Paleozoic Slates Research Articles

Landslide-dam paleolakes in the Central Pyrenees, Upper Gállego River Valley, NE Spain: timing and relationship with deglaciation

The production of a cartographic landslide inventory in the glaciated headwaters of the upper Gallego River, Axial Zone of the Spanish Pyrenees, revealed several paleolakes. These relict lake basins are related to the blockage of drainages by postglacial earthflows and slides, mainly developed on Paleozoic slates. The paleolakes are recorded either by non-dissected infilled basins or by hanging and incised lacustrine terraces that persisted for thousands of years. The development of lakes upstream of landslides, was favored, despite their erodibility, by high-displacement rates and the occurrence of paired landslides on both sides of the valley. Radiocarbon and single-grain optically stimulated luminescence (OSL) ages obtained on the lake sediments range between 41.5 ± 3.9 ka and 15.1 ± 0.3 ka. These chronologies indicate prolonged landslide activity long after the early deglaciation in the upper Gallego River Valley. The landslide-lake dating results support the interpretation that the regional maximum ice extent (MIE) in the Pyrenees occurred during the marine isotope stage 4 (MIS 4), long before the global Last Glacial Maximum (LGM).

1:5000 Landslide map of the upper Gállego Valley (central Spanish Pyrenees)

A 1:5000 scale geomorphological landslide inventory map of the glaciated headwaters of the Gállego River in the Spanish Pyrenees is presented. This map, covering an area of 57.6 km2 and mainly produced by direct mapping in the field, provides a more comprehensive and accurate picture of the distribution of slope movements than previous maps. Around 20% of the area is affected by large flow-dominated slope movements developed on Paleozoic slates. Our map shows that some of these post-glacial landslides have blocked the main drainage at several sites creating landslide-dammed lakes. The damage caused by landslides in the mapped area, with an estimated cost of greater 10 million euros, is mostly related to the activity of pre-existing slope movements, some of which have been reactivated or accelerated by adverse human alterations (e.g., excavation at the toe, overloading, higher water infiltration). This study illustrates that the incorporation of detailed cartographic landslide inventories in the planning and development process of alpine areas may contribute to reduce significant landslide-related damage in a cost-effective manner.

Ichnology, sequence stratigraphy and depositional evolution of an Upper Cretaceous rocky shoreline in central Chile: Bioerosion structures in a transgressed metamorphic basement

Exposures of upper Paleozoic slates of the metamorphic basement near Concepción, central Chile, are covered by transgressive deposits belonging to the Upper Cretaceous Quiriquina Formation. Presence of clusters of the bivalve boring Gastrochaenolites isp. at the irregular and erosive contact between these two units indicates the development of an ancient rocky shoreline, illustrating a rare example of bioerosion in a metamorphic substrate. Coarse-grained deposits mantling the bioeroded surface represent a transgressive lag produced due to ravinement. In sequence-stratigraphic parlance, the bioeroded surface is classified as a FS/SB or co-planar surface formed due to amalgamation of erosion during lowstand and the subsequent transgression. Unburrowed trough cross-bedded upper-shoreface to intensely bioturbated middle-shoreface deposits record continuous transgression. Logs bioeroded by Teredolites clavatus are also present. Middle-shoreface deposits are dominated by deep Ophiomorpha isp., commonly showing laminated infill. Thalassinoides suevicus occurs locally. Intense bioturbation also suggests that the shoreface developed in embayed shorelines, protected from oceanic waves. While rocky shorelines in limestone are characterized by a high abundance and diversity of bioerosion structures, those formed in other types of substrates contain less diverse, commonly monospecific, suites of borings. In terms of Seilacherian ichnofacies, the bioerosion structures analyzed are attributed to a low-diversity expression of the Trypanites ichnofacies. It is proposed that the Trypanites ichnofacies thus may display two expressions: an archetypal one characterized by high diversity in carbonate substrates, along with a depauperate expression in other types of substrates (e.g., metamorphic and igneous rocks). The extreme hardness of the substrate is regarded as the stress factor responsible for the reduction in ichnodiversity.

South American Global Geoscience Transect 7: Cordillera Frontal to Llanura Chaco Pampeana, Northern Argentina

The South American Global Geoscience Transect 7 is located in northern Argentina and traverses, from west to east, the Cordillera Frontal, Puna, Sierras de Famatina, Sierras Pampeanas, and Llanura Chaco Pampeana. Cenozoic stratovolcanoes that intrude Lower Paleozoic slates and Upper Paleozoic continental sedimentary rocks constitute the Cordillera Frontal. Upper Precambrian to lower Paleozoic metamorphie and sedimentary rocks intruded by Paleozoic granitoids comprise the Sierras de Famatina and Sierras Pampeanas. Restricted outcrops of Ordovician volcanic rock also appear in the Sierras de Famatina. Upper Paleozoic, Mesozoic, and Cenozoic continental deposits unconformably overlay the lower Paleozoic units. Tilted blocks bounded by lystric reverse faults that have formed in response to subduction of the Nazca plate constitute the main structure of the three ranges. Detailed studies of kinematic; markers from mylonitic belts within Paleozoic igneous and metamorphie basement indicate shortening and overthrusting of the Sierras Pampeanas onto the eastern border of the Sierras de Famatina. Quaternary sediments cover the Llanura Chaco Pampeana that extends to the east of 65° W. Magnetotelluric deep soundings were done from 1980 to 1993, between 65° and 68° W. The results of these soundings suggest a conductive layer (electrical resistivity ∼1 ohmm) at depths ranging from 8 to 25 km. Saline fluids produced where there is a large amount of free water released by metamorphie reactions have been proposed as an explanation for lower-crustal conductive anomalies. Beginning 1987, new gravimetric studies were performed between 63° and 68° W. The Bouguer anomaly map incorporates preexisting and new data (more than 700 gravity observations). The gravity field drops from −0.5 mGal at 64° W in the east to −280 mGal at 68° W and reaches nearly −400 mGal to the west in the Chilean part (˜69° W) at latitude 28° S. This regional low is related to crustal thickening within the Cordillera de los Andes. Active seismicity recorded during 1984-1994 defines part of the Benioff zone at depth.

Shallow landslides in deeply weathered slates of the Sierra de Collcerola (Catalonian Coastal Range, Spain)

Stability conditions in an area located NW of Barcelona (Spain) are discussed. Here, several mass movements were observed, mainly affecting weathered Paleozoic slates. Many of these failures involved slopes cut along recent infrastructures: debris flows, wedge and plane failures, generally surficial, occurred more frequently. After a detailed geological and geomorphologic survey, geomechanic characterization was carried out, according to RMR and SMR classifications. This rating gave a prediction of slope behaviour, in fairly good agreement with the real observed one. Stability numerical analysis was carried out for the main cut slopes, based upon the Limit Equilibrium Method. First of all, the deterministic factor of safety was computed using the mean values of parameters. After that, a simulation technique based upon the Monte Carlo Method was applied in order to obtain factor of safety distributions. The probability of failure was estimated as P( F<1). Finally, results from deterministic and probabilistic approaches were compared. The effectiveness of different possible remedial measures was highlighted by means of a sensitivity analysis, which showed that the more important parameters in the study area are the geometrical ones (height, slope and failure plane angles). The final technical solutions adopted are briefly outlined.

Limited, localized nonvolatile element flux and volume change in Appalachian slates

Geometric evidence for major nonvolatile volume losses at several Appalachian slate localities contradicts geochemical evidence for minimal compositional changes during low-grade metamorphism of shales. Relative to adjoining microlithons, spaced cleavage zones are depleted in Si (quartz), Na (albite), and, for carbonate-rich slates, Ca, Mn, and Mg (calcite and dolomite). Zr, Ti, Al, P, and Fe are enriched in cleavage zones; the greatest enrichments are in Zr. Proportional K gains and Na and Si losses suggest that cleavage fractionation combines stoichiometric reactions (e.g., K + + albite + chlorite = muscovite + SiO 2 + Na + ) with pressure solution of quartz and carbonate minerals. Cleavage and sorting (pelite to psammite) fractionation patterns are similar but can be distinguished by higher Zr in Al-rich cleavage zones relative to Zr in Al-rich pelitic rocks. The compositional similarities of homogeneous shales and slates do not indicate large volume losses during slate metamorphism. For Paleozoic slates from localities where large volume losses have been hypothesized on geometric grounds (Martinsburg slate belt of Pennsylvania and New Jersey, Meguma Group of Nova Scotia, and Taconic slate belt of Vermont and New York), slate compositions show no evidence of large nonvolatile volume losses relative to likely shale protoliths. Detailed sampling of slates folded at hand specimen to quarry scales indicate that substantial element and volume fluxes are limited to the submeter scale. In small-scale folds, volume losses in tight inner arcs appear to be balanced by volume gains in adjoining areas. The complications of metamorphic recrystallization and heterogeneous strain are probably responsible for erroneous interpretations of large nonvolatile volume losses in these Appalachian slate localities.

40Ar/39Ar illite dating of Late Caledonian (Acadian) metamorphism and cooling of K-bentonites and slates from the Welsh Basin, U.K.

The vacuum-encapsulation laser 40Ar39Ar technique allows extremely small (10−6 g) samples of fine-grained materials such as diagenetic clays to be dated. Here we show that the method can be extended to higher-grade clay minerals. The integration of transmission electron microscopic (TEM) characterization with 40Ar39Ar dating of vacuum encapsulated samples permits the resolution of the timing of metamorphic growth/cooling from the time of diagenesis. We have applied this technique to well characterized Lower Paleozoic slates and K-bentonites from the Welsh Basin, which span the transition from anchizonal to epizonal grade, which had been previously studied using RbSr and SmNd dating.TEM observations of epizonal K-bentonites and slate showed that illite in these samples is of 2M1 polytype, of muscovite-like composition, and oriented parallel to cleavage, suggesting that they are of metamorphic origin. Total gas ages (equivalent to conventional KAr ages) for encapsulated epizonal K-bentonites and slate (340–408 Ma) are considerably variable. The Ar retention ages (calculated from 39Ar and 40Ar atoms retained in the sample after irradiation) are more consistent (383–411 Ma). The 39Ar recoil losses are minor for illites from whole rock samples of epizonal K-bentonites but very significant for clay separates of epizonal slate. Plateaus in age spectra were observed in epizonal K-bentonites and slate. The plateau ages (414–421 Ma) and retention ages (383–411 Ma) can be correlated with the onset of Acadian metamorphism and culmination of uplift and inversion of the Welsh Basin, respectively. These ages are significantly younger than the ∼ 450 Ma ages previously reported for diagenetic clays using the same method, suggesting that diagenetic history has been lost in these epizonal K-bentonites and slate.TEM observations of anchizonal slates showed that there are two modes of illite. The first mode is similar to that observed in epizonal samples, suggesting a metamorphic origin. The second mode consists of the 1Md polytype, has typical diagenetic illite composition, and is oriented parallel to bedding, suggesting a diagenetic origin. Total gas ages for encapsulated anchizonal slates vary considerably (361–422 Ma). The retention ages are more consistent (413–432 Ma) than the total gas ages. The 39Ar recoil losses are more significant than those for epizonal K-bentonites and slate. Plateaus in age spectra are generally not observed. However, the consistent retention ages for the anchizonal slates correspond to the plateau ages for the epizonal samples, and are inferred to represent the onset of Acadian metamorphism.These data, when combined with our previously published results for diagenetic shales, suggest that thermal conditions near the boundary of anchizonal and epizonal grades are necessary to completely reset Ar systems in shales and slates.

Mesozoic-Tertiary weathering and soil formation on slates of the Rhenish Massif, Germany

Weathering of Paleozoic slates and sandstones of the Rhenish Massif in western Germany, which occurred during the Upper Mesozoic and Tertiary under warm, humid tropical to subtropical climatic conditions, led to the formation of a regolith up to 150 metres thick. In flat upland areas of the Hunsru¨ck and Eifel, where the tectonic uplift was relatively weak, remnants of this weathering mantle, more or less truncated by Upper Tertiary and Pleistocene erosion, are still preserved. On overlapping sections and drill cores of an autochthonous paleosoil and the saprolite underneath, the morphological, geochemical and mineralogical zonation of a complete profile of the weathering mantle has been reconstructed. A fossil pre-Oligocene Plinthitic Acrisol, covered by Oligocene fluvial sediments, displays characteristics formed under a high groundwater table. On the other hand the underlying saprolite can be subdivided into a lower reduction horizon and an upper oxidation horizon, each of them more than 40 meters thick. This indicates a polygenesis of the weathering mantle during the Tertiary, due to descending groundwater tables caused by the beginning tectonic uplift of the Rhenish Massif and drier climatic periods during the Middle Tertiary. During the Upper Oligocene the deposition of kaolinitic clays derived from removed horizons of the kaolinitic soils started in fault-block depressions. Periglacial processes during the Pleistocene led to a further removal of the weathering mantle and to the deposition of superficial layers on top of the autochthonous remnants of the saprolite. Presently the kaolinitic sediments as well as the saprolite are exploited as kaolin deposits.

Clays in paleoweathering processes: study of a typical weathering profile in the Hercynian basement in the Montes de Toledo (Spain)

AbstractA series of weathered Paleozoic slates was studied in an area southwest of the Montes de Toledo mountain range where the weathered slates are overlain by a raña formation and show three weathering levels. The fresh slate (at 30 m depth) is composed of ferrous chlorite, mica, quartz and feldspars. In the lowest part of the weathering profile the ferrous chlorite begins to evolve to smectite, and in the intermediate level, all the chlorite has been transformed into smectite. In the upper level (in contact with the raña formation), the smectites evolve to kaolinite, and the micas, which are unaffected at greater depths, begin to evolve to vermiculite, and there has been segregation of the free iron oxyhydroxides producing red, ochre and white zones. Two principal weathering processes, separated in time but superimposed, have been identified.

Die W-Sn-Lagerst�tte Chojlla, Cordillera Real, Bolivien Teil 1: Nebengestein und Tektonik

The W, Sn ore deposit of “Mina Chojlla” is situated in the Cordillera Real to the NE of La Paz within a thick pile of Lower Paleozoic slates near the contact to the alkaligranitic and granodioritic Taquesi-Mururata Batholith of Upper Triassic age. Due to the intrusion the slates, which during the Paleozoic had slightly been folded, became low grade metamorphic and were metasomatically turmalinized. The slates, which uniformly dip to the NE, are cut at right angle by a system of parallel orebearing quartz veins, which dip to the SW. They evidently are tensional features, but opening of joints was made possible only through a special orientation of stratification parallel to the tensional stress and normal to the compressional stress. The stress pattern was generated in a shear zone as a consequence of an upward motion of the batholith with respect to its surroundings. Younger Andean tectonics first caused frequently repeated small bedding plane faults, and lateron a system of reversed faults.

Petrochemistry of Paleozoic spilites of the eastern Alps (Austria)

SummaryIn the Karawanken Mountains (SE Austria) spilites (pillow lavas and sills) are found intercalated in a sequence of Paleozoic slates and graywackes. The petrogenesis of these spilites is interpreted as follows: The pillow lavas and sills consolidated as mugearites and hawaiites, which were derived from an alkali olivine-basaltic magma by fractional crystallization. Under low temperature metamorphic conditions water entered into the rocks predominantly from external sources. The primary minerals (Na-Ca plagioclase, pyroxene and glass) were thus replaced either partially or completely by minerals characteristic of spilites (albite, chlorite, epidote and others). The spilites analysed are of secondary origin. They are compared with spilites and basalts of other (continental and oceanic) areas.

X-ray fluorescent analysis of Rb, Sr, Y, Pb and Th in Japanese Paleozoic slates

The concentrations of Rb, Sr, Y, Pb and Th of Japanese Paleozoic slates were determined by means of X-ray fluorescent analysis. Among the analyzed elements, Rb shows a good correlation with K, but other elements do not appear to have clear systemmatic relations with major elements. Local variation in K/Rb ratio was not detected. The average K/Rb ratio is 251.

Chemical Composition of Paleozoic Slates:V., Comparison with Tertiary Siltstones

Chemical Composition of Paleozoic Slates:V., Comparison with Tertiary Siltstones

Chemical Compositions of Paleozoic Slates :III., Three Areas in the Inner Zone of Southwest Japan

Chemical Compositions of Paleozoic Slates :III., Three Areas in the Inner Zone of Southwest Japan

Chemical Composition of Paleozoic Slates:IV., Zonal Distribution of Geosynclinal Sediments and the Position of Regional Metamorphic Belts

Chemical Composition of Paleozoic Slates:IV., Zonal Distribution of Geosynclinal Sediments and the Position of Regional Metamorphic Belts

Isotopic Age Study, Dutchess County, New York

Research Article| August 01, 1962 Isotopic Age Study, Dutchess County, New York LEON E LONG LEON E LONG Lamont Geological Observatory (Columbia University), Palisades, N. Y 1 Present address: Department of Geology, University Museum, Oxford University, Oxford, England Search for other works by this author on: GSW Google Scholar Author and Article Information LEON E LONG 1 Present address: Department of Geology, University Museum, Oxford University, Oxford, England Lamont Geological Observatory (Columbia University), Palisades, N. Y Publisher: Geological Society of America Received: 07 Feb 1961 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1962, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1962) 73 (8): 997–1006. https://doi.org/10.1130/0016-7606(1962)73[997:IASDCN]2.0.CO;2 Article history Received: 07 Feb 1961 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 LEON E LONG; Isotopic Age Study, Dutchess County, New York. GSA Bulletin 1962;; 73 (8): 997–1006. doi: https://doi.org/10.1130/0016-7606(1962)73[997:IASDCN]2.0.CO;2 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 Rb-Sr and K-Ar isotopic age determinations on mica and whole-rock samples from Dutchess County, N. Y. are consistent with a period of metamorphism with a minimum age of 430 m. y. (million years), followed by a less intense regional reheating about 360 m. y. ago. Pre-existing radio-genic argon in detrital minerals in the isoclinally folded Paleozoic slates, west of Balk's (1936) biotite isograd, was driven out at the time of folding. Lower apparent ages in western Connecticut suggest a transitional zone to the area farther east affected by a 260 m. y. metamorphic event. 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.

STRUCTURAL ANALYSIS OF THE WEST BORDER OF THE DURHAM TRIASSIC BASIN

The Durham Triassic Basin in Piedmont North Carolina is a lowland area floored with Triassic rocks and defined on the east and west by older Paleozoic slates and Carboniferous granites. A narrow strip along the western border of the sediments was mapped, and the relationship of the pre-sedimentation and post-sedimentation structural features determined. A reconnaissance method of multiple-surface analysis was used which suggests that linears in the Triassic-crystalline contact are buried fault scarps. The method was also applied to the graphic solution of two otherwise indeterminate rotational fault problems. A figure of 1800 feet is established as the probable minimum amount of erosional stripping in the basin and on the Piedmont since faulting. An integrated structural and geomorphic history for the formation and erosion of the western part of the basin is developed. Evidence suggests that the basin was never much wider than its present western limit and certainly did not extend as far west as the Dan River Triassic Basin.