Southern Shelf of Belize: An Analog to Morrow and Atoka Formations, Permian Basin

Louis J. Mazzullo, S. J. Mazzullo

The Holocene and Pleistocene geology along the southern shelf of Belize displays a range of mixed siliciclastic and carbonate environments. The alluvial plain in southern Belize is supplied by sediment from the Maya Mountains, which are several to a few tens of miles inland of a clastic-dominated shoreline. Marshy tidal flats characterize the area immediately west of the shoreline. River-mouth processes along the southern shoreline vary in response to sediment load, inasmuch as the inner shelf is variously sheltered by a barrier reef, which lies up to 25 mi to the east, and tidal ranges are very low. The clastic shoreline grades seaward to rippled fine-grained sands and silts, which pass farther seaward into montmorillinitic green shales. In shallower parts of the marine helf, carbonates are intimately intermixed with, or grade rapidly to, carbonate banks and patch reefs. Submerged fluvial channels document relatively recent rises in sea level and transgression of marine over alluvial facies.

The Morrow formation of southeastern New Mexico and the Atoka Formation of the northern Midland basin display striking similarities to the southern Belize shelf in terms of depositional patterns, facies interrelationships, and scale. Detailed lithofacies mapping of the Morrow and Atoka reveal sequences of shallow marine carbonates interbedded with shallow marine and marine-transitional siliciclastic sedimentary rocks in both formations. These deposits are seaward of alluvial and marshy (primarily clastic) tidal-flat facies derived from low to moderate relief source areas. Deposition in both formations was affected by repeated minor fluctuations in sea level. Fluvial sandstones are hydrocarbon reservoirs in both the Morrow and Atoka, although the Morrow contains a wider range of reserv ir sandstone types.

AAPG Search and Discovery Article #91026©1989 AAPG Southwest Section, March 19-21, 1989, San Angelo, Texas.