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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 50 (1966)

Issue: 3. (March)

First Page: 652

Last Page: 652

Title: Sedimentary Regime of San Miguel Gap: ABSTRACT

Author(s): Frederick F. Wright

Article Type: Meeting abstract

Abstract:

San Miguel Gap is an offshore basin that intersects the continental margin at the extreme northwestern limit of the southern California borderland. The California current sweeps over the western portion of the gap, open to the deep sea through the Patton escarpment, whereas the eastern part lies close to the Channel Islands. Thus the bathymetry presents an enlargement of the continental slope, under both oceanic and terrestrial influences. A sedimentologic study of the basin and its surroundings was conducted.

Virtually all sediments of the gap region are sands. Foraminiferal tests, glauconite grains, and fine quartz-feldspar sand dominate the sand fraction. Locally, volcanic shards, terrestrial pebbles, tar, palagonite rubble, sponge spicules, and diatom tests are conspicuous. Cores show few obvious turbidity-current sands, but there is evidence of traction sediment movement. The clay fraction is significant only in the deepest part of the basin. Sub-bottom profiles suggest two generations of relatively undisturbed sediments overlying a "basement" of Miocene(?) volcanic and sedimentary rocks; the general characteristics of both sedimentary sequences are similar.

Biologic productivity, authigenesis of glauconite, and eolian introduction of terrestrial material, in that order, are the dominant sedimentary processes in the gap. These factors all can be directly related to climatic influences: productivity, to ocean currents and upwelling; glauconite, possibly to extreme weathering and low sedimentation rates; and the eolian sediments, to the occasional offshore windstorms. Because the ultimate control of sedimentation on the continental slope is climatologic, it is clear that valid paleoclimatic reconstruction in such areas may be based on the ancient sediments as well as on faunal data.

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Copyright 1997 American Association of Petroleum Geologists