Abstract: Thin-Bedded Turbidites in Modern Submarine Canyons and Fans

C. H. Nelson, W. R. Normark, A. H. Bouma, P. R. Carlson

Thin-bedded sand and silt turbidites are deposited in nearly all physiographic environments of submarine canyons and fans. At present they predominate in channelized areas because many submarine canyon and fan systems receive substantially less coarse-grained sediment during high sea-level stands. During glacial periods, most canyon-fan valley systems become active pathways for coarse-grained sediment transport and nonchannelized parts of fans are built by overbank deposition of thin-bedded turbidites.

The thin-bedded turbidite facies exhibit sufficient differences in overall characteristics to allow their recognition within ancient turbidite provinces. In channelized areas of upper and middle fans, thin-bedded turbidites are associated with thick-bedded thalweg sands and gravels; they are present in thin sequences that pinch out laterally and are subject to cutting, filling, and slumping from channel walls. Individual turbidites contain Bouma T_c-e sequences, cross-lamination, ripple drift, starved ripples, and lenticular sands. Sand/shale ratios are high because the fine-grained interbeds of turbidite and/or hemipelagic mud are thin.

Thin-bedded turbidite facies from levee crests, interchannel, and interlobe areas are finer grained and more laterally continuous than those from adjacent intrachannel or mid-fan lobe areas. They exhibit thicker sequences with lower sand/shale ratios and are less dominated by cross lamination. Truly distal turbidites of basin plains are in sequences hundreds of meters thick and are laterally continuous for tens of kilometers. Flat lamination dominates internal structure, and low sand/shale ratios prevail because of well-developed pelagic-mud interbeds.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA