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Notice Concerning Copyright Restrictions NOTICE CONCERNING COPYRIGHT RESTRICTIONS This document may contain copyrighted materials. These materials have been made available for use in research, teaching, and private study, but may not be used for any commercial purpose. Users may not otherwise copy, reproduce, retransmit, distribute, publish, commercially exploit or otherwise transfer any material. The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specific conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. MID-TERTIARY CONGLOMERATES AND THEIR BEARING ON TRANSVERSE RANGE TECTONICS, SOUTHERN CALIFORNIA By Robert G. Bohannon, U.S. Geological Survey, Denver, Colo. 80225 ABSTRACT rocks studied are shown in figure 2. Basalt dated in the Plush Ranch Formation coarse redbeds characterize mid-Tertiary yields ages of 17.4a3.7 and 19.6al.1 m.y. continental sedimentary rocks in southern (million years ), in the Vasquez Formation California. They include the Simmler, 23.9aO.8 and 24.9f2.1 m.y., and in the Sespe, Plush Ranch, and Vasquez Formations, formation of Diligencia 22.4a2.9 m. y. and the formation of Diligencia, which are (Crowell, 1973 ). Although the dated rocks probably in part contemporaneous. These are not precisely the same age, the sed- units contain locally derived conglomerates imentary sections containing these dated that accumulated in several fault-bounded rocks possibly overlap in age and appear basins. These east-west trending basins to be part of a unique tectonic and sed- and associated uplift areas apparently imentary phase which may have developed crossed the present trace of the San in different places through time. Andreas and San Gabriel faults and were later offset by them. BAS IN DESCRIPTIONS INTRODUCTION Simmler Formation Mid-Tertiary continental rocks in the The Simmler Formation in the La Panza Transverse Ranges are characterized by Range ( fig. 1, no. 1 ) consists of coarse coarse redbeds, which mark an interruption conglomerate and minor arkose. Angular in the extensive marine deposition that clasts of arkose and rounded clasts of prevailed in much of southern California medium-grained biotite quartz monzonite, duridg the Tertiary Period. This phase of granodiorite and devitrified porphyritic tectonics and sedimentation occurred about felsites are the predominant clasts. the same time as, or just prior to, the in- Pebble imbrication suggests transport ception of Tertiary volcanism in southern from southwest to northeast. California and triple junction migration A thick section of Simmler occurs along the coast (Atwater, 1970 ), and just immediately northeast of the Nacimiento prior to the inferred initiation of strike- (Rinconada) fault; however, none occurs slip faulting on the San Andreas system. on its southwest side. This distribution In order to understand the tectonic and the paleocurrent indicators suggest framework and sedimentologic history of that the Simmler Formation was derived off basins in existence at that time, the an active scarp at or near the Nacimiento Simmler, Sespe, Plush Ranch, and Vasquez fault (Vedder and Brown, 1968 ); however, Formations,·and the formation of Diligencia clasts in the Simmler indicate a conglom- were studied in 10 localities ( fig. 1 ). eratic provenance. According to T. W. Special attention was given the conglom- Dibblee ( personal commun., 1974 ), nearby erate facies and their clast types, prov- rocks across the fault are nearly all enance, and paleocurrent features. Con- sandstone and shale, not conglomerate. glomerate analysis helped document basin This problem could be alleviated by assum- history and development; using this infor- ing that conglomerate once existed in the mation, individual basins were compared proposed source but was now eroded, or stratigraphically and chronologically. that strike slip occurred on the Nacimiento fault during or after AGE RELATIONS deposition of the Simmler Formation. In the northern Cuyama badlands (fig. Age control comes from fauna in under- 1, no. 3 ), coarse conglomerate of the lying and overlying strata and from po- Simmler Formation contains clasts of tassium-argon age determinations taken on medium-grained muscovite-biotite quartz basalt flows in three of the areas. The monzonite, banded muscovite-biotite general age relations of the mid-Tertiary gneiss, rare aegerine-hornblende- 75 CALIFORNIA DIVISION OF MINES AND GEOLOGY e 1 La Panza Range 6 Canton Canyon 9 Abel Mountain \)J 2 Caliente Range 7 Charlie Canyon + and r, fB 3 Cuyama Badlonds 8 Texos Conyon 14,4 1 Mount Pinos area 078» 4 Lockwood Valley 9 Vasquez Rocks 5 Upper Sespe Creek 10 Orocopia Mountains 0 BLUE 2 MountainFrazier *'6 ROCKFAULT--..3 &40 4 <t FAULT RE SierraRidgePelona BIG PINE 4S San Gabriel DSanta•-'MNEFAULT•TN 6,•,I 8 - . .· ...::... Mountains Barbara 14 40 4. * -4«"*Ii'* San Bernardino FAULT 0 k, N =7 0LOS ANGELES F4 0 » 0/ .. C 2 /0 90 0,0 Mecca Hills 0 ..... 0el - 10 44/ 42#40, 1'4'(t \Re'. e ..67»ts \ »40<P 60 KILOMETRES '40 01 1 <h Figute 1.--Index map showing the location of the 10 study areas in southein California. muscovite granite and, at a few localities, that supplied detritus to the Simmler dacite, oxyhornblende welded tuff, and Formation. The silicic volcanic clast flow-banded rhyolite. Most of the section suite may have been derived from the east has paleocurrent indicators that indicate across the San Andreas fault. south to north transport; however, the few In the eastern Caliente Range (fig. 1, localities that contain abundant silicic no. 2 ), the Simmler Formation consists of volcanic clasts have pebble imbrication arkose and siltstone with only minor Suggestive of east to west and southeast conglomerate like that in the Cuyama to northwest transport. This transport badlands. Current lineations on sand- data, and the fact that the Simmler fines stone beds are consistent with south to to the northwest suggest that its principal north and southeast to northwest current source was to the south or southeast. An flow. exposure of banded biotite gneiss, biotite granodiorite, and quartz monzonite occurs Sespe Formation under the Caliente Formation just to the south across the Blue Rock fault, south of On upper Sespe Creek (fig. 1, no. 5 ), which the Simmler Formation, underlying conglomerates of the Sespe Formation have Pattiway Formation, and overlying Vaqueros clasts of coarse-grained arkose, medium- Formation are missing. This area could grained muscovite-biotite quartz monzon- have been a highland of basement rocks ite, a variety of recrystallized dacites 76 CALIFORNIA DIVISION OF MINES AND GEOLOGY YEARS NORTH PACIFIC LOCALITY MW (X106) AMERICAN COAST ij LAND FORAMAGE U) MAMMALAGE 2 3 4 5 6 7 8 9 I0 CLARENDONIAN Mohnion Monterey t-.--*-.-Modelo Fm C. Luisian Monterey Formaton Caliente Formation Formaton •_ M nt Canyon Format on U BARSTOVIAN -EBIann I HEMINGFORDIAN Saucesian Plush1/ R ncon Shole UN 1Tick ConyonU Formation Formation Voqueros Formation Ranch of ARIKAREEAN Zemorrian Formation Vaqueros Format on Vasquez Formation Diligencia WHITNEYAN j O03: -30 ORELLAN Refugian Smmler Format on Sespe Formation CHADRONIAN .= 10 DUCHESNEAN Narizlon ColdwaterCozy Dell Ss:Sh UINTAN ·· ··· ' 11110WW i Ulatizion Sandstone 1 11 1.I036ra036Formation 3 BRIDGERIAN Juncal UN n -50 Penution UN Formation WASATCHIAN -:IC Son m CLARKFORKIAN Bulitian UN Francisquito / TIFFANIAN Ynezion Pottiwoy Formation i' :: ·· Formation :: :: : 2f -60- TORREJONIAN m PUERCAN Danian U.K. -70- 1 .:1:r--uN--1. :: I..... 9 Of Carmon,(1964). 2/ Of Johns,(1940). 2/ Of Crowell and Susuki,(1959). Figure 2.---Correlation chart showing the relative ages of studied sections and age ranges of dated basalt samples. Line pattern in series column indicates zone of controversy of series boundaries; stippled pattern indicates nondeposition or erosion. UN, unnamed rocks. and rhyodacites, rare anorthosite (plagio- amphibolite, banded augite-biotite clase AN25 ), and mafic volcanics. Pebble gneiss, biotite-hornblende syenite, imbrication shows clast transport from the pyroxene gabbro, quartz syenite, norite, north across the Big Pine and Pine Mountain and unmistakable 220-m.y.-old Lowe faults. It is possible that the crystal- Granodiorite of Miller, 1946 (a biotite line clasts were derived from the highland monzonite, syenite, and granodiorite in the Cuyama badlands area, and the that is commonly sheared and contains arkose from Eocene sandstone exposures to garnet and large potassium feldspar the north; however, neither area is known phenocrysts ). Pebble imbrication data to contain anorthosite or mafic volcanics. Suggest west to east transport from It is also possible that the Nacimiento across the San Gabriel fault. Outcrops (Rinconada) and Pine Mountain faults were of anorthosite and related rocks occur at one time continuous and that right in the western San Gabriel Mountains to strike-slip occurred on them (T. W. Dibblee, the east; however, the large size of personal
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