149 The Devonian-Carboniferous Boundary at the section "Grune ...

149 Cour. Forsch.-Inst. Senckenberg, 100: 149-167, 4 text-figs., 4 pis. -

Frankfurt a. M., 2. 5. 1988

The Devonian-Carboniferous Boundary at the section "Grune Schneid" (Carnic Alps, Austria): A preliminary report HANS

P..

SCHONLAUB, RAIMUND FEI.sT & DIETER KORN

ABSTRACT At the section ~'Grline Schneid" (= "Green Crest";ital.: "Cresta Verde") in the Central Carnic Alps of Southern· Austria the passage from' the Devonian into the Carboniferous is well exposed and has long :been known. Conodonts and trilobites prove a continuous sedimentation across the boundary, however, a study of ammonoids has not yet been carried out in theupperm6st Devonian . During this interval uniform cephalopcrl limestones of an open marine·environment were deposited suggesting a stable offshore facies without anyobservable sedimentary breaks. In the studied 1 ,28 m thick ·bound,ary beds all known index conodonts were· recognized, i. e. Siphonodella praesulcata and its descendant S. sulcata, the Pratognathcrlus fauna and representatives of the genera Palmatolepis, Bispathodus, Pseudopolygnathus and Polygnathus . 'Their occurrence in this section lead us to the belief that most of them are related in an evolutionary relationship rendering this succession- in 'comparison to others. - as· one of the most valuable candidates for a worldwide stratotype of the DIC boundary. At present a 20 cm ·thick gap exists between both occurrences of the critical species of Siphonodella. It is planned to bridge this gap by additional samples in the near future.

INTRODUCTION '!be Carnic Alps of Southern Austria and Northern Italy represent one of the very few places in the world in which an almost complete fossiliferous sequence from the Ordovician to Middle Triassic times is exposed which has been well documented. 'Ibese rocks display three main facies which were affected by two orogenies: the older being the short lasting Variscan deformation in the Upper Carboniferous, while in the Tertiary Alpine tectonics caused considerable compression, faulting and local overthrusting. In the Central Carnic Alps, the Variscan sequence is well preserved, excellently exposed, fossiliferous and stratigraphically continuous with only a few exceptions, e. g. the Otdovician/Silurian boundary or within the Devonian. As early as 1931 H. R. v. GAERTNE~ proved continuous sedimentation from the Upper Devonian into the Lower Carboniferous. His conclusion was based on goniati t~s which occur in the uppermost limestone beds of the long ranging Cellon section at the locality "Grtine Schneid" (= Green Crest). Starting in the late 50-s se~eral authors found and published additional stratigra-

phic informations about this and other localities. The new data were mainly obtained by conodonts which were found at different places throughout the entire Carnic Alps on top of the Devonian limestone sequences. Recent comprehensive summaries about these activi ties were published by EBNER (1978), SCHONLAUB (1980, 1985) and ·.v. AMEROM et al. (1 984). 'Ihey are in good accordance with observations in other central European regions: During the Tournaisian as a result of only local uplifts stratigraphic gaps, erosion and reworking phenomena occurred while in deeper environmental settings sedimentation was unaffected and uninterrupted during the whole stage. The dominating lithology of Upper Devonian (Famennian) and Lower Carboniferous sequences of the Carnic Alps are various pelagic and micritic Flaser-type bedded cephalopod limestones. Without any observable lithologic change this rock type passes from the Devonian into the Carboniferous. In very few sections, however, the boundary is marked by a shaley intercalation of a few centimeter (SCHONLAUB, 1969) suggesting an equivalent of the Hangenberg Shale. Wher~ these shales are absent the Lower Carboniferous part of the limestone succession can only be dinstinguished from the Devonian by means of fossils. Neverthe-

150

Fig. 1. Cellon Mountain in the Central Carnic Alps from the northeast. '!he gorge in the middle part is the famous ItCellonetta-Lawinenrinne" in which a continuous Ordovician-Devonian sequence is exposed. Section Grune Schneid is marked by an arrow.

less both rocks on either side of the :boundary are named separately: The Famennian portion of the cephalopod limestones is termed Pal Limestone, the Tournaisian strata are the Kronhof Limestone. The latter reaches a thickness from less than a meter to a maximum of some 10 meters. rrhey are developed as mostly well bedded light grey or reddish pure micri tic limestones with less than 2 % clay content. The individual limestone beds are separated from each other by distinct or indistinct, mostly wavy bedding planes. Clayey up to 1 mm thick interlayers and partings are uncommon features in these rocks. The present day biostratigraphic requirements differ from older studies, in particular regarding the conodont sampling across any stratigraphic boundary. As indicated in our figure 3 we have recollected the section 11 Grune S'chneid" in closely spaced intervals to make sure to recover those forms which are needed for the definition of the boundary and to increase the knowledge about the true nature of this time unit.

L,O CAT ION 0 F THE SEC T ION uGRUNE SCHNEIDII

The section ItGrune Schneid" is located close to the Austrian/Italian border a few meters west of the marker point n-129 which is situated west of Cellon mountain at an altitude of 2142 m. The section comprises the uppermost limestone beds of a continuous Lower Paleozoic fossiliferous sedimentary sequence (fig. 1) ranging from the Upper Ordovician (Caradocian Stage) to the Carboniferous. The Tournaisian strata aredisconformably overlain by the clastic Hochwipfel Formation which is interpreted as a flysch deposi t and ranges from the Middle Visean to the Bashkirian or early Moscovian Stages (v. AMEROM et al., 1984 , SCHONLAUB, 1986). The outcrop and its surroundings have recently been re-mapped (SCHONLAUB, 1985). New geological maps exist for the whole Paleozoic area in the scale 1 : 50 000. Moreover, the classical Lower Paleozoic regions were mapped and published in the enlarged scale 1 :,1 0 000, for example the

151 area around Lake Wolayer and PlockenpaB, the latter being in the neighbourhood of our section at "Grtine Schneid". In the surroundings of this section additional boundary sections exist. Together with our section a second one has already been studied by GEDIK (1974). Several others can be found along the path running from PlockenpaB to Cellon mountain (GEDIK, 1974). Due to local tectonics the here reviewed section, 11 Grtine Schneid", is tectonically separated from the main sectionat-Cellon. The fault zone, however, is of minor importance and displacement occurred only along a few meters. Section "Grtine Schneid 11 (fig. 2) is easily accessible. The walking distance is about 1 1/2 hours along a good path on the Italian side from Plockenpan (Passo di Monte Croce, 1403 m). The section is a combination of a natural outcrop and an artificial trench (in the Devonian -part even a small cavern and a small tunnel) cut into the rocks during world war I. The individual beds can be traced laterally over several meters. Thus, the whole section is 100 % exposed. Reference samples can be collected without any limitations.

LITHOGRAPHY

AND BIOSTRATIOF THE SECTION

'The studied section is 1,28 m thick. As stated above only the boundary region was studied. in detail. Its lower portion which is equivalent to the Upper Famennian was not subject of this study. The section comprises 11 distinct beds wi th varying thicknesses. From each bed one conodont sample wi th an average weight of 2 kg was collected, but in two cases a bed was subdivided into a lower and an upper sample, e. g. 5B - 5e and 3A - 3B. Our conodont study is thus based. on 13 samples. The whole section consists of light grey and slightly pink colored dense biornicritic limestones. There is no variation or break in li thology. Most beds are separated ·by distinct bedding planes, however, in the Kronhof Limestone indistinct bedding occurs. Clay partings al though very thin occur at the base and on top of beds 5A, 6A and 6C.

Based on macroscopic and microfacies data, the studied sequence consists of the following lithologies (base to top, see figs. 3, 4; macrofacies/microfacies): Bed 7: Greyish - slightly pink colored limestone with faint black veines / micri-

Fig. 2. 'The limestone succession at Grtine Schneid. The left end of the scale is on bed 5 I the right end represents the top of the section.

tic wackestones with tiny cephalopod shells, ostracods, gastropods, trilobites, radiolarians and crinoid debris. -Bed 6A: Lightgrey to yellowish, weakly pink colored cephalopod limestones with few black veins / micritic wackestones with tiny cephalopod shells, ostracods, radiolarians, small bivalves and some crinoid debris. Bed 6B: Macroscopically the same as Bed 6A / biomicrite (radiolarian wackestone) with pressure solution residues of up to 1 mm thick local clay enrichment zones. Rare occurrences of cephalopods. Bed 6D: Greyish to light brownish weakly pink colored limestone, similar to Bed 6A / micri tic cephalopcrl wackestone wi th marly interlayers originated from pressure solution. Few crinoids, ostracods, gastropods , bivalves and trilobites. Inhomogeneous parts indicate bioturbation. Shell debris tiny and fragile. Bed 5A: Greyish to weakly pink limestone wi th pinkish portion in the lowermost 3 4 cm . In this portion pressure solution residues are more common than in the upper part. Solution effects can be seen along the rims of cephalopods / styloli tic radiolarian-cephalopod wackestone which is strongly bioturbated and reddish mottled in its lower part. Some ostracods, crinoid debris, few bivalves and trilobites. Bed 5B: Lightgrey to weakly pink colored limestone with few veins, macroscopically identical wi th Beds 7 and 6B / typical micritic goniatite wackestone with geopetal fabrics, ostracods, radiolarians, trilobites and perhaps bivalves.

152

Fig,,_ 3 _ 'Details of the section Grtine Schneid. Left side: Bed 7 from the Famennian _ Bed from the top of the 1 ,28 m thick boundary section in the lowermost Carboniferous.

5C: Lightgrey to yellowish-pinki,sh colored limestones similar to -Beds 6D or 6A, with few indistinct black veins / cephalopcrl-radiolarian wackestone with some ostracods, bivalves, trilobites and crinoids.

Bed

Bed 4:

Macroscopically the same as Beds SC, 6D or 6A / stylolitic cephalopcx:l limestone with large trilobite shells, ostracodes, bivalves and radiolarians.

Bed' 3: Lightgrey to yellowish-brownish and weakly pink colored limestone / trilobite -bearing goniatite-radiolarian wackestones with few ostracods, bivalves, crinoids and indication of bioturbation.

Beds 2, 1: Dense grey limestones, less pink colored than the' beds below / biomicritic limestone with mostly indistinct cephalopcrl shells_

Both the Pal and the Kronhof Limestone are fossiliferous . In varying abundances cephalopcrls, trilobites, brachiopcrls, ostracods and bivalves ("Estherians") have been found. The microfauna consists of abundant conodonts, fish teeth and radiolari'ans. Fossils, however, are more abundant in the Kronhof Limestone and here in parti-

cular in Beds 3, 4 and 5. 'The Upper Devonian Pal Limestone has as yet not been studied for trilobites, clyrneniids and other fossils satisfactorily. Our fossil data illustrates clearly that the "Grtine Schneid" section ranges from the Upper Devonian into the Lower Carboniferous. The rocks on either side of the systemic boundary are developed in uniform lithology of cephalopcrl limestone suggesting a modetately deep open marine pelagic environment with no indications of significant condensation. Based on conodonts the 1, 28 m thick limestone section can be subdivided into three faunal units: (1)

Conodonts Zone.

of

the

middle

praesulcata

This poorly defined Subzone is represented in the basal part of the section in samples 7 and 6A (fig. 3). In our collection ,from these to samples six specimens identified. as Siphonodella praesulcata were found. Two are complete adult specimens, the others are more or less fragmentary (in addition 12 specimens of S. praesulcata were found in the Carboniferous part of

153

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Fig. 4. Distribution of ammonoids, trilobites and conod.onts at Grtine Schneid (open circles: questionable occurrences); at present and provisionally the boundary is drawn between the two lines indicated in the figure. the section). For description see chapter "Remarks on the conodont fauna". The conodont fauna is equally dominated by representatives of the genera Palmatolepis, Bispathodus and Branmehlao Less abundant are. pseudopolygnathids (not true for sample 6A) and polygnathids. By far the most frequent species are Palmatolepis gracilis sigmoipalis, Bispathodus . costatus and Branmehla suprema but also Pseudopolygnathus marburgensis t:r:igonicus is a common species (e. g. in sample6A). These conodonts suggest a slope setting of the section 11 Grtine Schneid" in a .biofacies model (SANDBERG, 1976, SANDBERG & DREESEN, 1984, and others). However, Palmatolepis gracilis expansa has only been found in a sing~e fragmentary specimen suggesting an earlier extinction

in the strata below or possibly other reasons why it occurs so rare. Also failing in our association are representatives of the genus Protognathodus, i. e. Pr. collinsoni and Pr • rneischneri . They occur , however, in the succeeding bed.

(2) Conodonts Zone.

of

the

upper

praesulcata

'Ibis Subzone is well defined by the entry of Protognathodus kockeli. At the section "Grtine Schneid H , its first occurrence is in sample 6B. At this level the index conodont was found together with ~r • meischneri. The latter clearly dominates and the relationship is 6 : 1 in favour of Pr. meischneri. Co-occurring is Polygnathus conmunis conmunis while in the succeeding Bed 6C Pr. kuehni ,Polygnathus .purus purus and P. p. subplanus (?) have their first

154 appearances. In this horizon the relationship between Pr. rneischneri and Pr. kockeli changed significantly in favour of the latter (1 : 2). Strata equivalent to this Subzone are at "Grtine Schneid" 20 cm thick. Yet, Pr. collinsoni was not found. Also, nei ther Siphonodella praesulcata nor S. sulcata were yet discovered from thi.s small interval. As shown in fig. 4 at the base of sample 6B a very sharp faunal change took place. Above this level no representatives of the genus Palmatolepis occur . . Single elements of Bispathodusstill persist. '!here is no indication that they are reworked.

In samples SC, 2 and 1 S. sulcata co-occurs with its ancestor, S. praesulcata. 'This relationship is in agreement with observations in other areas (SANDBERG et al., 1978, QIANG;' 1987). REMARKS

ON

CONODONTS

With the exception of one new species treated here in open nomenclature all taxa have been well known in various regions. We add, however, some aspects which we observed in our fauna and which may extend and increase the knowledge about several taxa and their mutual relationships. Siphonodella praesulcata SANDBERG Siphonodella sulcata (HUDDLE)

(3) Conodonts of the sulcata Zone. The sulcata Zone and its equvalent rock sequence start at the base of Bed SA. The name bearer of this Zone ranges through the whole section and is still present in the uppermost sample 1. This part of the section, however, may belong to the lower duplicata Zone (see "Remarks"). In the sulcata Zone ( and above) the conodont fauna changed significantly. Three evolutionary sequences are obvious (for details see "Remarks"): the Protognathodus kockeli - Pr. licatus lineage,

praed~

the Polygnathus purus purus - P. p. subplanus lineage, the Pseudopolygnathus "dentilineatus" Ps. "primus" lineage.

-

In the lowerrnost sample SA Siphonodella sulcata is associated with abundant P.p. purus, Pr. kockeli and with rare questionable Pr. meischneri. The overlying sample yielded the same fauna; at this level Pr. kockeli disappeared. In the uppermost layer of Bed 5, i. e. in sample SC , Ps • dentilineatus and/or Ps. primus (cf. KLAPPER, 1981: 401) first appears. They·, persist to the top of the section' with a tendency to develop more "primus" than "dentilineatus" morphotypes. The two highest Beds 2 and 1 show the appearance of some new taxa .. We found Pseudopolygnathus marginatus, Polygnathus n. sp., P. conmunis bifurcatus, Siphonodella cf. duplicata and the re-appearance of the genus. Protognathodus. Representatives of the latter were assigned, to Pr. praedelicatus (for details see "Remarks").

As mentioned above, in the Upper Devonian part of the section six specimens were identified as S. praesulcata two of which are complete; the other forms are more or less fragmentary. 'These specimens permit the following observations: they are all slightly different from the holotype; they have short anterior blades; the platform is asymmetrical, curved and moderately wide; transverse ridges are well developed; the pseudokeel is narrow and raised; the anterior portion of the platform has deep furrows on each side of the carina with a tendency to form a very short rostrum. 'These characteristics lead us to believe that our specimens represent evolutionary advanced and hence transitional forms between' "typical" S. praesulcata and S. sulcata. In contrast to these differences in the Lower Carboniferous part of the section 12 specimens show all the characteristics of S. praesulcata. Interestingly, they resemble the holotype much more than the older forms.

s. sulcata first occurs in sample SA. At hand are four almost complete specimens and 1S fragments. In most cases the anterior portion of the platform is preserved. Our collection of S. sulcata is closely related to the type specimen. In oral view they are stronger curved and ornamented than. S. praesulcata. 'They have an asymmetrical platform and' a wider and more flat pseudokeel and in all cases a short but nevertheless distinct rostrum" This latter feature is apparently the main characteristic to distinguish S. sulcata from its ancestor.

155 Siphoncrlella cf. duplicata (BRANSON & MEHL) Two possible representatives of this species were found. They are preserved as fragments and the rostral part of the platform is missing. 'The illustrated specimen has a wide, flat and asymmetrical platform which resemble S. duplicata. However, since no complete specimens were found there remain certain doubts about the real occurrence of this species in our material. Hence, representation of the S. duplicata- Zone in the uppermost beds of section "Grline Schneid" is questionable. Polygnathus purus purus VOGES Polygnathus purus subplanus VOGES Between the two subspecies in our material an obvious relationship exist. P. p. purus wi th its typical platform and weakly developed adcarinal grooves and higher margins is replaced by forms with a considerable larger platform of varying outline. This platform is flat or bent in a convex manner. We named this morphotype P. p. sUbplanus. It is the dominating subspecies which starts in sample 3A. Protognathcrlus kockeli (BISCHOFF) Protognathcrlus praedelicatus LANE, SANDBERG & ZIEGLER LANE et al . ( 1980 ) have argued over the relationship between this species and its pr~ecessor as well as its descendants. Since then it has been clear that between Pr. kockeli, Pr. praedelicatus and Gnathodus delicatus and/or G. cuneiformis an evolutionary linkeage exist. Pr . kockeli is widely distributed in faunas of the sandbergi Zone in Germany and occurs rarely in faunas of the Lower crenulata Zone in North America. In the highest parts of this Zone Pr. kockeli gave rise to Pr. praedelicatus. Thus, the former gap of gnathodids between the first occurrences and the base of the Upper crenulata Zone was bridged. Our specimens in samples 2 and 1 cannot be objectively distinguished from Pr. praedelicatus. Very similar 'forms were already described by LUPPOLD et al. (1984: 101, pI. 6, fig. 2) and by MORY & CRANE (1982: 284, fig. 8 R -S). They named this species Gnathcrlus sp. and G. cuneiformis, respectively. Apparently they are all derived from the same level. In our collection 1 7 representati ves of this species occur. 10 additional specimens seem to represent juveniles which resemble Pr.meischneri. Apart from these forms our I

material is characterized by an oval shaped cup with mos tly unequal halves the anterior margins of which are slightly offset. The cup is ornamented by nodes which are in most cases arranged in indistinct elongate rows. On the inner side this row is always shorter and weaker developed than on the outer side. 'Ihe platform has a very sharp posterior termination. Provided that the two uppermost beels of section "Grline Schneid" still belong to the sulcata Zone (or perhaps to the Lower duplicata Zone) the first appearance of Pr. praedelicatus seems to be earlier than has previously been assumed by LANE et al. ( 1 980 ) . True and very characteristic representatives of Pr • kockeli 'are present in the lower samples. The collection from sample 6C, for example 1 is clearly different than the one derived from samples 2 or 1. Pseudopolygnathus primus BRANSON & MEHL Starting in sample SC Ps. primustogether with the Ps. dentilineatus l-morphotype occur. According to KLAPPER (1981: 401) there is no reason to separate the species because they are connected by intergrading morphotypes. Our material confirms KLAPPER S conclusion that Ps. primus is a highly variable species. However, we also found that there is a tendency to replace the Ps. "dentilineatus"-morphotype by the Ps. primus-morphotype in the upper samples. A clear distinction between the two cannot be drawn although in our collection mostly mature specimens occur. II

I

I

Polygnathus n. sp. In the uppermost sample 1 three polygnathid conodonts were found which according to the author s information have not as yet been described elsewhere. The have a long free blade the length of which extends the size of the small slender platform. The relatively large and elongated basal pit is located abouth the midlength of the conodont just anterior to the onset of the platform. Whether or not these forms represent juveniles of already known taxa cannot yet be concluded. I

Polygnathus conmunis bifurcatus HASS In our collection one single specimen occurs which we found in the uppermost sample 1. Contrary to the type or the illustration by LUPPOLD et al. (1 984) in oral view the spli tting of the carina is not developed. In aboral view, however, the keel shows distinct branching into two

156 directions, one to the posterior end of the platform and the other to a weakly developed lateral lobe.

Two juvenile specimens from Bed se show thickly discoidal conches with an open umbilicus. The diameter of the specimens is between 3 and 4 mm. Both show at 90 angles arranged constrictions on the shell surface and one specimen shows rather strong growth lines which run in an almost straight direction over the venter. 0

AMMONOIDEA At section IIGrtine Schneid" some ammonoids were found, but only a small number are well enough preserved to permit determination and description. 'The majority of the specimens are pieces of non characteristic very small conches. However, some more or less ··complete juvenile conches show characteristic features and can be placed in distinctive genera. The material at hand was mainly collected by the first author. Additional sampling was carried out by students from the University of Hamburg during an excursion. We greatly appreciate their help. Imitoceras sp. pI. 2, fig. 4 The specimen is a. juvenile conch of 3, 2 mm diameter from Bed se. It seems to be sUbglobose and has a completely closed umbilicus. Acutimitoceras cf. convexum (VOHRINGER, 1960) pI. 2 , fig. 1 a, b The single specimen from Bed SC has a diameter of 1 6 mm and shows a number of characteristic features. 'Ibe conch is thickly discoidal (ww: dm = 0,55) with a continuously rounded venter. The umbilicus is funnel-shaped but not completely closed. The surface of the shell has been destroyed due to diagenetic overprints and shows two very shallow constrictions with a convex shape. 'Ibese constrictions are on the flanks slightly deeper than on the venter. Acutimitoceras cf . substriatum (MUNSTER, 1839) pI. 2, fig. 3 a, b The shell surface is preserved on the specimen from Bed 5C. It has a diameter of 31 mm, but it could not be preparated off the rock completely. The conch is sUbglobose and the umbilicus seems to be closed . The ornamentation consists of fine growth lines which in the middle part of the flanks have distances of 1 mm. Their shape is convex with a deep external sinus. Constrictions are not perceptible. Acutimitoceras sp. pl.2, fig. 6

Gattendorfia cf. subinvoluta (MUNSTER, 1839) pI. 2, fig. 2 a, b This species occurs in Bed 4 and i t is a juvenile conch with a diameter of 8 , 5 mm. The specimen has an open umbilicus (uw: dm = ca. 0,5) and a trapezoidal whorl section. The venter is flattened and very broad. An ornamentation is not visible. Gattendorfia sp. pI. 2, fig. 5 'The small specimen from Bed se has a diameter of about 7 mm. 'The umbilicus is very wide and the whorls just touch the former one. The whorl section is rounded trapezoidal with a broad venter. Barely perceptible are fine growth lines on the shell. Age of the fauna Although not very well preserved these ammonoids can be placed in the stratigraphic scheme with minimal uncertainty. A comparison with the section in the Honne valley described by VOHRINGER (1 960) shows that the fauna from "Grtine Schneid" has an older Gattendorfia Stufe age. In the Honne valley "railroad cut" the species Acutimitoceras convexum, A. substriatum and Gattendorfia subinvoluta occur in the lower part of the section. 'Ibis age assignment is confirmed by the associated conodonts. TRILOBITA A· rich trilobite association comprlslng a dozen taxa has been known for a long time from the micri tic Upper Famennian (do V VI ) cephalopod limestones of the Carnic Alps. This fauna which had been studied in detail by Rud • & E • RICHTER in their famous monograph on Upper Devonian trilobites (1926) comes mainly from "Grosser Pal" (locality 6 km E of PlockenpaB) as well as from scattered neighboring localities such as "Kleiner Pal". Its occurrence W of the PlockenpaB is now reported for the first time: the same aSSOCiation, characterized by Typhloproetus carinthiacus (DREVERMANN , 1901), is quite common in the topmost

157 layers of the continuous Cellon mass which are displayed on the western side of the peak adjacent to "Grtine Schneid" where they are separated from the DIC boundary section described here by a minor fault zone. In the topmost Devonian praesulcata beds, however, trilobites are not so abundant. In this part further investigations are being planned for 1988 . At present, there is a continui ty in the trilobite record between the D/c boundary and the above mentioned trilobite horizon which does not extend beyond the expansa Zone ( = Middle costatuS Zone, SCHONLAUB, 1980). In contrast, trilobite remains of mainly disarticulated juvenile carapaces have been recognized in all micritic limestone beds above· the D/C boundary. Three taxa can be distinguished so far, which are known from elsewhere as index fossils of the lowermost Carboniferous Gattendorfia Stufe, i. e. A. (Phillibole) drewerensis, Liooole submonstrans and Globusia ? sp. This trilobite fauna is the first one known from the Gattendorfia Stufe in the Carnic Alps and in Austria. At "Grtine Schneid" it constitutes the second Tournaisian trilobite assemblages after the discovery of Liobole glabroides and A. (Waribole) sp. which are associated with the topmost Tburnaisian conodont faunas (K. J. MULLER, 1959). Archegonus (Phillibole) drewerensis (Rud. &E. RICHTER, 1951) pI. 2, fig. 11 - 1 7 This species is qui te common in beds 5C and 4 where 80 % qf the trilobi te remains belong to this taxon. Because well preserved adult specimens are insufficiently represented so far, a subspecific determination is still difficult. 'There are some slight differences to the type material from Drewer (Rhenish Slate Mountains) which concern essentially the size and the I;X)si tion of the palpebral lobe which is much larger in our material. This feature, however, may constitute a juvenile character. The narrow anterior glabella lobe and the shape of the anterior cephalic border, as well as the clearly ,developed posterior pleural bands in the pygidium are characteristic of the nominate subspecies. On the other hand, the granulose ornamentation of the exoskeleton is a feature of A. (Ph. ) drewerensis latepalpebratus OSMOLSKA, 1973 from Poland. 'The pygidium carries several continuous terrace ridges along the I;X)stero-lateral border which is a particular feature also occurring in the material from Montagne Noire (cf . FLAJS & FEIST, this vol.'.

Liobolina submonstrans Rud. & E. RICHTER, 1951 pI. 2, fig. 7 - 8 This species occurs in Beds SC, 4 and 2 • Only 1 cranidiurn and 3 pygidia had been found. The species which is known from the northeastern Rhenish Slate Mountains has recently been recorded from Mlissenberg (LUPPOLD et al., 1 984), where ist .appears much later than at "Grtine Schneid'" (sandbergi Zone versus sulcata Zone). Globusia ? sp. pI. 2, fig. 9 - 10 A juvenile cranidium and a single fragmentary librigena, associated withL. submonstrans in Bed 4 , may belong to Globusia OSMOLSKA, 1973 • '!his is suggested by the strongly downward-curved anterior glabella and the inflated genal spines. However, the glabella of the Polish material exhibit a more highly vaulted glabella and a narrow praeglabella field (sag.) which does not occur in our specimen. In addition the outline and form of the anterior fixigenae and the well defined anterior border are different and resemble certain representatives of Liobolina Rud. & E. RICHTER such as L. wurmi GANDL and L. ? oblativa OS~LSKA respectively . The adult cranidiurn of L. submonstrans, which has a longer and less vaulted glabella (sag.) can hardly be considered conspecific with the young cranidium. Nevertheless, at this stage, it is difficult to evaluate the significance of certain transitional juvenile features such as the degree of vaulting of the glabella. In contrast, the librigena displays the typical swollen distal portion of the genal spine which characterizes Globusia. However, even though Liobolina is thought to lack genal spines, this is not proven, especially, for L. submonstrans. More material is required to ascertain the taxonomic attribution of Globusia ? sp. from "Grtine Schneid" .

CONCLUSIONS At section Grtine Schneid" conodonts indicate continuous sedimentation across the Devonian-Carboniferous boundary. The boundary beds are within a uniform lithology of cephalopod bearing Flaser limestones. They represent a pelagic open-marine environment with abundant conodonts of the palmatolepid-bispathcrlid biofacies in the uppermost Devonian followed by a protognathodid-polygnathid-siphonodellid biofacies in the Tournaisian. Our association sug11

158 gests continui ty of a stable environment across the systemic boundary. 'The studied 1 ,28 m thick limestone sequence was deposited in an offshore open-marine pelagic setting in which major sedimentary breaks obviously ,did not occur. At the base of Bed SA the lowermost occurrence of Siphonodella sulcata was found. The index conodont for the base of the Carboniferous succeeds S. praesulcata which was found below but survived into the Tournaisian. Section "Grtine Schneid" exhibits several quali ties which render it as a candidate for a chronostratigraphic boundary strato-

type: (1) The passage from the Devonian into the Carboniferous is within a uniform lithology of pelagic cephalopod limestones. ( 2) Siphonodella praesulcata and S. sulcata are relatively abundant. Our present collection was recovered from less than 2 kg of rocks for each sample. (3) .The two index conodonts are connected by transitional forms.

boundary interval without index concxionts are being planned. for late spring 1988 . After this campaign more critical conodonts, trilobites and cephalopods will be available to establish the precise boundary plane between the Devonian and the Carboniferous systems.

REFERENCES AMEROM, van, H. W. J., FLAJS, G. & HUNGER, G. (1984): Die "Flora der Marinelli-Htitte" (Mittleres Vise) aus dem HochwipfelFlysch der Karnischen Alpen (Italien).Meded. Rijks Geol. Dienst., 37: 1 - 41. EBNER, F. (1978): Die sedimentare Entwicklung des Unterkarbons in Osterreich.Osterr. Akad. Wiss. , Erdwiss. Komm. , vol. 3: 1 79 - 190, Springer (Wien-New York) . FLAJS, G. & FEIST, R. ( 1988): Conodonts and trilobi tes of the Devonian-Carboniferous Boundary beds Montagne Noire, France. Stratigraphy and environment.(this vol.). I

(4) Our representatives of S. praesulcata may be evolutionary advanced forms.

GAERTNER, von, ·H. R. (1931): Geologie der zentralkarnischen Alpen.Denkschr. Osterr. Akad. Wiss., math. -naturw . Kl., 102: 11 3 - 199.

(5) The interval without siphonodellids is extremely short and not more than 20 cm thick.

GEDIK, I. (1974): Conodonten aus dem Unterkarbon der Karnischen Alpen.Abh. Geol. B.-A., 31: 1 - 29.

(6) The Devonian-Carboniferous boundary is presently drawn between samples" 6B and SA. This is a 10 cm interval wi thout siphonodellids, but with fairly abundant representatives of the genera Polygnathus and Protognathodus, e . 9 . , Pr • kuehni, and with lowermost occurrence of the trilobite species Archegonus (Ph.) drewerensis (?).

KLAPPER , (1981 ) : Pseudopolygnathus G. primus BRANSON & MEHL, 1934 b.- In: Catalogue of Conodonts IV: 401 - 408.

(7) In the Lower Carboniferous representatives of four genera are present and in most cases co-occurring, i . e. , Siphonodella, Protognathodus, Psetrlopolygnathus and Polygnathus. ( 8) CompletEness of this part of the succession is testified by evolutionary transitions from older to younger species or subspecies. (9) Section "Grtine Schneid" also other fossils such as amrnonoids, tes, bivalves, brachiopods and rians. The study of spores has been carried out.

contains trilobiradiolanot yet

(10) Detailed studies of the 20 cm

thick

LANE, H'. R., SANDBERG, C. A. & ZIEGLER, W. ( 1980 ): Taxonomy and phylogeny of some Lower Carboniferous concxionts and preliminary standard post-Siphonodella zonation.- Geologica et Palaeontologica, 14:117 - 164. LUPPOLD, F. W., HAHN, G. & KORN, D. (1984): Trilobiten- , Ammonoideen- und Conodonten-Stratigraphie des Devon/KarbonGrenzprofiles auf dem Mtissenberg (Rheinisches Schiefergebirge).-Cour. Forsch.Inst. Senckenberg, 67: 91 - 121. MULLER, K.J. ( 1959 ): Nachweis der Pericyclus-Stufe (Unterkarbon) in den Karnischen Alpen.- N. Jb. Geol. Palaontol. Mh. 1959: 90 - 94. OSMOLSKA, H. (1973): Tournaisian trilobites from Dalnia in the Holy Cross Mountains . - Acta geol. polonica, 23: 61 80.

159 QIANG, J. ( 1987): New results from Devonian-Carboniferous boundary beds in South China.- Newsl. Stratigr., 17: 155 - 167. RICHTER, Rud. & RICHTER, E. (1926): Die Trilobiten des Oberdevons.- Abh .. preuss. geol. Landesanst., 99: 1 - 314. (1951): Der Beginn des Karbons im Wechsel der Trilobiten.- Senck. leth., 32: 219 - 266 .. SANDBERG,C. A. (1976): Conodont biofacies of Late Devonian POlygnathus styriacus Zone in western United States.- In: BARNES, C. R. (ed.): Conodont paleoecology.- Geol. Ass.. Canada, Spec. Pap. 15: 1 71 - 186 . SANDBERG, C. A. & DREESEN, R. (1984): Late Devonian icriodontid biofacies models and alternate shallow-water conodont zonation.- Geol. Soc. America, Spec. Pap. 196: 143 - 178. SANDBERG, C . A., ZIEGLER , WOo, LEU'IERITZ , K. & BRILL, S. M. (1978): Phylogeny, speciation and zonation of Siphonodella (Conodonta, Upper Devonian and Lower Carboniferous).- Newsl. Stratigr. , 7: 102 - 120.

SCHONLAUB, H. P . ( 1969 ): Conodonten aus dem Oberdevon und Unterkarbon des Kronhofgrabens (Karnische Alpen, OsterreichJ.- Jb. Geol. B.-A., 112: 321 354. ( 1980 ): Field" Trip A, Carnic Alps.- In: Guidebook/Abstracts, Second Europ. Conodont Symp .. -ECOS 11, Vienna-Prague .. - Abh. Geol .. B.-A., 35: 5 - 57. (1985): Geologische Karte der Republik Osterreich, 197 Kotschach, 1 : 50 000, Erlauterungen 1 : 10 000.- Geol .. B.-A. Wien. (1986): Significant Geological Events in the Paleozoic Record of the Southern Alps (Austrian Part).- In: WALLISER, O. H. (ed.): Global Bio-Events.- Lecture Notes in Earth Sciences, 8: 163 - 167, Springer (Berlin-Heidelberg) .. VOHRINGER, E . ( 1960 ): Die Goniati ten der unterkarbonischen Gattendorfia-Stufe im Honnetal (Sauerland) . - Fortschr. Geol .. Rheinl. u. Westf., 3: 107 - 196 ..

H. P. SCHONLAUB Geologische Bundesanstalt Postf. 154, Rasumofskygasse 23 A-1031 Wierf --

R. FEIST Lab. de Paleontologie U.S.T.L., Place E. Bataillon F-34060 Montpellier D. KORN FeldstraBe 29 D-5768 Sundern1

160

PLATE Microfacies of the

Die

boundary beds at "Grtine Schneid

lf

Fig. 1. Wackestone (biomicrite) with cephalopod shells, ostracods and radiolarians. Sample 7; scale: 3 mm. Fig. 2. Wackestone (biomicrite) with cephalopod shells, ostracods and bivalves. Sample 6A; scale: 3 mm. Fig. 3. Radiolarian wackestone (biomicrite); strong influence of Sample 6B; scale: 5 mm.

pr~ssure

solution.

Fig. 4. Wackestone (biomicrite) with ostracods, bivalves and a large gastropod (right). Sample 6D; scale: 5 mm. Fig. 5. Stylolitic radiolarian wackestone (biomicrite), rich in insoluble residues; shelter porosity below the bivalve. Sample SA; scale: 6,5 mm. Fig. 6. Goniatite wackestone (biomicrite) with some ostracods. Sample 5B; scale: 6 mm. Fig. 7. Cephalopod-radiolarian wackestone (biomicrite) with orthoconic cephalopods. Sample se; scale: 3,5 mm~ Fig. 8. Radiolarian wackestone (biomicrite) with ostracods qnd a large trilobite; shelter porosity below the i:rilobite; a fenestral fabric (right) is filled at the base with internal sediment and on top with coarse-grained cement. Sample 3; scale: 4 mm

161

162

PLATE

2

Ammonoids and trilobites from the "Grtine Schneid n section; all specimens are reposited in the collections of the Senckeriberg Museum/Frankfurt Fig. 1 a, b. Acutimitoceras cf. convexum (VOHRINGER, 1960) SMF 51036, Bed 5C; x 3. Fig. 2 a, b. Gattendorfia cf. subinvoluta (MONSTER, 1832) SMF 51037, Bed 4; x 5. Fig. 3 a, b. Acutimitoceras cf. substriatum (MONSTER, 1839) SMF 51038, Bed SC; x 1,5. Fig. 4.

Imitoceras sp. SMF 51039, Bed 5C; x 5.

Fig. 5.

Gattendorfia sp. SMF 51040, Bed 5C; x 5.

Fig. 6.

Acutimitoceras sp. SMF 51041, Bed 5C; x 5.

Fig. 7-8.

Liobolina submonstrans Rud.

Fig. 9-10 .

Globusia? sp.

& E. RICHTER, 1951 7: Cranidium; SMF 49450, Bed 4; a: dorsal view, x 3,6; b: lateral view, x 3,3. 8: Pygidium; SMF 49451, Bed 4; a: dorsal view, x 6,4; b: lateral view, x 6,8.

9: Cranidium; SMF 49452, Bed 4; a: ,dorsal view, x5, 7; b: lateral view, x 5;6. 10: Librigena; SMF 49453, Bed 4; a: latex cast of external mOUld, x 5,2; b: x 4,9. Fig. 11-17.

Archegonus (Phillibole) drewerensis (Rud.

& E. RICHTER, 1951) 11: Cranidium; SMF 49454, Bed 4; x 5,8. 12: Small cranidium; SMF 49455, Bed 4; x 6,5. 13: Cranidium; SMF 49456, Bed 5C; a: dorsal view, x 5,2; b: lateral view, x 5,1 . 14: Small pygidium, SMF 49457, Bed 5C; x 8,2. 15: Pygidium; SMF 49458, Bed 5B; a: dorsal view, x 5,6; b: lateral view, x 5,8. 16: Librigena; SMF 49459, Bed 5C; latex cast of exterinal mould, x 6,4. 17: Pygidium; SMF 49460, Bed 5B; latex cast of external mOUld, x 6,5.

163

13a

15b

13b

9b

164

PLATE

3

Magnification: x 50, except figs. 7, 8, 16, 201 22, 27 (x 90)

Fig.

Palmatolepis gracilis gracilis BRANSON & MEHL; Bed 6A.

1 ..

Fig. 2.

Palmatolepis gracilis sigmoidalis ZIEGLER, Bed 7.

Fig. 3.

Psetrlopolygnathus· marburgensis trigonicus ZIEGLER; Bed 6A.

Fig. 4.

Bispathodus ziegleri muessenbergensis LUPPOLD; Bed 6A ..

Fig. 5.

Bispathodus costatus costatus (E. R. BRANSON); Bed· 7.

Fig. 6.

Polygnathus cf ... vogesi ZIEGLER; Bed 6A.

Fig. 7.

Palmatolepis gracilis expansa SANDBERG

Fig. 8, 9.

Polygnathus conmunis conmunis BRANSON & MEHL; Bed 6B.

Fig. 10.

Branmehla suprema (ZIEGLER); Bed 7.

Fig. 11-13.

Polygnathus purus .purus. VOGES

& ZIEGLER; Bed

11: Bed 6C. 12: Bed 4. 13: Bed 3A.

Fig.. 14-1 7 .

Polygnathus .porus subplanus VOGES 14: Bed 6C. 15, 16: Bed 3B. 17: Bed 1.

Fig. 18, 23. Siphonodella cf. sulcata (HUDDLE); Bed SA. Fig. 19, 20, Siphonodella sulcata (HUDDLE) 24. 19: Bed 5C. 20: Bed 2.

24: Bed 3A. Fig. 21, 22, Siphonodella praesulcata SANDBERG 26, 27. 21: Bed 5B. 22 1 26, 27: Bed 5C; 22: aboral view.

Fig .25.

Siphonodella cf • duplicata (BRANSON

&

MEHL); Bed 1.

7.

165

166

PLATE

4

Magnification: x 50, except figs. 1, 4, 5, 9, 12, 14, 17, 18 (x 90) Fig. 1, 2, 5. Protognathodus kockeli (BISCHOFF) 1: Bed 6C. 2: Bed SA. 5: Bed 5B.

Fig. 3, 7.

Protognathodus kuehni ZIEGLER & LEUTERITZ; Bed 6C.

Fig. 6.

Protognathodus kockeli - Protognathodus kuehni transi tional form; Bed 6C

Fig. 4.

Protognathodus meischneri ZIEGLER; Bed 6B.

Fig. 8-10.

Protognathodus praedelicatus LANE, SANDBERG & ZIEGLER; Bed 2.

Fig. 11-13.

Pseuiopolygnathus primus BRANSON & MEHL 11,12: Bed 1. 13: Bed. 3A.

Fig-. 14-15.

Pse1.rlopolygnathus dentilineatus E. R. BRANSON; Bed. 4.

Fig. 16.

Polygnathus conmunis bifurcatus HASS; Bed 1; aboral view ..

Fig. 1 7-18.

Polygnathus n. sp.; Bed 1; oral and lateral view.

167