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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. ...

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. ...

Speleology in Kazakhstan

Shakalov on 11 Jul, 2012
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 epilimnion is upper layer of stratified water [16].?

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Your search for geometry (Keyword) returned 138 results for the whole karstbase:
Showing 1 to 15 of 138
Assessing the importance of conduit geometry and physical parameters in karst systems using the storm water management model (SWMM), , Peterson Eric W. , Wicks Carol M. ,
SummaryQuestions about the importance of conduit geometry and about the values of hydraulic parameters in controlling ground-water flow and solute transport through karstic aquifers have remained largely speculative. One goal of this project was to assess the role that the conduit geometry and the hydraulic parameters have on controlling transport dynamics within karstic aquifers. The storm water management model (SWMM) was applied to the Devil's Icebox-Connor's Cave System in central Missouri, USA. Simulations with incremental changes to conduit geometry or hydraulic parameters were performed with the output compared to a calibrated baseline model. Ten percent changes in the length or width of a conduit produced statistically significant different fluid flow responses. The model exhibited minimal sensitivity to slope and infiltration rates; however, slight changes in Manning's roughness coefficient can highly alter the simulated output.Traditionally, the difference in flow dynamics between karstified aquifers and porous media aquifers has led to the idea that modeling of karst aquifers is more difficult and less precise than modeling of porous media aquifers. When evaluated against models for porous media aquifers, SWMM produced results that were as accurate (10% error compared to basecase). In addition, SWMM has the advantage of providing data about local flow. While SWMM may be an appropriate modeling technique for some karstic aquifers, SWMM should not be viewed as a universal solution to modeling karst systems

Hydrogeological investigations into discharge of salt-containing water from a stream into an aquifer., 1976, Neuss Matthias
An aquifer in a horseshoe bend of the Weser river was investigated regarding the processes of the river water infiltration. The geology and geometry of the aquifer was ascertained by means of numerous borings. The hydraulic situation before and after infiltration was determined by water table maps. The intrusion of a salt-freshwater lens could be reconstructed from the beginning of infiltration until ten years later by means of previous results of chemical analysis. By new chemical analysis it was proved that river water infiltrates into the aquifer. Additionally it was established that the relatively high concentration of chloride is reduced during the passage of the groundwater both by mixing with recharged groundwater and by adsorption of the ground. Furthermore temperature measurements in the groundwater at selected stations confirm qualitatively the river water infiltration into the polder.

A study of fresh water lens configuration in the Cayman Islands using resistivity methods, 1976, Bugg Sf, Lloyd Jw,
The problems of identifying the base of fresh water lenses in oceanic islands are discussed. A study carried out in the Cayman Islands is described in which the lens base is defined in relation to potable water standards and mapped using surface resistivity measurements with salinity profile controls in boreholes. Using depth-salinity ratios the piezometric surface is then determined. The technique is considered to provide a reliable cheap and rapid method of obtaining lens geometry in oceanic islands particularly where fairly homogeneous lithologies are present

Le karst jurassique du rebord subalpin dans les Alpes-Maritimes, 1989, Mangan, C.
Jurassic karst of the subalpine area in Maritime Alps Department (France) - The jurassic carbonated sediments represent the principal karst aquifer in front of the alpine range. This area is subdivided in three different sectors by the tectonic and paleogeographic evolution: subalpine arc of Castellane (Grasse Prealps), subalpine arc of Nice, Provence foreland. Through the comparative study of these areas, it appears a real diversity about the karst evolution, the geometry about the karst evolution, the geometry of waters reservoirs, the distribution of the underground flows, and therefore about the water supply and exploitation.

FLOW PARAMETERS IN A SHALLOW CONDUIT-FLOW CARBONATE AQUIFER, INNER BLUEGRASS KARST REGION, KENTUCKY, USA, 1991, Thrailkill J. , Sullivan S. B. , Gouzie D. R. ,
In the carbonate aquifers which underlie most karst terrains, groundwater flow is through a dendritic system of solution conduits. In such aquifers, termed shallow conduit-flow aquifers. the methods used to mode) granular and fracture aquifers are not generally applicable. Investigations were conducted in the Inner Bluegrass Karst Region of central Kentucky with the objective of developing methods of modeling shallow conduit-flow aquifers as well as obtaining quantitative information on a specific portion of the aquifer to assist in its management for water supply purposes. In the Inner Bluegrass Karst Region, groundwater basins are developed. in each of which there is an integrated system of solution conduits which conducts recharge to a major spring. One of the largest of these groundwater basins feeds Royal Spring, which serves as the principal water supply for the town of Georgetown. The basin extends over 15 km to the southeast and most of its flow is furnished by underground diversions of Cane Run, a surface stream with headwaters near the center of the City of Lexington. The principal objectives of the field investigation were to determine discharges at the spring and travel times to the spring from discrete recharge points within the basin, termed swallets. The spring is ungaged. and an attempt was made to obtain a continuous discharge record by the dilution of dye introduced at a swallet. Comparison of the dye-dilution discharge record with stage discharges at the spring revealed substantial discrepancies which are believed to be caused by as much as five-sixths of the low-flow discharge from the upper portion of the basin bypassing the spring. The dye-dilution method, therefore, provided significant insights into the geometry of the conduit system of the groundwater basin although it proved unsatisfactory as a method of determining discharges at the spring. Analysis of the travel times and stage discharges provided information on the conduit geometry by modeling the flow as open-channel flow in a rectangular channel. Flow in the system is rapid, ranging from 140 to 590 m h-1. Although the flow rate increases with discharge, the relationship is not simple owing to substantial increases in conduit cross-sectional area at higher discharges. Flow is turbulent and subcritical under all conditions. The most surprising result was the very low depth of flow calculated; less than 17 cm at even the highest discharge. Although this must be considered an 'equivalent' depth, it is believed to indicate that active flow in shallow conduit-flow aquifers is generally in a thin zone just beneath the water table

A MIDDLE PROTEROZOIC PALEOKARST UNCONFORMITY AND ASSOCIATED SEDIMENTARY-ROCKS, ELU BASIN, NORTHWEST CANADA, 1991, Pelechaty S. M. , James N. P. , Kerans C. , Grotzinger J. P. ,
A major palaeokarst erosion surface is developed within the middle Proterozoic Elu Basin, northwestern Canada. This palaeokarst is named the sub-Kanuyak unconformity and truncates the Parry Bay Formation, a sequence of shallow-marine dolostones that were deposited within a north-facing carbonate platform under a semi-arid climate. The sub-Kanuyak unconformity exhibits up to 90 m of local relief, and also formed under semi-arid conditions when Parry Bay dolostones were subaerially exposed during a relative sea-level drop of about 180 m. Caves and various karren developed within the meteoric vadose and phreatic zones. Their geometry, size and orientation were largely controlled by northwest- and northeast-trending antecedent joints, bedding, and lithology. Near-surface caves later collapsed forming valleys, and intervening towers or walls, and plains. Minor terra rossa formed on top of highs. Karstification was most pronounced in southern parts of Bathurst Inlet but decreased northward, probably reflecting varying lengths of exposure time along a north-dipping slope. The Kanuyak Formation is up to 65 m thick, and partially covers the underlying palaeokarst. It consists of six lithofacies: (i) breccia formed during collapse of caves, as reworked collapse breccia and regolith; (ii) conglomerate representing gravel-dominated braided-fluvial deposits; (iii) sandstone deposited as braided-fluvial and storm-dominated lacustrine deposits; (iv) interbedded sandstone, siltstone and mudstone of sheet flood origin; (v) dolostones formed from dolocretes and quiet-water lacustrine deposits; and (vi) red-beds representing intertidal-marine mudflat deposits. Rivers flowed toward the northwest and northeast within karst valleys and caves; lakes were also situated within valleys; marine mudflat sediments completely cover the palaeokarst to the north. A regional correlation of the sub-Kanuyak unconformity with the intra-Greenhorn Lakes disconformity within the Coppermine homocline suggests that similar styles of karstification occurred over an extensive region. The Elu Basin palaeokarst, however, was developed more landward, and was exposed for a longer period of time than the Coppermine homocline palaeokarst

GENERAL CENOZOIC EVOLUTION OF THE MALDIVES CARBONATE SYSTEM (EQUATORIAL INDIAN-OCEAN), 1992, Aubert O, Droxler Aw,
Analyses and interpretation of an industrial multi-channel seismic grid, a 2.3 km-deep industrial well (NMA-1) and two ODP (Sites 715 and 716), have generated new insights into the evolution of the Maldives carbonate system, Equatorial Indian Ocean. The present physiography of the Maldives Archipelago, a double chain of atolls delineating an internal basin, corresponds only to the latest phase of a long and dynamic evolution, far more complex than the simple vertical build-up of reef caps on top of thermally subsiding volcanic edifices. Through the Cenozoic evolution of the Maldives carbonate system, distinct phases of vertical growth (aggradation), exposure, regional or local drowning, and recovery of the shallow banks by lateral growth (progradation) have been recognized. The volcanic basement underlying the Maldives Archipelago is interpreted to be part of a volcanic ridge generated by the northern drift of the Indian plate on top of the hotspot of the island of Reunion. The volcanic basement recovered at well NMA-1 and ODP Site 715 has been radiometrically dated as 57.2 1.8 Ma (late Paleocene) by 40Ar-39Ar. Seismic and magnetic data indicate that this volcanic basement has been affected by a series of NNE-SSW trending subvertical faults, possibly associated with an early Eocene strike-slip motion along an old transform zone. The structural topography of the volcanic basement apprears to have dictated the initial geometry of the Eocene and early Oligocene Maldives carbonate system. Biostratigraphic analyses of samples, recovered by drilling in Site 715 and exploration well NMA-1, show that the Maldives shallow carbonate system was initiated during the early Eocene on top of what were originally subaerial volcanic edifices. The Eocene shallow carbonate sequence, directly overlying the volcanic basement at NMA-1, is dolomitized and remains neritic in nature, suggesting low subsidence rates until the early Oligocene. During this first phase of the Maldives carbonate system evolution, shallow carbonate facies aggraded on top of basement highs and thick deep-water periplatform sediments were deposited in some central seaways, precursors of the current wider internal basins. In the middle Oligocene, a plate reorganization of the equatorial Indian Ocean resulted in the segmentation of the hotspot trace and the spreading of the Maldives away from the transform zone. This plate reorganization resulted in increasing subsidence rates at NMA-1, interpreted to be associated with thermal cooling of the volcanic basement underlying the Maldives carbonate system. This middle Oligocene event also coincides with a regional irregular topographic surface, considered to represent a karst surface produced by a major low-stand. Deep-water carbonate facies, as seen in cuttings from NMA-1, overlie the shallow-water facies beneath the karst surface which can, therefore, be interpreted as a drowning unconformity. In the late Oligocene, following this regional deepening event, one single central basin developed, wider than its Eocene counterparts, and the current intraplatform basin was established. Since the early to middle Miocene, the shallow carbonate facies underwent a stage of local recovery by progradation of neritic environments towards the central basin. The simultaneous onset in the early middle Miocene of the monsoonal wind regime may explain the development of bidirectional slope progradations in the Maldives. During the late Miocene and the early Pliocene, several carbonate banks were locally drowned, whereas others (i.e. Male atoll) display well-developed lateral growth through margin progradations during the same interval. Differential carbonate productivity among the atolls could explain these diverse bank responses. High-frequency glacialeustatic sea-level fluctuations in the late Pliocene and Pleistocene resulted in periodic intervals of bank exposure and flooding, and developed the present-day physiography of atolls, with numerous faros along their rims and within their lagoons

HYDROGEOLOGY OF GRAND CAYMAN, BRITISH-WEST-INDIES - A KARSTIC DOLOSTONE AQUIFER, 1992, Ng K. C. , Jones B. , Beswick R. ,
On Grand Cayman, freshwater bodies present in the Bluff Formation are typically small and occur as thin lenses floating on top of dense saline water. Evaluation of the water resource potential of these freshwater lenses is difficult because of their variable hydrological conditions, complex paleohydrogeology and aquifer heterogeneity. Secondary porosity created by preferential dissolution of aragonitic fossil components is common. Open fissures and joints developed under tectonic stress and karst development associated with sea-level fluctuations are, however, the two most important causes of porosity and permeability in the aquifers on Grand Cayman. Fracture and karst porosity control the lens occurrence by: (1) acting as avenues for the intrusion of seawater or upward migration of saline water; (2) acting as recharge focal points; (3) enhancing hydrodynamic dispersion; (4) defining lens geometry; (5) facilitating carbonate dissolution along joints and fissures. A clear understanding of the hydrological and geological conditions is important in developing small lenses in a setting similar to that on Grand Cayman. This pragmatic approach can help identify the optimum location of the well field and avoid areas particularly susceptible to saline water intrusion

RELATIONSHIP BETWEEN FRACTURES AND KARSTIFICATION - THE OIL-BEARING PALEOKARST OF ROSPO MARE (ITALY), 1994, Soudet H. J. , Sorriaux P. , Rolando J. P. ,
The Rospo Mare oil field is located in the Adriatic Sea, 20 km off the Italian coast. The reservoir lies at a depth of 1300 m and consists of a paleokarst oi Oligocene to Miocene age which developed within Cretaceous limestones, now covered by 1200 m of Mio-Pliocene sequences. The oil column is about 140 m 8 high. The karstic nature of the reservoir was identified through vertical, cored drill holes which allowed us to analyse the various solution features and the sedimentary infilling (speleothems, terra rossa, marine clays), as well as their vertical distribution. Erosion morphology at the top of the karst is highly irregular, including in particular paleovalleys as well as many pit-shaped sink holes. Detailed geophysical knowledge of that morphology helped to optimize the development of the field through horizontal drilling. Observations concerning the upper part of the reservoir were compared to a palaeokarst of the same age, outcropping widely onshore, in quarries located nearby. The Rospo Mare paleokarst is an integral part of the ante Miocene paleokarst assemblages of the periphery of the Mediterranean which were formed in tropical conditions. Only the fractures enhanced by meteoric water during the formation of the karat are important for reservoir connectivity. During the formation of the karst there were several phases of dissolution and infilling which modified the geometry of the open fissures and only these fractures play an important role in the reservoir drainage. Vertically we can distinguish three very different zones from top to bottom: at the top the epikarst (0-35 m) in a zone of extension. All the fractures have been enlarged by dissolution but the amount of infilling by clay is substantial. The clays are derived either from alteration of the karat fabric or by deposition during the Miocene transgression; the percolation zone (15-45 m) is characterized by its network of large fractures vertically enlarged by dissolution which corresponds to the relict absorption zones in the paleokarst. These fractures, which usually have a pluridecametric spacing, connect the epi-karst with the former sub-horizontal river system. This zone has been intersected by the horizontal wells during the field development. In this zone there are local, horizontal barriers oi impermeable clay which can block vertical transmissibility. In these low permeability zones the vertical fractures have not been enlarged due to dissolution hence the horizontal barrier; the zone of underground rivers (35-70 m) is characterized by numerous horizontal galleries which housed the subterranean ground water circulation. When these fissures are plurimetric in extent this can lead to gallery collapse with the associated fill by rock fall breccia. This can partly block the river system but always leaves a higher zone of free circulation with high permeabilities of several hundreds of Darcys. These galleries form along the natural fracture system relative to the paleohydraulic gradient which in some cases has been preserved. The zone below permanent ground water level with no circulation of fluids is characterized by dissolution limited to non-connected vugs. Very locally these fissures can be enlarged by tectonic fractures which are non-connected and unimportant for reservoir drainage. Laterally, only the uppermost zone can be resolved by seismic imaging linked with horizontal well data (the wells are located at the top of the percolation zone). The Rospo Mare reservoir shows three distinct horizontal zones: a relict paleokarst plateau with a high index of open connected fractures, (area around the A and B platforms); a zone bordering the plateau (to the north-east of the plateau zone) very karstified but intensely infilled by cap rock shales (Miocene - Oligocene age); a zone of intensely disturbed and irregular karst paleotopography which has been totally infilled by shales. The performance of the production wells is dependent on their position with respect to the three zones noted above and their distance from local irregularities in the karst paleotopography (dolines, paleovalleys)

Contribution to geomorphological and hydrogeological study of karst in Mediterranean environment: the Aït Abdi plateau (central limestone High Atlas, Maroc),PhD thesis, 1995, Perritaz, L.

The Ait Abdi karstic plateau is located in the heart of the calcareous High Atlas (32°N/6°W). With an area of 160 km2, it is situated between 2,200 and 3,000 meters above sea level, i.e. 800 meters above the nearest valleys and canyons. It consists of a large series of massive Bajocian limestones which form a large brachysyncline, the axial plane of which dips gently to the NE. These limestones overlie a thick series of Toarcian-Aalenian detritic sediments forming the regional aquiclude and the top of the half captive Middle Liasic aquifer. The plateau is limited both in the N and S by strong changes in dip to the vertical of the sedimentary layers (ejective thrusted anticlines), and in the W and E by deep canyons created by major rivers. Therefore the plateau is a totally isolated calcareous compartment, from both a morphologic and a hydrogeologic point of view.
The climate of this region is Mediterranean with an altitude modification: maximum rainfall occurs in winter and in spring, snow cover is not durable but sometimes important, storms are common for dry season in summer. The precipitations comprise only 500 to 700 mm/year (subhumide zone) and the effective evapotranspiration is approximately 400 mm/year, including the losses due to sublimation. The snow coefficient is 60 %. This means that the recharge of the aquifer, occurring almost entirely during snow melting, is limited, but the large bare surfaces of the plateau with typical well developed karst forms (dolines, poljes, dry valleys, holes) improve the infiltration rate (40%). The specific discharge is only 8.1 L/s/km2.
The morphologic peculiarity of this nival karst consist of a succession of small parallel and asymmetric dry valleys forming some "waves". For that reason, the French geomorphologist Couvreur termed these climate controlled features "karst en vagues". The role of wind and snow in the genesis of these forms is predominant. The most of time structure controlled plateau's poljes are quasi inactive today. All kinds of high mountain karren landforms are present on the plateau and prove the great role of snow role in the microforms genesis.
An ancient speleological network with vertical shafts occluded lower down suggest of ancient more humid climatic conditions. U-Th dating indicates ages between 3,200 and 220,000 years, or outside the range of the method (more than 400,000 years). The lateral flow is conducted by an interstrata network, inactive and dry in the upper part, or active and phreatic at the base, near the regional aquiclude, attesting three karstification phases.
The water discharges as typically karstic hillfoot springs, most of the time oversaturated and forming tufas. Large doleritic vertical dykes cut the plateau and form major drainpipes. The physical-chemical and chemical signature of these spring waters is quite different of the signature of other springs of this area, which discharge whether from small local Toarcian-Aalenian aquifers or from the huge semi confined karstic Middle Liasic aquifer. The plateau springs hydrodynamic response is characteristic for an elevated karstic aquifer with rapid flow. The aquifer geometry does not allow important reserves, but the mean discharge from all perennial springs (about 1 m3/s) is a precious resource for the population of this far area of the Atlas Mountains.


Weathering crust and karren on exposed gypsum surfaces., 1996, Macaluso Tommaso, Sauro Ugo
The evolution of gypsum bare rock surfaces is the result both of changes of the outer rock layer and mass wasting by dissolutional processes. Some unusual weathering processes induce an increase in the of the outer gypsum layer, resulting in the development of a "weathering crust" and of characteristic forms such as small ridges and bubbles. However, the more typical erosional forms are dissolutional ones of karren type, which are commonly interconnected, or superimposed upon the previously described forms. In this chapter a classification system is proposed and discussed, within which the magnitude, order and geometry of the different karren forms are outlined, and the related lithofacies and main morphogenetic processes are examined.

Numerical multisource and multiscale imagery in the study of the topographic surface. Hydrogeological application in a karstic environment: Verneuil-sur-Avre (Perche, France), 1996, Sykioti O. , Deffontaines B. , Chorowicz J. , Obert D. , Demarsily G. , Lauverjat J. , Carvalho J. ,
We propose a new method revealing geological structures and their possible relationships with water percolation. It is based on a combination of (1) numerical analysis of the topography (satellite imagery Landsat TM, HCMM, SAR-ERS1; digital elevation model and derived data: drainage network, slope map, summit level surfaces...); (2) classic geological approach (field work, geological mapping, gravimetry); and (3) hydrogeological approach (piezometric map, tracer experiments). The superimposition of these data into a geocoded data base leads to the identification and the location of morphostructures (synthetic structural map). Field data and tracer experiments confirm the validity of the results. We propose to take into consideration the present day stress regime in order to define main orientations of open fractures. In conclusion, this method provides structural information allowing a better understanding of geometry in karstic aquifers

Statistical evaluation of glacier boreholes as indicators of basal drainage systems, 1996, Smart C. C. ,
Between 1988 and 1992 closely spaced arrays of boreholes were drilled at Small River Glacier, British Columbia. The borehole arrays have been used to investigate the interannual and spatial consistency of patterns of basal hydraulics beneath the glacier. A simple robust classification was devised identifying unconnected, high standing, low standing and dry base water levels in boreholes. Spatial and interannual comparisons were made using a simple nearest neighbour statistic, corrected for differences in frequency of different borehole types and evaluated using Monte Carlo confidence intervals to compensate for array form. Arrays in the lower ablation zone showed spatial and interannual coherence, with three distinct areas characterized by low water pressure, till-associated non-connection and high pressure. There was no indication of a dominant conduit. Slightly higher up-glacier borehole patterns were less coherent, and varied from year to year, probably a result of subglacial karst capturing basal waters at a number of low pressure points at the bed. Therefore both the upper and lower arrays at Small River Glacier appear to encompass unusual drainage conditions. The nearest neighbour analysis provides valuable constraints on more specific interpretation

Morphological affinities of the proximal ulna from Klasies River main site: Archaic or modern?, 1996, Churchill Se, Pearson Om, Grine Fe, Trinkaus E, Holliday Tw,
The Middle Stone Age (MSA) asociated hominids from Klasies River Mouth (KRM) have taken on a key role in debate about the origins of modern humans, with their craniofacial remains seen as either representing the earliest well-dated modern humans in southern Africa or orthognathic late archaic humans. Diagnostic postcranial remains from Klasies are few, but one specimen-a proximal right ulna from the lower SAS member-is useful For assessing the morphological affinities of these hominids. Canonical variates analysis using 14 proximal ulnar dimensions and comparative data from European, west Asian and African archaic humans, and Levantine Mousterian, European Upper Paleolithic, African Epipaleolithic and diverse recent modern human samples (many of recent African descent) were employed to assess the morphological affinities of this specimen. Results suggest an archaic total morphological pattern for the Klasies ulna. Analysis of diaphyseal cross-sectional geometry reveals an ulnar shaft with relatively thick cortical bone, but the specimen cannot be readily distinguished from Neandertals or early anatomically modem humans on the basis of shaft cross-sectional properties. If the isolated ulna from Klasies is indicative of the general postcranial morphology of these hominids, then the MSA-associated humans from KRM may not be as modern as has been claimed from the craniofacial material. It ii: possible also that the skeletal material from KRM reflects mosaic evolution-retention of archaic postcranial characteristics. perhaps indicating retention of archaic habitual behavior patterns, in hominids that were becoming craniofacially modern. (C) 1996 Academic Press Limited

Structure et comportement hydraulique des aquifers karstiques, DSc thesis, 1996, Jeannin, P. Y.

This thesis aims to provide a better knowledge of karst flow systems, from a functional point of view (behaviour with time), as well as from a structural one (behaviour in space). The first part of the thesis deals with the hydrodynamic behaviour of karst systems, and the second part with the geometry of karstic networks, which is a strong conditioning factor for the hydrodynamic behaviour.
Many models have been developed in the past for describing the hydrodynamic behaviour of karst hydrogeological systems. They usually aim to provide a tool to extrapolate, in time and/or space, some characteristics of the flow fields, which can only be measured at a few points. Such models often provide a new understanding of the systems, beyond what can be observed directly in the field. Only special field measurements can verify such hypotheses based on numerical models. This is an significant part of this work. For this purpose, two experimental sites have been equipped and measured: Bure site or Milandrine, Ajoie, Switzerland, and Holloch site, Muotathal, Schwyz, Switzerland. These sites gave us this opportunity of simultaneously observe hydrodynamic parameters within the conduit network and, in drillholes, the "low permeability volumes" (LPV) surrounding the conduits.
These observations clearly show the existence of a flow circulation across the low permeability volumes. This flow may represent about 50% of the infiltrated water in the Bure test-field. The epikarst appears to play an important role into the allotment of the infiltrated waters: Part of the infiltrated water is stored at the bottom of the epikarst and slowly flows through the low permeability volumes (LPV) contributing to base flow. When infiltration is significant enough the other part of the water exceeds the storage capacity and flows quickly into the conduit network (quick flow).
For the phreatic zone, observations and models show that the following scheme is adequate to describe the flow behaviour: a network of high permeability conduits, of tow volume, leading to the spring, is surrounded by a large volume of low permeability fissured rock (LPV), which is hydraulically connected to the conduits. Due to the strong difference in hydraulic conductivity between conduits and LPV, hydraulic heads and their variations in time and space are strongly heterogeneous. This makes the use of piezometric maps in karst very questionable.
Flow in LPV can be considered as similar to flow in fractured rocks (laminar flow within joints and joints intersections). At a catchment scale, they can be effectively considered as an equivalent porous media with a hydraulic conductivity of about 10-6 to 10-7 m/s.
Flow in conduits is turbulent and loss of head has to be calculated with appropriate formulas, if wanting any quantitative results. Our observations permitted us to determine the turbulent hydraulic conductivity of some simple karst conduits (k', turbulent flow), which ranges from 0.2 to 11 m/s. Examples also show that the structure of the conduit network plays a significant role on the spatial distribution of hydraulic heads. Particularity hydraulic transmissivity of the aquifer varies with respect to hydrological conditions, because of the presence of overflow conduits located within the epiphreatic zone. This makes the relation between head and discharge not quadratic as would be expected from a (too) simple model (with only one single conduit). The model applied to the downstream part of Holloch is a good illustration of this phenomena.
The flow velocity strongly varies along the length of karst conduits, as shown by tracer experiments. Also, changes in the conduit cross-section produce changes in the (tow velocity profile. Such heterogeneous flow-field plays a significant role in the shape of the breakthrough curves of tracer experiments. It is empirically demonstrated that conduit enlargements induce retardation of the breakthrough curve. If there are several enlargements one after the other, an increase of the apparent dispersivity will result, although no diffusion with the rock matrix or immobile water is present. This produces a scale effect (increase of the apparent dispersivity with observation scale). Such observations can easily be simulated by deterministic and/or black box models.
The structure of karst conduit networks, especially within the phreatic zone, plays an important role not only on the spatial distribution of the hydraulic heads in the conduits themselves, but in the LPV as well. Study of the network geometry is therefore useful for assessing the shape of the flow systems. We further suggest that any hydrogeological study aiming to assess the major characteristics of a flow system should start with a preliminary estimation of the conduit network geometry. Theories and examples presented show that the geometry of karst conduits mainly depends on boundary conditions and the permeability field at the initial stage of the karst genesis. The most significant boundary conditions are: the geometry of the impervious boundaries, infiltration and exfiltration conditions (spring). The initial permeability field is mainly determined by discontinuities (fractures and bedding planes). Today's knowledge allows us to approximate the geometry of a karst network by studying these parameters (impervious boundaries, infiltration, exfiltration, discontinuity field). Analogs and recently developed numerical models help to qualitatively evaluate the sensitivity of the geometry to these parameters. Within the near future, new numerical tools will be developed and will help more closely to address this difficult problem. This development will only be possible if speleological networks can be sufficiently explored and used to calibrate models. Images provided by speleologists to date are and will for a long time be the only data which can adequately portray the conduit networks in karst systems. This is helpful to hydrogeologists. The reason that we present the example of the Lake Thun karst system is that it illustrates the geometry of such conduits networks. Unfortunately, these networks are three-dimensional and their visualisation on paper (2 dimensions) is very restrictive, when compared to more effective 3-D views we can create with computers. As an alternative to deterministic models of speleogenesis, fractal and/or random walk models could be employed.


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