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: dimek@geology.bas.bg

(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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