New solenoporaceans from Upper Triassic ( ? Norian-Rhaetian ) reef limestones in central Iran

Two reef-building red algae of the family Solenoporaceae – Solenopora rectangulata n. sp. and Parachaetetes dizluensis n. sp. – are described from a ?Norian-Rhaetian section of the Nayband Formation exposed south of the town of Bagherabad, northeast of Esfahan, central Iran. These algae build reef structures or patches up to 17 m thick, either on their own or in association with other reef-building organisms including sponges, corals, etc. Such solenoporacean reef structures have not been described before, either from Iran or elsewhere in the world. Morphologically, both algae are easily distinguished by the different sizes of their thalli and particularly by their branching pattern.


INTRODUCTION
Upper Triassic (Norian-Rhaetian) deposits of the Nayband Formation are distributed over a large area in central and eastern Iran (SEYED-EMAMI, 1971, 2003).The type locality of the Nayband Formation crops out at the southern area of the Kuh-e Nayband (Nayband Mount), approximately 220 km south of the town of Tabas in northeastern Iran where it reaches a thickness of about 3000 m (FÜRSICH et al., 2005).
Reefs occur interbedded within the Nayband Formation and are usually biostromes, but small bioherms also occur (generally less than 50 m thick and less than 100 m laterally).The reefs are mainly sponge-coral or coral-sponge dominated.Other organisms are of minor importance (SENOWBARI-DARYAN, 1996, 2005a, 2005b).
Various groups of calcareous algae occur within the carbonate facies of the Nayband Formation.Solenoporaceans are usually found in reef facies while dasycladales occur main ly in bedded carbonates (SENOWBARI-DARYAN & HAME-DA NI, 1999NI, , 2000)).Until now, in Iran and elsewhere in the world, solenoporaceans have only been found as minor components of reefs or reef-like structures and never as the main reef -building organism.
In an outcrop section through the Nayband Formation northeast of , as well as sponges and corals, two erect and multi-branched species of solenoporacean red algae are the main reef builders to have acted as baffl ers to current-borne sediment grains.The two species can be distinguished in the fi eld by the different size of their thalli (Pl. 2,.The fi rst species (Pl. 2,Fig. b: small arrows) is described as Solenopora rectangulata n. sp. and has smaller and multi-branched thalli, the branching angle being up to 90 o and giving the appearance of a fi r-tree (Pl. 3,.The second species (Pl. 2,Fig. b: large arrows) has large and fi ngerlike multi-branched thalli and is described as Parachaetetes dizluensis n. sp.
Holo-and paratypes of both species are deposited in the Forschungsinstitut Senckenberg, Frankfurt am Main.(In ven tary -Nr.MB. 21123-21130; one rock piece and 7 thin sec tions).

LOCALITY AND SECTION
The outcrop of the Nayband Formation with the reef structures and solenoporaceans described in this paper is about 60 km northeast of Esfahan, south of the road from Esfahan to Ardestan (Fig. 1).The locality can be reached by car from Esfahan by taking the small side-road on the right after the town of Komschetsche.The locality is 7 km from the turn-off, at the base of the escarpment, on the left side of the road.
The stratigraphic section (Fig. 2) is well exposed in ridge "2" shown in Pl. 1, Figs. a-c.The Triassic Nayband Formation (about 130 m thick), forms the lower part of the section, and is overlain by Lower Jurassic beds and Orbitolina-bearing Cretaceous limestone (Barremian), the latter forming the main part of the escarpment (Pl. 1, Fig. 1).The lowermost part of the Nayband Formation, about 26 m thick, is concealed by a talus of reef boulders containing mainly small hypercalcifi ed sponges and tabular spongiomorphids.Coral-bearing bo ulders are not abundant.The exposed Nayband Formation succession starts with about 5.5 m of sponge-coral-dominated reef limestone passing up into about 9 m of coral-sponge-dominated, bedded, reefal limestone.This unit is overlain by 7.5 m of bedded reefal limestone in which the dominant organisms are small sphinctozoan sponges.This in turn is overlain by a limestone bed 2.7 m thick containing mainly tabular spongiomorphids which passes up into thick-bedded and sponge-dominated reefal limestone about 8 m thick.Bioclastic Limestone, 1.5 m thick, overlies the spongimorphid bed.This unit is overlain by bedded, sponge-dominated, reefal limestone about 21 m thick which passes up into a 6 m thick sequence of shaley sandstone beds which become calcareous in the upper part.The sandstone beds are overlain by a 1 m thick bed containing small brachiopods, and this passes up into about 10 m of sponge-dominated, reef limestone.That is overlain by about a 1.5 m thick, solenoporacean-dominated bed with some sponges and then a 2.5 m thick unit of spongiomorphid beds.These last fossiliferous beds containing the spongimorphids are overlain by about 30 m of Lower Jurassic deposits comprising in terbedded shales and sandstone without macrofossils.
The lower part of the Nayband Formation in ridge "1" (see Pl. 1, Figs. a-b) is not well exposed.The upper part of the section, however, does crop out and at the base of a sandstone unit the solenoporacean reefal build-ups reach a thickness of about 17 m.Remarks: According to RIDING (2004) the type species of Solenopora (S. spongioides) from the Ordovician is not a red alga but a chaetetid sponge.Therefore a careful revision of all species described as Solenopora is needed and a new generic name for the true algal solenoporaceans should be proposed.Meanwhile, the current generic name Solenopora is used here to describe the solenoporacean species from Iran.

SYSTEMATIC PALAEONTOLOGY
The following terms: main stem, branches of fi rst, second and third orders were used to describe the thallus of S. rectangulata in detail.These terms are shown in a thallus illustrated in Fig. 3. Diagnosis: Erect, slender and multi-branched, antler-or fi r-tree-like thallus.Several branches may radiate outward from the same level on the main stem and when viewed from above the angle between the branches varies from 30 to 90 degrees.The net-like appearance of the thalli in side view can be recognized in the fi eld and in thin-section, and results from lateral branches (i.e.branches from the side branches) tending to grow parallel to the main stem.Orientation of cells in the main stem and in the branches is different.No recognizable cross partitions.

Material:
In numerous rock samples and in thin-sections numbered 2/1, 2/2, 5, 6, 10, 11, 12, 13, 14/1, 14/2, and 16 Description: Colonies of erect and slender thalli of this gregarious species reach lengths of up to 10 cm with lateral extensions of 30 cm and more.Usually this species occurs alone (Pl.c Section through a thallus with branches of fi rst and second order.Legend: M) main stem, F) branches of fi rst order, S) branches of second order.Thin section 2.
a Longitudinal section through numerous thalli growing parallel to each other.The branching angle varies from 30 to 90°, mostly from branching points on opposite sides of the main stem.Thin section 16.
b Longitudinal section through a multi-branched, antler-like thallus.Legend: M) main stem, F) branches of fi rst order, S) branches of second order.Thin section 12.
c Longitudinal section through two thalli with branching angles approaching 90°.Numerous micrite-fi lled tube-like cavities in the axial part of the main stem run more or less parallel to the growth direction.These cavities may be interpreted as "fi laments" of the hypothallus in halymedaceans.Because these tubes cut the cells and the concentric layers, they are interpreted as the result of boring by certain organisms or even as the result of diagenesis.The large arrow points to the cells in a lateral branch, bending upward and oriented almost parallel to the main stem.Geopetal fabric in a brachiopod shell indicates the in situ growth position of the alga.Thin section 6.
d Section through the branching point of a thallus showing the micrite-fi lled tubes (partly branched in the growth direction) in the axial part of the main stem and at the base of a branch.Thin section 6.
e Numerous micrite-fi lled tubes, interpreted as borings or result of diagnesis, are oriented irregularly within a thallus.Thin section 6.
a Section through two main stems with fi rst branches amalgamated together without a recognizable boundary.Micrite fi lled large tube-like structures are the result of borings or even diagenesis.Thin section 6.
b Close-up from fi g. a (rectangle) shows the amalgamated area (arrow) without recognizable boundary.
c View similar to fi g. a exhibiting two main stems with fi rst branches amalgamated together without a recognizable boundary.Thin section 6.
d Arrow indicates the amalgamated area of two fi rst-order branches.
e The fi rst-order branches of a thallus (right side in photograph) penetrate into the main stem (left side in photograph) and are amalgamated with the stem without a recognizable boundary.Large micrite fi lled tube-or hoselike cavities -partly branched (arrow) -that are interpreted as the result of borings or diagenesis due to penetration of the growth bandings, thus destroying them.Thin section 6.  -c).By branching from a number of points on the main stem, the alga has the appearance in side-view of a fi r-tree (Fig. 5).Some of the secondary branches taper towards their terminations as shown in Fig. 5.The tendency of secondary branches (i.e.branches from the side branches) to grow parallel to the main stem produces a characteristic net-like appearance when viewed laterally (Pl.Individual thalli usually reach a diameter of 2 to 3 mm.The diameter of the main stem remains almost constant and does not increase during the growth stages.Hose-or tube-like, partly branched and micrite-fi lled cavities were observed in the main stems of several individuals (Fig. 4; Pl. 5, Figs.c-e; Pl. 6, Fig. e).These cavities are oriented more or less parallel or oblique and are usually branched upwards.They could be interpreted as "fi laments" of a hypothallus in halymedacean algae.The maximum diameter of these tube-like cavities is 0.07 mm but as they approach the periphery of the thallus they decrease to about 0.02 mm, i.e. approximately the cell diameter of the alga.We interpret these tube-like cavities as secondary products (the result of boring or diagenesis,).
Pronounced recrystallization makes recognition of cell details impossible in most specimens, but in well preserved thalli a weak annual growth banding is recognizable.The larger tube-like cavities pass through the cells and appear to destroy those (Pl.6, Fig. e).
The holotype (Pl.4, Fig. b/H) is a multi-branched specimen reaching a height of 22 mm.It exhibits all the characteristics of the alga, in particular its branching pattern and antleror fi r-tree-like appearance.Fig. 5 shows a reconstruction of S. rectangulata n. sp..

Discussion:
The larger (about 0.07 mm diameter) hoseor tube-like and micrite-fi lled cavities in the axial region of the main stems of Solenopora rectangulata n. sp. and at the base of the branches might be interpreted as borings of microorganisms, or else as cells of thallus differentiation in this alga, or even as "fi laments" of a hypothallus in halymedaceans.If the latter, this feature would justify the assignment of this alga to the halymedaceans.
Several features would support the interpretation of these tube-like cavities as cells or "fi laments" of halymedaceans: a) the micrite-fi lled tubes are concentrated in the axial region of the main stem and in the base of the branches and are rare in the peripheral part of the main stem; b) the cavities are oriented more or less parallel to the axis of the main stem or its branches; and c) branching directions of the tubes are ma inly consistent with the growth direction of the thallus.

Species
Remarks: All species of the genus Solenopora, known from Triassic deposits are listed with their diagnostic features in Table 1.All of these solenoporacean species have a nodular or club-shaped thallus.Only the antler-like multi-branched species Solenopora alcicornis OTT (1966) is comparable with this new species from Iran.The branching pattern (fi nger-like in S. alcicornis, fi r-tree-like in S. rectangulata) and the small size of the thallus clearly distinguish the Iranian species S. rectangulata from the Carnian species S. alcicornis OTT.Diagnosis: Erect and fi nger-like multi-branched thallus with a diameter up to 8 mm (at branching points up to 16 mm).Cells are oriented in the middle part of the thallus parallel to the axis, but toward the periphery of the thallus they diverge at an angle of 30 o -90 o .Concentric layers about 0.1 mm apart are produced by the thickening of the cell walls at the same height.Other kinds of cross partitions are missing.Cells are round or polygonal with a diameter of 0.04 mm.Reproductive organs were not observed.
Description: The erect and large thalli of this alga can easily be mistaken in the fi eld for recrystallized dendroid corals of a similar diameter.This alga grew together with Solenopora rectangulata n. sp. in patches several square metres in diameter.
The thallus of this fi nger-like multi-branched alga reaches heights of up to 20 cm with lateral extensions up to 20 cm long.The thallus of the holotype is at least 9 cm high with lateral extensions of at least 13 cm.
The holotype (Pl.7, Fig. a/H) is a multi-branched thallus with a length of at least 9 cm and with a diameter of 13 mm at branching points.The diameter of individual branches is usually 8 mm, reaching diameters of up to 16 mm at the branch ing points.
In cross-section the cells are round to polygonal and have a maximum diameter of 0.04 mm (0.02-0.04 mm).Concentric layers, produced by the thickening of the cell walls, are clearly visible in the axial parts of the thallus but not well developed in the peripheral parts.The concentric layers are a fairly constant 0.1 mm apart.The thickness of the cell walls is about 0.02 mm.
Thalli are generally recrystallised, particularly in the axial region.Peripheral parts are locally well preserved and may exhibit a thickening of the cell walls (Pl. 7,Fig. c;Pl. 8,Fig. b).This thickening is mainly on one side of the cell wall and the concentric layers are then indistinct or even absent (Fig. 6).In the axial region the cell walls are thickened on both sides  1975, P. cassianus (Solenopora cassiana FLÜGEL, 1961), and P. rhaeticus DRAGASTAN et al., 2000.Additionally the species P. clatratus, P. riedeli, and P. tauricus were described from Norian reef boulders in the Taurus Mountains of southern Turkey by SENOWBARI-DARYAN & LINK (2005).
Algae with erect and branched thalli -like P. dizluensis -are known from other Upper Triassic localities.The growth pattern and multi-branched thallus of Parachaetetes tauricus SENOWBARI-DARYAN & LINK ( 2005) is very similar to P. dizluensis n. sp., but it differs from this Iranian species by its smaller thallus diameter, wider spacing (0.6-0.8 mm) of its concentric layers and by its rounded cell outlines.In addition the concentric layers, refl ecting the thickening of the cell wal ls, are much better developed in P. tauricus and other species than in this Iranian species.Thickening of one side of the cell walls in P. dizluensis was not observed in other species of the genus.Different degrees of thickening of the cell walls in the axial and peripheral regions may refl ect the beginning of differentiation of the hypo-and perithallus.Such differentiation was also interpreted by PIA (1939) for the Tertiary species Parachaetetes asvapatii and for the Triassic species Solenopora alcicornis by OTT (1966).P. asvapatii, however, differs from P. dizluensis by well thickened cell walls and wider spacing of its concentric layers (see MOUSSAVIAN, 1989, pl. 5, fi gs. 3-4).Multi-branched pattern of the thallus in P. dizluensis and the stratigraphic range are further differences to P. asvapatti.
For comparison, the diagnostic features and dimensions of P. dizluensis n. sp. and other species of Parachaetes, known from Triassic deposits, are listed in Table 2.

ORGANISM ASSOCIATIONS AND MICROFACIES
In the sponge-coral dominated reefal parts of the succession, only a few individual thalli of the two species of algae described here occur.In the upper part of the section both algae occur, either alone or together, in algal patches, usually without any other reef builder.Several instances of geopetal fabrics (Pl.4, Fig. 1; Pl. 7, Fig. 1) indicate the in situ growth position of the algae.Spaces between the thalli are fi lled with micrite, indicating a quiet environment with limited water currents.
In the sediment between the thalli, small foraminifera including different species of Trocholina sp., Seminivoluta sp., and Coronipora sp.occur, along with rare small miliolids (Galaenella sp., "Sigmoilina" sp., Ophthalmidium sp.), brachiopods (including Gosaukammerella eomesozoicum (FLÜGEL)), gastropods and ammonites.An epifauna comprising sessile foraminifera and a few worm tubes was noted.The foraminiferal association of the investigated material in this locality differs from other localities of the Nayband Formation and will be published separately.A number of the foraminifera which occur here range up into the Lower Jurassic of the Te thy an realm but the association indicate late Triassic for this section.
Other organisms include hypercalcifi ed sponges (mainly small species), corals and other reef organisms.
Solenoporaceans occur in reefs together with other reef builders in the Upper Triassic Nayband Formation at other localities in central and northeast Iran.However, reefal buildups composed solely or mainly of algae, or where solenoporaceans are so abundant, have not been described before from the Nayband Formation.Moreover, such algal constructions are not known from any other Triassic localities in the world.The multi-kilometre sized Solenomeris reefs in the Pyrenean domain (S.France, N. Spain) are not classifi ed as algal reefs.Solenomeris, a taxon previously interpreted as a solenoparcean alga, is nowadays assigned to encrusting foraminifera (PER - RIN, 1987;PLAZIAT & PERRIN, 1992;MOUSSAVIAN & HÖFLING, 1993).Therefore the solenoporacean reefal structure in Iran seems to be a unique algal construction.

ACKNOWLEDGEMENT
The investigations were carried out under the terms of the research project "Stratigraphische, paläoökologische, paläontologische und fazielle Bearbeitung eines obertriassisch-liassischen?Riffes im Zentraliran, Se 416/17-1".Michael Ridd (London) is gratefully acknowleged for the English correction of the text.This paper benefi ted from the constructive reviews of Ovidiu Dragastan (Bucharest) and an anonymous review er.DARYAN & LINK 2005 (Norian).Legend: CD -cell diameter, TCWthickness of the cell walls, CO -cell outline (in cross section), DCLdistance apart of concentric layers.All measurements are in µm.Modifi ed from SENOWBARI-DARYAN et al. (2006).

Fi gu re 1 :
Geographic position of the locality south of the town of Dizlu, northeast of Esfahan (modifi ed from SENOWBARI-DARYAN & HAMEDANI, 2000).

Fi gu re 2 :
Columnar section of the Nayband Formation and overlying Lower Jurassic rocks through ridge '2' shown in Pl. 1, Fig. 2. The basal 26 m of the Nayband Formation is not exposed.It starts with spongedominated, thick bedded to massive limestones.Arrow indicates the solenoporacean horizon.
3, Figs.a-b), but may also occur together with Parachatetes dizluensis n. sp.(Pl.2, Figs.a-b).This alga builds communities occupying surfaces of several square metres.Even in the fi eld this alga is easily distinguished from the Fi gu re 3: Terms, used to described the thallus (drawn from Plate 3, Fig. B: rectagle) of Solenopora rectangulata n. sp. in detail.Legend: M) main stem, 1) branches of fi rst order, 2) branches of second order, 3) branches of third order.

Fi gu re 4 :abc 2 ab 3 ab
Figs. a-c: Solenopora rectangulata n. sp. a Thin-section photograph showing numerous branched and parallel-growing thalli with the almost constant diameter of the main stems.Several geopetal fabrics (large arrows) indicate the in situ position of the thalli.Small arrows indicate the branches of neighbouring thalli growing or fused together.For an enlargement of the holotype (H) and the part shown by the rectangle, see fi g. b.Thin-section 6.b Close-up from fi g. a (rectangle) shows three multi-branched thalli.Arrows indicate the branches of neighbouring thalli growing together.Legend: H) holotype M) main stem, F) branches of fi rst order, S) branches of second order.
companion species P. dizluensis n. sp. by its small thalli and particularly by the net-like appearance when viewed from the side Pl. 3, Pl. 4, Pl.5,.Individual thalli are more or less cylindrical and grow parallel to other individuals; the thallus diameter (diameter of main stem) does not increase during the growth stages(Pl.4,  Fig. a; Pl 5, Fig. b).Branches of the fi rst and second orders (see Fig.3) diverge from the main stem at varying distances and may radiate from one or all sides Pl. 3, Pl. 4, Pl. 5, Figs. a 2, Figs.a-b; Pl. 4, Fig. a).Branches of neighbouring thalli may grow or fuse together, with or without recognizable boundaries (Pl.4, Figs.4a-b: small arrows; Pl. 6, Figs.a-e).

Fibcabc
Figs. a-c: Parachaetetes dizluensis n. sp. a Longitudinal section through a colony of numerous thalli showing the fi nger-like branching pattern of individual thalli.H) Holotype.Thin section 9.b Enlargement of the axial part of a thallus showing the cells and the thickening of the cell walls at the same level producing the concentric layers.Thin section 2/0.cLongitudinal section at the edge of a thallus showing the thickening of the cell walls at the same level producing the concentric layers.Thin section 2/0.