Mineralogy and Origin of Sediments From Drill Holes on the Continental Margin Off Florida, 1965-1969 (NCEI Accession 7100714)

Drill cores obtained during the Joint Oceanographic Institutions' Deep Earth Sampling Program from the continental shelf, the Florida-Hatteras Slope, and the Blake Plateau off northern Florida are composed of sediments ranging in age from Paleocene to post-Miocene. Calcite is the dominant mineral in all the cores; dolomite is almost completely restricted to the shelf and slope cores. Aragonite persists in samples as old as Oligocene, but the magnesian calcite occurs only in post-Miocene samples. In general, only Miocene samples contain non-carbonate minerals in appreciable quantity. Phosphates are limited largely to the Miocene sediments. Here also, the clay minerals palygorskite, sepiolite, and montmorillonite are dominant. These clay minerals and the zeolites clinoptiolite and phillipsite in Miocene and older sediments suggest that volcanic activity was the principal source of non-carbonate deposition during much of the Tertiary. Heavy-mineral analyses suggest a southern Appalachian source for detrital materials. Terrigenous detrital material is scarce in most of the cores except for the surface samples on the continental shelf. The concentration of detrital quartz here probably resulted from reworking and winnowing by regression and transgression of the sea during Pleistocene rather than by increased influx of Terrigenous material.

Consolidated chertlike rocks consist of dominantly carbonate minerals in the near-shore holes and dominantly opaline cristobalite inthe Blake Plateau holes. Reflux dolomitization by dense brines produced in evaporative lagoons in the area of the continental shelf and later incursions of fresh ground water from the Florida peninsula may have lithified sediments in the near-shore holes. Only when conditions were favorable for silicification were sediments on the Blake Plateau appreciably consolidated.