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An integrated geophysical study was performed over a known cave in Colorado Bend State Park (CBSP), Texas, where shallow karst features are common within the Ellenberger Limestone. Geophysical survey such as microgravity, ground penetrating radar (GPR), direct current (DC) resistivity, capacitively coupled (CC) resistivity, induced polarization (IP) and ground conductivity (GC) measurements were performed in an effort to distinguish which geophysical method worked most effectively and efficiently in detecting the presence of subsurface voids, caves and collapsed features. Horseshoe Chimney Cave (HCC), which is part of a larger network of cave systems, provides a good control environment for this research. A 50 x 50 meter grid, with 5 m spaced traverses was positioned around the entrance to HCC. Geophysical techniques listed above were used to collect geophysical data which were processed with the aid of commercial software packages. A traditional cave survey was conducted after geophysical data collection, to avoid any bias in initial data collection. The survey of the cave also provided ground truthing. Results indicate the microgravity followed by CC resistivity techniques worked most efficiently and were most cost effective, while the other methods showed varying levels of effectiveness.
A fossil channel was filled by sandy sediments of light brown to ochreous color with dynamic structures and textures (lower sequence) unconformably overlain by remains of collapsed roof with brown and ochreous matrix (upper sequence). The sedimentary profile was about 5 m high. In all 38 samples taken from the profile, only one was cemented. Samples were demagnetised by alternating field (AF) at 10 to 1,000 Oe. The cemented one was demagnetised by gradual thermal process from 80 to 560 °C in the MAVACS apparatus. Detected remanent magnetisation in a natural state varied between 95 and 36,470 pT, values of volume magnetic susceptibility are from 55 to 998 x 10-6 SI. Rocks showed low or medium magnetisation. Normal and inverse polarization was detected after demagnetisation. The primary component of magnetisation and resulting polarity could not be stated in samples with expressive viscose component (up to 90 %). According to arrangement of individual magnetozone, it can be stated that sediments are older than the top of Olduvai chron (1.77 Ma), as the magnetostratigraphic profile at Kozina terminated by reverse polarised magnetozone and contains two normal polarised zones. The profile can be correlated with the Divača profile, not only from the palaeomagnetic point of view, but also from a lithological point of view. We suppose, as in Divača, that the cave is a result of the Messinian speleogenetic epoch and its fossilization was connected with rapid base level uplift after refilling of the Mediterranean basin by water. If this hypothesis is close to reality, the fossilization process can be dated from about 5.2 Ma up.
The Postojnska jama–Planinska jama cave system and number of smaller adjacent caves are developed in the Postojnski kras. These caves are located between two dextral strike-slip fault zones oriented in the Dinaric direction. The caves contain lithologically diversified cave fill, ranging from speleothems to allogenic fluvial sediments. The allogenic clastic material is derived from a single source, Eocene siliciclastics of the Pivka Basin. Small differences in mineral/petrologic composition between the sediments can be attributed to different degrees of weathering in the catchment area and homogenization of source sediments. Thick sequences of fine-grained laminated sediments, deposited from suspension are common. The depositional environment was mostly calm, but not completely stagnant. Such a sedimentary environment can be described as cave lacustrine, with deposition from pulsed flow. The homogeneity of the palaeomagnetic data suggests rapid deposition by a number of short-lived single-flood events over a few thousand years. This depositional style was favourable for recording of short-lived excursions in the palaeomagnetic field. The sediments were originally not expected to be older than Middle Quaternary in age (i.e. about 0.4 Ma). Later numerical dating (Th/U and ESR) indicated ages older than 0.53 ka. New palaeomagnetic data from selected sedimentary profiles within the cave system detected normal polarization in much of the profiles studied. Reverse polarized magnetozones, interpreted mostly as short- lived excursions of magnetic field, were detected in only a few places. Therefore, we interpreted most of the sediments as being younger than 0.78 Ma, belonging to different depositional phases within the Brunhes chron. Palaeomagnetic properties of two profiles in caves intersected by the artificial tunnel between Postojnska jama and Črna jama had reverse polarized magnetozones and of sediments in Zguba jama, may indicate an age much greater than 0.78 Ma. The cave system has evolved over a long period of time, governed by the functioning of Planinsko polje in the relation to the evolution of the resurgence area in Ljubljana Moor further to the east. General stabilization of the hydrological system with low hydraulic head led to the evolution of caves in epiphreatic and paragenetic conditions over a long time-span. Individual cave segments or passages were completely filled and exhumed several times during the evolution of the cave. Alternation of depositional and erosional phases may be connected with changing conditions within the cave system, the functioning of the resurgence area, collapse, climatic change, tectonic movement and the intrinsic mechanisms of contact karst.
An integrated geophysical study was performed over a known cave in Colorado Bend State Park (CBSP), Texas, where shallow karst features are common within the Ellenberger Limestone. Geophysical survey such as microgravity, ground penetrating radar (GPR), direct current (DC) resistivity, capacitively coupled (CC) resistivity, induced polarization (IP) and ground conductivity (GC) measurements were performed in an effort to distinguish which geophysical method worked most effectively and efficiently in detecting the presence of subsurface voids, caves and collapsed features. Horseshoe Chimney Cave (HCC), which is part of a larger network of cave systems, provides a good control environment for this research. A 50 x 50 meter grid, with 5 m spaced traverses was positioned around the entrance to HCC. Geophysical techniques listed above were used to collect geophysical data which were processed with the aid of commercial software packages. A traditional cave survey was conducted after geophysical data collection, to avoid any bias in initial data collection. The survey of the cave also provided ground truthing. Results indicate the microgravity followed by CC resistivity techniques worked most efficiently and were most cost effective, while the other methods showed varying levels of effectiveness.