Abstract: Geology of the Esquipulas, Chanmagua and Cerro Montecristo Quadrangles, Southeastern Guatemala

By

Burke Burkhart

Rice University Ph.D. thesis, 121 p., May, 1965

In southeastern Guatemala the sedimentary sequence is strikingly similar to that north of the Motagua Valley, with phyllites of the Santa Rosa Group (new designation) overlain by continental clastics of the Jurassic-Lower Cretaceous Todos Santos Formation and limestones of the Albian Coban Formation. Red beds of the Tertiary Subinal Formation are found in bands parallel to the tectonic fabric of the fold mountains of the Sierra, the locus of Tertiary volcanic activity as well. Post-Subinal pyroclastics and water-deposited tuffs, basalts and rhyolites form thick blanket deposits throughout the region.

The Esquipulas area is particularly important because of the insight that can be gained into the complex Late Cretaceous to Recent tectonics, where the pre-Tertiary rocks were folded and later block faulted into basins that paralleled the major fold mountains of Guatemala. The area was an important site of Tertiary volcanism centered almost wholly within an elongate graben basin parallel to the trend of the Motagua fault zone and the axes of the fold mountains. The graben was a basin of deposition for a thick (1000 + meters) sequence of Subinal red beds, composed almost entirely of Tertiary volcanic material. Distribution of Tertiary red beds along major fault zones of Guatemala is the result of volcanism along the zones of weakness and subsequent accumulation of volcanic (largely) detritus in basins that were controlled by normal faulting. 

Pyroclastic activity increased throughout the period of deposition of the Subinal in the Tertiary. A thick blanket of tuff was deposited throughout the map area on top of all but the most prominent peaks of pre-Tertiary rocks at the margins of the Subinal basins. A sequence newly designated here as the Padre Miguel Group is composed of massive and thin-bedded pyroclastics, the water-deposited facies controlled by deposition in graben basins that developed on an essentially north-south trend, transecting the older Subinal graben basins. Siliceous flows, basalts, lahars and pyroclastics which are the uppermost part of the Padre Miguel Group dominated in the Pliocene and Pleistocene.

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