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Deccan Traps volcanism dates + Bauru Cretaceous paleoenvironment in Brazil



Ben Creisler
bcreisler@gmail.com

New papers:


Blair Schoene, Kyle M. Samperton, Michael P. Eddy, Gerta Keller,
Thierry Adatte, Samuel A. Bowring, Syed F. R. Khadri & Brian Gertsch
(2014)
U-Pb geochronology of the Deccan Traps and relation to the
end-Cretaceous mass extinction.
Science (advance online publication)
DOI: 10.1126/science.aaa0118
http://www.sciencemag.org/content/early/2014/12/10/science.aaa0118

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 >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.

***

Richard Stone (2014)
The once-moribund idea that volcanism helped kill off the dinosaurs
gains new credibility.
Science 346 (6215): 1281-1283
DOI: 10.1126/science.346.6215.1281
http://www.sciencemag.org/content/346/6215/1281.summary

Forged nearly 66 million years ago in one of the largest episodes of
volcanism in Earth history, the rugged Deccan Plateau in southwestern
India is ground zero for a long-running and bitter scientific debate,
centered on the cataclysmic extinctions that took place at roughly the
same time. One camp argues that Deccan volcanism spewed enough carbon
dioxide to send temperatures soaring globally while sulfur fumes
turned the oceans to acid, with lethal results for three-quarters of
Earth's life forms, including all nonavian dinosaurs. The other camp,
in the ascendancy for decades, blames the die-off on a single killer:
the impact of an asteroid. Online this week in Science, volcanism gets
a big boost, and so does one of the most contentious figures in the
debate, Princeton University paleontologist Gerta Keller. In the
paper, she and her colleagues report precise dates for the main phase
of Deccan volcanism. Countering claims that the lava outpouring took
place too early to have played any role in the extinctions, they show
that it straddles the geological moment when many creatures from the
age of dinosaurs vanish from the fossil record.

***
News stories:

http://www.livescience.com/49097-lava-flows-led-dinosaur-extinction.html
http://www.washingtonpost.com/news/speaking-of-science/wp/2014/12/11/did-a-massive-volcanic-eruption-in-india-kill-off-the-dinosaurs/

====




Luiz Alberto Fernandes & Claudia Maria Magalhães Ribeiro (2014)
Evolution and palaeoenvironment of the Bauru Basin (Upper Cretaceous, Brazil).
Journal of South American Earth Sciences (advance online publication)
doi:10.1016/j.jsames.2014.11.007
http://www.sciencedirect.com/science/article/pii/S0895981114001618


Highlights

The paper tells about the Bauru Basin stratigraphy and its
depositional environments. We think that is significant because in the
Upper Cretaceous continental basin that where lived the main Brazilian
dinosaurs, matter of the special JSAES issue. The paper should be of
interest to readers in the areas of Paleontology, Stratigraphy and
South American Geology.



Abstract

The Bauru Basin was one of the great Cretaceous desert basins of the
world, evolved in arid zone called Southern Hot Arid Belt. Its
paleobiological record consists mainly of dinosaurs, crocodiles and
turtles. The Bauru Basin is an extensive region of the South American
continent that includes parts of the southeast and south of Brazil,
covering an area of 370,000 km2. It is an interior continental basin
that developed as a result of subsidence of the central-southern part
of the South-American Platform during the Late Cretaceous
(Coniacian–Maastrichtian). This sag basin is filled by a sandy
siliciclastic sequence with a preserved maximum thickness of 480
metres, deposited in semiarid to desert conditions. Its basement
consists of volcanic rocks (mainly basalts) of the Lower Cretaceous
(Hauterivian) Serra Geral basalt flows, of the Paraná-Etendeka
Continental Flood Basalt Province. The sag basin was filled by an
essentially siliciclastic psammitic sequence. In lithostratigraphic
terms the sequence consists of the Caiuá and Bauru groups. The
northern and northeastern edges of the basin provide a record of more
proximal original deposits, such as associations of conglomeratic sand
facies from alluvial fans, lakes, and intertwined distributary river
systems. The progressive basin filling led to the burial of the
basaltic substrate by extensive blanket sand sheets, associated with
deposits of small dunes and small shallow lakes that retained mud
(such as loess). Also in this intermediate context between the edges
(more humid) and the interior (dry), wide sand sheet areas crossed by
unconfined desert rivers (wadis) occurred. In the central axis of the
elliptical basin a regional drainage system formed, flowing from
northeast to southwest between the edges of the basin and the hot and
dry inner periphery of the Caiuá desert (southwest). Life in the Bauru
Basin flourished most in the areas with the greatest water
availability, in which dinosaurs, crocodiles, turtles, fish,
amphibians, molluscs, crustaceans, and charophyte algae lived. The
fossil record mainly consists of transported bones and other skeletal
fragments. In the northeastern and eastern marginal regions fossils
are found in marginal alluvial fan deposits, broad plains of braided
streams and ephemeral alkaline water lakes. In the basin interior the
fossil record is related to deposits in sand sheets with braided
streams, small dunes, and shallow lakes. In the great Caiuá inner
desert a few smaller animals could survive (small reptiles and early
mammals), sometimes leaving their footprints in dune foreset deposits.
The aim of this article is to present and link the basin sedimentary
evolution, palaeoecological features and palaeontological record.