Tertiary terrigenous depositional systems of the Mexican isthmus basins




Ricoy, José Ulises, 1948-

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Seismic stratigraphy and lithostratigraphic correlation of well logs were integrated to determine the regional distribution and hydrocarbon potential of the Tertiary lithofacies in the Saline, Comalcalco, and Mesozoic-Villahermosa geological Provinces of the Mexican Isthmus (States of Veracruz, Tabasco and Chiapas). Four principal seismic stratigraphic units or depositional sequences were defined and integrated with stratigraphic well log correlations. The ages of these units are: (I) Paleocene-Oligocene; (II) lower Miocene; (III) middle-upper Miocene; and (IV) Pliocene. These seismic sequences exhibit progradational facies from south-southeast (Mesozoic-Villahermosa province) to north-northwest (Comalcalco and Saline provinces). The progradation of sediments toward the northeast was restricted by the Sitio Grande-Samaria structural high, although the structures allowed by pass of finer sediments and induced a channelization of sediments toward the southeast structural low Platanal-Papiro, where a depositional lobe was formed. The predominant depositional systems in each sequence are interpreted as follows: prodeltaic shelf muds to submarine fans (I); deltaic/submarine fans (II); deltaic (HI) and fluvio/deltaic (IV). The southeast depositional lobe (Platanal-Papiro) is interpreted as being essentially formed by prodeltaic to submarine fan facies of sequence IV. The hydrocarbon producing intervals were located on respective sequence maps: net sand, structural tops, and seismic sedimentary facies. Within each sequence, areas with seismic-sedimentary facies similar to the hydrocarbon producing intervals, areas of greater thicknesses, and depocenters located on relative structural highs, - were extrapolated as potential hydrocarbon producing fairways. The seismic reflectors representative of the Jurassic salt and the top of Jurassic-Cretaceous carbonates document the carbonates wedging from the Mesozoic Province (south-southeast) toward the salt Province (north-northwest), as well as depositional change in the same direction; the carbonates of the Mesozoic Province are interpreted to be shelf/slope deposits, and in the Comalcalco Basin as slope/abyssal deposits. This regional variation in depositional systems initially stimulated and later allowed greater salt structures to develop progressively from the southeast (Comalcalco Basin) to the northwest (Saline Province) in response to the Tertiary terrigenous sediment input