This is a carbonate hardground from the Cretaceous
showing typical Mesozoic bioerosion. The top image is the upper
surface of the hardground with its round holes; the bottom image
is a cross-section of the hardground, showing that these holes
are clavate (club-shaped). These are the boring Gastrochaenolites,
usually produced by bivalves. These specimens are from the Glen
Rose Formation (Cretaceous) of Texas. (See a typical example
of Cenozoic bioerosion, examine a
diagram of Gastrochaenolites,
or return to the Geological History of Bioerosion
page.)
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