Nuclear Central America, Hub of Antillean Transverse Belt

Nuclear Central America is defined as comprising the eastern portion of the Sierra Madre del Sur, its ancient geanticline and the flanking geosynclinal portion of the Gulf Coast and Caribbean embayments. Southeastern Mexico, Guatemala, British Honduras, Honduras, and Nicaragua make up the principal land area. Nuclear Central America disappears to the east into the Caribbean Sea in east-trending tectonic lineaments. The north flank of this geanticline is the crucial area for regional geologic interpretation. The Mesozoic-Cenozoic Chapayal basin is the prime sedimentary area involved. Chapayal basin, the local extension of the Gulf embayment, is sharply asymmetric, having a steep and faulted south limb and a gentle opposing limb which shelves northward over the Yucatan platform. The shelf area is interrupted by the Maya Mountains uplift in British Honduras which developed during the Paleozoic. The Maya Mountains represent a remnant of an ancient landmass that provided a source for Mesozoic and Cenozoic sedimentation. The late Paleozoic-Mesozoic mobile belt, which sets the pattern for the geology of Nuclear Central America and the Antillean region, extends eastward from the mainland through the Greater Antilles. The main period of geosynclinal subsidence and sedimentation is Mesozoic in age; however, thick deposits were laid down during the Tertiary in the Chapayal basin and eastward in various island areas. In Nuclear Central America the sediments were derived primarily from the south, and from the ancient Maya Mountains-Misteriosa Ridge landmass lying on the northwest of the Caribbean. The partially foundered northwest Caribbean borderland, and the arcing of the late Paleozoic-Mesozoic and younger mobile belts provide the basic framework for the tectonic relationships between North and South America. The Lesser Antilles region is, principally, Late Cretaceous or early Tertiary in age. The foundering of the Gulf craton occurred with the beginning of the Mesozoic, and the initial deposits of the Gulf embayment are the red-bed clastics and associated sediments of Triassic-Jurassic age. Paleogeographic maps indicate that the Caribbean embayment probably had a related origin. The older and partially metamorphosed sediments in Nuclear Central America and its environs include undifferentiated Carboniferous and older Paleozoic, and possible Precambrian rocks. Younger unmetamorphosed sedimentaries are Permian, Jurassic, Cretaceous, early Eocene, late Oligocene, Miocene, and Pliocene in age, and include one of the thickest Mesozoic evaporite sequences in the world. Important orogenies are reflected in the sediments during all the major diastrophic events and during the early Oligocene. Intended as a principal contribution to the geology of the region is the introduction here of a supporting stratigraphic chart showing, in part, those formation names and ages which are accepted in Guatemala by the local Stratigraphic Nomenclature Committee. A late Tertiary and Quaternary volcanic belt follows the Sierra Madre axis for a short distance in eastern Mexico and Guatemala and diverges southeastward through the remainder of Central America, forming the physiographic Rocky Mountain backbone of today. Only slightly more than two dozen wells have been drilled for oil or gas in the northern Central America portion of Nuclear Central America. Although the results have been negative, there have been numerous encouraging shows. Evaporitic deposits in the Cretaceous and Jurassic limit the potential section of reservoir porosity.