The End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
One of the liveliest, contentious, and long-running scientific debates began over three decades ago with the discovery of an iridium anomaly in a thin clay layer at Gubbio, Italy, that led to the hypothesis that a large impact caused the end-Cretaceous mass extinction. For many scientists the discovery of an impact crater near Chicxulub on Yucatan in 1991 all but sealed the impact-kill hypothesis as proven with the impact as sole cause for the mass extinction. Ever since that time evidence to the contrary has generally been interpreted as an impact-tsunami disbturbance. A multi-disciplinary team of reserachers has tested this assertion in new cores and a dozen outcrops along the Brazos River, Texas. In this area undisturbed sediments reveal a complete time stratigraphic sequence containing the primary impact spherule ejecta layer in late Maastrichtian claystones deposited about 200-300 thousand years before the mass extinction.
Age and Origin of the Chicxulub Impact and Sandstone Complex, Brazos River, Texas: Evidence from Lithostratigraphy and Sedimentology
Published:January 01, 2011
Thierry Adatte, Gerta Keller, Gerald R. Baum, 2011. "Age and Origin of the Chicxulub Impact and Sandstone Complex, Brazos River, Texas: Evidence from Lithostratigraphy and Sedimentology", The End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas, Gerta Keller, Thierry Adatte
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Multidisciplinary investigations based on the lithology, sedimentology, mineralogy, and biostratigraphy of upper Maastrichtian to lower Danian boundary (KTB) sequences along 3.5 km of the Brazos River in Falls County, Texas, reveal depositional sequences, including an impact-spherule-rich sandstone complex, characteristic of sequence stratigraphic models applied to shallow shelf areas, such as incised valleys, lag conglomerate, storm deposits, and repeated bioturbation. The top of the Corsicana Formation coincides with a channel, which we interpret as an incised valley. The erosion surface marks a major depositional sequence boundary (SB) associated with the latest Maastrichtian sea-level fall. Initial channel deposits consist of coarse...