45 Brachiopod macrofaunal distribution through the upper Volkhov – lower Kunda (Lower Ordovician) rocks, Lynna River, St. Petersburg region JESPER HANSEN & DAVID A.T. HARPER Hansen, J. & Harper, D.A.T. 2003–04–30: Brachiopod macrofaunal distribution through the upper Volkhov – lower Kunda (Lower Ordovician) rocks, Lynna River, St. Petersburg region. Bulletin of the Geological Society of Denmark, vol. 50, pp. 45–53, Copenhagen. © 2003 by Geological Society of Denmark. ISSN 0011–6297. The ranges of 27 brachiopod species, through the upper Volkhov-lower Kunda interval of the Lynna River section, are presented on the basis of over 17,500 specimens. Three depth-related ecological associations are recognized within the succession of alternating limestones and marls forming part of an array of nearshore to mid-shelf communities in an intracratonic setting. Fau- nal diversity is relatively stable throughout the section with little evidence for abrupt local extinctions or originations. The dominant orthoid and clitambonitoid assemblages, however, form the basis of the distinctive Baltic brachiopod province developed during this time interval. Key words: Brachiopods, Volkhov, Kunda, Lynna River, biodiversity, brachiopod assemblages. Jesper Hansen, Geological Museum, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark (Present address: Tromsø University Museum, NO-9037 Tromsø, Norway) & David A.T. Harper [dharper@savik.geomus.ku.dk], Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark. 2 January 2002. ized by abundant, diverse and well-preserved shelly faunas, which not only have formed the subject of much monographic research, but also are providing data to frame and test models for biodiversification in the region. The Lower Ordovician successions are exposed along the Baltic-Ladoga Klint line in a series of quarries and river sections. The Lynna River pro- vides near complete and accessible exposure through the Lower Ordovician succession within Lamansky’s (1905) type area. Geological Setting The St. Petersburg region is located between the con- tinuation of the Baltic palaeobasin to the west (and northwest) and the Moscow palaeobasin to the south- east (Fig. 1); the successions are dominated by con- densed carbonates. Ordovician successions were de- posited in the eastern part of a relatively shallow, epicontinental sea, characterized by very slow rates of sedimentation (Lindström 1963, 1984; Männil 1966). Carbonate sources in the eastern part of the palaeo- basin may have competed with siliciclastic sources to The Ordovician rocks of the St. Petersburg region (Fig. 1) have, for nearly 200 years, been the focus for inten- sive palaeontological and stratigraphical studies. Al- though Kutorga published the first detailed geologi- cal map of the region in 1852 following initial over- views by Murchison and others, it was Schmidt (1881) who first developed a stratigraphical scheme for the Lower Palaeozoic rocks of the greater region; this, in a modified form, is the basis for modern correlation and interpretation of the succession (Bruton et al. 1997). Schmidt’s scheme was enhanced and modified by Lamansky (1905) and his units have helped define the regional stages, developed by Männil (1966) and others (e.g. Männil & Meidla 1994), that are currently in use. Nevertheless many of these units are based on a confusing mixture of litho- and biostratigraphy and to date have not been formally defined in type sec- tions in the Baltoscandian palaeobasin. Moreover their use outside the East Baltic region is restricted, where, for example, the development of siliciclastics and deeper-water facies limit their recognition. These units have, however, been used in this study together with the recognised lithostratigraphy because the Lynna River in fact falls within the type area for Lamansky’s units. These Ordovician units are typically character- Hansen & Harper: Brachiopod macrofaunal distribution Volkhov – lower Kunda ·