| Summary: | Scale of accompanying map 1:12,000 Title of accompanying map on Plate I: Geologic map of SW Isla Tiburon, Gulf of California, Mexico. Title of accompanying diagram on Plate II: Cross section A - A' Title of accompanying diagram on Plate III: Stratigraphic range of selected planktonic foraminifera. Title of accompanying diagrams on Plate IV: Distribution of selected foraminifera. Title of accompanying diagram on Plate V: Isla Tiburon measured sections. Title of accompanying diagram on Plate VI: Schematic illustration showing how unit designations are spatially associated with facies distribution patterns. The base map was constructed with aerial photographs by CETENAL. Coordinates for the geological map were estimated using Google-Earth-satellite imagery. Six folded plates in pocket Includes bibliographical references (leaves 50-[52]) A marine sedimentary section on the southwest corner of Isla Tiburon, Gulf of California, Mexico, consists of interbedded fossiliferous sandstone and conglomerate, conformably overlying fossiliferous marine sedimentary breccia. These marine sedimentary rocks are interbedded with a middle Miocene (12.9 + 0.4 Ma) volcanic debris flow and are unconformably overlain by a late Miocene (11.2 + 1.3 Ma) ignimbrite. They are interpreted as part of a subaqueous fan-delta system within the Miocene Gulf of California. Analysis of the microfossils indicate deposition during the late Miocene to early Pliocene time, conflicting with available K/Ar data. Megafossils indicate that deposition could have occurred as early as the middle Miocene. Integrated study of marine megafossils, benthic and pelagic fossil foraminifera, calcareous nannofossils, and sedimentologic characteristics found within the study area has allowed it to be subdivided into 7 units based on depositional environments and facies changes. The lowermost section, unit 1, consists of a fossiliferous marine breccia with a maximum thickness of 1,700 feet. Unit 2 conformably overlies unit 1, has a maximum thickness of ...
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