2005 Online Gallery  « Prev | Index | Next »

G. dehiscens
Laura K.O. Smith '05
Department of Civil and Environmental Engineering
Globoraquadrina dehiscens is a planktic foraminifera, which means that it is a floating microfossil. Its average size is about the size of a grain of sand. G. dehiscens first appears in the fossil record at the very beginning of the Miocene (24 million years ago) and is used world wide as an indicator of the Miocene/Oligocene boundary. This sample was collected from the Gee Greensand at from Campbell’s beach in Otago, New Zealand, in order to date the Greensand. The Gee Greensand also contains many macrofossils including corals, shark’s teeth, echinoderms, and brachiopods. The fossils, grain size, and mineral content of the Gee Greensand, as well as proximity to other rock formations, suggest that the Gee Greensand was deposited during a low sedimentation period and in very shallow water. G. dehiscens, along the presence of G. labicrassata, and G. woodi woodi, narrowed the age of the sediment to the base of the Waitakian Stage, the New Zealand stage for the beginning of the Miocene.