THE LARGE-SCALE STRUCTURE OF THE FOSSIL RECORD

Although the structure of the fossil record is well-understood at the geographic scale of a sedimentary basin and time scales of thousands to a few million years, less process-based attention has been given to larger and longer time scales. The roles of basin subsidence, eustasy, and sediment supply remain the governing factors over these larger and longer scales, although their relative importance differs from smaller and shorter scales. Initial examination of the large-scale structure of the fossil record indicates five important guiding principles. (1) Subsidence rates in most basins decrease over time, causing the stratigraphy to become more progadationally stacked, with a shift towards shallow marine and coastal plain sedimentation. Long-term stacking patterns are also modulated by variations in eustasy and sediment supply. (2) Sedimentary basins occupy a limited portion of Earth's continental surface today and likely so over the geological past. Only particular types of basins are common and likely to be preserved into deep geologic time. (3) Basins can be broadly divided into three categories, and these are fundamentally different in terms of geographic scale and longevity. Basins produced by cooling (passive margins, cratonic basins) occupy larger regions and are an order of magnitude longer-lived than flexural basins (pro-foreland and retro-foreland basins). Basins produced by stretching (rifts) are intermediate: they are large, but relatively short-lived. Marine records are common in all three categories of basins, but extensive terrestrial records are largely limited to flexural basins and rift basins. Upland terrestrial records are even more limited to rift basins and some flexural basins. (4) Preserving a deep-time fossil record requires basin subsidence, but modified by long-term eustasy. The more recent fossil record contains significant doomed sediments with little long-term chance of preservation. The deeper fossil record lacks most of these doomed sediment. (5) The long-term, global-scale fossil record is defined by the intersection of biogeographic provinces and the location of sedimentary basins. This heterogeneity must be considered in any interpretation of the long-term, global-scale fossil record.