Michelle M. Casey
Advisor: Ray Rogers
Senior Honors Thesis: 2003
Magnetostratigraphy of the Upper Cretaceous Maevarano and Berivotra Formations, Mahajanga Basin, Northwestern Madagascar
The Maevarano Formation and overlying Berivotra Formation cap the Upper Cretaceous section in the central Mahajanga Basin in northwestern Madagascar. The Berivotra Formation, which is marine in origin, yields an assemblage of fossils consistent with a Maastrichtian age (˜65Ma). The age of the Maevarano Formation is presently based on correlation with the Berivotra Formation. In an effort to test and further refine the current age interpretations I analyzed the paleomagnetic signal from a suite of samples collected from both formations using alternating field demagnetization. The results show a long interval of normal polarity followed by a single reversal located in the uppermost part of the Berivotra Formation. This simple pattern could place this stratigraphic section any number of places within the global polarity time scale, but fortunately the Cretaceous-Tertiary Boundary provides an independent datum in the local section. Preliminary results of this magnetostratigraphic analysis suggest that the Berivotra Formation and the underlying Maevarano Formation are late Maastrichtian in age. Additional samples throughout the Maevarano and Berivotra Formations as well as a conglomerate test are needed to test the validity of this interpretation.