Sedimentologic and stable isotopic evidence for rapid post-impact sedimentation in the chicxulub impact crater

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doi: 10.1130/abs/2017AM-299302
Author(s): Whalen, Michael T.; Bralower, Timothy J.; Gulick, Sean S. P.; Morgan, Joanna V.; Lowery, Christopher M.; Rodríguez-Tovar, Francisco J.
International Ocean Discovery Program, Expedition 364 Scientists, College Station, TX
Author Affiliation(s): Primary:
University of Alaska at Fairbanks, Department of Geosciences, Fairbanks, AK, United States
Other:
Pennsylvania State University, United States
University of Texas at Austin, United States
Imperial College London, United Kingdom
Universidad de Granada, Spain
Volume Title: Geological Society of America, 2017 annual meeting & exposition
Source: Abstracts with Programs - Geological Society of America, 49(6); Geological Society of America, 2017 annual meeting & exposition, Seattle, WA, Oct. 22-25, 2017. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: During spring 2016, International Ocean Discovery Program/International Continental Scientific Drilling Program Expedition 364 sampled facies recording the transition from high-energy, impact-related units to relatively normal marine deposits atop the Chicxulub impact crater peak ring at Site M0077. An 80 cm thick "transitional unit" records this change in a series of 0.5-3 cm thick, cyclic or episodic, light to dark brown, normally graded, silty calcareous laminated couplets with local basal scours. The upper transitional unit is interrupted by a 30 cm thick soft sediment fold overlain by 15 cm of laminae with trace fossils. Normally graded deposits from 4-60 cm thick also occur in the underlying, sand-sized suevite. Petrographic and stable C and N isotopic analyses from bulk organic matter provide insight into post-impact depositional processes and environment. We hypothesize that the normally graded packages record rapid deposition either from currents due to impact and slope failure-related tsunamis and ensuing seiches and/or from post-impact tidal or turbidity currents. The former processes would act on the order of hours to days while the latter might operate over weeks to years, post-impact. δ13C values fluctuate around -25 ppm throughout the transitional unit while δ15N values are mostly between 0 and 5 ppm except for a remarkable series of excursions ranging from -5 to -18 ppm in the upper portion of the unit. Rapid deposition is supported by the presence of the soft-sediment fold and repetition of the -18 ppm δ15N excursion within the fold reinforces interpretations of soft sediment deformation, rapid deposition, and mass wasting. Comparable negative δ15N excursions are not reported in terrestrial materials but relatively negative excursions were documented during atmospheric disturbances such as lightning or nuclear blasts where nitrogen is fixed, creating NOx. Prior modeling implies that 2% of NOx production is directly due to impact while 98% is related to atmospheric heating by ejecta reentry. The sedimentologic, ichnologic, and isotopic data thus appear to support very rapid deposition (hours to days post-impact) of the transitional unit up through the soft sediment fold. Rates of sedimentation above the soft sediment fold appear to be much lower than the underlying facies.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Chicxulub Crater; Emplacement; Expedition 364; Gulf of Mexico; IODP Site M0077; International Continental Scientific Drilling Program; International Ocean Discovery Program; Intrusions; North Atlantic; Ring complexes
Record ID: 2018022330
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States

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