Marine Basin Research Articles

The stability of present-day Antarctic grounding lines – Part 2: Onset of irreversible retreat of Amundsen Sea glaciers under current climate on centennial timescales cannot be excluded

Abstract. Observations of ocean-driven grounding-line retreat in the Amundsen Sea Embayment in Antarctica raise the question of an imminent collapse of the West Antarctic Ice Sheet. Here we analyse the committed evolution of Antarctic grounding lines under the present-day climate. To this aim, we first calibrate a sub-shelf melt parameterization, which is derived from an ocean box model, with observed and modelled melt sensitivities to ocean temperature changes, making it suitable for present-day simulations and future sea level projections. Using the new calibration, we run an ensemble of historical simulations from 1850 to 2015 with a state-of-the-art ice sheet model to create model instances of possible present-day ice sheet configurations. Then, we extend the simulations for another 10 000 years to investigate their evolution under constant present-day climate forcing and bathymetry. We test for reversibility of grounding-line movement in the case that large-scale retreat occurs. In the Amundsen Sea Embayment we find irreversible retreat of the Thwaites Glacier for all our parameter combinations and irreversible retreat of the Pine Island Glacier for some admissible parameter combinations. Importantly, an irreversible collapse in the Amundsen Sea Embayment sector is initiated at the earliest between 300 and 500 years in our simulations and is not inevitable yet – as also shown in our companion paper (Part 1, Hill et al., 2023). In other words, the region has not tipped yet. With the assumption of constant present-day climate, the collapse evolves on millennial timescales, with a maximum rate of 0.9 mm a−1 sea-level-equivalent ice volume loss. The contribution to sea level by 2300 is limited to 8 cm with a maximum rate of 0.4 mm a−1 sea-level-equivalent ice volume loss. Furthermore, when allowing ice shelves to regrow to their present geometry, we find that large-scale grounding-line retreat into marine basins upstream of the Filchner–Ronne Ice Shelf and the western Siple Coast is reversible. Other grounding lines remain close to their current positions in all configurations under present-day climate.

Heavy Metals in Sediments of Subarctic Meromictic Lakes of the White Sea as Possible Tracers of Environmental Changes

Meromictic lakes of the marine coast, quite widely distributed in the northern hemisphere, are the result of climate changes and glacier retreat. The bottom sediments of these lakes serve as a geological chronicle of the history of marine basin’s development with the geochemical occurrence forms of elements indicate various processes of their accumulation. This paper presents research results concerning the occurrence of forms of heavy metals in lake sediments along the coast of the White Sea. These results are based on a sequential seven step leaching procedure, followed by ICP-MS analysis and subsequent statistical data processing. To determine differences among the examined geochemical parameters, Pearson’s correlation analysis and Ward’s cluster analysis were utilized. The total content of Cr, Mn, Fe, Co, Ni, Zn, V, and Pb in the sediments did not exhibit significant differences based on their degree of isolation from the sea. The major contribution to deposition of these metals in sediments of the meromictic lakes studied is the residual form, encompassing the mineral matrix of the sediment. At the same time, the elevation of mobile forms for all the metals examined corresponds to an increase in the isolation of lakes from the White Sea. In the meromictic lake sediments, concentrations of Cu, Mo, and U demonstrated significant increases in forms tightly bound to organic matter, while Cd exhibited an association with Fe-Mn oxyhydroxides. Notably, a significant difference in the occurrence forms of Cu, Cd, Mo, and U was evident in the reduced sediments of meromictic lakes when compared to those of open sea bays. The meromictic lakes along the White Sea coast, positioned at various stages of isolation, hold promise for investigating the migration of metals in response to environmental changes.

PALEOCENE GLAUCONITE OF THE NEAR-VOLGA MONOCLINE OF SUBMARINE VOLCANIC-SEDIMENTARY GENESIS

A new concept of the formation of glauconite from the Paleocene deposits of the sedimentary cover of the southwestern part of the Near-Volga monocline is presented – it was formed as a result of halmyrolysis of ash material in lake conditions. Glauconitization is confined to the Paleogene thermal maximum and the periphery of active volcanism along the entire mobile belt. In this connection, it is widely distributed in the Paleogene deposits. Structural and crystal-chemical features of glauconite, stages of crystallization of its aggregates, paragenetic associations with smectite, kaolinite, and zeolite, as well as the presence of ore minerals, indicate its authigenic origin. The authigenic origin is confined to the formations of temporary, episodically submerging shallow marine basins. An applied scheme of discrimination of glauconites by their crystallochemical features has been developed. The discrimination diagram can be used to determine the specific conditions of the sedimentation basin, which are expressed in the progradation cycles of glauconite accumulation. The cycles were controlled by induced depressions within the Russian plate.

Structure and morphology of an active conjugate relay zone, Messina Strait, southern Italy

AbstractMessina Strait is a narrow fault‐bounded marine basin that separates the Calabrian peninsula from Sicily in southern Italy. It sits in a seismically active region where normal fault scarps and raised Quaternary marine terraces record ongoing extension driven by southeastward rollback of the Calabrian subduction zone. A review of published studies and new data shows that normal faults in the Messina Strait region define a conjugate relay zone where displacement is transferred along strike from NW‐dipping normal faults in the northeast (southern Calabria) to the SE‐dipping Messina‐Taormina normal fault in the southwest (offshore eastern Sicily). The narrow marine strait is a graben undergoing active subsidence within the relay zone, where pronounced curvature of normal faults results from large strain gradients and clockwise rotations related to fault interactions. Based on regional fault geometries and published age constraints, we infer that normal faults in southern Calabria migrated northwest while normal faults in NE Sicily migrated southeast during the past ca. 2–2.5 Myr. This pattern has resulted in tectonic narrowing of the strait through time by inward migration of facing normal faults and rapid mantle‐driven uplift.

Paleocene Glauconite of the Near-Volga Monocline of Submarine Volcanic Sedimentary Genesis

A new concept of the formation of glauconite from the Paleocene deposits of the sedimentary cover of the southwestern part of the Near-Volga monocline is presented. It was formed as a result of halmyrolysis of ash material in lake conditions. Glauconitization is confined to the Paleogene thermal maximum and the periphery of active volcanism along the entire mobile belt. In this connection, it is widely distributed in the Paleogene deposits. Structural and crystal-chemical features of glauconite, stages of crystallization of its aggregates, paragenetic associations with smectite, kaolinite, and zeolite, as well as the presence of ore minerals indicate its authigenic origin. The authigenic origin is confined to the formations of temporary, episodically submerging shallow marine basins. An applied scheme of discrimination of glauconites by their crystallochemical features has been developed. The discrimination diagram can be used to determine the specific conditions of the sedimentation basin, which are expressed in the progradation cycles of glauconite accumulation. The cycles were controlled by induced depressions within the Russian plate.

High primary productivity in an Ediacaran shallow marine basin influenced by strong seasonal to perennial upwelling

AbstractA significant area of late Neoproterozoic–early Cambrian seafloor hosted a ferruginous to euxinic condition as a result of expanded primary productivity-driven pumping of organic matter into subsurface water column and weak water column mixing in the concomitant sea. However, the cause and extent of increased marine primary productivity during this time interval remain unknown. To estimate the primary productivity in a late Neoproterozoic sea, this study investigated the Sirbu Shale, Vindhyan Supergroup, for trace elements, organic carbon isotopes and total organic carbon (TOC). Among the trace elements, cadmium (Cd), known for extremely low concentration in crustal rocks but higher abundance in biogenic organic matter, was the key parameter in the palaeoproductivity estimation. The Cd enrichment in the Sirbu Shale samples is comparable to that in modern marine sediments of the oxygen minimum zones in Chilean margins, Arabian Sea and Gulf of California characterized by high primary productivity and seasonal upwelling. In terms of Cd enrichment, the lower section of the Sirbu Shale was deposited under suboxic conditions, while the upper section was deposited under a relatively less reducing condition. Cd/Mo ratios > 0.36 in the shale sample indicate that the palaeoproductivity was strongly influenced by the nutrient supply through sea-shelf upwelling. Using non-detrital enrichment of Cd in Sirbu Shale samples, we calculated that the TOC exported to the floor of Sirbu Shale palaeodepositional setting through primary productivity ranged from 0.71 to 10.16%.

A high-resolution study of planktonic foraminifera during the Holocene at the Tilos-Symi sea basin in the SE Aegean Sea

High-resolution data for planktonic foraminifera and their groups of ecological interest, including Herbivores and Carnivores, combined with benthic foraminifera and a great variety of biogeochemical indices from the SE Aegean sediment core ST5, contribute to a detailed study concerning major and minor climatic episodes during Holocene. The ST5 sediment record, retrieved from the Tilos-Symi marine basin, evidences the impact of the nearby land, the local climate, and the Rhodes Gyre imprint on the eastern Mediterranean water circulation. Pronounced environmental changes are detected during a preconditioning period of ~400 years before the onset of sapropel S1 deposition and during the deposition phases S1a (10.0–8.4 ka BP) and S1b (8.0–6.1 ka BP). Major freshwater influx episodes (10.5 ka BP, 9.2–8.9 ka BP, 7.4 ka BP, 4.5–4.3 ka BP, and few additional during the Late-Holocene) are revealed, prominent oxygen deficiency time intervals (including a distinct brief anoxic period) as well as several drier, cooler and warmer climatic events. Herbivore planktonic foraminifera alternate their dominance with the Carnivores at the preconditioning period before the S1 onset and at the Late-Holocene (2.0–1.5 ka BP) when conditions of good seawater circulation, oxygenation, and productivity alternate with stratified low oxygenation waters and high freshwater influx from the land.

Storm or tsunamis: Boulder deposits on the rocky coasts of the Balearic Islands (Spain)

The origin of large imbricate boulders at the edge of coastal cliffs, by storm or tsunamis, is usually controversial. The Balearic Islands are a perfect place to elucidate this origin because the surrounding marine basins have low storm energy compared to oceans, and they are located 250 km N of the main tsunamigenic area of the Western Mediterranean. Thus, there have been recent and historical tsunamis affecting the Balearic Islands, especially in its southern and eastern parts. Tsunami simulations from submarine earthquakes on the North African coast predict the impact of tsunami waves on the Balearic Islands. Large coastal boulders of the Balearic Islands are located in the exact places numerical models predict they will be. Despite the fact that the height and energy of storm waves are much larger from the north and west, these boulders are located in the eastern and southern parts of the islands. Documentary sources confirm a very large tsunami affecting the southeast coast of Majorca in 1756, with a run-in up to 2 km and a run-up up to 45 m. Hydrodynamic equations applied to these boulders results in storm wave height values never recorded in 60 years. In February 2020, the highest storm wave ever recorded (14.33 m) was detected at Minorca buoy, related to storm Gloria. As predicted by hydrodynamic equations, none of the boulders studied moved significantly, and only three new boulders, located at sea level or at the cliff edge, were quarried. According to radiocarbon data and rate of growth of dissolution pans, the year of emplacement of boulders in the studied localities ranges between 1591 CE and 1894 CE. Thus, the distribution of the boulder sites along the islands, the historical record of a large tsunami, the run-up necessary for their placement, and the insignificant boulder movement produced by the highest storm recorded indicates that the cliff-top boulders of the Balearic Islands were quarried by North African tsunami waves.

Geological and energy potential analysis of Küplüce-Gökçesu basin rich in coal and other potential energy resources

The Küplüce-Gökçesu Basin, located in northwestern Anatolia, is an Eocene-aged shallow marine basin known for its rich carbonaceous sediments. The basin is underlined by Paleozoic metamorphic rocks, granites from the Sakarya Massif, and Jurassic-Upper Cretaceous turbiditic and carbonate rocks. The sedimentary deposits in the basin consist of two main lithological units, namely, the Tokmaklar and Sazlar Formations. The Tokmaklar Formation comprises marl, bituminous marl, clayey bituminous limestone, Nummulite limestone, and marl-clay-sandstone successions. Economic coal formations are found at the base of the Tokmaklar Formation, along with bituminous limestone and marl. The Sazlar Formation is composed of thick layered sandy limestones and marls, deposited in reefal conditions. Previous studies conducted in the 1980 s estimated the coal reserves in the Küplüce-Gökçesu Basin to be around 40 million tons. However, this study reveals the discovery of a new coal seam that was not previously identified, with a potential thickness of approximately 11 m. This discovery suggests that the coal reserves in the region could be significantly larger than previously known, potentially 5-6 times greater. The quality of the Küplüce-Gökçesu coals is classified as semi-bituminous hard coal of the lower bituminous coal group, based on chemical analysis results. This study contributes to the understanding of the geology and coal potential of Eocene basins in Anatolia and provides valuable information for future exploration and exploitation activities.

Dynamic process of turbidity current‐induced benthic‐marine oxygenation evidenced by sequential ichnocoenoses: An example from a Late Permian oxygen‐deficient basin

Turbidites and associated trace fossil assemblages have been extensively studied in modern and ancient sedimentary basins. However, benthic redox fluctuations induced by turbidity currents and relevant trace fossil suites (oxygen‐related ichnocoenoses) have rarely been demonstrated in geological records. Here, we present an example with a well‐preserved ichnocoenosis succession recording the detailed dynamic process of benthic marine oxygenation generated by turbidity currents in a Permian oxygen‐deficient basin. Millimetre‐ to centimetre‐scale sedimentological and ichnological analyses demonstrated that benthic‐marine oxygenation induced by distal turbidity currents recorded in fine‐grained calciturbidites from the anoxic basin began with a rapid, short‐lived oxygenation event marked by the Thalassinoides/?Scolicia ichnocoenosis, followed by a relative long‐term lower oxygen‐level stage indicated by the ichnocoenoses of Planolites‐Zoophycos and Zoophycos in turn, and ended with returning to the background anoxic benthic conditions represented by the laminated black shale. The sequential ichnocoenoses associated with turbidity current‐induced oxygenation events in the Permian oxygen‐deficient marine basin suggest that turbidity currents can prominently oxygenate anoxic/dysoxic bottom waters and have significant impacts on benthic communities in oxygen‐deficient basins.

Preservation of Soft-Bodied Organisms in Early Cambrian Carbonates

Abstract —Preservation of soft-bodied organisms as casts is common in the Ediacaran fossil record and extremely rare in Cambrian rocks. Among the factors, limiting fossilization of soft tissues, there is bioturbation–sediment disturbance by burrowing organisms. It is the emergence of burrowing metazoans and associated sediment bioturbation that is thought to be one of the major causes for the disappearance of Ediacaran soft-bodied organisms from the fossil record around ~540 Ma. Here, we study an assemblage of fossils preserved as casts in the Fortunian carbonates of the Olenek Uplift (northeastern Siberian Platform) in association with a typical Fortunian ichnoassemblage. The overall morphology and preservation of the fossils reveal that they comprise microbially induced sedimentary structures and soft-bodied holdfasts. The latter are vaguely reminiscent of some Ediacaran holdfasts, though it is unlikely that they include their phylogenetic descendants. Three-dimensional preservation of the studied fossils was caused by authigenic crystallization of calcite and its further early-diagenetic dolomitization. Our study confirms the critical importance of specific environmental conditions ensuring preservation of soft-bodied organisms as three-dimensional molds and casts. This unique interplay of environmental factors became rare in the Cambrian Period, which was caused by intensification and expansion of bioturbation in marine basins.

Versatile methanotrophs form an active methane biofilter in the oxycline of a seasonally stratified coastal basin.

The potential and drivers of microbial methane removal in the water column of seasonally stratified coastal ecosystems and the importance of the methanotrophic community composition for ecosystem functioning are not well explored. Here, we combined depth profiles of oxygen and methane with 16S rRNA gene amplicon sequencing, metagenomics and methane oxidation rates at discrete depths in a stratified coastal marine system (Lake Grevelingen, The Netherlands). Three amplicon sequence variants (ASVs) belonging to different genera of aerobic Methylomonadaceae and the corresponding three methanotrophic metagenome-assembled genomes (MOB-MAGs) were retrieved by 16S rRNA sequencing and metagenomic analysis, respectively. The abundances of the different methanotrophic ASVs and MOB-MAGs peaked at different depths along the methane oxygen counter-gradient and the MOB-MAGs show a quite diverse genomic potential regarding oxygen metabolism, partial denitrification and sulphur metabolism. Moreover, potential aerobic methane oxidation rates indicated high methanotrophic activity throughout the methane oxygen counter-gradient, even at depths with low in situ methane or oxygen concentration. This suggests that niche-partitioning with high genomic versatility of the present Methylomonadaceae might contribute to the functional resilience of the methanotrophic community and ultimately the efficiency of methane removal in the stratified water column of a marine basin.

Zircon age distributions and implied tectonic settings of early Cambrian to Early Devonian sedimentation in western and central Victoria

Age distributions among the detrital zircon populations in western and central Victorian Paleozoic metasedimentary rocks suggest that most were deposited in Andean-type back-arc environments, with variable proportions of arc and continental sediment sources. Notable exceptions are the upper Cambrian Knowsley East Shale and the Silurian(?) sample of ‘Glen Creek Lithic Sandstone’, which both contain unimodal zircon populations. In the case of the Knowsley East Shale, this age is very close to the inferred depositional age, implying a possible forearc environment, with sediment derived directly from the contemporary volcanic arc. On the other hand, the implied trench environment for the ‘Glen Creek Lithic Sandstone’ is most likely inherited from its very local sediment source in the fault-bounded and mainly Cambrian Glen Creek erosional window. The only analysed rock units that may have been deposited in non-arc settings are the middle Silurian Humevale Siltstone and the Lower Devonian Norton Gully Sandstone. The zircon populations in these units carry strong continental signals, and they may have been deposited in an extensional marine basin bounded by continental blocks. The upper Silurian Grampians Group may have been deposited in a similar rift setting, but the zircon age histogram for this unit suggests that it was more proximal to an arc terrane. These assignments of depositional/tectonic environment should be regarded as indicative only, particularly since the method provides only subtle distinctions between some extensional and convergent settings. However, if the assignments are correct, there are some important implications for the geological history of this part of the Lachlan Orogen. For example, contrary to present perceptions, the Stawell Zone rocks may not have been prominently uplifted during the Ordovician, and the basin in the Bendigo Zone may have been receiving sediment input from further west in the Grampians–Stavely Zone.

Link of the short-term temporal trends of Sr and Nd isotopic composition of aeolian dust over the Arabian Sea with the source emissions

Aeolian transport of continental dust from the Middle East and South Asia to the Arabian Sea (AS) is an important route for delivering key trace metals and nutrients. Despite being surrounded by several deserts, it is not clear which dust source is most likely contributing to mineral aerosols over this marine basin in winter. Substantial information on dust source emissions and transport pathways over the AS is, thus, needed for better constraining the biogeochemical effects in the sunlit surface waters. Here, we investigated the Sr and Nd isotopic composition (87Sr/86Sr and εNd(0)), respectively) of dust samples collected over the AS during a GEOTRACES-India expedition (GI-10: 13 January-10 February 2020). Both tracers, 87Sr/86Sr (0.70957–0.72495) and εNd(0) (−24.0 to −9.3), showed pronounced spatial variability. These proxies were further tagged with their source profiles of surrounding land masses based on the origin of air mass back trajectories (AMBTs). We also encountered two dust storms (DS), one on 27 January 2020 (87Sr/86Sr: 0.70957; εNd(0): −9.3) and the second one on 10 February 2020 (87Sr/86Sr: 0.71474, εNd(0):-12.5), which showed distinct isotopic signatures. AMBTs and satellite imagery together revealed that DS1 is from the Arabian Peninsula and DS2 is from Iran and/or the Indo-Gangetic Plain. Notably, the Sr and Nd isotope composition of DS1 is further consistent with other dust samples collected over the pelagic waters, suggesting the impact of dust outbreaks from the Arabian Peninsula during winter season. Such documentation based on the 87Sr/86Sr and εNd(0) over the Arabian Sea, hitherto, is lacking in literature and, thus, highlights the need for more measurements.

Red or green: Overprinting of the climatic signal in Miocene sediments, South China Sea (IODP Expedition 368, Site U1502)

AbstractSedimentary beds of alternating red and green colour are commonly interpreted to reflect orbitally‐forced cyclic climatic, syn‐depositional conditions, although colour changes caused by post‐depositional fluids are also documented. Results from IODP Hole U1502A marine sediments in the South China Sea exemplify post‐depositional reducing fluid–rock interactions that locally changed the sediment colour from red to green. Petrographic, rock magnetic and paleomagnetic data on cores show that the red colouration originates from an early, basin‐wide, pervasive diagenetic oxidation event (forming haematite), whereas the green colouration results from subsequent fluid‐driven reduction (forming pyrrhotite‐magnetite). The dense sulfidic stockwork in the basaltic basement underlying these sediments was the likely source of reducing fluids. Drilling deep holes into marine basin basements can thus provide useful information on fluid transfer from the basement to the overlying sedimentary layers.

The Late Cretaceous marine basin of platform Ukraine (morphometry, stages of development, lithology and stratigraphy of sedimentary formations)

Formulation of the problem. The relevance of the research is related to the formation of a holistic view of the Late Cretaceous Sea basin of the study area: its boundaries, area, the existence of probable land areas, conditions of sediment accumulation and historical development. The purpose of the article. Based on the results of exploratory, structural-exploratory and parametric drilling conducted during the State Geological Survey on scales of 1:50,000, 1:100,000 and 1:200,000 and own field research, we supplemented the information on the geohistorical chronicle of the Late Cretaceous of the southwestern part of the SEE. Methods. The material for writing the article was the results of drilling more than 10,000 exploration, structural and parametric drilling wells conducted during the State Geological Survey at scales of 1:50,000, 1:100,000 and 1:200,000, which are stored in the State Information Geological Fund of Ukraine. Also, the results of own field research of 47 most complete open sections of the Upper Cretaceous of Platform Ukraine were taken into account and a significant literature on the geological structure of the studied area was processed. Research methods: facies and formation analysis, lithological, petrographic, paleontological, litho-biostratigraphic, geophysical, etc. At the final stage of the mapping of the Upper Cretaceous sediments of Platform Ukraine, the methodology of sedimentary basin monitoring and modeling of formation units was used with the help of the domestic software package "Geomapping" with further conversion to the ArcView grid format. Results. To find out the spatio-temporal distribution of the Upper Cretaceous deposits of the study area, their composition, stratigraphic position and parameters of the Late Cretaceous sea basin, we analyzed the materials of mapping, structural search, exploratory and parametric drilling over the past 50 years were analyzed, our own studies of open sections of the Upper Cretaceous were taken into account, and significant stock material on the geological structure of the studied area was also processed. The most informative wells were selected as reference wells. Their number varied from 1179 for Early-Middle Cenomanian deposits to 1103 for Turonian deposits. The maximum density of the studied sections of support wells was recorded for the territory of Volyn-Podillia and individual blocks of the Ukrainian Shield (USH) and is 23.1 wells per 1000 km2, the minimum - in the water areas of the Ukrainian part of the Black and Azov Seas - about eight per 1000 km2. The absence of Upper Cretaceous deposits on a significant territory of platform Ukraine was established. Early-Middle Cenomanian and Turonian deposits have the largest distribution area, and Maastrichtian deposits have the smallest. In our opinion, areas with continental conditions of existence in certain ages or during the entire Late Cretaceous period have been identified. This made it possible to calculate the areas of land areas and areas covered by the sea with the help of software, with a certain percentage of error (up to 10%). The area of the sea basin was up to 80% of the territory of platform Ukraine. In the historical development of the Late Cretaceous Sea basin of the study area, two stages are distinguished: early-Middle Cenomanian and late Cenomanian-Maastrichtian, which differed significantly from each other in terms of hydrological, hydrochemical, temperature regimes and the nature of sedimentation. The lithological characteristics of the deposits according to the modern stratigraphic division of the Upper Cretaceous rock complex are given.

Hydrocarbon generation kinetics of salinized lacustrine source rocks in the upper Cretaceous-Paleocene South Yellow Sea Basin, offshore eastern China

Saline lacustrine source rocks have different enrichments in organic matter and hydrocarbon generation processes as compared with source rocks formed in freshwater and marine basins. We investigated the hydrocarbon generation kinetics of saline lacustrine source rocks and the physical properties of petroleum using immature source rocks from the Upper Cretaceous Taizhou Formation and Paleocene Funing Formation in the South Yellow Sea Basin. The source rocks were analyzed using PhaseKinetics approach.Our main results are as follows. (1) Compared with source rocks from freshwater and marine basins, the source rocks in the South Yellow Sea Basin have the same organofacies (i.e., generating Paraffinic-Naphthenic-Aromatic low wax oils) and a lower bulk activation energy (frequency factors of A = 9.66 × 1012 and 4.61 × 1012 s−1, with a dominant activation energy at 51 and 50 kcal/mol), with oil window conditions of 128–155°C and 98–146°C). (2) Compositional kinetic modelling indicates that the generated gas consists mainly of C1, C2, and C3 compounds, while the liquid phase is dominated by C7-15 and C16-25 compounds. (3) The physical properties of the two suits of source rocks show that the saturation pressure, gas/oil ratio and formation volume factor vary with maturation. The pressure−temperature envelope of different maturities defined by these experiments allowed their phase behavior to be predicted, with a liquid phase being generated by the Taizhou Formation, and an oil−gas phase fluid being transiently generated by the Funing Formation.These results provide new insights into the hydrocarbon generation kinetics of saline lacustrine source rocks, which are relevant to regional shale oil exploration.

26,000 years of environmental evolution of an incised valley in a rocky coast (La Janda wetland, SW Iberia).

The La Janda wetland record allows to expand the knowledge of the evolution of a restricted estuary since the Last Glacial Maximum. Multiproxy analysis of the sediments (facies, geochemistry, pollen, fossils) reveals that this system exhibits a classic incised valley sequence but differences with the adjacent estuaries can be established. The La Janda sedimentary infill can be split in four main sequences: (1) the Falling Stage Systems Tract (>20.6 ka BP) and (2) the Lowstand Systems Tract (16.7–20.6 ka BP) deposits record fluvial sedimentation in a narrow and incised valley, here seminally identified in the Gulf of Cádiz estuarine system; and (3) the Transgressive Systems Tract (7–16.7 ka BP), ending with the Holocene marine flooding surface at 7 ka BP, is composed of estuarine and marine basin deposits infilling a still steep and narrow topography coupled with the fast retreat of the river mouths. The (4) Highstand Systems Tract (0–7 ka BP) is composed of estuarine basin deposits with fluvial and tidal currents deposits in a wide a gentle sloped estuarine valley and it records the transformation of the basin into a terrestrial one. Comparison to other areas in the Gulf of Cádiz allows to correlate the different estuaries and to distinguish between open and restricted ones by the development of spit systems during the Highstand Systems Tract. But further work is needed to clarify the stratigraphy of the present eustatic cycle in the Gulf of Cádiz as the scarcity of data does not allow to determine the evolution of its estuaries during the last fall and rise of sea level. Such knowledge is crucial to disentangle the role of climate and tectonics in the future evolution of our coasts and design measures to adapt to sea level rise.

Sedimentary features of the gravity flow influenced shale deposit: A case study of Chang 7 member in the Ordos Basin, China

Black shale deposits are usually regarded to be deposited in a relatively slack and deep water environment. The gravity flows that can greatly affect the shale depositional process are well documented in many marine basins, with much less attention paid to the counterpart in lacustrine settings. The Upper Triassic Chang 7 Member in the Ordos Basin, which contains thick black shale and well developed gravity flow deposits provides a good opportunity to investigate the influence of gravity flows on shale development in lacustrine settings. We integrate X-ray diffraction, thin section petrography analysis, major and trace element analysis, total organic carbon testing, electron microscopy, and energy spectrum analysis on shale to reveal such complicated process. Based on the development of silty laminas and thickness of the laminaset/bedding, we classified the Chang 7 shale into five lithofacies. Each lithofacies was unique in terms of laminar morphology, texture, and composition, indicating different depositional processes. Proxies of paleo-water depth, paleo-settling rate, paleo-productivity, paleo-redox, and clastic influx also revealed that these five lithofacies deposited in different depositional settings. We propose new depositional models to explain such heterogenous shale deposits and suggest the paleo-productivity has the strongest influence on the accumulation of organic matter.

Plate convergence controls long-term full-depth circulation of the South China Sea

How plate tectonics may affect full-depth ocean/sea circulation is not well understood. We used seismic data plus drilling/core and geomorphologic data to examine the influence of regional tectonics on South China Sea circulation. The features of four contourite depositional complexes across the sea, continental shelf to abyssal plain, indicate that plate convergence has controlled circulation within this marginal sea since the beginning of its closure, primarily via Luzon Strait changes. Initially (late Miocene), South China Sea circulation was open, as a part of North Pacific ocean circulation. Later (Pliocene to early Pleistocene) creation of the Luzon Strait reversed the direction of South China Sea surface circulation but not its deeper circulation. Subsequent (middle Pleistocene to present) narrowing and shallowing of the strait weakened surface, intermediate, and bottom flows within the sea but strengthened deepwater flow. This contourite-based approach to elucidating tectonic effects on surface-to-bottom paleo-circulation can be applied to other marine basins within an active tectonic setting.