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IAWA Journal, Vol. 27 (2), 2006: 137–143

CRETACEOUS WOODS FROM THE FARAFRA OASIS, EGYPT

Marwah M. Kamal El-Din1, E.A Wheeler2 and J.A. Bartlett2

SUMMARY There are fewer than 200 angiosperm wood records for the whole of the Cre- taceous; the majority are from North America, Europe, and Asia. This paper describes two petrified woods from the Late Cretaceous Hefhuf Formation, Farafra Oasis, Egypt, a locality near the Campanian equator. Affinities of these two wood types cannot be determined with certainty. One wood has characteristics seen in the Lauraceae, Moraceae, and Anacardiaceae; the other wood has exclusively uniseriate homocellular rays, scalariform perforation plates, rare axial parenchyma, and alternate-opposite intervessel pitting. Key words: Egypt, Farafra, Late Cretaceous, petrified wood, Campanian, wood anatomy, paleobotany.

INTRODUCTION This is the second paper on petrified dicot wood from the Late Cretaceous Hefhuf Formation exposed at the Farafra Oasis, Egypt. In the first paper, three specimens were described and assigned to Celastrinoxylon celastroides (Schenk) Kräusel, another two specimens were described and assigned to Ficoxylon cretaceum Schenk (Kamal El-Din 2003). Schenkʼs (1883) and Kräuselʼs (1939) material came from sediments belonging to the upper member of the Nubia Formation (Queseir Clastic member), Egypt, which is Santonian–Campanian. Few Cretaceous woods have been described from equato- rial regions (Wheeler & Baas 1991). Kamal El-Din (2003) determined only 10 types of dicot woods had been reported for the whole of the Egyptian Cretaceous. The two woods described in this paper differ from previously described Egyptian Cretaceous woods and so expand our knowledge of the types of Late Cretaceous woody plants from low latitudes.

STUDY AREA

The study area lies in the Farafra Oasis (Fig. 1), in the Western Desert of Egypt, west of Asyut, between longitudes 27° 10' E and 28° 50' E and latitudes 26° 25' N and 27° 40' N. The lithostratigraphic section exposed in the study area (Geological Survey of Egypt 1982) is as follows: Farafra Limestone (Lower Eocene): White, hard, thick bedded, well developed at the top of El Qus Abo-Said plateau. Thickness 50 m. Esna Shale (Lower Eocene): Greenish-gray to green, including white marl bands at the top; makes the middle part of the scarp face of the El Qus Abo-Said and twisted northward to form the upstream of Bir El-Obeiyid. Thickness 20 m.

1) Department of Botany, Faculty of Science, Ain Shams University, Cairo, Egypt. 2) Department of Wood and Paper Science, North Carolina State University, Raleigh, NC 27695-8005, U.S.A.

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* Cairo 1 2 approximate 10°N paleolatitude 3 FARAFRA 4 Asyut

5 7

6 0 500 km

deeper marine sediments continental clastics nearshore / shallow marine Mesozoic volcanics coastal / nearshore [deltaic] exposed basement highlands / nondeposition [areas of erosion]

Fig. 1. Map of Egypt showing the location of the study area in the Farafra Oasis and other fossil wood localities of Egypt (1 = Fayum, 2 = Wadi El-Rayan, 3 = Bahariya, 4 = Bir Abu Munqar, 5 = Kharga, 6 = Bir Kiseib, 7 = Aswan) and the Giarabub Oasis locality in Libya (*).

Tarawan Formation (Paleocene): White to grayish, hard, thin bedded, forms 1/3 of the scarp, which overlooks Bir El-Obeiyid. Thickness 40 m. Khoman Chalk (Maastrichtian): Dazzling, white chalky, thick bedded, forms the pediment surface of the northern part of Bir El-Obeiyid. Thickness 15 m. Hefhuf Formation (Campanian): Clays and dolomitic limestone form the relics of the floor of Bir El-Obeiyid. Thickness 10 m.

The Hefhuf Formation consists primarily of dolomitized limestone with varying amounts of finegrained terrigenous clastic influx, preserving a variety of plant and ani- mal remains. It unconformably overlies the fluvial to marginal marine sandstones and claystones of the Quseir Formation, and is succeeded by a sequence of offshore carbon- ates and clastics (Geological Survey of Egypt 1982) representing a return to marine conditions after the onset of the major Campanian transgression (Hermina 1990). At this time the Farafra area lay at low paleolatitude north of a developing bay (Fig. 1; Reynolds et al. 1997), from which fossils may have been transported. The Hefhuf Formation is considered to be regionally correlative with the Upper Campanian Duwi Formation and may be synonymous with it (Tawadros 2001). The fossil woods reported in this paper are therefore probably slightly younger than specimens from other “Nubian Sandstone” localities (Kamal El-Din 2003). Large logs were found lying horizontally on the surface or half buried in sand at the collection site.

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MATERIALS AND METHODS

The material studied represents two trunks. 1FO was 1 m long and 20 cm in diameter; 6FO was fragmented into numerous, 5 to 15 cm long sections. Thin sections were prepared according to the method described by Lacey (1963). The specimens and prepared slides are numbered and deposited in the palaeobotanical collection of the Botany De- partment, Faculty of Science, Ain Shams University, Cairo, Egypt. The preservation of the samples is not very good, and it is not possible to observe some key features. The InsideWood (2005) web site was used to obtain lists of extant dicots with the combination of characters seen in the fossil woods.

DESCRIPTIONS

The following descriptions use the IAWA list of Microscopic Features for Hardwood Identification (IAWA Committee 1989).

Farafra Oasis Wood 1FO (Fig. 2–6) Growth rings indistinct. Wood diffuse-porous. Vessels mostly solitary, occasionally in radial multiples of 2, rarely 3; oval to round in outline, tangential diameter 120–195 μm, mean 160 μm, radial diameter of solitary vessels 240–300 μm, mean 275 μm; 4–7 vessels per sq.mm; perforation plates simple with oblique end walls, intervessel pits crowded alternate, polygonal in outline, 7–10 μm; vessel-ray parenchyma pits with reduced borders and round to oval in outline; mean vessel element length 560 μm, tyloses common. Axial parenchyma paratracheal, vasicentric, sometimes aliform (lozenge), and occasionally confluent between vessels near to one another; 4–8 cells per strand. Rays 1–4-seriate, usually 3–4-seriate, rarely uniseriate; uniseriate rays up to 7 cells high. Multiseriate rays 15–40 cells, 450–780 μm high; heterocellular, body composed of procumbent cells with 1 or 2 marginal rows of upright cells. Fibers with thin to thick walls; pits and septa not observed. No crystals observed.

Comparison to extant woods — The combination of vessels solitary and in short radial multiples, simple perforations, alternate intervessel pitting, vessel-ray parenchyma pitting with reduced borders, paratracheal parenchyma (vasicentric to aliform), and heterocellular rays with 1–2 marginal rows of upright cells occurs in members of the Anacardiaceae, Lauraceae, and Moraceae (InsideWood 2005). Some genera of Anacar- diaceae have radial canals, some genera of Moraceae have latex tubes or canals, and many genera of Lauraceae have oil cells and so these genera can be recognized as members of their respective families. However, this wood does not have any of these characters, so its affinities with a single extant family cannot be established with certainty.

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Fig. 2–6. Farafra Oasis Wood 1FO. – 2: Diffuse-porous wood, vessels solitary and in radial multiples of two, CS. – 3: Vasicentric parenchyma, CS. – 4: Intervessel pits crowded alternate, polygonal in outline. – 5: Vessel-parenchyma pits with reduced borders. – 6: Multiseriate rays, TLS. — CS = cross section, TLS = tangential section. — Scale = 200 μm in Fig. 2; 100 μm in Fig. 3 & 6; 25 μm in Fig. 4 & 5.

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Fig. 7–13. Farafra Oasis Wood 6FO. – 7: Vessels mostly solitary and occasional short radial multiples, CS. – 8: Ray composed of procumbent cells, RLS. – 9–11: Scalariform perforation plates and opposite-alternate intervessel pitting, probable vessel-ray parenchyma pits (vrp). – 12: Oppo- site-alternate intervessel pitting. – 13: Uniseriate rays, TLS. — CS = cross section, TLS = tangential section, RLS = radial section. — Scale = 100 μm in Fig. 7, 8 & 13; 50 μm in Fig. 9–12.

Farafra Oasis Wood 6FO (Fig. 7–13) Growth rings indistinct. Wood diffuse-porous. Vessels solitary, occasionally in pairs; solitary vessels generally with rounded outline. Tangential diameter 60–90 μm, mean 80 μm; radial diameter 60–105 μm, mean 90 μm; vessels per sq.mm 20–30. Perforation plates scalariform, apparently around 20 bars; intervessel pits alternate to opposite; vessel-ray parenchyma pitting likely similar to intervessel pitting. Tyloses not observed. Axial parenchyma absent or extremely rare. Rays exclusively uniseriate, 3–18 cells, 90–640 μm high; homocellular, composed of procumbent cells; more than 12 per mm.

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Fibers with thin walls, polygonal in shape, possibly septate (many septa), with simple to minutely bordered pits. No crystals observed.

Comparison to extant woods — The preservation and distortion of the sample made it difficult to be sure of the presence or absence of some features. Although this wood has some features that are not common in extant woods (scalariform perforations, axial parenchyma absent, numerous exclusively uniseriate homocellular rays), it is not clear what extant family it might be allied with. If septate fibers are present, only some species of Sonneratia (Lythraceae) have that feature in combination with randomly arranged vessels that are solitary and in radial multiples, scalariform perforations, alternate intervessel pits, scanty–rare axial parenchyma, and numerous exclusively uniseriate homocellular rays. However, no extant species of Sonneratia have exclusively scalariform perforation plates, but only rarely is there a mixture of simple and scalariform perforation plates (InsideWood 2005; Rao et al. 1987). The quantitative features of the wood (vessel tangential diameter, vessel density, rays per mm) and thin-walled fibers are consistent with those in the Sonneratiaceae. There did not appear to be any axial parenchyma in this wood; however, because of the contortion of the sample, we might have not been able to see parenchyma strands in the longitudinal sections. The combination of exclusively uniseriate homocellular rays, scalariform perforation plates, alternate to opposite intervessel pitting occurs in Alnus (Betulaceae). However, Alnus has obvious apotracheal parenchyma. Given that this wood came from near the paleoequator, it seems unlikely it would have relationships to extant Alnus. In the Late Cretaceous there were woods that have combinations of characters not found in any extant wood, and sample 6FO likely is another example of this phenomenon.

DISCUSSION

There are only four Cretaceous wood types at the Farafra Oasis (Table 1). The banded parenchyma and aliform parenchyma, characteristic of three of these woods, is not a characteristic of Late Cretaceous dicot woods from higher latitudes (e.g., Wheeler

Table 1. Characteristics of Farafra Oasis woods.

Species MTD/μm V/mm2 PP AP RW Celastrinoxylon celastroides 60 25–50 SC, 5–10 B, 2–4 1 Ficoxylon cretaceum 135 4–8 SI B, >6 2–3 “Lauraceae” type (1FO) 160 4–7 SI V, A, C 1–4 6FO 80 20–30 SC R 1

MTD = mean tangential diameter; V/mm2 = vessels per sq.mm; PP = perforation plate; AP = axial parenchyma type; RW = ray width (number of cells); SC = scalariform followed by number of bars; SI = simple; B = banded, number of cells wide; V = vasicentric; A = aliform; C = confluent; R = absent to rare.

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& Baas 1991). It is not surprising that the general characteristics of the Cretaceous wood from near the equator should differ from those growing at higher latitudes. The absence of distinct growth rings in the Farafra woods suggests that the climate was not markedly seasonal. The palaeoclimate of the Late Cretaceous in nearby localities south of the Farafra Oasis (Kharga Oasis and road between Kharga and Dakhla Oasis) is suggested to be tropical or subtropical as deduced from the study of fossil wood by Kedves et al. (2004) and Youssef and El-Saadawi (2004). Our observations are consistent with this interpretation.

ACKNOWLEDGEMENTS

M. Kamal El-Din wishes to thank Dr. Wagieh El-Saadawi, Professor of Botany at the Faculty of Science, Ain Shams University and Dr. Said Ghanem, Lecturer in Botany, Faculty of Science, Benha University for collecting the specimens from Farafra Oasis. M.K. wishes again to thank Prof. Dr. Wagieh El-Saadawi for illuminating criticism, and Dr. Rawhia Abd El-Latif, Assistant Professor of Botany, Faculty of Science (Girls), Al-Azhar University for photographic facilities.

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