Relationship between physical condition of the carbonate fraction and sediment environments: northern Puerto Rico shelf

Each of three sediment types recognizable on the northern Puerto Rico shelf and beaches is characterized by calcareous material in different physical condition. Dark terrigenous sand is accumulating at a relatively rapid rate and has a carbonate fraction containing fresh-appearing angular particles. The pure-carbonate skeletal-sand sediment type has a much lower rate of deposition, and its old-appearing calcareous particles have a dull surface luster. The third sediment type, a mixture of the first two, is largely from beaches and is characterized by highly polished, very well-rounded grains. Differences in length of sea-floor exposure and intensity of abrasion appear to be responsible for the variable physical condition of the carbonate fractions. We suggest that on other shelves having less distinctive sedimentary regimes, the physical condition of the carbonate grains could be used to interpret present shelf processes. ?? 1979.