Depositional Setting Research Articles

Zircon geochronology and Hf–O isotopes of the Nulliak supracrustal assemblage (Saglek Block–Canada): Constraints on deposition age and setting, metamorphic age and environments of zircon crystallization

The Archean Saglek Block, North Atlantic craton, is one of the oldest crustal segments preserved on Earth. This area records two granulite facies metamorphic events: one in the late-Eoarchean at ca. 3.7 Ga and one in the Neoarchean, at ca. 2.75 Ga. Here, we report the results of combined U–Pb/Hf/O in-situ isotope analyses of detrital and metamorphic zircon domains from two meta-sedimentary samples, one psammitic, and one pelitic. Both samples are components of the oldest supracrustal assemblage of the Saglek Block: the Eoarchean Nulliak supracrustal assemblage. The isotopic data presented in this study: (i) confirm deposition age of the Nulliak supracrustal assemblage before ca. 3.65 Ga, (ii) indicate local provenance of the detrital zircon, (iii) suggest deposition of the sedimentary protoliths in a convergent setting, such as an arc, (iv) crystallization of the oldest zircon during the early Eoarchean in a protolith derived from a depleted mantle component, (v) involvement of material that experienced prolonged low temperature alteration during the late Eoarchean granulite facies metamorphism and (vi) selective metamorphic overprinting during the Neoarchean granulite facies metamorphism.The new zircon U–Pb/Hf/O isotope data presented here in conjunction with previously published analyses suggest that a depleted mantle domain existed in the early Archean, as reflected in the positive εHf signature of zircon from the Saglek Block. Yet, such positive Hf isotope deviations are not the norm, but rather the exception in the preserved early Earth zircon record. In addition, mildly elevated zircon δ18O values, i.e. those ≥ 5.9 ‰, are as common in the early Archean as they are in the late-Archean zircon record, implying that crustal reworking was an active and efficient process all through the Archean. Hence, no significant variation in the nature of the reworking and broader geodynamic processes occurred during this period of time.

Branched glycerol dialkyl glycerol tetraethers as indicators for environmental parameters in a subtropical mountainous river, southern China

Indices based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) have been useful in paleo-environmental reconstructions, although their applicability in river-estuarine sediments remains unclear. This study aims to investigate the correlation between brGDGT-based indices and modern environmental parameters, and to discuss possible impact factors. In this study, we discussed the applicability of several brGDGT-based indices, with specific interests on the IRx’ (the relative abundance of 6- vs. 5-methylated brGDGTs) and CBT’ (cyclization index of branched tetraethers based on the separation of 5- and 6-methylated brGDGTs) for pH reconstruction, and MBT’5ME (the methylation index of branched tetraethers based on the separation of 5- and 6-methylated brGDGTs) for MAAT (mean annual air temperature) reconstruction. From the Jiulong River (JLR) catchment, we have analyzed both riverbank soil samples and riverbed surface sediment samples for brGDGTs, with the following main findings: Firstly, for pH reconstruction, the indices CBT’ and IRx’ are useful in soil and fluvial sedimentary settings. Secondly, for MAAT reconstruction, the MBT’5ME index is sensitive to the air temperature, and the BayMBT0 model performs relatively better than other global or regional calibrations in the study area; By employing the BayMBT0 model, MAAT reconstructed from soils are higher than the measured MAAT, but are generally lower than the measured MAAT when reconstructed from riverbed surface sediments. Thirdly, the disagreement between the reconstructed results from the two sedimentary archives suggests that: Signatures of brGDGTs in the aquatic environment are under strong impacts of in situ produced brGDGTs; Impacts of upper-reach brGDGTs input might have resulted in the increasingly negative offset for the reconstructed MAAT downstream; And influences of complex aquatic biogeochemical conditions on sedimentary brGDGT signals are site-dependent in this area. Finally, brGDGT-based indices are sensitive to the source of brGDGTs, e.g., soil vs aquatic in situ brGDGTs; And terrigenous brGDGTs have been exposed to a range of complex biogeochemical processes before their deposition in the estuary. Based on these findings, we suggest that at least the above impact factors need to be taken into consideration when interpreting the brGDGT signals from estuarine archives, and thus, multi-proxy studies are encouraged. The findings of this study provide a better understanding of the correlation between brGDGT-based indices and modern environmental parameters in subtropical river systems, and provide useful information for interpreting the paleo-environmental signals based on brGDGTs from fluvial-estuarine archives.

Unraveling the wheel of recruitment for salt-marsh seedlings: Resistance to and recovery after dislodgement

Elucidating bottlenecks at critical life stages and quantifying associated resilience (including resistance and recovery) to physical processes are central in inform restoration and attain sustainable development of coastal biogeomorphic ecosystems. Seedling establishment is a key life stage determines saltmarsh restoration potentials. However, the resilience of these recruits, especially through recovery, remains poorly understood. Here, two contrasting globally occurring saltmarsh species, namely Salicornia europaea and Spartina anglica, were employed to generate insights in i) seedling resistance against dislodgement, and ii) seedling recovery potential after dislodgement. Regarding resistance, we found that 1) root-shoot antagonism characterizes the growth rate of seedling resistance to dislodgement through hydraulic disturbance, 2) the root length determines seedling resistance to dislodgement through sheet erosion; 3) a 5 mm sedimentary setting amplifies seedling resistance without inhibiting their morphological evolution. Regarding recovery, we found that 4) dislodged seedlings have a high probability for achieving long-distance dispersal; 5) seedling age and the inundation-free period regulate the re-establishment potential of dislodged seedlings. Overall, S. anglica showed stronger resilience than S. europaea, characterized by stronger seedling resistance against dislodgement and higher re-establishment potential. Our results on seedling resilience suggest that seedling dislodgement is not an end-of-life cycle but a new spin on the “Wheel of Recruitment”, a proposed short-term cyclic behavior with alternating phases of seedling dislodgement, dispersal, and (re-)establishment. The Wheel of Recruitment concept is important for forecasting resilience and persistence of biogeomorphic systems such as salt marshes under global change and for guiding life cycle informed restoration.

Geochemical Characteristics and the Sedimentary Environment of Lower Cambrian Argillaceous Rocks on the Kongquehe Slope, Tarim Basin, China

The deposition of the Lower Cambrian argillaceous rocks on the Kongquehe slope provides a good opportunity to reconstruct the paleoenvironmental conditions of the Tarim Basin. To explore the paleoredox conditions, paleoclimate, and provenance of this deposit, 21 samples were collected from Well A, and the concentrations of major and trace elements were analyzed. The V/(V + Ni), V/Cr, Ni/Co, U/Th, Uau, and V/Sc ratios indicated that the sediments in the water body from the Lower Cambrian were in a reducing environment, and the degree of reduction weakened from the bottom to the top. The Sr/Cu, Mg/Ca, and Fe/Mn ratios in the sediments revealed that the Lower Cambrian was mainly characterized by a warm and humid paleoclimate, and there may be a paleoclimatic transition toward drought conditions as recorded by the sediments of Xidashan Formation. The chemical alteration index, compositional variation index, plagioclase alteration index values, and Th/U and K/Rb ratios of the Lower Cambrian mudstone all reflected that the parent rock in the study area was mainly subject to low- to medium-degree chemical weathering. Longitudinally, the Lower Cambrian gradually increased and then weakened from Xishanbulake Formation to Xidashan Formation. The ratios of trace elements and rare earth elements as well as Th–Sc–Zr/10, Th–Co–Zr/10, and ∑REE–La/Yb diagrams all showed that the mudstones of Xishanbulake and Xidashan Formations of the Lower Cambrian in the study area have a common parent rock type, mainly sedimentary rocks rich in felsic minerals. Additionally, the structural setting discrimination diagrams of SiO2–K2O/Na2O, Th–Sc–Zr/10, Th–Co–Zr/10, and La–Th–Sc showed that the structural setting of the Lower Cambrian mudstone deposition is mainly a continental island arc environment and has the characteristics of an active continental margin.

Community established best practice recommendations for tephra studies—from collection through analysis

Tephra is a unique volcanic product with an unparalleled role in understanding past eruptions, long-term behavior of volcanoes, and the effects of volcanism on climate and the environment. Tephra deposits also provide spatially widespread, high-resolution time-stratigraphic markers across a range of sedimentary settings and thus are used in numerous disciplines (e.g., volcanology, climate science, archaeology). Nonetheless, the study of tephra deposits is challenged by a lack of standardization that inhibits data integration across geographic regions and disciplines. We present comprehensive recommendations for tephra data gathering and reporting that were developed by the tephra science community to guide future investigators and to ensure that sufficient data are gathered for interoperability. Recommendations include standardized field and laboratory data collection, reporting and correlation guidance. These are organized as tabulated lists of key metadata with their definition and purpose. They are system independent and usable for template, tool, and database development. This standardized framework promotes consistent documentation and archiving, fosters interdisciplinary communication, and improves effectiveness of data sharing among diverse communities of researchers.

Authigenic clay mineral evidence for restricted, evaporitic conditions during the emergence of the Ediacaran Doushantuo Biota

The Ediacaran Period witnessed major environmental change and an expansion of eukaryotic life following the Marinoan glaciation. The Doushantuo Formation of south China has furnished much of our understanding of Earth System and biosphere evolution during this period, but its depositional setting–marine or non-marine–is still debated. Here we conduct mineralogical, petrographic and geochemical analyses of samples from the lower Doushantuo Formation in order to determine the origin of saponite clay minerals which are abundant in this interval. We find that the morphology and distribution of the saponite clays suggest they are of pre-compaction, authigenic origin. We infer that the lower Doushantuo sediments were deposited in a restricted, mildly evaporitic lagoonal basin, offering additional constraints on the environmental setting into which metazoan life emerged. Further, our findings confirm that Ediacaran seawater favored reverse weathering, with marine clay formation likely representing an important sink for various elements during the Precambrian.

Geochemical and organic petrographic analyses on the Late Eocene bentonitic shale bed in Kom Aushim vicinity, Fayum, Egypt; Paleoenvironmental implications

Bentonitic shale bed of the Qasr El Sagha Formation (Late Eocene), located in the Kom Aushim area, Fayum, composes of 5 m thickness of dark massive stratum intercalated with veins of iron bands. In this study, twelve fresh shale samples from this area were investigated concerning their geochemical and organic petrography analyses. A total organic carbon (TOC) of the shale samples is very low (0.07–0.39 wt%). Petrographic analysis of samples shows a dominance of the vitrinite maceral followed by either inertinite and/or liptinite macerals. Theoretically derived vitrinite reflectance (Rocal) reveals that the bentonitic shale bed was subjected to an abnormal increase in maturity toward the invasion of Fe, Zn, Cu rich hydrothermal sulfates and oxides veins. The composition and origin of these veins were investigated by XRD and XRF analyses. The results suggested that the Fe brought from these veins affected the main composition of the shale stratum to exhibit Fe-shale facies. Moreover, rich iron in the depositional medium leads to form siderite minerals (≈10%) and the replacement of lime associated clay to Ferron dolomite (≈25%). The dominant paleoclimate synchronized shale deposition was semi-arid and arid climate, as confirmed by the domination of evaporite (≈44% gypsum). The source area of shale components was found to be sedimentary and mafic igneous (basaltic trend). CIA-ICV and A–CN–K ternary diagrams showed that the shale components were subjected to a variety of intensive to moderate weathering, and they were probably coming from gabbro and tonalite igneous rock. An active sedimentary margin and island arc are the main provinces, as the shale was deposited at the marine anoxic condition of a clay-lime platform of a pro-delta sedimentary setting. The organic matters (OM) are of type III and IIIC that refer to terrestrial OM of marginal aquatic environments. Organic and inorganic studies confirm a prevailing depositional environment of a shallow shelf, shoreline mudflats and evaporitic lagoon that reflects the general trend of sea-level regression in the Fayum area during the Late Eocene.

Early diagenetic calcite replacement of evaporites in playa lakes of the Quiricó Formation (Lower Cretaceous, SE Brazil)

Evaporites are abundant in modern playa lakes, where efflorescence, inorganic and/or bioinduced precipitation coexist with siliciclastic deposition. Overall, the sensibility of salts to slight physicochemical changes results in partial to complete dissolution of evaporites in surface and shallow subsurface. However, in some cases, salt minerals are pseudomorphically replaced, providing a snapshot to depositional settings and diagenetic processes of evaporite-bearing successions. This is recorded in the Quiricó Formation (Lower Cretaceous), Sanfranciscana Basin, southeastern Brazil. This studied succession portrays a playa lake system subdivided in saline flat and saline lake deposits, whose diagenesis was marked by ubiquitous cementation and replacement reactions. Petrographic and geochemical techniques were undertaken to characterise primary and secondary textures, mineralogy and distribution of mudstone- and sandstone-hosted pseudomorphs. The pseudomorphs frequently underlie the stratigraphic contact of playa lake-aeolian beds. Pseudomorphs occur as coalescent nodules and as chaotically-distributed chevron crystals, composed of inequicrystalline calcite mosaics. Nodular pseudomorphs have cubic/sub-cubic “ghost” inclusions and displacive contacts with the matrix, whereas the contacts of chevron pseudomorphs and the matrix are undisturbed. Both types exhibit morphological replication of precursor minerals and non-luminescent euhedral relicts. Stable isotopic signatures are covariant and range between −1.6–0.6 ‰ δ13C and 1.4–2.5 ‰ δ18O for nodular pseudomorphs, and −2.2 to −1.5 ‰ δ13C and 0.3–1.3 ‰ δ18O for chevron pseudomorphs. Nodular crystals reflect subaerial and intrasedimentary crystallisation of Ca-sulphates in saline flats, whereas chevron-shaped pseudomorphs indicate bottom-growth halite in shallow lakes. Textural evidences from pseudomorphs and host lithologies constrain the diagenetic overprint to surface and shallow burial settings (syndepositional/eodiagenetic stages). Despite multiple generations of calcite, the constant isotopic signatures of pseudomorphs reflect water chemistry fractionation in a closed-lake basin. Widespread calcitisation of playa lake sediments was caused by calcium-rich groundwaters, influenced by limestones from the Precambrian basement. The playa lake deposits record the onset of aridification processes that culminated in the Thermal Cretaceous Maximum.

Sources and Fluxes of Organic Carbon and Energy to Microorganisms in Global Marine Sediments.

Marine sediments comprise one of the largest microbial habitats and organic carbon sinks on the planet. However, it is unclear how variations in sediment physicochemical properties impact microorganisms on a global scale. Here we investigate patterns in the distribution of microbial cells, organic carbon, and the amounts of power used by microorganisms in global sediments. Our results show that sediment on continental shelves and margins is predominantly anoxic and contains cells whose power utilization decreases with sediment depth and age. Sediment in abyssal zones contains microbes that use low amounts of power on a per cell basis, across large gradients in sediment depth and age. We find that trends in cell abundance, POC storage and degradation, and microbial power utilization are mainly structured by depositional setting and redox conditions, rather than sediment depth and age. We also reveal distinct trends in per-cell power regime across different depositional settings, from maxima of ∼10–16 W cell–1 in recently deposited shelf sediments to minima of <10–20 W cell–1 in deeper and ancient sediments. Overall, we demonstrate broad global-scale connections between the depositional setting and redox conditions of global sediment, and the amounts of organic carbon and activity of deep biosphere microorganisms.

Early Cretaceous Slump Deposits in Laiyang Group (Lingshan Island, East China): New Constraints for Provenance Identification and Tectonic Evolution

The sedimentary strata in the Lingshan Island area are gaining attention because of their unique sedimentary and tectonic characteristics. However, the provenance and the depositional and tectonic setting in this area remain the focus of controversy. There is a significant slump deposit with lateral length up to 250 m in the Laohuzui section at the top of the Laiyang Group, which differs from the underlying turbidite deposits in morphology and composition. The sandstone in the Laohuzui section was continuously sampled and analyzed for major trace and rare earth elements. The results showed that the Laohuzui section is mixed with a continental margin provenance from the re-cyclic deposition in the arid region, which is different from the continental island arc provenance in the lower part of the Laiyang Group. Through the geochemical study of the igneous gravel contained in the olistolite and the comparison with the igneous rocks in the surrounding area, it is observed that the properties of the igneous gravel are most like those of the igneous rock deposit in the Zhucheng-Taolin area. In addition, the Lingshan Island and the Zhucheng-Taolin areas have similar sedimentary processes, suggesting that both received provenance from the Jiaonan uplift at the end of the Early Cretaceous. This study clarified the depositional processes of the later period of the Laiyang Group deposition in the Lingshan Island area.

Facies Analysis and Geochemistry of Upper Cretaceous Carbonate Rocks, Wadi Feiran District, West Central Sinai, Egypt

The current study focuses on the geochemistry and facies analysis of the Upper Cretaceous carbonate rocks deposited in Wadi Feiran, West-Central Sinai, Egypt. The study area is defined by the careful petrographic and geochemical examination of four stratigraphic units, including Raha, Wata, Matulla, and Sudr formations. Ten microfacies types were recognized, listed from bottom to top; Fossiliferous-micrite, Bio-micrite, Pell-Bio-Micrite, Argillaceous Dolo-Biomicrite, Glauco- Dolo-Sparite, Glauco-Dolo-Microsparite, Dolo-Silty-Micrite, Bio- Pell-Sparite, Micrite and Foraminifera Biomicrite. The vertical distribution of these microfacies types indicates cyclic alternation between open and confined marine (bank interior deposits) deposition environments. The carbonate rocks were exposed to subaerial and submarine depositional settings diagenetically. The overflow dispersion of both main and minor components was determined by applying chemical and physicochemical parameter assessments to the selected samples. The review demonstrates that shallow sea conditions prevailed during the Upper Cretaceous.

Depositional Setting of Khurmala Formation (Paleocene-Early Eocene) in Nerwa section, Berat Anticline, Kurdistan Region, Northern Iraq

The depositional environment of the Khurmala Formation (Paleocene-Early Eocene) has been investigated in the Nerwa section, the southern limb of the Berat anticline in the High Folded Zone of Iraq. The thickness of the formation in the studied section was about 113m and can be divided into three units; fossiliferous bedded limestone unit (Unit A), massive dolomitic limestone unit (Unit B) and bedded marly dolomitic limestone unit (Unit C). The petrographic study of the 81 thin sections of the Khurmala carbonates revealed that the majority of skeletal grains are shallow marine derivative faunas and non-skeletal grains include peloids, cortoids and intraclasts. Depending on detailed field observations and petrographic study of the carbonate rocks, five main microfacies were recorded, these are; lime mudstone, lime wackestone, lime packstone, grainstone and boundstone in addition to one lithofacies which is an intraformational conglomerate. Based on the integration of the recognized microfacies and the field criteria of the Khurmala Formation, two facies associations were identified which elucidate deposition in a lagoonal environment including reef patches. Accompanying facies indicate that the formation's sedimentary model is a ramp carbonate platform.

Palaeoecology and depositional setting of an Early Permian (Artinskian) mire based on a multi-proxy study at the Jagannath coal mine (Talcher Coalfield), Mahanadi Basin, India

We report studies of petrography, palynofacies, charcoal and adpressed plant fossils for the coal-bearing Jagannath section in the Talcher Coalfield, Mahanadi Basin, India, to improve understanding of the age, palaeoecology and depositional setting of this palaeo-mire. Palynology is indicative of the Scheuringipollenites barakarensis assemblage, suggesting an Early Permian (Artinskian) age for the studied section. The age of the studied section is inferred based on correlation with coeval assemblages across Gondwana. Palynoassemblages have more similarity with those of Africa than South America. Petrographic indices suggest that peat-forming vegetation accumulated mainly in telmatic settings under ombrotrophic-mesotrophic (intermittent fluctuating) hydrological conditions. Palynofacies suggest that the deposition of organic matter (by high energy fluvio-deltaic agents) took place in an oxic to occasionally dysoxic setting. Megaflora comprise a low diversity assemblage dominated by Equisetales (Schizoneura and Paracalamites), with less common Glossopteridales (Glossopteris, Gangamopteris) and Filicales (Dichotomopteris) indicative of dense arborescent vegetation. Numerous fossil macrocharcoal fragments indicate the repeated occurrence of wildfires in the catchment area. The high abundance of pyrogenic inertinites in Permian coals of Gondwana may indicate a high-fire phase of Earth history linked to elevated atmosphere oxygen level, and our current study further substantiates this idea demonstrating the occurrence of fire, not only in seasonally dry ecosystems but also in peat forming ecosystems under humid conditions. Our multiproxy study is significant for understanding Permian peat-forming ecosystems and environments and provides a robust age assessment based on inter and intra-basinal correlations of coeval sequences across the Gondwana.

Origin and Provenance of Archean Keewaywin Formation clastic rocks at Sandy Lake, NW Ontario, Canada: Constraints on Archean weathering and depositional processes

Mesoarchean supracrustal sedimentary and volcanic rocks reflect provenance, depositional, tectonic and metamorphic conditions in Archean cratons. In the Sandy Lake Greenstone Belt within the North Caribou Terrane of the Superior Province, the Mesoarchean (∼2900 Ma) Keewaywin Formation is a metamorphosed siliciclastic deposit of mudstone, quartz-rich arenite, and volcaniclastic feldspathic litharenites and schists. Analysis of the petrography, mineralogy, and whole-rock and mineral geochemistry of sandstones and pelites indicate that precursor kaolinitic muds, dissolved iron, and quartz-rich sands were developed in soils by moderate to intense, long term weathering of felsic and mafic basement rocks in a tectonically stable environment. The detritus, half or more pelitic, was eroded from those soils and deposited as mud, some aluminous kaolinitic, some ferruginous, and as quartz-rich sands in a low relief setting. Volcaniclastic detritus from contemporaneous felsic volcanism was deposited with continually available kaolinitic mud and quartz- rich sediment. Kaolinitic aluminous muds were variously metasomatised at surface or near surface conditions with K, yielding muscovite-rich schists (as much as 95% muscovite); Ca and Na metasomatism yielded mm-scale, plagioclase rich laminae (up to 89% normative plagioclase) indicative of evaporite conditions. Ferruginous muds yielded chlorite rich schists (as much as 95 modal % chlorite). Reduced iron suggests the original sediments were deposited in an anoxic environment. New detrital zircon U/Pb age for a litharenite sample is 2930–2890 Ma is indicative of the age of an unconformity recognized in the North Caribou Core of the North Caribou Terrane. Detailed analysis of metamorphosed greenstone belt sedimentary rocks enables interpretation of their provenance, climate, weathering, depositional settings and post-depositional alteration. The shale compositions are particularly sensitive indicators of weathering conditions, hence climate. With age data, correlations between greenstone belts may allow recognition of regional large scale climate, weathering and sedimentation events.

Isotope compositions of dinosaur eggs and associated depositional settings in the Upper Cretaceous Huizhou Formation from the Qiyunshan area, Anhui Province, China: implications for paleoenvironmental reconstruction

ABSTRACT We analysed the stable isotope compositions of dinosaur eggshells and their associated depositional settings of the egg-bearing rocks in the Upper Cretaceous of the Qiyunshan area, Anhui Province, China. Data show that δ13C values for Similifaveoloolithus qiyunshanensis and Umbellaoolithus xiuningensis range between −5.94‰ and −3.55‰; this suggests that C3-type vegetation was consumed by dinosaurs with relatively high atmospheric CO2. δ18O values vary between −8.45‰ and −4.95‰, indicative of high temperature and low humidity within nesting areas. The lithological characteristics of the egg-bearing section evaluated in this study are dominated by red-brown fine sandy siltstone, correlating with pebbly medium-fine grained and medium-fine grained lithic sandstones. Grain size parameters, histograms, and sample probability cumulative curves are also all characterised by fine-grained sediments and suspension populations, likely indicative of floodplain and point bar environments. Therefore, the paleoclimate of the dinosaur nesting habitat was semiarid-to-arid based on food types as well as the colour and high Fe content of sediments. We suggest that this fluvial environment provided the best nesting and egg laying area for drought-adapted dinosaurs in the Upper Cretaceous of the Qiyunshan area and that the excavated nesting could be concluded in view of the periodic flooding events.

Early Neoproterozoic well-preserved stromatolites from southern Liaoning, North China: characteristics and paleogeographic implications

We report morphology and microstructure of the stromatolites of the Ganjingzi Formation in southern Liaoning. Sedimentologic and morphologic analyses indicate that the lower stromatolite mounds formed in a transgressive succession, while the stromatolite columns in the more complex upper biostrome changed vertically from dispersed growth to dense clumping. Biostratigraphic analysis shows that the stromatolites in the Ganjingzi Formation are similar to those from coeval strata in the Xuzhou-Huainan Region and in southern Jilin. Comparisons of the morphotype genera of stromatolites and the sedimentary setting between different areas, imply that sea-level was fluctuating in the east of the North China Craton (NCC) during the Ganjingzi interval and that the transgressions were beneficial to stromatolite growth, as indicated by the increased number of stromatolites in the study area.

Depositional Environment and Organic Matter Enrichment of Early Cambrian Niutitang Black Shales in the Upper Yangtze Region, China

Natural gas generation is the result of organic matter degradation under the effects of biodegradation and thermal degradation. Early Cambrian black shales in the Upper Yangtze Region are rich in organic matter and have shown great shale gas potentiality in recent years. Nevertheless, the enrichment mechanism and distribution of organic matter in these black shales between different sedimentary settings, such as intra-platform basin, slope, and deep basin, are still poorly understood. In this paper, based mainly on elemental geochemistry, a comprehensive study of the marine redox conditions, primary productivity, sedimentation rate, terrigenous input, hydrothermal activity, and water mass restrictions was conducted on the Early Cambrian Niutitang black shale in the Upper Yangtze Region. Our data showed that an intra-platform basin received a higher terrigenous input and that it deposited under more restricted conditions than the slope and deep basin settings. The primary productivity in the slope and deep basin settings was higher than that in the intra-platform basin setting. In the intra-platform basin, the productivity increased from its inner part to its margin. For the slope and deep basin settings, the high paleoproductivity generated large amounts of organic matter and its preservation was synergistically affected by the redox conditions. In contrast to the slope and deep basin, the preservation of organic matter in the inner part of the intra-platform basin was mainly controlled by redox conditions because the paleoproductivity in it was much lower than in the slope and deep basin settings. The intra-platform basin margin was the most favorable area for accumulating organic matter.

RETRACTED: Applying geoarchaeological principles to marine archaeology: A reappraisal of the “first marine” and “in situ” lithic scatters in the Dampier Archipelago, NW Australia

AbstractThe absence of known prehistoric underwater cultural heritage (UCH) sites on the Australian inner shelf stands in stark contrast to the thousands of sites revealed elsewhere in the world. Two recent claims—Dortch et al. (D2019) and Benjamin et al. (B2020)—put forward the first in situ (i.e., primary context) UCH sites in the shallow waters of the Dampier Archipelago, North West Australia, each arguing that the stone artefact scatters are at least 7000 years old and are now submerged because of postglacial sea‐level rise. We present new hydrodynamic modelling and data on coastal erosion and bathymetry, and reassess each site's sedimentary setting and archaeological site‐formation history. D2019 and B2020 clearly present lithic cultural artefacts, but the arguments for their sites being of primary context and reflecting early Holocene land surfaces are mistaken. Rather, these sites occur in the intertidal zone, and many or all artefacts are likely to have been reworked. Sites of secondary context, if treated appropriately, can inform our understanding of site‐formation process and change, and may support more powerful contributions to submerged archaeology than attempts to seek the first or the oldest.

Verification and Application of Sequence Stratigraphy to Reservoir Characterization of Horn River Basin, Canada

Shale reservoirs, the most important unconventional resource, are difficult to characterize. Shale formations require detailed interpretation of geological, petrophysical, and geochemical analyses, and an integration of these disciplines. In terms of geological interpretation, the commonly used sequence stratigraphy analysis includes a lithofacies analysis. The application of sequence stratigraphy to shales facilitates the ability to relate between lithofacies and mineral composition, petrophysical parameters, and kerogen contents, which are affected by depositional setting. The classification of lithofacies is indispensable for reservoir quality prediction. In this study, porosity, permeability, and TOC content largely depend on lithofacies, and their correlation coefficient is relatively high. The sequence stratigraphic interpretation shows that organic carbon content usually increases within the maximum flooding surfaces and decreases stepwise. However, the relationship between total organic carbon contents and systems tract is less direct and redox dependent.

Major, trace and rare earth elemental geochemistry of Santonian–Campanian onland‐offshore transition in a Gilbert‐type deltaic setting, Cauvery Basin, southern India

The spatially widely distributed and temporally protracted Santonian–Campanian stratigraphic records of the Sillakkudi Formation of the Ariyalur Group, Cauvery Basin, southern India represent an onland exposure of a Gilbert‐type delta. Here, we present geochemical, mineralogical, and petrographic analyses of two composite stratigraphic sections, and evaluate the climatic, tectonic, and other factors that contributed to the spatio‐emporal uniqueness of this formation. A range of low to intensive weathering, simultaneous exhumation/erosion, physical transport, and chemical weathering, prevalent at different parts of the source region and or the existence of multiple channels that drained varied source regions and hence varied lithologies at exhumation surfaces which in turn experienced seasonally varied flow conditions were interpreted. The prevalence of physical erosion during the initial stages of the deposition of the Sillakkudi Formation that progressed towards higher intensities of chemical weathering, in tune with the increase in atmospheric temperature and sea‐level rise during the later stages of the formation, is evidenced. Occurrences of positive and negative Eu anomalies and a progression from active to passive tectonic setting of samples, concomitant with change from tectonic control to relative sea‐level and the sediment influx controlled nature of deposition from Santonian–Campanian is recorded. Together, three sets of related factors namely, tectonics, increase of atmospheric temperature and sea‐level rise operated independently, and the enforced transience of transformation of the source terrain from active to passive margin, the transformation of depositional setting from fluvial to estuarine/intertidal to open marine, and shifting of principal loci of deposition from onland to offshore, are documented. The causal link between the progressive increase of sea‐level control over the depositional system during the Santonian–Campanian as recorded by this study could be due to the rise in atmospheric temperature that in turn might have been influenced by the movement of the Indian Plate from low latitudes towards the equatorial region. The second implication of the results is that the studies attempting to document tectonic setting, provenance, and weathering, with the help of geochemical discriminant diagrams, should also consider the spatial and temporal changes in the source area as well as depositional setting.