Paleo-canyons and contemdporaneous oil seeps at the Paleocene/Eocene boundary, Tampico-Misantla Basin, eastern Mexico

Abstract

At least five paleo-canyons have been identified on the western flank of the Tampico-Misantla Basin in eastern Mexico. These were formed at ~56 Ma when fluvial systems eroded into the subaerially exposed, unconsolidated Paleocene basin-floor sediments. Previous workers had not identified the Lower Eocene canyon-fills because of ubiquitous, reworked Upper Paleocene foraminifera and nannofossils. Our experience shows that detrital zircon analysis and palynology provide the most accurate depositional dates for the canyon-fill sequences. Following the drop in relative sea-level, a rapid rise provided the accommodation space for the deposition of hundreds of meters of coarse-grained, conglomeratic, and mud-rich canyon-fill sediments. The Acatepec canyon, was filled with more than 150 m of slumps, pebbly-mudstones, channel and channel-levee sediments. The upper part of the sequence also contains four paleo-karsted intervals which may indicate additional relative sea-level fluctuations. The Paleocene Eocene Thermal Maximum (PETM) has not yet been identified in the outcrops, but Wheeler diagram reconstructions indicate that it should be present near the canyon bases. The San Lorenzo paleo-canyon contains a mass transport complex at its base and overlies over 600 m of bathyal sediments. The pre-erosion and canyon-fill sediments are all deepwater sequences, begging the question of what caused the rapid fall and rise of relative sea-level. We have also identified two bitumen bed in outcrop which show evidence of desiccation in bathyal sediments, supporting a rapid fall of relative sea-level. This would have caused a pressure decrease in underlying sediments and, together with the removal of sediment caused by erosion, could be responsible for seal failure of hydrocarbon trap. This then caused subaerial oil seeps which fill in desiccation cracks and topography on a major unconformity

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018