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On the vertical distribution of Nummulites in the Paleogene deposits of Georgia

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R O C Z N I K P O L S K I E G O T O W A R Z Y S T W A G E O L O G I C Z N E G O A N N A L E S D E L A S O C I E T E G E O L O G I Q U E D E P O L O G N E

T o m ( V o l u m e ) X X X I X — 1969 Z e s z y t ( F a s c i c u l e ) 1—3 K r a k ó w 1969

IV A N E V. K A C H A R A V A *

ON THE VERTICAL DISTRIBUTION OF NUMMULITES IN THE PALEOGENE DEPOSITS OF GEORGIA

И. В. К А Ч А Р А В А

О вертикальном распределении нуммулитов в палеогеновых отложениях Грузии The N um m ulites are w ell represented in the Paleocene and Eocene deposits of the Georgian Soviet Socialist Republic (GSSR).

N um m ulite lim estones are w idely spread in the w est part of the GSSR (Racha, Lechkumi, Guria, Abkhasia). In the east part of Georgia they are replaced by the sandy-argillaceous and volcanic formations, in which the mentioned group of fossils occurs sporadically. On the southern slope of the Great Caucasus the terrigenous flysch exposed along the northern part of the Kartalinian depression also contains the m entioned fauna.

The Adjaro-Thrialethian folded system , situated southwards, consists of Paleocene and Lower Eocene flysch, Middle Eocene volcanic series and Upper Eocene sandy-argillaceous formation. The latter is replaced to the w est by the volcanic deposits of the Adigeni suite. N um m ulites were found at different levels of these deposits. They occur also in the deposits of the Akhaltsi'khe depression and in the rocks of the Som khithi Block, w hich is situated in the south-eastern part of Georgia.

In the above m entioned deposits, from the bottom to the top one can distinguish: 1. the horizon w ith Nummu lites fraasi d e l a H a r p e . This form has been discovered as yet in the argillaceous part of the section (4— 5 m), exposed in the Som khithi Block below the transgressive volcanic formation w ith the Middle Eocene N um m ulites near the district centre Thethri-Tskaro.

These clays w ere dated earlier as M ontian by N. M r e v l i s h v i l i (1965) and the present writer on the assum ption that the deposits w ith this fauna follow conform ably the ligh t-grey lim estones and marls of the Danian Stage.

But detailed investigation of the mentioned section (1967) proved that a gap exists betw een the Danian and the Paleocene. It appears now that the dark clays of the Paleocene here begin w ith coarse grained sand, w hile the clays im m ediately above contain redeposited Upper Cretaceous m icroforam inifers. The N um m ulites appear still higher, in the thinnest intercalations of arenaceous clays. And the clays them selves contain only the m icroforam inifers of the Globorotalia pseudomenardii zone, that is to say, the upper part of the Paleocene (Ilerdian).

* A d dress: Iv a n e V. K a ch a rava — Иване В. Качарава, T b ilisi, B arn ova 64, G SSR .

16 R o c z n i k G e o l o g i c z n y t o m X X X I X

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— 2.42 —

The stratigraphical position of Nummulites fraasi is more exactly defined in Austria w here according to G o h r b a n d t (1964) Nummu- lites cf. fraasi was found in the deposits exactly above the beds w ith rich Thanetian molluscs.

This N um m ulite has a sim ilar position in the east part of Egypt (the district o f Faraphrah Oasis), where dark Esnah shales are developed.

The m entioned N um m ulite was for the first tim e found and described in the low er part of these shales. According to the recent data (S c h a u b, 1964) the Esnah shales, unconform ably overlying the M aestrichtian lim e­

stones, contain besides the N um m ulites A lveolina fauna of the Ilerdian and m icroforam inifers O'f the Globorotalia pseudomenardii zone (Upper Palaeocene). Thus, the Upper Palaeocene age of Nummulites fraasi is beyond doubt. The Palaeocene N um m ulites are sm all-sized and repre­

sented by megaspheric forms.

2. The horizon w ith Nummu lites planulatus L a m a r c k . In the upper part of the Thrialethian flysch above the beds w ith Discocyclina cf. seunesi D o u v. of the Palaeocene a more abundant fauna of N um ­ m ulites is observed (N. planulatus, N. exilis, N. lucasi, etc.). The first tw o form s are more frequent and, moreover, both m egaspheric and microspheric forms are present.

3. The horizon w ith Nummulit es laevigatus B r u g u i e r e . The typical form of th is species has been known since long in Lutetian volcanic deposits of the northern slope of Thrialethi.

In the upper parts of the volcanic series in the districts of the villages D zegvi and Akhalkalaki a m ixture of some Lutetian (Numm ul ite s mille- caput) and Upper Eocene-O ligocene forms (N. incrassatus) was found together w ith N. aff. laevigatus L a m k , and species of N um m ulites of a wider vertical range. These deposits correspond to the Biarritzian stage (the upper part of the Middle Eocene) of W estern Europe.

A similar fauna w as found also in the equivalent beds of the w estern part of the Adjaro-Thrialethi in Guria ( K a c h a r a v a , 1964). In the carbonate deposits of the Middle Eocene of our Republic nongranulated species of N um m ulites are represented (N. murchisoni, N. irregularis, N. distans, etc.). They are rookforming in W estern Georgia, but in the volcanic deposits of the southern part of the Republic (Adjaro-Thrialethi, Som khiti Block) granulated representatives of this fauna prevail {N.

partschi, N. laevigatus, N. gallensis, etc.) widespread in the equivalent deposits of Armenia and southern Azerbaijan.

The Middle Eocene N um m ulites are larger and more variable.

4. The horizon w ith „Nummu lites fabianii,\ North of the Dzirula m assif, in the upper course of the K virila-river Num m ulite lim estones of sm all thickness w ith N. fabianii (type), N. incr\ass>atus, etc., are exposed overlain by the Maikop beds of the Oligocene, but southwards above the Biarritzian deposits of Thrialethi the Lyrolepis beds are developed (the low er part of the Upper Eocene) which in some places (Gori) cover discordantly the Cretaceous. Above follow sandstones inter­

bedded w ith clays. From the sandstones N. fabianii ssp. n., Discocyclina sella, etc., have been determined. H owever, in som e places (e.g. the southern slope of the Caucasus in Kartalinia) these deposits overlap directly beds of different ages. Probably, the m entioned unconform ities are of the same age, because in the Tskhanari syncline (Racha) N. fa­

bianii ssp. n. was found in the deposits of the Lyrolepis horizon. N. fa­

bianii ssp. n. takes its place above the rocks w ith N. fabianii Prev. In

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— 2.4,3

c o m p a r i s o n w ith the type — species this subspecies is sm aller and thinner, w ith thin granules on the surface. N. fabianii ssp. n. does not fu lly coincide w ith N. retiatus. On the surface of the latter the granules are scarcely noticable. N. fabianii ssp. n. and N. praefabianii M e n n e r ( = N. problemalicus T e 11 i n i?) belong to the same species. ,,N. pra e­

fabianii” is mentioned by the West European authors in the upper part of the Middle Eocene. It has nothing in common with N. praefabianii M e n n e r ( — N. fabianii ssp. n.), neither by its structure nor by its stratigraphical position.

Thus, the initial form of the series — ,,N. praefabianii” of the W est European authors — is of Middle Eocene age ( S c h w e i g h a u s e r , 1953—1954). More exactly, it is a form of the uppermost part of the M iddle Eocene. Stratigraphically above it is replaced b y N. fabianii (type).

Nummu lites fabianii ssp. n. is found in the highest part of the Upper Eocene (beds w ith Bolivina).

Stratigraphically higher N um m ulites are unknown in the deposits of Georgia, but in the equivalent deposits of West Europe N. retiatus occurs. It is described from the low est part of the Oligocene, or from the Upperm ost part of the Upper Eocene (R о v e d a, 1959).

A c a d e m i c i a n , G e or g i a A c a d e m y of Sc ience s

REFER EN CES

G o h r b a n d t K. (1964), A p ergu sur la su b d iv isio n du P a le o ce n e et de l ’E o c e n e le plus in ferieu r dans l ’H e lv e tic u m au nord de S a lzb ou rg (A utriche), b ase su r des F o ra m in iferes p la n cto n iq u es. M e m. B u r e a u rech. geol. min. C olloq u e sur le P a leog en e, 2.

K a c h a r a v a I. V. — К а ч а р а в а И. В. (1964), Вопросы стратиграфии среди е- эо ц еш в ы х отлож ений северной периф ерии С редизем ном орского бассейна.

В оор. геол. Грузии, АН ГС С Р, к XX II сессии МГК.

M r e v l i s h v i l i N .I . — М р е в л и т в и л и Н. И. (1965), П алеоценовы е нумму­

литы Ю го-Восточной Грузии. Из-в. Геол. общ . Грузии, т. IV, вып. 2.

R o v e d a V. (1959), N u m m u lites retia tu s n o u v e lle esp ece de N u m m u lite r e tic u le e des A bruzzes (Italie). Re v . Micr opal eont., nr 4.

S с h a u b H. (1964), L es b a ssin s p a leo g en es su isse s. C olloque p a leo g en e, B o rd ea u x , M e m . B R G M .

S c h w e i g h a u s e r I. (1953— 1954), M ik ro p a lao n tolo gisch e und str a tig r a p h isc h e U n tersu ch u n g en im P a leo ca en und E ocaen des V icen tin (N orditalien). S c h w e i z , pal eont. Abh. , 70.

Р Е ЗЮ М Е

На основе данных нуммулитовой фауны в палеоценовы х и эоценовы х отл о­

ж ен и ях республики выделяются следую щ ие горизонты: 1. Горизонт с N. f r aa s i в ер хн его палеоцена, 2. Горизонт с N. p l a n u l a t u s илрекого яруса, 3. Горизонт с N. l a e v i g a t u s лютета; в кровле ср едн его эоц ен а наблю дается фауна, характерная для биаррицского яруса, 4. Горизонт с ,,N. f a b i a n i i типичная ф орм а данного вида обн аруж ен а в нижней части отлож ений, выше ж е появляется N. f a b i a n i i ssp. n. { = N. p r o b l e m a t i c u s T e l l i n i (?)).

В олигоценовы х слоях республики нуммулиты не были обнаруж ены .

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