Conifer Woods of the Middle Jurassic Hojedk Formation (Kerman Basin) Central Iran

Home , Caytoniales, Jurassic, Middle Jurassic, Neocalamites, Nilssonia (plant), Shemshak (ski resort)

IAWA Journal, Vol. 26 (4), 2005: 489–505

CONIFER WOODS OF THE MIDDLE JURASSIC HOJEDK FORMATION (KERMAN BASIN) CENTRAL IRAN

Imogen Poole1* & Majid Mirzaie Ataabadi2, 3

SUMMARY This paper documents the first record of permineralised wood from Mid- dle Jurassic coal bearing deposits to the north of Kerman, Iran, deposited c. 170 million years before present. The coniferous woods have character combinations resembling, and thus have been assigned to, the genera Xen- oxylon Gothan and Agathoxylon Hartig. Since Xenoxylon is essentially Laurasian and Agathoxylon has been recorded from the Northern Hemi- sphere during the Mesozoic, these woods help confirm conclusions from recent geological studies that place the Kerman Basin of Iran in southern Laurasia during the Jurassic. Key words: Iran, Jurassic, conifer, Gondwana, Laurasia, fossil wood.

INTRODUCTION

Late Triassic–Middle Jurassic sediments extending from Central Iran northwards and east into Afghanistan have yielded excellently preserved floras. These Mesozoic plant- bearing deposits are important because they form a continuous, uninterrupted series from the Norian through to the Middle Jurassic (Schweitzer et al. 1997). The fossils originate from the mining areas in Northern Iran (Alborz), Central Iran (Kerman Basin) and Northeast Afghanistan (Hindukusch) (Schweitzer et al. 2000). In western and northern Alborz the deposits are completely terrestrial whereas in central and eastern Alborz and to the south in the Kerman Basin they have occasional marine intercalations (Schweitzer et al. 1997). During the last few decades plant microfossils (e.g. Kimiyai 1968; Arjang 1975; Ashraf 1977; Achilles et al. 1984) and macrofossils from this area have been com-prehensively studied. From the leaf floras alone c. 60 genera of plant macrofossils have been described, ranging from bryophytes, lycophytes, equisetales and ferns (Schweitzer 1978; Schweitzer et al. 1997) to caytoniales, cycadophytes, bennettites, ginkgophytes, czekanowskiales and coniferales (Poliansky & Safronov 1973; Barnard & Miller 1976 and references therein; Sadovnikov 1976; Vassiliev 1985; Schweitzer & Kirchner 1995, 1996, 1998, 2003; Schweitzer et al. 2000; Mirzaie Ataabadi 2002). Based upon these publications the Rhaeto-Jurassic sediments of the Alborz region

1) Wood Anatomy Section, National Herbarium of the Netherlands, University of Utrecht branch, P.O. Box 80102, 3585 CS Utrecht, The Netherlands & Palaeontological Museum, Univer- sity of Oslo, P.O. Box 1172 Blindern, N-0318 Oslo, Norway [E-mail: [email protected]]. *Author of correspondence. 2) University of Esfahan, P.O. Box 81745/188, Esfahan, Iran. 3) Present address: Division of Geology and Palaeontology, Department of Geology, University of Helsinki, P.O. Box 64, FIN-00014, Helsinki, Finland [E-mail: [email protected]].

Downloaded from Brill.com10/03/2021 06:57:34PM via free access 490 IAWA Journal, Vol. 26 (4), 2005 Poole & Mirzaie Ataabadi — Jurassic conifer woods 491 appear to be the most fossiliferous locality in Iran to date (cf. Schweitzer & Kirchner 1995, 2003) but more recent surveys by Mirzaie Ataabadi (2002) and Vaez Javadi and Mirzaie Ataabadi (2006) indicate that the Kerman area is also rich in fossils. Fossil wood from this geographical region is rare when compared with leaf floras. Seward (1912) reports the presence of Cupressinoxylon in the Saighan Series of North Afghanistan, and Sitholey (1940) and Jacob and Shukla (1955) document Mesembri- oxylon sp. from the same locality. Schweitzer and Kirchner (1996), however, synony- mise the latter with Xenoxylon barberi (Seward) Kräusel which they describe from the same series in Northeast Afghanistan. From Middle Jurassic deposits of the Ferizi area, northeastern Iran, Fakhr and Marguerier (1977) in Fakhr (1977) assigned woods to Prototaxoxylon. More recently Nadjafi (1982) described Jurassic woods of Alborz Mountains (Fig. 1) and assigned them to five genera,Xenoxylon , Prototaxoxylon, ʻMeta- taxodioxylonʼ, ʻProtosciadopitysʼ and ʻProtopinoxylonʼ. The last three genera were newly erected in Nadjafiʼs (1982) unpublished thesis and are thus invalid according to the rules laid down by the I.C.B.N. (Greuter et al. 2000). The fossil woods, which form the subject of this study, originate further to the south in Middle Jurassic deposits in the Kerman Basin of Central Iran (Fig. 1; Lapparent & Davoudzadeh 1972; Schweitzer & Kirchner 1995) known for the coal bearing deposits that cover an area of 700 to 1050 km2. Even though palaeobotanical investigations in this Basin have been undertaken, workers have concentrated on the leaf and fructifica- tion flora (see references listed above) and to our knowledge no wood specimens have been recorded to date.

GEOLOGICAL SETTING

The area around northern Kerman (Fig. 1) had, until the Triassic, formed part of the Ola- cogen Basin with a connection to Palaeotethys. Significant palaeogeographical changes subsequently occurred as a result of the Early Cimmerian tectonic movements of the Late Middle–Late Triassic (Carnian–Norian) and thus played a major role in the geological history of Jurassic deposits in this area. After these orogenic activities, faulting to the north and south of this area created a new basin in between the faults. The high amount of subsidence associated with these events caused the deposition of a thick sequence of terrigenous sediments that lasted until the Middle Cimmerian (Bajo- cian–Bathonian) (Berberian & King 1981). The detrital sediments in this basin vary in thickness from a few metres up to more than 3000 m. These sediments are known as the Shemshak group (formerly the Shemshak Formation) which includes the Nayband, Abhaji, Badamu and Hojedk Formations (Fig. 2) of Central Iran (Aghanabati 1977; Stöcklin & Setudenia 1991). The Hojedk Formation (Stöcklin & Setudenia 1991) comprises more than 1000 m succession of shale, sandstone, conglomerate and coal horizons (Fig. 2). The coal horizons are fossiliferous yielding beautifully preserved leaf floras. The woody material studied herein was found in the “coal bearing series, coal horizon D” in the Kerman Basin equivalent to the “Dansirit Series” of the Alborz region (Table 1 of Schweitzer et al. 2000). The ammonite fauna from the underlying marine limestones of the Badamu

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b 56° 24' 56° 35' 31° 15' 31° 15'

31° 31' 31° 31'

56° 24' 56° 35'

Fig. 1. – a: Map showing the position of the study area in relation to Kerman, in south central Iran, with the area north of Kerman enlarged indicating the fossil locality in relation to other major towns in the area. – b: Geological map of the immediate area showing the Jurassic coal- bearing deposits in which the fossil flora was found. The fossil locality is indicated.

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DESCRIPTION SUITE (MEMBER) STAGE LITHOLOGY FORMATION

Thick to medium bedded limestone

Asad Cal. Bidu Abad Red conglomerate and sandstone k

n h Alternation of greenish grey shale and

siltstones with black to medium bedded sandstones, k locally containing abundant plant macrofossils

n 100 meters

Alternation of thick and medium bedded sandstones with traces of tree trunks

Alternation of grey shales, siltstones and sandstones with rare plant macrofossils

Thick bedded sandstones G u m r d H o j e d k Alternation of greenish gray shales, siltstones and medium bedded gray sandstones with rare plant macrofossils

Thick bedded sandstones with fossil fragments

Alternation of sandstones, dark siltstones, coaly shales and coal seams (coal seams D9-D11) with abundant plant macrofossils Fig. 2. Stratigraphical Thick bedded gray sandstones column of the section

Alternation of dark siltstones, coaly shales and coal seams through the Hojedk (coal seams D2, D4 and D6) with abundant plant macrofossils Formation, North of Medium to thick bedded greenish gray sandstones with Kerman, with the strata invertebrate fossils and sedimentary structures

B a j o a n i B a c Pale yellow shales in which the fossils Medium to thick bedded yellowish oolithic limestones with were found indicated Badamu Babnizu abundant brachiopods, pelecypods, gastropods, ammonites by the wood symbol.

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Formation is dated as Toarcian–Lower Bajocian (Seyed Emami 1971) and Aghanabati (1998) concluded that the Hojedk Formation, covering an area from Southeast Central to East Central Iran, must have been deposited during the Middle Bajocian–Lower Batho- nian. Therefore, the fossil wood, found in the lower horizons of the Hojedk Formation, is probably Middle to Late Bajocian in age. This paper describes two gymnospermous taxa as yet undescribed from these deposits and thus increases the diversity of the flora preserved within the Hojedk Formation. This paper forms one of a series of publications focusing on the palaeobotany (predominantly leaf floras) of this Formation.

MATERIAL AND METHODS

Two specimens of fossil wood, one pyritized (EUGM–PC1574P) and one substituted with iron oxide (EUGM–PC1565P), deposited in the Palaeobotanical Collection at the Esfahan University Geology Museum, were collected from the Pabedana coalmine to the north of Kerman (Fig. 1). They originate from coal horizons D2–D4 (Fig. 2) of the Hojedk Formation which comprise the famous coal seams of this area. The wood specimens were thin sectioned along three planes, transverse section (TS), radial longitudinal section (RLS) and tangential longitudinal section (TLS) and studied using transmitted light microscopy. Descriptions follow the terminology of the IAWA Committee (2004) wherever possible. The material described has been referred, rather than assigned, to fossil species at this stage because not only are fossil conifer wood species ill-defined but both quantitative and qualitative anatomical characters can vary greatly throughout one tree (cf. Chapman 1994; Wheeler & Baas 1998; Falcon-Lang & Cantrill 2000) and furthermore each xylotype described below is only represented by one specimen.

RESULTS

XENOXYLON Gothan 1905 Holotype: Xenoxylon latiporosum (Cramer) Gothan 1905 Xylotype: Xenoxylon cf. latiporosum (Cramer) Gothan 1905 Material — This taxon is described from a single specimen, EUGM–PC 1565P. Description — An isolated piece of homoxylous secondary xylem (ʻtracheidoxylʼ, Creber 1972), with a total diameter of 4 cm and length of 10 cm, with 25 growth rings, composed predominantly of tracheids (Fig. 3). Parenchyma present and diffuse (Fig. 3). Growth increments predominantly narrow (c. 0.5 mm) although wider towards the outer edge (2.75 mm) and centre (5.5 mm) of the specimen. Ring boundaries distinct but de- marcated by only 1–2 layers of latewood tracheids, rectangular in cross section, thick- or thin-walled (double wall thickness 7–30 μm) when not compressed (Fig. 3). Latewood radial and tangential mean diameters measuring 18.5 μm (range: 12.5–25 μm) and 49 μm (range: 37.5–65 μm) respectively. Tracheids in the earlywood are thin-walled (double radial wall thickness 6–17 μm), regularly arranged in radial rows, square-rectangular in cross section with radial and tangential mean diameters measuring 51 μm (range:

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Fig. 3–9. Photomicrographs of Xenoxylon cf. latiporosum (EUGM – PC1565P). – 3: TS showing narrow growth increments with subtle ring boundaries. – 4: TLS showing relatively low rays. – 5: RLS showing a typical ray. – 6: TLS. – 7: Window-like cross-field pits in RLS. – 8: Intertracheary pitting in LS. – 9: Window-like cross-field pits in RLS. — Scale bar = 200 μm in Fig. 3; 100 μm in Fig. 4; 50 μm in Fig. 5; 25 μm in Fig. 6; 12.5 μm in Fig. 7; 10 μm in Fig. 8; 15 μm in Fig. 9.

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37.5– 67.5 μm) and 57 μm (range: 42.5–72.5 μm) respectively. No spiral thickenings present. Intertracheary pits (Fig. 8) on radial walls uniseriate, bordered, vertically contiguous, elliptical 15 –17.5 μm in diameter, with small round-oval apertures, of the abietinoid type (cf. Philippe 1995) usually separated by a distance of at least a quarter of the diameter of the radius if not adpressed, flattened; extremely rare subopposite biseriate pits. Pits on the tangential walls are rare but small, circular, bordered and up to 10 μm in diameter. Cross-field pits (Fig. 7 & 9) are predominantly solitary, occasionally 2, possibly even 3, seemingly of the large, simple, window-like ʻfenestriformʼ type (feature 90, IAWA Committee 2004) (cf. the ʻnormalʼ or ʻcircoporeʼ oopore of Philippe 1995) throughout the rays. Rays (Fig. 4 & 5) are homocellular, uniseriate, (1) 2–8 cells high, with no differentiation in shape of the marginal cells. Pith region absent. This specimen is from the inner portion of a branch/trunk as deduced from the growth ring cur- vature. One branchlet/twig/leaf trace can be seen running through at least 21 growth rings. Systematic affinities — Specimen EUGM–PC1565P is characterised by seemingly large, simple, circular cross-field pitting and contiguous uniseriate flattened intertracheary pitting on the radial walls. This pitting is characteristic of Xenoxylon, a Mesozoic northern hemisphere xylotype with uncertain systematic position (cf. Philippe & Théve- nard 1996). When this material is compared with other woods from this geographical region (Table 1), there are similarities (e.g. window-like cross-field pits, uniseriate intertracheary pits that are flattened when in contact) toXenoxylon latiporosum from Tazareh (Nadjafi 1982) and X. barberi from Ferizi (Schweitzer & Kirchner 1996). However, when the comparison is widened to include other material from other regions, this wood is more similar to X. latiporosum described by Suzuki and Terada (1992) from Japan (see Table 2). Thus, this specimen is referred to Xenoxylon latiporosum.

AGATHOXYLON Hartig Holotype: Agathoxylon cordaianum Hartig 1848 Xylotype: Agathoxylon sp. Material — This taxon is described from a single specimen, EUGM–PC 1574P. Description — An isolated piece of homoxylous secondary xylem (ʻtracheidoxylʼ, Creber 1972) (Fig. 10), measuring 15 cm in diameter and 20 cm in length. Growth rings present. At least three, wide (4–5 mm) growth-ring increments can be seen with distinct growth ring boundaries and a gradual transition from earlywood to latewood within the growth ring (Fig. 13). Parenchyma present as rare, diffuse cells. Latewood relatively wide, tracheids more or less rectangular in cross section, generally thick- walled (double radial wall thickness 12.5–25 μm) with respect to the tracheid diameter. Latewood radial and tangential mean diameters measuring 20 μm (range: 12.5–25 μm) and 31.5 μm (range: 22.5–40 μm) respectively. Tracheids in the earlywood, thin-walled (12.5–20 μm), regularly arranged in radial rows, rectangular in cross section (Fig. 13) with mean tangential and radial diameter measuring 37 μm (range: 27.5–45 μm) and 60 μm (range: 47.5–75 μm) respectively. Tracheids occasionally with features remi-

Downloaded from Brill.com10/03/2021 06:57:34PM via free access 496 IAWA Journal, Vol. 26 (4), 2005 Poole & Mirzaie Ataabadi — Jurassic conifer woods 497 m μ m × 15–38 μ Prototaxoxion feriziense Ferizi (Iran) Shemshak Fm, Dogger 1977 in Fakhr & Marguerier Fakhr 1977 silicified indistinct, numerous, 0.6–3 mm wide 22–50 absent uniseriate, rarely part biseriate; 1–13 cells high; tall marginal cells absent usually 1, rarely 2–3 in marginal cells; oculipores, weakly bordered RLS bordered, mainly uniseriate (contiguous or spaced), rarely biseriate (alternate or opposite) or mixed present — — true thickenings present, sometimes double

m) μ

m; μ

m μ

Xenoxylon barberi

Ishpushta (Afghanistan) Saighan series, Dogger Schweitzer & Kirchner 1996 — 0.25–2.1 mm wide; 103 in 5.5 cm (23) 48–57 EW 48 LW absent uniseriate, homocellular; 2–12 cells high (40–270 — usually 1, rarely 2, oval oopores, bordered RLS bordered, uniseriate, contiguous, flattened or spaced, round; protopinoid present — — seemingly present but preservation feature

sp.

Mesembrioxylon

Ishpushta (Afghanistan) Saighan series, Dogger Jacob & Shukla 1955 silicified narrow — present uniseriate, sometimes part biseriate; 3–25 (38–40) cells high — poorly preserved; 1–2 and fairly large uniseriate, bordered, irregu- larly distributed on radial walls, infrequently biseriate and opposite; podocarpoid present — ?bars of Sanio —

Cupressinoxylon orientale

Ishpushta (Afghanistan) Saighan series, Dogger Seward 1912 silicified narrow latewood — — uniseriate, rarely part biseriate; 1–20 (25–30) cells high — poortly preserved; 1–4, ?bordered, ?oopores RLS biseriate, opposite,flattened when in contact; sometimes uniseriate, occasional TLS uniseriate, groups of 3 contiguous in LW present — — —

Table 1. Table Summary of the anatomical characters of the Jurassic fossil = latewood; — not provided. = earlywood; LW region. – EW woods previously described from the Iran-Afghanistan geographical locality age reference preservation growth rings tracheids resin bodies rays indentures cross-field pits tracheid pits parenchyma tyloses ornamentation bar-like spiral thickening

Downloaded from Brill.com10/03/2021 06:57:34PM via free access 496 IAWA Journal, Vol. 26 (4), 2005 Poole & Mirzaie Ataabadi — Jurassic conifer woods 497 m μ m μ “Protopinoxylon fakhrii” Ferizi (Iran) Jurassic Nadjafi 1982 silicified 4–6 mm, distinct, numerous, latewood 1–3 cells 5–14 × 23–39 LW 28–62EW × 23–51 present as vertical canals in LW uniseriate, 1–22 cells high present 1–4, taxodioid RLS uniseriate (94%), flattened; biseriate (6%) alternate, araucaroid absent present — —

m μ

“Protosciadopityoxylon boureaui” (Iran) Tach Jurassic Nadjafi 1982 silicified distinct, 2 mm, latewood 1–2 cells 4–18(–30) 18– × (11) LW 44 (55) 26–67EW × 26–66 absent uniseriate, part biseriate (2%), 1–18 cells high — 1–3 (4), taxodioid, oculipores; oopores RLS uniseriate, biseriate (7%), araucaroid absent — — false thickenings

μ m

Prototaxoxylon “persicum” Sangroud (Iran) Jurassic Nadjafi 1982 — indistinct, c. 4 mm 7–22 × 26–33 (74) LW 26–48EW × 18–52 absent uniseriate, rarely biseriate (1%), 1–22 cells high — 1 (2–3), taxodioid, oculipores; ?oopore RLS uniseriate, flattened contigu- (55%); circular, ous (20%); biseriate alternate (20%); abietoid (4%) present — fine horizontal ʻcallitroidʼ bars present, double

μ m

“Metataxodioxylon iranicum” (Iran) Tazareh Jurassic Nadjafi 1982 silicified numerous, distinct, 2–5 mm, latewood 1–2 cells 5–23 × 23–48LW 32–46EW × 34–46 absent uniseriate, part biseriate (2%), 1–24 cells high — 1–2 (3–4) taxodioid RLS uniseriate (79%), flattened; biseriate (21%) alternate, araucaroid not observed — — —

Xenoxylon latiporosum (Iran) Tazareh Lias Nadjafi 1982 silicified numerous, distinct, 1–2.5 mm, latewood 1–3 cells 6–30 (42) × (9) 18–LW 48 (54) 30–66EW × 12–54 absent uniseriate, 1–10 cells — 1, occasionally 2 fenestriform pits occupying the whole cross-field area RLS uniseriate, contiguous, flattened, rarely biseriate, alternate uncertain due to the presence of tyloses and septae — — — TLS locally present

Table 1 continued Table locality age reference preservation growth rings tracheids resin bodies rays indentures cross-field pits tracheid pits parenchyma tyloses ornamen- bar-like tation spiral thickening

Downloaded from Brill.com10/03/2021 06:57:34PM via free access 498 IAWA Journal, Vol. 26 (4), 2005 Poole & Mirzaie Ataabadi — Jurassic conifer woods 499 m m μ μ with which specimen EUGM- Xenoxylon latiporosum Japan Early Cretaceous 1992 Terada Suzuki & — distinct, 0.25–1.35 mm latewood narrow, 2–several cells 60–80EW: × 40–80 20–30 × 40–80LW: dark occlusions in ray cells uniseriate, 1–10 cells high absent window-like (oopore) 1(–2), large, RLS: bordered, elliptical, round apertures, scattered contiguous to small, circular, bordered TLS: small, circular, absent present absent — Xenoxylon

m μ

EUGM-PC1565P Kerman Iran Jurassic Hojedk Fm, Dogger, herein iron oxide distinct, 0.5–5.5 mm latewood narrow 1–2 cells 37.5–67.5EW: × 42.5–72.5 12.5–25 × 37.5–65LW: absent (1) 2–8uniseriate, homocellular, cells high absent 1(–2), window-like (oopore) RLS: uniseriate, elliptical bordered TLS: very occasional small, circular, bordered present present absent absent

m m μ

m × 22.5–40 m × 47.5–75 μ μ

EUGM-PC1574P Kerman Iran Jurassic Hojedk Fm, Dogger, herein pyritized boundary, distinct with abrupt LW-EW 4–5 mm latewood wide with gradual transition EW-LW 27.5–45EW: 12.5–25 LW: absent 2–32 cells uniseriate, homocellular, high, rarely part biseriate present up to 6, bordered, cupressoid RLS: rarely uniseriate and triseriate, mainly biseriate, alternate, occasionally subopposite rare absent absent — TLS: rare uni–biseriate

Table 2. Table Summary of the anatomical characters of the woods described herein and the species = latewood; — not provided. of = earlywood; LW – EW shows greatest anatomical similarity. PC1565P locality age reference preservation growth rings tracheids resin bodies rays indentures cross-field pits tracheid pits parenchyma tyloses ornamentation bar-like spiral thickening

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Fig. 10–17. Photomicrographs of Agathoxylon sp. (EUGM – PC 1574 P). – 10: TS showing distinct rays. – 11: TS showing the remains of the pith. – 12: TLS showing rays. – 13: TS of growth ring boundary. – 14: RLS of cupressoid cross-field pits. – 15: RLS showing alternate intertracheary pitting. – 16: RLS showing pseudo-thickenings of the tangential wall of the ray cells. – 17: LS tracheid pitting and features caused by fungal decay of the cell wall that could be confused with spiral thickenings. — Scale bar = 50 μm in Fig. 10; 100 μm in Fig. 11–13; 15 μm in Fig. 14; 25 μm in Fig. 15 & 17; 10 μm in Fig. 16.

Downloaded from Brill.com10/03/2021 06:57:34PM via free access 500 IAWA Journal, Vol. 26 (4), 2005 Poole & Mirzaie Ataabadi — Jurassic conifer woods 501 niscent of spiral thickenings, although these are more likely to be features caused by fungal decay in the S2 layer of the cell wall (Fig. 17; cf. Kräusel & Jain 1964) or cell wall cavities associated with compression wood. Intertracheary radial wall pits (Fig. 15) are bordered, rarely uniseriate (<10%), predominantly biseriate (c. 85%), rarely triseriate (< 10%), predominantly polygonal and alternate when multiseriate, biseriate pitting is occasionally subopposite, 10.5–17.5 μm in diameter, with small round-oval apertures; uniseriate pitting is confined to the narrow latewood tracheids with pits usually contiguous, occasionally scattered. Multiseriate pitting occurs in the wide earlywood tracheids. Tracheid tangential wall pitting is rare but uni- to biseriate when present. Cross-field pits (Fig. 14) are bordered and of the ʻcupressoidʼ type (feature 93, IAWA Committee 2004) (cf. ʻcupressoidʼ oculipore of Philippe 1995) with up to six pits per cross field in both the marginal and central part of the rays. Cross-field pits poorly preserved but generally more or less circular when not touching; when adpressed, pits appear to be alternate. Rays are uniseriate, 2–32 cells high, rarely locally biseriate, with biseriate regions up to two cells in length with no difference between the cells of the margins and body (Fig. 12). Tangential walls of some ray cells appear to have thickenings (Fig. 16) but could represent ʻpseudo-thickeningsʼ formed by iron sulphide bacterial activity or, alter- natively, checking associated with compression wood. Pith is composed of thin-walled parenchyma cells (Fig. 11). Systematic affinities — Alternate biseriate tracheidal pitting, which is characteristic of specimen EUGM–PC1574P, is also found in the specimens of Prototaxoxylon and the invalid genera ʻMetataxodioxylonʼ, ʻProtosciadopityoxylonʼ and ʻProtopinoxylonʼ from the Alborz region of Iran (Nadjafi 1982; see Table 1). However, similar cross- field pits in combination with alternate tracheidal pitting occur only inPrototaxoxylon specimens from Alborz (Fakhr & Marguerier 1977 in Fakhr 1977; Nadjafi 1982). The differences between the specimens previously assigned to Prototaxoxylon and the specimen described herein include the abundance of biseriate and presence of triseriate tracheidal pitting, up to four cupressoid pits in the cross fields, and the absence of true spiral thickenings in EUGM–PC1574P; therefore this material cannot be assigned to this xylotype.

Alternate and subopposite radial intertracheary pitting and cupressoid crossfield pitting is also characteristic of araucariaceous fossil wood and wood of Brachyoxylon Hollick et Jeffrey (1909). However, the intertracheary pits are predominantly polygonal and alternate when multiseriate and the cross-field pits appear alternate when adpressed (although better preserved material will enable the determination of the precise pit characters of the cross fields) such that this fossil bears greater similarity to araucariaceous fossil woods than to those assigned to Brachyoxylon. Therefore this specimen has been assigned to the xylotype Agathoxylon erected for woods with araucarian radial wall pitting and araucarioid cross-field pits. No attempt has been made to place this specimen within an existing species since there are no other woods of this type yet found from Iran and the morphogenera for araucariaceous fossil wood are in need of revision (Bamford & Philippe 2001).

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DISCUSSION During the Middle Jurassic the habitats of Iran and Afghanistan were located on the southern coastal edge of the Middle Asian province of the Euro-Sinian region (Vakh- rameev 1991). Fakhr (1977) suggested that the Middle Jurassic basins of North Central Iran and North Afghanistan, once formed part of a basin-island complex along the coast of Laurasia and that the terrestrial deposits were laid down in the Caucausus–Turkistan geosyncline which branches into the eastern part of Central Iran. Studies by Repin (1985) concluded that the Kerman area was one such island situated in close proxim- ity to other land masses, which were periodically united into a large basin. Middle Jurassic vegetative remains were deposited in this basin and subsequently became the coal deposits of Central Iran. A study by Seyed Emami (1971) also considers the Kerman area to have been sited on the southern margin of Laurasia due to similarities between the terrestrial Rhäto–Jurassic deposits in North and Central Iran and those of Afghanistan, Turkmenistan and Armenia which are known to have been situated on the southern margin of Laurasia. However, Vozenin-Serra and Taugourdeau (1985) con- sider the Kerman area to have been connected to the northern part of Gondwana with migration from northern Gondwana prevented by the large expanse of water between India and this island complex (e.g. Delle 1967). The composition of the Jurassic floras within the Middle Asian province (extending south from the Karagandar-Turgay region in the north to the coast of the Jurassic sea in the south; Vakhrameev 1991) changed markedly along the north-south transect (Sykstel 1954). Floras of the Middle Jurassic are relatively species-rich, with a diversity of lycopods, horsetails, ferns and gymnosperms (Gomolitzky & Khudayberdyev 1976). Palaeobotanical evidence derived from the coal deposits of the Georgia-Transcaucasus region to the north indicates a typical rich and diverse Middle Jurassic flora similar to that found in the European floristic province (Barale et al. 199; Vakhrameev 1991). However, components characteristic of coeval floras growing in the Central Asian and Indian provinces were also present (Delle 1960; Junusov 1975). Understorey ferns (e.g. Coniopteris, Cladophlebis), ginkgos and conifers (e.g. Araucarioxylon, Podocarpoxy- lon and Xenoxylon) (Delle 1960; Barale et al. 1991 and references therein) occupied higher elevations whereas the cycadophytes (especially Nilssonia) and woody ferns grew at lower elevations, giving way to horsetails and neocalamites in moist swampy zones. A similar floral composition can also be found in Turkmenistan to the east (Delle 1960). To the south, the floras of northern and south-eastern (Kerman) Iran covering lowland areas adjacent to the marine basin can be referred to the Transcaspian subprovince (Vakhrameev 1991). The gymnosperm component of the vegetation from the Lower Jurassic comprised members of the Voltziaceae/Taxodiaceae (including Xenoxylon), Cheirolepidiaceae and Palissyaceae (e.g. Schweitzer & Kirchner 1996) with a decreasing Czekanowskiales (Delle 1967; Vakhrameev 1991; Barale et al. 1991). Palaeobotanical studies (Mirzaie Ataabadi 2002) of the Middle Jurassic macrofloras from the Kerman area of Iran show up to 50% similarity with those of Laurasian floras, the Transcauca- sus (Georgia; Delle 1967), East Urals (Russia; Genkina 1963) and the Saighan Series

Downloaded from Brill.com10/03/2021 06:57:34PM via free access 502 IAWA Journal, Vol. 26 (4), 2005 Poole & Mirzaie Ataabadi — Jurassic conifer woods 503 of North Afghanistan (Jacob & Shukla 1955) which also form part of the Euro-Sinian floral region (Vakhrameev 1991). By the Middle Jurassic the Czekanowskia and the Ginkgoales had become scarce in terms of number and diversity and the ancient Pinaceae were almost completely absent (Delle 1967; Vakhrameev 1991; Barale et al. 1991). The Lower-Early Middle Jurassic arboreal vegetation, as determined from the wood record, included Prototaxoxylon (Fakhr & Marguerier 1977 in Fakhr 1977; Nadjafi 1982), Xenoxylon (Nadjafi 1982, herein), Agathoxylon, and three other coniferous taxa assigned to the (unpublished and thus invalid-) genera ʻProtosciadopityoxylonʼ, ʻProtopinoxylonʼ and ʻMetataxodioxylonʼ (Nadjafi 1982).Xenoxylon survived into the Middle Jurassic and together with Agathoxylon and characteristic understorey ferns (such as Klukia, Eboracia and Coniopteris) and cycads, e.g. Nilssonia (Vakhrameev 1991) contributed to a more diverse and species-rich vegetation relative to the preced- ing Lower Jurassic flora (Gomolitzky & Khudayberdyev 1976). The presence of Xenoxylon, an essentially northern hemisphere (Laurasian) fossil wood taxon from the Middle Jurassic of Central Iran, may help substantiate the hy- pothesis that Central Iran was situated in the Middle Asian province of the Euro-Sinian floral region during the Middle Jurassic. However, the presence of a wood type in the Kerman Basin similar to Agathoxylon, which is distributed in both the northern and southern hemispheres, may indicate a connection enabling floral exchange between the Iran–Afghanistan region (forming the Iranian–Afghani Plate) and the northern edge of Gondwana at this time. Detailed studies of this and other palaeofloras will help further our understanding of the palaeogeography and vegetation dynamics across this region during the Mesozoic. The extensive survey of the fossil record of Xenoxylon by Philippe and Thévenard (1996) across the northern hemisphere shows this genus to favour cool, seasonally wet areas. The authors conclude that Xenoxylon favoured, and was later confined, to climates with a mean annual temperature of 5–15 °C during the Early Cretaceous. The presence of Xenoxylon wood in Pabedana along with other moisture loving plants such as bryophytes, equisetales and ferns (Schweitzer 1978; Schweitzer et al. 1997) and the relative abundances of Bennettites, Coniopteris and Nilssonia suggest that the palaeoenvironment was cool and at least locally moist – an observation which would agree with the Kerman area being an island at this time (Repin 1985) and evidenced by the vast coal deposits. The presence of growth rings in both specimens described here may suggest some seasonality. However, in the Xenoxylon specimen the rings are relatively indistinct rather than well-defined. Well-defined rings in Xenoxylon led some authors to believe that this taxon was deciduous (Philippe & Thévenard 1996 and references therein). Further growth ring analysis was not undertaken to explore this climatic aspect since there is debate as to the reliability of using such palaeoden- drochronological methods for fossil material (e.g. Brison et al. 2001).

CONCLUSION

Two coniferous taxa, Xenoxylon and Agathoxylon, are recorded from Middle Jurassic deposits of the Kerman Basin, Iran. This area was a lowland coastal zone located on the southern margin of Laurasia in the Middle Asian province of the Euro-Sinian floral

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region at this time. These specimens represent the first record of permineralised wood from these Middle Jurassic coal bearing deposits and provide information pertaining to the arboreal component of the vegetation. Additional studies focusing on fossil woods from sites across Iran and Afghanistan, the most southerly of all Laurasian localities, in combination with syntheses of the floras already described will further our understanding of the nature, affinities and palaeogeographical distribution of the Jurassic vegetation that grew along the edge of the Laurasian landmass. Moreover, palaeobotanic studies of fossil floras will enhance understanding of the spatial and temporal dynamics of the plate(s) on which they rode.

ACKNOWLEDGMENTS

We thank Dr Mohammad Sadegh Fakhr (Laboratory of Paleobotany, University of Tehran, Iran), Professor Han van Konijnenburg-van Cittert (Utrecht University), Professor Elisabeth Wheeler and especially Dr Marc Philippe (Université Claude Bernard, Lyon) for providing relevant literature, helpful discussions and comments that have improved this manuscript. Otto Stieckma (Utrecht University) is acknowledged for sectioning the fossil material. We are also grateful to Vachik Hairapetian (Islamic Azad University, Khorasgan branch, Esfahan, Iran) for his help in drawing the maps and the stratigraphic column used in this paper, and Iwona Rejniewicz for translating the Russian literature.

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