The Lake Izabal Basin in Guatemala is a major pull-apart basin along the sinistral Polochic Fault, which is part of the North American and Caribbean plate boundary. The basin infill contains information about the tectonic and sedimentological processes that have imparted a significant control on its sedimentary section. The inception of the basin has been linked to the relative importance of the Polochic Fault in the tectonic history of the plate boundary; yet, its sedimentological record and its inception age have been poorly documented. This study integrates diverse datasets, including industry reports, well logs and reports, well cuttings, vintage seismic data, outcrop observations and geochronological data to constrain the initial infill and age of inception of the basin. The integrated data show that during the Oligocene-Miocene, a marine carbonate platform was established in the region which was later uplifted and eroded in the early Miocene. The fluvial-lacustrine deposits above this carbonate platform are part of the initial infill of the basin and are constrained with zircon weighted-mean 206 Pb/ 238 U ages of 12.060 ± 0.008 from a volcanic tuff ~30 m above the unconformity. Sandstone, mudstone and coal dominate the interval from 12 to 4 Ma, with an increase in conglomerate correlating to the uplift of the Mico Mountains and San Gil Hill at 4 Ma. Fault switch activity between the Polochic and Motagua faults has been hypothesized to explain total offset along the Polochic Fault and the geologic and geodetic slip rates along the two faults. The 12 Ma age determined for the initial infill of the basin confirms this hypothesis. Consequently, our study confirms that at ~12 Ma the Polochic Fault served as the main fault of the plate boundary with inferred slip rates ranging from 13 to 21 mm/yr with a strong possibility that the Polochic Fault was, at some point between 15 Ma and 7 Ma, the only active fault of the plate boundary. The results of this study show that tectonic records preserved in sediments of strike-slip basins improve the understanding of the relative significance of individual faults and the implications with respect to strain partitioning throughout its tectonic history.
ResumenEl Bloque de Yucatán es una microplaca continental que cubre 450,000 km² en el sur de México, el norte de Guatemala y el norte de Belice. Su zócalo cristalino está cubierto por una plataforma evaporítica/carbonatada de hasta seis km de espesor depositada desde el Jurásico Tardío hasta el Reciente. El margen sur del bloque se suturó contra la microplaca Chortis en el Cretácico Tardío y siguió siendo afectado por movimientos relativos sinestrales desde el Mioceno hasta el Reciente. El margen oriental de Yucatán se modificó en el Paleoceno por el movimiento transcurrente del Arco Cubano hacia el norte.Ha habido muy poca sedimentación terrígena en Yucatán desde el Jurásico Medio por la falta de relieve local y el aislamiento de terrenos levantados desde la separación de América del Norte y Suramérica. Haciendo referencia a la geología económica, hay acumulaciones grandes de hidrocarburos al occidente del Bloque de Yucatán en las Tendencias Reforma y Campeche, y en la Cuenca de Macuspana. Se ha encontrado petróleo también al sur-occidente en la Faja Plegada de Chiapas y Guatemala (Sierra de Chiapas). Sin embargo, hasta la fecha se ha descubierto solamente un yacimiento comercial de aceite en el Bloque de Yucatán (el Campo Xan de Guatemala). La exploración para recursos metálicos se ha limitado a una pequeña área del zócalo cristalino expuesto en las Montañas Mayas de Belice.A pesar del modesto éxito económico logrado hasta la fecha, es la opinión del autor que el potencial del Bloque de Yucatán no debe ser menospreciado porque los esfuerzos exploratorios han sido esporádicos y sin la tecnología idónea. Hay una clara necesidad de adquirir nuevos estudios de sísmica regional de alta calidad para revelar la configuración estructural y la arquitectura sedimentaria del bloque. Entre los numerosos factores geológicos que aun no han sido entendidos se mencionan los siguientes: 1) la geometría de las estrucuras de rift (pilares y fosas) del Triásico-Jurásico.2) la presencia y las geometrías de las cuencas de plataforma interna, con sus probables rocas generadoras y crecimientos calcáreos.3) el paleoflujo de calor que afectaba la maduración orgánica. 4) los efectos adentro del bloque de la tectónica en sus márgenes, e.g., basculamiento, compresión, movimientos transcurrentes y movimientos en masa. 5) los efectos del impacto meteorítico "Chicxulub" del límite Cretácico-Terciario. Palabras Clave: Yucatán, Chicxulub, Xan, Petróleo AbstractThe Yucatan Block is a rifted continental microplate covering 450,000 km² of southern Mexico, northern Guatemala and Belize. The crystalline basement is mantled by a Late Jurassic through Recent carbonate/evaporite platform up to six km thick. The southern margin of the block was affected by Late Cretaceous suturing to the Chortis microplate followed by Miocene to Recent strike slip faulting. Its eastern margin was modified by Paleogene strike-slip against the Cuban Arc Terrane. The Yucatan Block has received very little terrigenous sedimentation since it was isolated from nearby landmas...
Outcrops of the Paleocene/Eocene Chicontepec Formation in eastern Mexico have provided a unique opportunity to study exposed time-equivalent sections of the deepwater Gulf of Mexico (GOM) Wilcox Formation. A 2012 study established a stratigraphic framework in the Tampico-Misantla Basin (TMB) and identified sequence boundaries that could not be correlated globally. Fieldwork in 2008 had also established a network of paleocanyons in the basin associated with a particular “54 Ma” sequence boundary. At that time, a Paleocene turbidite basin fed from the northwest was incised by a collection of northeast-facing erosional canyons that coalesced laterally into the main southeast-trending Chicontepec paleocanyon; this canyon network was filled in the Early Eocene. Using the 2012 study chronostratigraphic scheme, recent micropaleontological studies were performed on a unique outcrop containing a bitumen bed within one of these paleocanyons. The results suggest that the basin’s water level fell rapidly by at least 200 m, starting after 55.8 Ma and leading to subaerial exposure of the bathyal beds for a maximum of 850,000 years prior to canyon refill. Evidence of rooting (limonite tubes) occurs in the bathyal turbidites below the bitumen bed. At this time, the paleocanyons in the TMB were eroded by fluvial systems feeding directly into the central Gulf basin, probably a land-locked sea. The interpreted large and rapid fall and rise of the water level between 55.8 and 54.95 Ma supports the “GOM drawdown hypothesis,” i.e., that the GOM may have been isolated from the world’s oceans due to the closure of the Florida straits as the Cuban arc collided with the Bahamas and northeast Yucatán. The timing of the interpreted drawdown coincides with the Paleocene-Eocene thermal maximum (PETM), hinting that the PETM may have been caused or assisted by the release of methane from hydrates in the GOM margins and abyssal plain.
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