Paleogeographic Evolution and Non-Glacial Eustasy, Northern South America

Paleogeographic Evolution and Non-Glacial Eustasy Northern South America - Published eustatic cycle charts commonly call for eustatic fluctuations of more the 40 m every few million years or less. These cycles are interpreted as eustatic, but, so far, waxing and waning of continental glaciations is the only known mechanism which clearly has the ability to drive such large, short-term eustatic fluctuations. High-magnitude, high-frequency ?glacio-eustatic cyclicity? may be a valid concept for times of continental glaciations, but what about times when such glaciations was absent from Earth? Why do cycle charts have a similar form and style for time periods with and without glaciation? Is it that we have missed the identification of a fundamental driving cause which is as important as glaciation and which might have operated during non-glacial times? Or, is it that we are confusing local and eustatic drivers of relative sea-level change? These persistent questions, and others, continue to cast doubt on the entire subject of sequence correlatability. The papers in this book collectively address these questions.
Chronology, Relative Sea-Level History and a New Sequence Stratigraphic Model for Basinal Cretaceous Facies of Colombia
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Published:January 01, 1998
Abstract
Cretaceous strata of Colombia are primarily composed of siliciclastic sediments derived from the Guyana Shield to rhe east and, al times, from an ancestral Central Cordillera to the west. Organic-rich shales and pelagic limestones and cherts of the Vilieta Group and equivalent units comprise 60-70% of Lhe Cretaceous record and provide a good opportunity to study lhe interactions between tectonics, eustatic sea level, and sedimentation that regulate relative sea level in a basin. Rhythmic sedimentation, sediment accumulation, and relative sea-level history have been analyzed in four different regions: Sierra Nevada del Cocuy, Villa de Leiva, Bogoti (Eastern Cordillera) and Chaparral-Yaguara (Upper Magdalena Valley). Through the detailed study of cyclic sedimentation using modified accommodation space plots (Fischer plots), a quantitatively- defined relative sea-level history was interpreted. With this method, the relative sea-level history of different Colombian sub-basins can be objectively depicted and compared, permitting interpretation of tectonic, versus eustatic sea-level oscillations as regulating factors for the sequence stratigraphic record. Several transgressive-regressive cycles and a sequence stratigraphic interpretation of the Cretaceous are presented. Correlation and timing of these events is based on marker beds, deposition^ events (bentonites, mass mortality events, and concretion levels), cyclostrati graph y and on a composite macrofossil biostraiigraphy for northern South America. Results presented in this work modify regional paleogeographic concepts of the Cretaceous of Colombia.