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International audience; Since 2012, we have investigated a stratigraphic section encompassing the late Eocene–earliest Oligocene interval at Shapaja (Tarapoto area, Peruvian Amazonia, ca. 7°S), through paleontological and geological fieldwork. The measured sedimentary series (120 m-thick [West] plus 90 m-thick [East]), assigned to the upper member of the Pozo Formation, records fluvial micro-conglomeratic lenses intercalated with floodplain and evaporite-rich fine red deposits, estuarine/coastal-plain tidally-influenced fine sandstones, and oxbow lake nodule-rich blue clays. This sedimentary shift coincides locally with the demise of the large Eocene coastal-plain wetland known as Pozo System. The late Eocene–early Oligocene Shapaja section was extensively sampled for chemostratigraphy (δ13C on dispersed organic matter and pedogenic carbonate nodules), which in turn allowed for refining the location of the Eocene-Oligocene Transition (EOT) and other climatic events recognized at a global scale (i.e., Oi-1 and Oi-1a). The section has yielded nine fossil localities with plant remains (leaves, wood, charophytes, and palynomorphs), mollusks, decapods, and/or vertebrates (selachians, actinopterygians, lungfishes, amphibians, sauropsids, and mammals), documenting ~130 distinct taxa. Four localities of the upper member of the Pozo Formation at Shapaja predate the EOT, one is clearly within the EOT, while four are earliest/early Oligocene in age. The small leaf impressions found along the Shapaja section could be indicative of dry and/or seasonal conditions for this region throughout and after the EOT. Monkeys, indicative of tropical rainforest environments, are only recorded in a latest Eocene locality (TAR-21). Two biotic turnovers are perceptible in the selachian, metatherian, and rodent communities, well before the EOT [~35–36 Ma] and a few hundred thousand years after the EOT [~33 Ma]. The latter turnover seems to be primarily related to a global sea-level drop (ichthyofauna: marine-littoral elements replaced by obligate freshwater taxa) and/or the onset of a drier and more seasonal climate in early Oligocene times (terrestrial components). Changes in the structure of the Shapaja paleocommunities were mostly driven by the flexural subsidence during the late Eocene, and then globally driven by the earliest Oligocene climatic deterioration.

A high-resolution palynological analysis of the Cenomanian to Lower Campanian in the Trunch borehole, Norfolk (southern North Sea basin) is documented. This constitutes the most detailed continuous record of organic-walled dinoflagellate cysts (dinocysts) from a single Upper Cretaceous section to date. A revised stratigraphic framework for the Trunch succession is presented, integrating regional marker bed lithostratigraphy, macrofossil biostratigraphy and carbon-isotope chemostratigraphy. Palynological events at Trunch are compared to published records with an emphasis on NW Europe, and a new stratigraphy comprising 65 dinocyst events is proposed. A geochronological age model based on radioisotopic and astrochronological ages of macrofossil biostratigraphic datum levels and global carbon-isotope events (CIEs) is used to revise the age calibration of the Upper Cretaceous δ13Ccarb carbonate reference curve for the English Chalk, and to calculate absolute ages for the palynological events with an accuracy judged to be ± 500 kyr. The palaeogeographic distribution of key taxa is presented based on records obtained from the PALYNODATA database and additional records, summarised to 212 sites world-wide. Endemic NW Europe, Northern Hemisphere-wide and global species distributions are demonstrated. A taxonomic and detailed stratigraphic discussion is provided to determine the likelihood that the events may be considered as global first or last appearance datum levels, or are local to regional lowest and highest occurrences. Four global, 21 Northern Hemisphere and 40 NW Europe events are tabulated, including 29 inceptions or extinctions of marker species; an additional 36 events may be of regional significance.

Changes in the climate-sensitive carbon cycle during the major and second-order Late Devonian global events were more complex than usually expected, i.e., they were not characterized only by positive δ13Ccarb and δ13Corg excursions up to 5.5‰. In fact, the carbon (and oxygen) isotope signatures in lime mudstones are less susceptible to diagenetic bias and therefore several negative trends and spikes in different facies of distant continents are re-interpreted as primary biogeochemical signals. In addition to significant intra- and inter-regional variability resulting from diverse local carbon cycling factors, the initial phase of both Kellwasser Crisis events [Frasnian-Famennian (F-F) mass extinction] and end-Devonian Hangenberg Crisis confirms the predicted causal relationship between large-scale volcanic degassing (mainly in large igneous provinces?) and the response of global carbon cycle in 13C depleted signals. Potential volcanic signals were confirmed in more than 40% of the 73 F-F sites analyzed for C-isotope stratigraphy, as summarized in the global database. Lowered δ13C values characterize also onset of other less known Late Devonian events, exemplified particularly by well-documented Frasnian Middlesex/punctata Event. Thus, consistently recognized worldwide, paired negative δ13C and δ18O excursions, even only in carbonate signatures, can be cautiously regarded as a primary volcano-climatic (greenhouse) signal and additional proxy of the volcanic trigger. In addition, the repeated negative δ13C spike near the F-F boundary correlates with Hg anomalies considered to be the signature of the arc magmatism acme (and alkaline/carbonatite/kimberlite paroxysm?). However, both the carbon cycle response and time relationships between disturbances in C and Hg cycles during mass extinctions were certainly complex and required high-resolution studies in the most stratigraphically extended series and advanced quantitative modeling.

Recent studies on δ13C chemostratigraphy have produced a wealth of new information of major importance for clarification of local and global stratigraphic relationships. Currently, approximately 15 named positive and negative isotopic excursions have been identified in the Ordovician System. Some of these are significant and geographically widespread, whereas others are poorly developed and regional, thus hindering unambiguous usage. Because isotopic age data useful for precise excursion dating are rarely available in the Ordovician, biostratigraphic information from geographically widespread fossil groups such a graptolites and conodonts are of critical importance for correct identification of isotopic excursions. This study is a global review of the relations between Ordovician δ13C excursions and graptolite and conodont biostratigraphic units with special emphasis on Baltoscandia, North America, and Argentina, three large regions that have been centers of Ordovician chemostratigraphic research. In this report we review for each excursion its proper nomenclatural designation, relations to biostratigraphic units, its known geographic range, and key study localities.

This study presents C and Hg (Hg/TOC) chemostratigraphy data on identified Permian–Triassic successions across the globe with an aim to develop a better understanding on the “mass extinction” event during this time interval. Besides, it would also contribute to the global database on C and Hg stratigraphy and reinforce the application of the latter as a reliable proxy in global correlation, especially in cases of sedimentary sequences deposited coevally with LIP volcanism. In this endeavor, the δ13C chemostratigraphic curves from thousands of kilometers apart from nine classical marine sedimentary sections from various paleolatitudinal zones as well as Hg/TOC stratigraphic pathways of eight of these sections, were examined in a transect across the Pangea supercontinent (~ 252 Ma). A strong negative δ13Ccarb shift at the Late Permian Mass Extinction (LPME), in Meishan D, Guryul Ravine and several other (Permian Triassic Boundary) PTB sections worldwide, is probably due to voluminous CO2 degassing during volcanism in the Siberian Traps Large Igneous Province (STLIP). The C-isotope shift at the LPME is much stronger than in the PTB or Early Triassic Mass Extinction (ETME). The Hg/TOC peaks are observed at LPME and ETME horizons in the Meishan D section, whereas the peaks were recorded at LPME and PTB horizons in Hovea-3, Ursula Creek, Idrijca and Rizvanusa sections. The Rizvanusa section displays a single peak at the ETME horizon, Zal and Abadeh successions at the LPME and ETME horizons, while the Misci section shows Hg/TOC enrichment at the LPME horizon. The largest Hg/TOC peaks at the LPME, PTB and ETME can be associated with the beginning of Stage 2 (extrusive hiatus) of STLIP. The origin of a Hg/TOC spike in the LPME–PTB interval in seven of these sections is unclear as well as the Hg/TOC spike below the LPME at the Misci and Zal sections. The latter may, possibly be, linked to the STLIP (Stage 1) or some local volcanism. In the δ202Hg (MDF) vs Δ201Hg (MIF) cross plot, the majority of samples from the extinction interval plot within the “volcanic-emission box” and a few samples, in the “sediment/soil/peat box.” Hg isotope signatures underline mixing of volcanic and terrestrial Hg, generating four trends with negligible variation in Δ201Hg. Lesser terrigenous-Hg influx was noticed in sections closer to the STLIP (Rizvanusa, Idrijca and Seres/Misci, all in Europe), recording close to zero Δ201Hg (MIF) values. Marked influence is observed in sections far away from the STLIP (Meishan, Ursula Creek and Hovea-3) that exhibit negative a Δ201Hg (MIF). The Zal and Abadeh sections, at intermediate distance from the STLIP, exhibit the highest, positive Δ201Hg values (Abadeh) and the lowest, negative Δ201Hg values (Zal). The Δ199Hg (MIF) vs Hg (n ng− 1) cross plot testifies that volcanic Hg has been contaminated by terrigenously sourced-Hg influx, inducing the two major curved trends. The negative C-isotope excursions and Hg/TOC enrichments in these sections are nearly coeval, substantiating a synchronism between the P–T transition biotic crises (LPME and ETME) and the start of the stage 2 of the Siberian Traps (sill-intrusions).

Two negative carbon isotope excursions (3.5–6.5‰) across the Wuchiapingian-Changhsingian boundary (WCB) are observed globally (sections in China, Canada, and Iran); however, the causative mechanism of these excursions is debated. Here, high-resolution osmium isotope (187Os/188Os or Osi) chemostratigraphy of four globally correlated WCB sections (3 in China - Meishan, Shangsi and Lianyuan and 1 in Canada - Buchanan Lake) show two separate Osi excursions to less radiogenic compositions that are coincident with the carbon isotope shifts for two of the South China sections (Lianyuan, Meishan). In contrast, only a single Osi excursion to less radiogenic compositions, coinciding with the earliest Changhsingian carbon isotope shift, is observed for the Shangsi and Buchanan Lake sections. The Osi shift is interpreted to reflect increased unradiogenic Os input from basaltic magmatism in South China, possibly related to the Emeishan large igneous province (LIP). However, 187Os/188Os data suggest that only the earliest Changhsingian volcanism had global impact on both the ocean and atmosphere. The lack of any evidence for a biotic event associated with the WCB therefore may have been due to the more regional rather than global impact of volcanism during the latest Wuchiapingian. In contrast, during the earliest Changhsingian, volcanism was sufficient to cause a more global signal in the ocean osmium record, but was inadequate, or too prolonged, to drive any significant environmental change. Volcanism, however, may have provided the isotopically light carbon that drove the negative carbon isotope excursions across the WCB.

Shallow-platform settings with marked differences in paleoplatform bottom physiography influence the degree of connection with oceanic waters and overall circulation patterns, even when sharing the same palaeoclimatic conditions. Two Kimmeridgian shallow-marine settings have been explored to test the sensitivity and reliability of carbonate chemostratigraphy to detect such differences. An integrated overview of the obtained elemental trends depicted four major facies, shared along specific stratigraphic intervals of both depositional records. Diagenesis obliterated original geochemical signals only throughout the siliciclastics-rich interval, corresponding to the most landward setting. For the remaining facies, elemental features could be attributed to the differential action of forcing mechanisms operating along the south-Iberian paleomargin during Kimmeridgian times. The highest degree of continental influence can be recognized by a strong relationship between Fe and Mn for the most proximal setting, which fades out along the mixed carbonate-fine siliciclastic rhythmic deposition in more open settings. A characteristic geochemical signature of progressively more positive d13C values and significantly higher Sr content is identified for the interval dominated by biogenic sponge buildups., This research was supported by Projects CGL2008-05251-E and CGL2012-39835 (MINECO) and the Research Group RNM-178, Junta de Andalucía, Spain. R. Coimbra is currently supported by the Post- Doctoral Fellowship SFRH/BPD/92376/2013 (Fundação para a Ciência e a Tecnologia, Portugal) and the research units GeoBiotec - UID/GEO/04035/2013 and MARE- UID/MAR/04292/2013.

In recent years, δ13C and δ18O chemostratigraphy has become a powerful tool used to solve controversial results using different biological time markers from shallow-marine carbonate environments and establish long-distance correlations across proximal and distal settings. However, its reliability was recently questioned due to the impact of diagenesis on stable isotope records. The ammonite-calibrated, platform-to-basin transect of the late Barremian–early Aptian Urgonian Provence platform is made particularly relevant to challenge chemostratigraphy-based correlation methods in shallow carbonate series at different scales. The origin, preservation and stratigraphic potential of isotopic signatures are herein discussed along 11 shallow-marine and basinal sections. In the proximal settings of the Provence domain, tight carbonates—either resulting from muddy depositional textures or early cementation—likely preserve original marine signatures. Contrasting observations arise from porous carbonates whose stable isotope signal is heavily affected by micrite recrystallization (i.e., microporosity genesis) during a mid-Cretaceous tectonic uplift event. Locally, the C-isotope signal of microporous Urgonian limestones can be controlled by the vertical distribution of porosity. Although basinal series are more prone to preserve primary geochemical signatures, extreme values for carbon and oxygen isotopes are observed in correspondence with fine-grained bioclastic material input originating from the adjacent platform, following the latest Barremian demise of the rudist-dominated platform. This study suggests that stable isotope chemostratigraphy may not constitute a suitable tool for calibrating and correlating Urgonian shallow-marine series.

Cap Carbonates overlie the Marinoan Snowball Earth-related glacial diamictite, and possibly record the drastic surface environmental change and biological evolution after the Snowball Earth. We conducted on-land drilling from the Liantuo Formation, through the Nantuo, to the lower Doushantuo Formation in the Three Gorges area of South China to collect fresh, continuous samples in the Three Gorges area. We obtained high-resolution chemostratigraphies of δ 13 C and δ 18 O values of carbonates from the topmost part of the Nantuo Formation to the Cap Carbonate, in order to decode the detailed surface environmental change in the shallow marine setting. The δ 13 C chemostratigraphy possesses some unique characteristics: (1) stable δ 13 C values as a whole, but ubiquitous low δ 13 C anomalies through the Cap Carbonate, (2) increase of the δ 13 C values from −3 to +5‰ across the C2/C3 boundary, (3) no δ 13 C anomaly between the C1 and C2 boundary, and (4) presence of an anomalous high δ 13 C value (+2.3‰) and a faint positive correlation between δ 13 C and δ 18 O values in the C1 unit. Evidence of quite low δ 13 C anomalies (with a nadir of −41‰), ubiquitous negative δ 13 C anomalies through the Cap Carbonate, and a high δ 13 C anomaly accompanied with a faint positive correlation between δ 13 C and δ 18 O values in the C1 unit supports decomposition and formation of methane hydrate during Cap Carbonate formation. The drastic increase of δ 13 C values from the upper C2 to C3 units indicates enhancement of primary productivity and organic carbon burial, possibly due to high continental fluxes after the Snowball Earth event, evidenced by high Sr isotope values. The increase is restricted to the proximal side of the inner shelf in South China, and the timing of the increase of δ 13 C values of carbonates is earlier at Three Gorges area than any other area, suggesting that the enhancement of primary productivity started in the proximal environment because of higher continental influxes. The increase in oxygen contents of seawater due to the enhanced primary productivity possibly resulted in the emergence of multicellular animals soon after Cap Carbonate deposition.

The Neoproterozoic Huttenberg Formation in northeastern Namibia records a remarkable δ 13 C carb positive excursion with a sustained plateau of values up to +12‰ (i.e., the Huttenberg anomaly). High-resolution chemostratigraphic analyses of drill core samples spanning the upper Elandshoek and Huttenberg formations reveal multiple new observations: (1) overall high but oscillatory δ 13 C carb values; (2) δ 18 O carb values ranging from −8‰ to −2‰; (3) significant enrichment of 13 C in organic carbon and a broad co-variation between δ 13 C carb and δ 13 C org ; (4) a profound negative excursion in δ 34 S pyrite from +30‰ to −10‰; (5) an overall inverse δ 13 C–δ 34 S relationship; and (6) 87 Sr/ 86 Sr values down to 0.7074 in limestone samples. The new data suggest that the Huttenberg anomaly records dynamic fluctuations in marine redox conditions, which may include an oxygenation event during the height of the δ 13 C carb positive excursion and a deoxygenation event at its termination. The δ 34 S pyrite negative excursion suggests the buildup of the marine sulfate reservoir, likely due to enhanced pyrite oxidation during the oxygenation event. The δ 34 S pyrite increase at the end of the Huttenberg anomaly may result from a seawater sulfate concentration drawdown towards pre-anomaly conditions. On one hand, the Huttenberg anomaly may reflect restricted basin signals that are deviated from the Ediacaran open ocean; on the other hand, the Ediacaran Huttenberg anomaly, together with the Cryogenian δ 13 C carb positive excursions, suggests a stepwise pattern of the Neoproterozoic Oxygenation Event. Both local and global environmental factors may have contributed to the Huttenberg anomaly. The Huttenberg anomaly therefore represents a local enhancement of global oxygenation signals. Our data support the emerging view that the Neoproterozoic Oxygenation Event may have facilitated the evolution of early life at that time.

Expansive Late Cretaceous lacustrine deposits of East Asia offer unique stratigraphic records to better understand regional responses to global climate events, such as oceanic anoxic events (OAEs), and terrestrial organic carbon burial dynamics. This study presents bulk organic carbon isotopes ( δ 13 C org ), elemental concentrations (XRF), and initial osmium ratios ( 187 Os/ 188 Os, Os i ) from the Turonian–Coniacian Qingshankou Formation, a ∼5 Ma lacustrine mudstone succession in the Songliao Basin of northeast China. A notable δ 13 C org excursion ( ∼ + 2.5 ‰ ) in organic carbon-lean Qingshankou Members 2–3 correlates to OAE3 in the Western Interior Basin (WIB) of North America within temporal uncertainty of high-precision age models. Decreases in carbon isotopic fractionation ( Δ 13 C) through OAE3 in the WIB and Songliao Basin, suggest that significantly elevated global rates of organic carbon burial drew down pCO 2 , likely cooling climate. Despite this, Os i chemostratigraphy demonstrates no major changes in global volcanism or weathering trends through OAE3. Identification of OAE3 in a lake system is consistent with lacustrine records of other OAEs (e.g., Toarcian OAE), and underscores that terrestrial environments were sensitive to climate perturbations associated with OAEs. Additionally, the relatively radiogenic Os i chemostratigraphy and XRF data confirm that the Qingshankou Formation was deposited in a non-marine setting. Organic carbon-rich intervals preserve no compelling Os i evidence for marine incursions, an existing hypothesis for generating Member 1's prolific petroleum source rocks. Based on our results, we present a model for water column stratification and source rock deposition independent of marine incursions, detailing dominant biogeochemical cycles and lacustrine organic carbon burial mechanisms.

The Tonian-Cryogenian System boundary is to be defined at a GSSP (Global Boundary Stratigraphic Section and Point) beneath the first evidence of widespread glaciation. A candidate lies within the Dalradian Supergroup of Scotland and Ireland, which is least deformed and metamorphosed in Argyll, western Scotland. We present new stratigraphic profiles and interpretations from the Isle of Islay and the Garvellach Islands, update the chemostratigraphy of the Appin Group Tonian carbonates underlying the thick (ca. 1 km) glacigenic Port Askaig Formation (PAF) and demonstrate an environmental transition at the contact. The Appin Group forms a regionally extensive, >4 km-thick, succession of limestones, shales and sandstones deposited on a marine shelf. On Islay, the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure, oolite, stromatolitic dolomite and intraclastic microbial mounds. Significantly deeper erosion at the unconformity at the base of the overlying PAF is demonstrated in the southern section. Carbonate facies show a gradual decline in δ 13 C VPDB from +5 to +2‰ upwards. In NE Garbh Eileach (Garvellach Islands), a continuously exposed section of Appin Group carbonates, 70 m thick, here designated the Garbh Eileach Formation (GEF), lies conformably beneath the PAF. The GEF and the GEF-PAF boundary relationships are re-described with new sedimentological logs, petrological and stable isotope data. Interstratified limestone and dolomicrosparite with δ 13 C of −4 to −7‰ (a feature named the Garvellach anomaly , replacing the term Islay anomaly ) are overlain by dolomite in which the isotope signature becomes weakly positive (up to +1‰) upwards. Shallow subtidal conditions become peritidal upwards, with evidence of wave and storm activity. Gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the GEF. The basal diamictite (D1) of the PAF is rich in carbonate clasts similar to slightly deeper-water parts of the underlying succession. D1 is typically several metres thick with interstratified sandstone and conglomerate, but dies out laterally. Scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft-sediment deformation is interbedded with carbonate below and above D1. Dolomite beds with derived intraclasts and gypsum pseudomorphs are found above D1 (or equivalent position, where D1 is absent). Published and new Sr isotope studies, including successive leach data, demonstrate primary Tonian 87 Sr/ 86 Sr values of 0.7066–0.7069 on Islay, decreasing to 0.7064–0.7066 in the younger GEF limestones on the Garvellachs, with 1700–2700 ppm Sr. Other typically Tonian characteristics of the carbonates are the Sr-rich nature of limestones, molar tooth structure, and dolomitized peritidal facies with evidence of aridity. Seabed surveys suggesting uniformly-dipping strata and shallow borehole core material illustrate the potential for extending the Tonian record offshore of the Garvellachs. A candidate Tonian-Cryogenian GSSP is proposed on Garbh Eileach within the smooth δ 13 C profile at the cross-over to positive δ 13 C signatures, 4 m below the first occurrence of ice-rafted sediment and 9 m below the first diamictite. Although lacking radiometric constraints or stratigraphically significant biotas or biomarkers, the Scottish succession has a thick and relatively complete sedimentary record of glaciation, coherent carbon and strontium chemostratigraphy, lateral continuity of outcrops and 100% exposure at the proposed boundary interval.

The use of facies type, facies succession, and stacking pattern as proxies for assessment of habitat heterogeneity and dynamics was examined in this chapter. This approach may supplement the conventional assessment methods of habitats, which are often subjective, tenuous, discordant, and suffer from various biases. It was followed by the examination of stratigraphic variations of sediment geochemistry to characterize facies types and environmental settings. As the stratigraphic record is the outcome of an exogenic system consisting of geologic setting, changes in sea-level, changes in geochemical reactions between the sea and the earth, climate and processes of sediment formation, the ensuing sedimentary records show differences in bulk chemistry as a result of changes in different combinations of minerals, either bioproduced or brought into the depocenters, and neoformed during post depositional times. The results have shown the utility of facies characteristics, facies succession, and stacking pattern as visualized through chemostratigraphy as a tool for documenting habitat heterogeneity and dynamics.

The Permian and Triassic chronostratigraphic scales provide the basic temporal framework for understanding all geological and biotic events that took place during most of the Pangean interval of Earth history. Nearly two centuries of research have developed these chronostratigraphic scales, and their current integration with radioisotopic ages, magnetostratigraphy, and chemostratigraphy continues to refine and improve the resolution of geological age assignments and correlation during the Permo-Triassic. In 1841, Murchison coined the term Permian for strata in the Russian Urals. Recognition of the Permian outside of Russia and Central Europe soon followed, but it took about one century for Permian to be accepted globally as a distinct geological system. The work of the Subcommission on Permian Stratigraphy began in the 1970s and resulted in the current chronostratigraphic scale of nine Permian stages in three series: Cisuralian (lower Permian)—Asselian, Sakmarian, Artinskian, Kungurian; Guadalupian (middle Permian)—Roadian, Wordian, Capitanian; and Lopingian (upper Permian)—Wuchiapingian and Changhsingian. The first geological studies of Triassic rocks began in Germany in the late 1700s and culminated in 1834 when Friedrich August von Alberti coined the term Trias for the Bunten Sandsteins, Muschelkalk and Keuper, a thick succession of strata between the Zechstein and the Lias. Recognition of the Trias outside of Germany soon followed, and by the 1860s Austrian geologist Edmund von Mojsisovics began constructing a detailed Triassic chronostratigraphy based on ammonoid biostratigraphy. In 1895, Mojsisovics and his principal collaborators, Wilhelm Waagen and Carl Diener, published a Triassic timescale that contains most of the stage and substage names still used today. The work of the Subcommission on Triassic Stratigraphy began in the 1970s and resulted in current recognition of seven Triassic stages in three series: Lower Triassic—Induan, Olenekian; Middle Triassic—Anisian, Ladinian; Upper Triassic—Carnian, Norian, and Rhaetian. Further biostratigraphic development of the Permian and Triassic chronostratigraphic scales needs to focus on the remaining formal definition of some of the stages as well as definition and characterization of the substages, as these will provide a much more detailed basis for subdivision of Permian and Triassic time than do the stages. This chapter briefly reviews the development and current status of the Permian and Triassic chronostratigraphic scales.

Organic carbon (OC) isotope profiles from four sections of the Early Cretaceous continental Yellow Cat Member (YCM) of the Cedar Mountain Formation are presented to explore the constraints of studying and correlating continental sections. A significant body of research demonstrates that some continental chemostratigraphic profiles record global perturbations of the carbon cycle and specifically globally correlative carbon isotope excursions that can be correlated with well-constrained marine carbon isotope records to give some chronostratigraphic constraint. However, this is not always straightforward. Here we present our findings of four sections of the YCM and discuss some caveats of using continental OC isotope records, with an insight into some of the possible solutions. In this study a regionally extensive calcrete holds the key to resolving correlation of poorly reproducible carbon isotope profiles. Here, we tentatively correlate the YCM to the Barremian-lower Aptian.

Departamento de Ciencias de la Tierra, Universidad de Zaragoza, España, Instituto Geológico y Minero de España, España

A pioneer δ13Corg study through the upper Sandbian and Katian (Upper Ordovician) succession in the Rostanga 1 drill core in the classical geological outcrop area at Rostanga in southernmost Sweden produced a wealth of new carbon isotope data which are useful for local and regional correlations. Among the Upper Ordovician positive δ13C excursions, the Guttenberg (GICE), Waynesville (Saunja), Whitewater (Moe), Paroveja, and Hirnantian (HICE) isotopic carbon excursions are recognized but the Kope (Rakvere) δ13C excursion is missing, suggesting a stratigraphic gap. All these isotopic excursions are tied closely to biostratigraphy, especially graptolite biostratigraphy, and in the case of the Waynesville (Saunja) and Whitewater (Moe) excursions, for the first time anywhere in the world. The Rostanga GICE δ13Corg curve from the upper Sularp Shale shows a striking similarity to that of the Katian GSSP in Oklahoma, suggesting the potential of trans-Atlantic correlation. Based on a projection from the Katian GSSP, the previously poorly constrained position of the base of the Katian in southern Sweden appears to be in the uppermost Sularp Shale in strata of the upper Diplograptus foliaceus Zone. Previous interpretations of the relations between K-bentonite successions in southern Scandinavia are somewhat revised and the Kinnekulle K-bentonite is recognized for the first time in Scania. Based on new radiometric dates, this very prominent and widespread ash bed appears to be slightly older than the Deicke and Millbrig K-bentonites in eastern North America.

During the early Silurian, widespread anoxic graptolitic black shales developed predominantly on the northern margin of Gondwana. These black shales are attracting a considerable amount of scientific interest, as it is nowadays hypothesized that their genesis might be closely related to major changes within the paleogeographical configuration of continents, the oceanic circulation patterns, and also drastic global climatic perturbations. Furthermore, these black shale successions can be of highest economic significance, as some form the source rocks of the world's major oil reserves. For the present study, high-resolution whole rock geochemical data obtained from an early Silurian black shale source rock analogue (Formigoso Formation, Cantabrian Mountains, NW, Spain) are used to develop a chemostratigraphic framework and to reconstruct and further constrain the paleoenvironmental conditions that prevailed at the time of deposition. These chemostratigraphic interpretations and paleoenvironmental reconstructions are used, together with the results of previously published studies, to develop a detailed generic depositional model for the black shale successions of the Cantabrian Basin. This analogue model is compared and contrasted to previously proposed models. The new high-resolution chemostratigraphic data are combined with detailed biostratigraphic information from the published literature. The present study demonstrates that chemostratigraphic methods provide not only complementary but even vital information, especially where biostratigraphic data are absent or scarce, for larger scale intra- and interbasinal correlations.

Pedogenic nodules, calcitic shells, dispersed organic carbon and bulk rocks affected by low diagenesis are judged to be reliable tools for carbon-isotope chemostratigraphy. Up to now no systematic study has been carried out to check the reliability of fossil wood material for carbon-isotope chemostratigraphy in terrestrial settings. The 235-m thick Wealden facies sediments of the Danube-Bouchon quarry at Hautrage (Hautrage Clays Formation, Mons Basin, Belgium) encompass dark to grey clays and sands, rich in organic matter and coalified-charcoalified fragments of fossil wood, deposited in an alluvial plain during middle Barremian to earliest Aptian. We measured and compared the carbon-isotope ratios of 110 levels of the stratigraphic succession for dispersed organic carbon (δ13CDOC), and fossil wood (δ13CWOOD) collected in the same geological level. In the whole succession, the averages of δ13CDOC and δ13CWOOD have a significant difference of about 0.9‰. The δ13CWOOD is usually heavier than the δ13CDOC, which is consistent with measurements on different constituents of modern trees (branches versus leaves and tissues). In one single stratigraphic level, the variability of δ13CWOOD is much higher (up to 7.3‰) than that of δ13CDOC (0.4‰). Four main causes may explain these results. Firstly, the δ13CDOC averages the isotopic signal of different compounds and tissues (such as leaves, seeds, cuticles) as they become mixed and dispersed. The δ13CWOOD reflects the carbon-isotope ratio of a small part only of one single tree, which is a complex system with δ13C variations over a range of 4‰. Secondly, there is strong δ13C variability between different species of plants. In Hautrage, several gymnosperm genera were collected (including Podocarpoxylon, Taxodioxylon, Brachyoxylon, and Thujoxylon) and numerous fern taxa. Thirdly, coalification and charcoalification can affect the δ13C of the DOC and the various kinds of woods in a different way. Fourthly, the wood fragments may be reworked several times from more ancient geological levels, especially in the alluvial plain environment of Hautrage where thick levels of fluviatile coarse sand deposits are observed. However, in the whole succession, both δ13CWOOD and δ13CDOC curves show similar trends. This suggests that carbon-isotope curves on fossil wood can be matched to carbon-isotope curves on DOC. For the whole trend fossil wood is a relatively good chemostratigraphic tool when sufficient samples are measured in the succession. Whenever possible both control of the wood taxa, and estimation of degree of (char)coalification are however recommended. In one single level, charcoal has more stable δ13CWOOD values than δ13CWOOD of coalified fragments. The δ13C positive trend can be due to several causes, including global pCO2 variations and/or regional changes and/or local environmental conditions in the alluvial plain. If global, the dating of the Hautrage succession may be refined to the late Early Barremian-early Late Barremian by matching palynological and carbon-isotope chemostratigraphical data. © 2010 Elsevier B.V. All rights reserved.

Early diagenetic silicification and phosphatization of the Ediacaran Doushantuo Formation (ca. 635 to 551 Ma) in South China offer extraordinary taphonomic windows into the early evolution of multicellular eukaryotes, including various algal groups and potentially animals. In order to understand how the ecological and taphonomic distribution of these Ediacaran eukaryotes was controlled by oceanic redox conditions, it is critical to reconstruct the redox architecture of the sedimentary basin. Recently two alternative redox models have been proposed to account for the geochemical and sedimentary features of the Doushantuo Formation. One argues that the unit was deposited on a continental margin where a metastable sulfidic wedge was dynamically maintained by a sulfate concentration gradient between shelf and basinal environments. The other contends that the sulfidic water mass was largely restricted to the intra-shelf basin behind a rimmed margin. These two models make different predictions about the stratigraphic completeness and correlation of the Doushantuo Formation. To test these predictions, we generated high-resolution time-series trends of multiple isotopic and elemental tracers, including δ34S, 87Sr/86Sr and Ce/Ce*, to facilitate an integrated chemostratigraphic correlation between inner shelf (Xiaofenghe), intra shelf (Jiulongwan), and outer shelf (Yangjiaping and Zhongling) sections. Our correlations suggest that both the inner and outer shelf sections are stratigraphically incomplete relative to the intra shelf section. The euxinic wedge model should be reconsidered insofar as it is based on a miscorrelation between sections. Viewed from our revised chemostratigraphic framework, euxinic conditions on the platform appear to have been largely restricted to the intra shelf basin. Carbonates in the upper Doushantuo Formation at Jiulongwan and their stratigraphic equivalents are characterized by a profound negative carbon isotope anomaly (i.e., the Shuram Excursion) coincident with a drop in pyrite sulfur isotope values and a significant rise in 87Sr/86Sr from 0.7080 to 0.7090. The integrated stratigraphic data from South China suggest that the onset of the Shuram Excursion is associated with enhanced oxidative continental weathering that delivered radiogenic strontium, as well as sulfate, to the Ediacaran basin.

Sediments are reliable records of changes in physical, chemical, and biological conditions that take place before, during, and after their deposition and express the changes through constituent mineralogical and thus geochemical compositions. Individual sedimentary events create more or less homogeneous bulk chemistry of sediments at varying temporal and spatial scales. Distinguishing these homogeneities and for classification of stratigraphic records and correlation of the strata at varying spatiotemporal scales is emerging to be a reliable method of stratigraphy and is termed as chemostratigraphy a la chemical stratigraphy. This method helps stratigraphic correlation with ease where other formal stratigraphic methods have limitations or fail to achieve required spatiotemporal resolution. The study of geochemical variations in stratigraphic context has gained importance since the 1980s. Chemostratigraphy is, thus relatively a younger branch of geosciences. Attempts on distinguishing depositional units at varying spatiotemporal scales (from local to global and from tidal cycles to few tens of millions of years) have been influenced to a larger extent by the sequence stratigraphic concepts. Contemporaneous developments in sophisticated instrumentation for fast, accurate, and less expensive geochemical analyses have also contributed to the popularity and applications of chemostratigraphy. From a humble beginning of identification of similar geochemical values and similar pattern of geochemical profile, chemostratigraphy has traveled a long way. Currently, a wide variety of techniques and data from other subdisciplines of geosciences are used for distinction/recognition and correlation chemozones/geochemically distinguishable depositional units. Yet, chemostratigraphy consists of vaguely defined and often misleading and/or overlapping terminologies. Through an extensive review of published literature, this chapter attempts to enlist these terminologies namely, chemostratigraphy, chemical stratigraphy, geochemical fingerprinting, geochemical signature, geochemical fingerprint, geochemical marker, geochemical proxy, excursion, shift, fluctuation, perturbation, anomaly, trend, chemostratigraphic index, chemozone, chemochron, resolution, and scale of correlation and provides definitions/explanations. This attempt is made for initiating discussion among the practitioners that may lead to consensus on definitions and standardized usage. Despite, fulfilling the criteria required for any standard stratigraphic method and finding its applications in many different fields, this method/tool remains to be formally given its due. Elucidation of the traits and enlisting the terminologies of chemostratigraphy with the criteria for formal recognition prescribed by International Stratigraphic Commission suggests that chemostratigraphy deserves to be formalized as an independent stratigraphic method.

This study focuses on the geochemistry of the Permian–Triassic boundary (PTB) of three wells in the Persian Gulf region. The δ 18 O shows a negative shift at the PTB that is due to meteoric diagenesis. The δ 13 C shows a decrease to about −1.4‰ in this event, which is comparable with the other Permian–Triassic sections elsewhere. The negative δ 13 C excursion could be used as a marker and represents an input of the 12 C to the sediments. The subsequent gradual positive shift after the boundary is related to the biotic recovery following the end-Permian mass extinction. Changes in the Th/U ratio of the studied wells indicate an anoxic environment at the end-Permian time, followed by a sudden increase of oxygen content at the PTB. This was coupled with the increasing PCO 2 and the presumably acidic conditions that were increasing toward the PTB. The Sr concentration shows a decreasing trend toward the PTB indicating normal acidity and PCO 2 conditions at the Dzhulfian (Wuchiaingian), and change of acidic conditions below the PTB in Dorashamian (Changhsingian) are inferred from the deposition of aragonite or calcite as primary dominant mineral, respectively. After this boundary, both redox and acidic conditions have been changed, and the environment was favorable for biotic restoration. Concurrent with these situations, the sea level was falling and reached its lowest level at the end-Permian time as inferred from the increase in Fe elemental content and Sr isotope as well as the decrease in oxygen isotope data.

Correlation of the base of the Silurian System, which is defined by graptolite biostratigraphy, with the non-graptolitiferous carbonate shelf successions has been complicated due to rapid environmental changes and widespread unconformities of glacioeustatic origin in the end-Ordovician interval. The Hirnantian carbon isotope excursion (HICE) occurring in the Hirnantian Global Stage at a short distance below the Ordovician/Silurian boundary has been widely used in global and regional chemostratigraphic correlation of this boundary interval. In the present study we analyzed the δ 13 C trends in carbonates of the Ordovician/Silurian boundary interval from the drillcore sections of the Pandivere area in central Estonia. Comparison of the high-resolution Hirnantian and Rhuddanian δ 13 C curves suggests some changes in the traditional stratigraphic correlation scheme of Estonia. The new data demonstrate that the HICE crosses the traditional Ordovician/Silurian boundary, which should therefore be placed higher up in the Baltoscandian succession, in the lower part of the Juuru Regional Stage. The base of the Juuru Stage, traditionally correlated with the system boundary, has been defined by shelly fossil data. The second phase of the global Hirnantian extinction was followed by a slow faunal recovery with the appearance of postextinction biota in late Hirnantian that obviously included some “Silurian-type” shelly fossil groups. For that reason, the traditional position of the Ordovician/Silurian boundary in many regions with non-graptolitiferous successions, established by shelly fauna should be critically reevaluated.

Chemostratigraphy is concerned with the characterization and correlation of strata based on geochemical composition of the sediments, rocks, and rock components of interest. The geochemical data of biogenic carbonates are susceptible to time averaging and compositional averaging. The time-averaged assemblages are due to the temporal mixing of the fauna and may vary considerably in scale. For most geological records it is estimated to be hundreds to thousands of years. Compositional averaging is due to spatial mixing and variation in geochemistry of the shells and tests caused by varying life processes of the calcifying organisms. This chapter discusses how these two processes constraint the geochemical data in stratigraphic interpretation and correlation particularly at submillennial scales.

We report results of some of the latest cutting-edge research on traditional (C, O, S, N, Sr) isotope stratigraphy and some newer isotope systems (e.g., B, Ca, Mo, Fe, Cr, N), and elemental or elemental ratio (e.g., V, Mo, Hg, Rb/K, V/Cr, Zr/Ti, Mg/Ca, Mn/Sr, I/Ca) stratigraphy. The latter, in parallel with isotope stratigraphy, could be used as potential tracer for glacial events, buildup of volcanic gases (e.g., CO2) during glaciations, role of volcanism in mass extinction, salinity variation, redox state of the ocean and atmosphere, and provenance, among other applications. This paper also presents review on studies that are broad in both space and time, highlighting chemical events from the Archean to the Cenozoic. Special attention is given to Paleoproterozoic and Neoproterozoic isotope chemostratigraphy and problems including the reliability of the use of carbon isotopes for Neoproterozoic stratigraphic correlation. Some attention is also devoted to the early Paleozoic, K–T boundary, and Paleogene climatic and biogeochemical changes in the light of isotope chemostratigraphic studies.

The Lower Jurassic carbonate series of the Lusitanian Basin (Portugal), due to their remarkable exposure and high quality outcrops, are currently regarded as a pivotal point to the comprehension of the less-known offshore basins located along the Atlantic Margin. This study presents a detailed sedimentological and biostratigraphical framework and the carbon and oxygen isotopic record of one of the main organic-rich intervals of the Lusitanian Basin, the marly limestones with organic-rich facies member of the Vale das Fontes Formation (Pliensbachian). We report the occurrence of secular δ13C trend of the Lusitanian Basin concordant with the (second-order) Pliensbachian transgressive–regressive facies cycle. An overall increase in carbon isotopic record with transgression, reaching its maximum just above the maximum flooding interval and enhanced organic matter preservation is also observed. When compared with the defined third-order sequences, a transient δ13C increase during the onset of transgression is recognizable. Higher frequency variations in the carbon isotopic record can possibly be traced along the offshore studied sections and are interpreted to be the reflections of local controls which may eventually outpace the regional variation.

Based on bio and lithofacies characteristics and occurrences of hardground surfaces, iron-rich ooids, iron crusts, and shell lags, the Dhosa Oolite member deposited during Oxfordian in the Kachchh Basin of western India is traditionally considered to be equivalent of Fe-oolitic deposits formed as a result of eustatic sea-level maximum during Callovian-Oxfordian in southern Poland, Madagascar, France, and England. The regionally extensive and unique lithological characteristics of the Dhosa Oolite member made this member a regional marker interval. This member is also in use for correlation as marker interval in adjacent basins too. Yet, correlation of this member with regional and global equivalents is often mired with skepticism due to its condensed nature, occurrences of omission and hardground surfaces, mixed fauna typical of many biozones, and resedimented nature of sediments. In order to address this issue, this paper documents chemostratigraphic characteristics of this member to identify synchronicity of chemical signatures with regional and global signals. The geochemical profiles constructed with the present study recognized a major sea-level cycle spanning from upper part of the Dhosa Sandstone member that reached its zenith near the top of the Dhosa Oolite member. Individual short-term fluctuations represented by positive excursions of P and negative excursion of Ba were recognized within the studied sections. These excursions are regionally recognizable, and sedimentation pattern in the basin was found to be coupled with climate-sea-level fluctuations (as indicated by corresponding variations in source area weathering and detrital influx). However, correlating the Oxfordian oolite deposit of the Kachchh Basin with coinciding Fe-oolite deposits elsewhere requires adequate precautions.

The geodynamic reconstructions require accurate age determinations for the ancient sedimentary basins. Correlations between sedimentary deposits of different blocks of ancient oceans allow reconstructing the history of their development most accurately. This study is concerned with the investigations of Sr and C isotopic composition of Ediacaran and Cambrian carbonates of the Tuva–Mongolian and Dzabkhan (both in Mongolia now) continental blocks. These individual continental blocks evolved in the course of intensive carbonate sedimentation during the Late Neoproterozoic. At the base of these sections are deposits of glacial origin. Minimally altered carbonates (identified based on petrographic and geochemical criteria) of the Tuva–Mongolian block have Sr isotope values of 0.7073–0.7086 and δ 13 С values varying from −1.7‰ to +5.0‰. The primary 87 Sr/ 86 Sr ratios for Dzabkhan carbonate are 0.7072–0.7079 for Tsagaan Oloom Formation (δ 13 С varies from +3‰ to +14‰) and 0.7084–0.7086 for Bayan Gol Formation. We compared the 87 Sr/ 86 Sr curves of different coeval sections with the data generated by the present study and used geological data to establish that the deposits under study are accumulated asynchronously from the early Ediacaran (600 Ma) to middle of Cambrian (520 Ma).

Neoproterozoic banded iron formations (BIFs) are not restricted to the middle Cryogenian, c. 715 Ma glaciation, occurring in Tonian, Cryogenian, and Ediacaran successions. Many Neoproterozoic BIFs were deposited in glacially influenced settings, such as the Rapitan Group (Canada), Jacadigo Group (W Brazil), Chuos, and Numees Formations (Namibia) and Holowilena Ironstone (Australia). However, many occurrences are not related to glacial processes and can be assigned to the Algoma and Lake Superior types. Neoproterozoic Algoma-type BIF includes the Wadi Karim and Um Anab (Egypt), the correlative Sawawin BIF (Saudi Arabia), and the Jucurutu Formation of the Serido Belt (NE Brazil). Lake Superior type BIFs are represented by the Tonian Shilu Group (South China) and the late Ediacaran Arroyo del Soldado Group (Yerbal and Cerro Espuelitas formations, Uruguay). Useful chemostratigraphic tools for the study of BIFs include rare earth element distribution, especially Eu and Ce normalized concentrations, iron speciation, and Nd and Cr isotopes (δ53Cr). Whereas Rapitan type BIFs exhibit no Eu or Ce anomalies, the Algoma-type Neoproterozoic BIFs show both. Positive δ53Cr values characterize glacially influenced BIFs, and differentiates them from nonfractionated, mantle-like δ53Cr values of Algoma type BIF. The most positive δ53Cr values occur in the open-shelf, Lake Superior type BIF, especially that of Ediacaran age. We suggest that glaciation was not a prerequisite for deposition of BIF in the Neoproterozoic, and that hydrothermal activity related to Rodinia rifting played the key role in their reappearance after the Mesoproterozoic gap. Their deposition has more to do with the return to ferruginous conditions in the oceans than with near-global glaciation.

To understand the paleo-redox conditions that occurred during the Albian-Danian, we have analyzed major and trace elements from limestone samples collected from three sections of the Cauvery Basin. In the Vadugarpettai quarry section, coral algal limestone (CAL) and bedded limestone show small variations in CaO content (54.4–55.5%; 51.3–54.1%, respectively) than marl and gray shale (GS) (31.9–49.7%; 26.9–40.3%, respectively). In the Vellipirangiyam quarry section, oyster Gryphaea limestone (OGL) shows larger variations in CaO content (42.5–53.9%) than Inoceramus limestone and fossiliferous limestone (52.00–52.50%; 52.70–52.80, respectively). The concentrations of immobile trace elements (Zr and Th) varied significantly between different litho-units of the sedimentary rocks of Albian-Danian age. In addition, Al2O3 shows a positive relationship with immobile trace elements such as Zr and Th, suggesting a terrigenous origin for these elements. Enrichment of U and V contents is higher in the GS and particular intervals of CAL and marl bedded limestone (MBL) of the Vadugarpettai quarry section, lower and upper parts of the OGL of the Vellipirangiyam quarry section, and lower and middle parts of the limestone sequence of the Periakurichchi quarry section. The GS and lower part of MBL (Vadugarpettai quarry section); lower and upper parts of the OGL (Vellipirangiyam quarry section); and lower, middle, and upper parts of the Periakurichchi quarry section also show enrichment of Mo. Furthermore, high values of U/Th were noticed in the CAL and MBL of the Vadugarpettai quarry section, OGL of the Vellipirangiyam quarry section and certain intervals of the Periakurichchi quarry section. Such variations in U, V, and Mo contents and the U/Th ratio in the studied sections suggest that the Cauvery Basin experienced oxic to suboxic-anoxic conditions during Albian-Danian.

The environmental and climatic conditions prevalent during the transition from Cretaceous–Tertiary boundary (KTB) that caused extinction of marine and terrestrial fauna have been among the intensively studied geological phenomena. Cataclysmic meteoritic impact, Deccan volcanism, sea level fluctuation, acid rain, ocean acidification, contamination of marine and terrestrial ecosystems and atmosphere etc., by sulfur and methane are proposed to be the cause(s) of the extinction. In addition, the pattern of extinction itself, namely, sudden extinction due to extra-terrestrial catastrophic event and stepwise extinction due to multiple events and processes, is debated by the geoscientists. The Cauvery Basin, South India, contains more or less complete stratigraphic record of Barremian–Danian and thus has been studied by many researchers for the cause(s) of extinction pattern across K–T. This chapter presents the initial results of recently identified continuous K–T section located near Niniyur village in the Cauvery Basin and discusses the inferences in the light of regional and global models proposed as to the cause(s) of the extinction pattern. Results of the study indicate the predomination of influence of sea level fluctuations (which in turn might have been influenced by Deccan volcanism) over the depositional pattern of the Cauvery Basin. In addition, prevalence of many events namely off-seasonal floods, sharp, and sudden climatic reversals, destabilization of gas hydrates, and release of methane, all of which predating KTB and coincidental with similar events in geographically widely separated stratigraphic sections as indicated by geochemical anomalies are also recorded by the present study. Thus, present analysis supports the interpretation of regional and global scale, multicausal stepwise extinction pattern across KTB.

Litho-, bio-, and chemostratigraphy of the Cretaceous forearc basin sediments exposed in Hokkaido, northern Japan allow a synthesis of the faunal, sedimentological, and environmental history of the north-west Pacific margin. Although the succession, named the Yezo Group, has yielded an abundant record of mid- to late Cretaceous invertebrates, monotonous lithologies of sandstone and mudstone, showing occasional lateral facies changes, have caused confusion regarding the lithostratigraphic nomenclature. Based on our wide areal mapping of the sequence, and analysis of litho- and biofacies, a new lithostratigraphic scheme for the Yezo Group is proposed. In ascending order, the scheme is as follows: the Soashibetsugawa Formation (Lower Aptian mudstone unit); the Shuparogawa Formation (Lower Aptian–lower Upper Albian sandstone-dominant turbidite unit); the Maruyama Formation (lower Upper Albian tuffaceous sandstone unit); the Hikagenosawa Formation (Upper Albian–Middle Cenomanian mudstone-dominant unit); the Saku Formation (Middle Cenomanian–Upper Turonian sandstone-common turbidite unit); the Kashima Formation (Upper Turonian–Lower Campanian mudstone-dominant unit); and the Hakobuchi Formation (Lower Campanian–Paleocene shallow-marine sandstone-conglomerate unit). In addition, we designate two further lithostratigraphic units, the Mikasa Formation (Upper Albian–Turonian shallow-marine sandstone-dominated unit) and the Haborogawa Formation (Middle Turonian–Campanian shelf mudstone/sandstone unit), which correspond in age to the shallower facies of the Saku and Kashima formations, respectively. Despite a lack of so-called “black shales”, because of siliciclastic dilution, our stratigraphic integration has revealed the horizons of oceanic anoxic events (OAEs) in the Yezo Group. The OAE1a horizon in the Soashibetsugawa Formation is characterized by a lack of foraminifers, macrofossils and bioturbation, and a prominent positive excursion of δ 13 C org . A significant hiatus during the late Aptian and early Albian removed the OAE1b horizon. The OAE1c horizon in the Maruyama Formation shows a distinct negative excursion of δ 13 C org with a concomitant high productivity of radiolarians. The OAE1d horizon in the middle part of the Hikagenosawa Formation consists of weakly laminated, pyrite-rich mudstone. Planktonic and calcareous benthic foraminifers are absent, whereas radiolarians are abundant above the OAE1d horizon. The mid-Cenomanian event (MCE) horizon is identified at the top of the Hikagenosawa Formation. Stepwise extinction of calcareous benthic foraminifers and a decrease in radiolarian diversity become apparent above the MCE horizon. In the study area, the OAE2 horizon has been well documented, and is placed in the middle part of the Saku Formation.

Integrated analysis of the sedimentology, stratigraphy, and chemostratigraphy of the uppermost Devonian Chaffee Group of Colorado reveals the presence of two regionally extensive unconformity surfaces associated with globally recognized extinction/eustatic events. The contact between semi-restricted, marginal marine, mixed siliciclastic–carbonate deposits of the Parting Formation and open marine carbonate of the Dyer Formation is a major marine flooding surface across western Colorado. This flooding surface rests at the top of an ~ 5 m thick, transgressive, cross-bedded, shoreline sandstone unit that locally overlies a 2.5-m-thick paleokarst breccia. δ^(13)C values shift lighter across the formation contact, in some cases by as much as 5‰. Oxygen isotopic values are extremely variable between measured stratigraphic sections, in cases invariant across the contact, and in other cases covarying with the δ^(13)C values. At Ouray, CO, δ^(18)O covaries with δ^(13)C throughout the section, and reaches extreme values (< − 30‰) below the unconformity. An isotopic shift in rocks of this age in Utah, coined ALFIE, was previously correlated to the Parting–Dyer contact. This study demonstrates that the carbon and oxygen isotopic record of ALFIE is highly variable across western Laurentia, and that important carbonate chemostratigraphic variations result from diagenesis that is clearly linked to a regional unconformity and associated relative sea-level fall. This lowstand may be a signal of eustatic fall associated with the Dasberg Event, a late Famennian marine extinction event. Similar isotopic patterns exist for strata below and above a paleokarst breccia in the upper Dyer Formation that we link to the globally significant latest Famennian Hangenberg Event, which includes a eustatic lowstand and subsequent transgression. Similar to the Parting–Dyer contact, both carbon and oxygen isotopes in strata below this regional unconformity surface show the variable nature of diagenetic alteration of carbonate units during lowstand conditions. Our data also suggest that correlatable δ^(13)C chemostratigraphic shifts can be diagenetically produced during lowstands across a regionally widespread (western U.S.) basin, and that these δ^(13)C shifts may be expressed within outcrops that show no macroscopic sedimentological signature of subaerial exposure. This has broad implications for the evaluation of δ^(13)C data in the rock record, particularly the assumption that extensive correlatable isotopic anomalies reflect global marine signatures.

A combined sedimentological, lithological and chemostratigraphical (Mg/Ca, δ13C, δ18O) analysis of the Lower Pliensbachian marl–limestone platform successions exposed along the Asturias coastline (northern Spain) has resulted in the characterization of high-frequency cycles. The highest-order sedimentary cycles (i.e. elementary cycles) are centimeter- to deciemeter-thick alternations of bioclastic and muddy laminated/burrowed facies, which do not match the marl–limestone couplets. They encompass three sedimentary stages: deposition from storm-density currents (bioclastic facies), dominant lateral advection of continental terrigenous mud accumulated on to an oxygen-deficient seafloor (laminated facies), and recovery of bottom oxygenation involving the burrowing of laminated sediments (burrowed facies). The close match between the number of elementary cycles recorded during the Jamesoni Subzone in Asturias and Yorkshire (Northern England) gives support to the idea of the influence of a regional climatic factor (i.e. millennial-scale cyclicity). Decimeter- to meter-scale cycles formed by bundles of elementary cycles are thought to record orbitally driven climatic changes (precession or obliquity, depending on the time calibration considered). Lower hemicycles of bundles are dominated by marls/calcareous mudstones, with decreasing burrowing and eventual preservation of laminated facies. They formed during humid periods, which controlled an increase in freshwater and terrigenous input to the platform and quasi-estuarine circulation promoting bottom-anoxia. Upper hemicycles of bundles are dominated by burrowed and bioclastic limestones, thought to be formed under arid conditions with anti-estuarine circulation and an increase of shallow carbonate production and offshore resedimentation. Chemostratigraphic data from belemnites recorded in the muddy laminated and burrowed facies indicate that significant concomitant shifts in δ13C and δ18O occurred during the lower hemicycles of bundles (i.e., humid periods). Isotopic shifts are interpreted as reflecting changes in the balance between the proximity of the terrestrial sources, the local incursion of deeper cooler waters, the storage of organic matter within sediments, and the re-cycling of organic matter, due to long-term relative sea-level rise., Departamento de Ciencias de la Tierra, Universidad de Zaragoza, España, Unidad de Tres Cantos, Instituto Geológico y Minero de España, España, Museo del Jurásico de Asturias, España

Recent geochronological studies have raised concerns regarding the accuracy of regional and global correlations of Neoproterozoic sedimentary successions using relative dating methods such as carbon isotope chemostratigraphy and glaciogenic diamictite–cap carbonate lithological and geochemical characteristics. Precise and accurate radio-isotopic age constraints for Neoproterozoic sedimentary rocks thus remain a high priority for establishing a reliable Neoproterozoic chronostratigraphy. Here, we present a new Re–Os age of 640.7 ± 4.7 Ma from black shales of the upper Black River Dolomite (Togari Group, northwestern Tasmania) that represents a minimum age for deposition of the immediately underlying, diamictite-bearing Julius River Member. The upper Black River Dolomite Re–Os age is statistically identical to a Re–Os age of 643.0 ± 2.4 Ma previously determined for the Sturtian post-glacial Tindelpina Shale Member (Umberatana Group, Adelaide Rift Complex, southern Australia). Consistent with previous lithostratigraphic and stromatolite biostratigraphic evidence, the Re–Os ages suggest broadly coeval deposition of the Julius River Member and Sturtian diamictites and overlying organic-rich marine shales. Consideration of the Neoproterozoic geochronological database suggests that “Sturtian”-type diamictite–cap carbonate pairs cannot be used as chronostratigraphic marker horizons for global correlation of the Neoproterozoic rock record.

Carbon- and strontium-isotope data from the Mina Verdun, Arroyo del Soldado and Sierras Bayas groups are summarised and discussed. Mn/Sr ratios and δ 13 C versus δ 18 O crossplots for the Mina Verdun Group at its stratotype show that δ 13 C reflects seawater composition. The δ 13 C curve obtained for this unit suggests a late Mesoproterozoic to Tonian age. Four positive and negative δ 13 C excursions are recorded in the late Ediacaran Arroyo del Soldado Group. The middle Polanco N 1 excursion (−4.5‰ PDB) probably represents a non-snowball glacial event and is correlated to the Shuram–Wonoka anomaly. High-Sr limestones of the Polanco Formation yielded 87 Sr/ 86 Sr ratios between 0.7073 and 0.7086, and show secular variations of an amplitude of 0.0010. Similar δ 13 C and 87 Sr/ 86 Sr values for carbonates of the Sierras Bayas Group allow correlations at the formational level. The Cerro Victoria Formation yielded a δ 13 C curve consistent with an early Lower Cambrian age (

In this review we provide a correlation scheme for Neoproterozoic palaeoclimatic events in southwestern Gondwana based on combined carbon and strontium isotope variations informed by emerging radiometric constraints on glacial deposits. Strontium isotope ratios in particular hold promise as chronostratigraphic tools if well-preserved samples can be identified, and if long-term trends through the Neoproterozoic show a regular progression to more radiogenic values. Based on analyses of high Sr limestone samples from cap carbonate lithofacies, we recognise four discrete glacial events in southwestern Gondwana, including two Sturtian, one Marinoan and one Gaskiers ice age. Notably, the Namibian Maieberg cap carbonate – considered by many to be a Marinoan archetype – sits stratigraphically below a profound positive carbon isotope excursion (called the Huttenberg anomaly) and is correlated using Sr isotope ratios with an identical post-glacial cap in Brazil dated at ca. 740 Ma by Pb-Pb carbonate techniques. If correct, the Pb-Pb age constraint places the Ghaub ice age and its equivalents into the Sturtian epoch.

Carbonate muds deposited on continental shelves are abundant and well-preserved throughout the geologic record because shelf strata are difficult to subduct and peritidal carbonate units often form thick, rheologically strong units that resist penetrative deformation. Much of what we know about pre-Mesozoic ocean chemistry, carbon cycling, and global change is derived from isotope and trace element geochemistry of platform carbonates. Paleomagnetic data from the same sediments would be invaluable, placing records of paleolatitude, paleogeography, and perturbations to the geomagnetic field in the context and relative chronology of chemostratigraphy. To investigate the depositional and early diagenetic processes that contribute to magneitzation in carbonates, we surveyed over 500 core and surface samples of peritidal, often microbially bound carbonate muds spanning the last not, vert, similar 1000 yr and deposited on top of Pleistocene aeolianites in the Triple Goose Creek region of northwest Andros Island, Bahamas. Sedimentological, geochemical, magnetic and ferromagnetic resonance properties divide the sediment columns into three biogeochemical zones. In the upper sediments, the dominant magnetic mineral is magnetite, produced by magnetotactic bacteria and dissimiliatory microbial iron metabolism. At lower depths, above or near mean tide level, microbial iron reduction dissolves most of the magnetic particles in the sediment. In some cores, magnetic iron sulfides precipitate in a bottom zone of sulfate reduction, likely coupled to the oxidation of decaying mangrove roots. The remanent magnetization preserved in all oriented samples appears indistinguishable from the modern local geomagnetic field, which reflects the post-depositional origin of magnetic particles in the lower zone of the parasequence. While we cannot comment on the effects of late-stage diagenesis or metamorphism on remanence in carbonates, we postulate that early-cemented, thin-laminated parasequence tops in ancient peritidal carbonates are mostly likely to preserve syn-depositional paleomagnetic directions and magnetofossil stratigraphies.

The Late Devonian was an epoch of dramatic evolutionary and environmental changes linked primarily with the Frasnian-Famennian (F-F) mass extinction. Current data and ideas support a prolonged, multi-causal nature of the biodiversity crisis, which favor Earth-bound mechanisms rather than a global cosmic catastrophe. The better under-standing of the Late Devonian ocean-climate-biosphere system leads to several questions, and provides an agenda for future research. (1) Magnitude and rank of biotic changes : more detailed biodiversity studies are needed to place the end-Frasnian extinction in its Late Devonian context. In particular, the emerging severity of the end-Givetian and end-Famennian extinctions contrasts with the current overemphasis on the stepwise F-F crisis. (2) Timing of the key boundaries : a lack of radioisotopic dates hampers any estimation of true biodiversity dynamics, and the integrated comparison with reported ages of impact craters and magmatic events. (3) Marine vs. terrestrial events : insight into global ecosystem changes and correlation should be strengthened by chemostratigraphy, exemplified by the carbon isotope link between marine- and land-derived organic materials. (4) High-resolution (bio)geochemical patterns : isotope secular trends are poorly known at the intra-zonal and inter-basin scales, exemplified by prominent carbon isotope shifts across the Lower-Middle Frasnian passage. Further evidence is also awaited to verify cooling (vs. anoxia) pulses as the main stress factor in the F-F and end-Famennian marine settings, as well as climatic feedback with evolving weathering regimes on land and nutrient dynamic in marine realm. (5) Near-equatorial vs. high-latitude domains : refined data from extratropical successions, e.g. from the Kolyma Block, are still awaited. (6) Tectonic and volcanic-activity : an integrated analysis of tectonic and igneous events, possibly triggered by superplume activity. will serve to evaluate any possible link with the Late Devonian biospheric perturbations. (7) Cyclostratigraphical perspective: includes growing research on refined magnetosusceptibility (MS) and various sea-level signatures to test whether they result from variation in Milankovitch frequency orbital variability. In addition, eustatic sea-level trends and their assumed glacioeustatic forcing have only recently been subject to discussion.

The stratigraphic behavior of chemical elements (CaCO3, Mg, Sr, Fe, Mn, Zn, Cu, Ni, Cr, and V) in the Niobrara Chalk in western Kansas were studied using multivariate statistical techniques. The Niobrara Chalk, a sequence of rhythmically deposited carbonate sediments, is characterized by dilution cycles of terrigeneous clay and volcanic ash, which may be recognized as the chemical zone of volcanogenic Mn, in the chemical stratigraphy.

Stable isotope ratios combined with elemental compositions and molecular biomass data provide a powerful tool in Neoproterozoic palaeoenvironmental interpretations. Here, we report the results of an extensive organic and inorganic geochemical study performed in the Ediacaran sedimentary succession of the Corumba Group (CG) from SW-Brazil, deposited in a shallow marine basin in southwestern Gondwana. This sedimentary succession and in particular the Tamengo Formation, a unit bearing metazoan fossils, has been investigated by means of stable isotopes from carbonates (delta C-13(car) and delta O-18) and associated organic matter (delta C-13(ker) and delta N-15(ker)) together with hydrocarbon distribution and concentrations of major, trace and rare earth elements (REE). A short post-glacial delta C-13(car) negative excursion, interpreted as a period of water mixing, is recorded in the cap carbonates overlying diamictites of the Puga Formation, related to Gaskiers or end-Cryogenian glaciation. The overlying Tamengo Formation by contrast, represents a return to redox-stratified conditions in the basin before the Precambrian-Cambrian boundary. Two distinct biogeochemical modes alternate during deposition of Tamengo sediments: 1) an eutrophic, redox-stratified basin well defined by carbonaceous marls from the middle part of the unit but also recorded upwards, at the transition between bioclastic limestones and calcisiltites. 2) An anoxic basin well characterized in the shallow facies, particularly by bioclastic limestones of the upper Tamengo Formation. A positive Delta C-13(car-ker) (Delta C-13(car-ker) = delta C-13(car) - delta C-13(ker)) excursion of similar to 5% in the carbonaceous marls is explained by enhanced primary productivity in surface waters probably related to an increase of pCO(2), nutrient supply and possibly also changes of the primary producer communities. Abundant pyrite, a biomarker distribution characterized by the occurrence of gammacerane and a low Pr/Ph ratio (similar to 0.7) are also remarkable signatures of these facies, most probably associated with a sulfate-reducing microbial consortium in an anoxic and sulfidic (euxinic) environment. However, low concentrations in redox-sensitive trace elements in these fades suggest a largely oxygenated water column, thus constraining the euxinic setting to the sediments and/or bottom waters. The shallow-water bioclastic limestones record higher concentrations of redox-sensitive elements and Sigma REE as well as a positive Ce anomaly supporting reducing conditions. Oxygenated conditions and dominance of eukaryotic algae characterize the overlying Guaicurus Formation. Principal component analysis (PCA) was used to assess the major geochemical associations. The most significant component combines parameters involved in primary production, such as P concentrations and delta C-13(ker) values. The bio-chemostratigraphic variations in this part of SW-Gondwana point to a stratified ocean with oxic surface waters, alternating periods of high and low bioproductivity and anaerobic conditions at the bottom waters, in the aftermath of younger Neoproterozoic glaciations and close to the Precambrian-Cambrian boundary. (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Siliciclastic rocks of the Ruyang Group, southern Shanxi, and the broadly equivalent Gaoshanhe Group, Shaanxi, contain exceptionally well-preserved, large (empty set approximate to 150 mu m) acanthomorphic acritarchs recently interpreted as late Neoproterozoic (Sinian, c. 800-544 Ma) in age. This biostratigraphic interpretation is based on the presence of large acanthomorphs in Sinian successions of South China and elsewhere and the perceived absence of comparable forms in older rocks; it casts doubt on the long-accepted interpretation of Ruyang and correlative rocks as Mesoproterozoic in age (1600-1000 Ma). In contrast, thick marine dolomites in overlying units contain abundant radial fibrous fabrics and a narrow range of delta(13)C values (c. 0+/-1 parts per thousand vs. PDB), features which characterize unambiguously Mesoproterozoic carbonates elsewhere on the North China Platform and on other continents. Age estimates based on petrofabrics and chemostratigraphy are corroborated by a U-Pb zircon age of 999 Ma (no recorded error) for granites which intrude overlying carbonates. Thus, in combination, the available data constrain the Ruyang siliciclastics and overlying carbonates to be older than about one billion years, making Shuiyousphaeridium Yan and other large process-bearing acritarchs from these units among the oldest known distinctly ornamented eukaryotic microfossils., Organismic and Evolutionary Biology