Print this pageMicrobial Boundstone Slope Shedding—a Model for Carbonate Platform Growth
Kenter, Jeroen A. M.1, Paul (Mitch) Harris2, Giovanna Della Porta3 (1) Vrije Universiteit, Amsterdam, Netherlands (2) ChevronTexaco Energy Technology Company, San Ramon, CA (3) Universität Potsdam, Potsdam, Germany
Characteristics of two prograding
steep, high-relief margins fronting deep basins provide a depositional model
which may apply elsewhere. Seismic and well data from Tengiz,
one of the larger fields in the
Both examples share a highly productive microbial boundstone slope extending from the platform break to
nearly 300 m (or more) depth and a lower slope dominated by (mega)breccias and
grain flow deposits derived from the margin and slope itself. The broad depth
range of microbial and cement boundstone “factory”
increases the potential for production during both lowstands
and highstands of sea level and thereby facilitates progradation. Rapid in situ lithification
of the boundstone provides stability to the steep
slopes, but also leads to readjustment through shearing and avalanching.
Remarkable observations are the contrasts with the Bahamian highstand
shedding depositional model, little control by fluctuations in sea level or by paleo-wind directions due to their self nourishing nature,
and the accretion rates of in-situ boundstone.
This new model
of “slope” shedding has implications for slope readjustment, slope
architecture, sequence stratigraphic models,
reservoir characterization, and reservoir modeling, especially given that the
isotropic character of microbial boundstone will
reduce the potential for coherent seismic reflections to develop and possibly
invoke, under certain stress regimes, shattering and fracturing thereby
generating significant nonmatrix permeability.