Evolution Of Sedimentary Environments Research Articles

Late Quaternary sedimentation and neotectonics in Liaodong Bay, northern Bohai Sea

The Bohai Sea is a typical shelf sea, with obvious sediment differences in different regions. Although Liaodong Bay is the largest bay in the Bohai Sea, there lacks boreholes with precise dating. In this paper, the core sediments taken from YKC-2 borehole in the northeastern of Liaodong Bay are dated with AMS14C and OSL, in addition to grain size analysis, foraminifera and pollen identification, lithological characteristics and other testing results. Correlation is made with the global sea level change curve, and upon the basis the evolution of paleoenvironment in the northeast of Liaodong Bay is reconstructed. It is speculated that the age of the bottom of borehole YKC-2 is 150 kyr B.P., and two transgressions have been recorded, similar to the situation in JXC-1, a borehole 46.7 km to the west. It can be found that the sedimentation rate of YKC-2 borehole is obviously higher than that of JXC-1. The authors’ research found that it is mainly controlled by two factors: the provenance difference and the differential movement of basin controlling faults. In the west, sediments are mainly transported by the Bohai Sea current, with insufficient sediment supply, and the basin-controlling faults are rather stable and very weak in activity. In the east, sediments are transported mainly by the surrounding rivers with sufficient sediment supply; and the changes in accommodation space are under the control of the Tan-Lu fault zone. Affected by the strong extensional dynamic environment of the Bohai Bay Basin, the accommodation space, where the borehole YKC-2 is located, continuously increased for deposition of near-source river sediments. This article is an endeavor to study the evolution of the Late Quaternary sedimentary environment and the influence of tectonic activity on Quaternary sedimentation in the Bohai Sea.

Holocene Environmental Evolution Response to the Human Activities and East Asian Summer Monsoon Variation in the Liangzhu Ancient City Complex, Eastern China

The Liangzhu Ancient City Complex is located in a low-lying coastal delta area, and its environmental evolution would have had a significant impact on the human-environment interactions. In this study, element geochemistry and grain size of the sediment sequence from a dam section in Ganggongling (GGL) reveal crucial aspects of sedimentary dynamics, environmental evolution, human activities, and East Asian Summer Monsoon(EASM) variation in the Liangzhu area since 5500 a. Starting from the middle-to-late Holocene, the GGL section shows an overall transition from warm humidity to cold-dry, which is consistent with the climate record dimension in southern China. Through comprehensive analysis of the sedimentary environment before and after the dam’s completion, it can be found that the Ganggongling dam has played a positive role in regulating mountain torrents and met the needs of production and domestic water, such as rice planting through water storage. Further applications on the multi-decadal to centennial time scale demonstrate that variations in solar activity may control the EASM intensity mainly in southern China, which is subject to ENSO intensity changes.

Late Miocene-Quaternary sedimentary environment evolution of the Kerch seep area, Black Sea

A set of 2D high resolution seismic lines was acquired near the Kerch Peninsula during R/V Meteor Cruise M72/3 in March/April 2007 to the Eastern Black Sea. The high resolution seismic data were used for analysis of seismic facies and seismic sequences to gain insight into the sedimentary evolution of the study area. Seven seismic facies types were identified and six seismic units could be mapped. Based on seismic line interpretation, isopach and seismic facies distribution maps, a chronostratigraphic framework could be established for the study area. The study reveals that the sediment deposits were influenced by syndepositional tectonic movements, sea level and climate. During the late Miocene and the early Pliocene, possible slope fan deposits developed. At the boundary between the Miocene and Pliocene, the Messinian erosional truncation surface was observed. After the Messinian sea level fall, accompanied by a major transgressional phase during the Pliocene, the Paleo-Don and Kuban Rivers delivered a large terrigenous input to the Black Sea from the uplifted Crimean Mountains. This formed thick submarine fan deposits near the mouth of Kerch Strait during the late Pliocene. Facies variations within the seismic units are related to the sea-level and climate curves, and are reflected by grain size variations in the sediments and the shift of the river mouth. During the Quaternary, hemipelagic sediments interbedded with coarse-grained fluvial sediments developed in the study area, along with slumps, river channels and fan deposits.

Sedimentary environment of the Upper Cretaceous Yogou Formation in Termit Basin and its significance for high-quality source rocks and Trans-Saharan Seaway

The Yogou Formation of the Upper Cretaceous is a potential source rock in the Termit Basin of Niger, and the TOC content of the upper member is 1.8–9 times that of the lower member. However, the influence of the sedimentary environment evolution on its organic matter heterogeneity is still unclear. In this paper, the evolution of the sedimentary environment of the Yogou Formation profile was studied from the aspects of micropaleontology, element geochemistry and biomarkers. A total of three third-order sequences (YSQ1, YSQ2 and YSQ3, from bottom to top) were identified in the Yogou Formation. The distribution of micropaleontology in different sequences indicates that YSQ1 mainly deposited in the marine environment, while, the YSQ2 and YSQ3 mainly deposited in the marine-continental transitional environment. The elemental geochemical analysis shows that the water salinity of YSQ1 was higher than that of YSQ2 and YSQ3. From YSQ1 to YSQ3, the terrestrial input increased, the climate became warmer and wetter, and the reducibility of water generally weakened. The biomarker characteristics and organic geochemical parameters indicate that the YSQ1 generally deposited in a sub-anoxic to anoxic environment, while the YSQ3 deposited in the environment frequently alternating from reduction to oxidation, and the reducing environment may provide a good preservation condition for the enrichment organic matters. The abundant terrigenous materials input and good preservation conditions may be the basic reason to form the mudstone with high TOC content in the upper member of the Yogou Formation. The same micropaleontological species found in the Termit Basin, Benue Trough and Bornu Basin provide evidence for the hypothesis that there was a trans-Saharan seaway between the Tethys Sea and the South Atlantic during the Cenomanian and Turonian transgressions. This study not only helps to clarify the enrichment and distribution regularity of high-quality source rocks in the Yogou Formation, but also provides some evidence for the existence of trans-Saharan seaway.

Revisit the Sedimentary Stratigraphic Evolution and Environmental Changes on the Outer Shelf of the East China Sea Since MIS 5

The East China Sea (ECS) is featured by the broad continental shelf, huge terrigenous sediment input and striking river-sea interaction during the Quaternary. Despite the numerous studies, mostly on the delta, coastal and inner shelf areas, the late Quaternary stratigraphy and sedimentary environment on the mid-outer ECS shelf were poorly documented. In particular, it is still controversial in issues such as the recognition of marine transgression deposits in the interglacial period and the occurrence and ages of deposits in the glacial period. This study presents new data of high-resolution seismic reflection profiles and collective evidences from lithology, microfossil assemblages and geochronology of borehole SFK-1 on the ECS outer shelf, aiming to revisit the sedimentary stratigraphic evolution and environmental changes since the Marine Isotopic Stage 5 (MIS 5). Sixty-one ages were obtained by radiocarbon and Optical Stimulation Luminescence (OSL), providing robust constraints on the chronostratigraphy. Three marine regression/transgression cycles were identified, which primarily constrained the sedimentary environmental evolution over the past 100 kyrs. Although the strong river-sea interaction accompanied with sea level fluctuations characterized the late Quaternary depositional environment on the shelf, this study clearly identified the stratigraphic boundaries between MIS 1 and MIS 5, and confirmed the tide-influenced fluvial deposition formed during the Last Glacial Maximum on the outer shelf. We infer that tidal forcing significantly superimposed its influence on sea level change and thus formed the most striking feature on the late Quaternary stratigraphy of the open ECS shelf. With the combination of a large number of absolute depositional ages with high-resolution core records, the major findings of this study may allow better understanding of the Quaternary sedimentary evolution and river-sea interaction on open shelves dominated by siliciclastic sedimentation.

Influence of the depositional environment on the formation of organic-rich marine shale: A case study of the first discovery of Anisian shale in the Sichuan Basin

The Leikoupo Formation, which was deposited during the Anisian stage in the central Sichuan Basin, has produced significant amounts of conventional gas but there have been few studies on its unconventional resources. Organic-rich shale in the Leikoupo Formation was discovered for the first time in the wells of CT1 and JY1 in the central Sichuan region, but information on its sedimentary environment and climate evolution is scarce. A series of lithofacies, organic geochemistry and inorganic geochemistry analyses were used to analyse core samples of CT1 and JY1 to estimate their vertical changes. The organic matter characteristics, the sedimentary environment and the factors controlling the Leikoupo Formation shale in the Sichuan basin were revealed. The organic-rich shale of the Lei3-2 sub-member was formed in a semi-restricted lagoon environment. The sedimentary environment was dysoxic-anoxic, with high palaeoproductivity, a warm and humid to semi-arid and semi-humid climate. The vertical sea level decreased for a short period, led to an increase in oxygen content in the mixed shale, clayey shale and calcareous shale that were sequentially deposited from bottom to top. In the vertical direction, the palaeo-productivity and aridity decreased, and there was an increase in the salinity and terrigenous debris input. All of these corresponded well with TOC. According to Mo-TOC and Mo–U patterns, the mixed shale was characterised by the highest values of MoEF, UEF and MoEF/UEF, followed by clayey shale and calcareous shale, which indicated mixed shale was deposited in a moderately restricted water condition, which progressively became more restricted during the deposition of clayey shale and calcareous shale with the fall of relative sea level. Biomarker compounds (steranes, terpanes), Tmax and other pyrolysis parameters indicated that the organic matter had reached the stage of high-to over-maturity. The gammacerane to C30 hopane in the ratio indicated that it was the bottom water in which it was deposited was sratified.

Environmental Evolution and Human Adaption Recorded From a Salt Production Site at the Coastal Plain of Laizhou Bay, China

The southern coast of the Laizhou Bay is considered as one of important areas for the origin and development of sea salt production in Eastern China. Archaeologists have collected rich materials to better understand history of salt production in the region, but how environmental change influences early salt production is still unknown. Here we collected samples at the Shuangwangcheng (SWC) site in the southern plain of Laizhou Bay. We conducted grain size, mollusk and foraminifera analysis to examine the evolution of sedimentary environment and restored the human adaptions to environmental change. The results showed that the sedimentary environment of study area was lower tidal flat during 6400~5900 yr BP as indicated by coarse and well sorted grain size, high abundance of foraminifera, and the Ammonia beccarii vars. - Quinqueloculina akneriana foraminifera assemblage. Sedimentary environment changed from intertidal to supratidal flat with decreasing abundance of foraminifera and finer upward grain size at 5900~ 4300 yr BP. After 4300 yr BP, this area was less affected by seawater, which could be reflected by the appearance of freshwater mollusk and rarely discovered foraminifera. Our retrieved environment changes were closely related with ancient human activities. The Holocene transgression constrained the Dawenkou cultural sites within the inland areas with higher altitude. The exposed coast lowlands after sea retreat were initially not suitable for human survival except sporadic salt production sites of the Longshan culture. These conditions were improved during the Shang and Zhou Dynasties when humans widely used the particular natural resources of underground brine for salt production, and then a large number of salt production sites appeared, which made this region develop into an important origin center of salt production. Our research suggests that salt production was an economic activity that was adopted by people to adapt to the harsh environment, which is of great significance for understanding the evolution of the human-environmental relationship in the coastal area.

The geochemical characteristics of the Paleogene lacustrine source rock and Cenozoic oil in the eastern Huanghekou Sag, Bohai Bay Basin, China: An oil–source rock correlation

Oil source correlations were conducted through bulk carbon isotope composition, source-related biomarkers, and maturity-related parameters to characterize the differences between two Paleogene lacustrine source rocks the Shahejie third (Es3) and fourth (Es4) members, utilizing seven Cenozoic crude oils. Es3 is dominated by type II1 sapropel kerogen, and Es4 is dominated by type II2 humic kerogen. The Es4 source rock has high gammacerane content, low Pr/Ph, high C30 steranes, high dinosteranes, and low β-/γ- and α-/γ-methyltrimethyltridecylchroman (MTTC), indicating a transgression in a saline lake during sedimentation. The low abundance of short-chain n-alkanes, high carbon peak number, abundant perylene, cadalene, and retene indicate that the Es4 input included significant amounts of ferns and gymnosperms. In contrast, the Es3 source rock was deposited in a moderately deep freshwater lake and had relatively more angiosperm and algal input with high oleanane to C30 hopane and high 1,2,7-/1,2,6- trimethylnaphthalene (TMN) ratios. The oils have relatively high sulfur content except oil O1. The larger population of oils were derived from the Es4 system, and were mixed with the low sulfur oil produced by Es3. The oil maturity parameters are generally higher than those seen in the two source where sampled, indicating that the oils were generated from source kitchens of higher thermal maturity in the east and south. The results of this study will contribute to the understanding of the evolution of Paleogene sedimentary environments and regional oil and gas exploration.

The influence of Early Cretaceous paleoclimate warming event on sedimentary environment evolution and organic matter sources in Yin'e Basin: Evidence from petrology and molecular geochemistry

The lacustrine organic-rich fine-grained sedimentary rocks of the Early Cretaceous Bayingebi Formation are widely distributed in the Yin'e Basin and they have become important source rocks for oil and gas exploration. To reveal the influence of paleoclimate warming event on sedimentary environment evolution and organic matter sources, the petrological and molecular geochemical analyses of the upper member of the Bayingebi Formation (K1b2) were carried out using optical microscopy, X-ray diffraction, scanning electron microscopy, Rock-Eval pyrolysis and gas chromatography–mass spectrometry, in order to establish the paleoecological models of the Early Cretaceous freshwater and saline lakes. The oil shale and dark mudstone of K1b2 are both in the immature-early mature stage and have good potential for hydrocarbon generation, with a dominance of type I and type II1 kerogen. Two types of primary dolomite were found in this formation: microcrystalline dolomite with uniform structure, and the microbially originated spherical dolomite aggregates. The K1b2 can be divided into four units based on its lithology and logging curve characteristics. Unit II was deposited in the peak of lake development, under the warm-humid paleoclimate with abundant annual precipitation. There was greater influx of freshwater than other units, which resulted in the unstable stratification of the water column and less reducing condition of the lake bottom water body. Lower aquatic organisms and vascular plants were unprecedentedly prosperous, which were indicated by short-term thriving phenomena of telalginite, and the large input of terrestrial OM and highest abundance of the OM compared to other units. A lake water salinization event occurred during the sedimentation period of Unit III under the cooling climate, causing a transition from a freshwater lake to a high-salinity lake with reducing condition and stable stratification of the water column. Salinity of lake water increased the competitiveness of salt-tolerant algae and bacteria. The salty environment is beneficial for the thriving of single to halophilic genus of microorganism and lead to significantly lower abundance of telalginite. The biological sources of OM were mainly bacteria, algae and emergent plants, with limited contribution of terrestrial higher plants. The anoxic alkaline environment and high salinity condition at the lake bottom were beneficial for the formation of carbonate minerals and the preservation of OM. This were characterised by medium abundance of OM and high hydrocarbon generation potential. The study on the petrological and molecular geochemical characteristics of these organic-rich fine-grained sedimentary rocks is of great significance for investigating the genetic mechanisms and resource potential of oil and gas.

Hydrochemical Characteristics of Arsenic in Shallow Groundwater in Various Unconsolided Sediment Aquifers: A Case Study in Hetao Basin in Inner Mongolia, China

This study focused on the entire Hetao Basin, which can fall into four hydrogeological units, the Houtao Plain, Sanhuhe Plain, Hubao Plain, and South Bank Plain of the Yellow River, all of which are under different geological and environmental conditions. To systematically investigate the hydrochemical characteristics and spatial distribution of high-As groundwater (As > 10 μg/L), 974 samples were collected from shallow groundwater. As indicated from the results, high-As groundwater had an extensive distribution, and its spatial distribution in the four hydrogeological units exhibited significant variability. Three concentrated distribution areas were reported with high-As groundwater, which were all in the discharge areas of groundwater, and the arsenic contents in the groundwater were found to exceed 50 μg/L. The hydrochemical types of high-As groundwater in the HT Plain and the SHH Plain consisted of HCO3 SO4·Cl for anions and Na for cations, while those in the other two plains included HCO3 for anions as well as Na·Mg·Ca for cations. According to the pH values, the groundwater was weakly alkaline in the areas with high-As groundwater, and arsenic primarily existed as arsenite. Furthermore, high-As groundwater in the Hetao Basin was characterized by high contents of Fe (mean value of 2.77 mg/L) and HCO3− (mean value of 460 mg/L) and a low relative concentration of SO42− (average value of 310 mg/L). This study did not identify any significant correlation between groundwater arsenic and other ions (e.g., Fe2+, Fe3+, HCO3−, SO42−, NO2− and NO3−) in the entire Hetao Basin over a wide range of hydrogeological units. The results remained unchanged after the four hydrogeological units were analyzed. The special sedimentary environment evolution of the Hetao Basin was found as the prerequisite for the formation of high-arsenic groundwater. Furthermore, groundwater runoff conditions and hydrogeochemical processes in the basin were indicated as the factors controlling the formation of high-arsenic groundwater.

Benthic foraminifera distribution and sedimentary environmental evolution of a carbonate platform: A case study of the Guadalupian (middle Permian) in eastern Sichuan Basin

Benthic foraminifera are significant indicators of habitat changes and are useful for paleoenvironmental reconstruction. During the Permian period, the variation in species, individual sizes, and morphological characteristics of the different assemblages, such as the fusulinids, is a clue to paleoecological and paleoenvironmental interpretations. The eastern part of the Sichuan Basin, located near the equator in the middle Permian, Guadalupian period, was precipitated by thick beds of marine carbonate rocks with numerous benthic foraminifera. In this study, we record the species and calculate the frequency of benthic foraminifera from 445 thin sections of Guadalupian (Maokou Formation) marine carbonate rocks. Seven types of benthic foraminiferal biofacies are recognized and associated with five sedimentary microfacies in the Erya and Huilongchang sections, eastern Sichuan area. During the early Guadalupian period, small uniserial nodosariids and Endothyrida dominated the benthic foraminiferal assemblages; in the middle Guadalupian period, species of Miliolida, Ammodiscidae, and uniserial nodosariids were common; however, the species of Fusulinida, such as Schwagerina sp. and Verbeekina sp., were abundant in the late Guadalupian period. The associated sedimentary microfacies indicates a shallow open platform to marginal platform. In our study area, the early Guadalupian was deposited in an open platform to grain shoals. This was followed by gradual shallowing as the sedimentary environment shifted to marginal shallow shoals from the middle to late Guadalupian period until the paleoweathering abruptly terminated the deposition at the end of the Guadalupian period.

Geochemistry and Holocene Sedimentary Environment Evolution of Subaqueous Clinoform off Shandong Peninsula (Yellow Sea)

As a key sedimentary body connecting the north and South Yellow Sea, the subaqueous clinoform off Shandong Peninsula plays an important role in the sedimentary system of China seas, and it is also a studied example in the study among the major “source to sink” systems. Based on AMS 14C dating, sediment grain size, major and trace element contents from core WH-05 located at the edge of the clinoform, we discuss changes in the deposition rate, analyze sediment provenance and controlling factors, and reveal the environmental evolution of the source area since the Holocene. Results from core WH-05 show that marine sedimentation began at about 8.5 ka B.P. The deposition rate decreased from the initial 28.37 m/ka to 0.52 m/ka. Sediment provenance suggests that the Huanghe river sediments have been the main source for the study area since the Holocene. The As/Al, V/Sc indicators show that the environmental oxidation environment was gradually weakened and then increased slightly starting from 7.0 ka B.P. The change in redox is consistent with the change in sea level, the deposition rate, and depositional depth.

Sedimentary Environmental Evolution of the Western Taiwan Shoal Area since the Late Pleistocene

A new pollen analysis and major and trace element contents were conducted on a 40 m long gravity core recovered from the Taiwan Shoal (sand ridges), south of the Taiwan Strait, beginning in the Late Pleistocene. The changes in the pollen assemblage and concentration represent the climate change around the Taiwan Shoal and the strength of the Zhe-Min Coastal Current, whereas variations in major and trace element contents can imply the source of the sediments in the Taiwan Shoal, which are correlated with the rise or fall of the sea level with increased marine dinoflagellate cysts. The interval of 40–30 m was characterized by high pollen and spore concentrations, and evergreen Quercus was dominant taxon, which indicates a warm sedimentary environment, and the surrounding area of the Taiwan Shoal were covered by a tropical and subtropical broad-leaved forest. There were no pollen and spores from 30–24 m, which indicates a strong hydrodynamic sedimentary environment, and most of the Taiwan Shoal might have been experience subaerial exposure. The interval of 24–17 m was characterized by the reappearance of pollen and spores, as well as marine dinoflagellate cysts and foraminifera, suggesting the climate was warm and wet in the study area and an apparent marine sedimentary environment with relatively high sea level. Deciduous Quercus dominated the interval of 17–12 m, which indicated that the climate was relatively cool, corresponding to the end of Marine isotope stages3 (MIS3) to the Last Glacial Maximum accompanied by weathering and denudation. Above 12 m, the low pollen concentration with increased marine dinoflagellate cysts and foraminifera abundance suggested a marine sedimentary environment in the Taiwan Shoal. The high concentrations in Pinus corresponds to Holocene high sea level.

Stratigraphic Development and Sedimentary Environment Evolution in the Bohai Sea Since the Late Pleistocene

In recent years, there have been controversies in the evolution of sedimentary environment and stratigraphic division in the Bohai Sea since the Late Pleistocene. Based on the data (lithology, sedimentary structure, micro‐paleontology, and dating data) of 5 boreholes (core of BT113, BT114, BQ1, YRD-1101, and Lz908) in the Bohai Sea, the stratigraphic development and sedimentary environment evolution were revealed in the area since the Late Pleistocene: a marine bed of each borehole in study area was developed during MIS 5 (the MIS 5 bed of core BQ1 is not exposed); during MIS 4, there were fluvial deposits in the cores of BT113, BT114 and BQ1of the study area, but showed be a transitional sedimentary face in cores of YRD-1101 and Lz908,which may be due to the fact that the sea water has not completely withdrawn from the Bohai Sea with short time and temperature decline less than that of the Last Glacial Age. In the early MIS 3, a transgression has been occurred in cores of Lz908, YRD-1101, and BQ1 of the study area, but a fluvial deposit in cores of BT113 and BT114; from the middle and late MIS 3 to the Last Glacial Maximum, the study area was showed a regression during this period; there was have a marine bed due to wide transgression during the Holocene. According to the stratigraphic records of each borehole in the study area, we find that the evolution of the sedimentary environment is consistent with the trend of global sea level changes, indicating that stratigraphic development and the evolution of the sedimentary environment are mainly controlled by global sea level changes in the study area since the Late Pleistocene. In addition, we need further study to find out other factors.

The role of an ice-sheet, glacioisostatic movements and climate in the transformation of Middle Pleistocene depositional systems: a case study from the Reda site, northern Poland

ABSTRACT This study provides a new stratigraphic and palaeogeographic scheme for the time span between Marine Isotope Stages (MISs) 8 and 6. Based on detailed sedimentological and palynological studies, the roles of the Scandinavian Ice Sheet (SIS) advances and changing climate in the evolution of sedimentary environments is considered. At the Reda site, northern Poland, vertically stacked, 25 m thick glacigenic and fluvial successions were distinguished and divided into four depositional complexes. Two glacigenic units (R1 and R 2), representing two SIS advances in study area, are separated by two fluvial units (R2 and R3). The first SIS advance recorded at the Reda site took place at the end of MIS 8. Proglacial fluvial systems transported material along the ice margin towards the NW (R1 complex). Migration of the forebulge during deglaciation led to incision and opened the outflow towards the SW. During the younger part of MIS 7, the older fluvial unit (R2 complex) was deposited in a sand-bed braided fluvial system in boreal climate conditions. Local erosion and change in the sedimentation style into a meandering one under periglacial conditions took place (R3 complex). The progressive cooling of the climate towards the end of MIS 6 resulted in another SIS transgression and deposition of coarse-grained sediments (R4 complex) in the ice-marginal zone during deglaciation. SIS played a key role in the formation of R1 and R4 complexes. Glacial processes managed the reshaping the landscape through the erosion of older sediments and in the formation of accommodation space. Glacioisostatic movement controlled accommodation space, accumulation-erosion ratio, size of catchment and morphology of the valley.

Depositional controlling factors on pore distribution and structure in the lower Silurian Longmaxi shales: Insight from geochemistry and petrology

The present study investigates the lower Silurian (Rhuddanian-Aeronian) Longmaxi Formation of the Sangzhi block South China's Upper Yangtze Platform to establish the role of depositional environment as determinant of pore structure evolution. Research methods include clay grain microfabric analysis using a scanning electron microscope with cathodoluminescence, analysis of total organic carbon and major and trace element concentrations, X-ray diffraction analysis, and porosity measurements. Our results suggest that Rhuddanian shale accumulated in a suboxic environment that experienced relatively high paleoproductivity thereby enriching the sediment in organic matter (OM) and biogenic quartz. These combined to yield sediment characterized by relatively high porosity. OM appears to have been the main contributor to porosity with OM pores comprising the dominant pore type. Aeronian time was marked by an increased supply of terrigenous sediment, especially clay, and establishment of oxygenated bottom conditions. The increased supply of terrigenous sediment and decreased paleoproductivity resulted in sediment deficient in OM resulting in low porosity. Pore spaces in clay minerals are subordinate to interparticle pores, the dominant porosity of Aeronian shale. The transition of organic-rich Rhuddanian shale containing biogenic silica upward into clay-rich Aeronian shale deficient in OM is accompanied by a change in porosity and dominant pore type that reflects the changing depositional environments of these deposits. The up-section evolution of sedimentary environment reflects the effects of varying water depth and degree of water exchange with the open ocean related to sea level fluctuation. Documented changes in porosity related to depositional environment have a direct influence on shale gas reservoir capacity. Specifically, a suitable sedimentary environment creates the conditions for high-quality shale formation.

Evolution of sedimentary environments and geography of the Gavkhouni Playa during the Late Quaternary

Gavkhouni Playa, as lowland of the Zayandehrud River catchment area, is located in an inter-mountain basin in Central Iran. A total of 16 sedimentary cores were taken from the inner and outer parts of the basin, and surrounding areas to investigate depositional systems of the Gavkhouni Playa during the late Quaternary. Sedimentary facies were identified based on sedimentary texture, type of evaporite minerals, presence of organic materials, color changes, and other microscopic characteristics, and sampling was performed based on changes in types of sediment and sedimentary facies. A total of 80 sediment samples were selected for granulation analysis by two methods of wet sieving for coarse-grained particles and Laser Particle Sizer Analysette for smaller than sand (silt and clay) particles. Sedimentology parameters were measured by the Sedilizer software, and the results were statistically analyzed by the SPSS software. The major types of sediments in the Gavkhouni Playa sub-surface, mud and sedimentary environments included aeolian, fluvial, deltaic, lacustrine, and playa environments. According to 14C-AMS isotope dating analysis, the sedimentation rate for 40 ka period, is about 0.4 and 0.25 mm in western and eastern parts per year, respectively. Paleogeography of the Gavkhouni Playa and its extent have been reconstructed for the last 40 ka BP. The results showed that the Gavkhouni Basin extended to the western part of sand dunes during the late Pleistocene. During the early-middle Holocene, coastline regression and the Zayandehrud Delta progression toward the playa occurred in the northern part of the area. During this time, aeolian sands spread to the Gavkhouni Playa. In the Late Holocene, arid conditions caused a decrease in water level and coastline regression along with the domination of the playa environment in the Gavkhouni margin. But, there were still ephemeral lake conditions in the center of the Playa. Gavkhouni Playa experienced an increase in the level and progression of the coastline towards land about 3000 years ago. The presence of arid conditions about 1000 years ago (cal. BP) changed the Gavkhouni lands into a playa environment, and this situation was dominant in the area almost to the present day.

Multi-proxy reconstruction of the Holocene transition from a transgressive to regressive coastal evolution in the northern Jiangsu Plain, East China

The northern Jiangsu Plain (NJP) is an important part of the coastal plain in eastern China that has been affected by transgression and regression continuously throughout geological history; the region has well-recorded information on marine and terrestrial environmental changes since the Holocene. Previous studies have not reached a consensus regarding the timing and frequency of the occurrence of the Holocene transgression in the NJP, mainly due to the limitations of the dating methods and the difficulty in obtaining study materials. This study illustrated the results of integrated accelerator mass spectrometry 14C analyses, optically stimulated luminescence dating, grain size distribution, geochemical elements, total organic carbon, and diatoms from the Gangxi profile, located in the NJP, to elucidate the sedimentary environmental evolution characteristics and responses to the relative changes in sea levels during the Holocene. Our results indicate that the sedimentary environment in the study area has changed significantly since nearly 13,550 ± 127 cal yr BP and experienced the transformation of a lacustrine sedimentary environment, tidal flat–shallow sea sedimentary environment, and lacustrine sedimentary environment. The time at which the seawater reached the study area was 7270 ± 71 cal yr BP, while the occurrence of high sea levels was during 6570 ± 86–6260 ± 85 cal yr BP during the Holocene. In addition, six significant sea-level fluctuations occurred in the NJP during the Holocene. Consequently, the evolution of the sedimentary environment and the development of sedimentary strata in the coastal area of the NJP since 13,550 ± 127 cal yr BP were found to be related to global temperature and precipitation changes, sea-level fluctuations, and seawater intrusion. The research results provide an important reference for studying the land–ocean interaction zone respond to sea-level changes in the future.

Dominant Role of Sea Level on the Sedimentary Environmental Evolution in the Bohai and Yellow Seas Over the Last 1 Million Years

Transgression and regression deposits from the shallow continental margin provide information on orbital-scale variations in sea level, climate change, and local tectonics. In this study, we conduct a high-resolution chronological and sedimentological analysis of a 125-m core (NHH01) drilled in the southern Yellow Sea. We developed a high-resolution age model at the orbital timescale over the last ∼1 Myr by the astronomical tuning of the sediment grain size. Sedimentological analysis and environmental proxies reveal that the study area is characterized by cyclic alternations of neritic and littoral/fluvial deposits controlled by glacial–interglacial sea-level changes. These results confirm the earlier assumption that sea-level fluctuations play a dominant role in the sedimentary architecture of the southern Yellow Sea. Moreover, only low-frequency sea-level fluctuations (∼100 kyr) were preserved in the NHH01 sequence; however, additional high-frequency (∼40 kyr) sea-level variations were also present in the sediments of the shallower Bohai Sea. Despite the large spatial difference, this finding implies that the sedimentary environment in the eastern marginal seas of China had been influenced by the sea level as a whole over the last 1 Myr. The comparison of the sedimentary environment with other cores from the Bohai Sea, Yellow Sea, and coastal region, as well as records from Indonesia and Japan, reveals that a consistent initiation of large-scale marine transgression occurred at ∼0.8–1 Ma. This phenomenon was likely caused by the long duration of glacio-eustatic high sea-level stands following the Middle Pleistocene transition, which is characterized by a shift in glacial cycles from 40 to 100 kyr.

Eustatic and local tectonic impact on the Late Ordovician – early Silurian facies evolution on the SW margin of peri-Baltica (the southern Holy Cross Mountains, Poland)

AbstractThis paper provides insight into the Late Ordovician to earliest Silurian evolution of sedimentary environments in the southern Holy Cross Mountains (SE Poland), which at that time were a part of the SW periphery of Baltica. The facies layout in this area was influenced by the basement block faulting, which differentiated the basin bathymetry into submarine horst and grabens, controlling facies distribution. However, the local tectonism was insufficient to fully mask the global eustatic events. Therefore, it is possible to correlate some facies changes in the Upper Ordovician and lower Llandovery sedimentary record of the southern Holy Cross Mountains with eustatic and palaeoceanographic changes reported worldwide. The most noticeable influence of eustasy on the sedimentary record in the studied area occurs at the Ordovician/Silurian boundary. It is manifested by Hirnantian regressive coarse-grained clastic sediments overlain by a post-glacial anoxic/dysoxic interval represented by the Rhuddanian transgressive black cherts and shales. It is noteworthy that the pre- and post-Hirnantian sedimentary environments in the southern Holy Cross Mountains were affected by upwelling induced by the SE trade winds.