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Abstract

The lithic succession exposed in the Lampazos area of east-central Sonora comprises an irregular alternation of terrigenous shales and carbonates divisible into three lithic packages. Those rocks yielded abundant planktonic microfossils (foraminifera and colomiellids) allowing us to assign the succession to Biozones K-6 through K-15 of the standard planktonic zonation for the Cretaceous of Mexico (Longoria, 1984a) corresponding to the Comanchean Series (Aptian–Albian, 119–95.7 Ma). The succession was divided into three lithic units: (1) Cliff-forming, thick- to massive-bedded carbonates of Unit 1 (Biozones K6 through K-11) represent deposition on a carbonate platform; (2) slope-forming thin- to medium-bedded, nodular limestone packages of Unit 2, which yielded abundant favusellids and colomiellids indicative of deeper-water environments, ranging from K-12 to K-14; and (3) an alternation of thin- to medium-bedded limestone and thin-bedded shale, which yielded radiolaria and planktonic foraminifera indicative of deep-water facies that range from Biozone K-6 through K-15. Our biostratigraphic analysis demonstrated that the Lower Cretaceous succession as exposed on the west flank of Sierra Las Azules is involved in four structural segments separated by faults. West-verging thrust faulting is related to the mid-Cretaceous tectonic phase of this region. Both microfacies types and microfossils found in the Lampazos Comanchean succession are remarkably similar to coeval rocks from northeastern Mexico and are interpreted as indicative of the western extension of the Comanchean facies belts from Tamaulipas into eastern Sonora.

Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones

SEPM Special Publication No. 93, Copyright © 2009

SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 269-285.

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