Virtual Field Study
Calvert Rock Formations:There are three major units of rock that can be observed in Calvert County Maryland. These rocks are grouped into three major intervals that record changes in sea level.
The Calvert Formation:
The oldest sediments deposited in the Salisbury Embayment are grouped into a package of sediment known as the Calvert Formation. The Calvert is made up of three distinct marine units, each differing from the others in the nature of the sediment composition and fossil fauna. The Calvert Fm. sediments consist of thick clay beds with thin sand layers, which were deposited over a 10 million year period of time. The Calvert Formation is named after the location (Calvert County) where they were firstdescribed (Click for Photo).
The Choptank Formation:
Following a significant drop in sea level in the Salisbury Embayment, the clays that make up the Calvert Formation give way to marine sands, which form the Choptank Formation. This formation is named for the Choptank River, where exposures of this formation are found. The Choptank was deposited 13 to 12 million years ago. Sediments in the Choptank are made up of yellow sand and green-grey colored sandy clay (Click for Photo).
The St. Mary's Formation:
The St. Mary's Formation is named for St. Mary's County, where the original deposits were observed. The St. Mary's Formation consists of blue-colored sandy clay that grades into coarse sand. This change from clay to sand indicates a significant drop in sea level during the deposition of the St. Mary's Fm, 12 to 10 million years ago (Click for Photo).
Last modified October 06 2008 02:27 PM