Poor Sorting Research Articles

FORMATION OF LARGE‐SCALE CROSS‐BEDDING IN A CARBONATE UNIT

SUMMARYThe type Lindsey Bridge Member of the Moorefield Formation of northeastern Oklahoma consists of 24 ft. of massively cross‐bedded limestone. Cross‐bed shape, lithologic variation, grain size and sorting, distribution of insolubles, and distribution of fossils and fossil burrows can be explained with reference to a hydrodynamic model developed in recent flume studies.Three facies can be distinguished in this unit: (1 Thei) foresets, thick‐bedded, well‐sorted, fine to medium crinoidal grainstones, dipping at angles up to 1° (2) toesets, which are thin‐bedded, poorly sorted, skeletal packstones notably more fossiliferous than the foresets, with which they are laterally gradational; toesets dip at approximately 5°‐8° (3) bottomsets, composed of argillaceous, fine‐grained (mainly silt‐size), skeletal limestones. Foresets overlie previously deposited bottomsets; this geometry is typical of regressive sedimentation.The exposure is adjacent to a pre‐Moorefield topographic high. As currents crossing this high entered a basin on the downcurrent side, flow separation occurred. Bed material load was deposited mainly on the foreset slope, suspension material mainly in toeset and bottomset areas. The poor sorting of the toesets is in part due to reverse circulation, formed by the flow separation, which transported bottomset sediment back toward the foreset. Jopling (1965b) has shown that this depositional geometry produces tangential cross‐beds similar to those seen in this outcrop. Differential settling velocity, substrate stability, and abundance of organic detritus influenced other sedimentologic properties of the deposit.

Sediments of Crater Lake, Oregon

Crater Lake, in the collapse caldera of a Pleistocene composite volcano in the Cascade Range of Oregon, has a maximum depth of 1932 feet. Immature and generally unsorted volcanic sediments have been deposited on the steep slope and nearly flat floor of the lake. In locations protected from terrigenous influx, the sublittoral bottom and summits of volcanic cones have accumulations of diatomaceous and moss oozes. Poor sorting of patchy deposits of medium sand on the slope and shore suggests deposition by sublacustrine and subaerial mass movements. The thickest deposits, layers of mud and sand, are found on the flat floors of the basins. Organic content, poor sorting, and silt-size median diameters suggest that surface sediments of the basin floor, mud layers of the basin floor, and sediments of the intracaldera volcanic structures result from continuous sedimentation of suspended materials. These suspended particles are introduced into the water by winds picking up material from within and outside the caldera, and by streams, sheet wash, and mass movements down the caldera wall. Good sorting, median diameters of fine sand size, and the mineral composition of basin sand layers indicate that mass movements from the slopes occasionally generate turbidity currents that carry sand across the flat basins to the lake center. Different sources and varying mineral content of sand layers in the same core, and lack of correlation of sand layers from core to core indicate the limited lateral extent of turbidity currents. The thinner, finer-grained, better sorted, and fewer number of sand layers toward the center of the lake suggest that turbidity currents lose competence progressively away from their source. Crater Lake turbidites are most similar to those of the offshore ocean basins of Southern California.

Sediments of Sabine Lake, the Gulf of Mexico and Adjacent Water Bodies, Texas-Louisiana

ABSTRACT Sabine Lake, a lake estuary, and the adjacent parts of the Gulf of Mexico, a nearshore neritic environment, were cored and clam-shell sampled to determine if certain physical characteristics of their sediments could be used to differentiate between the two sedimentary environments. Megascopically, in the wet state, the sediments of the two environments appear mainly as grayish to blackish, very fine sandy and silty mud or silty and clayey mud. Some very fine sand and fine sand occur in the northern part of Sabine Lake; very fine sand also occurs along the western part of the Gulf of Mexico shoreline. The sediments of the two environments are usually soft with a high water content and contain variable amounts of shell and plant materials. In the dry state, megascopically, the sediments are seen to be sand, silt or clay, or admixtures of these types and exhibit lighter shades of gray or black color. Analysis of laboratory data shows that the dominant sedimentary type in the two environments, based on mean grain size, is silt with the secondary occurrence of very fine sand and fine sand. Poor sorting is usually characteristic of the sediments of both environments. Comparison of all data indicates that the described sedimentary characteristics would make poor criteria in differentiating between the two sedimentary environments.

Quiet Water Oolites from the Ordovician of Minnesota: NOTES

ABSTRACT Quiet water oolites, hitherto unreported from the geologic record, are present at three exposures of the Shakopee Formation (Lower Ordovician) in southeastern Minnesota. These unusual oolites are analogous to modern forms being generated in Laguna Madre, Texas. Protruding nuclei, ooolitic rings which abut against nuclei, and generally poor sorting suggest that these oolites were formed under low energy conditions.

Analyse mineralogique des sediments arenaces de l'Oxfordien superieur, de l'Albien et d'une formation intermediare dans la region de Lisieux (Calvados)

Abstract A heavy mineral analysis of sands reveals differences between Sequanian (upper Jurassic) and Albian (lower Cretaceous) formations of the Lisieux area, France. The heavy mineral suite in the horizontal well-sorted Sequanian Glos sands shows a predominance of tourmaline, zircon, rutile, and brookite. The Albian green sands differ from the Glos sands by the presence of glauconite, oblique stratification, and poor sorting at the base. A thin sandy bed intermediate between the Albian and Sequanian shows heavy mineral affinities for the Albian suite.

Permian

Permian

Squantum “Tillite”, Massachusetts—Evidence of Glaciation or Subaqueous Mass Movements?

The writer interprets the Boston Bay group as partially intertongued lithofacies of coarse conglomerate and associated volcanic rocks (Roxbury conglomerate) and finely laminated siltstone and mudstone (Cambridge “slate”). He regards the Squantum “tillite” as multiple discontinuous lenses of unsorted pebbly to bouldery mudstone of various ages interstratified within this complex. Although fossil evidence is inconclusive, stratigraphic relationships and clastic compositions suggest that these deposits were formed during middle Paleozoic diastrophism. The writer does not consider the Squantum as a temporal equivalent to southern hemisphere Permo-Carboniferous glaciation, as advocates of a glacial origin had supposed. Lack of glacial pavement and comparison of composition, graded bedding, gross stratigraphy, and tectonic setting with known submarine slide and mass-flow deposits render the glacial interpretation suspect. Origin by gravity movement of rapidly deposited, volcanic-rich sediments and periodic resedimentation by turbidity currents in a Paleozoic eugeosynclinal belt is a more plausible alternative. Very poor sorting, striated clasts, faceting, and even some rafted erratic fragments in fine, laminated mudstones can arise from mechanisms other than glaciation. A preserved, extensive, grooved and polished pavement overlain by poorly sorted, till-like material—particularly if nonmarine—is the most compelling glacial evidence. Very large erratic boulders are suggestive of ice movement, as are abundant rafted erratic fragments in fine muds, as in the Gowganda formation of Ontario. Independent biologic or isotopic cold-temperature indicators are sorely needed to strengthen glacial interpretations. General stratigraphic relationships and tectonic setting serve as important factors in judging probability of alternate interpretations, particularly in geosynclinal sequences. From these criteria, the writer judges that only the Permo-Carboniferous glaciation in certain parts of the southern hemisphere is firmly established. The Gowganda and some other Precambrian deposits are very likely glacial, but most postulated examples must be re-evaluated.

Petrography of Northeastern Lake Michigan Bottom Sediments

ABSTRACT A direct relationship between sediment properties and their environment of deposition, source material, and post-glacial history was shown by textural and mineralogical studies of cores and dredge samples obtained from northeastern Lake Michigan. The lake bottom topography of the area, which may be characterized as a valley-and-ridge province, exerts a very strong control on the distribution of sediments. In general the coarse sediments are found on the ridges and their adjacent flanks and fine sediments are restricted to the hollows between ridges. There is a regular variation in size with depth, but no regular variation in size with relation to distance from shore. The majority of bottom sediments are well sorted, but most of the samples from the lower portion of the flanks of troughs show poor sorting, probably the result of slumpage of coarser sediments from the higher portions on the flanks. Evidence for the Lake Chippewa low-water stage is shown by the following: Core samples taken from depths of water less than 275 feet contain coarse sediment overlying, underlying, or included within a sequence of much finer grained silty clay or clayey silt. The presence of shells of shallow-water forms in some of these coarse sediment zones and a peat deposit found in association with this coarse sediment give additional evidence of a low-water condition. The similarity of the mineralogy of the detrital sand-sized material in the lake sediments to that of the glacial drift from the adjacent shore shows that the lake sediments were derived mainly from that source. The general order of abundance of clay minerals in both the lake sediments and glacial till material from the adjacent shore is illite, mixed-layer chlorite and illite materials, and chlorite. Little variation in the clay mineral composition with changes in depth of water, distance from shore, or depth of burial was observed. In general the carbonate content of the lake bottom samples increases with a decrease in the median diameter of the sediment. There is, however, a lower carbonate content in the dark-gray sediments found in the deep troughs and in Little Traverse Bay: this is attributed to the solution of calcium carbonate as a result of a decrease in the pH within the sediment. Pyrite, in association with calcareous shell material, was found in many core samples, but not in glacial till samples from the adjacent land areas. The pyrite is interpreted as secondary, resulting from local reducing conditions produced by the decay of soft parts of the shelled organisms.

The term graywacke

A short history of the term graywacke is given, illustrating the circular reasoning this term has produced. An urgent plea is made for either abandonment or restriction of the term. If the term is to be abandoned, the new name usamerite is suggested to describe a large group of rocks characterized by a size range from breccias to sandstones, a substantial quantity of fine matrix, poor sorting, variable rockfragments, and angular to subangular grains.

Tarzana Fan, Deep Submarine Fan of Late Miocene Age Los Angeles County, California

The sandstone beds in the Modelo formation (upper Miocene) exposed on the north flank of the Santa Monica Mountains were for the most part deposited from turbidity currents. Evidence of rapid deposition is provided by poor sorting, high clay-silt content, grain angularity, high feldspar content, and load deformation. Evidence for great depth of water (about 3,000 feet) is provided by abundant foraminifers and fish remains in the interbedded shales. That the mechanism for transporting this poorly sorted sand-silt-clay mixture into waters of this depth was that of turbidity currents is borne out by the multitude of syngenetic textures and structures which these rocks have in common with accepted turbidites and with structures which have been produced in laboratory studies. Some of these structures are oriented with respect to the direction of travel of the current and thierefore provide a means of determining the direction of bottom slope along which the currents moved. When plotted on a map these directions reveal a pattern which is unmistakably that of a fan with its apex toward the north. The area studied constitutes a 16-mile-long section through this outcropping north-tlted fan. The point source was most logically the mouth of a submarine canyon. The canyon itself is thus far unrevealed, being concealed beneath the alluviated San Fernando Valley, but the eroding source area is tentatively identified on the basis of mineralogical studies in the San Gabriel Mountains about 22 miles northeast of the fan's apex. Further studies of this sort can not fail to provide valuable data on earth history and thus aid petroleum exploration in similar rock types elsewhere in California.

CONTRIBUTION TO THE PETROGRAPHY OF THE TANNER GRAYWACKE1

(Prepared by the Translator) Helmbold9s detailed study of the classic upper Devonian-lower Mississippian Tanner graywacke of the Harz Mountains is based primarily on analyses of three spot samples from quarries near Scharzfeld. Quantitative chemical analyses, petrographic description, and quantitative computation of principal constituents including estimates of mineral components of rock fragments, and measurements of sorting, shape, and orientation of grains are presented. The Tanner graywacke is a hard, tough, poorly sorted gray-green sandstone containing the following constituents (average of three analyzed specimens in volume per cent): quartz—24.6, feldspar—32.1, rock fragments—23.0, and matrix—20. Source rocks that supplied these constituents are estimated as follows (average of three analyzed specimens in volume per cent): igneous rocks—58, metamorphic rocks—29, and sedimentary rocks—13. The geologic setting, texture, composition, and sedimentary structures, such as graded bedding, indicate that the Tanner graywacke is a deposit of an orogenic belt, derived from the southeast, and deposited largely by periodic turbidity currents. The poor sorting and poor rounding of the grains, the abundant feldspar and rock fragments, and the postulated mode of origin of the Tanner graywacke agree with qualitative specifications of other graywackes, but its quantitative composition deviates from published analyses of them.

MUDFLOW OF 1941 AT WRIGHTWOOD, SOUTHERN CALIFORNIA

Research Article| May 01, 1953 MUDFLOW OF 1941 AT WRIGHTWOOD, SOUTHERN CALIFORNIA ROBERT P SHARP; ROBERT P SHARP CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIF.; NORTHWESTERN UNIVERSITY, EVANSTON, ILLINOIS Search for other works by this author on: GSW Google Scholar LAURENCE H NOBLES LAURENCE H NOBLES CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIF.; NORTHWESTERN UNIVERSITY, EVANSTON, ILLINOIS Search for other works by this author on: GSW Google Scholar GSA Bulletin (1953) 64 (5): 547–560. https://doi.org/10.1130/0016-7606(1953)64[547:MOAWSC]2.0.CO;2 Article history received: 07 Jul 1952 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ROBERT P SHARP, LAURENCE H NOBLES; MUDFLOW OF 1941 AT WRIGHTWOOD, SOUTHERN CALIFORNIA. GSA Bulletin 1953;; 64 (5): 547–560. doi: https://doi.org/10.1130/0016-7606(1953)64[547:MOAWSC]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract During early May of 1941 the southern California mountain resort of Wrightwood was partly inundated by surging flows of muddy debris which occurred daily for more than a week. The immediate cause of flowage was rapid melting of deep winter snow. Intense shattering and rapid weathering of the bedrock (Pelona schist) within the San Andreas rift zone at this location contributed materially to preparing debris for flowage.Field studies, eyewitness accounts, and movie films provide the following information. Debris was transported 15 miles by the mudflow, and on a gradient as low as 75 feet per mile at the outer extremity. The flow advanced in successive waves or surges of “slimy gray cement-like” mud containing abundant stones. Velocities of the surge fronts ranged from a few to nearly 15 feet per second and averaged close to 10 feet per second during the more fluid phases. The fronts of the more fluid surges slithered and splashed along about like a rapidly advancing tongue of water. No breaker-like motion was evident, although the top of the front tended to shoot ahead of the base. In more viscous surges a bouldery embankment developed at the front and was shoved along by the material following behind.One sample of the fluid debris had a density of 2.4, indicating a water content of 25–30 per cent by weight. Calculated viscosities range from 2 × 103 to 6 × 103 poises. An average sorting coefficient of 3.94 indicates poor sorting, although somewhat better than in many glacial tills which the flow deposits strongly resemble. Earlier mudflows have occurred here, and others will undoubtedly take place in the future. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Bottom Sediments of Green Lake, Wisconsin

ABSTRACT Green Lake is the deepest lake in Wisconsin. Its waters are hard and large quantities of calcium carbonate are precipitated. Deposits of this sediment are either in the form of shells of gastropods and pelecypods or small crystalline particles which have no known connection with the shells. Deposition of calcium carbonate extends from the shore to the greatest depth in the take--237 feet--with the most extensive distribution between depths of 12 and 30 feet. Sands deposited in the lake are not well sorted. Most characters of the sands were produced in other environments. Only the poor sorting and the stratification are due to lacustrine conditions.

IX.—St. Paul's School before Colet

To talk of St. Paul's School before Colet will to most people seem pure absurdity. Even those who know there was such a school think that it was only a poor sort of choir-boys' school, and would be inclined to apply to it, mutatis mutandis, the famous Scotch bull on the roads in the Highlands:If you'd seen these roads before they were made,You'd hold up your hands and bless General Wade.