Dolomitic Conglomerate Research Articles

The water-related work of William Smith (1769–1839)

Abstract In 1797 Smith recorded his first known ‘Order of Strata’. This was based on his work as a land, colliery and canal surveyor around Bath, Somerset. It already shows a clear awareness of the occurrence of spring lines (especially in the Fuller’s Earth, soon to cause such problems in the construction of the Somerset Coal Canal). In his better known June 1799 version, Smith much extended this, with a new third column showing springs, now tabulated for five of his 23 strata. Smith thus had a keen awareness of both the importance of, and the problems raised by, how water was, or was not, retained in rocks and how it was released at stratigraphically controlled spring lines. This paper briefly reviews five of his involvements with ‘water-related’ geology. The first was as canal engineer. Here one of the two branches of his first canal later had to be abandoned because it could not be made to retain water where it passed over the Dolomitic Conglomerate. The second was as a land drainer. This he first attempted at Camerton in about 1796. This skill brought him most of his early employments after his dismissal from canal work in June 1799. Third, Smith was next a significant exponent of the art of creating water meadows, particularly in Bedfordshire and Norfolk. Smith was active next in a fourth field, erecting sea defences along the east coast of England. Finally he was often consulted on how to find or control new water supplies, as at Swindon or Scarborough. It was this last work which used his stratigraphic skills to their fullest extent.

Catastrophic mass failure of a Neoproterozoic glacially influenced continental margin, the Great Breccia, Port Askaig Formation, Scotland

Abstract The Great Breccia is a thick (over 50 m) diamictite that occurs close to the base of the Neoproterozoic Port Askaig Formation in Scotland, and contains matrix-supported clasts up to 100 m across in a poorly sorted dolomitic matrix. Detailed logging and mapping of cliff and shoreline exposures through the Great Breccia on the Garvellach Islands show that it is not a simple ‘megabreccia’ but consists of three sedimentary units including a megabreccia (Unit 1), diamictites interbedded with dolomitic conglomerate, sandstone and mudstone (Unit 2) and a diamictite with metre-sized dolomite clasts (Unit 3). The sedimentological characteristics of the Great Breccia indicate that it formed by a variety of subaqueous sediment gravity flow processes, including matrix-rich debris flows and turbidites. Clasts up to 100 m across contained within the megabreccia unit record catastrophic collapse and failure of local calcareous siliciclastic deposits; other diamictite units were deposited by debris flows. Conglomerates were deposited from high-concentration turbulent flows, and sandstones and fine-grained facies also exhibit characteristics typical of turbidites. Continued downslope remobilization of sediment in the basin following deposition of the Great Breccia is recorded by overlying deformed diamictites, detrital dolomites and siltstones of the Disrupted Beds. The Great Breccia and associated facies within the lowermost part of the Port Askaig Formation are similar to those found in carbonate megabreccia successions that record catastrophic mass failure of carbonate platforms. Failure events in the Port Askaig Formation most likely relate to localized faulting and subsidence of the Dalradian Basin. Although the Port Askaig Formation is considered a Neoproterozoic ‘glacial’ succession, there is little direct evidence for glacial influence on sedimentation in the Great Breccia, making it difficult to fully assess paleoclimatic conditions.

Creation of functional ground models in an urban area

Rationale The ability to see the ground surface in an urban environment is limited by access and the amount of natural ground exposure. This is typically less than 10% by area. The assessment of the probable ground structure and the behaviour of critical ground elements can be achieved by comparison with non-urban environments exhibiting similar landforms. This model can be verified by a detailed study of historic maps and a review of existing local subsurface information. The site The City of Cardiff has largely been constructed in the last 150 years. The area studied relates to the whole city land area lying to the south of the A48T and between the west banks of the rivers Ely and Rhymney. Area model The area lies substantially on the Severn Levels, which comprise a recent tidal coastal margin zone of the Severn estuary. The area consists of a glaciated land surface comprising Mercia Mudstone and Dolomitic Conglomerate draped by a thin and partly discontinuous layer of glacial detritus that includes two identifiable layers of till and a consistent layer of fluvio-glacial sands and gravels which forms the dominant aquifer. These strata reflect Devensian and Flandrian glacial advance and recession. To the south of the historic natural shoreline a series of post-glacial foreshore alluvia are superimposed on the late-glacial surface and form a confining layer to the underlying fluvio-glacial sand and gravel aquifer. These alluvia represent a series of more recent marine transgressions modified by sea defence construction works of Bronze Age to late mediaeval antiquity.

Case histories of some effects of solution/dissolution in the Keuper rocks of the Severn Estuary region

Summary The Keuper strata in the Severn Estuary region can be divided into two fades, a scree/rock fan deposit known as the Dolomitic Conglomerate and a basin facies referred to as the Keuper Marl. Both facies contain gypsum or evidence indicating that gypsum was once present. As a result of diagenetic changes, such as the release of strontium when aragonite changes to calcite, and also calcite to dolomite, in some areas the initial gypsum, anhydrite accumulation has been replaced by celestine. Recent construction works have indicated that in parts of the area cavities occur in the Keuper rocks. Some of these cavities have caused engineering problems. Those near the top of the Keuper Marl in the Airport Road tunnel caused machine stress due to the Dosco boom attempting to deflect to the areas of nil resistance. In addition, there was some overbreak and increased grout take. Data obtained on samples from Llandough Quarry, Cardiff are presented to support the hypothesis that where dolomitic strata combine with gypsum, dedolomitization may occur resulting in degraded, very weak mudstone. Pronounced dolomitised ‘veins’ occur in one area of the quarry; these are described and X-ray diffraction traces are presented to support dolomitization from a joint outwards.

Quartz replaced anhydrite nodules (‘Bristol Diamonds’) from the Triassic of the Bristol District

SummaryQuartz nodules and geodes, known as Bristol Diamonds, occur in the Triassic Dolomitic Conglomerate of the Bristol district of England. They are composed of either, megaquartz, milky in the outer part and clear towards the centre, or fibrous quartz, chalcedony and lutecite. Much of the quartz, particularly in the outer parts, is full of anhydrite inclusions which are relics of larger lath-shaped anhydrite crystals. The Bristol Diamonds formed by silica replacement of anhydrite nodules, with replacement proceeding from the outside inwards. In many cases anhydrite solution was faster than silica replacement, so that a central void developed into which grew crystals with fine terminations. The anhydrite formed by precipitation of sulphate from hypersaline sediment-porewaters, probably in a marginal playa situation.

Foundation construction at the Bristol Royal Infirmary—Phase 1

Summary The Bristol Royal Infirmary is located on the south-easterly face of Kingsdown Hill overlooking the centre of Bristol. A series of extensions to the Infirmary have been constructed since 1966 and are planned for the future. The hill is underlain by alternating hard sandstones and mudstones of the Quartzitic Sandstone Group which dip towards the south-east at a steeper angle than the ground slope. The Carboniferous rocks are overlain by the Triassic Dolomitic Conglomerate in the upper part of the site, and by Triassic marls and fill at lower elevations. The hillside has a past record of instability both in superficial materials and in bedrock. The stability of the site had to be judged both overall and in relation to the design and construction of individual structures. The design of the foundations for each of these structures was based upon drilling coupled with a programme of laboratory and in situ tests. The largest building is the Outpatients Department which required major basements involving deep excavation into the hillside undercutting the bedding. The foundations for this structure were primarily created by buttresses formed in trench and combined with cross walls so ensuring total stability at all stages of excavation. In contrast, the Radiotherapy Centre is mainly founded on isolated bases carried down to bedrock and appropriately stepped in level. The thick walls between the treatment rooms in the basement were keyed into the quartzitic sandstone or very firm mudstone. The Maternity Hospital, located at the top of the site on thick Triassic deposits, has been founded on large diameter bored piles drilled into the Dolomitic Conglomerate. Attention is drawn to the special problems which arose during construction including the need for controlled blasting for excavation and the control of water, partly in relation to a medieval tunnel system.

A New Occurrence Of Celestite, Near Llantrisant, Glamorgan

An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The stratigraphy and sedimentary features of the Old Red Sandstone, portishead coastal section, north-east Somerset

Detailed examination of the Old Red Sandstone succession, which is unconformably overlain by Triassic Dolomitic Conglomerate, has permitted subdivision into twelve formations. The Lower Old Red Sandstone comprises cross-bedded sandstones but the younger rocks are more diversified and may be separated into conglomerate, sandstone and siltstone units. The Lower and Upper Old Red Sandstone contact is a conspicuous disconformity. The beds above and below the disconformable surface display layers of well-developed cornstone, which are interpreted as ancient caliche deposits. Cross-bedding studies show that the Old Red Sandstone sediments were mainly derived from the north-west.

XXVI.—A Late-Celtic and Romano-British Cave-dwelling at Wookey-Hole, near Wells, Somerset

The great cavern of Wookey-Hole is situated two miles to the north-west of the city of Wells, in the centre of Somerset, and immediately adjacent to the thriving- village which has taken the name of the cavern, and has depended for its prosperity on the existence of the copious and usually pellucid stream, which here bursts forth from Mendip's hidden reservoirs. This is the source of the Axe, which winds its way through the lower lands, and after uniting with the sister stream of Cheddar, flows into the sea near Weston-super-mare. From Wookey-Hole the southern slope of Mendip rises in an unbroken sweep till it reaches a thousand feet above the sea, commanding a magnificent view to the east, south, and west. It is not a limestone cave in the ordinary sense of the word, since every known cavity in the immediate vicinity is not in the Carboniferous Limestone, but in the Dolomitic Conglomerate, which here attains enormous thickness. To the north, the great mass of Carboniferous Limestone, receiving the water of innumerable springs from the Old Red Sandstone and Shales and from a generous rainfall, engulfs it in a countless number of swallets, many of which are insignificant, whilst some of the larger have been opened by our exploring parties during the past few years, and followed through unimagined beauties to profound depths.

On the Relation of Certain Breccias to the Physical Geography of their Age

Breccias and conglomerates have always attracted me, and the former especially since I had opportunities, about ten years ago, of examining one of the most interesting examples in Europe. They afforded problems, to which I failed to find answers in all respects satisfactory; so in the hope of obtaining further information I spent, during the summer of 1900, some days in the Western Thüringerwald, with my friend the Rev. Edwin Hill, in order to study the noted breccias of the Rothliegende, and last July again examined, and more fully than before, the beds of breccia, sections of which are well displayed along the high road in the Val des Ormonts above Le Sepey. In former years I had visited the Permian Breccias of the English Midlands and those now assigned to that period in Devon. All these exhibit certain features in common, some of which are also found in the so-called Dolomitic Conglomerate in the South-west of England. So I purpose to give a brief summary of the principal characters of each of these deposits, concluding with some comparatively modern breccias, in order that, if I cannot completely unravel their history, I may at least bring the more significant facts into a clearer focus.

On Abnormal Geological Deposits in the Bristol District

In making excavations at Redland, on the edge of Durdham Down, about 45 years ago, some conglomerates, associated with Carboniferous Limestone, were opened up, which contained the teeth and scattered and broken bones of reptilia, described by Messrs. Riley and Stuchbury in the ‘Proceedings of the Geological Society’ for 1836 under the names of Thecodontosaurus and Palæosaurus . As they were then the oldest known reptilia and of a high order, much interest has always attached to them. A few years since, in drainage-works at the same spot, this conglomerate was again crossed, and some other bones added to the series deposited in the Museum of the Bristol Philosophical Society. The collection has since been reviewed and described by Professor Huxley, F.R.S., and an account of the physical characters of the district given by Mr. Etheridge, F.R.S. Much uncertainty has prevailed as to the geological age of the Durdham-Down conglomerate. At first it was supposed to be Permian; but we have as yet no conclusive evidence of true Permian beds in the West of England. Mr. Etheridge has placed it on the horizon of the Dolomitic Conglomerate of the Keuper; whilst, owing to the discovery by myself of the same genera of reptilia, under somewhat similar physical conditions, in the Rhætic deposits of Holwell, and since then of true Rhætic remains on Clifton Down, I had referred them to the latter age—a point to be reviewed below. In my paper on the abnormal conditions presented in the Frome district I especially

III.—On the Occurrence of the Keuper Basement Beds in the Neighbourhood of Nottingham

Hitherto, exposures of the junction of the Bunter formation with the Keuper, in the Nottingham district, have shown the brown sandstones and red marls of the “Waterstones,” with a band of dolomitic conglomerate at the base, resting directly on an eroded surface of the Bunter Pebble Beds. Recently, howeve, between these formations there have been observed to intervene certain deposits that agree both in mineral composition and in physical characters with the white sandstones and conglomerates, known as the “Basement Beds,” that form so important a feature in the Keuper of the West Midlands.

On the Triassic Conglomerate near Cardiff

These beds are mapped by the Geological Survey as dolomitic conglomerate and marlstones, and appear to lie in a depression of the Carboniferous Limestone, by which they are bounded on all sides except the W., where they dip gradually into the sea. Immediately behind the village of Newton on the N. they are deposited close up to the base of the Limestone cliff; on which most of the village is built ; and they are shown all along the road to Nottage at intervals, forming a sort of natural pitching for the road. At Schorlon, where this stone was dug up, I was unable to examine them on account of the snow ; but in the small exposures I saw they seem to dip very slightly, perhaps 2 or 3 de~,oTees W. As it was useless, on account of the weather, to attempt any thing more here, I proceeded to Porth-Cawl, and strikingW, along the shore found that the Carboniferous beds still maintained the same genera] characters as at Newton, and had a slight dip W.N.W. of about 8 degrees.

On the Chronological Value of the Triassic Strata of the South-western Counties

I n no part of the south-western counties is a more detailed section of the Triassic rocks exhibited than on the South-Devon coast. It is the district in which the subdivisions seem to have attained their maximum thickness; and though they may be traced in unbroken conformity to Williton, near the shores of the Bristol Channel, the absence of the lower members of the group to the east of Taunton, and a study of the variable relations of land and water during the period in different parts of the area, render the proof of the following propositions a necessary supplement or second part of the paper which I have already had the honour of communicating to the Society*. F irst P roposition .—That the South-Devon and West-Somerset Triassic area was not connected with that of Gloucester and the midland counties till the later stages of the Keuper period. Proof. —(a) The tailing-off of Triassic. sediments towards the Mendip country. (b) The representation of the Trias on the north of the Poldens by marls alone, the Dolomitic conglomerate being a contemporary beach. (c) The abnormal thinning-out of the Trias on the north of the Mendips. Thus at Tyning pit, near Radstock†, it was bottomed at 186 feet; at Norton-Hill pit at 172 feet; at Batheaston (under Rhætic) at 54 feet ; in Mangotsfield cutting at 25 feet. The general results arrived at by Mr. Moore give an average thickness of 50 feet to the Trias within the coal-basin. (d) The fact that these marls, being in

On the Geological Position and Geographical Distribution of the Reptilian or Dolomitic Conglomerate of the Bristol Area

I t is so long since any communication has been made to the Society upon the Dolomitic Conglomerate in a physical sense, that it appeared to me the time had arrived when a paper in our Journal embodying some general notice or history of the conglomerate might not be unacceptable, especially as the Dinosauria of the Trias have lately been so ably treated by Prof. Huxley. This paper is therefore devoted to a consideration of the geological position and geographical distribution of the conglomerate so widely spread over the Bristol area, and containing the remains of the Dinosaurian reptiles Thecodontosaurus and Palæosaurus . I have little to communicate that has not been noticed by the older writers; and the mention of the names of Bright, Gilby, Buckland, Conybeare, De la Beche, and Murchison, will show how little is left for me to do; but uninviting as this nearly unfossiliferous rock may appear at first sight, it nevertheless possesses a history even yet not written, and its origin, date, and fauna are still matter for investigation and research. This old breccia is a grand and striking feature over many parts of the area where it is well exposed, and is a marked condition in the geological history and physical structure of Britain, to be studied and understood only over the limited and complicated area occupied. by the palæozoic rocks of the Bristol coal-basin.

On a Hyæna-den at Wookey-Hole, near Wells

Of all the ossiferous caverns of this country which have from time to time been explored since 1821, there are none, perhaps, which form so exact a parallel to the Hyæna-den at Kirkdale as that which I bring before your notice this evening. It is situated at Wookey-Itole, a village on the southern flanks of the Mendips, and about two miles to the north-west of Wells. The ravine in which it was discovered is one of the many which pierce the dolomitic conglomerate, or petrified sea-beach of the Permian (?) age, still lmderlying its ancient sea-cliffs of Mountain-limestone, and overlying the lower slopes of the Mendips. Open to the south, it runs almost horizontally into the mountain-side, until closed abruptly northwards by a perpendicular wall of rock, 200 feet or more in height, ivy-covered, and affording a dwelling-place to innumerable jackdaws. Out of a cave at its base, in which Dr. Buckland* discovered pottery and human teeth, flows the River Axe, in a canal cut in the rock. In cutting this passage, that the water might be conveyed to a large paper-mill close by, the mouth of the tty~ena-den was intersected some ten years ago; and from that time up to December 1859, it was undisturbed save by rabbits and badgers ; and even they did not penetrate far into the interior, or make deep burrows. Close to the mouth of the cave the workmen (employed in making this canal) found more than 300 Roman coins, among which were those

Notice of the Occurrence of an Earthquake Shock at Bristol

As some particulars relating to the shock of an earthquake which occurred on Saturday the 3rd of April in this district may not be wholly uninteresting to the Fellows of the Geological Society, I do not hesitate to submit to your notice such facts in connexion with the subject as I have been enabled to collect from unquestionable sources of information. The area principally affected comprises that portion of country extending from the Mendip Hills to Bristol, and the village of Henbury in Gloucestershire to the north, and probably on to the Severn; and from the Mendips to the Bristol Channel on the west. The geological features of this district consist of old red sandstone, carboniferous limestone, millstone grit, coal-measures, dolomitic conglomerate, new red sandstone, lias, and oolite, with alluvial patches of some extent. The principal line of disturbance appears to have been nearly north and south, running through the southern edge of the Mendips, the city of Wells, Cheddar, Pensford, and Dundry, in Somersetshire; Bristol, Westbury upon Trym, and Henbury in Gloucestershire. The chief focus of oscillation was at Cheddar, where the hill is said to have waved to and fro during several seconds; and in the alluvial flat or marsh below Cheddar, some houses had the plaster of the ceilings cracked, while in other houses the clocks struck, bells rang, &c.