Evolution of a Miocene half-graben basin, Colorado River extensional corridor, southeastern California
CHRISTOPHER M. FEDO Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 JULIA M. G. MILLER Department of Geology, Vanderbilt University, Nashville, Tennessee 37235
ABSTRACT INTRODUCTION western United States (Fig. 1; Howard and John, 1987; Hileman and others, 1990). At least The
Geological Society of America Bulletin, v. 104, p. 481 493, 6 figs., April 1992.
481
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1987). This extreme extension led to the struc- cover; these problems limit, but do not prohibit, (Spencer and Turner, 1983; Spencer, 1985). tural juxtaposition of locally ductilely deformed detailed study. This paper considers three in- Sense-of-shear indicators in a well-exposed out- mid-crustal rocks (footwall) beneath brittlely de- terrelated objectives: (1) to interpret the pa- crop of the fault zone near Browns Camp (Fig. formed supracrustal rocks (hanging wall) in fea- leoenvironments of the sedimentary deposits, 2) suggest top-to-the-east transport of the upper tures known as metamorphic core complexes (2) to reconstruct original stratigraphic relation- plate. Also, upper-plate rocks within the region (Crittenden and others, 1980). ships for the deposits, despite structural com- uniformly dip to the west-southwest, which sup- Within the Colorado River extensional corri- plexities, and (3) to document the tectonic/ ports top-to-the-east transport (Spencer, 1985). dor, brittlely deformed hanging-wall rocks in- sedimentologic evolution of these deposits. Poor exposure makes finding and assessing the clude kilometer-thick sections of Miocene syntec- importance of numerous other faults in the area tonic terrigenous clastic rocks intermixed with GEOLOGIC SETTING OF difficult to impossible. Normal faults accommo- volcanic rocks that accumulated in numerous THE NORTHERN SACRAMENTO dating rotation of the upper plate must be pres- extension-related basins (Nielson and Beratan, MOUNTAINS ent as pointed out by Spencer (1985), but none 1990; Miller and John, 1988; Knoll, 1988; has been unequivocally located. Knoll and others, 1986). The stratigraphic suc- Structure cessions are important in that they preserve a Lithology dateable account of the Earth's surface response The Sacramento Mountains detachment fault to crustal stretching. Specifically, the volume and splays (referred to together as SMDF) are Lower Plate. Very little is known about the and distribution of sedimentary facies relate di- the predominant structural features in the area. crystalline basement rocks that form the domed rectly to detachment fault (or boundary fault) They form part of an evolving, regional, east- core of the northwestern Sacramento Moun- geometry (Morley, 1989), and the sections pre- dipping detachment zone. John (1987) and tains. Spencer (1985) and Spencer and Turner serve information concerning paleoenviron- Nielson and Beratan (1990) correlated the (1983) mapped the basement near 1-40 as "Pre- ments, paleogeography, and paleoclimatology SMDF with detachment faults now exposed in cambrian undivided." Foster and others (1990) during extension. the Chemehuevi, Mohave, Whipple, Buckskin, dated hornblende and K-feldspar mineral sepa- This study focuses on discontinuous expo- and Rawhide Mountains, which emphasizes the rates from samples of the basement complex 40 39 sures of middle Miocene strata that crop out pervasive occurrence of detachment-related tec- using Ar/ Ar. They reported cooling ages over a 50-km2 area in the Flattop Mountain tonics in the Colorado River extensional corri- ranging from -14-88 Ma. Schweitzer (1991) region of the northern Sacramento Mountains, dor (Fig. 1). Near Flattop Mountain, the SMDF and Simpson and others (1991) described the southeastern California (Figs. 1 and 2). These divides the area into three plates: an autochtho- evolution of the crystalline footwall, which con- strata have not been critically examined until nous lower plate succeeded by two allochtho- sists of quartzofeldspathic gneiss intruded by now, perhaps because of locally severe structural nous sheets, referred to as the middle and upper granitoids (all variably mylonitized), in the problems combined with extensive Quaternary plates, each of which has distinct rock types Eagle Peak area (Fig. 2). Our reconnaissance,
Wl Miocene sedimentary and volcanic rocks
Precambrian — ?Mz XjLlì granitoids and gneisses
Low-angle normal V fault
High-angle normal fault
Location of measured section
0 km 3 L- Approximate Boundary Crestview Wash Basin Deposits
Figure 2. Simplified geologic map of the northern Sacramento Mountains, showing distribution of major rock types and structures. Filled circles show the locations of the measured sections discussed in text. BC, Browns Camp; CM, Cross Mountain; CW, Crestview Wash; DE, Devils Elbow; EP, Eagle Peak; FM, Flattop Mountain; FS, Flattop Mountain Springs; XC, Christmas Canyon. Geology after Spencer (1985).
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primarily near 1-40, reveals a heterogeneous Spencer and Turner, 1983, and Spencer, 1985, Facies Association 1: Boulder Breccia basement complex that consists of moderately to for true-scale cross sections). The basic distribu- and Conglomerate highly deformed coarse- and fine-grained quartz- tion of CWB deposits, however, is shown in ofeldspathic gneisses associated with coarse- and Figure 2. In general, the approximately north- Description. The first association occurs in fine-grained granitoids. east-trending outcrop area consists of strata that abundance in the vicinity of Flattop Mountain Middle Plate. Middle-plate strata are be- are found south of 1-40 and north of the approx- (Fig. 2) and is divisible into three variants. tween 200 and 300 m thick. Spencer and Turner imate latitude of Eagle Peak. Tertiary sedimen- Thickest accumulations (>300 m) are found in (1983) described basal beds that consist of tuffa- tary rocks in neighboring areas are discussed the southwest part of the basin, especially at ceous sandstone and conglomerate locally inter- below. Devils Elbow and Flattop Mountain Springs bedded with limestone, chert, siltstone, and tuff. The sedimentary and volcanic section near (Fig. 3). Above are thick felsic tuffs, which form the pre- the southern tip of the Dead Mountains and just Variant 1, which is the most abundant variant dominant lithology of the plate. One welded tuff north of Cross Mountain (Fig. 2) strongly re- of this association, consists predominantly of includes adularescent sanidine and sphene phe- sembles strata at Cross Mountain and probably dark red (green at Devils Elbow), matrix- nocrysts (D. C. Buesch, 1990, oral commun.) belongs to the CWB. The Tertiary sandstone supported, disorganized, boulder and cobble characteristic of the region-wide Peach Springs and conglomerate adjacent to a prominent re- breccia and conglomerate (Fig. 4A). Clasts are Tuff (Young and Brennan, 1974; Glazner and verse fault in the southwest Dead Mountains, dominated by ?Precambrian K-feldspar granite/ others, 1986). This tuff yielded an 18.5 ± 0.2 mapped by Spencer (1985), however, are not gneiss (99%) except in the Devils Elbow and Ma biotite K-Ar date (Spencer, 1985), which included in the CWB; these units contain clasts Crestview Wash sections where the conglomer- correlates well with the accepted Peach Springs probably derived from the CWB (sandstones ate is polymictic, but still composed of nearly all age of 18.5 ± 0.2 Ma reported by Nielson and and basalt) and underlie basalt dated at 12.1 ± ?Precambrian basement; boulders of Tertiary others (1990). An alternating sequence of vol- 0.3 Ma (Spencer, 1985). The rocks mapped as basalt occur sparingly. A chaotic internal fabric caniclastic rocks and volcanic-lithic tuffs com- "upper plate C" by McClelland (1984) and stud- dominates the deposit, although intervals show- pletes the middle plate. ied by Leach (1985) in the Eagle Peak area ing very crude clast alignment are present. Upper Plate. The upper plate consists pri- share a similar stratigraphic position, gross li- Where interleaved with the sandstone and mud- marily of texturally immature to submature thology, and probable age with the CWB but stone of facies association 2, beds range from sedimentary and less abundant volcanic strata are not included here, because during the Mio- 1-2 m thick and display sharp and flat upper that dip to the west-southwest. The tilted sedi- cene, a highland that supplied enormous boul- and lower contacts (Fig. 4B). Framework- mentary strata form the focus of the rest of this ders of gneiss and tuff to the southwest margin of supported intervals associated with crude clast paper. Volcanic rocks crop out at two locales: the CWB probably separated the northern and alignment and imbrication occur in the middle (1) as part of the Crestview Wash measured central Sacramento Mountains. Also omitted of the Crestview Wash section (Fig. 3). Over section (Fig. 3) and (2) near the Cross Mountain from the CWB are the smaller areas of Tertiary about 60 m in the Crestview Wash succession, section (Fig. 2). Spencer (1985) dated the basalt strata north of 1-40 in the Sacramento Moun- this facies coarsens from pebble- to meter-sized in Crestview Wash at 14.6 ± 0.9 Ma (whole tains and the small patch of strata near the west- boulders and thickens gradationally out of red rock K-Ar). Both the Crestview Wash and, in ern part of the range, through which 1-40 passes sandstones (facies association 2) that lie below. particular, the Cross Mountain basalts show (Fig. 2). These rocks possess substantially differ- The most intriguing characteristic of the suc- considerable alteration in thin section. The tilted ent clast assemblages from strata of the CWB cession at Flattop Mountain Springs is the pres- strata are overlain by pale gray, south-, west-, and perhaps represent smaller basins that ence of thick gravity glide blocks, or enormous and east-dipping (average dip 25°) cobble con- formed in irregularities on the detachment sur- single clasts, that display crackle or jigsaw- glomerate, which crops out as vertical cliffs be- face (see Spencer, 1985, for a minimum relief puzzle brecciation (variant 2; see Yarnold and neath the nearly flat-lying andesite (Simpson contour map of the SMDF; Davis and Lister, Lombard, 1989). Three of the blocks here are and others, 1991) of Flattop Mountain dated at 1988; John, 1987). composed of Precambrian basement, whereas 14.6 ± 0.2 Ma (whole rock K-Ar; Spencer, the other is made of felsic tuff. The blocks range 1985). Locations of Sections in thickness from about 10 to 30 m. The base- ment blocks are interstratified with conglomer- THE CRESTVIEW WASH BASIN Six stratigraphic sections were measured from ate and so are allochthonous. The felsic tuff across the basin, none of which show a deposi- block could, however, be a primary pyroclastic Definition tional base or top (Fig. 3). Locations of the flow. The basal contact of the tuff is altered and measured sections are shown in Figure 2. Typi- difficult to interpret; it might represent baking of Sedimentological data presented below sug- cal exposure of the sections is in narrow wash the underlying matrix-rich conglomerate, or it gest that upper-plate strata belong to a basin that cuts separated by extensive cover, thus making could be a comminuted shear zone that resulted evolved independently from rocks of the middle strike correlation between sections difficult. We from the catastrophic deposition of the 10-m- plate. We here designate the upper-plate sedi- have grouped the rocks into three abruptly inter- thick coherent block. mentary and volcanic rocks in the Flattop fingering facies associations, which correspond Variant 3 includes several distinct zones and is Mountain area as components of the Crestview to different environmental settings within the well exhibited in the lower transition from clay- Wash Basin (CWB). The actual areal extent of basin. Multiple depositional processes may be stone to breccia at about 75 m in the Christmas the basin remains uncertain, as basin-bounding represented within a single facies association, Canyon section (Fig. 3). Undisturbed shale depositional contacts have not been located. and thus environment. Reliable paleoslope and shows progressive internal deformation toward Even approximate boundaries are difficult to paleocurrent indicators are rare in the CWB; the base of the highly irregular contact zone, show on a map given the intricate structural all paleocurrent measurements are shown in which is ~1 m thick. In the contact zone, juxtapositioning of the different plates (see Figure 3. decimeter-scale plastically deformed shale frag-
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 LEGEND Devil's Elbow Crestview Wash bedding 160 .oó o';® •
/ very thin 280
1 medium 140 ! thick 260 d^OOy^p. very thick oó| 120 boulder cobble 240 oo o 0 o 0 pebble •poo'. •.-.'.'. po* granule 100 sand IS-CSSi silt 220 clay ISïËMâ 80
lithology 200 •• claystone r^-rmudstone ¿rsittstone 60 ••':': sandstone sandstone and conglomerate conglomerate breccia tuff 180 14.6+0.9 Ma v matrix-rich sandstone matrix-rich conglomerate 40 ^p^opoT o o QO on matrix-rich breccia ^SS. limestone 160 p^OjOgjO.'-' V v Od'-O-oV-1 O.OV V Vvolcani c glide block basement glide block O.Ö.O.Ö -Jji3 tf 20
structures 111 « 111 cross bedding = planar stratification = crude horizontal stratification
(} inverse to normal grading = break in section ba-°0<>aic * • " K/ V V V \/ *
200 * Il " // ^ •k » u *> // 1 " H Browns Camp II U II 1 100 ^i^zPjQrorqi OZO' ¿W, ; -o'o: £
X ; 50" 100 3 * n W // , Figure 3. Graphic logs of the measured sections discussed in text. Columns arranged from southwest to northeast. Double-barbed arrows represent a single paleocurrent measurement. Single-barbed arrows represent faults; queried where faults are uncertain. The small section in Christmas Canyon possibly represents an interval that is structurally omitted from the left section along a ?branching fault. Sections drawn at different scales. Note that the sections show representative lithology and bed thickness through a given interval. Individual bed thickness cannot be read from scale. See text for further description. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 EVOLUTION OF HALF-GRABEN BASIN, CALIFORNIA 485 Christmas Canyon Cross Mountain In variant 3, all five zones of the distal part of Toj>'oz°: cco-o~_ a large rock avalanche deposit (Yarnold and I Lombard, 1989) are preserved. The zones are 300 listed here from bottom to top, with the facies o ¿.r- association 1 or 2 counterpart at this locality shown in parentheses: (1) undisturbed substrate o'Ö^Q-b-ojpj (tilted lacustrine shale), (2) disturbed substrate 250 •f ù O 9 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 Figure 4. A. Disorganized, matrix-supported, red boulder conglomerate and breccia near Flattop Mountain Springs. All clasts of ?Precam- brian gneiss. Boulder breccia and conglomerate facies, variant 1. Rock hammer for scale. B. Tabular-bedded green sandstones (sandstone and mudstone facies, variant 1) interlayered with a normally graded (coarse tail) matrix-supported cobble to boulder conglomerate at Devils Elbow. Rock hammer for scale. C. Partial Bouma sequence (Ta-Tc), Christmas Canyon. Sandstone and mudstone facies, variant 1. Scale bar equals 10 cm. D. Alternating mudstone and immature sandstone, Devils Elbow. Sandstone and mudstone facies, variant 2. Rock hammer for scale. E. Fining-upward cycles in variant 4 (sandstone and mudstone facies), Crestview Wash. Pebbly mudstone at far left is overlain by horizontally stratified sandstone, which is overlain by siltstone. Marked cycle is about 2 m thick. Rock hammer for scale. F. Variant 5 (sandstone and mudstone facies) red sandstones showing distinct, coarser-grained, prominent ribs. Crestview Wash area. Rock hammer for scale. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 EVOLUTION OF HALF-GRABEN BASIN, CALIFORNIA 487 Figure 4. (Continued) G. Crudely stratified pebbly sandstone, Cross Mountain. Mixed pebbly sandstone and cobble conglomerate facies. Rock hammer for scale. H. Red, matrix-supported cobble conglomerate and breccia, Cross Mountain. Mixed pebbly sandstone and cobble conglomerate facies. Rock hammer for scale. Aside from its presence in the Christmas Can- yon, Crestview Wash, and Devils Elbow sec- tions (Fig. 3), only two isolated exposures (<5 m thick) exist, both in the vicinity of Flattop Mountain. Four variants of association 2 are recognized. The first consists of green matrix-rich and matrix-poor sandstone. Bedding contacts are smooth and generally flat with bed thicknesses ranging from 2-50 cm (Fig. 4B). Beds are later- ally persistent over the width of an outcrop (to as much as -15 m). Two beds preserve well- formed symmetrical ripple marks; other sedi- mentary structures include tool marks, flame structures, normal grading, and rare partial consists of many laminations, some of which are rocks are locally incorporated into the pebbly Bouma sequences (Ta-Tc; Christmas Canyon broken and curled up at the edge similar to des- mudstone. Planar-stratified, medium-grained, only; Fig. 4C). Bioturbation occurs locally as iccated mud chips. A several-meter-thick section matrix-free sandstone with a flat basal contact, vertical tubes (1 mm diameter by 20-50 mm of correlative dark gray limestone that contains or trough and planar cross-stratified, fine- to long; ?plant roots) and as sinuous horizontal orange chert nodules crops out about 1 km east coarse-grained, matrix-poor sandstone (each traces (0.5-1 cm wide by 1-5 cm long). of Christmas Canyon. There, we discovered sev- 20-50 cm thick) with an irregular erosive con- Numerous centimeter-thick beds consist of well- eral small unidentifiable bone fragments pre- tact, rests sharply on the pebbly mudstone. Hori- stratified units composed of alternating pebble served in the chert. R. Reynolds (1989, written zontally laminated siltstone (several centimeters lenses and matrix-poor sandstone. commun.) identified Merychippus fragments to —1 m thick) caps the sequence. The second variant consists of green, and less recovered from the same area, which suggests a The fourth variant is characterized by dark commonly tan and maroon, laminated siltstone, late Hemingfordian land-mammal age (17-16 red low-angle cross-stratified sandstone and mudstone, massive claystone, and rare 3- to 10- Ma) for the deposit. crops out primarily in the Crestview Wash cm-thick air-fall tuffs interbedded locally with Variant 3 crops out only at the bottom of the measured section, where it overlies variant 3. sandstone, pebbly sandstone, and pebble con- Crestview Wash measured section. Tan sand- Two thin, isolated, fault-bounded sections are glomerate (Fig. 4D). Sand and pebble grains are stone and mudstone are the predominant litho- exposed in the Flattop Mountain area. This var- locally common to abundant in the claystones types present. Numerous 1- to 2-m-thick, iant gradually coarsens and thickens upward and mudstones. Low-angle cross-stratification thinning- and fining-upward depositional cycles over about 60 m of section from sandstone in- occurs in some of the tan siltstone layers. Several characterize this variant (Figs. 3 and 4E). Disor- terbedded with mudstone, to sandstone with wood fragments and wood impressions 2-3 cm ganized pebbly mudstone (31%—36% matrix), minor pebble lenses, to pebbly/cobbly sand- long are present in Christmas Canyon, as well as 20-100 cm thick, forms the base of the cycle. stone. The unit grades into boulder and cobble two thin (2 and 10 cm) pale gray micritic lime- The lower contact ranges from flat to irregular breccia and conglomerate (facies association 1) stone interbeds. The thicker limestone bed (erosive). Deformed clasts of the underlying of Crestview Wash. A single camel track was Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 488 FEDO AND MILLER High-gradient gravity-dominated alluvial fans Uplifted footwall f\\ Lacustrine-margin sand flat Reworked alluvial deposits Low-gradient fluvial-dominated alluvial fans Hanging-wall dip slope Association 1 Association 2 Association 3 Figure 5. Paleoenvironmental reconstruction of the Crestview Wash Basin. Details explained in text. Scales approximate. noted on the sole of a sandstone bed. Above the the importance of sediment gravity flows as a ate turbidites (therefore Bouma sequences), al- sandstone/mudstone intercalations, prominent primary depositional mechanism for sand-grade though we cannot classify lake deposits in the rib-forming elongate lenses of coarse-grained material in the lake. Local accumulations of CWB as "saline" considering the deficit of trough cross-stratified sandstone punctuate the limestone containing land-mammal bone frag- chemical sedimentation. dark red sandstones and give this variant a dis- ments and rare desiccation cracks (variant 2) Variant 2 reflects the quiet-water accumula- tinct appearance (Fig. 4F). On the south slope of suggest that the lake was shallow. Sediment tion of fine-grained particles and limited produc- Flattop Mountain, the outcrop consists of the gravity flows, including turbidites, can form in tion of lacustrine limestone (Fig. 5). The poorly typical red sandstone interbedded locally with shallow lakes. For example, K. Beratan (1991, sorted mudstones may represent the fine-grained gray limestone at a centimeter to decimeter personal commun.) recognized graded beds and tails of the sediment gravity flows that deposited scale. Abundant millimeter-scale, amorphous, partial Bouma sequences in association with variant 1 graded beds and partial Bouma se- micritic clots (interpreted as ?algal fragments) flamingo trackways, carbonates, and other quences (compare with Hubert and Hyde, and poorly to moderately preserved ooids that shallow-water indicators in the coevally evolv- 1982). Desiccation features in one of the lime- show tangential and radial growth fabric com- ing Whipple Mountains basins. Hubert and stone beds indicate at least temporary subaerial pose the framework of the limestone. Hyde (1982) recognized numerous graded beds exposure of lake sediments. Interpretation. The variety of processes rep- in their study of semiarid rift-valley sediments Variants 3 and 4 of the sandstone and mud- resented in this association indicates that deposi- from the Triassic of Nova Scotia. They attrib- stone association are interpreted as the products tion occurred in a lacustrine (variants 1, 2) and uted grading to the rapid deceleration of sheet of a subaerial lacustrine-margin sandflat (Fig. 5; lacustrine-margin setting (variants 3, 4; Fig. 5). flows at the alluvial-fan toe/playa-mudflat tran- Hardie and others, 1978; Hubert and Hyde, Variant 1 records the deposition of sand by trac- sition where ponding of the flows can occur. 1982; Mertz and Hubert, 1990). The fining- tion and turbidity currents and mass-flow proc- Hardie and others (1978, p. 21), in their discus- upward depositional cycles of variant 3 record esses within the lake. Graded beds (including sion of saline lake depositional systems, consid- the deceleration of flood flows emanating from rare partial Bouma sequences) are more abun- ered that during storm conditions, sheet floods nearby alluvial fans. The pebbly mudstone dant than are muddy sandstone and well enter "shallow standing lake water as a waning bases, interpreted as mudflows (Lowe, 1979), stratified, matrix-free sandstone beds, indicating turbid underflow." Such conditions may gener- represent initial sedimentation from flood-stage Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 EVOLUTION OF HALF-GRABEN BASIN, CALIFORNIA 489 conditions (compare Mertz and Hubert, 1990; sandstone and conglomerate and (2) matrix- low-gradient fan-toe region (Hardie and others, Heward, 1978). Traction currents follow pro- supported conglomerate. 1978; Nilsen, 1982). Although debris flows may ducing well-stratified sandstones that overlie the In the crudely stratified sandstone and con- form anywhere on a fan (see Hooke, 1967), they mudflows. The well-washed horizontally strati- glomerate (Fig. 4G), bed thicknesses range from are most prevalent in the proximal to medial fied units record upper plane-bed "sheet flood" 3-50 cm; however, many beds are poorly de- reaches of the fan (Nilsen, 1982). The associa- conditions, typical where the distal margin of the fined, with diffuse, irregular contacts. Clast size tion of stream- and debris-flow deposits suggests fan grades into the sandflat environment (Nilsen, varies from medium sand to large pebbles. Local that the depositional slope of these fans was 1982; Hardie and others, 1978). The trough and gradual pinching out of beds laterally over ~10 gently inclined to allow for fluvial sedimentation tabular-planar cross-bedded sandstones are most m resembles the geometry of paleochannels. to take place and was expansive enough for likely lower flow regime, channelized counter- Combined with the centimeter- and decimeter- proximal and mid-fan deposits to occupy large parts of the planar-stratified sandstones. Consid- scale bed thickness, this indicates that the chan- areas. The gently dipping hanging wall of an ering the erosive lower contact of the cross- nels were probably shallow and broad. Sedi- asymmetrical half-graben basin provides an ex- bedded sands, it is plausible that the sands mentary structures are rare, although parting tensive, low-gradient depositional surface upon represent reworking of the mudflow tops. Mud- lineation, a set of asymmetrical ripple marks, which such alluvial fans may develop (Fig. 5; flow reworking also resuspends fines, which and poorly defined large-scale (~1 m) trough Mack and Seager, 1990). Leeder and Gaw- then settle to generate the horizontally laminated cross-beds were observed (Fig. 3). thorpe (1987) described similar low-gradient siltstone that rests on the cross-bedded sand- Matrix-supported, cobble (local boulder) con- "alluvial cones" and small, high-gradient alluvial stones (petrographic information in Fedo, glomerate is interstratified with the crudely strat- fans (equivalent to facies association 1) for ex- 1990). ified sandstone and conglomerate. Bed thick- tensional continental basins with interior Variant 4 represents deposition of sand by nesses range from 20-150 cm, and top and drainage. fluvial traction currents at the distal to distal bottom bed contacts are smooth and sharp. The mid-fan region of an alluvial fan (Hardie and matrix-supported conglomerates most common- STRATIGRAPHIC RECONSTRUCTION others, 1978). The red sandstones and pebbly to ly occur as single beds; multiple (amalgamated) cobbly sandstones of variant 4 grade into beds may exist, but internal contacts are difficult Structural complexities obscure the strati- proximal-fan boulder conglomerate/breccia, to recognize. The clast assemblage ranges from graphic relationships between measured sec- and thus preserve a complete section from lacus- monolithologic to polylithologic, but ?Precam- tions in the CWB. Any attempt to organize the trine margin to the proximal part of a small brian basement clasts dominate all others. The stratigraphy must consider the following: (1) fa- alluvial fan (Fig. 3, Crestview Wash section; deposits commonly show little internal organi- cies associations show dramatic, abrupt transi- coarsening upward over ~60 m). The algal/ zation (Fig. 4H), although scattered occurrences tions both vertically and laterally; (2) the oolitic limestone may be of primary fluvial of inverse or inverse-to-normal grading are different facies associations primarily occupy origin (McGannon, 1975) or a lacustrine- preserved. geographically restricted areas (lacustrine depos- margin deposit (Swirydczuk and others, 1979). Interpretation. Crudely and locally cross- its and high-gradient alluvial fans interfinger and Interbedding on a centimeter to decimeter scale stratified sandstone and conglomerate in this as- occupy the southwest part of the basin, whereas with terrigenous clastic fluvial sediments may sociation were deposited by traction currents, low-gradient alluvial fans occupy the entire favor the first option; however, the fluvial sys- and their abundance indicates that fluvial sys- northeast part of the basin); (3) the strata are tem does lie directly above a lacustrine-margin tems operated, probably through flashy dis- tilted to the west-southwest at generally constant sandflat succession and, thus, could have formed charge, for a long time period. Matrix-supported dips across the basin; (4) CWB deposits rest on a at the lake margin. conglomerate beds are interpreted as debris detachment fault today, and most likely were flows (Fisher, 1971; Lowe, 1979). This combi- deposited against one; and (5) the Colorado Fades Association 3: Mixed Pebbly nation of processes strongly suggests an alluvial- River extensional corridor experienced substan- Sandstone and Cobble Conglomerate fan setting for facies association 3 (Nilsen, tial Miocene extension during which the upper 1982). Yet these fans differ markedly from those crust segmented into numerous half-graben ba- Description. This association is volumetri- of the boulder breccia and conglomerate associ- sins (see Lister and others, 1986; Wernicke, cally the most abundant association within the ation: (1) sand-grade deposits generated by trac- 1985; Nielson and Beratan, 1990; Lister and CWB, constituting the entire upper plate from tion currents are found in abundance only in the Davis, 1989). Cross Mountain to just north of Christmas Can- sandstone and cobble conglomerate association, Several alternative reconstructions might ac- yon, or about 50% of the present areal extent of (2) the sandstone and cobble conglomerate as- count for the above. First, the deposits could the CWB (Fig. 2). Thin stratigraphic sections of sociation contains no significant thickness of represent a single tilted block, thus making Cross this association are present in the Browns Camp, strata deposited by rock avalanches or gravity Mountain strata the oldest deposits in the basin Crestview Wash, and Christmas Canyon meas- slides (this suggests a low-gradient depositional and Browns Camp strata youngest. Second, the ured sections (Fig. 3). The strata are dark red slope for the association), and (3) maximum av- CWB deposits could have been distributed and show the greatest clast heterogeneity of any erage clast size in the sandstone and cobble con- through the operation of a migrating depocenter. facies association of the CWB. Probable Pre- glomerate association debris flows is smaller Third, the deposits represent lateral sampling cambrian basement clasts of different types are than maximum average clast size in the boulder across a nearly complete but extended basin ex- most abundant, but Tertiary sandstone, lime- breccia and conglomerate association debris posed in numerous fault blocks. stone, and volcanic clasts and rare ?Mesozoic flows (cobble versus boulder). Assuming that the CWB is a single tilted plutonic clasts are present. Two depositional Significant accumulations of stream deposits block necessitates that the strata represent >4 styles are recognized, each forming a subequal that occupy broad, shallow channels or aggrade km of vertical stratigraphic section. Elsewhere in fraction of the association: (1) crudely stratified on flat interchannel areas form primarily in the the Colorado River extensional corridor, basins Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 490 FEDO AND MILLER that persisted for nearly 10 m.y. accumulated -2 accommodate all five parameters outlined BASIN EVOLUTION km of strata (for example, Nielson and Beratan, above. Lateral organization of the measured sec- 1990). Best age constraints suggest that the tions necessitates that the facies show abrupt lat- Figure 6 depicts the polyphase history of the CWB actively collected detritus for 2.5-4 m.y. eral transitions. Interfingering of the three facies CWB shown in increments of major sedimento- (discussed below). It is very unlikely that the associations, which is expected if they are later- logic and tectonic significance. The sections are CWB accumulated more than twice as many ally transitional to each other, is not well devel- oriented northeast-southwest, which is roughly strata as did adjacent basins with comparable oped but can be demonstrated in the CWB (see parallel to tectonic transport of the upper plate. geologic histories, in less than half the time. Fig. 3). The presence of small, high-gradient Six major phases can be deduced from data Another problem with this scenario is that the alluvial fans that interfinger with lacustrine de- presented herein combined with that from pre- present-day vertical thickness of the upper plate posits in the southwest end of the basin and vious studies. The evolution presented below is (and thus CWB) is -300 m (Spencer, 1985). If extensive, low-gradient alluvial fans in the north- simplified and restricted to the development of 4 km of sediment was deposited, it had to be east end of the basin argues for strong basin the upper plate only. Because a complete basin tilted and then nearly completely eroded to asymmetry, which is typical of half-graben ba- can be defined within the upper plate, exactly leave only 300 m prior to eruption of the se- sins (Leeder and Gawthorpe, 1987). Other how strata of the CWB and of the middle plate quence capping Flattop Mountain lavas. The evidence favoring strong basin asymmetry for relate remains unresolved. lavas of Flattop Mountain are 14.6 ± 0.2 Ma the CWB includes the following. In a half- (Spencer, 1985), which is within error of the age graben model, footwall-derived alluvial fans Phase A: Basin Opening of the dipping basalt exposed in the Crestview should prograde over basin depocenter deposits Wash section (14.6 ± 0.9 Ma; Spencer, 1985; (in this case, lacustrine) when tectonism dimin- Phase A represents the opening of the CWB. Fig. 3). This poses another problem. Given a ishes (Leeder and Gawthorpe, 1987; Blair and The stratigraphic reconstruction discussed above maximum average accumulation rate of 0.5 m Bilodeau, 1988; Mack and Seager, 1990). permits the interpretation that the CWB opened _1 ka for rift basins (Schwab, 1976), about 8 Within the CWB, the boulder breccia and along the SMDF, which dipped east at a low m.y. is needed to collect the 2 km of sediment conglomerate association alluvial fans do pro- angle (Spencer, 1985). The timing of opening that would overlie, and 2 km that would under- grade over lacustrine deposits (Fig. 3, Crestview and nature of initial sedimentary deposits are lie, the dipping basalt. Such a circumstance is Wash section). Additionally, lacustrine deposits, poorly constrained, as a basal depositional con- irreconcilable with documented age constraints which form over the locus of maximum subsid- tact has not been located. Several clasts of prob- for the CWB. ence (Leeder and Gawthorpe, 1987; Blair and able Peach Springs Tuff occur in CWB deposits. Bilodeau, 1988), are confined to the southwest Very thick sedimentary successions may ac- Thus the sedimentary succession must be older end of the CWB and intimately interfinger with cumulate in small, shallow (relative to strati- than 14.6 ± 0.2 Ma (flat-lying capping lavas) the small, high-gradient alluvial fans of associa- graphic thickness) basins when the depocenter and younger than 18.5 ± 0.2 Ma (probable tion 1, which are interpreted to have been de- of the basin migrates in response to syndeposi- Peach Springs Tuff equivalent in middle plate). rived from uplifted basement. tional tectonic transport of the basin fill. The Merychippus fragments found in the lacustrine Miocene Ridge Basin in southern California Basin asymmetry, uniform dips in the upper sediments suggest a 16-17 Ma age for the CWB. (Crowell, 1982) and the Devonian Hornelen plate, and sense-of-shear indicators in SMDF These radiometric ages and land-mammal fossils Basin in Norway (Steel and others, 1977) are fault gouge indicate that the CWB opened to the suggest that major extensional events occurred classic strike-slip basin examples. Because the east-northeast. Morley's (1989) recent study of between -16 and 18.5 Ma. depocenter migrates in the direction of transport synrift basin fill in East Africa reveals that basins with time, lacustrine deposits, if present, should bounded by low-angle faults are shallow owing Phase B: Basin Fill be areally extensive in that direction (approxi- to the predominance of horizontal over vertical mately northeast for the CWB). Depocentral translation; are dominated by coarse clastic de- Sedimentary rocks of the CWB filled the dep- deposits are limited in extent and confined to the tritus; contain restricted, short-lived lakes; and ositional trough generated by extension (Fig. southwest end of the CWB. This appears to re- may be associated with locally voluminous vol- 6B). Accumulation occurred during a time of ject the migrating depocenter hypothesis. Addi- canic rocks. Deposits of the CWB possess all relative tectonic quiescence. The lack of angular tionally, for basins bounded by detachment these characteristics, which suggests that the unconformities or fanning of dips strongly sug- faults, significant (kilometers) syndepositional SMDF moved at a low angle (^30°) all during gests that major syndepositional extension did transport in the direction of extension generates CWB deposition. Facies associations today oc- not take place during basin filling. Postdeposi- angular unconformities within the basin fill cupy relative positions to one another similar to tional structural dismemberment of the CWB, and(or) up-section fanning of stratal tilts from those they did during deposition; specific sites however, may be extensive enough to mask sub- steep to gentle (Frost, 1979; Nielson and Bera- are simply farther apart. Nielson and Beratan tle unconformities. On the basis of present expo- tan, 1990). Neither of these can be demonstrated (1990) demonstrated that intact relative posi- sures, it appears that a large depositional trough in the CWB. tions were maintained following extension- existed prior to the main sedimentation events We favor a reconstruction that makes the dif- related block faulting between four adjacent that filled the basin. We recognize only one epi- ferent measured sections partial lateral equiva- basins within the Colorado River extensional sode of lacustrine deposition, which also sug- lents of each other. Abrupt lateral facies corridor. In sum, lateral equivalence of the gests a single basin-opening phase, because transitions and the lack of widespread volcanic measured sections makes the most sedimento- multiple opening events tend to generate "tec- units make exact correlations impossible. Lateral logical sense and fits recent models for exten- tonic cyclothems" (for example, Blair and Bilo- equivalence, however, provides the most sensi- sional basins (Morley, 1989; Leeder and Gaw- deau, 1988; Leeder and Gawthorpe, 1987). The ble sedimentologic model and can reconcile or thorpe, 1987; Blair and Bilodeau, 1988). presence of large rock-avalanche deposits and Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 EVOLUTION OF HALF-GRABEN BASIN, CALIFORNIA 491 SW ne gravity glide blocks, however, suggests that the area was seismically active during sedimenta- tion. Because numerous coeval basins within a 100-km radius of the CWB were opening and filling through crustal extension, a single large- magnitude earthquake in one basin might trigger catastrophic depositional events in adjacent areas. This helps to explain the presence of tec- tonically driven sedimentation features in the CWB. Phase C: Block Rotation As Spencer (1985) pointed out and the strati- graphic reconstruction suggests, numerous faults accommodating rotation of the upper-plate blocks in the Flattop Mountain area must exist, but poor outcrop exposures hamper locating them. Crustal stretching segmented the basin into numerous blocks, which rotated and caused west-southwest stratal tilts. The uniformity of dips suggests that the faults strike north- northwest, thus indicating an east-northeast ex- tension direction (Spencer, 1985). The faults along which the strata were tilted cannot be lis- tric because tilts between individual blocks do not progressively steepen in the direction of transport; instead, constancy of stratal tilts sug- gests that the structures bound a family of planar fault blocks (Fig. 6C; Wernicke and Burchfiel, 1982). Phase D: Deposition of Perched Gravels A new depositional trough, or interconnected troughs, formed during phase C tilting, which adjusted local base level and caused renewed deposition. The result was the accumulation of <50 m of coarse conglomerate on top of the tilted red beds. Clasts in these "perched gravels" are the same as those found in the west- southwest-tilted deposits. Because the tilted strata are a probable source of the gravels, the lack of sedimentary rock clasts in the perched gravels could be due to the lack of induration of the west-southwest-dipping beds. Exposures of the gravels are limited to the bottom part of some vertical cliffs capped by overlying basalts. An angular unconformity between dipping red t>£ Facies Association 1 Facies Association 2 §°% Perched Gravels — Oo beds (CWB deposits) and the perched gravels is not visible in the field. Strata tilted at 35°-45°, however, strike into the topographically higher, oo°-'o Facles Association 3 J~|~]~ Lavas of Flattop Mountain . • OO o -U-J- less steeply east-, west-, and south-dipping (av- erage dip 25°) gravels, thus revealing the uncon- Figure 6. Polyphase depositional and tectonic history of the Crestview Wash Basin. A-F formity (see Spencer and Turner, 1983, for map correspond with phases A-F discussed in text. Drawing is highly exaggerated for clarity. details). We interpret the dip angles and scat- A. Basin opening. B. Basin infilling. C. Block rotation. D. Deposition of perched gravels. tered dip directions of the perched gravels as E. Eruption of Flattop Mountain lavas. F. High-angle faulting and modern erosional level. evidence of block adjustment following tilting. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021 492 FEDO AND MILLER Phase E: Eruption of Flattop Mountain Lavas west-southwest and are exposed in several fault REFERENCES CITED blocks; in general, stratal tilts vary slightly, and Eruption of the lavas of Flattop Mountain at there is no evidence for unconformities in the Blair, T. C., and Bilodeau, W. L., 1988, Development of tectonic cyclothems in rift, pull-apart, and foreland basins: Sedimentary response to episodic 14.6 ± 0.2 Ma followed deposition of the west-southwest-tilted deposits, suggesting that uctonism: Geology, v. 16, p. 517-520. Bull, W. B., 1972, Recognition of alluvial-fan deposits in the stratigraphic perched gravels. These lavas dip at <5° to the the basin filled during a phase of relative tec- record, in Rigby, J. K., and Hamblin, W. K., eds.. Recognition of east and cap the entire Tertiary sequence. The tonic quiescence, which was followed by an epi- ancient sedimentary environments: Society of Economic Paleontologists and Mineralogists Special Publication 16, p. 63-83. original lateral extent and source of the andesite sode of block faulting. An angular unconformity Crittenden, M. D., Jr., Coney, P. J, and Davis, G. H„ eds., 1980, Cordilleran metamorphic core complexes: Geological Society of America Memoir is uncertain, as it crops out only as erosional occurs at present-day topographically high ele- 153, 490 p. remnants. vations in the area, where less steeply dipping 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, conglomerate overlies tilted strata of the basin. southern California: Bakerefield, California, Society of Economic Pa- leontologists and Mineralogists, Pacific Coast Section, p. 25-42. Phase F: High-Angle Faulting and Erosion These perched gravels represent deposition fol- Davis, G. A., and Lister, G. S., 1988, Detachment faulting in continental lowing block faulting of the main body of strata. extension; perspectives from the southwestern U.S. Cordillera: Geologi- cal Society of America Special Paper 218, p. 133-159. High-angle faulting that crosscuts the entire The entire sequence is capped by the nearly flat- Fedo, C. M., 1990, Sedimentology and evolution of a Miocene half-graben basin, Colorado River extensional corridor, southeastern California upper plate is the last major tectonic event in the lying lava flows of Flattop Mountain, dated at [M.S. thesis]: Nashville, Tennessee, Vanderbilt University, 86 p. 14.6 ± 0.2 Ma. Fisher, R. V., 1971, Features of coarse-grained, high-concentration fluids and region. At Flattop Mountain, about 100 m of their deposits: Journal of Sedimentary Petrology, v. 41, p. 916-927. vertical displacement is estimated from offset of Results from this study indicate (1) that cur- Foster, D. A., Harrison, T. M., and Miller, C. F., 1990, Mesozoic and Cenozoic thermal history of the eastern Mojave Desert, California, and adjacent Flattop Mountain lavas. As shown in Figure 6F, rent evolutionary models for half-graben basins western Arizona: Insights from ^Ar/^Ar geochronology: Journal of Geophysical Research, v. 95, p. 20005-20024. significant erosion has taken place since the Mio- are applicable to the Sacramento Mountains in Frost, E. G., 1979, Growth-fault character of Tertiary detachment faulting, cene; thus deep parts of the upper plate are particular, and probably to the Colorado River Whipple Mountains, southeastern Califronia, and Buckskin Mountains, western Arizona: Geological Society of America Abstracts with Pro- now exposed. extensional corridor in general; (2) that signifi- grams, v. 11, p. 429. Glazner, A. F„ Nielson, J. E„ Howard, K. A., and Miller, D. M„ 1986, cant thicknesses of sedimentary strata can ac- Correlation of the Peach Springs Tuff, a large-volume ignimbrite sheet SUMMARY AND CONCLUSIONS cumulate and be tilted during a very short time in California and Arizona: Geology, v. 14, p. 840-843. Hardie, L. A., Smoot, J. P., and Eugster, H. P., 1978, Saline lakes and their interval; and (3) that detachment faults do not deposits: A sedimentological approach, in Matter, A., and Tucker, M. E., eds., Modern and ancient lake sediments: International Associa- Discontinuous exposures of middle Miocene necessarily act as growth faults; that is, the sedi- tion of Sedimentologists Special Publication Number 2, p. 7-41. sedimentary rocks within the northern Sacra- mentary response to extension may be slow Heward, A. P., 1978, Alluvial fan sequence and megasequence models: With 2 examples from Westphalian D-Stephanian B coalfields, northern Spain, mento Mountains, southeastern California, oc- enough so that a small (at least 50 km by 300 in Miall, A. D., ed., Fluvial sedimentology: Canadian Society of Petro- 2 leum Geologists Memoir 5, p. 669-702. cupy a present-day outcrop area of 50 km . m deep) depositional trough can be generated Hileman, G. E., Miller, C. F„ and Knoll, M. A, 1990, Mid-Tertiary structural prior to major basin filling. evolution of the Old Woman Mountains area: Implications for crustal Deposits in this basin, here named the "Crest- extension across southeastern California: Journal of Geophysical Re- view Wash Basin" (CWB), constitute the upper search, v. 95, p. 581-597. Hooke, R. LeB., 1967, Processes on arid-region alluvial fans: Journal of Geol- plate of a three-plate detachment-fault system ogy, v. 75, p. 438-460. ACKNOWLEDGMENTS Howard, K. A., and John, B. E., 1987, Crustal extension along a rooted system and lie in structural juxtaposition against older, of imbricate low-angle faults: Colorado River extensional corridor, Cali- middle-plate volcanic rocks, and lower-plate fornia and Arizona, in Coward, M. P., Dewey, J. F., and Hancock, P. L., eds., Continental extensional tectonics: Geological Society of variably deformed pre-Tertiary crystalline base- This paper represents the results of M.S. thesis London Special Publication 28, p. 299-311. Hubert, J. F., and Hyde, M. G., 1982, Sheet-flow deposits of graded beds and ment; a basal depositional contact is not exposed research by CMF while at Vanderbilt Univer- mudstones on an alluvial sandflat-playa system: Upper Triassic in the study area or surrounding regions. Sedi- sity. CMF thanks the Geological Society of Blomidon redbeds, St. Mary's Bay, Nova Scotia: Sedimentology, v. 29, p. 457-474. mentary rocks of the CWB are divisible into America, the American Association of Petro- John, B. E., 1987, Geometry and evolution of a mid-crustal extensional fault system, Chemehuevi Mountains, southeastern California, in Coward, three facies associations inferred to represent leum Geologists, Sigma Xi, and the Department M. P., Dewey, J. F., and Hancock, P. L., eds., Continental extensional (1) small, high-gradient, gravity-dominated allu- of Geology at Vanderbilt University for financial tectonics: Geological Society of London Special Publication 28, p. 311-335. vial fans; (2) lacustrine and lacustrine-margin support. JMGM acknowledges the donors of the Reefer, D. K., 1984, Rock avalanches caused by earthquakes: Source character- istics: Science, v. 223, p. 1288-1290. conditions; and (3) large, low-gradient fluvial- Petroleum Research Fund, administered by the Knoll, M. A., 1988, Tertiary basin evolution, eastern Mojave Desert [Ph.D. dominated alluvial fens. American Chemical Society, for financial sup- dissert.]: El Paso, Texas, University of Texas, 189 p. Knoll, M. A., Miller, C. F., and James, W. C., 1986, Mid-Tertiary stratigraphic Lacustrine deposits (facies association 2) in- port. CMF extends special thanks to his field and structural evolution of the Piute Mountains basin and adjacent areas of the Old Woman Mountains region, southeastern California, in Niel- timately mixed with small, high-gradient alluvial assistants Rob Scott and Rob Lewis. The au- son, J. E., and Glazner, A. F., eds., Cenozoic structure, stratigraphy, and thors' understanding of the Colorado River ex- mineralization of the Mojave Desert: Geological Society of America, fans (facies association 1) at the southwest end Cordilleran Section, Guidebook and Volume, p. 43-50. of the basin and extensive low-gradient alluvial tensional corridor has greatly improved through Leach, B. R., 1985, Petrology and depositional history of Miocene nonmarine sedimentary rocks, central Sacramento Mountains, San Bernardino fans (facies association 3) at the northeast end discussions with Kathi Beratan, Dave Buesch, County, California [M.S. thesis]: Nashville, Tennessee, Vanderbilt Uni- Rick Hazlett, Keith Howard, Barbara John, versity, 161 p. permit the interpretation that the basin opened Leeder, M. R., and Gawthorpe, R. L., 1987, Sedimentary models for exten- as an asymmetric half graben; such a configura- Calvin Miller, Jane Nielson, and Jack Yarnold. sional tilt-block/half-graben basins, in Coward, M. P., Dewey, J. F., and Hancock, P. L., eds., Continental extensional tectonics: Geological tion is consistent with regional trends that show Early versions of the manuscript benefited from Society of London Special Publication 28, p. 139-152. reviews by Calvin Miller and Jack Yarnold. Lister, G. S., and Davis, G. A., 1989, The origin of metamorphic core com- northeast-directed extension along northeast- plexes and detachment faults formed during Tertiary continental exten- dipping detachment faults. Sedimentation began GSA referees Greg Mack, Cal James, and Mar- sion in the northern Colorado River region, U.S.A.: Journal of Structural Geology, v. 11, p. 65-94. prior to 14.6 ± 0.9 Ma, the age of an inter- tin Knoll added many comments that improved Lister, G. S., Etheridge, M. A., and Symonds, P. A., 1986, Detachment faulting the manuscript. The authors thank Caltech/ and the evolution of passive continental margins: Geology, v. 14, bedded lava flow in the section; upper-plate p. 246-250. rocks are younger than the probable Peach JPL, via Kathi Beratan, for providing a high- Lowe, D. R., 1979, Sediment gravity flows: Their classification and some problems of application to natural flows and deposits, in Doyle, L. 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R., 1979, The Pliocene Glenns tectonic implications, Whipple detachment system, Colorado River ex- Ferry oolite: Lake-margin carbonate deposition in the southwestern MANUSCRIPT RECEIVED BY THE SOCIETY AUGUST 15,1990 tensional corridor, California and Arizona: Journal of Geophysical Re- Snake River plain: Journal of Sedimentary Petrology, v. 49, REVISED MANUSCRIPT RECEIVED SEPTEMBER 20,1991 search, v. 95, p. 599-614. p. 995-1004. MANUSCRIPT ACCEPTED SEPTEMBER 27,1991 Printed in U.S.A. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/481/3381542/i0016-7606-104-4-481.pdf by guest on 23 September 2021