The Shawangunk Formation (Upper OrdovicianC?) to Middle Silurian) in Eastern Pennsylvania GEOLOGICAL SURVEY PROFESSIONAL PAPER 744 Work done in cooperation with the Pennsylvania Depa rtm ent of Enviro nm ental Resources^ Bureau of Topographic and Geological Survey The Shawangunk Formation (Upper Ordovician (?) to Middle Silurian) in Eastern Pennsylvania By JACK B. EPSTEIN and ANITA G. EPSTEIN GEOLOGICAL SURVEY PROFESSIONAL PAPER 744 Work done in cooperation with the Pennsylvania Department of Environmental Resources, Bureau of Topographic and Geological Survey Statigraphy, petrography, sedimentology, and a discussion of the age of a lower Paleozoic fluvial and transitional marine clastic sequence in eastern Pennsylvania UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 74-189667 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 65 cents (paper cover) Stock Number 2401-2098 CONTENTS Page Abstract _____________________________________________ 1 Introduction __________________________________________ 1 Shawangunk Formation ___________________________________ 1 Weiders Member __________ ________________________ 2 Minsi Member ___________________________________ 5 Lizard Creek Member _________________________________ 7 Tammany Member _______________________________-_ 12 Age of the Shawangunk Formation _______ __________-___ 14 Depositional environments and paleogeography _______________ 16 Measured sections ______________________________________ 23 References cited ________________________________________ 42 ILLUSTRATIONS Page FIGURE 1. Generalized geologic map showing outcrop belt of the Shawangunk Formation in eastern Pennsylvania and northwestern New Jersey ___________________-_ 3 2. Stratigraphic section of the Shawangunk Formation in the report area ___ 3 3-21. Photographs showing 3. Conglomerate and quartzite, Weiders Member, Lehigh Gap ____ 4 4. Photomicrograph of lithic graywacke, basal Weiders Member, Lehigh Gap 4 5. Quartzite and conglomerate, Minsi Member, Delaware Water Gap _ 5 6. Conglomeratic quartzite and quartzite, Minsi Member, Delaware Water Gap 5 7. Photomicrograph of feldspathic sandstone, Minsi Member, Delaware Water Gap 6 8. Mud cracks in siltstone, Minsi Member, Delaware Water Gap ______ _ 6 9. Siltstone, shale, and quartzite, Lizard Creek Member, Lehigh Gap ___ 7 10. Laminated well-sorted calcitic sandstone, Lizard Creek Member, Delaware Water Gap _______________________. ___________________ 8 11. Flaser-bedded and lenticular sandstone and siltstone, Lizard Creek Member, Delaware Water Gap _________________________________ 8 12. Soft-rock convolutions, Lizard Creek Member, Delaware Water Gap ____ 9 13. Rippled sandstone, Lizard Creek Member, Delaware Water Gap ________ 9 14. Photomicrograph of fine-grained quartzite, Lizard Creek Member, Delaware Water Gap _______________________________________ 9 15. Burrows in siltstone, Lizard Creek Member, Delaware Water Gap ______ 10 16. Burrow in laminated red siltstone, Lizard Creek Member, Lehigh Gap ____ 11 17. Photomicrograph of hematitic orthoquartzite, Lizard Creek Member, Lehigh Gap 11 18. Nodule beds in Lizard Creek Member, Lehigh Gap ________________ 12 19. Shawangunk Formation at Delaware Water Gap _________________ 13 20. Photomicrograph of conglomeratic coarse-grained protoquartzite, Tammany Member, Delaware Water Gap __________________________- 14 21. Dolomite and dolomitic shale or shaly dolomite, Tammany Member, Delaware Water Gap ________________________________________ 14 in IV CONTENTS Page FIGURE 22. Block diagram showing sedimentary environments and major lithofacies in the Shawangunk Formation ____________________________________ 17 23. Histograms showing current trends from crossbedding _________________:___- 18 24. Photograph showing tidal-flat flaser bedding in Lizard Creek Member, Lehigh Gap __ 19 TABLE TABLE 1. Chemical and semiquantitative spectrographic analyses of rocks in the Shawangunk Formation ____________________________________________- 2 THE SHAWANGUNK FORMATION (UPPER ORDOVICIAN(?) TO MIDDLE SILURIAN) IN EASTERN PENNSYLVANIA By JACK B. EPSTEIN and ANITA G. EPSTEIN ABSTRACT Bake Oven Knob and from mapping between sec­ The Shawangunk Formation of Early and Middle Silurian tions. Maps of some areas are already published age, and possibly Late Ordovician age, in eastern Pennsyl­ vania and northwestern New Jersey forms a thick clastic Portland quadrangle (Drake and others, 1969) and wedge of sediments derived from sourcelands to the southeast Stroudsburg quadrangle (Epstein, 1971, 1972). uplifted during the Taconic orogeny. The formation is divided Some details from other quadrangles are given in into four newly denned members, from bottom to top: Weiders Epstein and Epstein (1967, 1969). Table 1 gives Member (coarse conglomerate and quartzose sandstone), Minsi Member (quartzose conglomeratic sandstone and minor chemical and semiquantitative spectrographic analy­ argillite), Lizard Creek Member (complex sequence of ses of rocks in the Shawangunk Formation. quartzose sandstone, siltstone, shale, and a few red beds, with The Shawangunk Formation consists predomi­ sparse fauna), and Tammany Member (quartzose conglom­ nantly of quartzose sandstone (quartzite), quartz-, eratic sandstone and minor argillite). The Weiders Member pinches out to the east near Smith Gap. The Tammany Mem­ chert-, shale-, and quartzite-pebble conglomerate, ber cannot be conveniently mapped west of Smith Gap because siltstone, and shale, as well as a few beds of sand­ of interfingering with and replacement by beds of the Lizard stone and siltstone containing nodules of cellophane, Creek Member. The contact of the Shawangunk with the siderite, and chlorite. Red beds are not uncommon underlying Martinsburg Formation is an angular unconform­ in the western part of the report area, and dolomite ity. The boundary between the Shawangunk and overlying Bloomsburg Red Beds is irregular and transitional through occurs at Delaware Water Gap. Fossils are rare. about 130-700 feet of red, green, and gray rocks. Sedimentary Four distinct lithic assemblages have been mapped. features in the Shawangunk indicate that the sediments were These are herein defined as members and include, deposited by streams and in a complex transitional marine- in general ascending order, the Weiders, Minsi, Liz­ continental environment, including tidal flats, barrier bars, ard Creek, and Tammany Members (fig. 2). estuaries, and lagoons. We wish to thank Gary E. Redline for assisting in INTRODUCTION measurement of stratigraphic sections. Wallace The Shawangunk Formation of Early and Middle deWitt, Jr., U.S. Geological Survey, and W. D. Sevon Silurian, and possibly Late Ordovician, age has been and D. M. Hoskins, Pennsylvania Geological Survey, mapped for 40 miles between Delaware Water Gap, made many helpful suggestions on the original N.J., and Bake Oven Knob, Pa. (fig. 1). It forms a manuscript. prominent ridge known as Kittatinny Mountain in SHAWANGUNK FORMATION the northeastern part of the area and as Blue Moun­ The Shawangunk Grit was named by Mather tain in the southwestern part. The Shawangunk is (1840) for sandstones and conglomerates in south­ folded, and in many places the rocks are overturned eastern New York that are part of the same outcrop to the southeast. The structure is more complex in belt as rocks in eastern Pennsylvania called Levant the southwest part of the report area; there the by Rogers (1858) and Oneida and Medina by White Shawangunk is faulted and in places doubly over­ (1882). Grabau (1909) first used the term Shawan­ turned to the northwest. Several wind and water gunk Conglomerate for these rocks in eastern Penn­ gaps transect the ridge; the formation is well ex­ sylvania. The lithic modifier was changed from con­ posed only in these gaps. Between gaps, good ex­ glomerate to formation in the Delaware Water Gap posures are generally lacking, but some lithologic area by Drake, Epstein, and Aaron (1969). A history information can be obtained by tracing float; thick­ of the early nomenclature is given by Schuchert nesses can be determined by constructing cross sec­ (1916) and Swartz and Swartz (1931). tions. Figure 2 shows a stratigraphic section of the Swartz and Swartz (1931) traced the Tuscarora Shawangunk compiled from sections measured at Sandstone and Clinton Formation from central Penn­ Delaware Water Gap, Wind Gap, Lehigh Gap, and sylvania eastward to Delaware Water Gap; there, SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA TABLE 1. Chemical and semiquantitative spectro graphic forms a tongue in the Shawangunk (fig. 2). Simi­ analyses of rocks from the Shawangunk Formation larly, the Tuscarora of Swartz and Swartz (1931) [Rapid-rock analyses by P. Elmore, G. Chloe, J. Kelsey, S. Bptts, H. Smith, (Weiders and Minsi Members of the Shawangunk J. Glenn, and L. Artis, U.S. Geological Survey. Semiquantitative speetro- graphie analyses by J. L. Harris, U.S. Geological Survey. N, not detected Formation of this report) can be traced beneath the or at limit of detection; L, detected but below limit of determination. The following elements were looked for and not detected or were found in Clinton. Because the name Shawangunk has priority amounts at the limit of detection: As, Au, Bi, Cd, Eu, Ge, Hf, In, Li, Nd, Pd, Pr, Pt, Re, Sb, Sm, Sn, Te, Th, Tl, U, W. The
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