About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 53 (1969)

Issue: 3. (March)

First Page: 743

Last Page: 743

Title: Coarse Channelized Deposits and Other Indicators of Slope and Base-of-Slope Environments in Ancient Marine Basins: ABSTRACT

Author(s): Daniel J. Stanley, Rafael Unrug

Article Type: Meeting abstract


Submarine slopes are distinctive depositional environments because of their gradients and their position between sediment source locales at their upper level and areas more favorable for preservation on basin floors beyond. The model for slope sedimentation must incorporate such factors as gradient, dissection, type and rate of sediment input, and processes. Slopes are most often represented as inclined planes reflecting depositional instability, i.e., relatively temporary resting places for sediments during their passage to depositional sites in more distal environments. Sediments are, however, preserved in a multiple set of slope subenvironments, and there are criteria for recognizing most of these.

Fine-grained pelagic deposits (some entirely reworked by benthonic organisms), hemipelagic materials influenced by bottom current activity, turbidites with mixed faunas and mineralogy, contorted slumped units, and allochthonous slabs which slid into deeper water generally are recognized as the dominant slope facies assemblage. However, the problem of Previous HitdistinguishingNext Hit slope from basin-floor sediment remains because criteria for Previous HitdistinguishingTop facies are found in both environments, especially near their juncture. Marine geologic investigations have detailed the three-dimensional geometry, vertical-lateral relation, sedimentary properties, and have defined processes on modern slopes. These investigations and studies of paleoslope deposits in certain Tertiary flysch formations of the Alps a d Carpathians, bring to light methods that permit more precise paleogeographic interpretations.

Channelized deposits, coarse units representing fills of submarine canyons and valleys and answering the description of fluxoturbidites, are important in this respect. They can be mapped regionally as shoestring bodies that migrate downslope and are incised in pelagic and bottom-current transported units and turbidite bundles. They are well developed on lower slopes, subsea fans, and rises, and can be traced well into basins; they are not necessarily proximal. Primary structures are generally indicative of traction processes. Their value in measuring primary dip and major slope trends, in pinpointing important source input along basin margins, and in serving as funnels in the transfer of sediments downslope can be demonstrated.

In association with these channels, wedges of pebbly mudstone are common at the base of slopes and, where concentrated, indicate the position of an important break (decrease) in gradient. Large, commonly rounded blocks and boulders enrobed in contorted mud suggest conditions of rapid sedimentation as off river mouths or along rapidly eroded coastlines, where materials are periodically moved across narrow shelves and then, en masse, on relatively steep slopes, perhaps between canyons.

End_of_Article - Last_Page 743------------

Copyright 1997 American Association of Petroleum Geologists