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Most concepts of conduit development have focused on telogenetic karst aquifers, where low matrix permeability focuses flow and dissolution along joints, fractures, and bedding planes. However, conduits also exist in eogenetic karst aquifers, despite high matrix permeability which accounts for a significant component of flow. This study investigates dissolution within a 6-km long conduit system in the eogenetic Upper Floridan aquifer of north-central Florida that begins with a continuous source of allogenic recharge at the Santa Fe River Sink and discharges from a first-magnitude spring at the Santa Fe River Rise. Three sources of water to the conduit include the allogenic recharge, diffuse recharge through epikarst, and mineralized water upwelling from depth. Results of sampling and inverse modeling using PHREEQC suggest that dissolution within the conduit is episodic, occurring only during 30% of 16 sampling times between March 2003 and April 2007. During low flow conditions, carbonate saturated water flows from the matrix to the conduit, restricting contact between undersaturated allogenic water with the conduit wall. When gradients reverse during high flow conditions, undersaturated allogenic recharge enters the matrix. During these limited periods, estimates of dissolution within the conduit suggest wall retreat averages about 4 × 10−6 m/day, in agreement with upper estimates of maximum wall retreat for telogenetic karst. Because dissolution is episodic, time-averaged dissolution rates in the sink-rise system results in a wall retreat rate of about 7 × 10−7 m/day, which is at the lower end of wall retreat for telogenetic karst. Because of the high permeability matrix, conduits in eogenetic karst thus enlarge not just at the walls of fractures or pre-existing conduits such as those in telogenetic karst, but also may produce a friable halo surrounding the conduits that may be removed by additional mechanical processes. These observations stress the importance of matrix permeability in eogenetic karst and suggest new concepts may be necessary to describe how conduits develop within these porous rocks.
Anomalous behaviour of specific electrical conductivity (SEC) was observed at a karst spring in Slovenia during 26 high-flow events in an 18-month monitoring period. A conceptual model explaining this anomalous SEC variability is presented and reproduced by numerical modelling, and the practical relevance for source protection zoning is discussed. After storm rainfall, discharge increases rapidly, which is typical for karst springs. SEC displays a first maximum during the rising limb of the spring hydrograph, followed by a minimum indicating the arrival of freshly infiltrated water, often confirmed by increased levels of total organic carbon (TOC). The anomalous behaviour starts after this SEC minimum, when SEC rises again and remains elevated during the entire high-flow period, typically 20–40 µS/cm above the baseflow value. This is explained by variable catchment boundaries: When the water level in the aquifer rises, the catchment expands, incorporating zones of groundwater with higher SEC, caused by higher unsaturated zone thickness and subtle lithologic changes. This conceptual model has been checked by numerical investigations. A generalized finite-difference model including high-conductivity cells representing the conduit network (“discrete-continuum approach”) was set up to simulate the observed behaviour of the karst system. The model reproduces the shifting groundwater divide and the nearly simultaneous increase of discharge and SEC during high-flow periods. The observed behaviour is relevant for groundwater source protection zoning, which requires reliable delineation of catchment areas. Anomalous behaviour of SEC can point to variable catchment boundaries that can be checked by tracer tests during different hydrologic conditions.
Unusual speleothems resembling giant mushrooms occur in Cueva Grande de Santa
Catalina, Cuba. Although these mineral buildups are considered a natural heritage, their
composition and formation mechanism remain poorly understood. Here we characterize
their morphology and mineralogy and present a model for their genesis. We propose that
the mushrooms, which are mainly comprised of calcite and aragonite, formed during four
different phases within an evolving cave environment. The stipe of the mushroom is an
assemblage of three well-known speleothems: a stalagmite surrounded by calcite rafts
that were subsequently encrusted by cave clouds (mammillaries). More peculiar is the
cap of the mushroom, which is morphologically similar to cerebroid stromatolites and
thrombolites of microbial origin occurring in marine environments. Scanning electron
microscopy (SEM) investigations of this last unit revealed the presence of fossilized
extracellular polymeric substances (EPS)—the constituents of biofilms and microbial
mats. These organic microstructures are mineralized with Ca-carbonate, suggesting that
the mushroom cap formed through a microbially-influenced mineralization process. The
existence of cerebroid Ca-carbonate buildups forming in dark caves (i.e., in the absence
of phototrophs) has interesting implications for the study of fossil microbialites preserved
in ancient rocks, which are today considered as one of the earliest evidence for life on
Earth.
The historical study of Australian caves and caving areas is fascinating although involving the expenditure of vast amounts of time. Australia's early days are unusually well-documented, but in the case of caves the early history is usually wrapped up in rumour, hearsay and clouded by lack of written record. Most research work means long hours poring over old newspaper files, mine reports, land department records and so on, little of which is catalogued. A small number of exploration journals and scientific studies have extensive material on special cave areas, and of these, the volume by Rev. Julian Edmund Woods, F.G.S., F.R.S.V., F.P.S., etc., and is one of the most interesting. This book gives the ideas and beliefs of 100 years ago concerning the origin, development and bone contents of caves and makes interesting reading in the light of more recent studies of cave origins. Wood's study "Geological Observations in South Australia : Principally in the District South-East of Adelaide" was published in 1862 by Longman, Green, Roberts and Green, London. In a preface dated November 15, 1861, Rev. Woods points out that the book was written while he was serving as a missionary in a 22,000 square mile district, and "without the benefit of reference, museum, library, or scientific men closer than England". Up to the time of writing, almost no scientific or geological work had been done in South Australia and much of the area was completely unexplored. The book, also, contained the first detailed description of caves in the south-east of the state. Father Woods writes about many different types of caves in South Australia, for instance, the "native wells" in the Mt. Gambier/Mt. Shanck area. These are caves, rounded like pipes, and generally leading to water level. Woods points out their likeness to artificial wells. He also writes of sea cliff caves, particularly in the Guichen Bay area, and blow holes caused by the action of the waves on the limestone cliffs. Woods discusses many other types of caves found further inland, particularly bone caves. Father Woods discusses cave origins under two sub-heads: 1. Trap rock caves generally resulting from violent igneous action, and 2. Limestone caves resulting from infiltration of some kind. He is mainly concerned with limestone caves which he sub-divides into (a) crevice caves - caves which have arisen from fissures in the rock and are therefore wedge-shaped crevices, widest at the opening, (b) sea-beach caves, caves which face the seashore and are merely holes that have been worn by the dashing of the sea on the face of the cliff, (c) egress caves, or passages to give egress to subterranean streams, (d) ingress caves, or passages caused by water flowing into the holes of rocks and disappearing underground. These caves would have entrance holes in the ground, opening very wide underneath, and having the appearance of water having entered from above, (e) finally a group of caves which he lists by use as "dens of animals".
Caves in the coastal aeolian limestone of Western Australia show two major types of morphology due to different groundwater conditions. The first type comprises linear caves with streams, and develops on a watertable which has pronounced relief because of an undulating impervious substratum. Cave systems of this type are thought to start developing as soon as coherence begins to appear in unconsolidated dunes, and develop rapidly by collapse while the dunes are still weakly cemented, to assume more stable mature forms when the rock is strongly cemented.
The clustering areas of bent-winged bats in limestone caves are frequently stained and etched. This staining is very intense, and covers large areas at breeding caves present in Palaeozoic limestones. Erosion of limestone is very conspicuous in these caves. Staining is not intense at breeding caves in Tertiary limestones, but a combination of chemical and mechanical erosion may, in part, account for the depth of dome pits in which the bats cluster. Certain caves that are characterised by extensive guano deposits and by conspicuously eroded and/or stained limestone, but which are currently without large colonies of bats, may represent ancestral breeding caves.
The caves of the Chillagoe District are well-known by repute, but have not been described in speleological literature to date. The author visited the area in April, 1964, in company with Mr. D. Fitzsimon, of Mareeba. This paper summarises the observations made on that occasion. Chillagoe is an almost deserted town, once the centre of an extensive mining industry, and is situated about 120 miles west of Cairns, North Queensland. Access may be gained either by road or rail from Cairns. It can be seen from Table 1 that the climate is monsoonal, with comparatively heavy summer rains, but with dry weather throughout the remainder of the year. The Silurian Limestone in which the caves occur forms a belt some 40 miles long by four miles wide, extending from Almaden in the south-east to the Walsh River in the north-west. Caves probably occur throughout much of this belt, but known caves are concentrated in the Chillagoe and Mungana areas. Mungana lies approximately ten miles north-west of Chillagoe.
Between July, 1960, and December, 1963, observations were made on the natural history of Rhinolophus megaphyllus Gray in north-eastern New South Wales. Typically the species occurs as small colonies in a wide variety of cave and mine roosts. It appears to be absent from available roosting sites at higher altitudes in this area. Seasonal changes in the sizes of testes and epididymides suggest that mating occurs in May and June. The single young are born at maternity colonies through November, and nursing lasts about eight weeks. Field weights do not reflect seasonal variation other than that associated with pregnancy. However, seasonal differences in daytime level of activity are noted and these correlate with behavioural changes apparently related to temperature selection. Changes in colony size are described for several roosts and three movements made by marked individuals are recorded. Males appear to be more sedentary than females. Considerable aggregation of females and their young at maternity colonies (size, 15 to 1,5000 individuals) characterises the spring and summer population.
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