VOLUME 19 (1)/February 1989

D. Kozhoukharov, B. Timofeev. Microphytofssil data on the Precambrian age of the Rhodope Supergroup (Sitovo and Asenovgrad Groups) in the Central and Western Rhodopes. Proterozoic microphytofossils have been found in the Rhodope Supergroup in the Central and Western Rhodopes which define Early Proterozoic age for Rupčos and Sitovo Groups. The microphytofossils in Sitovo Group - Lukovica Formation, belong to six genera: Protosphaeridium Tim., Leiosphaeridia Eis., Trematosphaeridium Tim., Synsphaeridium Eis., Stictosphaeridium Tim. and Phycomicetes of which g. g. Leiosphaeridia and Phycomicetes began to develop in the middle part of the Early Proterozoic. The rocks of Lukovica Formation are overlain by the marbles of Dobrostan Formation which contain Riphean microphytofossils.
   Asenovgrad Group, consisting of two formations - Dobrostan Marble Formation and Belaštica Carbonate Silicate Formation, contains the richest complex of microphytofossils which belong to 12 genera of the group of one-cell algae Sphaeromorphida and Scaphomorphida. The Sphaeromorphida Group is represented by 11 genera: Protosphaeridium Tim., Orgymatosphaeridium Tim., Stictosphaeridium Tim., Synsphaeridium Eis., Trematosphaeridium Tim., Trachysphaeridium Tim., Leiosphaeridia  Eis., Gloeocapsomorpha Zal., Pterospermopsimorpha Tim., Kildinella Tim. and Phycomicetes of which g. g. Kildinella and Scaphyta appear during the Upper Proterozoic - Riphean. The species Kildinella timanica Tim., Pterospermopsimorpha pileiformis Tim. and Scaphyta sp. define the age range of Asenovgrad Group as Early - Middle Riphean since the Late Riphean and Vendian are characterized by other species of g. Kildinella and new morphological groups of microphytofossils appear.
   The proven Riphean age of the rocks from Asenovgrad Group explains the position of the marbles from Dobrostan Formation upon different parts of the section of Rupčos and Sitovo Groups (until now always shown as divided by tectonic contact). This boundary marks in the Rhodope Massif one of the large breaks during the Precambrian - the break between the Lower and Upper Proterozoic (Riphean). These facts require a correct revision of the lower boundary of Asenovgrad Group, respectively Dobrostan Formation in the Rhodope Massif which in some outcrops is really tectonic and in others is not.

The marbles at the Asenova Krepost Castle in the Central Rhodopes lie about 10 km to the south of the town of Asenovgrad. They belong to a lithostratigraphic unit consisting of alternating calc schists, mica schists, marble and amphibolites. Marble surface have been shown to bear marks of palaeontological entities besides the numerous traces of weathering processes, lichens, etc. In several marble sample, examined in this study, specimens of Aspidella terranovica Billing, 1872, Atikokania lawsoni Walcott, 1912, and Chuaria Walcott, 1899, have been identified. These species occur in the Precambrian of North America, and the third one is found also in the Precambrian of Sweden and the Soviet Union. The finds are regarded as conclusive evidence of the Precambrian age of the Asenova Krepost marbles.