Middle Limb Research Articles

Steep shear zones in the basement and associated deformation of the cover sequence on Karmøy, SW Norwegian Caledonides

The allochthonous rocks of Karmøy, SW Norwegian Caledonides consist of three major geological units. The two oldest units (basement), the Karmøy Ophiolite intruded by the granitic rocks of the West Karmøy Igneous Complex (minimum age 445 Ma), were polyphasally deformed and metamorphosed prior to the deposition of the Skudeneset Group of Upper Ordovician/Lower Silurian age. During the end Silurian (Main Scandinavian Phase) orogenic deformation, the basement was cut by a series of linear steeply eastwards dipping shear zones with a NNW-SSE trend that can be followed on Karmøy and the off-shore islands for more than 40 km. Within the basement, mylonite zones with a well developed LS fabrics were formed, while the sediments were folded into asymmetrical folds with middle limb excision. In the sediments an axial planar cleavage and pronounced pebble orientation/elongation developed paralleling the LS fabric in the mylonites. Based on reorientation of dykes in the sheeted dyke complex of the Karmøy Ophiolite it can be shown that sinistral shear strain ( γ = 6−7) was operative across the zones. For the whole of the area the sense of shear was sinistral and the eastern blocks invariably moved upwards.

Post-mortem study of the hip joint. II. Histological basis for limited and progressive cartilage alterations.

This histological study is based on a macroscopical study of post-mortem hip joints (Byers, Contepomi, and Farkas, 1970) in which two categories of articular cartilage alterations, in addition to osteophytes, were described. One category consisted of 'limited' alterations which occurred frequently, had several subcategories, and rarely led to joint deformity. The other consisted of progressive alterations which caused bone exposure and joint deformity. Histological sections from both groups, including all the subcategories of the first, were studied. Initially the mechanisms that destroy cartilage were determined, and then their prevalence was assessed. Six mechanisms were found, all occurring in the group of limited alterations with varying prevalence and in varying combinations. Only one, fibrillation, occurred in the progressive group.

Single and Double Shading Rings in Single - Phase Magnets: A General Analysis

A mathematical relation between the least force and the shading ring resistance and the ratio of the shaded to the total area is developed. For every value of this ratio, there exists an optimum value of the shading ring resistance which would give maximum least force. In the case of an E magnet, although the middle limb does not have a shading ring, the magnet taken as a whole tends to increase the least force. A general theory of the double shading ring is suggested, and it is shown that the double shading ring develops up to 15 percent more least force for higher ratios of the shaded area to the total area. The theories are confirmed by measurements.

An interpretation of the structure of the Blatherskite Nappe, Alice springs, Northern Territory

Abstract The basal unit of the Amadeus Basin sequence is the Heavitree Quartzite, and this formation usually forms a single east‐west ridge along the northern side of the MacDonnell Ranges. However, at Alice Springs there are two such ridges. Basement rocks crop out on the northern side of each ridge, and dolomite and shale of the Bitter Springs Formation crop out on their southern sides. The northern outcrop of dolomite and shale is tightly folded, and is separated from the southern outcrop of basement by a major fault. The bedding of the sediments, the axial plane of the fold, and the fault all dip south at about 45°. Inverted facings on parasitic folds indicate that the northern outcrop of quartzite and dolomite plus shale is an antiform in inverted rocks. Hence the southern outcrop of basement and quartzite is synformal, and is interpreted as the frontal part of a fold nappe. The nappe started as a recumbent anticline whose middle limb of quartzite sheared out as the anticline travelled several kilome...

The structure of the Weymouth Anticline

An account of the structure of the Weymouth Anticline in south Dorset is based uppon a new survey. Fuller's Earth crops out in the Anticline core from the Fleet shore to the banks of the Wey. The numerous strike faults which cut the core are described and some new structural details along the Ridgeway Fault belt are given. Borehole evidence obtained by the British Petroleum Company at Chaldon Herring is recorded and the evidence it provides on the Tertiary reactivation of an Intra-Cretaceous fault is discussed. An Intra-Cretaceous age for the Broadwey Anticline, as suggested by Strahan, is confirmed following the connection by mapping of the Broadwey with the Hamcliff Anticlines. The suggestion of Arkell that faults downthrowing north in the lowland are Tertiary in age and those downthrowing south are Intra-Cretaceous is supported. The westward disappearance of the Purbeck Monocline is discussed and it is suggested that the Radipole Fault may be the westward continuation of a reversed fault which replaces the middle limb of the Monocline near White Nothe.

The Geology of Deudraeth. the Country between Traeth Mawr and Traeth Bâch, Merioneth

Summary Strip outcrops of Upper Cambrian strata in normal succession form the southeastern half of the Deudraeth peninsula. Garth Grit of Lower Arenig age follows with slight discordance. In echelon against the north-western face of the grit ridge are slabs of strata varying in age from Lower Bala at Ty-obry to Lingula Flags at Rhyd. Beyond these towards the north-west is the broad outcrop of the Crushed Slates group, enclosing separated lenses of ash and lava of late Arenig or Llandeilo age. Slip surfaces in this crush belt cut across the regional cleavage and slice the aureole of the Tan-y-grisiau intrusion. Late dolerite sills have entered along shear surfaces, but themselves are uncrushed. The shear zone is the broken middle limb of the main Caernarvonshire syncline, here thrust south-eastwards to override the margins of the Harlech Dome. I. Introduction The country described forms the north-western fringes of the Harlech Dome, immediately to the east of the type area of Tremadoc (Fearnsides 1910A). It lies between the Traeth Mawr and the Traeth Bach. It is mostly included on the six-inch sheets Merioneth XI and XIX NW. 1 The only detailed stratigraphical account of the district is that of J. W. Salter (in Ramsay 1866). At that time thrust movements were not suspected, although the section he described includes country which is very severely disturbed. On his map of North Wales, D. Sharpe (1846) indicated an outcrop of greenstone extending from Moelwyn to the Portmadoc embankment close to the position of the grit

Three Tectonic Problems of the Lulworth District: Studies on the Middle Limb of the Purbeck Fold

Of all the folds thrown up across the Chalk plains of North-West Europe during the Alpine orogeny, the most interesting and the most perfectly exposed is the Purbeck anticline. In the cliffs of the Dorset coast the sea has laid bare all parts of the structure, from the core or crestal region, through the vertical and overturned middle limb and the “foresyncline” (Busk 1929, p. 29), into the foreland, where the Upper Cretaceous rocks are seen reposing with sharp unconformity upon a previously folded and eroded Jurassic foundation. The general and some special aspects of the fold and its associated faults have been discussed in a previous paper (Arkell 1936). The present paper results from a study of the middle limb, where it is dissected by the sea cliffs of the Lulworth district. These cliffs have long been renowned for their beauty, but their marvellous tectonic features, both great and small, have been neglected, with the result that their value to students of tectonics has not been fully utilized. The first three parts of the paper attempt a solution of the three most outstanding problems : contortions in the Purbeck Beds, the Purbeck Broken Beds, and the abnormal attenuation of the strata towards Durdle Door. The fourth part offers an interpretative essay and synthesis. The area dealt with is included in sheet 342 of the Geological Survey one-inch map and sheet 141 of the Ordnance Survey one-inch map. The contortions in the Purbeck Beds at Stair Hole are illustrated in

Highly Folded between Non-Folded Strata at Trenton Falls, N. Y.

Previous articleNext article FreeHighly Folded between Non-Folded Strata at Trenton Falls, N. Y.W. J. MillerW. J. Miller Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 16, Number 5Jul. - Aug., 1908 Article DOIhttps://doi.org/10.1086/621529 Views: 30Total views on this site Citations: 4Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:A.J. Van Loon Chapter 3 The Recognition of Soft-Sediment Deformations as Early-Diagenetic Features – a Literature Review, (Jan 1992): 135–189.https://doi.org/10.1016/S0070-4571(08)70565-XJOHN L. CISNE, DANIEL E. KARIG, BRUCE D. RABE, BERNWARD J. HAY Topography and tectonics of the Taconic outer trench slope as revealed through gradient analysis of fossil assemblages, Lethaia 15, no.33 (Aug 1982): 229–246.https://doi.org/10.1111/j.1502-3931.1982.tb00647.xJohn Challinor The origin of certain rock structures near Aberystwyth, Proceedings of the Geologists' Association 60, no.11 (Jan 1949): 48–IN2.https://doi.org/10.1016/S0016-7878(49)80020-4W. J. Arkell Three Tectonic Problems of the Lulworth District: Studies on the Middle Limb of the Purbeck Fold, Quarterly Journal of the Geological Society 94, no.1-41-4 (Feb 1938): 1–NP.https://doi.org/10.1144/GSL.JGS.1938.094.01-04.03