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A Summary of the Late Cenozoic Stratigraphic and Tectonic History of the Santa Clara Valley, California

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A Summary of the Late Cenozoic Stratigraphic and Tectonic History of the Santa Clara Valley, California A New Three-Dimensional Look at the Geology, Geophysics, and Hydrology of the Santa Clara (“Silicon”) Valley Langenheim et al. A summary of the late Cenozoic stratigraphic and tectonic history of the Santa Clara Valley, California V.E. Langenheim1, R.C. Jachens1, C.M. Wentworth1, R.W. Graymer1, R.G. Stanley1, R.J. McLaughlin1, R.W. Simpson1, R.A. Williams2, D.W. Andersen3, and D.A. Ponce1 1U.S. Geological Survey, 345 Middlefi eld Road, Menlo Park, California 94025, USA 2U.S. Geological Survey, P.O. Box 25046, Denver, Colorado 80225, USA 3Geology Department, One Washington Square, San Jose State University, San Jose, California 95192, USA ABSTRACT Creek fault. Sometime between 9 and 4 Ma concealed basins that can amplify and prolong (9 and 1 Ma for the central block), the area shaking from local and distant earthquakes. The late Cenozoic stratigraphic and rose above sea level, and a regional surface This paper summarizes the late Cenozoic tectonic history of the Santa Clara Valley of erosion was carved into the Mesozoic and stratigraphic and tectonic history of Santa Clara illustrates the dynamic nature of the North Tertiary rocks. Alluvial gravels were depos- Valley as inferred from geologic, stratigraphic, American–Pacifi c plate boundary and its ited on this surface along the margins of the and geophysical data. This summary builds on effect on basin and landscape develop- valley beginning ca. 4 Ma, but they may not the more detailed and comprehensive papers ment. Prior to early Miocene time, the area have prograded onto the central block until in this theme issue and is illustrated by a series that became Santa Clara Valley consisted ca. 1 Ma, because no older equivalents of the of schematic cross sections (Fig. 3). Interpreta- of eroding Franciscan complex basement Pliocene–Quaternary Santa Clara gravels tions of the multiple geologic and geophysical structurally interleaved in places with Coast have been found there. Thus, either the cen- data sets indicate that the history of Santa Clara Range ophiolite and Mesozoic Great Valley tral block was high enough relative to the Valley is a tale of three sedimentary basins. The sequence, and locally overlapped by Paleo- surrounding areas that Santa Clara gravels youngest basin, called the Santa Clara Basin, gene strata. During early to middle Mio- were never deposited on it, or any Santa forms the present-day shape of the valley fl oor cene time, this landscape was fl ooded by the Clara gravels deposited there were stripped and during the past 1–1.5 m.y. has been accu- sea and was deformed locally into deeper away before ca. 1 Ma. Analysis of alluvium mulating debris from the Santa Cruz Moun- depressions such as the Cupertino Basin in on the central block implies a remarkably tains on the west and the Diablo Range on the the southwestern part of the valley. Marine uniform, piston-like, subsidence of the valley east. This alluvial basin conceals two deep late deposition during the middle and late Mio- of ~0.4 mm/yr since ca. 0.8 Ma, possibly Cenozoic basins that are revealed by analysis of cene laid down thin deposits in shallow extending north to northern San Francisco geophysical, primarily gravity, data. One is the water and thick deeper-water deposits in the Bay. Today, the central block continues to Cupertino Basin in the southwestern part of the Cupertino Basin. During this sedimentation, subside, the range-front reverse faults are valley, which records transtension associated the San Andreas fault system encroached active, and the major active faults of the San with the passage of the Mendocino triple junc- into the valley, with most offset partitioned Andreas system are mostly outside the valley. tion and development of the San Andreas fault. onto the San Andreas fault southwest of the The other is the Evergreen Basin in the east- valley and the southern Calaveras–Silver INTRODUCTION ern part of the valley, which is the product of a Creek–Hayward fault system in the north- right step within the East Bay fault system. The eastern part of the valley. A 6-km-wide right Santa Clara Valley, located within the broad margins of these concealed basins have been step between the Hayward and Silver Creek San Andreas fault system in northern Califor- largely overridden by thrust and reverse faults faults formed the 40-km-long Evergreen pull- nia (Figs. 1 and 2), hosts a population of nearly along the western and eastern edges of the val- apart basin along the northeastern margin of 2,000,000 people (U.S. Census Bureau, 2010). ley. The history of these three basins beneath the the valley, leaving a basement ridge between Groundwater from the valley provides this pop- urbanized Santa Clara Valley provides insight it and the Cupertino Basin. The Silver Creek ulation with nearly half of its water supply. The into the way in which the San Andreas fault fault was largely abandoned ca. 2.5 Ma in stratigraphy and structure beneath this highly system has developed in this region, illustrating favor of a compressional left step between urbanized valley provide a foundation for defi n- the dynamic nature of the plate boundary and the Calaveras and Hayward fault, although ing the boundaries of the groundwater fl ow sys- its effect on basin and landscape development. some slip continued to at least mid-Quater- tem because aquifer systems are a product of the nary time. Gravity, seismic, stratigraphic, interplay of depositional and deformational pro- REGIONAL GEOLOGIC SETTING and interferometric synthetic aperture radar cesses through time. The stratigraphy and struc- (InSAR) data indicate no other major San ture of the valley also provide a framework for Santa Clara Valley, a broad, mostly fl at allu- Andreas system faults within the central assessing seismic hazard by mapping locations vial plain extending southward from San Fran- block between the present-day range-front of faults concealed beneath urban development cisco Bay, is situated within the San Francisco faults bounding the valley and the Silver and young surfi cial deposits, and by defi ning Bay block (blue shaded region in Fig. 2). We Geosphere; February 2015; v. 11; no. 1; p. 50–62; doi:10.1130/GES01093.1; 4 fi gures. Received 19 June 2014 ♦ Accepted 8 December 2014 ♦ Published online 14 January 2015 50 For permissionGeosphere, to copy, contact February [email protected] 2015 © 2015 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/1/50/3334215/50.pdf by guest on 30 September 2021 Stratigraphic and tectonic history of Santa Clara Valley, California 124°W 123°W 122°W 121°W 120°W offset determined from analysis of gravity and LEGEND magnetic anomalies suggests even less offset COAST RANGES on the Peninsula segment, ~22 km (Jachens Vizcaino Quaternary Block and Zoback, 2000). The discrepancy between Tertiary sedimentary rocks 300 and 330 km of displacement on the San Tertiary volcanic rocks 39°N Andreas fault documented along the central Point Franciscan Complex part of the San Andreas fault and 124 km of Arena San Andreas Fault Mesozoic sedimentary rocks displacement along the Santa Cruz Mountains (Great Valley sequence east of segment is reconciled by adding displacement the San Andreas fault) taken up on faults east of the San Francisco Serpentinite and ophiolite Bay block. The Hayward and Calaveras faults Granitic and related rocks are part of the East Bay fault system, and they (Salinia) have 160–190 km of cumulative right-lateral BM displacement (McLaughlin et al., 1996) since Hayward Fault 38°N ca. 12 Ma (Graymer et al., 2002). This dis- GREAT VALLEY placement is further refi ned by offset gravity and magnetic anomalies to ~174 km (Jachens Calaveras Fault et al., 1998). The early development of the San Andreas SCV fault system was accompanied by slab-window volcanism in California and northern Mexico San Gregorio-Hosgri Fault YBR starting about 28–27 Ma that resulted from the 37°N deaths of a series of spreading ridge segments HV QS during piecewise destruction of an older sub- PACIFIC duction regime (Atwater, 1970; Wilson et al., OCEAN 2005; McCrory et al., 2009). In the vicinity of San Andreas Fault the Santa Clara Valley, the development of dis- crete faults and northwestward-younging vol- canism may have begun about 18–15 Ma in the COAST wake of a slab window that accompanied the PV northwestward-migrating Mendocino Triple 36°N Junction (Dickinson and Snyder, 1979; John- son and O’Neil, 1984; Fox et al., 1985; Stanley, Parkfield 1987b; McLaughlin et al., 1996). The distribution of basement beneath Santa RANGES PPP Clara Valley is not just the result of strike-slip faulting and transtension, but also earlier sub- duction. The basement within the San Francisco 0 50 100 150 200 KM Bay block consists of two main, often com- plexly interleaved coeval Mesozoic packages, 35°N the Franciscan complex (a subduction complex) Figure 1. Index map showing simplifi ed geology (modifi ed from Jennings, 2010). Box shows and the Coast Range ophiolite with its overlying location of Figure 2 centered on Santa Clara Valley (SCV). Black lines are Quaternary faults sedimentary section, the Great Valley sequence modifi ed from Jennings (1994). Abbreviations are for signifi cant localities discussed in text. (forearc-basin complex) of Bailey et al. (1964). BM—Burdell Mountain; HV—Hollister Valley; PPP—Palo Prieto Pass; PV—Priest Valley; Along the east side of the Coast Ranges for a QS—Quien Sabe volcanic fi eld; YBR—Yerba Buena Ridge. Thick red line near Point Arena distance of 600 km, these two packages are jux- marks the southern extent of the Vizcaino block.
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