Devonian Carbonate Platforms – Challenges and Potential for Integrated Chronostratigraphic Analysis
Devonian carbonates include some of world's most productive reservoirs as well as most illustrative exposures of ancient land-attached and isolated reefal platforms with diverse faunal assemblages. Most workers consider the Devonian a greenhouse system with minor cooling and transitional patterns developed in Givetian and Famennian stages. In contrast to other well-studied greenhouse systems such as the Early Ordovician and Cretaceous, Devonian platforms are developed in more active and isolated basins, thus requiring a combination of datasets for accurate correlation and identification of global signals. In addition, most of the “type” areas only contain exposures of one or two of the Devonian stages, making the development of common reference frames difficult. Fundamental questions that hold the key to predictability, such as the global vs. regional nature of stratigraphic sequences, frequency and amplitude of eustacy, the spatial and temporal extent of biotic crises, and the impacts of these phenomena on platform productivity and organic preservation, require integrated studies to unravel. The Devonian has been examined globally with a wide range of chronostratigraphic approaches to refine the hybrid stratigraphic signal. Conodont and vertebrate biostratigraphy, magnetostratigraphy, magnetic susceptibility, 13Corg and 13Ccarb, 18O/16O, and trace element chemostratigraphy have, in combination, been able to increase stratigraphic resolution, particularly in the Early and Middle Devonian where stratal architecture is subdued. Sequence analysis in this dominantly greenhouse system provides a first-order guide for comparison, such as in the Frasnian 3rd order frameworks of Australia and Canada, but detailed correlations and quantification of eustatic vs. biotic controlling functions is only now developing. Recent sequence framework for the Frasnian of the Canning Basin of Australia illustrates 6-7 3rd order units whereas the Western Canadian Sedimentary Basin workers now define 9 sequences. To what extent are these records truly different and to which driving processes do they owe their differences remain unknown, however tools and approaches are emerging to address these questions. Devonian carbonate platform-to-basin records throughout the world with their extensive multiproxy datasets may be the best test-case yet to examine the relative importance of eustatic, envinronmental/biotic, and tectonic drivers on a predominantly greenhouse succession.
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014