GSA Bulletin articles published online ahead of print on 30 April
In a new paper published online by GSA Bulletin on 30 April, researchers Mark Richards and colleagues address the "uncomfortably close" occurrence of the Chicxulub impact in the Yucatán and the most voluminous phase of the Deccan Traps flood basalt eruptions in India. Specifically, the researchers argue that the impact likely triggered most of the immense eruptions of lava in India -- that indeed, this was not a coincidence, but a cause-and-effect relationship.
This photo shows a spectacular sigmoidal jointing within a very thick lava flow from the Ambenali formation in the Western Ghats area of India. See related open-access article by M.A. Richards et al.
Credit: M.A. Richards and colleagues, and GSA Bulletin
Knowledge and study of the Deccan Traps eruptions have consistently cast a shadow of doubt on the theory that the Chicxulub impact was the sole cause of the end-Cretaceous mass extinction, most infamous for killing off Earth's dinosaurs. But Richards and colleagues write that historical evidence for the triggering of volcanoes by large earthquakes, coupled with a wide range of data, show that the massive outpouring of Deccan lavas are likely to have been triggered by the Chicxulub impact -- and thus following on as a secondary disaster.
"The chances of that occurring at random are minuscule," says Richards. "It's not a very credible coincidence."
Several of the authors visited India in April 2014 to obtain lava samples for dating, and noticed that there are pronounced weathering surfaces, or terraces, marking the onset of the huge Wai subgroup flows. This geological evidence likely indicates a period of quiescence in Deccan volcanism prior to the Chicxulub impact, which, says Richards, "gave this thing a shake," thus mobilizing a huge amount of magma over a short period of time.
Richards and colleagues write that while the Deccan eruptions probably spewed massive amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, "It's still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs."
This article is open access online. Co-authors of the paper are Paul Renne, Michael Manga, Stephen Self, and Courtney Sprain, all from UC-Berkeley; Walter Alvarez, a UC-Berkeley professor emeritus and the co-originator of the dinosaur-killing asteroid theory; Leif Karlstrom of the University of Oregon; Jan Smit of Vrije Universeit in Amsterdam; Loÿc Vanderkluysen of Drexel University in Philadelphia; and Sally A. Gibson of the University of Cambridge, UK. Learn more about this team's research via the UC-Berkeley newsroom. http://newscenter.
Triggering of the largest Deccan eruptions by the Chicxulub impact
Mark A. Richards et al., University of California, Berkeley, California, USA. Published online ahead of print on 30 Apr. 2015; http://dx.
Other GSA BULLETIN articles (see below) cover such topics as
1. A discussion of the coincidence of the eruption of the Siberian Traps with the end-Permian mass extinction;
2. An open-access article exploring a "brand-new" technique to understand the geochemistry of the Monterey Formation; and
3. New data regarding the Paleozoic evolution of western Marie Byrd Land, Antarctica.
GSA BULLETIN articles published ahead of print are online at http://gsabulletin.
Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GSA Bulletin in your articles or blog posts. Contact Kea Giles for additional information or assistance. Non-media requests for articles may be directed to GSA Sales and Service, email@example.com.
Siberian Traps volcaniclastic rocks and the role of magma-water interactions
B.A. Black et al., University of California, Berkeley, California, USA. Published online ahead of print on 30 Apr. 2015; http://dx.
The eruption of the Siberian Traps coincided with the end-Permian mass extinction. This work sheds light on the origin of unusual fragmental rocks from the Siberian Traps, their significance for the extent of Siberian Traps explosive volcanism, and implications for the delivery of volcanic gases to the upper atmosphere.
Diagenesis of phosphatic hardgrounds in the Monterey Formation: A perspective from bulk and clumped isotope geochemistry
H.J. Bradbury et al., Imperial College London, London, UK. Published online ahead of print on 30 Apr. 2015; http://dx.
Phosphorus is an essential element of the biological cycle, and can form a significant mineral fraction in sediment. This paper shows for the first time the temperature at which phosphorus nodules recrystallized within sediments of the Monterey Formation, shedding light on the geochemical processes taking place in a world-class source rock, and opening up the application of a brand new technique to understand phosphorus-rich sediments deposited on continental margins around the world.
Paleozoic evolution of western Marie Byrd Land, Antarctica
C. Yakymchuk et al., Laboratory For Crustal Petrology, University of Maryland, College Park, Maryland, USA. Published online ahead of print on 30 Apr. 2015; http://dx.
Understanding of the geological history of West Antarctica has been hindered by difficult access and the near absence of outcrops in this vast ice-covered region. Chris Yakymchuk and colleagues report new geochemical data from rare sedimentary and igneous rocks that crop out above the West Antarctica Ice Sheet that provide new insights into the Paleozoic tectonic and geological evolution of this poorly understood part of Antarctica. Cambrian-Ordovician sedimentary rocks preserve a history of sedimentation from source rocks now exposed in the Transantarctic Mountains and from rocks that now lie beneath the East Antarctic Ice sheet. Igneous rocks record Paleozoic subduction-related magmatism that is different to broadly contemporaneous magmatism in New Zealand and Eastern Australia -- regions that were once contiguous with West Antarctica along the former active margin of East Gondwana in the Pangean supercontinent. This indicates that different tectonic modes operated simultaneously along an ancient active continental margin system.
Are aragonite stalagmites reliable paleoclimate proxies? Tests for oxygen isotope time series replication and equilibrium
M.S. Lachniet, University of Nevada, Las Vegas, Nevada, USA. Published online ahead of print on 30 Apr. 2015; http://dx.
Cave deposits have been increasingly used to study past climate variations and have contributed important breakthroughs for understanding of the controlling factors that govern Earth's climate system. Most cave deposits are composed of the mineral calcite, but recent work has used aragonite stalagmites. However, how well aragonite stalagmites record climate variation is not well known, thus limiting paleoclimatologists' confidence in their oxygen isotopic records. In this new paper, Matthew S. Lachniet shows that aragonite stalagmites in some cases are exceptionally robust climate records, but that in other cases their oxygen isotopic composition may not reflect equilibrium, and hence climate, variations. Replicated aragonite stalagmite records are required to have confidence in their use as paleoclimate proxies.
A cold supergene zinc deposit in Alaska: The Reef Ridge case
L. Santoro et al., Università degli Studi di Napoli Federico II, Napoli, Italy. Published online ahead of print on 30 Apr. 2015; http://dx.
The Reef Ridge deposit (Alaska) is a typical supergene "nonsulfide" zinc mineralization, where smithsonite is the predominant ore mineral. The carbon and oxygen isotope values of smithsonite vary, and the delta-13C values are similar to those of the host rock, which is the predominant carbon source. The oxygen isotope ratios are more depleted in 18O compared to supergene nonsulfides from other parts of the world, formed under warm-humid, temperate or semi-arid climates. These values indicate that the delta-18O composition of Reef Ridge smithsonite is related to very low formation temperatures (approx. 10 degrees C), and strong depletion in 18O of the precipitating waters. The Reef Ridge nonsulfides were formed during cold/humid weathering episodes (late Tertiary to Recent). The "traditional" interpretation on the genesis of Zn nonsulfide deposits in warm-humid, temperate or semi-arid conditions, writes author L. Santoro, should be questioned where other climate zones are indicated.
New insights into the emplacement mechanism of the Late Triassic granite plutons in the Qinling orogen: A structural study of the Mishuling pluton
W. Liang et al., State Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China. Published online ahead of print on 30 Apr. 2015; http://dx.
From the abstract: Numerous geochronological and geochemical studies of the Late Triassic granite plutons in the Qinling orogen have been conducted over the past few decades. These studies have extensively discussed the genesis and correlations of granite plutons with the collisional processes between the North and South China blocks. However, several contradictory conclusions on the tectonic settings of these plutons (subduction, syn-collision, post-collision or intraplate) have been reached. Moreover, in all these studies, compressional or extensional structures have been always considered to control the magma emplacement, but no direct evidence has been presented so far. In order to clarify the emplacement mechanism of these Late Triassic plutons and avoid the ambiguities from pure geochemical studies, we conducted a multidisciplinary structural study on the Mishuling pluton in the West Qinling, one of the biggest Late Triassic plutons in the orogen.
Contact: Kea Giles
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