Late Transgression Research Articles

Changes in mesophotic carbonate‐platform export across the end of the last glacial cycle (Saya de Malha Bank, western Indian Ocean)

AbstractThe export of neritic material from the top of carbonate platforms is a key process in the construction of their slopes. However, our knowledge of the supply pattern of materials from platforms is dominantly based on platforms lying in the euphotic zone during the present sea‐level highstand. This is a somewhat biased perspective as through geological time not all platforms were euphotic. The Saya de Malha Bank in the Mascarene Plateau is an example of a modern mesophotic carbonate platform, and as such, its flooding and export patterns differ from those of euphotic ones. Using cores collected on the western slope of the Saya de Malha Bank, the export patterns of the platform since the last glacial maximum were explored. Material on the platform edge is winnowed and transported to the slope by multiple possible processes. The material on the platform is a combination of high and low magnesium calcite as well as high and low strontium aragonite, integrating pelagic and neritic sources. The ratio of these constituents varies over time with changes in the platform production capability as it was flooded and drowned during the Holocene transgression. The material from the platform is transported in both confined flows, mainly during lowstands, and unconfined flows, mainly during late transgression and early highstand. In the present state of the highstand, supply may have diminished, leading to erosion of the canyon shoulders.

Depositional processes of Marinoan-age diamictites and cap carbonates in northwestern Tarim, China: Implications for chemical weathering following the Marinoan deglaciation

The Marinoan diamictites and the overlying cap carbonates at continental margins bear key information on the paleo-environment evolution during the collapse of Snowball Earth, such as the timespan of intense chemical weathering. Such a sedimentary suite has been recently discovered in the northwestern Tarim Craton of China, but its depositional processes remain controversial. Here, we present stratigraphic and isotope geochemical studies on the diamictites of the Yuermeinak Formation and the overlying cap carbonates of the Sugetbrak Formation in the Aksu region of the northwestern Tarim Craton. Multiple unconformities in the region suggest major tectonic uplifting during the Cryogenian, probably resulting in a mountainous topography and varying dip directions of the overlying cap carbonates. The paleo-elevation of these mountains might have been higher and above sea level. We propose new depositional processes that involved four stages from glacial continental facies to neritic facies and/or alluvial fan systems. The first stage formed the massive diamictites and stratified siltstones with dropstones, recording cycles between glacier retreat and advance. The second stage involved the late transgression at the end of the deglaciation and the formation of calcareous massive diamictites with negative δ13C. The third stage included the onset of cap carbonate deposition and the alternating precipitation of calcareous mudstones and carbonates, reflecting frequent sea-level changes. The fourth stage was related to a widespread marine regression that developed a terrestrial environment and the sedimentation of the sandstones of the Sugetbrak Formation. Furthermore, we suggest that intense chemical weathering on exposed continents after the Marinoan deglaciation likely lasted for only hundreds of thousands of years, releasing ample alkalis into the ocean and facilitating the precipitation of the cap carbonates.

Sequence stratigraphy and sedimentary processes since the last glacial maximum in Nha Phu Bay and adjacent shelf, central Vietnam

Three sedimentary systems tracts (LST, TST, and HST) have been identified in Nha Phu Bay and the adjacent shelf, Khanh Hoa Province, Vietnam. These have been deposited since the Last Glacial Maximum (LGM) and interpreted in this study via the analysis of high-resolution acoustic data and sediment cores. The lowstand systems tract (LST) comprises sandy sediments exposed at seabed on the outer shelf as sand ridges, and underlying the transgressive systems tract (TST) on the middle shelf. The LST developed under shallow-marine settings during the sea-level lowstand and early sea-level rise before 14.6 cal kyr BP. The TST comprises primarily fine-grained sediments deposited during the transgression between 14.6 and 8.0 cal kyr BP in an incised trough of the outer shelf, on the middle shelf, and in Nha Phu Bay. Erosion of the seaward portion of the TST on the middle shelf might occur during the late transgression (9.0–8.0 kyr BP). The highstand systems tract (HST) comprises sediments deposited during the sea-level highstand between 8.0 and 0.0 cal kyr BP and is distributed widely in the bay, on the inner-middle shelf, and partially on the outer shelf. A paleo-coast zone, located in 100–120 m present-day water depth, is recognized through the appearance of sand ridges and sandy sediments. The seafloor sediment distribution is mapped via four major acoustic echo types, combined with seabed sediment samples. The coarse-grained sediment distribution, subaqueous outcrops, and thin deglacial sediment thickness on the inner shelf indicate erosion-dominated processes under vigorous hydrodynamic conditions. Nha Phu Bay and the middle shelf are interpreted as the depocentres. The estimated sediment load deposited in Nha Phu Bay is 0.18 Mt./yr, accounting for 15–35% of the annual sediment discharge from the Dinh River. The seabed morphology, muddy sediment distribution, and deglacial sediment thickness reveal a dominant sediment-transport pathway, across the inner shelf to the middle shelf, near the northern shoreline of Nha Phu Bay under the influence of the southwest monsoon.

Climate-Controlled Coastal Deposition of the Early Permian Liangshan Formation in Western South China

During the late Paleozoic ice age, tropical coastal depositions have been widely linked to high-frequency sea-level variations, but their linkage with the associated climate change was not fully understood. In the early Permian, two deglaciations occurred in the late Sakmarian and late Artinskian, respectively. During the late Artinskian deglacial warming and transgression, coal-bearing siliciclastic successions of the Liangshan Formation were developed in South China. Three facies associations were recognized from the Liangshan Formation successions in western South China and ascribed to coastal alluvial plain, estuarine, and deltaic environments. Detailed analysis of sedimentology, paleosol morphology, and sandstone petrology suggest a relatively dry-to-wet climate shift and estuarine to deltaic facies transition in the lower Liangshan Formation. This climate shift and facies transition can be temporally correlated based on regional stratigraphic correlations, although precise age constraints are needed to test this correlation. The estuarine interval of the lowest Liangshan Formation signified a rapid transgression during the late Artinskian deglaciation and likely formed during a relatively arid climate with locally small fluvial systems, which provided limited sediment supply. The subsequent transition to and initiation of deltaic deposition was broadly associated with the inferred climate shift and could be primarily resulted from a climate wetting-induced great increase in sediment supply, irrespective of the deglacial sea-level rise.

Low-accommodation foreland basin response to long-term transgression: A record of change from continental-fluvial and marginal-marine to open-marine sequences over 60,000 km2 in the western Canada foreland basin

Low-accommodation foreland basins have been of recent interest because their stratigraphic architectures provide insight into the interaction of tectonic subsidence and eustasy. Aptian-aged strata in Alberta, Canada (McMurray Formation and Wabiskaw Member) were deposited under the influence of a continental-scale river that longitudinally transported and debouched sediment into the southward-transgressing Boreal Sea in the distal, low-accommodation Western Canada Foreland Basin (WCFB). In this study, we present a high-resolution stratigraphic framework for the McMurray-Wabiskaw interval, which was deposited during a long-term transgression. Using wireline logs from >20,000 wells and more than 500 cores, regional mapping focused on resolving stratigraphic relationships and the distribution of depositional environments across approximately 60,000 km2 in the Athabasca Oil Sands Region of northeastern Alberta. The studied stratigraphic interval is part of a third-order sequence: the McMurray Formation developed during a period of relative sea-level fall, lowstand, and early transgression, while the overlying Wabiskaw Member was deposited during late transgression. Within the McMurray Formation, superimposed fourth-order sea-level fluctuations in this low accommodation setting created a complex amalgam of deltaic strata vertically and laterally juxtaposed with valley-fill deposits. Relative sea-level rises resulted in rapid transgressions in which the shorelines migrated >400 km landward. Thin (5–15 m thick), widespread deltaic parasequence sets were deposited during subsequent sea-level highstands. During relative sea-level falls, fluvial meandering channel belts developed in downcutting valleys, with associated shorelines dramatically prograding basinward. In the Wabiskaw Member, continued sea-level rise coupled with potentially decreasing sediment supply resulted in the development of tide-influenced/dominated channels and bars in estuaries. The final phase of the third-order transgression was marked by a regional transgressive ravinement event and several southwestward backstepping wave-dominated shorefaces/strandplains. This low-accommodation foreland basin succession demonstrates a transition from deposition in continental fluvial and marginal-marine settings subject to high-frequency eustatic changes, to open-marine conditions over a long-term transgression.

Impact of sedimentation, climate and sea level on marine sedimentary pyrite sulfur isotopes: Insights from the Valle di Manche section (Lower-Middle Pleistocene, southern Italy)

Variations in the isotopic composition of sulfur in sedimentary pyrite (δ34Spyr) are often used to reconstruct global sulfur biogeochemical cycling and Earth's surface oxidation state over Earth history. Recent work, however, has shown that δ34Spyr is strongly impacted by local depositional conditions, which both confounds attempts to reconstruct global sulfur cycling and provides a new proxy for investigating local paleoenvironmental conditions. We present a chemostratigraphic record of δ34Spyr in a detailed paleoenvironmental and sequence stratigraphic framework spanning the Early-Mid Pleistocene transition from the Crotone Basin (Calabria, Southern Italy). Bulk δ34Spyr data parallel transgressive-regressive cycles and enable the differentiation of progradational and retrogradational stacking patterns, where δ34Spyr values decrease toward −50‰ in outer shelf deposits during late transgression and become more positive and variable in prograding sedimentary units accumulated in shallower environments. In parallel with the observed variations in δ34Spyr, complementary data on organic carbon abundance and isotopic composition and total nitrogen abundance document changes in terrestrial delivery of sediment to the basin, as a consequence of glacial-interglacial eustatic sea-level changes, regional climate and local tectonics. The chemostratigraphic record of δ34Spyr appears sensitive to variations in sedimentation rates and local erosional surfaces and therefore may represent a powerful tool to assess stratal stacking patterns for sequence stratigraphic interpretations of siliciclastic successions. These results highlight the role of local conditions in controlling sedimentary δ34Spyr records and illustrate how isotopic data can be used to reconstruct key parameters of the sedimentary environment that might not otherwise be accessible, especially in deep-time strata.

ABOUT DATING OF PETROGLYPHS OF GOBUSTAN (AZERBAIJAN)

Since the discovery of the petroglyphs of Gobustan, there have been numerous studies of petroglyphs, field work on documentation, and archeological excavations. Despite the extensive literature on Gobustan, the issue of dating the rock paintings remains controversial. The author of the paper, using the results of radiocarbon dating and the 3D Studio Max software, classifies the petroglyphs by periods. As a result, the oldest date – 13 610 CD (calibrated date) – was revealed in Gobustan in the rocky shelter of Gaya Arasi on the Kichikdash mountain. The next oldest date is approximately 10,600 CD, which was obtained from the cultural layer of the Ana-zaga cave of the Beyukdash mountain. Considering that the Late Khvalyn transgression took place nearly 14,000 years ago, and during this period the waters of the Khvalyn Sea washed the Beyukdash, Kichikdash and Dzhingirdag mountains, the interval between these dates may be due to the fluctuations of the sea level. Based on the research carried out and the dates obtained, the author singles out 9 stylistic and chronological trends in the petroglyphs of Gobustan, including the period of the Middle Ages and the Modern Age. The author emphasizes that the uniqueness of the Gobustan archaeological complex lies in the fact that separate stones with petroglyphs identical to the rock carvings on the walls of the caves were discovered from dated cultural layers. In addition, stylistic and comparative analysis allowed the author to date the rock carvings of Gobustan.
 As a result of the research, it has been revealed that the settlements of the end of the Upper Paleolithic and Mesolithic Ages were mainly located on the upper terraces of the mountains. In the Neolithic and Eneolithic Ages, with the rise in the level of the Caspian Sea, the caves retained the status of the main place of residence. With the lowering of the sea level in the Bronze Age, the middle and lower terraces were inhabited. During this period, the settlers of Gobustan, who were engaged in cattle breeding, painted images of bezoar goats with large curved horns on the rocks. At the foot of the mountains, the round settlements and the tradition of kurgan burials emerged.

Coarse‐grained deltas approaching shallow‐water canyon heads: A case study from the Lower Pleistocene Messina Strait, Southern Italy

AbstractThe tide‐dominated Messina Strait (southern Italy) is a 3 km wide marine passageway, whose block‐faulted borders form steep subaqueous zones incised by canyons and gullies. These erosional features retreat towards the shorelines and are often in direct connection with subaerial valley‐bounded river deltas. High‐energy density‐flows generated by river floods periodically enter the canyon heads, attaining supercritical‐flow regime and accreting large, upslope‐migrating bedforms. Although these bedforms have been documented in recent studies, little attention has been paid to the definition of the type of delta entering canyon heads, the internal features of river‐influenced deposits accumulated in the nearshore zone, and their interplay with tidal currents flowing axially to the strait. This study focuses on a Lower Pleistocene coarse‐grained succession exposed along the north‐eastern margin of the modern Messina Strait, investigated using conventional facies analysis and sedimentological logging, integrated with photogrammetric techniques and interpretation of drone‐acquired imagery. Facies confinement between basement blocks suggests a subaqueous delta complex shed from the tectonically controlled margin of the ancient strait and entering shallowly submerged canyon heads. Basal breccias, conglomerates and pebbly sandstones exhibiting channel‐form discontinuities and upslope dipping backsets are interpreted as cyclic‐step and antidune deposits. Units composed of these facies are comprised between master erosional surfaces and tidal ravinement surfaces. The tidal ravinements suggest that canyon infill occurred during a major phase of sea‐level rise, punctuated by minor falls and stillstands. These surfaces are overlain by mixed bioclastic–siliciclastic, arenitic, trough and planar cross‐strata, representing dunes migrating roughly parallel to the palaeo‐coastline and originated by tidal currents amplified by the narrowing of the ancient Messina Strait. Tidal‐influenced sedimentation dominated over the fluvial‐influenced processes during the late transgression, overfilling the canyon relief. The exceptionally good exposure of depositional architectures and facies characteristics is key to outline the general features of a specific type of delta system, fed by valley‐bounded rivers and entering canyon heads in the nearshore of tectonically‐controlled, tide‐influenced steep strait margins. The pre‐existing subaqueous incised topography forced the delta front to be split into lobe branches during the canyon infilling, hampering clinoform architectures and preserving large supercritical‐flow sedimentary structures. This study suggests these as possible criteria for the recognition of similar systems in outcrop or subsurface.

Study on the Upper Paleozoic Source Rocks in Southwestern Henan, China

The Upper Paleozoic strata in Southwestern Henan have good prospects for unconventional oil and gas exploration. This paper takes the Upper Paleozoic source rocks in the Yuzhou area and the Pingdingshan area in Southwestern Henan as the research object, and tests 107 samples from the Upper Paleozoic coal rock, mudstone and carbonate rock. Combined with the sedimentary environment background, the Upper Paleozoic source rocks in Southwestern Henan are comprehensively evaluated. The results show that the Upper Paleozoic source rocks in Southwestern Henan, including coal rocks, mudstone and carbonate rocks, can be used as potential source rocks. Vertically, the source rocks are continuously distributed in the lower layer below the sandstone of Shanxi Formation. The Dazhan sandstone is only locally developed; the distribution of Upper Paleozoic source rocks in Southwestern Henan is mainly related to the Late Paleozoic transgression.

The Record of Environmental and Microbial Signatures in Ancient Microbialites: The Terminal Carbonate Complex from the Neogene Basins of Southeastern Spain

The Messinian microbialites of the Terminal Carbonate Complex (TCC) from the Neogene basins of southeastern Spain show both diversified morphologies and an excellent preservation of primary microbial microstructures. Their stratigraphic architecture, fabric (micro-, meso-, and macro-fabric), and mineralogical composition were investigated in eight localities from three sedimentary basins of southeastern Spain: The Sorbas and Bajo Segura basins and the Agua Amarga depression. Two recurrent microbialite associations were distinguished. Laterally linked low relief stromatolites predominated in Microbialite Association 1 (MA1), which probably formed in low energy lagoons or lakes with fluctuating normal marine to hypersaline water. The microfabrics of MA1 reflected the predominance of microbially induced/influenced precipitation of carbonates and locally (Ca)-Mg-Al silicates. Microbialite Association 2 (MA2) developed in high energy wave and tidal influenced foreshore to shoreface, in normal marine to hypersaline water. High-relief buildups surrounded by mobile sediment (e.g., ooids or pellets) dominated in this environment. MA2 microbialites showed a significant proportion of thrombolitic mesofabric. Grain-rich microfabrics indicated that trapping and binding played a significant role in their accretion, together with microbially induced/influenced carbonate precipitation. The stratigraphic distribution of MA1 and MA2 was strongly influenced by water level changes, the morphology and nature of the substratum, and exposure to waves. MA1 favorably developed in protected areas during third to fourth order early transgression and regression phases. MA2 mostly formed during the late transgressions and early regressions in high energy coastal areas, often corresponding to fossil coral reefs. Platform scale syn-sedimentary gypsum deformation and dissolution enhanced microbial carbonate production, microbialites being thicker and more extended in zones of maximum deformation/dissolution. Microbial microstructures (e.g., microbial peloids) and microfossils were preserved in the microbialites. Dolomite microspheres and filaments showed many morphological similarities with some of the cyanobacteria observed in modern open marine and hypersaline microbialites. Dolomite potentially replaced a metastable carbonate phase during early diagenesis, possibly in close relationship with extracellular polymeric substances (EPS) degradation. Double-layered microspheres locally showed an inner coating made of (Ca)-Mg-Al silicates and carbonates. This mineral coating could have formed around coccoid cyanobacteria and indicated an elevated pH in the upper part of the microbial mats and a potential dissolution of diatoms as a source of silica. Massive primary dolomite production in TCC microbialites may have resulted from enhanced sulfate reduction possibly linked to the dissolving gypsum that would have provided large amounts of sulfate-rich brines to microbial mats. Our results open new perspectives for the interpretation of ancient microbialites associated with major evaporite deposits, from microbe to carbonate platform scales.

Северо-западные берега Онежского полуострова Белого моря в голоцене: условия развития, динамика, хронология

According to detailed geomorphological studies, radiocarbon dating and Stolbovoe Lake sediments and terrace sedimentary cover diatom analysis three different stages of coastal zone development in the northwest of the Onega Peninsula had been identified and dated. The abrasion coastlines at elevations of 18.5–30 m were formed earlier ~9.5–8.5 cal kyr BP, during the Late Glacial transgression and the glacio-isostatic regression of the Early Holocene. A well-defined predominantly abrasion coastline at elevations of 14–18.5 m was formed ~8.2–5.8 cal kyr BP during the mid-Holocene Tapes transgression with insignificant fluctuations of the sea level with hydrodynamic activity greater than present. A short-term episode (~6.0–5.8 cal kyr BP) of the relative sea level rise on the shore of the Dvina Bay has been identified, probably associated with storm surges. Abrasion-accumulative coastlines at elevations up to 14–15 m were formed after ~5.8 cal kyr BP in the conditions close to modern. At all stages of development, the shores were dynamically young. The leading role of the postglacial uplift in the extension of the coast contour, and of the structure of the glacial relief–in the morpho- and lithodynamics of the coastal zone is shown. During the Tapes transgression, the rates of uplift of adjacent morphostructural blocks differed (~0.5 and 2.1–2.2 mm/year); then the uplift became uniform (~2.8–2.9 mm/year). The structure of the coastal forms indicates the constant prevailing directions of the waves and sediment transport, starting from the middle Holocene.

Evaluation of the hydrochemical evolution characteristics and renewable capacity of deep fresh groundwater in the Hangzhou Bay New Zone, China

The deep fresh groundwater in the Hangzhou Bay New Zone lies in a confined aquifer. The roof of the freshwater layer is 80–110-m deep, and its average thickness is 22 m. Freshwater occupies the downstream portion of the aquifer structure, while saline water occupies the upstream portion of the aquifer structure; this rare freshwater distribution characteristic causes widespread concern. Based on the hydrogeological conditions of the study area, the spatial and temporal evolution characteristics of groundwater in the Hangzhou Bay New Zone are researched by analyzing the hydrochemical characteristics and isotope tracing results of water samples. Furthermore, the formation mechanism of the fresh groundwater and its renewal capacity are evaluated. The results show that (1) the groundwater chemical type is influenced by the total dissolved solids (TDS). With an increase in the TDS of the groundwater, the main anions in the groundwater evolve from HCO3− to Cl−, and the major cations evolve from Ca2+ and Mg2+ to Na+. (2) The hydrogeological conditions, the hydrochemistry evolution characteristics, and the 2H, 18O, and 3H characteristics of the groundwater indicate that the freshwater does not receive a supplement of modern water and that no hydraulic connection exists between different layers. (3) According to 3H and 14C dating, the formation period of deep fresh groundwater and saline water in the study area was 13.0–17.9 Ka.B.P, and, 10.6–15.6 ka.B.P (the late Pleistocene), respectively. It is predicted that the fresh groundwater is the continental sedimentary water buried in the Pleistocene, as a result of sealing the well-isolated original sedimentary fresh water because of direct upstream infiltration and downstream salinization in the late transgression (mainly ice transgression in the later stage). (4) The fresh groundwater has little renewable capacity due to the absence of recharge sources.

Marine geological researches in the greater bay of Navarino area, Southern Ionian sea

This paper examines the marine area of the Bay of Navarino and the Ionian sea sector to the west of the bay, based on a collection of shallow and intermediate penetration seismic profiles and on three gravity cores. The Bay has a smooth sea bottom morphology with maximum depth (75m) toward the south. Two minor reefs penetrate the sea bottom, one of them rising above the sea level forming a rocky island. In the open sea area the sea bottom is anomalous, especially after the shelf break, that is distinguished at a depth of approx. 160m. Beyond this depth deep valleys and ridges alternate and produce a rough morphology. The examination of the three gravity cores indicated that their sediment sand composition is mainly biogenic with minor amounts of terrigenous material. Increased shell fragments and terrigenous material was found at the bottom of one core taken at a depth of 116m, related probably to wave action at an earlier sea level position. The study of the seismic profiles collected within the bay and in the shelf area revealed,the presence of two distinct sedimentation units, un upper A filling with loose sediments the basins that are formed in the lower Y which is the basement. Within unit A two distinct subunits are recognized Al and A2, separated by an unconformity. In the sector to the west of the bay and beyond the shelf break, alternating opaque and transparent sediment packages are present, that are attributed to earlier sedimentation phases of low/high sea level stages. An older shelf break feature correlated with sea level stage 6 was distinguished at approx. 250m. sea depth. Thus subsidence rate in the area is estimated between 1 and 2 mm/year. The comparison of all data with the known sea level change curve indicated that unit AI was deposited during and after the latest transgression (stage 1) the unconformity between Al and A2 is related to the previous regression (stage 2), while the deposition of the unit A2 took place probably during stages 3 and/or 5. The morphology of the basement Y in the bay and the shelf area is thus attributed probably to stage 6 when the area was again subaerially exposed.

Late Holocene wetland transgression and 500\xa0years of vegetation and fire variability in the semi-arid Amboseli landscape, southern Kenya

The semi-arid Amboseli landscape, southern Kenya, is characterised by intermittent groundwater-fed wetlands that form sedimentary geoarchives recording past ecosystem changes. We present a 5000-year environmental history of a radiocarbon dated sediment core from Esambu Swamp adjacent to Amboseli National Park. Although radiocarbon dates suggest an unconformity or sedimentary gap that spans between 3800 and 500 cal year BP, the record provides a unique insight into the long-term ecosystem history and wetland processes, particularly the past 500 years. Climatic shifts, fire activity and recent anthropogenic activity drive changes in ecosystem composition. Prior to 3800 cal year BP the pollen data suggest semi-arid savanna ecosystem persisted near the wetland. The wetland transgressed at some time between 3800 and 500 cal year BP and it is difficult to constrain this timing further, and palustrine peaty sediments have accumulated since 400 cal year BP. Increased abundance of Afromontane forest taxa from adjacent highlands of Kilimanjaro and the Chyulu Hills and local arboreal taxa reflect changes in regional moisture budgets. Particularly transformative changes occurred in the last five centuries, associated with increased local biomass burning coeval with the arrival of Maa-speaking pastoralists and intensification of the ivory trade. Cereal crops occurred consistently from around 300 cal year BP, indicative of further anthropogenic activity. The study provides unique insight in Amboseli ecosystem history and the link between ecosystem drivers of change. Such long-term perspectives are crucial for future climate change and associated livelihood impacts, so that suitable responses to ensure sustainable management practices can be developed in an important conservation landscape.

Clay Minerals Variations in Quaternary Sediments of Basrah City-Iraq

Mineralogical and chemical analysis of two well cutting in quaternary sediments at Basrah city. This study have been focused on the quaternary clay minerals variations which give a clear indication to marine transgression and or / regression in Hammar formation. Kaolinite, Illite, Palygoreskite, Illite-Palygorestike mixed layer, Chlorite, Montmorillonite, Vermiculte, and mixed layers of Illite- Smectite are the most quantitatively important phyllosilicates in soil studies in both boreholes. The mineralogical composition of cutting sediments shows significant variability in the different size fractions and depth distribution. Chlorite and kaolinite minerals were increase in the fine grain size especially in the clayey silt, whereas montmoriolllinite and vermiculite minerals were increase in coarse grains especially in silty sand texture. Kaolinite decrease in abundance with depth, which give indicative of a transition from non-marine in quaternary recent sediment ( fresh or brackish water silt) to marine facies in quaternary Hammar formation ( marine shelly silt) during last transgression of quaternary. Palygoreskite mineral percentages increasing at depths 27 and 28 meter , after decreased at 30, 32, 35 , and 40 m respectively , which give data indication that early quaternary marine transgression happened in 32m , and center of quaternary marine transgression detected in 27 and 28 meters , while late marine transgression detected in 17 m , and all of these represent by Hammar formation. Soil ageing also caused to downward increase of montmorillonite suggest to climate became more arid during the early quaternary. Variations ratio of montmorillonite versus kaolinite can be indicated to climatic fluctuation. Illite-Semectite featured indicates changes in both sediment source and paleoclimate. Illite transformation for Illite-Palygoreskite mixed layers with ageing. Vermiculite has strong susceptibility to increase with age. SiO₂, Al₂O₃, CaO, MgO, K₂O, and Fe₂O₃ were the major oxides that identified in present study and used as indicated of clay minerals in studied sediments.

Carbon isotope gradient of the Ediacaran cap carbonate in the Shennongjia area and its implications for ocean stratification and palaeogeography

The geochemistry and paleogeography of the Doushantuo succession in the Shennongjia area have been insufficiently studied. Here, we report on the carbon and oxygen isotope compositions of Ediacaran Doushantuo cap carbonates from four sections (Longxi, Muyu, Yazikou and Songluo) in the Shennongjia area. A large C-isotopic gradient (~5‰) between the Longxi and Songluo sections, here identified for the first time, is inferred to have been dynamically maintained by photosynthesis in surface waters and anaerobic oxidation of dissolved organic carbon (DOC) in deep waters. Spatial variation in C-isotope chemostratigraphy among the four sections was related to Marinoan post-glacial sea-level elevation changes. At Longxi, a positive δ 13Ccarb shift below the horizon containing tepee-like structure resulted from intense photosynthesis during early regression. A negative δ 13Ccarb shift within the tepee-horizon was triggered by sulfate reduction and freshwater mixing with 13C-depleted dissolved inorganic carbon (DIC) during late regression. A positive δ 13Ccarb excursion in the uppermost part of the cap carbonate was related to enhance primary productivity and organic matter burial during early transgression. At Muyu, the carbon isotopic variation tendency, which is similar to that at Longxi, may have been mildly influenced by the surface water environment. At Songluo, the positive δ 13Ccarb excursion, up to -4‰ in the lower part of the cap carbonate, was probably associated with methanogenesis in deep waters during late transgression to early regression and subsequently disappeared due to decomposition of methane hydrate during late regression. At Yazikou, the consistently stable δ 13Ccarb values around -4‰ indicate that the cap carbonate may have deposited at intermediate water depths. As evidenced by diagnostic sedimentary characteristics of the study sections, the palaeogeographic framework of the Shennongjia area exhibited deepening from SE to NW during the Early Ediacaran Period in the aftermath of Snowball Earth.

Systematic vertical and lateral changes in quality and time resolution of the macrofossil record: Insights from Holocene transgressive deposits, Po coastal plain, Italy

In siliciclastic marine settings, skeletal concentrations are a characteristic feature of transgressive intervals that provide insights into biological and sequence-stratigraphic processes. To investigate taphonomic signatures of transgressive intervals, we analysed three cores along a depositional profile from the high resolution chrono- and stratigraphic framework of the Holocene Po coastal plain, in northern Italy. Coupled multivariate taphonomic and bathymetric trends delineated spatial and temporal gradients in sediment starvation/bypassing, suggesting that quality and resolution of the fossil record vary predictably along the studied depositional profile. Moreover, integration of taphonomic, bathymetric, and fossil density trends across the study area reveals distinctive signatures useful in characterizing facies associations and determining surfaces and intervals of sequence-stratigraphic significance. Within the southern Po plain succession, taphonomic degradation of macroskeletal remains increases from proximal/nearshore to distal/offshore locations. This trend is discernible for both biologically-driven (bioerosion) and physically-driven (e.g., dissolution, abrasion) shell alterations. Compared to the up-dip (most proximal) core, the down-dip core is distinguished by shell-rich lithosomes affected by ecological condensation (co-occurrence of environmentally non-overlapping taxa) and by higher taphonomic alteration. The onshore-offshore taphonomic trend likely reflects variation in sediment-accumulation along the depositional profile of the Holocene Northern Adriatic shelf, with surface/near-surface residence-time of macroskeletal remains increasing down dip due to lower accumulation rates. These results indicate that, during transgressive phases, changes in sea level (base level) are likely to produce down-dip taphonomic gradients across shelves, where the quality and resolution of the fossil record both deteriorate distally. Radiocarbon-calibrated amino acid racemisation dates on individual bivalve specimens and the chronostratigraphic framework for this profile suggest jointly that the high levels of taphonomic degradation observed distally developed over millennial time scales (∼8ky). Whereas in proximal setting overall low taphonomic degradation and geochronologic constrains point to centennial-scale time-averaging during the late transgression phase. Patterns documented in the Holocene transgressive (and lowermost regressive) deposits of the southern Po Plain may be characteristic of siliciclastic-dominated depositional systems that experience high-frequency, base-level fluctuations.

Foraminifera eco-biostratigraphy of the southern Evoikos outer shelf, central Aegean Sea, during MIS 5 to present

The South Evoikos Basin is a marginal basin in the Aegean Sea which receives little terrigenous supply and its sedimentation is dominated by hemipelagic processes. Late Quaternary benthic and planktonic foraminifera from core PAG-155 are investigated in order to understand their response to the glacial-interglacial cycles in this region. The quantitative analysis of planktonic foraminifera, coupled with accelerator mass spectrometry (14C-AMS) radiocarbon date measurements, provide an integrated chrono-stratigraphic time framework over the last 90ka (time interval between late Marine Isotopic Stages 5 and 1; MIS5-MIS1). The temporary appearance and disappearance as well as several abundance peaks in the quantitative distribution of selected climate-sensitive planktonic species allowed the identification of several eco-bioevents, useful to accurately mark the boundaries of the eco-biozones widely recognized in the Mediterranean records and used for large-scale correlations. The established bio-ecozonation scheme allows a detailed palaecological reconstruction for the late Pleistocene archive in the central Aegean, and furthermore provides a notable contribution for palaeoclimatic studies, facilitating intercorrelations between various oceanographic basins. The quantitative analyses of benthic foraminifera identify four distinct assemblages, namely Biofacies: Elphidium spp., Haynesina spp. Biofacies, characterized by neritic species, dominated during the transition from MIS 5 to MIS 4; Cassidulina laevigata/carinata Biofacies dominated till 42ka (transgressive trend from MIS 4 to MIS 3); Bulimina gibba Biofacies dominated from 42ka to 9.5ka (extensive regression MIS 3,2 through lowstand and early transgression; beginning of MIS 1); Bulimina marginata, Uvigerina spp. Biofacies dominated from 9.5ka to the present (late transgression through early highstand; MIS 1)., This study showed that the South Evoikos Basin which is characterized by its critical depths and connections to the open sea, and its small volume water masses that nourished foraminiferal assemblages, accurately records 5th−4th order sea level and climatic fluctuations. Especially, the basin's limited communication with the open ocean implies that any climatic signals will be recorded in an amplified fashion, and therefore this heightened sensitivity to the effects of climate variability further underlies the prominent role of such marginal basins in the understanding of the global climatic evolution.

GIRKAN STAGE IN THE DEVELOPMENT OF THE CASPIAN SEA

Analysis of data on relief and geological structure of the continental part of the Dagestan coast of the Caspian Sea, and especially, aging of sediments of marine terraces by faunal data (shells) confi rm the existence of the independent Girkan stage of the sea development. Girkan transgression occurred in the time interval between Late Khazar and Early Khvalyn transgressions. As a result of the abrasion activity of Girkan transgression the topography of the coastal lowland and its morphological boundary with the foothills of the Greater Caucasus were fi nally formed. The boundary has an altitude of 100–105 m and 120–130 m. These altitudinal differences arose as a result of tectonic movements and accumulation of slope and alluvial-proluvial sediments at the foot of the escarpment separating the coastal plain from foothills. The Late Khazar and Girkan transgressions occurred in different climatic conditions: fi rst, in the era of MIS-5e (interglacial), second in MIS 5d-5a with repeated alternations of warming and cooling.

Appraisal of groundwater resource in Holocene soil deposits by resistivity, hydrochemical and granulomerial studies in the Gulf of Mannar Coast from Southern India

This article is aimed to delineate groundwater sources in Holocene deposits area in the Gulf of Mannar Coast from Southern India. For this purpose 2-D electrical resistivity tomography (ERT), hydrochemical and granulomerical studies were carried out and integrated to identify hydrogeological structures and portable groundwater resource in shallow depths which in general appears in the coastal tracts. The 2-D ERT was used to determine the two-dimensional subsurface geological formations by multicore cable with Wenner array. Low resistivity of 1-5 Omega m for saline water appeared due to calcite at the depth of about 5 m below the ground level (bgl). Sea water intrusion was observed around the maximum resistivity as 5 Omega m at the 8 m depth, bgl in the calcite environs, but the calcareous sandstone layer shows around 15-64 Omega m at the 6 m depth, bgl. The hydrochemical variation of TDS, HCO3-, Cl-, Na+, K+, Ca2+, and Mg2+ concentrations was observed for the saline and sea water intrusion in the groundwater system. The granulometic analysis shows that the study area was under the sea between 5400 and 3000 year ago. The events of ice melting an unnatural ice-stone rain/hail among 5000-4000 years ago resulted in the inundation of sea over the area and deposits of late Holocene marine transgression formation up to Puthukottai quartzite region for a stretch of around 17 km.