Is India's Infrakrol Formation the Same age as China's Ediacaran Doushantuo Formation?

Tianzhushania spinosa and other large acanthomorphic acritarchs of Ediacaran Period from the Infrakrol Formation, Lesser Himalaya, India

Authors:

Joshi et al

Abstract:

Covering a time span from Ediacaran (base of Blaini pink carbonates) to Early Cambrian (base of Tal Group), the Krol belt in the Lesser Himalaya (India), occurs as a series of synclines from Solan, Himachal Pradesh in the north-west to Nainital, Uttarakhand in the south-east. Various lithostratigraphic divisions of this belt reveal many palaeobiological entities, namely cyanobacteria, algae, acritarchs, small shelly fossils and trace fossils. Globally, large acanthomorphic acritarchs of the Ediacaran Period are used as significant biostratigraphic tools for global correlation. In the Krol belt, reports of acanthomorphic acritarchs from the Infrakrol and Krol ‘A’ formations of the Krol Group have further supported this notion. This paper reports well-preserved microfossils including acanthomorphic acritarchs, sphaeromorphic acritarchs, coccoids namely Tianzhushania spinosa, T. polysiphonia, Papillomembrana compta, Schizofusa sp., Gloeodiniopsis lamellosa, Sphaerophycus medium, and the unnamed forms A, B and C from the chert nodules of the Infrakrol Formation exposed in the Nainital Syncline of the Kumaun Lesser Himalaya. A biostratigraphic correlation based on acanthomorphic acritarchs suggests that the Infrakrol Formation is coeval to the lower Tianzhushania assemblage zone of the Doushantuo Formation of south China. Tianzhushania and Papillomembrana are significant additions to the previous record of the Ediacaran acanthomorphic acritarchs from the Lesser Himalaya of India and provide an independent evidence for construction of both biozonation scheme and paleogeography.

When did Mars Form a Crust and Mantle?

The age of Madumabisa (Zambia) Fossil Vertebrates From Permian

Resolving the age of Madumabisa fossil vertebrates: Palynological evidence from the mid-Zambezi Basin of Zambia

Authors:

Barbolini et al

Abstract:

Age estimates for Permian rocks in the mid-Zambezi Basin of Zambia have thus far yielded ambiguous results. Previously studied palynoassemblages from the Madumabisa Formation resemble spore-pollen suites from both the Cistecephalus Zone of North Luangwa (Lopingian) and the palynological Assemblage Sub-Zone IV H of Zimbabwe, proposed as Guadalupian. In order to improve age estimates and refine the biostratigraphy of the Madumabisa Formation, this formation together with the underlying Gwembe Formation, were sampled for palynomorphs. Assemblages from the Gwembe Formation are dominated by trilete spores with less common striate and non-striate bisaccate pollen, whereas the overlying Madumabisa Formation palaeoflora is composed predominantly of striate bisaccates. Ferns, pteridosperms, lycopods, sphenophytes, glossopterids and conifers are represented in the palynofloras. The upper Gwembe Formation palynoassemblage can be correlated with the Didecitriletes ericianus Zone of Backhouse (1991), the Guttulapollenites hannonicus–Protohaploxypinus rugatus Zone (Zone VI) of Aitken (1998), Assemblage Zone III of the mid-Zambezi Basin, Zimbabwe and Biozone KK 3 in the Kalahari Karoo Basin, Botswana, suggesting a Guadalupian (Wordian–Capitanian) age. The upper Madumabisa Formation palynoassemblage can be placed in the upper Dulhuntyispora parvithola Zone of Backhouse (1991)/APP5 of Price (1997), dated as Wuchiapingian (Lopingian) and correlates with Assemblage 2 of the Moatize–Minjova Basin, Mozambique and the McKinnon Member palynofloras of East Antarctica. It also resembles Daptocephalus (formerly Dicynodon) Assemblage Zone palynofloras of the lower and middle Balfour Formation in the Karoo Basin, South Africa, and is suggested to be Lopingian (Wuchiapingian–Changhsingian) in age. Although these palynological assemblages place lower and upper age constraints on Madumabisa Formation vertebrate fossils, uncertainty remains as to the exact correlation between the Madumabisa vertebrate assemblages and the assemblage zones of the main Karoo Basin.

Chilesaurus diegosuarezi is From the Tithonian Jurassic

Tithonian age of dinosaur fossils in central Patagonian, Chile: U–Pb SHRIMP geochronology

Authors:

Suárez et al

Abstract:

Three Tithonian concordant U–Pb SHRIMP zircon ages of 148.7 ± 1.4, 147.9 ± 1.5 and 147.0 ± 1.0 from tuffs intercalated in a clastic sedimentary succession with exceptional dinosaur bones including the new taxon Chilesaurus diegosuarezi gen. et sp. nov. exposed in central Chilean Patagonia (ca. 46°30′S) are reported herein. The fossiliferous beds accumulated in a synvolcanic fan delta reaching a shallow marine basin as indicated by glauconite present in some of the beds, and coeval with the beginning of the transgression of the Aysén Basin.

Snowball Earth Era Sedimentary Formations Found in China

U–Pb age and Hf isotope composition of detrital zircons from Neoproterozoic sedimentary units in southern Anhui Province, South China: Implications for the provenance, tectonic evolution and glacial history of the eastern Jiangnan Orogen

Authors:

Cui et al

Abstract:

Neoproterozoic sedimentary units at the southeastern margin of the Yangtze Block, South China, record a complex geological history including development of the Jiangnan Orogen during assembly of the Yangtze and Cathaysia blocks and later episodes of glacial activity. The timing of these events is controversial, and we have used U–Pb–Hf compositions of detrital zircons from the Lantian type section to constrain their ages in southern Anhui Province, at the eastern end of the Jiangnan Orogen. This section comprises the Xikou Group below an angular unconformity, and the Xiuning Formation and overlying glacial Leigongwu Formation above the unconformity. Detrital zircons in all three units are dominated by 2.6–2.4 Ga, 2.1–1.9 Ga and 960–740 Ma age populations suggesting erosion from similar source regions, and an increasing proportion of older grains up through the sequence reflects a change in depositional environment from syn-collisional to extensional. Pre-Neoproterozoic zircon grains were derived from the Yangtze Block basement, much of which is now concealed by younger rocks, while the Neoproterozoic population was eroded from local igneous rocks in the Jiangnan Orogen. Zircon Hf isotope compositions indicate that 2.6–2.4 Ga source rocks were a mix of juvenile and reworked crust, while 2.1–1.9 Ga source rocks were dominated by reworked crust. Neoproterozoic sources show a switch from 960–860 Ma juvenile crust to 860–740 Ma juvenile and reworked crust, reflecting a transition in the Jiangnan Orogen from subduction to collision and extension. The youngest detrital grains in the Xikou Group and overlying Xiuning Formation indicate deposition after ca. 810 Ma and ca. 732 Ma, respectively, correlating closely with comparable sequences elsewhere in the Yangtze Block. This demonstrates that the unconformity in South Anhui is part of a regional erosion surface that formed more or less synchronously throughout the orogen at 830–800 Ma, consistent with it dating the end of collision between the Yangtze and Cathaysia blocks. The age of the overlying glacial Leigongwu Formation is difficult to constrain from detrital zircons because of a paucity of post-720 Ma source rocks, but our data suggest the Leigongwu diamictite in the Lantian section is a single Marinoan-age glacial unit deposited after 649 ± 13 Ma. It follows that a carbonate layer in the middle of the Leigongwu diamictite in the Lantian section most likely reflects later faulting, rather than two separate glacial sequences, although we cannot rule out the presence of both Sturtian and Marinoan diamictite elsewhere in South Anhui.

Marine and Terrestrial Permian Extinctions Aren't Geochronologically Synchronous?

Is the vertebrate-defined Permian-Triassic boundary in the Karoo Basin, South Africa, the terrestrial expression of the end-Permian marine event?

Authors:

Gastaldo et al

Abstract:

The end-Permian extinction records the greatest ecological catastrophe in Earth history. The vertebrate fossil record in the Karoo Basin, South Africa, has been used for more than a century as the standard for understanding turnover in terrestrial ecosystems, recently claimed to be in synchrony with the marine crisis. Workers assumed that systematic turnover at the Dicynodon assemblage zone boundary, followed by the appearance of new taxa directly above the base of the Lystrosaurus assemblage zone, is the continental expression of the end-Permian event and recovery. To test this hypothesis, we present the first high-precision age on strata close to the inferred Permian-Triassic boundary. A U-Pb isotope dilution–thermal ionization mass spectrometry zircon age of 253.48 ± 0.15 Ma (early Changhsingian) is from a silicified ash layer ∼60 m below the current vertebrate-defined boundary at Old Lootsberg Pass (southern South Africa). This section yields newly discovered plants and vertebrates, and is dominated by a normal polarity signature. Our collective data suggest that the Dicynodon-Lystrosaurus assemblage zone boundary is stratigraphically higher than currently reported, and older than the marine extinction event. Therefore, the turnover in vertebrate taxa at this biozone boundary probably does not represent the biological expression of the terrestrial end-Permian mass extinction. The actual Permian-Triassic boundary in the Karoo Basin is either higher in the Katberg Formation or is not preserved. The currently accepted model of the terrestrial ecosystem response to the crisis, both in this basin and its extension globally, requires reevaluation.

Chinese Kayitou Formation is Latest Changhsingian Permian, not Triassic, & Witness to PT Extinction

The terrestrial end-Permian mass extinction in South China

Authors:

Zhang et al

Abstract:

The end-Permian mass extinction reflects the most severe life crisis during the Phanerozoic and was associated with major global environmental changes. However, the consistency of the time and pattern of the terrestrial and marine extinctions remains controversial. In this paper, we presented detailed analyses of the high-resolution biostratigraphical and geochemical data from terrestrial sections in South China. Our analyses show that the transitional Kayitou Formation actually recorded the process of terrestrial mass extinction as evidenced by the mass disappearance of the Gigantopteris megaflora in the lower part, the dramatic reduction in abundance of palynomorphs in the middle, and the last occurrences of plant remains and abundant charcoal fossils in the uppermost part. It is associated with a distinct negative shift of δ13Corg, beginning in the middle part of the formation, which is correlative with that in the top of Bed 26 at the marine Meishan section. In addition, the Kayitou Formation is characterized by a distinct shift of lithofacies of fresh lake-swamp or river flat environment from olive/grey/black mudstone, siltstone, fine to coarse sandstone in the lower part to gradually increasing maroon rocks, to purely maroon mudrocks with poorly-sorted breccia, calcic palaeosols and calcareous nodules in the lowest part of the Dongchuan Formation, which indicates a dramatic collapse of soil system associated with rapid deforestation and climatic warming and drying. In the coastal area, the Kayitou Formation contains marine beds with the typical Permian–Triassic mixed faunas and floras which are correlative with the latest Changhsingian marine mixed fauna 1 at Meishan. The Kayitou Formation also recorded a distinct transgression that began in the latest Changhsingian. All above phenomena suggest that the Kayitou Formation is actually the witness of the terrestrial end-Permian mass extinction; and it is mostly or entirely of latest Changhsingian (Permian), rather than Triassic age.

No Homo erectus Fossils in African Older Than 1.63 Million Years ago

Chronostratigraphy of KNM-ER 3733 and other Area 104 hominins from Koobi Fora

Authors:

Lepre et al

Abstract:

A magnetostratigraphy for ∼60 m of Koobi Fora Formation sediment in Area 104 was derived from 46 oriented samples that produced well-resolved characteristic magnetizations from progressive thermal demagnetization. Approximately 59 m below the Morte Tuff, previously dated to ∼1.51 Ma (millions of years ago), the Olduvai-Matuyama boundary (∼1.78 Ma) was found to be at the level of marker bed A2—inconsistent with the Area 102 type section and thus contrary to fossil dating schemes that utilize temporal equivalence between A2 [104] and A2 [102]. The magnetostratigraphic data, coupled with the Morte Tuff, provide a means to interpolate new ages for marker beds A2 [104] and the White Tuff, as well as multiple Area 104 hominin fossils. Noteworthy is the new date of ∼1.63 Ma for KNM-ER 3733, which now implicates KNM-ER 2598 as the sole early African Homo erectus fossil demonstrably older than Dmanisi and Java Homo specimens. Re-dating KNM-ER 3733 creates a ∼300-kyr gap at 1.9 to 1.6 Ma in the African fossil record of H. erectus, which might be partially spanned by hand axes recently dated at ∼1.76 Ma, if the Acheulian is indeed proprietary to this species.

Academic Bun Fights! The Anthropocene!

Ruddiman et al think the anthropocene is a useful, necessary concept, but one which ought to remain someone nebulous, but the start ought to be 1945 (first atom bomb blast):

Defining the epoch we live in

Authors:

Ruddiman et al

Abstract:

Human alterations of Earth's environments are pervasive. Visible changes include the built environment, conversion of forests and grasslands to agriculture, algal blooms, smog, and the siltation of dams and estuaries. Less obvious transformations include increases in ozone, carbon dioxide (CO2), and methane (CH4) in the atmosphere, and ocean acidification. Motivated by the pervasiveness of these alterations, Crutzen and Stoermer argued in 2000 that we live in the “Anthropocene,” a time in which humans have replaced nature as the dominant environmental force on Earth (1). Many of these wide-ranging changes first emerged during the past 200 years and accelerated rapidly in the 20th century (2). Yet, a focus on the most recent changes risks overlooking pervasive human transformations of Earth's surface for thousands of years, with profound effects on the atmosphere, climate, and biodiversity.

OTOH, Lewis and crew think definitions are really important for science and if we're going to use the term 'anthropocene' we ought to it down to a formal start geologically & according to the GSSP standards:

Definitions are one of the bedrocks of science. However, W. F. Ruddiman et al. (“Defining the epoch we live in,” Perspectives, 3 April, p. 38) propose that the geological term Anthropocene should remain deliberately undefined and ambiguous. They recommend not formalizing the term because some inception dates miss important earlier human-induced environmental impacts, particularly widespread farming. We have sympathy for this view. However, defining the Anthropocene as a geological epoch must be based on evidence, including changes to the Earth system lasting millions of years and the existence of stratigraphic evidence marking such changes (1). All other geological time-units have agreed-upon dated markers or agreed-upon dates. The Anthropocene should not be treated differently.

link.

Certini et al agree with Lewis and crew about needing to make the anthropocene into something formal, but they suggest the anthropocene subsueme the holocene:

In their Perspective “Defining the epoch we live in” (3 April, p. 38), W. F. Ruddiman et al. write that in spite of its popularity, the Anthropocene still lacks an official onset. They propose that the term anthropocene be used informally (without the initial capital), which would avoid the constraints of a formal designation. We disagree.

[...]

Even if the impact of humans was not immediately major and uniform across the planet, what are a few thousand years of discrepancy between the end of the last glacial period and the dawn of the Anthropocene in comparison to the entire geological scale? Most transitions between the formally defined epochs would be much longer than the Holocene. Anthropocene seems a more reasonable name than Holocene for this combined time span, whose most characteristic trait is the human pressure on the planet. Holocene could possibly be the first stage of the Anthropocene, the one characterized by a soft and spotty human impact on Earth.

link.

Ruddiman counters the formalism is 'silly,' but does point out if the anthropocene is going to go formal, when to date it. The atom bomb or the start of the megafauna overkills?

Certini and scalenghe and Lewis and Maslin seem convinced that geoscience must rely heavily on formal stratigraphic nomenclature to move forward. This view likely originates from the centuries-long effort to compile the relative geologic age sequence, which was a monumental achievement, especially given religious and social opposition. The compilation required careful attention to stratigraphic principles such as superposition, index fossils, diachroneity, and facies changes. Over time, the findings became formalized in geologic nomenclature.

link.

Revising the Frasnian–Famennian Devonian Boundary and Kellwasser Events

Revised correlation of the Frasnian–Famennian boundary and Kellwasser Events (Upper Devonian) in shallow marine paleoenvironments of New York State

Authors:

Bush et al

Abstract:

The Frasnian–Famennian boundary (Upper Devonian) is exposed in a 200 km-long outcrop belt in New York State, with deeper paleoenvironments to the west and shallower ones to the east. Geochronology in the eastern end of the outcrop belt has been based primarily on lithostratigraphic correlation with western sections, which were dated using conodonts. We collected conodonts and brachiopods from several measured sections and numerous other localities, and these collections suggest that these east–west lithostratigraphic correlations require revision. We correlate the Wiscoy Formation with the upper Angola Formation and the Canaseraga with the upper Hanover. Thus, the Canaseraga Formation contains the Frasnian–Famennian boundary and Upper Kellwasser Event, and the dark shale above the Wiscoy is equivalent to the Pipe Creek Formation and Lower Kellwasser Event. These new correlations imply that the Lower Kellwasser Event had greater impact on the shelly benthos of New York than the Upper Kellwasser, at least for the subset of taxa examined here. All strophomenid brachiopods and rugose corals were extirpated at the Lower Kellwasser, along with numerous other brachiopods. The final species of atrypid brachiopod persisted to the Upper Kellwasser.

Events of the Cambrian Period

Global climate, sea level cycles, and biotic events in the Cambrian Period

Authors:

Babcock et al

Abstract:

The developing high-resolution chronostratigraphy of the Cambrian provides an updated age model for various geologic and biotic events that occurred during this critical period of Earth history. Broad, time-specific patterns of lithofacies, such as organic-rich deposits, and biofacies appear to be consistent across all Cambrian paleocontinents. Records of important evolutionary events including first appearances of certain metazoan taxa, migrations, and extinctions, tend to coincide with changes in eustatic sea level, as do the positions of many Konservat-Lagerstätten, concretion horizons, agnostoid-rich beds, and other sedimentary features. Most of these events or horizons also show a relationship to perturbations in the global carbon cycle. The positions of organic-rich deposits bear strong relationship to both paleogeographic position and sea level history. Cambrian strata show evidence of cyclicity at multiple scales. Synchronous or near-synchronous global cyclicity is inferred to be associated with oceanographic and climatic cycles characteristic of glacial expansion and deglaciation.

Tightening up the Cryogenian Glaciation Chronology

A Cryogenian chronology: Two long-lasting synchronous Neoproterozoic glaciations

Authors:

Rooney et al

Abstract:

The snowball Earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion-year time scale. Geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons. Here we present four new Re-Os geochronology age constraints on Sturtian (717–660 Ma) and Marinoan (635 Ma termination) glacial deposits from three different paleocontinents. A 752.7 ± 5.5 Ma age from the base of the Callison Lake Formation in Yukon, Canada, confirms nonglacial sedimentation on the western margin of Laurentia between ca. 753 and 717 Ma. Coupled with a new 727.3 ± 4.9 Ma age directly below the glacigenic deposits of the Grand Conglomerate on the Congo craton (Africa), these data refute the notion of a global ca. 740 Ma Kaigas glaciation. A 659.0 ± 4.5 Ma age directly above the Maikhan-Uul diamictite in Mongolia confirms previous constraints on a long duration for the 717–660 Ma Sturtian glacial epoch and a relatively short nonglacial interlude. In addition, we provide the first direct radiometric age constraint for the termination of the Marinoan glaciation in Laurentia with an age of 632.3 ± 5.9 Ma from the basal Sheepbed Formation of northwest Canada, which is identical, within uncertainty, to U-Pb zircon ages from China, Australia, and Namibia. Together, these data unite Re-Os and U-Pb geochronological constraints and provide a refined temporal framework for Cryogenian Earth history

Complicating Human Evolution: Is Little Foot as old as Lucy?

New cosmogenic burial ages for Sterkfontein Member 2 Australopithecus and Member 5 Oldowan

Authors:

Granger et al

Abstract:

The cave infills at Sterkfontein contain one of the richest assemblages of Australopithecus fossils in the world, including the nearly complete skeleton StW 573 (‘Little Foot’) in its lower section, as well as early stone tools in higher sections. However, the chronology of the site remains controversial owing to the complex history of cave infilling. Much of the existing chronology based on uranium–lead dating and palaeomagnetic stratigraphy has recently been called into question by the recognition that dated flowstones fill cavities formed within previously cemented breccias and therefore do not form a stratigraphic sequence Earlier dating with cosmogenic nuclides suffered a high degree of uncertainty and has been questioned on grounds of sediment reworking . Here we use isochron burial dating with cosmogenic aluminium-26 and beryllium-10 to show that the breccia containing StW 573 did not undergo significant reworking, and that it was deposited 3.67 ± 0.16 million years ago, far earlier than the 2.2 million year flowstones found within it. The skeleton is thus coeval with early Australopithecus afarensis in eastern Africa. We also date the earliest stone tools at Sterkfontein to 2.18 ± 0.21 million years ago, placing them in the Oldowan at a time similar to that found elsewhere in South Africa at Swartkans and Wonderwerk.

This would have gone up yesterday, but April 1st...

Keller's Crew Strike:Tidal Wave From Chicxulub Impact Disputed

Mass wasting and hiatuses during the cretaceous-tertiary transition in the north atlantic: Relationship to the chicxulub impact?

Authors:

Mateo et al

Abstract:

Deep-sea sections in the North Atlantic are claimed to contain the most complete sedimentary records and ultimate proof that the Chicxulub impact is Cretaceous-Tertiary boundary (KTB) in age and caused the mass extinction. A multi-disciplinary study of North Atlantic DSDP Sites 384, 386 and 398, based on high-resolution planktonic foraminiferal biostratigraphy, carbon and oxygen stable isotopes, clay and whole-rock mineralogy and granulometry reveals the age, stratigraphic completeness and nature of sedimentary disturbances. Results show a major hiatus across the KTB at Site 384 with Zones CF1, P0 and P1a missing, spanning at least ~ 540 ky, similar to other North Atlantic and Caribbean localities associated with tectonic activity and Gulf Stream erosion. At Sites 386 and 398, discrete intervals of disturbed sediments with mm-to-cm-thick spherule layers have previously been interpreted as the result of impact-generated earthquakes at the KTB destabilizing continental margins prior to settling of impact spherules. However, improved age control based on planktonic foraminifera indicates spherule deposition in the early Danian Zone P1a(2) (upper Parvularugoglobigerina eugubina Zone) more than 100 ky after the KTB. At Site 386, two intervals of white chalk contain very small (less than 63 μm) early Danian Zone P1a(2) assemblages (65%) and common reworked Cretaceous (35%) species. In contrast, the in situ red-brown and green abyssal clays of this core are devoid of carbonate. In addition, high calcite, mica and kaolinite and upward-fining are observed in the chalks, indicating downslope transport from shallow waters and sediment winnowing via distal turbidites. At Site 398, convoluted red to tan sediments with early Danian and reworked Cretaceous species represent slumping of shallow water sediments as suggested by dominance of mica and low smectite compared to in situ deposition. We conclude that mass wasting was likely the result of earthquakes associated with increased tectonic activity in the Caribbean and the Iberian Peninsula during the early Danian well after the Chicxulub impact.

Did Something PaleoMagnetically Strange Happen to the Earth's Ediacaran NeoProterozoic Poles?

A paleomagnetic and U-Pb geochronology study of the western end of the Grenville dyke swarm: Rapid changes in paleomagnetic field direction at ca. 585 Ma related to polarity reversals?

Authors:

Halls et al

Abstract:

A paleomagnetic study of the western end of the ∼585 Ma Grenville dyke swarm shows that individual dykes are characterized by high coercivity and unblocking temperature magnetizations that can differ in direction by as much as 90°. Field tests including baked contact studies and the continuity of paleomagnetic direction along dyke strike, suggest that the magnetizations are primary. Precise U-Pb baddeleyite dating on these dykes indicates that changes in magnetization direction of ∼90° occur in less than 4 million years, and their close temporal association with reversals of the axial dipole field suggest that certain dykes are recording an equatorial dipole field as a transitional field between opposite polarity states. The documented instability in the Earth's field occurs less than 10 Myr before the first recorded appearance of macroscopic multi-cellular organisms on Earth, inviting speculation that an extended period of frequent magnetic reversals may play a part in faunal evolution.

Chaohusaurus is Oldest Known Ichthyopterygian

Ammonoid age control of the Early Triassic marine reptiles from Chaohu (South China)

Authors:

Ji et al

Abstract:

Here we described a series of ammonoid specimens from the Early Triassic of Chaohu, South China and recognized the occurrence of Procolumbites for the first time in this area. The Procolumbites layer is about one meter above the first appearance of Chaohusaurus, indicating that the oldest Chaohusaurus is within the Procolumbites Zone of middle Spathian age. This new age constrain is significantly older than the previously suggested Subcolumbites Zone assignment (early late Spathian). To date, Chaohusaurus is the oldest known ichthyopterygian.

Deccan Traps Geochronologically Synchronous With KT Extinction

U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction

Authors:

Schoene et al

Abstract:

The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply U-Pb zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that greater than 1.1 million km3 of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.

Geochronology of East Australian Gondwana Mapped From Middle Permian Through Lower Triassic

High-precision U-Pb CA-TIMS calibration of Middle Permian to Lower Triassic sequences, mass extinction and extreme climate-change in eastern Australian Gondwana

Authors:

Metcalfe et al

Abstract:

Twenty-eight new high-precision Chemical Abrasion Isotope Dilution Thermal Ionisation Mass Spectrometry U-Pb zircon dates for tuffs in the Sydney and Bowen Basins are reported. Based on these new dates, the Guadalupian-Lopingian/Capitanian-Wuchiapingian boundary is tentatively placed at the level of the Thirroul Sandstone in the lower part of the Illawarra Coal Measures in the Sydney Basin. The Wuchiapingian-Changhsingian boundary is at or close to the Kembla Sandstone horizon in the Illawarra Coal Measures, southern Sydney Basin, in the middle part of the Newcastle Coal Measures in the northern Sydney Basin, and in the middle of the Black Alley Shale in the southern Bowen Basin. The end-Permian mass extinction is recognised at the base of the Coal Cliff Sandstone in the southern Sydney Basin, at the top of the Newcastle Coal Measures in the northern Sydney Basin, and close to the base of the Rewan Group in the Bowen Basin and is dated at c. 252.2 Ma. The end-Permian mass extinction is interpreted to be synchronous globally in both marine and terrestrial environments, and in high and low latitudes (resolution < 0.5 my). The GSSP-defined Permian-Triassic boundary is interpreted to be approximately at the level of the Scarborough Sandstone in the lower Narrabeen Group, Sydney Basin, and in the lower Rewan Group, Bowen Basin. New dates presented here suggest that the P3 and P4 glacial episodes in the Permian of eastern Australia are early Roadian to early Capitanian, and late Capitanian to mid Wuchiapingian in age respectively. The greenhouse crisis in the uppermost Pebbly Beach and Rowan Formations of the Sydney Basin is interpreted as early mid Roadian, a mid-Capitanian age for the crisis at the base of the Illawarra/Whittingham Coal Measures is confirmed. Greenhouse crises in the upper Illawarra/Newcastle Coal Measures and lower Narrabeen Group of the Sydney Basin are dated as upper Changhsingian-Induan, and in the upper Narrabeen Group/lower Hawksbury Sandstone as upper Olenekian.

Bambuí Group (Brazil) is Ediacaran

New evidence of an Ediacaran age for the Bambuí Group in southern São Francisco craton (eastern Brazil) from zircon U-Pb data and isotope chemostratigraphy

Authors:

Macedo de Paula-Santos et al

Abstract:

Extensive carbonate-siliciclastic successions of the Bambuí Group, which overlie Neoproterozoic glaciogenic diamictites, cover most of the southern São Francisco craton (eastern Brazil). This group records sedimentation in a foreland setting related to the diachronic orogenic processes that formed the Brasília and Araçuaí marginal belts. The lowermost unit of the Bambuí Group, the Sete Lagoas Formation, comprises two shallowing-upward sequences of carbonate rocks with subordinated pelitic intercalations, overlying the glaciogenic diamictites in the southern São Francisco Craton. This study combines isotope chemostratigraphy (C, O, Sr) and U-Pb dating of zircon detrital grains retrieved from marls of the Sete Lagoas Formation. The basal sequence comprises low organic matter limestones and dolostones with δ13C values around 0‰, positioned above cap carbonates dated at around 740 Ma (Pb-Pb whole-rock isochron). The U-Pb ages obtained for this sequence show several age peaks between 1270-870 Ma and 625-550 Ma. The upper sequence includes dark limestones with δ13C values as high as + 10‰, best preserved 87Sr/86Sr ratios of around 0.7075 and U-Pb ages ranging from 625 Ma to 550 Ma. Our geochronological data suggest that the Araçuaí orogen is the main source of sediment for the Sete Lagoas Formation, and the youngest zircon population sets the maximum depositional age for its upper part at around 557 Ma. This suggests that the studied section of the Sete Lagoas Formation is not related to either the Sturtian or the Marinoan glacial events. Also, the 87Sr/86Sr ratios obtained from Sete Lagoas carbonates contrast with Sr evolution curves available in the literature, especially with those for the Ediacaran-Cambrian limit, when ratios higher than 0.7080 would be expected. The same discrepancy is reported for other Ediacaran carbonate successions, pointing to local disturbances in Sr composition of marine basins rather than global processes. Interbasinal correlations and blind dating based on isotope chemostratigraphy should proceed carefully, especially for Ediacaran marine deposits located on inner parts of large palaeocontinental regions, such as those found in western Gondwana.

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.