Coralline red algal limestones of the late Eocene alpine Foreland Basin in Upper Austria: Component analysis, facies and palecology |
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Authors: | Dr Michael W Rasser |
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Institution: | (1) Institute of Paleontology, University of Vienna, Geozentrum, Althanstrasse 14, A-1090 Vienna;(2) Institute of Geology and Paleontology, Karl-Franzens-University of Graz, Heinrichstrasse 26, A-8010 Graz |
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Abstract: | Summary Late Eocene sediments of the Upper Austrian Alpine Foreland Basin discordantly overlie Mesozoic and crystalline rocks, which
are deeply eroded and form a distinct pre-Eocene relief. Late Eocene deposits contain red algal limestones with a remarkable
lateral extent and a high diversity of sedimentary facies. Towards the south the algal limestones change into more clastic
sediments, which are characterized by larger foraminifera and bryozoans. Main components are coralline algal branches and
detritus, coralline crusts, rhodoliths, peyssonneliacean aggregates and crusts, nummulitid and orthophragminid foraminifera,
corals, bryozoans, as well as terrigenous components.
Rank correlation and factor analysis were calculated in order to obtain informations about relations between components. Hierarchical
cluster analysis allowed the designation of 17 facies, most of them are dominated by coralline algae. Actualistic comparisons
and correlations obtained from statistical analyses allowed the reconstruction of the depositional environments.
Main features of the northern area are huge accumulations of unattached coralline algae (branches, rhodoliths, detritus),
which are comparable to the present-day “Maerl”-facies. They formed loose frameworks cut by sand channels. The frequency of
coralline detritus decreases upsection. Peyssonneliacean algae in higher parts of the profiles show growth-forms that are
comparable to peyssonneliaceans of the Mediterranean circalittoral soft bottoms. This succession can be interpreted by an
increasing relative sea level. Besides, crustose coralline algal frameworks were growing on morphological highs which are
partially comparable to the present-day “Coralligéne de Plateau” of the Mediterranean Sea.
In contrast to the northern area, sedimentation rate of the southern area is too low to keep up with rising sea level. The
typical succession from nummulitid- to orthophragminid-and bryozoan-dominated facies can be interpreted by an increasing water
depth from shallowest subtidal to the deeper photic zone and finally to the aphotic zone. |
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Keywords: | Microfacies Analysis Component Analysis Facies Palecology Red Algal Limestones Coralline Algae Peyssonneliacean Algae Rhodoliths Larger Foraminifera Bryozoa Alpine Foreland Basin Upper Austria Late Eocene Paleogene |
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