Although the largest fans may be up to several hundred times the size of the smallest (Plate 1), most modern fans have the same basic facies associations. The general facies descriptions published and based mainly on late Pleistocene deposits of Astoria Fan have not been significantly modified (Nelson and Kulm, 1973); these will be summarized briefly and compared with more recent work on each of the general fan environments and associated facies. The interbedded blanket deposits from hemipelagic deposition and the more recently recognized widespread suprabed or debris-sheet facies also will be outlined. In addition, turbidite muds and proximal to distal thin-bedded-turbidite deposits will be differentiated from bottom-current-deposited contourites and shallow-water graded sands, both deposited by bottom currents.
For each facies association, the general morphology, acoustic character, and seismic stratigraphy will be summarized with the lithologic character to outline the complete facies-association characteristics for each environment.
The lithology of modern near-surface sediment on continental slopes typically is bioturbated or laminated hemipelagic mud with thin silt or very fine sand interbeds (Fig 6-1) (Maloney, 1965; Doyle and Pilkey, 1979). In deeper DSDP drill holes, however, the sediment often may be pure pelagic oozes Cook et al., 1982).
Three major slope sedimentary units made up of this generally monotonous lithology can be recognized: (1) undisturbed, in situ, pelagic and hemipelagic sediment draped on smooth undeformed slopes that exhibit seismic reflectors paralleling the upper slope but often thickening or diverging downslope into sigmoidal configurations (Fig. 6-1), (2) slides and other chaotically deformed
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Modern and Ancient Deep-Sea Fan Sedimentation
This course of modern and ancient deep-sea fan sedimentation provides the framework for understanding the morphology, physiography, geometry, depositional processes and reservoir potential of deep-sea fan deposits. Focus is chiefly on the principles that control fan sedimentation and the resultant morphology of fans deposited in various types of settings. Through the comparison of modern and ancient examples of deep-sea fan sedimentation, the authors hope to increase understanding of the principal characteristics of fans. The course is divided into four parts (1) the Introduction, which covers the organization of the course and history of fan studies, (2) modern deep-sea fan deposits, (3) ancient deep-sea fan deposits, and (4) the synthesis, in which the results of the separate modern and ancient examinations of deep-sea fan deposits are synthesized into models that may be applicable to petroleum exploration.