Upper Cretaceous (Campanian) and Cenozoic stratigraphic sequence, northeast Caribbean (St. Croix, U.S. Virgin Islands)

摘要

The stratigraphic sequence exhibited on St. Croix (United States Virgin Islands) constitutes the available data essential to interpretation of subsea stratigraphy in the northeast Caribbean. Stratigraphic columns define a sequence of Upper Cretaceous to lower Pliocene deposits containing six formally recognized rock units on St. Croix. Strongly folded Upper Cretaceous deep-water (oceanic) calcareous turbidites and volcaniclastics (>10.6 km thick; 34,700 ft) are divisible into the Caledonia, Allandale, Cane Valley, and Judith Fancy Formations, which are separated by gradational contacts. The top of the Judith Fancy Formation is marked by an unconformity. Between the Upper Creta- ceous formations and the two recognized Cenozoic rock units, the Jealousy Formation and the Kingshill Limestone, is an unexposed and unnamed lower Tertiary (Paleocene?) accumulation. This unit is 1.7 km thick (5,500 ft), and its earliest strata are of unknown origin but are inferred to be hemi-pelagic in nature, like the gently folded, overlying carbonates. The foraminiferal composition of the carbonate rocks indicates a shoaling (basinal) environment of deposition. The oldest named Tertiary rock unit, the Jealousy Formation, is composed of 430 m (1,400 ft) of blue, green, and gray clays; the youngest, the marly Kingshill Limestone, is 180 m (600 ft) thick. The unnamed lower Tertiary strata may be diachronous with the clay deposits; the clay and limestone strata are herein shown to be time-transgressive. An abrupt contact separates the Kingshill Limestone from an overlying lower Pliocene limestone, which is unconformably overlain by Quaternary coral reefs, alluvial sands, and beach deposits. Correlation of biochronologic ages of the exposed Cenozoic sediments with biostratigraphic zonations on the basis of planktonic foraminifera and calcareous nannofossils indicates that (1) the sediments correspond to respective early Eocene Zones P9 and NP13 through early Pliocene Zones N19 and NN15; (2) the Jealousy Formation appears to be at least early Eocene to early middle Miocene and is, in part, contemporaneous with the Kingshill Limestone; and (3) deposition of the mostly Miocene Kingshill Limestone began during late Oligocene time.