--> Abstract: Proximal Impact-Generated Stratigraphy of the Cretaceous Tertiary Boundary, Belize, Central America, by D. T. King, Jr.; #90950 (1996).

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Abstract: Proximal Impact-Generated Stratigraphy of the Cretaceous Tertiary Boundary, Belize, Central America

David T. King Jr.

Impact-generated Cretaceous-Tertiary boundary sediments of the Gulf Coast and Western Interior Seaway typically consist of a three-fold stratigraphy owing to the mechanism of emplacement. The primary ejecta curtain (class, spherules, and tektites) is overlain by two types of fireball" layers, a shocked-quartz bearing fine-grained clastic layer and an iridium-rich shale.

However, within exposures in Belize, approximately 350 km from the center of the Chicxulub impact crater, a unique two-fold spherulite-diamictite stratigraphy is developed between two carbonate units, the Maastrichtian Barton Creek Formation and the Paleocene-Eocene Doubloon Bank Group.

In Belize, a lower, 1-m thick dolomitic bed laden with carbonate and clay spherules (altered vapor-phase condensates) rests on fractured and fissured Maastrichtian bedrock. This spherulite bed is overlain by a 1 5-m thick breccia consisting of exotic and local carbonate and clay clasts in a dolomicrite matrix. The clasts have a wide range of angularities and sizes. Some clasts are mud-coated and others display surficial abrasion features. The breccia is very poorly sorted and apparently homogenous, thus making it appear as a diamictite.

Conspicuously absent in Belize are the fine-grained "fireball" deposits seen in North America. Instead, a coarse breccia, or impact-generated diamictite, occurs above the primary ejecta curtain (spherulite) deposits. Because of its proximity to the crater rim, Belize apparently received primary Chicxulub base-surge (or true ejecta blanket) material which is previously described only in wells penetrating the crater rim beneath Yucatan, Mexico.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas