3, 2009, p. 43-78. Gulf PetroLink, Bahrain. Refinements in biostratigraphy, chronostratigraphy, and paleogeography of the Mississippian (Lower Carboniferous).
GeoArabia, v. 14, no. 3, 2009, p. 43-78
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
Gulf PetroLink, Bahrain
Refinements in biostratigraphy, chronostratigraphy, and paleogeography of the Mississippian (Lower Carboniferous) Mobarak Formation, Alborz Mountains, Iran Paul L. Brenckle, Maurizio Gaetani, Lucia Angiolini and Maryamnaz Bahrammanesh ABSTRACT Detailed sampling of limestones from the Mobarak Formation at the Abrendan and Abnak measured sections in the eastern and central Alborz Mountains, northern Iran, yielded a diverse assemblage of Tournaisian – Lower Visean (Mississippian/ Lower Carboniferous) calcareous microfossils (foraminifers, algae, incertae sedis). The Abrendan locality contains Tournaisian foraminifers in the upper part of the formation that correlate to the Ivorian and upper Courceyan – lower Chadian substages of western Europe and the Kosvinsky Horizon of the Russian Platform. Brachiopods confirm a Tournaisian age for the lower part of the Mobarak, which lacks age-diagnostic calcareous microfossils. Lower Visean foraminifers at Abnak provide good correlation to the western European Moliniacian and Arundian substages and the Russian Bobrikovsky Horizon. Synthesis of foraminiferal data from this and other published reports indicates that the top of the Mobarak Formation becomes increasingly older across the Alborz to the southeast, caused most likely by Pennsylvanian (Upper Carboniferous) exposure and erosion in the south followed by a latest Pennsylvanian – Early Permian transgression from the north. The microbiota at both sections and the macrofossils at Abrendan show close affinity to the warm-water Paleo-Tethyan Ocean, seemingly contradicting Early Mississippian paleomagnetic reconstructions placing the Alborz region at 45–50° South latitude. The discrepancy is not resolvable at this time, but the answer may lie in the circulation of Paleo-Tethyan currents to the south along the Gondwanan shelf, rather than to repositioning the Alborz region to the northern side of the Paleo-Tethyan Ocean.
INTRODUCTION The Mississippian (Lower Carboniferous) Mobarak Formation of Assereto (1963) is a mixed carbonate-siliciclastic marine unit that crops out in an arcuate pattern along the flanks of the EWtrending Alborz Mountains of northern Iran (see location map in Bozorgnia, 1973, and Figure 1). The present definition of the formation (Stepanov, 1971; Bozorgnia, 1973) includes most Tournaisian and Visean rocks (Figure 2) that Assereto (1963, 1966) initially placed in the Mobarak and partly time-equivalent Geirud formations (Figure 3); the distinction between his two formations is based on lithologic differences that still require a more detailed stratigraphic nomenclature. Initial attempts at dating and locally correlating the Mobarak focused on macrofossil studies (see historical reviews in Gaetani, 1968; Stepanov, 1971; and Vachard, 1996) based primarily on brachiopod and coral occurrences. Most published microfossil investigations appeared in the latter part of the last century and concentrated on identifications and age interpretations of calcareous foraminifers, as will be explored further herein. Conodonts, another potentially useful microfossil group within the Mobarak (Ahmadzadeh Heravi, 1971; Ueno et al., 1997; Habibi et al., 2008), have yet to be examined in detail throughout the Alborz region. The objectives of this paper are to (1) provide new information on the distribution of calcareous microfossils (foraminifers, algae, and incertae sedis) from the Abrendan (eastern Alborz) and Abnak (central Alborz) measured sections located in Figure 1, (2) relate their occurrences to those published in previous Alborz foraminiferal studies, (3) comment on their relationship to other biotas within
43
Brenckle et al.
52º
Gonbad-e-Qabus
N
0
54º
Caspian Sea
50
km
Fazelabad
13
11
Aliabad
14
12
Gorgan
Chalus Sari Amol
1
EAN
ER VIS
PP TOP U
9 Figure 4
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36º
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Abrendan Damghan
EAN
ER VIS
Figure 6
OW TOP L
Abnak
6
4
Karaj
10
Firuzkuh
5
36º
7
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58°
IRAN
IRAQ
0 KUWAIT
34°
km
30°
26° Gulf of Oman
QATAR
Red Sea 38°
38°
N300
BAHRAIN UAE
Arabian Shield
22° SUDAN
46°
Figure 1
SYRIA CYPRUS 34° LEBANON Med Sea JORDAN 30° Gulf of Suez
Semnan
RNAISIA TOP TOU
38° 42° TURKEY
OMAN
SAUDI ARABIA
22°
Figure 1: Mobarak foraminifer localities in the Alborz Mountains: (1) Dozdehband (Bozorgnia, 1973; Pirlet and Conil, 1977); (2) Geirud (Bozorgnia, 1973; = Jajerud section of Lys et al., 1978); (3) Abnak (Stepanov, 1971; Bozorgnia, 1973; Pirlet and Conil, 1977; this paper); (4) Mobarakabad (Bozorgnia, 1973; Meissami et al., 1978); (5) Aruh (Bozorgnia, 1973); (6) Gaduk (Bozorgnia, 1973; Devuyst, 2006; Devyust and Kalvoda, 2007); (7) Shahmirzad (Bozorgnia, 1973; Ueno et al., 1997; Habibi et al., 2008); (8) Peyghambaran (Bozorgnia, 1973); (9) Abrendan (this paper); (10) Kalariz (Bozorgnia, 1973); (11) Kalate (Lys et al., 1978); (12) Viru (Lys et al., 1978); (13) Nodeh-Sud (Lys et al., 1978); (14) Khoshyeilagh (Bozorgnia, 1973). For localities above the uppermost dashed line, the top of the Mobarak Formation terminates in the Upper Visean; for those between the dashed lines the top of the Mobarak ends in the Lower Visean; and for those below the lowermost dashed line the top does not extend above the Tournaisian. See Figures 2 and 3 for stratigraphic terminology used in this paper. 18°34°
ERITREA
14°
ETHIOPIA
International Subsystem
Series
Stage
upper Middle
V2b-V3c
Visean
Mississippian (part)
Lower
Belgian Substage
Tournaisian
V1a-V2a
upper
Tn3a-c
Russian Horizon
Brigantian
Venevsky
Warnantian
Mikhailovsky Asbian
Livian lower
British Substage
Moliniacian
Tulsky
Arundian
Bobrikovsky
Chadian
Radaevsky Kosvinsky
Ivorian
Kizelovsky Courceyan
lower
Tn1b-Tn2
Hastarian
Aleksinsky
Holkerian
Cherepetsky Upinsky Malevsky Gumerovsky
44
42°
46°
50°
54°
Arabian Sea
YEMEN
Gulf of Aden SOCOTRA
14°
Figure 2: Chronostratigraphic terminology used in this paper, showing correlation between international and regional PaleoTethyan units. The position of the base of the Moliniacian substage follows the emendation of Poty et al. (2006).
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
the Paleo-Tethyan Realm, and (4) discuss their implication for regional and global paleogeography. Representative microfossils from the two measured sections are illustrated on Plates 1-12 and supplemental information on macrofossil occurrences (mostly brachiopods) and their significance is also included. This study developed from a project on Pennsylvanian (Upper Carboniferous) – Early Triassic stratigraphy in the Alborz (Gaetani et al., 2009) that was part of the Middle East Basin Evolution Programme (MEBE). The sections were sampled because of their relevance in establishing regional stratigraphic relationships at the Mississippian – Pennsylvanian boundary.
BIOSTRATIGRAPHY AND CHRONOSTRATIGRAPHY Foraminifers Foraminifers are the primary calcareous microfossil group used to correlate and date the Mobarak Formation, but little was done prior to the pioneering paper of Bozorgnia (1973). He described and illustrated the microfauna from numerous outcrop sections (Figure 1) and established a zonal scheme to correlate across the Alborz Mountains. His research showed the value of foraminifers in elucidating the local chronostratigraphy, e.g., identifying diachroneity along the top of the Mobarak, and also showed the feasibility of long-distance correlation by relating the assemblages to the better known Dinantian sequences in Belgium. Despite this promising start, only a few follow-up investigations have been published. Pirlet and Conil (1977) provided additional taxonomic information on the Dozdehband and Abnak sections as did Meissami et al. (1978) for the Mobarakabad area. Lys et al. (1978) published a generalized range chart and selected microfossil illustrations from localities in the central and eastern Alborz (Figure 1). In an excellent summary of progress to date, Vachard (1996) refined Bozorgnia’s foraminiferal zonal scheme by incorporating data from both published reports and dissertations (Jenny, 1977; Stampfli, 1978), and Kalvoda (2002) utilized this information in his analysis of the paleobiogeography of the Alborz region. Ueno et al. (1997) related the foraminiferal succession at the Shahmirzad section to major lithologic units in the Mobarak Formation, and Devuyst (2006) identified taxa within the Tournaisian – Visean boundary beds at the Gaduk section (Figure 1). Bozorgnia (1973) and Vachard (1996) established a credible zonal and chronostratigraphic framework but did not show the sample-by-sample distribution of individual taxa within the Mobarak Formation. Without that information, a high-resolution chronostratigraphy, now promoted by the Carboniferous Subcommission and by others to standardize series, stage and substage boundaries, cannot be
Visean
Tournaisian Famennian
Assereto (1963, 1966)
Mubarak Limestone
Geirud Formation
Stage/Age
Stepanov (1971)
Bozorgnia (1973)
Wendt et al. (2005)
Mobarak Limestone
Mobarak Formation
Mobarak Formation
Geirud Formation
Khoshyeilagh Formation
"D" member "C" member "B" member "A" member
Geirud Formation
Khoshyeilagh Formation
Figure 3: Name changes to strata assigned originally by Assereto (1963, 1966) to the Mobarak and Geirud formations. The Upper Devonian and the lowermost Tournaisian beds are composed of mixed arenitic and calcareous sediments, whereas during most of the Tournaisian and the Visean carbonate deposition prevailed. Assereto’s member C of the Geirud Formation appears to be a local dolomitized facies. Assereto’s member D was originally referred to the Early Permian, but since Stepanov (1971) is recognized as Visean. Relationships between the lithostratigraphic units are uncertain and need to be clarifed through new, detailed field work.
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developed. The work of Ueno et al. (1997) and Devuyst (2006) provided the first steps to create a precise foraminiferal biostratigraphy that is supplemented by material from the present report, although a comprehensive correlation scheme for the Mobarak Formation and adjacent Paleozoic strata awaits the results of future investigations. Diagnostic calcareous microfossils at the Abrendan section (Figure 4) are limited to the upper part of the Mobarak Formation (Figure 5, samples IR 1013-1020). The remainder of the formation is dominated by an assemblage of small, bilocular, earlandiin species (Earlandia elegans, E. minima, E. moderata) and cannot be dated precisely by the microfossils. The restricted composition of this microbiota possibly resulted from the relatively high terrigenous content and deposition on an high energy, current–swept substrate, unfavorable for the flourishing and preservation of foraminifers and algae. Reduction in water energy and the amount of siliciclastic clay eventually led to an influx of calcareous microfossils indicative of the latest Tournaisian, beginning in sample IR 1013. The presence of Eotextularia diversa, Darjella monilis, Loeblichia? fragilis, and Eoparastaffella specimens support correlation to the upper Kosvinsky Horizon of the Russian Platform and Urals and to the uppermost Ivorian or foraminiferal zone MFZ 8 in Belgium (Poty et al., 2006). Although elements of the assemblage extend into the Visean, diagnostic markers for that stage, such as Eoparastaffella simplex and Eoendothyranopsis donica, are not present. Bozorgnia (1973) indicated that the Mobarak Formation in the nearby Kalariz section (Figure 1) ended in the Lower Visean (V1a). His markers for that interval (Bozorgnia, 1973, p. 17 and opposite p. 20) included the first appearance of Dainella and Eoparastaffella along with Endothyra (=Spinoendothyra) recta, Endothyra (=Laxoendothyra) laxa and Endospiroplectammina conili. Subsequent work (e.g., Kulagina et al., 2003; Poty et al., 2006) has shown that all these taxa were widespread in the Paleo-Tethyan Ocean during the Late Tournaisian and are not reliable Visean markers. Research on Eoparastaffella for more than the past decade (e.g. Hance, 1997; Devuyst, 2006; Devuyst and Kalvoda, 2007) has produced a better understanding of the evolutionary history of that genus, which was once considered no older than Visean (Conil et al., 1977). Instead, the genus exhibits a complex development beginning in the Late Tournaisian, and knowledge of the species composition is now essential for placement of the Tournaisian – Visean boundary (Work, 2008). Because of its proximity to Abrendan and uncertainty about its foraminiferal content, the Mobarak Formation at the Kalariz section is herein considered no younger than Tournaisian (Figure 1), pending restudy of the microfossil sequence. For similar reasons the Mobarak in Bozorgnia’s Aruh section (Figure 1, locality 5) possibly ends in the Tournaisian, but because detailed occurrence data are not available, his V1a designation for the top of the formation is tentatively accepted in this report. Ueno et al. (1997) divided the Mobarak at the Shahmirzad section (Figure 1) into five members. The lower two and most of the third contained non-diagnostic earlandiin and tuberitinin microfossils; the upper part of the third, a Septabrunsiina foraminiferal assemblage; and the upper part of the fourth and fifth, a diverse foraminiferal assemblage not unlike that found in the upper Abrendan section. All the Mobarak beds beneath the upper assemblage at Shahmirzad are considered to be approximately equivalent to the lower non-diagnostic microfossil interval at Abrendan, although Septabrunsiina was not recovered at the latter locality because of either inadequate sampling or an unfavorable environment. Conodonts recovered from that same Shahmirzad interval (Ueno et al., 1997; Habibi et al., 2008) were dated as Early to Late Tournaisian in agreement with the brachiopod determination of a Tournaisian age for most of the lower Mobarak beds at Abrendan. Multilocular foraminifers from the upper two Shahmirzad members (Eoforschia moelleri, Eotextularia diversa, Inflatoendothyra sp., Uviella sp.) resemble some of the latest Tournaisian microfauna found in the upper Mobarak
Figure 4 (facing page): Lithology and stratigraphic position of samples at the Abrendan section. The base of the Mobarak Formation is not clearly defined in this area. Some of the lower Mobarak beds could as well belong to the Khoshyeilagh Formation whose upper member has similar lithologies extending from the Upper Devonian into the Tournaisian (Wendt et al., 2005). WGS84 coordinates of the base of the section 36°21’47.6”N and 54°18’59.9”E (Location 9 in Figure 1). The section may be reached in one hour walking from the road leading to the Kalariz mine.
46
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
Strat. Unit ?? Qezelqahleh Fm.
Thickness (m)
Age ? Pennsylvanian
ABRENDAN SECTION Lithology Sample
Description Grey medium litharenite and thin conglomerate
IR 1022 IR 1021
Conglomerate with large flat calcareous pebbles
IR 1020
Grey marlstone and mudstone, medium to thin bedded, with diffuse Zoophycos trace fossils
IR 1019
Thick bedded dark grey wackestone/packstone, with dark chert nodules. Steep wall
IR 1018 IR 1017 IR 1016
Dark grey wackestone/packstone, medium bedded, with marly and silty intercalations. Big solitary rugose corals
IR 1015 IR 1013 IR 1012
Grey and pinkish marlstone and thin bedded mudstone. Diffuse Zoophycos trace fossils
IR 1011
Mobarak Formation
Tournaisian
IR 1009
Packed, nodular grey packstone, medium bedded, with thin silty intercalations
IR 1008 IR 1007 IR 1006 IR 998 IR 997 IR 996 IR 995 IR 994 IR 993 IR 992 IR 990 IR 989 IR 988
Grey marlstone with mudstone and fine packstone intercalations, increasing in thickness upwards. Brachiopods abundant
Sandstone Marlstone Ooidal Limestone Marly Limestone Sandy Limestone Hybrid Sandstone Bioclastic Limestone Nodular Limestone Limestone Cherty Limestone Covered
Main creek Thin bedded grey mudstone alternated with marlstone and shale Pinkish, very thin arenites in cm-thick layers, with grey mudstone intercalations
IR 987 IR 986bis IR 986 IR 985
Grey medium bedded packstone with brachiopods and michelinid tabulate corals. Thin pinkish siltstone intercalations
Dev.
?
Khoshyeilagh Fm.
IR 984 IR 983 (debris) IR 1047 IR 1046 IR 1045 IR 982 IR 1044 IR 1044bis (debris) IR 981 IR 980 (debris) IR 1042 IR 1041 IR 1040 IR 1038
Grey recrystallized packstone in thin beds, intercalated with thin bedded laminated siltstone. Occasionally fine arenite. Brachiopods diffused, with shell lags of small productids. Sparse micheliniid tabulate corals
Marlstone and splintery siltstone with packstone lenses Thin bedded grey-brown quartzarenite with parallel lamination
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Brenckle et al.
at Abrendan; however, based on the identifications of Dainella and Eoendothyranopsis in the upper part of the fifth member, Ueno et al. (1997) assigned the top of the Mobarak at Shahmirzad to the Lower Visean. As mentioned above, the appearance of Dainella is not indicative of the Visean and the illustrated Eoendothyranopsis specimens, if truly belonging to that genus, are not characteristic of the E. donica assemblages typical of the Lower Visean. While an earliest Visean age cannot be ruled out for the uppermost Mobarak beds at Shahmirzad, the present interpretation of the evidence suggests that the formation is no younger than Late Tournaisian (Figure 1). After establishing the Geirud Formation in 1963, Assereto (1966) divided it in ascending order into the A, B, C, and D members, of which the last was described from the Abnak section (Figures 3 and 6). The oldest A member was Late Devonian. The middle B and C were Mississippian and Stepanov (1971) included them in the Mobarak Formation. The upper D member contained brachiopods (Fantini Sestini, 1966) that resembled Early Permian Gondwanan assemblages. Because of this discovery, member D was sampled extensively and those collections provide the material for this paper. In contrast, Stepanov (1971, p. 1518) reported that foraminifers examined by Soviet micropaleontologists from the same member were Visean and that brachiopods he collected were Late Visean. Vachard (1996) mentioned that conodonts supported the latter age interpretation. Bozorgnia (1973) countered that the interval actually contained early Middle Visean foraminifers and he assigned member D to the Mobarak. Specimens recovered from the present samples (Figure 7) replicate many of Bozorgnia’s identifications and confirm his age interpretation. “Member D” in the Abnak section contains an abundant assemblage of “primitive” archaediscids (Viseidiscus, Uralodiscus, Glomodiscus) and auxiliary forms that correlate to the Bobrikovsky Horizon of the Russian Platform, Arundian and upper Moliniacian substages of western Europe, and foraminiferal zone MFZ 11 of Belgium (Poty et al., 2006), chronostratigraphic intervals considered to be Early Visean in this report (Figure 2). Most Abnak limestones are composed of bioclastic-oolitic packstones and grainstones deposited in a warm, shallow-water environment that provided exceptionally fertile grounds for the development of calcareous foraminifers; green, red and cyanophytic algae; and incertae sedis. The foraminiferal composition is transitional between Late Tournaisian – Early Visean and Late Visean assemblages. Specimens of genera dominant in the older interval, including Bessiella, Biseriella?, Dainella, Eoparastaffella, Florennella, Latiendothyranopsis, Laxoendothyra, Lysella, and Pseudolituotubella, intermix with those of Endostaffella, Lituotubella, Omphalotis, and Plectogyranopsis that become prominent later in the Visean. Early representatives of “advanced” archaediscids, Kasachstanodiscus and Paraarchaediscus, occur jointly with the primitive archaediscids before replacing most of them in the Late Visean. Even within some specimens of the primitive archaediscids Glomodiscus and Uralodiscus a noticeable reduction in the thickness and distribution of the inner microgranular layer is observed, presaging the evolution of younger, double-walled archaediscids in which the inner dark layer became subordinate to the outer, hyaline-radial one. The few specimens tentatively assigned herein to Eostaffella (Figure 7; Plates 7 and 8) exhibit the morphology of that genus but possess a mostly homogeneous, microgranular wall in contrast to the typically layered wall. They may represent the transition from Eoparastaffella to Eostaffella that both Hance (1997) and Devuyst et al. (2003) observed in Early Visean specimens of southern China.
Algae and incertae sedis The algal flora is diverse and abundant throughout the Abnak section (Figure 7). Greens are represented by the Dasycladaceae (Coelosporella, Issinella and other unidentified genera), Palaeoberesellaceae (Kamaena, Kamaenella, Palaeoberesella), Umbellaceae (Protoumbella and indeterminate specimens) and spore cases (Calcisphaera, radiosphaerids); reds by the Aoujgaliaceae (Aoujgalia, Epistacheoides, Pseudostacheoides, Stacheoides and an indeterminate morphotype); and cyanophytes by Girvanella and an ortonellid. At least at the generic level most of these algae have a cosmopolitan distribution in the Northern Hemisphere during the Mississippian (Mamet, 1992). Protoumbella, which is the longest ranging of the umbellids (Mamet, 1990), is also one of the most widely dispersed of that group in the Early Visean, having been reported at that time from Iran (this paper), the northern Ural Mountains (under the name Grozdilovella Chermnykh, 1972), and the North American Midcontinent (Brenckle et al., 1982). Of the incertae sedis the most abundant are Diplosphaerina/Eotuberitina, Koninckopora and Proninella.
48
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
Upper Tournaisian (part)
Belgian Substage
→
British Substage
→
Upper Ivorian Upper Courceyan Lower Chadian
x
1011
1013
1015
x
1007
x
986
x
1006
x x
984
x
indeterminate Umbellaceae (algae) Spumisalebra spumosa (incertae sedis)
1047
?
Earlandia spp.
982
?
indeterminate Palaeoberesellaceae (algae)
1046
indeterminate foraminifer
980
IR Spl. No.
1038
Calcareous Microfossil
x
x
x
x
x
x
1020
Kosvinsky
1019
→
1018
Russian Horizon
Tournaisian?
1016
→
1017
International Stage
x
x
x
x
x
x
Eovolutina sp. (incertae sedis)
x
Kamaena delicata (algae)
x
x
x ?
x
x
x
Condrustella modavensis
x
x
x
Eogloboendothyra sp.
x
Eotextularia diversa
x
x
? x
?
Inflatoendothyra parainflata
x
x
x
?
Eoparastaffella sp.
x
Kamaena pirleti (algae)
? ?
Mediocris sp.
?
“Priscella” sp.
x
Pseudolituotubella spp.
?
radiosphaerid calcisphere (algae)
x
Septaglomospiranella sp.
?
x
Girvanella spp. (algae)
x
x
x
x
x
x
x
Aphralysia matthewsi (algae)
x
Diplosphaerina/Eotubertina sp. (incertae sedis)
x
x
x
x
?
x
x
x
x
x
x
?
x
Draffania sp. (incertae sedis)
x
Endospiroplectammina sp.
x
Eoforschia moelleri
?
Issinella devonica (algae)
?
Mediendothyra sp.
?
Tournayella vespaeformis
x
Uviella sp.
x
x
x
?
x x
x
x ?
x
x
x
x
x
x x x
x
x x
? x
Baituganella sp. (incertae sedis)
x
Bituberitina sp. (incertae sedis)
?
x
Calcisphaera spp. (algae)
x
Eoparastaffella florigena
?
x
x
Eotournayella kisella
x
x
Parathurammina/Parathuramminites sp. (incertae sedis)
x
Tournayella sp.
?
x
x
x
Dainella micula
x
x
Dainella sp.
?
Darjella monilis
x
Endothyra sp.
x
Kamaenella tenuis (algae)
x
Loeblichia ? fragilis
x
Loeblichia ? sp.
x
Palaeoberesella lahuseni (algae)
?
Proninella sp. (incertae sedis)
x
Pseudoammodiscus priscus
x
Tetrataxis sp.
x
x ? ? x
x
x x x
x
x x
x
Bessiella sp.
x
x
Brunsia sp.
x
x
Figure 5: Distribution of calcareous foraminifers, algae, and incertae sedis in the Mobarak Formation at the Abrendan section. Only samples containing calcareous microfossils are listed on the chart. Those examined but lacking microfossils include IR 981, 990, 992, 995 and 1009. See Figure 4 for sample locations. 49
Brenckle et al.
Thickness (m)
Strat. Dorud Group Unit
Latest Pennsylvanian Age
ABNAK SECTION
250 240
IR 1078 IR 1077
220
IR 1076
200 190
Mobarak Formation (Geirud Formation of Assereto, 1963, 1966) “Member D”
IR 1081 IR 1080 IR 1079
230
210
Early Visean
Lithology Sample
180 170
IR 1075
Description Whitish quartzarenite
Grey mudstone, marlstone and thin bedded grainstone/packstone
Coarsening-up cycles of marlstone and ooidal grainstone/packstone
IR 1074 IR 1073 IR 1072 IR 1071 IR 1070 IR 1069 IR 1068 IR 1067 IR 817 IR 813 IR 812 IR 810 IR 809
Medium bedded ooidal packstone/grainstone alternating with mudstone/wackestone
160
IR 808 150 140
IR 807
Light grey ooidal packstone/grainstone in medium to thick beds
130
IR 806 120 110
IR 805
Sandstone
100 90 80
Marlstone IR 804
Ooidal Limestone Marly Limestone
IR 803
Sandy Limestone Hybrid Sandstone
70 60
IR 801
Bioclastic Limestone
IR 800
Nodular Limestone Limestone
50
“Member C”
? Early Visean
Covered 40
IR 1084
30
IR 1066
20
Alternating medium bedded ooidal packstone/grainstone and mudstone/wackestone
10 0
IR 1065 IR 1062
50
Figure 6: Lithology and stratigraphic position of samples at the Abnak section. WGS coordinates of the base of the section 35°59’10.9”N, 51°36’54.9”E (Location 3 in Figure 1). The upper part of the section coincides with locality 4 of Fantini Sestini (1966, her fig. 1).
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
These microfossil groups are not as well represented in the Abrendan section even in the upper part of the Mobarak Formation (Figure 5) where foraminifers are common. The Palaeoberesellaceae are the most abundant and diverse algae, and Parathurammina/Parathuramminites specimens are the most common incertae sedis. The relative scarcity of algae is likely related to the turbid sedimentation (see lithologic descriptions in Figure 4) in contrast to the predominantly clear-water deposition for much of the Mobarak Formation at the Abnak section.
Brachiopods The brachiopod assemblages at Abrendan occur throughout most of the section and are comprised of 36 species in 27 genera of the orders Strophomenida, Productida, Orthotetida, Orthida, Rhynchonellida, Spiriferida and Spiriferinida (Figure 8). A single species of the molluscan order Conocardioida, Hippocardia alborza Hoare and Aghababalu, 2001, has also been found in the lower part of the section. Most of the taxa are cosmopolitan, especially at the generic level, and range from the Tournaisian to the Visean. However, some taxa are restricted to the Tournaisian such as Hemiplethorhynchus crassus Gaetani, 1968, Rossirhynchus adamantinus Gaetani, 1964, Cleiothyridina kusbassica Beznosova in Sarytcheva et al., 1963, Unispirifer (Unispirifer) striatoconvolutus (Benson & Dun in Benson et al., 1920), and the genera Ptychomaletoechia and Atylephorus (e.g., Gaetani, 1968; Sartenaer and Plodowski, 1996; Savage in Williams et al., 2002; Shi et al., 2005; Poletaev, 2006). In contrast to the calcareous microfossils, the latter brachiopods provide definitive proof that most of the lower Mobarak Formation at Abrendan is Tournaisian. Brachiopods from the lower part of the section (from samples IR 1040 to IR 987) are less diversified than the association found higher in the section and are dominated by pedicle attached species with few free-living spiriferinids and rare seminfaunal productids, indicating high-energy, shallow-water settings and high nutrient supply. Abundant and more diversified assemblages occur in the marlstone of the middle part of the formation (IR 988-IR 998); here pedicle attached species are still dominant, but concavo-convex seminfaunal productids significantly increase in abundance indicating quieter settings than previously. In the limestones from the uppermost part of the section, brachiopods are much scarcer and include few species found in the lower or middle part of the formation. Brachiopods in member D at the Abnak section comprise an enigmatic, low-diversity assemblage of relatively large and thick-shelled spiriferids (Frechella, until now known only in the Visean – Serpukhovian from North Africa) and productids (Fantini Sestini, 1966; Angiolini, unpublished data) that occur most abundantly with large solitary corals in the shaly and marly intercalations in the upper part of the member. The change from oolite-dominated lithologies in the lower beds (Figure 6) to mixed carbonate and fine-grained siliciclastics possibly suggests passage from well-oxygenated shoals to a more protected environment receiving siliciclastics from a new source, with periodic influx of coated grains from neighboring shoals. Furthermore, the low diversity and thick-shell structure of the brachiopods might indicate cooling water temperatures (Angiolini et al., 2005).
REGIONAL PALEOGEOGRAPHY From the age and locality information presented in Bozorgnia (1973), Lys et al. (1978) and this paper, the top of the Mobarak Formation becomes older in a southeasterly direction across the Alborz Mountains (Figure 1). On the northern flank, the upper Mobarak is Late Visean, whereas on the south flank the age varies from Early Visean to no younger than Tournaisian. Bozorgnia (1973) attributed this age discrepancy to differential uplift across the southern Alborz that started in the Late Visean and continued into the Early Permian. We propose instead that this situation resulted from the following scenario: (1) A progressive sea-level drop, linked to glacial episodes between latest Visean – Serpukhovian to early Moscovian (Fielding et al., 2008; Rygel et al., 2008; Haq and Schutter, 2008), exposed positive areas to the south that were also subject to tectonic uplift. Their erosion filled adjacent depressions in the northwest with clastic sediments intermingled with marine carbonates, now represented by the Bagherabad, Dozdehband and Qezelqaleh formations (Gaetani et al., 2009).
51
Brenckle et al.
Lower Visean?
Lower Visean (part)
International Stage
→
Russian Horizon
→
Bobrikovsky
Belgian Substage
→
Upper Moliniacian
British Substage
→
Formation Members
→
Mediocris mediocris Pseudoammodiscus priscus Pseudoammodiscus spp. Bessiella sp. Brunsia irregularis Endostaffella parva Endostaffella spp. Endotaxis spp. Eoparastaffella spp. Exvotarisella index (algae) Issinella devonica (algae) Kamaena delicata (algae) Koninckopora minuta (incertae sedis) Lysella spp. radiosphaerid calcisphere (algae) Uralodiscus rotundus ortonellid (algae) Lituotubella glomospiroides Pseudolituotubella spp. Uralodiscus spp. Endothyra spp. Eostaffella ? nalivkini Eostaffella ? sp. Pseudostacheoides spp. (algae) Endothyra obsoleta Florennella sp. Kamaena aff. pirleti (algae) Mediocris spp. Omphalotis spp. Plectogyranopsis regularis Forschia spp. Palaeospiroplectammina spp. Dariopsis curvisepta Endothyra prisca Kamaena pirleti (algae) Laxoendothyra laxa Tetrataxis spp. Dainella spp.
x
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x x ? x x
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Calcisphaera spp. (algae) Endostaffella discoidea Pojarkovella wushiensis Aoujgalia variabilis (algae) indeterminate Umbellaceae (algae) Latiendothyranopsis sp. Plectogyranopsis convexa Viseidiscus bozorgniae Viseidiscus monstratus Viseidiscus spp. Coelosporella spp. (algae) Glomodiscus spp.
?
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x x ?
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Figure 7: Distribution of calcareous foraminifers, algae and incertae sedis in the Mobarak Formation at the Abnak section. See Figure 6 for sample locations.
52
x
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?
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x
x x x x x x x x x x
1081
x
x x x x x x x x x x x x x x ? x x x x x
1080
x
x x x x x x x
1078
x x
x x x x x x x
1079
x
x x x x x x x x x x x x
1076
x
x x
x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x
1074
x x
1075
x x
1073
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1071
x
1072
x x
1069
x x
1070
x x
817
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1067
x x
812
808
809
x x ?
813
807
x
810
805
1066
x x x x x x x ? x x x x x x x x
806
Girvanella spp. (algae)
x
804
Earlandia spp.
802
Biseriella? bristolensis
803
Proninella spp. (incertae sedis)
x x x x x
800
"Priscella " spp.
x x x x cf. ? x x x x x x x x
801
indeterminate Dasycladaceae (algae) Palaeoberesella lahuseni (algae)
“D” 1084
Diplosphaerina/Eotuberitina sp. (incertae sedis)
1065
IR Spl. No.
“C” 1064
Calcareous Microfossil
Arundian
x
x ?
x
x
x
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
Lower Visean?
Lower Visean (part)
International Stage
→
Russian Horizon
→
Bobrikovsky
Belgian Substage
→
Upper Moliniacian
British Substage
→
Formation Members
→
Lapparentidiscus bokanensis Mediocris ? liae Epistacheoides spp. (algae) indeterminate Aoujgaliaceae (algae) Uralodiscus abnakensis Eovolutina sp. (incertae sedis) Spumisalebra sp. (incertae sedis) Omphalotis minima Kasachstanodiscus spp. Protoumbella elliptica (algae) Stacheoides meandriformis (algae)
x x x
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x
?
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1081
x
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? x x
Paraarchaediscus pachythecus
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Figure 7 (continued). (2) A marine incursion transgressed the Alborz from the north beginning in the latest Pennsylvanian (Gaetani et al., 2009), leading to deposition of the Gzhelian – Sakmarian Dorud Group (Jenny and Stampfli, 1978; Gaetani et al., 2009) that overlies progressively older rocks to the south and east.
GLOBAL PALEOGEOGRAPHY AND PALEOBIOGEOGRAPHY The paleoposition of the Alborz region during the Mississippian is controversial. The region has been positioned either at or near the margin of Gondwana (Meissami et al., 1977; Vachard, 1980; Sengör, 1990; Stampfli, 2000; Golonka, 2002; Webster et al., 2003; Torsvik and Cocks, 2004; Wendt et al., 2005; Muttoni et al., 2009) or closer to the Eurasian landmass (Kalvoda, 2002; Devuyst, 2006). Paleomagnetic data from Alborz indicate an Apparent Polar Wandering (APW) compatible with the West Gondwana APW (Wensink et al., 1978; Besse et al., 1998; Muttoni et al., 2009). The calculated paleolatitude for the base of the Tournaisian, about 45–50° South, although strikingly high, is in agreement with the Early Carboniferous loop of West Gondwana (McElinnhy et al., 2003; Figure 9). Also, the Permian and Early Triassic position of the Iran APW suggests that Iran and namely Alborz were on the southern border of the Paleo-Tethyan Ocean (Muttoni et al., 2009). The biota partly seems to contradict this inference. Foraminifers, algae, and brachiopods suggest warmer waters than should be expected at 45–50° South, although perhaps during the early stages of the Mississippian the temperate to semitropical climate belts were wider. Kalvoda (2002) and Devuyst (2006) argued that the Alborz foraminiferal faunas have Paleo-Tethyan affinities and were located along the northern side of that seaway. Indeed, the biotas at the Abrendan and Abnak sections contain many of the same calcareous microfossils recorded from other areas of the Paleo-Tethys (compare the present microfossil occurrences with those listed, for example, in Conil et al., 1991, p. 20-21; Mamet, 1992, p. 177; Reitlinger et al., 1996, p. 48-49; Kalvoda, 2002, p. 139-141). The Abnak section also contains Mediocris? liae and a Pojarkovella specimen resembling P. wushiensis, both of which species were considered possibly endemic to the Tarim Basin of western China and vicinity (Brenckle, 2004). Although older than the Tarim occurrences, the presence of these taxa in Iran point to communication between the two areas and to a wider distribution of these fossils along the Paleo-Tethyan corridor. Although mostly cosmopolitan, the Abrendan brachiopods are closer to coeval faunas of North America, western Europe and Russia than to cold-water Australian faunas, having six species in
53
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1078
x x
1079
x
1076
1074
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1073
1071
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1072
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817
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x cf. x ? x x x x x
Glomodiscus oblongus Koninckopora tenuiramosa (incertae sedis)
1067
812
x
1069
Stacheoides spp. (algae)
1070
x x
Kamaenella tenuis (algae)
813
810
808
809
807
805
806
804
802
803
800
801
1066
“D” 1084
1065
“C” 1064
IR Spl. No.
Calcareous Microfossil
Arundian
x
x
Brenckle et al.
common with the Kusnetsk and Moscow basins: (1) Tomiproductus elegantulus (Tolmachoff, 1924), (2) Cleiothyridina kusbassica Beznosova in Sarytcheva et al., 1963, (3) Syringothyris skinderi Sokolskaja in Sarytcheva et al., 1963, (4) Pustula cf. altaica Tolmachoff, 1924, (5) Pustula cf. kondomensis Sarytcheva in Sarytcheva et al., 1963, and (6) Composita megala (Tolmachoff, 1924); and four species in common with the Mississippian of Iowa, Missouri, and Illinois in North America: (1) Composita subquadrata (Hall, 1858), (2) Paraphorhynchus elongatum Weller, 1905, (3) Syringothyris carteri (Hall, 1857), and (4) Marginatia vaughani (Muir-Wood, 1928), the latter two occurring also in Europe. Most genera are widespread, occurring in America, Europe, China and Australia. Two are endemic to Iran and the Transcaucasus, and six occur elsewhere only in North America, Europe and Russia. The biogeographic similarity of brachiopods thus confirms the affinity of foraminifers and other biota (e.g., Webster et al., 2003) to the Paleo-Tethyan Ocean. Paleocurrent reconstructions, however, may provide an alternative explanation for these faunal similarities between the northern Paleo-Tethys and Iran. Kiessling et al. (1999, figure 6) showed for the Givetian – Frasnian a counterclockwise current flow around the Paleo-Tethyan Ocean along the northern part of the Iranian block, at the latitude of about 25° South. In that reconstruction, a current at the western end of the Paleo-Tethys continued southwesterly between the North European and North American blocks and the African-South American edges of Gondwana. This current could have promoted larval dispersal and thus explain similarities between European and North American faunas and Iranian ones. Northern and central Iranian Devonian stromatoporoids, rugose corals and brachiopods (Gaetani, 1965) were considered by Brice et al. (1999) to be similar to those of Armenia (Transcaucasia), the Central Mountains of Afghanistan and of Chitral (Karakorum). Moreover, according to Mistiaen et al. (2000), the Devonian Iranian biota (corals, stromatoporoids, charophytes, calcitic microproblematica, ostracods) has a cosmopolitan character and also shares affinities with northern regions (western Europe and Russian Platform). Angiolini et al. (2007) discussed a similar situation for the latest Carboniferous – Early Permian of Iran. Macrobiota having affinities with the northern shores of the Paleo-Tethys and Ural oceans occurred during Glacial Interval III (Isbell et al., 2003). They proposed a model in which a counterclockwise oceanic current brought warmer waters to the southern margin of the western Paleo-Tethys. However, the paleolatitude of Iran during the latest Carboniferous – Early Permian (c. 25° South in fig. 2 of Angiolini et al., 2007) was much further north than in the Mississippian. To apply the same model to the Early Mississippian implies that a Tournaisian – Early Visean equatorial current (Kutzbach et al.,
Plate 1 (facing page): Specimens are reposited in the Palaeontological Museum of the University of Milan, Italy. Museum numbers (MPUM) are assigned to thin sections containing the specimens illustrated herein. See Figures 4 and 6 for stratigraphic location of samples. (1, 2) Earlandia spp. (1) E. vulgaris (Rauzer-Chernousova & Reitlinger in Rauzer-Chernousova, 1937), x25, Abnak section, spl. IR 801 (MPUM 10055). (2) E. elegans (Rauzer-Chernousova & Reitlinger in Rauzer-Chernousova, 1937), x100, Abrendan section, spl. IR 1013 (MPUM 10087). (3–5) Pseudoammodiscus priscus (Rauzer-Chernousova, 1948d), x100. (3, 4) Abnak section, spl. IR 1065 (MPUM 10068). (5) Abrendan section, spl. IR 1017 (MPUM 10096). (6) Pseudoammodiscus sp., x100, Abnak section, spl. IR 1065 (MPUM 10068). (7) Brunsia sp., x100, Abrendan section, spl IR 1019 (MPUM 10100). (8, 15) Eotournayella kisella (Malakhova, 1956), x100, Abrendan section. (8) spl. IR 1017 (MPUM 10097). (15) spl. IR 1016 (MPUM 10093). (9, 10?, 17) Brunsia irregularis (von Möller, 1879), x100, Abnak section. (9) spl. IR 1066 (MPUM 10069). (10) spl. IR 801 (MPUM 10055). (17) spl. IR 1070 (MPUM 10072). (11–14) Lapparentidiscus bokanensis Vachard, 1980, x100, Abnak section. (11) spl. IR 817 (MPUM 10067). (12) spl. IR 1073 (MPUM 10075). (13) spl. IR 812 (MPUM 10065). (14) spl. IR 1074 (MPUM 10076). (16) Dariopsis curvisepta Malakhova, 1975, x100, Abnak section, spl. IR 803 (MPUM 10057). (18) Forschia? sp., x75, Abnak section, spl. IR 809 (MPUM 10063). (19) Tournayella vespaeformis Malakhova, 1956, x75, Abrendan section, spl. IR 1015 (MPUM 10091). (20, 21) Eoforschia moelleri (Malakhova in Dain, 1953), x75, Abrendan section, spl. IR 1017 (MPUM 10095).
54
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
Plate 1
5 4 3
7
6
2
1
12
11
10 9
8 14
13
16
17
15 18
19
20
55
21
Brenckle et al.
Macrofossil
IR Spl. No.
Pustula cf. P. kondomensis Schizophoria (S.) resupinata Composita megala Parallelora sp. ind. Rossirhynchus adamantinus Hemiplethorhynchus crassus Composita subquadrata Ectochoristites sp. ind. Syringothyris carteri Syringothyris skinderi Densalvus sp. ind. Pustula spp. Rhipidomella michelini Pustula cf. P. altaica Ptychomaletoechia sp. ind. Athyris sp. ind. Pseudosyrinx sp. ind. Marginatia vaughani Geniculifera sp. ind. Paraphorhynchus aff. P. elongatum Unispirifer (U.) sp. B Leptagonia analoga Tomiproductus elegantulus Martinia sp. ind. Hippocardia alborza Marginatia sp. ind. Cleiothyridina kusbassica Gerankalasiella sp. ind. Unispirifer (U.) striatoconvolutus Imbrexia sp. ind. Buxtonia sp. ind. Schellwienella sp. ind. Atylephorus sp. ind. Unispirifer (U.) sp. A Rhipidomella sp. A Rhipidomella sp. B Fusella sp. ind. Delepineinae gen. et sp. ind.
Tournaisian
1040 1041 1042 980 1044bis 1044 1045 1046 1047 983 984 985 987 988 989 990 992 993 994 995 996 997 998 1008 1009 1012
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Figure 8: Distribution of brachiopods and molluscs in the Mobarak Formation at the Abrendan section. Plate 2 (facing page): See Figures 4 and 6 for stratigraphic location of samples. Repository numbers (MPUM) are in parentheses. (1, 2) Eoforschia moelleri (Malakhova in Dain, 1953), x75, Abrendan section. (1) spl. IR 1017 (MPUM 10096). (2) spl. IR 1016 (MPUM 10094). (3, 4) Uviella spp., x75, Abrendan section. (3) spl. IR 1015 (MPUM 10090). (4) spl. IR 1017 (MPUM 10095). (5–8) Eotextularia diversa (Chernysheva, 1948b), x75 except as indicated, Abrendan section. (5) spl. IR 1017 (MPUM 10096). (6) spl. IR 1019 (MPUM 10101). (7) spl. IR 1015 (MPUM 10091). (8) x70, spl. IR 1013 (MPUM 10087). (9–11) Condrustella modavensis (Conil & Lys, 1967, emend. Brenckle & Hance, 2005), x100, Abrendan section. (9) 1013 (MPUM 10089). (10) spl. IR 1013 (MPUM 10088). (11) spl. IR 1015 (MPUM 10091). (12, 13) Mediendothyra? sp., x100, Abrendan section, spl. IR 1015 (MPUM 10091, 10092, respectively). (14–16) Endospiroplectammina spp., x100, Abrendan section. (14) spl. IR 1019 (MPUM 10099). (15, 16) spl. IR 1017 (MPUM 10096, 10097, respectively). (17) Palaeospiroplectammina? sp., x75, Abnak section, spl. IR 803 (MPUM 10057). 56
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
Plate 2
3 4 2 1
5
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11 10 9
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57
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Brenckle et al.
Scandinavia
Laurussia
Equ Pontides
North China
b Su
Adria
n io ct
du
Perunica
ator
HellenicMoesia
Rif
t
Armorica
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Apulia
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Si
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Central Iran
Arabia
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ad
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South America
Figure 9: Palaeogeographic sketch suggesting the position of Alborz near Gondwana, before rifting and detaching of the Cimmerian fringe (simplified and modified from Torsvik and Cocks, 2004). The counter-clockwise oceanic current (blue arrow) follows the concept of Kiessling et al. (1999).
Plate 3 (facing page): See Figures 4 and 6 for stratigraphic location of samples. Repository numbers (MPUM) are in parentheses. (1, 2) Darjella monilis Malakhova, 1963, x50, Abrendan section, spl. IR 1017 (MPUM 10096). (3–6) Lituotubella glomospiroides Rauzer-Chernousova, 1948a, x75 except as indicated, Abnak section. (3) x60, spl. IR 808 (MPUM 10062). (4) spl. IR 1072 (MPUM 10074). (5) spl. IR 806 (MPUM 10060). (6) spl. IR 801 (MPUM 10055). (7, 11) Pseudolituotubella spp. (7) Abnak section, x75, spl. IR 1084 (MPUM 10083). (11) Abrendan section, x100, spl. IR 1017 (MPUM 10095). (8, 9) Septaglomospiranella spp., x100, Abrendan section. (8) spl. IR 1015 (MPUM 10090). (9) spl. IR 1016 (MPUM 10094). (10, 12-14) Inflatoendothyra parainflata (Bogush & Yuferev, 1970), x100, Abrendan section. (10) spl. IR 1017 (MPUM 10096). (12–14) spl. IR 1015 (MPUM 10090, 10091, 10091, respectively).
58
Mississippian (Lower Carboniferous) Mobarak Formation, Iran
Plate 3
2
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Brenckle et al.
1990) flowed southeastward along the Gondwanan margin bringing warm water and Paleo-Tethyan taxa (larvae) to intermediate latitudes in the absence of glaciation during that time span (Isbell et al., 2003, figure 2). On the other hand, Webster et al. (2007) speculated that Early Mississippian currents hindered the dispersal of Paleo-Tethyan echinoderm larvae to Iran. In the Late Visean, the climate started to cool due to the onset of Glacial Interval II in western Gondwana (Isbell et al., 2003; Scheffler et al., 2006; Fielding et al., 2008). However, the current rotation toward the north of Iran might have compensated for that cooling and the biota continued to have a warmer signature as evidenced by microfaunas identified by Bozorgnia (1973), Lys et al. (1978) and Vachard (1996). A potential obstacle in applying the model of Angiolini et al. (2007) to the older Carboniferous is the fact that latest Pennsylvanian rifting changed the palaeogeography and possibly the current flow at the margin of this sector of Gondwana. Therefore, we do not at present have a full explanation to resolve the problem of these paleobiogeographically anomalous fossil occurrences in northern Iran, but the answer may lie in the southerly distribution of Paleo-Tethyan sea currents rather than in the position of the Alborz on the northern shore of the Paleo-Tethys.
ACKNOWLEDGEMENTS Field work was performed with assistance of the Geological Survey of Iran and financial support of the MEBE Programme. Dr. M. Ghassemi, GSI, organized field work facilities and A. Jalali, GSI, helped to collect macrofauna in the field. Luc Hance, Carmeuse Group, Belgium, and two anonymous reviewers helped to improve an earlier version of this paper. The authors thank Nestor Buhay II for designing the final graphics.
REFERENCES Ahmadzadeh Heravi, M. 1971. Stratigraphische und paläontologische Untersuchungen im Unterkarbon des zentralen Elburs (Iran). Clausthaler Geologische Abhandlungen, v. 7, p. 1-114. Angiolini L., H. Brunton and M. Gaetani 2005. Early Permian (Asselian) brachiopods from Karakorum and their palaeobiogeographical significance. Palaeontology, v. 48, no. 1, p. 1-18. Angiolini, L., M. Gaetani, G. Muttoni, M.H. Stephenson and A. Zanchi 2007. Tethyan oceanic currents and climatic gradients 300 MY ago. Geology, v. 35, no. 12, p. 1071-1074. Antropov, I.A. 1967. Devonian and Lower Carboniferous (Tournaisian) Algae from the central part of the eastern Russian Platform. Akademiya Nauk SSSR, Sibirskoe otdelenie, Trudy Instituta Geologii i Geofiziki, p. 118-125 (in Russian). Assereto, R. 1963. The Paleozoic formations in central Elburz (Iran). (Preliminary note). Rivista Italiana di Paleontologia e Stratigrafia, v. 69 , no. 4, p. 503-543.
Plate 4 (facing page): See Figures 4 and 6 for stratigraphic location of samples. Magnifications x100. Repository numbers (MPUM) are in parentheses. (1–3) Inflatoendothyra parainflata (Bogush & Yuferev, 1970), Abrendan section. (1) spl. IR 1020 (MPUM 10102). (2) spl. IR 1017 (MPUM 10095). (3) spl. IR 1015 (MPUM 10092). (4, 5) Loeblichia? sp., Abrendan section. (4) spl. IR 1019 (MPUM 10101). (5) spl. IR 1017 (MPUM 10095). (6–9) Loeblichia? fragilis (Lipina, 1951), Abrendan section. (6–9) spl. IR 1017 (MPUM 10095, 10097, 10097, 10096, respectively) (10–13) Dainella micula Postoyalko, 1970, Abrendan section, spl. IR 1019 (MPUM 10101, 10100, 10099, 10099, respectively). (14) Dainella sp., Abnak section, spl. IR 805 (MPUM 10059). (15–18, 20, 23) Bessiella sp. (15) Abrendan section, spl. IR 1019 (MPUM 10099). (16) Abrendan section, spl. IR 1020 (MPUM 10103). Remaining specimens from the Abnak section. (17) spl. IR 1066 (MPUM 10069). (18) spl. IR 803 (MPUM 10057). (20) spl. IR 1084 (MPUM 10083). (23) spl. IR 801(MPUM 10055). (19, 21, 22) Florennella sp., Abnak section. (19) spl. IR 801(MPUM 10055). (21) spl. IR 803 (MPUM 10057). (22) spl. IR 804 (MPUM 10058).
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