AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
A Reconstruction of Global Sediment Fluxes Since the Late Jurassic: Fact, Fiction or Wishful Thinking?
(1) GETECH, Leeds, United Kingdom.
The evolution of accommodation space is key to determining hydrocarbon potential. It is dictated by three factors: subsidence rate, which is a function of tectonic regime and sediment loading; eustacy; and sediment supply. Of these, sediment supply is perhaps the most complex, encompassing all of the processes that affect sediment from production (source) to delivery (sink), including tectonics, surface processes, climate, vegetation, weathering and autogenic effects. Uncertainty is further exacerbated by the fact that basin hinterlands, which supply sediment, have little or no preserved record since they are, by definition, erosional.
In this study we have used detailed palaeogeography as an alternative means of trying to reconstruct sediment supply. Maps have been constructed for each stage in the Cretaceous and Cenozoic, underpinned by a new global plate model. These have been built around a database of geological information. Each timeslice is represented by the following: GIS-based maps of palaeoenvironments and lithologies (contemporary sink areas); tectonophysiographic terrains (source areas, which are categorized according to the last thermo-mechanical regime to have affected that area); and intra-timeslice variations in shoreline. These are then converted into maps of palaeobathymetry, palaeoelevation and palaeodrainage.
Changes in elevation between adjacent timeslices are then calculated. This provides a first order indication of landscape evolution, but does not necessarily give an indication of denudation (the change in each crustal column, which then gives a measure of the sediment flux from each grid cell). This requires corrections for dynamic topography. Results are then checked against thermocronological, cosmogenic and sedimentological data. This is an iterative process, with derived sediment fluxes to basins then compared with measured sediment volumes, especially in areas of good well and seismic control. We have also made comparisons to the results of modeled fluxes using empirically derived equations, which have been applied to our palaeogeographies using our drainage basin reconstructions and the results of coupled Earth System models.
Whilst there are clearly uncertainties involved in this approach, the results are testable and we believe that this provides an effective method for predicting sediment supply in a robust, but inexpensive way.