Turbidites reworked by bottom currents : upper Cretaceous examples from St. Croix, U.S. Virgin Islands

Related Titles

Series: Smithsonian contributions to the marine sciences, no. 33

By

Stanley, Daniel J.

Type

Book

Material

Published material

Publication info

Washington, D.C, Smithsonian Institution Press, 1988

Notes

Sedimentological study of the Late Cretaceous volcaniclastic deposits in St. Croix, U.S. Virgin Islands, emphasizing primary structures and bedforms, reveals a remarkable suite of sandy lithofacies. An inventory of the different sand types in several formations shows that a natural continuum of deposits exists between downslope-directed gravity flow and bottom current-tractive “end-member” deposits. Most sandy strata, herein termed “intermediate variants,” record primary emplacement by turbidity currents, probably from the north, and a subsequent reworking of these layers by bottom currents flowing toward the west. The sand layers accumulated in a proximal setting, perhaps slope aprons, and these were then reworked along bathymetric contours. The lower portion of sand layers typically displays the original graded (A) turbidite division, while the texturally cleaner mid and upper parts of such strata usually show structures more typically associated with tractive transport. Photographs of polished slabs and large thin sections of the diverse Cretaceous sand layer types on St. Croix, reproduced at a 1:1 scale, may serve as a basis for comparison with other deep-water formations in the modern and ancient record. They may be most useful in interpreting sequences such as those on St. Croix where a solely turbidite or gravity-emplaced interpretation is inadequate.This petrologic investigation also sheds further light on the paleogeography of the region. Examination of the sandy volcaniclastic sequences supports earlier hypotheses that they accumulated in a tectonically active island-arc setting. A strong tectonic and volcanic imprint is displayed by the syndepositional deformation of fabric, bedforms, and primary structures. Paleocurrent analyses indicate that, in what was to become the northeastern part of the Caribbean, the predominant bottom-current trend during Late Cretaceous time was roughly parallel to the surface circulation pattern, i.e., directed toward the west. The vigorous reworking of coarse sand and granule turbidites, and the development of bioturbation structures in tractive deposits indicate that, although the paleo-Atlantic was geographically much narrower, bottom-water circulation in this region was not restricted nor were bottom waters anoxic. Recognition here of the diverse suite of reworked sandy turbidite lithofacies, poorly documented to date, can hopefully serve to clarify other cases in both the modern and rock record where there has been interaction between bottom currents and turbidity currents.

Subjects

Cretaceous , Geology, Stratigraphic , Saint Croix , Turbidites , Virgin Islands of the United States

Language

English

Identifiers

LCCN: https://lccn.loc.gov/87600196
OCLC: 16004819