Community news

Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

Did you know?

That gully is a deep erosional channel [16].?

Checkout all 2699 terms in the KarstBase Glossary of Karst and Cave Terms

What is Karstbase?



Browse Speleogenesis Issues:

KarstBase a bibliography database in karst and cave science.

Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
See all featured articles
Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
See all featured articles from other geoscience journals

Search in KarstBase

Your search for shear (Keyword) returned 38 results for the whole karstbase:
Showing 16 to 30 of 38
Existence of karsts into silicated non-carbonated crystalline rocks in Sahelian and Equatorial Africa, hydrogeological implications, 2002, Willems Luc, Pouclet Andre, Vicat Jean Paul,
Various cavities studied in western Niger and South Cameroon show the existence of important karstic phenomena into metagabbros and gneisses. These large-sized caves resulted from generalized dissolution of silicate formations in spite of their low solubility. Karstification is produced by deep hydrous transfer along lithological discontinuities and fracture net works. The existence of such caves has major implications in geomorphology, under either Sahelian and Equatorial climate, and in hydrogeology and water supply, particularly in the Sahel area. Introduction. - Since a few decades, several karst-like morphologies are described in non-carbonated rocks (sandstones, quartzites, schistes, gneisses...) [Wray, 1997 ; Vicat and Willems, 1998 ; Willems, 2000]. The cave of Guessedoundou in West Niger seems to be due to a large dissolution of metagabbros. The cave of Mfoula, South Cameroon, attests for the same process in gneisses. This forms proof that big holes may exist deeper in the substratum even of non-carbonated silicate rocks. Their size and number could mainly influence the landscape and the hydrogeology, especially in the Sahelian areas. Guessedoundou, a cave into metagabbros in West Niger. - The site of Guessedoundou is located 70 km south-west of Niamey (fig. 1). The cave is opened at the top of a small hill, inside in NNE-SSW elongated pit (fig. 2 ; pl. I A). The hole, 3 to 4 m deep and 20 m large, has vertical walls and contains numerous sub-metric angular blocks. A cave, a few meters deep, comes out the south wall. Bedrocks consist of metagabbros of the Makalondi greenstone belt, a belt of the Palaeoproterozoic Birimian Formations of the West Africa craton [Pouclet et al., 1990]. The rock has a common granular texture with plagioclases, partly converted in albite and clinozoisite, and pyroxenes pseudomorphosed in actinote and chlorite. It is rather fairly altered. Chemical composition is mafic and poorly alkaline (tabl. I). A weak E-W schistosity generated with the epizonal thermometamorphism. The site depression was created along a N010o shear zone where rocks suffered important fracturation and fluid transfers, as shown by its silification and ferruginisation. The absence of human activity traces and the disposition of the angular blocks attest that the pit is natural and was due to the collapse of the roof of a vast cavity whose current cave is only the residual prolongation. To the vertical walls of the depression and at the cave entry, pluridecimetric hemispheric hollows are observed (pl. I B). Smooth morphology and position of these hollows sheltered within the depression dismiss the assumptions of formation by mechanical erosion. In return, these features are typical shape of dissolution processes observed into limestone karstic caves. That kind of process must be invoked to explain the opening of the Guessedoundou cave, in the total lack of desagregation materials. Dissolution of metagabbro occurred during hydrous transfer, which was probably guided by numerous fractures of the shear zone. Additional observations have been done in the Sirba Valley, where similar metabasite rocks constitute the substratum, with sudden sinking of doline-like depressions and evidence of deep cavities by core logging [Willems et al., 1993, 1996]. It is concluded that karstic phenomena may exist even in silica-aluminous rocks of crystalline terrains, such as the greenstones of a Precambrian craton. Mfoula a cave into gneisses in South Cameroon. - The cave of Mfoula is located 80 km north-east of Yaounde (fig. 3). It is the second largest cave of Cameroon, more than 5,000 m3, with a large opening in the lower flank of a deep valley (pl. I C). The cavity is about 60 m long, 30 m large and 5 to 12 m high (fig. 4; pl. I D). It is hollowed in orthogneisses belonging to the Pan-African Yaounde nappe. Rocks exhibit subhorizontal foliation in two superposed lithological facies: the lower part is made of amphibole- and garnet-bearing layered gneisses, and the upper part, of more massive granulitic gneisses. Average composition is silico-aluminous and moderately alkaline (tabl. I). The cave is made of different chambers separated by sub-cylindrical pillars. The ceiling of the main chamber, 6 m in diameter, is dome-shaped with a smooth surface (D, fig. 4). The walls have also a smooth aspect decorated with many hemispherical hollows. The floor is flat according to the rock foliation. They are very few rock debris and detrital fragments and no traces of mechanical erosion and transport. The general inner morphology is amazingly similar to that of a limestone cave. The only way to generate such a cavity is to dissolve the rock by water transfer. To test the effect of the dissolution process, we analysed a clayey residual sampled in an horizontal fracture of the floor (tabl. I). Alteration begins by plagioclases in producing clay minerals and in disagregating the rock. However, there is no more clay and sand material. That means all the silicate minerals must have been eliminated. Dissolution of silicates is a known process in sandstone and quartzite caves. It may work as well in gneisses. To fasten the chemical action, we may consider an additional microbial chemolitotrophe activity. The activity of bacteria colonies is known in various rocks and depths, mainly in the aquifer [Sinclair and Ghiorse, 1989 ; Stevens and McKinley, 1995]. The formation of the Mfoula cave is summarized as follow (fig. 5). Meteoric water is drained down along sub-vertical fractures and then along horizontal discontinuities of the foliation, particularly in case of lithological variations. Chemical and biological dissolution is working. Lateral transfers linked to the aquifer oscillations caused widening of the caves. Dissolved products are transported by the vertical drains. Regressive erosion of the valley, linked to the epeirogenic upwelling due to the volcano-tectonic activity of the Cameroon Line, makes the cavities come into sight at the valley flanks. Discussion and conclusion. - The two examples of the Guessedoundou and Mfoula caves evidence the reality of the karsts in non-carbonated silicated rocks. The karst term is used to design >> any features of the classical karst morphology (caves, dolines, lapies...) where dissolution plays the main genetical action >> [Willems, 2000]. Our observations indicate that (i) the karst genesis may have occurred into any kind of rocks, and (ii) the cave formation is not directly dependent of the present climate. These facts have major consequences to hydrogeological investigations, especially for water supply in Sahelian and sub-desertic countries. Some measurements of water transfer speed across either sedimentary pelitic strata of the Continental terminal or igneous rocks of the substratum in West Niger [Esteves and Lenoir, 1996 ; Ousmane et al., 1984] proved that supplying of aquifers in these silico-aluminous rocks may be as fast as in a karstic limestone. That means the West Niger substratum is highly invaded by a karstic net and may hidden a lot of discontinuous aquifers. The existence of this karst system can be easily shown by morphological observations, the same that are done in karstic limestone regions (abnormally suspended dry valleys, collapses, dolines...). Clearly, this must be the guide for any search of water, even in desertic areas where limestones are absent

Engineering approaches to conditions created by a combination of karst and faulting at a hospital in Birmingham, Alabama, 2002, Cooley T,
Foundations for a major expansion and modification of a multistory hospital in Birmingham, AL, were founded on faulted and karst-dissolutioned dolomite. The foundation approach had to accommodate a high degree of uncertainty concerning local conditions due to limited access for exploration and extremely variable rock conditions. The scope of the construction included excavation of a subbasement into rock with associated tiebacks to support adjacent foundations, installation of rock-bearing shear walls and rock anchors under the existing hospital, and installation of rock-bearing caissons and wall foundations outside the existing hospital. Local complications included areas of highly shattered rock, a generally pinnacled rock surface with average relief of 3-6 m (10-20 ft), locally very deep cutters and pits, areas where dolomite was weathered to sand or weak rock up to 3 m (10 ft) thick, and pockets of flowing sand and mud near the rock surface. Because of the complexity of site conditions and limited initial access to the site, on-site geotechnical services required innovative approaches to gather additional information on the highly variable and ambiguous rock conditions and adapt detailed foundation design and foundation approaches to the actual conditions encountered. These approaches included triple-tube coring of shattered rock at selected caisson locations; development of a technique for installation of rock anchors into shattered rock, determination of required undercut depths, and remediation at individual foundations where rock was shattered, disaggregated, or steeply pinnacled; characterization of individual cutters by airtrack probing for remediation information in wall foundations; low-angle coring for cutter characterization in the tieback area; change in foundations from walls to caissons or caissons to mat foundations in select areas; and above all, careful judgment-based design. Limitations of characterization methods are also discussed. A fundamental understanding of karst processes and three-dimensional conceptualization was an essential part of the engineering required for this project. (C) 2002 Elsevier Science B.V. All rights reserved

The effects of the North Anatolian Fault Zone on the latest connection between Black Sea and Sea of Marmara, 2002, Oktay Fazli Y. , Gokasan Erkan, Sakinc Mehmet, Yaltirak Cenk, Imren Caner, Demirbag Emin,
The development of the Strait of Istanbul is also one of the principal results of the tectonics which led to the evolution of the North Anatolian Fault Zone (NAFZ) in the Marmara Region 3.7 Ma ago. High resolution seismic profiles from the Marmara entrance of the Strait of Istanbul show a folding which occurred after the deposition of the parallel reflected Tyrrhenian sediments. Over the Tyrrhenian strata, a fondoform zone of a deltaic sequence and marine sediments of the latest sea level rising are present. These sediments also display syn-depositional folding. This situation implies that a local compressional stress field was created over the area probably since the Wurm Glacial age. This recent variation of the tectonic regime in the northern shelf of the Sea of Marmara may indicate a significant change in the development of the NAFZ through the Sea of Marmara. This variation of evolution of the NAFZ affected the latest development of the Strait of Istanbul via clockwise rotation of the Istanbul and Kocaeli peninsulas by right-lateral shearing between two zone bounding faults. This rotation has led to the development of NNE-SSW left-lateral faults in the Strait of Istanbul and local compressional and tensional areas explaining the compressional structures seen in the southern entrance of the Strait of Istanbul. Therefore, the latest Mediterranean-Black Sea connection was established by means of the sufficient deepening of the Bosphorus channel by a variation in the evolution of NAFZ through the Sea of Marmara

Dachstein-Altflche, Augenstein-Formation und Hhlenentwicklung - die Geschichte der letzten 35 Millionen Jahre in den zentralen Nrdlichen Kalkalpen, 2002, Frisch W. , Kuhlemann J. , Dunkl I. , Szekely B. , Vennemann T. , Rettenbacher A.
The landscape of the central Northern Calcareous Alps (NCA) is largely determined by the celebrate elevated karst plateaus, which represent relics of the Dachstein paleosurface and can be followed as far as the eastern margin of the NCA. The Dachstein paleosurface formed in late Eocene to early Oligocene times as a karstic hilly landscape. It was modified by later erosional processes to a limited extent only and is preserved as such in the karst plateaus. In the Oligocene, the paleosurface subsided and was sealed by the Augenstein Formation, a terrestrial sequence of conglomerates and sandstones, which are only preserved in small remnants on the plateaus. The poorly and contradictingly defined terms Rax landscape" and Augenstein landscape" are not used any more. From the overall geological situation, the age of the Augenstein Formation can be inferred as Lower Oligocene to early Lower Miocene. Fission track dating on zircon support the Lower Oligocene age of the basal Augenstein sediments (only these are preserved). Their source area was situated in the south and mainly occupied by weakly metamorphosed Paleozoic sequences (Graywacke Zone and its equivalents) and the latest Carboniferous to Lower Triassic siliciclastic base of the NCA. To the west, the Augenstein Formation interfingered with the Tertiary sediments of the Lower Inn Valley. Thermal modeling of fission track data from apatite, which is contained in pebbles as an accessory phase, suggest that the Augenstein Formation attained thicknesses of locally 1.3 km, possibly even more than 2 km. Augenstein sedimentation probably ended in Early Miocene times with the onset of lateral tectonic extrusion in the Eastern Alps, which caused lowering of the relief in the source area and created a new, fault-bounded river network. In the following period, the Augenstein sediments were eroded and redeposited in the foreland molasse basin. From Pannonian times (ca. 10 Ma) on, the central and eastern NCA, and therefore also the Dachstein paleosurface, experienced uplift in pulses. The paleosurface remained preserved in those areas, where thick limestone sequences enabled subsurface erosion in cave systems and considerably reduced surface erosion. Augenstein sediments became washed into the widespread cave systems of the plateau-topped limestone massifs. The arrangement of the caves in three horizons shows that uplift of the NCA occurred in pulses separated from periods of tectonic quiescence. In our model of the evolution of the NCA since the late Eocene, the highest cave system, the surface-near ruin cave system, was probably formed during formation of the Dachstein paleosurface. The largest system, the giant cave system, formed in Upper Miocene times, i.e., in the early stage of the final uplift period of the NCA. The youngest and lowest system, the source cave system, formed in Pliocene to Quaternary times. We aimed to date material from the giant cave system by radiometric methods. U/Pb dating on speleothems from the Mammut cave (Dachstein) and the Eisriesenwelt (Tennengebirge) gave no formation age because of the low U contents; however, the isotope ratios allow to infer that the speleothems formed in pre-Pleistocene time. Quartz pebbles from the Augenstein Formation, washed into the caves before the formation of the speleothems, were analyzer for cosmogenic beryllium and aluminum isotopes in order to date the time of redeposition. The isotope contents, however, did no yield a sufficiently strong signal. Oxygen and carbon isotope ratios were determined on the Eisriesenwelt speleothem in order to receive information on climatic changes during speleothem growth. A 260 mm long core from the outer zone of the speleothem shower limited variation for the temperatures of the seeping rainwater, which caused the speleothems to form. This indicates moderate climate and thus, again, pre-Pleistocene formation of the speleothems. All these results are in accord with the supposed Upper Miocene formation age of the giant cave system. Displacement of a speleothem along a shear plane and normal faults visible on the plateaus by the offset of the actual surface testify young, partly Quaternary tectonics, which affected the NCA.

Sedimentologic, diagenetic and tectonic evolution of the Saint-Flavien gas reservoir at the structural front of the Quebec Appalachians, 2003, Bertrand R, Chagnon A, Malo M, Duchaine Y, Lavoie D, Savard Mm,
The Beekmantown Group (Lower Ordovician) of the Saint-Flavien reservoir has produced 162x106 m3 (5.7 bcf) of natural gas between 1980 and 1994. The conversion of the field into gas storage was initiated in 1992 and the pool became operational in 1998. Integration of structural and sedimentologic features, carbonate and organic matter petrography and geochemistry for 13 drill holes is used to define a tectonic-sedimentologic-diagenetic model for porosity evolution in these reservoir dolostones. The Beekmantown Group consists of numerous fifth-order shallowing-upward cycles 1.0 to 7.0 m thick (average of 2.4 m). Each cycle consists of a basal shale deposited during the initial flooding of the platform which was subsequently covered by a shoaling succession of subtidal and intertidal limestones to intertidal dolostones. Early dolomitization has produced intercrystalline porosity and preserved some moldic pores in the intertidal facies. Near surface, post-dolomite karstification has created vugs that were subsequently filled by early marine calcite fibrous cement based on the {delta}18O and {delta}13C ratios of calcite. Early burial elements consist of horizontal stylolites, pyrite and sphalerite. Late migrated bitumen was thermally altered or vaporized as native coke under deep burial conditions exceeding 240{degrees}C, partly due to overthrusting of Appalachian nappes. Under these conditions, breccias and fractures were generated and subsequently filled with K-feldspar, quartz, illite, and xenomorphic and poikilotopic calcite. The {delta}18O of the poikilotopic calcite and homogenization temperature of coeval fluid inclusions indicate formation under high temperatures (Th about 260{degrees}C). Horizontal shear zones and marcasite-rich vertical stylolites were produced during folding and thrusting. Dissolution has preferentially affected late fracture-filling calcite and generated most of the actual porosity during or soon after the Taconian Orogeny. The relationship between the occurrence of smectite and this type of porosity indicates the low temperature condition of this dissolution (T <100{degrees}C). Porosity in the Saint-Flavien reservoir has been mostly produced by fracture-controlled, late to post-Taconian dissolution of early to late calcite in the intertidal dolomitic slightly porous facies at the top of rhythmic cycles that compose the Beekmantown Group

Karst collapse related to over-pumping and a criterion for its stability, 2003, He K. Q. , Liu C. L. , Wang S. J. ,
Karst collapse, caused by natural or artificial abstraction of groundwater, has been an environmental geological problem. The origin of karst collapse has been described by the potential erosion theory and the vacuum absorption erosion theory. However, a mathematical prediction criterion for karst collapse cannot be established by these two theories. This paper, from a new perspective, attempts to explain the microcosmic mechanism of karst collapse on the basis of these two theories. At a certain point in the unconsolidated soil covered on karst caves, when shearing stress surpasses shear strength of the soil, it fails under the mechanic effects of water and gas as well as gravity pressure. With an increase in damage points, a break plane appears and the soil overlying the karst caves is completely damaged and, thus, the ground surface collapses. On the basis of Mohr-Coulomb damage theory and previous studies, a prediction criterion of karst collapse is presented. An example displays the calculating process of the model and proves its reliability by analyzing nine typical collapses caused by a pumping test in Guizhou Province, China

Testing for reach-scale adjustments of hydraulic variables to soluble and insoluble strata: Buckeye Creek and Greenbrier River, West Virginia, 2003, Springer G. S. , Wohl E. E. , Foster J. A. , Boyer D. G. ,
An open question exists as to whether channel geometries and hydraulics are adjusted in bedrock streams with stable, concave profiles in a manner analogous to alluvial rivers. As a test of this problem, a comparison was undertaken of channel geometries and hydraulics among reaches with substrates that are of high mechanical resistance, but of variable chemical resistance. Reaches were selected from Buckeye Creek and Greenbrier River, West Virginia, USA because these streams flow over sandstones, limestones, and shales. The limestones have Selby rock resistance scores similar to those of the sandstones. A total of 13 reaches consisting of between 6 and 26 cross sections were surveyed in the streams. HEC-RAS was used to estimate unit stream power (omega) and shear stress (tau) for each reach. The reaches were selected to evaluate the null hypothesis that that omega and tau are equal atop soluble versus insoluble bedrock. Hypothesis tests consisted of paired t-tests and simultaneous, multiple comparisons. Geomorphic setting was included for Greenbrier River because previous studies have suggested that bedrock streams are intimately coupled with hillslopes. Holding geomorphic setting constant, three separate comparisons of omega and tau reveal that these variables are lowest atop soluble substrates in Greenbrier River (significance less than or equal to 0.05) and that changes in and tau are mediated by changes in channel geometry. Similarly, headwater reaches of Buckeye Creek developed atop shale and sandstone boulders are statistically distinguishable from downstream reaches wherein corrosion of limestone is the primary means of incision. However, comparisons in each stream reveal that channel geometries, omega and tau, are not strictly controlled by bed solubility. For constant substrate solubility along the Greenbrier River, omega and tau are consistently higher where a bedrock cutbank is present or coarse, insoluble sediment enters the channel. The latter is also associated with locally high values of omega and tau in Buckeye Creek. Assuming that incision by corrosion requires lower values of omega and tau because the channel need not be adjusted for block detachment and tool acceleration, we posit that the statistically lower values of omega and tau are tentative evidence in favor of differential geometric and hydraulic adjustments to substrate resistance. We observe that these adjustments are not made independent of geomorphic setting. (C) 2003 Elsevier Science B.V. All rights reserved

Fallen arches: Dispelling myths concerning Cambrian and Ordovician paleogeography of the Rocky Mountain region, 2003, Myrow Paul M. , Taylor John F. , Miller James F. , Ethington Raymond L. , Ripperdan Robert L. , Allen Joseph,
High-resolution sedimentologic, biostratigraphic, and stable isotope data from numerous measured sections across Colorado reveal a complex architecture for lower Paleozoic strata in the central Cordilleran region. A lack of precise age control in previous studies had resulted in misidentification and miscorrelation of units between separate ranges. Corrections of these errors made possible by our improved data set indicate the following depositional history. The quartz-rich sandstone of the Sawatch Formation was deposited during onlap of the Precambrian erosion surface in the early Late Cambrian. The overlying Dotsero Formation, a regionally extensive carbonate- and shale-rich succession records blanket-like deposition with only minor facies changes across the state. An extremely widespread, meter-scale stromatolite bed, the Clinetop Bed, caps the Dotsero Formation in most areas. However, a latest Cambrian erosional episode removed 9-11 m of the upper Dotsero Formation, including the Clinetop Bed, from just east of the Homestake shear zone in the Sawatch Range eastward to the Mosquito Range. The overlying Manitou Formation differs in character, and thus in member stratigraphy, on the east vs. west sides of the state. These differences were previously interpreted as the result of deposition on either side of a basement high that existed within the Central Colorado Embayment or Colorado 'Sag,' a region of major breaching across the Transcontinental Arch. This paleogeographic reconstruction is shown herein to be an artifact of miscorrelation. Biostratigraphic data show that the northwestern members of the Manitou Formation are older than the members exposed in the southeastern part of the state and that there is little or no overlap in age between the two areas. This circumstance is the result of (1) removal of older Manitou Formation strata in the southeast by an unconformity developed during the Rossodus manitouensis conodont Zone, and (2) erosion of younger Manitou strata in central and western Colorado along Middle Ordovician and Devonian unconformities. Deciphering these complex stratal geometries has led to invalidation of long-held views on western Laurentian paleogeography during the Cambrian and earliest Ordovician, specifically the existence of the Colorado Sag and a northeast-trending high within the sag that controlled depositional patterns on either side. The mid- Rossodus uplift and resultant unconformity eliminated any and all Upper Cambrian and Lower Ordovician deposits in southern Colorado and northern New Mexico, and thus their absence should not be misconstrued as evidence for earlier nondeposition in this region. Lithofacies distribution patterns and isopach maps provide no evidence that highlands of the Transcontinental Arch existed in Colorado prior to the mid-Rossodus age uplift event. In fact, regional reconstructions of earliest Paleozoic paleogeography along the entire length of the purported Transcontinental Arch should be reevaluated with similarly precise biostratigraphic data to reconsider all potential causes for missing strata and to eliminate topographic elements not supported by multiple stratigraphic techniques. This study illustrates how seriously paleogeographic reconstructions can be biased by the presumption that missing strata represent periods of nondeposition rather than subsequent episodes of erosion, particularly in thin cratonic successions where stratigraphic gaps are common and often inconspicuous

Coastal cliff geohazards in weak rock: the UK Chalk cliffs of Sussex, 2004, Mortimore R. N. , Lawrence J. , Pope D. , Duperret A. , Genter A. ,
Geohazards related to chalk coastal cliffs from Eastbourne to Brighton, Sussex are described. An eight-fold hazard classification is introduced that recognizes the influence of chalk lithology, overlying sediments and weathering processes on location, magnitude and frequency of cliff collapses. Parts of the coast are characterized by cliffs of predominantly a single chalk formation (e.g. Seven Sisters) and other sections are more complex containing several Chalk formations (Beachy Head). Rock properties (intact dry density or porosity) and mass structure vary with each formation and control cliff failure mechanisms and scales of failures. The Holywell Nodular Chalk, New Pit Chalk and Newhaven Chalk formations are characterized by steeply inclined conjugate sets of joints which lead to predominantly plane and wedge failures. However, the dihedral angle of the shears, the fracture roughness and fill is different in each of these formations leading to different rock mass shear strengths. In contrast the Seaford and Culver Chalk formations are characterized by low-density chalks with predominantly clean, vertical joint sets, more closely spaced than in the other formations. Cliff failure types range from simple joint controlled conventional plane and wedge failures to complex cliff collapses and major rock falls (partial flow-slides) involving material failure as well as interaction with discontinuities. Other hazards, related to sediments capping the Chalk cliffs, include mud-slides and sandstone collapses at Newhaven, and progressive failure of Quaternary Head and other valley-fill deposits. Weathering, including the concentration of groundwater flow down dissolution pipes and primary discontinuities, is a major factor on rate and location of cliff collapses. A particular feature of the Chalk cliffs is the influence of folding on cliff stability, especially at Beachy Head, Seaford Head and Newhaven. A new classification for cliff collapses and a new scale of magnitude for collapses are introduced and used to identify, semi-quantify and map the different hazards. Climate (and climate change) and marine erosion affect the rate of development of cliff collapse and cliff-line retreat. This was particularly evident during the wet winters of 1999-2000-2001 when the first major collapses along protected sections of coastline occurred (Peacehaven Cliffs protected by an undercliff wall; Black Rock Marina the Chalk cliffs and the Quaternary Head). It is the geology, however, that controls the location and scale of erosion and cliff failure

Sediment entrainment and transport in fluviokarst systems, 2004, Dogwiler T, Wicks Cm,
The primary geomorphic process active in the development of karst stream systems is generally regarded as bedrock dissolution. However, physical erosional processes may also be an important geomorphic agent in karst development. The objectives of this study were to determine the sediment transport threshold in two fluviokarst streams. The source of the sediment was internal to the karst basins. The approach used was to calculate basal and critical shear stresses from streams in two karst systems to determine if, and how frequently, storm-induced flows are capable of mobilizing stream sediment. The fluviokarst systems investigated as a part of this research are capable of transporting 50-85% of their stream substrates during bankfull discharge conditions. Based on the discharge and precipitation frequency, stream flows capable of entraining d(50) and d(85) particles occur at intervals of 2.4 and 11.7 months (0.98 yr), respectively. Thus, the sediment transport threshold in fluviokarst streams is exceeded by relatively common discharge events. (C) 2004 Elsevier B.V. All rights reserved

A pipe-based, first approach to modeling closed conduit flow in caves, 2004, Springer Gregory S. ,
A closed conduit model is constructed for a discrete cave segment using the energy equation and the assumption that energy losses in the segment are generated by large-scale flow separation associated with expansions and bends. As employed, the model uses paleostage indicators and passage geometry to estimate total head loss across the study reach. Channel roughness is estimated using pipe-based equations and a skin friction factor estimated from secondary means. Discharge is varied in the model until calculated head loss matches observed head loss. The model is employed to estimate discharge for a flood recorded in Buckeye Creek Cave, West Virginia as high water marks consisting of silt lines. Under varying assumptions, the model yields paleodischarges in the range of 22-29 m3 s-1. Shear stress values calculated using model output are in general agreement with the size distribution of gravel on the stream bed and shear stress values are relatively insensitive to changes in discharge. The apparent friction factor for the study reach is estimated to be in the range of 0.4-0.7, which is in general agreement with previous studies of large conduits. The model is applicable to similar cave reaches, but requires further testing and validation because so little is known about conduit flow in karst

Mesozoic plate tectonic reconstruction of the Carpathian region, 2004, Csontos L, Voros A,
Palaeomagnetic, palaeobiogeographic and structural comparisons of different parts of the Alpine-Carpathian region suggest that four terranes comprise this area: the Alcapa, Tisza, Dacia and Adria terranes. These terranes are composed of different Mesozoic continental and oceanic fragments that were each assembled during a complex Late Jurassic-Cretaceous-Palaeogene history. Palaeomagnetic and tectonic data suggest that the Carpathians are built up by two major oroclinal bends. The Alcapa bend has the Meliata oceanic unit, correlated with the Dinaric Vardar ophiolite, in its core. It is composed of the Western Carpathians, Eastern Alps and Southern Alcapa units (Transdanubian Range, Bukk). This terrane finds its continuation in the High Karst margin of the Dinarides. Further elements of the Alcapa terrane are thought to be derived from collided microcontinents: Czorsztyn in the N and a carbonate unit (Tisza?) in the SE. The Tisza-Dacia bend has the Vardar oceanic unit in its core. It is composed of the Bihor and Getic microcontinents. This terrane finds its continuation in the Serbo-Macedonian Massif of the Balkans.The Bihor-Getic microcontinent originally laid east of the Western Carpathians and filled the present Carpathian embayment in the Late Palaeozoic-Early Mesozoic. The Vardar ocean occupied an intermediate position between the Western Carpathian-Austroalpine-Transdanubian-High Karst margin and the Bihor-Getic-Serbo-Macedonian microcontinent. The Vardar and Pindos oceans were opened in the heart of the Mediterranean-Adriatic microcontinent in the Late Permian-Middle Triassic. Vardar subducted by the end of Jurassic, causing the Bihor-Getic-Serbo-Macedonian microcontinent to collide with the internal Dinaric-Western Carpathian margin.An external Penninic-Vahic ocean tract began opening in the Early Jurassic, separating the Austroalpine-Western Carpathian microcontinent (and its fauna) from the European shelf. Further east, the Severin-Ceahlau-Magura also began opening in the Early Jurassic, but final separation of the Bihor-Getic ribbon (and its fauna) from the European shelf did not take place until the late Middle Jurassic.The Alcapa and the Tisza-Dacia were bending during the Albian-Maastrichtian. The two oroclinal bends were finally opposed and pushed into the gates of the Carpathian embayment during the Palaeogene and Neogene. At that time, the main N-S shortening in distant Alpine and Hellenic sectors was linked by a broader right-lateral shear zone along the former Vardar suture

Rock Mechanics for Underground Mining, 2004, Brady B. M. G. , Brown E. T.

The influence of the geological setting on the morphogenetic evolution of the Tremiti Archipelago (Apulia, Southeastern Italy), 2005, Andriani Gk, Walsh N, Pagliarulo R,
The Tremiti Archipelago (Southern Adriatic Sea), also called Insulae Diomedae from the name of the Greek hero who first landed there, is an area of high landscape and historical value. It is severely affected by significant geomorphologic processes dominated by mass movements along the coast that constitute the most important and unpredictable natural hazard for the population and cultural heritage. Coastal erosion is favoured by the peculiar geological and structural setting, seismic activity, weathering, development of karst processes, and wave action. The present paper reports on descriptive and qualitative evaluation of the factors controlling landslides and coastline changes based on medium-term in situ observation, detailed surface surveys at selected locations since 1995, and historic and bibliographic data. The Tremiti Archipelago is part of an active seismic area characterised by a shear zone separating two segments of the Adriatic microplate that have shown different behaviour and roll back rates in the subduction underneath the Apennines since middle Pleistocene. Although coastal morphology can be basically considered to be the result of wave action, the continual action of subaerial processes contributes effectively to the mechanism of shoreline degradation. Weathering mainly affects the marly calcisiltites and calcilutites of the Cretaccio Fm. and the friable and low cemented calcarenites and biomicrites of the San Nicola Fm. The cliffs are characterised by different types of failure such as lateral spreads, secondary topples, rock falls and slides. At the Isle of San Nicola, landslides are controlled by the contrast in competence, shear strength and stiffness between the Pliocene re-crystallised dolomitic calcarenites and calcisiltites and the Miocene marly calcilutites and calcisiltites. At the Isles of San Domino and Caprara rock falls are attributed to the undercutting of waves at the base of the cliffs

Variation of palaeostress patterns along the Oriente transform wrench corridor, Cuba: significance for Neogene-Quaternary tectonics of the Caribbean realm, 2005, Rojasagramonte Y. , Neubauer F. , Handler R. , Garciadelgado D. E. , Friedl G. , Gadodamas R. ,
In this study, we address the late Miocene to Recent tectonic evolution of the North Caribbean (Oriente) Transform Wrench Corridor in the southern Sierra Maestra mountain range, SE Cuba. The region has been affected by historical earthquakes and shows many features of brittle deformation in late Miocene to Pleistocene reef and other shallow water deposits as well as in pre-Neogene, late Cretaceous to Eocene basement rocks. These late Miocene to Quaternary rocks are faulted, fractured, and contain calcite- and karst-filled extension gashes. Type and orientation of the principal normal palaeostress vary along strike in accordance with observations of large-scale submarine structures at the south-eastern Cuban margin. Initial N-S extension is correlated with a transtensional regime associated with the fault, later reactivated by sinistral and/or dextral shear, mainly along E-W-oriented strike-slip faults. Sinistral shear predominated and recorded similar kinematics as historical earthquakes in the Santiago region. We correlate palaeostress changes with the kinematic evolution along the boundary between the North American and Caribbean plates. Three different tectonic regimes were distinguished for the Oriente transform wrench corridor (OTWC): compression from late Eocene-Oligocene, transtension from late Oligocene to Miocene (?) (D-1), and transpression from Pliocene to Present (D-2-D-4), when this fault became a transform system. Furthermore, present-day structures vary along strike of the Oriente transform wrench corridor (OTWC) on the south-eastern Cuban coast, with dominantly transpressional/compressional and strike-slip structures in the east and transtension in the west. The focal mechanisms of historical earthquakes are in agreement with the dominant ENE-WSW transpressional structures found on land. (C) 2004 Elsevier B.V. All rights reserved

Results 16 to 30 of 38
You probably didn't submit anything to search for