Conodont biostratigraphy and biofacies across the Devonian-Carboniferous boundary in the Kule section (Uzbekistan).

Cono dont biostratigraphy and biofacies across the De vo nian-Car bon if er ous

bound ary in the Kule sec tion (Uzbekistan)

Katarzyna NARKIEWICZ

*, Carlo CORRADINI

, Nuriddin ABDIEV

and Marek NARKIEWICZ

1 _{Pol ish Geo log i cal In sti tute – Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land} 2 _{Universit´ di Trieste, Dipartimento di Matematica e Geoscienze, via Weiss 2, 34128 Trieste, It aly}

3 _{Kitab State Geo log i cal Na tional Nat u ral Park, Kashkadarya Re gion, Kitab Dis trict, Ipak Yuli Street 9, 181300} Shakhrisabz, Uzbekistan

Narkiewicz, K., Corradini, C., Abdiev, N., Narkiewicz, M., 2021. Cono dont biostratigraphy and biofacies across the De vo -nian-Car bon if er ous bound ary in the Kule sec tion (Uzbekistan). Geo log i cal Quar terly, 2021, 65: 17, doi: 10.7306/gq.1588 As so ci ate Ed i tor: Micha³ Zatoñ

New cono dont data pro vide fur ther con straints on the oc cur rence of the De vo nianCar bon if er ous bound ary in the Kule sec tion through the car bon ate Novchomok For ma tion (Kitab Re serve, Uzbekistan). The stratigraphically con densed sec tion in -cludes the in ter val from the up per most Famennian Pseudopolygnathus granulosus–low er most Protognathodus kockeli zones to the mid dle Tournaisian Siphonodella crenulata Zone. In ad di tion to re vi sion of ear lier pub lished tax o nomic and biostratigraphic data, two pre vi ously un re ported taxa are de scribed: Polygnathus sp. n. A and a pe cu liar form prob a bly rep re sent ing a new ge nus (gen. et sp. indet.). The biofacies anal y sis doc u ments a suc ces sion of polygnathid, siphonodellid --polygnathid, polygnathid-siphonodellid to polygnathid-bispathodid, and again polygnathid-siphonodellid biofacies. The ge neric com po si tion of the sam ples and rel a tive abun dance of Polygnathus purus re flect deep ma rine en vi ron ments of the con ti nen tal slope and rise.

Key words: DCB, car bon ate fa cies, cono dont biostratigraphy, biofacies anal y sis, deep ma rine en vi ron ment.

INTRODUCTION

The De vo nianCar bon if er ous bound ary (DCB) is the sub -ject of con tin u ing re search fo cused on un re solved biostrati graphic prob lems (i.a. Flais and Feist, 1988; Ziegler and Sand -berg, 1996; Kai ser, 2009; Kai ser and Corradini, 2011; Corradini et al., 2011, 2017b, 2020). Much study is are also be ing de -voted to global events con nected with this bound ary, the Hangenberg Event in par tic u lar (Kai ser et al., 2009, 2016; Marynowski et al., 2012; Matyja et al., 2015; Becker et al., 2016; Kumpan et al., 2019; Paschall et al., 2019; Rakociñski et al., 2020; Shizuya et al., 2020). With re gard to these is sues, the Kule sec tion in Uzbekistan has been a fo cus of the work ing group es tab lished in 2008 by the In ter na tional Com mis sion on Stra tig ra phy to re de fine the bound ary and find a new GSSP (Global Bound ary Stratotype Sec tion and Point). The re sults of

early cono dont in ves ti ga tions of the sec tion, sug gest ing the pos si bil ity of doc u ment ing the DCB, were given dur ing a joint meet ing of the Subcommission on De vo nian Stra tig ra phy and IGCP Pro ject 499 (Yolkin et al., 2008: p. 46; Kim et al., 2008). The lo cal ity was in spected and resampled by par tic i pants of the ex cur sion or ga nized dur ing the meet ing (Matyja, 2011). There -af ter, it was mea sured and sam pled in 2015 by a field party from the Silesian Uni ver sity in Sosnowiec (Dubicka and Rakociñski, 2015, unpubl. re port). The pres ent study, based on the re sults of the lat ter field work, sup plied new cono dont data which al lowed up dat ing of the ear lier find ings (Erina, 2008a, b). Pre lim i nary data and in ter pre ta tions were pre sented dur ing the 4th In -ter na tional Cono dont Sym po sium in Va len cia (Narkiewicz et al., 2017). This pa per re ports new tax o nomic, biostratigraphic and biofacies re sults from the in ter val span ning the DCB and the lower Tournaisian (low er most Mis sis sip pian) strata.

REGIONAL AND STRATIGRAPHIC

SETTING

The Kule sec tion is lo cated in the Kitab Re serve Area in SE Uzbekistan, in the Zeravshan-Gissar Moun tains of the SW Tian Shan, not far from the Pragian-Emsian GSSP in the Zinzil’ban

Gorge (Yolkin et al., 1997; Fig. 1). The ex po sures oc cupy the south ern flank of the Dzhindy-Darya River near the east ern mar gin of the Kitab Nat u ral Park (Yolkin et al., 2008: p. 68).

The sec tion stud ied is a part of folded and faulted Mid dle De vo nian to Lower Car bon if er ous suc ces sion ex posed along the left slope of the Kule Gorge (Yolkin et al., 2008: fig. 15). The in ter val in ves ti gated cor re sponds to a part of the Novchomok For ma tion, the unit com pris ing the lo cal up per most Famennian and Tournaisian (Yolkin et al., 2008: p. 68). The for ma tion is de -vel oped as grey and light grey, vari ably bed ded, partly mas sive lime stones (Figs. 2 and 3). The de pos its are fine-grained and micritic, in places brecciated, bioclastic, with ir reg u lar bed ding sur faces. They con tain cri noids, rare brachi o pods and coral frag ments. Ac cord ing to an ear lier study (Yolkin et al., 2008: fig. 14), the DCB in ter val, from an un dif fer en ti ated praesulcata to the crenulata zones, is only 15 m thick, which sug gests some de gree of strati graphic con den sa tion.

MATERIAL STUDIED

Al to gether, 37 sam ples were taken in 2015 by Dubicka and Rakociñski from the Kule sec tion, out of which seven were ana -lysed in this study (Fig. 2). The sam ples, the weight of which var ied be tween 0.25 and 0.55 kg, were dis solved in 15% for mic acid and the heavy res i due with cono donts was sep a rated us ing so dium metatungstate. The to tal num ber of spec i mens ob

-tained is 250 and their pres er va tion state is mod er ately good to poor. Most spec i mens are bro ken, frac tured and in some cases the up per or na mented sur face has been scraped off, prob a bly due to tec tonic frac tur ing and shear ing.

The cono dont abun dance in the sam ples, sum ma rised in Ta ble 1, is mostly 20–40 spec i mens per sam ple, ex cept for sam ple 5B, where the abun dance reaches about one hun dred. The cono dont as sem blages con tain el e ments of dif fer ent ontogenetic stages, from early ju ve nile to ma ture. This in di cates in sig nif i cant post-mor tem, hy dro dy namic, sort ing which in turn sug gests the oc cur rence of in situ as sem blages (see the sec -tion on biofacies be low). The col our al ter a-tion in dex (CAI) of ma ture spec i mens is 3, cor re spond ing to palaeotemperatures 110–200°C (Ep stein et al., 1977).

Cono donts de scribed herein are stored at the Silesian Uni -ver sity in Sosnowiec, Po land.

BIOSTRATIGRAPHY

Ta ble 1 sum ma rises the cono dont taxa found in the sam -ples, their fre quency and the biostratigraphy of the microfossil as sem blages. The cono dont biostratigraphy is based on the lit -er a ture data cited be low, and is dis cussed in strati graphic or d-er. In ad di tion, the strati graphic ranges at trib uted to par tic u lar sam -ples are visu al ised with ref er ence to the cono dont zonation of the up per most De vo nian-low er most Car bon if er ous (Fig. 4).

The taxa im por tant for stra tig ra phy and in ter est ing from a tax o -nomic view point are il lus trated in Fig ures 5–8.

Var i ous cono dont zonation schemes are ap plied across the DCB. The clas si cal sub di vi sions by Ziegler and Sandberg (1990) for the Up per De vo nian and Sandberg et al. (1978) for

the Tournaisian have been up dated by Corradini (2008), Kai ser et al. (2009), and Spalletta et al. (2017). Also, due to dif fi cul ties in rec og niz ing the early siphonodellids, a new zonation across the DCB was in tro duced by Corradini et al. (2017b). This scheme is less de tailed than the pre vi ous one for the up per most

Fig. 2. Lo ca tion of the sam ples in ves ti gated and cor re spond ing cono dont biofacies (right) against the rel e vant part of the Novchomok For ma tion in the Kule sec tion (Dubicka and Rakociñski, 2015, unpubl. re port) com pared with the equiv a lent part (left) of the sec tion pub lished in Yolkin et al. (2008, fig. 14)

Famennian in ter val, as the Bispathodus ultimus Zone in cludes the pre vi ous Up per expansa, Lower and Mid dle praesulcata zones. There fore, Corradini et al. (2020) in tro duced in the up -per part of the Bi. ultimus Zone the Protognathodus meischneri Subzone, the base of which is ap prox i mately equiv a lent to the base of the for mer Lower praesulcata Zone of Ziegler and Sandberg (1990) and of the Siphodonodella praesulcata Zone of Kai ser et al. (2009). In this pa per we ap ply the most re cent zonation (Spalletta et al., 2017; Corradini et al., 2020), with the mod i fi ca tion sug gested by Becker et al. (2016) to re name the

Siphonodella hassi Zone as that of Siphonodella jii, due to tax o

-nomic prob lems with the in dex spe cies.

The biostratigraphic po si tion of the sam ple 04F as sem -blage is de fined by the to tal strati graphic range of Palmatolepis

gracilis sigmoidalis (Fig. 6A, B), that is, from the mid dle part of

the Pseudopolygnathus granulosus Zone to low er most part of the Protognathodus kockeli Zone (Spalletta et al., 2017, 2020). The pres ence of Pa. gracilis sigmoidalis above the Hangenberg Black Shale Event has been of ten con sid ered by Ger man au -thors as a re sult of re work ing from older sed i ments (e.g., Kai ser et al., 2009). It is doc u mented, how ever, in the lower part of the

Pr. kockeli Zone in sec tions where there is no sed i men ta tion

break and the se quence is con tin u ously car bon ate with out any

ev i dence of re work ing (e.g., Grüne Schneid, Sentiero Cresta Verde; Spalletta et al., 2020).

The stratigraphically im por tant spe cies in the sam ple 01A is

Siphonodella sulcata (Fig. 5J, K), the pres ent marker for the

base of the Car bon if er ous, the first ap pear ance of which in di -cates the base of the epon y mous zone. The up per biozonal limit is set by the biostratigraphy of the as sem blage from sam ple 1 higher in the sec tion (see be low) and thus sam ple 01A is re -ferred to an in ter val from the up per part of the Pr. kockeli Zone (sulcata/kuehni Zone of Kai ser et al., 2009) into the Sipho

-nodella duplicata Zone.

Sam ple 0 did not yield any char ac ter is tic cono donts. The lack of Si. jii (which ap pears higher in the sec tion) may point to an age older than the Si. jii Chron.

Sam ples 1 and 5B are at trib uted to the Siphonodella jii Zone based on the pres ence of rep re sen ta tives of Si. jii in both sam -ples (re spec tively: Fig. 5V, W, X–Z) and spec i mens at trib uted to

Polygnathus cf. P. tenuiserratus (Fig. 7F, G) found in the higher

sam ple. Siphonodella jii is the in dex spe cies for this zone (Becker et al., 2016), whereas Po. tenuiserratus has been found so far only in Sar dinia in the in ter val com pris ing the

Siphonodella bransoni to the Si. jii zones (Corradini et al., 2003,

2020; Mossoni et al., 2015). Other char ac ter is tic spe cies found in both sam ples are Si. sulcata (Fig. 5H, J) and Si. duplicata Morphotype 3 (Fig. 5R–U; see Ji and Ziegler, 1993).

Sam ple 8A has an im pov er ished fauna com pared to the pre vi ous sam ple, and does not in clude any stratigraphically di -ag nos tic taxa. Pseudopolygnathus multistriatus (Fig. 8P–R) and a ju ve nile stage of Ps. fusiformis (Fig. 8V, W) have their last oc cur rence within the Si. crenulata Zone (Ji and Ziegler, 1993). Con se quently, the as sem blage from sam ple 8A is at trib uted to the Si. jii–Si. crenulata in ter val.

The po si tion of sam ple 38 against the cono dont zonation is de ter mined by the co-oc cur rence of Siphonodella cf. Si.

isosticha (Fig. 6C–G), and Pinacognathus profunda (Fig. 6M,

N). Siphonodella isosticha is re ported from the base of the Si.

crenulata Zone (Klapper, 1971; Ji and Ziegler, 1993: p. 13;

Hogancamp et al., 2019), and Pi. profunda has its last oc cur rence within this zone (e.g., Klapper, 1966). In sam ple 38 a sin gle spec i men of Ps. micropunctatus (Fig. 8X–Z) has been de ter mined. How ever, this is a Famennian taxon with its LAD as -cribed to the lower part of the Bi. ultimus Zone (Hartenfels, 2011; Corradini et al., 2017; Spalletta et al., 2017). This un usual dis cov ery is prob a bly an ar ti fact of sam ple pro cess ing, oth er -wise it is dif fi cult to ex plain, as there is no ev i dence of re work ing in the sec tion stud ied.

BIOFACIES

Sev eral cono dont biofacies mod els have been pro posed for the lower Tournaisian (e.g., Dreesen et al., 1986; Dreesen, 1992; Kalvoda et al., 1999, 2015; Kai ser et al., 2009, 2017). They dem on strate that the Hangenberg Event and as so ci ated ex tinc tion of palmatolepids was fol lowed by a pro lif er a tion of two sur viv ing gen era, Polygnathus and Siphonodella, which dom i -nated early Tournaisian deep-wa ter en vi ron ments. Mi gra tion paths of the gen era, and global and lo cal en vi ron men tal chan -ges, in clud ing eustatic fluc tu a tions, con trolled the pro por tion of both taxa in cono dont as sem blages. In the lower part of the Tournaisian cor re spond ing to the mid dle part of the Pr. kockeli Zone (= lower and mid dle part of the sulcata/kuehni Zone ac cord ing to Kai ser et al., 2009; cf. Fig. 4) the proto gnathodid --polygnathid biofacies has been ob served. This biofacies grades in the up per part of the zone into the polygnathid

Fig. 3. Field photo show ing the DCB po si tion ac cord ing to the con cept of Yolkin et al. (2008: fig. 14)

biofacies. A dis tinct in crease in the pro por tion of siphonodellids, ac com pa nied by their tax o nomic di ver si fi ca tion, takes place from the Si. duplicata Zone up wards (Souquet et al., 2020). The

Si. jii to Si. crenulata zonal in ter val is char ac ter ized by the polygnathid-siphonodellid or siphonodellid-polygnathid bio -facies (Kai ser et al., 2009, 2017; Kalvoda et al., 2015).

The quan ti ta tive eval u a tion of the biofacies suc ces sion in the Kule sec tion is pos si ble ow ing to the suf fi cient cono dont

abun dance ex ceed ing 30 spec i mens in the sam ples 01A, 1, 5B, 8A, 38 (Table 1). The pres ence of rep re sen ta tives of var i ous ontogenetic stages, in clud ing ju ve nile and earlyju ve nile spec i mens (44%), at tests to the autochthonous na ture of the as sem -blages, thus sup port ing the re li abil ity of the biofacies anal y sis. This con clu sion could be chal lenged tak ing into ac count underrepresentation of ramiform el e ments rel a tive to plat form ones. The del i cate ramiforms, how ever, can be more eas ily

T a b l e 1 Tax o nomic com po si tion of cono dont as sem blages and their biostratigraphy in par tic u lar sam ples

Cono dont zones Ps. granul.–Pr.kockeli Pr. kockeli –Si. duplicata Siphonodella jii Si. jii –Si.cren cren. Si.

Sam ple num bers 04F 01A 0 1 5B 8A 38

Weight of sam ples (kg) 0.47 0.55 0.33 0.25 0.37 0.30 0.43

Palmatolepis gracilis sigmoidalis 2

Branmehla inornata 1 5 4

Branmehla cf. B. inornata 1 1

Branmehla sp. 2

Polygnathus purus purus 15 11 4 24 10 8

Polygnathus cf. P. purus purus 4 3 3 15 2 4

Pseudopolygnathus pri mus 1 1

Pseudopolygnathus cf. P. pri mus 1 1 1

Pseudopolygnathus fusiformis 1 Siphonodella sulcata 1 2 2 Sihonodella cf. sulcata 1 Siphonodella sp. (praesulcata›sulcata) 4 2 2 Siphonodella bransoni›duplicata 1

Siphonodella duplicata Morphotype 3 1 2

Siphonodella jii 1 1

Pseudopolygnathus multistriatus 1 1

Polygnathus n.sp. A 2 4 1

Pinacognathus profunda 1 1

ge nus and spe cies indet. 1

Bispathodus cf. B. stabilis 2

Bispathodus stabilis stabilis 1 1

Mehlina sp. 5

Protognathodus sp. 1

Polygnathus pupus sensu Bardashev

2004: pl. 12, figs. 12, 13 1

Polygnathus communis carinus 2

Polygnathus aff. P. tenuiserratus 2

Polygnathus aff. P. spicatus 1

Polygnathus aff. P. mehli 1

Pseudopolygnathus cf.

Ps. micropunctatus 1

Siphonodella cooperi 2

Siphonodella lobata 1

Siphonodella cf. Si. isosticha 1

Siphonodella sp. 2 1 6 11 8 Pseudopolygnathus sp. 2 1 7 1 2 Bispathodus sp. 1 2 Polygnathus sp. 1 3 4 11 7 4 Ramiforms 3 6 3 2 23 9 6 To tal of P1 el e ments 6 30 20 31 98 30 38

frag mented and re moved dur ing prep a ra tion of sam ples than the more ro bust plat form in di vid u als. In ad di tion, their hy dro dy -namic prop er ties could have led to their larger sus cep ti bil ity to lat eral trans por ta tion in a wa ter col umn, even un der a weak cur rent re gime, and par tic u larly at greater wa terdepths (Broad -head et al., 1990).

The re sults of the quan ti ta tive biofacies anal y sis are sum -ma rised in Fig ure 2. The anal y sis has been con ducted fol low ing the pro ce dure ap plied by Sandberg (1976, 1988) and Bultynck

et al. (1998). In di vid ual rep re sen ta tives of the gen era Pinaco

-gnathus, Protognathodus and ge nus indet. have been ne -glected in cal cu lat ing re spec tive per cent ages.

The as sem blage from sam ple 01A cor re sponds to the polygnathid biofacies with the Polygnathus per cent age as high as 73% while Pseudopolygnathus rep re sents 13% and

Siphono della 10% (see Fig. 2). Higher in the sec tion, in sam ple

1, the as sem blage in ves ti gated is as cribed to the siphono -dellid-polygnathid biofacies. Siphonodella, dis play ing in creased

Fig. 4. Strati graphic po si tion of the microfossil as sem blages in ves ti gated rel a tive to cono dont zonation schemes of the up per Famennian to lower Tournaisian

Fig. 5. Se lected cono dont el e ments (P1) of the ge nus Siphonodella from the Kule sec tion

Fig. 6. Se lected cono dont el e ments (P1) from the Kule sec tion

A, B – Palmatolepis gracilis sigmoidalis Ziegler, 1962: A, B – up per and lower views, sam ple 04F; C–G – Siphonodella cooperi Hass, 1959 M1, sam ple 38: C–E – up per, oblique and lower views, F, G – up per and up per/oblique views of a ju ve nile stage; H, I – Siphonodella cf. Si.

isosticha (Coo per, 1939): H, I – up per and lower views, sam ple 38; J – Siphonodella lobata (Branson and Mehl, 1934a), up per view, sam ple

Fig. 7. Se lected cono dont el e ments (P1) of ge nus Polygnathus from the Kule sec tion

Fig. 8. Se lected cono dont el e ments (P1) of the ge nus Pseudopolygnathus from the Kule sec tion

A–E, N, O – Pseudopolygnathus pri mus Branson and Mehl, 1934a: A–C – up per, lower and lat eral views, sam ple 01A, D, E – up per and lower views, sam ple 1, N, O – up per and lower views, sam ple 01A; F, M, P, R – Pseudopolygnathus multistriatus Mehl and Thomas, 1947: F–M – up per and lower views, sam ple 1, P, R – up per/oblique, up per and lower views of ju ve nile stage, sam ple 8A; G–I – ge nus and spe cies indetermined: G–I – up per, lower and lat eral views, sam ple 1; J–L – Pseudopolygnathus sp.: J–L – up per, lat eral, lower views, sam ple 01A; S–U – Pseudopolygnathus cf. Ps. pri mus Branson and Mehl, 1934a: S–U – up per, oblique and lower views of ju ve nile stage, sam ple 0; V, W – Pseudopolygnathus fusiformis Branson and Mehl, 1934a: V, W – up per and lower views of ju ve nile stage, sam ple 8A; X–Z –

Pseudopolygnathus cf. Ps. micropunctatus Bis choff and Ziegler, 1956: X–Z – up per, lower and lat eral views, sam ple 38; scale bar in all spec

tax o nomic di ver sity, com poses 55% of the en tire as sem blage, polygnathids 35%, and pseudopolygnathids 10%. In turn, sam -ple 5B is char ac ter ized by the polygnathid- siphono dellid biofacies with 62% of Polygnathus and 19% of Siphonodella. The 5B sam ple as sem blage is the most abun dant and di verse of all stud ied. In ad di tion to the gen era Polygnathus, Siphono

-della and Pseudopolygnathus, found also in lower sam ples, it

re cords the first en try of the bis pathodid group in clud ing Bis

-pathodus and the mor pho log i cally sim i lar Branmehla and

Mehlina (Ziegler and Sandberg, 1984). The bispathodid group

is third larg est in the 5B as sem blage, which also con tains a sin -gle rep re sen ta tive of Proto gnathodus.

The bispathodid group con tin ues higher in the sec tion peak -ing in sam ple 8A at trib ut able to the polygnathid-bispathodid biofacies. The per cent age of Polygnathus is 66% and that of bispathodids is 17% while Pseudopolygnathus and Sipho

nodella com pose 10 and 7%, re spec tively. The polygnathid

--siphonodellid biofacies re turns in sam ple 38, with Polygnathus form ing 46%, Siphonodella 32%, and bispathodids 14% of the whole as sem blage.

It is re mark able that Polygnathus is dom i nated by Po. purus

purus in all the as sem blages in ves ti gated. In sam ple 01A the

taxon rep re sents 100% of all polygnathids; in the up per sam ples 1 and 5B its pro por tion ranges to ~60%, while in the sam ples 8A and 38 it at tains 66 and 70% of all polygnathids, re spec tively. Some pub lished in ter pre ta tions sug gest that the sub spe -cies was adapted to en vi ron ments deeper than shal low-wa ter plat forms (Kai ser et al., 2009, 2017; Kalvoda et al., 2015).

The higher pro por tion and in creased di ver sity of siphono -dellids in sam ple 1 is con sis tent with the wider trend start ing from the Si. duplicata Zone (see above). It may have been con -nected with the eustatic post-Hangenberg rise (Kai ser et al., 2017) and col o ni za tion of emp tied mesopelagic niches dur ing the trans gres sion (Kalvoda et al., 1999, 2015). A lower pro por -tion of Siphonodella is ob served higher, in sam ples 5B and 8A. In the lat ter as sem blage all char ac ter is tic ear lier-oc cur ring

Siphono della spe cies have dis ap peared, ex cept for Siphono -della sp. (tran si tional form praesulcata®sulcata). The lack of

siphonodellids is not nec es sar ily ev i dence for shallowing of the Kule Ba sin, how ever, as the bispathodid group are char ac ter is -tic of the eupho-tic zone of the deep ma rine en vi ron ment (Kai ser et al., 2009; Gi rard et al., 2014; Kalvoda et al., 2015). The re -vival of Siphonodella, as so ci ated with the ap pear ance of new spe cies, is ob served higher, in sam ple 38.

The cono dont biofacies suc ces sion in the Kule sec tion de -scribed above is con sis tent with the uni ver sal mod els noted at the be gin ning of this chap ter. There is a no ta ble lack of the protognathodid-polygnathid biofacies, how ever, known from other lo cal i ties of the lower Tournaisian (Kai ser et al., 2009, 2017). This may sug gest that the low er most Tournaisian sam -ple in ves ti gated (01A), in which the polygnathid biofacies was found, cor re sponds to the up per part of the Pr. kockeli Zone. Such a sup po si tion is in agree ment with the re cent data on the DCB in the Kule sec tion, be ing placed lower than that in Yolkin et al. (2008; see also Fig. 2). The con sid er able pro por tion and di ver sity of Siphonodella start ing from sam ple 1 up wards is con sis tent with the global trend ini ti ated in the Si. duplicata Zone. Var i ous pro por tions of Siphonodella, Polygnathus and

Bis pathodus in the in ter val from sam ples 5B to 38 prob a bly re

-flect lo cal or re gional en vi ron men tal shifts.

In gen eral, the cono dont as sem blages ana lysed from the Kule sec tion, dom i nated by Po. purus purus and ac com pa ny ing siphonodellids and bispathodids, in di cate deep-wa ter ma rine en vi ron ments typ i cal of the lower con ti nen tal slope and rise (Ziegler and Sandberg, 1984; Savoy et al., 1999; Kai ser et al., 2008, 2009, 2017; Kalvoda et al., 2015).

COMPARISON WITH PREVIOUS DATA

The sec tion in ves ti gated is here cor re lated with the pre vi -ously pub lished log (Yolkin et al., 2008: fig. 14) based on the same lo ca tion of the DCB, and as sum ing the same ver ti cal scale (Fig. 2).

The strati graphic range of the 04F as sem blage (Ps.

granulosus to Pr. kockeli zones in ter val) is wider than but not in

-con sis tent with the range pre vi ously at trib uted to the roughly equiv a lent sam ples 96/2 to 96/3, which was placed within an un dif fer en ti ated expansa Zone (Fig. 2; Erina, 2008a: fig. 14). On the other hand, there is a dis par ity be tween the pres ent data on the 01A sam ple (kockeli–duplicata zones) and the cor re -spond ing 630-3 sam ple (praesulcata Zone; Fig. 2; Erina, 2008a: fig. 14). Con se quently, the DCB which was drawn by Yolkin et al. (2008) be tween their sam ples 96/4 and 6304, is lo cated lower in the sec tion, i.e. be tween the 04F and 01A sam ples ac cord ing to our study. Such a lower po si tion has been al -ready sug gested by Matyja (2011) and Narkiewicz et al. (2017) and has been de tailed by the new data of Erina (fide Salimova 2017, in for ma tion in an e-mail from De cem ber 14th, 2017). The lat ter au thor draws the DCB at the base of Bed 5 of Yolkin et al. (2008: fig. 14) cor re spond ing to the cen tral part of our Bed 04, above the po si tion of our sam ple 04F (Fig. 2).

Also, the pres ent biostratigraphic data from sam ple 1 (= Si.

jii Zone; Ta ble 1) dif fer from that for the slightly higher sam ple

630-4 (Fig. 2). Yolkin et al. (2008: fig. 14) at trib uted this sam ple to the sulcata Zone, but from that sam ple Erina (2008b: pl. 33, fig, 3) il lus trated as Si. angulata n. sp. an el e ment that ac tu ally is a ju ve nile of Si. lobata, which has its first oc cur rence within the

Si. jii Zone (Kalvoda et al., 2015; Corradini et al., 2020).

Con cern ing sam ple 5B, it is within the un dif fer en ti ated

duplicata Zone ac cord ing to Yolkin et al. (2008). So, both com

-pared datasets may cor re spond to each other as the Si. jii Zone is equiv a lent to the for mer Up per duplicata Zone. The same ap plies for our sam ple 8A, equiv a lent to sam ple 63010 in the pre -vi ous study.

Due to the sam pling gap we do not have data on the oc cur -rence of the Siphonodella sandbergi and Siphonodella

quadruplicata zones, while our up per most sam ple 38 be longs

to the un di vided Si. crenulata Zone. It fits in the in ter val where this zone was dis crim i nated by Yolkin et al. (2008).

The pres ent re sults con cur with the strati graphic con den sa tion of the in ter val around the DCB in the Kule sec tion. This ap -pears to be a uni ver sal phe nom e non as so ci ated with this bound ary (e.g., Kalvoda et al., 1999; Kai ser et al., 2009).

SYSTEMATIC PALAEONTOLOGY

(Fig. 7A–C, H–N)

Ca rina is quite strongly curved in wards; it reaches the pos te rior end of the plat form. It is ac com pa nied by shal low grooves deep en ing in the anteriormost part of the plat form. It is com posed of low nodes in the cen tral and pos te rior part of the plat form, and higher denticles in the an te rior part. Rounded, iso lated and low nodes (~9) are dis trib uted from 1/3 of the an te rior length of the ca rina to its pos te rior end. The dis -tance be tween nodes is larger in the pos te rior part than in the cen tral one. The nodes are con nected by a thin ridge, par tic u larly in the pos te -rior part. In the most an te -rior part of the plat form, nodes are re placed by dis tinctly higher, nar row, densely sit u ated denticles. There is no dis -tinct bound ary be tween the denticles of the ca rina and those of the free blade.

The blade is short, com posed of 4 to 6 denticles merged at their bases but with free peaks. The denticles are of al most uni form width but of var i ous heights. The first two or three denticles are higher than the re -main ing ones which are lower, grad ing into the denticles of the ca rina. A mod er ately large basal pit with raised flanges is lo cated in the an te -rior third of the plat form.

In dis tinct keel with a fur row ex tends from the basal cav ity to the pos te -rior end of the spec i mens. The basal cav ity with keel is sur rounded by a wide crimp with dis tinct edges.

In the phylo gen eti cally older forms (Fig. 7J, L) the plat form and ca rina are slightly curved in wards. The arclike bow ing in lat eral view is lack -ing. The outer part of the plat form may ex tend far ther an te ri orly than the in ner one. The lower sur face of a spec i men is nearly flat. The keel is lack ing but a dis tinct fur row ex tends from the basal cav ity to the pos -te rior end.

M a t e r i a l. – Seven spec i mens from sam ples 1, 5B and 8A. D i s c u s s i o n. – The taxon de scribed dis plays sim i lar i ties to the spec i men from the sandbergi Zone fig ured by Bardashev et al. (2004: pl. 11, figs. 16, 17) as Eucostapolygnathus sp. nov. 3. It dif fers from the lat ter, how ever, in the ab sence of an up turned outer plat form mar gin. In the taxon de scribed both an te rior mar gins are at the same level. S t r a t i g r a p h i c d i s t r i b u t i o n. – The taxon oc curs in the Si.

jii Zone, and pos si bly at slightly youn ger lev els.

Ge nus and spe cies indetermined (Fig. 8G–I)

D e s c r i p t i o n. – The in com plete spec i men with a bro ken an te rior part prob a bly be longs to a new taxon (ge nus ?) dis tin guished by a high blade, fixed to the right side of the plat form. The blade is in clined posteriorwards and con sists of two large merged denticles with free (sep a rated) api cal parts. The first denticle is con sid er ably higher and al most two times wider than the sec ond one which is con nected with a much lower ca rina.

The plat form is very nar row, slightly asym met ri cal and its pos te rior end is twisted in wards. The left an te rior part of the plat form is wider than the right one. Up per sur face is slightly con cave. The plat form mar gins are mostly nearly straight, ex cept for the most pos te rior twisted part, and run par al lel to the ca rina. Small nodes oc cur ring along the mar gins may merge caus ing thick en ing of the mar gins and a crenulate ap pear ance of the in ner mar gin in side view (Fig. 8G). On the in ner side of the plat form there are about eight dis tinct nodes while on the outer side only three weakly de vel oped nodes are ob served. Where the blade joins the ca rina there is a no ta ble con stric tion of both plat form mar gins (“waist line”). Start ing from the con stric tion, the an te rior in ner mar gin is in clined down -wards (see Fig. 8I).

Ca rina is strong, con sid er ably higher than plat form mar gins and ex -tends from its an te rior to pos te rior part. It con sists of nine denticles which are wide in side view, of un even size. They are con nected at their bases while their sharp peaks are free. Over all, they are lower posteriorwards, but the high est denticle oc curs in the pos te rior part while, both in front of it and be hind it, two small denticles oc cur. The de vel op ment of the basal cav ity is un clear as the crit i cal part of the spec i men is miss ing (bro ken). The lower side is sharply bev elled from keel to plat form mar gins. A high sharp keel with a nar row poorly vis i ble fur row runs from the pos te rior end of the plat form to wards its an te rior part. More or less in the place of the plat form mar gin con stric tions the

keel grades into a more clearly vis i ble fur row. Both struc tures are sur -rounded by a darker crimp with sharply out lined mar gins.

M a t e r i a l. – One spec i men from sam ple 1.

D i s c u s s i o n. – The gen eral shape of the el e ment may re call other lower Car bon if er ous gen era char ac ter ized by high and short free blades and a nar row plat form (Cavusgnathus, Clydagnathus, Patro

-gnathus, Taphrognathus), but dif fers by the pres ence of the ca rina

above the plat form. In fact, all these gen era have a dis tinct me dial trough on the plat form.

S t r a t i g r a p h i c d i s t r i b u t i o n. – The el e ment co mes from the Si. jii Zone.

SUMMARY AND CONCLUSIONS

Cono dont in ves ti ga tions of the Kule sec tion in SE Uzbekistan doc u ment the pres ence of sev eral zones com pris -ing Ps. granulosus–Pr. kockeli in ter val of the up per most Famennian and the Pr. kockeli–Si. crenulata in ter val of the lower–mid dle Tournaisian. The re sults of the pres ent cono dont study al lowed the au thors to re vise ear lier tax o nomic and biostratigraphic data (Yolkin et al., 2008; Kim et al., 2008). This re vi sion re sulted in plac ing the po si tion of the De vo nianCar -bon if er ous bound ary a few me tres lower within the Novchomok For ma tion rel a tive to the ear lier re sults. A new spe cies of

Polygnathus has been de scribed in open no men cla ture in ad di

-tion to a pe cu liar P1 el e ment re ported as ge nus and spe cies

indet., prob a bly con sti tut ing a new ge nus.

The pres ent anal y sis re vealed that the changes in cono dont biofacies in the sec tion stud ied are con sis tent with the lower Tournaisian biofacies suc ces sion gen er ally known from other bas ins world wide. The main dif fer ence is the ab sence of the protognathodid-polygnathid biofacies of the mid dle part of the

Pr. kockeli Zone, prob a bly cor re spond ing to a lack of ad e quate

data be low the low er most Tournaisian sam ple in ves ti gated. On the other hand, the low fre quency of Siphonodella and pre dom i -nance of polygnathids in sam ples 01A and 0 sug gests that the as sem blage is older than the Si. jii Zone. This would con strain the strati graphic at tri bu tion of the 01A and 0 as sem blages to the in ter val com pris ing the up per part of Pr. kockeli Zone to the Si.

duplicata Zone. The other dif fer ence is the rel a tive abun dance

of bispathodids which al lowed the au thors to dis cern a pre vi -ously un des cribed polygnathid-bispathodid biofacies. The high per cent age of Po. purus purus and the abun dance of siphonodellids and bispathodids are ev i dence of deep ma rine en vi ron ments of the lower con ti nen tal slope and rise in the Kule part of the sed i men tary ba sin.

Ac knowl edge ments. The au thors thank Z. Dubicka (Uni

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