Chemostratigraphic Profiles Research Articles

Linking anoxia, biotic events, and basin evolution in the Late Devonian Illinois Basin, North America: A geochemical approach

Epeiric seas and their sedimentary deposits are vital for understanding the history of Earth's oceans, but the lack of modern analogues and the frequent dominance of uniform mudrocks in these environments hinder our ability to identify key markers and interpret sea-level changes and past climatic/biotic events in epeiric sea successions. This study focuses on the Late Devonian Illinois Basin, where fine-grained mudrocks, occasionally organic-rich, were deposited in one of many variably interconnected epeiric seas that flooded much of the North American craton. Through the correlation of gamma logs from 50 wells across the basin and the generation of high-resolution chemostratigraphic profiles for four cores, a basin evolution model for the Upper Devonian New Albany Shale (NAS) in the southeastern depocenter of the Illinois Basin (USA) is established. Results indicate that NAS deposition occurred in three phases, characterized as one aggradational-progradational, one progradational, and one retrogradational package. The basin experienced an initial flooding event at the base of the NAS, followed by a second transgression immediately after the Frasnian-Famennian boundary (FFB). The mid- to upper Famennian interval witnessed progressive sea-level rise (a third transgression) and full basin inundation, extending nearly to the top of the NAS. Based on redox proxy data, four discrete anoxic pulses were identified during NAS deposition. By incorporating published biostratigraphic and geochemical datasets, we then correlate these signals observed in the Illinois Basin across the Appalachian, Michigan, Permian, and Anadarko basins of the broader North American Seaway. Additionally, some of the anoxic pulses are linked to key biotic crises of the Late Devonian, such as the Rhinestreet, Upper Kellwasser, and Enkeberg events, which caused substantial turnover in the marine biosphere. This study contributes an integrated basin evolution framework for the Late Devonian North American Seaway and serves as an exemplar of utilizing geochemical signals to correlate sea-level changes, anoxic pulses, and key biotic events in ancient mud-dominated epeiric seas.

Chemostratigraphic contributions to paleoenvironmental assessment of microbialites from neoproterozoic Capiru Formation, Southern Ribeira Belt – Brazil

The Capiru Formation records supracrustal metassedimentary rocks within the Southern Ribeira Belt. These rocks underwent heterogeneous deformation and metamorphism, resulting in an incomplete greenschist facies paragenesis. They are tectonically interbedded with strata that exhibit well-preserved primary structures. In the Morro Grande synform region, there is a continuous 150 m outcrop of metadolomites with preserved sedimentary records and was described in a stratigraphic profile (1:500) subsequently detailed (1:50). Dolomite, minor amounts of quartz, traces of ilite, graphite and zircon constitute the mineral assembly, defined by XRD, petrography and SEM-EDS. Distinct preserved facies are recognized by morphostructures: (1) lamina (parallel, discontinuous, crenulated); (2) stromatolites (homogeneous columnar, club-shaped, conical conophyton-like, pseudocolumnar, parallel-branching, divergent-branching, delicate-branching); (3) thrombolite (rugous) and (4) flat pebble conglomerate. Single-isotope data revials different microbial patterns, particularly in stromatolites (−1.57 to −0.40‰ δ13C; −8.21 to - 3.94‰ δ18O) and lamina (−1.89 to 1.29‰ δ13C; −7.32 to −3.55‰ δ18O). Facies associations suggest a shallow sea with a regressive trend. Tectonofacies are characterized by massive, venulated or brecciated carbonates. Chemostratigraphic profile is divided into two major intervals. At the bottom, the first does not exhibit a specific isotopic trend and can be subdivided in heterogeneous post-deformation venulas (Unit I, −1.75 to 0.40 δ13C; −2.34 to −8.16 δ18O), thrombolythic signals (Unit II, −1.43 to 0.40‰ δ13C; −6.35 to −4.11‰ δ18O), and facies variation, mainly supratidal (Unit III, 1.89 to 1.29‰ δ13C, −7.32 to −3.31‰ δ18O). Upwads in the profile, the second interval consists of microbial facies, displaying a more uniform signature with depleted values of δ13C and δ18O along with a slight enrichment marking the transition from intratidal to supratidal environments (Unit IV; −1.32 to −0.81‰ δ13C; - 8.17 to −6.25‰ δ18O) and supratidal lagoons (Unit V; −1.35 to −0.41‰ δ13C; −8.20 to −5.49‰ δ18O). Preserved EPS, graphite, and ilite confirm low-grade metamorphism, with clumped isotope thermometry temperatures ranging from 206.07 to 307.58 °C. Calcite is secondary, filling porosity and present in recrystallized facies. Isotopic signature of recrystallized facies differs from microbial ones, with the most depleted values (−2.16‰ δ13C; −14.02‰ δ18O) and lower formation temperature (122.29 ± 7.07 °C), indicating a late restricted event. This dolomitic succestion within Capiru Formation provides evidence of a shallow marine paleoenvironment with diverse microbial activity during its deposition.

Berriasian–Valanginian Geochronology and Carbon-Isotope Stratigraphy of the Yellow Cat Member, Cedar Mountain Formation, Eastern Utah, USA

The Early Cretaceous Yellow Cat Member of the terrestrial Cedar Mountain Formation in Utah, USA. has been interpreted as a “time-rich” unit because of its dinosaur fossils, prominent paleosols, and the results of preliminary chemostratigraphic and geochronologic studies. Herein, we refine prior interpretations with: (1) a new composite C-isotope chemostratigraphic profile from the well-known Utahraptor Ridge dinosaur site, which exhibits δ13C features tentatively interpreted as the Valanginian double-peak carbon isotope excursion (the so-called “Weissert Event”) and some unnamed Berriasian features; and (2) a new cryptotephra zircon eruption age of 135.10 ± 0.30/0.31/0.34 Ma (2σ) derived from the CA-ID-TIMS U-Pb analyses of zircons from a paleosol cryptotephra. Our interpretations of δ13C features on our chemostratigraphic profile, in the context of our new radiometric age, are compatible with at least one prior age model for the “Weissert Event” and the most recent revision of the Cretaceous time scale. Our results also support the interpretation that the Yellow Cat Member records a significant part of Early Cretaceous time.

Sea level changes and sequence stratigraphy of the Lower-Middle Jurassic Quse and Sewa formations in the Qiangtang Basin, central Tibet: Geochemical and palynological perspectives

ABSTRACT Sequence stratigraphy is a commonly used approach to understand basin-fill history and the occurrence of conventional reservoir and/or probable source rocks. Reconstructing a sequence stratigraphic framework in carbonates, marls, and organic-rich mudstones is challenging due to environmental, petrophysical, and sedimentological variations that can be subtle, whereas seismic data may be lacking or of limited use. For this reason, incorporation between palynological analysis and chemostratigraphic profiles is becoming increasingly common to facilitate sequence stratigraphic reconstruction. This study investigates the Quse (lower Toarcian) and Sewa formations (upper Bajocian-Bathonian) in the Bilong Co section from the Qiangtang Basin of central Tibet. Eighty-three rock samples were analysed for their whole-rock inorganic geochemical composition, of which 25 rock samples were tested for palynological and palynofacies analyses. The palynological composition defined two associations for the study section. The lower part of the Bilong Co section consisted is dominated by a moderate to high abundance of opaque phytoclasts versus low to moderate amorphous organic matter (AOM) content with a high concentration of sphaeromorphs pollen grains, revealing deposition of this interval at times of low relative sea level in fluvio-deltaic settings. The middle to upper parts of the section comprised of significantly high AOM content versus low phytoclasts and high content of sphaeromorphs pollen grains, but with increasing the relative abundance of dinoflagellate cysts, indicating a phase of high sea level. Chemostratigraphic variations relevant to changes in relative sea level delineated the subdivision of the Quse and Sewa formations into two and three third-order transgressive-regressive sequences, respectively. The collision between the Lhasa and Qiangtang blocks during the Early-Middle Jurassic is suggested to control consequent subduction and sea level highstand, especially during deposition of the Sewa Formation. Geochemical proxies that relate to shelf carbonate production are calcium, strontium, whereas proxies that relate to siliciclastics include titanium, zirconium, manganese, aluminium, and silicon, other redox-sensitive proxy like uranium is also implemented. This indicates that chemostratigraphic proxies are a promising tool for the interpretation of sea level cyclicity in terms of systems tracts and bounding surfaces.

Chemo stratigraphic Profile of a Reservoir in Well “X” of Field “Y” Offshore Southern Gabon

In a bid to evaluate the elemental and mineralogical content of reservoir samples from the “X” well in the “Y” oil field offshore Southern Gabon, analyses were performed using XRD and XRF. The log view profile of the result inferred that Na, Mg, and Calcite were absent in the shallower series of the reservoir sandstones studied, this observation implies that they are soluble ions that had eroded and refer to warm and humid paleoclimate and a depositional environment that is arid, which corresponds to the continental crust as their source. The plot of Ti and FeO+Mg discriminate the deeper series of the reservoir sandstone samples from the shallower samples. The lower series showed heavier values which implies their origin from Oceanic Crust. These are also the pre-salt facies while the shallower series were more of continental origin and represent the post-salt facies.

Ediacaran carbon cycling and Shuram excursion recorded in the Tarim Block, northwestern China

The largest perturbation of the carbon cycle in geological history, named as the ‘Shuram Carbon Isotope Excursion (SCIE)’, has been widely reported in the Ediacaran Period in different continents over the world. In the Tarim Block, a complete Ediacaran carbonate succession was deposited; however, whether it recorded the SCIE or not still remains controversial, hindering establishment of a reliable stratigraphic framework and understanding of environmental perturbations and evolution during the Ediacaran Period. Here, we present two high-resolution carbon isotopic stratigraphy profiles from the upper Sugetbrak through the Qigebrak formations in the northwestern Tarim Block. Two negative excursions (TN1, TN2), and two positive excursions (TP1, TP2) are identified from both sections and supposed to be of the primary origin. Of these, the TN1 was recorded in a storm-dominated inner-to-middle ramp beginning with the marine transgression. It marks the largest negative excursion with a nadir down to ca. −12‰ which can be correlated to the SCIE of late Ediacaran in terms of its similar magnitude, variation pattern, time constraints and depositional characteristics. Other carbon isotope anomalies can also be correlated with coeval anomalies elsewhere around the world. The temporal coincidence of TN1 (or SCIE) with onset of transgressive, storm-dominated successions suggests that enhanced oceanic upwelling and storm agitations together may have greatly increased the depth of ventilated seafloor and extent/volume of oxygenated DOC pool in shallow marine realms, leading to the extremely δ13C excursion of carbonates. Our new carbon isotopic chemostratigraphic profiles of upper Ediacaran from the Tarim Block thus not only provide a more reliable time stratigraphic framework helpful for documenting depositional history and environment-life evolution, but also promote comparisons with other continental blocks globally.

Re-Os geochronology for the Cambrian SPICE event: Insights into euxinia and enhanced continental weathering from radiogenic isotopes

AbstractThe late Cambrian Steptoean positive carbon isotope excursion (SPICE) represents a major perturbation to the global carbon cycle and was associated with trilobite extinctions and expansion of anoxic and/or euxinic water masses during episodes of eustatic sea-level change. We present a new Re-Os age together with Os and Nd isotope stratigraphy and major- and trace-element data from the Alum Shale Formation (Scania, Sweden). The Re-Os age of 494.6 ± 2.9 Ma is from the interval of peak δ13Corg values, providing the first radiometric age constraint for this Cambrian carbon isotope excursion, interpreted as a possible pre-Mesozoic ocean anoxia event, and the timing of biomere-level extinctions. The Os isotope chemostratigraphic profile can be explained by an increase in terrigenous weathering prior to the SPICE, potentially driven by sea-level fall, and in agreement with enhanced nutrient supply, primary productivity, and organic matter burial as the driver of the SPICE event. Post-SPICE, the Os isotopes become increasingly unradiogenic; however, invariant εNd(t) values argue against a change in provenance and instead support a decrease in the continental weathering flux, possibly related to eustatic sea-level rise.

Chemostratigraphy as a tool for sequence stratigraphy in the Devonian Hare Indian Formation in the Mackenzie Mountains and Central Mackenzie Valley, Northwest Territories, Canada

The Hare Indian Formation (HIF) is a late Eifelian to Givetian organic-rich mudstone constituting the lower portion of the Horn River Group (HRG), which has been minimally scrutinized in the literature. This paper proposes depositional environments and a sequence stratigraphic framework for the HIF. Using composition data collected via energy-dispersive X-ray fluorescence, geochemical proxies inform detrital input, silica source, and paleoredox conditions. Cross-plots and chemostratigraphic profiles of detritally sourced Al, Ti, and K and redox-sensitive Mo and V inform depositional and stratigraphic constraints. Silica proportions vary, indicating that sediment was derived from detrital and biogenic sources. Al, Ti, and K distributions increase upwards, showing increased continentally sourced minerals. Redox-sensitive metals are highest in the Bluefish Member (BM), suggesting intermittent euxinia. Based on the presence of continental and pelagic sediments, the sedimentary environment is interpreted as proximal- to mid-shelf. These proxies guide systems tract interpretations. Si and redox-sensitive metal concentrations peak higher in the BM, accompanied by lowered concentrations of Al, Ti, and K, suggesting a maximum flooding surface. At the top of the Prohibition and Bell Creek members, redox-sensitive enrichments are lower with higher concentrations of Al, Ti, and K, suggesting a maximum regressive surface. Transgression occurred during the initial deposition of the BM, followed by regression for the remainder of the HIF. The sedimentology of the HIF can be difficult to decipher; the use of chemostratigraphy supports its geological history (including sedimentation trends and a local record of relative sea level) using methods that may be applied to other fine-grained successions.

Stable isotope and chemical stratigraphy of the Eocene Tambaba Formation: correlations with the Paleocene–Eocene Thermal Maximum event

Abstract The Paraíba Basin has a well-defined carbonate depositional sequence from the Upper Cretaceous (Campanian) to the Eocene. The carbonate sequence consists of the Itamaracá, Gramame, Maria Farinha and Tambaba formations, which mainly contain calcareous sandstones and carbonates with siliciclastics, limestone–marl alternations, limestones and marls, and limestones, respectively. The Tambaba Formation is composed of reef limestones, ranging from fossil- and ichnofossil-rich calcilutite to calcarenite. We investigated rocks of this unit located in a representative geological section at the Tambaba Beach, northeastern Brazil, in order to elucidate the environmental responses recorded in geochemical proxies (C and O isotopic composition, and distribution of major and trace elements). The δ 13 C and δ 18 O values ranged from 1.0 to 2.7‰ VPDB and from −1.3 to 1.1‰ VPDB, respectively. The interpretation of this response suggests environmental changes, such as an increase or decrease in bioproductivity of the organisms that make up these reef limestones. These changes are also recorded in the behaviour of the major and trace elements – for example, the relationship between SiO 2 , Al 2 O 3 , MgO and CaO, characterizing two different cycles during the deposition of these limestones: the first one characterized by a predominantly carbonate deposition, and the second one presenting a pulse of siliciclastic content. In addition, palaeotemperature values (9–15°C, from δ 18 O data) obtained, together with chemostratigraphic profiles of previous studies (e.g. δ 13 C, CaO, MgO, SiO 2 , Al 2 O 3 ), indicate that the reef limestones of the Tambaba Formation were probably deposited about 5 myr after the Paleocene–Eocene Thermal Maximum event.

Global or regional? Constraining the origins of the middle Bambuí carbon cycle anomaly in Brazil

The Ediacaran-Cambrian Bambuí Group in Brazil records an anomalously positive excursion in carbonate carbon isotopes (δ13Ccarb) with a sustained plateau of ca. +15‰ (aka the Middle Bambuí Excursion–MIBE). Considering that the δ13Ccarb signals in Ediacaran-Cambrian seawaters do not typically exceed +6‰, the MIBE therefore represents a profound carbon cycle anomaly in Earth’s history. Although intensive studies have been done on the Bambuí Group, origins of the MIBE remain enigmatic. In order to better constrain the biogeochemical carbon and sulfur cycles during the MIBE, high-resolution chemostratigraphic analysis was conducted for both the plateau (i.e., Lagoa do Jacaré Formation) and the recovery part (i.e., lower Serra da Saudade Formation) of the MIBE. Chemostratigraphic profiles reveal remarkably different values in δ13Ccarb, δ13Corg, δ18Ocarb, and δ34Spyrite between these two studied MIBE intervals. The new data show that the plateau of the MIBE is characterized by coupled higher δ13Ccarb, higher δ13Corg, and higher δ34Spyrite signals compared with the recovery part of the MIBE. Based on multiple lines of sedimentological, geochemical, and model evidence, we propose that the possibilities of enhanced organic carbon burial and porewater methanogenesis are insufficient to explain the MIBE. Instead, local or regional controlling factors, including water-column methanogenesis, low-sulfate conditions, and enhanced carbonate recycling in a restricted basin may have played a role, independently or in unison, in generating this profound positive δ13Ccarb excursion. Therefore, the MIBE may reflect a regional event, instead of a global carbon cycle anomaly. We caution against the use of the MIBE in chemostratigraphic correlations on a global scale or any other attempt to infer global carbon cycling at that time. The biogeochemical landscape of the late Ediacaran-Cambrian basins and ocean margins may be more heterogeneous than previously thought.

Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China.

The late Ediacaran Dengying Formation (ca. 551.1-538.8 Ma) in South China is one of two successions where Ediacara-type macrofossils are preserved in carbonate facies along with skeletal fossils and bilaterian animal traces. Given the remarkable thickness of carbonate-bearing strata deposited in less than 12.3 million years, the Dengying Formation holds the potential for a relatively continuous chemostratigraphic profile for the terminal Ediacaran stage. In this study, a detailed sedimentological and chemostratigraphic (δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyrite, and 87Sr/86Sr) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of the southern Shaanxi Province, South China. Sedimentological results reveal an overall shallow marine depositional environment. Carbonate breccia, void-filling botryoidal precipitates, and aragonite crystal fans are common in the Algal Dolomite Member of the Dengying Formation, suggesting that peritidal facies were repeatedly karstified. The timing of karstification was likely early, probably soon after the deposition of the dolomite sediments. The presence of authigenic aragonite cements suggests high alkalinity in the terminal Ediacaran ocean. Geochemical analysis of micro-drilled samples shows that distinct compositions are registered in different carbonate phases, which should be considered when constructing chemostratigraphic profiles representative of true temporal variations in seawater chemistry. Integrated chemostratigraphic data suggest enhanced burial of organic carbon and pyrite, and the occurrence of extensive marine anoxia (at least in the Gaojiashan Member). Rapid basinal subsidence and carbonate accumulation during a time of elevated seawater alkalinity and increased rates of pyrite burial may have facilitated the evolutionary innovation of early biomineralizing metazoans.

Chemostratigraphy of the Cenomanian-Turonian shallow-water carbonate: new correlation for the rudist levels from north Sinai, Egypt

The present study aims to provide carbon-isotope curves for the Cenomanian to Turonian rudist-dominated successions in north Sinai. The high-resolution carbon-isotope curves obtained from north Sinai sections provide new insight for calibrating the age of rudists as well as for evaluating the effects of the oceanic anoxic event 2 (OAE2) on rudist communities. The primary goals are (1) to provide a high-resolution sequence stratigraphic framework for the Cenomanian-Turonian succession, (2) to use rudist and ammonite biostratigraphic data to distinguish the stratigraphic levels of the rudist species, and (3) to integrate the chemostratigraphic (δ13C) profile and the rudist levels to improve the biostratigraphy based on the rudist distributions and the carbon-isotope data. The recognition of three ammonite zones through the Cenomanian-Turonian succession was utilized to identify four temporally significant rudist levels indicative of the Lower Cenomanian, Middle Cenomanian, Upper Cenomanian, and Middle Turonian, respectively. Most of the rudists occur in the highstand deposits of medium-scale sequences. Carbon- and oxygen-isotopic analyses were carried out on both rudists and surrounding carbonate units. Based on the variations in the carbon-isotope signals, 12 chronostratigraphic segments were identified in the studied sections. The Cenomanian carbon-isotope segments (C23–C30) were obtained from the Halal Formation at Gabal Yelleg and Gabal Maaza sections, while the Turonian segments (C30–C34) were measured from the Wata Formation at Gabal Yelleg section. The carbon-isotope record from the studied sections is consistent with the trends documented in previous studies of the Tethyan realm. The Cenomanian-Turonian boundary is placed at the onset of falling carbon-isotope values (δ13C) from 2.61 to −0.25‰ in the upper part of OAE2 with the carbon-isotope segment C30 at Gabal Yelleg. The negative shift in δ13C values (C33) occurred in the Middle Turonian lowstand deposits characterizing the global sea level fall during this interval.

The use of chemostratigraphy to refine ambiguous sequence stratigraphic correlations in marine mudrocks. An example from the Woodford Shale, Oklahoma, USA

Application of sequence stratigraphy to fine-grained lithologies has previously been hindered by the difficulty of identifying distinct facies shifts within mudrocks. Three cores from Lincoln, Pottawatomie and Pontotoc Counties in Oklahoma and two outcrops at the Hunton Anticline Quarry in Murray County, OK record both proximal and distal regions of the Arkoma Basin. Handheld X-ray fluorescence data and gamma-ray profiles together with lithological descriptions can be used to develop sequence-stratigraphic interpretations. Stratigraphic successions that are challenging to correlate based on gamma-ray (GR) profiles alone can be correlated accurately by utilizing surfaces that are recognized within chemostratigraphic profiles. Within the Arkoma Basin, Oklahoma, the chemostratigraphic profile of the Woodford Shale is interpreted within a sequence-stratigraphic framework using the following general criteria. The Lowstand Systems Tract (LST) is defined by increasing concentrations of Ti, Zr, Al and K as well as high levels of Mo and V. The Transgressive Systems Tract (TST) is defined by declining concentrations of Ti and Zr, although Al and K may remain elevated; Mo and V also show general declines. The Highstand Systems Tract (HST) is defined by increasing concentrations of Ti, Zr, Al and K, but is distinguished from the LST by low levels of Mo and V. Supplementary material: Chemofacies profiles are available at http://doi.org/10.6084/m9.figshare.c.2849599 .

The geochemistry and petrogenesis of the Blue Draw Metagabbro

The Blue Draw Metagabbro (BDM) in western South Dakota, is an 800m thick, layered intrusion, which is interpreted to have been intruded as a rift-related subvolcanic sill during the Palaeoproterozoic. The age and tectonic setting of the BDM are similar to those recorded by the East Bull Lake Suite of layered intrusions in Southern Ontario. These similarities have led previous authors to suggest that the two sets of intrusions are cogenetic. The East Bull Lake Suite intrusions are relatively well studied and are known to host significant contact-type Ni–Cu–PGE sulphide mineralisation, however, prior to this work, relatively little was known of BDM both in terms of its geochemistry and mineralisation potential. Chemostratigraphic profiles through the BDM show that the intrusion is the product of at least two magma pulses which fractionated to produce a sequence of rocks which grade from peridotitic at the base of the intrusion to gabbronoritic at the upper margin. Closed-system fractionation following the intrusion of the second magma pulse caused the magma to become saturated in sulphur and precipitate Ni–Cu–PGE bearing sulphides—now preserved in a low-grade 50m thick zone near the top of the intrusion. Petrological modelling shows that the parental melt of the BDM was a low-Ti tholeiite, with a trace element chemistry defined by enrichments in large-ion lithophile and light rare-earth elements and prominent negative Nb, Ta, and Ti anomalies. This ‘arc-like’ geochemistry recorded by the BDM parent magma is shared with parent magmas of the East Bull Lake Suite and may suggest that the BDM and its potential Canadian relatives share a common magmatic source. However, the relative ubiquity of such geochemical signatures in Archaean–Palaeoproterozoic intracontinental magmatic rocks coeval with the BDM suggests that the geochemical similarities recorded by the BDM and East Bull Lake Suite are non-unique and hence, are not definitive evidence of a genetic link between the two sets of intrusions. Instead, this geochemical signature that is common to many ancient igneous provinces may indicate the presence of a transient and (currently) poorly understood Archaean–Palaeoproterozoic mantle reservoir which was a globally significant magma source.

Ediacaran chemostratigraphy and paleoceanography at a shallow marine setting in northwestern Hunan Province, South China

The geochemical and lithological features of the Ediacaran strata at Yangjiaping in northwestern Hunan Province, South China, record information about the depositional environments, redox conditions, and carbon cycling in a shallow-water setting in this region. The chemostratigraphic profile of the inorganic carbon isotope reveals three negative anomaly intervals in the Ediacaran section that comprises the thick (∼360 m) Doushantuo and the thin (∼110 m) Dengying Formations. Two of the three intervals, at the base of the Doushantuo Formation and the PC/C boundary, correspond to the global trend. Another anomaly interval in the uppermost 120 m of the Doushantuo Formation appears large-amplitude fluctuations of the inorganic carbon isotope, as well of the oxygen isotope. This interval can be correlated to one of the anomaly intervals of the Three George section, either at the upper, or at the middle Doushantuo Formation. The latter correlation scheme implies association with the Gaskiers glaciation, and demands a substantial hiatus at the Doushantuo/Dengying boundary. Decoupling between organic and inorganic carbon isotopes was recognized in two intervals of the lower Doushantuo Formation and the upper Doushantuo to the lower Dengying Formations. The lower and upper intervals were likely attribute to unusual carbon cycling, reflecting from development and diminishing of the dissolved organic carbon (DOC) reservoir, respectively. Shallow-water sedimentary facies and high organic carbon isotopic values are characteristic of the Yangjiaping section, especially in the oolitic facies of the middle Doushantuo Formation and in the supratidal facies of the lower Dengying Formation. In these intervals, Yangjiaping was in an isolated lagoonal setting where the carbon cycle was independent of that of the open ocean in the South China region.

Carbon isotope chemostratigraphy and sedimentary facies evolution of the Ediacaran Doushantuo Formation in western Hubei, South China

The Doushantuo Formation of South China, consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies, is one of the key sedimentary units in the world for understanding Ediacaran geobiological processes. However, stratigraphic correlation and sedimentary facies evolution of the Doushantuo Formation remain controversial. Sedimentary facies analysis of the well-known sections of the Yangtze Gorges area and new sections in northern Yichang, western Hubei indicate that the Doushantuo succession in the Yangtze Gorges area was deposited in an offshore intra-shelf basin within the Yangtze platform. In contrast, the Doushantuo Formation in the northern Yichang area which is characterized by one or a few phosphate-rich horizons represents deposition on the subtidal or intertidal shelf, and so is similar to the succession in the Weng’an area (central Guizhou Province). The carbon isotope profiles of the different sections exhibit significant variation, which is interpreted to result from facies differences. Sequence and high-resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the Doushantuo Formation on the Yangtze platform. The results confirm that a prominent negative δ13Ccarb excursion (BAINCE, nadir down to −5‰) in the middle portion of the second sequence of the Doushantuo Formation is a widely traceable event. BAINCE together with three other δ13Ccarb excursions, namely CANCE at the base, WANCE near the first sequence boundary near the middle, and DOUNCE at the top of the Doushantuo Formation, constitute a complete carbon isotope profile for the Doushantuo Formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the Ediacaran Period.

The Neoproterozoic Noonday Formation, Death Valley region, California

The Neoproterozoic–Cambrian succession in the Death Valley region of the southwestern United States is among the best exposed and easily accessible in the world. The largest single exposure of these strata occurs in the Panamint Range on the west side of Death Valley, and it, although variably metamorphosed, contains the most complete sections of the Noonday Formation cap carbonate sequence. New geological mapping, measured sections, and high-resolution carbon isotope data for the Noonday Formation in this range enable establishment of a unified stratigraphy across the Death Valley region that consists of three units. From the base upward, they include: the Sentinel Peak Member of light-gray, massive to laminated fine dolostone locally containing vugs and tubes variably filled with micrite, spar, or quartz (and rarely galena), and varying from 2 to 200 m in thickness; the Radcliff Member, composed of feldspathic shale and sandstone and thin-bedded limestone, 0–200 m thick; and the newly defined Mahogany Flats Member of gray, commonly stromatolitic, thin- to medium-bedded fine dolostone that is ~200 m thick at its type locality. Carbon isotopic trends in the Panamint Range match to within 1‰–2‰ reproducibility those known for the equivalent nonmetamorphosed strata in the eastern Death Valley sections. A composite section of the Noonday Formation displays a chemostratigraphic profile with values near −3‰ through the cap dolostone of the Sentinel Peak Member, a decline to −6‰ in the lower part of the Radcliff Member, followed by a recovery to near 0‰ and subsequent decline toward −2‰ in the remainder of the Radcliff units and lower Mahogany Flats Member, and then a return to positive values (4‰) through the remainder of the Mahogany Flats Member. This pattern matches the Ediacaran cap carbonate in Namibia remarkably well, and, assuming our carbon isotopic correlations are correct, it indicates that Noonday deposition occurred at the beginning of the Ediacaran Period, and that the immediately underlying Wildrose Diamictite of the Kingston Peak Formation probably represents the younger Cryogenian (Marinoan) glacial episode.

The Shuram and subsequent Ediacaran carbon isotope excursions from southwest Laurentia, and implications for environmental stability during the metazoan radiation

Research Article| July 01, 2011 The Shuram and subsequent Ediacaran carbon isotope excursions from southwest Laurentia, and implications for environmental stability during the metazoan radiation Charles Verdel; Charles Verdel † 1Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA †Current address: Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA; e-mail: cverdel@ku.edu Search for other works by this author on: GSW Google Scholar Brian P. Wernicke; Brian P. Wernicke 1Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA Search for other works by this author on: GSW Google Scholar Samuel A. Bowring Samuel A. Bowring 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (7-8): 1539–1559. https://doi.org/10.1130/B30369.1 Article history received: 08 Jul 2010 rev-recd: 10 Oct 2010 accepted: 12 Oct 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Charles Verdel, Brian P. Wernicke, Samuel A. Bowring; The Shuram and subsequent Ediacaran carbon isotope excursions from southwest Laurentia, and implications for environmental stability during the metazoan radiation. GSA Bulletin 2011;; 123 (7-8): 1539–1559. doi: https://doi.org/10.1130/B30369.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Current understanding of secular changes in the carbon isotopic composition of mid- to late Ediacaran carbonates suggests a relatively long, steady recovery of the global ocean from the Shuram negative excursion, followed by a smaller negative excursion at the Precambrian-Cambrian boundary. New radiometric, stratigraphic, and carbon isotope data from thick exposures of the upper Johnnie Formation in the Panamint Range of eastern California, combined with data from carbonate-rich facies of the Stirling Quartzite in the Funeral Mountains, confirm an Ediacaran age for these strata and provide a more complete record of isotopic variations during this time interval than previously determined from SW Laurentia and other key sections around the globe. A siltstone in the lower part of the Johnnie Formation yielded a detrital zircon grain with an age of 640.33 ± 0.09 Ma, lowering the maximum radiometric age constraint on the Johnnie Formation by >400 m.y., consistent with an Ediacaran age based on chemo- and biostratigraphic data. In contrast to previous C isotope compilations from this region, which were generally based on relatively thin portions of the Cordilleran miogeocline near its depositional hinge, the more basinward exposures exhibit a recovery from values near –12‰ to 0‰ within the upper part of the Johnnie Formation. Details in the shape of the chemostratigraphic profile through the upper Johnnie Formation closely match those in profiles through the Wonoka Formation in South Australia (which lies above the basal Ediacaran global stratotype section and point) and the Shuram-Buah interval in Oman, confirming temporal correlation and suggesting genesis through changes in the isotopic composition of the global ocean. The Shuram excursion in SW Laurentia is followed by at least three smaller Ediacaran to earliest Cambrian isotopic excursions recorded within, from oldest to youngest, the uppermost Johnnie Formation, the middle Stirling Quartzite, and the lower Wood Canyon Formation. These data indicate that the negative excursion associated with the base of the Cambrian is not a unique post-Shuram event, and that post-Shuram, pre-Cambrian animal evolution occurred in an environment of repeated large-magnitude fluctuations in the carbon isotopic composition of the global ocean. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chapter 41 Glaciogenic and related strata of the Neoproterozoic Kingston Peak Formation in the Panamint Range, Death Valley region, California

Abstract Glaciogenic deposits in the Death Valley region occur within the Neoproterozoic Kingston Peak Formation (Fm.). In the Panamint Range, immediately west of Death Valley, the formation is as much as 1000 m thick and is continuously exposed for nearly 100 km along the strike of the range. Although the strata are variably metamorphosed and locally exhibit pronounced ductile strain, original sedimentary textures are well preserved in many places. Diamictite occurs in two distinct intervals, a lower one comprising the Limekiln Spring and Surprise members, and an upper one, the Wildrose Sub-member of the South Park Member. Lonestones, bullet-shaped and striated clasts, and rare dropstones within these members, along with the impressive lateral continuity of diamictic units, support a glacial origin. Both diamictic intervals are succeeded by well-defined carbonates, the oldest is the Sourdough Member of the Kingston Peak Fm. and the younger one is the Sentinel Peak Member of the overlying Noonday Dolomite. The stratigraphic succession between the Sourdough Member and the Wildrose Sub-member (i.e. the Middle Park, Mountain Girl and Thorndike sub-members of the South Park Member) is c. 300 m thick and includes lithologies recording deposition in braided fluvial to platform carbonate settings. Lithostratigraphic and chemostratigraphic profiles of δ 13 C for the Sourdough (–3‰ to +2‰, increasing upward) and Sentinel Peak (–3‰ ±1‰) members suggest correlation with, respectively, the older Cryogenian (commonly referred to as ‘Sturtian’ in previous literature) and younger Cryogenian (commonly referred to as ‘Marinoan’ in previous literature) cap-carbonate sequences recognized worldwide. Potentially economic uranium deposits (secondary brannerite) occur in graphitic schist of the Limekiln Spring Member and sub-economic uranium and thorium (hosted by detrital monazite) occur within quartz-pebble conglomerate in the South Park Member. The Kingston Peak Fm. strata in the Panamint Range contain no fossils, radiometric age control or primary magnetizations.

Correlation of Aptian-Albian Carbon Isotope Excursions in Continental Strata of the Cretaceous Foreland Basin, Eastern Utah, U.S.A.

Abstract Nodular carbonates (“calcretes”) in continental foreland-basin strata of the Early Cretaceous Cedar Mountain Formation (CMF) in eastern Utah yield δ13C and δ18O records of changes in the exogenic carbon cycle related to oceanic anoxic events (OAEs), and terrestrial paleoclimate. Chemostratigraphic profiles of both forebulge and foredeep sections show two prominent positive δ13C excursions, each with a peak value of −3%0 VPDB, and having background δ13C values of about −6%0 VPDB. These excursions correlate with the global early Aptian (Ap7) and late Aptian–early Albian (Ap12-Al1) carbon isotope excursions. Aptian–Albian positive δ13C excursions in the CMF also correspond to 3–4 per mil increases in carbonate δ18O. These phenomena record local aridification events. The chemostratigraphic profile on the thinner forebulge section of the CMF is calibrated, for the first time, by a radiogenic U-Pb date of 119.4 ± 2.6 Ma on a carbonate bed, and by detrital zircon U-Pb dates on two bounding sandstone units (maximum depositional ages of 146 Ma and 112 Ma). Petrographic observations and diagenetic analyses of micritic to microsparitic carbonates from nodules indicate palustrine origins and demonstrate that they crystallized in shallow early meteoric phreatic environments. Meteoric calcite lines derived from CMF carbonates have δ18O values ranging between −8.1 to −7.5%0 VPDB, supporting an estimate of zonal mean groundwater δ18O of −6%0 VSMOW for an Aptian–Albian paleolatitude of 34° N. Furthermore, our two chemostratigraphic profiles exhibit a generally proportionate thinning of correlative strata from the foredeep on to the forebulge, suggesting that there were consistently lower rates of accumulation on the forebulge during the Aptian–Albian. Identification of the global Aptian–Albian δ13C excursions in purely continental strata, as demonstrated in this paper, opens a new avenue of research by identifying specific stratigraphic intervals that record the terrestrial paleoclimatic impacts of perturbations of the global carbon cycle.