--> Abstract: Patterns in Ice-House Carbonates; #90063 (2007)

Datapages, Inc.Print this page

Patterns in Ice-House Carbonates

 

Pollitt, David A.1, Peter M. Burgess2, V. Paul Wright1, Giovanna Della Porta1 (1) Cardiff University, Cardiff, United Kingdom (2) Shell Internation Exploration and Production, Rijswijk, Netherlands

 

Many 1D forward models of sedimentary cyclicity in carbonates have focused on strata produced during greenhouse periods, and have attempted to address the dispute over the relative importance of allocyclic versus autocyclic controls. There has traditionally been less investigation and dispute over the origin of ice-house cycles, where prominent exposure surfaces on sub-tidal facies are indicative of relative sea-level falls. The understanding of ice-house cyclothems, however, holds critical importance for super-giant fields in Central Asia, where cyclic platform carbonates form important reservoirs.

 

The aim of this study is to use a 1D forward model to investigate the impact of various controls on potential reservoir layering and heterogeneity.

 

We present a robust 1D numerical forward model incorporating euphotic, oligophotic and aphotic carbonate production, depth-dependent marine erosion, and linked sub-aerial pedogenesis, dissolution and diagenesis. Results demonstrate how modeled facies stacking-patterns depend on interactions of production, erosion and dissolution.

 

The modeling suggests that high-order orbital oscillations are unlikely to be manifest as stacked shallowing-upwards cyclothems. Furthermore, they are unlikely to be stacked to a ratio (e.g. 5:1) within a lower-order sequence, as some workers have previously suggested. It is more likely that high-order oscillations are manifest as a discrete facies changes, occurring within longer-term cyclothems of varying thicknesses and bounded by sub-aerial exposure surfaces. Statistical analysis suggests that cyclothem thickness occur as a continuum of values, lacking any evidence for a 3rd, 4th and 5th order heirarchy. These model scenarios are tested against classic Four Corners Carboniferous successions.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California