Origin of the Grayson micromorph fauna (Upper Cretaceous) of North-central Texas

摘要: The macrofauna of the Grayson Formation (Upper Cretaceous) Texas has been described as a micromorph fauna. Sedimentologic and paleontologic studies claystone in north-central show that it contains small shell size some oysters ammonoids is probably an adaptive strategy evolved by these organisms for survival soft substrate environment. oyster specimens Ilymatogyra arietina (Roemer) may be consequence progenesis, which one mechanism whereby can adapt to substrate. pyritized are result microreducing environments developed within individual shells mud.