Calcareous Siltstone Research Articles

On Convolute Bedding in the Lower Ludlovian Rocks of North-East Radnorshire

AbstractConvolute bedding is described from the Lower Ludlovian in north-eastern Radnorshire in calcareous siltstones probably of the Monograptus tumescenszone. Examples of true slump-structures from the same area are given for comparison. The mode of formation of the convolute bedding is discussed and reference made to such directional information as is available from a study of the sediments.

OVERTHRUST ORDOVICIAN AND THE NANNIE'S PEAK INTRUSIVE, LONE MOUNTAIN, ELKO COUNTY, NEVADA

The Lower Paleozoic rocks of the Great Basin consist of an eastern facies, composed of carbonate rocks, in eastern Nevada and western Utah, and a western facies, composed of clastic rocks, cherts, and volcanic rocks, in central and western Nevada. Major thrust faults have moved the rocks of the western facies eastward over the rocks of the eastern facies. The trace of one such thrust fault is exposed on the flanks of Lone Mountain in Elko County, Nevada. The rocks of the eastern facies lie beneath the thrust fault and are subdivided into the autochthonous McClellan Creek sequence and the allochthonous Coal Creek sequence. The McClellan Creek sequence is composed of Devonian? limestones; it is successively overthrust by the Devonian fractured limestone of the lower plate of the Coal Creek sequence and by the Upper Devonian limestones, shales, and calcareous siltstones of the upper plate of the Coal Creek sequence. The rocks of the western facies lie above the thrust fault in a series of thrust slices. The name Basco formation is proposed for mappable lithic units in one of the thrust slices. The Basco formation is Ordovician and contains four members: (1) basal calcareous siltstone with a sandstone bed and lenses of altered peridotite, (2) lower chert, (3) shale, and (4) upper chert. About 1750 feet of the Basco formation is exposed within the thrust slice. The calcareous siltstone member of the Basco formation contains Early Ordovician graptolites, and the shale member contains Middle Ordovician graptolites. The Basco formation is overlain by Silurian siltstone. The thrust fault at Lone Mountain is domed up by intrusive rocks of probable Miocene age. The most striking of these is the Nannie's Peak intrusive, which forms the crest of Lone Mountain; the intrusive is arcuate in map view, and it is interpreted to be a dike. Related stocks and dikes crop out on the east flank of the mountain. North, west, and south of Lone Mountain, the Paleozoic rocks are overlain by Cenozoic conglomerate that grades upward into welded tuffs. Normal faulting may bound Lone Mountain along its eastern margin, and the desert valley to the east is floored with vitric tuffs and with younger alluvium. The vitric tuffs are probably of late Miocene age, and they seem to grade laterally into the welded tuffs that lie north, west, and south of Lone Mountain.

Notes on the geology of the eastern slopes of Blackford Hill, Edinburgh

Carnethy-type porphyry and a thin band of ash have been uncovered in recent excavations on the north side of West Mains Road, Edinburgh, on the eastern slopes of Blackford Hill. Fissures in the chilled top of the porphyry are filled by calcareous siltstone, and it is considered that the porphyry was cooled under water. Peat and marl, probably rafted material, have been found in the boulder clay of the area.

Devonian-Mississippian Boundary in Canadian Rocky Mountains: ABSTRACT

Over most of the Alberta Rocky Mountain region, the Palliser formation, containing an Upper Devonian fauna, is overlain with disconformity by the Exshaw formation. The Exshaw, consisting of a lower black shale and an upper calcareous siltstone, has been considered to be Devonian but the faunal evidence of Devonian age is inconclusive. The Exshaw, though widespread, is not present throughout the region and in some sections the Mississippian Banff formation rests disconformably on the Palliser. The Exshaw occupies the same stratigraphic position and is lithologically similar to the Bakken of Saskatchewan. The Sappington of Montana which is reported to contain an early Mississippian fauna bears some lithological resemblance to the siltstone member of the Exshaw. It is sugges ed that the Devonian-Mississippian boundary be placed at the base of the Exshaw formation in the Alberta Rocky Mountains. End_of_Article - Last_Page 418------------

Cylindrical Structures in Permian(?) Siltstone, Eagle County, Colorado

In the East Brush Creek area a calcareous siltstone bed contains numerous cylindrical structures normal to the bedding. The bed is 35 feet above the conglomerate of other workers in the region. The conglomerate is here considered Permian(?) rather than Triassic, because the Shinarump of Arizona and Utah probably pinches out west of the area. The siltstone bed is in the transition from underlying continental conglomerates and sandstones to overlying marine red beds, and a littoral or estuarian environment is indicated. The cylinders occur throughout the total thickness of the bed but are restricted to the immediate locality. Cylinder contacts are sharp but slightly irregular, and the material they contain is identical to the surrounding sediment. A circular section of uniform diameter is commonly maintained throughout the length. The greatest exposed length is 4 feet. Diameters range from 1/2 to 8 inches. The cylinders are interpreted as fossil diagenetic springs. The bedding in pipe channels w...

A magnesian chamosite from the Wenlock Limestone of Wickwar, Gloucestershire

The Little Avon river rises on the scarp slope of the Cotswolds near Hawkesbury, 14 miles north-east of Bristol, and flows in a westerly direction over Mesozoic strata, until half a mile south-east of Wickwar it cuts through the Triassic mantle and exposes to view three inliers of Wenlock Limestone (Whittard & Smith, 1944, p. 65 and map). The West Gloucestershire Water Company was interested in the valley as a possible site for an impounded reservoir, and as part of a preliminary survey a trial-shaft was sunk into the Wenlock Limestone of the southernmost inlier situated near Sturt Bridge. The shaft penetrated 28 feet of dolomitized siltstones and crinoidal limestones, and at a depth of 4 feet it entered a band of calcareous chamositic siltstone averaging 9 inches in thickness. The shaft had been completed and the sides boarded before we heard it had been sunk; the hand-specimens were therefore obtained from the tip-heaps, but there is no doubt that all the material originated from the same horizon.

Marine Jurassic Formations of Sweetgrass Arch, Montana

The marine Jurassic rocks of the Sweetgrass arch in western north-central Montana have been assigned to the Ellis formation. As a result of measuring and sampling eleven Jurassic sections around the Sweetgrass arch and from examining numerous well cuttings, the writer concludes that the Ellis consists of three major lithologic divisions that should be recognized as formations, and that the Ellis should be raised to group rank. The formations of the Ellis group from oldest to youngest are herein named Sawtooth, Rierdon, and Swift. The Sawtooth formation consists of three members, a basal fine-grained sandstone, a medial dark gray shale containing a few dark limestone beds, and an upper member of light gray calcareous siltstone, fine-grained sandstone, or sandy, oolitic limestone. The Sawtooth is as little as 8 feet in thickness on the Kevin-Sunburst dome. It thickens eastward to 200 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The lower two members pass into redbeds east of the Sweetgrass Hills and on the southeast flank of the South arch. The Rierdon formation consists mainly of gray limy shale and nodular limestone. It seems to overlie the Sawtooth formation conformably. It is as little as 72 feet in thickness on the Kevin-Sunburst dome, but thickens eastward to 180 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The Swift formation is composed of two members along the Rocky Mountain Front and eastward across the Kevin-Sunburst dome at least as far as the Sweetgrass Hills. The lower member is dark non-calcareous shale, highly glauconitic at the base. The upper member is gray fine-grained flaggy glauconitic sandstone containing abundant black-gray micaceous shale partings. On the South arch the formation consists of fine-grained flaggy sandstone which is locally pebbly at the base. In the vicinity of the Little Belt Mountains the formation is massive fine-grained sandstone containing a prominent basal conglomerate. The Swift attains its maximum thickness of 166 feet in the Pondera field. The formation has been removed by pre-Kootenai erosion from most of the Cut Bank area, and from a small area west of the Whitlash field. All the formations are fossiliferous. According to Imlay, the Sawtooth is upper Bathonian, the Rierdon is upper Bathonian and Callovian, and the Swift is Divesian and Argovian. The South arch was an island through most of the Bathonian and Callovian stages. At the close of the Callovian the marine waters retreated from the area. During the early Divesian the Sawtooth and Rierdon formations were locally thinned by erosion and possibly removed from some areas. Later in the Divesian marine waters transgressed the entire area and remained until the close of the Argovian.

Marine Jurassic Formations of Sweetgrass Arch, Montana

The marine Jurassic rocks of the Sweetgrass arch in western north-central Montana have been assigned to the Ellis formation. As a result of measuring and sampling eleven Jurassic sections around the Sweetgrass arch and from examining numerous well cuttings, the writer concludes that the Ellis consists of three major lithologic divisions that should be recognized as formations, and that the Ellis should be raised to group rank. The formations of the Ellis group from oldest to youngest are herein named Sawtooth, Rierdon, and Swift. The Sawtooth formation consists of three members, a basal fine-grained sandstone, a medial dark gray shale containing a few dark limestone beds, and an upper member of light gray calcareous siltstone, fine-grained sandstone, or sandy, oolitic limestone. The Sawtooth is as little as 8 feet in thickness on the Kevin-Sunburst dome. It thickens eastward to 200 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The lower two members pass into redbeds east of the Sweetgrass Hills and on the southeast flank of the South arch. The Rierdon formation consists mainly of gray limy shale and nodular limestone. It seems to overlie the Sawtooth formation conformably. It is as little as 72 feet in thickness on the Kevin-Sunburst dome, but thickens eastward to 180 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The Swift formation is composed of two members along the Rocky Mountain Front and eastward across the Kevin-Sunburst dome at least as far as the Sweetgrass Hills. The lower member is dark non-calcareous shale, highly glauconitic at the base. The upper member is gray fine-grained flaggy glauconitic sandstone containing abundant black-gray micaceous shale partings. On the South arch the formation consists of fine-grained flaggy sandstone which is locally pebbly at the base. In the vicinity of the Little Belt Mountains the formation is massive fine-grained sandstone containing a prominent basal conglomerate. The Swift attains its maximum thickness of 166 feet in the Pondera field. The formation has been removed by pre-Kootenai erosion from most of the Cut Bank area, and from a small area west of the Whitlash field. All the formations are fossiliferous. According to Imlay, the Sawtooth is upper Bathonian, the Rierdon is upper Bathonian and Callovian, and the Swift is Divesian and Argovian. The South arch was an island through most of the Bathonian and Callovian stages. At the close of the Callovian the marine waters retreated from the area. During the early Divesian the Sawtooth and Rierdon formations were locally thinned by erosion and possibly removed from some areas. Later in the Divesian marine waters transgressed the entire area and remained until the close of the Argovian.

Stratigraphy of Northeastern Anzoategui, Venezuela

A reference section for the 40,000 feet of Cretaceous and Tertiary sediments of northeastern Anzoategui (Venezuela) was established several years ago on Rio Querecual and in the vicinity of the town of Santa Ines. Subsequent studies on the west and east have given a more complete three-dimensional picture of the original formations and their facies changes and have filled those parts of the stratigraphic section poorly represented on Rio Querecual. During the course of this work numerous fossil collections have been made and these have been submitted to specialists for study with the result that more authoritative data on the ages of the several formations are now available. The oldest rocks of northeastern Venezuela are the schists, phyllites, quartzites, and metamorphosed limestones of the Caribbean series, probably early Mesozoic in age. These rocks are in fault contact with unmetamorphosed Lower Cretaceous sediments which are well represented in northeastern Anzoategui and include about 5,000 feet of laterally variable shallow-water sandstones, shales, and reef limestones belonging to the Barranquin, El Cantil, and Chimana formations. These are followed by a deeper-water facies of 3,000-4,000 feet of black carbonaceous-bituminous limestone and calcareous shale with local sandstone and chert developments in its upper part, constituting the Guayuta group (Querecual and San Antonio formations) of Upper Cretaceous age. Conformably overlying the Guayuta gr up is the Santa Anita formation consisting of a lower sandstone member (Upper Cretaceous), a middle shale member (Upper Cretaceous-Paleocene), and an upper member of calcareous and dolomitic siltstones, glauconitic sandstones, and shales (Paleocene-Eocene). The whole formation is about 2,400 feet thick. The Santa Anita formation is overlain by the Merecure formation. In the eastern part of the area the contact between the two appears transitional but in the vicinity of Barcelona there may be an erosional unconformity. The basal Merecure contains orbitoidal foraminifera indicative of late Eocene age. The upper part of the formation is formed by the thick Naricual coal-bearing member and is probably in part Oligocene in age. The total thickness of the Merecure formation is 5,500-7,500 feet. The non-marine sediments of the upper part of the Merecure formation grade upward without a break into the more marine Santa Ines formation consisting of about 24,000 feet of sandstones, grits, conglomerates, shales, and claystones of middle Oligocene to late Miocene age. The marine character of this formation increases from west to east, and in the eastern part of the area it includes a fairly deep-water, highly foraminiferal shale member (Carapita shale). The Santa Ines formation is unconformably overlain by the Sacacual group (Pliocene) which is in turn unconformably overlain by the Mesa formation (Pleistocene). The sedimentary sequence of northeastern Anzoategui indicates that in early Cretaceous time a marine transgression began in this area which reached its culmination with respect to depth of water in Turonian time (Querecual formation). Toward the close of the Cretaceous (San Antonio and Santa Anita formations) there was a tendency toward emergence and a shallowing of the sea although its extent was still great. Marine deposition appears to have continued into Paleocene time, however, and in the eastern part of the area appears to have persisted with little or no indication of a break until the late Eocene. In the Barcelona area there may have been emergence and erosion in the early End_Page 1------------------------------ or middle Eocene (Santa Anita-Merecure unconformity). In the late Eocene (lower Merecure) marine deposition was widespread but was soon replaced by a coal-basin environment which continued into Oligocene time. In the middle Oligocene another major marine transgression began, during which the sediments of the Santa Ines formation were deposited. The area was then folded in late Miocene time before the deposition of the Sacacual group (Pliocene) and probably again in Pliocene time before Mesa (Pleistocene) deposition. The depositional history of the area is related to the pressure of the northern borderland of Paria against the continental nucleus of the Guayana shield and the consequent persistent southward shifting of the axis of the intervening Eastern Venezuelan geosyncline. During Cretaceous and early Tertiary time northeastern Anzoategui lay on the stable southern side of the geosyncline where deposition was relatively continuous, and formations follow each other without angular relation. In Oligocene and Miocene time it occupied a nearly axial position and received the thick flysch-like deposits of the Santa Ines formation. Toward the close of the Miocene it actually became a part of the northern flank of the geosyncline and as such its sediments were folded with each subsequent movement of he mobile northern borderland.

ON A BORING IN THE MILLSTONE GRIT SERIES AT HALLAM HEAD, SHEFFIELD

In the summer of 1938, a boring was made to supply the Hallamshire Golf Course with water. This borehole is situated in the disused Barncliffe Quarry adjoining Redmires Road at Hallam Head, 600 yards west of the Hallamshire Golf Club House. A small pump-house now stands a yard or two from the borehole. The boring was commenced at approximately 925 ft. O.D. The succession passed through is shown in Fig. 1. The lowest beds (145 to 200 ft.) are mainly soft, dark grey shales and mudstones, for the most part faintly banded. Pyrites and ironstone nodules are abundant at various horizons. Bands, an inch or two thick, of calcareous siltstone enclosing plant remains occur near the base of these beds. Goniatites, Lingula and Pterinopecten occur at certain horizons between 155 and 170 ft. and between 184 and 200 ft. Selected specimens were sent to Mr. W. S. Bisat who very kindly sent the following report:— “At 159 ft. Reticuloceras reticulatum mut. γ and an unknown species, possibly Gastrioceras sigma . At 165 ft. Reticuloceras reticulatum mut. γ , Gastrioceras sigma . At 167 ft. Gastrioceras sp. At 184 ft. to 187 ft. Reticuloceras reticulatum mut. γ , Gastrioceras sp. At 188 ft. Gastrioceras lineatum (?) At 190 ft. Reticuloceras reticulatum mut. γ of early type I cannot say if this last form is the same as W. B. Wright’s early mut. γ as I have no comparison material, and your material is not very well preserved, but there is a considerable difference between the ...

DummyChemical composition and ichnofacies of mudstones of the Lower Triassic Osawa Formation in the Ogatsu area, South Kitakami Terrane, northeast Japan

This study aims to reconstruct shelf environment of the Lower Triassic Osawa Formation in the Inai Group, the South Kitakami Terrane (SKT), on the basis of the vertical variations of chemical composition and ichnofacies. The Osawa Formation in the Ogatsu area is divided into the lower part (OL ; intensely bioturbated calcareous siltstones) and upper part (OU ; parallel laminated mudstones). The redox proxies (Zn/TiO2 and Ni/TiO2 ratios) and the benthic activity proxies (ichnofabric index and burrow diameter) suggest that the OL was deposited in a shelf where benthic activity was very high, whereas the OU was deposited in a relatively reductive environment that prevented benthic activity.