In the outcrops of central Saudi Arabia, Permian flora have been recovered from the Unayzah Formation and the Midhnab Member of the Khuff Formation. The Unayzah Flora is found in the Unayzah Formation (below the Khuff Formation), and it is a true Cathaysian-Euramerican mixed palaeoflora with a probable age of Middle Permian (either Roadian or/and Wordian). The Unayzah Flora would therefore be coeval with the Gharif Flora from the Al Huqf area of Oman (uppermost Gharif Formation). The Midhnab Flora is found in the continental Midhnab Member (subunit 4) of the Khuff Formation. It is a mixed Late Permian flora related to the Gondwanan, Euramerican and Cathaysian realms. New associations of the Midhnab Flora were discovered at Jal Khartam, Jal al Watah and Wadi al Batan in the Qasim area of central Saudi Arabia. The new Midhnab Flora are systematically described here for the first time. The combination of palaeobotanical and sedimentological data led to the characterisation and organisation of the various palaeoenvironments in which each palaeofloral association was growing. Comparison between the Permian flora of Saudi Arabia, Oman, Anatolia (Turkey) and surrounding realms provides the means for reconstructing a more complete palaeogeographic setting for the Arabian Plate in a global palaeobiogeography.
The Permian-Triassic Khuff Formation (Steineke and Bramkamp, 1952; Steineke et al., 1958; Powers, 1968; Vaslet et al., 2005) crops out in central Saudi Arabia along a N-S belt that is some 1,200 km in length (Figure 1). The formation rests everywhere unconformably (Pre-Khuff Unconformity, PKU) over Lower Palaeozoic or Proterozoic shield rocks (Powers et al., 1966; Powers, 1968; Vaslet et al., 2005). The Khuff Formation is conformably overlain by the clayey and evaporitic Lower Triassic (‘Scythian’) Sudair Shale Formation. Le Nindre et al. (1990a, b) published the first synthesis of field work and extensive systematic geological mapping, conducted in the 1980s by the Saudi Arabian Deputy Ministry of Mineral Resources (DMMR, now the Saudi Geological Survey - SGS) and the French geological survey (BRGM), including lithostratigraphy, biostratigraphy and palaeoenvironment reconstructions. More recent compilations from central Saudi Arabia, were interpreted in terms of sequence stratigraphy by Alsharhan and Nairn (1995), Al-Aswad (1997) and Sharland et al. (2001).
A complete revision, including new field acquisitions, and compilation of local studies for oil exploration (Senalp and Al-Duaiji, 1995, 2001), was prepared by Vaslet et al. (2005). It includes a reassessment of the biostratigraphy based on foraminifers and algae (Vachard et al., 2002, 2003, 2005), ostracods (Crasquin-Soleau et al., 2004, 2006) and palaeoflora (Broutin et al., 2002; this paper). Vaslet et al. (2005) divided the central Saudi Arabian outcrops of the Khuff Formation (some 200 m thick) into five members, from oldest to youngest: Ash Shiqqah, Huqayl, Duhaysan, Midhnab and Khartam members (Figure 2).
During field work in 1982, the DMMR and BRGM found several localities where fossil plants were recovered from the upper part of the Late Permian Midhnab Member of the Khuff Formation (Vaslet et al., 1985, p. 3 and 15; Banerji et al., 1987; Le Nindre et al., 1990b). In 1998, the present authors recovered additional material from the Midhnab locality, and found new localities in the Qasim area where fossil plants occur in the same stratigraphic level. These new central Saudi Arabian associations, known as the Midhnab Flora, are related to the Gondwanan, Euramerican, and Cathaysian realms (Broutin et al., 2002; Berthelin, 2002). They constitute one of the most significant assemblages to ever be discovered in the Arabian Peninsula, and are of primary importance for understanding the phytogeographic history of the Arabian platform, dynamics of vegetation, and palaeogeographical evolution of the Arabian Plate during the Permian times. This paper systematically describes, for the first time, the recently discovered palaeoflora in the upper part of the Midhnab Member. The location of the palaeoflora associations in the palaeoenvironments is also described. This allows us to reconstruct the palaeoecologic life conditions and discuss global palaeogeographic interpretations.
LITHOSTRATIGRAPHY, BIOSTRATIGRAPHY AND SEQUENCE STRATIGRAPHY OF THE KHUFF FORMATION
The Ash Shiqqah Member (nearly equivalent to the obsolete Unayzah member of Delfour et al., 1982) of the Khuff Formation consists of terrigenous sediments with secondary clayey dolomite, and local evaporite in the upper part of the member. The palaeoenvironments range from transitional to continental and supratidal. The Unayzah Flora (Figure 2; Hill and El-Khayal, 1983; El-Khayal and Wagner, 1985; Broutin et al., 1995), formerly described in the lower part of the Khuff Formation, is now attributed to the underlying Unayzah Formation (Vaslet et al., 2005). Rare benthic smaller foraminifers occur locally in the upper part of the Ash Shiqqah Member, indicating a possible ?Middle Permian ?Capitanian (?Midian) age for this lowest member of the Khuff Formation (Vachard et al., 2002, 2005; Vaslet et al., 2005).
The Huqayl Member is subdivided into two sequential units containing calcarenite, gypsiferous claystone, dolomite, and solution breccias related to subsurface evaporites. This marine transgressive unit is tentatively assigned a Late Permian ?Wuchiapingian (?Dzhulfian) age according to its benthic foraminifers content (Vachard et al., 2003, 2005; Vaslet et al., 2005).
The Duhaysan Member is the first true calcareous subtidal to littoral unit of the Khuff Formation (Le Nindre et al.,1990b), and interpreted as the transgressive unit of the overlying Midhnab Member (Vaslet et al., 2005). The Duhaysan Member has yielded benthic foraminifers, nautiloid embryos, and abundant bactritids. A Late Permian Wuchiapingian to Changhsingian age is tentatively assigned to the Duhaysan Member (Vaslet et al., 2003, 2005).
The Midhnab Member displays a succession ranging from marine fossiliferous limestones at the base, toward gypsiferous and dolomitic rocks deposited in restricted palaeoenvironments, in the upper part. The lower part of the Midhnab Member is dated by benthic foraminifers as Late Permian Changhsingian (Dorashamian) by Vachard et al. (2003, 2005). Locally, in northern central Saudi Arabia, the topmost continental facies of the Midhnab Member include lacustrine limestone, sandstone channels and claystone in meandering river systems and swamps. These facies contain drifted woods and plant remains (Figure 2; Hill and El-Khayal, 1983; Vaslet et al., 1985; Le Nindre et al., 1990b; Vaslet et al., 2005). Recent descriptions of the Midhnab Flora indicate a Late Permian mixed flora including Cathaysian, Euramerian and Gondwanian plant remains (Broutin et al., 1995, 2002; Berthelin, 2002; this paper).
The Khartam Member, the uppermost mainly carbonate unit of the Khuff Formation, is subdivided into two marine units characterised by littoral to tidal and intertidal palaeoenvironments. The Lower Khartam Member consists of claystone, dolomite and sands, deposited in supratidal to tidal palaeoenvironments. The Upper Khartam Member is an oolitic, peloidal and bioclastic limestone locally dolomitised, deposited in littoral to tidal and intertidal palaeoenvironments. The Lower Khartam Member yielded rare benthic foraminifers possibly dated as latest Permian (Changhsingian) by Vachard et al. (2003, 2005), while the Upper Khartam Member, consisting principally of reworked Dasycladacean algae ooids, is characterised by the appearance of Spirorbis phlyctaena Brönniman and Zaninetti (Figure 2), a serpulid that is particularly abundant in the Early Triassic rocks in Neo-Tethyan areas.
According to Vaslet et al. (2005), the Khuff Formation consists of four main depositional sequences (DS PKh, DS PKm, DS PKk and DS TrS, see Figure 2). The last depositional sequence starts with the Khuff Formation and continues in the overlying Sudair Shale Formation. The DS PKh (named after Permian-Khuff-Huqayl) includes the Ash Shiqqah and the Huqayl members. Its basal Sequence Boundary (SB) corresponds to the Pre-Khuff Unconformity (PKU) and it contains the first Late Permian flooding event over central Saudi Arabian outcrop areas (MFI PKh). This flooding interval is located in the basal part of the Huqayl Member and is followed by the regressive evaporitic palaeoenvironments of the Huqayl Member (Le Nindre et al., 1990a, b; Vaslet et al., 2005).
The DS PKm (named after Permian-Khuff-Midhnab) started with the deposition of subtidal to littoral Duhaysan Member above an erosive surface at the top of DS PKh, and ended with the regressive supratidal to continental deposits of the upper part of the Midhnab Member. A maximum flooding interval (MFI PKm) is clearly located in the outcrops at the base of the Midhnab Member, with abundant marine fauna including cephalopods, brachiopods (Angiolini et al., 2006; Chirat et al., 2005; Vaslet et al., 2005) associated with the ostracod fauna (Crasquin-Soleau et al., 2004, 2006).
The DS PKk corresponds to the Lower Khartam Member (Permian-Khuff-Khartam), and represents the terminal Late Permian depositional sequence in the outcrops of central Saudi Arabia. The basal SB is marked by a return to marine subtidal conditions after the continental break at the end of DS PKm. It contains a maximum flooding interval (MFI PKk) that is manifested by marine fauna, including abundant Permian ostracods (Crasquin-Soleau et al., 2004, 2006), bactritids and locally cephalopods (Chirat et al., 2006).
The DS TrS (named after the Sudair Shale Formation) starts with the littoral, tidal to intertidal deposits of the Early Triassic Upper Khartam Member of the Khuff Formation, and ends with the closed-basin, clayey to evaporitic rocks of the Lower Triassic Sudair Shale Formation (Le Nindre et al., 1990b; Vaslet et al., 2005).
PREVIOUS PALAEOBOTANICAL DATA AND STUDIES
Four main Permian floral realms are recognised: (1) Euramerica, (2) Gondwana, (3) Angara, and (4) Cathaysia (see Figure 8). Euramerica included North America, east and west Europe (Baltica). Gondwana consisted of South America, Africa, Arabia, Madagascar, India, south Tibet, New Guinea, Australia and Antarctica. Angara occupied the area east of the Urals, extending through Siberia to the Pacific Ocean, and from the Arctic Ocean south to outer Mongolia. Cathaysia consisted of present-day China, Japan, and other southeast Asian regions during the Late Carboniferous, Permian and possibly Early Triassic times (Utting and Piasecki, 1995). A number of Permian floral associations from the Arabian Plate include elements from two or more realms.
The Unayzah Flora occurs in the Unayzah Formation (Figure 2), below the Khuff Formation (Vaslet et al., 2005). This flora is a true Cathaysian-Euramerican mixed flora (El-Khayal et al., 1980; Lemoigne, 1981a, b; Hill and El-Khayal, 1985; Broutin et al., 1995), and includes relevant Cathaysian forms such as Lobatannularia lingulata Halle, Lobatannularia sp. cf. heianensis Kodaira, Fascipteris hallei (Kawasaki) Gu and Zhi 1974, Gigantonoclea sp., Pecopteris phegopteroides Feistmantel, Qasimia schyfsmae (Lemoigne) Hill, Wagner and El-Khayal. These forms are associated with northern elements belonging mainly to Filicophyta and Cordaites. The Dadoxylon spp. figured by Lemoigne (1981a, b) clearly corresponds to the Euramerican Araucarioxylon genus (Broutin et al., 1995). The microfloral data (Fauconnier inLe Nindre et al., 1990b) indicate a Middle Permian Wordian (late Murghabian) age. The age of the Unayzah Flora was initially interpreted as Late Carboniferous but was later revised to Middle-Late Permian (Broutin et al., 1995). Broutin (based on ongoing studies) suggests that the Unayzah Flora is of Middle Permian age, either Roadian (Kubergandian) or/and Wordian (Murghabian).
The Jal Khartam Flora was discovered in the upper part of the Midhnab Member, in the northern Qasim region of central Saudi Arabia (Hill and El-Khayal, 1983, 1985; El Khayal and Wagner, 1985). It also consists of mixed associations of palaeofloras and was dated as Late Permian. Conifers are predominant in the association (fragments of leafy shoots only) such as Ullmannia bronnii Göppert., Pseudovoltzia sp., Culmitszchia sp. This poor floral assemblage resembles the conifers of the Zechstein Flora from the latest Permian Euramerican arid zone (Schweitzer, 1986). The occurrence of these morphogenera, considered as meso-xerophytic, is well reflected in the microflora: Lueckisporites virkkiae, Klausipollenites schaubergeri, Lunatisporites noviaulensis, Nuskoisporites sp. Protohaploxypinus spp. (Fauconnier in Le Nindre et al., 1990; Broutin et al., 2002).
The Midhnab Flora was discovered in 1982 during field mapping south of the Qasim region, at Jal Khartam in the Midhnab area and was published with the geological map of the Al Faydah quadrangle (Vaslet et al., 1985, p. 3 and 15). It was later on described by Banerji et al. (1987). The Midhnab Flora, like the Jal Khartam Flora, also occurs in the upper part of the Midhnab Member (Figure 2). The name Midhnab Flora refers to its stratigraphic position in the Midhnab Member and its discovery close to Midhnab city in central Saudi Arabia. By stratigraphic position, the Midhnab Flora is dated as Late Permian Changhsingian (Dorashamian), possibly ?early Dorashamian (Vachard et al., 2003, 2005; Crasquin-Soleau et al., 2004, 2006; Vaslet et al., 2004, 2005).
Charophytes remains have been described from the lacustrine limestone in the topmost part of the Midhnab Member (Delfour et al., 1982; Hill and El-Khayal, 1983; Vaslet et al., 1985; Le Nindre et al., 1990b; Vaslet et al., 2005), including the new species Palaeonitella tarafiyensis (Hill and El-Khayal, 1983). These lacustrine sediments are the lateral equivalents to the sediments bearing the Midhnab Flora (Vaslet et al., 2005).
Outside Saudi Arabia, Permian flora were described in several localities in the Arabian Peninsula. The Gharif Flora from the Gharif Formation in the Al Huqf area of Oman is dated as late Roadian to early Wordian (Broutin et al., 1995; Berthelin, 2002; Berthelin et al., 2003). The “Hazro Flora” from the Hazro Formation, Eastern Anatolia in Turkey, is dated as Late Permian (Wagner, 1962; Archangelsky and Wagner, 1983).
NEW PALAEOBOTANICAL DATA
The Midhnab Flora assemblages, including numerous taxa, were discovered in three localities; namely: (1) Jal Khartam, (2) Wadi al Batin, and (3) Jal al Watah (Figure 3). All the species found in these three localities, from the Midhnab Member of the Khuff Formation, are coeval and characterise the mixed Midhnab Flora.
(1) At Jal Khartam (25°57′23″N, 44°12′25″E) in the Al Faydah quadrangle (Vaslet et al., 1985), the original locality of the discovery of the Midhnab Flora (Figure 1), two assemblages of fossil plants were found in two different lithologies and palaeoenvironments (Figure 4). The first assemblage was found, together with drifted trunks, in oblique beds of a beige siltstone channel interpreted as a crevasse-splay expanded into greenish-grey claystone, with secondary gypsum exudations. The second assemblage occurs in the greenish-grey claystone around the siltstone channel, and represents a quieter palaeoenvironment in the upper part of the Midhnab Member (subunit 4 of Vaslet et al., 2005). The Midhnab macrofloral assemblages at Jal Khartam comprise fossil plants related to the Cathaysian, Euramerican and Gondwanan floras: fertile forms of Euramerican conifers (Ullmannia frumentaria Göppert 1850, Ullmannia bronnii Göppert 1850 and Ullmannia spp., and Culmitzschia sp. Plate 1.a–1.c), Gondwanan Sphenophytes (Phyllotheca australis Brongniart 1828; Plate 1.f) and Cathaysian Pteridophytes (Pecopteris chihliensis Stockmans and Mathieu 1957; Plates 1.d and 1.e).
(2) To the south of Wadi al Batin (26°14′08″N, 44°04′44″E; Figures 1 and 3) in the Buraydah quadrangle (Manivit et al., 1986), an accumulation of plant remains was found in a beige finegrained sandstone channel, including seamlets of greenish claystone (Figure 5), in the topmost part of the Midhnab Member (subunit 4 of Vaslet et al., 2005). The Midhnab floral assemblage at Wadi al Batin is dominated by Cathaysian-like Sphenophytes (Lobatannularia heianensis Kawasaki 1927, Plate 2.c), Lobatannularia multifolia Kon’no and Asama 1950, Plate 2.b, 2.f and 2.g), Lycophytes cones (Plate 2.a, basal part of a cone produced by an arborescent Lycophyte) and few Voltzia-like fertile shoots (Euramerican conifers, typical of the Euramerican realm, Plate 2.d and 2.e).
(3) At Jal al Watah (26°26′34″N, 43°59′02″E) in the Buraydah quadrangle (Manivit et al., 1986), plant remains were found at the top of a meander bar of white fine-grained sandstone (Figure 6), located in a greenish to red-brick pedogenetised silty claystone succession, at the upper part of the Midhnab Member (subunit 4 of Vaslet et al., 2005). At Jal al Watah (Figure 3), the new data are exceptional and include the leafy shoots of Ullmannia bronnii Göppert 1850 (Plate 3.h–3.j), Pseudovoltzia liebeana Florin 1927 (Plate 3.f), and Culmitzschia sp. (Plate 3.e) first observed by Hill and El-Khayal (1983, 1985) in the locality of Jal Khartam. The data also now includes the fructifications (cones) found in connection with the shoots. To these Euramerican forms are added some morphogenera considered as Cathaysian; such as Pelourdea sp. cf. P. halleiGu and Zhi 1974, (Plate 3.g and 3.k) and Discinites sp. cf. D. orientalisGu and Zhi 1974 (Plate 3.d). Finally, for the first time in the Permian of Saudi Arabia, vegetative and fertile forms of Glossopteris were discovered including Glossopteris formosa Feistmantel 1881 (Plate 3.b), Glossopteris decipiens Feistmantel 1879 (Plate 3.a), and Arberia sp. (Plate 3.c), which are typically Gondwanan elements. M. Stephenson (Stephenson and Filatoff, 2000) was surprised by the abundance of Protohaploxypinus spp. pollen grains found in the palynological assemblages from core samples of the Khuff Formation in Saudi Arabia. These pollen grains were also found in the Midhnab outcrops (cf. Plate 4), although the macrofloral remains of Glossopteris which produced them is missing. This paradox results from incomplete macrofloral sampling.
The first palynological data (work in progress) attests to the occurrence of monosaccates and bisaccates pollen grains (Protohaploxypinus microcorpus, P. amplus, P. hartii, P. bharawadjii, P. diagonalis etc., cf. Plate 4), spores (Calamospora breviradiata, Laevigatosporites vulgaris, Punctatisporites fongosus, Leiotriletes sp. etc.). The microfloral assemblage of the Midhnab Member is dominated by bisaccates pollen grains and that indicates a Late Permian age (Broutin et al., 2002). The microfloral assemblages are equivalent to those described in the Salt Range in Pakistan (Balme, 1970) and in Australia (Foster, 1979; Backhouse, 1991).
PALAEOBOTANICAL AND SEDIMENTOLOGICAL DATA: THE PALAEOENVIRONMENT
The coniferous plants common in the Euramerican realm represented dry-adapted vegetation, which for example flourished in the Zechstein Flora. These conifers grew in a warm and dry climate. In contrast to the latest Permian Euramerican plants, Cathaysian species could not endure without precipitation. As demonstrated by Fluteau et al. (2001), the ecological requirements of the Cathaysian flora could have been similar to those of the present-day rainforest. Therefore these Cathaysian plants required warm environments (temperatures exceeding 18°C for the coldest month) with relative or constant humidity (swampy environments, with a dry season reduced to less than four months (Fluteau et al., 2001)).
Because Early Permian Glossopterids occurred predominantly in high latitudes in Gondwana, some authors (for a long time) interpreted them as indicating cool temperate conditions for the whole Permian (Ziegler, 2001). However, their occurrences in the Arabian Peninsula during the Middle Permian (Gharif Formation, Oman, Broutin et al., 1995; Berthelin, 2002; Berthelin et al., 2003) and Late Permian (Midhnab Member), indicates their wider palaeogeographical distribution. Furthermore, their occurrence in Arabia implies they adapted to (or/and survived) various ecological and climatic conditions.
The succession of Glossopterids elements from Oman to Saudi Arabia shows that Glossopterids survived and better adapted to a warmer and dryer climate during the Late Permian, than the typical Gondwanan forms. Their association with Cathaysian plants in the Gharif and Khuff formations, provides evidence for their development and adaptation to warm environments, with relative or constant humidity (swampy environments). Their persistence until the Late Permian demonstrates that environmental conditions (climates and temperatures) where meso- to xerophytic plants (Otovicia, Voltzia) were growing.
The detailed sedimentological studies of each fossiliferous locality of the Midhnab Member (Jal Khartam, Wadi al Batin and Jal al Watah), and the composition of the macrofloral assemblages, can be used to reconstruct the depositional environments and their sequential evolution. The strata that contain the palaeofloras indicate humid, lagoonal and fluvio-lacustine palaeoenvironments, where abundant and specific vegetation grew in swamps and interdistributary bays, or on emerged sand bars, shores and embankments. The predominant palaeofloral elements are different in each locality: the composition of these assemblages, dominated by autochthonous to sub-autochthonous plants, was driven by the local palaeoenvironments.
Thus depositional environments of the assemblages vary (Figure 7).
(1) In the Jal al Watah alluvial system within the point bar environments, the Progymnospermophytes (Noeggerathiaceae: Discinites), and Gymnospermophytes (Glossopterids: Arberia, Glossopteris; Conifers: Pseudovoltzia, Culmitzschia) are found together, and are considered to be an allochthonous assemblage of drifted plant remains (point bar in Figure 7).
(2) In the Wadi al Batin sandy deltaic environments, the Cathaysian Sphenophytes (Lobatannularia) and Lycophytes grew. The Sphenophytes are the predominant palaeofloral elements at this locality and are clearly autochthonous or “sub-autochtonous” fossil plants. Their habitat was restricted to a fluvio-lacustrine environment where they usually colonised sandy embankments and shores (alluvial plains in Figure 7).
(3) In the Jal Khartam clayey swampy environment Cathaysian plants grew (e.g. the Pteridophytes such as Pecopteris chihliensis, the predominant autochthonous palaeofloral elements of this locality) in association to Sphenophytes (Gondwanan and Cathaysian, claystone in Figure 7) and drifted small fragments of Conifer shoots (Culmitzchia). This swampy environment was locally disturbed by stream channels reworking plants (trunks of Euramerican conifers).
The diversity and the composition of the palaeofloral associations were strongly controlled by the depositional environment. The various macrofloral associations depend on the palaeoenvironment in terms of sandy or clayey deposits. In spite of the lateral facies variations, both associations belong to the same stratigraphic level. We stress that without any sedimentological information on the palaeoenvironmental context, the biostratigraphic and palaeobotanical conclusions would have been different. Therefore, it is very important to take into account the sedimentary context for the biostratigraphic implications of the fossil plant assemblages.
PHYTOGEOGRAPHICAL SEQUENCE FOR THE TETHYSIAN OCCIDENTAL MARGIN (TETHYS TIME SCALE)
Based on the study of the mixed palaeoflora, a phytogeographical sequence for the Tethyan margin is proposed (correlation between the Gharif and Unayzah floras is still in progress):
At the Kubergandian-Murghabian (Wordian/Roadian) transition, the first Cathaysian and Euramerican incoming floral elements settled on the Arabian Platform; i.e. into the northern floral Gondwanan realm (Gharif Formation, Oman).
During the ?Kubergandian (Roadian) or/and Murghabian (Wordian), the floral Euramerican and Cathaysian elements developed or persisted under an increasing climatic aridity (Unayzah Formation, Saudi Arabia, work in progress). These two groups of plants grew in their own favourable biotopes (more or less drained slopes for Euramerican ones, flood plain and deltaic river for Cathaysian ones).
During the Dorashamian (Changhsingian), the Euramerican elements (more xerophytic) became increasingly predominant in Saudi Arabia (Midhnab palaeoflora) and in South China. However, the occurrence of Gondwanan forms (belonging to Glossopteris) and the persistence of Cathaysian plants – where the biotopes remained favourable for the growing of plants – adapted to a warm and humid climate.
The Midhnab Flora shows a different composition than the older Gharif Flora of Oman. The Midhnab Flora represents those plants that could have grown in Oman during the Dorashamian (Changhsingian), with increased aridity, had this area not been flooded. The mixed palaeofloras reflect locally the influence of global geodynamic events; namely the formation of the Pangea supercontinent in the Permian and its subsequent northward drift.
Because the relative position of Gondwana with respect to Laurassia remains uncertain, several Permian Pangea models have been proposed. Some of them strongly affect the interpretation of the Palaeo-Tethyan area; e.g. by the location of the Chinese blocks and palaeobiogeographic relationships with the southwestern Palaeo-Tethys Ocean. One of the most commonly adopted Pangea model is the “Pangea A” (Jurassic Wegenerian Pangea, Scotese and McKerrow, 1990; Scotese and Langford, 1995). Another model is the “Pangea B” (Irving, 1977; Besse, 1998) where South America faces North America (Figure 8). The “Pangea B” model is based on palaeomagnetic data.
The mixed Midhnab Flora of Saudi Arabia and the Gharif Flora of Oman resulted from Middle and Late Permian floral migrations in Arabia. Such mixed palaeofloras are useful tools for testing models of palaeogeographical reconstructions. Moreover, the discovery of Cathaysian and Gondwanan fossil plants, intermingled with Euramerican ones, strongly links the Midhnab Late Permian floral assemblage with the Gharif and Hazro floras.
The Gharif Flora (Wordian) of central Oman contains rich macrofloral elements with a mixture of Euramerican, Cathaysian and Gondwanan taxa (Broutin et al., 1995; Berthelin et al., 2003). Typical European forms are Otovicia hypnoides (Brongniart) Kerp et al., Sigillaria brardii Brongniart and Calamites gigas Brongniart and its fructification Metacalamostachys dumasii (Zeiller) Barthel. Cathaysian elements include Gigantopteris sp., Gigantonoclea lagrellii (Halle) Koidzumi, Catahysiopteris whitei (Halle) Koidzumi, Tingia sp., Tingiostachya sp., Lepidodendron acutangulata (Halle) Stockmans and Mathieu, and Sphenophyllum sino-coreanum Yabe. Gondwana taxa include six species of Glossopterids, e.g. Glossopteris occidentalis White, G. damudica Feistmantel, G. taeniopteroides Feistmantel, G. angustifolia Brongniart, G. clamarginata Anderson and Anderson, and G. browniana Brongniart. Several types of Glossopterid fructifications have also been found. Sphenophyllum speciosum (Royle) McClelland is another species that is widely distributed in Gondwana but that has also been reported from China and Korea. Comia is another remarkable genus from the Gharif Flora. It was originally described from the Petchora Basin (Angara), but is also known from Cathaysia (Huang, 1966; Gu and Zhi, 1974), and the eastern United States (from Kerp: personal communication, W.A. DiMichele, 2000). The silicified wood remains and the palynoflora also show a mixture of elements from different floral realms (Broutin et al., 1995; Berthelin et al., 2003).
The Hazro Flora has been described from the uppermost Permian of Hazro, Eastern Anatolia, Turkey (Archangelsky and Wagner, 1983; Wagner, 1962). The composition of this palaeoflora, which includes numerous sphenopsids and ferns, suggests a warm and humid environment. This palaeoflora contains a number of typical Cathaysian taxa (e.g. Lobatannularia and Gigantopteris), and Gondwanan elements such as Glossopterids (Glossopteris anatolicaArchangelsky and Wagner 1983) and Botrychiopsis. The Gondwanan component of the Hazro Flora has been regarded for a long time as controversial, because Glossopteris anatolica is the most representative of the Gondwanan flora in Hazro. Accordingly, the Glossopteris anatolica from Hazro is the most northerly known occurrence of this Gondwanan genus. The palaeogeographical position of the Hazro Flora was more or less equatorial (Ziegler et al., 1997). Moreover, the occurrence of Glossopterids on the Arabian Peninsula and in Turkey, during the Middle and Late Permian, implies extending their geographical distribution during the Permian. It also requires re-evaluating their ability to adapt and survive various ecological and climatic conditions.
The occurrence of such mixed palaeofloras (intermingled Gondwanan, Cathaysian and Euramerican elements) provides important constraints for the main changes of the vegetational cover, and its relationship with the geographic and climatic evolution throughout southern Pangea during Permian times. It shows that the Arabian Plate shifted northwards from about 50° south in the Late Carboniferous, to intertropical to subequatorial latitudes in the late Middle and Late Permian.
The Midhnab Flora represents a new control point that supports a migration route (Figure 8) for the Permian Cathaysian plants from South China to Turkey through the Arabian Peninsula (Broutin et al., 1995; Berthelin et al., 2003). Combined with Oman’s palaeontological (Crasquin-Soleau et al., 2001, 2006) and palaeobotanical data (Gharif Flora), the Midhnab Flora clearly supports a palaeogeographical model with reduced oceanic space for the Palaeo-Tethys. In conclusion, these data are in accordance with the Pangea B reconstruction.
This study is based on geological field data acquired in 1998 as part of the framework for geological mapping of central Saudi Arabia by the Saudi Arabian Deputy Ministry for Mineral Resources (DMMR, now Saudi Geological Survey) and the French Bureau de Recherches Géologiques et Minières (BRGM). Dr. M.A. Tawfiq (President of the Saudi Geological Survey), and the SGS and BRGM are acknowledged for supporting this work. Special thanks to P. Lebret and J. Roger (BRGM) for their help in logistic support and organisation of the field mission, and to S. Crasquin-Soleau and A. Lethiers for their help in drawing Figure 7. Improvement of the manuscript is due to review by M. Stephenson and M.I. Al-Husseini. Finally, the GeoArabia team is thanked for the preparation of the text and the final design of the paper.
ABOUT THE AUTHORS
Martine Berthelin obtained a PhD in 2002. Her thesis was based on the Permian Flora of Oman. She has since spent two years at University of Münster, working on Permian floras and microfloras from the Arabian Peninsula. One of Martine’s main aims is to understand the climates of the past and the kinetics of ancient vegetation, so as to provide a tool for testing palaeoclimate and palaeogeographic modeling. She uses biogeochemical studies for characterising fossil organic molecules and determining their biological origin in relation to plant remains of fossiliferous beds.
Jean Broutin is Professor of Palaeobotany and Palaeoecology at the University of Paris, and is a specialist of Late Paleozoic micro and macroflora. His field of research extends over both the northern and southern margins of the Tethys Ocean, from Europe to the Urals, and from Brazil to Morocco and Oman. Jean has developed associations between palaeobotany and palaeoenvironments, so that analysis of the dynamic distribution of the plant cover can be used to determine palaeoclimatic and biogeographic changes through time. In this respect, palaeobotanical data are used for testing global geodynamic and palaeoclimatic modelling.
Denis Vaslet is Head of the Geology and Geoinformation Division at the Bureau de Recherches Géologiques et Minières (BRGM), the French Geological Survey. He has 30 years of experience in the geology of the Middle East. From 1977 to 1979 Denis was involved in geological mapping and phosphate prospecting in Iran for the Geological Survey of Iran and the National Iranian Oil Company. From 1979 to 1991, he was responsible for the Cover Rocks mapping program in Saudi Arabia for the Saudi Arabian Deputy Ministry for Mineral Resources. Denis has been involved in the complete lithostratigraphic revision of the Phanerozoic rocks of central Saudi Arabia, for which he received his Doctorate of Sciences from the University of Paris in 1987. He is currently in charge of geological and geophysical mapping both in France and overseas, and for the production and distribution of digital geological information at BRGM. Denis remains involved in several research projects in the sedimentary geology and stratigraphy fields within the Arabian Peninsula.
Yves-Michel Le Nindre has more than 10 years of experience in the geological mapping of the Phanerozoic rocks of Saudi Arabia. He received his Doctorate of Sciences from the University of Paris in 1987. Yves-Michel’s dissertation was on the sedimentation and geodynamics of Central Arabia from the Permian to the Cretaceous. He is currently working with the Bureau de Recherches Géologiques et Minières on sedimentary basin analysis and modelling, particularly in hydrogeology, and is also involved in present-day littoral modelling.
Mohammed Halawani is a Geologist in the Saudi Geological Survey (SGS), which is part of the Saudi Arabian Ministry of Petroleum and Mineral Resources. He received a BSc from the Faculty of Earth Sciences at King Abdulaziz University, Jeddah in 1981. After graduating he worked on various projects in the Arabian Shield. Since 1990, he has been involved in the mapping of Phanerozoic rocks, especially in the Palaeozoic of northern and northwestern Saudi Arabia. Mohammed is presently working on the Palaeozoic stratigraphy of Saudi Arabia.