Permian Conglomerates Research Articles

Petrology and Diagenesis of Broughton Sandstone (Permian), Kiama District, New South Wales

ABSTRACT The Broughton Sandstone, a 500-foot thick horizontal sequence of Permian conglomerates, sandstones, and siltstones, interstratified with contemporaneous submarine volcanics (latites) occurs at Kiama, N.S.W. The sequence contains authigenic mineral assemblages characteristic of the laumontite zone of the zeolite facies. Albite, calcite, chlorite, quartz, clay minerals, and laumontite are the common authigenic minerals in the sediments, whereas in addition, prehnite, pumpellyite, epidote, and sphene occur in the latites. The clean-washed sediments are largely composed of volcanic rock fragments and detrital plagioclase with minor amounts of ferromagnesian minerals and quartz. The composition, sedimentary structures, and faunal assemblage indicate that the sediments were derived from a volcanic provenance, and deposited in a shallow-water marine, possibly near-shore environment. Physicochemical parameters of the early diagenetic environment appear to have significantly influenced the nature of the final authigenic minerals. Connate water and the breakdown of detrital constituents, especially calcic plagioclase, provided the chemical elements for the formation of the authigenic minerals. The low-grade 'burial' metamorphism, induced by increasing temperatures in response to increasing load pressures, alone, could not have produced the observed mineral assemblages, since the rocks have been buried to a maximum depth of only about 3000 feet.

Tippett Field, Crockett and Pecos Counties, Texas

The Tippett field comprises a group of eight pools located in northwestern Crockett County and adjacent Pecos County, Texas. The field was discovered in 1947, and to January 1, 1960, has produced about 2,700,000 barrels of oil and 1,540 million cubic feet of gas. The chief producing zones are conglomerates in the basal Permian at 5,800-6,300 feet. Minor producing zones are found in middle Permian dolomite from 3,800 to 4,500 feet. The trap is formed by an anticline about 6 miles long and 4 miles wide, the axis of which trends northwest and southeast. The structural relief on the basal Permian pay zones is about 300 feet. The anticline is clearly discernible at the surface, so that discovery may be credited to both surface work and shallow stratigraphic drilling. Total pro uctive area is about 2,540 acres. Though water is found in the basal Permian conglomerate reservoirs, a large gas cap in most of them probably furnishes most of the oil-producing energy. Some conglomerate reservoirs contain only gas. The pay conglomerates appear to be derived from Devonian and Ordovician cherty limestones and dolomites, which were truncated by Pennsylvanian erosion. The residual cherts seem to have been reworked into shingle beaches and then consolidated into porous conglomerates containing very little calcareous cement. Future productive prospects lie chiefly in gas reservoirs on the structurally higher part of the anticline.

BORINGS IN THE PERMIAN AND COAL MEASURES AROUND HARTLEPOOL

Seven borings have recently been put down in S.E. Durham in search of coal and water, and I have been privileged to examine the cores and reports of most of these through the kindness of the Horden Collieries, Ltd. and the Hartlepool Gas and Water Company. The strata and fossils met with in these borings are of considerable interest and have a bearing on such matters as the southern limit of the Durham Coalfield and the arrangement of the various facies of the Permian Formation. BORING ABOUT ¼ MILE N.W. OF THORPE BULMER FARM. No. 1 on sketch map, fig. 1. Altitude about 250 feet | | Depth | |:-------------------------------------------------------------------------------------------------------------------------- | ----- | --- | | | ft. | in. | | | Boulder clay; the red and brown Northern or Cheviot drift | 146 | 10 | | | Soft dolomite, grinding up in core; Schizodus schlotheimi and Liebea hausmanni | | | }Upper Magnesian Limestone | | Yellow, soft, non-porous dolomite | | | | Yellow, oolitic dolomite | | | | Yellow, dense, hard, thinly-bedded dolomite; a thick mass | | | | Yellow dolomite, brecciated | | | }Middle Magnesian Limestone | | Yellow, dense dolomite, partly massive, suggestive of reef rock | | | | Grey and buff, brecciated dolomite | | | | Grey, brecciated dolomite | | | | Yellow and grey, dense, bedded dolomite | | | }Lower Magnesian Limestone | | Hard, grey, dolomitic limestone; Serpula pusilla near the base | | | | Marl Slate, grey-black dolomitic marl, traces of fish remains | 707 | | }Marl Slate and Yellow Sands | | “Yellow Sands”; greyish-green sandstone with dull, rounded grains cemented with calcite, 10 ft. 6 in. thick | 719 | 6 | | Grey Sandstone | | | }Basal Permian Conglomerate | | Grey conglomerate and grit; 10 or 15 ft. thick, dull, rounded quartz grains and pebbles and a piece of siliceous crinoidal | | |

A Remarkable Quartzite Implement

The gravel-pit in which the implement was found in November, 1929, is known as the Bilford Pit, and is situated about a mile due east of the river Severn, in the Bilford Road, and a mile and a half due north from the centre of Worcester City. The surface level is 100 feet O.D., and the pit is owned and worked by the Worcester Corporation.The area in the immediate vicinity of Worcester could not have been exempt from some of the effects of the abnormal climate that prevailed over the British Islands during the Ice Age, yet we have at present no clear evidence of an invasion of the district by ice-sheets. The drift deposits around Worcester comprise a great variety of pebbles, beds of sand, and a few boulders. The pebbles are similar to those obtained from the Permian and Bunter conglomerates, and the pebble-beds of the Lickey and Clent district (about sixteen miles to the north of Worcester). They include yellow, brown, and liver-coloured quartzites, vein quartz, sandstone, chert, limestone, slate and various igneous rocks.The occurence of marine shells, Cretaceous flints, Liassic fossils, and other drift materials in the gravels extending from Cheshire to Gloucestershire, led Murchison to believe they were laid down by a marine current flowing from the north. Few geologists now accept this explanation.

III.—On some Chalk-pebbles from the Floor of the English Channel

In 1908 Mr. R. H. Worth described a number of stones which had been dredged by Mr. T. R. Crawshay, of the Marine Biological Association, from the floor of the English Channel to the east and south-east of the Lizard. These stones included a great variety of rocks such as granites, felsites, diorites, and other igneous rocks, gneisses, schists, slates, and quartzites, Devonian grits, Permian conglomerate, Triassic marl, sandstones of different kinds, Liassic limestones, hard chalks, and flints.

The Permian Conglomerates of the Lower Severn Basin

I. I ntroduction . B etween the River Severn and the village of Enville in South-east Shropshire, and again round the southern half of the South Staffordshire Coalfield, there are certain bands of rocks cemented and hardened by calcareous matter—namely, calcareous conglomerates, cornstones, and calcareous sandstones—which constitute parts of the group classified by the officers of the Geological Survey as Middle Permian. The object of this paper is to trace the materials composing these calcareous rocks to their sources. The typical Permian sequence of the Shropshire type is, according to Prof. Hull, as follows, in descending order:— Murchison stated that at Coton and Bowhills the calcareous horizons of the Middle Permian consist of ‘( a ) coarse conglomerate, composed chiefly of fragments of Carboniferous Limestone, generally rounded ; . . . . some of them are of an oolitic structure . . . . ( b ) conglomerate, with fewer fragments of limestone, but pebbles of quartz, Old Red Sandstone, ere . . . . . and minute fragments of jasper.’ He pointed out that ‘the nearest known masses of similar [Carboniferous\ rock are in the Carboniferous Limestone of the Clee Hills.’ Ramsay collected from conglomerates, included by him in the Middle Permian, at Gatacre Hall and Four Ashes, near Enville, pebbles of He states that ‘the Carboniferous Limestone pebbles by far predominate,’ and that ‘the nearest Carboniferous Limestone is that of the Titterstone Clee :Hills . . . . The Coalbrookdale limestone contains chert . . . . and in the same district occur igneous and

Ancient Ice Ages

MESSRS. BLANFORD, in their letter (NATURE, p. 101) called forth by Dr. Wallace's notice of a palaeozoic glacial conglomerate in Victoria, Australia, say:—“It has become an accepted article of faith amongst most European geologists that no ice-age occurred before the last glacial epoch.” There is no doubt that the tendency of opinion has been in that direction, notwithstanding the evidences to the contrary brought forward by Dr. Blanford and others. The late Sir Andrew Ramsay was the first, so far back as 1855, to suggest that the Permian conglomerate of Abberley and the Clent hills was an ancient glacial deposit. Although this reading was accepted by so cautious a philosopher and critic as Sir Chas. Lyell (“Principles,” 10th ed., vol. i. p. 223), the idea has languished from disfavour. Having devoted a considerable portion of the last twenty years to the study of glacial phenomena, I early this year paid my first visit to the district. The best section I saw is an excavation at Abberley in what may be called boulder-gravels, and, except for its prevailing red colour, the deposit, if dropped down on the coast of Wales, would, in general appearance and arrangement of the materials, be undistinguishable from many of the glacial deposits to be found there. Many of the stones have flattened faces, and in general shape resemble glaciated boulders, but the striae, so far as I could observe in the limited time at my disposal, were not very pronounced. Since then I have found a deposit of glaciated gravels on the top of the Screes, Cumberland, 1600 feet above the sea, which on comparison with the specimens brought home from Abberley enables me to understand the latter better. The volcanic rocks of the lake district of which these gravels are composed break up into very similar shapes, and are planed and striated in a very similar way to those of Abberley. I also brought home from Abberley two specimens of the “paste” which fills up the interstices of the finer gravel. On washing and riddling this clayey matter, well waterworn and smooth gravel was separated from it up to about the size of a bean, and on many of these minute pebbles, with the aid of a microscope of low power, beautifully-developed striae are to be seen, sometimes on more than one face. This latter fact appears to have been unnoticed before. The conclusion I have come to is that Ramsay had reasonable grounds for his belief in this being a Permian glacial deposit, and think that if he had given more details in his otherwise able paper, geologists would probably have followed him more freely.

On a Permian Conglomerate Bed at Markington

There is in the parish of Markington a small bed of Permian Conglomerate, the existence of which seems to be worth recording. It consists of waterworn pebbles of Carboniferous Limestone arid Sandstone, with angular fragments of Magnesian Limestone, embedded in a matrix of harder Magnesian Limestone. The thickness of this bed, where it is exposed, is about a yard, and its width a few yards, as far as it is traceable. The difficulty of tracing it further arises from its position. It occurs a little below the top of a steep bank about 50 feet in height, overgrown with a rather dense plantation, in which two out-crops appear. This conglomerate bed and another well-marked bed, upon which it lies, reaches to the bottom of the valley; and upon its eroded surface there runs the Markington Beck, a great part of which shortly disappears in swallow-holes and crevices of the Limestone. After passing underneath the hili, which is between Markington and Bishop Monkton, the stream bursts out in the latter parish. That this conglomerate bed once extended further to the west is clear from the occurrence there of boulders of this rock among the other boulders of the drift. There is clear evidence at hand that the loss by denudation has been very great, probably to the extent of 200 feet or more. The well-marked limestone I have mentioned is easily recognized amongst the other Permian beds, and consists of smoothed lumpy blocks of greyish-brown limestone, containing many sparry cavities, and ...