Atmospheric halogen and acid rains during the major Deccan episode: magnetic and mineral evidences

Environmental and climatic changes linked to Deccan volcanism are still poorly known. A major limitation resides in the paucity of direct Deccan volcanism markers and in the geologically short interval where both impact and volcanism occurred, making it hard to evaluate their contributions to the mass extinction. We investigated the low magnetic susceptibility interval just below the Iridium-rich layer of the Bidart (France) section, which was recently hypothesized to be the result of palaeoenvironmental perturbations linked to paroxysmal Deccan phase-2. Results show a drastic decrease of detrital magnetite and presence of fine specular akaganeite, a hypothesized reaction product between FeCl2 from the volcanic plume with water and oxygen in the high atmosphere. A weathering model of the consequences of acidic rains on a continental regolith reveals nearly complete magnetite dissolution after about 33,000 years, which is consistent with our magnetic data and the duration of the Deccan phase-2. This discovery represents an unprecedented piece of evidence of the nature and importance of the Deccan-related environmental changes

Atmospheric halogen and acid rains during the main phase of Deccan eruptions: magnetic and mineral evidence

Environmental changes linked to Deccan volcanism are still poorly known. A major limitation resides in the paucity of direct Deccan volcanism markers and in the geologically short interval where both impact and volcanism occurred, making it hard to evaluate their contributions to the mass extinction. We investigated the low-magnetic-susceptibility interval just below the iridium-rich layer of the Bidart (France) section, which was recently hypothesized to be the result of paleoenvironmental perturbations linked to paroxysmal Deccan phase 2. Results show a drastic decrease of detrital magnetite and presence of scarce akaganeite, a hypothesized reaction product formed in the aerosols derived from reaction of a volcanic plume with water and oxygen in the high atmosphere. A weathering model of the consequences of acidic rains on a continental regolith reveals nearly complete magnetite dissolution after ~31,000 yr, which is consistent with our magnetic data and falls within the duration of the Deccan phase 2. These results highlight the nature and importance of the Deccan-related environmental changes leading up to the end- Cretaceous mass extinction

The Paleocene-Eocene GSSP at Dababiya, Egypt – Revisited

We investigated the Paleocene-Eocene boundary GSSP (Dababiya quarry) near Luxor, Egypt, in two nearby (25m and 50m) sequences based on highresolution biostratigraphy, lithostratigrapy, mineralogy and geochemistry. Results confirm the many positive aspects of the Dababiya GSSP but also show potentially serious limiting factors: (1) the GSSP is located in the deepest part of a ~200 m wide submarine channel, which limits its use as global type section. (2) Some lithologic units identified at the GSSP are absent or thin out and disappear within the channel and beyond. (3) The P-E boundary is placed at the base of a clay layer above an erosion surface with variable erosion of latest Paleocene and earliest Eocene sediments. (4) The current definition of the P-E boundary as marked by the abrupt onset of the carbon isotope excursion at the base of a clay layer is not supported at the GSSP because 50m to the left the excursion begins gradually 60cm below the P-E boundary and reaches minimum values in the boundary clay. With awareness of these limiting factors and recognition of the gradual onset of the PETM excursion the GSSP can contribute significantly to a more complete understanding of this global warm event

Chicxulub impact spherules in the NW to SW Atlantic: age constraints and KTB hiatus

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. Copyright © Cambridge University Press 2013

Stratigraphy of the Cenomanian-Turonian Oceanic Anoxic Event OAE2 in shallow shelf sequences of NE Egypt

Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated to evaluate the response to OAE2. Age control based on calcareous nannoplankton, planktic foraminifera and ammonite biostratigraphies integrated with delta(13)C stratigraphy is relatively good despite low diversity and sporadic occurrences. Planktic and benthic foraminiferal faunas are characterized by dysoxic, brackish and mesotrophic conditions, as indicated by low species diversity, low oxygen and low salinity tolerant planktic and benthic species, along with oyster-rich limestone layers. In these subtidal to inner neritic environments the OAE2 delta(13)C excursion appears comparable and coeval to that of open marine environments. However, in contrast to open marine environments where anoxic conditions begin after the first delta(13)C peak and end at or near the Cenomanian-Turonian boundary, in shallow coastal environments anoxic conditions do not appear until the early Turonian. This delay in anoxia appears to be related to the sea-level transgression that reached its maximum in the early Turonian, as observed in shallow water sections from Egypt to Morocco. (C) 2011 Elsevier Ltd. All rights reserved