The Biogeochemical Aftermath of Neoproterozoic Ice Ages

University Of Maryland, College Park, College Park MD

Investigators

Abstract

ABSTRACT The Biogeochemical Aftermath of Neoproterozoic Ice Ages The proposed research aims to critically test the celebrated Snowball Earth hypothesis, which predicts that several times in the Neoproterozoic (543-1000 million years ago), the entire planet was blanketed from the poles to equator with continental glaciers and sea ice. To overcome such extreme conditions it has been suggested that over millions of years atmospheric carbon dioxide concentration must have risen to over 100 times its present inventory, eventually building up enough greenhouse gas to warm the frozen planet. On one hand, the materials required for the enigmatic carbonates (which cap these Neoproterozoic glacial sediments worldwide) may have come from the intense weathering of the continents under such a CO2-charged atmosphere. Alternatively, the source of these materials may have derived from the deep ocean where sulfate-reducing bacteria dominated the water column - similar to the present-day anoxic Black Sea - during widespread, yet less severe and shorter glacial epochs. Testing the validity of either of these end-member hypotheses will require detailed study of the elemental, mineralogical, textural, and stable isotopic compositions of the cap carbonates. Samples from the Otavi Group in Namibia (where the critical evidence for global glaciation was first amassed), and in demonstrably equivalent strata from the Bambui and Macaubas groups of Brazil will be analyzed. Regional mapping and high-resolution stratigraphic studies of the thick, carbonate-dominated Brazilian successions will aid in the evaluation of models that seek to explain these severe oscillations of Precambrian climate.