Estimations of Clarkes for Carbonaceous biolithes: World averages for trace element contents in black shales and coals

Black shale and coal Clarke values are the average trace element contents in the World black shales and coals. These calculations are made in Russian geochemistry but up to now are poorly known in the West.

Modern tables of black shale and coal Clarkes are presented, based on comprehensive calculations using very large amount of information (thousands analyses of black shales, coals, and coal ashes for trace elements). In black shale geochemistry, three figures were calculated for each main lithologies: terrigenous (+ tuff), chert, and carbonate. Two Clarke estimations are presented, named “lithological” (K1) and “lithostratigraphical” (K2). In coal geochemistry, seven figures were calculated for each trace element: average content in hard coals and their ashes; average content in brown coals and their ashes; average content in all coals and their ashes; and coal affinity index (or “coalphile index”) = average content in all ashes/Clarke values of sedimentary rocks.

The black shale and coal Clarkes presented here provide an important scientific base for many geochemical comparisons and issues.