP (after 28.0–27.0 cal ka). With the Exception of the last stage, which is associated with a microblade industry, the main industry of each stage was affiliated with denticulate tools. As such, there was no discontinuity in the technological traditions found between these stages in northern China. Rather, industries continuously and gradually shifted from the MP to UP; that is, UP techno-elements were incrementally introduced. To understand the drivers behind this industrial transition, it is first necessary to verify whether anatomically modern humans migrated to northern China during the MP and if they then maintained the group of denticulate tool industries until the UP.

The first direct Pb–Pb dating of carbonate rocks of the Kamo Group has been carried out. The Pb–Pb age of carbonates of the lower units (the Madra, Jurubchen, Kuyumba, and Vingold formations) of this sedimentary sequence is 1510 ± 50 Ma, while the age of the upper unit (the Iremeken Formation) is 1490 ± 50 Ma. The ages obtained show that all the carbonate formations of the Kamo Group are Lower Riphean (Early Mesoproterozoic), and their deposition continued for a period of no longer than several tens of millions of years. The new geochronological data allow us to correlate the Riphean deposits of the Baikit Anteclise with the rocks of the Riphean cover of the Anabar Uplift.

Research subject. The article considers the Famennian‑Tournaisian sequence of the South-Eastern part of the Tchernyshev Uplift (North Cis-Uralian). The sequence corresponds to the Izyayu Formation.Materials and methods. The article is focused on the clarification of the stratigraphy, composition and depositional environment of this formation. Research data about the Izyayu Formation in the type area (Izyayu River) were used. The stratigraphic framework of this study included data on conodonts, foraminifers and carbonate carbon isotopic shifts.Results. In the type area under study, the Izyayu Formation corresponds to the interval from the upper part of the Famennian (upper part of the Palmatolepis marginifera utahensis conodont Zone) up to the middle part of the Tournaisian (Lower crenulata conodont Zone). The formation is 100– 120 m thick. The Izyayu Formation grades to the upper part of the deep-water Syvyu Formation in the east, and to the shallow-water Kamenka Formation and the lower part of the Ydzhid Formation. The areal of the Izyayu Formation comprises the South-Eastern part of the Tchernyshev Uplift. The Formation was deposited in the environment of a gentle prograding slope of a carbonate platform.Conclusions. The Izyayu Formation in the type area is composed of thin clayey-carbonate graded cycles. It covers the stratigraphic interval from the Zelenets Regional Stage through the Tcherepet Regional Stage. This formation is easily distinguishable by lithological features in outcrops and borehole cores.

Coseismic surface fault displacement presents a serious potential hazard for structures and for lifeline infrastructure. Distributed lifeline infrastructure tends to cover large distances and may cross faults in multiple locations, especially in active tectonic regions like California. However, fault displacement measurements for engineering applications are quite sparse, rendering the development of predictive models extremely difficult and fraught with large uncertainties. Detailed fault surface rupture mapping products exist for a few documented cases, but they may not capture the full width of ground deformations that are likely to impact distributed infrastructure. The 2019 Ridgecrest earthquake sequence presented an ideal opportunity to collect data and evaluate the ability of different techniques to capture coseismic deformations on and near the fault ruptures. Both the M 6.5 and 7.1 events ruptured the surface in sparsely populated desert areas where little vegetation is present to obscure surficial features. Two study areas (~400 m × 500 m each) around the surface ruptures from the two events were selected. Teams of researchers were deployed and coordinated to gather data in three ways: field measurements and photographs, imagery from small uninhabited aerial systems, and imagery from airborne light detection and ranging. Each of these techniques requires different amounts of resources in terms of cost, labor, and time associated with the data collection, processing, and interpretation efforts. This article presents the data collection methods used for the two study areas, and qualitative and quantitative comparisons of the results interpretations. While all three techniques capture the key features that are important for displacement design of distributed infrastructure, the use of remote sensing methods in combination with field measurements presents an advantage over the use of any single technique.

Despite long-standing recognition of high-amplitude, high-frequency sea-level variation resulting from repeated glaciations of Gondwanaland, recorded as “cyclothems” in late Paleozoic strata worldwide, major questions remain concerning their precise timing and expression in the stratigraphic record. A deep meandering canyon in southern Utah cut by the San Juan River exposes cyclic Pennsylvanian (Moscovian) carbonate strata of the Paradox Formation of the Hermosa Group in three dimensions. These peritidally to subtidally deposited strata archive a long record of Pennsylvanian sea-level change that was important to the early development of sequence stratigraphy. Their interpretation with respect to sea level is complicated by lateral variations in sequence thickness and a lack, until recently, of precise geochronologic control. In this study, we use Structure from Motion photogrammetry (SfM) to quantify lateral stratigraphic variation in three dimensions (3D) in the inner gorge of the canyon, then integrate these data with published U-Pb geochronology and conodont biostratigraphy to assess magnitude and temporal significance of depositional cyclicity. 3D SfM models were used to precisely measure the thickness of sixteen depositional sequences in the Barker Creek and Akah intervals, which constitute the lower Paradox Formation. Bioherms ranging from 2–18 m in relief occur within five sequences, and are typically constructed by either microbialites, the sponge Chaetetes, or a mixture of both. On average, bioherms containing Chaetetes are steeper and thicker than those without them. Bioherm-generated bathymetric highs can influence overlying strata in several characteristic ways: 1) by serving as a nucleation site for bioherms in overlying sequences, 2) sequences often onlap bioherms, leading to local stratal truncations, and in some cases, 3) progradational geometries extend laterally outward from preexisting highs in underlying units. Sequence thickness can vary laterally by up to four times in areas with no obvious bioherms; sequences tend to be thickest in the vicinity of bioherms. To better understand the potential orbital significance and correlation of Paradox Formation cyclicity to an increasingly precise global record, we projected photogrammetry-generated average sequence thicknesses onto an age framework using conodont and fusulinid biostratigraphy and CA-TIMS U-Pb zircon ages for correlative strata in Eastern Europe. To mitigate the influence of local variability of accumulation rate, SfM-based average sequence thicknesses in the study area were used to construct a relative-sea-level history that can be compared to global records. While regional averaging cannot correct for the unknown durations of sequence-bounding unconformities, underfilled accommodation, or autocyclicity due to shoal migration, it does provide a more quantitative means to consider timescales of deposition and mechanisms responsible for cyclicity than is possible with a one-dimensional section or core. Paradox Formation cyclicity shares a broad similarity with the global record, suggesting coherent glacio-eustatic sea-level variation across several different tectonic regimes. If one explores a thickness to duration relationship in these sequences, it is plausible that eight thin (2–4 m) sequences in the investigated strata (S2.6–11; S3.5–6) have apparent durations ranging from 100 to 350 kyr, within the plausible range of short and long eccentricity. In contrast, four thicker (6–12 m) sequences in the middle Akah interval (S3.1–S3.4) contain deeper-water lithofacies and have apparent durations ranging from 500 to 1000 kyr, implying that they may be down-dip composites of multiple documented cyclothems in the North American Midcontinent, Urals–Donets, and South China Block successions.

Dense seismic networks provide the opportunity to better understand seismogenic processes in tectonically active regions. The Algerian Digital Seismic Network was strengthened following the 10 October 1980 Ms 7.3 El Asnam and 21 May 2003 Mw 6.8 Bournerdes earthquakes, such that the source parameters of small- to moderate-magnitude earthquakes in northern Algeria can now be computed. Here we examine the 2007 seismic sequence recorded in the Medea region (north-central part of Algeria). We calculate the seismic sources of three moderate events that occurred between May and August 2007 using near-field waveform modeling, and obtain moment magnitudes of 4.4, 4.1, and 4.6, with fault planes oriented N63°E, N15°E, and N219°E, respectively. We use displacement spectra to estimate the corner frequency fc and spectral flat level then use these to recalculate the seismic moment and moment magnitude. The stress tensor obtained by inverting 13 focal mechanisms from events near the 2007 sequence exhibits a well-constrained compressional axis with a subhorizontal N335°E-trending σ1 axis (plunge 7°). We calculate the static stress changes to understand the connections between these three events. The results indicate an interaction between the faults related to these events during the earthquake sequence. We conclude that these events likely occurred on the unstudied extensions of mapped faults, and that the epicentral area therefore has moderate seismogenic potential.

The tempo and mode of Homo sapiens dispersal in Eurasia and the demise of Neanderthals has sparked debate about the dynamics of Neanderthal extinction and its relationship to the arrival of H. sapiens. In Italy, the so-called ‘Transition’ from Neanderthals to H. sapiens is related to the Uluzzian technocomplex, i.e. the first archaeological evidence for modern human dispersal on the European continent. This paper illustrates the new chronology and stratigraphy of Uluzzo C, a rock shelter and Uluzzian key site located in the Uluzzo Bay in southern Italy, where excavations are ongoing, refining the cultural sequence known from previous excavations. Microstratigraphic investigation suggests that most of the deposit formed after dismantling of the vault of the rock shelter and due to wind input of loess deflated by the continental shelf. The occasional reactivation of the hydrology of the local karst system under more humid conditions further contributed to the formation of specific layers accumulating former Terra Rossa-type soil fragments. Superposed on sedimentary processes, strong bioturbation and the mobilization and recrystallization of calcite have been detected. Optically stimulated luminescence (OSL) ages from Uluzzo C Rock Shelter are congruent with previously published radiocarbon ages obtained on shell beads and tephrachronology from adjacent sites preserving the Uluzzian technocomplex such as Grotta del Cavallo, confirming the onset for the Uluzzian in the area to ca. 39.2–42.0 ka. The OSL chronology from Uluzzo C also provides a terminus post quem for the end of the Mousterian in the region, constraining the disappearance of the Neanderthals in that part of Italy to ≥46 ± 4 ka.

The Chavanon metamorphic sequence in the Variscan French Massif Central contains marble lenses that have been exploited since at least the 18th century to produce lime. They provided an opportunity to some major pioneers among nineteenth century French geologists to understand how metamorphic rocks are formed. The intimate association between marbles and gneisses led them to propose that the initial pile of rocks was deposited as a single unit under water. They thoroughly described the attitude, folding and mineralogy of the marbles, making their works of great historical value. Originally written in French, their translation into English and the reproduction of original figures from the works they published will be very useful to the international community of geologists interested in the history of their science.

The article is devoted to paleogeothermal and paleotectonic reconstructions based on the results of processing the vitrinite reflectance data array of coal organic matter of the Upper Paleozoic sediments from the Don-Dnieper Downwarp (within the Dnieper-Donets Depression and adjacent areas of Donbass). It was found that paleogeothermal parameters changed under the influence of geotectonic, magmatic and lithofacies formation conditions of the Upper Paleozoic deposits. Analysis of changes and regularities distribution of paleogeothermal characteristics made it possible to assess the evolution of the thermal field, changes in the tectonic movements character, to identify the role of volcanism, deep faults geodynamics, lithosphere thickness in the thermal history of the region under study. It is shown that with the help of paleostructural analysis, based on data on the thermal maturity degree of coal organic matter, it is possible to judge the activity changes of tectonic structures in time, the formation sequence, to establish the amplitudes of their mutual displacement and rank according to oil and gas potential. Based on the results of the work, maps of the paleogeothermal gradients distribution and the amplitudes of rock masses vertical displacements were constructed. The presented maps should be considered as a universal information material that can be used to determine the features of the regional distribution of the above parameters, as well as become an important tool in the study of tectonic and thermal history, identification changes trends and distribution patterns of paleo­geothermal characteristics.

Late Visean foraminiferal assemblages from a section in the Sikasya (Sikaza) River Valley (South Urals) are studied to provide a reliable framework for stratigraphy and correlation of the Visean-Serpukhovian boundary beds on the western slope of the South Urals. The middle–upper Visean deposits on the Sikasya River are composed of shallow shelf carbonates with abundant foraminifers, corals, and brachiopods, and are represented by four regional substages: Tulian, Aleksinian, Mikhailovian, and Venevian. This section is known as the “Sikaza Section”. The upper Visean deposits are overlain by Serpukhovian beds composed mainly of dolomites. The Tulian and Aleksinian successions consist of bioclastic and foraminiferal wackestone and packstone. In the Mikhailovian, there are packages of dolomites with interbeds of bioclastic grainstone to packstone, containing foraminifers. The Venevian is represented by bioclastic and foraminiferal grainstone and packstone. The following foraminiferal units are discussed: in the middle Visean: (1) Paraarchaediscus koktjubensis–Endothyranopsis compressa; in the upper Visean: (2) Ikensieformis proikensis–Archaediscus gigas, (3) beds with Vissarionovella (corresponding to the Ikensieformis ikensis Zone), and (4) Ikensieformis tenebrosa; the Serpukhovian is represented by (5) beds with Eostaffellina decurta.

Biozonation and sequence stratigraphic characterization of sediments in X-well, JV-Field Greater Ugheli Depo belt Niger Delta Basin were carried out using a total of One hundred and ninety (190) Ditch cutting samples, with the aim of identifying palynological and foraminiferal bio-events such as abundance, zones, paleoenvironment, age and also identify sequence stratigraphic key surfaces such as Maximum Flooding Surfaces (MFS) and Sequence Boundaries (SB) of sediments penetrated by the drill. Diagnostic Palynomorphs such as Praedapollis africanus, Peregrinipollis nigericus, Retibrevitricolporites obodoensis aided in the establishment of three P-zones which are P620, P580, P560 Zones in the well. P620 and P580 Zones were lumped together and occur at depth 4680ft-7620ft while P560 occur at depth 7620-11580ft, species of foraminifera recorded are calcareous and arenaceous benthic Foraminifera species. Planktic Foraminifera specie are generally absent. Species recorded include Sproplectammina wrightii, Florilus atlanticus, Florilus costiferum, Eponides cf eshira, Quinqueloculina rhodiensis, Nonion centrosulcatum, and Alveolophragmium crassum. Foraminiferal zones established are Nonion centrosulcatum (N9), Fursenkoina punctata (N5) planktic and N8-N5 zone. the well records the occurrence of Two maximum flooding surfaces (Mfs) and two sequence boundary(SB) which was establish in P620/P580 zones and one maximum flooding surface which was established in the P560 Zone. The Sequence boundaries, Maximum flooding surfaces and their respective ages in these palynological zones occurred at various depths, P620 and P580 occurred at 26.2Ma Alabamina 1 Mfs at (6397ft) and 28.1Ma BOLIVINA 27Mfs at (7401ft) and the Sequence boundaries occurred at 6750ft at 27.3Ma SB,7553ft at 29.3Ma SB, P560 occurred at depth 31.3Ma UVIGERINELLA 5Mfs at (11200ft).

Rio graben is a region of significant stratigraphic and palaeontological interest where several environmental changes have been recorded during the Quaternary. These changes are a result of active tectonism, related to the well-known rifting process that has been occurring in the geotectonic region of the Corinth-Patras Rift, as well as of the influence of continuous eustatic and climatic changes. Fossil assemblages from Middle to Upper Pleistocene transitional to marine and terrestrial sedimentary sequences located at Sichaena (Rio Graben) on the west side of Charadros river in NW Peloponnesus, Greece, are analyzed herein in order to distinguish tectonic and eustatic controls. The name of the studied section is Vigla 1 (50 m thickness), belonging to the NE-trending Rio graben, a structure bridging the Corinth graben to the east and the Patras graben to the west. The presence of two normal antithetic second order faults and an unconformity were identified separating the studied stratigraphic section into four distinct sedimentological sequences. The purpose of this work is to determine the palaeoenvironmental conditions of the studied section and to unravel the Middle-Late Pleistocene palaeoenvironmental changes. The micro-fauna evidences oligohaline lagoon sediments at the lower sequence (Sequence 1). Conversely, at the middle (Sequence 2) and at the upper sequence (Sequence 3), the recorded species indicate lagoonal to shallow marine depositional environments. At the top of the section, an unconformity brings into contact Sequence 3 with a sequence consisting a red conglomerate (Sequence 4) that indicates an alluvial fan environment. In order to constrain chronologically the sediments Optically Stimulated Luminescence (OSL) dating was applied. According to the OSL dating results, an Upper Middle Pleistocene age has been attributed for the studied sequences. Moreover, projecting the dating results to the marine isotope curve, a high degree of consistency can be seen between the OSL ages and MIS 7e, 7c and 6d, where the transition from lagoonal facies to shallow marine alternations in sequence 2 correlates well with the MIS 7c highstand, and sequence 3 with MIS 7e and the MIS 6d low stand. Thus, our results indicate the spatial palaeoenvironmental evolution of the studied area which during the Upper Middle Pleistocene is characterised by intense local tectonic movements in conjunction with eustatic sea level changes.

Research has shown that fluvial systems exhibit a rapid response to extreme events, such as floods or climate-tectonic interplay, the evidence of which is recorded in fluvial sediments. This article provides new data and insights into the reconstruction of the Anthemountas River depositional environment. The study was conducted with granulometric analysis and with the lithostratigraphic and chronostratigraphic description of approximately 20000 yr B.P., the area's most extended sedimentary sequence to date. The evolution of the Anthemountas River Valley during the Late Pleistocene and Holocene is closely linked to tectonic activity and changes in the sea-level and climate. The interpretation of grain size cumulative curves, frequency curves, and the Passega C-M diagram is used in conjunction with the textural parameters of the sediments to obtain information about the means of transport and the intensity of environmental conditions. In addition, the loss on ignition method was used to estimate two parameters; organic matter and carbonates. Chronostratigraphic details were also obtained from the A.M.S. dating of charcoal samples. The analysis has identified the Late Pleistocene aggradation materials and the transition to the Holocene. Sedimentation can be described as a fluvial valley-fill sequence with periodical in-channel, off-channel, and floodplain series. After 3500 cal. B.P., the area is affected by the possible formation of a bay-head delta, with fluvial-dominated sands and the development of stable floodplains. Finally, the fluvial records of the Anthemountas River reveal phases of hydrological activity and stability.

Waters at seventeen mud volcanoes of the Kerch–Taman province in the Northwestern Cis-Caucasus region have been analyzed for Sr isotope composition. The 87Sr/86Sr ratios vary from 0.70734 to 0.71076 and show positive correlation with δ18О, as well as with fluid generation temperatures estimated using the Mg–Li geothermometer. The results revealed that the mud volcano system of the province was separated from the fluid systems of deeper Mesozoic sedimentary strata that fill the West Kuban Basin. The mud volcano water budget includes a major contribution from dehydration waters that release during illitisation of smectite, which occurs within the Maykop Shale sedimentary sequence. At the same time, 87Sr/86Sr ratios reflect lithological and geochemical heterogeneity of shallow sedimentary strata of the West Kuban Basin.

The article presents the results of investigations conducted by members of SSC RAS on the Dolgaya Spit in 2019–2020. The following types of data are analyzed: satellite imagery, coastal current measurements, borehole drilling, malacofauna research, and absolute age determinations of coastal sediments. In accordance with the extension of ancient longshore bars and the sequence of their connection to each other, six geomorphological generations are distinguished, reflecting the course of the Nymphaean and, partly, earlier transgressions. The radiocarbon dating data on mollusk shells suggests that the main part of the accumulative body of the spit was formed over 1 ka, in the interval of 2.5–1.5 ka ago. Based on field observations, it was concluded that the current velocities at the western coast of the spit are two to three times higher than at the eastern coast. A list of about 20 species and supraspecific taxa of shellfish from the coastal sediments of the Dolgaya Spit is presented. It is noted that the bulk (more than 90%) of shell sediments making up the longshore bars are valves of Cerastoderma glaucum shells.

Coeval changes in the reconstructed bog surface wetness and the pollen record of a peat sequence extracted from an ombrothropic bog (Calul de Piatra, 1630 m, Apuseni Mountains) allowed the natural ...

Shells from Neolithic shell midden sites have been routinely dated in Korea, but they have not been calibrated based on the correction values (ΔR) for the marine reservoir effect (MRE). A lack of proper calibration has left dates on shells incomparable to those on terrestrial samples, and thus unusable in building the chronological sequence of shell middens. Here, we report the two new ΔR values of a pre-bomb (pre-1950) blue mussel from the south coast. We applied the two new and the two previously reported ΔR values to the three dates on marine shells from the Bibongri shell midden in southeastern Korea. Our ΔR adjusted calibration and the comparison to dates on charcoal and bone remains clarify an ambiguity in the stratigraphy and the Early Neolithic chronology at Bibongri. Our contribution is to provide the ΔR values that can be further applied to other Neolithic shell middens along the south coast.

Reinforced concrete intake towers are considered as main hydraulic structures constructed in dams’ reservoirs, connected to the dam or as a separate structure. If an intake tower is damaged, the po...

This article presents the ceramic sequence and chronology resulting from a multi-year program of survey, excavation, and analysis of pre-Hispanic settlement and exploitation within the Zinapécuaro-Ucareo (“U-Z”), Michoacan obsidian source area. Pottery analysis and classification aided by seriation analysis identified nine ceramic complexes and seven ceramic phases and sub-phases that both expand and refine the ceramic sequence previously established for the region by Gorenstein's (1985) investigations at nearby Acámbaro, Guanajuato. Initially established by ceramic cross-dating, the U-Z ceramic chronology has been largely confirmed by 30 radiocarbon dates and spans over 2,000 years of pre-Hispanic settlement, which included at least two notable episodes of trait-unit and site-unit intrusion from the eastern El Bajío and central Mexico. One of these episodes involved the appearance of two enclaves settled by individuals from the Acambay valley c. 90 km to the East, most likely from the site of Huamango, which our data indicate would have been occupied during the Middle Postclassic period.