Boulder, Colo., USA - Since the Cambrian Explosion, ecosystems have suffered repeated mass extinctions, with the "Big 5" crises being the most prominent. Twenty years ago, a sixth major extinction was recognized in the Middle Permian (262 million years ago) of China, when paleontologists teased apart losses from the "Great Dying" at the end of the period. Until now, this Capitanian extinction was known only from equatorial settings, and its status as a global crisis was controversial.
David P.G. Bond and colleagues provide the first evidence for severe Middle Permian losses amongst brachiopods in northern paleolatitudes (Spitsbergen). Their study shows that the Boreal crisis coincided with an intensification of marine oxygen depletion, implicating this killer in the extinction scenario.
The widespread loss of carbonates across the Boreal Realm also suggests a role for acidification. The new data cements the Middle Permian crisis's status as a true "mass extinction." Thus the "Big 5" extinctions should now be considered the "Big 6."
An abrupt extinction in the Middle Permian (Capitanian) of the Boreal Realm (Spitsbergen) and its link to anoxia and acidification
David P.G. Bond et al., University of Hull, Hull, UK. Published online ahead of print on 14 Apr. 2015; http://dx.
Other GSA Bulletin articles (see below) cover such topics as
- Three strikes and you're out: Environmental deterioration in Pangea and the "Great Dying";
- The history of earthquake-induced liquefaction in Christchurch, New Zealand; and
- The evolution of the Arctic Ocean.
GSA Bulletin articles published ahead of print are online at http://gsabulletin.
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Progressive environmental deterioration in NW Pangea leading to the Latest Permian Extinction
S.E. Grasby et al., Geological Survey of Canada, Natural Resources Canada, Calgary, Alberta, Canada. Published online ahead of print on 14 Apr. 2015; http://dx.
Three strikes and you're out! New results presented by S.E. Grasby and colleagues show that the Latest Permian Extinction, the worst extinction in Earth's history, was related to progressive environmental deterioration rather than a single cause. There were three main events: Initial lowered ocean pH limited the ability of marine animals to build calcareous shells prior to the main extinction. The extinction boundary itself is marked by a massive release of toxic metals related to eruption of the Siberian Traps, the largest volcanic eruption in Earth's history. The final blow to life was development of anoxic (oxygen deficient) ocean waters related to rapid global warming that lead to final extinction of the last holdout survivors, representing a total net loss of over 90% of marine species.
Paleoliquefaction in Christchurch, New Zealand
S.H. Bastin et al., University of Canterbury, Christchurch, New Zealand. Published online ahead of print on 14 Apr. 2015; http://dx.
Liquefaction during the 2010-2011 Canterbury earthquake sequence caused extensive damage to infrastructure and prompted major residential land rezoning in Christchurch, New Zealand. This paper presents the first evidence of a liquefaction event in Christchurch prior to the 2010-2011 Canterbury earthquake sequence. The timing of liquefaction event(s) is dated to between 1660 and 1905 AD. Modeling of the ground motions for five well-documented historic earthquakes indicates that the 1869 Mw ~4.8 Christchurch earthquake may have triggered the observed historic liquefaction. Other possible sources include the 1717 Alpine Fault and ~500 years B.P. (before present) Porters Pass earthquakes. Houses in Christchurch built between the mid-19th century and 2005 were located atop geological evidence for liquefaction, highlighting the importance of paleo-liquefaction studies in determining the likely location of future liquefaction, contributing to seismic hazard assessments and informing land use planning.
An imbricate mid crustal suture zone: The Mojave-Yavapai province boundary in Grand Canyon, AZ
M.E. Holland et al., University of New Mexico, Albuquerque, New Mexico, USA. Published online ahead of print on 15 Apr. 2015; http://dx.
New geochronologic data from the oldest rocks in Grand Canyon help resolve a persistent uncertainty in Precambrian geology of southwestern North America. The Paleoproterozoic Yavapai and Mojave crustal provinces have been identified as distinct crustal blocks in the literature for over 20 years, but the difference between them and the location of their boundary has been debated. By analyzing the hafnium isotopic composition of zircons from 1.84- to 1.70-billion-year-old rocks in the Grand Canyon, a collaborative team led by researchers from the University of New Mexico has identified the Mojave-Yavapai province boundary to be located along the Crystal shear zone in the Upper Granite Gorge of the Grand Canyon. Granitic rocks of the Mojave province west of the Crystal shear zone were derived from Archean crust (older than 2.5 billion years), whereas granitic rocks east of the shear zone were derived from 1.8- to 1.7-billion-year-old terranes.
Wind-driven bottom currents and related sedimentary bodies in Lake Saint-Jean (Québec, Canada)
A. Nutz et al., CNRS-Université de Strasbourg, Strasbourg, France. Published online ahead of print on 3 Apr. 2015; http://dx.
Fine-grained sedimentary rocks (i.e., shales or mudstones) are by far the most common sedimentary rocks preserved in the geological record, a large part of them result from paleo-lakes evolution. However, processes related to mud sedimentation have remained largely overlooked with only rare detailed inspection even implications are wide and may call for reinterpretation of processes at the origin of numerous offshore successions. In this study, sedimentation modalities in offshore domain of Lake Saint-Jean (Québec, Canada) are investigated. As a result, the development of wind-induced bottom currents that generated large-scale sediment bodies onto the lake floor are evidenced suggesting more energetic conditions in deep part of some lakes than previously expected. This highlights impact of wind well below the wave base in some enclosed water bodies through the emplacement of basin-scale internal circulation. Thus, scientists have an alternative vision concerning sedimentation in lake systems.
Evidence for protracted HALIP magmatism in the central Sverdrup Basin from stratigraphy, geochronology, and paleodepths of saucer-shaped sills
C.A. Evenchick et al., Geological Survey of Canada (GSC-Pacific), Vancouver, British Columbia, Canada. Published online ahead of print on 14 Apr. 2015; http://dx.
The evolution of the Arctic Ocean between the Canadian Arctic Islands, Alaska, Arctic Norway, and Siberia is uncertain because conventional methods of determining the timing and geometry of new ocean basin formation cannot be applied with confidence. The creation of a new ocean basin is accompanied by the formation of igneous rock; therefore, an understanding of the types and ages of igneous rocks in the Canadian Arctic will help our understanding of the evolution of the Arctic Ocean. In this paper, C.A. Evenchick and colleagues document and interpret newly recognized igneous rock occurrences on Ellef Ringnes Island, Nunavut, Canada. These include volcanic rocks that resulted from extrusion of magma at Earth's surface and intrusive rock that resulted from solidification of magma below the surface. Evenchick and colleagues document igneous activity between 130 and 101 million years ago. The ages include periods of igneous activity not recognized in other regions of the Arctic.
Geochronological and Hf isotopic variability of detrital zircons in Paleozoic strata across the accretionary collision zone between the North China Craton and Mongolian Arcs, and its tectonic implications
P.R. Eizenhöfer et al., The University of Hong Kong, Hong Kong, SAR China. Published online ahead of print on 15 Apr. 2015; http://dx.
This article presents substantial new detrital zircon U-Pb and Hf isotopic data that provide insights into understanding the broad Paleozoic accretionary collision between the Mongolian Arcs and the North China Craton. The paper not only sheds a light on an important regional tectonic problem in East Asia, but also on the issue of cryptic suturing with respect to "soft" wedge-wedge accretionary collision. The results of this paper will resolve many long-standing issues of when and how the Paleo-Asian Ocean was closed and North China and Siberia collided, which are important for reconstruction of East Asian continents in Pangea.
Petrogenesis of Malaysian granitoids in the Southeast Asian Tin Belt: Part 1. Geochemical and Sr-Nd isotopic characteristics
Samuel Wai-Pan Ng et al., The University of Hong Kong, Hong Kong. Published online ahead of print on 3 Apr. 2015; http://dx.
The Malaysian tin granites have traditionally been recognized as two distinct granitic provinces: (1) The Permo-Triassic "I-type" Eastern Province, and (2) the Late Triassic "S-type" Main Range Province. In Part 1, new geochemical data show that Chappell and White's (1974) I-S granite classification adopted in the existing model does not adequately distinguish the two provinces from one another, as previously thought. Trace element geochemistry and Sr-Nd isotopic compositions show that the Malaysian tin granites in both provinces have common transitional I-S characteristics, but that they are different in terms of the proportion of igneous and sedimentary protolith involved in melt formation. In addition, they are both enriched in high field strength elements; possibly a within-plate signature inherited from Gondwana-related source rocks.
Petrogenesis of Malaysian granitoids in the Southeast Asian Tin Belt: Part 2. U-Pb zircon geochronology and tectonic model
Samuel Wai-Pan Ng et al., The University of Hong Kong, Hong Kong. Published online ahead of print o 3 Apr. 2015; http://dx.
Previous ages of the Malaysian tin granites, obtained in the 1970s and 1980s, were largely obtained by whole rock Rb-Sr and biotite K-Ar geochronology. We re-sampled the entire Malaysian Peninsula and 40 samples were collected for high-precision U-Pb SIMS dating on extracted zircon grains. The crystallization ages of the Eastern Province granitoids have been constrained to between 220 to 290 million years ago, while the Main Range Province granitoids have ages ranging from 200 to 230 million years ago. A progressive westward younging trend is apparent across the Eastern Province, which is still evident but less obvious in the Main Range Province. Our model proposes two eastward dipping subduction zones. We suggest that subduction roll-back along the Bentong-Raub suture might account for the westward younging trend, in the Eastern province. A second Late Triassic east-dipping subduction zone beneath western Malaysia is proposed in order to explain the "I-type" components to the Main Range Province granitoids.
Strontium isotope (87Sr/86Sr) stratigraphy of Ordovician bulk carbonate: implications for preservation of primary seawater values
C.T. Edwards et al., School of Earth Sciences, The Ohio State University, Columbus, Ohio 43210, USA. Published online ahead of print on 3 Apr. 2015; http://dx.
This study compares 230 bulk carbonate strontium isotope (87Sr/86Sr) measurements to a high-resolution conodont apatite-based Ordovician seawater 87Sr/86Sr curve in order to assess the reliability of bulk carbonate to preserve seawater 87Sr/86Sr and its utility for 87Sr/86Sr chemostratigraphy. Well-preserved bulk carbonate can faithfully record the 87Sr/86Sr seawater trend, but sample variability is about twice that for conodont apatite. The difference between bulk carbonate and seawater 87Sr/86Sr (delta-87Sr/86Sr) is used to show that minimally altered bulk carbonate either contains high Sr concentrations ([Sr] > 300 ppm) or experienced burial temperatures below ~150 °C. Bulk carbonate that meets these criteria can be useful for high-resolution measurement of 87Sr/86Sr seawater, particularly for successions where well-preserved fossils are not available. These criteria must be considered in the context of whether a limestone formed in Calcite Seas (high seawater Sr/Ca) or Aragonite Seas in which case the diagenetic transformation of aragonite to calcite may incorporate non-seawater Sr.
Late Paleozoic Woniusi basaltic province from Sibumasu terrane: Implications for the breakup of eastern Gondwana's northern margin
S.-Y. Liao et al., Chinese Academy of Sciences, Nanjing, China. Published online ahead of print on 3 Apr. 2015; http://dx.
The breakup of northern Gondwana and rifting of Cimmerian terranes are, and will continue to be a hot and debatable topic. Our paper provides a new perspective to this issue by reporting an investigation of Late Carboniferous to Early Permian Woniusi basaltic province in the northern Sibumasu, eastern Cimmerian. We explored its whole distribution (~12,000 km2), precise emplacement age, petrogenesis and tectonic implications. We demonstrate that the Woniusi basaltic province belonged to a fragmentized LIP that may have original distribution comparable to those of Ontong-Java, Deccan or Siberian traps. We suggest that this LIP was most probably triggered by a Late Carboniferous to Early Permian huge mantle plume that centered in the northern Greater Indian. This plume system may have important bearings on the rifting of eastern Cimmerian terranes (e.g. Sibumasu, southern Qiangtang) from the northern Indian and Australian Gondwana margins respectively.
Stratigraphic correlations using trace elements in apatite from Late Ordovician (Sandbian-Katian) K-bentonites of eastern North America
B.K. Sell et al., Syracuse University, Syracuse, New York, USA. Published online ahead of print on 3 Apr. 2015; http://dx.
This research suggests substantial revisions to the larger stratigraphic correlation framework for the Sandbian to Katian interval in eastern North America. The results highlight the importance of considering regional unconformities when using interval biozones and chemostratigraphy for stratigraphic correlation. The use of trace elements in apatite for correlating tephra is extensively tested and is shown to be a robust and reliable stratigraphic correlation method.
Anatexis of UHP eclogite during exhumation in the North Qaidam UHP terrane: Constraints from petrology, zircon U-Pb dating and geochemistry
Yu Shengyao et al., Chinese Academy of Geological Sciences, Beijing, PR China. Published online ahead of print on 3 Apr. 2015; http://dx.
The UHP metabasite in the NQD UHP terrane experienced initial partial melting under eclogite-facies conditions triggered by dehydration melting involving zoisite and rare muscovite.