Iridium anomaly at the Cretaceous-Tertiary boundary in Texas

A sequence of events across the Cretaceous-Tertiary boundary

“…Ganapathy et al [31] did not recognize this unit as such, but our examination of the outcrop shows that the only turbidite in the Upper Cretaceous and Lower Tertiary in the Brazos river occurs exactly at the K/T boundary, and the lr anomaly occurs on the top of it [34]. This may be the first evidence of impact (?tsunami) -triggered sediment.…”

Shelf hypoxia in response to global warming after the Cretaceous-Paleogene boundary impact

“…This complex shows a normal gradation and has been interpreted to be deposited within a time span of 24 hours to a couple of weeks, as part of the settling phase of the tsunami complex deposited directly after the K-Pg boundary bolide impact in the Gulf (Smit et al, 1996). However, the iridium records already show elevated levels at the base of Unit E (Ganapathy et al, 1981;Hansen et al, 1987;Asaro et al, 1982;Rocchia et al, 1996). Since it may take days to years to deposit the very fine-grained impact-derived Platinum Group Elements (PGEs) on the sea floor (Robin et al, 1991;Kring and Durda, 2002), longer than the dissipation of the impact-triggered tsunami waves, the complex of Units E-G probably represents a rapid depositional event that occurred at least weeks after the K-Pg boundary tsunamis, possibly as the deposition of suspended material after the waning of large storms and hurricanes that occurred in the decades following the K-Pg boundary impact (Vellekoop et al, 2014;Hart et al, 2012).…”

“…The sedimentary successions in this region comprise the Maastrichtian Corsicana Formation and the Paleocene basal and upper Littig members of the Kincaid Formation. The K-Pg boundary deposits outcropping along the Brazos River between Waco and Hearne, Texas, comprise an exceptionally well-preserved and frequently studied sedimentary succession (Smit et al, 1996;Woelders and Speijer, 2015;Hansen et al, 1987;Bourgeois et al, 1988;Yancey, 1996;Heymann et al, 1998;Vellekoop et al, 2014;Ganapathy et al, 1981). In most previous studies, the K-Pg boundary interval has been subdivided in a series of lithological units (Units A to J) first described by Hansen et al (1987).…”

“…The high-resolution age model used in this study is based on the Ir-anomaly and calcareous nannoplankton, planktic foraminifer and organic-walled dinoflagellate cyst (dinocyst) biostratigraphy presented in (Vellekoop et al, 2014). Various studies have been published on iridium anomalies in the Brazos River area (Ganapathy et al, 1981;Asaro et al, 1982;Rocchia et al, 1996;Hansen et al, 1993), showing a series of irregular peaks in lithological Units E, F and G. It is likely that the PGE bearing impact dust settled within months to years after the impact and was subsequently reworked in the lag deposits of post-impact storms (Vellekoop et al, 2014;Hart et al, 2012), explaining the scattered and smeared out nature of the iridium profile. Since the enhanced contrast between warm oceans and cold atmosphere, triggering the storms after the impact, likely lasted for less than a century (Vellekoop et al, 2014;Galeotti et al, 2004), we assume that this is the maximum amount of time represented by units E, F and G. Normal sedimentation resumed in Unit I, which therefore represents the first millennia following the K-Pg boundary impact winter event.…”

Terminal Cretaceous Environmental Events

“…A relatively small iridium anomaly was measured at the K/T Brazos River section in Texas (22). The lithology is a silty shale, characteristic of a shelf environment.…”