Lacustrine Basin Research Articles

Terrestrial records of the early Albian Ocean Anoxic Event: Evidence from the Fuxin lacustrine basin, NE China

The early Albian Oceanic Anoxic Event 1b (OAE 1b) is well documented in the Tethys, Pacific and North Atlantic, but few studies have evaluated whether or not terrestrial records of OAE 1b exist. In order to identify terrestrial records of the early Albian OAE 1b and to infer possible driving mechanisms, an integrated multi-proxy study from the late Aptian to Albian in the Fuxin lacustrine basin was conducted, including thick, organic-rich black mudstones, total organic carbon (TOC), organic carbon isotopes (δ13Corg), mercury concentration (Hg) and results from pyrolysis analyses (S2, Tmax and HI). Results show three distinct short-term negative δ13Corg excursions corresponding with relatively high TOC values, which could be counterparts of the Kilian, Paquier and Leenhardt sub-events of the early Albian OAE 1b. Atmospheric CO2 concentration (pCO2) recovered from C3 plant δ13Corg compositions indicates an increasing trend in Unit C during the early Albian, and there are three short-term increases of pCO2 corresponding to the three sub-events of OAE 1b at this time interval. We infer that a trend of increasing pCO2 during the Kilian sub-event in the study area is closely related to volcanism. Continental weathering calculated using chemical weathering indices (CIA, WIP and MIA(O)) show an increasing trend during the OAE 1b interval, likely resulting from warmer and more humid conditions. Mixed sources of terrestrial plants and lacustrine plankton demonstrated by pyrolysis analyses (HI vs. Tmax and S2 vs. TOC), indicate a terrestrial contribution to the organic-rich sediments of the Kilian, Paquier and Leenhardt sub-events of OAE 1b. We suggest that a CO2-forced greenhouse effect during the early Albian might have triggered the relatively warm and humid palaeoclimatic conditions, and intensified chemical weathering that combined to create high nutrient and organic matter levels that were flushed into lakes contributing to eutrophication and anoxia in lacustrine and in contemporaneous oceanic systems.

Las Cabras volcano, Michoacán-Guanajuato Volcanic Field, México: Topographic, climatic, and shallow magmatic controls on scoria cone eruptions

Scoria cones are abundant in most volcanic fields on Earth, such as the Michoacán-Guanajuato Volcanic Field, in the central-western sector of the Trans-Mexican Volcanic Belt. However, there are few in-depth studies on their eruptive style and controlling factors, despite of their diversity in shape and composition which implies a wide range of hazards. Here, we present results of morphologic, stratigraphic, sedimentary, petrographic, and geochemical studies of the prominent Las Cabras scoria cone located west of the Zacapu lacustrine basin in the center of the Michoacán-Guanajuato Volcanic Field. This basaltic andesitic to andesitic volcano formed between 27 and 26 kyrs BP on the steep slopes (>10º) of the lava shield of El Tule volcano. Over time, its dominant eruptive style changed from Strombolian to effusive. Initial explosive activity built a 170-m-high scoria cone and deposited thick tephra fallout on the surrounding sloping terrain. Structures in the deposits indicate that early friable fine-grained tephra underwent significant erosion due to syn-eruptive heavy rain coupled with the sloping nature of the underlying ground. This erosion generated lahars that very likely reached the Zacapu lake based on the pre-eruptive topography. As the explosivity dropped, lava was emitted from the base of the cone first to the S and SE, forming a thick, viscous lobe that filled a pre-existing E-W valley. The flow direction then deviated to the N and NE, to form thinner, less-viscous lobes fed from the vent by an open-channel. The lavas are covered by hummocks made of agglutinates and bombs that indicate that the eruption terminated by catastrophic collapse of the SE sector of the cone, possibly triggered by the intrusion of magma within the cone, which destabilized its downslope segment. The sudden flank failure was potentially associated with a late effusive event and the hummocks may have been carried away by the lava surge. Whole-rock chemical variations and crystal disequilibrium textures point toward a complex magma feeding system, involving mixing and mingling between different magma batches. This study shows that the formation of scoria cones on a terrain with a marked slope (>10°) has profound impacts on the eruption dynamics and related hazards due to its effect on cone stability and ash erosion. It also evidences the erosive effect of syn-eruptive rain on fine-grained tephra, especially when deposited on a slope. Finally, it reveals the complex magmatic processes that may occur in the shallow plumbing system of monogenetic andesitic volcanoes, which could be particularly important in inland areas of continental arcs.

Plausible Emergence and Self Assembly of a Primitive Phospholipid from Reduced Phosphorus on the Primordial Earth.

How life arose on the primitive Earth is one of the biggest questions in science. Biomolecular emergence scenarios have proliferated in the literature but accounting for the ubiquity of oxidized (+ 5) phosphate (PO43-) in extant biochemistries has been challenging due to the dearth of phosphate and molecular oxygen on the primordial Earth. A compelling body of work suggests that exogenous schreibersite ((Fe,Ni)3P) was delivered to Earth via meteorite impacts during the Heavy Bombardment (ca. 4.1-3.8 Gya) and there converted to reduced P oxyanions (e.g., phosphite (HPO32-) and hypophosphite (H2PO2-)) and phosphonates. Inspired by this idea, we review the relevant literature to deduce a plausible reduced phospholipid analog of modern phosphatidylcholines that could have emerged in a primordial hydrothermal setting. A shallow alkaline lacustrine basin underlain by active hydrothermal fissures and meteoritic schreibersite-, clay-, and metal-enriched sediments is envisioned. The water column is laden with known and putative primordial hydrothermal reagents. Small system dimensions and thermal- and UV-driven evaporation further concentrate chemical precursors. We hypothesize that a reduced phospholipid arises from Fischer-Tropsch-type (FTT) production of a C8 alkanoic acid, which condenses with an organophosphinate (derived from schreibersite corrosion to hypophosphite with subsequent methylation/oxidation), to yield a reduced protophospholipid. This then condenses with an α-amino nitrile (derived from Strecker-type reactions) to form the polar head. Preliminary modeling results indicate that reduced phospholipids do not aggregate rapidly; however, single layer micelles are stable up to aggregates with approximately 100 molecules.

SEDIMENTATION PATTERN OF SOILS SOUTH EL-AMIRIA, ALEXANDRIA GOVERNORATE, EGYPT

The current study aims to identify the sedimentation pattern of soils south El-Amiria, Alexandria Governorate, Egypt. This includes study of grain size parameters, depositional environments and hydrodynamic conditions of these soils. The study area is located between longitudes 29o 47` 55``and 30o 30` 05`` East and latitudes 29o 29` 30`` and 30o 30` 05`` North and comprise an area of about 571168 Feddan. The area is characterized by two main physiographic units namely Lacustrine plains and Windblown sand. The obtained results indicated that: I. Soils of lacustrine plains appeared that: 1-Grain size parameters as follows: The fine silt was the predominant constituent of median (Md) as average size. Graphic mean (Mz), generally, differed from fine to medium and coarse silt. Measure of uniformity appeared very poorly sorted values (σ1) which indicated that the sediments are transported and deposited by water. Measure of symmetry cleared that, the sediments have values of strongly coarse skewed (SKI). These values indicate that, the examined sediments have a tail of coarse grains. Measure of peakedness showed that, the distribution of grains between platy & very platykurtic and lepto & very leptokurtic. 2- The depositional environments of lacustrine plain soils were fluvial or deltaic. 3- The hydrodynamic conditions, in general, were pelagic suspension (T). II. Soils of windblown sand showed that: 1-Grain size parameters as follows: Coarse sand was a median (Md) and graphic mean (Mz). Moderately and moderately well sorted values (σ1) represented the measure of uniformity. This indicated that, sediments are transported and deposited under a combined action of both water and wind. Strongly fine skewed class was the measure of a symmetry, which indicated that the examined sediments have a tail of fine grains. Lepto and very leptokurtic were the measure of peakedness. 2-The depositional environment of soil of windblown sand was either fluvial or deltaic. 3-The mechanism of transportation was rolling (N-O).

Characterization of lacustrine basin paleosalinity and its control on calcareous lithofacies distribution: a case study in the eastern Dongying Sag, China

Characterization of lacustrine basin paleosalinity and its control on calcareous lithofacies distribution: a case study in the eastern Dongying Sag, China

Discovery of lacustrine shale deposits in the Yanshan Orogenic Belt, China: Implications for hydrocarbon exploration

The mechanism of formation of lacustrine deposits within stable orogenic belts and their potential for shale oil and gas exploration are frontier themes of challenge in the fields of sedimentology and petroleum exploration. Orogenic belts witness strong tectonic activities and normally cannot host stable lacustrine basins and deep shale formations. Therefore, basins in orogenic belts are considered to have no potential to form shale hydrocarbon reservoirs. Here we investigate the Luanping Basin located in the Yanshan orogenic belt where previous studies regarded rivers and fan deltas as the major main Mesozoic deposits. Based on detailed field exploration and scientific drilling, we report the finding of a large number of lacustrine shale continental deep-water deposits in the Mesozoic strata. Our finding of the occurrence of active shale oil and gas also in this basin also subvert the previous perceptions.We report SHRIMP zircon U-Pb age that define the bottom boundary of the target interval as 127.6 ± 1.7 Ma belonging to the early Cretaceous strata. Tectonics and climate are considered to be the main factors that controlled the deep-water sedimentation during this period. The drill cores revealed evidence of shale gas and the TOC of shale is 0.33%–3.60%, with an average value of 1.39% and Ro is 0.84%–1.21%, with an average value of 1.002%. The brittleness index of shale is between 52.7% and 100%. After vertical well fracturing, the daily gas production is more than 1000 m3. Our findings show that the basin has considerable potential for shale oil and gas. The geological resources of the shale gas in the Xiguayuan Fm. are estimated as 1110.12 × 108 m3, with shale oil geological resources of 3340.152 × 104 t. Our findings indicate that the Yanshan orogenic belt has potential exploration prospect. This work not only redefines the Luanping Basin as a rift deep-water Mesozoic Lake Basin, but also rules out the previous notion that the basin is dominated by shallow water sediments. The discovery of shale oil and gas also provides an important reference for subsequent petroleum exploration and development in this basin. Our study shows that shale oil and gas reservoirs can be found in the lacustrine basins of orogenic belts which were strongly influenced by volcanism. These results have significant implications for the sedimentology and oil exploration in the Qinling and Xingmeng Orogenic Belts of China, as well as those in other terranes of the world including the New England Orogenic Belt in Australia.

In-situ U-Pb dating of Ries Crater lacustrine carbonates (Miocene, South-West Germany): Implications for continental carbonate chronostratigraphy

The Nördlinger Ries Crater lacustrine basin (South-West Germany), formed by a meteorite impact in the Miocene (Langhian; ∼14.9 Ma), offers a well-established geological framework to understand the strengths and limitations of U-Pb LA-ICPMS (in situ Laser Ablation-Inductively Coupled Plasma Mass Spectrometry) geochronology as chronostratigraphic tool for lacustrine (and more broadly continental) carbonates. The post-impact deposits include siliciclastic basinal facies at the lake centre and carbonate facies at the lake margins, coevally deposited in a time window of >1.2 and <2 Ma. Depositional and diagenetic carbonate phases (micrites and calcite cements) were investigated from three marginal carbonate facies (Hainsfarth bioherm, Adlersberg bioherm and Wallerstein mound). Petrography combined with C and O stable isotope analyses indicate that most depositional and early diagenetic carbonates preserved pristine geochemical compositions and thus the U-Pb system should reflect the timing of original precipitation. In total, 22 U-Pb ages were obtained on 10 different carbonate phases from five samples. The reproducibility and accuracy of the U-Pb (LA-ICPMS) method were estimated to be down to 1.5% based on repeated analyses of a secondary standard (speleothem calcite ASH-15d) and propagated to the obtained ages. Micrites from the Hainsfarth, Adlersberg and Wallerstein facies yielded ages of 13.90 ± 0.25, 14.14 ± 0.20 and 14.33 ± 0.27 Ma, respectively, which overlap within uncertainties, and are consistent with the weighted average age of 14.30 ± 0.20 Ma obtained from all the preserved depositional and early diagenetic phases. Data indicate that sedimentation started shortly after the impact and persisted for >1.2 and <2 Ma, in agreement with previous constraints from literature, therefore validating the accuracy of the applied method. Later calcite cements were dated at 13.2 ± 1.1 (nw=2), 10.2 ± 2.7 and 9.51 ± 0.77 Ma, implying multiple post-depositional fluid events. This study demonstrates the great potential of the U-Pb method for chronostratigraphy in continental systems, where correlations between time-equivalent lateral facies are often out of reach. In Miocene deposits the method yields a time resolution within the 3rd order depositional sequences (0.5–5 Ma).

Ultimate expellable potentials of source rocks from selected super basins: What does “world class” look like?

An important step in the evaluation of a play or prospect is to consider the potential supply of petroleum charge, which is ultimately constrained by masses and volumes supplied by the source bed. The two factors limiting the mass of petroleum expelled from the organic matter in the source bed are (1) its initial expulsion potential and (2) the cumulative fraction of potential that has been expelled up to its maximum state of maturation. To evaluate the initial expulsion potential, we introduce a workflow to estimate the ultimate expellable potential (UEP), divided into an oil potential (UEO) and a gas potential (UEG), which represent the cumulative masses of oil and gas that can be expelled upon complete maturation of the source rock. For use in resource estimation, these masses can be converted to surface volumes of oil and gas per unit area (million stock tank barrels per square kilometer and billion standard cubic feet per square kilometer or million barrels of oil equivalent per square kilometer, respectively). The UEP (UEO, UEG) can be mapped across the depositional extent of the source bed, just as a reservoir depositional system is mapped. These potentials per unit area constitute the first level of quantitative resource estimation in the evaluation of a play or prospect. We show examples of UEP (UEO, UEG) mapping based on available public data. Three of the example source rocks are aquatic organofacies that have charged major conventional petroleum systems: the Callovian to Oxfordian marine organofacies of the Arabian Basin, Saudi Arabia; the Volgian marine organofacies Bazhenov Formation of the West Siberian Basin, Russia; and the Eocene–Oligocene lacustrine freshwater organofacies Shahejie Formation of the Bohai Basin, China. We also include an unconventional system: the uppermost Devonian–lowermost Mississippian marine organofacies Bakken Formation of North Dakota, United States. The UEPs of the studied source rocks in the Arabian Basin and West Siberian Basin, with tens of millions of barrels of oil equivalent per kilometer over large areas, define world class in marine source rocks since these basins are ranked number one and number two in the world by oil endowment. Until more data are available on other lacustrine basins, we offer the UEP of the studied Bohai Basin source rock as an example. In contrast, the UEP of the Bakken Formation source rocks (combined Upper and Lower Members) is relatively modest despite its world class unconventional oil endowment. The Bakken's effectiveness, despite its relatively low UEP, reflects the negligible migration saturation losses involved in charging the Middle reservoir Member. This illustrates that the commonly touted term world class can be rather meaningless. It needs to be considered in context given the task in hand: the greater the (vertical) migration losses incurred in charging reservoirs, the higher the UEP needed to create the charge needed to overcome them.

Anatomy of a Catastrophe: Reconstructing the 1936 Rock Fall and Tsunami Event in Lake Lovatnet, Western Norway

Rock falls and landslides plunging into lakes or small reservoirs can result in tsunamis with extreme wave run-ups. The occurrence of these natural hazards in populated areas have encouraged a recent sharp increase of studies that aim to mitigate their impact on human lives and assess infrastructure lost. This paper amalgamates in a novel fashion and at an unprecedented detail in situ historic measurements, geological data and numerical modeling of a rock fall event and associated tsunami wave that occurred in Lake Lovatnet (western Norway) in September 1936. Historical records report an event that released ca. 1 million m3 of rocks and debris from Ramnefjellet Mountain at an altitude of 800 m above Lake Lovatnet. The fragmented material plunged into the lake, causing a tsunami that reached a maximum run-up of 74 m and killed 74 people. In fact, the settlements of Bødal and Nesdal were wiped out as a result of the catastrophic wave. Sediments resulting from the 1936 rock fall and associated tsunami were identified in the subsurface of Lake Lovatnet by shallow geophysical investigations and were retrieved using gravity coring equipment. A set of high resolution physical and geochemical measurements were carried out on the cores with the aim of reproducing a highly detailed reconstruction of this catastrophic event in order to better understand and learn about the processes involved. The cores were retrieved in the northwestern sub-basin of the lake and its chronology was constrained by 210Pb and radiocarbon dating. A specially tailored physically based mathematical model was applied to better understand the tsunami event. Integration of the geophysical record, the sedimentological data and numerical modeling provide a comprehensive background to better understand the effects of such event in a deep fjord-like lacustrine basin and to generate information for better mitigation of similar events elsewhere.

Lower cretaceous avian-dominated, theropod, thyreophoran, pterosaur and turtle track assemblages from the Tugulu Group, Xinjiang, China: ichnotaxonomy and palaeoecology.

Rich tetrapod ichnofaunas, known for more than a decade, from the Huangyangquan Reservoir (Wuerhe District, Karamay City, Xinjiang) have been an abundant source of some of the largest Lower Cretaceous track collections from China. They originate from inland lacustrine clastic exposures of the 581–877 m thick Tugulu Group, variously divided into four formations and subgroups in the northwestern margin of the Junggar Basin. The large Huangyangquan track assemblages occur in the Lower layer/Subgroup II. Similarly-composed track assemblages also occur at the smaller Asphaltite site in the Upper Layer/Subgroup III. The Huangyangquan assemblages have yielded more than 1,500 identified tracks including abundant tracks of avian and non-avian theropods, pterosaurs and turtles and less abundant tracks of stegosaurs. Previous avian track identifications have been reassessed to conclude that Moguiornipes robustus is a taphotaxon and Koreanaornis dodsoni might be better accommodated in the ichnogenus Aquatilavipes which appears to be the dominant avian ichnotaxon. The avian track Ignotornis is also recognized and represents the first occurrence of this ichnogenus in China. Although the Huangyangquan assemblages lack some of the larger components (e.g., sauropodan and ornithopodan tracks) known from other Lower Cretaceous localities, the association of abundant tracks of smaller tetrapods (avian and non-avian theropods, pterosaurs and turtles) appears to be representative of lacustrine basin faunas of this region, and are an excellent example of the shorebird ichnocoenosis/ichnofacies concept. This is the first comprehensive review and re-analysis of an important Lower Cretaceous ecosystem.

A semi-confined turbidite system in the eocene lacustrine: An example from Niuzhuang Sag, Bohai Bay Basin, Eastern China

This paper establishes the sedimentary facies distribution model in the middle of the third member of the Shahejie Formation (Es3z), deep-lacustrine and turbidite fans in the Niuzhuang Sag. Lacustrine turbidite systems can form high-quality oil and gas reservoirs and the understanding of these systems is of great significance for lacustrine basins exploration. We identified a series of turbidite fans by comprehensive analyzing core, well log, 3-D seismic data and grain size variations. These fans can be further divided into lobe axis, lobe fringe, and lobe distal fringe settings. The lobes developed in both directions: the vertical fault strike (east-west) direction and parallel fault strike (northeast-southwest) direction. Porosity and permeability data showed that massive sandstone was mainly developed in the middle lobe axis that has better reservoir physical properties. The paleoclimate was determined using geochemical data. The paleoclimate was warm and humid in the highstand system tract (HST), contributing to the development of the turbidite system.

Geoenvironmental Implications and Biocenosis of Freshwater Lakes in the Arid Zone of East Kazakhstan

Steppe and semi-desert lakes of Central Asia represent unique and still poorly known aquatic ecosystems. The paper provides summaries of multi-proxy environmental and biological investigations of the previously unexplored ground of Sibe lakes in the naturally pristine zone of East Kazakhstan, and of their contributions to people. Data on the taxonomic composition of zooplankton and zoobenthos of these freshwater lacustrine basins are presented in terms of the species’ frequency of occurrence; the abundance of the aquatic biomass and the analyzed water geochemical variables insofar as they are dependent and correlative. The qualitative and quantitative records display variability in the biocenosis diversity due to the lakes’ geochemistry and hydrology differences—some lakes being oligotrophic and others being moderately trophic. In the latter case, the lakes characterized by an increased macrozoobenthos biomass are favourable for local ichthyofauna. Sapro-biological analysis reveals the predominance of β-saprobic species in the zooplankton composition pointing to slight or moderate pollution of surface waters due to natural biotic substances. This observation is in agreement with differences in the water quality of solitary lakes. The uneven distributions of benthic invertebrates (in terms of taxonomy and species populations) in the water bodies suggest specific hydro-ecological conditions that predetermine the structure of the lakes’ biocenosis. The littoral part of the lakes is characterized by the highest abundance of zooplankton and benthic fauna. The Sibe lakes are an example of an autonomous functioning of the lacustrine basins in the upland arid steppe zone, which is characterized by pronounced climate “continentality” and a high level of the sub-aquatic flora and fauna endemism. The present results are relevant to the understanding of the ecosystems’ dynamics and the modern anthropogenic impacts upon the pristine parkland-steppe landscapes of Central Asia, with implications for regional nature protection and sustainable eco-recreation.

Decoding a complex record of anthropogenic and natural impacts in the Lake of Cavazzo sediments, NE Italy

The Lake of Cavazzo is a natural, lacustrine basin in the Friuli-Venezia Giulia region (NE Italy), which occupies a fluvio-glacial suspended valley of the Tagliamento river, at the southern front of the Alpine chain. The lake formed after the melting of major glacial tongues at the end of the Last Glacial Maximum, and has been affected in recent years by natural and anthropogenic events, with economic, cultural and environmental consequences. According to local witnesses, the lake environment has changed dramatically after the 1950s, when the basin was connected to a hydroelectric power plant collecting waters from a wider catchment area, as it served as its final discharge basin.In this work, based on a densely-spaced grid of high-resolution seismic reflection profiles complemented by sediment cores, we analysed the uppermost lake stratigraphy, highlighting major changes occurring at a decadal scale. Our main purpose is to verify whether and how the lake sediments record the transition from pristine/natural to artificial conditions, as well as the effects of multiple natural impacts including the 1976–77 Friuli earthquake sequence. The results of our analysis suggest varying environmental conditions of the lake after the 1950s indicated by changing sediment mineralogy, increased deposition of allochthonous clastic sediments, and recurrent episodes of anoxic conditions at the lake's floor, likely triggered by hyperpycnal flows derived from the hydroelectric power plant discharges. We also observe that the effects of the 1976–77 seismic sequence are recorded in the lake as resedimented levels, likely due to shaking, in situ deformation, landslides, and turbidity currents. Our results stress the importance of lacustrine environments as efficient recorders of anthropogenic and natural events.

Evaluation of the Shale Oil Reservoir and the Oil Enrichment Model for the First Member of the Lucaogou Formation, Western Jimusaer Depression, Junggar Basin, NW China

The Lucaogou Formation (Fm) in the Jimusaer depression is the first large-scale development of a terrigenous clastic sedimentary shale oil reservoir in China. Nearly one billion tons of shale oil resources have been discovered. However, the current exploration and development is concentrated in the eastern part of the sag. The limited geological understanding in the western area has restricted the prediction and development of “sweet spots” for shale oil. To help rectify this, we have studied the petrology, geochemistry, oil content, and pore properties of the second part of the first member (Mbr) of the Lucaogou Fm (P2l12) in a typical well (Ji-X) in the western part of the sag. The results show that P2l12 in the Jimusaer sag is a mixed fine-grained sedimentary system composed of sandstone, mudstone, and carbonate, which can be divided into seven types: dolomitic mudstone, calcareous mudstone, mudstone, mixed fine-grained rock, argillaceous limestone, sandstone, and argillaceous dolomite. The organic matter type of P2l12 in well Ji-X is dominated by types I and II, and this is the best source rock in the whole exploration area of the Jimusaer sag. The overall oil saturation is relatively high, but the maturity of crude oil is low, and the overall oil quality is heavy, which is mainly controlled by the sedimentary environment and maturity of source rocks. Lithology and reservoir physical properties are the key to control oil content. The high-quality light oil reservoir lithology is argillaceous dolomite and sandstone. The higher the content of macropores and mesopores, the weaker the heterogeneity of the pore structure, and the better the oil content in the reservoir. There are four light oil sweet spots in the upper part (burial depth less than 4366 m), and there are excellent source rocks with high HI and high organic matter content near each sweet spot. This discovery of shale oil enrichment regularity will effectively guide the development of shale oil in continental lacustrine basins in other parts of the world.

Introduction to special section: Mapping mixed clastic and carbonate depositional systems in lacustrine basins

Introduction to special section: Mapping mixed clastic and carbonate depositional systems in lacustrine basins

Wave and storm signals in a lacustrine succession and their relationship to paleowind direction (Tanan Depression, Mongolia, early Cretaceous)

Existing fan-delta depositional models for lacustrine basins do not adequately address significant wave- and storm-related processes. However, in many lakes, such high-energy processes can be effectively driven by winds. As such, the prevailing wind direction determines the propagation direction of wind-induced waves. Observations from modern examples show that wave-dominated deposits commonly exist on one side of the lake, and their sedimentary processes are completely distinct from those on the opposite side. However, equivalent deposits have seldom been identified from subsurface data. We present an ancient example from the Upper Tongbomiao Formation in the Tanan Depression (Tamtsag Basin, Mongolia), which was previously interpreted as a fan-delta depositional system. Based on extensive core investigations, eighteen lithofacies, six lithofacies associations and two genetic deposition systems are identified, and a new sedimentological interpretation is proposed comprising a wave-dominated clastic littoral system in the western half-graben dip slope and a fluvial-dominated fan-delta system in the eastern half-graben. Sediments within the eastern half-graben unit include braidplain, fan-delta front and prodelta environments, while those within the western half-graben dip slope unit comprise dominantly alluvial fan, wave-reworked beach, storm-affected shoreface and offshore sediments. The strikes of the sediments in the western half-graben dip slope unit are parallel to the westward shoreline trend, while the progradation direction of sediments in the eastern half-graben unit is perpendicular to the eastern shoreline. This indicates approximately northwestward-propagating waves that were possibly driven by southeasterly winds, which has implications for understanding the prevailing wind direction in Northeast Asia during the depositional period. Other factors contributing to the preservation of these two distinct sedimentary systems are the paleotopography and subsequent climate shift towards more humid climatic conditions which intensified sediment supply and hydrodynamic conditions that were able to rework the sediments.

Palaeoclimate of the Paleogene Dongying Formation in Bozhong Sag of Bohai Bay Basin

It was showed that the sedimentary environment of lacustrine basins is more susceptible to basin size than that of marine basins, leading to frequent changes in sedimentary environment and large differences in sediment supply and types. Based on the comprehensive analysis of clay minerals, spore pollen, major elements and trace elements, the sedimentary environment of Dongying Formation and its evolution in Bozhong Sag were studied. The results showed that during the sedimentary period of Dongying Formation, the study area was in a subtropical warm and humid climate as a whole. In addition, the vertical distribution of spore pollen and algae was divided into four zones and each one represents different sedimentary environments. Combination zone I is characterized by a large number of spore pollen and algae, including juglanspollenites verus, ulmipollemites minor, abietineaepollenites and pinuspollenites, taxodiaceaepollenites hiatus, leiosphaeridia and granodiscus, and it indicates a relatively hot and dry climatic; Combination zone II mainly contains juglanspollenites verus, ulmipollemites minor, abietineaepollenites and pinuspollenites, pediastrum and leiosphaeridia. Compared with I, the number of spore pollen and algae decreases, but the number of pediastrum increases a lot, which represents warm and humid climate. The combination zone III is dominated by abietineaepollenites and pinuspollenites and chaetosphaeridium, and the species and quantity decrease significantly. It indicates a relatively hot and humid climate at that time. Combination zone IV contains a small amount of spore pollen and algae, and it means the climate was warm and humid at that period. The frequent changes of sedimentary environment in lacustrine basins are influenceded by regional tectonic environment and basin scale. Using S/A and E-T parameters, the paleoclimate in the study area was delineated and 10 sedimentary environment interfaces were identified, which further illustrated the characteristics of frequent fluctuations of sedimentary environment in lacustrine basins.

Turbidite Reservoirs in the Dongying Sag, Bohai Bay Basin: Interactions between Carbonate Cementation and Hydrocarbon Charge

AbstractTurbidite sandstones have become increasingly significant in hydrocarbon exploration. Carbonate cementation occur commonly in turbidite reservoirs developing within the Paleocene lacustrine basins, Northeastern China. This study utilizes core data, thin section data and production data to investigate the interaction between the carbonate cementation and hydrocarbon charge within turbidite reservoirs in the Niuzhuang Sub‐sag of the Dongying Sag, Bohai Bay Basin, East China. The results reveal that the carbonate cementation is mainly developed at the top and bottom of the turbidite sandbodies, and even forms carbonate cement shells. Three stages of hydrocarbon accumulation are identified based on fluid inclusion analysis: stage I (27.5–24.6 Ma), stage II (14.0–5.0 Ma), and stage III (5.0–0 Ma). The interaction between the carbonate cementation and hydrocarbon charge has significant controls on the formation of a turbidite reservoir. The temporal relations and intensity relations between the two factors should be considered significantly. Moreover, hydrocarbon charge during the early stage can inhibit the carbonate cementation, favoring the hydrocarbon accumulation in turbidite reservoirs. Many deep‐lacustrine turbidite sandbodies surrounded by source rocks with abnormal high pressure, are also favorable for hydrocarbon accumulation. These results suggest that some deeply buried turbidite sandbodies with similar geological settings have high potential for hydrocarbon exploration.

Late Holocene Malpaís de Zacapu (Michoacán, Mexico) andesitic lava flows: rheology and eruption properties based on LiDAR image

Few monogenetic eruptions that produced lava flows have occurred in historical times, limiting the observations of their impact on human settlements. However, rheological models based on morphological and petrological datasets can contribute to decipher the eruptive dynamics and durations of ancient eruptions. The Malpaís de Zacapu, a temporal-spatial monogenetic volcano cluster at the western margin of the Zacapu lacustrine basin (Michoacán, Mexico), offers a good opportunity to apply such models because of the availability of a high-resolution LiDAR topography from which detailed morphological data was extracted. The Malpaís de Zacapu comprises late Holocene lava flow fields emplaced in the last 3200 years by four different low magnitude volcanic eruptions: Infiernillo, Malpaís Las Víboras, Capaxtiro, and Malpaís Prieto. Jointly these eruptions produced thick andesitic block lava flows covering an area of 38.3 km2 with a volume of ~ 4.4 km3. The lava viscosities at eruption vents were estimated from petro-textural analyses and range between 103 and 106 Pa s, while the final flow apparent viscosities, obtained from dimensional analyses, vary from 108 to 1010 Pa s. We estimated the mean effusion rate and lava flow emplacement duration for each flow field. Results revealed that the more viscous flows, Malpaís Las Víboras and Malpaís Prieto, could have been emplaced in less than 3 years, while the more fluid Infiernillo probably took less than 1 year. In stark contrast, the morphologically different and more voluminous Capaxtiro flow field could have been emplaced in ~ 27 years. These findings can help to evaluate the impact that these eruptions had on adjacent pre-Hispanic populations, known to have inhabited the region since at least 3000 years ago.

Environmental evolution, faunal and human occupation since 2\xa0Ma in the Anagni basin, central Italy

We present the study of a composite, yet continuous sedimentary succession covering the time interval spanning 2.6–0.36 Ma in the intramontane basin of Anagni (central Italy) through a dedicated borecore, field surveys, and the review of previous data at the three palaeontological and archaeological sites of Colle Marino, Coste San Giacomo and Fontana Ranuccio. By combining the magneto- and chronostratigraphic data with sedimentologic and biostratigraphic analysis, we describe the palaeogeographic and tectonic evolution of this region during this entire interval. In this time frame, starting from 0.8 Ma, the progressive shallowing and temporary emersion of the large lacustrine basins and alluvial plains created favorable conditions for early hominin occupation of the area, as attested by abundant tool industry occurrences and fossils. This study provides new constraints to better interpret the hominin migratory dynamics and the factors that influenced the location and spatial distribution during the early occupation of this region.