John M. Dennison

Evidence of non-vascular land plants from the early Silurian (Llandoverian) of Virginia, U.S.A.

Abstract Evidence is presented for the earliest known occurrences of non-vascular land plants and of higher, septate fungi. Macerates of carbonaceous silstone lenses from the lower Massanutten Sandstone, early Silurian (Llandoverian) of Virginia, have yielded a diverse assemblage of microfossil elements. Parallel aligned, banded tubes with annular to spiral ribbing and rounded to papilliform ends, membranous cellular sheets, cuticles, trilete spores, small spore tetrads, and septate higher filamentous fungi were recovered from the macerates. The banded tubes are probably a significant analogue with supportive or conductive cell types, but are not considered tracheidal. The heterogeneous plant assemblage may represent a thalloid, non-vascular land plant, in part, with a tubular-filamentous (nematophytic) organization associated with a membranous cellular layer and cuticular covering. While no spores were established as nematophytic, the presence of trilete spores adds to the indirect evidence of multiple evolutionary convergence toward land-plant characters. This assemblage is interpreted as of land-plant origin, based on the inferred fluvial depositional model of the fossiliferous rocks. A glacio-eustatic sea-level drop in the late Ordovician is suggested as a stimulus to the advent of land plants in the early Silurian.

Tertiary Intrusions and Associated Phenomena near the Thirty-Eighth Parallel Fracture Zone in Virginia and West Virginia

Recognition of Eocene igneous intrusions in Highland County, Virginia, by Fullagar and Bottino (1969) prompted a search for related phenomena. The temperature culmination of a group of thermal springs, the site of maximum uplift of the Schooley erosion surface, and a regional simple Bouguer gravity anomaly in excess of —80 mg occur within 20 mi of the common juncture point of Highland and Bath Counties, Virginia, and Pocahontas County, West Virginia. The Highland County intrusive rocks of Eocene age are the most recent surface expression of volcanism along a deep-seated crustal fracture that lies transverse to the Appalachians near the 38th parallel. Surficial rocks above the fracture zone contain igneous injections, flows, and pyroclastic deposits of late Precambrian, Devonian, Triassic, Jurassic, and Eocene age. Radiometric dating data now available suggest westward migration with time of intrusive centers. The fracture zone seems to have been present and sporadically active for more than 0.8 b. y. and may still be a zone of deep crustal weakness.

Stratigraphic Cross Section of Hamilton Group (Devonian) and Adjacent Strata along South Border of Pennsylvania: GEOLOGIC NOTES

A cross section of the strata between the top of the Oriskany Sandstone and the base of the Brallier Formation is based on 13 wells and 5 outcrops and extends for 150 mi (242 km) at lat. 39°43^primeN from the Ohio River eastward along the south border of Pennsylvania to the most eastern Appalachian outcrop belt. The two best time markers in the section are the Tioga Bentonite and Tully Limestone; the intervening strata thicken from a minimum of 490 ft (149 m) at the west end to a maximum of 1,850 ft (564 m) near the east end. Thickening is caused by stratigraphic divergence accompanying eastward increase in grain size of the clastic deposits which entered the Appalachian basin from the east. The stratigraphic section illustrates facies changes and thickness relations of these formations and their members: Needmore Shale, Huntersville Chert, Marcellus Shale, Mahantango Formation, Harrell Shale, Millboro Shale, and Brallier Formation.

Sedimentary response to Mississippian tectonic activity at the east end of the 38th Parallel fracture zone

Carbonate fades of the Greenbrier Group establish the presence of an east-west-trending Mississippian uplift and record the timing of late Paleozoic tectonic movement in the east-central Appalachian basin at the east end of the 38th Parallel fracture zone. This fracture zone has been defined by previous workers from the alignment of igneous intrusive and volcanic rocks, ore mineralization zones, major fault systems, and Landsat lineaments across eastern and central North America. This fracture system is apparently associated with displacement along faults in the Precambrian basement rock. Movement along the fracture zone occurred periodically throughout the Phanerozoic. The lineament may be distinguished both geomorphically (on Landsat imagery and side-looking airborne radar) and stratigraphically. Mississippian tectonic activity along the eastern section of the fracture zone is indicated by anomalous thinning of sediments, facies patterns, and stratigraphic relations of uppermost Devonian to Upper Mississippian strata of the eastern Appalachian Plateau.

Devonian eustatic fluctuations in Euramerica: Discussion

No Abstract Available. The article discussed appeared in the Bulletin , v. 96, p. 567–587. The authors of that article declined to write a Reply to this Discussion.

Lithofacies of the Silurian Keefer Sandstone, east-central Appalachian basin, USA

Abstract Fourteen lithofacies of the Keefer Sandstone in the area of northeastern West Virginia and western Maryland were identified. Depositional environments of the lithofacies include storm-dominated marine shelf/basin, barrier island, and backbarrier tidal flat and lagoon. Coastal lithofacies document a dominant basinward progradation, with some sea-level rise, which placed backbarrier lithofacies above barrier island lithofacies. Shelf lithofacies, as stacked coarsening-upward sequences, document as many as four fluctuations within the major progradation. Coarsening-upward sequences are typically capped by transgressive sands which represent material eroded from relatively landward environments and transported basinward during coastal retreat. Deposition of cycles within the Keefer occurred under conditions of tectonic quiescence, dominant steady or falling sea level followed by rise in sea level, and in a climate which was warm and humid.

Gravity tectonic removal of cover of Blue Ridge anticlinorium to form Valley and Ridge province

Chiefly on the basis of comparative amounts of foreshortening of the Valley and Ridge and Blue Ridge provinces, it is proposed that the eastern Valley and Ridge strata are the remnants of the former cover of the Blue Ridge anticlinorium. This cover slumped to the northwest (by gravity tectonic denudation) as the western Piedmont-eastern Blue Ridge was tilted gently to the northwest during the Alleghany orogeny, probably during the Permian Period. In a later phase of the Alleghany deformation, the Blue Ridge anticlinorium formed, and throughout much of its length it was thrust over the Valley and Ridge province as a result of continued pressure from the southeast. Arguments are presented that the anticlinorium configuration of the Blue Ridge area did not develop until after deposition of the Paleozoic strata in the Appalachian basin.

Expected Paleozoic Stratigraphy Beneath Western Part of Metamorphic Overthrust in Southern Appalachians: ABSTRACT

A stratigraphic cross section from Roanoke, Virginia, to Alabama shows the formations and facies of the easternmost Valley and Ridge outcrops. This cross section, coupled with 3-dimensional insights on facies changes, siliciclastic sources, and regional unconformity patterns, delimits stratigraphic expectations directly beneath the metamorphic over-thrust of the Blue Ridge-Great Smoky-Piedmont terrain as far east as the Brevard zone. These strata are in the Saltville structural block south of central Tennessee and in the Pulaski block to the north. The stratigraphic column in the block directly beneath the metamorphic overthrust is up to 5,100 m (17,000 ft) thick and contains Upper Precambrian (Chilhowee Group) to middle Mississippian beds. The Chilhowee in the block beneath the metamorphic overthrust is probably less shaly and thinner than equivalent Chilhowee exposed along the leading edge of the metamorphic overthrust block. The Shady Formation becomes less dolomitic eastward, passing into dark, shaly limestone east of the carbonate bank edge. Rome-Conasauga siliciclastics change to carbonates eastward and northeastward. The Knox Group changes to limestone beneath the overthrust, and the post-Sauk unconformity probably disappears. Middle Ordovician siliciclastics coarsen eastward toward the Blount delta. The Wallbridge discon inuity expands eastward, so that Silurian and Lower Devonian strata probably do not occur beneath the metamorphic overthrust. The pre-Upper Devonian unconformity truncates more section eastward, so that Chattanooga Shale locally rests on Middle Ordovician Bays Formation in southeastern Tennessee. In Tennessee, Georgia, and possibly North Carolina, Mississippian strata include sandstone, dark shale, limestone, and bedded chert passing beneath the Great Smoky-Cartersville fault. End_of_Article - Last_Page 470------------

Effects of Mississippian Tectonic Movement on Sedimentation and Diagenesis of Greenbrier Group in Eastern Appalachian Plateau: ABSTRACT

The Greenbrier Group of eastern West Virginia consists of marine carbonates interbedded and mixed with siliciclastics that were deposited on a shallow shelf in the Late Mississippian. The Denmar Formation is the lowest unit of the Greenbrier Group present in east-central West Virginia, and it represents a shallow tidal-flat and platform sequence deposited by a transgressing sea during the Meramecian. This transgression was followed by a regression with progradation of Taggard Formation terrigenous clastics onto restricted tidal flats during the earliest Chesterian. The Denmar tidal-flat deposits are characterized by pelleted mudstones, limited and depauperate fauna, calcite-filled and dolomite-filled geodes, caliche crusts, fenestral structures, dolomite, burrows, and channel deposits. The platform deposits include more diverse fauna, less micrite, cross-bedded and massive oolitic grainstones, and cross-bedded quartzarenites. Most of the siliciclastics were derived from the north and east of the Appalachian basin. Additional quartz silt, sand, and pebbles were eroded from an uplifted area within the basin and were incorporated into the tidal-flat and platform sediments. This Meramecian tectonic uplift, considered to be part of the 38th parallel lineament, created a subaerial and submarine topographic high that affected sedimentation patterns dur ng the remainder of Greenbrier deposition. Early phreatic cementation occurred along the flank of the uplift in at least two stages. There is evidence of both penecontemporaneous and later replacement dolomite. In certain strata in the western outcrops, hydrocarbons migrated through permeable layers and filled remaining pores. End_of_Article - Last_Page 318------------

Folds Along Junction of Central and Southern Appalachian Trends in Southeastern West Virginia and Adjacent Virginia: ABSTRACT

Field mapping of crest and trough lines of the larger folds clarifies the junction between central Appalachian structural trends (striking about N25°E) and southern Appalachian trends (striking about N65°E) in southeastern West Virginia and adjacent Virginia. Previous interpretations have argued whether the change in orientation is gradual or abrupt, whether the two trends formed simultaneously, whether the more obviously overthrust southern Appalachians overrode the central trend, whether the central Appalachians were overprinted across the southern trend, whether the junction of the two trends is caused by rotational movement, or whether the differences result from a major basement fracture zone separating the two blocks. Our mapping shows that the folds are continuous across the junction of the trends, with a gradual bending of the fold traces. For tens of miles north of the junction of the two trends, gentle folding striking about N35°E can be mapped within the relatively flat major synclines of the central Appalachian area, but cannot be readily traced into the steeper flanks and more sharply folded crests of the major anticlines. We believe that these gentle anticline folds trending N35°E are related to the initial folding of the southern segment that trends N65°E. Subsequent to the development of the southern Appalachian folds, the central area was simultaneously folded and rotated, reorienting the northern extension of the southern fold generation to their present position of N35 76;E. This suggests that the southern fold and fault trend was overprinted by the central trend, a conclusion consistent with studies of stylolites by Dean and Kulander. Near the junction of the central and southern trend, structural domes and depressions formed as a result of fold interference. End_of_Article - Last_Page 1444------------