Discussion and Correlation (former Soviet Union): FUSULINID SUCCESSION FROM THE MIDDLE-UPPER CARBONIFEROUS BOUNDARY BEDS ON SPITSBERGEN, ARCTIC NORWAY

DISCUSSION AND CORRELATION

The Middle/Upper Carboniferous boundary in the stratotype area of the Moscow Basin is placed at the base of the Krevyakinian Horizon (Ivanov 1926, Dan'shin 1947) (Figure 10). This boundary was traditionally defined by fusulinids in the 1950's (Rauser-Chernousova et al. 1951; Rauser-Chernousova and Reitlinger 1954; Rauser-Chernousova and Scherbovich 1974; Ivanova and Khvorova 1955), and the base of the Protriticites pseudomontiparus-Obsoletes obsoletus Zone was assigned to correspond to the base of the Kasimovian (i.e. base of Krevyakinian Horizon). This definition is accepted and widely used.

Former Soviet Union

In the Russian Platform, Timan-Pechora Basin, Urals, Donets Basin and Central Asia the Middle/Upper Carboniferous boundary is defined by the first occurrence of Obsoletes and accompanying advanced Protriticites and Quasifusulinoides (Rauser-Chernousova and Scherbovich 1974; Davydov 1986, 1990a, 1990b, 1997a, 1997b; Konovalova 1991; Remizova 1995). However, representatives of the latter two genera first appear in the underlying upper Myachkovian beds (i.e. uppermost Moscovian). Protriticites, Quasifusulinoides, and Obsoletes can be identified only if their tests are well preserved. Even slight recrytallization hampers recognition of these genera. Some specialists deny the independence of these genera for this reason (Villa et al. 1993). Distinct changes in fusulinid wall structure (i.e., well-defined trabecularity of keriotheca) are observed at the base of the Montiparus montiparus Zone, and some investigators prefer therefore to place the Moscovian/Kasimovian boundary at the base of this zone (i.e., at the base of the Khamovnichenian Horizon in the stratotype section of the Moscow Basin area; Remizova 1997; Villa et al. 1993).

The problem of the Moscovian/Kasimovian boundary has recently been discussed by Davydov (1997a). Several variations of the Moscovian/Kasimovian boundary position were considered:

At the base of Praeobsoletes burkemensis-Protriticites ovatus Zone corresponding to the base of the Protriticites Genozone and Peskovskyi Fm. of Myachkovian Horizon in the Moscow Basin.
At the base of Protriticites pseudomontiparus-Obsoletes obsoletus Zone that places the classical Moscovian/ Kasimovian boundary at the base of Krevyakinskian Horizon.
At the base of the Montiparus montiparus Zone corresponding to the base of Khamonicheskian Horizon.

Based on the latest fusulinid and conodont studies in the region of the Moscow Basin (Alekeseev et al. 1994; Davydov 1997a) the best correlation potential is shown by the following boundaries:

A) at the base of the Suvurovskaya Fm. (or probably base of "liska" bed of the Peskovskaya Fm. of the Myachkovian Horizon) - the base of the Protriticites pseudomontiparus, Obsoletes obsoletus Zone and its equivalent the Streptognathodus subexcelsus conodont Zone;

B) at the base of the Montiparus paramontiparus Zone and its equivalent the Streptognathodus oppletus conodont Zone (Villa et al. 1997; Davydov 1997a).

Based on evidence mentioned above, we can conclude that the Moscovian/Kasimovian boundary problem still is unresolved in the stratotype area and the boundary therefore should be left at an accepted level, i.e. at the base of the Krevyakinian Horizon, that corresponds to the base of the Protriticites pseudomontiparus-Obsoletes obsoletus Zone and base of Streptognathodus subexcellsus conodont Zone.

Spain

In the Cantabrian Mountains lower Myachkovian assemblage with Fusulinella bocki occur in the middle portions of Picos de Europa Formation (Villa et al. 1997). In the upper portion of this formation, primitive Protriticites first appear together with conodonts resembling Streptognathodus subexcellsus. The base of the Kasimovian is established based on the occurrence of Protriticites pseudomontiparus and other advanced Protriticites, and by the first appearance of Praeobsoletes. First Obsoletes occur together with Montiparus (i.e., higher in the section than in the stratotype area). The same phenomena is observed in the Kolosseum section at Spitsbergen, where Praeobsoletes and Obsoletes appear slightly later than in the stratotype area.

Carnic Alps

The lower most portion of the Upper Paleozoic succession in the Carnic Alps has been restudied recently (Krainer and Davydov 1998). The Bombaso Formation and basal Meledis Formation in the central Carnic Alps near Straniger Alm and Zollnersee (Austria/Italy border) consist of shallow marine clastic and carbonate sediments that are arranged to form two fining and deepening upward sequences. Limestones in particular and even breccias of the Bombaso and lower Meledis Formation yield a rich fusulinid fauna composed of 33 species that are attributed to the following zones: Quasifusulinoides quasifusulinoides-Protriticites ovatus; Protriticites pseudomontiparus, and Montiparus montiparus. Breccia of the Bombaso Formation west of Straniger Alm contains the oldest fusulinid fauna of the Carnic Alps, belonging to the Quasifusulinoides quasifusulinoides - Protriticites ovatus Zone corresponding to the Peskovskaya Formation of the Myachkovian Horizon in the Moscow basin indicating uppermost Moscovian age. A similar assemblage is found in limestones from depositional sequence 1 at Zollnersee (Krainer and Davydov 1998). Limestones and calcareous sandstones-siltstones of the basal Meledis Formation of depositional sequence 2 near Zollnersee and at Cima Val di Puartis are characterized by fusulinids of the Protriticites pseudomontiparus Zone (Protriticites globulus, Pr. pseudomontiparus, Pr. sphaericus, Pr. rotundatus, Pr. ovoides, Pr. lamellosus, and Praeobsoletes burkemensis) and by Montiparus paramontiparus Zone (Praeobsoletes pauper, P. burkemensis, Obsoletes timanicus, O. obsoletus, Montiparus paramontiparus, M. umbonoplicatus, M. montiparus, M. likharevi, M. rhombiformis, and M. priscus) indicating correlation to Krevyakinian (Lower Kasimovian) and Khamovnichenian Horizons (Middle Kasimovian) of the Russian Platform, respectively. In the Carnic Alps, Praeobsoletes and Obsoletes first occur in the Khamovnichenian Horizon (i.e., later than in the stratotype area).

Northeast Greenland (Wandel Sea Basin)

New fusulinid collections from Amdrup Land have recently been studied by Davydov and Nilsson. Beds with Beedeina paradistenta, Fusulinella praebocki, Pseudofusulinella eopulchra and primitive Protriticites are correlated with the Peskovskaya Formation of the upper Myachkovian Horizon in the Moscow Basin. These beds are overlain by beds with advanced Protriticites, Quasifusulinoides, rare Praeobsoletes, Obsoletes, and Plectofusulina. This assemblage corresponds to the Krevyakinian Horizon of the Lower Kasimovian in the Moscow Basin. Higher in the section Quasifusulina, Montiparus, and rare Protriticites occur. This assemblage is correlative with the Khamovnichenian Horizon (Middle Kasimovian) in the Moscow Basin. Beds with assemblages of Quasifusulina, Montiparus, and rare Protriticites are overlain by beds with numerous Quasifusulina and the first Rauserites, that correlate with the Dorogomilovian Horizon (Upper Kasimovian) in the Moscow Basin. Moscovian-Kasimovian fusulinid assemblages in Northeast Greenland show strong similarities with those in Spitsbergen and correlate well with the Moscovian-Kasimovian transition in the stratotype sections of the Moscow Basin.

Canadian Arctic

In the Canadian Arctic (Sverdrup Basin) fusulinids from the Middle/Upper Carboniferous boundary beds are reported by Rui Lin et al. (1991), Nilsson (1993) and Rui Lin and Nassichuck (1994). An upper Moscovian Fusulinella eopulchra assemblage, a lower to middle Kasimovian Protriticites-Pseudofusulinella ex. gr. usvae assemblage and an upper Kasimovian Rauserites aff. quasiarcticus assemblage are recorded from the Canyon Fiord Formation (Nilsson 1993). Rui Lin et al. (1991) defined two upper Moscovian fusulinid zones in the type section of the Nansen Formation: Wedekindellina lata-W. uralica longa Zone (units F-G) and "Fusulinella" eopulchra Zone (units H-L). The former zone is correlated by Rui Lin et al. (1991) with the Podolskian Horizon and the latter zone with the Myachkovian Horizon. We kindly were permitted by Dr. Nassichuk and Dr. Rui Lin to study the thin sections from the type section of the Nansen Formation. This study enabled us to propose another correlation of this section. We consider fusulinid assemblages from the units F-G most similar to the Myachkovian of the Moscow Basin. In particular, units F-G comprise species of Wedekindellina, Neostaffella, and Fusulinella, that are characteristic for the Myachkovian of the Moscow Basin (Rauser-Chernousova and Reitlinger 1954). The fusulinid taxa notably change in the units H-L. Typical Moscovian genera such as Wedekindellina and Neostaffella completely disappear while Fusulinella and Pseudofusulinella predominate. In unit L we recognized Nodosaria aff. longissima Suleimanov and Raphconilia sp. Until now these small foraminifera were not known in deposits older than Kasimovian (Davydov 1988; Brenckle and Whalman 1993; Groves and Whalman 1997). Also in Spitsbergen Nodosaria has not been reported in beds older than Krevyakinian (Nilsson and Davydov 1992). "Fusulinella" eopulchra Zone of Rui Lin et al. (1991) is therefore partly of early Kasimovian and may be middle Kasimovian in age.

Rui Lin and Nassichuk (1994) describe two new fusulinid assemblages above unit L in the type section of the Nansen Formation. Both "Protriticites" sp. A Zone (thickness 1.5 m) and Eowaeringella placitasensis Zone (thickness 23 m) are correlative with the Lower Missourian of the American Stratigraphic Scale and with the Krevyakinian Horizon of the Lower Kasimovian of the Moscow Basin . In our opinion however, their "Protriticites" fauna should belong to the genus Rauserites , because those specimens have a true keriothecal wall structure; sometimes slightly recrystallized. Rauserites occurs only from the beginning of the upper Kasimovian in the Moscow Basin, Urals, Donets Basin, Central Asia, North Greenland and Spitsbergen (Villa et al. 1994). Rauserites assemblage from type Nansen seems to correlate well to the Rauserites quasiarcticus Zone of the stratotype area (i.e., Dorogomilovian Horizon of Moscow Basin). Consequently, the proposed Moscovian/Kasimovian boundary in type Nansen by Rui Lin and Nassichuk (1994) is actually closer to the middle Kasimovian/upper Kasimovian boundary. In our opinion the Moscovian/Kasimovian boundary in the type Nansen should be placed at the base of unit H.

North America

Correlation of fusulinids from Russia and Spitsbergen with North America can be performed only conventionally. Traditionally the Moscovian/Kasimovian boundary is correlative with the Desmoinesian/Missourian boundary, with Missourian being the approximate equivalent of the Kasimovian (Ross and Ross 1987). Rosovskaya (in Ivanova and Rosovskaya 1967) noted, however, that fusulinids from the base of Missourian, according to their evolutionary level, correspond to Upper Kasimovian fusulinids. Rosovskaya assumed a gap between the Desmoinesian and Missourian corresponding to the Krevyakinian and Khamovnicheian Horizons (Ivanova and Rosovskaya 1967). Accepting Rosovskaya's idea of the correspondence of the Lower Missourian and Upper Kasimovian, we propose a correlation between the Desmoinesian with the Lower and Middle Kasimovian and the Lower Missourian with the Upper Kasimovian (Figure 11).

In Eurasia Fusulinella predominates at the end of the Myachkovian. It is simultaneously displaced by Protriticites and Praeobsoletes, that later are gradually followed by Montiparus and Rauserites in the first line (Figure 11), and by Obsoletes and Triticites in the second one respectively (Davydov 1990b). It is also at the end of the Myachkovian that Fusulina is displaced by Quasifusulinoides, that is followed by Quasifusulina in the Khamovnicheian (Chen-Tzin-Shi 1963). Beedeina disappears completely at the end of the Myachkovian.

The following fusulinid succession in the Upper Moscovian-Kasimovian in Eurasia is shown in Table 1.

In North America Fusulinella is scarce in the upper part of the Desmoinesian and disappears relatively quickly. Beedeina and Fusulina predominate during most of Desmoinesian. The evolution these genera in North America is very different from their evolution in Eurasia. Specialization and gigantism characterize evolution of Beedeina in North America. At the beginning of the Missourian in North America, Triticites abruptly occurs, perhaps as a result of migration. Triticites instantaneously displaces super-specialized Fusulina and Beedeina. Recently Wahlman et al. (1997) discovered Protriticites and probably Praeobsoletes fauna co-occur with Bartramella bartrami in the middle Desmoinesian. Table 2 shows recorded fusulinid zones of Desmoinesian (DS) and Missourian (MS) in USA by Wilde (1990).

Comparison of the Myachkovian-Kasimovian fusulinid succession of Eurasia with the Desmoinesian-Missourian fusulinid succession shows the following. Fusulinids from DS-1a,b and DS-2a zones of the Desmoinesian are, according to their evolutionary level, correlative with those from the Myachkovian in the Russian Platform and to Fusulinella bocki and Protriticites ex. gr. ovatus-Quasifusulinoides quasifusulinoides zones in Spitsbergen. Fusulinids in succeeding Desmoinesian fusulinid zones (DS-2b, DS-3, DS-4, and DS-5) differ essentially in a more advanced shell structure.

The first Missourian Eowaeringella and Triticites Fusulinid Zone replace Desmoinesian successions of Beedeina and Fusulina in the USA. According to their development these Triticites correspond to Triticites and Rauserites from the Upper Kasimovian (Dorogomilovian) of the Moscow Basin (Ivanova and Rosovskaya 1967). Position of DS-4, DS-5, DS-6 and DS-7 enables us to assume that the major part of the Desmoinesian corresponds to the Krevyakinian and Khamovnichenian Horizons of the Russian Platform. Desmoinesian Fusulinid Zones DS-4, DS-5, DS-6, DS-7 correspond to Protriticites pseudomontiparus and Montiparus montiparus fusulinid zones in Spitsbergen respectively. In summary, we propose that the Moscovian/Kasimovian boundary is correlative with the base of DS-3 (Middle-Upper zone of Beedeina and upper zone of Wedekindellina) by Wilde (1990) (Table 3).

Similar conclusions can be drawn based on ammonoids. Ammonoids in the Moscovian/ Kasimovian transition are, however, insufficiently studied because of their scarcity. Rare Moscovian ammonoids occur in the region of the Moscow Basin, Donets Basin and Pai-Khoi (Ruzhenzev 1974). The earliest assemblage of Upper Carboniferous ammonoids (Dunbarites and Prouddenites) occurs in the lower part of the Kasimovian in Cape Chaika of the Pai-Khoi (Ruzhenzev 1974), where early Kasimovian fusulinids occur (Villa et al. 1994). This ammonoid assemblage is correlative with the Wewoka Formation of the middle Desmoinesian. According to Boardman et al. (1990), Dunbarites, Prouddenites, and Wewokites occur within the Marmaton Group, and these genera also correspond to the Desmoinesian. This enables correlation of the middle and upper portion of Marmaton Group with the Lower and Middle Kasimovian of the Russian Platform.

The proposed correlation is also supplemented by conodont data. Conodonts in the Moscovian and the Kasimovian are also inadequately studied, especially in North America. Streptognathodus exelsus and St. oppletus, that occur in the Krevyakinian in the Moscow Basin (Alekseev et al. 1994; Villa et al. 1997), are also known in the Desmoinesian of North America (Merrill 1975). Idiognathodus saggitalis Kosenko, that is characteristic of the upper part of the Khamovnicheian and Dorogomilovian in the Moscow Basin (Alekseev et al. 1994), occurs at the base of the Missourian in North America (Barrick et al. 1996). These observations also suggest an approximate correspondence of Upper Desmoinesian and Lower-Middle Kasimovian strata.

To compare the above-mentioned Eurasian zonation and North American fusulinid zonation of Wilde (1990), it is possible to conclude that the Fusulinella bocki Zone approximately corresponds to DS-1 of the Desmoinesian. The Rauserites quasiarcticus Zone can be correlated with MS-1 of the Missourian. According to their position in the section, the Protriticites ovatus-Praeobsoletes burkemensis, Obsoletes obsoletus-Protriticites pseudomontiparus and Montiparus montiparus zones correspond to DS-2, DS-3, DS-4, and DS-5 zones of the Desmoinesian, respectively.

Recent data from the Arctic region support this correlation. In the lower and middle Kasimovian of Northern Timan and Kolguev Island Wedekindellina occurs (Remizova 1995; Davydov 1997b). This type of Wedekindellina in North America is known from the middle Desmoinesian. Also, occurrences of Plectofusulina and Oketaella in the lower Kasimovian of Kolguev Island were reported recently (Davydov 1997b). Both genera previously were known only in North American sections. Plectofusulina first appears in the middle Desmoinesian and range to Missourian. Oketaella ranges from Missourian to the Permian. Therefore Arctic sections are perhaps the key to solving the problem of correlation of Upper Carboniferous between Russian Platform and North America.