Abstract

Petrographic studies from 140 sandstone samples from the four largest oil fields of the Salina Basin, on the southern Gulf of Mexico, were used in this study. Subsurface sandstones of the Encanto Formation (middle to late Miocene age), ranging in depth from 1850 to 3100 meters, are mainly poorly cemented lithic arkoses and feldspathic litharenites. Feldspar rich plutonic and volcanic rock fragments are the most abundant framework grains, with minor metamorphic and clastic rock fragments and traces of carbonate grains. Similar composition is inferred toward the marine portion of this basin.

Provenance analyses show that most of the sediments in the basin came from an evolved dissected or transitional magmatic arc, including very rich feldspar samples coming from an exhumed basement. This evidence supports the idea of having the Chiapas Massif as the main source of the sediments. On the other hand, basically no detritus are inferred to have come from the Chiapas Foreland and Thrust Belt or the Yucatan Platform. The amount of volcanic rock fragments of these sandstones seems to indicate a larger volcanic source area than that ever reported for the region. Therefore, we infer that Chiapas Batholith had a thicker sequence of calcakaline tertiary volcanics, which were eroded and deposited toward the north, in the Salina Basin.

Carbonate grain absence would require a strong channelized sedimentation directly from the south, with almost no input of sediments from the Chiapas Foreland and Thrust Belt, the Yucatan Platform or from western terranes on continental Mexico.