Calcareous algae , foraminifera and sequence stratigraphy of the Fahliyan Formation at Kuh-e-Surmeh ( Zagros Basin , SW of Iran )

Palaeontological, environmental and sequence stratigraphic studies were carried out on the shallow carbonate platform facies of the Berriasian to Hauterivian Fahliyan Formation and the lower part of the Gadvan Formation, at Kuh-e-Surmeh. The studies were based on calcareous green algae (mainly Dasycladales) and accompanying benthic foraminifera, focusing on revision of the considerable, pioneering work of GOLLESTANEH (1965, 1979), initially undertaken on behalf of the National Iranian Oil Company (NIOC). Thirty two species of calcareous green algae and thirty four species of benthic foraminifera were identifi ed from the Fahliyan Formation and from the lower part of the Gadvan Formation. A number of the recognized calcareous green algae were previously given different names by other authors working in SW Iran. Additional taxa were also recorded for the fi rst time in the Zagros basin, including Clypeina dragastani, C. estevezii, C. solkani, C. parasolkani, Holosporella arabica, Otternstella lemmensis, Salpingoporella circassa, S. istriana and S. katzeri. Salpingoporella circassa is quite common and apparently recorded for the fi rst time from Southern Tethys. Also Salpingoporella? inopinata n. sp., (originally named Iranella inopinata by GOLLESTANEH, a nomen nudum) appears to be quite common in the Fahliyan Formation, although apparently endemic to SW Iran. Three main depositional environments were recognized based on the faunal/fl oral association, lithological and sedimentological characteristics: inner ramp/restricted platform, mid ramp/margin to open platform, and outer ramp/platform slope, with water depths ranging from about 5m to 20m, rarely reaching 40m. Facies changes facilitated the recognition of three large scale sequences throughout the studied succession, bringing interesting relationships with the sequence bundles identifi ed in the Arabian Plate.


INTRODUCTION
This paper deals with the calcareous green algae (mainly Dasycladales) and foraminifera from the Zagros Basin (SW of Iran) which aims as a tool to recognize the depositional environments and to contribute to the understanding of algal palaeoecology.The section studied is located at 52° 34' longitude and 28° 32' latitude, in Kuh-e-Surmeh, south of the town of Firouzabad (Fig. 1).The exposed section is 212m thick and a total number of 254 thin-sections were prepared from the collected samples.Systematic description of the whole microfossil assemblages is beyond the scope of this paper which focuses on sequence stratigraphy, benthic foraminifera and the newly identifi ed dasycladalean algae.
The Fahliyan Formation has already been documented in previous articles and in several unpublished internal reports of the National Iranian Oil Company (NIOC), dealing with biostratigraphy and facies analysis.A preliminary report on this formation was carried out by Ali Gollestaneh in 1965 2. TAXONOMIC DESCRIPTION Among many known dasycladalean algae, the Fahliyan Formation yielded a new species, herein tentatively assigned to the genus Salpingoporella PIA.The species was fi rst described and properly illustrated by GOLLESTANEH (1965), in his unpublished PhD thesis, under the name of Iranella inopinata gen.and sp.nov.Yet, adequately combining new observations on the present material with illustrations provided by GOLLESTANEH remains a diffi cult task.Hypothetically, more than one species may be present and certainly, additional material must be identifi ed and investigated.Nevertheless, this opportunity is taken to formally introduce and provisionally describe the new species dedicated to Dr. Ali Gollestaneh.Material and stratum typicum: Up to 24 specimens, from different localities (Kuh-e-Surmeh), all from the Zagros fold belt, Iran.The specimen illustrated in Pl. 1, Fig. L is the holotype, an oblique section from sample JHT 1353 in the upper, Valanginian part of the section.Type location is at Kuhe-Surmeh, 50 km south of Kazerun city, SW Iran (Fig. 1).

Genus
Depository: Materials (rock samples and thin-sections) are housed in the department of Geological and Geochemical (NIOC internal report no.1056), as his PhD thesis, later published in London (GOLLESTANEH, 1965).It includes the systematic description of benthic foraminifera and calcareous green algae, along with a range chart distribution of the microfossils.Therefore, the present paper is a partial revision of Gollestaneh's report, focusing on the calcareous green algae.Most of the internal reports of the NIOC also centre on biostratigraphy and age determination, following the zonation scheme introduced by WYND (1965) for the exploration/production agreement area.The Cretaceous rock units (such as the Fahliyan and Gadvan formations) have been analyzed for microfossils and age determination by several geologists (GOLLESTANEH, 1974; SETUDEHNIA, 1978; WYND,  1965 1 ; WELLS, 1965 2 ; KHERADPIR, 1975 3 ).However, additional, new, detailed palaeoecological and palaeobathymetric studies are essential for comprehension of the Fahliyan Formation and other Lower Cretaceous successions in the Zagros Basin, in order to ensure better correlations and improve our understanding of the regional geology.Diagnosis: Thallus and axial cavity cylindrical to slightly club-shaped.Laterals horizontal, forming quincunxes, four to fi ve per verticil, connected to the main axis by a short and narrow pore (peduncle).Laterals then abruptly widen out, fi rst elliptical, horizontally elongated, then circular in tangential section, where they are loosely adjacent to each other.Weak imprints of cysts, whenever present, are located in the lower part of the laterals (cladospory), or at the periphery of the axial cavity (endospory).Calcareous coat colourless, made of interlocking calcite crystals (originally aragonite), solid around the axial cavity, weak, forming a pellicle at the calcifi ed periphery of the laterals.

Dimensions:
Outer diameter (  (CARRAS et al., 2006, pl.V, fi g. 1-5), the laterals are fi rst rectangular in section, then hexagonal, horizontally elongated.The proximal pores (peduncles) of S. hispanica are eccentrically located, laterally to the axis of the corresponding laterals.In certain sections (Pl. 4,Fig. P), the laterals show the presence of questionable "holes", possibly corresponding to eccentrically located proximal pores.In other sections, on the other hand (Pl. 1,Fig. L;Pl. 4,Fig. D), the pore is clearly located on the axis of the lateral.Based on a single tangential section (Pl. 4,Fig. O), the laterals of the new species are not adjoined beyond the calcareous coat.In other words, they do not or do not always form the distal, continuous assimilatory cortex typical of Salpingoporella.So far, the questionable endospory is based on a single oblique section (Pl.3, Fig. F).Cladospory (e.g. in Salpingoporella genevensis CONRAD et al.) is part of the defi nition of the genus Salpingoporella.Also in Salpingoporella turgida RADOIČIĆ the axial cavity and the thallus may be slightly club-shaped.One section, of S.? inopinata (GOLL-ESTANEH, 1965, pl. 68, fi g. 3) not illustrated here,suggests the possible presence of a much wider, possibly aberrant "head" of thallus.

MICROPALAEONTOLOGICAL ASSEMBLAGES
The total thickness of the studied succession is 212m.The Fahliyan Formation is 150m thick and the remainder belongs to the Gadvan Formation which overlies the Fahliyan Formation in this area.Based upon the micropalaeontological data, the following three geological age intervals can be separated.

PLATE 4
Calcareous algae of the Kuh-e-Surmeh section

PLATE 7
Carbonate facies types  As shown by the range chart distribution (Fig. 2), most of the benthic foraminifera and calcareous green algae found in the Berriasian interval are also present in the Valanginian.The main difference is the fi rst occurrence of some benthic foraminifera and dasycladalean algae such as: Choffatella sp., Debarina  Hauterivian-Barremian: The third, 62m thick interval of the studied surface section belongs to the lower part of the Gadvan Formation.This formation mainly comprises marl and some thin to medium size intercalations of clean limestone (bioclastic packestone).Most of the Gadvan Formation (the shaly portions) is covered by vegetation so that no samples could be taken.Only two surface samples were prepared from the limestone horizons of this formation which are dominated by: Palorbitolina lenticularis BLUMENBACH, Salpingoporella dinarica RADOIČIĆ, Debarina hahounerensis FOURCADE et al., Choffatella decipiens SCHLUMBERGER, Trocholina sagittaria ARNAUD-VANNEAU et al, T. oduk paniensis DES-SAUVAGIE, Aulotortus sp., Novalesia distorta ARNAUD-VANNEAU, Dukhania sp., Falsogaudryinella tealbyensis BARTENSTEIN, Dukhnia conica HENSON and oncoids of Lithocodium aggregatum ELLIOTT with Bacinella irregularis RADOIČIĆ, associated with echinoid remains, mollusc fragments and corals.Based upon the aforementioned microfossils, an Hauterivian -Barremian age is assigned to this part of the Gadvan Formation in this area.

DEPOSITIONAL ENVIRONMENTS
Based on the analysis of the faunal and fl oral content of 254 thin-sections, and also on standard facies analysis criteria (texture, grain types and sedimentary features), three main depositional environments have been identifi ed (Fig. 3).
Inner ramp/restricted platform: The inner ramp (shallow subtidal) depositional environments generally include the open lagoon, inner shoal and restricted lagoon.In the studied section, most of the deposits belong to the inner ramp environment, especially the open lagoon and inner shoal, which are characterized by the presence of bioclastic wackestonepackstones and bioturbated wackestone-packstones (Pl.7, Fig. A).Peloidal-bioclastic fenestral packstones to grainstones are also observed, indicative of the upper subtidal environments (Pl.7, Figs.B-C).Most of the deposits are dominated by Lithocodium/Bacinella bindstones which are interpreted as typical shallow subtidal deposits (Pl.7, Fig. I).The inner ramp deposits are represented by a highly diversifi ed fauna and fl ora (Fig. 4) such as: calcareous green algae (Salpingoporella, Actinoporella, Clypeina, Otternstella, Zergabriella and rare Selliporella, associating with Lithocodium/Bacinella).Among the large benthic foraminifera, Pseudocyclammina, Choffatella, Cuneolina, Trocholina and miliolids are common, while Dukhania and orbitolinids are rarely observed.These are associated with abundant mollusc fragments, dissolved gastropods, corals and rare echinoid remains.The calcareous green algae dominate and prevail over benthic foraminifera in this environment.The serpulid limestone is also present in some parts, marking a transition from carbonate ramp stage to a platform stage (Pl.7, Fig. L).The occasional presence of tintinnids (Tintinnopsella carpathica MURG & FILIP) and echinoids (Saccocoma) indicates a temporally limited connection to open platform environments.The miliolid-ostracod carbonates which indicate restricted lagoonal environments are extremely rare.They occur in the middle part of the section and are mainly mud supported, with wackestones.Based upon the abundant calcareous green algae, it is suggested that the water depth varies from 5m to 10m in this environment.
Mid ramp/margin to open platform: This depositional environment is characterized by the presence of abundant large benthic foraminifera associated with calcareous green algae.The texture of these deposits varies from bioclastic wackestones (low energy) to peloidal-bioclastic packstone-grainstones indicative of high energy conditions.The main faunal content of this depositional environment includes benthic foraminifera such as Pseudocyclammina, Cuneolina, Trocholina, orbitolinids and Dukhania, associated with abundant echinoid remains, ammonite shells and rare sponge spicules.Among the dasycladalean algae, Salpingoporella pygmaea, Salpingoporella katzeri, Salpingoporella?inopinata n. sp., Salpingoporella istriana and Selliporella neocomiensis are rather common, whereas other species of Salpingoporella as well as Clypeina, Actinoporella, Otternstella and Lithocodium/Bacinella are rarely present.In our opinion, a water depth of 10-20m is estimated for this depositional environment.
Outer ramp/platform slope: In the Kuh-e-Surmeh section, the deposits containing pelagic organisms (sponge spicules, Saccocoma, ammonite shells and abundant echinoid remains), rare in situ benthic foraminifera (Dukhania and small Valvulinids) and very rare Salpingoporella?inopinata n. sp., Salpingoporella pygmaea, S. katzeri and S. istriana have been assigned to the outer ramp to platform slope depositional environment.Other benthic foraminfera in this environment including species of Trocholina, Falsogaudryinella, Choffatella, Cyclamminids, Praechrysalidina, Debarina, Rummanolo culina, Nautiloculina, Cuneolina and calcareous green algae such as other species of Salpingoporella and Clypeina (Fig. 3), were probably brought in by storms and are not in situ.The lithology of these deposits is marked by mud supported car-bonates, commonly with wackestones and packstones (Pl.7, Fig. E).Based on the faunal composition, it is expected that the water depth ranges from 20m to some 40m.

SEQUENCE STRATIGRAPHY
The presented sequence stratigraphic model is based on the defi nition of VAIL et al. (1991).Herein we have amalgamated possibly low stand and transgressive system tracts as transgressive deposits.Three 2 nd and 3 rd order sequences have been recognized throughout the studied section, ranging from about 2 to 8 MY (Fig. 2 and Fig. 4).Each sequence is shown by two triangles or polygons, differently coloured.If A/S > 1 (Accommodation more than Sediment supply), this indicates the transgressive trend, and if A/S < 1, the regressive trend is represented.As for the sequence boundaries, two inferred categories are shown in Fig. 2 and Fig. 4: SB I, corresponding to the Type I with evidence of exposure; SB II, corresponding to the Type II with a shallowing upward trend.Fig. 4 shows the benthic foraminiferal diversity increases during the transgressive phases, reaching a maximum value before the maximum fl ooding surfaces, and decreases or remains constant during the regressive stages, fi nally reaching the minimum at the sequence boundaries.Instead, the maximum diversity of calcareous algae occurs in the fi rst phase of transgression as well as in the last phase of highstand, when the sea level is intermediate.Conversely, their lowest diversity occurs in or close to the maximum fl ooding surface (mfs), since during the sea level rise, the environmental conditions (light, temperature, salinity and substrate) were not suitable for fl oral productivity (Fig. 4).
Sequence A: The thickness of this sequence is 106m.The lower sequence boundary is a regional discontinuity located between the Hith Anhydrite and the Fahliyan Formation (Late Jurassic-Early Creataceous) in the Zagros basin as well as in the Arabian Plate (SHARLAND et al. 2001(SHARLAND et al. , 2004)).Tentatively this sequence boundary is placed in Type І, corresponding to an exposure.The sequence represents a deepening-shallowing trend, with shallow subtidal (inner ramp), inner to mid ramp and outer ramp environments.The maximum fl ooding surface (mfs) is marked by the presence of abundant sponge spicules and echinoid remains, with rare benthic foraminifera and calcareous green algae; it is assigned to the mid to outer ramp environments.The highstand deposits show a seaward stepping and regressive cycle, with a decreasing diversity of the benthic foraminifera and an increasing diversity of the calcareous green algae (Fig. 4).The sequence is assigned a Berriasian -Lower Valanginian age, quite comparable with the Arabian Plate sequence stratigraphy scheme of SHARLAND et al. (2001SHARLAND et al. ( , 2004)).
Sequence B: The second partly covered sequence of the Fahliyan Formation has a thickness of about 44m.It includes deepening and shallowing upward deposits, with inner ramp/ lagoonal to mid ramp and also outer ramp deposits.The transgressive trend begins with bindstone mats overlain by high energy and low energy deposits denoting mid ramp environments.The maximum fl ooding surface is dominated by sponge spicules, ammonite shells, Saccocoma and echinoid remains.
The highstand deposits are marked by seaward stepping with the presence of inner ramp deposits.The lower sequence boundary is normal (SB II, or Type II), whereas the upper sequence boundary is of Type I, with evidence of subaerial exposure (iron oxide-rich, karstifi cation and hard ground) illustrated in Pl. 7, Fig. O.This sequence is given an Early Valanginian age, again showing an interesting relationship with the sequ ence bundle identifi ed in the Arabian Plate (SHARLAND et al., 2001(SHARLAND et al., , 2004)).
Sequence C: This 62m thick sequence belongs to the lower part of the Gadvan Formation.As mentioned above, most parts of the Gadvan Formation are covered.The soft materials in the basal part of the Gadvan Formation are interpreted as being transgressive deposits with a deepening upward trend.In the mid part of the Gadvan Formation, at the top of the sampled section, some thin to medium sized, clean limestone beds occur indicating inner to mid ramp depositional environments.This interval is formally called the Khalij Member.It can be traced over the whole of the Zagros basin as well as in the Arabian Plate.By similarity with the sequence stratigraphic model for the Arabian Plate (SHARLAND et al., 2004), the upper sequence boundary is placed at top of the limestone horizon of this member.At present, there is no data, in the studied section, to document the transgressive trend and the maximum fl ooding surface.
Fi gu re 3: Environmental distribution of the main calcareous green algae (especially dasycladalean), some benthic foraminifera and other biota (sponge spicules and echinoids) in the studied succession.

PALAEOECOLOGY AND PALAEOBATHYMETRY
Environmental indicators used in this study are shown in Fig. 3. Concerning the dasycladalean algae, extant species usually live in normal (euhalyne) waters, within the 20°C isocryme, in the infralittoral environment defi ned as corresponding to the habitat of the marine phanerogams.There are exceptions however, which were reviewed by BERGER & KAEVER (1992).The same applies to the fossil record.Most species identifi ed in the Kuh-e-Surmeh section lived in the Inner Ramp environment, while three species deserve special interest.The fi rst species, Salpingoporella dinarica RADOIČIĆ, was very tolerant, as shown by the fact that it fl ourished in low energy, restricted marine environments (for a review of the genus Salpingoporella, see CARRAS et al., 2006) RENARD (1979), when associated with charophytes, the species indicates a hypersaline environment, rather than a brackish one as would be suggested by biotic and facies data.
The benthic foraminifera and calcareous green algae diversity curves are shown in Fig. 4. The diversity index of benthic foraminifera ranges from 1 (minimum) to 15 (maximum), whereas this index varies from 0 (minimum) to 17 (maximum) for calcareous green algae.This study reveals that each depositional environment has a typical assemblage of benthic foraminifera and calcareous green algae.Concerning the benthic foraminiferal diversity, the maximum value is observed throughout the mixed sediments of the inner ramp to mid ramp environments (index from 4 to 15).The lowest diversity corresponds to the shallower subtidal and lagoonal environments, and, also to the outer ramp (index from 1 to 8).By comparison, the highest diversity values of calcareous green algae are found in open lagoon and shoals, with indexes ranging from 3 to 17, while the least values refer to the platform slope environments, with values ranging from 0 to 4. Among the calcareous green algae, the order Dasycladales is frequently represented.Some species of the family Dasycladaceae are reported for the fi rst time from the Zagros Basin, e.g.Zergabriella embergeri, Salpingoporella katzeri, S. istriana, S. pygmaea, and S. circassa.The latter species is apparently reported for the fi rst time from southern Tethys.The family Acetabulariaceae is also present, with the subfamily Clypeineae including species such as Clypeina estevezi, C. solkani, C. parasolkani and C. dragastani, which are reported for the fi rst time from the Zagros Basin.

CONCLUSIONS
Based on micropalaeontological data from the Kuh-e-Surmeh section, the ages of the Fahliyan and Gadvan Formations have been determined.The Fahliyan Formation is of Berriasian and Valanginian age, while a Hauterivian to Barremian age is assigned to the Gadvan Formation in the study area.Sequential interpretation reveals the presence of at least three sequences comprising several parasequences throughout the studied succession.Two sequence boundaries are considered to belong to the Type I, with subaerial exposures believed to correspond to regional discontinuities.One sequence boundary belongs to the Type II.Species of the Dasycladaceae and the subfamily Clypeineae are reported for the fi rst time from the Zagros Basin and/or from southern Tethys.One new species of Dasycladalean algae, Salpingoporella?inopinata GOLLESTAN-EH, n. sp. is provisionally described, awaiting additional material.Palaeoecological and palaeobathymetric investigations indicate that the studied samples were deposited in shallow water, internal subtidal (open lagoon) to external subtidal (inner to mid ramp) and platform slope (outer ramp) environments, in water depths of 5m to 40m, with salinities ranging from normal marine to saturated (hypersaline).