VOLUME 20 (2)/April 1990

D. Kozhoukharov, M. Konzalova. First finds of microphytofossils in the marbles of Dobrostan Formation. Nothem and Southern Pirin. Preliminary results of the studies on 12 samples from Dobrostan Formation along three profiles in Northern and Southern Pirin Mountain, as well as on one sample from the stratotype of the Formation in the Central Rhodope Mountains, revealed different amounts of organic matter. The latter consists of organic coats, plant detritus, graphite crystals and kerogene matter, and contains also specimens of microphytofossils in differing state of preservation. The following taxa have been determined: Protosphaeridium sp., Protosplweridium den sum Tim., Kildinella sp., Kildinella cf. sinica Tim., Kildinella cf. hyperboreica Tim., and Trachysphearidium (?) sp. These microphytofossils are characteristic for the Upper Proterozoic (Riphean). The presence of the genus Kildinella – a guide fossil for the Riphean of Eurasia, confirms the Riphean age of Dobrostan Formation in Pirin Mountain, i.e. the same age already establi shed for this Formation in its type region.

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Some velocity characteristics of the crust and upper mantle in the central part of the Balkan region are studied on the basis of about 1000 local and teleseismic earthquakes, registered on the 32 seismic stations. An approach for estimation of the large anisotropic structures effects is used together with the general consideration about the connection between the time residuals and velocity inhomogeneities. The main features of the inhomogeneities in the crust and upper mantle are drscussed in relation with some gravity, heat flow and seismotectonic data. The distribution of the crustal inhomogeneities in general corresponds to the configuration of the morphotectonic structures in Bulgaria. The subcrustal inhomogeneities are discordant with the surface structures, but their orientation is in coincidence with the Trans-Balkan seismolineament system. This fact indicates that the crustal seismicity in the region is probably controlled by the upper mantle structures. The high-velocity structures in the deep upper mantle beneath the Rhodope massif probably represent a paleosubduction at a depth more than 300 km.