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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 64 (1980)

Issue: 3. (March)

First Page: 441

Last Page: 442

Title: Mass Movement Effects on a Bathyal Macrofaunal Population, California Borderland: ABSTRACT

Author(s): Brian D. Edwards

Article Type: Meeting abstract


The benthic macrofauna of Santa Cruz basin, a dysaerobic bathyal basin in the California borderland, is subject to frequent substrate disturbances that erode the muddy surficial deposits, bury more deeply burrowing infauna, and transport shallow-water fauna to deeper environments. The effects on infaunal distributions have been examined through trophic-group and life-habit analyses.

X-ray radiography and textural distributions of surficial sediments recovered at 211 box-core stations are complemented by acoustic profiling records. These data indicate that the basin is presently filling by both hemipelagic sedimentation and gravity-induced mass movements. Failures are frequent, and many dislocations involve the uppermost 1 cm of the sediment pile.

A single ridge-crest to basin-floor transect of 10 stations has been quantitatively analyzed for macrofauna (> 0.5 mm). Species richness, density, and standing crop decrease from the ridge crest across the slope and fluctuate on the basin floor proper. Polychaetous annelids dominate the benthic macrofauna; crustaceans are second in abundance on the slopes, and mollusks are second on the basin floor.

The sand-and-gravel covered crest is equally partitioned by epifaunal suspension feeders and surface-deposit feeders. In comparison, the silty slope is dominated by infaunal, surface, and subsurface deposit feeders. Upper slope populations are evenly divided among sessile and motile species; motile species become more common toward the base of the slope. The basin floor is dominated by motile, infaunal surface-deposit feeders.

Substrate instability produces confused and patchy

End_Page 441------------------------------

trends at the slope-basin floor boundary. For example, population explosions of the oweniid Myriochele at the base of the slope suggests opportunism related to substrate instability. Significant macrofaunal populations are supported throughout this environment. Repeated disturbance by mass movements produces a downslope trend toward an infaunal, motile life habit.

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Copyright 1997 American Association of Petroleum Geologists