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- Title: Silurian Reefs of Gotland
- Author: A. A. Manten
- Publisher: Elsevier
- Pages: 554
The Swedish island of Gotland, in the Baltic, has long attracted the attention of many geologists. Of these, several have visited the island, and more than a few have contributed to the extensive literature concerning its Middle Palaeozoic sediments and fossils. A large number of museums and institutions contain beautiful petrifactions derived from Gotland.
Nevertheless it took a long time before a more or less definite stratigraphy of this island could be established. Although the stratigraphical subdivision, proposed by Hede, has been rather generally accepted since 1921, a few dissentient views were still subsequently recorded (Wedekind and Tripp, 1930; Jux, 1957).
These stratigraphical difficulties stem from the variable genesis of the sediments involved. The stratigraphical column of the Middle Palaeozoic of Gotland shows an alternation of sediments, typical of deposition in a shallow sea, bordered by a base-levelled continent. Small sized epeirogenetic movements of the sea floor resulted in very marked differences in the facies of the sediments (marlstone, limestone, oolite, sandstone). Moreover, in several localities in Gotland, the succession of sediments which is normal for an epicontinental basin, is overshadowed by the occurrence of reefs. These reefs formed protruding elevations on the sea bottom and influenced the process of sedimentation. This caused a number of local differences in the facies of the deposits, even within a certain bathymetrical zone. Besides, each of the several facies may contain a fauna largely typical of the special environment, more so than of the time of deposition, making stratigraphical work even more difficult.
It is clear from these short remarks, that for a good understanding of the sedimentary succession of Gotland, it is highly important that the distribution of all the different kinds of sediments be carefully mapped and their faunal contents intensively studied. This has been done especially by Hede. But this alone is not sufficient. An attempt should also be made to deduce the mode of formation of the various sediments, both stratified and unstratified, and to study their interrelationships.