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Geologic Investigation of the Lincoln and Bluemont Virginia

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Geologic Investigation of the Lincoln and Bluemont Virginia COMMONWEALTH OF VIRGIN IA DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT DIVISION OF MINERAL RESOURCES GEOLOGIC INVESTIGATION OF THE LINCOLN AND BLUEMONT QUADRANGLES, VIRGINIA PIERRE E. PARKER REPORT OF INVESTIGATIONS \4 VIRGINTA DIVISION OF MINERAL RESOURCES James L. Colver Commissioner of Minerol Resources ond Stote Ceologist CHARLOTTESVILLE, VI RGI N IA r 968 COMMONWEALTH OF VIRGINIA DEPARTMENT OF CONSERVAT]ON AND ECONOMIC DEVELOPMENT DIVISION OF MINERAL RESOURCES GEOLOGIC INVESTIGATION OF THE LINCOLN AND BLUEMONT QUADRANGLES, VIRGINIA PIERRE E. PARKER REPORT OF INVESTIGATIONS 14 VIRGINIA DIVISION OF MINERAL RESOURCES Jomes L. Colver Commissioner of Minerol Resources ond Stote Ceologist CHARLOTTESVI LLE, VI RGi N IA 1968 ConrvoNweeLTH or Vrncrrre DepenruBNr on Puncnasrs aNn Suppr-r RrcnltoNo 1968 DEPARTMENT OF CONSERVATION AND ECONOMIC DEVELOPMENT Richmond, Virginia Ment'tN M. SursnnrtNo, Director Cnenr-Bs A. CnntsropHERSEN, Deputy D'irector A. S. Recser, JR., Executiae Assistant BOARD Cenrrsr-B H. HururBrsrNr, Williamsburg' Chairrnan ANonrw A. Fenrev, Danville, Yice-Chairman Joe P. Grus, Roanoke Arr-en M. HBvu'ant, NewPort News L. SreNrBv Hoocns, Virginia Beach Cr-euoo A. Jnssun, Jn., Charlottesville W. MennN Jonxsou, Lynchburg Wrr-rrenn H. Kruc, Burkeville Genr,eNo E. Moss, Chase CitY EnNpsr L. Sl-nn, Grundy JoHN S. TuonNrox, CulPePer Ancnrc L. W-ENxrcH, Hopewell PUBLISHER'S NOTE This will acknowledge the good work of one of Loudoun coun- ty's public spirited citizens. pierre E. parker, a recognized "with professional geologist, spent many hours hecoming acquainted tte geologic envrronment of his county and prepared this map and manusiript on his own time and without remuneration. He was most Eracio'us in supplying these materials to the Division of Mineral Resorirces. This study is a significant contribution to the knowledge and understand_ ing of the geologic history of northern Virginia. _J.L.C. CONTENTS Peco Abstract .......""""'i"':""' 1 Introduction 1 Rocks in the area .. 3 5 Precambrian rocks . , Marshall Formation ) Cambrian or Precambrian rocks. 7 Swift Run Formation' Catoctin Formation t3 Cambrian rocks 15 Weverton Formation 15 Hampton (Harpers) Formation. "''"' 15 Erwin (Antietam) Formation 16 t6 Triassic rocks . Structural geology t7 Geologic history 18 Economic geology 20 2l References 22 Index . ILLUSTRATIONS Pr,erp Pacn 1. Geologic map of the Lincoln and Bluemonr quadrangles, Virginia . .In pocket Frcunp l. Index map showing locations of Lincoln and Bluemont quadrangles 2 Marshall 2. gneiss that has marked schistosiry and lineation.... + 3. Felsite dike in metabasalt of the Catoctin Formation. 5 4. Marshall gneiss that has pronounced lineation 6 5. Marshall Formation with well-developed rineation in gneiss. 6 Boulder 6. beds in the Swift Run Formation. .. 8 Boulder 7. beds in the Swift Run Formation. .. 8 8. Platy-bedded, fine-grained arkosic sandsrone in the Swift Run Formation .. g 9. Boulder bed in the Swift Run Formation. .. l0 10. Cross-bedding in a fine-grainecl arkosic sandstone in the Swift Run Formation. l0 ll. Phyllite in the Swift Run Formarion. il Limestone 12. in the Swift Run Formation. .. lz 13. Swift Run limestone... 13 1,1. Tuff of dacitic or andesitic composition in the Catoctin Formation lj GtsOLOGIC INTVESTIGAfiON OF THE LINCOLN AND BLUEMONT QUADRANGLES, VIRGIITIA By Prnnnn E. Pemrnl ABSTRACT Reconnaissance mapping of the Lincoln and Bluemont quld- rangles in Loudoun co"-nty in northern Virginia has clarified rela- tiorirhip, befween the Precambrian Marshall Formation, the overlying swift Run Formation, and metabasalt of the catoctin Formation which intruded fractures in the older formations and flowed over them. The catoctin is oveilain by the weverton Formation; no intervening Loudoun-type rocks #ere found. Hampton (Harpers) and Erwin of the (Antietamj'formations are Present in thi northwest Portion Blo"*or* quadrangle. Basali dikes of Triassic age occur throughout much of tlie area,-and Triassic sedimentary rocks are Present in the southeast part of the Lincoln quadrangle. Gneiss, alaskite, greenstone' and graywacke have been qlarried in the area for use as ioad metal. Limestone in the Swift Run Forma- tion was burned for the production of lime, and this material has also been worked for marble. INTRODUgfION The Lincoln and Bluemont quadrangles are located in northern Virginia in Loudoun counqy and are bounded by parallels 39"o0' and 3g""07'Jo" and meridians 7i"37'30" and 77"52'30" (Figure 1)' The quadrangles include small porrions of the Piedmont and valley and d1ag. ptysiographic provinces, but most of the area is within the Blue Rid[e prt"in-ce.^ The principal physiographic features are the Blue extension of Catoctin Rid[e ilountains ott ih" -isq " southward Mointain on the east, and a dissected intervening valley locally known ul- as Loudoun valley. All drainage flows into Goose Creek, which timatelv drai's eaitward into thi Potomac River. The greenstone and "weather al- gneiss to rich heavy soils that-.make excellent pasturage, Ihoogn in many places the land is too hilly for corn growing. Prosper- ous dairy, beef, and horse farms abound' l Paeonian Sprinp, VL 22129. Vrncrxre Drvrsron on Mrunner Rnsouncrs Figure 1. Index map showing locations of Lincoln and Bluemont quadrangles. geologic map of the Lincoln and Bluemont quadrangles (Plate 1) is the resuli of a reconnaissance areal studv made inter- mittendy from 1960 to 1966. Because of deep weatherin-g, there are few outcrops in the more level areas; however, along G-oose Creek and Beaverdam Creek there are some excellerrt ."poruir. The author felt it desirable to complete the generaliied phase of the mapping in order to provide a basis for mori detailed rtndi", in the wirt, few ex-ceptions, all the data on the map were based on fierd"t.". determina- tions. Numbers preceded by "Rl' in parentheses (R-3436) correspond to sample localities on_Pfa1e r. These samples are on file in the reposi- tory of the virginia Division of Minerai Resources where thev are available for examination. The author's work confirms the southward extension of the Blue Ridg_e-catoctin Mountain anticlinorium as interpreted by cloos (1951) and Nickelsen (1956). It also confirms conditions observed iarther south and described by Bloomer and Bloomer (1947), King (1950), and. others. The principal effort in this mapping p.ogr"ri was to -the clarify_the relationships within Loudoun valley^beiween Marshall, Swift Run, and Catoctin formations. Much of the confusion over the succession of formations in this area has arisen from the widespread occurrence of the catoctin Forma- tion, and its various Not only was ir intruded "rp-."!r. through the Marshall-gneiss and swift Run Formation, but also during subslquent stages of intense folding the feeder dikes and ramifyinf veins were broken up into isolated blocks and masses contained wiiniritrre Marshall and the Swift Run. where the basalt was the predominant rock, the Lrucor,n exo Br,unnronr QueoneNcr,us rela- hosr gneisses were isolated as blocks within the catoctin. These tions-of the basalt to the host rock, combined with the fact that along and zones of greatest movement the basalt was sheared into phyllites almost colpletely chloritized, make detailed rnapping a lecessity for determining the superposition of beds. Therefote, on the basis of a I- Valley- would preliminarf investigation, Portions of oudoun ]Ppear io be und"rlain by-the Catoctin Formation because all the conspicuous outcrops are greenstone. Yet a more detailed study of some of these though ,r"r, *ry rev-eal soils ccntaining tiny fragments of gneiss even or l""tt the most obvious rock' gr..trrorr" is the predominant iock," "i L, , *"r,", of mapping procedure, the Catoctin is indicated on the geologic -rp only'*nu"t" t"tg" ar-e1s oj metabasalt were clearly dis- Z.rrri6't.. It m"y b" doe to ,ori" of the foregoing reasons. that previous investigators of the Blue Ridge province the sericitic phyllites TtPP"q where of the Swift Run within ot oltt,Lp of the Catoctin. In this area, to Catoctin' no Loudoun Weverton quartzite is present "dj"..ttt Formation has been found between them' The author gratefully acknowledges the g-:"-t-".git interPretanon of the Potomac {iu., Gorge and i\Iar-yland's Middletown Valley-by He had ;. E. Cil his ,rrociit.s of Johns Hopkins "nd 9nt:tt:fty: able rhe srear advanrage during his first forays lnto the field of the Barbara Toan, l"ia?""" *orlk of Dr."Richard Nickelsen and l\4iss two of Dr."rrd Cloos' students. The Virginia Division of Mineral Re- generously provided thin sectio-ns and spectrographic analyses' sources ind and Dr. L. Calver, Commissioner 'of Mineral Resources James work' State Geologist, gave ample encouragement to. complete the to Many thanki go io the landowners who allowed the author access Mrs' Milton thei-J propertf frtti.otar mention is due General and Attol'd, #ho'p.r*itted numerousitraverses of their plirperty^by +: On and author and the use of their home for shelter and provisions' to to their land' there are exPosures of all of the rock types be"dj"."rra found in Loudoun ValleY. ROCKS IN THE AREA PnrcelrsnrlN Rocrs Marshall Formation Forma- The oldest recognizable unit in this region is the Marshall tion. There variations in texture and structurel however' "ra -"-tty granodiorite its general composition aPPears to approximate that of of and it is gneissic in ,t o"ior". Excelfent petrographie deseriptions 4 VrRGrNr;\ I)rvrsrox or i\,{rxrinar RnsourcBs this gneiss have been presented bv Nickelsen (1956, p.242-243). rt is characteristi.l]ll p"tpt-tvroblastic, with white feldipar phenocrysts having very difiuse outlines 0.5 inch or more in criameter. In the eastern half of Loudoun valley, considered to be the sl-rallor.ver portion of the basement, the feldspar phenccrysts do not exceed 0.5 inch in cross section (Figure 2).
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