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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 777

Last Page: 777

Title: Channelized Submarine Carbonate-Debris Flow, Cretaceous, Mexico: ABSTRACT

Author(s): Paul Enos

Article Type: Meeting abstract


Carbonate platforms, fringed by rudistid reefs, rose to more than 1,000 m above contemporaneous basinal carbonates in the middle Cretaceous of central Mexico. The platforms are surrounded by halos of debris forming wedges which extend as much as 5-15 km from the platform margin. An exception to the wedge morphology is a breccia-filled channel exposed in section perpendicular to the paleoslope, 1 km from the marginal escarpment of the El Doctor platform, Queretaro, Mexico.

The main part of the channel deposit is 225 m wide and 16 m thick. Breccia clasts are 75% basinal components (pelagic limestone and chert) and 25% platform derived. The bedded clasts form flat plates up to several meters in maximum dimension. A few clasts are deformed, indicating that they were at most slightly lithified and presumably of low density; nevertheless, most are neatly stacked with little distortion. Unstable clast postures, with long axes approaching normal to bedding, and imbrication are common. Content of dolomitized muddy matrix is low; the deposit is grain supported.

The morphology of the breccia deposit and truncation of pelagic limestone at the channel edge demonstrate erosional competence of the depositional mechanism. Locally in the channel base an incipient slump of slightly folded pelagic limestone and chert indicates slope instability and suggests a mechanism for incorporating basinal carbonates in the breccias. In the top few meters of the deposit, breccia grades upward into fine-grained, skeletal-fragment packstone, which extends several hundred meters beyond the channel limits as thin, graded bed. At least 3 episodes of channel fill are suggested by internal structure.

This evidence places the following constraints on the depositional proces--high competence (large clasts, erosion), high viscosity (unstable clast postures), low turbulence (slight deformation and platy form of unconsolidated clasts), high clast concentration (grain support, clast interaction) and channelization (form of deposit, multiple episodes). A high velocity submarine debris flow is suggested. The nonchannelized part of the last depositional episode is a typical turbidite.

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