White Hall DRAFT
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U.S. DEPARTMENT OF THE INTERIOR OPEN-FILE REPORT U.S. GEOLOGICAL SURVEY OF 2010-1265 SEA LEVEL SEA CORRELATION OF MAP UNITS DESCRIPTION OF MAP UNITS WHITE HALL Qa QUATERNARY Alluvium (Holocene and Pleistocene?)—Clay, silt, and lesser sand with angular to QUADRANGLE 1000 Qa 1000 2000 18 FEET W. VA. 70 48 subrounded clasts, derived from local bedrock. Pebble-size (4–64 mm) fragments of 20 27 23 67 Unconformity sandstone, siltstone, quartzite and weathered shale are scattered throughout the deposits. W.VA. SM VA. 83 Dm 35 62 35 Winchester 21 34 In area underlain by the Martinsburg Formation, consists of light-olive-gray, yellowish- 17 72 57 78 B 62 \ 72 61 t TERTIARY ? gray, and pale-yellowish-orange, well-bedded to crudely bedded, planar-bedded clayey 27 84 _O 73 VIRGINIA 25 silt, with weathered shale fragments as much as an inch long. Thickness as much as 40 ft 75 25 Unconformity 30 Qa DSls 61 ANTICLINORIUM 30 ZONE 31 Terrace deposits (Tertiary?)—Rounded to subrounded, highly weathered cobbles, sand, MAP LOCATION Dm b t PERMIAN ? silt, and clay exposed along State Route 681 near the confluence of Isaacs Creek and Back PROVINCE Z_ Swbm Strasburg 70 30 FAULT Skr Creek 73 70 FORD St SD Dh Om SYNCLINORIUM 33 22 60 68 Breccia (Permian?)—Brecciated massive dolomite or dolomitized limestone; may be 42 Df b 28 82 Df silicified in places and contain black stringers or staining (Fe-Mn oxide?). Exposures Ojo Dfu 25 36 83 Df 29 CREEK occur in fields east of Frog Hollow and along the axis of the Welltown syncline FAULT PROVINCE 18 Dfl Dfu MOUNTAIN 16 18 Db BAILEY 31 _O BRANCH Dmch Dmc Dmch Dm Df Hampshire Formation (Upper Devonian)—Sandstone, mudstone, siltstone, and minor 19 Dh Dh shale. Sandstone, reddish-gray to brownish-gray, medium- to thick-bedded, in part mica- _O 18 Dm Dfl Dfl SD 30 ceous and (or) arkosic, commonly crossbedded, unfossiliferous. Mudstone, maroon red, 71 18 BACK Mount Pleasant syncline 32 weathers into small lumps. Siltstone and shale, reddish-brown to gray, exhibits strong Om 70 77 76 Db RIDGE 70 80 MEADOW B 37 \ cleavage. Exposed thickness of unit as much as 850 ft. Upper part of formation not SM 16 30 MOUNTAIN 17 Db 25 33 exposed in quadrangle. Lower contact placed at base of red-beds and at top of highest Z_ Probable unconformity WEST VIRGINIAVIRGINIA 66 70 80 Qa 78 72 81 Dmc DEVONIAN Harrisonburg 65 82 81 89 gray, fossiliferous sandstone and shale of the underlying Foreknobs Formation 78 90 34 Dm VALLEY FAULT 85 60 85 Dmch 81 83 05 Dmc SM 24 35 30 MASSANUTTEN Dmc 28 Foreknobs Formation (Upper Devonian)—Interbedded sandstone, siltstone, and minor 32 Dmch 24 Dm 88 Dfu shale; locally fossiliferous. The main unit (Df) contains coherent packages of thick- Om 30 42 24 75 16 Dmch bedded to massive sandstone which occur as two ridge-forming units that are mappable BLUE Mountain 18 42 BAILEY FORD ANTICLINORIUM 22 CREEK 22 51 75 22 55 Df throughout the study area. The upper ridge-forming unit (Dfu) consists of 5 to 6 masses of NORTH 15 15 70 Dm Dm 15 MEADOW BRANCH SYNCLINORIUM 16 Back Creek fault Dm thick, resistant interbedded sandstone, siltstone, and shale that form a prominent ridge in 22 DSls 14 80 the upper part of the formation; locally two or more masses form distinct ridges. The Qa 15 54 14 Dmn Dfl Om 85 66 SM 15 24 Db Swbm lower ridge-forming unit (Dfl) consists of 3 to 4 packages of thick-bedded to massive 21 North 15 85 20 70 Dmch Skr 16 43 22 resistant interbedded sandstone, siltstone, and shale which form a prominent ridge at the Om Unconformity BACK 19 St base of the formation. The interval (Df) between the two ridge-forming units consists of 10 47 36 thin- to medium-bedded sandstone, siltstone, and shale and typically occupies the drain- _O 12 DSls 65 15 Little North Mountain age area between the two ridges; commonly not well exposed. The lower contact with the GREAT 75 Ojo 47 62 58 Brallier Formation is gradational through about 300 ft and is mapped where an abrupt Z_ 85 Swbm 21 SILURIAN increase in fossiliferous sandstone beds greater than 6 in. occurs. Thickness about 1,700 ft Little 46 ZONE 23 18 60 72 _O 20 Skr SYNCLINE 50 Brallier Formation (Upper Devonian)—Interbedded shale, siltstone, and sandstone, 20 70 67 45 Db 17 35 dark-gray to greenish-gray, weathers light brownish-gray, sparsely fossiliferous. Grain FAULT 82 17 77 St FAULT 75 size increases irregularly upward in section; sandstone beds, 2 to 6 in. thick, become more Silurian through Mississippian rocks of the Valley and ANTICLINORIUM 70 73 SM 70 52 77 Ridge Province 16 42 abundant near top of formation. Shale that is thickly laminated with scattered siltstone 69 Qa Unconformity 74 SURFACE beds up to 3 in. thick makes up the bulk of the formation. The lower contact with the FAULT _O 80 80 74 DS Devonian and Silurian rocks of Massanutten Mountain 19 Om MOUNTAIN 77 Om underlying Mahantango Formation is a disconformity above a massive sandstone unit 87 Ojo 32 50 50 (Dmc) at the top of the Mahantango. A mappable contact is placed at the top of this RIDGE Oc Upper and Middle Ordovician Martinsburg PLEASANT 26 52 70 Om 87 57 45 sandstone. Thickness approximately 1,100 ft Formation On 35 MOUNTAIN 68 63 Om 32 34 On SM Cambrian through Middle Ordovician rocks, mainly MOUNTAIN Dfl 37 _O GREAT NORTH Oc 40 Op Mahantango Formation (Middle Devonian)—Mudstone, shale, siltstone, and minor 85 35 65 Dmc carbonate Oc PIE 26 SYNCLINE 30 45 Oc sandstone. Mudstone, dark-gray to olive-gray, hackly weathering, locally very fossilifer- SM Qa 29 52 23 Neoproterozoic and Lower Cambrian rocks Oc Z_ 22 Op ORDOVICIAN ous; bedding obscure, spheroidal weathering common. Sandstone (Dmc, equivalent to Df Df 52 On of the Blue Ridge Province 11 Dm Clearville Siltstone Member of Jolley, 1983), medium-gray, fine-grained, medium- to MOUNT NORTH B' _O FAULT 75 On thick-bedded, generally massive, locally fossiliferous; occurs as two units near top of 64 70 Dmc Unconformity Figure 1. -- General geologic map of the Great Valley Province in WELLTOWN Dfu Dmch formation separated by mudstone; total thickness as much as 380 ft. Chaneysville NORTH APPLE 10 85 Or northern Virginia showing the location of the White Hall 7.5-minute 60 Op Siltstone Member (Dmch) is predominantly massive darkgray siltstone and black 70 67 35 43 Apple Pie Ridge Fault Op quadrangle, and inset map of the White Hall quadrangle showing shaded Dfu 20 mudstone occurring in the lower part of the formation, locally fossiliferous, up to 850 ft LITTLE 10 72 77 _e relief and selected structural elements. Lithotectonic units on inset map: Om Or thick, grades into calcareous shale at base. Total thickness of entire formation ranges from WELLTOWN 62 70 41 Or MS, Mississippian through Silurian rocks of Valley and Ridge Province; 22 Df B’ 15 90 35 1,600 to 1,800 ft. Lower contact gradational; placed at base of olive-gray beds above Df Oc 28 _O, Cambrian and Ordovician rocks of the Great Valley Province to the Thrust fault -- teeth on upthrown block 55 45 62 underlying Marcellus Shale 1000 2000 FEET SEA LEVEL SEA \ 1000 70 83 Os east of Little North Mountain, bounded by the North Mountain fault 67 14 Strike-slip fault -- arrows indicate relative motion 40 35 zone. Major folds in the Devonian shales, siltstones, and minor 40 On 35 Marcellus Shale and Needmore Shale, undivided (Middle and Lower Devonian)— 39 44 45 O_c Dmn sandstones are also shown. Anticline -- arrow indicates direction of plunge 90 70 88 90 Op 80 50 Black shale, silty shale, calcareous shale, and minor limestone. Thickness as much as 800 40 63 25 Db 39 34 80 CAMBRIAN ft; however, units are not well exposed in the quadrangle due to faulting and colluvial Syncline -- arrow indicates direction of plunge 12 40 _e 38 cover. Descriptions below are based upon mapping conducted in adjacent quadrangles 60 40 33 Overturned anticline 47 74 56 20 22 Marcellus Shale (Middle Devonian)—Shale, black to dark-gray, highly fissile, with Overturned syncline Dfl DSls 38 46 EXPLANATION OF MAP SYMBOLS 45 63 75 localized beds or concretions of dark-gray, argillaceous limestone or calcareous shale. 84 Forms thin, platy chips and weathers dusky yellowish-gray in exposed outcrops. Base of Db 81 Bedrock contacts -- Dashed where approximately located; dotted where concealed A Or 90 70 Alluvial contacts -- Identity and existence certain, location inferred Marcellus is marked regionally by the Tioga Metabentonite; not seen in outcrops but may 90 Swbm 45 82 be present in covered intervals. Thickness up to 700 ft _e 80 83 13 Faults -- Dashed where approximately located, dotted where concealed 40 72 APPROX. STRATIGRAPHIC COLUMN 50 75 Needmore Shale (Middle and Lower Devonian)—Calcareous shale, dark-greenish-gray 45 30 49 THICKNESS 50 to olive-gray, and dark-gray fissile silty shale; locally fossiliferous. Thickness about 100 68 Thrust fault -- teeth on hanging wall FORMATION and MEMBER LITHOLOGY 25 30 Skr (in feet) EXPLANATION Period 75 Stage ft. Grades upward into the Marcellus Shale through a series of thin limestone beds. Base Fossils 25 53 ZONE b placed at top of coarse sandstone of underlying Oriskany Sandstone. Qa 75 St Strike-slip fault -- arrows indicate relative sense of movement Ojo 65 Alluvium and colluvium 0–40 ft 54 20 Regional unconformity 40 51 5 U Oriskany Sandstone, Helderberg Group, and Tonoloway Limestone, undivided 48 40 b Normal fault -- U, upthrown side; D, downthrown side SYNCLINE DSls Hampshire Formation Dmc 36 49 D (Lower Devonian and Upper Silurian)—Sandstone, limestone, and shale.