GEOLOGICA BALCANICA, 30, 3-4, Sofia, Febr. 2001, p. 59-63
New fossil evidence for the Lower Paleogene ( Krumovgrad Group) in the East Rhodope Mountains, SE Bulgaria
Ek. Dimitrova, A. Goranov, Iv. Boyanov
Geological Institute, BAS, 1113 Sofia; E-mail: [email protected]
(Submitted 15.12.1999; accepted for publication 23. 06.2000)
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Abstract. Ek. Dimitrova, A. Goranov, Iv. Boyanov. New fossil evidence for the Lower Paleogene (Krumovgrad Group) in the East Rhodope Mountains, SE Bulgaria. An Algal detritus which is the basic rock-forming material is established in the organogeneous limestones among the coarse-terrigenous deposits of the Krumovgrad Group of the Mandritsa depression to the South of lvaylovgrad along the Kostilkovska river valley. A various foraminiferal assemblage is found in these rocks consisting mainly of the representatives of the families of Lagenidae, Discorbidae, Miliolidae, Textulariidae, Rotaliidae, Acervulinidae, Linderinidae. These bioassociations are typical of the reef(marine shallow-depth) facies. They contain most of the bioelements of the co-assemblages of the intraplatform facies of the Paleocene and the Early up to Middle Eocene basins of the South Tethys. Furthermore, they are analogous to the assemblages described in the Upper Paleocene of the West Carpathians and the Middle and Upper Paleocene in the Dinarides. Following these comparisons, the age of the coarse-clastic deposits along the Kostilkovo river valley could be referred to the span Upper Paleocene - Middle Eocene. Thus, the presence of marine Lower Paleogene sediments is proven also in the West part of the East Thracian depression.
Dimitrova, Ek., Goranov, A., Boyanov, lv. 2000. New fossil evidence for the Lower Paleogene (Krumovgrad Group) in the East Rhodope Mountains, SE Bulgaria - Geologica Bale., 20, 3-4; 59-63 Key words: SE Bulgaria, East Rhodope Mountains, Krumovgrad Group, Lower Paleogene, fossil evidence.
Introduction
Finding of the Paleocene in Krumovgrad area, East Rhodope Mountains (Atanasov, Goranov, 1984) led to intensive investigations which proved the presence of that system in many more places in the same region. Boy-
anov and Goranov (1994) published a generalization about the presence of the Late Paleogene deposits in the East Rhodope Mountains and described for the first time the presence of marine Paleocene - Eocene sediments proven by pelagic microfauna in the Asenovgrad area.
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Geological background and faunistic data The present paper reports new faunistic information about the sediments of the Krumovgrad Group (Goranov, Atanasov, 1992). They fill in the South margin of the Mandritsa depression located to the South of Ivaylovgrad along the Kostilkovska river valley and to the North of Petrova Mogila peak in the areas of Kostilkovo, Oreshino, Mandritsa, Dolno Lukovo and Meden Bukvillages (fig. 1). In respect of geotectonics that depression builds up the westernmost periphery of the wide East Thracian depression developed widely on the territory of Greece and Turkey where a presence of a marine type of Paleocene is proven (Suemengen, Terlemez, 1991). The Krumovgrad Group is undifferentiated in the range of the Mandritsa depression. It is mainly represented by boulder-block, poligenic breccia consisting of olistolites and olistoplacas of high-grade metamorphic and low-metamorphic Phanerozoic
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rocks which are various in respect to composition and sizes. There are a sand-conglomerate bands into the Lower Paleogene depositions as well as organogenous limestones lenses with thickness from 0,6 up to 7-8 m that contain a big amount of terrigeneous components. These biodetrital limestones are exposed in the Kostilkovo river valley and along the ridge near by Petrova Mogila peak (fig. 1).
The limestones are composed mainly by algae, bryozoans, corales and microfossil detritus. A relatively diverse foraminiferal association of representatives of the families Lagenidae, Discorbidae, Miliolidae, Textulariidae, Rotaliidae, Acervulinidae and Linderinidae was established. Sections of Rotalia sp., Pyrgo sp., Eoanularia cf. eocenica Cole & Bermudez, Sphaerogypsina cf globulus (Reuss), Eofabiania cf grahami Kueper, Planorbulina sp. (Table I, II) were determined. The stratigraphic distribution of the last four species is considered as Paleocene - Eocene up to Holocene (Loeblich, Tappan, 1988).
The main rock-forming organogenous com-
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Fig. l . Geological map of the Paleogene, (Krumovgrad Group) in lvaylovgrad area, East Rhodope Mountains l - Mezozoic low-crystalline fundament; 2 - Paleocene- Middle Eocene, Krumovgrad Group; 3 - Upper Eocene, conglomerates, sandstones, limestones; 4 - Fault; 5 - transgresive boundary; 6 - Fauna sample number
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Fig. 2. Scheme of the Lower Paleogene depositions distribution in the East part of the Rhodope Mountains area Pre-Paleogene fundament: l - Rhodope super unit; 2 - Sredna Gora super unit. Paleocene - Middle Eocene (Krumovgrad Group); 3 - Continental fresh water depositions; 4 - Marine depositions; 5 - Paleogene - Neogene sediment cover; 6 - Geological boundary; 7 - Faults; 8 - Reverse-slip faults and overthrusts
PLATE I
1. Nummulites sp., sample 2255, Topolovo Formation, Paleocene ; x60. 2. Eofabiania cf. grahami Kueper, sample 94/21", Kostilkovska River, Paleocene - Middle Eocene; x60. 3. Planorbulina sp., sample 94/65, Kostilkovska River, Upper Paleocene - Eocene; x70. 4. Miliolidae, ?Peneroplidae, Rotaliidae (Rotalia sp.), Algae, sample 94/65, Kostilkovska River, Paleocene; x60. 5. Miliolidae, Linderinidae (part), sample 94/65a, Kostilkovska River, Paleocene - Eocene; x60. 6. Miliolidae, (Pyrgo sp.), Algae, sample 94/65a, Kostlkovska River, Paleocene- Eocene; x60.
PLATE II
Mandritsa Regoin, Krumovgrad Group
1,2. Eoanularia sp. (in the association on the fig. 2: Lagenidae and Anomalinidae), sample 94/67, NW Petrova Mogila Pike, Eocene; x80. 3. Sphaerogipsina cf. globulus (Reuss), sample 94/67, NW Petrova Mogila Pike, Eocene; xSO. 4, 4a.Remanellina cf. eocenica Tappan & Loeblich, sample 94/67, NW Petrova Mogila Pike, Eocene, XSO; fig. 4ax120. 5. Eoanularia sp. , sample 94/64, N Petrova Mogila Pike, Eocene;x60. 6. Algae (Distichoplax cf. biserialis Dietrich), sample 94/64, N Petrova Mogila Pike, Eocene;x80.
PLATE Ill
Topolovo Formation
l. Heterohelicidae (Chiloguembelina), Globigerinidae, ? Bolivina sp., sample 2255, Paleocene; x80. 2. Globigerinidae, sample 2255, Paleocene; XSO. 3. Globoconusa daubjergensis (Bronnimann), sample 2254, Paleocene; x80. 4. Globigerinidae (Globigerina gr. triloculinoides Plummer), sample 2257, Paleocene; x80. 5. Globigerinidae, sample 2259; x80. 6. Globigerinidae, ?Globigerinella sp., sample 2257, Paleocene; x80.
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PLATE I
Ek. Dimitrova, A. Goranov, Iv. Boyanov, Geologica Balcanica, 3-4/2000
PLATE II
PLATE III
ponents are the algae and some of them are determined as Distichop/ax biserialis Dietrich and Peyssonella antiqua Johnson (pl. I, fig. 6; pll. fig. 6). They are widely represented in the Paleogene biofacies (AGIP, Atlas, 1988; Samuel et al., 1972). A section of calpionelides was found, tappanstoeblich and determined as -Remanel/ina cf. eocenica (pl. II, fig. 4, 4a).
The available fossil material is badly preserved and is often strongly recrystallized. The non-characteristic foraminiferal sections do not allow a more exact species determination. Most of the cited taxa appear in the Late Paleocene and attain a wide occurrence during the Middle Eocene. The associations determined in the region are characteristic for marine shallow-depth (reef) facies and as a whole are analogous to that ones described for the Upper Paleocene of the West Carpathians (Samuel et al., 1972) and for the Middle and Upper Paleocene of the Dinarides (Radoicic, 1960). Those associations consist most of the typical bioelements of the intraplatform facies assemblages if the Paleocene and Early-Middle Eocene basins of the South Tethys. (AGIP - Atlas, 1988; Salay, Maamouri, 1988).
For a difference of the limestones in the investigated area the limestones of the Northern margin of the East Rhodope Mountains depressions (the area of the village of Topolovo) associating with Early Paleogene coarse-terrigenous sediments have a pelagic character (Boyanov, Goranov, 1994). A foraminiferal planctonic association was found in them: Globigerinidae, Globoconusa daubjergensis (Bronnimann), G/obigerina gr. triloculinoides Ftummer, G/obigerinella sp. Heterohelicidae (Chiloguembelina sp.). It indicates also a Paleocene - Middle Eocene age, and a relatively deeper marine conditions of sedimentation.
The Lower Paleogene deposition distribution in the east part of the Rhodope Mountains area is shown in fig. 2 where the marine and continental sediments are separated.
Conclusions
The comparisons performed in this paper allow the coarse-clastic depositions of the area along the Kostilkovska river valley, Mandritsa subsidence, to be referred in respect of their age to the age span Late Eocene- Middle Eocene. In that way for the first time a marine Lower Paleogene presence is proven in the western part of the East Thracian depression.
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