Lithofacies and depositional environment spanning the Cretaceous-Paleogene boundary on the New Jersey coastal plain.

摘要

The sedimentary record spanning the Cretaceous-Paleogene (K/Pg) boundary was examined in outcrop and in seven cores recovered from a 50 km long transect along the outcrop belt on the New Jersey coastal plain. The objectives were to: (1) conduct a high-resolution study of the K/Pg lithofacies, (2) document spatial and temporal changes in composition and texture of the sediments, and (3) interpret any changes in the depositional environment across this important geological boundary when a mass extinctions occurred. Analyses include core description, textural, petrographic, microprobe, and XRD analyses. Five lithofacies were interpreted in the Upper Cretaceous sediments and three lithofacies were recognized from the lowermost Paleogene deposits.;Microprobe studies show the chemistry of Upper Cretaceous and lowermost Paleogene glauconite are identical (∼7-8% K2O), but their color difference may suggest different redox condition. XRD analyses show the Upper Cretaceous clay contains more land-derived detritus than the lowermost Paleogene clay.;The following sequence of events is interpreted from the sediment record spanning the K/Pg boundary: (1) deposition in near-shore setting and slow sedimentation in middle shelf when sea level was falling, albeit still shelfal depth; (2) deposition of K/Pg lithofacies when sea level was falling possibly creating a diastem but not a sequence boundary, per se; (3) a transgression above the K/Pg boundary; and (4) deposition in middle shelf possibly with decreased ocean productivity and a more reducing environment.;There is no sedimentological evidence above the K/Pg boundary, suggesting tsunami-related deposition associated with a bolide impact. Either a tsunamite was eliminated by bioturbation, or NJCP was too far from the impact site to be affected. A transgressive lag, instead, was formed by normal sedimentation during the subsequent transgression in the early Paleocene.