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The Importance of High-Frequency Tectonic Control during Greenhouse Times of Earth History

Boyan Vakarelov1, Janok Bhattacharya2, and Dragana Nebrigic1
1 University of Texas at Dallas, Richardson, TX
2 University of Houston, Houston, TX

The relative importance of tectonism in the stratigraphic record should be exaggerated during Greenhouse times of Earth history. During such periods, even minor pulses of uplift or subsidence should potentially leave a clear imprint in the stratigraphic record, due to the lack of high-frequency high-amplitude changes in sea level. Unfortunately, establishing the importance of tectonism, especially at temporal scales comparable to typical transgressive - regressive cycles, has been plagued by problems of poor temporal resolution. An outcrop and subsurface-based study of a Cenomanian shallow marine siliciclastic interval, constrained by excellent bentonite-based geochronology and detailed biostratigraphy, allows the evaluation of this problem. In a 2.2 million year interval, we identify four tectonically-driven erosional surfaces, which dominate preserved stratigraphy. Biostratigraphic correlation to a high-resolution sea-level curve for the Cenomanian, where coeval high-frequency low-amplitude eustatic variation has previously been demonstrated, allows the first direct comparison of the effects of eustasy and tectonics in a Greenhouse time. The results of this study suggest that even minor tectonic pulses can locally overshadow the effects of eustasy and exert dominant control over preserved stratigraphy. Care therefore must be taken when interpreting driving mechanisms, unless external criteria such as diagnostic stratigraphic architecture or coeval base-level change at far removed localities can be demonstrated. While subtle tectonic control on sedimentation has been documented throughout the Cretaceous Western Interior, results of this study suggest that much of that deformation might be occurring at sub-million year frequencies at time-scales comparable to typical transgressive-regressive cycles.