Neogene current-modified submarine fans and associated bed forms in Mexican deep-water areas




Arce Perez, Luis Enrique

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The Mexico’s Gulf of Mexico Neogene record reflects the dynamic interaction between high rates of sedimentation and tectonic processes. Distinctive Pliocene to Miocene-age shingled seismic clinoforms reflections were identified in a previous study using older data and interpreted as contourite drift deposits located east of the Mexican Ridges in paleowater depths exceeding 400 meters. The database for this thesis includes new and recently reprocessed seismic data, well logs and core information. Large scale bedforms with seaward-dipping accretion sets (SDAS) are documented in several geobodies mapped in the study area.
The objectives of this research are to evaluate the paleogeographic evolution of the southwestern Gulf of Mexico and deepwater systems during Neogene, evaluating several hypotheses for development of these unique SDAS deepwater bedforms, placing observations in a regional context, and interpreting likely sediment sources and transport pathways. The SDAS were present in four geobodies, two of Upper Miocene (UM) age, one in the Mio-Pliocene (PL1) and another in the Pliocene (PGa) genetic sequence. Time structure maps show progressive infill of the deep-water Veracruz Trough from the southwest. Isochron maps show individual SDAS geobodies thinning basinwards, paralleling trends of adjacent submarine fans. The geobodies were likely formed during an episode of high precipitation and river discharge, modulated by tectonics, and a steep slope that may have allowed frequent bypass of sediments to the basin. SDAS show a series of internal structures climbing upward and landward that are interpreted as cyclic steps bedforms deposited by high-velocity, supercritical turbidity flows. Geobody 2 is associated with an adjacent channel complex and may be a product of unconfined, levee overbanking flows. Other geobodies are associated with submarine fan mounds.
The Mexican Ridges foldbelt may have steered southerly longshore and along slope flow into the nearby Cañonero Canyon, then diverting turbidity flows to the east. The early forming Mexican Ridges may also have created a steep slope gradient and bottom roughness that facilitated local development of hydraulic jumps, a prerequisite for generation of cyclic steps bedforms. Identification of these unusual bedforms in Pliocene and Miocene strata of deepwater Mexico represents one of first documented occurrence in subsurface settings.


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