Carbonate Platform to Basin Transitions on Seismic Data and in Outcrops: Great Bahama Bank and the Maiella Platform Margin, Italy
Gregor P. Eberli, Flavio S. Anselmetti, Christian Betzler, Jan-Henk Van Konijnenburg, Daniel Bernoulli, 2004. "Carbonate Platform to Basin Transitions on Seismic Data and in Outcrops: Great Bahama Bank and the Maiella Platform Margin, Italy", Seismic Imaging of Carbonate Reservoirs and Systems, Gregor P. Eberli, Jose Luis Masaferro, J. F. “Rick” Sarg
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The comparison of seismic and core data from the western Great Bahama Bank with the exhumed Maiella Platform margin and its adjacent slope in the Apennines of Italy relates the seismic facies to depositional facies and processes. Both platforms evolved similarly from an escarpment-bounded, aggrading platform in the Cretaceous to a prograding platform in the Tertiary. This comparison helps to improve seismic interpretation of isolated carbonate platform systems.
Platform interior deposits are typically horizontally layered cycles of shallow-water carbonates, but the seismic sections from Great Bahama Bank are dominated by a chaotic to transparent seismic facies. Synthetic seismic sections of the Maiella Platform margin demonstrate that the chaotic to transparent seismic facies is a product of low-impedance contrasts in the platform carbonates. Both platforms were bounded in the Cretaceous by an escarpment that separated the platform from onlapping basinal and slope sediments. This juxtaposition of facies is recorded in the seismic facies by the lateral change from chaotic platform toinclined continuous reflectionsof the slope. The outcrops of the Maiella Platform margin help assess the processes that formed these escarpments. Small concave scallops and associated megabreccias in the basinal section document episodic erosion during the platform growth, indicating that the escarpment was growing simultaneously with the platform.
Both platforms prograde after burial of the escarpment by basinal sediments. On the western margin of the Great Bahama Bank, progradation started in the middle Miocene and advanced the platform margin approximately 25 km westward to its present position. Progradation is documented on the seismic data by clinoform geometry and the expansion of the interpreted platform seismic facies. The prograding system of western Great Bahama Bank consists of sigmoidal clinoforms with foresets that are approximately 600 m high. The foresets are characterized by reflections with variable amplitude and continuity. Discontinuous high-amplitude packages are interrupted by low-amplitude, nearly transparent units of periplatform ooze. Channels of variable size dissect the entire slope but deep incisions with a persistent cut-and-fill geometry occur preferentially at sequence boundaries. These incised submarine canyons are oriented downslope perpendicular to the strike of the platform margin. Most of the gravity-flow deposits bypassed the upper and middle slope and are deposited on the lower slope and on the toe-of-slope. These redeposited carbonates are seismically characterized by discontinuous to chaotic high-amplitude reflections that suggest a heterogeneous environment of depositional lobes.
Core data indicate that a tripartite facies succession of slope, reef margin, and platform interior deposits forms the topsets of the prograding clinoforms on Great Bahama Bank. This facies succession is also found in the Maiella Platform margin that prograded across the underlying slope during Eocene time. Synthetic seismic sections show that the reefal units appear as transparent zones on the seismic data, corroborating the calibration made by a core-to-seismic correlation in the Bahamas.
Along the Maiella Platform margin, incised slope canyons are exposed, revealing the lithologies of the channel fills. The Maiella canyons are filled with coarse, fining-upward mass gravity-flow deposits that fine upward. The outcropsinthe Gran Sasso area display the heterogeneityof the toe-of-slope environment thatischaracterizedbysmall, amalgamated lobes with feeder channels in largely pelagic background sediment.