THE WIDESPREAD OCCURRENCE OF AGGLUTINATED FORAMINIFERA IN BLACK SHALES

Diverse forms of agglutinated foraminifera, identified with the help of scanned cathodoluminescence, are observed to occur widely in black shales. These forms have been observed within a variety of shale lithologies in the Barnett Shale of central Texas (lower Mississippian), the Ohio Shale of Kentucky (Devonian), the Kimmeridge Clay and Oxford Clay Formations (Upper Jurassic) exposed in southern and central England, and the Mancos Shale (Cretaceous) of Utah. Extreme compactional flattening in the plane of bedding is a prominent characteristic. A common type of test is composed dominantly of silt-size quartz that is cemented with authigenic quartz (possibly former opal). The small crystal size of the test materials gives these fossils a chert-like appearance in transmitted light microscopy. Together with the complications of compaction, their appearance in light microscopy makes it possible for these fossils to be easily mistaken for silt-filled burrows or silicified collapsed spores or algal cysts. Cathodoluminescence reveals clearly however the dominantly detrital nature of the material that makes up the shell wall. Detrital quartz and feldspar dominate the grain assemblages within the shells whereas detrital micas, abundant in the surrounding matrix, are largely rejected by the organisms. Given their widespread occurrence of these foraminifera, investigations into their ecological significance could contribute to important advances in our understanding of the complex facies variations within black shales.