Influence of Compaction on Alluvial Architecture

Stephen Anderson

Two- and three-dimensional studies of alluvial architecture were undertaken on laterally continuous coastal exposures of the Middle Jurassic nonmarine Scalby Formation of North Yorkshire, England. Sandstones and mudstones were collected and analyzed to quantify the processes involved in compaction and to investigate the influence of differential compaction on alluvial architecture.

The original geometry of alluvial deposits is distorted during burial due to the juxtaposition of sediments of different compressibilities inherent in the alluvial environment. Mudstones, having higher initial porosities, compact at a greater rate than sandstones, with the result that small faults and folds may develop within the mudstone to accommodate the different compaction rates. More importantly, differential compaction affects the flood-plain topography during sedimentation and, therefore, influences the subsequent pattern of facies distribution, most notably channel-sandstone body stacking patterns.

The Scalby Formation consists of a basal, complex, multilateral sheet sandstone that passes upward into meandering stream deposits, which exhibit both inclined homolithic and heterolithic stratification.

Decompaction models of the sedimentary rocks reveal the original depositional architecture before differential compaction produced the present-day geometry. The decompacted sandstone/mudstone geometry provides a more accurate estimate of mudstone channel-fill thickness and inclined homolithic and heterolithic stratification dimensions, both of which are used in estimating paleochannel dimensions.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.