ORDOVICIAN ERRATIC TRILOBITES (ARTHROPODA, TRILOBITA)FROM PLEISTOCENE DEPOSITS OF BELARUS (PRELIMINARY DATA)

Abstract

Analysis of geographic distribution and determination of geological age of erratic pre-Quaternary sedimentary
megaclasts (blocks, boulders and pebbles) enclosed in Quaternary deposits is especially important for localizing their possible sources and native areas. Except for some varieties of rocks that can be identified by their unique petrographic features, definite stratigraphic systematization of the majority of sedimentary megaclasts can be carried out only by means of paleontological study. However, petrographic features have been used solely in almost all previous publications dealing with sedimentary erratics from the territory of Belarus, so it is questionable whether the results can be considered reliable without paleontological confirmation.

Identification of trilobites (Trilobita Walch, 1771) is applied here for the purpose of ascertaining the geological
age of Ordovician sedimentary blocks, boulders and pebbles redeposited in Pleistocene strata of Belarus. At this time, trilobites belonging to 15 genera and subgenera have been identified in the studied area. They represent the major part of the Ordovician carbonate bedrock succession typical for the East-European Platform. Strata of this succession are subjacent to various younger deposits in north- and southwestern parts of Belarus and in the Baltic States and crop out in northern Estonia and the St. Petersburg Region of Russia.

We propose that the studied Ordovician erratic material is not necessarily the result of long-distance transport,
which is usually presumed according to the theory of Pleistocene continental glaciations, but might have been
redeposited from nearby buried Ordovician bedrock sources as well. Taxonomic composition of the “Ordovician erratic trilobite complex” of Belarus denotes its similarity to the “erratic trilobite association” from northern Germany, northern Poland and Kaliningrad Region of Russia (formerly East Prussia). At the same time it also shows clear affinity to trilobite assemblages from Middle and Upper Ordovician bedrock outcrops in northern Estonia and the St. Petersburg Region (East Baltics), although it is not entirely typical for them. It is also notable that several of the collected trilobite specimens show morphological dissimilarity with typical trilobite material described in paleontological literature.

Fig. 28. Table 1. Ref.: 41 titles.