Abstract

Ancient deep-sea fans, consisting of channel, levee, overbank, and fringe deposits are recorded in Brushy Canyon, Cherry Canyon, and Bell Canyon Formations (Guadalupian) of the Delaware Basin. Sediment economics and depositional processes that characterized the Delaware Basin were very similar to those operating in modern continental borderland basins off southern California.

Margins of the Delaware Basin were incised by numerous submarine canyons whose associated deep-sea fans coalesced around the basin margin to form a compound submarine apron or bajada.

Proximal fan deposits consist predominantly of deeply incised channels which are filled with thin, laminated and small current-rippled flow units and thick avalanche and mudflow deposits. Intermediate fan deposits consist of channel — levee — overbank deposits. Intermediate fan channels contain thick, clean, well-sorted, current ripple crossbedded sandstones deposited as major flow units (3–10 feet thick). Distal fan deposits also consist of aggradational channel — levee — overbank deposits, but the distal channels contain thinner flow units. Overbank deposits consist of laminated and small current-rippled siltstones. A peripheral aureole of finely laminated silty shale, deposited by dilute suspensoid clouds which traveled beyond the limits of the channels, formed a fringe around the fans.

Strong circumstantial evidence indicates that throughout most of Guadalupian time the geologic history and sediment economics of the Delaware Basin and Northwest Shelf may be related within the context of glacially controlled eustatic sea level changes.

During times of low standing sea level large volumes of clastic sediment were prograded across constricted shelf lagoons, swept into heads of submarine canyons by longshore and tidal currents, and introduced into the Delaware Basin via the channel — levee — overbank system. Carbonate production and reef growth ceased on the outer platform. Subaerially exposed, permeable backreef carbonates became converted to vadose caliche pisolites as sea level fell. Introduction of progressively larger volumes of clastic sediment into the Delaware Basin during lagoonal constriction is recorded by basinward expansion and progradation of fan over fringe deposits and erosion in submarine canyon and proximal fan.

As sea level rose during deglaciation, shelf lagoons expanded and the volume of clastic sediment reaching the outer platform progressively diminished; carbonate production and reef growth resumed. Distribution of progressively smaller volumes of clastic sediment to the basin caused fans to “shrink” or recede toward canyon mouths. Fringe deposits were laid down over the shrinking fans as the locus of sediment accretion migrated toward the canyon mouth and finally, up the canyon. Smaller carbonate fans then prograded relatively short distances basinward.