Delta front gravity flow deposits in the middle submember of the third member of the Shahejie Formation in the Dongying depression:Lithofacies and lithofacies association types and their distribution

Exemplified by the delta front deep-water gravity flow deposits in the middle submember of the third member of the Shahejie Formation in the Dongying depression, the emphasis in the present paper is placed on the classification and distribution of the lithofacies and lithofacies association types according to 3-D seismic data, core data, well logs and analytical results. The deep-water gravity flow deposits are divided into 13 lithofacies types according to mud contents and sedimentary structures, and 20 lithofacies association types which are involved into five categories, i. e., the lithofacies associations (1) with primary sedimentary structures;(2) with synsedimentary deformational structures;(3)with the massive beddings and abundant clasts;(4)with the lower debris flow deposits and upper turbidity current deposits, and (5)with imcomplete Bouma sequences. Judged from the lithofacies and lithofacies associations types and distribution of delta front gravity flow deposits types, there are gradations of slide-slump-debris flow-turbidity current from the slope to the deep-water plain. The slide-and slump-dominated lithofacies and lithofacies association types are observed in the proximal part;the debris flow-and mixed debris flow-turbidity current dominated lithofacies associations appear in the central part, and turbidity current-dominated lithofacies associations are common in the distal part. The redivision of lithofacies and lithofacies associations types may be helpful to the prediction of the gravity flow sandstones and future petroleum exploration in the study area.