| Abstract [eng] |
The regional horizon of Geluva has been characterized in the written materials (Paškevičius and others, 1994) of the second conference of Baltic stratigraphists which took place in Vilnius, Lithuania in the year 1993. Earlier it was recognized as a separate stratigraphic element only in conjunction with Euripterus (Schmidt, 1891) layers and those layers were correlated with the lower part of Ludlov. Later on those layers were given the name of Rootsikülos (Bekker, 1925). The stratotype of the regional horizon of Rootsikülos was in the extinct quarry of Viitos (Sidaravičienė, 1999). The neostratotype has been characterized in the exposures of Vesiku stream near the village of Rootsikülos, the hipostratotype – in the boring of Kipio (interval between 25.6 and 53.6 meters) (Эйнасто, 1970). The regional horizon of Rootsikülos is characterized in shallow-water facies which are being dominated by layered lagoonal dolomites, dolomites containing with bioturbations, by layered stromatopors and coarse-fragmented limestone. The boundaries of this horizon were determined by referencing the cycle of sedimentation. The sectional view of the regional horizon of Rootsikülos in Estonia does not have correlational features that are required for a chronostratigraphic element. The stratotype is in lagoonal facies. The sectional view contains stratigraphic breaks and gaps which, in conjunction with the incomplete geological sectional view, is the cause for unclear boundaries of the regional horizon in the entire basin and vague correlations. The boundaries and the scope in the global graptolithical stratigraphical scale do not correlate with the boundaries and scopes of biozones due to the missing accurate correlation of the regional horizon in the entire basin. The boundaries do not relate to sedimentary cycles in all the facies. Based on the above, during the second conference of Baltic stratigraphists it was decided to replace the regional horizon of Rootsikülos with another one – the regional horizon of Geluva which satisfies all the requirements for a regional horizon that could be treated as a chronostratigraphic element. Although the regional horizon of Geluva was already proposed in 1999, the Estonian geologists are still clinging on to the old incorrect chronostratigraphic element of Rootsikülos which does not have a defined stratographic scope and is very hard to correlate with international stratographic scale. It is advisable to use it as a chronostratigraphic element of the eastern basin of Baltic Silur for stratigraphists from other countries (Cramer and others, 2011). Sometimes, by changing the upper boundary of this regional horizon, it is advisable to characterize the regional horizon of Rootsikülos in shallow facies (Kiipli ir kt., 2011). In this case, the eastern basin of Baltic Silur would have two regional horizons of similar scope which, in turn, is inconsistent with the stratigraphical canons. The purpose of this work is to review the stratigraphy of the regional horizon of Geluva and to clarify its standing (correlation) in the international stratigraphic scale. The following tasks have been raised: 1. To examine the graptolites from Vidukles – 61 boring, 2. To segregate the biozones of graptolites, 3. To correlate the biozones of graptolites with the geochemical and geophysical data, 4. To discover reliable chronostratigraphic benchmarkfor the correlation of regional horizon of Geluva with other regions. |
