ABSTRACT Upwards-propagating collapse pipes typically form sinkholes where they meet the land sur... more ABSTRACT Upwards-propagating collapse pipes typically form sinkholes where they meet the land surface. Renewed dissolution of breccia in ancient pipes can have a similar effect. For these cases, probability-based models of sinkhole hazard are closely related to the expected mature architecture of the collapse-pipe field. We present a case study of the architecture of a square-kilometre field of collapse-pipes from the Carboniferous-Permian in which the pipes are documented in outcrop and using shallow geophysical methods. The study site is located on the Wordiekammen plateau in the Carboniferous Billefjorden half-graben basin on Spitsbergen. Cliffs bounding the plateau expose breccia pipes cutting a gently-dipping 200-m-thick series of platform carbonates, in turn underlain by stratiform breccias and residual pods of gypsum. Many of the breccia pipes are tall (>250 m) and postdate several shallow karstification episodes. Most pipes are inferred not to have reached the surface based on a lack of terrigenous material and fluvial structure, although several pipes show indications of such surface communication. Although the pipes are generally attributed to gypsum dissolution, a deep carbonate karstification event is inferred based on high temperature calcite cement, and burial dehydration of gypsum, may also have contributed to void formation. On the plateau top the collapse pipes are obscured by thick scree, thus km-scale size and spacing data for the pipes and faults was collected by mapping the bedrock with 2D ground-penetrating radar (GPR). GPR profiles were acquired on a grid with 25-meter line spacing, using 50 MHz antennas and achieving 30-40 m penetration. Breccia bodies were identified by steep-sided zones of complex diffraction patterns interrupting bedding-related continuous reflections. Two pipes were further studied in 3D using high-resolution GPR, tomographic seismic and geo-electric. These geophysical data were merged into a comprehensive 3D framework including helicopter-borne lidar and photo scans of the plateau rim geology, thus allowing an integrated visualization and interpretation of the different datasets. The GPR data show the breccia pipes to be slightly oblate with diameters ranging from 20 to over 100 m; 60 meters is a typical value. Approximately 10 pipes are identified in cliff-side outcrops bordering the GPR area, whereas 30 more are identified within the plateau by the GPR data. The GPR volume lies about 200 m above the pipe base, hence the pipe-length frequency-distribution data are incomplete. The strata are cut by small-offset (<5m) faults related to collapse processes and larger-offset faults related to regional basin extension. The breccia pipe field appears to be delimited by these more regional faults, in turn inferred to control the thickness of syn-rift gypsum and/or the hydrology of its dissolution. Collapse breccia pipes form strong vertical heterogeneities in rock properties such as porosity and perme- ability, matrix density, cement, mechanical strength and lithology, affecting fluid-flow characteristics on a meter to hundred-meter scale. It is rare that pipe fields are well exposed at the kilometre scale. Although some scaling data can be obtained from 3D oil-industry seismic reflection data but the resolution insufficient to visualize critical details. The outcrop combination of seismic, electric and geologic techniques facilitates the interpretation of 3D facies architectures and by proxy porosity-permeability relationships. Studies at the km scale are fundamental for understanding basic karst and collapse processes, and yield petrophysical models that can be applied predictively to natural hazards and groundwater or hydrocarbon exploitation in paleokarst settings.
Relict phreatic caves, in hanging positions within a glacial topography, pose an enigma with resp... more Relict phreatic caves, in hanging positions within a glacial topography, pose an enigma with respect to the speleogenetic interpretation. A glacier ice mass may provide liquid water and create caves anywhere in the adjacent rock, making glacier ice-contact as well as interglacial, meteoric speleogenesis feasible. The problem is reviewed with relevant glacier rheology, hydrology, and chemistry. The glacial environment was certainly able to overprint and widen already existing caves (sensu lato speleogenesis), while the full evolution of caves from tight fractures (sensu stricto speleogenesis) was slow and inefficient (about 1/40) as compared to nonglacial conditions. Off-print available upon request
El Soplao cave (Cantabria, northern Spain) was discovered in the mid-nineteenth century as result... more El Soplao cave (Cantabria, northern Spain) was discovered in the mid-nineteenth century as result of mining activity in La Florida mine. Spectacular helictites, anthodites and huge vadose speleothems are the most relevant aesthetic features of this show mine-cave. In some of its karst conduits there are also several evidences of palaeoflood that has intruded fine-grained detrital materials into the cave. Flowstones composed by aragonite laminas interlayered within successive thin strata of cemented silt and clay show clear evidences of these different events. The oldest sedimentary body is currently hung up about 30 cm above the cave floor. Discontinue aragonite layers formed under quiet vadose conditions by laminar flow on the detrital materials are alternated with alluvial deposits looped with a decrease of clastic material upwards and marked by sharp erosional surfaces. Close to the top of the flowstones, Fe-Mn oxide precipitation also occurred. Results from U-Th dating of the lo...
... Presumably the visible charcoal fragments (10-50 uM) were carried into the cave with theminor... more ... Presumably the visible charcoal fragments (10-50 uM) were carried into the cave with theminor flood event but Page 274. Z70 SE LAURITZEN & J. LUNDBERG it is impossible to know if the pollen and carbonized dust were carried in on air currents. ...
ABSTRACT In this paper we present and examine a comprehensive series of dates (> 200), whi... more ABSTRACT In this paper we present and examine a comprehensive series of dates (> 200), which underpins a new reconstruction of ice-sheet fluctuations along nine transects extending from inland to the coast in Norway. Sediments with low organic content dominate the dated materials, particularly from the inland sites, some of which may have a marine origin. Consequently, the new dates reported here, include mainly 14C-dates of bulk organic sediment samples. The geochronology of sites located in coastal areas is mainly based on shell dates. A considerable number (> 100) of previously published dates are also employed, both as 'control dates' for the new synthesis, and as components of the overall geochronological data base. The data base also includes 14C-dates of bones and calcareous concretions, U/Th-dates of speleothems and calcareous concretions, and TL/OSL-dates of wind-blown and water-lain sand. Brief reference is also made to relative age estimates based on amino acid analyses and correlation using magnetostratigraphy. The accuracy and precision of the chronology is examined on a millennium scale. The dates give ranges of ages which provide a coherent chronology of the stratigraphic succession and of the main events, which span the Middle to Late Weichselian interval.
ABSTRACT Upwards-propagating collapse pipes typically form sinkholes where they meet the land sur... more ABSTRACT Upwards-propagating collapse pipes typically form sinkholes where they meet the land surface. Renewed dissolution of breccia in ancient pipes can have a similar effect. For these cases, probability-based models of sinkhole hazard are closely related to the expected mature architecture of the collapse-pipe field. We present a case study of the architecture of a square-kilometre field of collapse-pipes from the Carboniferous-Permian in which the pipes are documented in outcrop and using shallow geophysical methods. The study site is located on the Wordiekammen plateau in the Carboniferous Billefjorden half-graben basin on Spitsbergen. Cliffs bounding the plateau expose breccia pipes cutting a gently-dipping 200-m-thick series of platform carbonates, in turn underlain by stratiform breccias and residual pods of gypsum. Many of the breccia pipes are tall (>250 m) and postdate several shallow karstification episodes. Most pipes are inferred not to have reached the surface based on a lack of terrigenous material and fluvial structure, although several pipes show indications of such surface communication. Although the pipes are generally attributed to gypsum dissolution, a deep carbonate karstification event is inferred based on high temperature calcite cement, and burial dehydration of gypsum, may also have contributed to void formation. On the plateau top the collapse pipes are obscured by thick scree, thus km-scale size and spacing data for the pipes and faults was collected by mapping the bedrock with 2D ground-penetrating radar (GPR). GPR profiles were acquired on a grid with 25-meter line spacing, using 50 MHz antennas and achieving 30-40 m penetration. Breccia bodies were identified by steep-sided zones of complex diffraction patterns interrupting bedding-related continuous reflections. Two pipes were further studied in 3D using high-resolution GPR, tomographic seismic and geo-electric. These geophysical data were merged into a comprehensive 3D framework including helicopter-borne lidar and photo scans of the plateau rim geology, thus allowing an integrated visualization and interpretation of the different datasets. The GPR data show the breccia pipes to be slightly oblate with diameters ranging from 20 to over 100 m; 60 meters is a typical value. Approximately 10 pipes are identified in cliff-side outcrops bordering the GPR area, whereas 30 more are identified within the plateau by the GPR data. The GPR volume lies about 200 m above the pipe base, hence the pipe-length frequency-distribution data are incomplete. The strata are cut by small-offset (<5m) faults related to collapse processes and larger-offset faults related to regional basin extension. The breccia pipe field appears to be delimited by these more regional faults, in turn inferred to control the thickness of syn-rift gypsum and/or the hydrology of its dissolution. Collapse breccia pipes form strong vertical heterogeneities in rock properties such as porosity and perme- ability, matrix density, cement, mechanical strength and lithology, affecting fluid-flow characteristics on a meter to hundred-meter scale. It is rare that pipe fields are well exposed at the kilometre scale. Although some scaling data can be obtained from 3D oil-industry seismic reflection data but the resolution insufficient to visualize critical details. The outcrop combination of seismic, electric and geologic techniques facilitates the interpretation of 3D facies architectures and by proxy porosity-permeability relationships. Studies at the km scale are fundamental for understanding basic karst and collapse processes, and yield petrophysical models that can be applied predictively to natural hazards and groundwater or hydrocarbon exploitation in paleokarst settings.
Relict phreatic caves, in hanging positions within a glacial topography, pose an enigma with resp... more Relict phreatic caves, in hanging positions within a glacial topography, pose an enigma with respect to the speleogenetic interpretation. A glacier ice mass may provide liquid water and create caves anywhere in the adjacent rock, making glacier ice-contact as well as interglacial, meteoric speleogenesis feasible. The problem is reviewed with relevant glacier rheology, hydrology, and chemistry. The glacial environment was certainly able to overprint and widen already existing caves (sensu lato speleogenesis), while the full evolution of caves from tight fractures (sensu stricto speleogenesis) was slow and inefficient (about 1/40) as compared to nonglacial conditions. Off-print available upon request
El Soplao cave (Cantabria, northern Spain) was discovered in the mid-nineteenth century as result... more El Soplao cave (Cantabria, northern Spain) was discovered in the mid-nineteenth century as result of mining activity in La Florida mine. Spectacular helictites, anthodites and huge vadose speleothems are the most relevant aesthetic features of this show mine-cave. In some of its karst conduits there are also several evidences of palaeoflood that has intruded fine-grained detrital materials into the cave. Flowstones composed by aragonite laminas interlayered within successive thin strata of cemented silt and clay show clear evidences of these different events. The oldest sedimentary body is currently hung up about 30 cm above the cave floor. Discontinue aragonite layers formed under quiet vadose conditions by laminar flow on the detrital materials are alternated with alluvial deposits looped with a decrease of clastic material upwards and marked by sharp erosional surfaces. Close to the top of the flowstones, Fe-Mn oxide precipitation also occurred. Results from U-Th dating of the lo...
... Presumably the visible charcoal fragments (10-50 uM) were carried into the cave with theminor... more ... Presumably the visible charcoal fragments (10-50 uM) were carried into the cave with theminor flood event but Page 274. Z70 SE LAURITZEN & J. LUNDBERG it is impossible to know if the pollen and carbonized dust were carried in on air currents. ...
ABSTRACT In this paper we present and examine a comprehensive series of dates (> 200), whi... more ABSTRACT In this paper we present and examine a comprehensive series of dates (> 200), which underpins a new reconstruction of ice-sheet fluctuations along nine transects extending from inland to the coast in Norway. Sediments with low organic content dominate the dated materials, particularly from the inland sites, some of which may have a marine origin. Consequently, the new dates reported here, include mainly 14C-dates of bulk organic sediment samples. The geochronology of sites located in coastal areas is mainly based on shell dates. A considerable number (> 100) of previously published dates are also employed, both as 'control dates' for the new synthesis, and as components of the overall geochronological data base. The data base also includes 14C-dates of bones and calcareous concretions, U/Th-dates of speleothems and calcareous concretions, and TL/OSL-dates of wind-blown and water-lain sand. Brief reference is also made to relative age estimates based on amino acid analyses and correlation using magnetostratigraphy. The accuracy and precision of the chronology is examined on a millennium scale. The dates give ranges of ages which provide a coherent chronology of the stratigraphic succession and of the main events, which span the Middle to Late Weichselian interval.
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