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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 9. (September)

First Page: 1667

Last Page: 1668

Title: Signatures of Surficial Sand and Small-Scale Mass Wasting of Sediments at Shelf Break and Upper Slope Seaward of Baltimore Canyon Trough: ABSTRACT

Author(s): Terry A. Nelsen, Richard H. Bennett

Article Type: Meeting abstract


Sedimentary processes were investigated for the continental margin between Wilmington and Lindenkohl Canyons. Sediment sampling was carried out in a series of closely spaced shelf-break-normal transects from the outer shelf to the upper rise.

Q-mode factor analysis of the sieved sands identified three significant end-member (E-M) size distributions. E-M I dominates the slope below 400 m south of and 200 m north of Spencer Canyon. The shelf, shelf break, and upper slope to the foregoing respective depths are dominated by E-M II and III sands. These boundaries are breached on the slope in at least two places. The breaches appear to be pulses of shelf sand which extend down the slope to at least 500 m, producing load casts at the contact between the sands and the underlying muds.

The most dramatic soft-sediment deformation structures were recovered in a box core taken 400 m north of Wilmington Canyon. A thick sandy surface layer extended downward as

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load casts interdigitating with the underlying muds to > 30 cm. Below this, isolated sand pillows up to 10 cm in diameter extend into the matrix mud to > 50 cm. Ratios of E-M I and II sand in the pillows were significantly different from the sand above. Trends in the E-M ratios in the surficial and load-cast sands and comparisons with other earlier studies suggest that dynamic emplacement of the shelf sand produced these structures. Owing to the size and isolation of the sand pillows in three dimensions, and lack of primary structures in the mud, a bioturbation origin was ruled out.

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