T100 Impact Cratering on Earth and in the Solar System

Monday, 2 November 2015
8:00 AM - 12:00 PM
Room 344

NEW JERSEY, A MOST HABITABLE PLACE DURING AN ASTEROID STRIKE: SHOCKED QUARTZ AND IRIDIUM SPIKE CO-OCCUR BELOW A MAASTRICHTIAN MOLLUSK COMMUNITY ON THE NJ COASTAL PLAIN

Paper number: T100-9
Program: Technical Sessions
Time: 9:55 AM – 10:15 AM

Authors

Abstract

Previous studies have identified K/Pg boundary sites on the New Jersey Coastal Plain. The Agony Creek section (30-45m paleodepth) in the Manasquan River Basin is of particular interest because there is a discrepancy in the biotic and physical indicators of the impact [1]. Here, an Ir anomaly is located at the base of a Maastrichtian assemblage, the ~20 cm thick “Pinna Layer”, which includes ammonites [2]. Another impact indicator is identified at the base of the Pinna Layer: Pyrite framboids enriched in Ni and Co up to 100x above background [3]. We find similar framboids and shocked quartz with planar deformation features (PDFs) at Crosswicks Creek (50-75m paleodepth), coincident with an Ir spike and the biostratigraphic boundary [4, 5]. The occurrence of quartz grains with PDFs below or above the Pinna Layer at Agony Creek would resolve conflicting evidence for whether this fauna survived the impact.

Samples were obtained from exposed stream banks at Agony Creek [1], collected at 1 cm intervals from the base of the Ir anomaly upward (~24 cm) to the base of the Hornerstown Formation (earliest Danian[6]). Samples were leached in HCl to remove iron staining and sieved to isolate grains between 62 -150 µm. Quartz grains were magnetically separated from glauconite and observed under a petrographic microscope to determine PDFs. Universal stage measurements confirm that the planar features observed in quartz from the Ir-rich layer are PDFs related to the Chicxulub impact [7]. Shocked quartz grains occur at the same horizon as the Ir anomaly but not above it. This coincidence suggests that the Ir (and Ni, Co) did not diffuse downward after deposition. The overlying Pinna Layer fauna are in life position and are not reworked [2]. Our new findings therefore suggest that this community may have flourished for a brief time (10’s of years) after the Chicxulub impact.

[1] Aldoroty R. J. et al. 2013. Abs. #1703, 44th Lunar Planet. Sci. Conf.

[2] Landman N. H. et al. 2012. Acta Palaeontologica Polonica 57:703-715.

[3] Bigolski et al. 2010. Abs. #116-3. GSA Abs. Prog 48:305.

[4] Ebel et al. 2010. Abs. #116-4. GSA Abs. Prog 48:305.

[5] Miller K. G. et al. 2010. Geology 38:867-870.

[6] Landman N. H. et al. 2004. Bull. AMNH 287:1-107.

[7] French B. M. 1998. LPI Contribution #954, 120p.