John C. Ferm

Permo-Triassic Sedimentation Patterns, Sydney Basin, Australia

Fluvial, deltaic, and marine-shelf sediments were deposited in a 100- by 200-mi, north-south oriented trough centered around Sydney, where up to 12,000 ft accumulated during the Permo-Triassic. A basin analysis was made using depositional models based on rock outcrops and closely spaced boreholes. These depositional models were used to form a best fit-of-environment correlation along three lines of section through the basin using 21 deep boreholes as control. Patterns of sedimentation can be delineated from the correlation charts at several intervals through the sequence. Lower Permian sediments were derived mainly from the north and, except for minor delta-plain facies in the nearshore area, were principally deposits of a marine shelf and delta front with an abundant fau a of thick-shelled pelecypods, brachiopods, and bryozoans. Most of these marine sandstones and siltstones contain predominantly lithic fragments but some, apparently representing subaqueous bars, are distinctly quartzose. From the Middle Permian into the Early Triassic, the sediments were deposited in a southward prograding delta and were derived mainly from the north. Two fluvial wedges formed which merged southward into a deltaic plain facing a shallow sea. Close borehole control within the fluvial system establishes channel-bar sandstones and conglomerates 50-200 ft thick grading laterally into levee and lacustrine siltstones and back-swamp coal beds. Alluvial deposits grade seaward into delta-plain sediments consisting of distributary-mouth bar sandstones 30-50 ft thick which interfi ger laterally with interdistributary bay sequences. These bay sequences commonly grade from fine to coarse upward and commonly are capped by intensely burrowed sandstones or root claystones and coal beds. Delta-front sandstones flank the delta-plain deposits and merge with mottled gray siltstones of the open shelf. Several episodes of delta outbuilding separated by periods of marine transgression can be delineated with the last most widespread progradation followed in the Triassic by an equally extensive transgression of shallow marine water. Fluviodeltaic deposits in this latest episode lack coal, and the sedimentary sequence is dominated by an orthoquartzitic barrier bar-tidal delta system locally 1,000 ft thick which grades laterally into marine red claystones and gray tidal-flat silt tones and fine sandstones.

Exploration Model for Pennsylvanian Upper Delta Plain Coals, Southwest West Virginia

The Lower Stockton coal seam of the Upper Pennsylvanian Kanawha Formation, studied in a small area in southwestern West Virginia, is 6 ft (2 m) thick at the center of the coal body, and thins in at least one direction by a combination of splitting and thinning of individual benches. Clastic intervals between coal benches become less extensive upward, suggesting coal-body deposition during the abandonment phase of an upper delta plain distributary channel. Rates of splitting vary through the coal body, necessitating closer drill hole spacing near the edges, where variations are greatest. Documentation of such coal bodies leads to an understanding of their lateral variability. A knowledge of seam variability, types of splitting, and seam characteristics can lead to an effec ive exploration model.

Stratigraphic Variation in Some Allegheny Rocks of Western Pennsylvania: GEOLOGICAL NOTES

Recent stratigraphic studies of Allegheny rocks [Pennsylvanian] of western Pennsylvania seem to show that the marine Kittanning rocks are analogous with Freeport rocks of fresh-water origin. Detrital sediments dominate Allegheny rocks but nondetrital coals, ironstones, and limestones do occur and they separate detrital facies. The couplets of detrital and non-detrital rocks can be considered as records of cyclic sedimentation.

Estuarine-Coastal Plain Coal Deposition in Southern West Virginia; Pennyslvanian Beckley Seam: ABSTRACT

Current studies of the Beckley (Pennsylvanian) seam in an area 60 by 30 km in southern West Virginia indicate that the Beckley was formed in a back-barrier depositional setting. Examination of about 1,800 core records as well as underground workings shows that the Beckley stratigraphic position is characterized by linear northeast-southwest-trending orthoquartzitic sandstone bodies about 1,500 m wide representing stranded barriers on a prograding coastal plain. Areas between the barrier sandstones are about 15 km wide and are occupied by coal and shale of estuarine and tidal-creek origin. The thick bodies of coal, which are relatively small (4.8 by 9.6 km or less), are located on the flanks of the barrier and thin toward the shaly central part of the interbarrier area. Ad acent to the barriers, the coal is split by small linear tongues of sandstone produced by erosion of the barrier. Where the coal adjoins estuarine and tidal-creek sediments, it interfingers and thins into shale and sandy shale. Within the interbarrier areas, the thickest coal is near the headward parts of the tidal creeks; closer to the major estuary the coal bodies are thinner and smaller in areal extent. Knowledge gained from exploration and mining of the Beckley seam should aid in searching for and developing coals in similar depositional settings. End_of_Article - Last_Page 533------------

Late Paleozoic Clastic Wedges in Appalachian Province: ABSTRACT

Late Paleozoic clastic wedges, arrayed from north to south along the western edge of the Appalachian tectonic welt, differ in age as well as spatial relations. The northern, Catskill, wedge is the oldest and apparently was derived from the north, whereas the succeeding Warrior-Arkoma wedge was apparently derived from a southern or Ouachita source. The youngest, Pocahontas and Dunkard, wedges are located between the older two and were derived from only a relatively small area in the central Appalachian Blue Ridge and Piedmont. Although the style of sedimentation differs among these large sedimentary prisms, all were governed by similar tectonic controls of differential subsidence and growth faulting. Significantly, the trend of tectonic complexes from which the sediments w re derived is nearly at right angles to most of the present structures and suggests predrift tectonic connection. End_of_Article - Last_Page 778------------

Tectonic Chronology of Pennsylvanian Borderlands: ABSTRACT

Pennsylvanian sedimentary rocks that are exposed in the eastern United States were deposited as a broad undulating blanket from highly deformed borderlands--Appalachia on the east and Ouachita on the south. These rocks were universally involved in borderland folding. Two separate sedimentological investigations of essentially undeformed rocks closely adjoining the borderland indicate that regionally distinct segments affected depositional patterns at various times during the Pennsylvanian, and that other segments were not active until latest Pennsylvanian or Permian time. The first study indicates that the Ouachita deformed belt, now buried beneath Gulf Coastal Plain sediments, was one of the earliest Pennsylvanian tectonic welts and provided the major source of sediments for the Black Warrior basin of northern Alabama and Mississippi. Contrasts in mineral composition of these sediments as compared with correlative sediments in northern Arkansas indicate that this tectonic welt probably plunged northwestward, with the deepest portions of the structure thus being exposed at the southeastern terminus. Exposed Appalachian structures in the southeast are definitely post-early Pennsylvanian and did not affect Pennsylvanian sedimentation in this area. A second study of paleogeographic patterns in Allegheny and late Pottsville sediments of Pennsylvania, Ohio, West Virginia, and Kentucky shows that major source areas lay to the south, probably related to a tectonic highland paralleling the present Pine Mountain fault. Major structural deformation in the classical fold area of Pennsylvania and northern West Virginia is clearly post-Pennsylvanian and Permian. End_of_Article - Last_Page 340------------