Carboniferous Cover Research Articles

COAL RANKS IN THE HARTON BOREHOLE: A REPLY

(Short communication) Unfortunately, it appears possible that Dr. Suggate has taken the term “higher-than-expected”, quoted in the last sentence of the section on coal rank in the paper by Ridd, Walker and Jones (1970, p. 91), rather out of context. The term was used relative to coal ranks in the nearby Northumbrian Trough where seams lower in the succession than the bottom of the Harton well are of very low rank. The authors in that paper wished to emphasize the difference that exists between the rank gradient at Harton and that in the Northumbrian Trough. While Dr. Suggate appears to agree with the authors in their interpretation of early, pre-Whin Sill, imposition of rank profile, he attributes this to thick Upper Carboniferous cover rather than high heat flow through the basement. This would necessitate a much greater thickness of Upper Carboniferous sediment in Durham than in Northumberland, which is unlikely in view of the pattern of earlier Carboniferous sedimentation. In addition, although the presence of a greater thickness of Upper Carboniferous strata at Harton would possibly increase the overall rank levels of the coals it would have the result of decreasing the rank gradient. The authors still feel that their interpretation, dependent on differences in the thermal properties of the basement, is the most probable explanation of the high rank gradient at Harton relative to that existing in the Northumbrian Trough.

A gravity survey of a region of the Highland Boundary Fault in Scotland

The results of 1591 gravity measurements made in parts of the Midland Valley and the Grampian Highlands of Scotland, flanking the Highland Boundary Fault-zone between Callander and Cowal are described and density units in the Palaeozoic rocks of the area distinguished on the basis of some 800 laboratory measurements. Steep gravity gradients across the Highland Boundary Fault at Callander and Aberfoyle show that its small hade to the north-west, observed at surface, is maintained to a depth of 2400 ft below sea-level, indicating that the fault behaved as a high-angle reversed fault in mid-Devonian times. West of Loch Lomond, the fault continues in general alignment with its course to the east and is inferred to underlie the Carboniferous cover in the Greenock–Inverkip region. The existence of a deep sedimentary basin bounded to the north-west by three step faults and to the south-east by the Highland Boundary Fault is revealed by a gravity low west of Loch Lomond. The basin is probably partly filled by Lower Old Red Sandstone. The maximum thickness of the Lower Old Red Sandstone sediments in the surveyed area is between 5000 and 6000 ft and the formation thins south-eastwards in the region of the Ochil Fault. On the flanks of the Highland Boundary Fault, the survey has provided information of regional importance: the slate-belt probably occupies a downfolded synform within the Dalradian rocks; the Ochil Fault can have only a small magnitude in the surveyed area; the maximum thickness of the Lower Old Red Sandstone sediments in the area is between 5000 and 6000 ft and the formation thins south-eastwards in the region of the Ochil Fault.

Stratigraphy and Paleogeography of Mabou Group and Related Middle Carboniferous Facies, Nova Scotia, Canada

Marine and nonmarine facies in Nova Scotia, Canada, of Visean through Westphalian A (middle Carboniferous) age are closely related to a tectonic framework that consists of a narrow region of highly mobile blocks surrounded by a broad region of stable blocks. Defining and mapping new lithogenetic units and a more precise method of time control (fossil microspores) supports this hypothesis. Middle Carboniferous units of previous workers, the Windsor, Canso, and Riversdale “groups,” are time-stratigraphic and hence inadequate for defining facies. New lithogenetic units of group rank were defined in a previous report (Belt, 1964) to include strata represented by those time-stratigraphic units. The new units are termed the Windsor Group (restricted Windsor “group”), the Mabou Group (previously a formation), and the Coarse Fluvial Facies (an informal term). Existing formations have, wherever possible, been regrouped into these new units. A new formation (Emery Brook Formation) and a tongue (Glengarry tongue of the Pomquet Formation) are herein proposed. Windsor, Canso, and Riversdale time-stratigraphic units are redefined as Windsorian, Cansoan and Riversdalian Stages. The term Mabou Group is applied to fine-grained “red” and “gray” fluvial and lacustrine strata that succeed the widespread marine and evaporite deposits of the Windsor Group. The Mabou facies represent basin-fill sediments that underlie and also are laterally equivalent to coarse marginal deposits of the Coarse Fluvial Facies. The major zone of mobility during middle Carboniferous time, the Fundy Basin, was irregular in shape and not entirely a region of subsidence. The Caledonia and Cobequid arches, narrow upthrown blocks within the basin, supplied much of the sediment. The New Brunswick and Meguma platforms, bordering the Fundy Basin on the northwest and south, respectively, do not represent a major source of sediment, although much sediment moved across them from outside the Maritime region. The platforms are distinguished from the basins by a thin veneer of relatively undeformed strata; they alternated between gentle uplift and gentle subsidence. In contrast, the subsiding portions of the Fundy Basin received up to 20,000 feet of middle Carboniferous sediment that was subsequently highly folded and faulted and locally mildly metamorphosed. The margin of the Fundy Basin is interpreted as a region of high-angle faults because the thickness of Carboniferous sediment decreases abruptly from the basin onto the platform, Mabou facies grade laterally from “gray” (lacustrine) to “red” (fluvial) facies toward the margin of the basin, and coarse alluvial fans were deposited on the basin side of long, sinuous faults. The margin is believed to parallel the area of long faults that today separate the area of pre-Carboniferous platform, with its thin, slightly deformed Carboniferous cover, from the area of the basin, with its thick, highly deformed Carboniferous strata.

The Location of the Southern Uplands Fault in Central Ireland

AbstractIt has been suggested that the Southern Uplands fault of Scotland does not continue across central and western Ireland. Published geophysical evidence, however, strongly suggests that the fault does continue, under the Carboniferous cover, at least as far as the neighbourhood of Galway.

An Outline of the Geomorphology of Murrisk and North-West Galway

AbstractThe denudation chronology of the mountainous district of south-west Mayo and north-west Galway is closely linked with drainage superimposition from a deformed Carboniferous cover. Small outcrops of basal Viséan sandstones and conglomerates, lying on bevelled summits and wide bevelled tablelands demonstrate unequivocally that the west Connaught summit level corresponds to the base of the Carboniferous. Uplift, to produce a pre-glacial divide, is believed to have occurred in Mid-Tertiary times. Upon the uplifted, faulted, and warped Carboniferous cover a consequent drainage was developed. Superimposition on to the Caledonian basement followed and during the Pleistocene considerable glacial modifications of the pre-glacial drainage pattern took place.