Rates of Instrastratal Solution of Heavy Minerals in Southeast Atlantic Coastal Plain and Their Potential for Dating Sedimentary Events
Robert E. Carver
The heavy mineral content of sedimentary deposits depends on provenance, the effect of chemical and mechanical weathering during transport, grain size of the host sediments, and postdepositional intrastratal solution that selectively removes, over time, the less stable minerals. Giles and Pilkey pointed out that two types of sand-sized sediment arrive at the southeast Atlantic Coast: sediments originating in the Piedmont with immature heavy mineral assemblages, and sediments derived from older coastal plain sediments with mature heavy mineral assemblages. Most of the coastal sands are mixtures of these two types, and the heavy mineral suites of well-mixed coastal sands are reasonably predictable, as are the suites of Piedmont sands.
For sands from similar sources and with similar transport histories, the mineralogy of fine-grained sand samples differs from that of coarse-grained samples. For example, fine-grained samples invariably have more zircon. Examination of a single size fraction of the samples eliminates the size effect. For well-mixed coastal sands, postdepositional intrastratal solution is the only variable producing significant differences in heavy mineral suites.
Of the common heavy minerals in southeast Atlantic coastal and Piedmont suites, hornblende and epidote appear to be the most susceptible to intrastratal solution, hornblende more so than epidote. The rate of intrastratal solution is progressive, but because of variation in vertical and horizontal permeability and other factors, the rate is rarely, if ever, linear with time. However, under certain circumstances, heavy mineral suites indicate relative areas of coastal plain sand units and rough estimates of absolute ages.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.