Marine stratigraphy and paleontology of southwest Isla Tiburon, Gulf of California, Mexico

Scale of accompanying map 1:12,000Title 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.Northwest geographic corner for the map: W 112??34???09??? -- N 28??53???07??? = -112.569167?? -- 28.885278??Northeast geographic corner for the map: W 112??30???28??? -- N 28??55???26??? = -112.507778?? -- 28.923889??Southwest geographic corner for the map: W 112??33???51??? -- N 28??51???22??? = -112.564167?? -- 28.856111??Southeast geographic corner for the map: W 112??28???42??? -- N 28??53???57??? = -112.478333?? -- 28.899167??Center coordinates of accompanying map in decimal degrees [longitude/latitude]: -112.547500?? and 28.890000??The mapped area is a polygon that is not parallel to latitude and longitude grid. Latitudes and longitudes are given for each corner of the map.The base map was constructed for this project using aerial photographs and a photogrammetric stereoplotter. The aerial photographs were provided by CETENAL, a Mexican government agency. Contour interval for the geological map is 20 feet. Jay Robert Neuhaus??? and Cassidy's theses use the same geological base map. Scale of the geological map is: 1:12,000. Coordinates for the geological map were estimated using Google-Earth-satellite imagery.Two, satellite-imagery scenes were used. Scene one: Digital Globe Catalog ID: 10 100 100005042602; Acquired Date: 08 January 2006; Latitude: 28.80959??; Longitude: -112.49215??; Off-Nadir Angle: 5??; Target Azimuth: 60??; Cloud cover: 0%; Environmental quality: 99. Scene two: Digital Globe Catalog ID: 10 100 10000205A203; Acquired Date: 26 June 2003; Latitude: 28.94923??; Longitude: -112.48258??; Off-Nadir Angle: 10??; Target Azimuth: 27??; Cloud cover: 0%; Environmental quality: 90Six folded plates in pocketIncludes 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. \ud 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. \ud 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. \ud 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 820 feet, and consists of interbedded conglomerate containing neritic megafossils. Unit 3 conformably overlies unit 2 and consists of 250 feet of interbedded, inversely graded conglomerate and sandstone, both of which contain neritic megafossils. Unit 4 conformably overlies unit 1, is 590 feet thick and consists of three sub-units: unit 4A, the bulk of the unit, which consists of fine to coarse-grained sandstone containing both benthic and pelagic foraminifera and neritic marine megafossils, unit 4B, a volcanic debris flow, and unit 4C, a rhyolite flow. Unit 5 conformably overlies and is interbedded with unit 4 and unit 6 and consists of interbedded conglomerates and sandstones which contain neritic megafossils. \ud Unit 6 conformably overlies and is interbedded with both unit 4 and unit 5, and consists of interbedded conglomerates which contain neritic megafossils. Unit 5 and unit 6 have a combined maximum thickness of 1,954 feet. Unit 7 conformably overlies unit 6, and consists of fine to coarse grained sandstones which contain neritic megafossils. \ud The marine sedimentary section exposed on Isla Tiburon represents neritic marine deposition of the subaqueous portion of a fan-delta system during the Miocene, possibly as early as the middle Miocene. \ud Work in progress on interbedded and overlying volcanic rocks should shed further light on the age of the section