Sedimentology and stratigraphy of the Upper Cretaceous-Paleocene El Molino Formation, Eastern Cordillera and Altiplano, Central Andes, Bolivia: implications for the tectonic development of the Central Andes
Master of Science (MS)
Geology and Geophysics
The Upper Cretaceous-Paleocene El Molino Formation of the Bolivian Central Andes consists of mixed siliciclastic and carbonate strata alternately interpreted as syn-rift, post-rift thermal sag and foreland basin deposits. These deposits can be divided into two lithostratigraphic sequences. The first sequence consists of a carbonate, carbonate sand and mudrock lower member, a middle member consisting entirely of mudrock and an upper member containing carbonates and mudrocks. The second lithostratigraphic sequence contains a lower member composed of carbonate sands, carbonates and mudrocks, and an upper member consisting of a coarsening upwards sequence of sandstones and mudrocks. Within these lithostratigraphic sequences, five facies associations can be identified: 1) an open water facies; 2) a nearshore facies; 3) a beach, bar and shoal facies; 4) a floodplain facies; and 5) a fluvial facies. A regional study of El Molino Formation stratigraphic stacking patterns and facies association geographic distributions suggests that deposition occurred within a dominantly lacustrine basin. For most of El Molino Formation deposition, the lacustrine system remained hydrologically-closed and perennial, although evidence indicates that depositional systems experienced periodic ephemeral lacustrine conditions as well as hydrologically open lacustrine and/or shallow marine depositional environments. While lacustrine systems exist in syn-rift, post-rift thermal sag and foreland basin systems, sedimentological and stratigraphic data, in addition to an absence of key indicators of tectonic activity (e.g. faulting, growth strata) limit the El Molino Formation tectonic setting to post-rift thermal sag and/or foreland basin back-bulge settings. Paleocurrent and provenance data further support the interpretation for post-rift thermal sag and/or back-bulge basin deposition, indicating flow of continental block provenance sediment into a central depositional basin while clast count data show a simple unroofing sequence indicative of the tectonic quiescence associated with post-rift thermal sag and foreland basin back-bulge tectonic settings.
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Fink, Richard John, "Sedimentology and stratigraphy of the Upper Cretaceous-Paleocene El Molino Formation, Eastern Cordillera and Altiplano, Central Andes, Bolivia: implications for the tectonic development of the Central Andes" (2002). LSU Master's Theses. 3925.