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End-Triassic extinction tied to Central Atlantic Magmatic Province and other papers



From: Ben Creisler
bcreisler@gmail.com

A number of recent papers not directly related to dinosaurs:

Terrence J. Blackburn, Paul E. Olsen, Samuel A. Bowring, Noah M.
McLean, Dennis V. Kent, John Puffer, Greg McHone, E. Troy Rasbury &
Mohammed Et-Touhami (2013)
Zircon U-Pb Geochronology Links the End-Triassic Extinction with the
Central Atlantic Magmatic Province.
Science (advance online publication)
DOI: 10.1126/science.1234204
http://www.sciencemag.org/content/early/2013/03/20/science.1234204.abstract


The end-Triassic extinction is characterized by major losses in both
terrestrial and marine diversity, setting the stage for dinosaurs to
dominate Earth for the next 136 million years. Despite the approximate
coincidence between this extinction and flood basalt volcanism,
existing geochronologic dates have insufficient resolution to confirm
eruptive rates required to induce major climate perturbations. Here,
we present new zircon U-Pb geochronologic constraints on the age and
duration of flood basalt volcanism within the Central Atlantic
Magmatic Province. This chronology demonstrates synchroneity between
the earliest volcanism and extinction, tests and corroborates the
existing astrochronologic time scale, and shows that the release of
magma and associated atmospheric flux occurred in four pulses over
~600,000 years, indicating expansive volcanism even as the biologic
recovery was under way.


***
[This one contrasts with results in the recent paper that dated sites
in Montana.]

GERTA KELLER, HASSAN KHOZYEM, THIERRY ADATTE, NALLAMUTHU MALARKODI,
JORGE E. SPANGENBERG and WOLFGANG STINNESBECK (2013)
Chicxulub impact spherules in the North Atlantic and Caribbean: age
constraints and Cretaceous–Tertiary boundary hiatus.
Geological Magazine (advance online publication)
DOI: http://dx.doi.org/10.1017/S0016756812001069
http://128.232.233.5/action/displayAbstract?fromPage=online&aid=8871600&fulltextType=RA&fileId=S0016756812001069

The Chicxulub impact is commonly believed to have caused the
Cretaceous–Tertiary boundary mass extinction and a thin impact
spherule layer in the North Atlantic and Caribbean is frequently cited
as proof. We evaluated this claim in the seven best North Atlantic and
Caribbean Cretaceous–Tertiary boundary sequences based on
high-resolution biostratigraphy, quantitative faunal analyses and
stable isotopes. Results reveal a major Cretaceous–Tertiary boundary
unconformity spanning most of Danian subzone P1a(1) and Maastrichtian
zones CF1–CF2 (~400 ka) in the NW Atlantic Bass River core, ODP Sites
1049A, 1049C and 1050C. In the Caribbean ODP Sites 999B and 1001B the
unconformity spans from the early Danian zone P1a(1) through to zones
CF1–CF4 (~3 Ma). Only in the Demerara Rise ODP Site 1259B is erosion
relatively minor and restricted to the earliest Danian zone P0 and
most of subzone P1a(1) (~150 ka). In all sites examined, Chicxulub
impact spherules are reworked into the early Danian subzone P1a(1)
about 150–200 ka after the mass extinction. A similar pattern of
erosion and redeposition of impact spherules in Danian sediments has
previously been documented from Cuba, Haiti, Belize, Guatemala, south
and central Mexico. This pattern can be explained by intensified Gulf
stream circulation at times of climate cooling and sea level changes.
The age of the Chicxulub impact cannot be determined from these
reworked impact spherule layers, but can be evaluated based on the
stratigraphically oldest spherule layer in NE Mexico and Texas, which
indicates that this impact predates the Cretaceous–Tertiary boundary
by about 130–150 ka.

***


K. T. Bates, R. Savage, T. C. Pataky, S. A. Morse, E. Webster, P. L.
Falkingham, L. Ren, Z. Qian, D. Collins, M. R. Bennett, J. McClymont
and R. H. Crompton (2013)
Does footprint depth correlate with foot motion and pressure?
Journal of the Royal Society Interface 10 no. 83 20130009
doi: 10.1098/rsif.2013.0009
http://rsif.royalsocietypublishing.org/content/10/83/20130009.abstract?sid=01dddfad-8a52-4191-a2c7-eda4e4fc1c09

Footprints are the most direct source of evidence about locomotor
biomechanics in extinct vertebrates. One of the principal suppositions
underpinning biomechanical inferences is that footprint geometry
correlates with dynamic foot pressure, which, in turn, is linked with
overall limb motion of the trackmaker. In this study, we perform the
first quantitative test of this long-standing assumption, using
topological statistical analysis of plantar pressures and experimental
and computer-simulated footprints. In computer-simulated footprints,
the relative distribution of depth differed from the distribution of
both peak and pressure impulse in all simulations. Analysis of
footprint samples with common loading inputs and similar depths
reveals that only shallow footprints lack significant topological
differences between depth and pressure distributions. Topological
comparison of plantar pressures and experimental beach footprints
demonstrates that geometry is highly dependent on overall print depth;
deeper footprints are characterized by greater relative forefoot, and
particularly toe, depth than shallow footprints. The highlighted
difference between ‘shallow’ and ‘deep’ footprints clearly emphasizes
the need to understand variation in foot mechanics across different
degrees of substrate compliance. Overall, our results indicate that
extreme caution is required when applying the ‘depth equals pressure’
paradigm to hominin footprints, and by extension, those of other
extant and extinct tetrapods.