Millstone Grit Research Articles

THE HASLINGDEN FLAGS (NAMURIAN G 1 ) OF SOUTH-EAST LANCASHIRE: BAR FINGER SANDS IN THE PENNINE BASIN

Summary The sedimentary sequence between the Gastrioceras cancellatum Marine Band and the Rough Rock in south-east Lancashire comprises a wide range of lithologies ranging from mudstone through siltstone to ripple cross-laminated and cross-bedded medium-grained sandstones. The sequence consists broadly of two coarsening upwards sequences, each dominantly of mudstone and siltstone in its lower part and each capped by a sandstone member, the Lower and Upper Haslingden Flags respectively. Isopachytes on these sandstones show them to form elongate lobes thinning eastwards from a maximum exposed development around Blackburn. Palaeocurrent directions are dominantly towards the east. Both sandstones are cross-bedded in their central upstream regions and, in the Upper Haslingden Flags, a complex internal geometry involves large scale, low-angle cross-bedding up to 27 metres thick. The overall geometry and lithofacies assemblage is compared with that of a modern bar-finger sand and, in the Upper Haslingden Flags, the internal structure of the actual distributary mouth bar is shown. These deltas differ in type from the usual Millstone Grit delta in their finer grain size, their body geometry and in their palaeocurrent pattern. These points of difference raise the possibility of a western source area for at least some of the Millstone Grit and also imply that a different hydrological regime may have operated there.

Solution Subsidence Mechanisms and End-Products in South-East Breconshire

Low-dipping Carboniferous Limestone and Basal Grit (Millstone Grit) provide the structural framework for stepped scarp faces and intervening elevated dip-slopes on this segment of the North Crop of the South Wales coalfield. Fully half the extent of the limestone country is veneered with the jumbled and highly-broken remnants of a former grit cover. This has been largely derived through solution-subsidence agencies, but has been appreciably modified by periglacial influences. It is considered that concentrated solution along or directly beneath a former up-dip extension of the irregular plane of unconformity separating the two main formations of this area was, in the first place, largely responsible for the collapse of the overlying beds. Accelerated rates of solution directed from the base of depressions within this subgrit surface probably initiated the production of most of the numerous 'pockets' of collapsed grit blocks, while a notable proportion of the spectacular collapse dolines pitting the present in situ Basal Grit exposures are likely to reflect roof falls in underlying major caverns developed along or immediately below the down-dip continuation of this same plane. THE relatively narrow outcrops of the Carboniferous Limestone and Basal Grit (Millstone Grit) which fringe the North Crop of the South Wales coalfield show specific karstic landforms on more impressive scales than are recorded elsewhere in Britain.1 Foremost amongst such landforms are the slumped masses of Basal Grit let down throughout a long history of solution subsidence so as to lie at present at highly anomalous levels well within the Carboniferous Limestone outcrop and in extreme cases up to 250 m below their original in situ position. They vividly reflect the potency of solution-collapse processes as erosive agents where calcareous beds are present, but on the other hand when closely spaced over wide areas they have the effect of creating a form of derived scenery which can be differentiated from that featuring drift-covered Carboniferous Limestone terrain. The mapping of these collapsed Millstone Grit masses has previously been recorded for the western half of south Breconshire and the adjoining sectors of south-east Carmarthenshire.2 Recent re-surveys of the Ammanford (230)3 and Merthyr Tydfil (23 )4 One-Inch Sheets by the Institute of Geological Sciences have also confirmed that slumped Basal Grit derived by this means is much more prevalent than was indicated by the earlier surveys. Within the 20-km stretch of high moorland country lying between the Taf Fechan valley to the north of Merthyr Tydfil and the northern slopes of the Clydach valley to the east of Brynmawr (Figs. I and 2) there are significant differences between the collapsed Basal Grit deposits and those occurring in the areas located farther west. In these western areas the extraction of siliceous materials from a number of open pits has revealed that bedding planes are still discernible in the collapsed grit and beds of excessively-rotten, quartzose sandstone or seams of loose quartz sand make up a notable proportion of the stratigraphic sequence which may attain a vertical thickness in excess of 25 m. In contrast, in the area under review the deposits invariably comprise a jumble of large to medium-sized blocks of quartzitic sandstone or quartz conglomerate with little or no interstitial material. Pocket deposits of Millstone Grit blocks are also more prevalent in this eastern

A geophysical study of Pleistocene buried valleys in the Lower Swansea Valley, Vale of Neath and Swansea Bay

The distribution of drift in the Lower Swansea Valley, Vale of Neath and Swansea Bay has been studied by geophysical surveying. Onshore, detailed gravity surveys have been used to detect small negative Bouguer anomalies associated with areas of thick drift; offshore, the distribution of drift has been mapped by continuous seismic profiling. A contour map of concealed bedrock topography is presented. The surveys indicate a series of drift-filled, buried valleys characterised by overdeepened basins, the deepest of which occurs in the Vale of Neath and extends to a depth of approximately — 160 m. O.D. In the onshore area the position of the buried valleys and, in particular, the overdeepened basins is closely controlled by the prevailing geological structure and lithology. On the assumption that the distribution and geometry of the offshore buried valleys is similarly controlled, an attempt is made to infer the bedrock geology of parts of Swansea Bay floored by a virtually continuous sediment cover. It is suggested that the Neath Disturbance courses south-westwards across Swansea Bay, passing seawards of Mumbles Head, and that Millstone Grit in the core of the Pwll-du syncline subcrops over a substantial area of the sea-bed immediately to the south-east of Gower.

Discussion on W. B. Evans

E. J. Arrowsmith, A. G. Morris and L. Bradley (North Western Road Construction Unit) described slips and remedial measures in cuttings at three localities on the M62. With major slips occurring either during construction or after completion of excavation, and with the need rapidly to establish stable slopes, detailed investigations could not be undertaken. Subsequent observations showed that the slopes had certain features in common. The strata consist of alternating beds of sandstone and shale of the Millstone Grit and beds at the base of the Lower Coal Measures. Bedding dips gently into the cuttings at 6° to 20°. Modes of failure appeared to have been similar in all cases and were interpreted as translational slides on low shear strength materials in a geological setting of partially confined aquifers and potentially high seepage forces. The authors assumed a general form of wedge failure illustrated in Fig. 1, and presented simplified diagrams and geological cross-sections showing the slope profiles and the suggested limits of rock movement behind the face (Figs. 2, 4 & 5. Piezometers were installed in boreholes in the north batter of Windy Hill Cutting (Fig. 2) and the recordings from them gave some indication of the response of the several perched water tables to the incidence of rainfall (Fig. 3). They were used to check the effectiveness of the drainage measures in depressing the water-levels below critical values. Low strength materials encountered in the cuttings were probably clay mylonites and appeared in each case to have been the

A DEEP BOREHOLE AT HARTON ON THE MARGIN OF THE NORTHUMBRIAN TROUGH

Summary The deep Harton borehole on the north Durham coast penetrated 73 metres of Permian beds underlain by Coal Measures (367 metres), Millstone Grit (98 metres), Upper Limestone Group (341 metres), Middle Limestone Group (410 metres), an un-named limestone group (76 metres), and an un-named sandstone group (302 metres). In addition three quartz-dolerite intrusive bodies totalling 99 metres in thickness were present. The hole reached a total depth of 1,769 metres (5,804 feet) without reaching the base of the Carboniferous. The rank and texture of coal seams in the succession have been altered by the igneous intrusions and there is evidence that the lower coals had attained anthracitic rank before the bottom intrusion, or possibly before all of the intrusions, had been emplaced. Until Harton No. 1 was drilled it was believed on the evidence of a gravity survey that the borehole would penetrate an Alston Block type of succession and that the boundary between the block and the Northumbrian Trough coincided with the Ninety Fathom Fault, six kilometres (4 miles) north of the borehole. However, the thickness of the Lower Carboniferous succession and its lithology indicate that Harton No. 1 was drilled in the Northumbrian Trough. The boundary between block and trough is probably gradational and not a sharp boundary such as occurs over the Stublick Fault farther west.

Petrology, Provenance and Silica Diagenesis of the Penrith Sandstone (Lower Permian) of Northwest England

ABSTRACT The Penrith Sandstone (Lower Permian) of north west England is a continental red bed sandstone, deposited as barchan sand dunes in a hot, arid desert environment. The rock displays a high degree of mineralogical and textural maturity, being a coarse, well sorted orthoquartzite, composed of rounded unstrained, strained and polycrystalline quartz grains, with subordinate feldspar and rock fragments. Distinct petrographic features of the detrital grains suggest derivation from the Millstone Grit (Upper Carboniferous) sandstones of Yorkshire, and perhaps County Durham. In the southern part of the area non-silicified sandstones are interbedded with calcite cemented alluvial fan breccias (brockrams). This contrasts markedly with northern areas where brockrams are absent, in that the sandstones are tightly cemented with secondary quartz, occurring as overgrowths of optically continuous, bipyramidal quartz crystals around detrital grains. Many varieties of overgrowth are present, their structure being pre-determined by the internal structure of the detrital grains. Thus, unicrystaline unstrained and strained, and polycrystalline overgrowths can be recognised. Overgrowths of secondary feldspar occur occasionally on detrital orthoclase and microcline. It is suggested that the source of the secondary quartz is due to the solution of the siliceous dusts produced during aeolian abrasion of the quartz grains. Alkaline desert groundwaters are considered to be responsible for taking the siliceous dust into solution, which, upon evaporation, precipitated the silica as optically continuous quartz overgrowths around the detrital grains. The inverse relationship between silicification of the Penrith Sandstones and brockram distribution is attributed to differences in compositon of the groundwaters in the two facies.

Jointing, Aspect and the Orientation of Scarp-Face Dry Valleys, near Ivinghoe, Buckinghamshire

The relationships between the orientations of scarp-face dry valleys, elements in the geological structure (particularly joints) and the aspect of the scarp are examined in respect of the Chiltern escarpment at Ivinghoe. Both joints and dry valleys show preferred orientations which are unlikely to be the result of chance but there is only a very weak correlation between preferred joint and preferred dry-valley directions. Even the most deeply incised valleys cannot be related to the joint pattern in any convincing way. The only relationship detected is between the orientations of the regional strike and dip and those of a few valleys or segments of valleys, including parts of the most deeply incised ones. It appears that, in this area, joints do not determine dry-valley orientations but that in some instances strike faults may do so. The evidence does not support an hypothesis of spring sapping for the origin of the valleys. There is a marked tendency for the dry valleys to run either near-normally down the scarp or obliquely from right to left as the scarp is viewed from below. Linear erosion, probably by niveo-fluvial processes and largely controlled in direction by the slope of the scarp face, is a possible mode of origin for those valleys trending normal to the scarp. The obliquely trending valleys may have been inherited from an earlier valley system. THAT JOINT planes serve as avenues of attack for the process of weathering has long been a matter of general field observation. All standard text books in physical geology and geomorphology make reference to their importance (A. Holmes, 1965, p. I03; B. W. Sparks, I960, p. 33). It has further been suggested that in some instances, notably in granite areas, the distribution and frequency ofjoints are important indirect controls of landform. D. L. Linton (1955) concludes that the selection of a particular mass of rock for survival as a tor, while neighbouring masses are decomposed, is a function of the wider spacing of joints at the site of the tor. R. S. Waters (I957) has argued that, complementarily, the relatively broad valley widenings or basins that feature in the morphology of Dartmoor, are the morphological antitheses of upstanding tor-crowned hills, the consequence of differential lowering where joints are most closely spaced. It is also probable thatjoints may in some circumstances be created by erosion; in particular, pseudo-bedding planes or sheet joints are thought to result from pressure release consequent upon the removal of an overburden by erosion. This would appear to be a situation where joints actively contribute to the fashioning of surface form (C. A. Chapman, 1958; Chapman and R. L. Rioux, 1958) in contrast to their predominantly passive role in the formation of tors. The influence of jointing upon fluvial erosion has seemingly excited much less interest. But in an early statistical study of successive 25-foot (7.6 m) segments along the Rivers Wharfe, Ure, and Derwent and the Newtondale glacial meltwater channel, K. Harrison and A. D. Thackeray (1940) confidently suggested a causal relationship between segments with preferred orientations of 024-o25°, II2-1I6° and 163° true bearing, and joints in the Magnesian Limestone, Millstone Grit and Corallian having preferred orientations of o24°, II5° and I63°, as measured by S. Melmore (I938).

Saline ground-waters in the Carboniferous Rocks of the English East Midlands in relation to the geology

Summary The Carboniferous system in the East Midlands is comprised of a limestone-shale series or a massive limestone (the Carboniferous Limestone) overlain by a cyclic sequence of sandstones, mudstones, seat-earths and coals (the Millstone Grit and Coal Measures). The geology is described briefly and modifications are made to correlations of the Millstone Grit and Lower Coal Measures in the light of recent studies of information obtained by deep drilling for oil. Most of the Carboniferous ground-waters discussed are saline with total concentrations ranging up to 246 000 mg/1. The concentration in all formations increases from the Eakring-Kelham Hills area towards Gainsborough, that is from SW to NE, and the variation in ionic content associated with this increase is discussed. The ground-waters are believed to have originated from the diagenesis of Carboniferous marine and brackish waters and possibly some Permian marine waters. They have probably been concentrated by argillaceous beds acting as semi-permeable membranes and it is suggested that the increase in the Ca/Cl and Mg/Cl ratios as the total ionic concentration increases is due to the selective concentration of calcium and magnesium ions by argillaceous beds. In the south-west and south of the East Midlands the saline water has been diluted, probably by meteoric water moving through the aquifers from the outcrop areas and discharging into Permo-Triassic rocks, where these overlie Carboniferous aquifers at depth in the south-east of the region.

The Ecology of Saltmarsh Acarina

Llanrhidian saltmarsh is situated on the north coast of the Gower Peninsula in South Wales at the southern edge of the Burry River estuary. It is an ancient marsh composed of post-glacial alluvial deposits with boulder clay. The hills behind are composed of red sandstone conglomerate, carboniferous limestone and millstone grit. Very little reclamation has taken place since 1750 (Plummer 1960), although the marsh turf is now designated as common land and is grazed closely by sheep, cattle and horses. The immediate effect of this is to cause the saltmarsh plants to assume dwarf proportions producing a compact turf. Primary and creek-type pans are numerous in all phases of the marsh and the larger creeks are susceptible to erosion owing to the rather sandy subsoil. Soil profile studies show that the surface layers of soil are composed of organic gleys which overlie sand at all levels. The marsh gleys become thinner towards the sea and eventually disappear on the sand flats. As on most saltmarshes the vegetation exhibits a marked zonation. The lowest zone, established in 1957 in the sampling area, consists of Spartina townsendii H. & S. Groves growing in sand. These Spartina clumps have caused the deposition of a small amount of silt which provides a substrate for Salicornia europaea L. The next zone, submerged by tides every day, is mainly composed of S. europaea, together with some Puccinellia maritima (Huds.) Parl., Suaeda maritima (L.) Dum., and strands of the alga Enteromorpha. Next to this is a Puccinellio-Salicornietum (or Puccinellio-Suaedetum near the creeks) containing a high proportion of Aster tripolium L. From here the Puccinellietum proper extends as far as the High Water Spring Tide mark and has an abundant associated vegetation of typical saltmarsh plants. Above this is a sward of Festuca rubra L. (the Festucetum) which is the most heavily grazed area. Plants such as Armeria maritima (Mill.) Willd., Plantago maritima L., Aster tripolium and Cochlearia officinalis L., which are found in large numbers here, are always very low-growing and dwarfed. The climax vegetation is Juncus maritimus Lam. with Festuca rubra and Puccinellia maritima as

Deposition of Peat from Aqueous Suspensions; Natural Occurrence of Stalactitic and Related Forms

IN the course of study of a line of caverns at Ystradfellte, Breconshire, described previously1,2 the occurrence of a hitherto unrecorded type of stalactite formation was noted. Most of the formations are unconsolidated, conical in shape and hang vertically from the Millstone Grit caprock forming the roofs (Fig. 1). They range in length from 0.4 to 30.0 cm and in mean diameter from 0.1 to 5.5 cm respectively, and are composed of a non-fibrous size-fraction of blackish brown peat transported from the surface peat bog overlying the grit. In most cases cross-sections reveal a series of concentric growth rings. These are co-axial with the core when it is present. The formations occur in two main types: joint-orientated lines extending across the roofs (type I); randomly distributed and isolated formations (type II).

Aisled Houses in the Halifax Area

The houses with which this paper is concerned belong to the small segment of the eastern slopes of the Pennines known as the ‘Ancient Parish of Halifax’. It is not known when the ‘Ancient Parish’ was formed but the first recorded vicar of Halifax was inducted in 1274 and in that same year the Wakefield Manor Courts ceased to meet in Sowerby Town and made Halifax their centre.The Ancient Parish covers ten miles of the valley of the river Calder and its tributaries, Halifax itself lying on the Hebble. The area is bleak; it lies, all except the extreme eastern part, on Millstone Grit and rises from a height of some 200 feet above sea level in the valley to an altitude of 1,400 feet. The old settlements mostly lie on the sloping hillsides at an average height of 700 feet.

Les minéraux argileux dans le tertiaire du bassin de Paris. Problèmes d'origine et de genèse

Montmorillonite, probably detrital, predominates in the formations which cover the chalk in the north and west of the Paris Basin (Thanetian and Sparnacian stages). Detrital kaolin, ori¬ ginating from the Massif Central, has been spread out in two layers in the Paris Basin (Sparnacian plastic clays and Miocene "granitic" sands). The Lutetian sequence of clays : kaolinite -illite montmorillonite -attapulgite is characteristic of the only complete geochemical cycle in the Tertiary layer of the Paris basin. The lagoon formations of the Ludian and Sannoisian stages consist chiefly of magnesium clays , attapulgite and sepiolite. Illite is predominant in the Oligocene, except in the continental formations (Millstone Grit clays) which contain mostly kaolinite. This latter is probably recently formed as is in part the kaolinite from flint clays.

A Non-Marine Lamellibranch from the “Millstone Grit” in Northumberland

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The Millstone Grit succession between Brynmawr and Blorenge, South Wales, and its relationship to the Carboniferous Limestone

The Namurian and lowest Westphalian beds of the Millstone Grit are mapped between Brynmawr and Blorenge, South Wales. It is shown that a phase of secondary dolomitisation is related to zones of close jointing of post-Carboniferous age. This has led to easier weathering of the more friable dolomite which in turn has resulted in irregularities along the Millstone Grit-Carboniferous Limestone junction. Details of an easterly directed overstep of Namurian B (R 2) age are described together with a further possible overstep of early Westphalian ( lenisulcata Zone) age.

The palaeogeographic significance of isotopic age determinations on detrital micas from the triassic of the Stockport-Macclesfield district, Cheshire, England

A trial investigation of the possible geological application of isotopic age determinations to sedimentary studies. Forty-one new potassium-argon age determinations on detrital mica concentrates from the Triassic of the Stockport-Macclesfield district, Cheshire, and two determinations on detrital micas from the Millstone Grit of north Derbyshire are reported. A general discussion of the theoretical problems involved in the interpretation of isotopic results from detrital micas is followed by a detailed analysis of the sedimentation, petrology and subsequent history of the Triassic samples used in the study. It is shown that the isotopic results can be used to supplement stratigraphical and heavy mineral studies and make palaeogeographic interpretation both easier and more certain. In particular, it is concluded that the bulk of the Triassic of the Stockport-Macclesfield district was almost certainly derived from the south, being the deposits of a river that drained the Wessex-Channel Basin via the Worcester Graben. Differences in their isotopic patterns enable a clear distinction to be made between the Bunter and Keuper deposits, and it is suggested that this kind of work may have economic applications.

X.—A Gravity Survey in Ayrshire and its Geological Interpretation

SynopsisBouguer anomaly maps covering most of Ayrshire at a density of about one station per sq. km., show a close relationship between anomalies and the distribution of the Upper Palæozoic rocks in the area south of the Inch-gotrick Fault, but are less clearly interpreted to the north, where thick dense igneous masses are present.In central and south Ayrshire the gravity field may be largely interpreted in terms of the known density-contrasts at the interfaces separating Upper and Lower Old Red Sandstone, and Lower Old Red Sandstone and Lower Palæozoic rocks. The major structure, the Mauchline Basin, is reflected clearly in the largest anomaly, and there is evidence of a culmination of its south-western limb near Kirkoswald. The important N.E.–S.W. faults also give rise to large anomalies, which may be connected with the known geology. It is inferred that they moved as normal faults in Carboniferous times, and that the adjacent synclines are essentially sags associated with the fault displacements. There is geophysical evidence that both the Southern Upland and Kerse Loch Faults existed in Middle O.R.S. (proto-Armorican) times. It is concluded that a hypothesis of N.–S. Armorican stress is not valid in south Ayrshire.In north Ayrshire, many of the anomalies are best explained by changes of thickness of the Millstone Grit lavas and of the Clyde Plateau lavas, and by the presence of thick dolerite intrusions. Additional evidence is needed, however, before final conclusions may be drawn.

A study of the depositional area of the Glamorgan lias

Orientation studies of echinoid spines and sponge spicules, coupled with a study of small-scale sedimentary structures, suggest that a principal direction of Lias sedimentation in the Vale of Glamorgan was from the south. The absence of northerly derived Coal Measure or Millstone Grit lithoclasts in the nearshore and offshore Liassic sediments in Glamorgan support this view. The present South Crop of the South Wales Coalfield was presumably not exposed during the Lias.

THE CARBONIFEROUS SUCCESSION IN THE KIRKBY MALZEARD AREA, YORKSHIRE

Summary Beds described range from the Sabdenian (H) to the Halifaxian (G 2 ) stage. The sequence is thinner stage for stage than in the Bradford area, with the most marked attenuation in R 2 . A shelly siltstone in R 1 , the Ure Shell Bed, and its associated shales yield a fauna rich in brachiopods. Above the persistent Brimham Grits are fifty feet of measures with two Lingula bands, thought to be the sole representatives of R 2 . Measures in G 1 and G 2 , include the Gastrioceras cumbriense band and two beds with Lingula. Some eight square miles of country hitherto mapped as Millstone Grit are considered to be of Westphalian age.

Note on recent spore and goniatite evidence from the Passage Group, of the Scottish Upper Carboniferous succession

A break in the deposition of the Passage Group, formerly Scottish Millstone Grit, has been inferred by many authors. This was based on the lack of faunal evidence of the Namurian stages between the top of the Arnsbergian (E2) and the Coal Measures. Recent evidence from spores and goniatites has shown, however, that some, at least, of the missing stages are present. The spore evidence is from coal samples collected by Messrs P. J. Brand and D. K. Graham from Bonnyside No. 2 Mine by kind permission of the owners, Messrs James Dougall and Sons Ltd. The mine is sited one mile south-east of Bonnybridge, close to Bonnyside Estate Bore (1954–55). It starts in beds just below the local base of the Coal Measures and cuts down through the greater part of the Passage Group. From the record of the bore, the strata in the mine can be correlated with successions in the Clackmannan syncline (Fig. 1). A study, by the first-named author, of the spore assemblages obtained from the coals indicates that a more complete Namurian succession is present in Scotland than was formerly supposed. The samples were taken from fourteen thin coals, numbered as on Fig. 1, which range in horizon from just below No. 2 Marine Band up to the Bowhouse-bog Coal, near the top of the Passage Group. A moderate diversity of well-preserved miospores was obtained from most of the coals. Many of the spores are species of the genera Lycospora, Densosporites, Calamospora, Savitrisporites and ...

Notes on the Millstone Grit of the North Crop of the Pembrokeshire Coalfield

The two cliff sections, one at Marros and the other between Settling Nose and Druidston Haven, at the eastern and western ends of the north crop of the Pembrokeshire Coalfield, are described in detail. Several undescribed marine horizons, including goniatite bands, are reported. The strata are correlated with the Millstone Grit of the north crop of the South Wales Coalfield, and the sub-Namurian unconformity is discussed.