F 1-ELD T R I P G U I 0 E 8 0 0 K - FOR PITTSBURGH GFOLOGICtL ~OCIETY PREPARED BY KAKTINS AND WILLIAM R. BRICE UNIVERSITY OF PITTSBURGH AT JOHNSTOWN JOHNSTOWN, PENNSYLVANIA MAY 4, 1985 I TABLE OF CONTENTS • iii List of Figures • • • • • • • • • 2 Introduction .. • • • • • • • • • • • • • • • 2 Regional Structure • • • • • • • 2 Geologic Summary • • • • • • • • • • • Devonian • • • • • • • • • • • • 5 6 :t'Iississippian • • • • • • • • • • • • • • • 10 Pennsylvanian • • • • • • • 16 References • • • • • • • • • • • Geistown Qu•d~angle Geologic, Map. • • • :. • • • • • • • 18 Vintondale Quadrangle Geologic Map • • • • • • • 19 Johnstown Quadrangle Geolbgic ~3p • • • • • 20 • 21 Road Log • • • • • • • • • • • 21 Stop 1 • • • • • • • • • • 22 Stop 2 • • • • • • • • • • • • • • • • • • 22 Stop 3 • • • • • • • • • • • • • • • • • • Stop 4 . • • • • • • • • • • • • • • • • • • .. • 23 Stop 5 . • • • • • • • • • • • • • • • • Stop 6 • • • • • • • • • • • • • • • • • • • • • 24 • 24 Stop 7 • • • • • • • • • • • • • • • • • Stop 8 • • • • • • • • • • • • • • • • • • • • • 25 ii LIST OF FIGURES Figure 1: Location Map • • • . • • • • • • • 1 Figure 2: Topographic map of Conemaugh Gorge • . • • • . • . • 3 Figure 3: Generalized stratigraphic section • • • • • • • • • 4 Figure 4: Generalized Devonian section in Conemaugh Gorge 7 Figure S: Stratigraphic correlation - Devonian to Pennsylvanian 8 Figure 6: Depositional environments • • • • • • • • • • • • • 9 Figure 7: Stratigraphic section at Clark Run - }Jauch Chunk • • 11 Figure 8: Plant fossils of the Johnstown area . • . • • • • 12 Figure 9: Stratigraphic section at Widman Street Exit • • • • 13 Figure 10: Stratigraphic sections at Gee Bee outcrop . • • • 14 Figure 11: Marine fossils of the Brush Creek Limestone • • •• lS iii ·o(\ sec.'' 1-l,~c.~ \.ov.e v~o ,e~<' _.a\.JI.~Q . ~o'> ..._o'{'l ~- c.~~'\~JI.\. _t.PPALAfljiAN PL_AJEAUS r~ ....JY """"~ c==: ) , lPOTTER ----, ?'Jiii,.?"' \ __ .:::::1\i •~u~am:'""kANk \ I r·i'. I"""', ( 'f-'~ ~\,.. \,.. (..,~ c:,'\'t-~,~ (,o'f-~~o , ___ _ APPALACHIAN PLATEAUS VAllEY AND RIDGE BLUE RIDGE PIEDMONT PROVINCE PROVINCE Figure 1. Location map within the state of Pennsylvania. Page 2 INTRODUCTION The purpose of this field trip is to examine the general geology of the Johnstown area. The route and stops have been chosen to give you as much yariety as possible. The trip will begin near the Clark Run Nature Area on Route 403, and with time permitting, it will end on Route 56 near the intersection with Route 219. REGIONAL STRUCTURE The field trip area is within the Allegheny Mountain section of the Applachian Plateau Province <see figure 1). The city of Johnstown lies in a syncline between Laurel Hill anticline and the less visible Ebensburg Anticline <see the attached geologic maps; Geistown, Johnstown, and Vintondale Quadrangles). The UPJ campus is situated almost on the crest of the Ebensburg Anticline and the Conemaugh River water gap is cut through the Laurel Hill Anticline, an open. slightly asymmetric fold. Laurel and Chestnut Mountains are the only two major "wrinkles" or folds on the Allegheny Plateau. In the Johnstown area the Laurel Hill anticlinal axis closely follows the ridgeline with a strike of approximately N 43 E with a plunge to the NE varying from 0.5 to 1.5 degrees. The southeastern limb has a maximum dip of approximately 13 degrees while the northeastern limb dips a maximum of only about 10 degrees <Keirn 1983). The Conemaugh Gorge is approximately 4.5 miles long and has a maximum relief of about 1400 feet which is the greatest local relief in Pennsylvania (see figure 2). The gorge has been formed by the down-cutting action of the Conemaugh River as the landscape developed since the uplift of the Plateau. Sub-surface data suggest it is fault controlled (Personal Communication - Peoples Natural Gas Company), but there appears to be little surface expression of the fault. Since the uplift of the Plateau Region, down-cutting and erosion have kept pace with the exposure of the fold. GEOLOGIC SUMMARY The surface rocks exposed in this part of Pennsylvania consist of Lower Paleozoic strata ranging in age from Upper Devonian to Upper Pennsylvanian <see figure 3). While most of the area is underlain by rocks of the Pensylvanian System, older rocks are exposed in the Conemaugh Gorge where the Conemaugh River has cut through from the Pennsylvanian to rocks of the Upper Devonian. This is one of the few places on the Plateau where rocks of this age are exposed. The environments of deposition in the Johnstown region vary from marine to fluvial, but the majority are of freshwater origin, and many provide a rich supply of plant fossils. Inter-bedded with these freshwater fluvial materials are a few fossiliferous marine limestones. Coal is commonly found in many of the road cuts in the area. One of the outstanding features of the rocks of Western Pennsylvania is the cyclic nature of the sediments. A composite "normal" cyclothem for the Johnstown area would include: Fio-Jl,..P ?_ (From never ~ Bolles 1979 GENERALIZED SECTION OF ROCKS IN THE JOHNSTOw"'N AREA scale: 1" = 400' SYS- FORMATION SECTION thick CHARACTER OF FORMATION TEM ness OR GROUP (ft ) hf".r;-:~ ~-~.:.:. CONEMAUGH !-- --850 Upward fining sequences GROUP .-------- to of sandstone, silts tine, and 960 shale; with thin beds of coal r---.:.-~--__..:,--- __,_ and a few thin limestones ~--;"T·~ ~ ......... !... -·- ~ '*• -:- -r':-- ---·•.,•.:: ·······: r--~--- -.:.::::= ~ - ~ H - ~·· .. -:-.. ~ ~ '\ ....-: ~ .-o:-.-~ ~ ;:::=:-=. - tf.l I ~ ~;o;;::!.:.Jo.~--:Z!. j;il ALLEGHENY ---....&i - .:.-=--- 220 Coal cyclothems; with up tc 5 p.., ~~___. GROUP ~-·--'~ -- to workable seams ~- ---- 290 POTTSVILLE ...' ·: ............. ,,,. '·... 175 Upward fining sequences of • • ,. • • I •• • GROUP . ·. .• ·i •: .. •. to sandstone, siltstone and shale ·::,. ·.,....... !It ~.:-:'...· unconformity .... .. ·.... "' ... 250 - Red and green silty shale; sand MAUCH CHUNK Fm. ~~- 1£~ ~'M' 200 stone 1Loya.1nanna LJ.mest:on -.. .. N .)U cross-oeaaea ca.tcaronJ.t;e \ · ..... ..... .. ' . medium to coarse sandstones Burgoon . .. .... ·. .. .... predominate; some conglomeratic ~ sandstone . V\350 H . p.., ::::::-- . - ~ = sandstone and interbedded H ----~ siltstone tf.l . tf.l ... .. .. H . tf.l .. tf.l • • . .. H .. .. ~ j .. , . :-::._-..:...!:-· --= undifferent. ' . .. .,650 Grayish-green sandstone, silt- Shenango and .. .. .~ ... • stone and shale; lower units Oswayo Fms. .....--=-.-:_...... ~ include thin fossiliferous and -.. ; . .. .. _.. ___: .. '. _.,L_::..: . calcareous beds • .<lfL. .!,..=- . .. ... ~ . .. H . z = Red siltstone and inter 0 CATSKILL Fm. '==:::::::. ·- 400+ shale; :> - ~ j;il r;::. bedded sandstone ~ - Figure 3. Generalized stratigraphic section of the Johnstown area, including the Conemaugh Gorge. (Various sources) Page S. 5. Shale, non-marine/or sandstone with an erosional base representing the start of the next cycle. 4. Coal 3. Underclay 2. Shale without marine fossils 1. Sandstones, with noncomformable base Although it is rare to find a complete sequence at any one location, regional mapping has produced the composite listed above. In addition to the non-marine cycle listed above, in a few locations in the Johnstown area, the cycles have been interrupted by a marine transgression producing a composite cycle like this: 8. Shale; non-marine 7. Shale/limestone; brackish/marine 6. Coal 5. Underclay <Paleosol) 4. Limestone <Freshwater) Siltstone/shale Fine sandstone/shale <Planar bedding, small scale cross stratification 1. Medium-coarse sandstone <Trough cross-bedding~ erosional base Note that Units 1-6 represent an upward fining, meandering stream sequence This cyclic nature is well exposed along Rt. 56 as you enter Johnstown from Rt. 219. At the Widman Street exit you can see several coal seams exposed in the road cut; each produced by a different sedimentation cycle. The following descriptions will give a brief geologic summary of each of the major units to be examined on this trip. DEVONIAN The oldest rocks of the area belong to the Catskill Formation of the Upper Devonian Period. These are primarily red shales and sandstones, rather rich in mica, with some plant fossils and root markings. The rocks suggest a nearshore, mudflat type of environment with freshwater or at most brackish water deposition. The Catskill rocks exposed in the Conemaugh Gorge are very similar to the ones seen along Route 30 in Bedford County. The next sequence of beds, the Oswayo Formation, represent a sudden Page 6. change in relative sea-level to deeper water. In this sequence are inter-bedded shales~ sand- and siltstones, and an occasional limestone layer. In several of these are e>:amples of washed in fossil pieces, mostly brachiopods, and strong evidence of bioturbation. Current ripples, both climbing and in-phase~ are dominate_in the lower beds. Several beds have small layers of shale rip-up clasts. Several times these thin-bedded sequences are punctuated by a massive sandstone (up to 2 feet thick) with well developed cross-bedding, all dipping the same direction, truncated by a series of planar sandstone beds. Plant fossils are found at the bases of these massive sands. The combination of beds suggest a location at or near the distal delta slope in the beginning of the sequence, but then with time, the sea slowly regressed. Figure 4 is a stratigraphic section illustrating the Oswayo and the upper portion of the Catskill beds that are exposed in the Conemaugh Gorge. MISSISSIPPIAN In this area, the lower