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Erin Blackwood, M.Ed. Romberg Tiburon Center for Environmental Studies San Francisco State University [email protected] The Formation of San Francisco Bay April 10, 2014 Plate Tectonics Glaciation Sediments Bathymetry Estuaries Human Impacts Romberg Tiburon Center for Environmental Studies 2 100 million years agopresent day Romberg Tiburon Center for Environmental Studies 3 Long, long ago…before ANY of us were born! North America paleogeography 100 million years B.P. Romberg Tiburon Center for Environmental Studies 4 North Pacific Plate Tectonics Several QuickTime animations can be viewed here simply by clicking on them. http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html#GlobalTectonics If you do not have QuickTime, you can download for free at http://www.apple.com/quicktime/?cid=oas-us-domains-quicktime.com It works for both Mac and PC. Romberg Tiburon Center for Environmental Studies 5 Plate tectonics of western North America Romberg Tiburon Center for Environmental Studies 6 Subduction tectonics and sedimentation Sediment is scraped off the descending plate and piles up in an accretionary prism Romberg Tiburon Center for Environmental Studies 7 04.07b: The accretionary prism Romberg Tiburon Center for Environmental Studies 8 Volcanic Activity Pillow basalt (visible at Pt. Bonita, & in S.F!) Result of volcanic lava cooling quickly in the ocean Romberg Tiburon Center for Environmental Studies 9 California’s Geologic History Cenozoic - ca. 50 million years ago The ancestral Nevadan Mountains had eroded down to relatively low-lying hills. Large rivers flowed through the region and deposited gravels rich in gold. The southern Sierra Nevada and Mojave region were elevated enough to allow for the erosion and deposition of thick layers of marine sedimentary rocks in what are now the southern Coast Ranges and western Transverse Ranges. Romberg Tiburon Center for Environmental Studies 10 Cenozoic – ca. 20 million years ago Volcanic activity, related to extension and thinning of the crust, became widespread in the Sierra Nevada and Mojave regions. Around 10-15 mya a series of deep marine basins formed along the coast between Orange County and the San Francisco region. The appearance of the basins may have signaled the passage of what is now coastal southern and central California over the spreading zone. The rocks formed in these basins (Monterey Formation) are composed mainly of material derived from marine organisms, rather than terrestrial sediments. These marine deposits are known as the Monterey Shale, targeted for natural gas extraction through fracking. Romberg Tiburon Center for Environmental Studies 11 Cenozoic – ca. 5 million years ago Mountain-building activity rapidly accelerated, and finally most of the modern mountain ranges were uplifted, including the Sierra Nevada and the large fault-block ranges to the east, the Coast Ranges, the Transverse Ranges, and the Peninsular Ranges. San Andreas Fault jumps inland. Subduction continued in the north forming the major volcanoes of the Cascades. Pleistocene glaciation in the Sierra Nevada and, to a minor extent, in the San Bernardino Mountains; recent volcanic eruptions in the Mojave and Great Basin regions; and the widespread volcanic activity that created the southern Cascade volcanoes (Mt. Shasta and Mt. Lassen) and the lava flows of the Modoc Plateau region. Romberg Tiburon Center for Environmental Studies 12 Earthquake faults Romberg Tiburon Center for Environmental Studies 13 Lake Corcoran – ca. 1 mya A million years ago, there was no San Francisco Bay, just rolling grasslands. The middle of California—what is now the Central Valley—was covered by an enormous inland sea called Corcoran Lake. Rivers from Corcoran Lake emptied to the south through the Salinas River into Monterey Bay. About 560,000 years ago, tectonic shifting (likely at the Garlock fault) caused the Bay Area land to sink, and the southern end of Lake Corcoran to rise. Water from Lake Corcoran spilled over its western ridge, near the present day city of Martinez, completely draining the lake. This cataclysmic event carved out the Carquinez Strait and began to shape the basin that would become San Francisco Bay. Romberg Tiburon Center for Environmental Studies 14 Classification of Marine Sediments Lithogenous- also includes quartz sand, estuarine mud *CCD=Carbonate (CO3) Compensation Depth, b/w 4 an 5 km deep (2.5-3 miles) Hydrogenous-precipitation of minerals often caused by bacteria Romberg Tiburon Center for Environmental Studies 15 River input of silt to oceans Which sediment type does this create?Terrigenous or lithogenous Romberg Tiburon Center for Environmental Studies 16 Siliceous Oozes Which type of sediment does this create? Biogenous! Romberg Tiburon Center for Environmental Studies 17 Microfossils make up siliceous and calcareous oozes Radiolarians (above) make up siliceous oozes, foramaniferans (top right) and coccolithophores (right) make up calcareous oozes Romberg Tiburon Center for Environmental Studies 18 Deep-sea sediment distribution Manganese mining operation was based at RTC in the 1960s. Good cover to search for a downed Soviet submarine Romberg Tiburon Center for Environmental Studies 19 Hydrogenous Sediments a) Manganese nodules. Contain a variety of valuable metals including iron, nickel, copper, cobalt, zinc and lead. Origin is unclear, but they are created at the watersediment interface b) Cross-section of a nodule revealing the nucleus (arrow) around which concentric layers are laid down at the rate of 1-4mm per million years. The nucleus may be sand grains, gravel, or even shark teeth! Romberg Tiburon Center for Environmental Studies 20 Bulk Emplacement Terrigenous sediment extends to the continental slope Turbidity currents are sediment-laden slurries aided by gravity moving rapidly downslope Speed increases as more sediment is scoured and suspended, increasing the density of the slurry relative to surrounding water Turbidity currents create and deepen submarine canyons As the slope flattens and the turbidity current slows, sediment is dropped out of suspension according to particle size, creating graded bedding. These beds are called turbidites. Romberg Tiburon Center for Environmental Studies 21 Monterey Canyon Submarine canyons such as Monterey Bay’s are too deep to have been creating by ancient rivers (the deep canyon was never above sea level) Turbidity currents are a likely explanation Romberg Tiburon Center for Environmental Studies 22 Ice rafting Another form of bulk emplacement Romberg Tiburon Center for Environmental Studies 23 Romberg Tiburon Center for Environmental Studies 24 Distribution of shelf sediments by size The smaller the sediment size, the farther it can be carried, especially if currents are weak. Larger gravel and cobbles need high wave energy to be transported any distance. 25 Romberg Tiburon Center for Environmental Studies Glaciation and sea level Romberg Tiburon Center for Environmental Studies 26 Once Upon a Time…. Romberg Tiburon Center for Environmental Studies 27 Post-Glacial Flooding of SF Bay QuickTime animation http://emvc.geol.ucsb.edu/2_infopgs/IP2IceAge/cSFBayFlood.html Romberg Tiburon Center for Environmental Studies 28 Melting Glaciers, Changing Shoreline Romberg Tiburon Center for Environmental Studies 29 The Mermaid Takes Shape Romberg Tiburon Center for Environmental Studies 30 The Formation of San Francisco Bay KQED Saving the Bay video clip http://education.savingthebay.org/the-formation-of-san-francisco-bay/ Romberg Tiburon Center for Environmental Studies 31 Types of Estuaries Chesapeake Bay Puget Sound North Carolina Coast Tomales Bay Romberg Tiburon Center for Environmental Studies 32 Which type is San Francisco Bay? Romberg Tiburon Center for Environmental Studies 33 Which type is San Francisco Bay? Drowned river mouth Romberg Tiburon Center for Environmental Studies 34 Estuary Circulation Which type does San Francisco Bay follow? NOT a salt wedge, correction from lecture! Romberg Tiburon Center for Environmental Studies Puget Sound Gulf of California 35 Partially to well-mixed estuary depending on season well-mixed partially mixed Romberg Tiburon Center for Environmental Studies 36 The Gold Rush From 1854-1884, 1.5 billion cubic yards of soil and rocks were blasted from the Sierra hillsides and dumped into nearby rivers and ultimately San Francisco Bay. Between 1850 and 1900, 26 million pounds of mercury were used to extract gold KQED Saving the Bay segment, “The Aftermath of the Gold Rush: Mining and Mercury in the Bay” at http://education.savingthebay.org/the-aftermath-of-the-gold-rush-mining-and-mercury-in-the-bay/ Romberg Tiburon Center for Environmental Studies 37 San Francisco Bay, 1800 vs 1998 Romberg Tiburon Center for Environmental Studies 38 The changing shoreline of San Francisco Romberg Tiburon Center for Environmental Studies 39 Habitat Alteration Gold Rush increased sediment on Bay floor, smothering native filter feeders and wiping out kelp beds in Central Bay Filling and diking wetlands for development and agriculture has reduced these natural flood control areas by over 90% Reduced fresh water and normal sediment flow due to water diversions for agriculture (80% of diversions) and urban needs Romberg Tiburon Center for Environmental Studies 40 Current Depth of SF Bay Romberg Tiburon Center for Environmental Studies 41 Bathymetry of the Central Bay Romberg Tiburon Center for Environmental Studies 42 Blasting of Arch Rock Arch Rock, around 1900 Blasting of Arch Rock, 1901 Romberg Tiburon Center for Environmental Studies 43 Submerged Rocks at the Golden Gate Currently less than 40 feet below the surface at low tide Romberg Tiburon Center for Environmental Studies 44 But container ships are now much larger, with deeper draft This could be a problem Romberg Tiburon Center for Environmental Studies 45 Sand Waves Undersea sand waves are created by subsurface currents. Sand waves like this exist in San Francisco Bay, just inside and outside the Golden Gate Romberg Tiburon Center for Environmental Studies 46 Fly Over the Seafloor of SF Bay U.S. Geological Service YouTube video at https://www.youtube.com/watch?v=GySUAMuj-cY Romberg Tiburon Center for Environmental Studies 47 Salt Ponds-Remediation Challenge Replaced and doubled natural South Bay Restoration Project Flyover http://youtu.be/GOEUSJwTu8M (1.5 min) salt panne habitats. Vary in size, depth, salinity, and most importantly, invertebrate characteristics, resulting in the highest diversity of shorebird species of any other habitat in the Bay. Significant roosting and nesting sites for a wide variety of non marsh-dependent species, and the ponds themselves became important foraging areas for millions of shorebirds and other species of waterfowl. Romberg Tiburon Center for Environmental Studies 48 Eelgrass Habitat Restoration Living Shorelines Program Coordinated by CA Coastal Conservancy RTC’s Dr. Kathy Boyer is lead scientist-experimental design, harvest, replanting, monitoring Eelgrass plots alternating with oyster reefs Over 2 million oysters have been “recruited” Habitat could also alleviate sea level rise Romberg Tiburon Center for Environmental Studies 49 San Francisco Bay Today Urban Estuary Creates opportunities and challenges Romberg Tiburon Center for Environmental Studies 50
