Fold Lines Research Articles

Discussion

Dr Gordon Taylor stated that there were certain similarities between the structural history of the North Achill area and that found in the Dalradian rocks of the Slieve Gamph area, which was situated some 50 km approximately due east. Evidence has been deduced for the following structural sequence of events in the latter area: Phase I produced tight to isoclinal minor folds, a prominent schistosity (S₁) and a lineation (L₁). A major tectonic slide was formed (Lough Talt Slide) parallel to S₁. Phase II produced tight minor folds with subvertical axial planes which trend ne–sw, a crenulation foliation (S₂) parallel to the axial-planes of the minor folds and an elongation of pebbles and a rodding of quartz veins (L₂) sub-parallel to the hinge lines of the minor folds. A major tectonic slide was formed (Glennawoo Slide) parallel to S₂. Phase II produced a conjugate set of structures: (a) an earlier, more prominent series of open folds with a pronounced crenulation foliation (S_3a) which trends nne–ssw and dips to the east. (b) a later series of open folds with an e–w trending axial plane trace (S_3b) which dips to the north. Both sets of folds share a crenulation lineation (L₃). Phase IV produced kink-bands, conjugate and open folds with nw–se trending axial-plane traces. The sequence closed with the formation of ne–sw trending faults followed by nw-se trending faults. However, structures similar to those of Dr Kennedy’s second phase had not been observed in the Slieve Gamph

Basic Framework, Deformation, and Petroleum in Middle East: ABSTRACT

The most prolific oil-producing area of the Middle East lies on the southern flank or extension of the ancient Asiatic Tethyan geosyncline and was at least partly subjected to the same tectonic forces which produced the Alpine-Taurus-Himalayan Mountains. The importance of these tectonics is second only to depositional conditions in the Arabian-Persian Gulf geosyncline during which occurred the proper distribution of salt and anhydrites in time and place. To emphasize the importance of the evaporites, most if not all of the large gentle structures of Arabia and the southern gulf are salt-generated and the remaining structures in Iran and Iraq were created or modified by plastic deformation of salt and anhydrite. The Hith Anhydrite caps Jurassic oil in Arabia; the Fars Anhydrite caps Cretaceous-Miocene oil in Iran and Iraq. Late Tertiary deformation and fracturing of the Cretaceous Bangestan and Miocene Asmari Limestones created the long lines of story-book folds of the Zagros Mountains and oil reservoirs in Iran and Iraq. Fractured Bangestan oil reservoirs leaked much of their contents upward into fractured Asmari reservoirs where oil finally was trapped by the plastic Fars Formation. End_Page 469------------------------------ Zagros deformation not only determined the size and shape of reservoirs but also their permeability and porosity. The economic importance of this area is obvious. The Middle East, especially the Arabian-Persian Gulf and its periphery, is presently producing more than one third of the world's oil. Recent discoveries and extensions of known reservoirs have increased production to the point that the area produces more than North America. More than half of the world's proved reserves are in this area. Communist-block countries, in spite of tremendous potential, are contributing less than one-sixth of total world oil. Doubtless this is partly a result of the fact that these countries still have not attained the same wide use of petroleum products as the free world. Also, oil commerciality depends on the proper balance between a stable growing market and cheap transportation. The unique accessibility and availability of Middle East oil from this gulf guarantees its rising importance in world-energy needs. A plethora of oil is here and available; transportation is cheap. Extensive oil discoveries in new, inaccessible, or distant inland areas, even in the Middle East, world conditions permitting, should in no way threaten this source for many years to come. End_of_Article - Last_Page 470------------

Two-Dimensional Acoustic Fields and Amplitude-Phase Space

A mapping of two-dimensional real space, in which a time harmonic acoustic field exists, into a polar amplitude-phase space is considered. This mapping defines a set of “folding lines” that partition real space into connected regions over which the mapping is one to one. The “folding lines” are shown to be those curves along which the circulation of the vector intensity is zero. A computer has been used to determine these lines for plane-wave scattering from hard and soft cylinders for ka values of 0.5–6.0. The results yield an insight into the nature of the diffracted wave not obtainable from amplitude and phase calculations alone. [Work supported in part by a National Science Foundation grant.]

Development of Laramide Structure in Laramie Basin, Wyoming: ABSTRACT

The triangular Laramie basin lies between the Medicine Bow Mountains and the Laramie Range, and south of the Como Bluff fold. The stratigraphic column ranges in age from Pennsylvanian to Recent and is more than 15,000 feet thick. Hydrocarbons are produced commercially from fourteen fields and from six stratigraphic zones. The basin is asymmetric with a gently dipping east and southeast flank, a steeply folded and faulted west margin, and an indefinite northern boundary. Faulted northwest-trending folds interrupt the southern margin of the basin. Fault blocks in which Precambrian is exposed delimit the southwest margin of the basin south of Centennial. Faults bounding the blocks dip both east and west; individual blocks are elevated as much as 8,000 feet; and are bounded by fault complexes which might be anticipated in drilling. North of Centennial the basin is delimited by the Arlington thrust fault. The Centennial Valley syncline extends north-northwest parallel with the Rock River line of folding. Asymmetry of the anticline changes along strike from southwest at Seven Mile to northeast at Rock River. The Centennial syncline is in part overridden by the west-dipping Arlington thrust fault which dips 15° near Centennial and steepens to more than 45° near Arlington. The hanging wall plate is segmented by northeast-trending tear faults. Cooper Hill appears to be a gravity-emplaced klippe detached from the front of the thrust plate. The Laramie basin is segmented by the basinward extension of the Mullen Creek-Nash Fork shear zone in Precambrian rocks of the Medicine Bow Mountains. North of this zone the dominant feature is the Rock River line of folding and the Cooper Lake depression. Cross sections of the anticlines reveal a systematic pattern of internal deformation of the anticline, involving Triassic Chugwater and Cretaceous Niobrara and Frontier formations. The position of the major anticline was probably controlled by basement fracturing. Interference of three structural trends--Como Bluff (N. 30° E.), Seminoe fault zone (N. 65° W.), and Rock River (N. 20° W.) results in the complex of folds characterized by recurved fold axes near Medicine Bow. The mutual relationships between existent structural trends suggest that the first stage of development was broad crustal up-arching aligned north and south and probably extending to the base of the crust. The second stage developed along northeast-trending basement features and resulted in segmentation of the basement and in limits for the overthrusting. The third stage deformed the west margin of the basin either by faulting and folding (north half) or by development of fault blocks (south half). In this stage east-dipping faults appear to antedate west-dipping faults. The fourth stage involved complex reaction to compression in the Medicine Bow area, resulting in folds with variable orientation. Rocks correlated with the Hanna formation (Earliest Eocene) but not definitely dated rest with marked angular unconformity on the Cretaceous Medicine Bow formation. The Arlington thrust may be in part overlapped by the Hanna. Rocks of definite Wind River age are slightly folded. Rocks of Oligocene age are offset by normal faults. Younger Cenozoic deposits exist but have not been definitely dated. End_of_Article - Last_Page 115------------

Structure and Oil Possibilities of the West Flank of the Denver Basin: ABSTRACT

A seismic survey was conducted by members of the geology and geophysical departments of the Colorado School of Mines in the summer of 1951 along the west flank of the Denver basin. Its purpose was to determine the subsurface structure and relate it to surface features. Most of the work was correlation reflection shooting with some refraction work near the mountain front. A number of pertinent structural data were obtained. The Golden fault, a major reverse fault cutting across the steep west flank of the basin is a low angle overthrust, and not a high angle upthrust as commonly believed. The diagonal and en echelon plunging folds common along the mountain front north of Denver are present in the underthrust block of the fault. At least two lines of folding exist parallele to the axis of the Front Range, one of which is effectively concealed by thrust faulting. The deepest part of the Denver basin lies just southeast of the Denver city limits with the lowest closing contour on the Dakota sandstone at about -4,900 feet, or roughly 10,000 feet deep. End_of_Article - Last_Page 966------------

Structural Trends and Fault Systems in Eastern Interior Basin: ABSTRACT

The Eastern Interior basin is a structural basin cradled between the Ozark uplift and the Cincinnati arch-Nashville dome uplift. The two most conspicuous structural features indicated by an areal geology map are the La Salle anticline and the nearly separated lobe of the basin in Kentucky. A cross section indicates that the area acquired its basin character early and retained it through most of geologic history. A study of the folding and faulting within the basin reveals two different types of structure. One consists of a series of faults trending S. 20° W. and paralleling lines of anticlinal folding. Cross sections show these faults to be normal diagonal shears and the folds to be similar to the granite ridge and related lines of folding in the Mid-Continent area. The other is the Shawneetown-Rough Creek fault zone and associated faults extending across the south end of the basin. Cross sections and data gleaned from the literature dealing with this and the Kentucky River fault zone, to which it appears closely related, show this to be an entirely different type of faulting from the system first described. On the basis of the evidence presented, the writers suggest an explanation and classification of this zone of faulting different from any that has been proposed in the past.

The Geology of British Oilfields 3. The Oilfields of Burma

The oilfields of Burma lie almost entirely within the elongated Tertiary basin which runs approximately north-south and is bordered on the west by the Arakan Yoma and on the east by the ancient plateau of the Shan Hills. Most of the oil has been obtained from fields lying on a single line of folding and in a belt only 50 miles long between latitudes 20° 20′ and 21° 10′, the remainder being found in small fields situated at various places between latitudes 19° 25′ and 23° 45′.

The Tectonic Development of the Western Weald in Lower Cretaceous Times

Modern detailed stratigraphical studies have demonstrated very clearly the long and involved tectonic history of the majority of the main structural units of England. It has been proved that, in certain areas, the thickness and the lithology of the sediments were partly determined by repeated pene-contemporaneous folding along definite axes, and thus it has been possible to trace the gradual growth of some of the main fold lines of the country. The Weald is typical of these areas, whose structure, at first sight simple enough, reveals on closer study much complexity of the minor folding and faulting and also gives evidence of long continued movement along certain lines; movement contemporaneous with the deposition of beds which were involved in the final crescendo of tectonic activity.

Source and Date of Accumulation of Oil in Granite Ridge Pools of Kansas and Oklahoma

All oil pools extending from El Dorado, Kansas, to Oklahoma City along the Nemaha granite ridge and the southern extension of that line of folding have important oil accumulations at an unconformity beneath the Pennsylvanian shales. This relation, together with evidence from later folds in the region, furnishes data from which the approximate date of oil migration and accumulation can be determined. Consideration of various possible sources for this oil indicate that it was not generated until long after the sediments were deposited, and that its source can not logically and consistently be sought in the rocks in the immediate vicinity of the pools. Generation of the oil by metamorphic agencies during the Appalachian revolution and its migration, in some regions through l ng distances, to its present reservoirs through porous carrier beds is a suggested hypothesis which seems to accord better with the data from the fields than do any of the hypotheses of local origin of the oil.

Involutions of Order n with an n - 2 Fold Line and Their Mapping

Involutions of Order n with an n - 2 Fold Line and Their Mapping

Involutorial Transformations in S 3 of Order n with an (n-1)-Fold Line

Involutorial Transformations in S 3 of Order n with an (n-1)-Fold Line

Geology of Vermilion Creek Gas Area in Southwest Wyoming and Northwest Colorado

The Vermilion Creek gas area, located on both sides of the state line between southwest Wyoming and northwest Colorado, is now the field terminus of a 330-mile $20,000,000.00 gas line built in 1929 and supplying Salt Lake City, Utah, and adjacent towns with natural gas. The gas developed here is the first important commercial gas developed in the Tertiary formations of the Rocky Mountain region. Six closed domes, three of which are associated with considerable faulting and four of which are controlled by one main line of anticlinal folding, are developed. The folding in the gas area is a direct consequence of the older and more severe regional structural movements in the Uinta Mountains on the south and west and the Rock Springs uplift on the northwest. To date two of the domes have been proved for commercial gas, one well yielding a total of 65,000,000 cubic feet per day from four separate sands. The gas is produced from irregular sand bodies, very lenticular and physically different, in the lower Wasatch formation of Eocene Tertiary age. The producing horizons are of fresh-water origin only. Gas accumulation is controlled by the folding of the Tertiary beds into closed structures. The source of the gas, which is of excellent quality, is not exactly known. Examination of outcrops and of drill cuttings reveals comparatively scanty evidence of organic life in the lower Tertiary beds. It has been suggested that the underlying Cretaceous beds are the source, but the preponderance of evidence does not support this view. Production from the gas area commenced in September, 1929. Insufficient gas has been run to date to make possible accurate estimates on the life of wells and total reserves.

U-Shaped Mountain and Fold Line: Review

U-Shaped Mountain and Fold Line: Review

Rumanian Oil Fields

The distribution of the Rumanian oil fields is governed by lines of folding related to the major Carpathian overthrust faulting. Along these lines of folding, the production tends to focus around salt masses that form local highs. The source of the salt is unknown. Its rise is due to lateral pressure. The source of the oil is disputed, but the writer believes that it is Pliocene. A comparison of these fields with those of the American Gulf Coast region shows that, although there are some resemblances which may indicate the action of like causes to a limited extent, the dissimilarities are greater. The lateral pressure, which is proved for Rumania, cannot be accepted as the entire, or even as the major, cause of the American domes.

The Status of Americans in Petroleum Developments of Europe and Asia

This paper deals with the major known petroleum regions of Asia, also the fields of Southern Europe, such as Rumania and Russian Caucasia, which are geographically related to Asiatic districts east of the Caspian Sea. Consideration is given to future prospects, rather than to a review of the past. Geological conditions are set forth briefly and industrial and political matters are touched upon in so far as they have a bearing upon future developments and may affect American participation in them. Such facts as may indicate the relative importance of the oil regions are cited, and events of recent history are reviewed which show the reasons for the failure of Americans to become established in these countries. The oil regions will, so far as possible, be grouped geological y into provinces, and the extent of these provinces defined by reference to political subdivisions. By grouping into the stratigraphic and structural provinces as shown by the heavy lines on the accompanying map (Plate 19), the areas are indicated in which there is a continuity of conditions, such as major lines of folding and general similarity of formations, but not, of course, a continuity of oil accumulations. The map, however, aims to indicate roughly the lines along which future oil fields are most likely to be developed. The lines connecting developed oil regions do not represent continuous single anticlines, but in some cases groups of folds or other structural conditions favorable to oil accumulation, also areas of similar stratigraphy. The writer has spent a number of years recently in both the Far East and the Near East, having visited many of the regions discussed, conferred with government geologists and others associated with American or British companies, fresh from the study of some of the more important oil districts, and has also had some experience with negotiations for oriental oil lands. The following discussion is built upon such sources of information as those mentioned and upon a certain amount of personal knowledge, more largely than upon a search of petroleum literature. Dependence has been placed upon reliable oil journals for recent events. It is admitted that others, especially English geologists, have much more detailed information upon the fields discussed, but the writer feels that the conclusi ns expressed are sufficiently justified by the information in his possession.

Pre-Cambrian Folding in North America

Introduction Any serious attempt to decipher the pre-Cambrian paleogeography of the continents, even if only in broad outline, should be commended. An elaborate effort of this kind has very recently been made[2][1] by R. Ruedemann, whose paper is valuable mainly because of its highly suggestive features. In it he “ventures to. suggest some possible fundamentals of pre-Cambrian paleogeography.” It is not too much to say that Ruedemann has opened up a new and important field of geological inquiry. The present purpose is to confine attention to one very important aspect of the subject, in which the writer has been interested for some years, and this in its application to North America only. This aspect of the subject is the folding and foliation of pre-Cambrian age, with special reference to their trend-lines. This is a fundamental consideration in Ruedemann’s paper, and in his. summary regarding the principal lines of pre-Cambrian folding . . . [1]: #fn-1

Intra-Jurassic Movements and the Underground Structure of the Southern Midlands

Summary1. The occurrence of anticlinal folding during Jurassic times has been demonstrated by Mr. Buckman's detailed zonal work in the Vale of Moreton and in the North Cotteswolds. These anticlines are indicated on the map by marked bends in the outcrops of the Lower Jurassic formations.2. Similar bendings of outcrops are seen at several localities in the Eastern and Southern Midlands, and the structure at one such locality—Melton Mowbray—has recently proved to be anticlinal.3. Intra-Jurassic folding betrays itself by non-sequences and reduced thicknesses of Lower Jurassic zones along anticlinal axes. Such evidence suggests the existence of anticlinal structures in the neighbourhood of Banbury, Weedon, and perhaps also Market Harborough, in addition to the cases mentioned above.4. Movement was probably almost continuous along some or all of these axes, at least from Rhætic to Bajocian times. Outcrops of post-Bathonian formations are not affected by the flexures, although the folding was perhaps renewed in later Jurassic or even Tertiary times.5. Several of these lines of Jurassic folding probably follow the lines of earlier and more powerful movements. The bearing of such flexures on the structure of the Palæozoic floor is discussed.6. Attention is called to a curious symmetry in the disposition of the Palæozoic formations on either side of a prolongation of the Pennine axis.

XXIX. The “Green Beds” on Sron Aonaich and near Ardlui, Argyllshire

Stratigraphically the “Green Beds” occur in a position near the top of the lower arenaceous zone, and occupy a horizon not far below the Loch Tay limestone. It was not until considerable advances had been made in the mapping of the Highlands that the Officers of the Survey were enabled to recognise the importance of the rocks as a definite and well-marked horizon amongst the schists to the south of the Loch Tay limestone, below which and towards the great central facker or fan structure the “Green Beds” dip in simple outcrops below the Loch Tay limestone. Between the great axial line of folding and the frontier Highlands they are repeated again and again in isoclinally-folded strata as outliers between the folds of the Ben Ledi grits. In Cowal there appear to be two sets. The particular specimens from which those exhibited have been taken are on Sron Aonaich, a shoulder of Ben Lomond, and in the railway cutting on the West Highland line north of Ardlui, the principal interest attached to them being the increasing metamorphism seen in the rocks from the latter locality. The Sron Aonaich “Green Beds” are principally pale yellowish greeny grits, the original clastic structures being quite apparent, as they often enclose large pebbles of quartz and felspar. Examined in a thin slice under the microscope the rock is seen to be composed of epidote, quartz, felspar, chlorite, biotite, and two sets of long needle-shaped crystals, one of which gives straight extinction and has a This 250-word extract was created in the absence of an abstract