Date of Award

Spring 1993

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Geology

Committee Director

Stephen J. Culver

Committee Member

Carl F. Koch

Committee Member

Daniel J. Stanley

Call Number for Print

Special Collections LD4331.G4L86

Abstract

Two hundred and forty-six species of benthic foraminifera have been recognized in fourteen short cores (≤ 24cm) taken from within the Wilmington and South Heyes submarine canyons along the slope and rise of the United States Atlantic Continental Margin. Of these one hundred and forty-five species were identified to the species level, thirty were closely related to known species, sixty-six could not be assigned specific names, and five species were of uncertain generic placement. The petrologic character of the sediments was determined for each of the seventy-eight micropaleontogical samples.

Cluster analysis of benthic foraminiferal data identified twelve groups which, together with planktonic to benthic foraminiferal ratios, indicate that distribution patterns are depth related. The consistent distribution of benthic foraminifera down and between cores and the occurrence of species, which have been considered previously to inhabit shallower water depths within samples shielded from potential down-slope transport processes, indicate that nearly all species observed have accumulated at lower bathyal or abyssal depths. The known depth range of these species must be increased accordingly.

Marked variations in sedimentary characteristics observed across meanders throughout Wilmington Canyon contrast with the ubiquitous occurrence of the abundant foraminifera, which show a clear depth-related variation in abundance, but do not show significant cross-canyon variation. This indicates that mass-wasting processes (including creep) and bottom (perhaps tidal) or density current action are altering the sedimentary characteristics, particularly along the outside of meanders, while leaving the observed distribution of foraminifera relatively unaffected. The lack of significant variation in sedimentary and foraminiferal characteristics across-canyon in South Heyes Canyon, along with a low percent terrigenous material and a low rate of deposition relative to Wilmington Canyon, indicate that these processes are less important in South Heyes Canyon than in Wilmington Canyon. This is probably the result of the simple morphology of South Heyes Canyon.

The previously proposed stop-and-go down-slope transport mechanism for sedimentary particules (including foraminiferal tests) involving active transport of material by turbidity or high density gravity flows from the outer shelf to the lower slope requires some modification. The observations used to formulate this theory are better explained by deeper species ranges, more limited displacement by bioerosion of steep canyon walls and redeposition of allochthonous fauna and sediments, and minor bottom current action. There is no direct evidence that powerful erosive turbidity currents have traversed the Wilmington Canyon in the past 200 years. The stop-and-go transport mechanism may be more correctly restricted to the slope and may utilize less obvious bottom (possibly tidal) and density currents as a vehicle for transport.

The processes which recent models of submarine canyon maturation have proposed as the cause for the transformation of youthful straight slope canyons (e.g., South Heyes Canyon) to mature meandering shelf-indenting canyons (e.g., Wilmington Canyon) have apparently been inactive in Wilmington and South Heyes canyons in the past 200 years. However, the time period represented by cores in this study is brief, and these processes (major mass wasting and headward erosion in straight canyons, and active scouring by major turbidity currents in meandering canyons) may well take place at time scales far greater than those examined in this study.

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DOI

10.25777/2mya-sx76

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