Karst Depressions Research Articles

Surface hydrology and soil movement in an arid karst: the Nullarbor Plain, Australia

The Nullarbor Plain is the largest karst area in Australia (220,000 km2) and one of the largest in the world. Its climate is arid (Koppen BWk and BWh), and the surface relief is less than 10m. The landscape is divided into extensive closed karstic depressions separated by low rocky ridges, and the dominant vegetation is chenopod shrubland. The extent and severity of soil degradation has been assessed using remote sensing. GPS rectified images from 1972–1973, 1979, 1983, 1988, and 1991 have been compared for two sites on the Nullarbor. Over the 19 years the total extent of bare soil has reduced significantly, but some areas around water points have degraded and there is some disturbance due to fossorial wombats. Sheet-flow processes occur during intense rainfall events, which happen two or three times per decade. Runoff only occurs after the 10− or 50− year return frequency events, and at these times turbid water ponds in depressions and enters caves. Surface soil sorptivity and hydraulic conductivity differ markedly between ridges and depressions; the ridges are clearly zones of groundwater recharge, while ponding is evident in most depressions. Sorptivity is influenced by the extent and nature of ground cover and cryptogam crusts on the soil. The landscape has been divided into classes on the basis of vegetation type and percentage of foliage cover. In each class the activities of fallout radionuclides will be determined by high resolutionγ spectroscopy. Preliminary results suggest that in undisturbed sites little sediment movement has occurred over the time scale of cesium-137 (the last 35 years) but that the landscape has been well sorted over a much longer time scale. Future work will investigate disturbed sites to estimate relative soil loss during the pastoral period.

Exploration and Development of Ground Water from the Stone Forest Karst Aquifers of South China

AbstractStone forest aquifers are the most widely exploited sources for ground water in the vast south China karst belt. These aquifers occupy a thin epikarst zone that has been infilled with clastic sediments. The aquifers are characterized by large lateral permeabilities and small reservoir capacities owing to their thinness. The carbonate rocks which comprise the framework for the aquifers are usually buried under the karst plains and large karst depressions where development is desired.The stone forest aquifer exploration procedure must first locate saturated zones. Second, those parts of the saturated zone having the greatest dissolution porosity must be identified because the infilled dissolution voids contain the water.The best indicators of saturation include the combination of low topography and the presence of active karst features such as springs, karst windows (natural openings exposing the water table), and live surface streams. These elements are readily observed on intermediate scale (1:20,000) aerial photography.The depth and degree of carbonate dissolution porosity is a function of several geologic and hydrologic factors including carbonate rock type, carbonate purity, fracture density, specific discharge, age of the circulation system, etc. These variables cannot be measured directly because the carbonate rocks are usually buried under a thin mantle of clastic sediments. However, if it is recognized that the ground‐water system has already exploited the most favorable geology and that dissolution is an ongoing process, a simple indirect method can be used to identify the areas having the greatest porosity. The presence of karst depressions and recent sinkholes are indicative of the most intensely karstified and hydraulically active parts of the epikarst zone. Mapping of these surface features from stereo aerial photography is a simple geomorphology exercise that can be used to directly identify the most favorable well sites.Current well construction practices in the south China karst belt involve both dug and drilled wells. Dug wells are preferred in many locations owing to both cost‐effectiveness associated with cheap labor and lack of available drilling equipment. The dug wells look and function identically to karst windows and thus conform to timeless water use traditions in the region.

Hydrogeologie Characteristics and Deforestation of the Stone Forest Karst Aquifers of South China

AbstractStone forest aquifers comprise an important class of shallow, unconfined karstic aquifers in the south China karst belt. They occur under flat areas such as floors of karst depressions, stream valleys, and karst plains. The frameworks for the aquifers are the undissolved carbonate spires and ribs in epikarst zones developed on carbonate strata. The ground water occurs within clastic sediments which infill the dissolution voids.The aquifers are thin, generally less than 100 meters thick, and are characterized by large lateral permeabilities and small storage. The result is that the aquifers are difficult to manage because recharge during the rainy season moves rapidly out of the aquifers. Water levels fall sharply as the dry season progresses and the ground‐water supply falls off accordingly.The magnitude and duration of the seasonal recharge pulse that replenishes the stone forest aquifers have been severely impacted by massive post‐1958 deforestation in the south China karst region. Water that was formerly retained beyond the wet season in the forested uplands, later to be released to the stone forest aquifers under the lowland plains, now passes quickly through the system during the wet season. The loss of this seasonal upland storage has resulted in both a reduction in the volume of recharge to the lowland stone forest aquifers and a shortening of the seasonal recharge event. The result is accelerated water‐level declines in the stone forest aquifers as the dry season progresses which, in turn, causes premature dewatering of wells and decreased spring discharges. This response is compounded by increased ground‐water withdrawals as the people attempt to offset the declining supply. Management of the total water‐supply system requires not only tinkering with the aquifer, but massive reforestation efforts to restore dry season water retention in the upland parts of the watersheds.

Contribution to the geochemistry of the rare earth elements in the karst-bauxite deposits of Yugoslavia and Greece

Distribution of the rare earth elements (REE, including La-Lu, Y) along vertical profiles is presented for four well-studied karst-bauxite deposits from Yugoslavia and Greece. For one deposit from Jamaica, La and Y contents are given. All deposits a downward enrichment of the REE culminating at the base, where authigenic REE minerals have been formed. This REE pattern is characteristic for karst-bauxites formed in situ through the bauxitization of argillaceous material collected in karstic depressions. In this way, the highest enrichment of the REE in the sedimentary cycle has been achieved. Both light REE (LREE) and heavy REE (HREE) were “mobile” during the bauxitization process and were concentrated at the alkaline barrier of the carbonate footwall. In four out of five studied deposits, the ratios ΣLRE/ΣHREE and La/Y in bauxites decrease downwards, showing an enrichment of the HREE relative to LREE. A further fractionation of the REE took place in the formation of authigenic REE minerals, which exhibit a very high enrichment of LREE relative to HREE. In spite of this, these minerals and bauxites in four studied deposits have a general similarity of the REE distribution patterns, which indicate a close genetic relationship.

Late Neogene sequence stratigraphy of a carbonate-siliciclastic transition: Southwest Florida

A network of high-resolution seismic profiles and 23 lithologically and/or geophysically logged boreholes have been analyzed in order to evaluate the effects of sea-level cyclicity, karstification, and an intercalated, carbonate to siliciclastic transition on the late Miocene to Quaternary stratigraphy of the Charlotte Harbor area in southwest Florida. Six late Neogene disconformity-bounded depositional sequences are identified between two regional unconformities. The lower regional unconformity (R-3) varies from about 20 m to more than 115 m below sea level. The lows are present as northwest-southeast- and northeast-southwest-trending troughs, and the high areas as sharp, irregular reflections and isolated sinkholes indicative of subaerial exposure. The R-2 unconformity, which overlies and truncates the late Neogene sequences, occurs as a strong, flat-lying reflector seaward of the present coastline and a series of downcutting channel complexes in back-barrier areas. The six depositional sequences prograde to the south-southeast with a proximal-distal transition from short, steeply dipping oblique clinoforms to long, low-angle clinoforms. Three lithofacies, which generally occur in a vertical sequence, are (from the bottom up) (1) quartz-dominated sand with phosphate sand and gravel; (2) calcareous clays; and (3) poorly indurated to well-indurated, sandy, molluscan calcirudite. The pebbley sand facies are transgressive lags gradationally overlain by prograding, laminated clays deposited in an estuarine to prodelta shoreface environment. The calcirudite transitionally overlies the clay facies and was deposited in a shallow subtidal to subaerial chenier-like setting which may be indurated and/or indicate subaerial exposure and may form the base of another sequence. The karstified antecedent topography has controlled the distribution of the depositional sequences in two ways. First, fluvial systems are localized in the antecedent lows, which restricts the distribution of fluvially transported sands. Second, the relatively impermeable clays, which occur as thin beds outside the lows, thicken to 20-40 m within the karstic depressions. The clay deposits limit vertical drainage and initiate the development of fluvial systems on the carbonate terrain. The sequences were deposited during the late Miocene Tortonian Stage, which is increasingly viewed as a time of high-frequency, glacio-eustatic sea-level fluctuations. Although high-resolution chronostratigraphic data are not available, the sequences contain thin and/or poorly preserved transgressive sands, overlain by prograding regressive sediments, and they represent discrete sea-level cycles. A regional pattern of karstic dissolution has controlled the transition by localizing deposition of impermeable prodelta clays and the developing paleo-fluvial system. The introduction of quartz sand into the carbonate terrain was, in turn, controlled by the karstic relief and a localized sediment supply derived from the paleo-fluvial systems.

Karstification and pedogenesis on a late Dinantian carbonate platform, Anglesey, North Wales

SUMMARY The late Dinantian (Lower Carboniferous) carbonate succession on Anglesey, North Wales, comprises over 20 transgressive/regressive shoaling upwards cycles. Cycle tops are marked by distinctive hummocky surfaces, interpreted as palaeokarstic, commonly overlain by green bentonitic clay palaeosols with fossil rootlets, and locally by red terra-rossa clays. Limestones immediately below the karstic surfaces display structures and fabrics typical of calcretes, including rhizoliths, calcrete ooids, micrite pellets, micritised grains and micritic vadose cements. These pedogenically altered limestones are commonly capped by laminar calcrete crusts of accretionary origin. The effects of contemporary brecciation and growth of microspar further contribute to a variety of emergent profiles developed at minor cycle tops. Profile development was in two stages. During the early syn-lithification stage, closely following emergence, plants and soil-dwelling faunas colonised unconsolidated platform carbonates. Micritic coatings and cements were deposited and wind-blown volcanic fines accumulated at the surface. During the ensuing post-lithification stage, roots and downward percolating rain waters could no longer penetrate the underlying case-hardened carbonates. Micrite was deposited as sheets at the soil/rock interface, building laminated crusts rich in rhizoliths, whereas elsewhere, or at other times, sub-soil dissolution led to the formation of the characteristic karstic morphology. Preferential dissolution within broad karstic depressions generated localised pockets of reddened insoluble residues. Brecciation re-exposed lower parts of some profiles to secondary phases of calcretisation and, with concomitant dissolution and downward infiltration of clay palaeosol material, created deep, regolith-like rubbly profiles within which there was extensive replacive and displacive growth of microspar.

Murettes et terrasses de culture dans les régions karstiques méditerranéennes

Stone-walls and land-terraces in the mediterranean karst areas. After analysis on the functions of stone-walls and terraces, the paper show many types of agrarian arrangement in limestone slopes and table-land, in rapport with the quality of soils, and in little karst depressions. They make up «agro-karstic landscapes». In the dolines and uvalas particularly, the contouring and removal of blocks give «anthropo-geomorphological forms». This researches are continued in the outline of I.G.U. Study Group on «Man's impact in Karst», now «Environmental Changes in Karst Areas».

Quaternary stratigraphy of the Charlotte Harbor estuarine-lagoon system, southwest Florida: Implications of the carbonate-siliciclastic transition

Charlotte Harbor is a complex lagoon and estuarine system in southwestern peninsular Florida that is underlain by Tertiary carbonates and Quaternary siliciclastic sedimentary sequences. High-resolution seismic profiling, vibracores, and sediment samples from modern environments have been used to interpret the Quaternary stratigraphy and evolution of this system. The underlying Tertiary carbonates have undergone extensive dissolution and collapse which has created isolated karst depressions and fracture-controlled, elongated troughs. Although late Neogene deposition infilled most of the pre-Quaternary relief, the Quaternary drainage system was controlled by the poorly integrated, vertical drainage of the karstified limestones which is unlike the well-integrated paleofluvial drainage systems of the mid-Atlantic and northern Gulf coastal plains. Despite these differences, paleotopography and sediment availability have controlled locations and sedimentary environments as has been noted in other published studies on purely siliciclastic systems. The distribution of three interpreted Quaternary depositional sequences (fluvial to upper estuarine point bar fining upward sequence (FUS), transitional estuarine sequence and tidal channel-delta FUS) and the mapped distribution of an early-middle Pleistocene seismic unconformity indicate that Quaternary sea-level fluctuations have repeatedly caused coastal systems to migrate through the area, leaving records of at least two Pleistocene barrier-lagoon systems. These systems straddled the infilled karst depressions and were apparently controlled by the availability of erodible sediment that infilled the depressions. The modern barrier system is perched upon one of the Pleistocene barrier platforms which has been preserved as a result of lithification of carbonate-rich inlet-tidal delta deposits. These platforms should preserve the backbarrier deposits from future shoreface incision but localized channelization will cause extensive reworking. Because the paleofluvial channels do not extend offshore, preservation on the inner shelf (> 5–7 km offshore) is limited to isolated karst depressions where Tertiary limestones are exposed.

The genesis of allochthonous karst-type bauxite deposits of Southern Europe

Some Mediterranean bauxite deposits in karst, considered to be allochthonous originating from neighboring silicate rocks, reveal the following common features of fluvial transport and sedimentation: (1) The SiO2 content increases in the direction of the transport; (2) the trace elements indicate the area of origin; (3) the bauxite was deposited in depressions of a slightly karstified coastal plain in a lagoonal or estuarine environment; (4) the karst relief became accentuated after the bauxite was covered by sediments; and (5) the depth of the karstic depressions was controlled by the former groundwater level. Therefore, the thickness of the orebodies increases with the distance from the former shoreline. These factors have an implication on the strategy of exploration. The following examples are taken from central Greece and Montenegro and comparisons are made with the bauxite districts of France, Italy, and Jamaica.

The karst contagion model: Synopsis and environmental implications

The contagion model of karst terrane evolution focuses on the environmental implications for a large karst depression population on the Pennyroyal Plain (southern Kentucky) and the adjacent Western Highland Rim (Tennessee) immediately south of the Mammoth Cave Plateau. In karst terranes where the contagion model applies, there is a well-defined infrastructure comprised of hydrologic, structural geologic and geomorphic interacting elements that result in clustered depressions underlain by a radial conduit system. Clusters tend to be randomly distributed and typically contain a parent depression surrounded by numerous daughters.

Ancient Maya Wetland Agriculture: New Insights from Ecological and Remote Sensing Research

Abstract Despite claims that ancient Maya canals are found throughout the central Maya Lowlands, our study of satellite and aircraft imagery indicates that canals are concentrated in three regions: northern Belize, southern Quintana Roo, Mexico, and along the upper Candelaria River and its tributaries in Campeche, Mexico. Earlier reports of lattices of small canals in the karstic depressions, or bajos, of Peten, Guatemala, based on the analysis of airborne radar imagery, have not been verified with other remote sensing data or by field research. Our analyses of this same airborne imagery and Seasat satellite radar imagery demonstrate that the spatial resolution of, and speckle noise in, existing radar imagery make it inadequate for mapping lattice patterns of small canals. Radar imagery and Landsat Thematic Mapper imagery were, however, useful in mapping large canals, which in most cases are connected to lattices of smaller canals. Furthermore, our analyses of wetland soils, vegetation, and hydrology conf...

TALEMZANE: ALGERIAN IMPACT CRATER DETECTED ON SIR‐A ORBITAL IMAGING RADAR

In November, 1981, NASA's first Shuttle Imaging Radar mission (SIR‐A) began producing maplike photographic strips of Earth scenes from orbital altitude. A Saharan radar image acquired over Algeria clearly delineates two sedimentary basins, Erg Occidental and Erg Oriental, separated by an elongated zone of exposed bedrock, the M'Zab Chebka. At the NE margin of the Chebka, rimrocks, slopes, and ejecta deposits of Talemzane meteorite impact crater appear as a distinct two km wide radar‐bright ring. This unique circle of strong radar backscatter distinguishes the solitary impact structure from numerous dayas (similarly appearing karstic depressions) which characterize the region. The crater is prominant on radar, but is obscure on optically obtained satellite and aircraft images, as are partly buried fluvial drainage systems and fault‐block traces developed in bedrocks of the Chebka. Radar detection of an annular drainage system indicates possible presence of a ring graben at the crater. Brightest radar signals on the image are cultural features at recently developed gas fields near Hassi er R'Mel.

Slope form, erosion, and hydrology in some Belizean Karst depressions

AbstractDetailed slope surveys were made in seven karst depressions in central Belize. Four major slope types were identified—inclined bedrock slopes, staircases, broken cliffs, and talus slopes. Depression bases are dominated by inclined bedrock and talus slopes, midslopes largely by broken cliffs, and near hill summits by staircases. Erosional weight loss tablets deployed in 1975–1981 and 1980–1985 show significant variations between the different slope types, with a maximum near depression bases. Throughfall measurements in 1980 and 1985 show that midslope and near‐summit sites receive 10–20 per cent less water than do depression bases. Surface runoff, monitored using coloured dyes, is of limited distance and duration but still contributes to surface corrosion and morphology. Vadose seepage, monitored by tracing water from the surface to a small, shallow cave, is rapid, and subsurface corrosion exceeds that at the surface.Overall, near‐surface form and process are consistent with hydrological models of depression development (Williams, 1983, 1985) and surface processes contribute significantly to overall depression form. Moreover, surface activity complements that in the subcutaneous zone by directing recharge into the epikarstic aquifer.

Palynostratigraphy and Th/U ages of upper Pleistocene interglacial and interstadial deposits on Cape Breton Island, eastern Canada

Research Article| July 01, 1986 Palynostratigraphy and Th/U ages of upper Pleistocene interglacial and interstadial deposits on Cape Breton Island, eastern Canada A. de Vernal; A. de Vernal 1Laboratoire de Géochimie isotopique et de Geochronologie (GEOTOP), Université du Québec à Montréal, B.P. 8888, succ. A, Montréal, Québec H3C 3P8, Canada Search for other works by this author on: GSW Google Scholar C. Causse; C. Causse 1Laboratoire de Géochimie isotopique et de Geochronologie (GEOTOP), Université du Québec à Montréal, B.P. 8888, succ. A, Montréal, Québec H3C 3P8, Canada4Permanent address: Laboratoire de Geologic du Quaternaire, CNRS Lummy, Case 907, 13288 Marseille Cedex 09, France Search for other works by this author on: GSW Google Scholar C. Hillaire-Marcel; C. Hillaire-Marcel 1Laboratoire de Géochimie isotopique et de Geochronologie (GEOTOP), Université du Québec à Montréal, B.P. 8888, succ. A, Montréal, Québec H3C 3P8, Canada Search for other works by this author on: GSW Google Scholar R. J. Mott; R. J. Mott 2Terrain Science Division, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE6, Canada Search for other works by this author on: GSW Google Scholar S. Occhietti S. Occhietti 3Laboratoire de Géochimie isotopique et de Géochronologie (GEOTOP), Université du Québec a Montréal B.P. 8888, succ. A, Montréal, Quebec H3C 3P8, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information A. de Vernal 1Laboratoire de Géochimie isotopique et de Geochronologie (GEOTOP), Université du Québec à Montréal, B.P. 8888, succ. A, Montréal, Québec H3C 3P8, Canada C. Causse 1Laboratoire de Géochimie isotopique et de Geochronologie (GEOTOP), Université du Québec à Montréal, B.P. 8888, succ. A, Montréal, Québec H3C 3P8, Canada4Permanent address: Laboratoire de Geologic du Quaternaire, CNRS Lummy, Case 907, 13288 Marseille Cedex 09, France C. Hillaire-Marcel 1Laboratoire de Géochimie isotopique et de Geochronologie (GEOTOP), Université du Québec à Montréal, B.P. 8888, succ. A, Montréal, Québec H3C 3P8, Canada R. J. Mott 2Terrain Science Division, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE6, Canada S. Occhietti 3Laboratoire de Géochimie isotopique et de Géochronologie (GEOTOP), Université du Québec a Montréal B.P. 8888, succ. A, Montréal, Quebec H3C 3P8, Canada Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1986) 14 (7): 554–557. https://doi.org/10.1130/0091-7613(1986)14<554:PATAOU>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. de Vernal, C. Causse, C. Hillaire-Marcel, R. J. Mott, S. Occhietti; Palynostratigraphy and Th/U ages of upper Pleistocene interglacial and interstadial deposits on Cape Breton Island, eastern Canada. Geology 1986;; 14 (7): 554–557. doi: https://doi.org/10.1130/0091-7613(1986)14<554:PATAOU>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 SocietyGeology Search Advanced Search Abstract On Cape Breton Island (Nova Scotia), near the margin of the Wisconsinan ice sheet, karst depressions in Mississippian gypsum-bearing rocks contain interglacial and interstadial organic-rich deposits. Three palynostratigraphic units have been observed and tentatively dated by Th/U measurements on embedded fossil wood. The first, dated at ca. 125 ka, may be assigned to the oceanic 18O substage 5e; thermophilous forests (Quercus, Ostrya, Pinus strobus) developed in response to a climate warmer than the present. The second unit, rich in Abies balsamea pollen and dated at ca. 87 ka, may relate to the 18O substage 5a; it reflects a cool and wet climate not unlike that of today. The third unit probably spans part of the mid-Wisconsinan (18O stage 3); it shows alternating boreal forest-tundra forest assemblages indicative of climatic oscillations during a generally cold interval. 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.

Exploring a contagion model for karst-terrane evolution

Theoretical and geomorphic implications of a contagion model of karst depression and initiation are explored with particular emphasis on (1) identifying parent versus daughter depression subpopulations; (2) analyzing spatial characteristics of each subpopulation; and (3) defining the contagious karst mechanism and how it is transmitted along solution-enlarged joints. The contagious karst mechanism suggests that the presence of one or more parent depressions increases the probability of daughter depressions developing along solution-enlarged joints that radiate outward from beneath parent depressions. In karst terranes where the contagion model applies, there is a well-defined infrastructure with several important elements. Interaction among elements of the infrastructure (hydrologic, structural geologic, and geomorphic) result in clustered depressions. Clusters tend to be randomly distributed and consist typically of a centrally located parent depression surrounded by numerous daughter depressions.

Origin of Red Clay over Dolomite in the Loess‐Covered Wisconsin Driftless Uplands

AbstractRed clays associated with Prairie du Chien and Sinnipee (Galena) dolomites and loess were studied stratigraphically and geomorphically at 10 locations. The clay content (&lt; 2 µm, 82 ± 9.1%; &lt; 0.2 µm, 70 ± 10.4%, n = 15) relative to the overlying loess (&lt; 2 µm, 28 ± 4.4%; &lt; 0.2 µm, 16 ± 4.9, n = 4) and the dolomite insolubles (&lt; 2 µm, 47 ± 11%; &lt; 0.2 µm, 34 ± 9.6%, n = 7) indicate fine clay enrichment. Smectite‐rich oriented clay coatings on dolomite sands suggest illuviation. Undisturbed chertlines from dolomite through red clay bodies necessitate a volume‐for‐volume replacement. Periglacial activity during the Wisconsinan frequently produced loess (i), over a mixed zone of loess and red clay (ii), over in‐situ red clay (iii), and dolomite (iv). For the 1‐to 10µm quartz; euhedral grains indicated by x‐ray diffraction I(100)/(101) = 0.23, 0.54, 1.02, 0.70, respectively; nine trace element contents = 2.15 ± 0.40, 1.61 ± 0.18, 0.78 ± 0.10 relative to dolomite (1.0); and oxygen isotopes expressed as δ18O = 18.6, 19.7, 26.9, 26.4%. The values for the mixed zone (ii) fall between those for the loess (i) and insitu red clay (iii). Optical data for the morphology of the fine sand fractions (50–250 µm) were corroborative. The silt and sand of in‐situ red clay (protected in karst depressions and by chert lag gravels) are from the dolomite.

Doline Morphology and Development in Barbados

ABSTRACT In Barbados, dolines developed on an uplifted series of raised reef terraces provide a unique opportunity to investigate the long-term formation and change of karstic depressions. In a 124.5 km2 area, 1179 dolines were located and 360 surveyed. Dolines occupy only about 1 percent of the total area. There are spatial controls on doline development, but dolines in areas of different elevation and age differ from one another in a way that suggests sequential development. Doline densities increase up to an altitude of 150 m and decline thereabove. Distributions indicate clustering, but there is little evidence of structural controls producing preferred long-axis orientation. Doline and dry valley development is competitive, and there are two doline subpopulations: a larger one in interfluve areas and a smaller one in valleys. Doline complexes develop through time partly by expansion, interference, and coalescence and partly by subdivision.

Quaternary interglacial and associated deposits in southwest Newfoundland

A coastal cliff section near Codroy, Newfoundland exposes five distinctive lithologic units, which are defined lithologically and structurally as colluvial, lacustrine, or glacial in origin. They have been preserved in a gypsum karst depression, but continuing karst evolution has disturbed their original attitudes.The two oldest units, 5 and 4, were formed by sidewall slumping of local bedrock and earlier glacial material from the failing rim of a newly formed sinkhole. Unit 3 represents tranquil sedimentation of thin sand and silt–clay laminae, first in a freshwater sinkhole pond, then in brackish marine waters that entered after breaching of its seaward wall, and finally again in fresh water as sea level fell below the sill of the small embayment. Units 2 and 1 are glacial deposits laid down over older units after a second major sinkhole collapse. Collapse has continued to the present day.Pollen and spores from unit 3 indicate that during its deposition regional vegetation changed from tundra (Zone A) to boreal forest (Zone B), and back to tundra (Zone C), through an interglacial cycle of vegetation change. Balsam fir wood from Zone B is radiocarbon-dated to &gt; 40 000 BP (I-10203).Foraminifera from unit 3 indicate that brackish marine conditions prevailed before Zone B times, and that nearshore fully marine conditions briefly prevailed in Zone B times. Zone B is thus assigned full interglacial status, based on pollen and foraminiferal evidence, and is tentatively assigned to the Sangamonian for want of indications to the contrary and for economy of interpretation. The overlying glaciogenic units 1 and 2 are thus probably of early Wisconsinan age.Calcite crystals, possibly pseudomorphous, found within Zone B of unit 3, were radiocarbon-dated at 30 000 ± 1450 BP (UQ-115). δ18O values of −6.8 to −7.5‰ (versus PDB) indicate replacement by calcite under conditions similar to present. δ13C values of −24.00 to −26.24‰ (versus PDB) indicate that carbonate carbon was supplied by decay of local organic matter. The date is thus a minimum and supports the contention that the sediments are of at least last interglacial age.Gypsum karst has thus been evolving in this area since before the last interglacial and has preserved a record of environmental change for that period that is unique in the Atlantic Provinces of Canada. Unit 3 is proposed as the stratotype for the "Codroy Interglacial Beds" (new name).

Spatial analysis of a karst depression population: Clues to genesis

A detailed analysis of depression spatial distribution on the parts of the Western Highland Rim and Pennyroyal Plain underlain by the St. Louis and Ste. Genevieve Limestones indicates the presence of a depression infrastructure. The major geomorphic elements of the infrastructure include depression density (no./km 2 ), doline swallet order, and interdoline spacing. A multigenerational diffusion and competition process model best explained: (1) the presence of two lognormally distibuted depression density subpopulations; (2) discrete, clustered depression sets containing second-order swallet dolines surrounded by first-order swallet depressions; (3) geomorphic competition between adjacent second-order swallet dolines for runoff and catchment area; and (4) a positive correlation between interdoline rim spacings of the small swallet order and the sum of their respective major axial lengths.

Hydrological processes in karst depressions

Hydrological processes in karst depressions