Conglomerate Layers Research Articles

A study of high temperature crack growth in nickel-aluminide

The mechanism of high-temperature intergranular embrittlement in a nickel-aluminide intermetallic alloy has been investigated. Crack propagation rates were measured as a function of stressintensity in four-point bend specimens loaded in air at 500–760°C. Cracking and oxidation processes were examined using a variety of analytical techniques, including scanning, transmission and scanning-transmission electron microscopy, secondary-ion mass spectroscopy, and Auger-electron spectroscopy. Failure of the bend specimens occurred by stable intergranular crack growth at rates of up to 10 −4 ms −1 at 760°C. An activation energy for the process was estimated at 110 kJ mol −1, which is consistent with interfacial oxygen diffusion as the rate determining step. The crack and oxidation product morphology suggests that crack growth took place by a discontinuous step-wise mechanism, in which oxygen penetrates the grain boundary ahead of a stationary crack tip until the boundary is sufficiently embrittled to fracture locally under the prevailing stress intensity. The crack jumps forward into fresh unembrittled material and arrests, upon which the process is repeated. Mechanisms of embrittlement are discussed. Subsequent oxidation of the crack faces produces a multi-layered infill comprising a central conglomerate layer of unoxidised nickel, flanked by aluminium oxide containing sub-micron nickel particles.

Subaqueous deposition of accretionary lapilli: Significance for palaeoenvironmental interpretations in Archaean greenstone belts

Accretionary lapilli from phreatomagmatic eruptions are abundant in the late Archaean Fortescue Group of the Pilbara Region, Western Australia. Where the sequence is uncleaved and gently folded, well-preserved depositional structures include densely packed accretionary lapilli in trough cross-beds and sparse accretionary lapilli in trough and wedge to tabular cross-beds. Accretionary lapilli also occur in conglomerate layers and localised pebbly-channel-fills associated with granite and pegmatite clasts up to 10 cm in diameter. These lapilli are clearly robust being capable of withstanding fairly energetic aqueous transport in contrast to the opinion of many authors who consider that all accretionary lapilli would disintegrate if settled through extensive water columns or incorporated in turbidite deposits. Accretionary lapilli indicate subaerial or very shallow water eruption but their presence cannot be used alone to support very shallow water or subaerial deposition. Accretionary lapilli are found throughout many volcanic piles and are probably widespread in Archaean greenstone successions but their environmental significance has to be assessed carefully using a variety of associated features.

Strain distribution in a fold in the West Norwegian Caledonides

Strain has been measured from clasts within a deformed conglomerate layer at 17 localities around an asymmetric fold in the Rundemanen Formation in the Bergen Arc System, West Norwegian Caledonides. Strain is very high and a marked gradient in strain ellipsoid shape exists. To either side of the fold, strain within the conglomerate bed is of the extreme flattening type. In the fold, especially on the lower fold closure, the strain is constrictional. Mathematical models of perturbations of flow in glacial ice have produced folds of the same geometry as this fold, with a strikingly similar pattern of finite strain. The fold geometry and strain pattern, as well as other field observations, suggest that the fold developed passively, as the result of a perturbation of flow in a shear zone, where the strain was accommodated by simple shear accompanied by extension along Y.

Shelf Sedimentation Across Precambrian-Cambrian Boundary: Chapel Island Formation, Southeastern Newfoundland: ABSTRACT

The upper Precambrian-Lower Cambrian Chapel Island Formation consists of medium- and fine-grained siliciclastics and minor limestones that record the early evolution of shelly fossils and complex trace fossils. Deposition of these Avalonian sediments occurred in a variety of shelf environments. Temporal and spatial changes in the conditions of sedimentation during the deposition of this sequence resulted in a wide spectrum of sedimentary and biogenic structures. Facies transitional with underlying terrestrial and shallow-marine red beds were deposited in foreshore and upper-shoreface settings under tidal influence and display tidal channels, shrinkage cracks (desiccation and synaersis), abundant current ripples (bimodal-bipolar current distribution), and phosphatic nodules. Sandstones and siltstones deposited in shoreface to outer-shelf settings contain evidence of storm and wave reworking. Features present include: gutter casts, thin granule lag zones, phosphate nodules, slump-fold zones, hummocky cross-stratified beds, and thin to medium-grained sandstones with sharp bases and gradational tops, wave-rippled upper surfaces, climbing wave ripple laminations, and draping laminations. These features indicate deposition on a storm- and wave-dominated shelf with locally variable topography. Thick massive siltstone beds and pebbly mudstones are interpreted as debris flows formed on a gentle slope. Red and green mudstones, nodular limestones, and medium to thick (up to 60 cm) limestones were deposited during periods of low siliciclastic input. The limestone beds--micrites to packed biomicrites--contain oncolitic and planar stromatolites, sheet-crack cavities (containing the oldest known coelobiontic fauna), iron-manganese encrusted surfaces, authigenic barite, mudcracks, intraformational and extraformational conglomerate layers, and small channels. These are interpreted as intertidal and supratidal deposits. End_of_Article - Last_Page 291------------

Porosity in Giant Gas Field, Ellenburger Formation, Puckett Field, Pecos County, Texas: ABSTRACT

The Lower Ordovician Puckett field has produced nearly 2.5 Tcf of gas from the Ellenburger Dolomite since the discovery of the field in 1952 by Phillips Petroleum Co. Production is from a depth interval of approximately 12,000 to 15,000 ft (3,600 to 4,500 m), and the estimated ultimate recovery is 3.3 Tcf. The Ellenburger facies are interpreted to have been deposited in several major environmental settings--subtidal, intertidal-channel belt, and supratidal. Subtidal deposition is represented by burrowed, irregularly laminated mudstones and wackestones and by oolitic grainstones. In the intertidal-channel belt, intraclastic packstones and stromatolitic boundstones accumulated. Laminated mudstones and algal-laminated mudstones were deposited on the supratidal flats in which desiccation produced mud cracks and thin layers of flat-pebble conglomerates. During Ellenburger sedimentation there were many periods of subaerial exposure which resulted in formation of soil zones and karst terranes as deep as 20 ft (6 m). Solution collapse produced thick brecciated zones. Maximum porosity in the reservoir is 12% and the greatest permeability is 117 md. Porosity originated dominantly from tectonic and karst fractures and karst vugs. The generally low porosity is locally enhanced by intercrystalline, moldic, and interparticle porosity. The greatest porosity and permeability is commonly in the facies of the supratidal and intertidal environments most affected by tectonic fractures and by soil and karst development. End_of_Article - Last_Page 488------------

Studies on the Occurrence Mechanism of Surface Landslide in Kuchinotu Landslide area

The relation between the creep upper yield stress τu of cohesive soil near the landslide face and the effective overburden pressure ρε on the landslide face can be expressed as follows:τu=Cc+ρe tanφcwhere Cc φc are coefficient.A factor of the development of surface landslide in the region of Kuchinotu is the heavy rains amounting to over 250mm. That is, the decrease of effective overburden pressure due to the generation of pore water pressure of artesian condition from the ground water flows in permeable sandstone layers or conglomerate layers is the cause for the decrease of upper yield stress, and landslide is caused by the creep breakage of cohesive soil.After landslide occurred, when the static water pressure due to ground water in the slideface has over constant value by the heavy rains, the slide of layer begins again.

Performance of a Miscible Flood in the Bear Lake Cardium Unit, Pembina Field, Alberta, Canada

Field data and interpretation of project performance are given on a rich gas-drive miscible flood project that has been in progress for more than 5 years. Production has been good, but early solvent breakthrough occurred at two wells. In developing explanations for the breakthrough, computer models were used to analyze field data and the displacement mechanism. Introduction In Feb. 1968, a secondary recovery project was begun in the Pembina Bear Lake Cardium Unit 1 in Alberta, Canada. The major part of the secondary scheme was a rich gas-drive miscible flood conducted in the central region of the unit. The miscible process was used because of its potential for recovering oil unrecoverable by conventional waterflooding. This potential results from displacement efficiencies approaching 100 percent in the region of the reservoir swept by the solvent. Presented here is a general description of the reservoir, followed by a discussion of the miscible project scheme. The performance of the project is reported and analyzed. Information derived from reservoir simulation studies is also presented. The paper is a summary of several engineering studies and progress reports that are on file as public documents with the Energy Resources Conservation public documents with the Energy Resources Conservation Board of Alberta. These documents contain detailed reservoir data not reported in this paper. General Description of the Reservoir Reservoir Location and Layout The Pembina Bear Lake Cardium Unit 1 is located in the northwest portion of the Pembina field in Alberta, Canada, as shown in Fig. 1. The unit boundary and well locations are indicated in Fig. 2. Originally, the wells were developed on 160-acre spacing, but in the last 2 years some infill wells have been added. Currently, there are 29 wells in the unit; three are used as injectors, 25 are producers, and one well has been shut in. producers, and one well has been shut in. Formation Description The Cardium oil reservoir occurs at an average depth of 4,857 ft (-2,054 ft subsea). The oil accumulation is found in a sand bar development about 1 1/2 miles wide and 6 miles long. The Cretaceous sand was deposited under a deltaic condition and then was deeply eroded over most of the unit area. A highly permeable conglomerate-type chert was deposited over the eroded area. Fig. 3 is a cross-section of the reservoir showing the geometry of the sand and conglomerate layers. Maximum thickness of the conglomerate along the major axis of the bar is 41 ft. The underlying sand varies in thickness from 0 to 35 ft. The conglomerate layer is thickest in the northwest, and thins down and disappears in the southeast. It is important to note the vertical scale exaggeration on Fig. 3. The reservoir is actually extremely thin compared with its areal extent. Fig. 4 shows the depth to the top of the pay zone. The crest of the structure follows close to the major axis and dips downward from southeast to northwest. The amount of relief is small compared with the areal extent. Typical or average characteristics for the formation are included in Table 1. In the conglomerate layer, the average horizontal permeability is about 700 md. Permeability in the sand averages only about 20 md. The Permeability in the sand averages only about 20 md. The porosity is about 11 percent in both the conglomerate and porosity is about 11 percent in both the conglomerate and the sand. Permeability data taken from tests on core samples indicate that horizontal permeability of the conglomerate is generally 10 to 20 times greater than the vertical permeability. Geological analysis of core samples indicates that this difference results from the presence of essentially horizontal lithologic zones (beds) of relatively low permeability. In most cases, these zones consist of permeability. In most cases, these zones consist of conglomerate containing abundant sandstone matrix. JPT P. 672

Upper Cretaceous Resedimented Conglomerates at Wheeler Gorge, California: Description and Field Guide

ABSTRACT A field map and measured stratigraphic sections revise the geology of Wheeler Gorge. There are three layers of conglomerate, each of which passes upward into massive sandstones, classical turbidites, and/or dark mudstones with thin distal turbidites. Clast long axis orientation on conglomerate layers 1 and 3 gives vector means of 282 and 287 degrees respectively. This agrees closely with flutes (285) and grooves (279) on layer 1, and hence gives a paleocurrent direction for layer 3 for the first time. The conglomerates do not contain as much inverse grading as has previously been suggested, and none of the conglomerates is stratified. Inverse grading was measured in one bed, indicating a continuous upward coarsening of both the smaller and larger clasts in the population. The Wheeler Gorge conglomerates do not fit precisely with the three generalized models of conglomerates recently proposed by Walker, but are closest to the disorganized-bed model.

Sedimentation of deep water conglomerates in lower Ordovician rocks of Quebec; composite bedding produced by progressive liquefaction of sediment

ABSTRACT A Sequence of Lower Ordovician conglomerates and sandstones outcrops on the south shore of the St. Lawrence River, northeast of the village of Grosses Roches, Quebec. Detailed measurement of a section 100 meters thick shows that the conglomerate facies, which includes conglomerates, conglomeratic sandstones, and sandstones, occurs above a sequence of claystones, and alternates with a sandstone-shale turbidite facies. The conglomerates erode both the claystones and the turbidites. Rip-up structures, channeling of underlying sediments, grading, poor sorting, very large clasts, and chaotic clast fabric in some conglomerates suggest formation by deposition from gravity-controlled slides or flows. The conglomerates display two types of bedding: (1) Beds with no marked internal textural cha ges from top to bottom. These are termed simple beds in the present study. (2) Beds with several thin discontinuous sandstone layers in them. These layers can be traced up to 80 m along strike, but most layers are of limited lateral extent. These conglomerate beds are termed compound beds. Sandstone layers within compound conglomerate beds generally have flat tops and irregular bases. Where they wedge out, they invariably thin from the base upwards. They are not eroded by overlying conglomerate layers, although erosive features are common at the bases of both simple and compound beds. Thin fine-grained turbidites and thick medium to coarse-grained quartzose sandstone beds occur between compound conglomerate beds but not between layers within compound beds. This suggests that deposition of individual compound beds occurred as a series of events which were closely related in time and space, i.e., the beds are composite. It is likely that the development of such a series of events is related to the mechanism of initiation of a slide or flow rather than to the transp rt or depositional mechanism. This implies some type of progressive failure of the sediment mass at source. Recent advances in the field of experimental soil mechanics, and observations during recent earthquakes, suggest that the phenomenon of progressive liquefaction may account for relatively rapid but discontinuous failure of unconsolidated sediment. Considering the grain size of the material involved and the structures in the conglomerates, it is suggested that the composite beds in the Grosses Roches section result from deposition from a submarine slide or flow which was caused by progressive liquefaction of sandy layers in a series of unconsolidated sands and gravels, perhaps during an earthquake.

The development of the wustite-fayalite scale on an iron-1.5 wt.% silicon alloy at 1000�C

An investigation has been carried out on the morphological development and structure of the wustite-fayalite scale formed on a ferritic Fe-1.5 wt.% Si alloy exposed to carbon dioxide-carbon monoxide atmospheres at 1000°C. The amorphous silica film formed on the metallographically polished specimens crystallized to β-cristobalite at the reaction temperature. Wustite and fayalite developed within nodules which grew laterally to cover the alloy surface. Concurrent with growth of the nodules externally, oxygen diffusion into the underlying alloy led to precipitation of silica as α-tridymite. This internal oxidation zone was sufficiently depleted in silicon for its transformation to an austenitic phase. A fully developed scale was composed of an external wustite layer and an inner wustite-fayalite conglomerate layer, interspersed with discontinuous fayalite bands.

The Oxidation Properties of an Iron‐1.5 wt.% Silicon Alloy in Carbon Dioxide‐Carbon Monoxide Atmospheres at 1000°C

AbstractAn investigation is reported on the growth and structure of the scale formed on a ferritic Fe‐1.5 wt.% Si alloy exposed to carbon‐dioxide‐carbon monooxide atmospheres at 1000°C. The amorphous silica film on the metallographically polished specimens crystallized to β‐cristobalite. Wustite and fayalite developed within nodules which grew laterally to cover the alloy surface. Oxygen diffusion into the underlying alloy led to precipitation of silica as α‐tridymite. This internal oxidation zone was sufficiently depleted of silicon for its transformation to an austenitic phase. A fully developed scale was composed of an external wustite layer and an inner wustite‐fayalite conglomerate layer, interspersed with discontinuous fayalite bands. A model and a reaction sequence are advanced to account for the form of the oxidation curves and the reaction rate constants in terms of surface reaction steps similar to those for wustite formation on pure iron in these atmospheres.

Kinetics of wustite-fayalite scale formation on iron-silicon alloys

A superficial duplex scale consisting of an inner wustite-fayalite conglomerate and an outer layer of wustite was formed on an iron-1.5wt.% silicon alloy upon its exposure in carbon dioxide-carbon monoxide atmospheres at 890and 1000°C. Variations in the oxidation curves before onset of linear reaction kinetics could be correlated with appearance of fayalite bands in the scales. The linear rate constants for the overall reaction kinetics showed a proportional dependence on the pressure of carbon dioxide due to reaction control by surface reaction steps for dissociation of carbon dioxide and incorporation of chemisorbed oxygen into the wustite lattice. Growth of the wustite-fayalite conglomerate was not dependent upon the oxidizing potential of an atmosphere. Wustite growth involved iron migration while the growth of the inner wustite-fayalite conglomerate layer involved inward migration of oxygen resulting from a dissociative reaction of wustite at its inner surface.

Structural evolution of taiwan

The island of Taiwan is the site of Tertiary geosynclinal deposition on a basement of metamorphic complex. The structural evolution can be divided mainly into a pre-Tertiary orogeny and a post-Tertiary orogeny with a controversial intervening mid-Tertiary orogenic episode. Other local breaks and some conglomerate layers have been recorded in the Tertiary sequence, but their structural significance still leaves much room for discussion. Early Tertiary sediments were deposited in a eugeosynclinal basin with a metamorphic basement formed probably by Late Mesozoic movements. Neogene clastic sedimentation took place separately in a west miogeosynclinal basin and an east eugeosynclinal basin, each on one side of the cordillera made up of Paleogene and older metamorphic rocks. The main orogenic period occurred in Early Pleistocene time during which all the earlier formed rocks were folded and thrust-faulted. Continuation of this orogeny to the present is evidenced by the frequent earthquake shocks and other earth movements.

Arabiens arkæologi

Arabiens arkæologi

Nouvelles observations stratigraphiques sur le Cretace superieur du synclinal de Glandage-Creyers (Drome); repercussions paleogeographiques

Abstract New paleontologic data, especially the discovery of Globotruncana concavata (foraminifer) and an Inoceramus (I. sp. ex gr. muelleri) in the gray-blue upper Cretaceous limestones of Glandage-Creyers (Drome, French Prealps), indicate that the limestones are essentially Santonian, possibly extending upward into the lower Campanian. The underlying Gas conglomeratic complex is now assigned to the upper Turonian and, at the top, to the Coniacian. The Gas complex consists of two conglomerate layers separated by sandy limestones. Thus the so-called pre-Senonian orogeny apparently took place in at least two phases, one early Turonian (pre-Senonian), the other late Coniacian (early Senonian). The Coniacian, not the Turonian, is the major phase.

Lower Cretaceous Albian Rocks in Northern Great Plains

Rocks of Lower Cretaceous Albian age in Montana, North and South Dakota, and northeastern Wyoming have an average thickness of about 1,000 feet and can be divided into three major facies: (1) the Dakota facies in eastern South Dakota, (2) the Blackleaf facies in northwestern Montana, and (3) the basin facies lying between and intertongued with the other two. A study of the lithofacies, paleontology, and tectonic aspects of the basin facies suggests that two major transgressive-regressive marine cycles occurred during Albian time. After a period of non-deposition, marine waters from the Gulf region invaded the northern Great Plains. As this sea transgressed into Wyoming and Montana, the continental Aptian sands were reworked and redeposited into a blanket type sand called Fall River and First Cat Creek. The Fall River Sandstone has been and still is called Dakota; this terminology should be avoided because the Fall River is the basal sandstone of the basin facies and is not correlative with the entire Dakota facies on the east. As waters became deeper black shale (Skull Creek) was deposited, and finally the sea retreated, and a vast delta was built out from central South Dakota into eastern Wyoming and southeastern Montana. The Newcastle Sandstone is a typical delta distributary sand, and the Birdhead Sandsto e is a shelf deposit marginal to the Newcastle delta complex. A study of the sedimentary structures in the Newcastle suggests that at least four delta lobes can be ascertained. Much of the northern Great Plains then became land for a short period of time, and a very thin conglomerate layer was deposited at the top of the Birdhead sand. Before much erosion took place, a sea from the north invaded the area. In eastern Montana and western North Dakota a blanket type sand called Dynneson (new name; previously called Newcastle) was deposited. Some of the sand probably was derived from the upper part of the Newcastle delta, but much of it no doubt came from land areas on the east. The upper part of the Dynneson was deposited as a series of northeasterly trending features resembling off-shore bars. Then the waters became deeper, and the sea spread farther east and south. Much volcanic ash fell and apparently changed the muds to highly siliceous clays resulting in t e distinctive gray Mowry shale. Near the end of Albian time the northern sea retreated, but probably not all areas became emergent before another marine cycle began in Cenomanian (possibly late Albian) time.

Revision of Colorado Group on Sweetgrass Arch, Montana

The writers propose that the rocks formerly assigned to the Colorado shale on the Sweetgrass arch of northwestern Montana be divided into a lower unit, the Blackleaf formation with four named members, and an upper unit, the Marias River shale with four named members. The Blackleaf formation, of Early Cretaceous age, consists of marine and non-marine rocks that include much sandstone and sandy shale. It is divided into the Flood, Taft Hill, Vaughn, and Floweree members. The oldest member, the Flood, consists of brown-weathering ledge-forming sandstone beds and dark gray fissile shale probably marine in origin. It is 138 feet thick at its type section. The Taft Hill member, a marine sequence that is 240 feet thick as its type locality, consists of greenish gray glauconitic sandstone and gray soft bentonitic siltstone and shale. The Vaughn bentonitic member is characterized by light-colored bentonitic and tuffaceous siltstone that contains small crystals of orange-red heulandite. This non-marine unit is 97 feet thick at its type locality. The Bootleg er member, 330 feet thick at its type locality, is a marine sequence of interbedded sandstone, siltstone, and shale, but includes some layers of bentonite and chert-pebble conglomerate. The Marias River shale, of Late Cretaceous age, consists of 900-1,200 feet of dark gray marine shale. It is divided into the Floweree, Cone, Ferdig, and Kevin members. The Floweree (basal member) is mostly non-calcareous shale and siltstone; it is 63 feet thick at its type locality. The Cone calcareous member, 54 feet thick, consists of calcareous shale, thin beds and concretions of limestone, and some layers of bentonite. Sandy non-calcareous shale characterizes the Ferdig shale member which is 225 feet thick at its type locality. The Kevin shale member, 620 feet thick, contains numerous gray, yellow, and brown limestone concretions and dusky red dolostone concretions as well as many thin layers of bentonite. The middle of the member is marked by the MacGowan concretionary bed, a thi unit of dolostone and limestone that contains pebbles of chert and phosphatic siltstone.

STRATIGRAPHY OF THE COW HEAD REGION, WESTERN NEWFOUNDLAND

Seashore exposures in the Cow Head area display a succession of limestone conglomerates interbedded with shales and limestones. Conglomerate layers range in thickness from 1 foot to more than 200 feet. The material consists of flat angular chips or moderately rounded boulders of fine-grained gray or white limestone. Fossiliferous boulders from any one layer yield trilobites of the same limited age. Boulders from the lowest fossiliferous conglomerate at Broom Point contain Kootenia, Zacanthoides, Orriella, Agraulos, and Peronopsis. Succeeding bedded limestone yields Meneviella and Tomagnostus. A boulder in the overlying conglomerate also contained Meneviella and Tomagnostus. Cambrian conglomerates at Cow Head yield younger trilobites in successive layers: Tricrepicephalus appears in the lower, then Taenicephalus, followed by Ctenopyge, Rasettia, and Keithiella. Above are beds with Staurograptus and Dictyonema, overlain by conglomerates with early Ordovician trilobites. Successively higher black shales contain graptolites of the Levis Shale zones, and interbedded conglomerates yield successively younger Ordovician trilobites. Shale with Trigonograptus and Isograptus underlies the highest conglomerate which yields Nileus, Bathyurellus, Remopleurides, and Ectenonotus. The thick limestone conglomerate at Lower Head includes enormous boulders, one of which contains many of the trilobites described by Billings (1861–1865) as from Cow Head. This layer is underlain by black shale with Isograptus. The Cow Head Group, therefore, is not a single formation but a succession of conglomerates and intervening beds ranging in age from Middle Cambrian to Middle Ordovician. With few exceptions the boulders of any conglomerate are approximately the same age as the immediately underlying strata. The limestones of the fossiliferous boulders formed in shallow water; the beds intervening between the conglomerate layers formed in deeper water and consequently are almost devoid of fossils other than graptolites.

Palæomagnetic Measurements of the Keweenawan

RECENTLY, it has been possible to collect specimens from the Keweenawan system and measure their directions of magnetization. This system is a thick sequence of late Pre-Cambrian volcanics and sediments which outcrop along the margins of the Lake Superior syncline. It is divided into three series, Lower, Middle and Upper Keweenawan. At the type locality on the Keweenawan Peninsula, where most of the specimens were collected, only the Middle and Upper series are represented. Here the Middle Keweenawan consists of 11,000 ft. of basalt and andesite flows known as the Portage Lake Lava Series. There is a total of about three hundred successive flows with occasional interstratified layers of rhyolitic conglomerates and thin beds of sandstone. Succeeding the Portage Lake Lava Series conformably is the Upper Keweenawan, which consists of three divisions. The lowermost is the Copper Harbor Conglomerate, which consists principally of very coarse conglomerates and subordinate amounts of coarse reddish sandstone, but there are also some 500 ft. of interbedded lava flows. The total thickness of the Copper Harbor Formation is 4,500 ft. Lying conformably above the Copper Harbor is the Nonesuch Shale, which in this region consists of 700 ft. of thin bedded sandstones and siltstones. It grades upward into the third of the three divisions of the Upper Keweenawan, the Freda Sandstone. This formation consists of reddish, finegrained sandstones and siltstones. It is well bedded and consolidated, and usually only shows cross-bedding on a very small scale. One can find ripple marks, mud cracks and raindrop imprints, which clearly indicate a terrestrial deposition. On the Keweenawan Peninsula the Freda Sandstone is approximately 2,500 ft. thick, but in other localities it may reach a thickness of as much as 12,000 ft.

Stratigraphy of Plattin Group, Southeastern Missouri

Restudy of the Middle Ordovician Plattin formation of southeast Missouri to determine the mode of its northward thinning has led to the establishment of the Plattin group of four formations. The group consists of the following units, from older to younger. 1. Bloomsdale formation--oolitic and carbonate pebble-bearing calcilutite, commonly with green shale layers and beds of dolomite rock 2. Beckett formation--fucoidal fine-textured calcite limestone with many layers of intraformational conglomerate in the upper member 3. Hager formation--mainly of fine-textured calcite rock which grades northward into calcarenite and calcilutite 4. Macy formation--fucoidal calcite rock and succeeding fossiliferous calcite rock, the latter with shaly partings and a widespread metabentonite near the top Northward thinning of the Plattin group, from approximately 400 feet at Cape Girardeau to approximately 125 feet in southern Lincoln County, is by convergence within units and offlap and overlap of units. The Beckett formation overlaps the oolite-bearing Bloomsdale. The Hager formation disconformably offlaps the Beckett. The Macy formation thins by the reduction of the fucoidal part; the upper member is essentially plate-like. The Plattin has been classified as Bolarian, Black River in age, and correlated with the Platteville of the upper Mississippi valley. Faunules from the upper Macy suggest that those beds are lower Trentonian. Lower formations resemble the Bolarian in central Kentucky and central Pennsylvania.