Foraminifera: New approaches to their paleobiology, biology and evolution

oth fossil and living foraminifera have been investigated in this study. Late Cretaceous age foraminiferal assemblages have been used to examine the relationship between high-frequency sea level change, biotic response and paleoceanography, in the U.S. Western Interior Sea. Living planktic foraminifera were also studied in order to test a novel hypothesis on the evolution of cellular organelles known as fibrillar bodies. The major findings of this dissertation are: (1) The third-order Greenhorn tectono-eustatic cycle (late Cenomanian-middle Turonian) in the Cretaceous Western Interior Basin is superposed by fourth-order relative sea level cycles and fifth-order parasequences that are reflected in foraminferal assemblages and carbonate content of shales and mudrocks. The study interval includes the Cenomanian/Turonian (C/T) boundary event (93.3 Ma) and the highest stand of sea level in the western interior during early Turonian time. Calcareous benthic foraminiferal assemblages show marked shifts in taxon dominance which is interpreted as ecologic replacement indicating change from a food-controlled to an oxygen-controlled environment. Acmes of the genus Gavelinella are related to the initiation of fourth-order transgressive episodes early in the third-order transgression and late highstand phases of the Greenhorn Cycle. The rapid proliferation of this taxon is thought to be a response to pulses of food. Warm, oxygen-poor Tethyan waters spread across the WIS during the late transgression and highstand phases of the Greenhorn Cycle. A rapid ecologic shift to Neobulimina dominance is the benthic foraminiferal response to this Tethyan incursion. The relative abundance of Neobulimina shows a highly significant correlation to carbonate content (p...