Provenance of the upper Miocene Modelo Formation and subsidence analysis of the Los Angeles basin, southern California: Implications for paleotectonic and paleogeographic reconstructions
Peter E. Rumelhart Department of Earth and Space Sciences, University of California, Raymond V. Ingersoll* } Los Angeles, California 90095-1567
ABSTRACT tion was transferred to the San Andreas fault; transpression has dom- inated the Los Angeles basin since 6 Ma, including rapid uplift, flexural The Los Angeles basin has undergone three stages of development subsidence due to tectonic loading, and rapid sedimentary filling. The related to complex plate interactions within the evolving San Andreas rapid subsidence and filling and the sudden switch between transten- transform system: transrotation (16Ð12 Ma), transtension (12Ð6 Ma), sion and transpression in the Los Angeles basin are typical of strike-slip and transpression (6Ð0 Ma). Timing of these stages correlates with basins in general. However, initiation of the Los Angeles basin by tran- microplate-capture events along the continental margin, and is ex- srotation reflects the uncommon process of microplate capture along pressed in changes in subsidence rates and provenance within the Los the rapidly evolving California margin. Angeles basin. The Modelo Formation and related units were deposited in the INTRODUCTION northern part of the Los Angeles basin at bathyal depths during late Miocene time. The northern Los Angeles basin was segmented into The compositional evolution of siliciclastic sediment of strike-slip basins three subbasins, in each of which coarse sediment was deposited as sub- is not well understood. Other than studies by Link (1982) of the Ridge basin marine fans (Puente, Tarzana, and Simi). A fourth fan system (Piru) in southern California, by Ridgeway and DeCelles (1993) of the Burwash formed in the Ventura basin, just north of the Los Angeles basin. The basin in the Yukon, and by Critelli et al. (1995) of the Puente Formation of Puente, Tarzana, and Piru fans were derived from the San Gabriel the Los Angeles basin in southern California, there is a dearth of detailed block, which consists primarily of crystalline basement and lesser vol- petrologic studies of strike-slip basins. canic and sedimentary components. Sandstone within the Puente fan The Los Angeles basin is recognized as an excellent example of sedi- reflects unroofing of the central and eastern San Gabriel block. The mentation in a strike-slip setting (Biddle, 1991). It has been proposed that Tarzana fan was derived primarily from the central San Gabriel block, the basin formed as the result of clockwise crustal rotations during middle and the Piru fan was derived primarily from the western San Gabriel and late Miocene time (Luyendyk and Hornafius, 1987). As such, it is one block, which is distinctly characterized by Ca-rich plagioclase derived of the only known examples of a transrotational basin (Ingersoll, 1988). from Proterozoic anorthosite and related bodies. The lack of Ca-rich Furthermore, because of its prolific hydrocarbon production, the Los Ange- plagioclase in the other fans eliminates the western San Gabriel block les basin has been the subject of intense industry interest over the past cen- as a possible source area, and confirms differentiation of the Ventura tury (Biddle, 1991). Despite its eminence, many of the important lithologic basin from the Los Angeles basin by late Miocene time. The Simi fan units have not been petrographically investigated, nor have petrographic was derived from locally uplifted Cretaceous and Paleogene strata; data been incorporated into stratigraphic and tectonic interpretations of the sandstone composition reflects the recycling of these sediments. basin. In this paper we summarize an investigation of sandstone within the Subsidence and provenance analyses are consistent with the follow- upper Miocene Modelo Formation of the Santa Monica Mountains. Using ing paleogeographic and paleotectonic reconstruction. Beginning at ap- petrologic data, as well as microprobe compositional data from detrital pla- proximately 16 Ma, transrotation of the Western Transverse Ranges in- gioclase grains, we suggest a possible provenance within the San Gabriel duced extension and thermal subsidence of the Los Angeles basin area. Mountains. Similarly, very few subsidence studies of the Los Angeles basin A second pulse of extension and thermal subsidence occurred when have been published (e.g., Mayer, 1987, 1991; Sawyer et al., 1987). On the motion began along the San Gabriel fault at 12 Ma. Right slip of basis of our provenance and subsidence data, we propose a paleotectonic 60Ð70 km occurred along the San Gabriel fault, which produced and paleogeographic reconstruction for the northern Los Angeles and east- transtension in the Los Angeles basin area and deposition of the ern Ventura basin regions during middle to late Miocene time. Puente, Tarzana, Simi, and Piru fan systems. At 6 Ma, transform mo- The Los Angeles basin is one of many Neogene basins along the western margin of California (e.g., Blake et al., 1978; Crowell, 1974, 1987; Dickin- *Corresponding author. E-mail: [email protected] son et al., 1987; Luyendyk and Hornafius, 1987; Mayer, 1987, 1991; Yeats,
Data Repository item 9733 contains additional material related to this article.
GSA Bulletin; July 1997; v. 109; no. 7; p. 885Ð899; 8 figures; 3 tables.
885
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
Figure 1. Generalized geologic map of Los Angeles basin and San Gabriel Mountains and locations of Modelo Formation outcrops. C—Cal- abasas area; EVB—eastern Ventura basin; MCF—Malibu Coast fault; SMS—Santa Monica Slate; TA—Topanga anticline; L—location of Laubacher #1 well (actual location is the western edge of the Santa Monica Mountains (SMM), approximately 15 km west of figure margin); R— location of Rancho #1 well; S—location of Simi #33 well. Inset: LA—Los Angeles basin; SB—Santa Barbara basin.
1987; Biddle, 1991; Wright, 1991). It is located at the northern end of the PreÐLos Angeles basin strata consist mostly of material associated with Peninsular Ranges, and is bounded on the north by the San Gabriel fault, on the Mesozoic-Paleogene convergent margin. The basement includes Juras- the east by the San Andreas fault, and on the west by the southern Califor- sic to Cretaceous metasedimentary rocks of the subduction complex (e.g., nia continental borderland (Fig. 1). The Los Angeles basin is a small (30 km Catalina schist, Pelona schist), as well as granodiorite and tonalite associ- wide) rhombohedral basin southwest of the San Andreas fault zone, which ated with the Mesozoic magmatic arc (Fig. 2; Yerkes et al., 1965). Locally, forms the present boundary between the Pacific and North American plates Precambrian metamorphic rocks (gneiss of the San Gabriel Mountains) are (Atwater, 1970, 1989; Bohannon and Parsons, 1995). The Los Angeles also part of the basement (Ehlig, 1981). Pre-basin rocks also include sedi- basin formed in a former forearc area, which encompassed the length of the mentary and volcanic rocks of the forearc basin (e.g., Tuna Canyon, Coal west coast of North America during the Mesozoic and Paleogene (Dickin- Canyon, Trabuco, Ladd, Williams, Silverado, Santiago, Santiago Peak, son, 1976, 1981; Crouch and Suppe, 1993). Transform tectonism initiated Sespe and Vaqueros formations; Fig. 2). approximately 25 Ma, when the Pacific-Farallon ridge reached the conti- The oldest sedimentary unit in the Los Angeles basin proper is the lowerÐ nental margin (Atwater, 1970, 1989; Dickinson, 1981; Bohannon and Par- middle Miocene Topanga Group. The Topanga Group consists of conglom- sons, 1995). The basin began subsiding approximately 18Ð16 Ma (Horna- erate, sandstone, and mudstone deposited at middle-bathyal to nonmarine fius et al., 1986; Mayer, 1991; Rumelhart, 1994a), probably in association depths (Yerkes et al., 1965; Lane, 1987; Blake, 1991). Interfingering with with the onset of clockwise rotation of the western Transverse Ranges and included within the Topanga Group are several volcanic units (e.g., (Luyendyk and Hornafius, 1987; Crouch and Suppe, 1993), and continued Conejo and El Modeno volcanic rocks) that reflect crustal extension (Yerkes until about 3 Ma, when north-south shortening resulted in regional uplift et al., 1965). The middle-bathyal to nonmarine San Onofre Breccia both in- (Atwater, 1970; Mayer, 1991; Rumelhart, 1994a). terfingers with and lies unconformably on the Topanga Group (Vedder and
886 Geological Society of America Bulletin, July 1997
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 SUBSIDENCE ANALYSIS OF THE LOS ANGELES BASIN
Figure 2. Generalized strati- graphic chart for Los Angeles basin (modified from Blake, 1991). Note nonlinear vertical scale.
Howell, 1976; Stuart, 1979; Blake, 1991). The San Onofre Breccia contains Formation and below the Pico Formation in the northeastern Ventura basin. clasts, derived from the west, of Catalina Schist, indicating that the metamor- Kew (1924) redefined the Modelo Formation to include parts of the Vaque- phic basement was exposed and shedding sediment into the Los Angeles ros, resulting in the unit being about 2745 m thick in the type area. In 1931, basin by early middle Miocene time. The middle to upper Miocene Mon- Hoots defined middle to upper Miocene strata, which unconformably over- terey Formation lies unconformably on the Topanga Group and locally the lie the Topanga Group (i.e., Calabasas Formation) and are overlain by the San Onofre Breccia (Blake, 1991). The Monterey Formation consists of Pico Formation, as the Modelo Formation (about 1750 m thick). Dibblee siliceous hemipelagic shale deposited at bathyal depths (Pisciotto and Garri- (e.g., 1991, 1992) defined middle and upper Miocene strata of the Santa son, 1981). Coeval with Monterey deposition, the Modelo and Puente for- Monica Mountains as the Monterey Formation. This interpretation is vari- mations were deposited as turbidites on submarine fans at bathyal depths ably accepted and many workers are continuing to call these strata the (Sullwold, 1960; Durham and Yerkes, 1964; Yerkes et al., 1965; Yerkes, “Modelo Formation.” Fritsche (1993) divided the Modelo Formation in the 1972; Rumelhart, 1994a; Critelli et al., 1995). The upper Miocene to lower Santa Monica Mountains into the Modelo Formation (Mohnian) and the Pliocene Capistrano Formation in the southern part of the basin (San Joaquin Sisquoc Formation (upper Mohnian to Delmontian), on the basis of the HillsÐNewport Bay) rests conformably on the Monterey Formation and in- higher diatomaceous shale content in the upper unit. We use Hoots’ (1931) cludes a sand-rich turbidite system (e.g., Walker, 1975). The final infilling of terminology; the main outcrops of Modelo Formation are located in the the Los Angeles basin is represented by the Pliocene to Holocene Repetto, Santa Monica Mountains and the eastern Ventura basin (Fig. 1). Fernando, Pico, and La Habra formations (Yerkes et al., 1965; Yerkes, 1972), which range from bathyal-turbidite to inner-neritic to nonmarine deposits. Sedimentology and General Geology
STRATIGRAPHY OF THE MODELO FORMATION The Modelo Formation in the Santa Monica Mountains is angularly un- conformable on the middle Miocene Topanga Group and older units (Lane, The Modelo Formation (Fig. 2) was originally defined by Eldridge and 1987). The maximum thickness of the Modelo in the Santa Monica Moun- Arnold (1907) as a sequence of shale and sandstone above the Vaqueros tains is 1650 m in the Calabasas area and decreases to zero to the east and
Geological Society of America Bulletin, July 1997 887
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
west (Sullwold, 1958). The unit has been identified as Mohnian to Del- TABLE 1. CATEGORIES USED FOR SANDSTONE POINT COUNTS OF montian by many workers, using planktic and benthic foraminifers (Hoots, FRAMEWORK GRAINS AND RECALCULATED PLOTS Grain category definitions Categories* Recalculated 1931; Sullwold, 1958, 1960; Blake, 1991); the Delmontian section is only parameters exposed locally in the Santa Monica Mountains (Sullwold, 1958). The Qp Aphanitic polycrystalline quartz ➞ Qp QFL: lower member (10 m thick) is a poorly sorted dark gray to black shale and Qm Monocrystalline quartz ➞ Qm Q = Qm + Qp conglomerate, which contains many angular fragments of the Jurassic Santa P Plagioclase feldspar ➞ P F = P + K K Potassium feldspar ➞ K L = Lv + Lm + Ls Monica Slate, as well as rounded granitoid, sedimentary, and volcanic clasts Lvv Vitric volcanic lithic fragments ➞ Lv (cobbles to boulders). The middle and upper members (1640 m thick) con- Lvf Felsitic volcanic lithic fragments ➞ Lv LmLvLs: sist predominately of white punky diatomaceous shale. Lvml Microlitic volcanic lithic fragments ➞ Lv Lm = Lm Lmi Low-grade metaigneous ➞ Lmv Lv = Lv Both the middle and upper members of the Modelo contain lenses of light lithic fragments Ls = Ls yellowish-tan to buff sandstone; they are most prevalent in the middle mem- POLYM Polycrystalline phyllosilicates ➞ Lms QMF(T) Quartz-mica-feldspar aggregate ➞ Lms QpLvmLsm: ber. The lenses consist of medium-grained, poorly sorted, highly angular with tectonite fabric Qp = Qp sandstone (Sullwold, 1958). The beds vary in thickness from a few centime- QMF(A) Quartz-mica-feldspar aggregate ➞ Lms Lvm = Lv + Lmv ters to 10 m and are generally normally graded (Sullwold, 1958). The sand- without tectonite fabric Lsm = Ls + Lms Ls(Arg) Argillaceous sedimentary lithic ➞ Ls stones were called “arkosic graywackes” by Hoots (1931) and Sullwold fragments QmKP: (1958, 1960) because of the high feldspar content (reported 30%Ð85%) and Ls(Cb) Aphanitic carbonate lithic fragments ➞ Ls Qm = Qm high matrix content (15%Ð25%). This relatively high percentage of matrix is Mica Monocrystalline phyllosilicates ➞ M K = K Dense “Dense” mineral grains ➞ Misc. P = P probably the result of mistaking deformed lithic grains (pseudomatrix) for Matrix Interstitial matrix and cement ➞ I true matrix. Actual matrix values are 5%Ð10% (see below). (not a grain category) Ratio parameter: The environment of deposition for the middle member of the Modelo in P/F the Santa Monica Mountains was a submarine fan (Sullwold, 1958, 1960). *After Ingersoll (1983). Sullwold determined, on the basis of benthic foraminifers, that the Modelo was deposited at about 1000 m depth. Furthermore, he inferred that gravity- flow structures within the sandstones were evidence for turbidite deposition. Suczek, 1979). All of the reported recalculated parameters based on the The lenticular nature of the sandstone units indicates that they were proba- lithic percentages are derived from the lithic counts (i.e., LmLvLs and bly deposited in channels (e.g., Dibblee, 1992). We infer, therefore, that the QpLvmLsm; see Table 1). Modelo was probably deposited in a channelized mid-fan depositional en- Petrographic Results. On the basis of gross lithologic characteristics vironment (e.g., Ingersoll, 1978). The shaley deposits are interchannel de- (e.g., composition, depositional environment, percent sandstone), Dibblee posits, which were deposited during times of low rates of clastic sedimen- (1991, 1992) tentatively divided the Modelo Formation (Monterey Forma- tation or as a result of channel migration. tion) in the Santa Monica Mountains into three members which were used Sullwold (1958, 1960) took hundreds of paleocurrent measurements on to assign each sandstone sample to one of three units: lower, middle, or up- cross-beds in the Modelo in the Santa Monica Mountains. His work indicates per. In the following discussion, lower, middle, and upper members refer to that Modelo sandstone was derived from the north, with the exception of the only the sandstone parts of the section. The means and standard deviations lowest part of the section. The paleocurrents for the middle and upper mem- of sandstone recalculated parameters are listed in Table 2. bers have 180¡ of dispersion centered in the Tarzana area (Sullwold, 1958, Recalculated data are presented as means and fields of variation in Fig- named the feature the “Tarzana fan”). Isopach data from Nagle and Parker ure 3 (AÐD). The data cluster moderately well, indicating that the sediment (1971) show that upper Miocene strata are thickest between the Santa Mon- had a restricted source and/or has been homogenized. Both the data and the ica Mountains and the crystalline rocks of the San Gabriel Mountains. marine depositional environment suggest that sand has been homogenized (third-order sampling) (cf., Ingersoll, 1990; Ingersoll et al., 1993). There- SANDSTONE COMPOSITION fore, it is appropriate to apply global provenance fields to the data (e.g., In- gersoll and Suczek, 1979; Dickinson, 1985). This is not true, however, for Petrology and Petrographic Methods the lower member of the Modelo Formation, which is interpreted to be in- trabasinal (see discussion below). The lower member is included in the Sandstone samples were cut perpendicular to bedding, and impregnated ternary plots for the purposes of comparison. to make thin sections. Each thin section was etched in concentrated hydro- The mean QFL value (see Table 1) of the lower Modelo plots within the fluoric acid for 3 s to distinguish plagioclase and stained for potassium dissectedÐmagmatic-arc field near the recycled-orogen field (Fig. 3A; Dick- feldspar. The samples were counted randomly, and grid spacing was selected inson et al., 1983; Dickinson, 1985). The mean LmLvLs value of the lower that allowed 300 framework counts per thin section without counting any Modelo plots close to the metamorphic apex, reflecting the high proportion single grain more than once. The Gazzi-Dickinson method of point counting of QMF(A) (see Table 1) metamorphic lithic material present in most sam- was used (Gazzi, 1966; Dickinson, 1970; Ingersoll et al., 1984); crystals ples (Fig. 3B). The mean QpLvmLsm value of the lower Modelo plots in greater than 0.0625 mm within lithic fragments were counted as monocrys- the mixed magmatic arcs and rifted continental margin field, also reflecting talline grains. In all cases, the effects of diagenesis (compaction and incipient the high percentage of metasedimentary lithic fragments (Fig. 3C). The clay formation) were “mentally removed” so that original detrital composi- mean QmKP value (see Table 1) of the lower Modelo plots in the granite tion was determined. Counting parameters and calculations are based on In- field, toward the quartz apex on a modified Streckeisen diagram (Fig. 3D; gersoll (1983) and Dickinson (1985), and are summarized in Table 1. Streckeisen, 1976). The lower Modelo has low P/F (0.40) (see Table 1) As a result of the low percentage of lithic grains in many of the samples, compared to the rest of the formation (Table 2). Except for the easternmost a second count was performed on each of the Santa Monica Mountains sam- samples, the lower member of the Modelo is generally rich in metasedi- ples. For each thin section, 100 lithic grains were counted in order to mini- mentary lithic fragments. The eastern samples are low in metasedimentary mize the effect of anomalous grains (e.g., Graham et al., 1976; Ingersoll and lithic material and relatively enriched in volcanic lithic material.
888 Geological Society of America Bulletin, July 1997
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
TABLE 2. RECALCULATED MODAL POINT-COUNT DATA FOR THE MODELO FORMATION Sample QFL% LmLvLs% QpLvmLsm% QmKP% P/F No. Q F L Lm Lv Ls Qp Lvm Lsm Qm K P Lower ModeloÐSanta Monica Mountains PR91-61 16 9 74 87 2 11 0 13 87 64 22 14 0.39 PR92-62 45 36 20 69 18 13 0 36 64 56 33 11 0.25 PR92-63 56 28 16 62 17 21 4 31 65 66 21 12 0.37 PR92-71 55 30 15 77 18 5 2 35 63 64 26 10 0.28 PR93-97 51 35 15 83 6 11 0 33 67 60 27 13 0.33 PR93-100 46 23 31 79 9 12 4 14 82 67 23 11 0.33 PR93-120 24 21 56 94 3 3 0 3 97 53 24 22 0.48 PR93-122 21 21 58 86 10 4 2 13 85 50 20 31 0.61 PR93-125 49 40 11 42 50 8 5 66 29 55 23 22 0.49 PR93-127 44 45 11 39 51 11 1 71 28 49 30 21 0.42 x 41 29 31 72 18 10 2 31 67 58 25 17 0.40 SD 15 11 23 19 18 5 2 23 23 7 4 7 0.11 Middle ModeloÐSanta Monica Mountains PR92-31 33 53 14 28 71 1 0 83 17 39 20 42 0.68 PR92-33 35 58 8 34 62 4 0 81 19 37 20 42 0.68 PR92-36 30 57 13 40 57 3 0 75 25 35 22 43 0.66 PR92-38 33 56 11 35 62 3 1 82 17 37 21 42 0.66 PR92-42 32 54 14 38 61 1 2 77 21 37 19 45 0.71 PR92-43 29 57 14 38 56 6 0 72 28 34 22 45 0.67 PR92-45 37 52 11 27 71 2 1 88 11 41 22 38 0.63 PR92-60 40 48 11 42 51 7 1 61 38 45 16 39 0.71 PR92-64 27 60 13 24 66 10 0 76 24 31 22 47 0.68 PR92-65 32 55 13 43 44 12 0 60 40 37 20 43 0.68 PR92-67 30 64 7 46 42 12 1 57 42 31 19 50 0.73 PR92-68 31 58 11 49 42 8 0 59 41 34 23 43 0.65 PR92-70 34 58 8 68 28 4 0 53 47 37 18 46 0.72 PR92-73 32 54 14 48 45 7 0 76 24 37 20 43 0.68 PR92-74 34 57 9 59 34 7 0 72 28 37 23 40 0.63 PR92-75 34 55 12 51 38 11 0 64 36 38 22 40 0.64 PR92-76 32 59 10 51 40 9 0 75 25 35 16 49 0.75 PR92-76B 28 64 8 49 47 4 0 74 26 31 19 50 0.72 PR92-77 28 53 19 30 65 5 0 89 11 35 20 45 0.70 PR92-78 31 58 10 70 20 to 0 40 60 35 24 41 0.63 PR92-79 26 63 11 43 52 5 0 85 15 29 30 41 0.58 PR92-80 29 53 17 51 46 3 0 79 21 36 17 48 0.74 PR92-81 26 57 17 41 55 4 1 82 16 31 22 47 0.68 PR92-82 35 56 9 38 55 7 0 69 31 39 17 44 0.72 PR92-83 33 57 10 29 63 8 0 75 25 37 17 46 0.73 PR92-84 29 64 8 44 48 8 0 60 40 31 22 47 0.68 PR92-85 29 64 7 40 52 8 0 66 34 31 23 46 0.66 PR92-86 25 67 8 64 36 0 0 68 32 27 28 45 0.62 PR92-87 29 66 5 42 50 8 0 74 26 31 24 45 0.65 PR92-88 32 62 6 52 46 2 0 62 38 34 22 43 0.66 PR92-89 38 50 12 43 53 4 0 75 25 43 16 40 0.71 PR92-90 35 59 7 60 38 2 0 62 38 37 27 36 0.57 PR93-99 35 53 12 17 82 1 0 85 15 39 24 37 0.61 x 32 58 11 43 51 6 0 71 28 35 21 43 0.67 SD 4 5 3 12 13 3 0 11 11 4 3 4 0.04 Upper ModeloÐSanta Monica Mountains PR92-72 32 64 4 92 8 0 0 24 76 34 17 50 0.75 PR93-91 28 68 3 67 13 21 0 28 72 29 23 47 0.67 PR93-92 34 64 2 69 24 7 0 34 66 34 19 47 0.71 PR93-93 29 70 1 98 8 4 0 62 38 29 30 41 0.58 PR93-94A 28 70 2 77 20 3 0 53 47 28 32 40 0.55 PR93-94B 29 68 4 61 28 11 0 44 56 30 29 41 0.58 PR93-95 30 66 3 71 24 4 0 37 63 31 24 45 0.65 PR93-96 28 69 2 73 24 3 3 37 61 29 22 4,9 0.69 x 30 67 3 75 19 7 0 40 60 31 25 45 0.65 SD 2 3 1 11 8 7 1 13 13 2 5 4 0.07 Modelo-Ventura basin PR93-101 38 59 4 73 18 9 0 55 45 39 26 34 0.57 PR93-102 37 59 4 64 36 0 0 64 36 39 25 36 0.58 PR93-103 45 48 7 89 0 11 10 29 62 48 18 34 0.65 PR93-104 42 52 6 67 0 33 21 11 68 44 26 30 0.54 PR93-106 41 54 5 73 9 18 15 15 69 43 24 33 0.58 PR93-107 44 53 3 89 0 11 0 33 67 46 28 26 0.48 PR93-108 36 61 3 86 0 14 0 14 86 37 18 45 0.72 PR93-109 11 85 3 100 0 0 0 11 89 12 9 80 0.90 PR93-1 10 39 56 6 93 0 7 22 0 78 40 15 45 0.75 PR93-1 11 22 73 5 77 15 8 7 21 71 23 14 63 0.82 PR93-112 44 51 5 93 0 7 12 12 76 46 17 37 0.68 PR93-113A 43 48 8 58 17 25 0 21 79 47 16 37 0.70 PR93-113B 51 43 6 65 35 0 6 61 33 54 21 24 0.53 PR93-114 10 79 11 100 0 0 0 0 100 I 1 18 71 0.80 PR93-115 12 84 5 73 0 27 0 0 100 12 14 74 0.84 PR93-116 11 83 6 100 0 0 0 0 100 12 14 74 0.84 x 33 62 5 81 8 11 6 22 73 34 19 46 0.69 SD 14 14 2 14 13 11 8 21 21 15 6 19 0.13 Note: See Table 1 for explanation of abbreviations; x = mean, SD = standard deviation.
Geological Society of America Bulletin, July 1997 889
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
Figure 3. QFL, LmLvLs, QpLvmLsm, and QmKP diagrams of Modelo Formation sandstones from the Santa Monica Mountains and eastern Ventura basin (see Tables 1 and 2 for explanation of symbols). U—upper Modelo member, Santa Monica Mountains; M—middle Modelo mem- ber, Santa Monica Mountains; L—lower Modelo member, Santa Monica Mountains; V—Modelo, eastern Ventura basin. Polygons indicate one standard deviation about the mean. Arrows show compositional trends within the middle member. Following are the provenance fields. QFL tri- angles (Dickinson, 1985): 1, craton interior; 2, transitional continental; 3, basement uplift; 4, dissected arc; 5, transitional arc; 6, undissected arc; 7, recycled orogen. LmLvLs and QpLvmLsm triangles (Ingersoll and Suczek, 1979): 1, magmatic arcs (forearc areas); 2, mixed magmatic arcs and rifted continental margins (backarc basins); 3, mixed magmatic arcs and subduction complexes; 4, rifted continental margins; 5, suture belts (remnant ocean basins). QmKP triangles (modified after Streckeisen, 1976): 1a, quartzolite; 1b, quartz-rich granitoids; 2, alkali-feldspar gran- ite; 3, granite; 4, granodiorite; 5, tonalite; 6, alkali-feldspar quartz syenite; 7, quartz syenite; 8, quartz monzonite; 9, quartz monzodiorite; 10, quartz diorite; 11, alkali-feldspar syenite; 12, syenite; 13, monzonite; 14, monzodiorite; 15, diorite.
In contrast to the lower Modelo, the middle member is relatively enriched Data from the upper member of the Modelo cluster tightly within the in volcanic lithic material and plagioclase. The middle member QFL mean basement-uplift field (Fig. 3A). The data on both the LmLvLs plot and the plots on the border of the dissectedÐmagmatic-arc field and the basement- QpLvmLsm plot are located near the suture-belt field, which clearly shows uplift field (Fig. 3A). The lithic composition of the member varies up-sec- that the lithic composition of the upper Modelo is dominated by metamor- tion. The LmLvLs mean plots in the magmatic-arc (forearc) field (Fig. 3B). phic and sedimentary lithic material (Fig. 3, B and C). The P/F is indistin- The lowest part of the member tends to be the most volcanic rich; up- guishable from the middle member (Table 2). The QmKP mean plots on the section, the proportion of volcanic lithic material declines and metasedi- granodiorite-granite boundary (Fig. 3D). mentary lithic material increases (Fig. 3B). The up-section decrease in vol- Provenance. The lower member of the Modelo is interpreted to be locally canic sediments can also be seen in the QpLvmLsm ternary plot (Fig. 3C). derived. The lower Modelo contains chips of Santa Monica Slate (Fig. 1) and The composition varies from abundant volcanic material at the base of the rounded granitic cobbles and boulders, which reflect directly underlying member to dominantly sedimentary-metasedimentary lithic material at the rocks. Point counts of thin sections of granitic clasts from the lower member top. The P/F for the middle member is relatively high (0.67), possibly re- show a P/F ratio (0.45) similar to that of the sandstone (0.40; Table 2), and un- flecting the high volcanic content or granodiorite in the source region like that of sandstone from the other members (0.66, Table 2). It is unlikely (Table 2). The QmKP mean plots in the granodiorite field, reflecting the that these granitic clasts came from the same source areas as most of the Mod- high percentage of plagioclase and moderate quartz (Fig. 3D). elo. This is further evidence for a local source, perhaps the granitic bodies in
890 Geological Society of America Bulletin, July 1997
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 SUBSIDENCE ANALYSIS OF THE LOS ANGELES BASIN
the eastern Santa Monica Mountains (Hoots, 1931; Fig. 1). The lithic popula- TABLE 3. DETRITAL PLAGIOCLASE-FELDSPAR tion of the lower member also suggests local derivation. Most of the sandstone COMPOSITIONAL DATA FOR THE MODELO FORMATION is rich in metasedimentary lithic fragments, probably derived from the Santa Sample Ca Na K Monica Slate. To the east of exposures of Santa Monica Slate, Modelo sand- Santa Monica Mountains 68, A 0.15186 0.86693 0.00410 stone is relatively poor in metasedimentary lithic material and enriched in vol- 68, B 0.05474 0.95159 0.00767 canic lithic material, consistent with derivation from underlying Topanga vol- 72, A 0.20546 0.80279 0.01398 72, B 0.12998 0.88651 0.00904 canic rocks. The relatively high proportions of monocrystalline quartz and 72, C 0.12189 0.89629 0.01145 potassium feldspar (QFL%Q = 41; P/F = 0.40; Table 2) in the lower sandstone 83, A 0.07667 0.93158 0.00819 are key differences between the lower member and the rest of the formation. 83, B 0.29379 0.70533 0.01125 83, C 0.17404 0.82520 0.01001 The source of the lower member is thought to have been a submarine 88, A 0.14694 0.84942 0.01014 high in the eastern Santa Monica Mountains (Dibblee and Ehrenspeck, 88, B 0.10417 0.99864 0.00531 1993), which Rumelhart and Ingersoll (1994) called the Griffith Park uplift 88, C 0.13880 0.87526 0.00618 88, D 0.06385 0.95186 0.00970 (or Griffith Park high). Critelli et al. (1995) also inferred the presence of the x 0.15585 0.86005 0.00898 Griffith Park high on the basis of the identification of intrabasinal clasts in SD 0.08893 0.10029 0.00270 Eastern Ventura Basin the Puente Formation. The high K-feldspar content of westernmost lower 101, A 0.34336 0.65167 0.01762 Modelo sandstone suggests the possibility that the lower member may have 101, B 0.27526 0.73440 0.01262 also received significant detritus from reworked Cretaceous and Paleogene 101, C 0.31086 0.67484 0.02523 101, D 0.00364 1.00881 0.00280 strata of the Simi uplift area (Rumelhart, 1994b). 109, A 0.48439 0.52289 0.00332 The middle member of the Modelo is rich in plagioclase and moderately 109, B 0.48200 0.52558 0.00514 low in quartz (e.g., QFL%Q = 32; QFL%F = 58 and P/F = 0.67; Table 2), in- 109, C 0.39835 0.61462 0.00286 109, D 0.48291 0.50937 0.00312 dicating a potential granodioritic-tonalitic or a diluted anorthositic source 109, E 0.46284 0.55191 0.00254 (Fig. 3D). The Lowe Granodiorite (Triassic) and/or the anorthosite in the 109, F 0.48817 0.52916 0.00208 114, A 0.46817 0.54323 0.00273 western San Gabriel Mountains probably contributed the majority of sand- 114, B 0.28035 0.73836 0.00521 stone to the area (see Fig. 1). The moderately high percentage of volcanic 114, C 0.49697 0.51037 0.00241 lithic fragments (LmLvLs%Lv = 51) (Fig. 3B) suggests a nearby volcanic 115, A 0.31847 0.67868 0.01821 115, B 0.33557 0.65137 0.02861 center. Although the main volcanic center of the middle Miocene Conejo 115, C 0.52516 0.47971 0.00325 Volcanics was nearby, the volcanic rocks were probably not subaerially ex- 115, D 0.45782 0.55866 0.00560 posed, thus would not have contributed much sediment into the eastern Santa 115, E 0.42365 0.58937 0.00130 115, F 0.33127 0.66905 0.01952 Monica Mountains (Dibblee and Ehrenspeck, 1993). Furthermore, pale- 115, G 0.39507 0.61348 0.00299 ocurrent and isopach data indicate that the sandstone was derived from the x 0.38821 0.61778 0.00836 north. The currently exposed middle Miocene GlendoraÐEl Modeno and/or SD 0.12073 0.12027 0.00861 Note: Ca = calcium, Na = sodium, K = potassium, x = mean, the OligoceneÐMiocene Vasquez volcanic strata or their equivalents in the SD = standard deviation. San Gabriel Mountains are a potential source for the volcanic material within the middle member. The proportion of volcanic lithic fragments decreases stratigraphically up-section, whereas metasedimentary lithic material in- creases. This probably represents unroofing of the San Gabriel Mountains. plutonic complex that contained a high proportion of plagioclase, moderate As the volcanic cover was removed, the composition became progressively quartz, and moderate potassium feldspar. Potential major source rocks dominated by plutonic and metamorphic detritus. within the San Gabriel Mountains (Fig. 1) include the Precambrian anortho- The upper member of the Modelo was derived from plutonic and meta- site body in the western San Gabriel Mountains, Lowe Granodiorite, and morphic basement within the San Gabriel Mountains. This interpretation is other Mesozoic granitoids in the central and eastern San Gabriel Mountains supported by low lithic percentages (QFL%L = 3; Fig. 3A) and the high per- (Ehlig, 1981), and/or a mixture of sources. On the basis of the modal com- centage of metasedimentary lithic material (LmLvLs%Lm = 75 and positions of the sandstone, it is equivocal as to which source terranes dom- QpLvmLsm%Lsm = 60; Fig. 3, B and C). High P/F (0.65) and moderate inated. However, detailed composition data of detrital plagioclase help as- quartz (QFL%Q = 30) suggest that the plutonic source was similar to that for certain whether the sediments were derived from the dominantly the middle member (i.e., Lowe Granodiorite or diluted anorthosite from the Ca-plagioclaseÐrich anorthosite complex of the western San Gabriel Moun- San Gabriel Mountains). Note that, although there is overlap in Figure 3 be- tains or the Na-plagioclaseÐrich granodiorite, tonalite, and diorite of the tween the lower and upper members, the key differences are P/F values (0.40 central San Gabriel Mountains. vs. 0.67 respectively) and lithic percentages (31% vs. 3%, respectively). Analytical Methods. Plagioclase analyses were conducted at the Univer- It is not likely that sandstone in the middle and upper members was derived sity of California at Los Angeles (UCLA), on the Cameca Camebex micro- from sources east of the San Andreas fault (>50 km away), because sandstone probe, operated in both wavelength- and energy-dispersive modes at an ac- compositional and textural immaturity suggests that the sediment was not far celerating voltage of 15 kV and at sample currents of approximately traveled (Sullwold, 1960). Furthermore, it is evident from the buttress uncon- 10Ð15 nA. Natural and synthetic mineral-oxide standards are from the formity at the eastern end of the Ventura basin that the San Gabriel Mountains UCLA collection; wet chemical analyses are available upon request. ZAF were a topographic high during late Miocene time (Stitt, 1986). corrections were used for all analyses in order to correct raw intensities. The limit of detectability is about ±0.02 wt% for the wavelength-dispersive Detrital Feldspar Compositions mode and is somewhat higher for the energy-dispersive mode. Sources of error include the precision to which the concentration of standard elements On the basis of sandstone petrographic analysis, it is probable that the is known, the accuracy of the ZAF corrections, machine drift, and counting main source for Modelo sandstone in the Santa Monica Mountains was a statistics. Counting errors were maintained at less than 1% for the standards
Geological Society of America Bulletin, July 1997 891
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
The data suggest that much of the Modelo in the eastern Ventura basin was partially derived from the anorthosite complex in the western San Gabriel Mountains. The samples that are almost entirely plagioclase (Table 2) were probably derived directly from the complex.
SUBSIDENCE ANALYSIS
Methods and Assumptions
The following discussion addresses the results of subsidence analyses of the northern Los Angeles basin from data provided by Unocal Corporation. These analyses were conducted using the BasinWorks software package (Marco Polo Software, Inc., 1988Ð1991). For our purposes, the goal of per- forming subsidence analyses is to ascertain the timing and style (thermal, flexural, or mechanical) of the tectonic events that affected the basin. The BasinWorks software package aids in this by removing the subsidence due to sediment and water loading, leaving only the effects of tectonics (tectonic subsidence). By backstripping progressively older units, the total and tec- Figure 4. CaNaK diagram of plagioclase compositions of sandstone tonic subsidence can be calculated through time (see Steckler and Watts, from Santa Monica Mountains and eastern Ventura basin (see Table 3 1978). for data set). In order to perform a subsidence analysis, four types of information are required: (1) present stratigraphic depth, (2) lithology, (3) stratigraphic age, and (4) paleobathymetry. In this case, stratigraphic depth and lithology were (counting time, 20 s in all cases). taken directly from the well descriptions. The subdivisions for each strati- Reproducibility of analyses was checked by running the garnet standard graphic section were defined generally on the basis of formation or benthic- as an unknown, both before and after the series of unknown minerals, and foraminiferal stage boundaries. Each subdivision was assigned a gross comparing the ratio of the corrected intensities (Table 3). The observed er- lithology (e.g., sandstone or siltstone), which was given a compaction coef- ror was less than 2%, well within acceptable standards (R. Jones, 1993, per- ficient by BasinWorks (see Data Repository1 for compaction parameters). sonal commun.). The depth:porosity relation used in the analysis was from Bond and Kom- Microprobe Analysis. Table 3 contains the microprobe analyses (only inz (1984) and Dickinson et al. (1987). During the backstripping process, Ca, Na, and K) for the middle and upper members of the Modelo Formation the porosity for each unit was recalculated as the overlying units were se- of the Santa Monica Mountains, and a ternary diagram (Fig. 4) illustrates quentially removed (e.g., Van Hinte, 1978). The assumption that the base- the composition of the feldspars. Plagioclase composition in the Modelo of ment is completely lithified may result in an overestimate of the amount of the Santa Monica Mountains ranges from 0.64 Ab to 0.95 Ab and averages tectonic subsidence if the basement compacted during burial. 0.86 Ab; the standard deviation is 0.10 (Table 3). The plagioclase clearly Stratigraphic age based on planktic foraminifera and paleobathymetry was derived from rocks that contained significant Na-plagioclase, similar to based on benthic foraminifera were provided by Unocal (G. Blake, 1992, the Lowe Granodiorite, tonalite, and diorite in the central to eastern San personal commun.). Paleobathymetric zones are based on Ingle (1980). Un- Gabriel Mountains (Sullwold, 1958). There does not seem to be any sys- less more specific information was available (e.g., lower part of the upper tematic variation of plagioclase composition within the Santa Monica bathyal zone) the average depth for that zone was used in the analysis; in Mountains samples. general, the error is considered to be ±500 m, assuming that the original Sandstone samples were also collected from the eastern Ventura basin. foram interpretation is accurate. As Dickinson et al. (1987) discussed, the These were analyzed both petrographically and by using the microprobe (as greatest potential error in this type of analysis involves the paleobathymet- described above). Figure 3 (AÐD) and Table 2 illustrate that framework ric data. compositions of the sandstone are similar to those of the middle and upper In all analyses except Rancho #1, no unconformities or faults are known. members of the Modelo from the Santa Monica Mountains. The composi- In Rancho #1, there is an intra-Modelo unconformity which was assumed tion (high QFL%F = 62%, high P/F = 0.69, and low QFL%L = 5%) sug- to have little or no section removed because of the middle bathyal water gests that the Modelo in the Ventura basin had granodioritic to anorthositic depths of strata above and below the unconformity. source rocks, similar to those of the Modelo in the Santa Monica Moun- tains. However, some samples contain very high QFL%F (79%Ð85%; Northern Los Angeles Basin Table 2) and P/F (0.85; Table 2), suggesting a source extremely rich in pla- gioclase. These few samples contrast with all samples in the Santa Monica The wells (Signal-Richfield-Rancho #1 [sec. 36, T. 1 S., R. 15 W.; Ran- Mountains. cho #1 herein], Doheney-Richfield-Laubacher #1 [sec. 5, T. 1 N., R. 22 W.; The eastern Ventura basin plagioclase compositional data are variable, Laubacher #1 herein], and Simi #33 [sec. 10, T. 3 N., R. 18 W.]; Fig. 1) were from 0.48 Ab to 1.00 Ab, and average 0.62 Ab; the standard deviation is selected for completeness of section and quality of paleobathymetric data. 0.12 (Table 3; Fig. 4). The data suggest that a significant amount of plagio- In all of the wells, the Modelo Formation is present. The subsidence histo- clase in the eastern Ventura basin Modelo had a source containing relatively calcic plagioclase (andesine-sodic labradorite). Ehlig and Crowell (1982) 1GSA Data Repository item 9733, data for subsidence analyses, is available reported that plagioclase within the anorthosite complex in the western San on request from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301. Gabriel Mountains is “intermediate to calcic andesine” (60%Ð 70% Ab). E-mail: [email protected].
892 Geological Society of America Bulletin, July 1997
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 SUBSIDENCE ANALYSIS OF THE LOS ANGELES BASIN
ries for the wells are shown in Figure 5 (AÐE). Basement for all three wells is considered to be whatever unit underlies the Topanga Group. Rancho #1. Rancho #1 is located directly south of the Santa Monica Mountains near Beverly Hills (Fig. 1). It is at the southernmost part of the northern block of the Los Angeles basin (Yerkes et al., 1965). The well is 3750 m deep and bottoms in the upper part of the Topanga Group. It shows the most total subsidence of the wells studied on the northern block, more than 6000 m. The tectonic-subsidence curve indicates that rapid subsidence began about 12 Ma and tapered off from 10 to 6 Ma (Fig. 5A). The concave- upward shape of the tectonic-subsidence curve from 12 to 6 Ma suggests that the subsidence mechanism may have been thermal (Turcotte and McAdoo, 1979; Pitman and Andrews, 1985; Dickinson et al., 1987; Ange- vine et al., 1990). Another period of rapid subsidence occurred between 6 and 3 Ma, when the basement reached its maximum depth. The tectonic- subsidence curve during this time may be convex upward, suggesting that subsidence was driven by flexural loading. Since 3 Ma, the basin has un- dergone tectonic uplift and sediment infilling. Laubacher # 1. Laubacher #1 is located at the west end of the Santa Monica Mountains. The stratigraphic section was deposited at the western margin of the basin (Fig. 1). The well is 2940 m deep and bottoms in the nonmarine Sespe Formation. To facilitate comparison with the Rancho #1, the Sespe was considered to be part of the basement. The base of the section used for the analysis was the base of the Topanga Group. Although there is probably some section missing above the Sespe Formation, we feel justified in using the lowest marine strata in the Topanga Group as indicators of the initiation of rapid subsidence. The tectonic-subsidence curve (Fig. 5B) in- dicates that significant subsidence had begun by 16 Ma. Subsidence contin- ued until 3 Ma, by which time basement had subsided to 3000 m. Uplift oc- curred between 3 and 2 Ma. Simi #33. Simi #33 is located at the northern edge of the Los Angeles basin in the Santa Susana Mountains (Fig. 1). The well is 2080 m deep and, similar to the Laubacher #1, it bottoms in the nonmarine Sespe Formation. For the Simi #33, we also treat the Sespe Formation as part of the basement. The subsidence history of the well (Fig. 5C) contrasts with those of the other sites. In this area, the basin subsided rapidly from 16 to 14 Ma. From 12 to 8 Ma, the basement underwent slight tectonic uplift. Since 8 Ma, the tec- tonic-subsidence curve has remained relatively flat, and there has been grad- ual filling of the basin. The basement reached a maximum depth of 2000 m about 13 Ma.
Central Los Angeles Basin
Figure 5, D and E, shows subsidence analyses from Mayer (1987, 1991) and Sawyer et al. (1987), respectively. Mayer obtained his data from his own composite stratigraphic column and from Yerkes et al. (1965); base- ment is the base of the Vaqueros Formation. Sawyer et al. (1987) obtained their data exclusively from Yerkes et al. (1965); basement is the base of the Monterey Formation. Mayer (1991). Two main episodes of increased subsidence, at 18 and 5 Ma, are interpreted from the tectonic-subsidence curve (Fig. 5D). Mayer (1987) inferred a 12 Ma event on the basis of the period of peak volcanism; his tectonic-subsidence curve is inconclusive regarding this interpretation. Although the data are sparse, the concave-upward nature of the tectonic- subsidence curve supports a thermal subsidence mechanism from 18 to Figure 5. Subsidence curves (decompacted) used to infer subsidence tim- 5 Ma. The subsidence mechanism of 5 to 3 Ma is equivocal due to the lack ing and style. See Figure 1 for locations and text for discussion. Note that of resolution. Uplift and increased sedimentation rate are characteristic of basement varies for each analysis. (A) Base of Calabasas; (B) base of Cal- 3 Ma to the present (Mayer, 1987). Basement is currently at a maximum abasas; (C) base of Calabasas; (D) base of Vaqueros; (E) base of Monterey. depth of 11 000 m. Vertical bars indicate paleobathymetric uncertainties where available. Sawyer et al. (1987). Sawyer et al. (1987) presented Yerkes et al.’s
Geological Society of America Bulletin, July 1997 893
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
(1965) data as subsidence curves (Fig. 5E). Although the data are sparse, tributing sediment to the Tarzana Fan system (Rumelhart, 1994a, 1994b). they indicate rapid subsidence in progress by 11 Ma and continuing until Furthermore, the middle Miocene upper Topanga Group and the lower Mo- around 2 Ma, when tectonic subsidence ceased. The subsidence mechanism delo Formation (outcrops south of the Simi Hills; see Fig. 1) contain clasts is difficult to interpret. It is probable, however, that there was an increase in from the Cretaceous and Paleogene units in the Simi area (Rumelhart, the rate of subsidence between 5 and 2 Ma. Shallowing of water after 2 Ma 1994b). and a slowing of tectonic subsidence suggest increased rates of sedimenta- tion as the result of uplift of the Transverse Ranges. The maximum base- Proposed Tectonic Processes ment depth is 10 300 m. Tectonic-subsidence curves for strata from the Los Angeles basin (Fig. 5, Subsidence History of the Los Angeles Basin AÐE) are segmented and seem to show three episodes of subsidence. On the basis of the tectonic-subsidence curves of Angevine et al. (1990), it is clear On the basis of the subsidence analyses, we recognize three episodes of that only basins formed in strike-slip settings have rapid enough rates of tectonism within the Los Angeles basin. Not all of these events are shown subsidence to match those of the Los Angeles basin. Unfortunately, there in every analysis, but all analyses are consistent with our proposed tectonic are no published tectonic-subsidence curves for supradetachment basins events. The first episode seems to have initiated at approximately 16 Ma, as (basins formed in the hanging walls of low-angle detachments; Friedmann shown by rapid subsidence in Simi #33 (Fig. 5C). The preserved marine and Burbank, 1995), and therefore these cannot be dismissed as a possible section in Laubacher #1 is consistent with this interpretation (Fig. 5B). The tectonic setting. Although tectonic-subsidence curves for the Los Angeles major episode of rapid vertical-axis rotations seems to have occurred be- basin show extremely rapid, concave-upward (likely thermal) initial subsi- tween 16 and 12 Ma in the Santa Monica Mountains (i.e., southern Trans- dence, the basin is not a simple transtensional basin. The basin has had dif- verse Ranges; Hornafius et al., 1986). It is likely that the initiation of subsi- ferent episodes of subsidence, each with its own subsidence mechanism, dence in the northern Los Angeles basin was associated with extension between crustal blocks during the rotations (Luyendyk and Hornafius, 1987; Luyendyk, 1991; Crouch and Suppe, 1993). We therefore interpret the initial phase of subsidence as the result of extension associated with transrotation (Ingersoll, 1988; i.e., vertical-axis rotations of the Transverse Ranges). The second phase of tectonism started about 12 Ma and is best illustrated by the Rancho #1 well (Fig. 5A), which shows an episode of rapid subsi- dence beginning at approximately 12 Ma and ending about 6 Ma. An age of 12 Ma is consistent with Mayer’s (1987) interpretation of an event associ- ated with increased volcanism. Crowell (1982) and Yeats et al. (1994) re- ported that the San Gabriel fault was active between 12 and 5 Ma. It is pos- sible that in the northern Los Angeles basin, transtension (and subsequent thermal subsidence) resulted from movement along the San Gabriel and as- sociated faults. The last phase of subsidence began about 6 Ma. It is best illustrated in Rancho #1 (Fig. 5A), although it can be seen in the Laubacher #1, and the Mayer (1987) and Sawyer et al. (1987) curves as well (Fig. 5, B, D, and E). It roughly corresponds to the initiation of the modern San Andreas fault sys- tem at approximately 5 Ma (Crowell, 1987). The upward convex shape of the Rancho #1 during this time suggests flexural subsidence, which resulted from compression due to increased convergence within the San Andreas fault system (e.g., Atwater, 1970; Engebretson et al., 1985; Luyendyk, 1991). A switch from extensional to compressional tectonism around the beginning of the Pliocene in the northern Los Angeles basin is also sup- ported by structural and stratigraphic relationships reported by Schneider et al. (1996). Very rapid tectonic uplift and shallowing bathymetry about 3 Ma (Fig. 5, A, B, and D) indicate either increased rates of contraction or that a finite amount of time following the 6 Ma initiation of transpression was needed before contraction led to tectonic uplift. Because the Simi #33 well is on the far northern edge of the Los Angeles basin, most of its subsidence history contrasts with the other wells. Uplift after 13 Ma was possibly caused by convergence between crustal blocks Figure 6. Timing and style of tectonism and/or subsidence in south- during rotations within the Transverse Ranges. Thin upper Miocene strata ern California. Abbreviations: SGF—San Gabriel fault; SAF—San in the Simi Hills indicate that uplift resulted in a topographic high (Nagle Andreas fault; WTR—western Transverse Ranges; SMM—Santa and Parker, 1971). Thus, the Ventura and Los Angeles basins probably were Monica Mountains; LAB—Los Angeles basin; CLAB—central Los partitioned into two basins about 13Ð12 Ma (Yeats, 1987). This is consistent Angeles basin; NLAB—northern Los Angeles basin. Stippled areas with the high K-feldspar content within the lower Modelo Formation of the show times of transition between tectonic phases indicated at bottom Santa Monica Mountains, which suggests that the Simi Hills area was con- (see text).
894 Geological Society of America Bulletin, July 1997
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 SUBSIDENCE ANALYSIS OF THE LOS ANGELES BASIN
Figure 7. Palinspastic reconstruction at 12 Ma for northern Los Angeles basin, Ventura basin, and San Gabriel Mountains. Fault offsets are based on May and Walker (1989). EVB—eastern Ventura basin; MCF—Malibu Coast fault; SFV—San Fernando Valley. Vertical lines indicate areas where significant postÐ12 Ma tectonic shortening has occurred.
creating the complex polyphase basin we see today (Crowell, 1987). They also noted, however, that outcrops of Catalina, Orocopia, and Pelona The rhombohedral shape and rapid thermal tectonic subsidence of the schist resemble “metamorphic core complexes,” which have been isostati- Los Angeles basin (Pitman and Andrews, 1985) suggest that it formed as a cally uplifted along low-angle detachment faults. Nothing in our study dis- pull-apart basin. However, the lack of an obvious releasing bend and the allows detachment faulting associated with transrotation as a mechanism for dominance of rotational tectonics in the area suggest that the basin may initial subsidence in the Los Angeles basin. However, S. J. Friedmann have initiated as a transrotational basin (i.e., Ingersoll, 1988). The concave- (1995, personal commun.) indicated that the greatest known subsidence of upward shape of the tectonic-subsidence curves during the oldest subsi- any supradetachment basin is approximately 3 km. This suggests that sub- dence episode (16 to 12 Ma) suggests that the subsidence mechanism was sidence of more than 10 km in the central Los Angeles basin was not en- thermal. There may have been a transition from transrotation to transtension tirely the result of extension along low-angle detachment faults, although at 12 Ma, when the rotation of western Transverse Ranges slowed (Luyen- this process may have played a role. dyk and Hornafius, 1987). The youngest event (6Ð0 Ma) may be character- ized by generally convex-upward tectonic-subsidence curves, similar to DISCUSSION those from flexural basins (i.e., Angevine et al., 1990). Crouch and Suppe (1993) suggested that the present rhombohedral shape Los Angeles Basin Paleotectonics of the Los Angeles basin is a function of post-Miocene movements on bounding strike-slip faults and that the basin formed by extension along The middle to late Miocene paleotectonics and paleogeography of south- east-dipping low-angle detachments. Crouch and Suppe (1993) noted, as ern California in the vicinity of the Los Angeles basin are among the most did Luyendyk and Hornafius (1987), that subsidence in the Los Angeles complex in the world (e.g., Crowell, 1987). Keys to reconstructing the pa- basin accompanied Neogene clockwise rotation of the Transverse Ranges. leotectonics and paleogeography of the area include the timing, style, mag-
Geological Society of America Bulletin, July 1997 895
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
declination data could equally be explained by a constant rotation rate of 5.79¡/m.y. from 16 Ma to the present. We prefer the variable-rate model, based on changes in plate motion during the late Tertiary (Engebretson et al., 1985), and the model of microplate capture (Nicholson et al., 1994; Bo- hannon and Parsons, 1995). Our interpretation applies only to the southern Transverse Ranges (e.g., the Santa Monica Mountains). In the Santa Mon- ica Mountains, the southerly paleocurrent directions within the Modelo For- mation (Sullwold, 1958, 1960) suggest that the Modelo Formation in the Santa Monica Mountains has not been rotated. It is likely that the Santa Monica Mountains stopped rotating earlier than other parts of the western Transverse Ranges. Luyendyk (1991) suggested that extension (and subsi- dence) may have been a major component of the crustal rotations. The slow- ing of vertical-axis rotations by 12 Ma (Hornafius et al., 1986) suggests that continued subsidence may have been transtensional rather than transrota- tional. It is likely that active extension (and subsidence) continued, rather than simple postrift thermal subsidence, because the rate of tectonic subsi- dence increased during late Miocene time (12 Ma), as shown in Rancho #1 (Fig. 5A). A third episode of subsidence began in the Los Angeles basin about 6 Ma. The shape of the tectonic-subsidence curve for the Rancho #1 well (convex upward, see Fig. 5A) suggests that the mechanism of subsi- dence was flexural. This is supported by Schneider et al.’s (1996) structural and stratigraphic analyses. The compression was probably in response to oblique convergence between the Pacific and North American plates (En- gebretson et al., 1985; Luyendyk, 1991), as major activity was transferred from the San Gabriel to the southern San Andreas fault. The timing of the tectonic events described above (16 Ma, 12 Ma(?), 6 Ma; Fig. 6) corresponds well with the times of microplate capture reported by Nicholson et al. (1994). They suggested that the “capture” of partially subducted Farallon microplates by the Pacific plate and subsequent basal drag on the overlying North American plate along low-angle detachment faults resulted in rotation of the Transverse Ranges and inland migration of the transform boundary (Nicholson et al., 1994). The completion of indi- vidual capture events corresponds well with initiation of subsidence events, as documented in the present study (Fig. 6). Provenance data from this study indicate that along the San Gabriel fault, displacement of 10 km is too small and displacement of 60Ð70 km is con- sistent with palinspastic reconstruction of the source areas. Petrologic and Figure 8. Paleogeographic block diagram of northern Los Angeles compositional data from the Modelo Formation in the Santa Monica Moun- and eastern Ventura basins during deposition of middle member of tains suggest that the sandstones were derived from rocks with abundant Modelo Formation. TA—Topanga anticline; SGF—San Gabriel fault; Na-rich plagioclase. Possible source rocks can be found in the central and SL—sea level; GPH—Griffith Park high. See text for discussion. eastern San Gabriel Mountains (Sullwold, 1960; Ehlig, 1981). It is signifi- cant that Santa Monica Mountains Modelo Formation sandstone has almost no Ca-plagioclase. This suggests that none of the Modelo Formation sand- stone was derived from the anorthosite body in the western San Gabriel nitude and mechanism(s) of basin subsidence; the timing and amount of dis- Mountains. A minimum displacement of 50 km (the amount of displace- placement on strike-slip faults; locations and ages of paleohighs (and lows) ment required to get the anorthosite body past the Simi uplift; Fig. 1) is that affected sedimentation; and identification of major source terranes and therefore required on the San Gabriel fault. Less offset would have allowed sediment dispersal systems (fan deltas and submarine fans) which con- sediments derived from the anorthosite body in the western San Gabriel tributed sediment to the Los Angeles basin. Mountains to contribute to the Tarzana Fan (Sullwold, 1960; Ehlig, 1981). The provenance, sedimentologic, and subsidence data presented in this Petrologic and compositional data from the Modelo Formation in the east- paper provide constraints on various aspects of paleotectonic and paleogeo- ern Ventura basin indicate that the anorthosite body contributed significant graphic reconstructions for the Los Angeles basin area. Figure 6 is a com- Ca-rich plagioclase to that basin during late Miocene time. parison of timing of fault movements, block rotations, microplate capture, Our geologic and paleotectonic map for late Miocene time (Fig. 7) is and subsidence in southern California and the Los Angeles basin. Subsi- based on fault displacements from May and Walker (1989) and assumes dence data from the Los Angeles basin (Fig. 5, AÐE) suggest that rapid sub- 60 km of net displacement on the San Gabriel fault. The gaps (filled with sidence began in the area at approximately 16 Ma. This is consistent with vertical lines) within the San Gabriel Mountains imply that significant tec- paleomagnetic data (Hornafius et al., 1986), which indicate that rapid rota- tonic shortening has occurred in the southeastern San Gabriel Mountains tions began in the San Gabriel block and the western Transverse Ranges since 12 Ma. The direct evidence for shortening is either unrecognized or about 16 Ma and slowed at 12Ð11 Ma. Luyendyk (1991) suggested that the destroyed by uplift and convergence along the Sierra Madre fault (P. Ehlig,
896 Geological Society of America Bulletin, July 1997
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 SUBSIDENCE ANALYSIS OF THE LOS ANGELES BASIN
1995, personal commun.). This is consistent with the reconstruction of Cri- tonic and paleogeographic reconstructions for southern California during telli et al. (1995), who suggested that significant shortening and uplift are middle to late Miocene time. required in the eastern San Gabriel Mountains to account for the volume of Furthermore, we think that this study illustrates the complex polyphase sediment in the Puente Hills area (see Fig. 1). tectonic evolution of the Los Angeles basin. The transrotational (16Ð12 Ma), transtensional (12Ð6 Ma), and transpressional (approximately 6Ð0 Ma) Los Angeles Basin Paleogeography phases of tectonism are only now being recognized in one of the best studied and most complex basins in the world. This serves to emphasize the need for Our late Miocene paleogeographic reconstruction of the northern Los detailed sedimentologic, petrologic, and structural studies in other strike-slip Angeles and eastern Ventura basins (Fig. 8) includes four main submarine- basins, which commonly have polyphase histories. Our results provide im- fan systems. Three were derived from the San Gabriel Mountains, a signif- portant constraints on the timing and character of deformation in southern icant topographic high during late Miocene time (Crowell, 1982; Stitt, California, as well as an example for future comparable studies of other 1986). The other system was derived from the Simi uplift, which separated strike-slip basins. the Los Angeles and Ventura basins (Nagle and Parker, 1971; Yeats, 1987); the Griffith Park high segmented the Los Angeles basin (Rumelhart and In- ACKNOWLEDGMENTS gersoll, 1994; Critelli et al., 1995). The Piru fan was deposited in the eastern Ventura basin during late Mio- Much of this paper could not have been written without the generosity of cene time (Dibblee, 1989). The fan received coarse detritus from the San Gregg Blake and Unocal Corporation for the use of their well data and fi- Gabriel Mountains, including a high percentage of Ca-plagioclase from the nancial support. Ingersoll thanks the Committee on Research of the Acade- anorthosite complex. Sedimentation was both nonmarine (fan delta) and mic Senate of the University of California, Los Angeles, for financial sup- marine (Stitt, 1986). port. We thank Mike Campbell, Salvatore Critelli, Jon Davidson, Jeff The Puente fan (Puente Formation) accumulated in the Los Angeles basin Geslin, Steve Graham, Theresa Heirshberg, Jim Ingle, Connie Mongold, and was derived from the northeast (Dibblee, 1989). Critelli et al. (1995) sug- and Ted Reed for helpful and interesting discussions and comments. We gested that the formation represents an unroofing sequence of volcanic rocks thank Gary Axen, Bill Dickinson, Becky Dorsey and Paul Heller for ex- and crystalline basement from the southeastern San Gabriel Mountains. tremely helpful comments during the revision process. We also thank Kim- The Tarzana fan (Sullwold, 1960) entered the northern Los Angeles basin berly Holland for her support and talents as a field assistant. from the north. Both paleocurrent and isopach data suggest that the fan head was north of the Santa Monica Mountains on the northeastern edge of the REFERENCES CITED San Fernando Valley (Figs. 7 and 8; Sullwold, 1960; Nagle and Parker, 1971). Paleobathymetric data from the Santa Monica Mountains indicate Angevine, C. L., Heller, P. L., and Paola, C., 1990, Quantitative sedimentary basin mod- eling: American Association of Petroleum Geologists Short Course Notes, that the basin floor was middle to upper bathyal in depth throughout late p. 1Ð133. Miocene time (Fig. 5; M. Cotton, Unocal, 1992, personal commun.). Lat- Atwater, T., 1970, Implications of plate tectonics for the tectonic evolution of western eral variations in clast types of the lower member of the Modelo Formation North America: Geological Society of America Bulletin, v. 81, p. 3513Ð3536. suggest that a submarine topographic high (Griffith Park high) existed at the Atwater, T., 1989, Plate tectonic history of the northeast Pacific and western North Amer- ica, in Winterer, E. L., Hussong, D. M., and Decker, R. W., eds., The eastern Pacific eastern end of the Santa Monica Mountains. This high probably served to Ocean and Hawaii: Geological Society of America, Geology of North America, funnel the submarine fan to the west and separated it from the Puente fan to v. N, p. 21Ð72. the east. This high was also a significant source of coarse detritus within the Biddle, K. T., 1991, The Los Angeles basin: An overview, in Biddle, K. T., ed., Active margin basins: American Association of Petroleum Geologists Memoir 52, p. 5Ð24. lower member of the Modelo Formation. West of the Tarzana fan, the west- Blake, G. H., 1991, Review of the Neogene biostratigraphy and stratigraphy of the Los ern Santa Monica Mountains uplift (Nagle and Parker, 1971; Topanga anti- Angeles basin and implications for basin evolution, in Biddle, K. T., ed., Active cline?, in Fig. 8) further segmented the Los Angeles basin during deposition margin basins: American Association of Petroleum Geologists Memoir 52, p. 135Ð184. of the upper Topanga and lower Modelo Formation (Simi subbasin; Rumel- Blake, M. C., Jr., Campbell, R. H., Dibble, T. W. Jr., and five others, 1978, Neogene basin hart, 1994b). South of the Santa Monica Mountains, the submarine fans formation in relation to plate-tectonic evolution of San Andreas fault system, Cali- probably merged on the lower-bathyal floor of the central Los Angeles basin fornia: American Association of Petroleum Geologists Bulletin, v. 62, p. 344Ð372. (Wright, 1991). Bohannon, R. G., and Parsons, T., 1995, Tectonic implications of post-30 Ma Pacific and North American relative plate motions: Geological Society of America Bulletin, v. 107, p. 937Ð959. CONCLUSIONS Bond, G. C., and Kominz, M. A., 1984, Construction of tectonic subsidence curves for the early Paleozoic miogeocline, southern California: Geological Society of Amer- ica Bulletin, v. 95, p. 155Ð173. On the basis of this study, it is clear that most of the Modelo Formation of Critelli, S., Rumelhart, P. E., and Ingersoll, R. V., 1995, Petrofacies and provenance of the eastern Santa Monica Mountains was deposited as a submarine fan the Puente Formation (middle to upper Miocene), Los Angeles basin, southern Cal- (Tarzana Fan), which had two distinct depositional histories. During the ifornia: Implications for rapid uplift and accumulation rates: Journal of Sedimen- early history, sediment was derived from local sources (such as the Griffith tary Research, v. A65, p. 656Ð667. Crouch, J. K., and Suppe, J., 1993, Late Cenozoic tectonic evolution of the Los Angeles Park high), including the rocks upon which the Modelo Formation was de- basin and inner California borderland: A model for core complex-like crustal ex- posited. This was followed by deposition of sediment derived from grano- tension: Geological Society of America Bulletin, v. 105, p. 1415Ð1434. diorite and/or tonalite from the east-central part of the San Gabriel Moun- Crowell, J. C., 1974, Sedimentation along the San Andreas fault, California, in Dott, R. H., Jr., and Shaver, R. H., eds., Modern and ancient geosynclinal sedimentation: So- tains. The absence of detrital input from Precambrian anorthosite in the ciety of Economic Paleontologists and Mineralogists Special Publication 19, western San Gabriel Mountains implies that the San Gabriel fault had ap- p. 292Ð303. proximately 50Ð60 km of displacement on it between 12 and 5 Ma. In con- Crowell, J. C., 1982, The tectonics of Ridge basin, southern California, in Crowell, J. C., and Link, M. H., eds., Geologic history of Ridge basin, southern California: Los trast, samples taken from the eastern Ventura basin indicate that they, in part, Angeles, California, Society of Economic Paleontologists and Mineralogists, Pa- were derived from the anorthosite complex in the western San Gabriel cific Section Book 22, p. 25Ð41. Mountains. The above information is important for constraining paleotec- Crowell, J. C., 1987, Late Cenozoic basins of onshore southern California: Complexity
Geological Society of America Bulletin, July 1997 897
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 RUMELHART AND INGERSOLL
is a hallmark of their tectonic history, in Ingersoll, R. V., and Ernst, W. G., eds., ern and central California: American Association of Petroleum Geologists Bulletin, Cenozoic basin development of coastal California: Englewood Cliffs, New Jersey, v. 67, p. 1125Ð1142. Prentice-Hall, Rubey Volume VI, p. 207Ð241. Ingersoll, R. V., 1988, Tectonics of sedimentary basins: Geological Society of America Dibblee, T. W., Jr., 1989, Miocene conglomerates and breccias in the northeastern Ven- Bulletin, v. 100, p. 1704Ð1719. tura basin and northern Los Angeles Basin and their tectonic significance, in Col- Ingersoll, R. V., 1990, Actualistic sandstone petrofacies: Discriminating modern and an- burn, I. P., Abbott, P. L., and Minch, J., eds., Conglomerates in basin analysis: Los cient source rocks: Geology, v. 18, p. 733Ð736. Angeles, California, Society of Economic Paleontologists and Mineralogists, Pa- Ingersoll, R. V., and Suczek, C. A., 1979, Petrology and provenance of Neogene sand cific Section Book 62, p. 207Ð226. from Nicobar and Bengal fans, DSDP Sites 211 and 218: Journal of Sedimentary Dibblee, T. W., Jr., 1991, Geologic map of the Beverly Hills and Van Nuys (south half) Petrology, v. 49, p. 1217Ð1228. quadrangles, Los Angeles County, California: Santa Barbara, California, Dibblee Ingersoll, R. V., Bullard, T. F., Ford, R. L., Grimm, J. P., Pickle, J. D., and Sares, S. W., Geological Foundation, scale 1:24 000. 1984, The effect of grain size on detrital modes: A test of the Gazzi-Dickinson Dibblee, T. W., Jr., 1992, Geologic map of the Topanga and Canoga Park (south half) point-counting method: Journal of Sedimentary Petrology, v. 54, p. 103Ð116. quadrangles, Los Angeles County, California: Santa Barbara, California, Dibblee Ingersoll, R. V., Kretchmer, A. G., and Valles, P. K., 1993, The effect of sampling scale Geological Foundation, scale 1:24 000. on actualistic sandstone petrofacies: Sedimentology, v. 40, p. 937Ð953. Dibblee, T. W., Jr., and Ehrenspeck, H. E., 1993, Field relations of Miocene volcanic and Ingle, J. C., Jr., 1980, Cenozoic paleobathymetry and depositional history of selected se- sedimentary rocks of the western Santa Monica Mountains, California, in Weigand, quences within the southern California continental borderland: Cushman Founda- P., Fritsche, A. E., and Davis, G. E., eds., Depositional and volcanic environments tion for Foraminiferal Research Special Publication 18, p. 163Ð195. of middle Tertiary rocks in the Santa Monica Mountains, southern California: Los Kew, W. S. W., 1924, Geology and oil resources of a part of Los Angeles and Ventura Angeles, California, Society for Sedimentary Geology (SEPM), Pacific Section counties: U.S. Geological Survey Bulletin 753, 202 p. Book 72, p. 75Ð93. Lane, C. L., 1987, Provenance and petrology of Tertiary arkoses of the Santa Monica Dickinson, W. R., 1970, Interpreting detrital modes of graywacke and arkose: Journal of Mountains, southern California: Implications for tectonic history [Ph.D. dissert.]: Sedimentary Petrology, v. 40, p. 695Ð707. Los Angeles, University of California, 252 p. Dickinson, W. R., 1976, Sedimentary basins developed during evolution of Mesozoic- Link, M. H., 1982, Petrography and chemistry of sedimentary rocks, Ridge Basin, south- Cenozoic arc-trench system in western North America: Canadian Journal of Earth ern California, in Crowell, J. C., and Link, M. H., eds., Geologic history of Ridge Sciences, v. 13, p. 1268Ð1287. basin, southern California: Los Angeles, California, Society of Economic Paleon- Dickinson, W. R., 1981, Plate tectonics and the continental margin of California, in tologists and Mineralogists, Pacific Section Book 22, p. 159Ð180. Ernst, W. G., ed., The geotectonic development of California: Englewood Cliffs, Luyendyk, B. P., 1991, A model for Neogene crustal rotations, transtension, and trans- New Jersey, Prentice-Hall, Rubey Volume I, p. 1Ð28. pression in southern California: Geological Society of America Bulletin, v. 103, Dickinson, W. R., 1985, Interpreting provenance relations from detrital modes of sand- p. 1528Ð1536. stones, in Zuffa, G. G., ed., Provenance of arenites: Dordrecht, Netherlands, D. Rei- Luyendyk, B. P., and Hornafius, J. S., 1987, Neogene crustal rotations, fault slip, and del, p. 333Ð361. basin development in southern California, in Ingersoll, R. V., and Ernst, W. G., eds., Dickinson, W. R., and eight others, 1983, Provenance of North American Phanerozoic Cenozoic basin development of coastal California (Rubey Volume VI): Englewood sandstones in relation to tectonic setting: Geological Society of America Bulletin, Cliffs, New Jersey, Prentice-Hall, p. 259Ð283. v. 94, p. 222Ð235. Marco Polo Software, Inc., 1988Ð1991, BasinWorks: Houston, Texas, Marco Polo Soft- Dickinson, W. R., and eight others, 1987, Geohistory analysis of rates of sediment accu- ware, 42 p. mulation and subsidence for selected California basins, in Ingersoll, R. V., and May, D. J., and Walker, N. W., 1989, Late Cretaceous juxtaposition of metamorphic ter- Ernst, W. G., eds., Cenozoic basin development of coastal California: Englewood ranes in the southeastern San Gabriel Mountains, California: Geological Society of Cliffs, New Jersey, Prentice-Hall, Rubey Volume VI, p. 2Ð23. America Bulletin, v. 101, p. 1246Ð1267. Durham, D. L., and Yerkes, R. F., 1964, Geology and oil resources of the eastern Puente Mayer, L., 1987, Subsidence analysis of the Los Angeles basin, in Ingersoll, R. V., and Hills area, southern California: U.S. Geological Survey Professional Paper 420-B, Ernst, W. G., eds., Cenozoic basin development of coastal California: Englewood 62 p. Cliffs, New Jersey, Prentice-Hall, Rubey Volume VI, p. 299Ð320. Ehlig, P. L., 1981, Origin and tectonic history of the basement terrane of the San Gabriel Mayer, L., 1991, Central Los Angeles basin: Subsidence and thermal implications for Mountains, central Transverse Ranges, in Ernst, W. G., ed., The geotectonic devel- tectonic evolution, in Biddle, K. T., ed., Active margin basins: American Associa- opment of California: Englewood Cliffs, New Jersey, Prentice-Hall, Rubey Volume tion of Petroleum Memoir 52, p. 185Ð195. I, p. 253Ð283. Nagle, H. E., and Parker, E. S., 1971, Future oil and gas potential of onshore Ventura Ehlig, P. L., and Crowell, J. C., 1982, Mendenhall gneiss and anorthosite-related rocks basin, California, in Future petroleum provinces of the United States: Their geol- bordering Ridge basin, southern California, in Crowell, J. C., and Link, M. H., eds., ogy and potential, Volume 1: American Association of Petroleum Geologists Mem- Geologic history of Ridge basin, southern California: Los Angeles, California, So- oir 15, p. 254Ð297. ciety of Economic Paleontologists and Mineralogists, Pacific Section Book 22, Nicholson, C., Sorlien, C. C., Atwater, T., Crowell, J. C., and Luyendyk, B. P., 1994, Mi- p. 199Ð202. croplate capture, rotation of the western Transverse Ranges, and initiation of the Eldridge, G. H., and Arnold, R., 1907, The Santa Clara valley, Puente Hills, and Los An- San Andreas transform as a low-angle fault system: Geology, v. 22, p. 491Ð495. geles oil districts, southern California: U.S. Geological Survey Bulletin 309, 266 p. Pisciotto, K. A., and Garrison, R. E., 1981, Lithofacies and depositional environments of Engebretson, D. C., Cox, A., and Gordon, R. G., 1985, Relative motions between oceanic the Monterey Formation, California, in Garrison, R. E., and Douglas, R. G., eds., and continental plates in the Pacific Basin: Geological Society of America Special Pa- The Monterey Formation and related siliceous rocks of California: Los Angeles, per 206, 59 p. California, Society of Economic Paleontologists and Mineralogists, Pacific Section Friedmann, S. J., and Burbank, D. W., 1995, Rift basins and supradetachment basins: In- Book 15, p. 97Ð122. tracontinental extensional end-members: Basin Research, v. 7, p. 109Ð127. Pitman, W. C., and Andrews, J. A., 1985, Subsidence and thermal history of small pull- Fritsche, E. A., 1993, Middle Tertiary stratigraphic terminology for the Santa Monica apart basins, in Biddle, K. T., et al., eds., Strike-slip deformation, basin formation, Mountains, southern California, in Weigand, P., Fritsche, A. E., and Davis, G. E., and sedimentation: Society of Economic Paleontologists and Mineralogists Special eds., Depositional and volcanic environments of middle Tertiary rocks in the Santa Publication 37, p. 45Ð49. Monica Mountains, southern California: Los Angeles, California, Society for Sed- Ridgeway, K. D., and DeCelles, P. G., 1993, Petrology of mid-Cenozoic strike-slip imentary Geology (SEPM), Pacific Section Book 72, p. 1Ð12. basins in an accretionary orogen, St. Elias Mountains, Yukon Territory, Canada, in Gazzi, P., 1966, Le arenarie del flysch sopracretaceo dell’Appennino modenese; corre- Johnsson, Mark J., and Basu, A., eds., Processes controlling the composition of lazioni con il flysch di Monghidoro: Mineralogica e Petrographica Acta, v. 12, clastic sediments: Geological Society of America Special Paper 284, p. 67Ð89. p. 69Ð97. Rumelhart, P. E., 1994a, Petrology and provenance of the Modelo Formation, Santa Graham, S. A., Ingersoll, R. V., and Dickinson, W. R., 1976, Common provenance for Monica Mountains, California: Implications for paleotectonic and paleogeographic lithic grains in Carboniferous sandstones from Ouachita Mountains and Black War- reconstructions [Master’s thesis]: Los Angeles, University of California, 165 p. rior basin: Journal of Sedimentary Petrology, v. 46, p. 620Ð632. Rumelhart, P. E., 1994b, Evidence for Los Angeles basin segmentation: Implications for Hoots, H. W., 1931, Geology of the eastern part of the Santa Monica Mountains, Los An- basin formation and evolution: Geological Society of America Abstracts with Pro- geles County, California: U.S. Geological Survey Professional Paper 165-C, grams, v. 26, no. 7, p. A-192. p. 83Ð134. Rumelhart, P. E., and Ingersoll, R. V., 1994, Petrology and provenance of the Modelo Hornafius, J. S., Luyendyk, B. P., Terres, R. R., and Kamerling, M. J., 1986, Timing and Formation, Santa Monica Mountains, southern California: Constrains on displace- extent of Neogene tectonic rotation in the western Transverse Ranges, California: ment along the San Gabriel fault: American Association of Petroleum Geologists Geological Society of America Bulletin, v. 97, p. 1476Ð1487. Bulletin, v. 78, p. 674. Ingersoll, R. V., 1978, Submarine fan facies of the Upper Cretaceous Great Valley se- Sawyer, D. S., Hsui, A. T., and Toksoz, M. N., 1987, Extension, subsidence and thermal quence, northern and central California: Sedimentary Geology, v. 21, p. 205Ð230. evolution of the Los Angeles basin: A two-dimensional model: Tectonophysics, Ingersoll, R. V., 1983, Petrofacies and provenance of late Mesozoic forearc basin, north- v. 133, p. 15Ð32.
898 Geological Society of America Bulletin, July 1997
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021 SUBSIDENCE ANALYSIS OF THE LOS ANGELES BASIN
Schneider, C. L., Hummon, C.,Yeats, R. S., and Huftile, G. L., 1996, Structural evolution Vedder, J. G., and Howell, D. G., 1976, Review of the distribution and tectonic implica- of the northern Los Angeles basin, California, based on growth strata: Tectonics, tions of Miocene debris from the Catalina Schist, California continental borderlands v. 15, p. 341Ð355. and adjacent coastal areas, in Howell, D. G., ed., Aspects of the geologic history of Steckler, M. S., and Watts, A. B., 1978, Subsidence of the Atlantic-type continental mar- the California continental borderland: American Association of Petroleum Geolo- gin off New York: Earth and Planetary Science Letters, v. 41, p. 1Ð13. gists, Pacific Section Miscellaneous Publication 24, p. 6Ð11. Stitt, L. T., 1986, Structural history of the San Gabriel fault and other Neogene structures Walker, R. G., 1975, Nested submarine-fan channels in the Capistrano Formation, San of the central Transverse Ranges, California, in Ehlig, P. H., ed., Neotectonics and Clemente, California: Geological Society of America Bulletin, v. 86, p. 915Ð924. faulting in southern California: Los Angeles, California, Geological Society of Wright, T. L., 1991, Structural geology and tectonic evolution of the Los Angeles basin, America Cordilleran Section, p. 43Ð102. California, in Biddle, K. T., ed., Active margin basins: American Association of Pe- Streckeisen, A. L., 1976, To each plutonic rock its proper name: Earth Science Reviews, troleum Geologists Memoir 52, p. 35Ð134. v. 12, p. 1Ð34. Yeats, R. S., 1987, Changing tectonic styles in Cenozoic basins of southern California, in Stuart, C. J., 1979, Lithofacies and origin of the San Onofre Breccia, coastal southern Cal- Ingersoll, R. V., and Ernst, W. G., eds., Cenozoic basin development of coastal Cal- ifornia, in Stuart, C. J., ed., A guidebook to Miocene lithofacies and depositional en- ifornia (Rubey Volume VI): Englewood Cliffs, New Jersey, Prentice-Hall, vironments, coastal southern California and north-western Baja California: Los An- p. 284Ð298. geles, California, Society of Economic Paleontologists and Mineralogists, Pacific Yeats, R. S., Huftile, G. J., and Stitt, L. T., 1994, Late Cenozoic tectonics of the east Ven- Section, p. 25Ð42. tura basin, Transverse Ranges, California: American Association of Petroleum Ge- Sullwold, H. H., 1958, The Tarzana fan, a deep submarine delta of late Miocene age, Los ologists Bulletin, v. 78, p. 1040Ð1074. Angeles County, California [Ph.D. dissert.]: Los Angeles, University of California, Yerkes, R. F., 1972, Geology and oil resources of the western Puente Hills area, southern 159 p. California: U.S. Geological Survey Professional Paper 420-C, p. 1Ð63. Sullwold, H. H., 1960, The Tarzana Fan, a deep submarine fan of late Miocene age, Los Yerkes, R. F., McCulloch, T. H., Schoellhamer, J. E., and Vedder, J. G., 1965, Geology of Angeles County, California: American Association of Petroleum Geologists Bul- the Los Angeles basin: An introduction: U.S. Geological Survey Professional Paper letin, v. 44, p. 433Ð457. 420-A, 57 p. Turcotte, D. L., and McAdoo, D. C., 1979, Thermal subsidence and petroleum genera- tion in the southwestern block of the Los Angeles basin, California: Journal of Geo- physical Research, v. 84, p. 3460Ð3464. Van Hinte, J. E., 1978, Geohistory analysis: Application of micropaleontology in explo- MANUSCRIPT RECEIVED BY THE SOCIETY DECEMBER 19, 1995 ration geology: American Association of Petroleum Geologists Bulletin, v. 62, REVISED MANUSCRIPT RECEIVED OCTOBER 15, 1996 p. 201Ð222. MANUSCRIPT ACCEPTED DECEMBER 11, 1996
Printed in U.S.A.
Geological Society of America Bulletin, July 1997 899
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/885/3382736/i0016-7606-109-7-885.pdf by guest on 29 September 2021