Quartzite Pebbles Research Articles

Une nouvelle méthode pour la paléopodologie du Pliocène et du Villafranchien des Pyrénées centrales : l'étude des galets de quartzite à cortex d'altération

It is shown that each weathered corona surrounded quartzite pebbles and some characteristics of the matrix can be regarded as the result of the same pedogenesis. Consequently each individualized pedological evolution, can be jointly studied on the matrix (classical pedological method) and on the cortex which presents two peculiar advantages : 1. individualization and relative localization in the course of time, of the great weathering periods ; the former are responsible for the cortex of the nearest of the heart of the pebble, the later for the peripherie coronas. 2. Characterization of each pedogenesis, thanks to the possible establishment of geochimical balances. This method applied to the pedology of the Pliocene and Pyrenean Villafranchian shows that two main evolutions have succeeded each other : the first one being of ferrallitic type and the other one of podzolic type.

Highly Quartzose Pebble Gravels in the London Basin

Wooldridge (1927) recognised two subdivisions of the Hertfordshire Pebble Gravels; a third is now described. Its deposits lie at lower levels than the other Pebble Gravels and are therefore younger, and they contain a much higher proportion of pebbles of quartz, quartzite, sandstone and Carboniferous chert. They have been traced discontinuously from the Goring Gap to Bishop's Stortford, and are thought to have been laid down by an ancestral Thames. It is believed that the ‘exotic’ materials came from the Midlands, the southern Pennines and other more remote areas, and were introduced through the Goring Gap. There is some evidence that the deposits are older than the North Sea Drift of East Anglia. It is pointed out that these results provide direct confirmation of a hypothesis of Wooldridge (1938) concerning the very early course of the Thames.

Relationship between volume and axes of some quartzite pebbles from the Olean conglomerate, Rock City, New York

Measurements of 110 quartzite pebbles from two layers in the Olean Conglomerate to determine the relationships of variation in axial dimensions, logarithm of the volume, and bulk density show that, given constant composition and density, it is possible to define particles formed in different environments through precise measurements of variation in volume (size and shape).

Crushed Pebble Conglomerate of Southwestern Montana

Many quartzite pebbles in the Tertiary Beaverhead Formation in southwestern Montana are scarred or deformed in two distinctive ways: (1) at points of mutual pebble contact, dents (or depressions) have been formed as a result of squeezing of the strata; and (2) at localities where deformation has been the greatest, individual pebbles have been sheared (and commonly rehealed), in some instances showing ten or more shear planes in a single stone. The direction of motion inferred from sheared pebbles supports the hypothesis of pronounced lateral (strike-slip) displacement in the area. Drag folds yield the same result. Vertical offset, although more spectacular, must be relatively minor. Sandstone lenses and beds within the conglomerate show little evidence of deformation. If resistant pebbles in contact with each other had not been common in the Beaverhead, the large-scale horizontal displacement would have gone unnoticed, and only the vertical motion would have been recorded. The width of the zone of shattered pebbles indicates that much of the displacement was taken up in the strata, rather than by dislocation along an adjacent fault plane. These observations tend to confirm the hypothesis that, in deformed regions, measurements of offset produce results that are conservative by one or more orders of magnitude.

Precambrian Rocks at North Franklin Mountain, Texas

At North Franklin Mountain in the western tip of Texas, more than 5,000 feet of sedimentary and volcanic rocks lie unconformably beneath the Bliss sandstone (Upper Cambrian). Except for algal structures, these older rocks are non-fossiliferous, and are thought to be Precambrian in age. Granite, probably Precambrian, is intruded into the sequence. In ascending order the Precambrian rocks consist of the Castner limestone (new name), the Mundy breccia (new name), the Lanoria quartzite, and an unnamed rhyolite unit. The Castner is 1,100 feet thick and includes limestone, hornfels, and chert, as well as diabase sills. It contains mound-like algal structures near the base and rests on intrusive granite. The Mundy, ranging from a trace to 250 feet thick, consists of basalt rubble of unknown source resting unconformably on the Castner. The Lanoria quartzite, 2,600 feet thick, is composed of fine-grained sandstone, siltstone, and shale, all metamorphosed. It is divided into three members by a middle unit of massive quartzite. The rhyolite unit contains rounded pebbles of Lanoria quartzite at its base and attains its maximum known thick ess, 1,400 feet, at North Franklin Mountain. The Castner limestone may be equivalent to the Allamoore limestone of the Van Horn area, 100 miles to the east. However, other Precambrian formations in the two areas are so unlike that positive correlation can not be made.

Observations et hypotheses a propos des cailloutis eleves de Saint-Restitut (Drome) et de la Caume (Alpilles, Bouches-du-Rhone)

Abstract Reconstruction of the Pliocene paleogeographic setting of the Saint-Restitut and Caume plateaus, France, shows that the quartzite pebbles found on those heights cannot be Pliocene. It is suggested that they are pre-Plaisancian, dating from the continental period marking the boundary between the Miocene and Pliocene sedimentary cycles.

Basin-and-Range Structure Reflects Paleozoic Tectonics and Sedimentation: ABSTRACT

Upper Paleozoic tectonism and sedimentation are the key factors which influenced the relation between valleys and ranges in northeastern Elko County, Nevada. The Mississippian orogeny which formed the Manhattan geanticline, a northeast-southwest welt in central Nevada, was also responsible for the formation of an east-west-trending positive feature in northern Elko County, Nevada. This feature, here named the Northeast Nevada high is probably an eastward extension of the Manhattan geanticline. The presence of the Manhattan geanticline divided the Cordilleran geosyncline into an eugeosyncline on the west and an unstable shelf on the east. Acting as a buffer zone for the compressive forces from the west, the shelf was gently folded into a series of essentially north-south-trending synclines and anticlines. Rapid erosion of the Manhattan geanticline and Northeast Nevada high fed coarse clastics east and south, depositing the Tonka and Diamond Peak formations on the shelf which was surfaced by the folded Mississippian Chainman shale. Maximum clastic deposition occurred in a foredeep parallel with the east side of the geanticline, while minor amounts from the Northeast Nevada high were being channeled southward into the folded geosynclinal shale basin. Contemporaneous with the clastic deposition in the synclinal folds, erosion was attacking the adjacent shale-capped anticlinal folds and many of the anticlines were eroded as deeply as the Ordovician Eureka quartzite and equivalents. Filling of the synclines and erosion of the anticlines continued through most of Morrowan time. By middle to late Morrowan time, erosion had reduced the anticlines to approximately the same level as the clastic-filled synclines. A veneer of chert and quartz gravels and grits remained as pediment deposits over this nearly peneplaned surface. By early Atokan time, the orogeny was limited to spasmodic unrest, supplying minor amounts of chert and quartzite pebbles into the newly formed limestone depositional basin (Moleen, Tomera, and Ely formations). In middle Des Moines time, the entire Great Basin was gently uplifted permitting erosion and non-deposition until at least middle Missourian time. By Virgil-Wolfcampian time, partial relaxation of positive forces in the Great Basin again permitted the seas to invade most of eastern Nevada and adjacent Utah (upper member of Oquirrh form tion, and equivalent carbonate formations). Leonardian time was characterized by quiescence and the deposition of a fusulinid-bearing carbonate formation over approximately 9,000 square miles of northeastern Nevada and adjacent Utah. This heretofore unnamed limestone sequence, dated lower Leonard to lower Guadalupian, is here named the Pequop formation. The Pequop formation is 1,525 feet thick at its type section in Sec. 3, T. 33 N., R. 65 E., Elko County, Nevada. Composed of purplish gray, irregularly bedded, platy, silty limestones with interbedded fusuline coquinas, the lower contact is placed at the red silt member which overlies the massive Wolfcampian limestones (unnamed formation), and the upper contact placed at the base of an unnamed massive dolomite sequence which is overlain by the Phosphoria formation. Subsidence continued, depositing the Phosphoria and Gerster formations, until uppermost Guadalupian time when once again the rejuvenated Manhattan geanticline and Northeast Nevada high shed minor amounts of limestone, chert, quartzite pebbles and gravel east and south into the western part of the Phosphoria depositional basin in Nevada. Episodes of tectonic unrest in northeastern Nevada occurred during Jurassic-Cretaceous (Nevadian) and Cretaceous-Tertiary time (Laramide). Not until post-middle Miocene was the area once again subjected to major compressive forces of the Cascadian (Basin-and-Range) revolution. The north-south-trending anticlines, eroded of their Mississippian, Devonian, Silurian and in some places Ordovician sediments, together with continued compressive forces from the west, acted, as the jaws of a vise on the thicker Paleozoic sedimentary piles within the synclines. Weaker sediments in the synclines were forced topographically higher than the adjacent anticlines with shearing occurring along the flanks of the anticlines. Thus, in northeastern Nevada, present ranges were born from a thick sedimentary section once protected in the synclines, while valleys were developed from eroded anticlines stripped of their lower and middle Paleozoic ection. End_of_Article - Last_Page 1105------------

Cretaceous and Tertiary Orogeny in Jackson Mountains, Humboldt County, Nevada

A formation of Early Cretaceous age composed of locally derived clastic rocks, including pebble to boulder conglomerate, siltstone, coarse graywacke, and finely crystalline limestone is exposed at several places in the central and northern part of the Jackson Mountains, Humboldt County, Nevada. This formation was folded and at two places probably completely eroded before deposition of the next younger unit--a pebble conglomerate composed of exotic pebbles of chert and quartzite derived from rocks of early Paleozoic age. This younger pebble conglomerate may be of Late Cretaceous or early Tertiary age and may be equivalent to rocks of similar stratigraphic position and lithologic character exposed over a considerable area of eastern Nevada and western Utah. Both of these co rse clastic formations have been overriden by a thrust sheet of Permian or older volcanic rocks. The dimensions of the thrust sheet are not known exactly but remnants are exposed over a 25-mile-long segment of the range. Upper Tertiary volcanic rocks exposed in the range are not involved in the thrusting. The Cretaceous and younger rocks of the Jackson Mountains record a long period of orogenic unrest that included: (1) uplift of the source area of and deposition of the Lower Cretaceous rocks; (2) folding and beveling by erosion; (3) deposition of the exotic-pebble conglomerate; (4) thrusting of the Permian or older volcanic rocks over the two coarse clastic formations; and (5) later folding, faulting, and erosion providing the present outline of the range.

On the Deformation of the Funzie Conglomerate, Fetlar, Shetland

The Funzie conglomerate in northeast Shetland is a very large body of deformed metaconglomerate of pre-Middle Old Red Sandstone age. Its elongated and flattened pebbles, which are mostly of quartzite and occasionally of marble, lie in a subgraywacke matrix. A plot based on the measurement of 548 quartzite pebbles shows that the shapes of the pebbles vary systematically over the area. A minimum value for the deformation of the conglomerate at any point is found by comparing the average pebble shape at that point with the average pebble shape in the area of least deformation. Compression in the plane normal to the elongation direction has forced the pebbles to elongate by flow (Einengung). It is shown that the consistency of direction of the pebble axes is related to the elongation of those axes and is due to differential flow of the matrix against the pebbles. During the deformation of the pebbles their constituent quartz grains, the clastic quartz grains in the matrix, and the calcite grains in the marble...

Reinterpretation of Supposed Late Tertiary Chert Gravels North of Atchison, Kansas

Todd referred to these chert gravels as marking the level of preglacial drainage and thus reaffirmed the Tertiary dating he had made earlier (Todd, 1918) of similar chert gravels along Kaw Valley and in the Missouri Valley bluffs. Subsequently the chert gravels of Atchison County have been described and referred to as Tertiary (?) (Frye, 1941; Frye and Walters, 1950; Frye and Leonard, 1952). Frye and Leonard (1949) contrasted the lithology of these gravels with the pre-Nebraskan David City gravels farther north at the Iowa Point section in Doniphan County, and Davis (1951) in his study of Pleistocene gravel lithologies examined a colllection from the basal 1 foot at this locality and reported 0.5 percent quartz but no pink quartzite, granite, or other igneous rock types. Examination of chert gravels in this section in recent years has been limited to the basal 1 to 11/2 of gravel exposed at the top of the limestone face in the abandoned quarry. It had been impossible to examine the 8-10 feet reported by Todd or the contact relations with the overlying fine sands which are classed as the pro-Kansan Atchison formation. However, in October 1953 we revisited this locality with a group of graduate students and found that a small pit had been opened in these gravels and that about a quarter of an acre of area was exposed. This new excavation revealed a total thickness of 7 to 8 of gravels and the contact of the chert gravel with the overlying Atchison formation. A careful examination of the lithology of the gravels was made and the presence of pebbles of pink quartzite and igneous rocks in place in the

Hominids, Pebble Tools and the African Villafranchian

Hominids, Pebble Tools and the African Villafranchian l F. CLARK HOWELL Washington University School of Medicine (St. Louis) T HE greatly accelerated pace of prehistoric research in the postwar years has made it necessary to reexamine certain problems in paleoanthropol­ ogy. This is especially true for Africa where primitive hominids and pebble tools have been discovered in deposits of recognized Villafranchian age. These discoveries raise the question of the relationship, if any, between these earliest stone implements and the Villafranchian hominids. A related problem is the place of the Pliocene-Pleistocene boundary and the age of the Villafranchian stage in Africa ith reference to the Pleistocene sequence in other parts of the Old World. A review of the evidence for Pleistocene man south of the Sahara will be presented at another time, but it is worth while here to clarify certain points about the Villafranchian stage in Africa in view of some misconcep­ tions present in the literature. The first evidence of tool-making is found in deposits of the first pluvial (Kageran) stage in equatorial and southern Africa. Pebble tools of this age have been found on the eastern shores of Victoria basin at Kanam (Leakey 1936a, 1936b), and in the Kagera and Kafu river valleys west of the basin in Uganda (Wayland 1934; Lowe 1952); artifacts of comparable age have recently been found sealed in situ in ancient gravel deposits in the Vaal river basin (Lowe 1953). These implements, referred to the Kafuan stage of the Pre-Chelles­ Acheul industry, were manufactured from waterworn pebbles of quartz or quartzite with stone percussion flaking in one direction, and on only one side, to produce a single, adze-like cutting edge. Although artifacts of Kafuan type are found rolled and abraded in deposits of post-Kageran age at various locali· ties south of the Sahara, the industry may well be restricted to the first pluvial stage. The Oldowan, a derivative stage of the African Pre-Chelles-Acheul, is found in deposits of the early part of the second pluvial (Kamasian) stage. Some Oldowan implement types are found in the final phases of the Kafuan (Lowe 1952), however, so it is possible that this industry had its beginnings in the later part of the first pluvial stage. This problem may be clarified by future field work in northwestern and central Africa. Pebble tools of first end­ pluvial age (Kageran-Kamasian interpluvial) have been found recently in southern Morocco (Mortelmans, Choubert and Hollard 1952) and also in the vicinity of Casablanca (Biberson 1953). An industry termed the Kafilian, more advanced than the Kafuan, is known from the Congo and is of the same ap­ proximate age (Mortelmans 1947, 1949). These assemblages may well fill the gap between the Kafuan and the Oldowan.

GEOLOGY OF THE BARRILLA MOUNTAINS, TEXAS

The Barrilla Mountains, in the northeastern part of the Davis Mountains of Trans-Pecos Texas, are composed of Tertiary volcanic materials. Five tuffs and five lava flows, 1500 feet thick occurring throughout the mountains, persist in thickness and lithologic characteristics. Their upper surfaces show little erosion. The lavas are chiefly Silicic and soda rich. The volcanic succession is underlain by a Tertiary sandstone above Upper Cretaceous marine formations. These were slightly deformed by the Laramide revolution, subsequently beveled, and everywhere covered by the sands of coalescing streams. The sandstone contains well-rounded chert and quartzite pebbles. Broad folds and normal faults succeeded the extrusions of the youngest lava.

The Age of the Neptunian Dyke at Hazler Hill

During the Easter Field Meeting of the Sedgwick Club, portions of the Neptunian dyke at Hazier Hill, near Church Stretton, were collected and brought back to Cambridge for further examination. The material consisted of a buff-coloured, sandy mudstone with scatters of facetted pebbles of quartzite and igneous material, including weathered rhyolite, up to a centimetre in diameter. The material proved to be richly fossiliferous and the following fauna was obtained which, we believe, throws some light on the age of these sand-filled fissures :—

Wealden petrology : The Top Ashdown Pebble Bed and the Top Ashdown Sandstone

Wealden petrology : The Top Ashdown Pebble Bed and the Top Ashdown Sandstone

On the Relationship between “Fronts” of Regional Metamorphism and “Fronts” of Granitization

Two important papers, relating to “fronts” of metamorphism, appeared in theBull. Soc. Géol. Franceduring the war years, and may, in consequence, have escaped the notice of many petrologists. The contents of both papers are so closely bound up with the important subject of granitization as to render their review desirable. In the first of these papers, Perrin and Roubault (1941) describe an apparently unconformable boundary between a Triassic conglomerate and an underlying schist. The Triassic conglomerate consists of red quartzite pebbles in a sandy matrix, whilst the schist is a normal low-grade sericite-chlorite-schist of a green colour. Detailed examination of the contact, however, shows that the relations between the two rock types are by no means so straightforward as a cursory examination suggests. Although the contact between the conglomerate and the schist is generally sharp, a close scrutiny establishes the following local but remarkable apparent anomalies: (1) “Xenoliths” of the conglomerate, and isolated pebbles from it, occur within the schist. (2) “Veins” and pods of the schist occur within the Triassic conglomerate. (3) Gradational contacts are sometimes found between the schist and the Triassic sandstone, the schist facies dying out within the space of a few centimetres. On the basis of these observations Perrin and Roubault reach the inevitable conclusion that the metamorphism which gave rise to the schist actually post-dated the deposition of the conglomerate.

The ultimate shape of pebbles, natural and artificial

Flint pebbles that have been worn down enough to be symmetrical may be spherical, or may approximate to prolate or oblate spheroids or to ellipsoids. When, however, the section is at all elongated, it is not as a rule accurately elliptical, but except at the axial points it lies entirely outside an ellipse adjusted to the same axes. Thus, if one of the axes is much smaller than the other, the pebble is much flatter than an ellipsoid. Considering the quasi-spheroidal pebbles, whether prolate or oblate, these are always flattened at the poles, and the very oblate ones become tabular or even concave at the poles. These statements hold for flint pebbles, but a large quartzite pebble is figured which is pretty accurately an oblate spheroid, the meridional sections being truly elliptical. Experiments are described with chalk pebbles, initially shaped as prolate or oblate spheroids, and the change of figure under abrasion is observed. This depends in some degree on what is the abrasive. Steel nuts, nails ('tin tacks’) and small shot were used. In general the axes tend to approach equality, but not rapidly enough for the spherical form to be attained before the pebble has disappeared. The form initially spheroidal becomes flattened at the poles just like the natural flint pebbles, and may become concave, as flints sometimes do. The circumstances determining the rate of abrasion at any point are considered, and it is shown that this abrasion cannot be merely a function of the local specific curvature. The figure at points other than the one under consideration comes into question, so that the problem in this form has no determinate answer. It is shown by simple mechanical considerations how the concave form arises.

The Tectonics of Tregarth

Most of the Cambrian of Arvon has the “Caledonian” strike which is dominant in Snowdonia. But there is a tract at Tregarth, about a square mile in extent, where the beds trend in any direction: that is, have no strike at all. Nothing in the beds themselves is any explanation whatever: there seems no reason for this anomaly. We have to seek an explanation in the underlying floor, and there, I think, we win some light. That floor has more than one component: Mona Complex and Arvonian. In the chapter of the Anglesey Memoir on the Age of the Mona Complex, I have thrown out a suggestion (then in explanation of nothing but the pebbles), that hills of Gwna Quartzite stood up through the Arvonian lavas. Now, in the great conglomerate of the crest and dip-slope of Y Pare, pebbles of quartzite are so numerous as to outnumber those of the rhyolite. It seems legitimate to infer that, underneath this Tregarth tract, these buried knobs of quartzite were exceptionally numerous and exceptionally high, and made the sub-Cambrian floor so uneven that the beds which rested on it could not acquire the usual strike, but were driven hither and thither, in all sorts of irregular ways. The same irregularity, though to a somewhat less degree, affects the Arvonian tuffs themselves.

Contact Metamorphism by a Tertiary Dyke at Waterfoot, Co. Antrim

Close to Waterfoot and about one and a quarter miles south of Cushendall, in Co. Antrim, a bifurcating dolerite dyke of Tertiary age outcrops on the shore approximately 750 feet south-west of Red Bay pier (see text-fig. 1). The dyke is intruded into practically horizontal beds of Triassic sandstone which contain abundant fragments and pebbles of schist and quartzite. As shown on the map, text-fig. 1, the dyke bifurcates and encloses a lenticular portion of these Triassic beds. Where unaltered by the dyke, that is in the low cliff adjoining the sea-wall to the south-west of the dyke and in that portion of the enclosed mass adjoining the south-western branch of the dyke, the Trias is a friable yellow sandstone, rich in fragments of schist and quartzite ranging in size from a few inches down to microscopic dimensions. On the south-western side of the north-eastern branch of the dyke, however, a marked change takes place. The Trias here changes in colour from yellow to grey and becomes hard and compact; and, as the dyke is approached, the fragments and pebbles become less distinct and eventually merge into the matrix of the rock. This change begins between eight and nine feet from the contact. Within a foot from the contact the alteration is so intense that the main part of the rock has a compact homogeneous appearance, so that at first glance it resembles an igneous rock with sparse xenoliths of white quartzite. The schist fragments are here represented by dafk patches which merge, often imperceptibly, into the matrix of the rock.

THE TERTIARY HISTORY OF EAST YORKSHIRE

Since the discovery of the so-called Bridlington Crag in 1835 (2) the possible existence of Tertiary rocks in Yorkshire has been a matter of speculation but Phillips’ conclusion that Tertiary strata did not occur in Yorkshire has been accepted by most Yorkshire geologists. In 1904, Stather (13) reported the presence of scattered pebbles of quartzite over the Wolds even above the drift limit and concluded that they represented either the relics of an early glaciation or even of a Tertiary stratum. There exists in the Hull Museum a map produced by R. Mortimer, never officially published, showing a distribution of masses of sand and gravel covering the Chalk of the Wolds and allocated by him to the Eocene, Miocene and Pliocene periods. There is now no indication of such sand being exposed so far as the writer has been able to discover but the late Mr. Stather gave the author a sample of sand collected some thirty or forty years ago from Thixendale, one of the localities marked by Mortimer. The analysis of this sand is given later in this paper. Others of Mortimer’s areas seem to be simply the ordinary chalk gravel of glacial date. Among the many tumuli which are scattered on the Yorkshire Wolds and were excavated by J. R. Mortimer (10) there are some, 12 in all, which are described as having been dug, not in Chalk, but in sand which existed as a pipe in the Chalk. All these tumuli are found above the drift ...

Derbyshire Caves Exhibition

ON behalf of the Derbyshire Caves Exploration Committee appointed by the British Association, Mr. Leslie Armstrong has excavated Pin Hole, a cave in Creswell Crags inhabited in Upper Palaeolithic times and exceptionally rich in prehistoric remains. A preliminary report was published in the Transactions of the Hunter Archaeological Society, 4, part 2, with av diagram showing the brick-earth, red above and yellow below, which underlay the present stalagmitic floor, with layers of slabs fallen from the roof marking periods of exceptional cold. The palaeolithic cultures ‘represented are Le Moustier and Aurignac, the latter persisting through the glaciation associated elsewhere with La Madeleine; and the fauna shows severe and temperate conditions alternating. There are chipped pebbles of quartzite, and flint implements of excellent workmanship, nearly all with white patina; also slight engravings on bone, a bone blade regarded as a bull-roarer, as well as a cowrie shell and piece of mother-of-pearl. Mr. Armstrong has also excavated Mother Grundy's Parlour in the same valley, and published an account in the Journal of the Royal Anthropological Institute, 55, Jan.-June 1925, with eight pages of careful drawings of the stone implements mostly of Aurignac types, but with a micro -lithic industry in the uppermost layer, and chipped quartzite at the base. The cave-earth of the Parlour has large stones from the roof incorporated throughout, not at intervals, and shows the same difference in colour as Pin Hole. Engravings of animals on bone in the Aurignac style and the best of the finds from both sites are now exhibited in the Department of British and Mediaeval Antiquities at the British Museum, near the top of the main staircase, and will, by the kindness of Mr. Armstrong, remain there for the rest of the year.