STRATIGRAPHY AND PALEONTOLOGY OF LATE CRETACEOUS VERTEBRATE AND INVERTEBRATE DISCOVERIES IN NORTHWESTERN MADAGASCAR.

HARTMAN, Joseph H., Energy & Environ. Res. Ctr., Univ. North Dakota, Grand Forks, ND 58202; WELLS, Neil A., Geology Dept., Kent State Univ., Kent, OH 44242; KRAUSE, David W., Dept. Anat. Sci., SUNY-Stony Brook, Stony Brook, NY 11794; BUCKLEY, Gregory A., Dept. Geology, Field Museum, Chicago, IL 60605.

In a 1993 search for Late Cretaceous mammals in the Mahajanga Basin of northwestern Madagascar, a number of significant vertebrate and invertebrate discoveries were made in nonmarine and marine strata. The stratigraphic evaluation of about 100 fossil localities, in the vicinity of Berivotra village, resulted in a reassessment of Malagasy lithostratigraphic nomenclature, which is a mix of chronostratigraphic terminology, geochronologic correlation, and undelimited lithic-based units referred to as series. Three map units in this area are the Campanian, Maastrichtian, and Danian. The uppermost strata of the Campanian map unit had been subdivided, in part, into the Marovoay and Maevarano Series. From the sections measured and localities studied in 1993, four distinctive lithic units can be recognized. These units (in ascending order) are preliminarily referred to as the Marovoay, Maevarano (both "Campanian"), and Berivotra ("Maastrichtian") Formations, and an unnamed carbonate unit ("Danian"). The Marovoay Formation consists of variably colored sandstones and finer-grained lithologies. The fauna includes possible nonmarine invertebrates, bony fishes, turtles, crocodilians, and dinosaurs. The occurrence of pycnodont fishes suggests a marine to brackish influence in a fauna otherwise dominated by terrestrial taxa. The overlying strata of the Maevarano Formation consist of red and green fine-grained lithologies and sandstones, which in turn are overlain by fossiliferous white sandstones. The vertebrate fauna includes fishes, frogs, turtles, snakes, lizards, crocodilians, and sauropod and theropod dinosaurs, plus a mammal, while the invertebrate fauna includes conchostracans and nonmarine mollusks. In the study area, the Maevarano Formation may represent a distributary channel complex, with minor green claystones representing river-dominated estuarine deposition. The fossiliferous marine strata of the overlying Berivotra Formation consist primarily of marine claystones. In the lower portion of the unit, the fauna is dominated by large gryphaeids and ostreids, while the upper part includes neogastropod snails, bivalves, ammonites, and echinoids. This research was supported, in part, by NSF Grant DEB-9224396.