SEARCHING FOR EVIDENCE OF THE K-T IMPACT IN CALIFORNIA: A SYNTHESIS

Previous empirical evidence and modeling indicate that the following events occurred as a result of the K-T impact at Chicxulub, Yucatan, Mexico: 1) Impact blast; 2) ejecta fallout; 3) a tsunami sequence; 4) rapid atmospheric heating, followed by atmospheric cooling; and 5) acidic aerosol generation and rain-out. We hypothesize that heretofore unrecognized evidence of some of these events are preserved in the stratigraphic record in California.

In California (and elsewhere), lowest Tertiary rocks are characterized by kaolinitization. Examples in California include the Paleocene Silverado, Simi Conglomerate, and Goler Formations; and basal units of the “Eocene” Ione, Walker, and Maniobra Formations. Components common to most of these formations include kaolinitized sediment and basement (saprolite); pisolitic claystone; lignite; and small lenses of hematite-rich rock.

The classical (uniformitarian) interpretation is that these deposits formed as a result of an extended period of weathering and paleosol formation in a warm, humid environment. However, kaolinitized continental lower units of the Silverado Formation are tightly bracketed stratigraphically by an erosional unconformity on the Upper Cretaceous (upper Campanian Stage) marine Pleasants Sandstone Member of the Williams Formation, below; and the lower Paleocene (Martinez Stage) transgressive marine member of the Silverado Formation, above. The Simi is similarly constrained.

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

Research is proceeding to identify evidence in the K-T boundary transition in California¯such as the presence of shocked quartz¯to potentially establish a direct link with the Chicxulub impact.