Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9463178 | Palaeogeography, Palaeoclimatology, Palaeoecology | 2005 | 17 Pages |
Abstract
We propose a hypothesis in which anoxic conditions were initiated beneath the halocline in a salinity stratified water column; a fresher surface layer resulted from ice meltwater generated during early deglaciation. During the initial stages of marine incursion, nutrients in the monimolimnion were isolated from the euphotic zone by the halocline. Increasing total organic carbon (TOC) and δ13Corg up section indicates the organic carbon content of the shales was controlled mainly by increasing bioproductivity in the mixolimnion (the Strakhov model). Mixolimnion nutrient levels were sustained by a continual and increasing supply of meltwater-derived nutrients, modulated by obliquity changes in high latitude insolation. Anoxia was sustained over tens to hundreds of thousands of years. The formation of black shales on the north Gondwana shelf was little different to those observed in modern black shale environments, suggesting that it was the nature of the Ordovician seas that pre-disposed them to anoxia.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth-Surface Processes
Authors
Howard A. Armstrong, Brian R. Turner, Issa M. Makhlouf, Graham P. Weedon, Mark Williams, Ahmad Al Smadi, Abdulfattah Abu Salah,