5 Sedimentology and Stratigraphy (Posters)

Monday, 4 April 2016
8:30 AM - 5:30 PM
Ballroom C

EVIDENCE OF THE K-PG IMPACT IN CALIFORNIA

Paper number: 5-1
Program: Technical Sessions
Time: 8:30 AM – 5:30 PM

Authors

Abstract

Empirical evidence and modeling indicate that the following events occurred as a result of the K-Pg impact at Chicxulub, Mexico: Impact blast, ejecta fallout, tsunami sequences, acidic aerosol generation and rain-out. We theorize that evidence of these events is preserved in the sedimentary record in California.

Paired clay-rich “ejecta” and Iridium-rich “fireball” layers occur globally. Impact-tsunami deposits are documented in the Gulf of Mexico. Elsewhere, tsunamis would likely be generated by seismically induced submarine landslides (Atlantic and Pacific coasts), and possibly by antipodal geoid displacement (southeast Asia).

Researchers have quantified a volumetric-range for acidic aerosols generated by the K-Pg impact into Yucatan’s anhydrite target rocks. The estimated volume of acid is deemed sufficient to have produced, via enhanced weathering, the “spike” in sea-water strontium isotope values across the K-Pg boundary. These acidic solutions would likely reside in basins and lagoons until neutralized.

In California (and elsewhere), Paleocene rocks are characterized by kaolinite. Examples include: the Paleocene Simi Conglomerate, Silverado, and Goler Formations; and basal units of the “Eocene” Ione, Walker, and Maniobra Formations. Features common to these formations include laterization, pisolitic claystone, kaolinitized sediment and basement (saprolite), and lignite.

The classical interpretation is that these lateritic “paleosols” result from an extended period of weathering in a warm, humid environment. However, the laterite-bearing Silverado Formation and Simi Conglomerate are bracketed between Danian and Maastrichtian marine strata, which suggests a period of lowered sea level — and a cooler, drier climate.

We propose a model in which the observed intensive corrosion and kaolinitization of sediment and basement resulted when impact-generated acidic solutions collected in and saturated sediment-filled fluvial channels, basins, and lagoonal environments.

In this model, economic clay deposits in the Alberhill area represent sediment and basement variably altered by ponded acidic run-off. The Claymont Clay Bed, which consists exclusively of kaolinite and angular sub-mm quartz, may represent a deposit from a down-range ray of the clay-rich K-Pg impact “ejecta layer.”

Geological Society of America Abstracts with Programs. Vol. 48, No. 4

doi: 10.1130/abs/2016CD-274222

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