Nearshore Facies Research Articles

Variations in Late Pennsylvanian Molluscan Faunas: ABSTRACT

Certain nearshore facies of the upper half of the Pennsylvanian System in the Mid-Continent region are characterized by faunas which are dominantly molluscan. Although individual faunules are reasonably well known, few comparisons have been made between successive faunas. Five molluscan faunules ranging in age from Desmoinesian to Virgilian were examined on the specific and supra-specific levels. The abundance of individual species, genera, and families within each formation, variations in the abundances with time, and the phylogenetic changes aid in the interpretation of the paleoecologies of these unusual populations. End_of_Article - Last_Page 731------------

Evaporite Basin Configuration--Structural versus Sedimentary Interpretation: ABSTRACT

This paper presents different interpretations of the structural and/or stratigraphic criteria which are the bases for understanding evaporite-basin sedimentation and its subsequent role in oil exploration. The gross profile and configuration of Devonian Famennian, Givetian, and Eifelian evaporite basins in North America have induced the a priori conclusion that these lenses and wedges are the result of differential sedimentary tectonics with contemporaneous evaporite-carbonate deposition. Such basins are viewed as culminating in uniform subsidence and conformable deposition of superjacent successions--generally of open-marine and nearshore facies. Although this hypothesis deserves equal consideration with any other as a basis for interpreting evaporite-basin sedimentation, its preponderant acceptance without benefit of local and regional detailed stratigraphic studies hardly endows it with any real validity. In testing, this hypothesis should be examined seriously by the following considerations: (1) Walther's Law of Correlation of Facies demands that an unconformity must be recognized between the evaporites and the overlying transgressive redbed, sand, and/or carbonate succession; (2) related to Walther's Law--contemporaneous carbonate-evaporite deposition generally is impossible; the concept of cyclical superposition is much more rational; and (3) the offset axes of superjacent successions demand End_Page 550------------------------------ interdepositional tectonics and not subsidence contemporary with sedimentation. The above three points support the validity of the concept that the Devonian Famennian, Givetian, and Eifelian evaporite-basin configurations are not simply the result of differential sedimentary tectonics but are mainly eroded structural remnants. Supporting this concept are detailed stratigraphic subdivisions suggesting that these basins or lenses are only remnants of originally much more expansive evaporite depositional regions. These basins are analogous to structural basins in contemporaneous open-marine sedimentary provinces. Post-depositional epeirogenic movement and vast areal erosion have left thick broad lenses or wedges of evaporite sections--regionally defined as evaporite provinces of deposition. In searching for hydrocarbon accumulations among structural and stratigraphic traps within the evaporite complex, one has to consider these critical factors--the supra-evaporite basin unconformities and their tectonic origin. End_of_Article - Last_Page 551------------

Role of Compaction in Development of Geometry of Superposed Elongate Sandstone Bodies: ABSTRACT

End_Page 455------------------------------Pennsylvanian and Permian nearshore facies on the eastern shelf of north-central Texas contain channel-fill sandstone bodies, which have been mapped from the outcrop westward down the paleoslope for 50 miles. These elongate sandstone bodies range in width from several yards to 3-4 miles and in a few places are more than 100 feet thick. Where the thickness values of the subsurface dendritic (distributary) sandstone bodies are unusually great, sandstone from subjacent bar-finger deposits probably has been included. Within shallow, poorly developed synclines, which apparently provided primary paleotopographic control of channels, superposed channel systems commonly are offset laterally as a result of (1) interchannel subsidence by differential sandstone (channel)-shale (interchannel) compaction and (2) channel subsidence by compaction of sediments beneath massive channel-fill sandstones. The common offset patterns of superposed channel pairs is mainly a result of dominant interchannel compaction. Stacked or cross-over relations of channel pairs are less common and occur where the lower member is unusually thick. Channel-pair intersect maps illustrate the persistent geographic position of stacking and cross-overs, which may reflect tectonic control of channel location. Because of differential sandstone-shale compaction, axes of sandstone bodies commonly coincide with maximum thicknesses of thin, conformity-bounded sequences which enclose the elongate sandstone body. Axes representing maximum thickness of these enveloping strata, supplemented by high sandstone percentage trends, and synclinal axes, are useful in outlining the general position of channel-fill sandstone systems, but sandstone isopachous maps, paleotopographic maps, and cross sections (necessitating denser well control) are more definitive. End_of_Article - Last_Page 456------------

Pennsylvanian and Permian Basins in Northwestern Utah, Northeastern Nevada and South-Central Idaho: REPLY

The Pennsylvanian and Permian basins in northwestern Utah, northeastern Nevada, and south-central Idaho are downwarped segments of the Cordilleran geosyncline superposed on a complex structural pattern of Precambrian and early and middle Paleozoic age. The Oquirrh basin contains Pennsylvanian and Lower Permian sedimentary rocks as much as 26,000 feet thick; the area of maximum sedimentation was in northwestern Utah. Three principal parts are recognized: a lower part of clastic limestone, sandy limestone, and minor shale; a middle cyclically bedded limestone and sandstone; and an upper sandstone, chert, and shale unit. The lower part was deposited in an offshore shallow-water environment; the middle and upper parts in offshore moderately deep water; these grade laterally both eastward and westward into shallow-water nearshore facies. The Permian Phosphoria basin was partly coextensive with the Oquirrh basin, but the area of maximum sedimentation was in northeastern Nevada and southern Idaho, where locally 3,500 feet of shale, cherty shale, chert, dolomite, and limestone accumulated. This facies was deposited in an offshore deep-water environment, favoring formation of thick sponge-spicule chert and cherty shale units; these grade southward and eastward into carbonates and shales that were deposited in a shallow nearshore environment. In Cretaceous time the Paleozoic and lower Mesozoic rocks of northeastern Nevada and western Utah moved eastward on great thrust plates that extended from southern Utah into Idaho. Movement took place on the Willard-Charleston-Nebo thrust belt in the Wasatch Mountains. Westward continuations of these thrusts crop out in northwestern Utah and eastern Nevada. Imbricate thrusts and tear faults within the upper plate have resulted in complex distribution of upper Paleozoic rocks.

Pennsylvanian and Permian Basins in Northwestern Utah, Northeastern Nevada and South-Central Idaho

The Pennsylvanian and Permian basins in northwestern Utah, northeastern Nevada, and south-central Idaho are downwarped segments of the Cordilleran geosyncline superposed on a complex structural pattern of Precambrian and early and middle Paleozoic age. The Oquirrh basin contains Pennsylvanian and Lower Permian sedimentary rocks as much as 26,000 feet thick; the area of maximum sedimentation was in northwestern Utah. Three principal parts are recognized: a lower part of clastic limestone, sandy limestone, and minor shale; a middle cyclically bedded limestone and sandstone; and an upper sandstone, chert, and shale unit. The lower part was deposited in an offshore shallow-water environment; the middle and upper parts in offshore moderately deep water; these grade laterally both eastward and westward into shallow-water nearshore facies. The Permian Phosphoria basin was partly coextensive with the Oquirrh basin, but the area of maximum sedimentation was in northeastern Nevada and southern Idaho, where locally 3,500 feet of shale, cherty shale, chert, dolomite, and limestone accumulated. This facies was deposited in an offshore deep-water environment, favoring formation of thick sponge-spicule chert and cherty shale units; these grade southward and eastward into carbonates and shales that were deposited in a shallow nearshore environment. In Cretaceous time the Paleozoic and lower Mesozoic rocks of northeastern Nevada and western Utah moved eastward on great thrust plates that extended from southern Utah into Idaho. Movement took place on the Willard-Charleston-Nebo thrust belt in the Wasatch Mountains. Westward continuations of these thrusts crop out in northwestern Utah and eastern Nevada. Imbricate thrusts and tear faults within the upper plate have resulted in complex distribution of upper Paleozoic rocks.

Oquirrh and Phosphoria Basins in Northwestern Utah, Northeastern Nevada, and Southern Idaho: ABSTRACT

The Oquirrh and Phosphoria basins in northwestern Utah, northeastern Nevada, and southern Idaho are downwarped segments of the Cordilleran geosyncline superposed on a complex structural pattern of Precambrian and early and middle Paleozoic age. End_Page 1878------------------------------ The Oquirrh basin contains Pennsylvanian and Early Permian sedimentary rocks as much as 26,000 feet thick; the area of maximum sedimentation was in west-central Utah. Three principal units are recognized: a lower unit of cyclically bedded bioclastic limestone and sandy limestone, a middle unit of interbedded limestone and quartzite, and an upper unit of quartzite. The lower and middle units were mostly deposited in an offshore shallow water environment; the upper unit in offshore moderately deep water; these grade laterally both eastward and westward into shallow nearshore facies. The Middle Permian Phosphoria basin was partly coextensive with the Oquirrh basin, but the area of maximum sedimentation was in northeastern Nevada and southern Idaho, where locally 3,500 feet of shale, cherty shale, chert, dolomite, and limestone accumulated. This facies was deposited in an offshore deep-water environment, favoring formation of thick sponge-spicule chert and cherty shale units; these grade southward and eastward into carbonates and shales that were deposited in shallow nearshore environment. In Cretaceous time the Paleozoic and early Mesozoic rocks of northeastern Nevada and western Utah moved eastward on great thrust plates that extended from southern Utah into Idaho. Movement took place on the Willard-Charleston-Nebo thrust belt in the Wasatch Mountains. Westward continuations of these thrusts crop out in northwestern Utah and eastern Nevada. Imbricate thrusts and tear faults within the upper plate have resulted in complex distribution of late Paleozoic facies. End_of_Article - Last_Page 1879------------

A sedimentary and faunal study of the Blue Lias of Dorset and Glamorgan

The rocks of the Blue Lias in Dorset and Glamorgan can be divided into off-shore and near-shore facies. The off-shore facies has a characteristic pattern of regular, small-scale alternations of argillaceous calcilutites, marls and sometimes bituminous shales, the main variable being CaCO3content. Two distinct types of limestone are recognized and termed laminated and normal limestone, respectively. The marls are generally comparable with the limestones in all respects except their much lower CaCO3content. The bituminous shales are rich in bituminous matter which is arranged in fine laminae parallel to the bedding. Determinations of percentages of insoluble residues reveal a consistently large difference between the limestones and marls. Fuller chemical analyses of major constituents indicate, among other things, that nearly all the carbonate is present as CaCO3. The clay mineral content consists almost entirely of illite, with subsidiary kaolinite. The strontium content of the carbonate fraction of the marls appears to be markedly higher than that of the limestones. Vertical variation in Dorset, Glamorgan and Somerset is studied and compared by a graphical method based on the limestone-shale ratio. It has been established that the Blue Lias rhythm is primary in origin, but that there has also been a limited amount of early diagenetic segregation of CaCO3to produce nodular structures. The limestone textures are accounted for by recrystallization from an original lime mud and the respective importance of several processes including drusy and grain growth and granular and rim cementation assessed. Pyrite is considered to have been formed early in diagenesis under anaerobic conditions within the sediments. Its association in some drusy cavities with calcite is explained as due to the local fall in pH of interstitial fluids. The difference between the normal and laminated limestones and marls is considered to be the result of aerobic and anaerobic bottom conditions, respectively. The microlaminae in the bituminous shales are interpreted as varves due to the annual fall of plankton into anaerobic bottom waters. Evidence is put forward that the Blue Lias rhythm may be the result of repeated epeirogenic oscillations. Rocks of the near-shore facies are confined to Glamorgan. They include (besides calcilutites and subsidiary marls) skeletal limestones, oolites, conglomerates and cherty beds; locally the rocks lie unconformably on Carboniferous Limestone. Silica is found in the form of bands of nodules and silicified limestone pebbles and shells. The facies relationships of the different rock types can be satisfactorily related to the approach of an old shoreline. The silica was almost certainly derived from detrital chert weathered from the Carboniferous Limestone. Although there is a broad similarity in the fauna between Dorset and Glamorgan, a number of important differences are recognizable. Differences between the off-shore and near-shore facies are also described; whereas the former has pelecypods and ammonites as its most conspicuous elements the latter is notable for the abundance of corals and gastropods and, locally, of ribbed pectinids. A relationship between the fauna and the sediments is recognized in three cases: (1) shell enrichment in condensed beds (with glauconite and/or collophane); (2) dwarfing and general faunal impoverishment in the laminated rocks, related to poor aeration of the sea bottom ; and (3) variations in sedimentary rate and depth of sea probably account for the faunal differences between Dorset and Glamorgan in the off-shore facies. On the other hand, no relationship can be perceived in three other cases: (1) the increase in size up the succession in a number of forms, which is evolutionary; (2) the succession of different organisms due to ecological replacement and extinction; and (3) certain shell enrichments which may be due to population fluctuations. In a summary of the Blue Lias environment deductions are made about temperature, salinity, rate of sedimentation, depth of sea and current strengths.

Stratigraphy and structure at Three Forks, Montana

Research Article| January 01, 1943 Stratigraphy and structure at Three Forks, Montana GEORGE W. BERRY GEORGE W. BERRY Search for other works by this author on: GSW Google Scholar Author and Article Information GEORGE W. BERRY Publisher: Geological Society of America Received: 17 Feb 1942 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 1943 Geological Society of America GSA Bulletin (1943) 54 (1): 1–30. https://doi.org/10.1130/GSAB-54-1 Article history Received: 17 Feb 1942 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 GEORGE W. BERRY; Stratigraphy and structure at Three Forks, Montana. GSA Bulletin 1943;; 54 (1): 1–30. doi: https://doi.org/10.1130/GSAB-54-1 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 The northwest part of the Three Forks sheet, mapped by Peale (1896), has been remapped. The Pebbly limestones (Cambrian) of Peale's section could not be identified. The contact of the Dry Creek shales with the overlying Jefferson limestone represents a hiatus involving the Ordovician, Silurian, and Lower Devonian. The Jefferson is correlated with the Devils Gate of Nevada; upper Middle Devonian age is indicated in the lower beds by Spirifer cf. S. engelmanni (Spirifer argentarius zone, Devils Gate), and the base of the Upper Devonian is marked by the occurrence of Phillipsastraea, 175 feet above the base of the formation. Sixty feet of yellow sandstone overlying the Cyrtospirifer zone of the Three Forks shale (Upper Devonian), and previously included in that formation, contains a Lower Carboniferous Syringothyris fauna (Kinderhook) and is lithologically a recognizable unit. The name Sappington sandstone is here proposed. The Belt is not present in the southern part of the area but is represented by 4000 feet of conglomerate, arkosic sandstone, and micaceous shale in the northern part. A relatively steep shore line is indicated, and the section probably is the near-shore facies of one or more of the formations distinguishable farther north. The Belt shore line is marked by an east-west zone of Laramide high-angle thrusting, including the Jefferson Canyon fault, with an apparent throw of approximately 12,000 feet. The faulting was probably controlled by the declivity in the basement surface, which in turn was localized by a zone of weakness within the basement. North of the Jefferson Canyon fault, the structures conform to those of the Northern Rockies in their orientation and plainsward thrusting. South of it, the trends are west and northwest, and thrusting and overturning are to the southwest. This conforms to the general structural pattern of southern Montana and is not explainable by local resolution of east-northeastward Laramide stresses. 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.