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Abstract

One-dimensional and two-dimensional basin modeling has been performed along a regional transect crossing the Córdoba Platform allochthons and the autochthonous Veracruz Basin in order to infer the burial and kinematic evolution and to determine timing of hydrocarbon migration and charge in this famous Mexican petroleum province. Vitrinite reflectance, Rock-Eval data, and bottom-hole temperatures have been used to calibrate the heat flow and thermal evolution of the Veracruz Basin, where no erosion occurred.

The Córdoba Platform and Veracruz Basin in Eastern Mexico comprise the southern most extent of the Laramide foreland fold-and-thrust belt,which developed along the eastern border of the North American Cordillera from Late Cretaceous to Eocene. Unlike in the Canadian Rockies, where pre-orogenic strata are relatively isopachous, this segment of the North American craton has been strongly affected by the Jurassic rifting and opening of the Gulf of Mexico. Substantial thickness and facies changes between horsts and grabens control the lateral and vertical distribution of Mesozoic source rocks and hydrocarbon reservoirs.

In the east, thick Paleogene and Neogene sequences in the Cordilleran foreland provide a continuous sedimentary record in the Veracruz Basin. In the west, however, the Middle Cretaceous carbonates of the Córdoba Platform generally constitute the main outcropping horizon in the adjacent thrust belt, making it difficult to reconstruct its burial evolution from the Laramide orogeny onward.

Cemented veins were sampled in reservoir intervals of the thrust belt. Petrography, stable isotope analyses, and fluid inclusion studies (microthermetry, Synchroton Fourier Transform Infra-Red analyses) on these samples revealed the diagenetic history of the reservoirs. Where diagenetic phases could be constrained in time and with respect to the tectonic evolution, fluid inclusion temperatures provide an additional paleothermometer in areas where major erosion occurred. Pressure-temperature modeling of simultaneously entrapped aqueous and oil-bearing inclusions indicates more than 4.5 km of erosion of Late Cretaceous-Paleocene sequences in the thrust belt, which can be accommodated in palinspastic sections only by restoring a hypothetical foredeep basin. This implies that the current east-dipping attitude of the basement beneath the Córdoba Platform developed after Laramide deformation, accounting for a major change in paleofluid dynamics. Fluid flow and basin modeling of the Veracruz section has been performed using CERES2D to infer the paleofluid dynamic associated with the petroleum system evolution. Following the initial phase of geometric model building and calibration against the thermal and burial history inferred, the modeling accounted for the past migration pathways for both water and oil and gas fluids. Unlike in most other foreland fold-and-thrust belts, hydrocarbons generated in Jurassic source rocks from the Veracruz foreland are currently migrating westward toward the thrust belt, accounting for a post-Laramide charge of the frontal duplexes of the Cordilleran thrust belt.

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