Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

More documents

Recommendations

Info

116 ADVANCES IN PALAEOICHTHYOLOGY upper part of the formation, suggest that continental conditions similar to semidesert or desert prevailed at the very end of the Šķervelis time (Stinkulis 2004). The results of the analysis of rocks of the Pavāri Member indicate their forming in alternating hydrodynamic regime. A powerful stream flowing from NNE to SSW formed the erosional channels. Some of them were filled by moderately or well-sorted very fine-grained to fine-grained sand containing no admixture of clay particles. Judging from the size and sorting of clastic particles, the material was probably transported in a low concentration flow. According to data of the grain-size analysis the clastic material has been sorted by stream and, possibly, also influenced by wave action. Deformations of sandstone bedding and intrabasinal conglomerate consisting of clay pebbles indicate the role of slump processes on sides of the erosional channels. Cross-bedding is characteristic for the infilling of the channels and clearly demonstrates high angle of dip and bipolar orientation, which is usually explained by the influence of inter-tidal streams (Reineck and Singh 1980). The structure and poor sorting of the overlaying beds of clayey silt and sandy-clayey silt suggest accumulation in calm water. Fining upwards sequence of sedimentary structures is characteristic for the coarsegrained point bar deposits in fluvial systems (apart of bidirectional orientation of cross beds) or shallow channels in tidal inlets and tidal deltas in a coastal marine environment (Reineck and Singh 1980). The remarkable orientation of fossils indicate transportation in a medium-strong stream with velocity about 1-20 cm/sec, and deposition of remains on the bottom of an erosional channel at the moments of drastic decrease in stream power. Considering the results of taphonomic and sedimentologic analysis of the Pavāri locality it is concluded that it formed in relatively shallow sea conditions dominated by stream, not wave influence. The deposits were not accumulated in continental or coastal freshwater environment, and there is not enough evidence to support the delta hypothesis regarded previously (Lebedev and Lukševičs 1996). Most likely, vertebrates from the Ketleri Formation existed in a coastal marine environment, although the possibility that the remains have been transported for a more considerable distance can not be excluded. Possibly, rocks of the Pavāri locality formed in a low-tidal terrigenous shelf environment between low islands where shallow channel might be formed in tidal processes. It is worth noting that Acanthostega gunnari from East Greenland, morphologically the most closely resembling Ventastega curonica, have been interpreted as a mainly aquatic animal dwelling in an active fluvial channels in a fluvial-dominated environment (Bendix-Almgreen et al. 1990). Comparison of the faunal composition of the Britta Dal (locality ‘A’) and Ketleri (Pavāri locality) formations shows clear taphonomic differences between these two localities. The fossil assemblage from the Britta Dal Formation is dominated by abundant remains of Acanthostega represented by isolated bones and articulated, sometimes exceptionally well-preserved material including skulls and even articulated postcranial parts in association with skulls. On the contrary, the fish material is poorly preserved, consisting only of disarticulated scales, teeth and placoderm trunk armour plates. The fish fauna of this particular fauna is represented only by some taxa including Holoptychius, lung-fishes Soederberghia and perhaps Oervigia, as well as rarely found placoderm Remigolepis. Probably, taphonomic peculiarities of the formation of Britta Dal oryctocoenosis resulted in the elimination of a significant part of information on the ancient biocoenosis. In contrast, composition
E. Lukševičs, I. Zupiņš. Sedimentology, fauna, and taphonomy of Pav āri 117 of the fossil assemblage from the Pavāri locality is supposedly much more informative about the content of the palaeobiocoenosis, where dominant placoderms played the role of prey for diverse predators among sarcopterygians and tetrapod. Acknowledgements. - This study was supported by the Latvian Council of Science, grant No. 02.0871. The 2001 expedition to the Pavāri site was financed by the Natural History Museum of Latvia and The Natural History Museum (London). Sincere thanks to Drs P.E. Ahlberg, H. Blom, O.A. Lebedev, Mrs. L. Vyushkova, and staff of the Natural History Museum of Latvia who participated in excavations of 1988, 1991 and 2001. Special thanks to Drs H. Blom and Ģ. Stinkulis for reviewing the manuscript, productive discussions and valuable comments on sedimentological and taphonomical aspects of this research. References Ahlberg P., Lukševičs E. 1998. The new data on the head and shoulder girdle skeletons of the primitive tetrapod Ventastega curonica. - Latvijas ģeoloģijas vēstis, 4. 36-42 p. (in Latvian with English summary) Ahlberg P.E., Lukševičs E., Lebedev O. 1994. The first tetrapod finds from the Devonian (Upper Famennian) of Latvia. Phil.Trans.R.Soc.Lond.B, 343: 303-328 p. Behrensmeyer A.K. 1975. The taphonomy and paleoecology of Plio-Pleistocene vertebrate assemblages of Lake Rudolf, Kenya. Bulletin, Museum of Comparative Zoology, 146: 31-108. Behrensmeyer A. K. 1991. Terrestrial vertebrate accumulations. – In: Allison, P.A., Briggs, D.E.G., eds. Taphonomy: Releasing the Data Locked in the Fossil Record. Plenum, New York, p. 291- 335. Bendix-Almgren S.E., Clack J.A., Olsen H. 1990. Upper Devonian tetrapod palaeoecology in the light of new discoveries in East Greenland. Terra Nova 2: 131-137. Coates M.I., Clack J.A. 1995. Romer’s gap: tetrapod origins and terrestriality. Bulletin du Muséum national d’Histoire naturelle, Paris, 4-e ser., sect. C, 17 (1-4): 373-388. Esin D., Ginter M., Ivanov A., Lebedev O., Luksevics E., Avkhimovich V., Golubtsov V., Petukhova L. 2000 Vertebrate correlation of the Upper Devonian and Lower Carboniferous on the East European Platform. Courier Forschungsinstitut Senckenberg, 223: 341-359. Gross W. 1933. Die Fische des baltischen Devons. – Palaeontographica, Abt. A, 79: 1-74. Gross W. 1942. Die Fischfaunen des baltischen Devons und ihre biostratigraphische Bedeutung. – Korrespondenzblatt des Naturforscher-Vereins zu Riga, 64: 373-436. Ivanov A., Lukševičs E. 1994. Famennian Chondrichthyans from the East European Platform. - Daba un muzejs, 5: 24-29. Lebedev O.A., Lukševičs E. 1996. Attempted correlation of the upper part of the Famennian deposits of Baltic and Central Russia by vertebrates. The Third Baltic Stratigraphical Conference. Abstracts and Field Guide. Tartu, pp. 35-36. Lebedev O.A. 2004. A new tetrapod Jakubsonia livnensis from the Early Famennian (Devonian) of Russia. Acta Universitatis Latviensis, this volume. Riga, pp. 79-98. Liepiņš P. 1959. Famenskie otlozheniya Pribaltiki [Famennian deposits of the Baltic area]. Riga, Academy of Sciences of SSR of Latvia. 140 p. [in Russian] Lukševičs E. 1991. Bothriolepids from the Ketleri Beds of the Upper Devonian of Latvia (Pisces, Placodermi). Daba un muzejs, 3. – Riga: Gandrs. Pp. 38-50. Lukševičs E. 1992. Palaeoichthyocenoses of the Famennian brackish seas of the Baltic area. - Academia, 1. Tallinn: 273-280 p. Lukševičs E. 2001. Bothriolepid antiarchs (Vertebrata, Placodermi) from the Devonian of the north-western part of the East European Platform. – Geodiversitas, 23 (4): 489-609.
Page 1 and 2:
LATVIJAS UNIVERSITĀTES RAKSTI 679.
Page 3 and 4:
LATVIJAS UNIVERSITĀTES RAKSTI 679.
Page 5 and 6:
Contents Ervīns Lukševičs and Ģ
Page 7 and 8:
ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 9 and 10:
Ervīns Lukševičs, Ģirts Stinkul
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Olga Afanassieva. Microrelief on th
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
D.K. Elliott, E. Mark-Kurik, E.B. D
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
C.G.Miller, T. Marss, H. Blom. New
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 59 and 60:
H.-P. Schultze, T. Marss. Revisitin
Page 61 and 62:
Page 63 and 64:
Page 65 and 66: H.-P. Schultze, T. Marss. Revisitin
Page 79 and 80: ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 81 and 82: O.A. Lebedev. A new tetrapod from R
Page 99 and 100: ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 101 and 102: E. Lukševičs, I. Zupiņš. Sedime
Page 115: E. Lukševičs, I. Zupiņš. Sedime
Page 121 and 122: J. Valiukevičius. Silurian acantho
Page 149 and 150: V. Pernegre, V. Dupret. Biostratigr
Page 159 and 160: Ž. Žigaite. New telodont from Tuv
show all

Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?