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Post-1968 Research on the Great Valley Group Geological Society of America Special Paper 338 1999 Post-1968 research on the Great Valley Group Raymond V. Ingersoll Department of Earth and Space Sciences, University of California, Los Angeles, California 90095; e-mail: [email protected] INTRODUCTION Subsequent sedimentological research has refined interpretations of processes and products of submarine deposition, paleoecology, Ojakangas (1964, 1968) documented paleocurrent directions and paleogeography (e.g., Garcia, 1981; Cherven, 1983; and associations of sedimentary structures, stratigraphic changes Suchecki, 1984; Ingersoll and Nilsen, 1990; Graham and Lowe, in sandstone composition primarily reflecting changes in prove- 1993; Williams et al., 1998). nance, and overall stratigraphic-structural relations of the Sacra- mento Valley. These three components (sedimentology, petrology, PETROLOGY AND PROVENANCE and structure) formed the basis for Ingersoll’s (1976) dissertation (both Ojakangas and Ingersoll were supervised by W. R. Dickin- Bailey and Irwin (1959) first recognized systematic strati- son at Stanford University). Fundamental breakthroughs in under- graphic changes in sandstone composition in the Sacramento Val- standing occurred between the times of Ojakangas’ and Ingersoll’s ley, and Brown and Rich (1961) utilized these petrologic intervals dissertations, which allowed the latter to integrate these fields in a for mapping. Following Ojakangas’ (1968) refinement of these way not previously possible. petrologic intervals, Rich (1971) and Dickinson and Rich (1972) named five petrofacies along the west side of the Sacramento Val- SEDIMENTOLOGY ley. At the same time, Mansfield (1971, 1979) studied compara- ble petrofacies of part of the San Joaquin Valley. This petrofacies Following Ojakangas’ (1968) suggestion that turbidite sedi- work overlapped publication of the definitive method of petro- mentation produced the upper Mesozoic strata of the Great Val- graphic analysis of graywacke and arkose by Dickinson (1970a). ley, Swe and Dickinson (1970), Mansfield (1971, 1979), and Dickinson et al. (1969) also documented in greater detail diage- Lowe (1972) confirmed this general conclusion with detailed netic changes in Great Valley strata, as previously discussed by analyses of local deep-marine components of the Great Valley Ojakangas (1968). basin. Meanwhile, researchers of both modern and ancient deep- Ingersoll (1978a, 1983) refined the Sacramento and San marine sedimentation were developing models for the four- Joaquin petrofacies and designated petrostratigraphic units, dimensional evolution of submarine fans (e.g., Normark, 1970, which are mappable over the entire Great Valley. Ojakangas 1974; Walker, 1970; Haner, 1971; Nelson and Kulm, 1973; (1968), Dickinson and Rich (1972), Ingersoll (1978a, 1983) and Walker and Mutti, 1973; Mutti, 1974; Nelson and Nilsen, 1974), Mansfield (1979) all related changes in petrofacies to provenance culminating in the seminal model for ancient submarine fans of changes in the Sierra Nevada and Klamath Mountains (Fig. 1). Mutti and Ricci-Lucchi (1972). Additional work by Bertucci (1983), Seiders (1983, 1989), Ingersoll (1978b) utilized the model of Mutti and Ricci-Luc- Suchecki (1984), Seiders and Blome (1988), and Short and Inger- chi (1972) to delineate horizontal and vertical trends in subma- soll (1990) refined provenance interpretations through combined rine-fan facies of the Upper Cretaceous part of the Great Valley study of sandstone and conglomerate petrofacies. Additional Group. This facies analysis was combined with a synthesis of all detailed insight regarding evolution of the Sierra Nevada mag- available paleocurrent and paleoecological data to outline the matic arc was provided by analysis of radiogenic isotopes of depositional history of the Great Valley basin (Ingersoll, 1979). Great Valley petrofacies (Linn et al., 1991, 1992). Ingersoll, R. V., 1999, Post-1968 research on the Great Valley Group, in Moores, E. M., Sloan, D., and Stout, D. L., eds., Classic Cordilleran Concepts: A View from California: Boulder, Colorado, Geological Society of America Special Paper 338. 155 156 R. V. Ingersoll Hamilton (1969) suggested that Pacific oceanic plate “under- flowed” California throughout the Mesozoic and created the Franciscan subduction complex, as well as the Sierra Nevada batholith, by generating melts at depth. Ernst (1970) proposed that the fault contact between the Franciscan Complex and the Coast Range ophiolite was the crustal remnant of the late Meso- zoic subduction zone. At the same time, radiometric dating of plutons in the Sierra Nevada was delineating migrating patterns of magmatism (e.g., Evernden and Kistler, 1970) (Fig. 2). Dick- inson (1970b, 1971, 1973, 1974a, 1974b) discussed how forearc basins such as the Great Valley formed between growing subduc- tion complexes and active magmatic arcs. In fact, the Great Val- ley forearc basin has served as the type forearc basin in subsequent discussions (e.g., Dickinson and Seely, 1979; Inger- soll, 1982; Dickinson, 1995). The most enigmatic aspect of Great Valley geology is the ori- gin of the Great Valley ophiolite, which in places depositionally Figure 1. Schematic paleogeographic block diagram looking northeast, underlies the western Great Valley Group. Bailey et al. (1970) and showing north end of Sacramento forearc basin during Early Cretaceous Moores (1970) proposed that the ophiolite represented oceanic (early Hauterivian). Black trough represents Franciscan trench, where crust accreted to the continental margin prior to initiation of the oceanic lithosphere is being subducted beneath Klamath terranes to Great Valley forearc basin. Schweickert and Cowan (1975) pro- north, and Coast Range ophiolite underlying Great Valley Group (GVG) to south. Sierra Nevada magmatic arc is east of forearc basin. Diagram posed a model involving the collision of the west-facing continen- illustrates relations prior to extensive transgression of Klamaths. Note tal-margin arc with an east-facing intraoceanic arc with backarc mixing of Klamath-derived (Platina petrofacies) and northern Sierra- spreading; collision created the Nevadan orogeny, which immedi- derived (Stony Creek petrofacies) detritus in northwest part of forearc ately preceded and overlapped with initiation of Franciscan sub- basin (from Short and Ingersoll, 1990). duction in the latest Jurassic (Fig. 3). Ingersoll and Schweickert (1986) integrated this model with the contrasting Nevadan tec- tonic history of the Klamath area (e.g., Harper and Wright, 1984) STRATIGRAPHY and showed how a wide oceanic forearc basin could have formed in the Great Valley area at the same time that no such forearc basin Stratigraphic nomenclature of the Great Valley has a complex formed in the Klamath area (Fig. 4). Dickinson et al. (1996) history (discussed in Ingersoll, 1990). The enormous thickness, reviewed ongoing controversy concerning origin of the Great Val- lithologic homogeneity, and lateral stratal lenticularity have ley ophiolite. Godfrey et al. (1997) provided seismic and gravity resulted in proliferation of lithostratigraphic names of local util- data consistent with thrust emplacement of the Great Valley ophi- ity, and alternatively, designation of individual units several kilo- olite over Sierran basement during the Nevadan orogeny, as pre- meters thick, with little structural or stratigraphic utility. Following dicted by Schweickert and Cowan’s (1975), Moores and Day’s the mapping of Brown and Rich (1961), Rich (1971), and Mans- (1984), and Ingersoll and Schweickert’s (1986) models. field (1971, 1979), Ingersoll et al. (1977) and Ingersoll and Dick- Additional insights regarding the Great Valley forearc basin inson (1981) proposed using petrofacies to define regionally were provided by subsidence and thermochronologic analyses. extensive petrostratigraphic formations; these formations consti- Dickinson et al. (1987) suggested that Cretaceous subsidence was tute the Great Valley Group, as formalized in Ingersoll (1990). primarily due to isostatic sediment loading on top of the residual Chronostratigraphic units have been refined since 1968, deep oceanic crust, followed by rapid shallowing during flat-slab based on megafossils, microfossils, geochronology, and subduction. Moxon and Graham (1987) documented Late Creta- magnetostratigraphy (e.g., Douglas, 1969; Imlay and Jones, ceous thermal subsidence along the east side of the basin, corre- 1970; Pessagno, 1976, 1977; Ward et al., 1983; Haggart and sponding to eastward migration of the magmatic arc (i.e., Ward, 1984; Almgren, 1986; Verosub et al., 1989; Bralower, Ingersoll, 1979) (Fig. 3), and latest Cretaceous uplift along the 1990). Moxon (1988, 1990) reinterpreted the Great Valley west side of the basin, corresponding to initiation of Laramide Group in terms of sequence stratigraphy, as summarized by flat-slab subduction. Bostick (1974) and Dumitru (1988) docu- Williams (1993, 1997). mented low geothermal gradients within the Great Valley forearc, as predicted by the forearc model. BASIN ANALYSIS AND TECTONICS By the end of the Cretaceous, most of the Sacramento fore- arc basin had been filled nearly to sea level, to form a broad shelf During the plate tectonics revolution of the late 1960s and early (Dickinson et al., 1979; Ingersoll, 1982). Diverse depositional 1970s, major aspects of California geology were reinterpreted. environments, ranging from nonmarine to coastal and deltaic to Post-1968 research on the Great Valley Group 157 Figure 3. Schematic map
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