. Bulletins of American paleontology. 86 Bulletin 371 of the coral Pontes califomica Verrill from the U|5per Pleistocene +12-m terrace deposit were reported hy Ashby et al. (1987, 1988) as 124,000 ± and ± years. Ashby ( 1984) and Ashby and Minch (1987) presented detailed stratigraphic and pa- leoecologic data Irom the area of iItc Miiicize estuary. Loreto embayment (Text-tigs. 2. 56. 62. 63) Overview The Loreto embayment extends from approximately 30 km to 5 km north of Loreto. and from the base of the Sierra la Giganta on the west to Isla del Carmen. 14 km (9 mi) offshor
. Bulletins of American paleontology. 86 Bulletin 371 of the coral Pontes califomica Verrill from the U|5per Pleistocene +12-m terrace deposit were reported hy Ashby et al. (1987, 1988) as 124,000 ± and ± years. Ashby ( 1984) and Ashby and Minch (1987) presented detailed stratigraphic and pa- leoecologic data Irom the area of iItc Miiicize estuary. Loreto embayment (Text-tigs. 2. 56. 62. 63) Overview The Loreto embayment extends from approximately 30 km to 5 km north of Loreto. and from the base of the Sierra la Giganta on the west to Isla del Carmen. 14 km (9 mi) offshore. The area is highly significant in the history of the modern Gulf of California because of its sequence of Miocene arc volcanic and volcani- clastic sediments overlain by a thick wedge of Plio- cene marine, nonmarine. and deltaic facies that was deposited during the transition from extensional to transtensional regimes. The onshore Loreto embay- ment was mapped by McLean (1988) at a scale of 1 and as part of detailed sedimentary and tec- tonic studies by Dorsey el al. (1997). Zanchi (1994). and Bigioggero et al. ( 1995). Long recognized as an important key to the geologic history of the central Gulf of California, the offshore Loreto embayment represented by the sediments on Isla del Carmen needs further detailed mapping. Isla del Carmen Plate 2. Column 37 (Text-figs. 56. 62. Appendix 1) Column modified from the geologic sketch map of Anderson ( 1950: fig. 4). Isla del Carmen is 28 km long by 3-8 km wide, composed of unnamed volcanic and volcaniclasiic rocks oxerlain miconlormably by a number of facies of marine clastic deposits that were described by An- derson ( 1950). We are unable to separate two of these in the onshore basin, shown in Plate 2. Coknnn 38 as the Carmen-Marquer Formation, undifferentiated. Stnitiiiraphy Basement roeks. Oligocene or Mioeene.âThe old- est rocks that crop out on northeastern Isla Carmen are the reddish tuff breccias and lava flows
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