Journal of African Earth Sciences 95 (2014) 168–174

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Journal of African Earth Sciences

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Wood remains from the Late Triassic (Carnian) of Jordanand their paleoenvironmental implications

http://dx.doi.org/10.1016/j.jafrearsci.2014.03.0111464-343X/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: Senckenberg Forschungsinstitut und Naturmuseum,Senckenberganlage 25, 60325 Frankfurt am Main, Germany. Tel.: +4969970751611.

E-mail address: dieter.uhl@senckenberg.de (D. Uhl).

Abdalla M.B. Abu Hamad a, André Jasper b, Dieter Uhl c,d,⇑a Department of Applied and Environmental Geology, The University of Jordan, Amman 11942, Jordanb Programa de Pós-Graduação em Ambiente e Desenvolvimento da UNIVATES (PPGAD/UNIVATES), Centro Universitário Univates, Rua Avelino Tallini, 171 – CEP 95.900-000,Lajeado, RS, Brazilc Senckenberg Forschungsinstitut und Naturmuseum, Senckenberganlage 25, 60325 Frankfurt am Main, Germanyd Senckenberg Center for Human Evolution and Palaeoenvironment, Institut für Geowissenschaften, Universität Tübingen, Sigwartstraße 10, 72076 Tübingen, Germany

a r t i c l e i n f o

Article history:Received 18 December 2013Received in revised form 11 March 2014Accepted 13 March 2014Available online 24 March 2014

Keywords:TriassicCarnianJordanFossil woodCharcoalPaleo-wildfire

a b s t r a c t

During field work in the Triassic of Jordan fossil wood remains have been discovered at five horizons (S-1AR–S-5AR) of the Late Triassic (Carnian) Abu Ruweis Formation in NW Jordan. In most horizons woodremains are too badly preserved to allow for a detailed xylotomic investigation. Only two horizons pro-vided material which exhibited anatomical details: (1) in horizon S-1AR we found rare and rather smallfragments of woody charcoal exhibiting cellular details (representing the first macroscopic evidence ofpaleo-wildfires from the Late Triassic of the Middle East), and (2) in horizon S-5AR surfaces of partly com-pressed (gagatized) and partly permineralized wood fragments exhibited anatomical details that could beinvestigated by means of scanning electron microscopy. All wood remains that allow for a detailed inves-tigation show features typical of gymnosperms, but at the moment nothing can be said about a more spe-cific taxonomic affinity of most of the woods, although wood from horizon S-5AR exhibits characteristicsof protopinoid wood. Our data provide evidence that gymnospermous woody vegetation cover hasexisted in the source areas of the sediments deposited in the Abu Ruweis Formation in Jordan and thatthis woody vegetation occasionally experienced wildfires. This, together with lithological data, providesevidence for a seasonally dry (maybe even arid) climate during deposition of the Abu Ruweis Formation.On a larger scale our findings contribute to the very scarce current knowledge about Late Triassic wild-fires on the entire continent Gondwana, from where so far only three records of macro-charcoals, asundisputed evidence of paleo-wildfires, have been published from this period.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction Abu Hamad, 2004; Dill et al., 2012; Bandel and Abu Hamad, 2013;

Although a number of studies have dealt with the palynology ofTriassic sediments from the Middle East region (e.g. Cirilli andEshet, 1991; Abu Hamad, 2004; Buratti and Cirilli, 2007), not muchis currently known about macroscopic plant fossils from this periodand region. So far several authors briefly mentioned the occurrenceof unspecified fossil plant remains and especially ‘‘driftwood’’ (e.g.Bandel and Khoury, 1981; Abu Hamad, 2004; Makhlouf andEl-Haddad, 2006) as well as charcoal (Abu Hamad et al., 2013) insediments of the Middle Triassic (Anisian) Mukheiris Formation inJordan. Also ‘‘driftwood’’ and fern remains, provisionally assignedto the genus Phlebopteris, were mentioned (but not figured) forthe Late Triassic (Carnian) Abu Ruweis Formation in Jordan (e.g.

Bandel and Salameh, 2013) without providing any further informa-tion about this material. Additionally Dill et al. (2012) mentionedthe occurrence of isolated xylem fragments (tracheids?), as wellas cuticles within individual coal layers within massive gypsumbeds from this formation. To improve the scarce knowledge aboutthe Triassic vegetation of Jordan and adjacent areas, as well as therather scarce knowledge about Triassic paleo-wildfires on the en-tire continent of Gondwana, we provide a first detailed descriptionand paleoenvironmental interpretation of fossil wood remains,including fossil charcoal as direct evidence for paleo-wildfires, fromthe Carnian Abu Ruweis Formation.

2. Geological and stratigraphical setting

The material investigated for this study comes from five differ-ent horizons from the Abu Ruweis Formation (Carnian) of Jordan.The geographic position of the sampling site is given in Fig. 1;

Fig. 2. Photograph of the so called eastern quarry in the Zarqa river area showingthe typical sedimentary succession of the Carnian Abu Ruweis Formation. Thelength of the arrow equals approx. 10 m. All wood samples come from horizonsabove the arrow.

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the stratigraphic positions of the different wood bearing horizons(3 siltstone and 2 marly limestone) sampled for the present studyare indicated in the lithological log presented in Fig. 3.

The Abu Ruweis Formation was introduced by Bandel and Kho-ury (1981) to describe the youngest Triassic outcrop in Jordan. Theformation crops out only at the core of an anticline within the wes-tern reaches of the Zarqa River (Fig. 1). The total thickness of theformation exposed in Wadi Zarqa is about 42 m as measured inthe so called eastern quarry (Figs. 2 and 3). It consists predomi-nantly of massive gypsum beds with small intercalated coalylayers; however, interbeds of black shale and dolomite are notuncommon. The formation is unconformably overlain by a redlateritic soil of an assumed Jurassic age (Makhlouf et al., 1996).

The Abu Ruweis Formation is of Carnian age (Blake, 1936; Ban-del and Khoury, 1981; Druckman et al., 1982; Keegan et al., 1987).Earlier palynological studies assigned a late Cordevolian–Julian(latest early Carnian–middle Carnian) age to the upper part ofthe formation exposed in the so called eastern quarry (Abu Hamad,2004). Based on a limited number of samples and palynomorphsDill et al. (2012) assigned a Tuvalian age (uppermost Carnian) tothe same part of the formation. This contradiction cannot beresolved here, but a critical reinterpretation of the data presentedby Abu Hamad (2004) does not contradict an assignment of theformation to the uppermost Carnian (or even early Norian)(C. Heunisch, Hannover, pers. comm. 2013).

The depositional environment of the outcrop is interpreted asshallow marine shelves interchanging with intertidal flats andsupratidal sabkhas (Makhlouf and El-Haddad, 2006). The sameauthors interpreted the climate as relatively stable arid, althoughthe occasional occurrence of thin coal beds within the evaporites(Dill et al., 2012) may point to occasional phases which elevatedhumidity, at least in the hinterland.

Fig. 1. Map of Jordan showing the geographic position of the sampling locality atthe Zarqa River.

Fig. 3. Columnar section of the Carnian Abu Ruweis Formation in the Zarqa riverarea. Arrows point to the horizons containing macroscopic wood remains.

3. Methods

Sediment samples were collected during field work in the socalled eastern quarry during February 2011. Wood samples wereextracted mechanically from the sediment with the aid of

Table 1Published records of macrocharcoal and inertinites in coals as evidence of palaeowildfires during the Carnian (modified from Abu Hamad et al., 2012). Evidence from Gondwana ishighlighted with light-grey background.

Macrocharcoal

Locality/area Country Age References

Franconia Germany Carnian Kelber (2007)

Allan Hills Antarctica (Ladinian ?) Carnian –Norian ? Kumar et al. (2011)

Ischigualasto Basin Argentina Carnian Colombi and Parrish (2008)

Prince Charles Mountains Antarctica Carnian ? Cantrill et al. (1995)

Petrified Forest National

Monument, Arizona

USA Carnian–Norian Jones et al. (2002)

Inertinites

Locality/area Country Age References

Mungaroo Fm Australia Ladinian–Norian Cook et al. (1985)

Ipswich Coal M. Australia Carnian Cook and Taylor (1963); Chern (2004)

Tasmania Australia Carnian Bacon (1986a, 1986b)

Lunzer Coal/Lunzer Decke Austria Carnian Sachsenhofer (1987)

Wayaobao Fm China Carnian Yang et al. (1996)

Exmouth Plateau Australia Late Triassic Cook et al. (1985)

Sichuan Basin China Late Triassic Wang (2009)

Jiangxi China Late Triassic Querol et al. (2001)

(See above-mentioned references for further information.)

Fig. 4. Permineralized wood fragments from sample S5-AR from the Carnian AbuRuweis Formation. Scale bar = 2 cm.

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preparation needles and tweezers under a binocular microscope inthe laboratory. Table 1 Silty sediment from horizon S-1AR, alsocontaining layers of isolated leaf fragments and dispersed cuticles,were soaked in water which led to the disintegration of the sedi-ment within a few hours. Woody fragments were extractedmechanically from the residue after repeated careful washingand decanting with water.

Due to the very fragile nature of these particular specimens(which turned out to represent charcoal, see below), these couldnot be cleaned further with acids to remove adhering mineral re-mains, as even very careful treatment has led to the total fragmen-tation of this material into even smaller fragments (cuticles thathave been isolated from horizon S-1AR are currently under investi-

gation and these results will be published in a forthcoming study).Wood samples that showed evidence of anatomical preservationunder the binocular microscope were mounted on standard stubswith LeitC (Plano, Münster, Germany), and subsequently examinedwith the aid of a JEOL JSM 6490 LV Scanning Electron Microscope(SEM; accelerator current 15 or 20 kV respectively) at the Sencken-berg Forschungsinstitut und Naturmuseum Frankfurt (Germany).

Unfortunately it has not been possible so far to get any informationfrom thin sections or polished surfaces of the wood remains thatcould be used for anatomical studies in transmitted or reflected light.

4. Results and discussion

Wood remains occur in several horizons of the Carnian Abu Ru-weis Formation in a variety of preservational states. In some hori-zons there are only highly compressed remains of woody axes, onlya few centimetres in diameter that show no anatomical details,whereas in other horizons wood remain occur that have been com-pressed and coalified or that have been (partly) permineralizedwith unidentified minerals. Especially (partly) permineralizedspecimens are usually relatively large with up to several centime-tres in diameter and up to several decimetres in length. The mate-rial is rather hard and lumina of tracheids are filled with minerals(cf. Fig. 6B). The material fractures irregularly in smaller fragmentsalong preformed cracks, which follow zones where wood structureseems to have been compressed (Fig. 4). When broken outsidethese preformed cracks, specimens fracture conchoidally.

During our analysis it turned out that only wood material fromhorizon S-1AR and S-5AR were well enough preserved to allow forthe investigation of anatomical details by means of SEM.

4.1. Horizon S-1AR

4.1.1. PreservationWood fragments are scattered within horizon S-1AR, about

10–12 fragments occur per dm2 on the surface of hand-specimens.

Fig. 5. SEM images of charcoal from the Carnian Abu Ruweis Formation. (A) Overviewof shattered tracheids in tangential view, with wood ray and fragment of a radial (?)tracheid wall with uniseriate (?) bordered pits; (B) enlargement of A) showing detailsof bordered pits and homogenized cell walls (arrow); (C) shattered tracheid walls,showing uniseriate (?) bordered pits and homogenized cell walls (arrow).

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These fragments are compressed due to sediment compaction.They are relatively small, ranging from approximately 1 to 5 mmin diameter, with generally well rounded edges, pointing to trans-portation prior to sedimentation (Nichols et al., 2000). Due to thesmall size and mechanical instability only 4 specimens could beinvestigated by means of SEM.

The following characters indicative of charcoal (Scott, 2010),can be observed in this material: black streak, silky lustre, splinteryappearance, preservation of anatomical details (Fig. 5) and homog-enized cell walls under the SEM (Fig. 5B and C). Based on this, thematerial can reliably be identified as fossil charcoal or fusain (Scott,1989, 2000, 2010).

4.1.2. Description and taxonomic affinityThe charcoal consists of pycnoxylic wood, with tracheids ap-

prox. 20 lm wide, exhibiting (most likely) uniseriate pitting on

the (radial?) walls (Fig. 5B and C). Pits seem to be contiguous, withelliptical apertures (Fig. 5C). Wood rays are unicellular, only 3–4cells high (Fig. 5A). Cross-field pitting as well as growth rings couldnot be observed due to the fragmentary nature of the material.

The observed anatomical characters indicate a gymnospermousaffinity of the material, but a more specific identification is not pos-sible due to the very fragmentary nature of the specimens.Anatomical characters of all specimens (5) investigated are veryuniform and thus it is not possible to differentiate between differ-ent wood types, which may belong to different taxa or would comefrom different parts/growth stages of a single taxon.

4.2. Horizon S-5AR

4.2.1. PreservationPartly compressed (gagatized) and partly permineralized wood

remains are abundant in horizon S-5AR (Fig. 4). This material is blackwith a slight silky shine and has a blackish–brownish streak. In somespecimens fairly good preservation of anatomical details (Figs. 6 and7) can be seen under the SEM in parts of this material on fracturedsurfaces. Cell walls clearly exhibit a three-layered composition andare not homogenized (e.g. Fig. 7D), as seen in charcoal.

4.2.2. Description and taxonomic affinityPycnoxylic wood (Figs. 6 and 7), with tracheids, 15–20 lm wide,

with uniseriate pitting on the (radial?) walls (Figs. 6D and 7A–C).Pits are mostly contiguous but sometimes separated by small gaps(Fig. 7C), with round to elliptical apertures (Fig. 7A–C). Wood rayspresent, cross-field pitting seems to be araucarioid or cuppressoid,with 3–5 pits per cross-field (Fig. 6C). Growth rings could not beobserved.

The observed anatomical characters also indicate a gymno-sperm affinity of the material from this horizon, and an unequivo-cal specific identification is not possible due to the fragmentarynature and the particular preservation of the specimens. The occur-rence of contiguous pits on radial tracheid walls together withoccasional small gaps between pits points to a protopinoid affinityof this wood (e.g. Philippe and Bamford, 2008). Anatomical charac-ters of all specimens investigated are very uniform and thus it isnot possible to differentiate between different wood types, whichmay belong to different taxa or which could originate from differ-ent parts/growth stages of a single taxon.

5. Paleoecological interpretation

So far detailed macropaleobotanical data are lacking for the LateTriassic for the entire Middle East region, although unspecifiedoccurrences of plant remains (i.e. the fern Phlebopteris) and espe-cially driftwood have occasionally been mentioned in the literature(e.g. Bandel and Khoury, 1981; Abu Hamad, 2004; Makhlouf andEl-Haddad, 2006; Bandel and Abu Hamad, 2013).

Our data demonstrate that during the Carnian woody vegeta-tion existed somewhere in the source region of the sedimentsdeposited near the eastern rim of the Dead Sea in Jordan. As forthe previously reported charcoal from the Anisian Mukheiris For-mation of Jordan (Abu Hamad et al., 2013) nothing can be saidabout the type of vegetation that existed in this region at themoment based on these wood remains, although woody gymno-sperms have been a component of this vegetation. The abundanceof pollen belonging to the Circumpolles-group, which wereproduced by cheirolepidiacean conifers, in sediments from theAbu Ruweis Formation (Abu Hamad, 2004) as well as the Carnianof southern Israel (Eshet, 1990), also demonstrates thatgymnosperms (i.e. conifers) were an important component of theCarnian floras in this region.

Fig. 6. SEM images of a broken surface of permineralized wood from sample S5-AR. (A) Overview of secondary wood in radial view; (B) tracheids with (partly broken) mineralinfillings; (C) tracheids with (partly broken) mineral infillings and remains of cross-field pitting (arrow) in radial view; (D) detail of uniseriate pitting on the surface of amineral cast.

Fig. 7. SEM images of permineralized wood from sample S5-AR. (A) Tracheids in tangential view; (B) detail of uniseriate pitting; (C) uniseriate pits with ‘‘shades’’ of the tori,pits separated by small gaps; (D) cell walls showing typical layered composition (arrow).

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Additionally the material from horizon S-1AR can be identifiedas fossil charcoal and thus represents the direct evidence for paleo-wildfire during deposition of the sediments of the Abu Ruweis For-mation. Recently Dill et al. (2012) isolated pyrogenic polycyclicaromatic hydrocarbons (PAHs) from the same outcrop, alreadypointing to the possible occurrence of wildfires. However, as thematerial used by these authors for geochemical analysis came fromsurface samples these authors could not exclude anthropogeniccontamination due to burnt fuels. Our material has definitely beenisolated from undisturbed sediments, thus it represents the firstunequivocal evidence for the occurrence of wildfires in the region(i.e. the entire Middle East region) during the Carnian, supportingearlier assumptions of Dill et al. (2012).

Due to the transport of the charcoal prior to sedimentation it isclear that we have to consider taphonomic biases, including sortingand filtering (e.g. Nichols et al., 2000). Therefore nothing can be sta-ted at the moment about the type of vegetation that experiencedfires, although woody gymnosperms (the source plants of the char-coal investigated here) must have been a component of these eco-system(s). The occurrence of wildfire during the deposition of theAbu Ruweis Formation support previous interpretations of a gener-ally arid climate (Makhlouf and El-Haddad, 2006), with more humidconditions after deposition of the main evaporite (i.e. gypsum) beds.

So far, only three occurrences of macroscopic charcoal as anindicator of paleo-wildfires have been published from the Carnianof Gondwana (Table 1). Interestingly these three records represent

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also the only records of Gondwanan macrocharcoal for the entireTriassic (cf. Abu Hamad et al., 2012). Additional evidence for Car-nian wildfires comes from inertinites, a group of coal maceralswith mainly pyrogenic origin (Scott and Glasspool, 2007; Glasspooland Scott, 2013), from a number of coals, mostly from Gondwana(Table 1). Although some inertinites may have originated throughother oxidative and/or biochemical processes than fire (cf. O’Keefeet al., 2013) we use the presence of inertinites as a proxy for wild-fires, following evidence that links the origin of many macerals ofthe inertinite group (i.e. fusinite, semifusinite and even some fun-ginites) to a pyrogenic origin (Scott and Glasspool, 2007; Glasspooland Scott, 2013).

Not only for Gondwana, but also on a global scale, only a rathersmall number of records of Carnian wildfires have been publishedso far (Table 1; Abu Hamad et al., 2012). However, for several ofthese occurrences the exact stratigraphic position is not knownand it is not clear, whether the records really come from the Car-nian or slightly older or younger upper Triassic strata (cf. Table 1).Even if we assume that these records can be counted as Carnian, itis noteworthy that most of these records come from localities lo-cated on Gondwana (Australia, Antarctica, Argentina), as well asfrom China (Table 1). All of these records come from comparablyhigh latitudes (i.e. north and south of the tropical zone), whereasthe new evidence from Jordan represents the first record of char-coal from the semi-arid to arid tropics of Northern Gondwana.

Based on this scarce data-set it is difficult to provide sound inter-pretations concerning the occurrence of fires on a larger regional oreven global scale during the Carnian, as global and regional climatewas not uniform throughout the Carnian. For example, although amore or less arid climate prevailed in large parts of northernPangaea during this period, i.e. in the Germanic basin and Tethysarea, there was at least one significant humid pulse in the middleCarnian (sometimes called the Carnian pluvial event), that can berecognized at least in the Germanic basin and the Tethys realm(e.g. Kozur and Bachmann, 2010 and citations therein). However,this pluvial event is probably older than the sediments from whichthe wood remains described here originate and thus it is not possi-ble to connect the existence of woody vegetation after deposition ofthe Abu Ruweis evaporates to this climatic oscillation.

On a global scale most records of Late Triassic wildfires, espe-cially records of macrochacoal, come from the Northern hemisphere(cf. Abu Hamad et al., 2012), thus the Carnian is somewhat unusualin this respect. As fire is a global phenomenon it should be expectedthat evidence for fires can be found more or less equally distributedon all hemispheres, if the basic prerequisites for fires (e.g. occur-rence of fuel [biomass], lightning strikes as ignition source, a moreor less pronounced dry season and enough atmospheric oxygen)are given. However, considering the smaller number of studies onfossil macro-charcoal from the Paleozoic and Mesozoic of Gondw-ana compared to studies presenting evidence for wildfires on thenorthern hemisphere (e.g. Abu Hamad et al., 2012; Uhl et al.,2012; Jasper et al., 2013; Brown et al., 2012) it is possible that thegeneral scarcity of Triassic (and the relative abundance of Carnian)charcoal from Gondwana has to be explained to a large extent by thisfactor as well as (other) taphonomic factors.

6. Conclusions

Based on our investigations of wood remains from the Late Tri-assic (Carnian) Abu Ruweis Formation in Jordan we can summarizethe following conclusions:

� Some kind of vegetation cover, including (arborescent) gymno-sperms (some of which show a protopinoid affinity), must haveexisted in the semi-arid to arid environments of NorthernGondwana during the deposition of the Abu Ruweis Formation.

� Our data represent the first paleobotanical evidence of paleo-wildfires for the Late Triassic of the entire Middle-East regionas well as the paleo-tropics of Northern Gondwana.� The occurrence of wildfires during the deposition of the Abu

Ruweis Formation support previous interpretations of a gener-ally arid climate, with more humid conditions after depositionof the massive evaporite beds which dominate this formation.

Acknowledgments

We thank Claudia Franz, Senckenberg Forschungsinstitut undNaturmuseum Frankfurt am Main/Germany, for technical assis-tance with SEM facilities, Dr. Carmen Heunisch, NLFB Hannover/Germany, for comments on the palynostratigraphy of the Abu Ru-weis Formation, as well as the University of Jordan, Amman/Jordan,for logistic support during field work; DU acknowledges funding bythe Deutsche Forschungsgemeinschaft/Germany (UH 122/3-1, UH122/5-1) that enabled parts of the fieldwork in Jordan. Last butnot least we thank two anonymous reviewers for their constructivecomments, that helped to improve the manuscript.

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