SEQUENCE STRATIGRAPHIC ARCHITECTURE, THE DICHOTOMY OF TIME, AND THE IMPORTANCE OF EPICONTINENTAL BASINS

The differences between ice- and greenhouse modes have long been appreciated with respect to the climatic differences associated with each of them. An area, however, that has received less attention is how those variations in climate impact the stratigraphic records through the effects of changing sea-level regimes. The established amplification of Milankovitch-scale, sea-level changes during icehouse intervals has led to geologically rapid and dramatic fluctuations in sea level reflecting both changes in eccentricity (~100 ka) and obliquity (~41 ka). In terms of sequence stratigraphy, this implies that sequence boundaries occur with a much higher temporal frequency during icehouse intervals resulting in records that are likely to be much more hiatus dominated than those from greenhouse periods. At least during the Cenozoic, the degree of stratigraphic completeness is further negatively impacted by the lack of widespread epicontinental seas, areas were the combination of tectonic and sedimentary loading generally produced broad regions of increasing accommodation space. Therefore, despite the overall abundance of Cenozoic, especially Neogene deposits, our ability to place these into a robust chronostratigraphic framework is limited by not only the nearshore setting of many of these deposits, which often limits the presence of biostratigraphically important taxa, but also by the inability or difficulty in using a range of other tools, such as magnetostratigraphy and potentially strontium-isotope stratigraphy. These differences in temporal stratigraphic patterns have tremendous influence on a variety of paleobiologic questions, especially on reconstructing evolutionary tempo and mode.