The Upper Cretaceous part of the Great Valley Sequence provides a unique oppor- ... facies associations, and tectonic setting of the Late Cretaceous fore-arc ...
Sedimentary Geology, 21 (1978) 205--230
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© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
S U B M A R I N E F A N FACIES O F T H E U P P E R C R E T A C E O U S G R E A T VALLEY SEQUENCE, NORTHERN AND CENTRAL CALIFORNIA
RAYMOND V. INGERSOLL
Department of Geology, University of New Mexico, Albuquerque, N.M. 87131 (U.S.A.) (Received August 8, 1977; revised and accepted December 21, 1977) ABSTRACT Ingersoll, R.V., 1978. Submarine fan facies of the Upper Cretaceous Great Valley Sequence, northern and central California. Sediment. Geol., 21: 205--230. The Upper Cretaceous part of the Great Valley Sequence provides a unique opportunity to study deep-marine sedimentation within an arc--trench gap. Facies analysis delineates submarine fan facies similar to those described from other ancient basins. Fan models and facies of Mutti and Ricci-Lucchi allow reconstruction of the following depositional environments: basin plain, outer fan, midfan, inner fan, and slope. Basin plain deposits are characterized by hemipelagic mudstone with randomly interbedded thin sandstone beds exhibiting distal turbidite characteristics. Outer fan deposits are characterized by regularly interbedded sandstone and mudstone, and commonly exhibit thickening-upward (negative) cycles that constitute depositional lobes. The sandstone occurs as proximal to distal turbidites without channeling. Midfan deposits are characterized by the predominance of coarse-grained, thick, channelized sandstone beds that commonly are amalgamated. Thinning-upward (positive) cycles and braided channelization also are common. Inner fan deposits are characterized by major channel-fill complexes (conglomerate, pebbly sandstone, and pebbly mudstone) enclosed in mudstone and siltstone. Positive cycles occur within these channel-fill complexes. Much of the finegrained material consists oLlevee (overbank) deposits that are characterized by rhythmically interbedded thin mudstone and irregular sandstone beds with climbing and starved ripples. Slope deposits are characterized by mudstone with little interbedded sandstone; slumping and contortion of bedding is common. Progressions of fan facies associations can be described as retrogradational and progradational suites that correspond, respectively, to onlapping and offlapping relations in the basin. The paleoenvironments, fan facies associations, and tectonic setting of the Late Cretaceous fore-arc basin are similar to those of modern arc--trench systems.
INTRODUCTION
The Upper Cretaceous part of the Great Valley Sequence is exposed nearly continuously from near Redding in the north to near Coalinga in the south (Fig. 1) and provides a unique opportunity to study deep-marine sedimentation within an arc--trench gap (Dickinson, 1971, 1974; Ingersoll, 1975, 1976b; Ingersoll et al., 1977). Upper Cretaceous thicknesses exceed 8 km locally in the San Joaquin Valley, where Lower Cretaceous and Upper
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the late Mesozoic arc-trench system and geographic locations. The Great Valley Sequence is primarily Upper Cretaceous in the San Joaquin Valley, and is Upper Jurassic through Upper Cretaceous in the Sacramento Valley. Small outcrops of uppermost Cretaceous strata occur along the east side of the Sacramento Valley, but are too small to show at the scale of this map.
Jurassic strata generally are absent due to a combination of non-deposition, erosion and tectonic displacement. One of the thickest (exceeding 15 km) and most complete Upper Mesozoic sections in North America is exposed along the west side of the Sacramento Valley (Lachenbruch, 1962). This thick sequence of interbedded mudstone, sandstone and conglomerate accumulated in a deep fore-arc basin bounded on the west by an active trench with an associated growing subduction complex (the Franciscan complex) and on the east by an active magmatic arc, the roots of which are exposed today as the Sierra Nevada batholithic complex. The volcanic, plutonic and metamorphic terranes within the arc provided the majority of the detritus deposited within the fore-arc basin (Dickinson, 1971). Recent advances in knowledge of both modern and ancient deep-marine clastic sedimentation allow for the delineation of submarine fan paleoen-
207
vironments through the application of submarine fan facies models (Mutti and Ricci-Lucchi, 1972; Ingersoll, 1976a). Petrologic studies of the Great Valley Sequence have delineated vertical as well as horizontal trends in sandstone composition that facilitate stratigraphic correlations and reveal provenance characteristics during the Late Cretaceous (Ingersoll, 1978). Integration of sedimentary, petrologic, and paleoecologic data into a coherent picture of basin evolution is facilitated by knowledge of modern arc--trench systems in the context of plate-tectonic theory (Hamilton, 1969, 1974; Ernst, 1970; Dickinson, 1973a, b, 1974, 1976; Scholl and Marlow, 1974; Karig and Sharman, 1975). This paper deals with the analysis of submarinefan facies and the recognition of fan subenvironments, as expressed by facies associations, within the Great Valley Sequence. In another paper (Ingersoll, 1979) I will discuss the spatial and temporal distribution of submarine fan environments, and the relationships between submarine fan deposition and the tectonic evolution of the Late Cretaceous fore-arc basin. (See Ingersoll et al., 1977 for a summary of basin evolution and stratigraphy of the Great Valley Sequence.) DEEP-MARINE SEDIMENTATION AND FAN FACIES MODELS
Previous models
Previous workers have attempted to classify submarine fan facies and fan morphologies by two separate and at times conflicting approaches. Landbased geologists have developed schemes utilizing vertical sequences of lithified strata (Bouma, 1962; Walker, 1967, 1970; Mutti and Ricci-Lucchi, 1972, 1975; Walker and Mutti, 1973; Ricci-Lucchi, 1975a) while marine geologists studying modern deep-marine environments have based their classifications on surface morphologies and horizontal variations in surface sediments (Normark, 1970, 1974; Haner, 1971; Nelson and Kulm, 1973; Nelson and Nilsen, 1974). One result of this dual approach has been a confusion of nomenclature used in describing fan features. Fig. 2 compares terminologies and conceptual models of various workers. Combination of terminologies and conceptual models from ancient and modern examples has the advantage of unifying the two approaches. On the other hand, application of terminology and models derived from either modern or ancient examples may facilitate additional studies of other modern or ancient fan systems, respectively, because the terminology and models are best suited for one or the other situation (Mutti, 1974). For instance, a marine geologist can detect more easily changes in fan-surface morphologies using reflection profiling than he can detect changes in sand-to-mud ratios obtained from widely spaced, shallow-penetration cores. In contrast, a field geologist can measure more easily sandstone-to-shale ratios from outcrops than he can study subtle changes in bed surface geometries over great distances. Consequently, in this study a model based on ancient submarine fans (Mutti and Ricci-Lucchi,
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Fig. 2. C o m p a r i s o n o f p u b l i s h e d fan classifications based on m o r p h o l o g i e s and facies. Normark's and Haner's classifications are based on m o d e r n fans, whereas the other classifications are based on primarily ancient facies analyses, but with s o m e input from m o d e r n e n v i r o n m e n t s . Ricci-Lucchi's classification m o s t c l o s e l y resembles that a d o p t e d for the present s t u d y .
1972, 1975; Ricci-Lucchi, 1975a) is used as it is the best suited to reconstruction of the depositional environments of the Late Cretaceous basin. Regardless of which fan model is used there are significant variations among individual fans which must be incorporated into the model. Important variables in fan settings include: type of sediment supply (coarse-grained versus fine-grained, for instance), nature of basin (confined versus unconfined), basin size, and tectonic setting. Voluminous input of coarse-grained material may result in steeper, more conical fans, whereas a predominance of fine-grained material may result in a poorly defined fan geometry. Wellsorted sediment supply may result in relatively greater overbank and levee deposition whereas poorly sorted, coarse-grained supply may cause the formation of a suprafan with backfilling of the main channel, thereby resulting in a less stable configuration (Normark, 1970). Deposition at the front of
209
a deltaic complex with predominantly coarse-grained supply may result in a rapidly prograding, steep sandy slope that has few typical fan features, but which shows indisputable evidence of deposition by sediment gravity flow processes {e.g., Link, 1975). Mufti and Ricci-Lucchi's fan facies model from the Apennines is applicable to the Upper Cretaceous of California because of similarities in tectonic setting (arc--trench-related basins) and sediment supply ("immature" clastic sediments with variable compositions and grain sizes). Both basins formed within active tectonic settings and the fans formed in generally unconfined situations (progradation onto basin plains rather than confinement in a small basin). Both basins were elongate and relatively narrow during most of the deep-marine clastic sedimentation. Details of the tectonic settings of the Apennine basins remain obscure (Sagri and Zanzucchi, 1975), but recent basin analyses have illuminated temporal changes in basin geometries (Ricci-
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Fig. 3. Submarine fan model used in the present study (primarily after Ricci-Lucchi, 1975a). See text for discussion of modifications necessary when sediment supply is primarily coarse grained (development of suprafan) or fine grained (development of dune bypass). C M = Channelized Midfan, F = Fan Fringe, F C = Fan Channel, I C = Interchannel Area, I F = Inner Fan, L = Depositional Lobe, L S = Lower Slope, M F = Midfan, O F = Outer Fan, O V B = Overbank Area, P S = Passive or Prograding Slope, S A = Slump Accumulation, S C = Slope Channel, S S = Slump Scar, U S = Upper Slope. (+) indicates parts of the fan characterized by positive cycles, and (--) indicates parts of the fan characterized by negative cycles.
210
Lucchi, 1975b). In addition, dimensions of the fan systems in both settings are of the same order of magnitude (tens to a few hundreds of kilometers in width and length). The salient features of the fan model I have used are summarized below and in Fig. 3. The model consists of the following primary environments: basin plain, outer fan, midfan, inner fan, slope, and shelf. Locally, incised channels (sometimes more properly termed canyons) are found on slopes and cutting shelf edge and fan surfaces. Aggrading meandering channels are found on the inner fan and midfan, whereas aggrading braided channels are confined to the midfan. Overbank deposits form near major channels as levee deposits or between braided channels as interchannel deposits. Depositional lobes are the primary depositional areas on the outer fan. Slump scars and areas of slump accumulations are c o m m o n on the slope as well as within channels and on fan fringes near slopes. Upper and lower slopes may be differentiated on the basis of slump features and by proximity to basin plain, fan fringe, channel, and shelf environments. Under conditions of rapid coarse-grained sedimentation, a suprafan may form which combines characteristics of both the midfan and the outer fan (Mutti, 1974). In this situation differentiation of midfan and outer fan may be impossible except at the proximal and distal ends of the suprafan where the braided and channelized midfan is clearly distinguishable from the nonchannelized outer fan. However, in the Great Valley Sequence thick-bedded, channelized, massive sandstone of the midfan usually is distinguishable from non-channelized, interbedded sandstone and mudstone of the outer fan. Another variant of midfan deposits may occur where sediment supply is predominantly fine-grained and little sand deposition occurs on the midfan. Under these conditions a "dune-bypass" area may form (E. Mutti, personal communication, 1974). "Dune-bypass" areas are characterized by the predominance of mud with lenticular sand bodies showing traction features similar to shallow marine cross-bedding. These dune features are analogous to channel-mouth bars of delta complexes, and c o m m o n l y contain climbing and starved ripples. The variations in midfan characteristics mentioned above can be incorporated into the model presented in Fig. 3 b y replacing the channelized midfan and depositional lobes by a suprafan or by a "dunebypass" area and lobes, depending on local details.
Characteristics of submarine fan facies Mutti and Ricci-Lucchi (1972, 1975), Walker and Mutti (1973) and RicciLucchi (1975a) classified submarine fan facies into seven categories (Facies A through G). These often are called turbidite facies, although n o t all submarine fan sedimentation is by the process of turbidity flow. Middleton and H a m p t o n (1973) discussed mechanisms by which gravity flow deposits occur. Mutti and Ricci-Lucchi's fan and facies classification is applicable to the Great Valley Sequence with little modification. Because these facies
211 TABLE I Simplified facies classification used in the present study (After Mutti and Ricci-Lucchi, 1972, 1975; Walker and Mutti, 1973; Ricci-Lucchi, 1975a) Bouma sequence not applicable
Facies A: Coarse-grained conglomerate and pebbly sandstone Facies B : Medium- to coarse-grained massive sandstone
Bouma sequence not applicable
Facies C: Interbedded sandstone and mudstone, proximal turbidites Facies D: Interbedded mudstone and sandstone, distal turbidites Facies E: Interbedded sandstone and mudstone, overbank and interchannel deposits
Bouma sequence not applicable
Facies F : Chaotic deposits, olistostromes Facies G: Mudstone, pelagic and hemipelagic deposits
have been described thoroughly by the above-mentioned workers, I will illustrate each facies as it occurs in the Upper Cretaceous part of the Great Valley Sequence with only brief descriptions of the most important characteristics. Table I summarizes the lithologic characteristics of each facies. Facies A consists of coarse-grained conglomerate (clast-supported) and pebbly sandstone (matrix-supported) (Fig. 4a and b). Walker and Mutti
Fig. 4. (a) Facies A: pebbly sandstone and imbricated conglomerate (current flowed toward the right), hammer parallels bedding; Santonian, Formation B (Schilling, 1962) (San Luis Reservoir area). (b) Facies A: conglomerate; same location as (a). (c) Facies B: massive sandstone showing amalgamation due to pinch-out of mudstone interbeds, "H" of graffiti approximately 30 cm high; Turonian, Venado Member, Cortina Formation (Ingersoll et al., 1977) (Stone Corral Creek). (d) Facies B: massive amalgamated sandstone, thickest bed approximately 2 m thick; Cenomanian, Juniper Ridge Member, Waltham Formation (Mansfield, 1971, 1972) (Coalinga area).
212 (1973) and Mutti and Ricci-Lucchi (1975) subdivided this facies on the basis of whether beds are "organized" or "disorganized", and Ricci-Lucchi (1975a) only included "organized" beds in his Facies A. Moreover, Mutti and RicciLucchi (1975) included pebbly mudstone (which they had previously included in their Facies F) in their "disorganized" Subfacies A. Although the presence of "organization" provides a valid descriptive classification and may have paleoenvironmental significance (Walker, 1975a), it does n o t seem particularly useful in classifying facies or fan facies associations of the Great Valley Sequence. This lack of applicability of Walker's scheme is due in part to difficulty in finding three-dimensional exposures of channels that would allow changes in "organization" to be observed. I have used "organization" as a descriptive term w i t h o u t paleoenvironmental significance, although further studies in the Great Valley Sequence may prove its worth. Facies A c o m m o n l y occurs as lenticular bodies within channel-fill complexes. As a result, bases are usually erosional and amalgamation of separate depositional units is common. Sandstone-to-shale ratios are extremely high as bedding is thick and massive. Outsized clasts are c o m m o n in both conglomerate and pebbly sandstone. The Bouma sequence generally is not applicable to the description of bedding features. Deposition of Facies A occurred by the processes of debris flow or grain flow, although fluidization and turbulence may have played a role in deposition of the finer-grained portions (Middlet o n and H a m p t o n , 1973). Facies B consists of coarse- to medium-grained massive sandstone ("fluxoturbidites" and "grain-flow deposits") with local thin interbeds of mudstone (Fig. 4c and d). Walker and Mutti (1973) and Mutti and Ricci-Lucchi (1975) subdivided this facies on the basis of bed thickness, lenticularity, and the presence of "dish" structures and thick diffuse laminae. I follow the simpler usage of Mutti and Ricci-Lucchi (1972) and Ricci-Lucchi {1975a), because the subfacies do n o t seem to be useful in differentiating fan facies associations within the Great Valley Sequence. Bedding in Facies B c o m m o n l y is lenticular and shows evidence of channelization. Bases are generally erosional and amalgamation is c o m m o n , b u t sole markings are seldom observed due to lack of thick interbedded mudstone. Sandstone-to-shale ratios are high, and beds are generally thick and massive. Sorting is better than in Facies A, b u t n o t as good as in Facies C. Graded bedding and inverse grading may occur in conjunction with laminations, ripples, convolutions and fluid-escape structures, c o m m o n l y in no predictable sequence. Ripped-up and redeposited m u d chips, and cut-and-fill structures are common. The Bouma sequence generally is n o t applicable, although progressions of laminations, ripples, and convolutions may resemble Bouma sequences. Facies B beds were deposited primarily through the processes of fluidization, grain flow, and high-density turbidity flow (Middleton and Hampton, 1973). Upward movement of escaping fluid and traction flow may have characterized the waning period of deposition. Facies B usually occurs in channel-fill complexes. Facies C consists of interbedded mudstone and coarse- to fine-grained
213
Fig. 5. Facies C: interbedded sandstone and mudstone, amalgamation of sandstone, tops to the right; part of measured section 74-13, and part of progradational sequence at Cache Creek (Fig. 17b); Coniacian, Sites Member, Cortina Formation (Ingersoll et al., 1977) (Cache Creek).
sandstone ("classical proximal turbidites") (Figs. 5 and 6a). Mutti and RicciLucchi (1975) subdivided this facies on the basis of characteristics of the Bouma sequence, b u t this approach is n o t followed in the present study. Facies C beds show little or no channelization as tops and b o t t o m s of beds are even and parallel. Each event of sand deposition usually was followed by mud accumulation that was not easily removed by subsequent flows. As a result, amalgamation is not c o m m o n , and sole marks are usually well preserved. Sandstone-to-shale ratios are m o d e r a t e ( g r e a t e r than one). The complete Bouma sequence is c o m m o n l y present. Facies C sandstone beds
Fig. 6. (a) Facies C: interbedded sandstone and mudstone, thickest bed approximately 2.5 m thick; same location as Fig. 5. (b) Facies D: interbedded sandstone and mudstone, hat for scale; part of measured section 74-30; Cenomanian, Boxer Formation (Ingersoll et al., 1977) {Salt Creek).
214
were deposited primarily by "classical" turbulent flow, generally in nonchannelized settings. Facies D consists of thinly interbedded mudstone and fine-grained sandstone ("classical distal turbidites") (Fig. 6b). Mutti and Ricci-Lucchi (1975) and Ricci-Lucchi (1975a) subdivided this facies into three subfacies on the basis of bedding thickness, sandstone-to-shale ratios, bedding characteristics, and sedimentary structures, b u t these subdivisions are n o t adopted in the present study. Bedding surfaces in Facies D are parallel for great distances and individual sandstone layers are laterally extensive and generally thin. Individual sandstone beds are easily differentiated; typically, these beds are graded, with the upper part of the Bouma sequence present (base cut-out). Sole marks are c o m m o n on the thicker sandstone beds. Sandstone-to-shale ratios are generally less than one, b u t are variable. Facies D sandstone beds probably were deposited by low-density " m a t u r e " turbulent flows far from channel sources. Facies E consists of thinly interbedded sandstone and mudstone that superficially resembles Facies D (Fig. 7). Facies E is differentiated from Facies D by the following characteristics (Mutti and Ricci-Lucchi, 1972, 1975; Nelson et al., 1974, 1975; Mutti, 1977): (1) higher sandstone-to-shale ratios (greater than or near one), (2) thinner, b u t more numerous sandstone
Fig. 7. (a) Facies E: thinly interbedded sandstone and mudstone, hammer for scale, part of retrogradational sequence at Monticello Dam (Figs. 16 and 17a); Turonian, Venado Member, Cortina Formation (Ingersoll et al., 1977) (Putah Creek). (b) Facies E: pinching and swelling sandstone with climbing and starved ripples with interbedded siltstone and mudstone; close-up near hammer of (a). (c) Facies E: laminated and rippled sandstone with gradational base and sharp top; part of measured section 74-8; Cenomanian, Boxer Formation (Ingersoll et al., 1977) (Putah Creek area). (d) Facies E: similar to (c); Cenomanian, Boxer F o r m a t i o n (Ingersoll et al., 1977) (South Fork Cottonwood Creek area).
215
beds, and (3) more discontinuous bedding with wedging and lensing. Surfaces of sandstone beds are wavy, b u t in sharp contact with mudstone on both tops and bottoms. Climbing ripples are characteristic of sandstone beds and c o m m o n l y result in extremely wavy upper bed surfaces due to "starving" of the ripples. The Bouma sequence generally is applicable. Facies E beds are inferred to be local lag deposits in or near channels (overbank and interchannel deposits) that were deposited b y high-concentration gravity flows that bypassed the lag deposits. Facies F consists of chaotic deposits exhibiting evidence of mass slumping and resedimentation (Figs. 8a and b). There is disagreement whether certain conglomerate and pebbly mudstone should be included in Facies F or Facies A. I follow Walker's and Mutti's suggestion and restrict Facies F to those chaotic deposits that " s h o w clear evidence of having been previously deposited elsewhere in the basin, and also, evidence of having been remobilized and moved en masse to their present location" (Walker and Mutti, 1973, p. 133). Bedding, if present, is lensoid. Beds may reach enormous thicknesses, b u t are n o t laterally extensive. Blocks within this facies c o m m o n l y are highly variable in composition, size, and origin (formed both within and without
Fig. 8. (a) Facies F: pebbly mudstone within channelized sequence, large block directly above figure consists of Facies E (channel levee deposit that collapsed into the channel}, chaotic mixture of diverse clasts; part of measured section 75-1, and part of retrogradational sequence at Monticello Dam (Figs. 16 and 17a); Turonian, Venado Member, Cortina Formation (Ingersoll et al., 1977) (Putah Creek). (b) Facies F: contorted slumps of interbedded sandstone and mudstone, fold axes parallel presumed paleoslope contours, hat for scale; Cenomanian, Upper Oak Flat Member, Oak Flat Formation (Mansfield, 1971, 1972} (Coalinga area}. (c) Facies G: mudstone with interbedded thin sandstone (less than 10 cm thick); Turonian, Gas Point Member, Budden Canyon Formation (Murphy et al., 1969) (Dry Creek). (d) Facies G: mudstone with interbedded thin sandstone, possible slump features above figure; Cenomanian, Boxer Formation (Ingersoll et al., 1977) (Putah Creek area).
216 the basin). The matrix (usually mudstone) c o m m o n l y is featureless, b u t may show flow and deformation features. Facies F formed b y gravity slumping and sliding which may have taken the form of debris flows in channelized situations or of semicoherent slump accumulations in or near lovcer-slope environments. Facies G consists of pelagic and hemipelagic mudstone with a few interbedded thin siltstone beds (Fig. 8c and d). Bedding is parallel and very thin, if present at all. Facies G mudstone tends to blanket all surfaces uniformly, b u t may be concentrated and thickened in channels and depressions. The Bouma sequence is n o t applicable. Under proper environmental conditions these mudstone beds are extensively bioturbated. Very thin siltstone turbidites within the predominant mudstone may be describable by the Bouma sequence. Deposition of Facies G was from dilute suspensions (fine-grained turbidity and nepheloid flows) and by the continuous rain of hemipelagic sediment. Facies G mudstone is most prominent in slope and basin plain settings. Under the proper conditions it may be possible to differentiate turbiditic from non-turbiditic mudstone in any of the above facies (Hesse, 1975). However, the probable conditions of deposition for the Great Valley Sequence ("terrigenous turbidite basins below the CCD") are the least desirable conditions under which to make this distinction (Hesse, 1975). Therefore, this approach was not attempted.
Facies analysis: examples from the Great Valley Sequence Purpose and methods. Detailed measurements were made of fifteen vertical sequences from the Cenomanian through Coniacian parts of the Great Valley Sequence exposed on the west side of the Sacramento Valley. This area was chosen for initial analysis because of its good exposures and intensity of previous investigation (i.e., Ojakangas, 1964, 1968). Sections were chosen for measurement that are well exposed and which represent a variety of facies and facies association types. Nonetheless, outer fan and basin plain assemblages were measured more c o m m o n l y due to their abundances in the initial study area. At each locality tape measurements were made, sedimentary structures and grain sizes noted, and beds classified according to the Bouma sequence or other descriptive categorizations. This detailed study of a variety of facies and facies associations served two purposes: (1) it resulted in graphic summaries of important facies characteristics, and (2) it tested which facies classifications and methods of analysis are most applicable to the Great Valley Sequence. After measurement was completed each section was classified as to facies (following the scheme outlined above), and sandstoneto-shale ratios and Walker's ABC Index (P~) (Walker, 1967) were calculated. Table II contains this and other information. Ingersoll (1976b) and Ingersoll et al. (1977) discuss stratigraphy and petrofacies as well as presenting the detailed measured sections and their locations. Some of the measured sections are thin enough or uniform enough that no
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