NEW EARLY AND MIDDLE JURASSIC COCCOLITH TAXA AND BIOSTRATIGRAPHY FROM THE EASTERN PROTO-ATLANTIC (MOROCCO, PORTUGAL AND DSDP SITE-547-B)

Lower to Middle Jurassic basinal marl/limestone sections in the Lusitanian Basin of Portugal and the High Atlas of Morocco contain nearly continuous successions of calcareous nannofossil assemblages. Many of the nannofossil bioevents identified in this paper have been calibrated to the ammonite biostratigraphy in these basins. The definition of precise species concepts is fundamental to recognizing these events and eliminating diachroneity apparent in the published stratigraphic ranges of previously-described taxa. The marine sediments in these basins also provide new information about the origin and early evolution of a major group of Mesozoic coccoliths, the Order Podorhabdales. Early developments within this order are related to changes in coccolith rim construction. This is reflected in significant taxonomic revisions of the two oldest families within this order of coccoliths, the Bussoniaceae and the Biscutaceae. One new genus and nine new species are described: Similiscutum, Similiscutum orbiculus, Similiscutum avitum, Similiscutum cruciulus, Similiscutum precarium, Similiscutum gephyrion, Biscutum profundum, Triscutum sullivanii, Triscutum tiziense, and Triscutum pricatillus. Two families, four genera, and one species are emended. Five new combinations are proposed.