Typical Triassic Gondwanan Floral Elements in the Upper Permian Of
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Typical Triassic Gondwanan ¯oral elements in the Upper Permian of the paleotropics Hans Kerp Forschungsstelle fuÈr PalaÈobotanik, UniversitaÈt MuÈnster, Hindenburgplatz 57, 48143 MuÈnster, Abdalla Abu Hamad* Germany Birgit VoÈrding Klaus Bandel Geologisch-PalaÈontologisches Institut, UniversitaÈt Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany ABSTRACT from a nearby locality in the upper part of the Permian ¯oras of the Middle East often show a mixture of Euramerican, Cathaysian, Um Irna Formation contains several typical and Gondwanan elements. We report several species of Dicroidium, a seed fern typical Late Permian Cathaysian taxa, including Lob- for the Triassic of Gondwana, from the Upper Permian of the Dead Sea region. This is atannularia and Gigantonoclea (Mustafa, the earliest unequivocal record and the most northerly occurrence of this genus, suggesting 2003). The Ma'in Formation, which overlies that it may have evolved during the Permian in the paleotropics. With the decline and the Um Irna Formation with an erosional con- eventual extinction of the typical Permian Glossopteris ¯ora, Dicroidium may have mi- tact, yielded a low-diversity micro¯ora, dom- grated southward. As the climate ameliorated in the Triassic, Dicroidium could have inated by lycopsid spores (Endosporites pap- spread farther, eventually colonizing all of Gondwana, where it became one of the dom- illatus, Densoisporites nejburgii) and inant ¯oral elements. acritarchs (Veryhachium sp.), an assemblage typical for the Lower Triassic (Eshet, 1990; Keywords: ¯oral provinces, Permian-Triassic transition, migration, pteridosperms. Looy et al., 1999). INTRODUCTION channel ®lls of a distal braided river system THE UM IRNA FLORA Paleozoic ¯oral provincialization began in (Makhlouf et al., 1991). Mummi®ed leaves with excellently pre- the Early Carboniferous and culminated in the The rich and well-preserved micro¯ora is served cuticles are abundant in the lower part Permian (Wnuk, 1996). At the end of the dominated by Falcisporites, occurring in large of the Um Irna Formation, including up to 30 Permian, locally, 95% of the peat-forming clusters and as individual pollen grains. Fal- cm long, almost complete, bifurcated fronds. plant species became extinct (Michaelsen, cisporites is known from the Upper Permian, Based on gross morphology and cuticle struc- 2002), although it also has been argued that but percentages of up to 50% are normally ture, two species of Dicroidium can readily be the scale and timing of effects of the end- only found in Triassic rocks. This pollen type distinguished; bulk macerations have yielded Permian biotic crisis varied markedly between has been attributed to Dicroidium (Balme, at least three other possible Dicroidium spe- different regions (Rees, 2002). Several groups 1995), the dominant constituent of the Wadi cies. Although the generic assignment of the became extinct, whereas others suffered a Himara macro¯ora. In addition, nearly sixty plant remains is clear, they cannot be attribut- strong decline. Therefore, the discovery of a other palynomorph taxa have been identi®ed ed to previously described species of Dicro- Late Permian ¯ora from the Middle East with that clearly indicate a Late Permian age, in- idium. Apart from Dicroidium, the plant- foliage assignable to the Gondwanan seed fern cluding Lueckisporites virkkiae, Klausipollen- bearing beds contain a few unidenti®able fern genus Dicroidium, which is generally consid- ites schaubergeri, Nuskoisporites dulhuntyi, fragments and relatively large amounts of ered to be restricted to the Triassic (Anderson and Jugasporites delasaucei. Another ¯ora charcoal. et al., 1999), is most remarkable. This is not only the earliest record of Dicroidium, but also the most northerly occurrence of a genus that became highly successful in Gondwana in the Triassic. GEOLOGICAL SETTING AND AGE Plant remains were collected from the Um Irna Formation in Wadi Himara, Dead Sea re- gion, Jordan (Fig. 1). This 67 m thick clastic sequence unconformably overlies the Cambri- an Um Ishrin Formation (Bandel and Khoury, 1981) and consists of a series of predomi- nantly sandy ®ning-upward sequences with paleosols with ferruginous pisoliths. In the lower part of the formation, grayish-brownish siltstone and claystone lenses, with abundant plant material, are interpreted as abandoned *Current address: The University of Jordan, De- partment of Environmental and Applied Geology, Figure 1. A: Geographical position of Wadi Himara locality (arrow). B: Stratigraphic subdi- Amman 11942, Jordan; E-mail: Abdalla80@ vision of the Upper Permian±Lower Triassic in Dead Sea region with a schematic section hotmail.com. of lower part of the Um Irna Formation and position of the plant-bearing horizon (arrow). q 2006 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. Geology; April 2006; v. 34; no. 4; p. 265±268; doi: 10.1130/G22187.1; 6 ®gures. 265 Figure 3. Stratigraphic ranges of the genus Dicroidium in the Middle East and various parts of Gondwana. 1ÐJordan; 2ÐAustralia and New Zealand; 3ÐAntarctica; 4ÐIndia; 5ÐSouth America; 6Ðsouthern Africa. ing of Cathaysian taxa, is known from the Up- Ï Figure 2. A±C: Dicroidium sp. A. A: Frond showing typical bifurcation (arrow). B: Cuticle of per Permian of western Iraq (CtyrokyÂ, 1973). a pinna. C: Cuticle of lower pinnule surface stomata with ring of equally strongly cutinized The ¯ora of the Unayzah Member (Khuff For- subsidiary cells. D±F: Dicroidium sp. B. D: Frond showing typical bifurcation (arrow). E: mation, early Late Permian) of Qasim Prov- Pinna apex. F: Cuticle of lower pinnule surface showing stomata with weakly cutinized ince, Saudi Arabia, is dominated by pecopter- lateral subsidiary cells. ids and sphenopsids, suggesting a warm and humid climate. Several taxa, e.g., Lobatan- The two species represented by larger spec- cal representatives of the genus (D. narrabee- nularia and a gigantopterid, are typically Ca- imens, here informally named Dicroidium sp. nense, D. zuberi) are known from the thaysian. The overlying Khuff Member yield- A and Dicroidium sp. B, have bifurcated, bi- Narrabeen Group and the Newport Formation ed taeniopterid leaves and Euramerican-type pinnate fronds. Dicroidium sp. A (Figs. 2A± (lower Olenekian) of eastern Australia (Retal- conifers (El-Khayal and Wagner, 1985). An- 2C) has densely spaced, tongue-shaped pin- lack, 1977), whereas the last occurrences are other mixed ¯ora from the Upper Permian of nules with broadly tongue-shaped terminal in the Rhaetian (Fig. 3). Dicroidium is a typ- Hazro, southeast Turkey (Wagner, 1962; Ar- pinnules, whereas Dicroidium sp. B (Figs. ical Gondwanan taxon, occurring at paleola- changelsky and Wagner, 1983), predominantly 2D±2F) has narrower, triangular pinnules and titudes above 358 S in southern Africa, Aus- consisting of sphenopsids and ferns, includes narrow, acute terminal pinnae. The two spe- tralia, New Zealand, India, Argentina, Chile, a number of typical Cathaysian taxa, e.g., cies are easily distinguishable by their sto- southern Brazil, and the Antarctic (Fig. 4). Lobatannularia and Gigantopteris, but also mata. Dicroidium sp. A has stomata with a The material reported here thus represents Gondwanan elements such as Glossopteris ring of four to seven equally strongly cutin- both the earliest and the most northern occur- and Botrychiopsis. Middle and Late Permian ized subsidiary cells, whereas Dicroidium sp. rence of a genus that is traditionally regarded ¯oras from the Middle East thus often show a B. usually has stomata with four subsidiary as a typical Triassic Gondwanan element. mixture of elements from several ¯oral prov- cells, of which the lateral ones are weakly cu- inces. Not only Cathaysian elements reached tinized (Figs. 2C and 2F). In both species, cu- MIDDLE AND LATE PERMIAN the limits of their geographical distribution, ticles are of medium thickness and stomata are FLORAS OF THE MIDDLE EAST but also Gondwanan elements such as not sunken. In the Late Permian, the Arabian plate was glossopterids. The absence of typical wetland plants and connected to the African plate, and the Dead In contrast, Late Permian ¯oras from the the low percentage of spores (,20% of the Sea region was a lowland area located in the southern Alps (Italy), which are ;258 north total assemblage) are indicative of extrabasin- equatorial belt at ;158 S (Scotese and Lang- of the paleoequator (Scotese, 2002; Ziegler et al vegetation sensu Pfefferkorn (1980). The li- ford, 1995; Ziegler et al., 1997). Comparisons thology points to a tropical summer wet cli- with other Permian ¯oras from the Middle al., 1997), are dominated by conifers, with mate; soils with ferruginous pisoliths are East (Fig. 5) are of special interest with regard peltasperms and ginkgophytes as additional typically formed in hot and humid climates to paleophytogeography. elements (Visscher et al., 2001). Plants display with a high annual rainfall and a short dry In the Middle Permian (Wordian) Gharif xeromorphic features, i.e., thick cuticles, often season (Driessen et al., 2001). Formation of central Oman, Euramerican taxa with prominent papillae, sunken stomata, and (e.g., the conifer Otovicia hypnoides) are as- strongly cutinized subsidiary cells; leaves are STRATIGRAPHIC AND GEOGRAPHIC sociated with Cathaysian elements such as Gi- often thick and ¯eshy. Typical conifer prepol- DISTRIBUTION OF DICROIDIUM gantopteris and Tingia, and with Gondwanan len known from the Upper