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Slumps and Debrites in the Paleocene Chicontepec Formation, Mexico: Implications for Subsurface Identification

Stephen P.J. Cossey
Cossey and Associates Inc, Durango, CO

The Paleocene Chicontepec Formation crops out along the western margin of the Tampico embayment, also known as the Tampico-Misantla basin, located in northeastern Mexico. The sequence records deposition in a deep-marine, foreland basin between the Golden Lane Atoll and the Sierra Madre Oriental. In the northern part of this outcrop belt, slope deposition is recorded primarily by undeformed and deformed thin-bedded turbidites with occasional sand-rich lobes, channel-fills and debrites. Sediment transport and slumping direction was to the east and southeast. The slumped, thin-bedded turbidites show the complete spectrum of deformation, including coherent slumps, semi-coherent, chaotic, faulted and boudinaged slumps. Several of these types of slumps can occur in a single outcrop. All the slumps have extremely flat upper surfaces, indicating that the tops of the slumps were either all planed-off or continued moving after the main body of the slump froze in-place. A unique, flat-topped toe-thrust, is also preserved at one of the outcrops. Several large, spectacular debrites up to 30 m (98 ft) thick show faulting at their erosional margins, pressure ridges and evidence that the debris flow did not create the void that it occupies.

These spectacular outcrops provide a unique opportunity to study the detailed characteristics of geological seafloor hazards and slumped reservoirs. Evidence from these outcrops indicates that sub-seismic scale slumps could be extremely difficult to identify, even in core or on FMI logs.