Clay Diagenesis in the Chesapeake Bay Area

Abstract

The rivers of the Chesapeake Bay area carry in suspension predominantly a well formed to degraded illite with minor amounts of kaolin and accessory degraded chlorite. Montmorillonite is rare.Electron microscope photographs of suspended and bottom sediment clays in the James estuary indicate a decrease in floccular size and an increase in crystal size with increasing salinity.A chlorite-like clay is forming in the Chesapeake Bay estuaries. Its thermal stability increases with increase in the salinity of the environment and with depth in the sediments. This material seems to arise from the diagenesis of degraded illite in the Chesapeake Bay area, but it has also been observed to result from diagenesis of a montmorillonoid in the Atchafalaya region of the Gulf Coast.The geochemical relations of chloride, sodium, calcium, potassium, and magnesium in the clays of the James estuary support the hypothesis that chlorite is forming in the estuarine and marine environment.