5

to the Llandovery-Wenlock boundary) this boundary lies not below the middle part of the Ust'Durnayu Stage. However, several specialists in the region still argue against the dates based on conodonts, and try to explain the problems connected with correlation of the sea-level curve of the Timan-Urals basin with those from other regions by specific conditions in the basin (all over the world the Telychian is known as a time of maximum transgression, but in the Timan-Urals regions it seems to be the opposite - the Telychian is represented by the most shallow- water sediments).
3. Ordovician and Silurian intervals of the Palaeozoic sequence from different parts of the Timan-Pechora region will be demonstrated.
4. Melnikov and Zhemchugova are preparing a manuscript "Lower Silurian of Timan-Ural region (the problems of global correlation)" dealing with the problems of evolution of the basin, and stratigraphy. Their studies of sedimentology are based on the method of sequence stratigraphy. The analyses of the distribution of various faunas in the sections on the Kozhym River allowed the authors to recognise 31 distinct levels (named as datums) which are marked by appearance(s) and/or disappearance(s) of taxa, and can be used in correlations. Field meeting in the Subpolar Urals (Kozhym River basin)
Time:July 12 - August 2, 1999.
Participants:
T. M. Beznosova, leader of the team, Institute of Geology of the Komi Science Centre, Ural Division of Russian
Academy of Sciences, Syktyvkar;
V.Yu.. Lukin, Institute of Geology of the Komi Science Centre, Ural Division of Russian Academy of Sciences,
Syktyvkar;
S. V. Melnikov, Timan-Pechora Scientific Research Centre, Ukhta;
V. P. Savel'ev, Timan-Pechora Scientific Research Centre, Ukhta;
P. Männik, Institute of Geology at Tallinn Technical University (Tallinn, Estonia).
Main tasks of the field meeting:
One of the main tasks of this field meeting was to work out the routes and subjects of geological excursions in the national park Yugyd Va. The tasks of this expedition included also:
1) detail study of sections, and bed-by-bed collecting of fauna, from the Orodvician-Silurian boundary interval; 2) investigation of different sedimentary environments on the shelf margin of the Early Palaeozoic Timan-Urals
palaeobasin;
3) study of faunal associations and their relations to the different palaeoenvironments.
The study of the sections started in the region of mouth ofthe Balban''yu River (sections 73, 74, 75, and 76) where Ordovician and Silurian reefal facies are exposed. According to previous data, these reefs developed in Ashgill and in Ludlow times. Additional samples of conodonts were taken to specify the age of reefs, and of basinal sediments (black bedded limestones with chert) also exposed in this region.
Also, sections 86, 87 and 89 (region of mouth of the Tavrota River) were briefly examined. Here, Middle and Upper Ordovician strata are well exposed. In the region of mouth of the Bet'yu River (Gur'ev Pool), the Ordovician and Silurian contact (section 108) was studied, as were lower Silurian strata (sections 108, 109, 795); detailed collecting of faunas (brachiopods, tabulate and rugose corals, and samples for conodonts) was undertaken to identify the precise age of the exposed strata.
In section 108, a continues sequence across the Ordovician-Silurian boundary is exposed. Here, the oldest rocks are represented by stromatolitic limestones of the Malaya Tavrota Formation. These strata formed in extremely shallow-water conditions during the late Ashgill regression. The uppermost Ordovician strata in this section are represented by various, mainly massive, limestones of the Yaptikshor Formation. Relatively rich faunas occurring in this formation indicate that these strata formed in normal marine environments, probably in a time of a transgression. The Ordovician beds are overlain by bedded, strongly dolomitised limestones of Silurian (Llandovery) age. The precise position of the Ordovician-Silurian boundary in the section is not yet known. Between the uppermost strata with Ordovician pentamerids and the lowermost occurrence ofundoubtedly Silurian pentamerids is an interval (about 100-150 m in thickness) of strongly dolomitised limestones where macrofauna is completely destroyed. A series of conodont samples was taken from this interval to identify the age of these strata. The study of the Ashgill and Llandovery strata is particularly important to investigations of the evolution of and crises in faunal successions. As is well known, the extinction in many groups of faunas at the end of the