Hundreds of high-quality drill cores have been extracted in Estonia since 1958 in the course of geological mapping and prospecting for mineral resources and groundwater supplies. However, the material obtained has been analysed to a greatly variable degree, depending on the particular geological task.
Detailed restudy of selected drill cores was started at the Geological Survey of Estonia in 1995. Until now ten issues of the journal Estonian Geological Sections have been published, each dealing with one core (Fig. 1). The bedrock succession studied ranges from the Proterozoic (Palaeoproterozoic–Neoproterozoic) to the Palaeozoic (Cambrian–Devonian). The stratigraphic subdivision of the sections (Table 1) has been improved mainly on the basis of data on the distribution of chitinozoans, conodonts, ostracods and acritarchs in the Cambrian, Ordovician and Silurian, and acanthodians in the Devonian. Rock composition has been specified, using different chemical and mineralogical analyses (Table 2). Stable isotope data of Ordovician and Silurian rocks were first included in the 2003 issue.
The issue on the Soovälja (K–1) core includes data from the deepest drill hole (815.2 m) in Estonia, made in the Kärdla meteorite crater in the course of geological deep mapping of Hiiumaa Island in 1990.
From 2003 onwards the appendixes of issues are available on the CD-ROM. These include photo-logs of the core, photos of selected intervals and thin sections with descriptions, laboratory data, and drawings illustrating the rock types in combination with fossil distribution and stratigraphic scale.
The photo-log of the Viki drill core (tenth issue) with depths and positions of the studied samples has been included in the database of the Institute of Geology at Tallinn University of Technology (accessible online at http://sarv.gi.ee/attachments/locality/1464/1464_2.pdf). Explanations to the samples are available on the CD-ROM of the Viki bulletin: selected intervals (Appendix 2), thin sections (Appendix 3), chemical composition (Appendixes 4, 12, 14), chitinozoans (Appendixes 5–8) and conodonts (Appendixes 9–11). All material on the Ordovician and Silurian of the Viki drill core is contained in the bulletin.
More than 70 people contributed to the publication of the journal, among them over 55 authors from twelve geological institutions of the USA, Denmark, Sweden, Finland, Lithuania, Austria and Estonia (Table 3). A large dataset has been compiled as a result of long-term collaboration between the authors, and thus the journal can be considered as a kind of Estonian geological heritage from the older generation to the younger.
Infoisik: Anne Põldvere, Tartu Regionaalosakond, vanemgeoloog, tel: 733 9004