Stratigraphy and structure of the San Lucas area, Michoacan and Guerrero states, southwestern Mexico

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Geology and Geophysics

First Committee Member

Christopher G. A. Harrison - Committee Chair


Mesozoic marine rocks and Cenozoic continental red beds were mapped at 1:50,000 scale in a 900 km$\sp2$ area around San Lucas, in the Balsas River basin between Ciudad Altamirano, Guerrero State, and Huetamo, Michoacan State, Mexico. Interpretation of Landsat Thematic Mapper images, combined with extensive field work, enabled refinement of the stratigraphy and a new interpretation of the structure of the region south of the Mexican Volcanic Belt. A sedimentary sequence nearly seven kilometers thick crops out in the study area. Mesozoic marine rocks consist of a shallowing-upward sequence approximately 3.5 km thick, with previously unreported laminated cherts at the base, progressing upward through turbidite facies clastic rocks, and shallow water carbonates of middle to late Cretaceous age at the top. More than three kilometers of continental clastic rocks are exposed above the marine sequence. A major angular unconformity within the red beds is interpreted to record the end of intense Laramide (late Cretaceous-early Tertiary) folding and thrusting. Structural repetitions observed in the Cretaceous marine sequence require reinterpretation of the Laramide tectonic evolution of the area, involving thin-skinned tectonics. These conclusions have important implications for the regional tectonic interpretation of southwestern Mexico, the interrelationship between the structural and stratigraphic development of the area, depth to basement, and perhaps most importantly, the lack of compelling evidence for Laramide accretion of tectonostratigraphic terrances in the region. A three-part tectonic model was constructed to explain pre-Laramide, Laramide, and post-Laramide tectonics and sedimentation in the region, constrained by the new stratigraphic and structural data. The model is similar to others developed to explain the evolution of the North American Cordillera during the Laramide Orogeny. It is also consistent with models of the Caribbean region that predict large eastward displacements of the Chortis block of Central America along the southern margin of Mexico, resulting in gradual truncation of the margin, transcurrent faulting, exposure to subduction, and uplift.



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