Version 2.0 (2004)
(Originally published in 1997)
Cross section G–G’ is the sixth in a series of restored stratigraphic cross sections drawn by the senior author to show the stratigraphic framework of Cambrian and Ordovician rocks in the Appalachian basin from Pennsylvania to Tennessee. The sections show complexly intertongued carbonate and siliciclastic lithofacies, marked thickness variations, key marker horizons, unconformities, and stratigraphic nomenclature of the Cambrian and Ordovician sequence. Several of the drill holes along the cross sections have yielded a variety of whole and (or) fragmented conodont elements. The identifiable conodonts are used to differentiate strata of Middle Cambrian, Late Cambrian, and Early Ordovician age, and their conodont color alteration index (CAI) values are used to establish the thermal maturity of the sequence. Macrofossil collections from drill holes and (or) outcrop sections along the restored sections provide additional biostratigraphic data. In addition to providing lithologic, nomenclatural, and paleontologic details of Cambrian and Ordovician strata, these cross sections also help to define and delineate the structure of the block-faulted Proterozoic basement rocks beneath the sedimentary cover of the Appalachian basin. Previously completed cross sections in this series are F–F’ (Ryder and others, 1996), E–E’ (Ryder, 1992a), D–D’ (Ryder, 1991), C–C’ (Ryder and others, 1992), and B–B’ (Ryder, 1992b) (fig. 1).
Section G–G’ is about 255 mi (410 km) long. The section is constructed on the basis of eleven drill holes that are from 6 to 80 mi (10–129 km) apart and range in depth from 2,480 to 19,591 ft (756–5,971 m) (fig. 1, table 1). Eight of the eleven drill holes bottomed in crystalline basement rocks of Middle Proterozoic age or sandstone of Middle(?) Proterozoic age. Drill holes 10 and 11, which are located east of the St. Clair thrust fault, were restored 15 to 20 mi (24–32 km) southeastward to compensate for tectonic transport along underlying Alleghanian thrust faults (Woodward and Gray, 1985; Kulander and Dean, 1986).
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Miscellaneous Investigations Series Map I-2530 [5.2 MB PDF file]
Miscellaneous Investigations Series Map I-2530 [32.8 MB EPS file] — CAUTION: LARGE FILE SIZE
Miscellaneous Investigations Series Map I-2530 [5.6 MB AI file]
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Contact: Robert T. Ryder or Erika E. Lentz
U.S. Department of the Interior, U.S. Geological Survey
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Last modified: 10:39:00 Mon 23 Feb 2004
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