High Terrestrial Input Research Articles

Właściwości złoża jurajskiej formacji Khatatba: Pole naftowe Tut, Pustynia Północno-Zachodnia, Egipt

The Tut oil field is in the North-western part of the Western Desert. This work aims to study the reservoir characteristics, to evaluate the hydrocarbon potentiality of the Upper and Lower Safa Members based on the available subsurface data obtained from open-hole well log records of four wells distributed in the study area. Numerous isopach and lithofacies maps have been constructed. The petrophysical evaluation, in terms of determining reservoir net-pay thickness, shale content (Vsh), effective porosity (∅eff), water saturation (Sw) and hydrocarbon saturation (Sh), were estimated. The vertical and the lateral distribution of the reservoir characteristics, in the form of litho-saturation cross-plots, iso-parametric maps and lithologic-matrix cross-plots were constructed. Three hydrocarbon charged zones in the Khatatba Formation were defined and represented by the Upper Safa-Top, Upper Safa-Bottom and Lower Safa-Top. The upper most part of Upper Safa Member (Upper Safa-Top) reservoir represents an oil producing zone where it consists of shallow marine to alluvial sediments. The Lower most part of Upper Safa Member (Upper Safa-Bottom) reservoir represents gas producing zone where it consists of a thick alluvial sand body. Finally, the upper most part of Lower Safa Member (Lower Safa-Top) reservoir represents an oil-gas producing zone consisting of shallow marine sediments with high terrestrial input. The iso-parametric maps show that Northern and central parts of the study area are the most favorable parts for hydrocarbon accumulation due to the increase in net-pay thickness and average effective porosity and decrease in water saturation toward these parts.

Source rock characterization and biomarkers analysis of Adar and Galhak Formations, Rawat central sub-basin, White Nile basin, Sudan

Geochemical analysis was conducted on shaly-cutting samples from various formations in Rawat Central Sub-Basin using Rock-Eval pyrolysis, vitrinite reflectance, and GC-MS to determine the characteristics of different source rocks in the basin, including their hydrocarbon potential, maturity, and organic facies. It can be inferred that most samples exhibit characteristics of gas-prone source rocks. Only Adar and the shaly upper section of the Campanian Galhak formation are promising in having excellent source rocks with TOC reaching up to 12%, HI (563–919 mg/g TOC) Tmax (443–445 °C), and S2 (77 mgCO2/g rock) with a potential to generate oil. The maturity data of both Tmax and vitrinite reflectance revealed that these source rocks are within the early mature to early peak mature with dominant kerogen type of a mixed type II-III kerogen. Few samples reflect a pure type I and type II kerogen.The biomarkers data revealed that three possible organic faces can be identified. Slightly brackish anoxic to sub-anoxic deep lacustrine/marine shale to marginal marine shale (coastal plain estuary) characterized by (Pr/Ph < 1, High Hopanes, C23 TT, Pr/Ph < 1, C25TT/C26TT and C24TeT/C26TT < 1, C27 ∼ C29 sterane, high Gammacerene and β-carotane) (Organofacies I). Mixed facies of distal lacustrine to coastal plain proximal lacustrine (Organofacies II) characterized by (High waxiness, Pr/Ph > 2, C25TT/C26TT and C24TeT/C26TT > 1, high C28 sterane). Sub-oxic terrestrial to coastal plain estuary/bay facies characterized by (Pr/ph ∼1, C25TT/C26TT and C24TeT/C26TT > 1, low Gammacerane, High C29 sterane) (Organofacies III). Lower Galhak formation was deposited in slightly brackish, clay-rich, deep lacustrine to mixed marginal marine shale estuary representing Organofacies I with an average terrestrial input forming type II & III kerogen. For Galhak formation, the depositional environment ranged from proximal sub-oxic sallow lacustrine to distal sub-oxic lacustrine (Organofacies II) with a high terrestrial input in the Lates. Adar formation was deposited in a clay-rich, sub-oxic, terrestrial (Fluvial) to coastal plain (estuary/bay) (Organofacies III) with an average terrestrial input generating a mixed type II/III kerogen. The relatively low 20S/(20S + 20R) and ββ/(ββ + αα) C29 suggest an early maturation in Adar formation and early to peck mature source rocks in Galhak formation.

Dynamic evolution of marine productivity, redox, and biogeochemical cycling track local and global controls on Cryogenian sea-level change

The Cryogenian period of the Neoproterozoic was marked by two Snowball Earth glaciations that bookended a non-glacial interval that lasted roughly 10 million years. The break-up of Rodinia in the early Neoproterozoic gave rise to numerous rift basins whose time-varying redox dynamics, linked to marine productivity and biogeochemical cycling, were likely controlled by varying degrees of basin restriction in response to sea-level change. Those drivers were associated with both global glaciations (Sturtian deglaciation and the possibly early onset of the Marinoan) and local tectonics (regional basin uplift/subsidence). To explore these relationships, we focus on the Datangpo Formation, an exceptional shale sequence deposited in a marginal rift basin in South China. The Datangpo succession comprises lower organic-rich black shales and upper organic-lean gray shales/siltstones. As elucidated by our integrated data, the former were deposited in H2S-rich, deep-water settings underlying highly productive surface waters. We attribute this productivity to elevated nutrient supplies replenished from the open ocean following a sea-level rise, as augmented by high terrestrial input of phosphate in the wake of the Sturtian deglaciation. By contrast, the gray shales/siltstones were associated with relatively shallow deposition in an oxic/suboxic water column with suppressed primary production. The major driver of this dramatic shift in water chemistry may lie with a greater extent of basin isolation and the corresponding reduction in nutrient fluxes from the global ocean due to a significant sea-level fall—possibly linked to regional basin uplift. At this time, the basin experienced an elevated influx of detrital clays and organic material, perhaps triggered by lower sea level. Surprisingly, we found that euxinic conditions prevailed in the water column for a substantial period following the onset of more isolated conditions. This relationship can be attributed to redox-dependent phosphorus cycling. Specifically, H2S-replete conditions facilitated regeneration of bioavailable phosphorus, initiating a positive feedback that allowed the persistence of anoxic waters. This study advances our understanding of nutrient cycling and biogeochemical evolution during the Cryogenian under the influence of large-scale sea-level fluctuations and associated time-varying connectivity to the open ocean that must have been common in many basins at this time. Furthermore, our study sheds novel light on the iron proxy and early sulfur cycling. Almost all of the terrestrial silicate-bound iron was likely converted into highly reactive phases due to strong chemical weathering, while sulfur data revealed isotopic stratification in the wake of Sturtian deglaciation, with important messages for interpretations of analogous data in the aftermath of other climate upheavals in Earth history.

Oceanic Redox State During the Early Cambrian: Insights From Mo‐S Isotopes and Geochemistry of Himalayan Shales

AbstractThe Precambrian‐Cambrian (Pc‐C) boundary marks significant biological, atmospheric, and oceanic changes. These changes include extinction of the Ediacaran fauna, initiation of complex lifeforms, and oxygenation of the atmosphere and oceans. In this contribution, elemental and Mo‐S isotopic compositions of organic‐rich shales overlying the Pc‐C boundary from the Tal Formation, Lesser Himalaya, have been investigated. These datasets are used to reconstruct past oceanic redox state and sulfate concentrations. The principal component analysis of the elemental dataset identifies six major factors, with factors associated with organic matter and sulfide phases accounting for about half of the total variance. Iron speciation and Mo/U data suggest that the shales were deposited in anoxic and ferruginous deep water conditions. The δ98Mo data (1.5 ± 0.2‰) and their mass balance calculations indicate that the areal extent of sulfidic waters and pyrite burial rates were about 2–4 times higher during the Pc‐C transition than in the modern ocean. The pyrite‐δ34S values (3.6–8.3‰) for the Tal shales are isotopically heavier compared to modern‐day sedimentary pyrites (∼−21‰). Calculations involving earlier‐reported δ34S values for early Cambrian seawater and our measured pyrite‐δ34S data estimate the seawater sulfate concentration (8 ± 3 mM) during their deposition. This sulfate value for the Tal basin is higher than that reported for the late Neoproterozoic ocean (&lt;5 mM), attributable to increasing oxygen availability and continental supply during this time. The observed basinal conditions and high terrestrial input may have influenced metazoan diversification.

Controlling factors of organic matter accumulation and lacustrine shale distribution in Lianggaoshan Formation, Sichuan Basin, SW China

The lacustrine shale, represented by the Lianggaoshan Formation, is widely distributed in oil and gas basins of China and will be a key target for unconventional hydrocarbon exploration in the future. Due to the complexity of geological conditions, the distribution of lacustrine shale and the mechanism of organic matter (OM) enrichment show significant differences between different basins. In this study, seismic interpretation, core observation, high-frequency geochemical analysis and other methods are integrated to reveal factors controlling lacustrine shale distribution and OM accumulation in lacustrine shale. The results suggest that six bottom-to-top organic-rich shale intervals are identified within the Lianggaoshan Formation due to lake-basin migration. The migration process of depocenters controls the planar distribution of lacustrine organic-rich shale. The organic-rich lacustrine shale within 1st Member and 2nd Member is characterized by relatively high paleoproductivity and dysoxic condition. The lacustrine organic-rich shale of the upper to the top of 3rd Member is characterized by relatively low paleoproductivity, relatively high terrestrial input, and dysoxic condition. Paleoproductivity and preservation condition caused by lake-level rise are generally the major influencing factor of organic matter accumulation in 1st Member and 2nd Member organic-rich shale. The input of terrestrial OM, and the condition of preservation caused by rapid deposition are the major factors controlling OM accumulation in 3rd Member of Lianggaoshan Formation.

Volcanism intensity and associated climate-ocean-land dynamics during the Cryogenian interglaciation: Insights from mercury isotopes

The Cryogenian interglaciation (ca. 660 Ma to 650 Ma) was an interlude between the Sturtian glaciation (ca. 717 Ma to 660 Ma) and Marinoan glaciation (ca. 650 Ma to 635 Ma). Recent observations of anomalously high mercury (Hg) concentrations in Cryogenian interglacial sediments at basinal settings in the Nanhua Rift Basin, South China, imply that large volcanism can be a possible driving force of the Cryogenian interglaciation. To test this hypothesis and understand the potential linkage between large volcanism and climate-ocean-land dynamics during the Cryogenian interglaciation, we investigate mercury (Hg) concentrations and isotopic composition of Cryogenian interglacial sediments at shallow water (shelf/slope) settings in the Nanhua Rift Basin, South China. The basal Mn-bearing black shales show an increased pattern in Hg concentrations (318 to 4400 ppb) and Hg/TOC ratios (243 to 1730 ppb/wt%), and overall positive Δ199Hg values (0.00 to 0.10‰), suggesting increasing volcanic Hg input into the ocean via atmospheric Hg(II) deposition in the early Cryogenian interglaciation. The upper siltstone samples show a dramatic decrease in Hg concentrations (from 5110 to 459 ppb) and a drop of Δ199Hg values (from 0.04 to −0.05‰), suggesting weakened volcanism during the middle-late Cryogenian interglaciation. Combined with the analyses of major and trace elements proxies, we demonstrate that (1) greenhouse climate in the early Cryogenian interglaciation induced high oceanic productivity, high organic burial on the seafloor and high terrestrial sulfate input into the ocean, which favors the deposition of Mn-bearing black shales in the ocean; and (2) weakened volcanism and continued continental weathering exhausted atmospheric CO2 and drove the global climate to the Marinoan glaciation. This study, therefore, provides important insights into the climate-ocean-land dynamics during the Cryogenian interglaciation.

Palynological evidence for the Middle Jurassic environmental evolution in the eastern part of the Alborz Mountains (northern Iran)

The palynological assemblages of the Dalichai Formation were studied to reconstruct the paleoenvironmental evolution of the Middle Jurassic interval in the eastern part of the Alborz Mountains (N Iran). Dinoflagellate cyst biozones, planktonic foraminifera, and ammonites suggest a Bajocian-Callovian age for the Dalichai Formation. The palynodebris, mostly of terrestrial origin, are dominated by black opaque phytoclasts. Dinocysts, spores, pollen grains, and amorphous organic matters (AOM) are minor components in most samples. Terrestrial palynoflora are mainly represented by coastal gymnosperms (Araucariaceae, Cheirolepidiaceae), lowland simple monosulcate pollen producers (Cycadales/Bennettitales), ferns, upland seed ferns and conifers (Corystospermales and other bisaccate pollen producers). These assemblages indicate a warm climate with seasonally-dry conditions. However, an increase in Cheirolepidiaceae (Classopollis) in Bathonian assemblages reflects higher temperature during this interval. The dominance of the land-derived phytoclasts and presence of brackish water Botryococcus colonies with cells arranged irregularly suggest a proximal setting with high terrestrial and freshwater input during the Bajocian. The palynofacies analysis suggests a sea-level rise during the Bathonian, reflected by higher abundance and diversity of dinocysts as well as the presence of degraded small phytoclasts. This transgression phase is related to the increased subsidence of the Alborz region due to ongoing Neotethys subduction and creation of a large extensional back arc basin in the Eurasian margin. The syn-rift deposits are characterized by ammonitico rosso facies as well as hemipelagic carbonates containing planktonic foraminifera and pelagic bivalves.

Source and sequestration of sediment organic carbon from different elevation zones in estuarine wetland, North China

Estuarine wetland plays an important role in regulating global carbon cycle due to high terrestrial carbon input and burial. However, it is unclear how the source and sequestration of sediment organic carbon (SOC) in estuarine wetlands changes under the anthropogenic impact in the past century. In this study, combining parameters of TOC/TN ratios, δ13C, δ15N and 210Pb-chronology, temporal trends of SOC source and sequestration flux in Liaohe estuarine wetland were studied. The results showed that the source of organic carbon in Liaohe estuarine wetland was dominated by terrestrial input (contribution >60 %). Due to vegetation, TOC in shallow reed marsh was significantly higher than that of bare beach and subtidal flat. Affected by elevation, the sediment mass accumulation rate (MAR, kg·m−2·yr−1) showed differences in reed marsh (C1), bare beach (C2) and subtidal flat (C3), which were 6.57, 13.56 and 13.25 respectively in the past century. MAR fluctuated over time, it showed an overall increasing trend, especially since the 1980s. Correspondingly, the sequestration flux of SOC (SF-SOC, g·m−2·yr−1) showed an overall increasing trend with average of 82.84 (reed marsh), 151.93 (bare beach) and 123.71 (subtidal flat). Comparing to TOC, the higher MAR had a more distinct effect on carbon sequestration in Liaohe estuarine wetland. The difference in sedimentation rate and carbon sequestration are linked to the changes in sediment flux of riverine input and land utilization in the catchment area due to human activities in recent decades, including the construction of reservoirs, dams and local ditch wharf.

Temporal and spatial variations of high-resolution strontium, carbon, and oxygen isotopic chemostratigraphy at the end-Permian crisis boundary in South China

Variable degrees of strontium, carbon, and oxygen isotopic perturbations related to the end-Permian mass extinction (EPME) were recorded from the Latest Permian (i.e., the Lopingian stage prior to the extinction event) to the Earliest Triassic recovery (i.e., the Induan stage), while the underlying causes for their temporal and spatial variations and marine paleoenvironmental indications were poorly understood. In this study, integrated high-resolution 87Sr/86Sr, δ13C, and δ18O proxies are presented across the Wuchiapingian/Changhsingian and Permian/Triassic boundaries within the stratigraphic framework calibrated with high-resolution conodont biostratigraphy and high-precision geochronology in three South China sections, i.e., the Liangfengya, the Meishan, and the Shangsi sections. High-resolution strontium isotopes revealed that the water-mass segregation and accelerated precipitation rate of strontium probably resulted in local heterogeneity and provincial features of 87Sr/86Sr values at short-time interval less than 1 Myr. This provincialism of 87Sr/86Sr values can serve high-resolution chemostratigraphy. Integrated δ13C and 87Sr/86Sr isotopes from the studied sections at the Wuchiapingian/Changhsingian boundary (WCB) revealed that spatial heterogeneity with respect to drift magnitudes and peak values of δ13C negative excursion was not associated with oceanic stratification or high terrestrial input, while the releasing of 13C-depleted CO2 by deep-marine volcanism could be a plausible cause. Moreover, integrated δ18O and 87Sr/86Sr isotopes indicated that the “cooling event” occurring at the WCB was a provincial event, which was influenced by water depth and marine volcanism. The integrated high-resolution 87Sr/86Sr, δ13C, and δ18O proxies confirmed that the oceanic stratification was an ultimate cause for shallow-to-deep-water δ13C gradient at the Permian/Triassic boundary (PTB), but having no link to paleoproductivity increase. The positive excursion of 87Sr/86Sr postdated negative shift of δ13C by ∼ 40 Kyr across the PTB from the studied intervals. This temporal chemostratigraphic variation revealed that terrestrial influx was not a major cause for negative excursion of δ13C. The shallow-to-deep-water 87Sr/86Sr gradient was observed across the PTB in the studied sections, which was probably caused by water segregation resulting from oceanic stratification and distances from high- or low-radiogenic strontium sources supplied by terrestrial input or marine volcanism.

Palaeosedimentary Environment and Formation Mechanism of High-Quality Xujiahe Source Rocks, Sichuan Basin, South China

AbstractTriassic Xujiahe source rocks, the main gas source of shallow tight gas, are the most typical continental coal-bearing source rocks in the Sichuan Basin, South China. However, the organic matter enrichment section cannot be identified easily, leading to limited progress in the exploration of coal-bearing tight gas. This paper reveals the main controlling factors of the organic matter enrichment, reconstructs the evolution process of the Xujiahe palaeosedimentary environment, proposes a dynamic enrichment mechanism of the organic matter, and determines the organic matter enrichment section of the high-quality coal-bearing source rocks by geochemical characteristics of the source rocks, major elements, and trace elements. The results show that the Xujiahe sedimentary environment can be divided into a fluctuating stage of transitional sedimentation, stable stage of transitional sedimentation, fluctuating stage of continental sedimentation, and stable stage of continental sedimentation. The Xujiahe source rocks were featured with high-quality coal-bearing source rocks with high total organic carbon and maturity and good parent material in the stable stage of transitional sedimentation and fluctuating stage of continental sedimentation, in which the water was connected with the Palaeo-Tethys Ocean with abundant terrestrial organisms. The water was shallow in the fluctuating stage of transitional sedimentation with a low sedimentation rate, leading to poor organic matter enrichment. The Palaeo-Tethys Ocean withdrew westward from the Yangtze plate in the late period of the fluctuating stage of continental sedimentation, leading to the absence of algae and dinosteranes and a decrease in biological productivity in the stable stage of continental sedimentation. Therefore, high terrestrial inputs and biological productivity and high sedimentation rate were conducive to the organic matter preservation in the coal-bearing source rocks.

Geochemical Characterizations of Source and Depositional Environment of Hydrocarbons in the Lake Albert Rift Basin

AbstractDespite the upsurge in hydrocarbon exploration in the Lake Albert Rift Basin (LARB) over the past three decades, systematic characterization of hydrocarbon compositions remains lacking, leading to uncertainties in source rock and oil generation determination. We characterized crude oil compositions and oil sand samples in the northern and southern subbasins of LARB. The relative abundance of normal and branched linear alkanes, hopanes, steranes, and aromatic hydrocarbon suggest that northern and southern hydrocarbons were deposited in anoxic to suboxic lacustrine environments and share similar biological source compositions (i.e., a mixture of plants and aquatic algae and bacteria). Relative to southern samples, northern samples show more negative δ13C values for oils, saturates and aromatics, indicating longer migration paths, and exhibit higher MPI‐1, DNR‐1 and 4‐/1‐MDBT ratios, indicating higher maturity. Between the two possible sets of source rocks (upper Miocene and Jurassic strata), the positive δ13C values of saturated hydrocarbons (average = –20.5‰) suggest that the upper Miocene lacustrine shale is the most likely candidate. Oleanane index (&lt;5% in our samples) does not exclude either source rock possibility, and C28/C29 regular sterane (average = 0.63) may be biased by high terrestrial inputs in a lacustrine setting. Together, our data show that northern and southern oils originate from the same source rocks but different oil kitchens. Given the similar geochemical characteristics of southern and northern oils, previous exploration successes in the northern subbasin likely suggest similar potential in the southern sector, while other elements influencing exploration success must be also evaluated.

Using microplankton proxies to evaluate marine palaeonvironmental changes during late Maastrichtian: Evidence from the Møre Basin (Norwegian continental shelf)

This work presents high-resolution palynological and micropalaeontological analyses of a cored succession across the upper Maastrichtian from a well in the Møre Basin (Norwegian continental shelf). Diverse assemblages of dinoflagellate cysts and foraminifera provide insights into the palaeobiogeography and palaeoenvironmental conditions during the late Maastrichtian in this region. An outer neritic setting is interpreted based on the general high abundance of planktonic foraminifera. A subdivision of the biostratigraphic record into three Ecozones has allowed for a detailed documentation of the phytoplankton communities during the late Maastrichtian until the K-Pg boundary. Ecozone A is characterised by a predominance of peridinoid cysts which together with abrupt fluctuations in planktonic foraminifera suggests high nutrient availability and, possibly, high terrestrial input potentially associated with regional turbiditic currents. Also, the occurrence of taxa characteristic of boreal affinity suggests colder waters for this Ecozone. Ecozone B is characterised by consecutive influxes of areoligeracean species such as Palynodinium grallator, Areoligera senonensis and Circulodinium distinctum in the dinoflagellate cyst assemblages. The increase abundances of planktonic foraminifera across this interval suggests an increase in palaeowater depth into a more outer shelf to upper slope. Immediately before the K-Pg boundary (Ecozone C), an increase in abundance of low latitude dinoflagellate species and the planktonic foraminifera Pseudotextularia elegans may represent the local signal of the global latest Maastrichtian Warming Event. Two new dinoflagellate cyst species restricted to the late Maastrichtian, Glaphyrocysta turgida sp. nov. and Heterosphaeridium silybum sp. nov. are also formally described.

Sedimentary environment and model for lacustrine organic matter enrichment: lacustrine shale of the Early Jurassic Da'anzhai Formation, central Sichuan Basin, China

Based on the analysis of element geochemistry and total organic carbon (TOC), this study investigates the main factors controlling organic matter (OM) enrichment, reconstructs the evolution process of the sedimentary environment, and proposes a dynamic OM enrichment model of the Jurassic Da'anzhai (D) Formation, Sichuan Basin. The results indicate that the Sichuan Basin was generally dominated by a warm and oxidizing sedimentary environment, but with some peculiarities, such as a hotter climate in the D1 member and more anoxic lake water in the D2a member. The sedimentary evolution of the Da'anzhai Formation can be divided into a fluctuating sedimentary stage, a stable sedimentary stage and a reef-building stage. The D2a member showed the strongest hypoxia, the weakest weathering, the largest amount of terrestrial inputs, and the highest TOC content. The TOC is positively correlated with reducing conditions and terrestrial inputs, negatively correlated with weathering. Based on these findings, it is suggested that the global climate in the Early Jurassic period had a complex regional effect and the global oceanic anoxic events of the Toarcian did not spread to the Sichuan Basin. Thus, the anoxic deep water, high terrestrial inputs, and weak weathering were conducive to rapid deposition and preservation of lacustrine OM.

Three Gorges Reservoir construction induced dissolved organic matter chemistry variation between the reservoir and non-reservoir areas along the Xiangxi tributary

As one of the most dynamic and reactive compound pools, DOM plays a crucial part in various biochemical processes such as element cycling and nutrient export. Although the reservoir DOM has been investigated extensively, the variation of DOM between reservoir area and non-reservoir area induced by reservoir construction is not comprehensively assessed. By the combination of a series of complementary techniques including stable carbon isotope, optical spectroscopy, and ultrahigh-resolution mass spectrometry, here we show that hydrological alterations induced by Three Gorges Reservoir (TGR) construction were responsible for the variation in DOM molecular composition between reservoir area and non-reservoir area in Xiangxi tributary. With water intrusion from mainstream induced by reservoir construction and operation, reservoir area had relatively higher terrestrial input and more recalcitrant DOM than those in the non-reservoir area with limited influence of reservoir operation, whereas, relatively more autochthonous source and higher molecular lability of DOM were observed in the non-reservoir area. The water intrusion from mainstream to tributaries induced by reservoir construction is likely the main factor controlling DOM variation between reservoir area and non-reservoir area, and might devote to the organic carbon burial in the reservoir. This research provides new insight into spatial variations of riverine DOM composition induced by reservoir construction, underlining the important role of the reservoir in DOM cycling.

A multi-proxy study of the Cerro Piche Graben - A Lower Jurassic basin in the central North Patagonian Massif, Argentina

The volcano-sedimentary succession of the Cerro Piche Graben, Río Negro province, Patagonia (Argentina), was studied U–Pb and Lu–Hf in zircon. As well, a stratigraphic, sedimentological, palynology and a review of the paleoflora content was made. The combined stratigraphic and geochronological study on the volcano-sedimentary succession indicates that the Cerro Piche Graben was developed during the Early Jurassic and allow us to propose the Cerro Piche Formation. This formation is composed of a lower volcanic succession (named the Loma Blanca Member) that is restricted to the tectonic depression and that was probably emplaced during the Sinemurian (ca. 191 Ma), and an upper sedimentary succession (named the El Tono Member) that was unconformably deposited over the lower sequence during the Pliensbachian (ca. 183 Ma). The sedimentological study of the upper sequence allows to recognition of nine sedimentary cycles related to the evolution of an alluvial fan. The palynofacies interpretations reflect intermittent exposure to weathering and/or intense reworking of organic components as a result of a dynamic sedimentary system with a high terrestrial input, sediment reworking, and/or intermittent subaerial exposure. The paleoflora preserved in this sedimentary succession is composed exclusively of conifers and assigned to Cupessinoxylon sp., and probably corresponds to an arboreal paleocommunity. The U–Pb data on Early Jurassic detrital zircon grains from the El Tono Member indicate a maximum depositional age (MDA) of 185 Ma for this sequence, and the Lu–Hf data support a reworked continental crust for the zircon source. . Additionally, the U–Pb and Lu–Hf data obtained during this work together with data from the North Patagonian Massif supports the recognition of four magmatic cycles, called C0, C1 (including C1i source), C2 and C3. The C1 (172–180 Ma) and the C3 (155–162 Ma) cycles indicate mixing of juvenile mantle-derived and reworked crustal components in the parental magma of zircons and the C0 (182–192 Ma) cycle, which includes the distal volcanism identified in the Cerro Piche Graben, the C1i (172–180 Ma) and C2 (166–169 Ma) cycles seemingly represent three episodes of crustal reworking.

Integrated bio-chemostratigraphy of Lower and Middle Triassic marine successions at Spiti in the Indian Himalaya: Implications for the Early Triassic nutrient crisis

In this paper we study the Lilang Super Group in the Spiti area, Indian Himalaya to understand environmental changes in the aftermath of the end-Permian mass extinction. We focus on the Mikin and Kaga Formations, which span the Induan to Ladinian stages of the Lower and Middle Triassic. These strata formed on the southern mid-palaeolatitude margin of East Gondwana and are interpreted as condensed, mixed carbonate – siliciclastic ramp deposits that deepened distally. Carbon isotope ratios of carbonate (δ13Ccarb) show an increase from −2.6 to 0‰ from the Griesbachian substage to the Dienerian-Smithian transition, followed by a negative shift to −3‰ in the Smithian substage and a large positive excursion from −3.0 to 3.5‰ across the Smithian-Spathian boundary. A short negative shift to −1.0‰ occurred in the early Spathian substage, and is followed by a positive trend from ~−1.0 to 1.0‰ in the Middle Triassic, with several minor excursions occurring during the Aegean substage. Carbon isotope ratios of total organic carbon (δ13Corg) co-vary with δ13Ccarb, suggesting that both proxies represent the original isotopic signatures. Sedimentary and palaeontological evidence, as well as trace metal geochemistry (Mo/Al ratio), indicate anoxic conditions developed from the late Griesbachian to the Dienerian substages, and dysoxic to probably fully oxic conditions from the late Dienerian substage onward. Anoxic conditions only very briefly reoccurred in the late Smithian substage. Ti/Ca and Zr/Al ratios suggest a consistently high terrestrial input in the first three substages of the Early Triassic, followed by a decrease across the Smithian–Spathian boundary. Thus, in the Spiti area, the positive δ13Ccarb excursion across the Smithian–Spathian boundary is recorded in generally well‑oxygenated sediments and coincides with a decrease in terrestrial input. While evidence for enhanced weathering is lacking, observations are strongly at odds with studies postulating eutrophication as a universal kill mechanism for the Smithian–Spathian crisis. The strata in the Spiti area contain an Early Triassic gap in phosphorite deposition indicating a ~ 5 Myr waning of coastal upwelling in an otherwise persistent (>100 Myr) upwelling zone of the East Gondwana margin. The phosphorite gap suggests low P availability, low rates of organic matter degradation, and a reduction in nutrient exchange between deep and surface water masses. Altogether, the phosphorite gap, the paucity of sessile and filtering fauna in oxygenated waters, and low organic carbon burial rates indicate a collapse in marine productivity in the aftermath of the end-Permian mass extinction.

Hydrological management constraints on the chemistry of dissolved organic matter in the Three Gorges Reservoir

Reservoirs are well known as a far-reaching human modification on the functions of natural river networks. However, changes in the chemistry and reactivity of dissolved organic matter (DOM) responding to hydrological management for water retention structures, and its influence on the river carbon cycle, remain poorly understood. Here we show that hydrological management does shape the molecular composition of DOM in the world's largest Three Gorges Reservoir, as revealed by optical spectroscopy and ultrahigh-resolution mass spectrometry. Relatively higher terrestrial input, molecular complexity, isomeric complexity, and environmental stability of DOM were observed during the storage period, whereas the inverse occurred during the drainage period. The results demonstrate that the hydrodynamic processes, which are mainly controlled by water intrusion from mainstream to tributaries, are likely the underlying mechanism controlling DOM chemistry. Integrated with observations from worldwide river reservoirs, the DOM degradation experiments suggest that reservoir hydrological management would enhance DOM mineralization, thereby increase CO2 emission and change the river carbon cycle.

Lacustrine environmental evolution and implications on source rock deposition in the Upper Cretaceous-Paleocene of the South Yellow Sea Basin, offshore eastern China

Lacustrine source rocks are well developed within the Upper Cretaceous-Paleocene in the South Yellow Sea Basin (SYSB) in offshore eastern China. Understanding the deposition of these source rocks could provide critical information for hydrocarbon exploration in the SYSB, as well as reveal the paleoenvironment across the Cretaceous/Paleogene boundary in eastern China. This study investigates the lacustrine environmental evolution during the Upper Cretaceous Taizhou Formation (K2t) to Paleocene Funing Formation (E1f) within the SYSB and its implications on source rock deposition based on core observation combined with organic geochemical indicators. Multiple maturity parameters (vitrinite reflectance, Tmax and biomarker isomerization ratios) reveal that the organic matter (OM) has reached early oil window maturity. The OM of source rocks is dominated by kerogen Type II-III (liptinite and vitrinite). Anoxic, saline-brackish deep to semi-deep lacustrine environments prevailed during the deposition of K2t2 (second member of the K2t), E1f2 (second member of the E1f) and E1f4L (lower unit of fourth member of the E1f). The deposition of three intervals was influenced by marine incursion, as evidenced by geochemical and paleontological results. Low to moderate TOC contents (avg. 0.78 wt% to 1.91 wt%), which corresponds to low to moderate terrestrial OM input, are observed through three intervals. Abundant freshwater, together with high terrestrial OM flowed into the lacustrine environments during the deposition of E1f4U (upper unit of fourth member of the E1f), leading to dysoxic-oxic and freshwater conditions. High terrestrial OM input is probably the major controlling factor for relatively high TOC contents (avg. 2.49%) in the E1f4U. An evolution from balanced-fill to overfilled lake-type is observed in the Upper Cretaceous-Paleocene of SYSB, consistent with an evolution from semi-arid to humid paleoclimate conditions. The E1f4U and E1f2 source rocks exhibit fair to good potential, whereas poor to fair potential is present in the E1f4L and K2t2 source rocks. Compared with the Paleogene source rocks in onshore eastern China, the Upper Cretaceous-Paleocene source rocks in the SYSB probably hold good potential for generating commercial quantity of oil, although further study on hydrocarbon generation kinetics of source rocks and overall basin history are needed.

Origin of hydroxyl GDGTs and regular isoprenoid GDGTs in suspended particulate matter of Yangtze River Estuary

Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (OH-GDGTs) were found having the potential to track past sea surface temperatures (SST), in analogy to the TEX86 – a paleothermometer based on isoprenoid GDGTs (iGDGTs). Especially in estuarine regions with high terrestrial input, the ring index of OH-GDGTs (RI-OH) was more robust to trace the summer SST than TEX86. In order to clarify the potential sources of sedimentary GDGTs and to further elucidate the potential of OH-GDGTs as SST proxy, we investigated the seasonal distribution of core OH-GDGTs and iGDGTs in the suspended particulate matter in a transition section in the Yangtze River Estuary. The concentrations of OH-GDGTs and iGDGTs were higher in the estuary than those in the lower Yangtze River, which suggested the OH-GDGTs and iGDGTs in estuarine sediment mainly came from marine autochthonous organisms, whereas the terrestrial contribution was relatively low. The higher content of OH-GDGTs and iGDGTs in summer than in winter indicated that sedimentary OH-GDGTs and iGDGTs mainly originated from the summer SPM deposition. In addition, the ratio of OH-GDGTs versus iGDGTs suggested that OH-GDGTs were relatively abundant in the upper water layer compared to iGDGTs, regardless of season. Furthermore, the distributions of iGDGTs and OH-GDGTs were found to be influenced by hydrodynamics. The increasing warm bias of iGDGT and OH-GDGT reconstructed temperatures with water depth suggested that either GDGTs in deeper waters derive mainly from surface water or GDGTs cyclization in deeper waters was influenced by reduced ammonium oxidation rates in response to the limited supply of ammonium and oxygen, especially in summer.

Impact of rift dynamics on palaeoenvironmental conditions and hydrocarbon system development (northern Upper Rhine Graben, SW Germany)

The Upper Rhine Graben (URG), a classical hydrocarbon (HC) province, is part of the European Cenozoic Rift System. The rift graben development has led to a complex basin fill of terrestrial and marine Cenozoic deposits, providing several HC source and reservoir units. The aim of this study is the multidisciplinary analysis of the palaeoenvironmental conditions and source-rock development within the transgressive marine intervals, and the palaeothermal history of the graben system to improve the understanding of the HC system development. Palaeoenvironmental conditions are strongly influenced by rift-related tectonic activity. Transgressive marine intervals in times of major subsidence show high terrestrial input from the graben shoulders, leading to mainly terrigenous gas-prone kerogen, while transgressive marine intervals during weak tectonic activity are dominated by marine–brackish palaeoenvironments and oil-prone kerogen. This differs clearly from the previously suggested HC potential of these intervals. Thermal maturation analysis shows nearly constant maturation with depth, which is atypical for burial-controlled maturation. It indicates significant secondary thermal overprinting related to long-lasting very hot hydrothermal fluid systems, concentrated along fault zones. Therefore the development of the depositional setting, kerogen composition, thermal maturation and the HC potential is directly linked to the dynamics of the rift system development. Supplementary material: detailed results of all three wells are available at https://doi.org/10.6084/m9.figshare.c.4183106