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Masters Thesis

Stratigraphic analysis and paleogeography of the Hurricane Deck Formation, San Rafael Mountains, Santa Barbara County, California

Detailed geologic mapping in the central San Rafael Mountains, Santa Barbara County, California revealed that the rocks are comprised, from oldest to youngest, of the Franciscan Complex, undifferentiated Cretaceous rocks, the Simmler Formation, the Quail Canyon Sandstone and Soda Lake Shale Members of the Vaqueros Formation, the Hurricane Deck Formation, and the Saltos Shale Member of the Monterey Shale. Stratigraphic analysis of the Hurricane Deck Formation indicates that it is underlain conformably and intertongues with the Soda Lake Shale Member and is overlain conformably and intertongues with the Saltos Shale Member. The formation is 1,170 m thick at the type section in the White Ledge Canyon area and thins westward to 690 m thick in the Potrero Canyon area. The formation also thins toward the north and south to 92.5 (Bald Mountain Canyon section) and 35 m (Zaca Lake section), respectively. Within the Hurricane Deck Formation the following eight lithosomes were recognized: lithesome A (pebble conglomerate, channel-shaped geometry), lithesome B (graded sandstone, planar to slightly scoured base), lithesome C (graded to structureless, bedded sandstone, scoured base). Lithosome E (mudstone intraclast-bearing sandstone), lithesome G (contorted interbeds of sandstone and mudstone), lithesome I (structureless mudstone), lithesome J (laminated mudstone), and lithesome K (bentonite). Lithosomes B and C are most abundant and occur in 0.2- to 5.0-m-thick beds that form laterally continuous sandstone units that are separated from one another by intertonguing mudstone units of lithesome I or J. The sandstone units also pinch out into the mudstone. These mudstone units contain lower middle bathyal, Saucesian-age foraminifera. The coarser grained lithosomes (A, B, C, E, G) are interpreted to mostly represent high concentration turbidity currents that were deposited on a middle fan depositional lobe environment. A minor amount of the coarser grained deposits represents an interlobe or lower fan environment. Lithesome C also represents depositional lobe channel deposits. The mudstone of lithosomes I and J is interpreted to represent pelagic and hemipelagic deposition in interlobe, lower fan, and basin plain environments and on submarine highs. Lithesome K is interpreted to represent settling from suspension of volcanic ash in all the environments mentioned above. Thin-section and heavy-mineral analyses indicate that the source area consisted mainly of felsic plutonic rocks with minor amounts of volcanic, metamorphic, and sedimentary rocks. The depositional basin within which the depositional lobe to basin plain sediment accumulated was a confined, west-trending trough with submarine highs running along the north and south sides. Sediment supplied from the upper fan was generally confined to a westward paleocurrent direction due to the geometry of the basin. Lower fan and basin plain deposits occur mostly in the western portion of the study area where the length of the trough sometimes exceeded the distance of transport for the middle fan depositional lobes.

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