Stratigraphic Record of Pliocene-Pleistocene Basin Evolution and Deformation Within the Southern San Andreas Fault Zone, Mecca Hills, California
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Tectonophysics 719–720 (2017) 66–85 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Stratigraphic record of Pliocene-Pleistocene basin evolution and deformation within the Southern San Andreas Fault Zone, Mecca Hills, California James C. McNabb a,⁎, Rebecca J. Dorsey a, Bernard A. Housen b, Cassidy W. Dimitroff b, Graham T. Messé b a Department of Earth Sciences, 1272 University of Oregon, Eugene, OR 97403-1272, USA b Department of Geology, 516 High Street, Western Washington University, Bellingham, WA 98225-9080, USA article info abstract Article history: A thick section of Pliocene-Pleistocene nonmarine sedimentary rocks exposed in the Mecca Hills, California, pro- Received 30 July 2016 vides a record of fault-zone evolution along the Coachella Valley segment of the San Andreas fault (SAF). Geologic Received in revised form 28 February 2017 mapping, measured sections, detailed sedimentology, and paleomagnetic data document a 3–5 Myr history of Accepted 24 March 2017 deformation and sedimentation in this area. SW-side down offset on the Painted Canyon fault (PCF) starting Available online 28 March 2017 ~3.7 Ma resulted in deposition of the Mecca Conglomerate southwest of the fault. The lower member of the Keywords: Palm Spring Formation accumulated across the PCF from ~3.0 to 2.6 Ma during regional subsidence. SW-side San Andreas fault up slip on the PCF and related transpressive deformation from ~2.6 to 2.3 Ma created a time-transgressive angu- Mecca Hills lar unconformity between the lower and upper members of the Palm Spring Formation. The upper member ac- Gulf of California cumulated in discrete fault-bounded depocenters until initiation of modern deformation, uplift, and basin Strike-slip basins inversion starting at ~0.7 Ma. Magnetostratigraphy Some spatially restricted deposits can be attributed to the evolution of fault-zone geometric complexities. How- Tectonostratigraphy ever, the deformation events at ca. 2.6 Ma and 0.7 Ma are recorded regionally along ~80 km of the SAF through Coachella Valley, covering an area much larger than mapped fault-zone irregularities, and thus require regional explanations. We therefore conclude that late Cenozoic deformation and sedimentation along the SAF in Coachel- la Valley has been controlled by a combination of regional tectonic drivers and local deformation due to dextral slip through fault-zone complexities. We further propose a kinematic link between the ~2.6–2.3 Ma angular un- conformity and a previously documented but poorly dated reorganization of plate-boundary faults in the north- ern Gulf of California at ~3.3–2.0 Ma. This analysis highlights the potential for high-precision chronologies in deformed terrestrial deposits to provide improved understanding of local- to regional-scale structural controls on basin formation and deformation along an active transform margin. © 2017 Elsevier B.V. All rights reserved. 1. Introduction and regional (plate boundary-scale) kinematics. Sedimentary rocks de- posited and subsequently uplifted along strike-slip faults record the ba- The formation and deformation of sedimentary basins is widely doc- sinal response to fault-zone processes, offering unique insights into the umented along continental transform faults (Crowell, 1974; 4-D evolution of strain in these settings. Christie-Blick and Biddle, 1985; Sadler et al., 1993; Weldon et al., The Mecca Hills on the northeast side of Coachella Valley, southern 1993; Aksu, 2000; Seeber et al., 2006, 2010), yet the controls on California, superbly expose a N1.3 km-thick section of Pliocene-Pleisto- strike-slip basin evolution remain incompletely understood. Models cene terrestrial sedimentary rocks along the southern San Andreas fault that predict transpression and transtension due to relative plate-motion and associated strike-slip faults. Recent uplift and erosion in the Mecca obliquity along strike-slip faults fail to describe observed patterns of up- Hills allow for detailed sedimentological and stratigraphic analysis, lift and subsidence along the San Andreas fault (SAF) (e.g., Spotila et al., making it an excellent natural laboratory to study the stratigraphic re- 2007a, b), suggesting the influence of additional factors such as struc- cord of deformation along strike-slip faults. Previous workers have doc- tural complexity, rock strength, crustal anisotropy, or changes in local umented the stratigraphy and modern structure of the Mecca Hills (summarized below), but until this study the evolution and chronology of depositional systems in response to fault-zone evolution through ⁎ Corresponding author at: ExxonMobil, Exploration Company, 22777 Springwoods Village Parkway, 77389 Spring, TX, USA. time have not been fully understood. We combine geologic mapping, E-mail address: [email protected] (J.C. McNabb). stratigraphic analysis, magnetostratigraphic data, and determination http://dx.doi.org/10.1016/j.tecto.2017.03.021 0040-1951/© 2017 Elsevier B.V. All rights reserved. J.C. McNabb et al. / Tectonophysics 719–720 (2017) 66–85 67 of sedimentary provenance to reconstruct past landscapes and environ- 2010; Dorsey et al., 2012; Fattaruso et al., 2016), which transferred a sig- ments in response to crustal deformation. This allows us to interpret a nificant but uncertain fraction of relative plate motion from the south- 3–4 Myr history of basin formation and deformation in the Mecca ern SAF to the San Jacinto fault zone (Fig. 1). Hills, and assess the underlying controls on vertical crustal motions The modern Salton Trough and Coachella Valley basin fill consists of along this section of the southern SAF zone. a sediment wedge that onlaps basement rocks of the Santa Rosa Moun- tains in the southwest, and thickens northeastward to 4–5 km against 2. Geologic setting and prior work the SAF (Langenheim et al., 2005; Dorsey and Langenheim, 2015). Strong oblique extension and possible lithospheric rupture beneath 2.1. Southern San Andreas Fault Zone the Salton Trough appears to have deflected the Moho to shallower depths leading to the ongoing creation of young metasedimentary The southern SAF zone (Fig. 1) has been the locus of relative plate rocks (Fuis et al., 1984; Elders and Sass, 1988; Parsons and McCarthy, motion between the Pacific and North American plates since its incep- 1996; Dorsey, 2010; Lekic et al., 2011). In contrast, transpression and tion in the Coachella Valley between ca. 6 and 12 Ma (e.g., Atwater, crustal shortening northwest of the Coachella Valley at the San 1970; Stock and Hodges, 1989; Ingersoll and Rumelhart, 1999; Oskin Gorgonio Pass restraining step-over has thrust Mesozoic and Cenozoic and Stock, 2003a, b; Dorsey et al., 2011). The Coachella Valley segment basement rocks over young basin sediments (Matti and Morton, 1993; of the SAF consists of a main strand that bounds the northeast Coachella Dibblee, 1997; Yule and Sieh, 2003; Langenheim et al., 2005). Recent Valley and Salton Trough, and terminates in the southeast Salton Sea at studies document northeast tilting of the crustal-scale block between the Brawley seismic-zone releasing step-over (Fig. 1). Northwest of the the SAF and San Jacinto fault over the past ~1.2 Ma, which likely is study area, the southern SAF zone splits into the Banning and Mission caused by crustal loading from highly oblique transpression along the Creek faults near a major restraining step-over in San Gorgonio Pass SAF in Coachella Valley (Fattaruso et al., 2014; Dorsey and (Fig. 1). Langenheim, 2015). Late Cenozoic oblique transform tectonics has produced large-scale Discrete elongate zones of fault-bounded uplift along the southern transtensional and transpressional features within the southern SAF SAF in the Indio Hills, Mecca Hills, and Durmid Hill define the northeast system since late Miocene time. Regional transtension was partitioned boundary of Coachella Valley and Salton Trough (Fig. 1). Between areas into extension on the low-angle west Salton detachment fault and of uplift, the geomorphic expression of the SAF varies from expression- strike-slip offset on the SAF from latest Miocene to early Pleistocene less in lowland areas to vegetation lineaments, dextrally offset geomor- time (e.g., Axen and Fletcher, 1998; Dorsey et al., 2011). At ~1.3 to phic features, fault sags, and scarps (e.g. Sylvester and Smith, 1976; 1.1 Ma a major tectonic reorganization resulted in initiation of the San Keller et al., 1982; Sieh and Williams, 1990; Dibblee, 1997; Behr et al., Jacinto fault zone and termination of the West Salton detachment 2010; Gray et al., 2014). Recent studies of InSAR and GPS data fault (e.g. Morton and Matti, 1993; Lutz et al., 2006; Janecke et al., (Lindsey and Fialko, 2013), seismic hypocenter relocation (Lin et al., Fig. 1. Geologic map of the Coachella Valley. Modified from Dorsey and Langenheim (2015). Abbreviations: BF, Banning fault; BSZ, Brawley seismic zone; DH, Durmid Hill; EFZ, Extra fault zone; IH, Indio Hills; MCF, Mission Creek fault; MH, Mecca Hills; PMF, Pinto Mtn. fault; SAF, San Andreas fault; SGP, San Gorgonio Pass; SJF, San Jacinto fault; SJP, San Jacinto Peak; WSDF, West Salton detachment fault. 68 J.C. McNabb et al. / Tectonophysics 719–720 (2017) 66–85 2007; Fuis et al., 2012), and kinematic finite-element fault modeling Wilcox et al., 1973; Sylvester and Smith, 1976; Sheridan and Weldon, (Fattaruso et al., 2014, Fattaruso et al., 2016)suggesta60°–70° north- 1994; Miller, 1998). east dip for the Coachella Valley segment of the SAF, previously assumed Sedimentary strata N1300 m thick in the Mecca Hills includes the to be sub-vertical. Fattaruso et al. (2014) concluded that modeling a NE- Mecca Conglomerate, Palm Spring Formation, and Ocotillo Conglomer- dipping SAF through Coachella Valley better aligns seismic hypocenters ate (Figs. 2, 3), which were first described and named by Dibblee with the fault at depth, and generates patterns of deformation that (1954). The main exposures of Mecca Conglomerate in the central closely match modern subsidence and uplift.