The Oneonta Formation (Catskill Magnafacies) in south-central New York is composed of two lithofacies associations: (1) Medium- to very fine-grained, cross- and planar-stratified sandstone bodies, with bedsets (lithofacies) arranged into one or (usually) more erosively based storeys. Individual storeys generally have upward-fining lithofacies, also lateral-accretion bedding and channel fills: (2) Interbedded mudstones and erosively based sandstones with a diversity of primary sedimentary structures, calcareous concretions, plant remains and trace fossils. Upward-fining bedsets (lithofacies) are sheet-like or channel-filling, and are arranged in meter-scale lithofacies sequences. The sandstone bodies are interpreted as deposits of laterally migrating and aggrading single-channel (perennial) rivers. Vegetated point-bar tops were subjected to both sheet floods and chute-channel formation. Minor low-flow deposition occurred on bar surfaces. Quantitative reconstruction of bankfull channel geometry and hydraulics gives channel widths, mean depths and slopes of approximately 60 m., 2.5 m., and 10 −4 respectively: low reconstructed bend sinuosities (1.1 to 1.2) are supported by paleocurrent data, and help to explain the dominantly coarse-grained channel fills associated with chute cut-off. Sinuosity changes during lateral migration are documented quantitatively. The sandstone-mudstone lithofacies association is interpreted as overbank flood deposits, on levees, crevasse channels and splays, and flood basins. Plant and faunal activity, and soil-forming processes, were abundant. Periodic channel-belt diversions (avulsions) caused the meter-scale lithofacies sequences in this association, also the cyclicity of the two lithofacies associations. If avulsion frequency averaged about once per 10 3 years, floodplain deposition rates are estimated at about 2 × 10 −3 m/year.

Abstract Synergetic depositional and . deformational phenomena have resulted in large concentrations of oil and gas in the upper Miocene and Pliocene sections of the Gulf Coast geosyncline. Most of these accumulations have been found trapped in the sandstone and sand- stone-shale magnafacies. The gulfward limit of future exploitation can be determined reasonably from present data, and should extend to water depths of 600 ft (180 m). Any significant future discoveries are most likely to be in the offshore. Development of these facies in Louisiana is approaching maturity, but there should be limited extensions gulfward and eastward of present production. Offshore Texas is largely unexplored, but results of drilling have been disappointing. Exploration for turbidites in the shale magnafacies gulfward of present trends is a challenge both to explorationists and to management. Turbidites will be difficult to locate and drilling will be expensive. They must be thick and prolific reservoirs in order to be commercial—but it is possible that such thick sequences are present. A possible future source exists in the shale magnafacies where turbidite sandstone reasonably can be expected on the updip flanks of salt structures and in the lows between them. The search for reservoirs of this type, particularly in the younger sections, will involve operations beyond the continental shelf in water depths that increase abruptly from 600-ft (180 m) depth. Exploration in the older beds will require increasingly deeper drilling. Exploration for turbidites requires complex seismic techniques and the best efforts of geologists, paleontologists, and geophysicists. No realistic estimate of favorable sedimentary-rock volume in the shale magnafacies is possible at this time. Present economics barely have justified the oil industry's exploration of the sandstone and sandstone-shale magnafacies in water less than 600 ft deep. Thus, more costly exploration in the deeper waters beyond the continental shelf will depend on increased incentives. Otherwise, economic considerations may jeopardize all future exploration in the Gulf of Mexico.

The Devonian Catskill Formation has been divided into four magnafacies (Mf) which have been correlated throughout Pennsylvania. Lithologies in 28 sections and wells were assigned to 10 facies on the basis of grain size, color, bed forms, fossils, and other sedimentary features. Repeating patterns of facies were used to identify magnafacies. Mf-A, the basal magnafacies, is composed dominantly of interbedded marine and non-marine shale and fine sandstone and is inferred to have been deposited mainly in a mud-rich tidal-flat environment. Mf-B is dominated by thick red shales accompanied by thin, fine-grained sandstones and is interpreted as a low-energy fluvial deposit on an inactive arid coastal plain. Mf-B is interrupted occasionally by thin, transgressive sandstones of tidal origin. Mf-C is composed of thick sandstones deposited by braided rivers and localized in three major northwest-trending zones of sediment input. Mf-D is composed of thick, fining-upward cycles with sub-equal amounts of sandstone and red shale. It is inferred to have been deposited by meandering rivers and is thickest in the same areas that Mf-C is thick. Mf-A and Mf-B are richer in sand near the sediment-input centers. In most sections, the Mf are present in the order A, B, C, and D upward, with C missing in many areas and more complex relations in extreme northeastern Pennsylvania. All Mf tend to thin northwestward. This pattern of distribution presumably results from northwestward progradation of the fluvial environment. Numerous small non-economic Cu-U occurrences are concentrated in areas of thick, shale-rich Mf-B lying between the major sediment-input areas. Most are closely associated with marine transgressions. A few occurrences are in the upper part of Mf-A and in Mf-D, but none is in Mf-C. Most of the Cu-U occurrences are localized by small accumulations of plant trash in shallow fluvial or tidal channels. In contrast, Wyoming-type, roll-front uranium occurrences are localized near Jim Thorpe in large channel sandstones of thick Mf-D in the sediment-input areas. The Cu and U occurrences appear to have formed during diagenesis by migration of metalliferous pore fluids.

Abstract Newly acquired U–Pb magmatic zircon dates from silicic tuffs within the Old Red Sandstone (ORS) magnafacies of the Munster Basin (SW Ireland) are intercalibrated with newly discovered (late Givetian) and reappraised (mid-Frasnian) miospore assemblages to provide the first biostratigraphically constrained numerical ages in the Irish Devonian succession. The weighted mean 207 Pb/ 206 Pb isotopic age determined for the Keel Tuff Bed (385.0 × 2.9 Ma) is indistinguishable from that of the previously investigated Enagh Tuff Bed (384.9 × 0.7 Ma). In conjunction with very similar rare earth element (REE) signatures, this confirms their correlation, placing a minimum age of 384.9 × 0.4 Ma on the newly discovered Reenagaveen microflora, which is assigned to the late Givetian TCo Oppel zone. The equivalence of the Keel and Enagh Tuffs constrains a vertebrate fauna containing Bothriolepis and the Valentia Island tetrapod ichnofauna to pre-date this event. Isotopic dating of thickly bedded subaerial tuffs from the Lough Guitane Volcanic Complex, a major accumulation of rhyolites and silicic volcaniclastic rocks, reveals ages of 384.5 + 1.0 Ma (Killeen Volcanic Centre), indistinguishable from the Keel–Enagh Tuff Bed, and 378.5 × 0.2 Ma from the Horses Glen Volcanic Centre, previously considered to be the oldest of the complex. The Horses Glen Centre post-dates the Moll's Gap Quarry microflora, the only current biostratigraphical control on the age of the early ORS in the east of the basin depocentre, thus indicating a minimum age for the (mid-Frasnian) IV Oppel zone, the revised biostratigraphic age of this assemblage. These controls on the early ORS (1) suggest that Munster Basin initiation occurred before late Givetian time and (2) give time-averaged (compacted) accumulation rates of c. 0.17–0.25 and 0.18 mm a –1 for eastern and western Iveragh, respectively. The minimum basin duration time was c. 23 Ma to the end of the Devonian period. The implications of these data for the depocentre stratigraphy, volcanic events, proposed ORS cyclicities and the geohistory of the Munster Basin are examined.