Detrital Flux Research Articles

Elemental Geochemical Characteristics of Shales from Wufeng-Longmaxi Formations in the Southern Margin of the Qinling Orogenic Belt, China: Implications for Depositional Controls on Organic Matter.

The tectonic background and sedimentary environment during the transition period from the Ordovician to Silurian have been widely studied by many scholars. This study focuses on the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in the Bajiaokou profile at the southern margin of the Qinling Orogenic Belt in southern China. In order to study the aggregation mechanism of organic matter, geochemical proxies were proposed, including redox proxies (V, V/Al, U, U/Al, Mo, and Mo/Al), paleoproductivity proxies (P, P/Ti, Ba, Ba/Al, and SiXS), paleoclimate proxies (CIA), and terrigenous flux proxies (Al, Zr, and Zr/Al). In addition, Al-Co[EF] × Mn[EF] is used to provide information on paleoenvironmental parameters such as watermass restriction conditions. The redox proxies show that the Wufeng-Longmaxi shale is mainly accumulated under oxic-dysoxic conditions. During the shale deposition period of Wufeng-Longmaxi formations, the marine surface primary productivity in the southern Qinling area is generally low to moderate. The paleoclimate proxies show that from the Late Ordovician to the Early Silurian the southern Qinling area generally had a warm and humid climate. The upwelling current is widely developed in the northern margin of the Sichuan Basin and the southern margin of the Qinling area. Although the upwelling current was highly developed during the deposition of the Wufeng Formation in the Bajiaokou profile, the concentrated accumulation of a large amount of volcanic ash resulted in the low primary productivity of the ocean. During the sedimentary period of the Longmaxi Formation in the Bajiaokou profile, the development of seasonal upwelling currents and a small amount of volcanic ash supply increased the primary productivity to moderate, which provided a good material basis for the enrichment of organic matter, but the high detritus flux and the water body condition of oxic-dysoxic resulted in the slight enrichment of organic matter.

Effect of Paleoenvironmental Conditions on the Distribution of Lower Carboniferous Shale in Yaziluo Rift Trough, South China: Insights from Major/Trace Elements and Shale Composition

Paleoenvironmental conditions significantly influence the distribution patterns and organic matter enrichment of shale. This study investigated the vertical variations of major elements, trace elements, and total organic carbon (TOC) in the Lower Carboniferous marine shale from the Yaziluo Rift Trough, South China, to understand the paleoenvironmental conditions, including redox conditions, terrigenous detrital input, paleoproductivity, and paleo-seawater depth. The Lower Carboniferous formation consists of three sedimentary facies: basin facies, lower slope facies, and upper slope facies. From the basin to the lower slope and then to the upper slope facies, TOC, quartz, and pyrite contents gradually decrease, whereas the carbonate mineral content shows an increasing trend. A continuous decline in paleo-seawater depth transformed a deep-water anoxic environment with high paleoproductivity and low detrital input in the basin facies into a semi-deep-water environment with dysoxic-oxic conditions and moderate detrital influx in the lower slope facies, evolving further into a suboxic environment with high detrital flux in the upper slope facies. The geochemistry results suggest that anoxic conditions and high paleoproductivity were the primary controls on organic matter enrichment in the siliceous shale of the basin facies. In contrast, redox conditions significantly influenced organic matter accumulation in the mixed shale of the lower slope facies, attributed to relatively low paleoproductivity in a more restricted marine setting. Additionally, the adsorption of carbon components by clay minerals facilitated the preservation of organic matter in the calcareous shale of the upper slope facies.

The timing and magnitude of the British–Irish Ice Sheet between Marine Isotope Stages 5d and 2: implications for glacio‐isostatic adjustment, high relative sea levels and ‘giant erratic’ emplacement

ABSTRACTThe extent, chronology and dynamics of the pre‐Marine Isotope Stage (MIS) 2 last British–Irish Ice Sheet (BIIS) are not well known. Although the BRITICE‐CHRONO Project has detailed the maximum extent and retreat phases of the last BIIS for the period after 30 ka and into the Last Glacial Maximum (LGM), the Project identified several pre‐existing datasets and generated new data that implied glaciation pre‐dating the LGM but which post‐dated the Last Interglacial (Eemian; MIS5e); these data are reviewed here. There are no dated till units but are other indicators clearly indicative of glaciation: deep‐sea ice‐rafted detritus flux into the adjacent NE Atlantic, cosmogenic rock‐exposure age dating from glaciated surfaces in Wales and the island of Lundy (Bristol Channel), and optically stimulated luminescence (OSL) ages of proximal glacifluvial sequences on the Isle of Lewis (Outer Hebrides) and in the Cheshire Basin. Taken together these indicate BIIS inception during MIS5d, growth into MIS4 and evidence for dynamic retreat–advance phases during MIS3. OSL evidence for high relative sea level indicated by raised beaches in southern Ireland during MIS4 and 3 at a time of lowered glacio‐eustatic sea level indicates substantial glacial isostatic loading, explained by the early growth of the BIIS during the last cold stage. High relative sea level during MIS4 and 3 coincident with adjacent calving ice sheet margins provides an explanation for the rafted giant erratics found around the shores of southern Britain and Ireland.

Palygorskite in Indian tropical soils: a clay mineral of pedogenic, geogenic, or climate-induced origin – a mechanistic review

Abstract Most clay minerals are characterized by a platy morphology. By contrast, palygorskite has a fibrous morphology and is structurally distinct from the typical 1:1 and 2:1 layer structures. Diverse opinions exist on the origin of palygorskite in soils. Many authors suggest that palygorskite forms after smectite. Others favor its authigenesis during pedogenic processes or its inheritance from the parent material. This review provides a critical synthesis on the origin of palygorskite in the semi-arid-tropical (SAT) Vertisols and arid calcic soils of the Thar Desert of India. It also highlights the specific genetic pathway for the presence of palygorskite in the soils. The ubiquitous association of smectite with palygorskite is inadequate to explain the formation at the expense of smectite, because at pH 8.2 and above the smectite structure is subjected to dissolution to create soluble Si and Al, and the recrystallization of the soluble Si and Al to form palygorskite may not be possible in the Vertisols of the Indian SAT environment. Thus, mildly to moderate alkaline pedochemcial environments of the SAT Vertisols do not favor authigenic precipitation of the palygorskite in such soils. This review shows that the presence of palygorskite in the SAT Vertisols is due to its inheritance from the exhumed inter-trappean beds, infra-trappean beds, and bole beds. This view on the genesis of the palygorskite is also justified by its presence in weakly developed calcic soils of the Thar Desert as detrital flux from the adjoining marine sedimentary rocks.

Petrographic and geochemical characteristics of the Middle Devonian Eifelian Nabiao Formation in the Youjiang Basin, South China: Implications for paleoenvironment and organic matter accumulation mechanism

The Nabiao Formation of the Middle Devonian Eifelian period has been identified as a promising site for shale gas exploration in the Youjiang Basin, South China. And yet, little is known about the accumulation mechanism of organic matter under transgression in the archipelago paleogeography. In this study, the core samples were analyzed by thin section microscopy, field emission-scanning electron microscopy, pyrite morphology, X-ray diffraction, and geochemical analysis (total organic carbon (TOC) content, sulfur content, organic petrography, inorganic carbon isotope and major and trace elements) to understand changes in and controls on the mineralogy, lithofacies, depositional environments, as well as the organic matter accumulation mechanism of the Nabiao Formation. The study indicates that organic-rich sediments were deposited during the two transgressions of the Chotec Event and the Kacak Event. The deposition of carbonaceous mudstone occurred in water columns with weak upwelling, while siliceous mudstone and siliceous shale were developed in a strong upwelling water column. The correlations between multiple geochemical proxies (paleoredox, paleoproductivity, and terrestrial detrital influx) and TOC content indicate that the Chotec Event is more conducive to organic matter enrichment of the Nabiao Formation than the Kacak Event. In stage 1, TOC content is low due to oxic water columns and low productivity. In stage 2, the Chotec Event causes the relative sea-level of Member 2 to rise rapidly and the basin bottom water to quickly change to dysoxic conditions. This is the key to organic matter enrichment. In stage 3, the oceanic upwelling is crucial in organic matter enrichment by increasing paleoproductivity. Under the protection of dysoxic condition, organic matter is accumulated in stage 4. Organic matter of the Nabiao Formation is not significantly affected by the terrigenous detrital flux. By taking into account the changes in paleoproductivity, redox conditions, upwelling events, and terrigenous detrital flux, an evolution model is proposed in this paper to elucidate the paleoenvironmental change and the organic matter enrichment under transgression in the archipelago paleogeography.

Paleoenvironmental constraints on shallow-marine carbonate production in central and West Texas during the Albian (Early Cretaceous)

The Albian Glen Rose Formation in central and west Texas records carbonate sedimentation in a broad epicontinental sea partly contemporaneous with Oceanic Anoxic Event 1b. The paleogeographic setting of the Comanche Platform facilitated the deposition of carbonate sediments that resulted in carbonate matrix-rich facies, with various amounts of allochems, which permitted the interpretation of shallow lagoon depositional settings. Geochemical proxies for environmental conditions (nutrient supply, detrital input, redox conditions) were calculated from the elemental geochemical analysis of samples, while their carbon and oxygen isotope composition was used to evaluate the impact of diagenesis. The statistical analysis of this dataset helps identify three intervals within the Glen Rose Formation where the matrix-rich carbonate sedimentation was modulated by environmental parameters. First, the strong correlation between MgO concentration and δ18O vectors on a Principal Component Analysis for the whole dataset confirms the deposition of dolomitic series with stromatolites in a restricted environment. Second, moderately high nutrient input and low detrital flux suggest that part of the sedimentation in west Texas was affected by upwelling. Third, mesotrophic conditions associated with a patch reef made of rudist bivalves support their suspension feeder ecological behavior. Conclusions drawn for this research may apply to other shallow-marine series deposited in broad epicontinental seas affected by greenhouse conditions.

Controls on the stratigraphic distribution of organic carbon in ancient deep-marine levees

Modern deep-marine levees have been shown to be an important reservoir of the world's total buried organic carbon; however, few studies have attempted to assess this in ancient systems. Deep-marine levees are extensive features that experience high rates of sedimentation, making them ideal sites for significant carbon burial, and therefore examining the distribution of organic material in ancient levee deposits could provide insight into paleoenvironmental conditions and the evolution of ancient ocean and climate systems. In this study, a 350-m-thick succession of mudstone-dominated levee deposits of the Windermere Supergroup in British Columbia, Canada, was stratigraphically logged in centimeter-scale detail and samples taken with 4–10 m spacing. X-ray fluorescence (XRF) and total organic carbon (TOC), were conducted to evaluate the elemental composition and distribution of organic carbon to evaluate trends in paleoenvironmental conditions such as primary productivity, ocean redox, weathering intensity, and detrital flux. TOC ranges from <0.2% to 15.55% (corrected for the effects of metamorphism). Organic-rich strata, taken to be ≥ 1% TOC, are principally confined to a single 60 m-thick stratigraphic interval, and typically occur as anomalously thick, mud-rich sandstone turbidites, with organic matter occurring mostly as micro-scale carbon sorbed onto the surface of clay grains. In this same interval, trends in XRF data indicate an increase in primary productivity, weathering intensity, and detrital influx, and a decrease in ocean oxygenation levels. These data suggest that intense continental weathering, high terrigenous input, elevated sea level, and relatively low oxygenation conditions all act to enhance organic matter production, accumulation, and preservation. However, although all these components contributed to increased organic production, accumulation, and preservation on their own, the results of this study suggest that it is the temporal coincidence of all of them in a “perfect storm” that is required for significant organic carbon enrichment.

Decoupling of physical and chemical erosion in the Himalayas revealed by radiogenic Ca isotopes

Determining the rate of CO2 consumption associated with the Himalayan uplift is an essential prerequisite to understanding climate evolution throughout the Cenozoic. The riverine fluxes of dissolved calcium can be used to quantify uptakes of atmospheric CO2 by chemical weathering, but this approach requires deciphering the silicate-derived Ca flux from the generally dominant carbonate-derived Ca flux. Here we present high-precision radiogenic calcium (40Ca) analyses of bank sediments and dissolved loads from a network of rivers in central Nepal Himalaya and Bangladesh, to constrain the sources and relative contributions of carbonate and silicate-derived calcium to the dissolved loads of Himalayan rivers. Calcium isotope analyses were performed in multidynamic mode by thermal ionization mass spectrometry, yielding an external precision of ±0.4 ε-units (2 S.D.). Our results show that silicate catchments exposed in the Himalayan range have variably radiogenic ε40Ca compositions relative to seawater, ranging from +0.7 in the TSS to +14 in the LH. In contrast, sedimentary carbonates, including metamorphosed dolomites with variably radiogenic 87Sr/86Sr, exhibit uniform ε40Ca identical to modern seawater. The homogeneous ε40Ca composition of sedimentary carbonates confirms the relative resistance of radiogenic Ca signatures to post-depositional alteration and provides a robust baseline against which the contribution of silicate weathering to the riverine Ca flux can be evaluated. Dissolved load compositions of rivers draining LH catchments exhibit ε40Ca values ranging from 0 to +11, reflecting the relative contribution of unradiogenic carbonates and highly radiogenic metapelitic units of the LH sequence. HHC rivers show a more moderate range, from 0.5 to +2, reflecting the less radiogenic composition of HHC paragneisses. Himalayan front rivers draining all three lithotectonic units of the Himalayan range exhibit moderately radiogenic ε40Ca, ranging from +0.5 to +1.4 and overall similar to the average composition of the Ganga mainstream in Bangladesh. Using an approach combining conventional alkalinity budgets with isotopic mass balance calculations, we show that the dissolved silicate Ca flux of major Himalayan front rivers is primarily derived from the weathering of metapelitic rocks of the lesser Himalaya. In contrast, regions of the high range that generate the bulk of the detrital flux to the Gangetic floodplain represent a subordinate source of silicate-derived Ca. This result demonstrates that the chemical weathering of Ca-silicates in the Himalayan system is decoupled from physical erosion. The extensive erosional activity observed in the high range may thus play a limited role in promoting CO2 consumption and global cooling by silicate weathering.

Factors Controlling Brittleness of the Wufeng–Longmaxi Shale in the Yangtze Platform, South China: Insights from Geochemistry and Shale Composition

Brittleness index is an important parameter used to select favorable fracturing intervals during shale gas exploitation. Mineral compositions exert a significant influence on rock brittleness, and various grain assemblages can be deposited under different paleo-environmental conditions. The Wufeng–Longmaxi marine shale is a hot spot of shale gas exploitation in China. However, for the Wufeng–Longmaxi shale, the relationship between sedimentary environments, grain assemblages, and shale brittleness are rarely discussed. To address these problems, a series of experiments including petrographic observations, mineral compositions, rock mechanics, and major (trace) element analyses were carried out on shale samples from the Wufeng–Longmaxi formations. The Wufeng–Longmaxi formations are divided into upper Longmaxi formation (ULMX), lower Longmaxi formation (LLMX), and Wufeng formation (WF). The results show that WF shale samples deposited under a sedimentary environment with low terrigenous detrital influx, suboxic depositional water, and high paleoproductivity are characterized by the highest energy-based BI, compared to ULMX and LLMX shale samples. Dolomite in the samples grew in situ during early diagenesis. Redox conditions, terrigenous detrital flux control authigenic carbonate contents, and the oxic depositional water of the ULMX formation restrain carbonate mineral formation. In contrast, the suboxic sedimentary environment of the LLMX and WF allowed the generation of carbonate minerals. Compared with the WF, the larger terrigenous detrital flux of LLMX formation do favor more authigenic carbonate formation. The paleoproductivity affects biogenic quartz generation, and abundant biogenic quartz, primarily occurring in the form of micron-size microcrystalline quartz in the shale matrix, and can connect the silt-size brittle minerals to form a mechanical framework, which makes a strong positive contribution to shale brittleness. Terrigenous detrital influx decreases brittleness because the weakening effect of terrigenous clay minerals on shale brittleness is greater than the strengthening effect of terrigenous brittle minerals on shale brittleness.

Sponges sneeze mucus to shed particulate waste from their seawater inlet pores

SummarySponges, among the oldest extant multicellular organisms on Earth,1 play a key role in the cycling of nutrients in many aquatic ecosystems.2, 3, 4, 5 They need to employ strategies to prevent clogging of their internal filter system by solid wastes,6, 7, 8 but self-cleaning mechanisms are largely unknown. It is commonly assumed that sponges remove solid waste with the outflowing water through distinct outflow openings (oscula).3,9 Here, we present time-lapse video footage and analyses of sponge waste revealing a completely different mechanism of particle removal in the Caribbean tube sponge Aplysina archeri. This sponge actively moves particle-trapping mucus against the direction of its internal water flow and ejects it into the surrounding water from its seawater inlet pores (ostia) through periodic surface contractions that have been described earlier as “sneezing.”10,11 Visually, it appears as if the sponge is continuously streaming mucus-embedded particles and sneezes to shed this particulate waste, resulting in a notable flux of detritus that is actively consumed by sponge-associated fauna. The new data are used to estimate production of detritus for this abundant sponge on Caribbean coral reefs. Last, we discuss why waste removal from the sponge inhalant pores may be a common feature among sponges and compare the process in sponges to equivalent mechanisms of mucus transport in other animals, including humans.

87Sr/86Sr Isotopic Ratio of Ferromanganese Crusts as a Record of Detrital Influx to the Western North Pacific Ocean

In this study, the Sr isotope ratios (IRs; 87Sr/86Sr) of ferromanganese (Fe–Mn) crusts are analyzed through laser ablation inductively coupled plasma multiple-collector mass spectrometry. A sample collected from off Minamitorishima Island showed uniform Sr IRs (0.70906–0.70927) similar to that of present-day seawater with more than 36 mm thickness. Meanwhile, a detritus-rich sample collected from off northeast (NE) Japan showed a wide variation in Sr IRs (0.707761–0.709963). The Sr IR variation in the Fe–Mn crust from off NE Japan suggests detrital influx contributions from both the NE Japan arc (&lt;0.708) and aeolian dust from China (&gt;0.718). Detrital flux from the NE Japan arc increases from the bottom to middle layers, possibly due to the uplift of the Ou backbone range that occurred after ~2 Ma. The increased influx of the aeolian dust in the outer layer is attributable to global cooling in the Quaternary that increased the loess dust transportation from China to the western North Pacific Ocean. Meanwhile, the influence of the detrital influx on the sample from off Minamitorishima Island appeared to be negligible. The Sr IR analysis with high spatial resolution proposed in this study possibly improves the burial history of Fe–Mn nodules.

Charcoal Whirlwinds and Post-Fire Observations in Serengeti National Park Savannahs

Whirlwinds and visible dust devils occur over semi-arid ecosystems and entrain particles from the ground surface. Fires produce abundant charcoal across savannahs and the resulting blackened surfaces create a large albedo contrast. Whirlwinds have been observed associated with active fires; yet, there are few published observations on post-fire landscapes. Spatiotemporal patterns of whirlwinds have been documented for a limited number of regions and have not been made for the ecosystems of eastern Africa. From field-based sightings in the Serengeti National Park, Tanzania, we report on whirlwinds over burned savannah patches that entrained large quantities of charcoal to produce black coloured charcoal devils that lofted charcoal into the atmosphere. Two occurrences of charcoal devils were sighted and photographed, one each in the Western Corridor (Bunda District) and Lamai (Serengeti District), Mara Region. The observations were compared with regional scale meteorological data and remote sensing satellite imagery and albedo estimates of the land cover conditions. Although direct meteorological or particulate matter measurements were not made, the observations show that both charcoal devils differed in colour, funnel shape, height, and savannah land cover types (different woody to grass fuel canopies), and thus different charcoal morphologies. Charcoal laden whirlwinds require further study and characterization to analyse the contribution to local-scale redistribution of matter and regional-to-global fluxes of terrestrially derived atmospheric particulates. Future research focusing on the spatiotemporal patterns of whirlwinds over burned patches of savannah, the formation, duration and dissipation mechanisms, and characterisation of the entrained material would contribute to our understanding of the phenomena. The redistribution of organic and clastic material would contribute to understanding of detrital fluxes to depositional environments, such as lakes, wetlands, and snow.&#x0D; Keywords: Atmospheric boundary layer; Convection; Detritus; Dust devils; Fires; Particulate matter.

Quantification of Asian Dust Source Variabilities in Silt and Clay Fractions since 10 Ma by Parallel Factor (PARAFAC) Endmember Modeling at IODP Site U1425 in the Japan Sea

Abstract Japan sea sediments consist of various detrital materials of eolian and riverine origin. Understanding the provenance of eolian dust is vital for reconstructing the variability of wind patterns and monsoons in the past. New and complete eolian accumulation rates from Taklimakan, Gobi, and Ordos are reconstructed at Integrated Ocean Drilling Program (IODP) Site U1425 in the Japan Sea using parallel factor (PARAFAC) endmember modeling. Our results show that Taklimakan dust is dominated by the silt fraction, while Gobi dust is dominated by the clay fraction, and they are controlled by the relative contributions of different pathways of dust transport, such as the westerly winds and East Asian winter monsoon (EAWM). Clay-size dust from Gobi increased during three periods, late Miocene global cooling (LMGC), intensification of Northern Hemisphere Glaciation (iNHG), and mid-Pleistocene Transition (MPT), which reflected increased EAWM winds associated with global cooling and glaciation. Taklimakan became the major dust contributor to the Japan Sea sediments during the warmer climate periods in the latest Miocene to early Pliocene and the Late Pleistocene, where westerly wind activity dominated eolian transport. Dust from Ordos increased greatly 0.95-0.85 Ma due to enhanced Asian aridification since 2 Ma in Northwest China. Detrital flux from Japanese islands suggests that the East Asian summer monsoon (EASM) was stronger 9.6-8 Ma and weakened from 8 Ma to the Pleistocene.

A Novel Tracer Technique to Quantify the Lithogenic Input Flux of Trace Elements to Qinghai Lake

Thorium (Th) isotopes were applied to quantify the contributions of lithogenic inputs to the Qinghai Lake (QHH). Concentrations of dissolved 232Th and 230Th were measured in 59 water samples collected from Qinghai Lake and its exogenous recharge rivers. There are significant differences in the concentration of 232Th of the sampled water in QHH that confirm the input of variable lithogenic material sources. The 230Th concentrations were used to calculate a scavenging residence time for Th, which was then applied to calculate the flux of dissolved 232Th by matching the measured concentrations of dissolved 232Th. Then the 232Th content of lithogenic material was used with the solubility of Th from the preliminary particle data from the Qinghai–Qaidam district. When using a Th solubility from particles of 1%, the fluxes of lithogenic material range from 0.03 to 25.25 g/m2/yr in the surface water, consistent with the flux results of settled particles from the previous study. When a large number of exogenous recharge rivers are mixed into the northwest basin of Qinghai Lake, the 232Th content and lithogenic flux of the lake water are mainly influenced by the type and content of the particles in the Buha and Shaliu rivers. Conversely, in south basin with limited recharging rivers, the 232Th content of the lake water away from the estuary is mainly influenced by atmospheric dust. Furthermore, based on the 230Th normalization method (combining with 232Th and τTh), the Buha and Shaliu rivers located in the northwest basin contribute about 90% of the detrital flux to the lake. The lithogenic flux in the southeast lake is dominated by dust flux with a value of ∼0.109 g/m2/yr, while the higher lithogenic flux at the bottom of the lake was likely generated by accumulated sinking particulate matter and resuspension of bottom sediments in September. This study confirms the utility of long-lived Th isotopes to quantify lithogenic inputs based on the Th content of the dissolved lake water and also supply deposition resolution information for QHH sediment records with some certainty.

First record of the early Toarcian Oceanic Anoxic Event in the Hebrides Basin (UK) and implications for redox and weathering changes

The early Toarcian (~183 Ma) was characterized by a prominent volcanism-induced warming event associated with a massive addition of 12 C-enriched carbon to the ocean-atmosphere system. This warming likely contributed to marked ocean deoxygenation during this time, giving the event its name: the early Toarcian Oceanic Anoxic Event (T-OAE). Although the T-OAE has been recognized globally, clear geographic differences in the character of the event and its environmental effects have been noted. Here we present new carbon isotope, element abundance and organic geochemical data from a lower Toarcian succession on the Isle of Raasay, Scotland (Hebrides Basin, Northwest European Shelf). These data provide the first evidence of the T-OAE in Scotland. The succession is generally enriched in organic matter through the T-OAE interval, though redox-sensitive trace element data indicate that oxic-suboxic bottom water conditions prevailed, potentially interspersed with ephemeral anoxic episodes. Our elemental data contrast with evidence for persistent anoxia/euxinia in nearby basins, and emphasize how deoxygenation was spatially variable and dependent on water depth and basin hydrography. Similarly, the data emphasize how anoxia was not a prerequisite for the deposition of organic-rich lithologies during the T-OAE. Sedimentological evidence, coupled with inorganic geochemical data, indicates increased coarse-grained detrital flux and enhanced chemical weathering during the T-OAE. Our findings support emerging evidence for a marked strengthening of hydrological cycling and increased storminess at tropical and subtropical latitudes globally in response to global warming during the T-OAE. • Toarcian Oceanic Anoxic Event described from Hebrides Basin (sub-Boreal realm) for the first time. • Negative organic carbon isotope excursion (~-2.7‰) during the early Toarcian • Oxic to suboxic conditions through the T-OAE, in contrast to strong anoxia in nearby basins • Significant strengthening of continental weathering through T-OAE at sub-tropical latitudes

Hydroclimate change in the Garhwal Himalaya, India at 4200\xa0yr BP coincident with the contraction of the Indus civilization

High-resolution analysis of a 3.80 m sediment core recovered from Deoria Tal, a mid-elevation lake located at 2393 m a.s.l. in the Garhwal Himalaya, documents long-term and abrupt hydroclimate fluctuations in northern India during the mid- to late Holocene. The sediment chronology, based on ten 14C dates, indicates the core spans 5200 years. Non-destructive, radiological imaging approaches (X-ray fluorescence (XRF), X-ray imaging, and CT scans) were used to assess the response of the lake system to changing hydroclimatic conditions. Variations in elemental concentrations and sediment density evidenced notable hydroclimate change episodes centered at 4850, 4200, and 3100 cal yr BP. Elevated detrital input, greater sediment density, decreased lake ventilation, and lower autochthonous productivity reflects lake deepening between 4350 and 4200 cal yr BP. An abrupt shift in elemental concentrations and sediment density indicated the onset of lake drawdown at 4200 cal yr BP and a negative hydroclimate anomaly between 4200 and 4050 cal yr BP. Lower detrital flux, decreased sediment density, increased oxygenation, and higher autochthonous productivity, reflects a reduction in lake volume between 3200 and 3100 cal yr BP. The potential link between abrupt climate change at 4200 cal yr BP and the contraction of the Indus civilization is explored.

Simulated Global Coastal Ecosystem Responses to a Half‐Century Increase in River Nitrogen Loads

AbstractCoastal ecosystems are increasingly threatened by anthropogenic stressors such as harmful algal blooms and hypoxia through the combined effects of eutrophication and warming. As a major terrestrial nitrogen source to the ocean, rivers play a key role in shaping coastal nitrogen budgets and biogeochemical cycling. Combining an enhanced‐resolution, global ocean biogeochemical model with temporally changing river inputs, we estimate that elevated river nitrogen loads alone resulted in a 5.8% increase (16.6 Tg) in the global coastal nitrogen inventory from 1961 to 2010, accompanied by increases in coastal net primary productivity (+4.6%) and benthic detrital flux (+7.3%). The ecosystems most sensitive to added nitrogen were those with long residence times and strong nitrogen limitation. While even enhanced‐resolution global models remain limited in their capacity to resolve shelf‐scale responses, these basic factors provide two relevant axes for frameworks assessing the comparative coastal ecosystem susceptibility to enhanced nitrogen loads, and the effectiveness of mitigation strategies.

Rock magnetic evidence of tectonic control on the sedimentation and diagenesis in the Andaman Sea over ~1 million years

We evaluate the sedimentary (magnetic, mineralogical, geochemical, grain size) records of a long sediment core (NGHP-01-17 A) to elucidate the tectonic control on the sedimentation and diagenesis in the Andaman Sea (AS) over the past ~ 1 Ma. Two distinct sedimentary magnetic zones (Z-I and Z-II) are identified based on the rock magnetic signatures. A significant shift in the depositional environment is observed around ~90 ka which is marked by a rapid change in magnetite susceptibility (χlf), Fe, Ti and organic carbon content in Z-I. A trend of upward increase in χlf from ~90 ka to 3 ka in core NGHP-01-17 A suggest increase in detrital flux to the AS and represents the onset of a new sedimentary regime following most recent event of tectonic uplift in Indo-Burman Ranges (IBR) which occurred at ~ 150 ka. Methane influenced progressive diagenetic dissolution of detrital iron oxides and subsequent precipitation of iron sulfides in Z-II is clearly evident in the rock magnetic and mineralogical data. Multiple bands of diagenetically formed iron sulfide nodules at different periods in Z-II indicate episodic intensification of anaerobic oxidation of methane (AOM) due to enhanced methane-flux. We propose that fluid migration forced by tectonic processes facilitated episodic release of methane from deep reservoir that led to the formation of iron-sulfide nodules in the AS.

Multiple Controls on the Accumulation of Organic-Rich Sediments in the Besa River Formation of Liard Basin, British Columbia, Canada

The Late Devonian Besa River Formation is an organic-rich shale sequence in Liard Basin, northeastern British Columbia, Canada, with significant natural gas reserves. High-resolution elemental geochemistry of three long continuous cored intervals of the Besa River Formation was used to better understand the paleodepositional environment of organic-rich intervals in this thick marine shale. The studied core intervals were divided into five chemostratigraphic units based on organic and inorganic geochemical proxies. The highest total organic carbon (TOC) content (up to 13 wt.%) was identified in the upper part of the Patry member (Unit III) within the Liard Basin. During the deposition of Unit III, low clastic influx and euxinic bottom conditions mostly contributed to the high accumulation of organic carbon. Moreover, a high productivity and organic influx may have increased organic-rich basinal sediments, which further depleted the seawater column oxygen content in the presence of a large amount of organic matter. This took place within the oxygen-deficient bottom water from the Patry–Exshaw stratigraphic units. This high TOC interval was most likely deposited through abundant biogenic silica production by radiolarians, thereby utilizing the supply of nutrients from the upwelling. Sea level change was also an important factor that controlled organic matter accumulation in the Besa River Formation. The transgression in sea level changed the residence time of the organic matter in oxic zones within the water column, which limited its supply in deeper water; this decreased the TOC content in Unit IV. Before the deposition, silica production collapsed and was replaced by terrestrial sedimentation of clay minerals in the upper part of the Exshaw member, which caused organic matter dilutions in Unit V (under 5 wt.%). These results provide new insights into the effects of relative sea level changes on redox conditions, productivity, and detrital flux, which are related to organic matter enrichment patterns and their geographic variations. Unit III is characterized by an organic-rich interval as well as an abundance of biogenic silica that is closely related to fracturing. Thus, Unit III is expected to have the highest shale gas potential in the Devonian Besa River Formation. The high-resolution geochemical data integrated with well log and/or seismic data can be used to determine the distribution of the perspective interval for shale gas production in the Liard Basin.

Major, trace-elemental and sedimentological characterization of the upper Ordovician Wufeng-lower Silurian Longmaxi formations, Sichuan Basin, south China: Insights into the effect of relative sea-level fluctuations on organic matter accumulation in shales

The relative sea-level fluctuations play a vital role in the organic matter enrichment of black shales across the world. The Wufeng-Lower Longmaxi shales deposited during the Late Ordovician to Early Silurian stage are accompanied by the global transgression and regression, whereas the role of relative sea-level changes on organic matter accumulation has been rarely discussed. In this study, we integrated TOC content, X-ray diffraction (XRD) mineralogical composition, thin section and scanning electron microscope (SEM) images, elemental geochemical data, and petrographic features of pyrite framboids to investigate the varying paleoenvironmental conditions and the effect of relative sea-level changes on organic matter accumulation under a robust sequence stratigraphic framework.Based on detailed petrographic observations and mineralogical analysis, six major lithofacies are identified in the Wufeng-Lower Longmaxi formations, including siliceous mudstone, clay-rich siliceous mudstone, siliceous-argillaceous mixed shale, silty mudstone, siltstone, and bentonite. TOC content is generally higher in the transgressive systems tracts (relative sea-level rise stage) than in the highstand systems tracts and falling stage systems tract (relative sea-level fall stage). Multiple geochemical proxies indicate contrasting paleoenvironmental changes between relative sea-level rise and fall stage. Relative sea-level rise resulted in elevated productivity, predominantly anoxic conditions, low detrital flux, and moderate water mass restriction, as indicated by high biogenic Si content, high Mo-EF (enrichment factor of element Mo), small-sized pyrite framboids, low Al content and moderate Mo/TOC ratio. On the contrary, relative sea-level fall generally resulted in decreased productivity, dysoxic conditions, increased detrital flux, and strongly restricted conditions. The correlations between TOC content and geochemical proxies suggest that organic matter accumulation was a combined effect of paleoproductivity, paleoredox conditions, detrital influx, and water mass restriction. The variation of these factors was strongly influenced by relative sea-level fluctuations related to Hirnantian glaciation and regional tectonic movements during the Late Ordovician-Early Silurian transitional stage.