An area of fine-grained sediments south of Martha's Vineyard, Massachusetts, has been interpreted as a contemporary deposit. Textural analysis of cores from this area indicates that the deposit consists of sandy to clayey silts overlying a well sorted relict sand. The maximum thickness of the fine sediments is about 6 meters as determined from a core near the center of this deposit.
The mineralogy of the <2 um size fraction is similar in both the fine sediments of the contemporary deposit and the underlying coarse sands. The assemblage consists of about 60% illite, 20% chlorite, and 10% kaolinite with minor amounts of mixed-layered clay and smectites.
Heavy mineral analysis from a core near the center of the deposit reveals that opaque minerals, framboidal pyrite, muscovite, hornblende, garnet, and tourmaline constitute over 65% of the total downcore assemblage.
Pyrite concentrations vary widely at some intervals and may reflect areas of micro-reducing conditions within the core or changes in source area with time. A persistent mica content indicates the presence of a low-energy environment throughout the depositional history of these fine sediments.
Downcore organic carbon concentrations are generally uniform in the fine sediments and average about 1.5 percent. Surficial concentration from a core near the center of this feature is about 10 times greater than concentrations for coarse-grained sands on the surrounding shelf.
