Quaternary history of the Kiseiba Oasis region, southern Egypt

Accepted Manuscript Quaternary history of the Kiseiba Oasis region, southern Egypt

Ted A. Maxwell, C. Vance Haynes, Kathleen Nicoll, Andrew K. Johnston, John A. Grant, Ali Kilani PII:

S1464-343X(17)30168-1

DOI:

10.1016/j.jafrearsci.2017.04.024

Reference:

AES 2892

To appear in:

Journal of African Earth Sciences

Received Date:

31 October 2016

Revised Date:

02 April 2017

Accepted Date:

20 April 2017

Please cite this article as: Ted A. Maxwell, C. Vance Haynes, Kathleen Nicoll, Andrew K. Johnston, John A. Grant, Ali Kilani, Quaternary history of the Kiseiba Oasis region, southern Egypt, Journal of African Earth Sciences (2017), doi: 10.1016/j.jafrearsci.2017.04.024

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ACCEPTED MANUSCRIPT

Fluvial channels detected by radar are correlated with near-surface sedimentary units Inverted topography coupled with paleodrainage is responsible for the these channels Quaternary drainage from south to north was responsible for fluvial deposits Topographic inversion led to local drainage reversal in the late Pleistocene

ACCEPTED MANUSCRIPT March 31, 2017

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Quaternary history of the Kiseiba Oasis region, southern Egypt

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Ted A. Maxwell1, C. Vance Haynes Jr2, Kathleen Nicoll3, Andrew K. Johnston1,4, John A.

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Grant1, Ali Kilani4

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Institution, Washington DC 20013 ([email protected])

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85721

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Department of Geography, University of Utah, Salt Lake City, UT 84112

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Adler Planetarium, Chicago, IL 60605

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Egypt Geological Survey and Mining Authority, Cairo, Egypt

Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian

Departments of Anthropology and Geosciences, University of Arizona, Tucson, AZ

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Submitted to Journal of African Earth Sciences, Special Issue to honor Professor Bahay Issawi Abstract

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Kiseiba Oasis and depression are located in southern Egypt between the Selima Sand

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Sheet to the west and the Nile to the east, an important area that hosted Late Cenozoic

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drainage, Middle Pleistocene lakes, and numerous Paleolithic and Neolithic cultural sites.

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A synthesis of orbital data, field surveying and near-surface stratigraphy provides new

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insights into the Quaternary history of this region. Shuttle Imaging Radar data show a

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complex of fluvial channels that are due to stringers of surficial fluvial lag, subsurface

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fluvial deposits, and areas of deep alluvium. Three topographic surfaces are described: 1)

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the Atmur El-Kibeish, above 230 m elevation, which displays a linear pattern of light

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radar returns, possibly formed from northeast drainage; 2) the Acheulean Surface, at 200

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m elevation, that has dark radar patterns resulting from thick alluvium bounded by pebble

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sand and calcrete strata, and 3) the Kiseiba Surface, below 190 m, that has a complex

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series of surface and subsurface fluvial and aeolian sediments. Initial drainage from the

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Early through Middle Pleistocene was to the northeast, which may have lasted through

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the Last Interglacial. Later reworking of sediments during the Last Glacial Maximum

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and the Holocene resulted in topographic inversion, with any subsequent local drainage

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on the Kiseiba Surface to the southwest, towards the Kiseiba Scarp.

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Keywords: Egypt, Quaternary landforms, SIR Radar, Paleochannels, Drainage evolution,

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Kiseiba Oasis

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1. Introduction

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Kiseiba Oasis (22° 41’ 45” N, 29° 55’ 30” E) is a small, uninhabited oasis along the Darb

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El-Arba’in caravan route in southern Egypt (Fig. 1). Throughout at least the last two centuries, it

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was the primary watering hole between Selima Oasis in northern Sudan and oases in central

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Egypt. Kiseiba Oasis and its bordering scarp are located at the western edge of the Kiseiba-

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Tushka depression near the southern border of Egypt (the northern part of the “Selima-Toshka

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Trough” of Thurmond et al., 2004). The depression stretches 180 km south of the scarp (Sinn

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El-Kaddab) that marks the southern margin of the limestone plateau, to Wadi Tushka near the

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Nile (Fig. 1). The Kiseiba Scarp forms a breakpoint between the Atmur El-Kibeish (the eastern

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edge of the Selima Sand Sheet) and the Nile. The depression is important for several reasons: it

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contains numerous archaeological sites, particularly those at Nabta Playa (Wendorf and Schild,

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1998) and Bir Kiseiba (Wendorf et al., 1984), as well as Paleolithic artifacts north of the oasis

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(Haynes et al., 1997; 2001). This area also occupies an important part in several theories for the

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evolution of the Nile, being the area that once may have seen westward drainage from the Red

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Sea Hills to the Western Desert (Issawi and McCauley, 1992; Issawi and Osman, 2008), that

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once possibly hosted a drainage basin that fed the Nile (Haynes, 1980), and that may have been

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the site of mega-lakes during the Middle Pleistocene (Maxwell et al., 2010). In recent years

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parts of the depression were flooded and later desiccated (Abdelsalam et al., 2008) and new

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roads and cultivation have irrevocably modified the near-surface stratigraphy and Bir Kiseiba

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itself.

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Imaging radar data from the 1994 Shuttle Imaging Radar C (SIR-C) mission revealed a

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complex network of fluvial paleochannels in the Kiseiba region. Unlike the smaller bedrock and

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calcrete incised radar-detected channels in the Selima Sand Sheet (McCauley et al., 1982; Davis

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et al., 1993), channel traces of the Kiseiba region are formed in alluvium and in some cases are

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visible to the radar because of a pebble lag on the surface. These paleochannels and the local

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playa basins in the depression emphasize the importance of the geologic setting to cultural sites,

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and like the numerous archaeological sites of the “radar rivers” (McHugh et al., 1988; 1989),

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indicate a relation between the geomorphology of the region as revealed by SIR data and early

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human habitation.

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Early studies of this area concentrated on geologic mapping (Issawi, 1969) and

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archaeological sites (Schild and Wendorf, 1984; Haynes et al., 1997; 2001). Our initial work

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with ground-penetrating radar (GPR) documented the existence of subsurface fluvial point bars

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(Grant et al., 2004). However, no work to date has concentrated on the Quaternary evolution of

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the region. Consequently, the purpose of this paper is to address that period of landscape

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formation, with particular respect to the role of fluvial activity. The most recent aeolian

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modification of the region is beyond the scope of this paper, and is reported in Hamdan et al.

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(2016).

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1.1 Methods

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The work reported here concentrates on the stratigraphy of the near surface sediments,

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the formation of multiple erosion surfaces, the origin of the paleochannels, and a model for the

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fluvial history. To address these topics, we have used a combination of data from Landsat, SIR-

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C, and the Shuttle Radar Topography Mission (SRTM) coupled with near-surface stratigraphy,

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topographic surveying, and GPR. Field studies were correlated with orbital data by repeated

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global positioning system (GPS) locations that were used to geometrically correct and coregister

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Landsat (Landsat 7 ETM, 176/44, acquired 2003) with SIR-C (Data Take 66.50) and SRTM (3

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arc-seconds, 90 m spatial resolution) data. Field topographic surveying was done by a laser

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theodolite (~1 cm accuracy), and by differential GPS (DGPS) at the Kiseiba Scarp. We used 400

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MHz ground-penetrating radar (GPR) to characterize the subsurface and interpolate the shallow

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stratigraphy between numerous trench (to 2 m depth) and pit (50 cm depth) lines, and to compare

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with the orbital (SIR-C) radar image. To address the roles of surface and subsurface backscatter

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in SIR-C data, we documented the size range of armoring fragments on the surface of the sand

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sheet, and use the term “gravel” in this paper to include a deposit of poorly sorted lag larger than

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64 mm.

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2. Prior Studies of the Bir Kiseiba Region

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Some of the earliest geographic observations of the Kiseiba-Tushka region were made by

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Ball (1927) as a result of extensive topographic surveying in southern Egypt. At that time, the

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topographic slope of the sand sheet towards the northeast, and the basic outline of the depression

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south of the limestone plateau were mapped. The possibility of an ancient river connecting

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Dongola (in northern Sudan) with the Mediterranean through the Western Desert was thoroughly

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discounted by Ball, although the reverse of this hypothesis with easterly drainage from the

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Western Desert through Wadi Tushka was introduced by Haynes (1980).

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The basic stratigraphic framework of bedrock and surficial strata in the Kiseiba-Tushka

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depression comes from the geologic field studies of the Geological Survey of Egypt (GSE) in the

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1960s (Issawi, 1969) and the archaeological investigations of Kiseiba Oasis and Nabta Playa by

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the Combined Prehistoric Expedition (CPE; Wendorf et al., 1984). The depression is floored

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primarily by the Upper Cretaceous Dakhla Shale (a variegated, friable sandy claystone with

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interlayered sandstone beds), overlain by Paleocene through Eocene limestone that creates the

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caprock of the “limestone plateau,” which comprises the physiographic divide between the Nile

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valley and the “New Valley” to the west (Issawi, 1969).

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In 1979 and 1980, the CPE, led by Fred Wendorf and Roman Schild, concentrated on the

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Bir Kiseiba region to compare local archaeological assemblages found there with those of Nabta

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Playa, 90 km to the east (Wendorf and Schild, 1998). The Neolithic artifacts from several

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trenches indicate a prolonged settlement from ca: 10 to <5 Ky. The sediments underlying the

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sand sheet just below the Kiseiba Scarp (sites E 79-1 to 3 of Schild and Wendorf, 1984) consist

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of basal sands overlain by planar cross-stratified pebble-rich sand, which is in turn overlain by

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colluvial wash deposits from the scarp (Fig. 2). Those authors interpreted the basal sands (which

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contained transported Paleolithic artifacts) as deltaic remnants of a complex (fluvial) system,

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probably associated with the Acheulean and Middle Paleolithic wet phases.

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The combined work of the GSE and CPE documented both the archaeology and geology

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of several playas in the depression. In addition to Nabta Playa and those of Kiseiba, there are

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numerous playas south of the Sinn El-Kaddab. Typically, the playas are surrounded by clusters

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of Neolithic artifacts, and have been interpreted as originating from surface runoff into deflated

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hollows during the Holocene (Issawi and Hinnawi, 1984; Haynes, 2001). One such playa is in

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the lee of Two Hills (Fig 2), where a bench on the south side of one hill is flanked by a playa pan

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containing grinding stones and numerous other Neolithic artifacts (Two Hills playa of Haynes et

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al., 1997).

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In contrast to the setting of Neolithic materials, an older assemblage of Acheulean

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artifacts was discovered at the margin of the Acheulean Surface (Fig. 2) (Haynes et al., 1997).

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Here, a cluster of 30 cleavers, handaxes and flakes suggest a much older and 10 m higher artifact

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surface than the Neolithic playas. Subsequent mapping of the distribution of these and other

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sites showed that they occur preferentially on the edges of the surface, indicating that the

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artifactural material is weathering out of a shallow subsurface stratigraphic stratum (Haynes et

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al., 2001).

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The combination of in situ artifacts coupled with fluvial channels detected by SIR led us

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to investigate the region using GPR in 2002. We found that the Kiseiba Trough (Fig. 2) at the

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base of the scarp is incised as much as 12 m into bedrock, and contained a stream that was

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laterally migrating towards the northwest, steepening the Kiseiba Scarp (Grant et al., 2004).

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Although that paper proposed a southwest drainage direction for the fluvial channel based on

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present-day local topography, analysis of the regional topography instead favors a northeast

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direction, at least for the oldest regional paleochannels (Maxwell et al., 2010).

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Consequently, the oldest, early to Middle Paleolithic artifacts seem to be located within

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discrete sedimentary strata, whereas the younger Neolithic remnants are confined to blow-outs

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and depressions hollowed out well before the Holocene. The archaeological remains support a

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climatic history that varies from active fluvial and lacustrine environments of deposition during

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the interglacials, and aridity to hyperaridity in the glacial periods, and add a temporal framework

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for the several erosion surfaces and paleochannels of the region.

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3. Stratigraphy of Quaternary Sediments

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In this paper we divide the geomorphic surfaces of the area into three topographic units:

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the Atmur El-Kibeish, the Acheulean Surface (described by Haynes et al., 1997), and what we

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term here the Kiseiba Surface (Fig. 2). Over several years of field seasons we excavated three

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trench lines and numerous shallow pit lines (Fig. 3), whose locations were determined by

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apparent fluvial patterns detected by SIR-C. Below, we present the geologic setting and near-

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surface stratigraphy of these relict surfaces. A summary of the characteristics of each stratum

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and our interpretation is presented in Table 1.

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3.1 Atmur El-Kibeish

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Although sometimes termed the Selima Sand Sheet, we use the term Atmur El-Kibeish

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for the flat sand sheet surface immediately west of the Kiseiba Scarp, and separated from the

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Selima Sand Sheet by a N-S line of granitic exposures that occur 50 km to the west in the Bir

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Safsaf region (Fig. 1). Like the Selima Sand Sheet, its surface is made of horizontally-laminated,

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bimodal sand at various stages of pedogenesis (Haynes et al., 1993; Maxwell and Haynes, 2001).

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Following Haynes et al. (1997) this northeast-trending strip of sand sheet is the oldest continuous

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surface exposed in the region based on its elevation (230 m) and the advanced degree of

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pedogenic alteration beneath the sand sheet. The only older surface is that represented by small

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remnants on the top of Two Hills (Fig. 2a), as shown in Figure 2 of Haynes et al. (1997).

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Sediments of the Atmur El-Kibeish are underlain by the Dakhla Shale (Issawi, 1971),

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which is fractured and pedogenically altered at its upper surface. Auger holes in the plateau

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surface typically bottom out with fragments of shale, and where exposed in the face of the

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Kiseiba Scarp, the section shows an upward transition to calcified bedrock (Fig. 4). The upper

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parts of the carbonate-rich strata are almost completely modified by root casts and tubular insect

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burrows. Occasional rounded 5-10 cm gravels are embedded in the matrix, and the calcrete is

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overlain by iron- and manganese-rich alluvium (equivalent to stratum C1 (calcareous alluvial

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sand) of Haynes et al., 1993).

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The 10-km wide strip of smooth sand sheet that borders the Kiseiba Scarp displays

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variegated NE-trending lineations in SIR-C L band radar (Fig. 2b), the cause of which we have

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not been able to determine in the field. The surface here consists of rounded calcrete and quartz

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gravels (Fig. 4) and broad (100’s of meters) shallow troughs between bedrock exposures that

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have a meter or more of granule-armored sand sheet. Beneath the active surface layer, the sand

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sheet displays desiccation cracks several 10’s of cms wide, a bimodal grain size, and little or

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none of its original horizontal lamination.

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3.2 Acheulean Surface

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Below the Kiseiba Scarp and 5 km east of Bir Kiseiba, the Acheulean Surface (Fig. 2) is

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an isolated 5-km wide plateau at 200 m elevation, barely 10 m above the local desert surface, and

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nearly indistinguishable from the surrounding sand sheet under certain lighting conditions.

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Unlike the sand sheet layers of the inter-bedrock lows of the Atmur El-Kibeish or the Selima

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Sand Sheet that can range up to several 10’s of cms thick (Maxwell and Haynes, 2001), there is

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commonly only a monolayer of 1 cm of horizontally-laminated sand sheet on this surface.

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Closely spaced lag pebbles have a median grain size of 0.4 to 0.8 cm with a maximum of 2.5 cm

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(Fig. 5). Underlying that armor, the primary near-surface sediment consists of an unstratified

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granule rich alluvium (Table 1). Typically the stratigraphic sequence consists of a basal yellow

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to white fine sand occasionally mixed with white clay that directly overlies the Dakhla Shale.

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Although auger holes commonly reach bedrock after a few meters, there are some areas where a

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hard carbonate zone is impenetrable at the base. Three sandy alluvial strata of a few cms to over

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a meter in thickness occur above the basal sand: a light brown granule sand, which is in turn

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overlain by reddish and brown alluvial strata (Fig. 5). A vesicular horizon typically less than 20

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cms thick occurs directly beneath the pebble lag in some areas.

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Using numerous shallow pits, auger holes, and a grid survey of the uppermost alluvium,

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we documented the stratigraphy associated with the Paleolithic artifacts (Haynes et al., 2001),

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and investigated the physical causes responsible for the variations in (SIR-C) radar reflectivity.

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Although we initially thought the present surface was the host for the 27 archaeological sites

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(hence the term Acheulean Surface; Haynes et al., 1997), we later confirmed that the artifact–

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rich stratum is in the subsurface, specifically a light brown granule-rich sand stratum that

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overlies the basal yellow-white sand (Haynes et al., 2001). Overlying the granule-rich sand are

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two alluvial strata, a lower, reddish granule alluvium (RGA), and an upper light brown granule

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alluvium (BGA; Fig. 5d). At the margin of the Acheulean Surface, the NW portion of the KAS-

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15 line, sand dominates the section. Both the stratigraphy and the distribution of artifacts

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indicate that the artifact-bearing stratum is of late Acheulean age, an imprecise time, but at least

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older than the Last Interglacial based on comparison with younger Middle Paleolithic artifacts

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from below the surface of the Kiseiba Trench (Wendorf et al., 1984) and sites at Bir Tarfawi, 100

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km to the west (Wendorf et al., 1993).

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We located several GPR lines, shallow pit cross sections and auger holes on the

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Acheulean Surface at an east-west, linear ~200 m wide strip that appears dark in SIR-C radar. In

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this desert, radar-dark zones typically indicate complete attenuation of the signal by

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homogeneous sand, either aeolian or fluvial, both of which have been observed in southern

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Egypt (Schaber et al., 1986). As opposed to the distinct near-surface calcrete-bounded channels

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prevalent near Bir Safsaf (Schaber et al., 1997; Paillou et al., 2003), the dark “channel” here is

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composed of 1-2 m of BGA underlain by either bedrock or an extremely hard clay and calcrete

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layer (Fig. 6). The 400 MHz GPR section indicates that bedrock, clay and calcrete vary from 1

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to >3 m beneath the surface with the channel margins bounded by calcrete within 1 m of the

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surface (Fig. 6). Both orbital and ground-based radar indicate an irregular calcrete and bedrock

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surface beneath the plateau, possibly formed from fluvial erosion and deposition, and modified

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by aeolian and pedogenic processes.

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3.3 Kiseiba Surface

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The Kiseiba Surface varies from 150-190 m in elevation, extending from the Kiseiba

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Scarp to Wadi Tushka, and consists of sand sheet surfaces several kms wide broken by bedrock

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(Dakhla Shale) exposures, local granitic exposures, playas, and chains of barchan dunes. Several

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100-400 m wide shallow deflated basins in the area are surfaced with firm playa sediments,

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particularly those south of the Sinn El-Kaddab (Issawi and Hinnawi, 1984) (Fig. 1), and Nabta

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Playa, halfway between Bir Kiseiba and Lake Nasser. Nabta Playa is the most well-known such

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deposit in the area because of the work by the CPE, establishing it as a Neolithic age settlement

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(Wendorf and Schild, 1998) complete with an ancient stone calendar (Malville et al., 1998).

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The SIR-C L band radar displays an extensive dendritic pattern of small channels

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between Bir Kiseiba and Bir Ayed (Fig. 2b), prompting our investigations of the near-surface

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stratigraphy. Both hand-dug trenches to 2 m (Salah Line in Fig. 3) and numerous 20-30 cm

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shallow pits were used to document near-surface sediments along and across the E-W strike of

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the channels. Overall, the sedimentary strata mapped in the trenches are consistent with fluvial

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aggradation, but have additional characteristics that support a more complex history.

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A schematic of the major sedimentary strata and their stratigraphic relations is shown in

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Figure 7. Field designations of strata A to D were based on sand texture, color, grain surface

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characteristics, and superposition relations seen in the Salah Line (Table 1). The trenches are

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dominated by fluvial sands with cm-scale pebble lenses (stratum C) that underlie 10-30 cm of

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sand sheet (stratum D) with varying degrees of pedogenic modification. Stratum C is typically

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poorly sorted subangular medium- to fine-grained sand that varies from brownish yellow to very

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pale brown (10YR 8/4) with increasing depth (Fig. 7). Stratum C pebbles are composed of

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rounded quartzite and quartz, and are either disbursed throughout the trenches or in 1-4 cm thick

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lenses. A slight dip of pebble lenses was noted in a few of the trenches, but showed no

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consistent direction. In addition to the transitional contacts between aeolian and fluvial sands,

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pedogenic modification is also evidenced by root casts in stratum C (Fig. 7b).

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The lower contact of stratum C is transitional to a soft, pale brown to white bimodal sand

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(stratum B) present in only some of the trenches, or to a carbonate and clay-rich medium fine

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sand with carbonate cemented nodules (stratum A). In those trenches where we did not reach a

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basal stratum A, auger holes up to an additional 2 m bottomed out in stratum B, where caving of

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the soft white sand made further penetration impossible. However, in most cases, stratum C

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directly overlies stratum A, in which both quartz pebbles and rounded carbonate nodules occur,

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the latter originating as fluvial reworking of indurated fragments. In some trenches, a manganese

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stained sand with angular carbonate and shale fragments directly overlies the Dakhla Shale.

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The surface of the north Kiseiba area where we trenched and surveyed is characterized by

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spreads of gravel tens to hundreds of meters wide. The gravel is composed of 3-6 cm subangular

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quartz, flint and carbonate fragments set in a medium to coarse sand matrix, with sharp lateral

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contacts against the more typical granule- or pebble-armored sand sheet (Fig. 8). The angular

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shape of the surficial lag fragments contrasts with the subrounded to rounded clasts found in

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stratum C of the Salah Line, suggesting a shorter transport distance or less reworking. In some

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cases, the gravel spreads are superposed on the sand sheet, and are not laterally continuous

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beneath it. Elsewhere, however, the gravel lag is part of a thick (10-20 cm observed) stratum

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that unconformably overlies an older, pedogenically altered sand sheet (Fig. 8).

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Three shallow pit lines in the Kiseiba Surface north of the Salah Line display local

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stratigraphic variations not seen in the deeper trenches. In general, these 20-30 cm pits were not

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deep enough to reach the fluvial sand of stratum C. Instead, two classes of sand were identified,

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each with minor variations within the class. Beneath the sand or pebble sheet, the uppermost

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stratum is primarily a brown (7.5YR 6/6), bimodal fine sand with widely dispersed granules

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(brown granule sand), in some cases incorporating an Av horizon up to 20 cm thick, consisting

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of a vesicular, clayey stage 3 sand sheet, or anhydrite. In several pits, the contact between the

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sand sheet and brown granule sand is extremely sharp, mimicking other discontinuities between

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the pebble sheet and the granule sand (Fig. 8e). A lower stratum consists of a soft yellow-brown

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(5YR 7/3) fine sand and granule mixture that caves easily, making further excavation difficult.

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In some pits, this lower stratum consists of a coarser sand with rounded pebbles, an apparent

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fluvial unit.

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The Dreadnaught Hill pit line is 3 km north of the Salah Line, and is closest to the

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Kiseiba Scarp of any of the survey lines. It is also at a lower elevation (168-171m) than the other

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lines, reflecting its location along the Kiseiba Trough. As opposed to the pits farther out in the

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basin, those here contain additional silty clay and playa mud strata at the expense of the granule

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sands (Fig. 9). The playa clays in particular, are local topographic highs in the survey line,

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bordered by more erodable vesicular strata and pebble sand.

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3.4 Summary and Interpretation The extensive pedogenic modification of the sediments of the Atmur El-Kibeish suggest

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in situ modification of local alluvium during wetter climates such as those of the Middle

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Pleistocene (Szabo et al., 1995). In contrast to those sediments, the record of the lower surfaces

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is much more varied. For the Acheulean Surface, the combination of indistinct drainage patterns

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seen in the SIR-C image and the extensive, flat-lying plain with alluvium overlying sand strata

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suggest their origin as fluvial and aeolian sand, capped by low-energy overbank deposits

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modified by aeolian processes. The granule alluvial strata (RGA and BGA) may have originated

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as fluvial deposits, but their bimodal sand size fraction indicates mixing with aeolian sand sheet.

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The admixture of silt and clay in both strata suggests additional reworking and pedogenic

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mixing.

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Several observations of Kiseiba Surface stratigraphy suggest a complex depositional

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history. From the auger holes in the vicinity of the Salah Line, it is apparent that the bedrock and

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calcrete surface beneath the fluvial sands is irregular, having 2-4+ m total Quaternary

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sedimentary fill. Both the deep (strata A and B) and shallow (strata C and D) sands suggest a

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varied energy and climatic environment. Stratum A, with its rounded carbonate and bedrock

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pebbles, indicates a fluvial environment capable of dislodging and transporting indurated mud

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near the top of the Dakhla Shale. In contrast, the unimodal, fine sand and soft packing of stratum

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B is more indicative of aeolian dune sand. Although the individual grains are more angular than

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modern dune sand, the above characteristics as well as the patchy occurrence of stratum B points

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to either a minor fluvial reworking of dune sand, or aeolian deposition of fluvial sand.

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The stratigraphy and archaeology from CPE trenches 6 km northwest of the Salah Line provide an age context for the stratum C sands. There, Schild and Wendorf (1984) reported the

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occurrence of a basal, poorly-sorted pebble sand, which we interpret as the lateral equivalent to

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stratum C. Middle Paleolithic artifacts from the upper part of the sands, and rolled artifacts from

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an upper stratum help to establish its age, albeit within the wide error bars (115-130 kya;

303

Wendorf et al., 1993; Nicoll, in press) of that cultural period. The numerous climate shifts over

304

the late Pleistocene preclude assigning a specific marine isotope stage to strata A and B. In

305

addition, several lines of evidence support sporadic stability and post-depositional groundwater

306

effects in the upper few meters in this area: 1) root casts in several trenches, typically 25-40 cm

307

below the present surface; 2) Mn and CaCO3 cementation of sand; and 3) bleaching of sand with

308

depth (Fig. 7c).

309

The detailed stratigraphy of the pits north of the Salah Line provides more specific

310

evidence for Holocene fluvial activity. Both the yellow-brown and brown granule sands were

311

likely deposited as sand sheet, with subsequent pedogenic processes destroying the initial

312

bedding, and shallow groundwater percolation modifying the sand color. In several pits,

313

however, a sharp upper contact between the granule sand and either sand sheet or fluvial pebble

314

sand indicates an erosional discontinuity that we attribute to fluvial planation of the older

315

alluvium. An ostrich eggshell (most likely a water container) from the North Line in the upper

316

sand sheet yields an average 14C age of 6870 ± 40 BP based on unweathered fragments (AA-

317

42539 and AA-42540). A Neolithic grinding stone and small blade found in the sand sheet just

318

above the pebble sheet on the same line provide further evidence that this latest fluvial reworking

319

and deposition occurred during the Holocene pluvial, ca: 5-10 ky (Haynes, 2001; Nicoll, 2004).

320

The near-surface playa deposits and near-surface bedrock of the Dreadnaught Hill Pit

321

Line suggest that the most recent fluvial activity modified the surface closest to the Kiseiba

322

Scarp, although those pits do not help to define the direction of drainage. In addition, the E-W

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15

323

linear trends of the fluvial lag on the Kiseiba Surface contrasts with the variable dip directions of

324

foreset planar stratification noted on the Salah Line. Thus, the question remains as to the source

325

of fluvial sediments on that surface, as well as the varying direction of drainage revealed in the

326

trenches and on the surface. To address these questions we turn to the wider view provided by

327

both regional topography and SIR-C.

328

4. Paleodrainage and Inverted Channels

329

Several lines of evidence for varying scales, types and directions of paleodrainage are

330

apparent from the SRTM DEM, the SIR-C image and our field studies. In addition to the

331

topographically lower trough at the foot of the Kiseiba Scarp that once hosted a stream channel,

332

two types of inverted channels are present on the Kiseiba Surface. The linear patterns of

333

surficial lag gravels seen in SIR-C and noted in the field north of the Salah Line are 1-2 m above

334

the surrounding sand sheet, and are presently graded towards the scarp, allowing the possibility

335

that the most recent (Holocene?) drainage was westward, possibly removing the fine-grained

336

sand sheet, remobilizing the earlier fluvial deposits and forming the present surficial lag.

337

The second type of inverted channel is revealed by the SIR-C image and is only apparent

338

in the field by siting locations based on those data. At the regional scale, SIR-C shows that local

339

sand sheet deposits are connected by broad, 10’s of meters wide curvilinear channels that are

340

recognizable because of the thick sand sheet that completely attenuates the radar signal, bordered

341

by near-surface bedrock. In the field, it is apparent that these curving sand masses are inverted

342

paleochannels, with the sand sheet of the center of the channels elevated 1-3 m above the

343

channel margins. We noted their presence in the field southeast of Bir Kiseiba and east of the

344

Acheulean Surface, where they lead from one featureless sand sheet patch to another.

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345

16

In addition to these inverted paleochannels, the regional drainage direction has been

346

interpreted based on SRTM and SIR data. Using a SRTM DEM coupled with a drainage model

347

for the Selima Sand Sheet, Ghoneim and El-Baz (2007) interpreted the most recent drainage

348

direction of that surface (90 km west of Bir Kiseiba) towards the northeast. The SRTM data for

349

the Kiseiba region also suggests northeast drainage at the regional scale (Maxwell et al., 2010),

350

but with additional complexity. Northward draining channels near Selima Oasis terminate at 247

351

m, well above the 190 m Kiseiba Surface, implying a base level of a mega-lake that covered

352

much of the area in the Middle Pleistocene (Maxwell et al., 2010). However, these northeast

353

trending channels at the regional scale conflict with the present westward gradient of inverted

354

gravel lag on the Kiseiba Surface noted above. Consequently, both the flow direction and the

355

timing of fluvial activity are not as well constrained as the ages of the relict surfaces.

356

The interpretations of drainage direction in the Kiseiba Trough also vary. Schild and

357

Wendorf (1984) interpreted the trough as the result of northeast drainage based on an apparent

358

northerly dip of basal sands seen in their trenches, consistent with the drainage direction of a

359

truncated channel north of Selima noted by Maxwell et al. (2010). Based on GPR surveys, Grant

360

et al. (2004) concluded that a southwest drainage was possible, noting that the undulating relief

361

along the trough precludes any continuous drainage direction along the present surface.

362

To address the age of the channel within the Kiseiba Trough relative to the neighboring

363

surfaces, we used DGPS to measure the topographic profiles of several gravel-armored pediment

364

surfaces and thalwegs of drainage channels along the scarp. As shown in Figure 10, the highest

365

pediments (closest to the head of the scarp) project to elevations above the present trough, but

366

lower than the Acheulean Surface, suggesting that the scarp had assumed its present position

367

prior to the Paleolithic occupations and deepening of the trough. The difference in slopes

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17

368

between higher and lower pediments is consistent with a long-term westward (scarpward)

369

migration of the channel and the preservation of the Acheulean Surface located farther from the

370

scarp. The profiles of two channel thalwegs near the foot of the scarp coincide with the present

371

surface of the trough, as would be expected from sporadic Holocene (and Recent) rainfall.

372

These various observations from subsurface, surface, and remote sensing data reflect the

373

changing environment from Middle Pleistocene to Middle Holocene; one in which the intensity

374

of fluvial modification varied considerably. Below we present a model for the drainage

375

evolution based on observations at these various scales.

376

4.1 Drainage Evolution

377

Neither the shallow trenching reported above nor the remote observations address the

378

formation of the Kiseiba Scarp itself, which may have formed as a structural break due to uplift

379

along the Tushka-Dongola high (Thurmond et al., 2004), or as an erosional scarp due to drainage

380

to the southwest from Wadi Qena (Issawi and McCauley, 1992; Issawi et al., 2016), or to the

381

northeast from an ancestral Nile (Williams and Williams, 1980; Abdelkareem et al., 2012;

382

Abdelkareem and El-Baz, 2015). Based on the pediment profiles, it is apparent that the scarp

383

was at its present position prior to the Middle Pleistocene surfaces and sediments described here.

384

In the Kiseiba area, the earliest possible drainage remnants observed are the discontinuous linear

385

trends on the Atmur El-Kibeish, that are oriented SW-NE, consistent with the northward regional

386

tilt of the Egypt platform that started late in the Eocene (Said, 1993, p. 34; Underwood et al.,

387

2013), and may have continued on the plains beneath the Selima Sand Sheet (Ghoneim and El-

388

Baz, 2007). Whether these linear patterns on the Atmur El-Kibeish noted in the SIR-C image are

389

truly fluvial channels has yet to be confirmed. The few pits we have examined have not shown

390

any systematic orientation of bedding, although the rounded pebbles incorporated into the

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18

391

calcrete-cemented stratum at the face of the Kiseiba Scarp indicate an ancient (pre-Pleistocene?)

392

period of fluvial activity.

393

The oldest unambiguous fluvial paleochannels in the study area are the remnants of

394

northward drainage 150 km to the south at Selima Oasis, and Wadi Mareef, an incised channel

395

on the limestone plateau that flowed to the west. Both paleochannels terminate near 247 m

396

elevation, well above the Atmur El-Kibeish and surrounding surfaces. Both sets of channels may

397

have helped feed a lake at that level during the late Cenozoic. Later drainage to the north during

398

the last interglacial, either preceding or following a 190 m mega-lake (Maxwell et al., 2010)

399

likely deposited the fluvial sands in the Kiseiba Trough and the lower fluvial strata (B and C)

400

noted beneath the Kiseiba Surface (Fig. 11).

401

The hyperaridity of the Last Glacial Maximum modified the fluvial landscape by

402

emplacement of erosion-resistant sand sheet deposits between the linear eroded remnants of

403

fluvial lag on the Kiseiba Surface. With intermittent drainage, channels became choked with

404

sand, eventually becoming inverted as wind erosion denuded the more erodible Dakhla Shale.

405

Aeolian activity accentuated and deepened the Kiseiba Trough, aided by downslope winds across

406

the Kiseiba Scarp.

407

The onset of the Neolithic Pluvial (Nicoll, 2004) saw a different landscape than the

408

preceding humid periods. The deepened Kiseiba Trough became a depocenter for fine-grained

409

sediment emplaced by sporadic rains (Fig. 11), now preserved as playa deposits. Areas of the

410

sand sheet that had become inverted now allowed runoff towards the trough, eventually leaving

411

behind stringers of lag deposits on the surface as aridity took over the landscape. This local

412

reversal of drainage is responsible for varying interpretations of drainage directions, and explains

413

the surficial lag that could have been a distributary pattern from a NE flowing stream, now left

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414

abandoned with a present-day topographic slope towards the scarp. Finally, any throughgoing

415

drainage now ran towards Kiseiba Oasis to the southwest, where it served to maintain the high

416

water table of the oasis.

417

5. Conclusions

418

19

Three surfaces in the Kiseiba Oasis region are characterized by varying degrees of fluvial

419

and aeolian sedimentation. The Atmur El-Kibeish, at 230 m elevation is composed of calcified

420

rounded pebble/gravel clasts beneath an iron and manganese stained sand, which is in turn

421

overlain by sand sheet. The upper stratigraphy of the Acheulean Surface, at 200 m elevation is

422

dominated by aeolian and fluvial strata capped by alluvial deposits of the Last Interglacial.

423

Below that, the Kiseiba Surface, below 190 m displays a complex of surficial deposits of gravel

424

and pebble lag, underlain by mixed fluvial and aeolian sand.

425

Field investigations of fluvial patterns seen in the SIR-C image of the Kiseiba region

426

reveal several causes for the light- and dark-toned linear channel patterns. In contrast to Bir

427

Safsaf where channel margins are located by a shallow carbonate layer that was eroded or

428

dissolved by fluvial activity, the patterns in the Kiseiba area are created by surface lag gravels,

429

by 10-30 cm deep strata of fluvial pebble and gravel deposits, and by lateral margins of alluvial

430

deposits against subsurface calcrete strata and shallow bedrock.

431

Numerous trench and pit lines on the Kiseiba Surface reveal sedimentary strata that

432

generally consist of reworked shale at the base, overlain by a mixture of fluvial and aeolian sand

433

with some tabular fluvial pebble lenses, capped by a more typical sand sheet of aeolian granules

434

(and pebbles) stratified with fine sand. In contrast, the Acheulean Surface is dominated by fine-

435

grained alluvium mixed with aeolian sand above a layer of mixed fluvial and aeolian sand with

436

associated early Paleolithic artifacts. Coupled with GPR transects, this shallow stratigraphy and

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20

437

associated artifacts indicate surfaces emplaced and pedogenically altered during humid periods,

438

later modified during times of aridity.

439

A model for drainage evolution consistent with field and orbital observations suggests

440

that northeast flowing Middle Pleistocene drainage through the Kiseiba Trough deposited the

441

fluvial sands of the Kiseiba Surface, which was later left inverted as the hyperarid climate of the

442

Last Glacial Maximum was dominated by aeolian processes. The penultimate surface

443

modification during the Holocene consisted of drainage reversal on the Kiseiba Surface, with

444

reworking of coarse fluvial gravel left as inverted lag channel deposits now surrounded by sand

445

sheet.

446 447

Acknowledgements

448

The field research reported here would not have been possible without the help, advice, and

449

many illuminating discussions with Dr. Bahay Issawi. He has been instrumental in supporting

450

our research throughout the past 4 decades. Stephen Stokes aided with field work and

451

discussions during various field seasons, as did Mohamed Askalany, Ali el Hawari, Peter Patton

452

and Richard Sebastion. Donald L. Johnson, late of the University of Illinois was instrumental in

453

defining the extent and character of insect burrows and root casts in the trench and pit lines. We

454

thank Barbara Tewksbury, Mohamed Abdelkareem, and Robert Giegengack for their helpful

455

reviews of this paper. This research was supported by NASA, NSF, and the endowments of the

456

Smithsonian Institution.

457 458

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459

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Said, R., 1993, The River Nile: Geology, Hydrology and Utilization. New York, Pergamon, 320 p. Schaber, G.G., McCauley, J.F., Breed, C.S. and Olhoeft, G.R., 1986, Shuttle Imaging Radar:

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Wendorf and R. Schild, edited by A.E. Close, pp. 9-40, Southern Methodist Univ. Press,

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566

Table 1.

567

Quaternary stratigraphic strata of the Kiseiba Oasis region Stratum D

Characteristics

Interpretation

Bimodal fine to medium sand with admixture of

Predominantly aeolian

medium granules to medium pebbles; typically

sand sheet with scattered

Stage 0 and 3 sand sheet strata of Haynes et al.

areas of playa mud

(1993), with intermediate stages. Also includes

deposits

fine grained, hard silty clay deposits in some trenches and pits. Occurs on all surfaces in the region Atmur El-Kibeish C1

Carbonate rich matrix enclosing rounded 5-10 cm

Alluvial sand of fluvial

gravel, with extensive root and insect tubes.

origin with extensive

Overlain by calcareous iron and manganese stained

pedogenic modification

poorly sorted medium sand equivalent to stratum C1 of Haynes et al., 1993 Acheulean Surface BGA

Poorly sorted fine to medium sand with admixture

Fluvial (overbank?)

of silt and clay capped by granule to pebble sand

alluvium modified by

sheet. Light brown in color (7.5YR 7/8)

aeolian and pedogenic mixing

RGA

Similar characteristics to stratum BGA, but with a

Fluvial (overbank?)

reddish coloration (5YR)

alluvium modified by aeolian and pedogenic mixing

Kiseiba Surface C

Poorly sorted, medium to fine grained sand;

Fluvial sand with

contains subhorizontal lenses of pebble to gravel

occasional point bar

size rounded clasts. Color varies from brownish

deposits, subject to post-

ACCEPTED MANUSCRIPT March 31, 2017

B

26

yellow (10YR6/6) at top to very pale brown

depositional leaching

(10YR8/3) at base

from groundwater

Well-sorted fine to medium subangular sand with

Fluvial sand reworked by

minor admixture of medium rounded and frosted

aeolian processes

grains. Pale brown to near white color (10YR 8/4). Caves easily in trenches and auger holes A

Pebble size (2-4 cm) carbonate cemented sand

Groundwater modified

nodules in a carbonate rich medium sand matrix.

clay-rich sand of fluvial

Extremely hard to excavate

or aeolian origin mixed with weathered Dakhla Shale

568 569

ACCEPTED MANUSCRIPT March 31, 2017

27

571

Figures

572

Fig. 1. Google Earth image of southern Egypt showing locations discussed in text. The Kiseiba-

573

Tushka area is bounded by the south-facing scarp of the Sinn El-Kaddab, Wadi Tushka to the

574

east, and the Kiseiba Scarp that borders Bir Kiseiba to the west. East Oweinat is an agricultural

575

project started in the 1990s utilizing groundwater beneath the Sand Sheet. Box is location of

576

Figure 2.

577 578

Fig. 2. (a) Landsat 7 ETM image (Bands 7,4,2 composite) of Kiseiba region showing locations

579

discussed in text. The sand sheet surface of the Atmur El-Kibeish is the highest surface in the

580

region, followed successively by the lower Acheulean and Kiseiba Surfaces. (b) SIR-C Data

581

Take 66.50 (L-band) image of the Kiseiba region showing NE-trending linear light toned texture

582

of the Atmur El-Kibeish, faint dark channel markings on the Acheulean Surface and a dendritic

583

pattern on the Kiseiba Surface. (c) SRTM DEM showing surface texture (illuminated from the

584

NW) combined with color coded topography. The Atmur El-Kibeish, at an average elevation of

585

230 m is the oldest of the surfaces based on the degree of pedogenesis of the local bedrock and

586

alluvium. Below the scarp in the vicinity of Bir Kiseiba, the Acheulean Surface is a local 5-km

587

wide plateau at 200 m elevation. The Kiseiba Surface varies from 150-190 m, and extends

588

eastward to Wadi Tushka at the Nile Valley, locally interrupted by playa depressions.

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Fig. 3. Landsat 7 ETM image (Bands 7,4,2 composite) of the Kiseiba area showing locations of

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trenches, pits, auger holes, ground-penetrating radar (GPR) lines and differential global

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positioning system (DGPS) locations used to infer the stratigraphic and geomorphic history.

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Boxes show locations of Figures 6 and 10.

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Fig. 4. Near surface strata of the Atmur El-Kibeish: (a) Coarse, subrounded bedrock gravels of

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the surface armoring a desiccation cracked sand sheet, (b) Close-up of (a) showing sand sheet

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overlying Fe-Mn alluvium, (c) Calcified alluvium near the face of the Kiseiba Scarp with

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incorporated gravel (g) and root casts (r). (Photos by Don Johnson).

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Fig. 5. (a) Acheulean Surface with Two Hills and Kiseiba Scarp in the background. Foreground

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rock is an Acheulean handax weathering out of the surface. (b) Site KAS-15 handaxes and

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cleavers overlying a red sandy alluvium. (c) Typical granule-pebble surface lag of the

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Acheulean Surface. (d) Brown granule alluvium (BGA) overlying red granule alluvium (RGA)

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typical of the Acheulean Surface.

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Fig. 6. NW-SE GPR profile across SIR-C radar dark, east-west linear (channel) feature of the

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Achulean Surface (see Fig. 3 for location). Only the central 295 m of the line are shown,

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centered around the channel and auger holes. (a) Enlargement of SIR-C L-band radar showing

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locations of KAS-15 survey line and NW-SE auger and GPR lines. (b) Close up of the dark, E-

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W linear feature and GPR line. (c) 295 m GPR profile of the dark feature. (d) Enlargements of

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the GPR section with auger hole stratigraphy at the same vertical scale. The most prominent

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reflectors are bedrock and calcrete strata, and the alluvial strata are featureless in this 400 MHz

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GPR section.

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Fig. 7. Schematic ~2m thick section of Kiseiba Surface stratigraphy. (a) Contact between

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stratum D (sand sheet) and stratum C (fluvial sand), (b) Rhizoliths in stratum C at a depth of 75

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cm, with red root structures surrounded by a white sand matrix, (c) Progressive whitening with

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depth in stratum C shown by samples taken from depths noted on a trench shovel. (d) Section of

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sand sheet (D) overlying fluvial sand (C), over clay and carbonate-rich sand (A).

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Fig. 8. Stratigraphic variations of fluvial pebble lag and sand sheet on the Kiseiba Surface. (a)

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Looking north along North Line (Fig. 3), showing dark lag interspersed with lighter sand sheet in

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the far ground. (b) Widely spaced subangular fluvial pebble fragments on the Dreadnaught Hill

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Line. (c) Surficial pebble lag (left of dashed line) abutting granule sand sheet (stratum D).

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Coarse lag does not extend under the sand sheet at this location. (d) Monolayer of pebble lag

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overlying 7 cm of sand sheet (stratum D), which in turn overlies 20 cm of brown granule sand

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(stratum C). (e) Sharp contact between sand sheet and erosional surface of brown granule sand.

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(f) Thick, cross stratified pebble sand unconformably overlying yellow-brown sand. Such

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relations suggest an initial erosion surface on top of the brown granule sand (old, pedogenically

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altered sand sheet), with subsequent fluvial deposition of pebble sand. Repeated wetting and

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drying resulted in fluvial deposits both superposed on, and superposed by aeolian sand sheet.

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Fig. 9. Dreadnaught Hill pit line (location shown in Fig. 3) is closest to the Kiseiba Scarp and

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the only one of the pit and trench lines to show playa clays. (a) Topographic variations of >3 m

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are present along this line. Boxes show locations of photos below. (b) View of pit 1 showing

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pebble sheet directly overlying silty clay. (c) Sand sheet (ss) overlying playa clay (p); (d)

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Monolayer of sand sheet overlying playa clay (p) and Dakhla Shale (DS). The higher parts of

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the cross section show evidence for inversion in the form of prismatic (playa) clays that are more

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resistant to erosion than the Dakhla Shale.

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641

Fig. 10. N-S pediment profiles from Kiseiba Scarp (right) projected through the Kiseiba Trough.

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Location is shown in inset box of Figure 3. SRTM topographic reference is derived from a 1-

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km-wide SRTM elevation profile perpendicular to the topographic profiles measured in the field,

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hence the mismatch between the individual profiles and the SRTM reference. The relict

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pediments highest along the scarp project farthest into the basin, but still below the level of the

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Acheulean Surface. The Kiseiba Scarp was likely at its present location prior to the isolation of

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the Acheulean Surface.

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Fig. 11. Perspective views to the southwest for stages of Late Pleistocene drainage. Base image

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is a shaded relief rendition of SRTM data with lighting from the northwest. (a) Probable

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intermittent lake at 190 m elevation isolated the Acheulean Surface prior to the Last Interglacial

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(Haynes et al., 1997; Maxwell et al., 2010). Possible northeast drainage existed during or prior

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to this period on the Atmur El-Kibeish. (b) During the Last Interglacial drainage to the northeast

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on the Kiseiba Surface resulted in a distributary fan north of the Acheulean Surface and

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deposition of fluvial sands. (c) Sporadic drainage of the Latest Pleistocene/Holocene towards

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Bir Kiseiba isolated gravel stringers on the sand sheet. North-South linear features at bottom of

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base image are chains of barchan dunes (see Hamdan et al., 2016).

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659 660

Fig.1

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Fig. 2 a,b

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Fig. 2 c

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Fig. 3

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Fig. 4

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668 669

Fig. 5

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Fig. 6

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673 674

Fig. 7

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Fig. 8

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Fig. 9

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Fig. 10

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Fig. 11

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