Actualistic approaches for the interpretation of clastic ...€¦ · Main focus was set on sampling...
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Actualistic approaches for the interpretation of clastic deposits of the Mühlbach Cave, Germany Martin Trappe, Eichstaett The Mühlbach Cave was discovered in 2001 by speleologists after intense digging activities. With a length of more than 7 km today it is among the longest caves in Germany. The cave is located in the South Franconian Alb (Fig. 1), a karstic area showing limestones and dolomites of Jurassic Age. Most cave passages show active streams discharging 300 l/s and transporting gravels and sandy-silty sediments (Fig. 2, 4). The Mühlbach cave offers the opportunity to study undisturbed fluvial cave sediments in relation to the hydrological conditions. Main focus was set on mapping and sampling of different sedimentary environments of clastic cave deposits to characterise a broad spectrum of cave sediments directly related to the sedimentary facies (Fig. 3-5). These samples act as reference material for the interpretation of samples which did not show any relation to fluvial or other facies (actualistic approach). Especially fine sand to silt outcrops at the cave walls or similarsuccessions drilled by a manual auger at the bottom of abandoned passages had to be identified (Fig. 6). A rough distinction between channel-fill, channel and point bar, natural levée and overbank deposits was made along the active streams. Although only minor fragments of carbonate rocks occur (strongly corroded limestones, speleotheme fragments) higher portions of dolomite grains are observed within the sand fractions. It can be concluded that these grains result from a granular disintegration of dolomitic rocks at higher levels of the cave (Fig. 8). Except of silt and fine sand transported as suspension load no important dislocation of sedimentary material was observed within the Mühlbach Cave. Although larger floods were documented for historic times the depositional setting of this cave has to be interpreted as a calm fluvial environment. Due to its lower hydrological dynamics it is different from the typical Fluviokarst. Abandoned passages behind natural levées show a continuous grain size decrease with increasing distance to the levées. Often the sedimentary environment changes to lacustrine conditions which are disturbed by fluvial input only in a few episodic cases. Mostly the connections to the main passage are interrupted and water supply is fed mainly by drip water. The facies separation is confirmed by the sedimentpetrographic data (Fig. 7, 9). Facies diagrams (e.g. BOSCH & WHITE 2004) can be used for sediment differentiation (Fig. 9, 10). Fig. 3: Geological map of cave deposits observed at the confluence of the main cave passage and an abandoned passage. Fig. 4: View to the main cave passage with a central stream bed showing fine gravels and fine-grained overbank deposits (Foto: Armin Schnobrich, Copyright: KGM e.V.). Fig. 7: Cumulative grain size curves of fluvial cave deposits from different facies domains at the Mühlbach cave site (actualistic approach). Unfilled quadrangles – limnic deposits, grey triangles – overbank deposits, black quadrangles – side bar or point bar, unfilled rhombi – channel bed deposits. Fig. 8: Typical variation of lithology across the grain size distribution of a selected sample. BOSCH, R.F. & WHITE, W.B. (2004): Lithofacies and transport of clastic sediments in karstic aquifers. -In: SASOWSKY, I.D. & MYLROIE, J.W. (eds.): Studies of cave sediments: Physical and chemical recorders of climate change: 1-22, Kluwer. TRAPPE, M. (2007): Gliederungsmöglichkeiten und Systematik von klastischen Höhlensedimenten (Beispiel Südliche Frankenalb). – Laichinger Höhlenfreund, 42 73-88. TRAPPE, M. (2009): Sedimentpetrographie, Gliederung und Entstehung von Karstsedimenten am Beispiel der Südlichen Frankenalb. – Unpublished Habilitation Thesis, Catholic University Eichstaett-Ingolstadt. Danube Rhine Munich Berlin 0 50 100 kilometres Northern Franconian Alb Eichstaett Southern Franconian Alb Muehlbach Cave Catholic University of Eichstätt-Ingolstadt, Department of Geography Introduction Fig. 1: Regional overview of the research area. Methodology First results N 0 10 [ m ] escarpment stream direction boulder medium - coarse sand fine gravel medium gravel coarse gravel loam / silt carbonate cemented deposits stalagmites bed-rock Fig. 6: Sedimentpetrography of cave deposits drilled in an abandoned cave passage. Fig. 10: Discrimination of fluvial facies domains applied to samples from abandoned passages and thick sequences of unknown origin. Fig. 9: Discrimination of recent samples taken with respect to the fluvial facies due to BOSCH & WHITE (2004). depth lithology samples granulometry carbonate content 0,0 0,5 1,0 1,5 50 0 0 m ÖAMb07041 ÖAMb07042 ÖAMb07043 ÖAMb07044 ÖAMb07045 ÖAMb07046 ÖAMb07047 ÖAMb07048 ÖAMb07049 ÖAMb07050 1,30 m 100 wt-% clay silt sand gravel grain size silt loam silt - fine sand flowstone layer fl fl S 0 0 2 -2 -6 -8 -4 4 6 8 10 10 20 30 50 [ wt - % ] [ Phi ] 40 0,002 0,063 2,0 63,0 [ mm ] Reptation Saltation Suspension carbonate rock loam cherts with Fe-coating cherts quartz Author adress: Dr. Martin Trappe Department of Geography Catholic University Eichstaett-Ingolstadt Ostenstr. 18 D-85072 Eichstaett, Germany email: [email protected] References Fig. 11: Laminated fine silt and flowstones (Foto: M. Trappe).. Fig. 2: Typical view of cave passages in the Mühlbach cave (Foto: Armin Schnobrich, Copyright: KGM e.V.). Fig. 5: Sequence of laminated fine silt exposed at an abandoned passage (Foto: Martin Trappe). Acknowledgement: I thank the members of the caving club “Karstgruppe Mühlbach” (KGM e.V.) for their technical and personal support during the field campaigns and the owner of the Mühlbach cave for the permit to enter the cave.
Transcript of Actualistic approaches for the interpretation of clastic ...€¦ · Main focus was set on sampling...
Actualistic approaches for the interpretation of clastic deposits of the Mühlbach Cave, Germany
Martin Trappe, Eichstaett
The Mühlbach Cave was discovered in 2001 by speleologists after intense digging activities. With a length of more than7 km today it is among the longest caves in Germany. The cave is located in the South Franconian Alb (Fig. 1), a karsticarea showing limestones and dolomites of Jurassic Age. Most cave passages show active streams discharging 300 l/sand transporting gravels and sandy-silty sediments (Fig. 2, 4). The Mühlbach cave offers the opportunity to studyundisturbed fluvial cave sediments in relation to the hydrological conditions.
Main focus was set on mapping and sampling of differentsedimentary environments of clastic cave deposits tocharacterise a broad spectrum of cave sediments directlyrelated to the sedimentary facies (Fig. 3-5). Thesesamples act as reference material for the interpretation ofsamples which did not show any relation to fluvial or otherfacies (actualistic approach). Especially fine sand to siltoutcrops at the cave walls or similarsuccessions drilled bya manual auger at the bottom of abandoned passageshad to be identified (Fig. 6).
A rough distinction between channel-fill, channel and point bar, natural levée and overbank deposits was made along theactive streams.
Although only minor fragments of carbonate rocks occur (strongly corroded limestones, speleotheme fragments) higherportions of dolomite grains are observed within the sand fractions. It can be concluded that these grains result from agranular disintegration of dolomitic rocks at higher levels of the cave (Fig. 8).Except of silt and fine sand transported as suspension load no important dislocation of sedimentary material was observedwithin the Mühlbach Cave.Although larger floods were documented for historic times the depositional setting of this cave has to be interpreted as acalm fluvial environment. Due to its lower hydrological dynamics it is different from the typical Fluviokarst.
Abandoned passages behind natural levées show a continuous grain size decrease with increasingdistance to the levées. Often the sedimentary environment changes to lacustrine conditions which are disturbed by fluvialinput only in a few episodic cases. Mostly the connections to the main passage are interrupted and water supply is fedmainly by drip water. The facies separation is confirmed by the sedimentpetrographic data (Fig. 7, 9). Facies diagrams(e.g. BOSCH & WHITE 2004) can be used for sediment differentiation (Fig. 9, 10).
Fig. 3: Geological map of cavedeposits observed at the confluenceof the main cave passage and anabandoned passage.
Fig. 4: View to the main cave passage with a central stream bedshowing fine gravels and fine-grained overbank deposits (Foto:Armin Schnobrich, Copyright: KGM e.V.).
Fig. 7: Cumulative grain size curves of fluvial cave deposits from different facies domainsat the Mühlbach cave site (actualistic approach). Unfilled quadrangles – limnic deposits,grey triangles – overbank deposits, black quadrangles – side bar or point bar, unfilledrhombi – channel bed deposits. Fig. 8: Typical variation of lithology across the grain size distribution of a selected sample.
BOSCH, R.F. & WHITE, W.B. (2004): Lithofacies and transport of clastic sediments in karsticaquifers. -In: SASOWSKY, I.D. & MYLROIE, J.W. (eds.): Studies of cave sediments: Physicaland chemical recorders of climate change: 1-22, Kluwer.
TRAPPE, M. (2007): Gliederungsmöglichkeiten und Systematik von klastischenHöhlensedimenten (Beispiel Südliche Frankenalb). – Laichinger Höhlenfreund, 42 73-88.
TRAPPE, M. (2009): Sedimentpetrographie, Gliederung und Entstehung vonKarstsedimenten am Beispiel der Südlichen Frankenalb. – Unpublished Habilitation Thesis,Catholic University Eichstaett-Ingolstadt.
Danube
Rhin
e
Munich
Berlin
0 50 100 kilometres
Northern
Franconian
Alb
EichstaettSouthern
Franconian
Alb
Muehlbach Cave
Catholic University of Eichstätt-Ingolstadt, Department of Geography
Introduction
Fig. 1: Regional overview of the research area.
Methodology
First results
N0 10[ m ]
escarpment
stream direction
boulder
medium - coarse sand
fine gravel
medium gravel
coarse gravel
loam / silt
carbonate cemented deposits
stalagmites
bed-rock
Fig. 6: Sedimentpetrography of cave deposits drilledin an abandoned cave passage.
Fig. 10: Discrimination of fluvial facies domains applied to samples from abandonedpassages and thick sequences of unknown origin.
Fig. 9: Discrimination of recent samples taken with respect to the fluvial facies due to BOSCH & WHITE(2004).
depth lithology samples granulometry carbonatecontent
0,0
0,5
1,0
1,5
5000m
ÖAMb07041ÖAMb07042
ÖAMb07043
ÖAMb07044
ÖAMb07045
ÖAMb07046
ÖAMb07047
ÖAMb07048
ÖAMb07049
ÖAMb07050
1,30 m
100wt-%
clay
silt
sand
gravel
grain size
silt
loam
silt - fine sand
flowstone layer
flfl
S
002 -2 -6 -8-446810
10
20
30
50
[ w
t -
% ]
[ Phi ]
40
0,002 0,063 2,0 63,0[ mm ]
Reptation
Saltation
Suspension
carbonate rock
loam
cherts withFe-coating
cherts
quartz
Author adress:
Dr. Martin TrappeDepartment of GeographyCatholic University Eichstaett-IngolstadtOstenstr. 18D-85072 Eichstaett, Germany
email: [email protected]
References
Fig. 11: Laminated fine silt and flowstones (Foto: M. Trappe)..
Fig. 2: Typical view of cave passages in theMühlbach cave (Foto: Armin Schnobrich,Copyright: KGM e.V.).
Fig. 5: Sequence of laminated fine silt exposed at anabandoned passage (Foto: Martin Trappe).
Acknowledgement:I thank the members of the caving club “Karstgruppe Mühlbach” (KGM e.V.) for their technicaland personal support during the field campaigns and the owner of the Mühlbach cave for thepermit to enter the cave.
Geophysical Research Abstracts,Vol. 11, EGU2009-10425, 2009EGU General Assembly 2009© Author(s) 2009
Actualistic approaches for the interpretation of clastic deposits of theMühlbach Cave, GermanyM. TrappeUniversity Eichstaett-MGF/Geography, Eichstaett, Germany ([email protected])
The Mühlbach Cave was discovered in 2001 by speleologists after intense digging activities. With a length ofmore than 7 km today it is among the longest caves in Germany. The cave is located in the South Franconian Alb, akarstic area showing limestones and dolomites of Jurassic Age. Most cave passages show active subsurface streamsdischarging 300 l/s and transporting gravels and sandy-silty sediments. Because of lacking of a natural cave en-trance there is the opportunity to study undisturbed fluvial cave sediments in relation to the hydrological conditions.
Main focus was set on sampling of different sedimentary environments of clastic cave deposits to charac-terise a broad spectrum of cave sediments. These samples act as reference material for the interpretation ofsamples which did not show any relation to fluvial or other facies (actualistic approach). Especially fine sand to siltoutcrops at the cave walls or similar successions drilled by a manual auger at the bottom of abandoned passageshad to be identified.
A rough distinction between channel-fill, channel and point bar, natural levee and overbank deposits wasmade along the active cave streams. Referring to the distinct hydrological conditions a detailed morphological andgeological mapping was performed for a few localities. Streambed samples show often rounded gravels of mediumsize or sandy gravels. Lithologically they comprise mainly cherts and quartzites derived from the karst surface.Although only minor fragments of carbonate rocks occur (strongly corroded limestones, speleotheme fragments)higher portions of dolomite grains are observed within the sand fractions. It can be concluded that these grainsresult from a granular disintegration of dolomitic rocks at higher levels of the cave. They were displaced throughvertical shafts into the active streams. Grain size data from point bars, natural levees and marginal overbankdeposits exhibit clear sorting of the unimodal sediments and a gradual shift of cumulative grain size curves to finermaterial.
Abandoned passages behind natural levees show a continuous grain size decrease with increasing distanceto the levees. In case of flooding the natural levee deposits are highly affected by the dynamics of the adjacentcave stream (proximate facies). More distant areas display finer grain sizes due to the reduced current velocities(distal facies). Often the sedimentary environment changes to lacustrine conditions which are disturbed by fluvialinput only in a few episodic cases. Mostly the connections to the main passage are interrupted and water supplyis fed mainly by drip water. The limnic cave sediments are often fine laminated and consist of fine silt and minorclay. The discrimination between different sedimentary environments was also performed by facies diagramsusing sorting and grain size parameters.
Except of silt and fine sand transported as suspension load no important dislocation of sedimentary mate-rial was observed within the Mühlbach Cave. Although larger floods were documented for historic times thedepositional setting of this cave has to be interpreted as a calm fluvial environment. Due to its lower hydrologicaldynamics it is different from the typical Fluviokarst.
