- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
The Besa River Formation of Middle Devonian (Givetian) to Late Mississippian (Chester) age ranges in thickness from less than 1,000 to more than 7,000 feet. The thinner sections, which were continuously deposited in deep water represent the fondothem. Thicker sections on the east and south represent the clinothem. Barrier reef complexes, blanket shelf carbonates, and interbedded calcareous shale and limestone represent the undathem. The predominant fraction of the shale, comprising quartz, carbonate, pyrite, and carbonaceous matter is indigenous to the basin of deposition and is largely of organic or chemical origin. The subordinate clay fraction was either derived from volcanic ash and moved to shelf margins or was generated within the basin from dilute solutions of its constituents. Depth of water is not critical to formation of thin transgressive black shales.