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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 458

Last Page: 458

Title: Previous HitPaleoenvironmentalNext Hit Previous HitAnalysisTop of Late Cretaceous Active Margin Continental Slope Deposits, Southern California: ABSTRACT

Author(s): Steven P. Buck, David J. Bottjer


Extensive active margin, continental slope and upper fan deposits are not commonly preserved in the rock record. The Holz Shale (Ladd Formation, Black Star Canyon, Santa Ana Mountains) represents such a sequence where shale and mudstone strata are dissected by numerous coarse-grained channel-fill deposits. Channels preserve evidence of filling primarily by conglomerate debris flows, high-density turbidites, and classic Bouma low-density turbidites; slumping and traction-current mechanisms were less important. Associated with channels are submarine chutes, pebbly mudstones, and poorly developed levee facies. Interbedded turbidites, contourites, and hemipelagic sediments dominate interchannel strata. Hemipelagic sediments exhibit sedimentologic textures that range from biol gically dominated (homogenous, bioturbated) to physically dominated (fine-scale, planar-laminated, anaerobic) fabrics. This variation in texture and associated diagenetic information indicates that the anaerobic/aerobic boundary was generally at some depth below the sediment-water interface, but at times migrated up into the overlying water column.

Foraminiferal assemblages within hemipelagic sediments are dominated by agglutinated forms which indicate deposition at bathyal depths. Macroinvertebrates include (1) the interchannel paleocommunity, dominated by the bivalve Inoceramus and the deposit-feeding trace fossil Chondrites, and (2) the submarine channel paleocommunity, comprised mainly of the trace fossils Thalassinoides and Ophiomorpha.

Previous studies have demonstrated that these active margin environments included a narrow continental shelf. Abundance of terrestrial plant material, paucity of displaced shelf faunas, well-rounded conglomerate clasts, and the coarse-grained texture of these deposits suggest that one or more of the Holz Shale submarine channels was receiving sediment directly from terrestrial environments.

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