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| Titel |
Upper Devonian vertebrate taphonomy and sedimentology from the Klunas fossil site, Tervete Formation, Latvia |
| VerfasserIn |
J. Vasiļkova, E. Lukševičs, Ģ. Stinkulis, I. Zupins |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059921
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| Zusammenfassung |
| The deposits of the Tervete Formation, Famennian Stage of Latvia, comprising
weakly cemented sandstone and sand intercalated with dolomitic marls, siltstone
and clay, have been traditionally interpreted as having formed in a shallow, rather
restricted sea with lowered salinity. During seven field seasons the excavations
took place in the south-western part of Latvia, at the Klunas site, and resulted in
extensive palaeontological and sedimentological data. The taphonomical analysis
has been performed, having evaluated the size, sorting, orientation of the fossils,
articulation and skeletal preservation as well as the degree of fragmentation and abrasion.
The sedimentological analysis involved interpretation of sedimentary structures,
palaeocurrent direction reconstruction, grain-size analysis and approximate water depth
calculations.
The vertebrate assemblage of the Klunas site represents all known taxa of the Sparnene
Regional Stage of the Baltic Devonian, comprising placoderms Bothriolepis ornata
Eichwald, B. jani LukševiÄs, Phyllolepis tolli Vasiliauskas, Dunkleosteus sp. and
Chelyophorus sp., sarcopterygians Holoptychius nobilissimus Agassiz, Platycephalichthys
skuenicus Vorobyeva, Cryptolepis sp., Conchodus sp., Glyptopomus ? sp., "Strunius" ? sp.,
and Dipterus sp., as well as an undetermined actinopterygian. Placoderms Bothriolepis
ornata and B. jani dominate the assemblage.
The fossils are represented in the main by fully disarticulated placoderm plates and plate
fragments, sarcopterygian scales and teeth, rarely bones of the head and shoulder
girdle, and acanthodian spines and scales. The characteristic feature is the great
amount of fragmentary remains several times exceeding the number of intact bones.
The horizontal distribution of the bones over the studied area is not homogenous,
distinct zones of increased or decreased density of fossils can be traced. Zones of the
increased density usually contain many elements of various sizes, whereas zones of the
decreased density might be subdivided into two types: 1, with limited number of
large bones; 2, with scattered relatively small scales or fragments. The shape and
size of zones of increased density of fossils slightly resemble that of subaqueous
dunes.
Within the Klunas fossil site three taphonomically distinct oryctocoenoses can be traced,
differing in the compactness of accumulation, size, disarticulation and fragmentation of bones
and showing various degree of mixing of repeatedly buried and very fresh, partially
articulated material. Analysis of similarities and differences between these oryctocoenoses
demonstrates that all are sedimentary concentrations and have to be assessed as
allochtonous assemblages. However, despite these differences, the 1st and the 3rd
oryctocoenoses, which have been formed as vertebrate bone accumulations on the bottom of
an erosional channel, have much in common contrary to the 2nd oryctocoenosis,
which exemplifies the lens of fossil bearing cross-stratified sandstone formed in
subaqueous dunes. The concentrations of vertebrate remains have been formed under the
influence of fluvial and tidal processes in the shallow water environment, most
probably deltaic or estuarine settings. It has been found also that elongated placoderm
and sarcopterygian bones might be better indicators of the palaeoflow direction in
comparison with very elongated, but dense acanthodian spines or sarcopterygian
teeth. |
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