Shallow Shelf Research Articles

Coupling between Source Rock and Reservoir of Shale Gas in Wufeng-Longmaxi Formation in Sichuan Basin, South China

In order to analyze the main factors controlling shale gas accumulation and to predict the potential zone for shale gas exploration, the heterogeneous characteristics of the source rock and reservoir of the Wufeng-Longmaxi Formation in Sichuan Basin were discussed in detail, based on the data of petrology, sedimentology, reservoir physical properties and gas content. On this basis, the effect of coupling between source rock and reservoir on shale gas generation and reservation has been analyzed. The Wufeng-Longmaxi Formation black shale in the Sichuan Basin has been divided into 5 types of lithofacies, i.e., carbonaceous siliceous shale, carbonaceous argillaceous shale, composite shale, silty shale, and argillaceous shale, and 4 types of sedimentary microfacies, i.e., carbonaceous siliceous deep shelf, carbonaceous argillaceous deep shelf, silty argillaceous shallow shelf, and argillaceous shallow shelf. The total organic carbon (TOC) content ranged from 0.5% to 6.0% (mean 2.54%), which gradually decreased vertically from the bottom to the top and was controlled by the oxygen content of the bottom water. Most of the organic matter was sapropel in a high-over thermal maturity. The shale reservoir of Wufeng-Longmaxi Formation was characterized by low porosity and low permeability. Pore types were mainly <10 nm organic pores, especially in the lower member of the Longmaxi Formation. The size of organic pores increased sharply in the upper member of the Longmaxi Formation. The volumes of methane adsorption were between 1.431 m3/t and 3.719 m3/t, and the total gas contents were between 0.44 m3/t and 5.19 m3/t, both of which gradually decreased from the bottom upwards. Shale with a high TOC content in the carbonaceous siliceous/argillaceous deep shelf is considered to have significant potential for hydrocarbon generation and storage capacity for gas preservation, providing favorable conditions of the source rock and reservoir for shale gas.

Reconstruction of oceanic redox structures during the Ediacaran-Cambrian transition in the Yangtze Block of South China: Implications from Mo isotopes and trace elements

To explore paleo-ocean redox variations and Mo biogeochemistry across the Ediacaran–Cambrian transition (E-C), continuous fresh core shale samples of Ediacaran to Cambrian were collected from a well drilled in the upper slope region of the Yangtze Block in South China and analyzed for δ98/95Mo and δ13Corg values, TOC, as well as the concentrations of trace and rare earth elements. The Mo–U covariations, Th/U and Re/Mo ratios as well as published iron speciation data indicate a redox stratified ocean with oxic surface waters and anoxic/euxinic deep waters prevailing across the E-C transition. During the time of Cambrian Fortunian and Stage 2, the bottom water in the upper slope became oxic due to the deepening oxycline. Afterwards, widespread anoxia and/or euxinia occurred during latest Age 2 and early Age 3. The Mo concentrations and Mo/TOC ratios suggest that the Yangtze Block was well connected with the open ocean during the late Ediacaran, and then became strongly restricted at the beginning of Cambrian. Following a large-scale transgression during Cambrian Age 2, its connection with the open ocean was enhanced again. The negative δ98/95Mo values may reflect preferential adsorption of isotopically light Mo by Mn oxides particles above the chemocline and their subsequent shuttling to euxinic sediments in the redox stratified late Ediacaran ocean; whereas the relatively low δ98/95Mo values during the Cambrian Fortunian and Age 2 indicate the decrease of δ98/95MoSeawater values in the restricted basin. The operation of local Mn particulate shuttles could also be stimulated by inflow of oxic waters into restricted basin during marine transgression, resulting in negative δ98/95Mo values. In conjunction with previous published Mo isotope data, the variations of sedimentary δ98/95Mo values from shallow shelf to deepwater slope regions draw the outline of ‘sandwich’-like model with euxinic waters (e.g., [H2S]aq > 11 μM) sandwiched by oxic surface waters and anoxic deep waters during the E-C transition. The shuttling of isotopically light Mo to euxinic sediments by Mn oxides in the redox stratified Ediacaran-Cambrian ocean may play a role in driving heterogeneous heavy seawater Mo isotopes and variable sedimentary δ98/95Mo values.

PONTO-CASPIAN AND MEDITERRANEAN FAUNAL AND FLORAL RECORDS OF UPPER PLEISTOCENE-HOLOCENE SEDIMENTS FROM THE İZMİT GULF (MARMARA SEA, TURKEY)

İzmit Gulf is located between Kocaeli and Armutlu peninsulas at east of Marmara Sea and the interaction area of North Anatolian Fault Zone (NAFZ) and Marmara Graben systems. In this study, the faunal and floral contents (ostracod, foraminifer, mollusc and diatom) of the samples belonging to seven drilling cores were studied and obtained the radiocarbon and optically stimulated luminescence (OSL) age data in order to establish on the Black Sea – Marmara Sea - Mediterranean water connections and palaeoenvironmental changes. The sediments in this study are Late Pleistocene-Holocene aged and only cover the Marine Isotope Stages MIS-5 (interglacial), MIS-3 (an interstadial period between MIS-4 and MIS-2 glacial epochs) and MIS-1. The determination of ostracod and mollusc fauna of the Mediterranean and Ponto-Caspian origin provide important clues to water exchange between the Mediterranean and the Black Sea. Although some Mediterranean originated ostracods occur sporadically with low abundance, absence of foraminiferal fauna and existence of Ponto-Caspian ostracods together with fresh water and cosmopolitan diatom flora indicate that the area strongly interacted with the Black Sea waters during MIS-5. The faunal and floral characteristics of the sediments deposited during MIS-3, clearly denote that the Izmit Gulf was connected with the Black Sea and the Mediterranean Sea at the beginning of MIS-3 (ca. 52.0 - 40.0 ky BP) and the shallow shelf areas were frequently affected by both the Black Sea discharge and Mediterranean input. A thick Holocene sedimentary sequence recovered from the southern Hersek Burnu drilling cores reflects the environmental changes after the latest Black-Mediterranean seas connection. The studied ostracod and mollusc assemblages are mainly characterized by the Mediterranean originated species with a few relict Ponto-Caspian fauna. Also, the benthic foraminiferal assemblages are dominated by normal marine and euryhaline species, reflecting the salinity fluctuations in the Holocene interval.

Comparing the Upper Triassic Deep‐sea Flysch of the Shannan Terrane with the Coeval Shallow Shelf Sediments of the Tethys Himalaya, Southern Tibet

AbstractThe provenance and paleogeography of the Upper Triassic deep‐sea flysch Langjiexue Group (LG) of the Shannan Terrane in the northeastern Himalaya orogen, south of Yarlung Zangbo, have been disputed in recent years since its affinity to the Tethys Himalaya was suspected during the early 2000s. Based on the earlier discoveries of the Upper Permian–Triassic basalts and mafic dykes from the LG and of coeval detrital zircons from the Qulonggongba Formation (QF) in shallow shelf sediments of the Tethys Himalaya, the previous viewpoints on the basin and tectonics of the LG have been recently rejected. We compared the two units of the Upper Triassic, and our results reveal a number of differences, discrepancies, and inconsistencies in the debate, raising crucial questions on the postulation and provenance model of the remote Gondwanide Orogen for the LG. It is suggested that more observations and evidence are needed to further improve the paleogeographic understanding and relationship of the two units.

Provenance and tectonic settings of the Eze-Aku Sandstone (Turonian) in Awajir and adjoining areas, Southern Benue Trough, Nigeria: evidence from petrography and geochemistry

Eighteen representative samples for petrographic (6) and geochemical (12) studies were collected from the Turonian (Eze-Aku Formation) sandstones outcropping within Awajir and adjoining areas in the northern section of the Southern Benue Trough. Sandstones of different textural variety underlie the study area: fine-, medium- and coarse-grain sandstones facies. Field study revealed an overall coarsening upward succession, ripple bedding surfaces, cross-stratification and bioturbation, which suggest prevalence of a shallow shelf with relict shoreline environmental settings. Petrographic study show that the sandstones are subarkosic to arkosic and deposited in a humid to semi-humid paleoclimatic condition. Polygenic (mixed) provenance source is inferred for the sandstones and the insignificant presence of sedimentary rock fragments in the framework constituents suggests the Precambrian Basement complex of southern Nigeria as the most likely source area. This result is consistent with trace element ratios such as Cr/Zr (< 0.6) and Cr/Th (0.3–15.7) as well as La/YbN versus CeN diagram which points all the sandstone facies to an intermediate Igneous provenance, unambiguously ruling out the chances of mafic igneous rocks being present in the source terrain. The most probable provenance for the sandstones is the continental Basement complex rocks of Obudu plateau and Oban massifs. The study showed that there was a mild influence of diagenetic alteration on the sandstone facies after deposition in an active continental margin-continental island arc setting.

Depositional environments and sequence stratigraphy of post-last glacial maximum incised valley-fill, Malay Basin, northern Sunda Shelf

The alternating submergence and subaerial exposure of the low-gradient, shallow Sunda Shelf of southeast Asia during Quaternary interglacial-glacial cycles played an important role in ocean circulation and monsoonal climate through the interchange of Indian Ocean and Pacific Ocean waters. The Quaternary stratigraphic development of this margin is, however, poorly understood. This study uses a multi-proxy approach (AMS radiocarbon, bulk sediment magnetic susceptibility, X-ray fluorescence spectrometry, and foraminiferal assemblage data) to characterize environmental change and late Pleistocene to Holocene sequence stratigraphic architecture in 16 cores from the northern Sunda Shelf off the east coast of Peninsular Malaysia.Five chronostratigraphic units are recognized. Unit 1 is an inner shelf deposit dating from a late Pleistocene sea-level highstand (the highstand systems tract of the pre-LGM base-level cycle). Units 2–4 represent different paleoenvironmenal components of the transgressive systems tract (TST) of the most recent base-level cycle. Unit 2 is a late Pleistocene shallow open embayment deposit that formed during the post-LGM inundation of the paleo-Chao Phraya River valley as sea level rose. Unit 3 is composed of late Pleistocene to early Holocene paralic peat and organic-rich mud and is capped by a transgressive ravinement surface. Unit 4 is a shallow shelf unit deposited during the early Holocene transgression on the Sunda Shelf prior to ca. 6500 cal yr BP (the onset of the regional Holocene sea-level highstand). Unit 5 represents the mid-Holocene to recent highstand systems tract (HST) deposited from ca. 6500 cal yr BP to present.The incised paleovalleys of the paleo-Chao Phraya River and its tributaries provide more accommodation space for sediment accumulation than the surrounding shelf. However, the thinness of the Holocene sedimentary record, 2–3 m in the incised valleys compared to <1 m over the adjacent shelf, indicates that the LGM incised valleys were almost filled by fluvial and coastal plain sediments before open marine conditions returned near the beginning of the Holocene. The multi-proxy approach of this study elucidates the geologic response of this shelf to sea-level rise and the sequence stratigraphic development of tropical, siliciclastic-dominated shallow shelf depositional sequences.

Current state and long-term changes in the mesozooplankton community of the Ukrainian and Georgian parts of the Black Sea as indicators of its ecological status

Water quality assessment is a key task of any measures in the field of water use, environmental management and protection. Thus, it is necessary to conduct systematic monitoring to assess the ecological state in the marine waters and to develop a strategy for its recovery. Anthropogenic impacts of various types leading to eutrophication and pollution of the Black Sea are changing the main characteristics of all components of the aquatic ecosystem. Zooplankton plays a key role in the pelagic food web. This article presents the results of the research on the state of zooplankton which was conducted during the Ukrainian-Georgian expedition in the framework of the international project “Emblas-plus” during 2016, 2017 and 2019. The ecological quality class of the investigated Black Sea waters was determined by the zooplankton integrated index (IZI). In Ukrainian waters in total, 49 taxa of zooplankton were registered. In 2017 taxonomic composition of zooplankton was more diverse (36 taxa in 2016, 35 in 2019). In Georgian waters in 2019, 40 taxa of mesozooplankton were registered, most of them are widespread forms in the Black Sea. The most diverse group is Crustacea (Cladocera and Copepoda).The most prevalent crustaceans were the eurythermic species, an important representative of forage zooplankton – Acartia (Acartiura) clausi Giesbrecht, 1889 and two thermophilic species of Calanoida – Acartia (Acanthacartia) tonsa Dana, 1849 and Centropages ponticus Karavaev, 1895. In Ukrainian waters average abundance and biomass of zooplankton in 2019 was similar to those in 2016 and much higher than in 2017. Dominant taxa and spatial distribution of zooplankton in 2019 were similar to those in 2016 and 2017. Average biomass of forage zooplankton in 2019 was approximately 10 times higher than in 2016 and 2017. In the Georgian coastal waters annual average abundance and biomass of mesozooplankton decreased, due to a sharp decline in the abundance of Noctiluca scintillans (Macartney) Kofoid &amp; Swezy, 1921. It was found that at most of the stations the dominant role in the formation of zooplankton biomass was played by the organisms of forage zooplankton. By the IZI index, the subdivision Northwestern Black Sea Bays had “Good”, “Poor” and “Moderate” water quality in spring, summer and autumn respectively. The subdivision’s deepwater shelf and shallow shelf had “Bad” water quality. The subdivision Danube-Dnieper interfluve coastal waters had “High” water quality. The Danube Avandelta area had “High”, “Good” and “High” water quality in spring, summer and autumn respectively. The best ecological class status was in 2019 and the worst – in 2016. The main tendencies in changes in the mesozooplankton community in the Black Sea are decrease in the percentage of N. scintillans in the total zooplankton biomass and increase in the percentage of Copepoda. Those tendencies indicate decrease in the pressure of the negative eutrophication factor and show positive changes in the forage base of commercial planktophagous fish and the ecological status of the Black Sea waters.

Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms sampled by experimental trawling in the Iberian Mediterranean Sea

Ascidians form aggregations in soft bottoms, thereby creating a complex habitat and increasing the biodiversity by providing new substrates, food, and refuge. As sessile and filtering organisms, they are extremely vulnerable to bottom trawling, which exerts a strong pressure on the circalittoral soft bottoms and could be used as bioindicators of this impact. During the MEDITS surveys of 2010 and 2017, the ascidiofauna of the Iberian Mediterranean Sea was studied from Alborán Sea to Catalonia at depths ranging from 37.5 to 693 m. A total of 3810 specimens belonging to 10 families and 38 species were assessed. Taxocenosis demonstrated that Southeast (SE) and Northeast (NE) Iberian Peninsula host a high diversity, specific richness, and abundance of both colonial and solitary species; however, in the Gulf of Valencia, the rates were lower than those previously recorded, and the colonial strategies were scarce. This may have occurred as a result of the continental shelf being steeper in the Alborán Sea and the SE and NE zones coasts than in the shallow shelf of Gulf of Valencia, which is more prone to bottom trawling. Moreover, differences were found in terms of depth, with the highest values of the previous rates being lower than 50 m, where Spanish legislation prohibits bottom trawling at depths lower than that mentioned. For the results obtained, both the taxocenosis of the ascidians and their strategies could be good indicators of the condition of the circalittoral soft bottoms of the Mediterranean Sea impacted by bottom trawling.

Deeper-water deposition in intrashelf basins: Example from the Lower Cretaceous (Albian) upper Glen Rose Formation in the Houston trough, eastern Texas

In easternTexas, a thick (150-200 ft) interval of Lower Cretaceous upper Glen Rose D strata was deposited in the Houston trough intrashelf basin landward of the Stuart City reef margin and seaward of the main eastern Texas intrashelf basin. The stratigraphic section in this intrashelf basin forms a primarily oil-bearing hydrocarbon system where porous grainstones in the Alabama Ferry and Fort Trinidad fields were deposited coevally with organic-rich calcareous argillaceous mudstones. Here, we present evidence to suggest that the depositional setting within the Houston trough and the contained ooid grainstone beds were of deeper-water origin (400-500 ft), below storm wave base. Further, the water column was stratified, allowing dysaerobic to anaerobic conditions to develop, fostering accumulation and preservation of organic matter. Grain-rich gravity flows consisting of ooids, intraclasts, and thin-walled mollusks, derived from the shallower shelf to the northwest, were deposited in the basin, forming the Alabama Ferry and Fort Trinidad fields. The upper Glen Rose interval is composed of lithofacies that vary laterally within the Houston trough. Five lithofacies are recognized on the basis of sedimentary features, texture, fabric, biota, and organic-matter content: (1) laminated to nonlaminated argillaceous lime mudstone to lime wackestone; (2) laminated to nonlaminated calcareous siliciclastic mudstone to siltstone; (3) intraclast–ooid skeletal lime packstone; (4) intraclast–bivalve–ooid lime grainstone; and (5) oyster lime floatstone and rudstone. Grain-rich lithofacies laterally adjacent to and interbedded with organic-rich argillaceous lime mudstones and calcareous siliciclastic mudstones were previously interpreted as being deposited in a tidally influenced, high-energy, shallow-water shoal environment; however, reconstruction of the depositional setting and interpretation of the vertical and lateral distribution of lithofacies suggest that these lithofacies were deposited as grain-rich gravity flows into the deeper-water Houston trough. This interpretation suggests a new conceptual framework integrating facies models from submarine channel and fan complexes to explore for grainstone reservoirs similar to Alabama Ferry and Fort Trinidad fields.

The Impact of Methane Seepage on the Pore-Water Geochemistry across the East Siberian Arctic Shelf

East Siberian Arctic Shelf, the widest and the shallowest shelf of the World Ocean, covering greater than two million square kilometers, has recently been shown to be a significant modern source of atmospheric methane (CH4). The CH4 emitted to the water column could result from modern methanogenesis processes and/or could originate from seabed deposits (pre-formed CH4 preserved as free gas and/or gas hydrates). This paper focuses primarily on understanding the source and transformation of geofluid in the methane seepage areas using ions/trace elements and element ratios in the sediment pore-water. Six piston cores and totally 42 pore-water samples were collected in the East Siberian Sea and the Laptev Sea at water depths ranging from 22 to 68 m. In the active zones of methane release, concentrations of vanadium, thorium, phosphorus, aluminum are increased, while concentrations of cobalt, iron, manganese, uranium, molybdenum, copper are generally low. The behavior of these elements is determined by biogeochemical processes occurring in the pore-waters at the methane seeps sites (sulfate reduction, anaerobic oxidation of methane, secondary precipitation of carbonates and sulfides). These processes affect the geochemical environment and, consequently, the species of these elements within the pore-waters and the processes of their redistribution in the corresponding water–rock system.

Conodont biostratigraphy of Upper Devonian–Lower Carboniferous deposits in eastern Alborz (Mighan section), North Iran

The Devonian/Carboniferous (D/C) transition is characterized by a major transgressive/regressive cycle which led to a widespread ocean anoxia known as the Hangenberg Black Shale Event (HBSE), as well to a major sea-level fall (Hangenberg Sandstone Event, HSSE), recognized around the world. Both events are known as the Hangenberg Crisis. In order to examine the D/C transition in shallow water environment, the Mighan section in eastern Alborz was studied in terms of conodont biostratigraphy and stable isotope geochemistry. Twenty-five conodont species belonging to seven genera were identified and 5 conodont zones discriminated; namely, the Bispathodus aculeatus aculeatus Zone, Bispathodus costatus Zone, Bispathodus ultimus Zone, Siphonodella praesulcata Zone, costatus-kockeli Interregnum, and the sulcata Zone. Below the Devonian–Carboniferous boundary (DCB), the Hangenberg Black Shale and Hangenberg Sandstone equivalents were recognized, representing the Hangenberg Crisis that highly affected trilobite, ammonoid, brachiopod and conodont faunas at Mighan and worldwide. The kockeli Zone of the latest Famennian is missing at Mighan due to the lack of conodonts, probably related with the major environmental changes linked with the Hangenberg Crisis recognizable worldwide. Carbon isotopes measured of micrites from Mighan indicate a proximal depositional environment of a shallow shelf with terrestrial input and the oxygen isotope values from conodont apatite suggest warm seawater temperatures of tropical and subtropical setting in the study area.

Patterns in Benthic Microbial Community Structure Across Environmental Gradients in the Beaufort Sea Shelf and Slope.

The paradigm of tight pelagic-benthic coupling in the Arctic suggests that current and future fluctuations in sea ice, primary production, and riverine input resulting from global climate change will have major impacts on benthic ecosystems. To understand how these changes will affect benthic ecosystem function, we must characterize diversity, spatial distribution, and community composition for all faunal components. Bacteria and archaea link the biotic and abiotic realms, playing important roles in organic matter (OM) decomposition, biogeochemical cycling, and contaminant degradation, yet sediment microbial communities have rarely been examined in the North American Arctic. Shifts in microbial community structure and composition occur with shifts in OM inputs and contaminant exposure, with implications for shifts in ecological function. Furthermore, the characterization of benthic microbial communities provides a foundation from which to build focused experimental research. We assessed diversity and community structure of benthic prokaryotes in the upper 1 cm of sediments in the southern Beaufort Sea (United States and Canada), and investigated environmental correlates of prokaryotic community structure over a broad spatial scale (spanning 1,229 km) at depths ranging from 17 to 1,200 m. Based on hierarchical clustering, we identified four prokaryotic assemblages from the 85 samples analyzed. Two were largely delineated by the markedly different environmental conditions in shallow shelf vs. upper continental slope sediments. A third assemblage was mainly comprised of operational taxonomic units (OTUs) shared between the shallow shelf and upper slope assemblages. The fourth assemblage corresponded to sediments receiving heavier OM loading, likely resulting in a shallower anoxic layer. These sites may also harbor microbial mats and/or methane seeps. Substructure within these assemblages generally reflected turnover along a longitudinal gradient, which may be related to the quantity and composition of OM deposited to the seafloor; bathymetry and the Mackenzie River were the two major factors influencing prokaryote distribution on this scale. In a broader geographical context, differences in prokaryotic community structure between the Beaufort Sea and Norwegian Arctic suggest that benthic microbes may reflect regional differences in the hydrography, biogeochemistry, and bathymetry of Arctic shelf systems.

Facies and stratigraphic associations of Sinjar and Khurmala Formation, Dohuk Area, Kurdistan Region, Iraq

The carbonate facies of the Lower Eocene Sinjar and Khurmala Formations are stratigraphically interrelated and forms part of the shoaling stage sediments of the Zagros Foreland Basin. This work aims at investigating their stratigraphic associations at Dohuk area of NE Iraq. Both Formations are well exposed in three sections examined from Dohuk area including Spindar (Gara Mt.), Birkyat (Khair Mt.) for Khurmala Formation, and Barbuhar (Bekhair Mt.) for Sinjar Formation. The thickness of the Khurmala Formation varies from 90.7 m at Spindar and 81 m at Birkyat. The thickness of the Sinjar Formation is 36.5 m at Barbuhar section. The focus of this study is to determine the carbonate microfacies in order to construct their sedimentary facies model and to interpret the depositional environment. Lithologically, Khurmala Formation in Spindar and Birkyat sections is closely similar and consisting of buff to gray, medium to thick, well-bedded microbialites dolostone, alternating with thin beds of soft shale and marlstone interlayer. The Barbuhar section consists mainly of three reefal limestone horizons alternating with siliciclastic interlayers. Four intensively dolomitized microfacies were recorded from Khurmala Formaton sections. These are dolo-mudstone, microbial dolo-mudstone, foraminiferal algal dolo-packstone, and foraminiferal dolo-wackestone, whereas Sinjar Formation shows eight carbonate microfacies, which are coraline framestone, bioclastic coralgal rudstone, coralgal foraminiferal bioclastic packstone, foraminifera bioclastic algal packstone, bioclastic forminiferal packstone, dolomitic microbial bindstone, dolomitic microbial laminite, and bioclastic sandy limestone. Field observations, along with microscopic investigations, have resulted in identifying facies types of the two formations. The Khurmala Formation in Spindar and Birkyat seems to be deposited in a shallow shelf setting of supratidal, intertidal, and semi-restricted lagoonal facies with siliciclastic-dominated coastal plain. The section of Barbuhar represents the Sinjar Formation which is deposited at further seaward position of the shelf as a patch reef limestone which is intermixed with the Kolosh Formation sandstone in a further deeper position.

Quantifying the relative influence of ice sheets, faults, and instability on channel and gully cross-profile shapes in the Gulf of Alaska

Convergent tectonics and glaciomarine sedimentary processes in the northern Gulf of Alaska have produced a variety of troughs, canyons, channels, gullies, and other drainage related features over a range of spatial scales. To evaluate the effects of glaciomarine and fault processes on observed drainage morphology we measured regional drainage feature cross-profile shape characteristics across the area. Our results show overlap between U-shaped feature cross-profile locations, ice sheet extents, and instability zones on the shallow shelf and slope that were previously inferred by observations of potential mass-movement structures such as slumps, slides, and debris flows. U-shaped profiles were also observed in areas of recent slope progradation such as the flank of the proximal deep-sea Surveyor Fan. We used principal component analysis (PCA) and geographically weighted regression (GWR) to relate drainage cross-profile morphology to proxy variables for ice sheets, faults, and instability zones. This method enables quantitative evaluation of the effects on cross-profile shape explainable by each variable as indicated by the magnitude, distribution, and variation of parameter coefficients both at the local and regional scale. Our multiple variable GWR model can explain most of the regional variability in cross-profile shape with the contribution of each parameter varying throughout the study area. Parameters associated with ice sheet extent have the strongest overall relationship with drainage shape, while the distance from an instability zone is the strongest local relationship. The fault proxy parameter shows relatively strong correlations with cross-profile shape near the Transition Fault, and the narrowest zone of morphologic influence overall.

Signals of combined chromium–cadmium isotopes in basin waters of the Early Cambrian – Results from the Maoshi and Zhijin sections, Yangtze Platform, South China

The combination of authigenic chromium and cadmium stable isotopes in marine sedimentary archives enables reconstruction of the redox conditions and levels of primary productivity in past oceans and basins. The Ediacaran to Cambrian Nanhua Basin (Yangtze Platform, South China) and its sedimentary sequences have been studied intensively in the past with respect to investigating the effects of post-Snowball Earth glaciations on the oxygenation of Earth's atmosphere, and intimately related, on the consequences of climate changes on the evolution of the ocean environment and of life during the Precambrian-Cambrian transition. Following recent propositions of using cadmium isotopes as a novel proxy for reconstructing the extent of primary productivity in paleooceans, we here present results from a combined cadmium (Cd)‑chromium (Cr) isotope study on metalliferous black shale, black shale and phosphorite sediments deposited during the Early Cambrian Niutitang Formation at the Maoshi and Zhijin sections. Results point toward strongly oxidized and highly productive surface water layers in the Nanhua Basin during this period. The samples have strongly positively fractionated δ114Cd and δ53Cr values up to +0.6‰ and + 1.4‰, respectively, similar to such values from carbonaceous sediments in modern oceans. The association of Cd with sulfides in the sediments, together with high Cd/TOC ratios particularly in the metalliferous black shales, implies a sulfide-controlled enrichment of Cd under restricted euxinic conditions. The lower Cd/TOC values in phosphorites and barren black shales and negatively fractionated δ114Cd values down to −0.33‰ point to less effective precipitation of Cd under more suboxic conditions as likely prevailing in an open shallow shelf. The Cr content in the sediments is mostly close to average shale, and the δ53Cr values are little fractionated in the 0–0.2‰ range, corroborated by flat shale-like rare earth element + yttrium (REE + Y) patterns. However, some metal-rich shale samples have clearly authigenic Cr isotope signatures with up to +1.4‰ δ53Cr, and the authigenic Cr component in the phosphorite samples is around 1‰ δ53Cr, indicating oxic surface waters. The latter sediments also depict seawater-like, middle REE enriched REE + Y patterns with distinct negative Ce and positive Y anomalies indicative of an oxygenated surface water layer, and with positive Eu anomalies which they likely received during phosphatogenesis in the euxinic bottom water environment. In accord with previous studies reporting on extreme trace metal enrichments (Mo, Ni, V, Hg, etc.) in these Early Cambrian sediments, our Cd and Cr isotope signatures favor a scenario of a strongly stratified basin in which high primary productivity thrived in an oxidized surface water layer, potentially as a result of increased nutrient supply from a strongly weathering continental hinterland in the aftermath of the last Snowball Earth glaciations in the Ediacaran.

Native biodiversity collapse in the eastern Mediterranean.

Global warming causes the poleward shift of the trailing edges of marine ectotherm species distributions. In the semi-enclosed Mediterranean Sea, continental masses and oceanographic barriers do not allow natural connectivity with thermophilic species pools: as trailing edges retreat, a net diversity loss occurs. We quantify this loss on the Israeli shelf, among the warmest areas in the Mediterranean, by comparing current native molluscan richness with the historical one obtained from surficial death assemblages. We recorded only 12% and 5% of historically present native species on shallow subtidal soft and hard substrates, respectively. This is the largest climate-driven regional-scale diversity loss in the oceans documented to date. By contrast, assemblages in the intertidal, more tolerant to climatic extremes, and in the cooler mesophotic zone show approximately 50% of the historical native richness. Importantly, approximately 60% of the recorded shallow subtidal native species do not reach reproductive size, making the shallow shelf a demographic sink. We predict that, as climate warms, this native biodiversity collapse will intensify and expand geographically, counteracted only by Indo-Pacific species entering from the Suez Canal. These assemblages, shaped by climate warming and biological invasions, give rise to a ‘novel ecosystem’ whose restoration to historical baselines is not achievable.

Barotropic and baroclinic tides in Panay Strait, Philippines

The Panay Strait constitutes a bathymetrically complex system with intense tidal currents. The four major tidal constituents in the total energy spectra inferred from sea level and current profiles are K1, O1, M2, and S2. Spatially, O1 and M2 dominate over K1 and S2, respectively. The diurnal tide accounts for highest amplitude variability over the shallow shelf while semi-diurnal tides over the deeper channel of the strait. Rotary spectra of surface currents shows inertial frequency peaks and exhibit an unusually broad peak in both the clockwise (CW) and counterclockwise (CCW) rotating components, indicating frequency shift by the vorticity of sub-inertial currents prevalent in the region. Vertically, variance of the horizontal velocity explained by the major tidal constituents peaks in two distinct depth bands; the upper layer centered at 110 m (11% variance) dominated by semi-diurnal tide (M2) and the lower layer at 470 m (26% variance) dominated by diurnal tides (O1). Semi-diurnal tidal current ellipses (M2 and S2) exhibit a dominance of CW motions at near-surface depth (110 m), indicative of downward energy propagation and implying a surface energy source. These features from Acoustic Doppler Current Profiler (ADCP) deployed close to the sill is consistent with the dominant semi-diurnal tide (M2) over the channel of the strait from the High Frequency Doppler Radar (HFDR). Comparison of incoherent to coherent tidal energy shows K1 dominated the incoherent tidal band. Spatially, incoherent energy is dominant over the channel particularly near the sill and the constricted part of the strait. The incoherent portion of the tide is presumably attributable to the surface expression of the internal tide which seems to be generated near the sill and then topographically steered west over the edge of the shallow shelf where incoherent energy is dominant.

БИОСТРАТИГРАФИЯ И ЛИТОЛОГИЧЕСКИЕ ОСОБЕННОСТИ НИЖНЕКАМЕННОУГОЛЬНОЙ УРМУГТЭЙУЛЬСКОЙ СВИТЫ (ОРХОНСКИЙ ПРОГИБ, СЕВЕРНАЯ МОНГОЛИЯ)

The results of a biostratigraphic and lithological studies of the terrigenous Carboniferous Urmugteyul Formation in the stratotype area (left bank of the Sharyn-Gol River, Orkhon Trough) are presented in this research paper. Four members are distinguished in the composition of the formation; the first three members are assigned to the Lower Urmugteyul Subformation, the fourth is to the Upper Urmugteyul Subformation. The first palynological studies made it possible to limit the accumulation time of the Lower Urmugteyul Subformation to Late Tournaisian, and the Upper Urmugteyul Subformation to Late Visean. The nature of the structure and lithological features of the section, considered as part of two terrigenous facies associations, as well as the paleontological characteristics and analysis of palynofacies, indicate that the accumulation of the Lower Urmugteyul Subformation occurred in the alluvial-delta plain settings, and the Upper Urmugteyul Subformation is in the shallow shelf basin.

Stratigraphic and sedimentological aspects of the worldwide distribution of Apectodinium in Paleocene/Eocene Thermal Maximum deposits

Abstract The Paleocene/Eocene Thermal Maximum (PETM) is characterized by pronounced global warming and associated environmental changes. In the more-or-less two decades since prior regional syntheses of Apectodinium distribution at the PETM, extensive biological and geochemical datasets have elucidated the effect of rising world temperatures on climate and the biome. A Carbon Isotope Excursion (CIE) that marks the Paleocene/Eocene Boundary is associated with an acme of marine dinocysts of the genus Apectodinium in many locations. Distinctive foraminiferal and calcareous nannofossil populations may also be present. For this updated, dinocyst-oriented view of the PETM, data from worldwide locations have been evaluated with an emphasis on stratigraphic and sedimentological context. What has emerged is that a change in lithology is common, often to a distinctive siltstone or claystone unit, which contrasts with underlying and overlying lithotypes. This change, present in shallow marine/coastal settings and in deep-water turbidite deposits, is attributed to radical modifications of precipitation and erosional processes. An abrupt boundary carries the implication that some time (of unknowable duration) is potentially missing, which then requires caution in the interpretation of the pacing of events in relation to that boundary. In most instances an ‘abrupt’ or ‘rapid’ CIE onset can be attributed to a data gap at a hiatus, particularly in shallow shelf settings where transgression resulted from sea-level rise associated with the PETM. Truly gradational lower boundaries of the PETM interval are quite unusual and, if present, are poorly known so far. Gradational upper boundaries are more common, but erosional upper boundaries have been reported. Taxonomic changes have been made to clarify identification issues that have adversely impacted some biostratigraphic interpretations. Apectodinium hyperacanthum has been retained in Wetzeliella , its original genus. The majority of specimens previously assigned to Apectodinium hyperacanthum or Wetzeliella ( Apectodinium ) hyperacanthum have been reassigned to an informal species, Apectodinium sp. 1. Dracodinium astra has been retained in its original genus as Wetzeliella astra and is emended.

Cenozoic volcanism, tectonics and mineralisation of Woodlark Island (Muyuw), eastern Papua

Cenozoic geology of Woodlark Island was influenced by events prior to the onset of continental rifting at ca 8 Ma and the slightly later commencement of seafloor spreading in the eastern Woodlark Basin between ca 6 and 3.6 Ma. The embryonic Woodlark Island consisted of latest Paleocene(?)–Eocene shallow marine, deep-water shelf and turbidite deposits (Loluai Formation) and small submarine and emergent mafic volcanic centres (Utavai Basalt Member). Platform carbonates extended across the Woodlark Basin in the late Oligocene–middle Miocene (Nasai Limestone). Onset of middle Miocene eruptions in the north-northeast-trending Okiduse Volcanic Zone (OVZ) was localised in the similarly trending Kulumadau Horst and Graben Zone (KHGZ). Volcanic centres flanked major structures in the 12.5 km wide horst and graben zone, suggesting a link between volcanism and extensional tectonics. It was not an island arc settling, and there are neither andesites nor an obvious subduction zone. Offshore the KHGZ is connected with the similarly trending Nubara Fault, the plate boundary between the Solomon Sea Plate and Woodlark Plate. Contrasting volcanic deposits were erupted from volcanoes of the OVZ, viz. Mt Kabat Eruptive Centre, Uvarakoi Caldera, Watou Mountain Eruptive Centre and Suloga Harbour Tuff Cone. The epithermal Busai and Kulumadau gold deposits are located in the KHGZ. They are hosted by porous and permeable crystal lithic lapilli tuff beds in the Monasiy Tuff (Uvarakoi Caldera). Emplacement of thick dolerite sills (Auyed Dolerite) occurred post-middle Miocene. Sill emplacement coincided with the ca 6–3.6 Ma commencement of seafloor spreading in the eastern Woodlark Basin. A major phase of extensional tectonics along the KHGZ commenced post-middle Miocene and has persisted to the Holocene. Uplift was accompanied by rapid erosion and the widespread deposition of poorly to chaotically sorted gravels (Na’ku’iel Conglomerate). KEY POINTS Middle Miocene volcanism occurred from four volcanic centres in the north-northeast-trending Okiduse Volcanic Zone. Volcanism was confined to the similarly north-northeast-trending Kulumadau Horst and Graben Zone. Volcanism was not located in an island arc setting, as there are neither andesites nor an obvious subduction zone. A major phase of extensional tectonics along the horst and graben zone commenced post-middle Miocene and has persisted to the Holocene. Both the epithermal Busai and Kulumadau gold deposits exhibit lithological controls (porosity and permeability) on ore deposition.