Showing papers in "International Journal of Earth Sciences in 1972"

Absolute water depth limits of late devonian paleoecological zones

Abstract: A refined scheme of reefal limestone classification, which places more emphasis on the > 2 mm components (conglomeratic fraction) and on the mode of organic binding, allows for a more detailed facies description of organic buildups. The classification has been applied to Late Devonian organic buildups which outcrop on northeastern Banks Island, Canadian Arctic Archipelago. The distribution and sequences of facies in one organic buildup has led to the determination of absolute water depth limits of three major Late Devonian paleoecological zones. Corals were the dominant fauna below 70 feet (21 m.); tabular stromatoporoids flourished between 70 feet (21 m.) and 30 feet (9 m.) of water depth; massive stromatoporoids were the dominant fauna between 30 feet (9 m.) and sea level. The main controlling factor on the depth limits of the zones was wave energy (normal wave base, 30 feet [9 m.]; storm wave base, 70 feet [21 m.]).

Sediment rejection by recent scleractinian corals: a key to palaeo-environmental reconstruction

Abstract: 26 of the 59 living species of scleractinian corals found in Western Atlantic and Caribbean waters, less than 68 metres deep, and two fungiid genera from the Pacific are analysed in terms of their behaviour, sediment rejecting properties, functional morphology and distribution patterns.

Pacific coral reefs of panamá: Structure, distribution and predators

Abstract: Structural coral reefs of Recent age are undergoing vigorous growth on the eastern Pacific continental shores of Panama. Coelenterate hermatypes include 20 species; 3 are hydrocorals in the genusMillepora, a notable new record for the eastern Pacific region; the abundant scleractinians arePocillopora (4 spp.),Pavona (6 spp.) andPorites (5 spp.).Pocillopora is the chief constructor of mound and fringing reefs with massivePavona andPorites sometimes important at the reef base. UninterruptedPocillopora growth characterizes some fringing reefs, forming a vertical framework with observed maximum thickness of 6 m. Binding of coral by encrusting coralline algae imparts a more rigid and coherent structure to the reef crest and peripheral faces. Intra-reef and flanking sediments contain over 90% calcareous matter; the predominant grain constituents arePocillopora, cirriped and mollusk fragments. Reefs attain their greatest development in the Gulf of Chiriqui; the reason for this is sought in the high and stable thermal conditions of this area. Radiometric dating indicates that net vertical reef growth may approach 1 m/250 years or 4000 B. Important coral predators include fishes, a gastropod, paguran decapods andAcanthaster (in certain areas). Quantitative measurements of the feeding rates and population densities of corallivores indicate that predators may destroy approximately one-third of the annual growth of aPocillopora coral community.

Fabrics and sequences of submarine carbonate cements in Holocene Bermuda cup reefs

Abstract: A variety of precipitative synsedimentary CaCO3 cements lines or fills cavities and surrounds sediment particles within Recent algal cup reefs which dot the rim of the Bermuda platform. These include aragonite needle, spherulitic, and lath cements as well as calcite micrite, palisade, scale, and blocky cements, listed according to respective relative abundances. No distribution pattern of cements is apparent; various combinations of three or four cements are found in almost every sample or thin section. From the occurrence of various cements, factors determining composition and fabric are deduced: Various sequences of two or three precipitative cements result from changes in microenvironment; the only cause of such change recognized is the entrance of endolithic algae into partly cemented cavities. This study provides some insight into the origin of submarine cements and a basis for comparative interpretation of cements in fossil marine environments, especially fossil reefs.

Recent algal stromatolitic deposits, Andros Island, Bahamas. Preliminary report

Abstract: After some introductory comments on fresh water bluegreen algal calcareous formations, the general features and the ruling mecanisms of which are of fundamental importance for the interpretation of stromatolites, the distribution and general features of algal deposits across Andros Id, Bahama, and adjacent marine platforms are briefly reported. Morphological differenciations characterizing Recent stromatolitic biostromes in process of formation over the flats of seasonal lakes (N-Eastern Andros) are then briefly analyzed. The interpretation of structures relies on the various data gathered during an observation period of three months encompassing the phase of prolific stromatolitic growth during the complete flooding of the lakes, and ending with the progressive drying up and exposure of the algal flat at the beginning of the dry season.

Seismotektonische Traverse von der Nordsee bis zum Apennin

Abstract: Die auf ihre Erdbebentatigkeit hin untersuchte Traverse ist 1300 km lang und erstreckt sich von der Doggerbank (54° N) bis zum nordlichen Apennin (44° N). In einem Tiefenschnitt entlang der Traverse wird die raumliche Verteilung der Erdbebenherde betrachtet. In der Zahl der Herde und ihrer Anordnung zeigen sich Unterschiede zwischen den verschiedenen Teilgebieten der Traverse (Niederrheinische Bucht, Oberrhein-Graben, Schwabische Alb, Alpen, Apennin). Bezuglich der Herdtiefe ist ein gemeinsames Merkmal fast aller Gebiete, das sich die Erdbebenherde auf die oberen 20–25 km der Erdkruste beschranken. Die starkste seismische Aktivitat ist im Tiefenbereich von 2–12 km festzustellen. Dieses Ergebnis ist fur das Verhalten der einzelnen Krustenabschnitte bei rezenter Bruchtektonik von Bedeutung. Lediglich im Bereich der Doggerbank scheinen die Herde an der Basis der Erdkruste oder im obersten Erdmantel zu liegen, was auf besondere seismotektonische Verhaltnisse in diesem Gebiet hindeutet. Demgegenuber zeigt die Herdtiefenverteilung im Alpengebiet trotz abweichender Krustenstruktur keine Besonderheiten gegenuber dem nordlichen und sudlichen Vorland. Vergleicht man den aus seismographischen Messungen abgeleiteten rezenten Spannungszustand von Erdbebengebiet zu Erdbebengebiet, so ergibt sich fur die Alpen und das nordlich anschliesende Gebiet bis zur Nordsee ein sehr einheitliches Bild fur die Orientierung der horizontalen Hauptspannungen (groste Hauptspannung NW-SE, kleinste Hauptspannung SW-NE). Im Apennin ist die Spannungsverteilung gerade umgekehrt.

Recent investigations of surficial and deeper crustal structures of the Eastern and Southern Alps

Abstract: After a review of the surficial structures of the Eastern and Southern Alps a discussion of some important theories of the Alpidic Orogeny is presented. Geological cross sections, based as far as possible on the latest data, are then presented in detail.

Rythme et Modalités des Plissements Superposés dans les Chaînes Subalpines Méridionales des Alpes Occidentales Françaises

Abstract: Les chaines subalpines des Alpes francaises offrent un bon exemple de plis de couverture decolles au niveau du Keuper a evaporites. Leur partie meridionale, au S du Vercors et au N et NE des Chaines Provencales, montre en outre l'entrecroisement de deux systemes plisses presque orthogonaux: un systeme E-W, dit pyreneoprovencal, dont la genese s'etale du Cretace superieur a l'Eocene moyen, et un systeme N-S a NW-SE, dit alpin, qui date de l'Oligocene et du Neogene. Il y a donc eu deux etapes majeures de plissements qui se sont succedees dans le temps; mais on doit se demander si chacune de ces etapes etait faite d'une succession de phases tectoniques courtes separees par des intervalles relativement plus longs de calme tectonique, ou bien si elles correspondent a de longues periodes de deformations continues; ces deux postulats paraissent ici egalement vraisemblables. La premiere periode, celle des plis pyreneens, semble avoir fait naitre des plis droits assez simples, parfois de style ejectif, dont les anticlinaux ont souvent, des l'Eocene, ete erodes jusqu'au Jurassique superieur. A l'Oligocene et au Miocene, des plis N-S a NW-SE sont nes, dans les domaines qui n'etaient pas deja plisses, tandis que les plis E-W deja existants ont ete accentues et rompus, degenerant parfois en chevauchements caracterises par des troncatures des flancs inverses des plis. A l'echelle des Alpes Occidentales comme a celle des Chaines Subalpines Meridionales et des « arcs » elementaires qui les composent, les structures plissees disposees en arc ne sont pas simples, mais sont l'aboutissement d'une evolution tectonique longue et complexe.

Interaction of genetic processes in holocene reefs off North Eleuthera Island, Bahamas

Abstract: The inner shelf platform off North Eleuthera consists of a series of terraces at 6 m, 8 m, 20 m, and 35 m depth, respectively. The boundary between 6 and 8 m terraces is marked by a near continuous reef ridge, landward and seaward of which isolated reef structures are found. Reefs are aggregates of pillar structures, which in turn are composed of columnar, club-shaped or mushroom-shaped pillars of corals. The dominant primary framebuilder above 3 m depth isAcropora palmata; below corals of the generaMontastrea andDiploria, Porites astreoides andP. porites also contribute to the frame, as does the hydrozoanMillepora. The secondary framebuilders start developing and changing the shape of the frame as soon as they find suitable substrates; most important are coralline red algae, which encrust internal and external surfaces, but also may fuse the components of the frame; other organisms just add to the frame. In contrast boring and rasping organisms destroy the frame. Constructing or destructing organisms were found living on every surface, external or internal, accreting or diminishing.

Horizontal-Stylolithen im französisch-schweizerischen Tafel- und Faltenjura und ihre Einpassung in den regionalen Rahmen

Abstract: Stylolithen entstehen vorwiegend in Karbonaten meistens durch Drucklosung, wenn Losungsunterschiede im Gestein vorhanden sind. Stylolithen konnen senkrecht zur noch flach liegenden Schichtung infolge Uberlagerungsdruck als Vertikal-(V-)Zapfen entstehen oder parallel zur Schichtflache als Horizontal-(H-)Stylolithen (Abb. 1 und 2). Die H-Zapfenflachen sind zum Teil sehr uneben entwickelt. Die Lange der Einzelzapfen schwankt zwischen weniger als 1 mm und mehr als 10 m (im Eis). Die Richtung der jeweiligen Zapfenachse entspricht der der angreifenden Krafte.

The roles of bryozoans in modern coral reefs

Abstract: Contrary to impressions gained from the literature, collecting in the living reefs of Bermuda, Eniwetok, and Eleuthera implies that bryozoans are common and diversified in at least some modern coral reefs.

Transform faults in Island

Abstract: In Iceland the mid-Atlantic ridge rises above sea-level for a north-south-extension of 350 km. One or two east-west-directed transform faults may be expected on land in Iceland, since the mid-Atlantic ridge is offset by transform faults every 100–200 km. Two of these faults, the Reykjanes Fracture Zone in southern Iceland, and the Tjornes Fracture Zone in northern Iceland, have been located by recent seismological activity (Ward, 1971). There are no strike-slip faults within the Tjomes Fracture Zone that support transform faulting on land. En echolon faults may indicate a status nascendi of lateral offset for the Reykjanes Fracture Zone. A third transform fault, the Snaefellsnes-Vatnajokull Fracture Zone, however, was already active about 3 m.y. ago, when the rift system in southern Iceland began to spread faster than in northern Iceland. The features resulting from this process can be observed in (1) a change in strike from a northerly trend in northern Iceland to a north-easterly direction in southern Iceland; (2) the separation of the rift axis in southern Iceland into two branches; (3) right lateral strike-slip movements along the Snaefellsnes-Vatnajokull Fracture Zone with an offset of about 100 km. Field mapping and observations from air photographs have enabled the construction of a detailed tectonic pattern for the latter zone. The Pleistocene to Postglacial volcanic activity, the offset of magnetic anomalies, and recent active seismicity support the mechanism of transform faulting. At least 3 m.y. ago the west-wandering Icelandic Rift System started with higher spreading rates, revealing a trend to connect directly the Reykjanes- and the Iceland-Jan Mayen Rift Systems. Since that time three crustal plates proceeded from the Vatnajokull Triple Junction with different drift velocities, inducing the activity of the Snaefellsnes-Vatnajokull Transform Fault, which separates the north-western from the south-western Icelandic plate.

Environmental distribution of calcareous algae in Upper Devonian reef complexes

Abstract: Calcareous algae are important constituents in reef complexes of Frasnian and Famennian ages in the Canning Basin of Western Australia and in reef and bank developments of Frasnian age in western Canada. At least 17 genera of skeletal calcareous algae occur in Upper Devonian carbonate facies in these two regions. Many algae are quantitatively significant constituents in various facies and some forms functioned as framebuilders in reef facies. Algae in back-reef facies includeGirvanella nodules and crusts, dasycladacean (Vermiporella) segments, radiosphaerid calcispheres, and solenoporacean red algae (Parachaetetes andSolenopora). Reef facies are characterized by encrusting forms, such asRenalcis (a problematic alga),Sphaerocodium (=Rothpletzella) (a green or blue-green alga), andKeega (an “ancestral coralline“ red alga).Renalcis andSphaerocodium are principal framebuilders in Western Australia reef complexes, but are subordinate to stromatoporoids in most western Canada occurrences. Fore-reef facies contain deeperwater species ofSphaerocodium andParachaetetes. A similar distribution of Upper Devonian skeletal calcareous algae has been reported from the USSR; this same pattern probably occurs in carbonate complexes of this age in other regions of the world where diagenetic processes have not destroyed the fossil evidence.

Outline of the geology of the Cape Verde Archipelago

Abstract: The Cape Verde Archipelago, totalling 4033km2, lies some 460km WNW from Dakar, West Africa. Topography, relief and geomorphologic development enable the islands to be placed into two major groups, indicative of their respective ages. The islands are overwhelmingly of igneous constitution, with basic volcanics and pyroclastics comprising some 83% of the total area, and sedimentary rocks amounting to some 9%. Volcanics and plutonics are distinctly basic in character, the archipelago representing a soda-alkaline petrographic province, with a petrologic succession similar to that in other Atlantic islands. Rocks perhaps as old as the Mahn, most certainly Neocomian, are present in the island of Maio, and here are found the highest dips and greatest thicknesses of sedimentary rocks. Post-Aptian Cretaceous, Palaeogene and Neogene are only sporadically represented, and indeed it can be questioned wheter any sediments are of these ages. Fogo is an active volcano, last erupting in 1951. The 8 km diameter caldera, at an elevation of 1600 m with an interior cone rising to 2829 m, is thought to have resulted from subsidence of a large cylindrical block, the “feeding” magma chamber lying at a depth of some 8 km. The archipelago probably dates back some 180 m. y., with an older and younger volcanic episode, the latter probably of late Neogene times.

Pennsylvanian stratigraphic reefs in Kansas, some modern comparisons and implications

Abstract: Broad platformlike buildups in the Stanton Limestone in southeastern Kansas are composed primarily of lime mud and phylloid algae and are rimmed with skeletal calcarenite composed largely of echinoderm and algal debris. Bordering the buildups are large (1×30 km) channels, lined or filled with similar calcarenite, and a broader basin containing shaly skeletal calcilutite. Grain abrasion and spar cement in the rimming calcarenites indicate water agitation and suggest wave resistance of the buildups during growth. Wave resistance may have been provided by 1) stalked echinoderms, which are resilient when alive and bind sediment with their roots, and also by 2) early drusy cementation of loose sediment to a coherent mass. Comparison to modern channel-separated buildups in the Persian Gulf and the Great Barrier Reef complex brings out the relative significance of organic frameworks in these different geologic settings. Recognized organic frameworks range from absent or insignificant in the Pennsylvanian examples through locally present but insignificant in the Persian Gulf, to apparently important in maintaining the buildups in the Great Barrier Reef. All three examples, however, exhibit patterns of original hydrodynamic control over initiation and gross form of the buildups. Determining significance of organic frameworks to overall buildup growth involves examining both their positions relative to evidence of wave action and the nature of binding in contemporaneous talus produced by wave action on the buildup.

Facies and development of the Meggen Reef (Devonian, West Germany)

Abstract: In the course of an exploration program in 1965 in the subsurface of the southeastern Elspe Syncline (Sauerland, Rhenish Schiefergebirge) was discovered a Middle Devonian reef, unknown up to now. The foundation is not yet drilled. The Meggen Reef forms a bioherm-like table reef which is completely surrounded by basinal sediments. According to organisms, matrix and primary voids within the reef limestones 7 facies types can be distinguished. The reef core is built of stromatoporoids and crinoids, the reef flank types are characterized by corals and crinoids. The subsided reef is covered with thin, partly condensed pelagic limestones. At the same time in the adjacent basin the stratiform pyrite-sphalerite-barite ore of Meggen is deposited. At the end of Middle Devonian time the Meggen reef and the overlying pelagic limestones are brecciated and transected by numerous sedimentary dikes. As in the sedimentary dikes the same acid tuffs are occurring, which follow immediately above the pyrite-sphalerite-barite ore of Meggen, there is a close connection between submarine destruction of the Meggen Reef, acid tuff eruptions and ascent of metall-bearing hydrothermal solutions. The Meggen Reef is due to the compression while the Variscan orogeny is deformed to an overturned and thrusted anticline and itself is thrusted over from the adjacent basin facies. With respect to the development of diagenetic processes, the following stages are distinguished: (1) during reef growth, (2) between reef growth and sedimentary dike formation, (3) between sedimentary dike formation and Variscan deformation and (4) during Variscan deformation.

Der südwestliche Randbereich der Espinhaço-Zone, Minas Gerais, Brasilien

Abstract: Die vorliegende Arbeit umfast eine Kartierung in prakambrischen Metamorphiten und Metasedimenten am SE-Rand des Sao-Francisco-Beckens. Als alteste Einheit finden sich die Praminas-Gesteine, die von der miogeosynklinalen Quarzitfazies der MinasSerie uberlagert werden. Die jungere Sao-Francisco-Serie liegt diskordant uber den alteren Einheiten. Sie gliedert sich in eine grobklastische Randfazies, das Macaubas, und eine feinklastische, karbonatische Beckenfazies, das Bambui. Die Sao-Francisco-Serie wurde noch in die ausklingende Minas-Orogenese einbezogen. Die Minas- und Macaubas-Quarzite wurden tektonisch intensiv verschuppt und uber das Bambui uberschoben. Im Bambui entwickelte sich nur ein flacher Faltenbau. Aufgrund der tektonischen und sedimentologischen Beziehungen wird angenommen, das die Sao-Francisco-Serie die Molasse des Minas-Orogens darstellt.

Cavity formation in living scleractinian reef corals and fossil analogues

Abstract: The origin of cavitous fabrics in some living scleractinian coral-dominated communities from the Florida Reef tract is examined in terms of comparative laboratory growth experiments designed to distinguish the micro-environmental role of living organic matter.

About deep-sea volcanism

Abstract: Hyoclastites mainly result from underwater comminution of molten basalts initially explosively erupted out of the sea-floor and instantaneously pulverized by closely succeeding phreatic explosion (s). Many sea-mounts probably never were the alleged volcanic islands, later sea-level eroded into truncated cones and eventually drowned several km down, they are claimed to be. They are here considered as submarine polygenic volcanoes, the shape of which is congenital. Their building up probably started by accumulation of numberless flows of basalt, quietly poured out from a long-lived central vent; when this lava-volcano's crater, so progressively carried higher and higher, reached depths where explosive phenomena became possible because of lowered hydrostatic pressure, magmatic explosions occurred due to violent release of primitively dissolved (or combined) gases. Shattering of lava, 1∘) increases by several orders of magnitude lava's surface to volume ratios, so allowing huge quantities of super-heated steam to be engendered; 2∘) this super-heated steam trapped below the lava-lumps, as well as in their numberless holes, immediately explodes and comminutes the primary lavalumps; 3∘) so other super-heated steam is produced and further steam explosions are resumed in confined room until almost all the primitive heat content of the magma is transformed into kinetic energy and the lava is comminuted into glassy, ashy, hyaloclastites. This process also works above fissural eruptions. The difference is that fissural volcanoes, contrarily to large central ones, are usually monogenic (i. e. delivering one eruption only through the same vent instead of numberless ones for polygenic volcanoes). Linear effusive eruptions also produce quietly flowing basaltic flows but — because being monogenic — they cannot build up big, and eventually steep, reliefs as polygenic volcanoes do. When not poured over steep slopes where pillowlavas develop, submarine flows are characterized by 1∘) the lack of any scoriaceous, more or less thick, upper part (or jacket), and 2∘) a regular pavingstone-like surface, each polygon of which being the upper face of short prisms similar to ordinary columnar prismation, but one or two orders of magnitude shorter. As for central volcanoes, explosive activity along submarine fissures produces huge quantities of hyaloclastites, but these cannot be heaped up into steep ridges, as happens for subglacial eruptions, because sea-currents spread them far and wide.

Cavities in the reefs of the Wenlock Limestone (Mid-Silurian) of Shropshire, England

Abstract: Studies of the growth attitudes and internal structure of organisms in the Wenlock reefs show that cavities existed during reef growth between knobs of reef builders, between individual reef builders, between the branches of reef builders and within skeletons. Only the well sealed growth cavities escaped fill by particulate sediment on burial. The location and nature of diagenetic cavities are governed by the growth fabric of the reefs. Diagenetic cavities were formed by the dislocation of reef components during compaction and by dissolution of organisms, particularly bryozoans, that neighboured growth cavities.

The preservation of scleractinian corals by calcite in the corallian beds (Oxfordian) of southern England

Abstract: Corals in the Oxfordian barrier-reef complex of southern England show great variations in the style and quality of preservation. Preservation was influenced by differences in the structure and chemical composition of the skeleton and by diagenetic effects such as the production of fibrous aragonite overgrowths and micrite cement. In all cases, however, the aragonite dissolved. Calcite usually precipitated in the resultant voids.

Structural evolution of the Simla klippe in the lower Himalayas

Abstract: The rocks of the Jutogh Series in the Simla area have been involved in folding of three generations and metamorphism in two phases The earliest structures are isoclinal, recumbent/reclined folds (F1) with a shallow plunge toward east or west where least reoriented The axial surfaces of these folds have been folded coaxially into open, upright antiforms and synforms (F2), which become tight to isoclinal in the northern part, causing local involution The F1 and F2 folds have been affected by conjugate and chevron folding (F3) with an overall NS strike of axial planes, resulting in axial culminations and depressions of the early folds Axial plane foliation related to F1 folding and transposition schistosities parallel to the axial planes of the F2 and F3 folds are the planar deformation structures that have developed Cross stratification at one contact of two rock-units suggests that the structure of the Jutogh Series in the largest scale is a recumbent syncline, the peaks of Taradevi, Jutogh and Prospect Hill representing the inverted limb The Jutogh rocks are surrounded and structurally underlain by the rocks of the Chail Series The open, synformal nature of the Jutogh-Chail boundary in contrast with the complex fold-geometry within the Jutogh Series, tearing-off of the largescale early folds and sharp break in the first metamorphism at the Jutogh-Chail contact, and widespread cataclasis all along the border prove that the Jutogh Series has been thrust over the Chail Series forming a klippe in the Simla area Continuation of the second metamorphism and the third folding across the Jutogh thrust indicates that the thrusting preceded F3 and was broadly coeval with the F2 movement An unrestricted southward transport could generate the F1 recumbent folds The F2 folds point to a flattening in the waning phase of the overthrust movement in broadly the same plan of deformation The F3 folds indicate a compression in an EW direction in the last phase of deformation

Sind detritische Zirkone rötlicher Farbe auch in Mitteleuropa Indikatoren für präkamhrische Liefergebiete

Abstract: Detritische Zirkone rotlicher Farbe wurden erstmals in Grosbritannien vonMackie (1923) als sicherer Hinweis auf prakambrische Liefergebiete gewertet. Unter diesem Gesichtspunkt wurde nun auch in Mitteleuropa in Sandstein- und Konglomeratproben vom Kambrium bis zum Tertiar der Anteil an rotlichem Zirkon bestimmt. Untersucht wurden drei stratigraphische Richtprofile aus dem Hohen Venn, aus der Saar-NaheSenke sowie aus dem Harz und Harzvorland, ferner Proben aus dem Massiv von Rocroi, dem Massiv von Brabant und aus Nordspanien. Auch in den Sedimentgesteinen Mitteleuropas nimmt der Anteil an rotlichem Zirkon, statistisch gesehen, mit dem geologischen Alter zu.

Beiträge zur Sedimentologie des kontinentalen Mesozoikums am Westrand des Murzukbeckens (Libyen)

Abstract: Am Westrand des Murzukbeckens ist uber marinem Karbon eine etwa 800 m machtige kontinentale, vorwiegend fluviatile Sedimentfolge von roten und braunen Sandsteinen und zwischengelagerten Tonsteinen aufgeschlossen. An der Messak-Schichtstufe wurden an drei Stellen korrelierbare Profile aufgenommen. Die Schichtfolge lies sich nach feldgeologischen Befunden von unten nach oben in Tilemsin-Schichten und Messak-Sandstein gliedern.

A note on the mullion structures from the Ardennes and North Eifel

Abstract: The structures first described as boudinage byLohest at the type locality near Bastogne in the Ardennes are the results of layer parallel compression of the competent beds Since at present the term boudinage is almost invariably associated with stretching of the bedding, inspite of the usual priority rules, the author has used the term mullions for these structures, because their descriptions fit the accepted definition of mullions These mullions are regarded to be produced by further modification of gentle sinusoidal buckles initiated at the boundary of a competent layer by compression Examples of progressive deformation are cited, where the mullions, which originated at an earlier stage of deformation, are “refolded” by folds developed at a later stage A quantitative determination of strain has been made from the mullion structures at the well known exposure near Dedenborn

Tektonische Untersuchungen an Molasse-Geröllen

Abstract: An einer orientiert entnommenen Kollektion von Gerollen aus der Unteren Suswasser-Molasse bei Immenstadt (Allgau, Bayern) wird ein neues Verfahren zur Messung von Gerollen angewandt. Die Gerolle werden in Gerolldiagrammen dargestellt, die es ermoglichen, Form, Grose und Orientierung und alle Gefugemerkmale der Gerolloberflache exakt abzubilden und zu vergleichen. Striemen und Losungsgruben auf den Gerollen werden geometrisch erfast und statistisch ausgewertet. Danach ergeben sich Ruckschlusse auf die felsmechanische Beanspruchung des Gerollverbandes durch die Alpen.

Fazieswechsel und Metamorphose in der westlichen Serra Negra (Espinhaço-Zone, Minas Gerais, Brasilien)

Abstract: Es wird eine Ubersichtskarte fur die Serra Negra (Ostrand der Espinhaco-Zone) im Masstab 1∶250 000 vorgelegt. Lithologische Faziesubergange und das Vorkommen ultrabasischer bis basischer Gesteine belegen einen mio-/eugeosynklinalen Ubergangsbereich der Minas-Geosynklinale. In der jungeren, die Minas-Serie diskordant uberlagernde Sao-Francisco-Serie (Macaubas-Fazies) wurden erstmals magmatische Gesteine nachgewiesen. Die metamorphen Mineralneubildungen in der Minas-Serie weisen auf eine nach Osten zunehmende Regionalmetamorphose hin. Der groste Teil des Arbeitsgebietes liegt im Ubergangsbereich Grunschiefer-/Amphibolit-Fazies.

Sedimentology and ecology of the horn plateau formation: A middle devonian coral reef, Northwest Territories, Canada

Abstract: The Horn Plateau Formation is a Middle Devonian limestone reef approximately 0.4 miles in diameter and 400 feet thick which crops out on the Interior Plains about 110 miles west of Yellowknife, Northwest Territories. The study is based upon examination of material collected from the outcrop and 5 core-holes drilled on and near the reef.

Deformation of the rocks of Simla Hills

Abstract: Simla Hills form a part of Lesser Himalaya. Metamorphic rocks of this area (Pre-Cambrian), forming Chail-Jutogh nappe, are thrust over a series of mostly unfossiliferous rock formations ranging in age from Palaeozoic to Eocene. The rocks of the area are characterised by meso-structures belonging to three phases of deformation. The second phase structures, both in the allochthon as well as in the para-autochthon units are synchronous with the nappe formation. The third structure in the para-autochthon unit has been related with the movement of nappe. A model explaining the probable kinematics of thrusting in the Simla Hills has been suggested.

Die Minas-Gruppe in Nordost-Bahia, Brasilien

Abstract: Die Quarzite und Phyllite der prakambrischen Serie Jacobina, deren geologische Beziehung zum umgebenden hochmetamorphen Kristallin bisher ungeklart war, wurden in verschiedenen Teilgebieten kartiert und petrographisch untersucht. Im Gebiet von Juacema (Abb. 1) bildet die Serie Jacobina den Westflugel einer fast isoklinalen, schwach westvergenten Mulde. Sie wurde Jacobina-Synklinorium genannt und erstreckt sich vom Rio Sao Francisco im Norden rund 300 km weit nach Suden (s. Abb. 3 und 6). Auf dem Ostflugel der Mulde sind die Phyllite durch Kalifeldspatisation granitisiert worden (Reliktgefuge!); die eingeschalteten Quarzite sind denen der Serie Jacobina im sedimentaren Mineralbestand, z. B. der Turmalin- und Hamatitfuhrang, sehr ahnlich. Im Gebiet von Campo Formosa (Abb. 2) konnte nachgewiesen werden, das die Serie Jacobina mit der Serie Lavras stratigraphisch identisch ist: Die Abfolge der Formationen Rio do Ouro — Cruz das Almas — Serra do Meio (der Serie Jacobina) entspricht der Abfolge Tombador — Caboclo — Morro do Chapeu in der Serie Lavras. Beide Serien mussen damit altersmasig in die Minas-Gruppe eingestuft werden.