Ediacaran Oceanic Oxygenation may be Older Than Previously Thought

Stratigraphic position of the Ediacaran Miaohe biota and its constrains on the age of the upper Doushantuo δ13C anomaly in the Yangtze Gorges area, South China

Authors:

An et al

Abstract:

The siliceous shale unit that hosts the Ediacaran Miaohe biota in the Yangtze Gorges area, commonly referred to as the Miaohe Member, has an age of 551 ± 0.7 Ma. This unit is thought to be time-equivalent with the Doushantuo Member IV, which marks the top of the upper Doushantuo negative δ13C excursion. New bio-, sequence- and chemostratigraphic studies presented here demonstrate that the Miaohe Member is significantly younger than the Doushantuo Member IV, most likely time-equivalent with the lower Shibantan Member of the Dengying Formation. The new findings indicate that the top of the Doushantuo Formation, i.e., the top of the upper Doushantuo/Shuram δ13C excursion, should be much older than 551 Ma (likely ≥ 560 Ma). The ocean oxygenation event documented from the Doushantuo Member IV black shales should also be older than 560 Ma and predate the Miaohe biota for more than 10 Ma.

The Stratigraphy of Mass Extinctions

The stratigraphy of mass extinction

Authors:

Holland et al

Abstract:

Patterns of last occurrences of fossil species are often used to infer the tempo and timing of mass extinction, even though last occurrences generally precede the time of extinction. Numerical simulations with constant extinction demonstrate that last occurrences are not randomly distributed, but tend to cluster at subaerial unconformities, surfaces of forced regression, flooding surfaces and intervals of stratigraphical condensation, all of which occur in predictable stratigraphical positions. This clustering arises not only from hiatuses and non-deposition, but also from changes in water depth. Simulations with intervals of elevated extinction cause such clusters of last occurrences to be enhanced within and below the interval of extinction, suggesting that the timing and magnitude of extinctions in these instances could be misinterpreted. With the possible exception of the end-Cretaceous, mass extinctions in the fossil record are characterized by clusters of last occurrences at these sequence stratigraphical horizons. Although these clusters of last occurrences may represent brief pulses of elevated extinction, they are equally likely to form by stratigraphical processes during a protracted period (more than several hundred thousand years) of elevated extinction rate. Geochemical proxies of extinction causes are also affected similarly, suggesting that many local expressions of mass extinction should be re-evaluated for the timing of extinction and its relation to environmental change. We propose three tests for distinguishing pulses of extinction from clusters of last occurrences produced by stratigraphical processes.

Using Impacts on Mars to Probe Subsurface Stratigraphy

Using martian single and double layered ejecta craters to probe subsurface stratigraphy

Authors:

Jones et al

Abstract:

Martian craters with fluidized ejecta – including single-layered, double-layered and multiple-layered craters – have been studied extensively, with their formation generally suggested to require some presence of volatiles in the subsurface. However, experimental reproduction of these morphologies, impact modelling, and the occurrence of layered ejecta in putative volatile poor regions suggests that other factors may also play important roles. A recent extensive catalogue of martian impact craters (Robbins, S.J., Hynek, B.M. [2012a]. J. Geophys. Res. 117, E05004) classifies crater ejecta along with their location, diameters and ejecta extents, potentially providing new information on the links between these morphologies and the subsurface. We utilise this catalogue to examine the regional variation in ejecta mobility, onset diameter and the correlation between ejecta mobility and diameter for single- and double-layered ejecta craters on Mars. A simple regional stratigraphic model is developed to explain the observed trends through the viscosity of the layers within the target. Using this model, the potential relative thickness and burial depths of low viscosity layers in the martian subsurface are hypothesised, and compared to other observations and models of subsurface volatiles and how they have varied throughout time.

Revised Chronostratigraphy of Chinle Formation has Implications for Late Triassic Dinosaur Evolution

Revised chronostratigraphy of the Lower Chinle Formation strata in Arizona and New Mexico (USA): High-precision U-Pb geochronological constraints on the Late Triassic evolution of dinosaurs

Authors:

Ramezani et al

Abstract:

The early history of dinosaurs in North America is obscured by an incomplete fossil record, taxonomic uncertainties and speculative correlations of tetrapod-bearing rocks, as well as poor calibration of the Late Triassic time scale. High-precision U-Pb geochronology provides a reliable means of correlating terrestrial rock formations independent of equivocal lithostratigraphy or vertebrate biostratigraphy, and hence the possibility of properly evaluating models for the early radiation and diversification of Dinosauria. Here we present new, high-precision, U-Pb ID-TIMS zircon geochronology from the presumed lowermost strata of the Upper Triassic Chinle Formation of the Colorado Plateau in Southwest United States, including a mean 206Pb/238U date of 219.39 ± 0.16 Ma from the renowned Placerias Quarry Bone Bed in eastern Arizona. The new results prompt revisions to the chronostratigraphy of the lower Chinle and provide a new temporal context for its rich tetrapod fauna.

The oldest documented dinosaurs of North America coexisted with their non-dinosaurian near-relatives for a minimum of 12 m.y., from ca. 223 Ma to ca. 211 Ma, in the Norian. This early dinosauromorph record follows a ca. 6 m.y. period from which no tetrapod fossils have been documented and which was itself preceded by a ca. 10 m.y. depositional hiatus spanning nearly the entire Ladinian and Carnian stages of the terrestrial North America. The supposed late appearance of dinosauromorphs in North America compared to those in South America thus appears to be an artifact of incomplete preservation, as well as unsubstantiated age interpretations. This, together with the conspicuous biogeographic distinctions among the Triassic dinosauromorph assemblages, invalidates a simple diachronous model for the transcontinental radiation of early dinosaurs.

The Jiyuan Tetrapod Fauna of the Upper Permian China

The Jiyuan tetrapod fauna of the Upper Permian of China—2. stratigraphy, taxonomical review, and correlation.

Authors:

Liu et al

Abstract:

Reexamination of the specimens from the Jiyuan tetrapod fauna, shows that this assemblage is dominated by the pareiasaur Honania complicidentata and comprises three chroniosuchian species including Bystrowiana sinica, Jiyuanitectum flatum gen. et sp. nov., and Dromotectum largum sp. nov., one cynodont species and possibly one gorgonopsian. It is roughly correlated to the Ilinskoe Subassemblage of the Sokolki Assemblage of Russia and the Cistecephalus Assemblage Zone of South Africa.

Should the Berriasian Cretaceous Really be the Berriasian Jurassic?

New constraints on the Jurassic–Cretaceous boundary in the High Andes using high-precision U–Pb data

Authors:

Vennari et al

Abstract:

The Jurassic–Cretaceous (J–K) boundary is poorly constrained, and is the only Phanerozoic system boundary that lacks an internationally accepted reference stratigraphic section (GSSP). Precise radio-isotopic U–Pb data are unavailable for the earliest stage of the Cretaceous— the Berriasian. The age of the Jurassic–Cretaceous boundary was based on several assumptions, including the relative duration of ammonite zones, the constant spreading rates of magnetic anomalies, and the extrapolation of Rb–Sr or K–Ar isotopic data. This paper discusses a site in an Andean Basin of Western Gondwana showing the J–K boundary interval with geographically widespread nannofossil markers which are here uniquely combined with precise radiometric dates. The recent finding of a sequence of marine black shales in the High Andes of Argentina, interbedded with ash-fall tuffs, provides important constraints on this boundary. This succession bears calcareous nannofossils and ammonites, which allow correlation with well-established Tethyan floras and faunas in the northern hemisphere. The Tithonian–Berriasian transition in the Andes was recognized on the basis of ammonite zones and nannofossil bioevents for the first time in the southern hemisphere. The new ages obtained are 137.9 ± 0.9 Ma by sensitive high-resolution ion microprobe (SHRIMP), and 139.55 ± 0.09/0.18 Ma by chemical-abrasion isotope-dilution thermal ionization mass spectrometry (TIMS) near the base of the Berriasian. These new ages can be interpreted in two different ways. The first alternative would indicate that the present geological time table is correct and the fossil levels should be late Berriasian. The second alternative is that the J–K boundary is 5 Ma younger than the recently published geological time scale. The authors support the last alternative and propose that the J–K boundary should be close to 140 Ma.

NeoProterozoic to Ordovician Strata in Bhutan

Documenting basin scale, geometry and provenance through detrital geochemical data: Lessons from the Neoproterozoic to Ordovician Lesser, Greater, and Tethyan Himalayan strata of Bhutan

Author:

McQuarrie et al

Abstract:

Detrital zircon (DZ) ages, augmented with εNd(0) and δ13C isotopic values from 18 new and 22 published samples collected from Lesser Himalayan (LH), Greater Himalayan (GH) and Tethyan Himalayan (TH) rocks in Bhutan, support deposition of > 7 km of sedimentary rock in late Cambrian–Ordovician time and provide a stratigraphic framework for the pre-collisional Indian margin. Youngest GH DZ grains become younger upsection from 900 Ma to 477 Ma. Youngest DZ grains in TH samples are ~ 490–460 Ma. Both the LH Jaishidanda Formation (Fm), and the LH Baxa Group overlie Paleoproterozoic LH rocks. The Jaishidanda Fm exhibits distinct populations of youngest DZ peaks, 475–550 Ma, and 800–1000 Ma. The Baxa Group (Manas, Pangsari, and Phuntsholing formations) contains youngest DZ peaks at both 500–525 Ma and 0.9–1.0 Ga. However, most samples from the Baxa Group in western Bhutan contain no grains younger than 1.8 Ga. Samples from the LH Paro Fm, which sits directly under the MCT in western Bhutan, have youngest DZ peaks at 0.5, 0.8, 1.0, 1.7, 1.8 Ga. εNd values generally match DZ spectra, with samples that contain old, youngest grain populations corresponding to more negative εNd signatures. The Paro Fm is an exception where εNd (0) values from quartzite samples are quite negative (− 19 to − 24) whereas the εNd (0) values from interbedded schist contain younger detritus (− 12 to − 17). δ13C values from the Jaishidanda, Paro and Manas formations have δ13C values (− 1.8 to + 6) suggestive of deposition over late Neoproterozoic to Ordovician time. δ13C values from the Pangsari Fm vary from − 2.8 to + 1.8, compatible with deposition in the early- to middle Neoproterozoic. The young, latest Cambrian–Ordovician grains preserved in TH, GH and LH rocks suggest that the late Cambrian–Ordovician orogeny, documented in GH rocks throughout the orogen, served as a significant sediment source in Bhutan.

Huaibei, Huainan, and Feishui Groups are Tonian Neoproterozoic (and may have an interesting vase shaped fossil)

Biostratigraphic and chemostratigraphic constraints on the age of early Neoproterozoic carbonate successions in North China

Authors:

Xiao et al

Abstract:

Thick carbonate successions of Proterozoic age were deposited in the Huaibei and Huainan regions along the southern margin of the North China Block. These successions, including the Huaibei Group in the Huaibei region and the Huainan and Feishui groups in the Huainan region, have been correlated with the Qingbaikou Group which outcrops in the Jixian area of North China and is the eponymous succession of the Qingbaikouan System (traditionally regarded as 1000–800 Ma). Recently, it has been shown that lower Qingbaikouan strata in the Jixian area may be as old as 1300–1400 Ma. By correlation, the Huaibei, Huainan, and Feishui groups may include Mesoproterozoic strata, but these units have also been interpreted as Tonian or Cryogenian–Ediacaran–Cambrian in age. These contradictory age interpretations hamper our ability to explore the rich paleontological and sedimentary records preserved in these rocks and to assess paleogeographic reconstructions. In this report, we describe new microfossils and stable isotope data (δ13Ccarb, δ18Ocarb, δ34SCAS) from the Huaibei, Huainan, and Feishui groups. Possible vase-shaped microfossils from the Jiayuan Formation of the lower Huaibei Group and characteristic early Neoproterozoic acritarchs (particularly Trachyhystrichosphaera aimika) from the Gouhou and Liulaobei formations are consistent with a Tonian age for the Huaibei and Huainan groups. Similarly, carbon isotope trends in the Huaibei, Huainan, and Feishui groups are comparable with Tonian δ13Ccarb patterns in South Australia and Laurentia, with a plateau of moderately positive (1–5‰) values followed by pronounced negative δ13Ccarb excursion in the Gouhou Formation, which may be equivalent to the Bitter Springs anomaly in South Australia. δ34SCAS values of the Huaibei Group are mostly 25–40‰, similar to values from the stratigraphically equivalent Jingeryu Formation in the Jixian area. Overall, the combination of biostratigraphic, chemostratigraphic, and available radiometric data suggests that the Huaibei, Huainan, and Feishui groups are early Neoproterozoic (Tonian) in age

The Middle Permian of North America was Very Dusty

Climatic and Palaeogeographic Significance of Aeolian Sediment in the Middle Permian Dog Creek Shale (Midcontinent U.S.)

Authors:

Foster et al

Abstract:

Middle Permian fine-grained redbeds of Midcontinent North America are analogous to many Permian units globally. They archive an interesting time in Earth history, but the lack of fossils and the fine grain size have confounded attempts to refine the age and depositional setting, respectively. Here we focus on the Dog Creek Shale and correlatives of Oklahoma and Kansas (palaeo-tropical western Pangaea), which are representative of many analogous Permian units across the region and globe, to assess the age, depositional environment, and provenance of siliciclastic material.

These mudstone-dominant units have long been interpreted to record marine deltaic or tidal flat deposition based primarily on the presence of evaporites and an inferred relationship with sandstone units southward. However, the uniform grain size, and occurrence of common palaeosols, together with the lack of typical deltaic attributes such as hyper/hypo-pycnites, proximal deltaic channels, and large-scale upwardly coarsening trends, in addition to the problematic correlation, complicates this interpretation. Sheet-like tabular siliciclastic units thin northward from the Anadarko foredeep (Oklahoma) onto the Anadarko shelf (Kansas), and undergo lateral facies changes into marginal marine evaporites of the San Andres Formation in the Palo Duro Basin (Texas Panhandle). The fine and uniform grain size, massive bedding, and sheet-like geometry indicate that the siliciclastic units are aeolian in origin, but at times were transported by wind and deposited and reworked in mudflats. Abundant Vertisols within the Dog Creek Shale indicate periods of wetting and drying in a low-relief setting. Major detrital zircon age populations reflect a dominantly east to southeasterly Appalachian-Ouachita source, with minor input from derivative sediment from the Ancestral Rocky Mountains to the west and northwest. These data indicate prevailing easterlies, and some westerly and southwesterly winds in western equatorial Pangaea, possibly representing north to south shifting of the Inter-Tropical Convergence Zone (ITCZ), likely associated with monsoonal circulation. The predominance of aeolian-transported material and its capture in a series of mudflats and soils indicates that midcontinent North America (western equatorial Pangaea) formed a major sink for large volumes of atmospheric dust in middle Permian time, quite unlike the modern and recent tropics.

A Maastrichtian Through Paleogene (?) Section on Vega Island, Antarctica

Stratigraphy and vertebrate paleoecology of Upper Cretaceous–?lowest Paleogene strata on Vega Island, Antarctica

Authors:

Roberts et al

Abstract:

The Upper Cretaceous (Maastrichtian) Sandwich Bluff Member of the López de Bertodano Formation is well exposed on Vega Island in the James Ross Basin off the northeastern coast of the Antarctic Peninsula. Although this unit is one of the richest sources of end-Cretaceous vertebrate fossils in Antarctica, it is also one of the least sedimentologically and stratigraphically characterized units in the basin. New facies and stratigraphic analyses of the Sandwich Bluff Member and the underlying Cape Lamb Member of the Snow Hill Island Formation were performed in tandem with intensive prospecting for fossil vertebrates and stratigraphic assessment of historic paleontological localities on Vega Island. This effort has led to a revised stratigraphy for the Sandwich Bluff Member and the precise stratigraphic placement of important terrestrial and marine vertebrate fossil localities.

Facies analysis reveals a fining and shallowing upward trend through the section that culminates in a newly recognized sequence boundary near the top of the Sandwich Bluff Member, followed by the deposition of a previously unrecognized, 6 m-thick, matrix-supported pebble-cobble conglomerate of probable alluvial origin. Immediately overlying this unit, well-developed Thalassinoides burrow networks in fine-grained transgressive sandstones and siltstones indicate a rapid return to marine conditions. A similar stratigraphic pattern is well documented at the top of the López de Bertodano Formation and the base of the overlying (Paleocene) Sobral Formation on Seymour Island in the southern part of the basin. Although no fossils were recovered to constrain the age of the upper 10–15 m of the succession on Vega Island that preserves the newly recognized upper sequence boundary, strata below this level can be confidently placed within the Manumiella bertodano interval zone, which extends to a short distance below the K–Pg boundary on Seymour Island. Hence, based on sequence stratigraphic and lithostratigraphic evidence, the uppermost 10–15 m of the succession on Vega Island may encompass the Cretaceous–Paleogene boundary together with a few meters of the Paleocene Sobral Formation.

Global Seawater Chemistry Changes During Lower to Middle Ordivician

Carbon isotope (δ13Ccarb) stratigraphy of the Lower–Middle Ordovician (Tremadocian–Darriwilian) in the Great Basin, western United States: implications for global correlation

Authors:

Edwards et al

Abstract:

New stable carbon isotope data (δ13Ccarb) from Lower–Middle Ordovician (Tremadocian to Darriwilian) carbonate mudstone and wackestone rocks of the Pogonip Group are presented from two sections in the Great Basin region (USA) - Shingle Pass (east–central Nevada) and the Ibex area (western Utah). The Pogonip Group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the Late Cambrian (Furongian) to Middle Ordovician (Darriwilian). The Shingle Pass and Ibex area sections have been previously studied for their conodont biostratigraphy and contain a North American Midcontinent conodont fauna that range from the Cordylodus intermedius Zone (uppermost Cambrian) to the Phragmodus polonicus Zone (Darriwilian). The δ13C trend has four distinct characteristics recognized in both Great Basin sections: 1) a drop in δ13C from + 1‰ at the base of the Ordovician (Tremadocian) to -0.7‰, 2) a 1 to 2‰ positive δ13C shift in the uppermost Rossodus manitouensis Zone during the late Tremadocian, 3) a gradual δ13C increase from -2‰ to ca. 0‰ during the end of the Early Ordovician (Floian), and 4) a steady δ13C decrease from 0‰ to -4 to -5‰ during Middle Ordovician (Dapingian–Darriwilian).

In the Lower Ordovician, δ13C trends reported here from the Great Basin are not consistent with a causal mechanism involving sea level change and the migration of isotopically distinct water bodies. Instead, these Lower Ordovician isotope data most likely reflect primary seawater chemistry and changes in δ13C on a global scale. This interpretation is supported by the excellent correlation of δ13C in the Lower Ordovician to other δ13C trends reported from the sections in the Argentine Precordillera (La Silla and San Juan formations) and in western Newfoundland (St. George and Table Head groups). These correlations using δ13C are consistent with published biostratigraphic data and provide an integrated and high-resolution chemo-biostratigraphic framework for the Lower Ordovician sedimentary record of the Laurentian margin. The Middle Ordovician portion of the δ13C curves in the Great Basin represented by the Kanosh and Lehman formations shows significant isotopic depletion relative to the section in Argentina. Thus, although there is some indication that minima and maxima in the Middle Ordovician curves can be correlated, the Great Basin sections show clear evidence of overprinting by local variables related to both diagenesis (dolomitization) and platform restriction.

Assessing and Correlating Assemblage Zones in Chinese Terreneuvian Cambrian

Terreneuvian small shelly faunas of East Yunnan (South China) and their biostratigraphic implications

Authors:

1. Ben Yang (a)
2. Michael Steiner (a)
3. Guoxiang Li (b)
4, Helmut Keupp (a)

Affiliations:

a. Department of Earth Sciences, Freie Universität Berlin, Malteserstrasse 74–100, Haus D, Berlin, 12249, Germany

b. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China

Abstract:

The study discusses the detailed composition of Terreneuvian small shelly fossil (SSF) assemblages of eastern Yunnan Province (Meishucun, Xianfeng and Huize regions). The described sections represent shallow water deposits of the Yangtze Platform that include a number of stratigraphical hiati. The reported SSF assemblages can be assigned to the regional SSF biozones I-III (Anabarites trisulcatus-Protohertzina anabarica Assemblage Zone; Paragloborilus subglobosus-Purella squamulosa Assemblage Zone; Watsonella crosbyi Assemblage Zone). Zones II and III are slightly redefined based on new data. Two subzones of Zone II are proposed here, namely, Annelitellus yangtzensis-Obtusoconus honorabilis Subzone and Maikhanella cambriana–Oelandiella korobkovi Subzone. Claviconchella qianyii gen. et sp. nov. and Bubiites simplex gen. et sp. nov. are reported. Here we also provide a critical revision of the SSF distribution for the well-known Meishucun section. The correlation scheme for East Yunnan documents the extent and duration of stratigraphical hiati. The distribution of SSFs and the lithological characterization indicates three major events of exposure of the carbonate platform resulting in sedimentary breaks and possible karstification. This prompts new consideration of the previously described stable isotope stratigraphy of shallow platform strata. Considering the complexity of the Terreneuvian Earth history as well as the uniqueness of SSF, an integration of sedimentology, geochemistry and palaeontology is needed for future SSF study.