(1) Vrij University, Amsterdam, Netherlands
(2) University of Wisconsin, Madison, WI
Abstract: Long-term Drowning of Carbonate Platforms by Geodynamic Processes
The rule that sedimentation rates decrease with increasing time interval has recently been examined by procedures that avoid the mathematical problem of ratio correlation. These tests confirm that the dependence of sedimentation rates on the time scale is a physical property of the sediment record and not an artifact of data transformation. In the time range of 10-1-108 yr, sedimentation rates change roughly in proportion to the inverse of the square root of time. One probable consequence of rate scaling is that the growth potential of reefs and carbonate platforms is also scaled such that relative sea-level rises extending over long time may be able to drown a platform even though the rate of rise is far below the short-term growth potential of the system. We present examples that supporting platform drowning by long-term tectonic subsidence.
In the Alpine Mesozoic, rapid subsidence during rifting correlates with a gradual change from restricted to open marine and finally to deep-water conditions. Drowning extended over 30.10 yr. On other passive margins and in foreland basins we observed phases of repeated backstepping extending over 10-20.106 yr. The change from progradation to backstepping and vice versa frequently coincides with changes of subsidence by factors of 2-4 but overall rates remain in the range of 102 Bubnoffs when averaged over 106 yr (1 Bubnoff=1 micron/yr). We estimate that the growth potential of reefs and platforms is about 200-300 Bubnoffs for growth intervals of 106 yr and 75-150 Bubnoffs for intervals of 107 yr.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana