Chapter 3. the Early Palaeozoic Glacial Deposits of Gondwana

Home , Iherir, In Amenas, Tamadjert, Tibesti Mountains

CHAPTER THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA: OVERVIEW, CHRONOLOGY, AND 3 CONTROVERSIES

D.P. Le Heron1, S. Tofaif1 and J. Melvin2 1Royal Holloway, University of London, Surrey, United Kingdom, 2Saudi Aramco, Dhahran, Eastern Province, Saudi Arabia

3.1 INTRODUCTION 3.1.1 OVERVIEW There is a widespread record of deposits of Early Palaeozoic age that provide evidence for glaciation (Fig. 3.1). As this chapter will show, much of the record of the Early Palaeozoic is restricted to the Ordovician, although there is some evidence for glaciations of early Silurian age in some regions. Much of the sedimentary record is archived in present-day North Africa and Arabia, providing an interesting contrast between these modern-day hyper-arid settings and an ancient, 443- million-year-old (Hirnantian) glacial record. As a result of the outcrop distribution in these modern desert settings, rock exposure is typically excellent, and superb examples of ancient glacial landforms and successions can be documented. In this chapter, we provide illustrated examples throughout from the North African and Arabian record in particular, paying particular attention to exploring what makes this glacial sedimentary record unique and important. Compared to other Precambrian and Phanerozoic glacial records, that of the Hirnantian is unusually sandy. This simple observation demands an explanation, not least because the very sand-prone nature of the deposits accounts for their major resource importance as regional oil and gas reservoirs (Huuse et al., 2012).

3.1.2 PALAEOGEOGRAPHIC CONTEXT AND ORIGINS OF THE GLACIATION The palaeogeographic context at 443 Ma, during the Hirnantian, explains the present-day distribution of glaciogenic deposits of this age, including how extensive outcrop belts occur in the modern-day Sahara and Arabian deserts. At 443 Ma, parts of the Gondwana supercontinent became glaciated. This supercontinent, which comprised South America, Africa, Madagascar, Arabia, India, East Antarctica, and Australia (Fig. 3.2)(Allen, 2007; Torsvik and Cocks, 2009), extended from the South Pole to the tropics during the Early Palaeozoic (Torsvik and Cocks, 2009), and hence it records the full spectrum of warm to polar climate indicators in its sedimentary archive (Scotese et al., 1999).

FIGURE 3.1 Outline of present-day countries which contain Early Palaeozoic glacial deposits highlighted in yellow, with the black arrows indicating the direction of palaeo-ice flow. From Hambrey, M., 1985. The Late OrdovicianEarly Silurian glacial period. Palaeogeogr. Palaeoclimatol. Palaeoecol. 51, 273289; Hambrey, M.J., Harland, W.B., 1981. Earth’s pre-Pleistocene glacial record. Cambridge University Press, London, 1022 pp.; Ghavidel-syooki, M., A´lvaro, J.J., Popov, L., Pour, M.G., Ehsani, M.H., Suyarkova, A., 2011. Stratigraphic evidence for the hirnantian (latest ordovician) glaciation in the zagros mountains, Iran. Palaeogeogr. Palaeoclimatol. Palaeoecol. 307, 1À16. doi:10.1016/j. palaeo.2011.04.011; Grahn, Y., Caputo, M.V., 1992. Early Silurian glaciations in Brazil. Palaeogeogr. Palaeoclimatol. Palaeoecol. 99, 9À15. doi:10.1016/0031-0182(92)90003-N; Le Heron, D.P., Craig, J., 2008. First-order reconstructions of a Late Ordovician Saharan ice sheet. J. Geol. Soc. Lond. 165, 19À29. doi:10.1144/0016-76492007-002; Le Heron, D.P., Craig, J., Etienne, J.L., 2009. Ancient glaciations and hydrocarbon accumulations in North Africa and the Middle East. Earth-Sci. Rev. 93, 47À76; Monod, O., Kozlu, H., Ghienne, J.F., Dean, W.T., Gu¨nay, Y., Le Heriss´ e,´ A., et al., 2003. Late Ordovician glaciation in southern Turkey. Terra Nov. 15, 249À257. doi:10.1046/j.1365-3121.2003.00495.x; Robardet, M., Dore,´ F., 1988. The Late Ordovician Diamictic Formations from SW Europe: N Gondwana Glaciomarine Deposits. Palaeogeogr. Palaeoclimatol. Palaeoecol. 66, 19À31; Storch,ˇ P., 1990. Upper Ordovician—lower Silurian sequences of the Bohemian Massif, central Europe. Geol. Mag. 127, 225À239. doi:10.1017/S0016756800014503; Vaslet, D., 1990. Upper Ordovician glacial deposits in Saudi Arabia. Episodes 13, 147À161. 3.1 INTRODUCTION 49

FIGURE 3.2 Reconstruction of Gondwana during Early Ordovician and Mid-Silurian from Torsvik and Cocks (2009).

The formation of Gondwana resulted in widespread amalgamation of terranes, intracratonic mountain building, and consequently extensive weathering (Berry and Finney, 2001; Smith, 1997). The decrease of atmospheric CO2 (by increased organic activity and continental weathering (Brenchley et al., 1994; Young et al., 2004) is considered to be one of the key drivers for the Hirnantian glaciation. The increase in weathering activity could be responsible for the decrease in atmospheric CO2 and in turn induced the start of the Hirnantian glaciation (Kump et al., 1999; Berry and Finney, 2001). In addition, the formation of high grounds could have accelerated the formation of mountain glaciers which in turn helped increase the weathering rate (Young et al., 2004; Raymo and Ruddiman, 1992). The opening and closure of oceanic gateways is presumed to be an important contributor to cooling and was possibly a primary cause of the Hirnantian glaciation (Smith and Pickering, 2003). The closure of an isthmus in central America may have isolated Gondwana from the warming effects of circumpo- lar currents, promoting insulation and thus refrigeration (Smith and Pickering, 2003). 50 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

3.2 EXTENT OF GLACIATION AND CHRONOLOGY 3.2.1 OVERVIEW Two end-member scenarios were proposed by Ghienne (2003) with regard to ice sheet extent in the Late Ordovician. These were (1) a large, pan-African ice sheet and (2) disconnected, though likely synchronous, ice sheets (Fig. 3.3). These ideas were tested by Le Heron and Dowdeswell (2009) who calculated the likely volume of water stored in the ice sheets in both end-member cases, concluding that the smaller scenario was probably the most realistic based on available data. In a similar way, it is important to establish whether the ice caps around GondwanaÀparticularly those that extended into South AmericaÀwere part of a single, ‘short snap’ Hirnantian event, or whether they evolved, and persisted, during a longer cold phase (Delabroye and Vecoli, 2010). The debate concerning whether the South American deposits are latest Ordovician or early Silurian is considered below, where we explain ‘the essentials’ of regional subdivisions in the Late Ordovician record, in order to communicate our understanding of the glacial sedimentary system and to explain the controversies surrounding timing and extent of ice masses on Gondwana. We will briefly explain, with reference to Fig. 3.4, the glacial stratigraphy of four key areas: (1) North Africa, (2) Arabia, (3) southwest Europe, and (4) South America.

3.2.2 NORTH AFRICA: MOROCCO, ALGERIA, LIBYA In North Africa, Late Ordovician glacial deposits sit unconformably above a paralic succession of variable age (typically mid-Ordovician to preglacial Hirnantian (Loi et al., 2010; Moreau, 2011), exhibit name changes across regional borders (Fig. 3.4), and are characterized by their internal stratal complexity. Not all authors recognize or even use the official formation terminology, owing to the dramatic facies changes and inferred depositional setting over several kilometres. Nevertheless, in Libya, the Mamuniyat Formation is widely recognized. This is correlated with the Tamadjert Formation in Algeria and with the Upper Second Bani Formation in southern Morocco (Fig. 3.4). Strata in northern Morocco are assigned to a multitude of different formations owing to their location within disparate basement inliers (see Le Heron et al., 2007). Study has focused particularly on the Libyan successions around the borders of Al Kufrah Basin in the east (Le Heron et al., 2010, 2014; Le Heron and Howard, 2010), and the Murzuq Basin in the west (Le Heron et al., 2004, 2005, 2013; Ghienne et al., 2003, 2007, 2010a, 2013; Girard et al., 2013a,b, 2015). The westernmost flank of the Murzuq Basin is part of the extensive Tassili N’Ajjer outcrop belt, where the classic studies of Beuf et al. (1971) have motivated highly detailed, recent efforts to unravel the complexities of the glacial sedimentology and stratigraphy (Deschamps et al., 2013). In this latter paper, the recognition of two main types of glacial erosion surface associated with glacial palaeovalleys: (1) a sharp, irregular contact recording predominantly meltwater processes, and (2) a ‘smoother’ type of surface associated with soft-sediment striations (see Box 3.1) and soft-sediment deformation, primarily recording subglacial shearing. These ideas have simultaneously been developed on the equivalent succession in the Anti-Atlas of Morocco (Clerc et al., 2013; Ravier et al., 2015). 3.2 EXTENT OF GLACIATION AND CHRONOLOGY 51

FIGURE 3.3 Reconstruction of Gondwana during the Hirnantian with the location and size of posited ice sheets superimposed. Distribution of ice sheets initially from Ghienne (2003). Figure from Le Heron, D.P., Craig, J., Etienne, J.L., 2009. Ancient glaciations and hydrocarbon accumulations in North Africa and the Middle East. Earth-Sci. Rev. 93, 47À76. 52 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

FIGURE 3.4 Regional Early Palaeozoic stratigraphy of North Africa and part of the Middle East, with particular focus on glaciogenic strata of Hirnantian age. Note the complex regional variance in stratigraphic names. Modified after Le Heron, D.P., Craig, J., Etienne, J.L., 2009. Ancient glaciations and hydrocarbon accumulations in North Africa and the Middle East. Earth-Sci. Rev. 93, 47À76 and updated to reflect new subdivisions of Melvin, J., 2015. Lithostratigraphy and depositional history of Upper Ordovician and lowermost Silurian sediments recovered from the Qusaiba-1 shallow core hole, Qasim region, central Saudi Arabia. Rev. Palaeobot. Palynol. 212, 3À21. doi:10.1016/j.revpalbo.2014.08.014 in Saudi Arabia.

3.2.3 ARABIAN PLATE Early Palaeozoic glacial deposits crop out in a vast belt in three main regions of Saudi Arabia: the NW, Central, and SW regions (Vaslet, 1990). The syn-glacial deposits are predominantly confined to palaeovalleys cutting down to Cambrian-age strata (the Saq Sandstone (Clark-Lowes, 2005; Vaslet, 1987, 1990)). Melvin (2015) refined the Upper Ordovician stratigraphy in central Saudi Arabia (Fig. 3.4), recognizing four members of the Sarah Formation, namely, from oldest to youngest: Sarah Sandstone Member, Hawban Member, Baq’a Shale, and Baq’a Sandstone (Melvin, 2015). The Sarah Sandstone member contains two megafacies, which represent the glacial advance followed by a glacial retreat. The Hawban Member represents another glacial advance followed by the Baq’a Shale Member as the terminal glacier retreat facies. The Baq’a Sandstone lacks any indication for glaciation and possibly represents the postglacial isostatic rebound separating the lower unit from the upper unit of the Baq’a Sandstone (Melvin, 2015). The syn-glacial deposits are attributed to Late Katian to Late Hirnantian age (Le Heriss´ e´ et al., 2015; Melvin, 2015; Paris et al., 2015). The syn-glacial deposits found in Saudi Arabia are relatively similar to those in Jordan (Abed et al., 1993; Armstrong et al., 2005; Vaslet, 1990), with spectacular palaeovalley occurrences (Douillet et al., 2012). In SE Turkey, the syn-glacial deposits appear to show a comparatively ice- marginal signature. Basal deposits are transitional and a fining upward motif is the general trend (Monod et al., 2003). These glacial deposits start with channelized sandstone deposited in ice proxi- mal settings and end with sandstone, siltstone, and shale with some rare lonestones representing 3.2 EXTENT OF GLACIATION AND CHRONOLOGY 53

relatively glaciomarine settings with rare dropstones (Monod et al., 2003). In Iran, on the other hand, the glacial deposits are described by Ghavidel-syooki et al. (2011) as clast-rich, massive to crudely stratified diamictite units alternating with moderately sorted, fine- to coarse-grained sandstone units reflecting two or possibly three cycles of ice advanceÀretreat.

3.2.4 SOUTHWEST EUROPE Many regions in present-day Europe occupied a ‘peri-Gondwanan’ position toward the present-day north of Africa, either as terranes of uncertain position or potentially welded to the Gondwana land- mass (Fig. 3.3). As such, Early Palaeozoic glacial deposits are widespread across southwestern Europe and are found in the Iberian Peninsula (Portugal and Spain), Armorican Massif (France), Thuringia (Germany), and the Prague Basin in the Bohemian Massif (Czech Republic, Germany, and Poland) (Bernardez´ et al., 2006; Brenchley and Storch,ˇ 1989; Couto et al. 2013; Fortuin, 1984; Gutierrez-Marco´ et al., 2010; Robardet and Dore,´ 1988; Storch,ˇ 1990). They are widely accepted as glaciomarine deposits of Hirnantian age (Brenchley and Storch,ˇ 1989; Couto et al., 2013; Fortuin, 1984; Gutierrez-Marco´ et al., 2010; Robardet and Dore,´ 1988). They comprise diamictites and shales bearing outsized clasts (dropstones) deposited in a shallow marine shelf environment (Brenchley and Storch,ˇ 1989; Fortuin, 1984; Robardet and Dore,´ 1988; Storch,ˇ 1990). Two localities described in northern Portugal and northwestern Spain show uniquely coarser sediments within northÀsouth-oriented palaeovalleys with evidence for direct ice contact (Couto et al., 2013; Gutierrez-Marco´ et al., 2010). The thickness of the syn-glacial deposits varies significantly within short distances, ranging from 0 to 250 m (Brenchley and Storch,ˇ 1989; Fortuin, 1984; Robardet and Dore,´ 1988). The internal structure is generally massive, poorly stratified to nonstratified with possible slumped or convoluted bedding (Robardet and Dore,´ 1988). The evidence for a glacial origin is supported by (1) presence of faceted and striated clasts, (2) characteristics of the quartz grains under scanning electron microscopy, (3) dropstones, (4) the possible presence of varves, (5) extensional microfaults, (6) sheath folds, and (7) small-scale intraformational grooves. These deposits are thought to have accumulated in a shallow marine shelf environment (Couto et al., 2013; Fortuin, 1984; Gutierrez-Marco´ et al., 2010; Robardet and Dore,´ 1988).

3.2.5 SOUTH AMERICA Early Palaeozoic glacial deposits are widespread in South America. They occur in central and NW Argentina (dated at ,485 Ma, based on detrital zircons: Van Staden et al., 2010). They occur as continental deposits in Brazil, and as glaciomarine facies (with reworked deposits also) in the Peru-Bolivian Basin (D´ıaz-Mart´ınez and Grahn, 2007; Grahn and Caputo, 1992). In Brazil, continental deposits occur in the Amazonas Basin, Cariri Valley, Jacoba Basin, Parnaiba Basin, and Parana Basin (Grahn and Caputo, 1992). The glacial deposits are interpreted as true tillites (deposited in direct contact with the ice) deposited in two major advanceÀretreat glacial cycles with smaller-scale interglacial events (Grahn and Caputo, 1992). Gray et al. (1985) and Grahn (1991) indirectly dated the oldest Silurian glaciation in Brazil as early Llandovery and early to middle Llandovery, respectively, based on shelly fossils obtained from the beds overlying the glacial deposits. Younger glaciation events in the Amazonas Basin were dated as early Telychian (based on chitinozoan) and late Telychian to earliest Wenlock (based on shelly fauna) (Grahn and Caputo, 1992; Grahn and Paris, 1992). 54 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

The Early Palaeozoic deposits are also found in the Peru-Bolivian Basin, which extends over Venezuela, Colombia, Ecuador, North Argentina, Paraguay, and western Brazil (D´ıaz-Mart´ınez and Grahn, 2007). In this basin, D´ıaz-Mart´ınez and Grahn (2007) found diamictite interbedded with lami- nated shales and fine-grained turbidites indicating deep-marine settings and therefore concluded the reworked glaciomarine nature of these deposits. The age of these deposits, however, is still contro- versial. D´ıaz-Mart´ınez and Grahn (2007) concluded that the age of these deposits derived from chitinozoan and palynology as Early Sillurian (Llandovery), while Rubinstein and de la Puente (2008) questioned the chitinozoan assemblage presented by both Grahn and Gutierrez´ (2001) and D´ıaz-Mart´ınez and Grahn (2007), settling on a Late Ordovician age on the basis of trilobite fauna (Monaldi et al., 1986) and palynomorphs with some cryptosphores (de la Puente and Rubinstein, 2013).

3.3 THE SEDIMENTARY RECORD 3.3.1 OVERVIEW The expansion of ice sheets over the southern supercontinent of Gondwana was dominantly over a substrate comprising stratified siliciclastic series of rocks which are colloquially described as the Gondwana superfan system (Meinhold et al., 2013). The superfan deposits crop out across North Africa and Arabia, and highly comparable stratigraphies in Cambrian through Ordovician strata are characteristic. Intercalated shallow marine and fluvial intervals are dominant in this interval from Morocco (Ghienne et al., 2007) to Turkey (Ghienne et al., 2010b). Detailed examination of each outcrop belt in between reveals a similar pattern: for instance, in southern Libya, all studies of Hirnantian glacial deposits show that they rest unconformably on mid-Ordovician to early Hirnantian shallow marine sandstones and subordinate mudrocks (Girard et al., 2015). Therefore, at a regional level, the homogeneity of the substrate over which Hirnantian ice sheets advanced is therefore striking. As we will explore later in this chapter, this homogeneity had a direct impact on the sedimentary record, most particularly on the paucity of diamictites across Gondwana of Hirnantian age. Across the margins of Gondwana, the stratigraphic architecture of the substrate, in concert with its composition, can be argued to have played a key role both on palaeo-ice sheet dynamics and on the composition of strata produced during the Hirnantian glaciation.

3.3.2 GLACIAL CYCLES Ghienne et al. (2007) suggested that the North African region was glaciated at least five times, with five glacial cycles being recognized. On the most simple level, the outer reaches of the platform (i.e., the most northward, and furthest from the ice centre) were glaciated only once (e.g., northern Morocco: Le Heron et al., 2007), whereas areas closest to the ice centre were subject to multiple glacial cycles (e.g., the Ghat area of Libya: Moreau, 2011). An outer, a medial, and an inner glaciated shelf (Fig. 3.5) were hence recognized. Examining the stratigraphic record reveals that the outer glaciated shelf exhibits only one soft-sediment striated surface (and hence interpreted subglacial erosion surface), whereas those corresponding to the inner glaciated shelf comprise high complex architectures with cross-cutting subglacial erosion surfaces in places (Moreau, 2011). 3.3 THE SEDIMENTARY RECORD 55

FIGURE 3.5 Model of the glaciated shelf system of North Africa and Arabia during the Hirnantian glaciation after Ghienne et al. (2007). (A) Database. (B) Recognition of zones within the glaciated shelf region: an inner, middle, and outer shelf. Numbers correspond to the number of glacial cycles interpreted within each area, such that to the north (e.g., Morocco and Turkey) only one glacial cycle is recorded (and only at the glacial maximum). Repeated ice margin oscillations explain the greater number of glacial cycles in the inner glaciated shelf.

3.3.3 PALAEOVALLEYS: MELTWATER-DOMINATED SEDIMENTARY RECORD (FIG. 3.6) Le Heron (2016) viewed the Hirnantian sediment-landform system as meltwater-dominated. This view is based on the ubiquity of tunnel valley incisions that can (1) be observed at outcrop, (2) that can be mapped using aerial photography or satellite imagery, or (3) which can be imaged in the subsurface using seismic reflection data. Examples of tunnel valleys examined by these methods are shown in Fig. 3.6. Note that the recognition of Hirnantian tunnel valleysÀincisions produced 56 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

FIGURE 3.6 Palaeovalleys in three separate parts of the North Africa and Middle East region, interpreted to have been cut by subglacial meltwaters as tunnel valleys. (A) The El Eina palaeovalley, Tabuk region, NW Saudi Arabia. (B) The Dider palaeovalley, Tassili N’Ajjer, Algeria (truck for scale). (C) The Foum Larjame palaeovalley, Anti-Atlas mountains, Morocco. In each case note (1) the undulose, complex basal surface to the glacial deposits (demarcated by an unconformity), (2) the occurrence of very similar, stratiform, paralic deposits beneath the glacial successions, and (3) the cliff-forming (sandstone-rich) character to the syn-glacial deposits above the unconformity. All photos: D.P. Le Heron. under elevated hydrostatic pressures beneath an ice massÀrelies on them being geomorphologically identical to their famous Pleistocene counterparts on the north European plain (Van der Vegt et al., 2012). For example, from the western Sahara in Mauritania, Ghienne and Deynoux (1998) published a very useful table allowing the geometries of tunnel valleys with incisions produced through other mechanisms (e.g., nonglacial fluvial valleys) for comparison. In a practical sense, aside from the geometric differences in scale and aspect ratio when compared with fluvial valleys and submarine canyons (Ghienne and Deynoux, 1998), establishing that incisions in the Hirnantian record are subglacial in character revolves around the following criteria. Evidence for soft-sediment deformationÀtypically downward flexure of preglacial strata or fluidizationÀis often apparent (Fig. 3.7). This deformation is attributable to the effects of ice-loading. Similarly, the base or margins of the palaeovalleys commonly exhibit evidence for the ice sheet overburden, with intraformational striated pavements preserved in a number of cases (cf., Le Heron et al., 2004). FIGURE 3.7 (A) Detail of a tunnel valley margin in southern Algeria (the Iherir East palaeovalley). Note the stratiform nature of the In Tahouite Formation, and their flexure immediately below, and adjacent to, the tunnel valley incision (marked by red undulating line). Basal deposits of the glaciogenic Tamadjert Formation are, at this locality, composed of massive, muddy sandstones. Width of photo c. 50 m. (B) Seismic section showing a tunnel valley cutting into the stratiform deposits of the Qasim Formation in the subsurface of Saudi Arabia. Note that this is an identical stratigraphic relationship to that shown in Fig. 3.6A. From McGillivray, J.G., Husseini, M.I., 1992. The Palaeozoic petroleum geology of central Arabia. Am. Assoc. Petrol. Geol. Bull. 76 (10), 1473À1490. 58 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

Finally, in planform, an anastomosing character is typical, and can be recognized both by surface and subsurface mapping, although individual/isolated tunnel valleys are not uncommon. The best-studied region for tunnel valleys is probably North Africa, although it should be recognized that examples are also reported from Jordan (Douillet et al., 2012), Spain (Gutierrez-Marco´ et al., 2010), and Saudi Arabia (Vaslet, 1990). In the North Africa area, Le Heron and Craig (2008) tried to document the regional distribution of these features and it was found that ‘swarms’ of tunnel valleys corresponded to palaeo-grounding lines. There remain large areas where no tunnel valleys appear to be present (eastern Al Kufrah Basin: Le Heron et al., 2010), although other important types of incision are recognized. Mostly, the picture seems to be one of meltwater incisions cradling the Hirnantian glacial deposits, and wider incisions produced by palaeo-ice streams (Moreau et al., 2005; Ghienne et al., 2007; Le Heron and Craig, 2008) are more than an order of magnitude greater than the tunnel valleys in terms of length and width ( . 50 km wide and .200 km length). Establishing the nature and dimensions of these incisions is important because it sets the scene for, and hopefully allows us to understand, the origins if the Hirnantian glacially related sediments that sit within them.

3.3.4 REGIONAL ICE SHEET DYNAMICS Le Heron and Craig (2008) developed the initial hypothesis of Ghienne et al. (2007) to propose a map of the Hirnantian glacial maximum which integrated observations from outcrops across North Africa, subsurface information (well and seismic observations) and satellite imagery (Fig. 3.8). The location of palaeo-ice stream pathways was posited, and these were mapped across the region. Some of these more speculative palaeo-ice stream pathways are now confirmed by very high- quality mapping interpretations from wide desert areas of North Africa, such as in the Murzuq Basin in Libya (Moreau and Ghienne, 2016). Whilst hopefully still a useful compilation 8 years on, the availability of new proprietary data, and ongoing research, necessarily implies that this palaeogeographic snapshot of this glaciation requires local refinement (see, e.g., Deschamps et al., 2013; Ravier et al., 2015). It is thus a far from perfect map; the presence of large gaps in outcrop to constrain this model cannot be overcome, and never will be! It should be noted that no such map has hitherto been published from the Arabian Peninsula: this remains a research priority. The starting point for this might be considered to be the work of Aoudeh and Al-Hajri (1995), who systematically mapped palaeovalley incisions in NW Saudi Arabia, demonstrating a general radiating pattern around the Arabian Shield (Fig. 3.9). The significance of this remains to be properly investigated, although detailed work in the Jordanian sector suggests that these palaeovalleys are also tunnel valleys in character (Douillet et al., 2012). It could be speculated, therefore, that the Arabian Shield acted as a stable pinning point for the ice sheet. The NW Saudi Arabian region has a high-quality archive of glacial deposits represented by the Sarah Formation (Fig. 3.10). The glacial features include clear examples of intraformational striated surfaces (Fig. 3.10A and B) which in places bear well-expressed plough marks (Fig. 3.10C), confirming their soft-sediment origin. Many of these striated surfaces were documented, as least in a preliminary sense, by Senalp and Al-Laboun (2000). These commonly exhibit postdepositional deformation structures, including centimetre-scale extensional faults (Fig. 3.10D). Furthermore, boulder pavements of exceptional quality (Fig. 3.10E) occur in places, providing proxy evidence for subglacial erosion. In Saudi Arabia, the boulder pavements are rich in granite that was derived 3.3 THE SEDIMENTARY RECORD 59

FIGURE 3.8 Palaeogeographic reconstruction of North Africa at the Hirnantian glacial maximum, emphasizing the location of palaeo-ice streams. The occurrence of mega-scale glacial lineations helps to constrain these but, in reality, there is commonly a huge data gap between areas. This is most obvious in Libya where a large basement uplift, the Tibesti Mountains, separates the Dur al Gussa and Jabal Eghei data control points. The smaller map shows the location of tunnel valley incisions which demarcate grounding line positions in a stepwise retreat. Map from Le Heron, D.P., 2016. The Hirnantian glacial landsystem of the Sahara: a meltwater-dominated system. In: Dowdeswell, J.A., Canals, M., Jakobssen, M., Todd, B.J., Dowdeswell, E.K. & Hogan, K.A. (Eds.), Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient. Geological Society, London, Memoirs, redrawn after Le Heron, D.P., Craig, J., 2008. First-order reconstructions of a Late Ordovician Saharan ice sheet. J. Geol. Soc. Lond. 165, 19À29. doi:10.1144/0016-76492007-002.

from the Arabian Shield. Individual boulders exhibit striations that crosscut both quartz and alkali feldspar crystals, testifying to their subglacial or englacial transport (Fig. 3.10E).

3.3.5 PALAEOVALLEYS VERSUS INTERFLUVES Much of the interest in Hirnantian glacial successions has revolved around their regional significance throughout North Africa and the Middle East as hydrocarbon reservoirs (Le Heron et al., 2009). In this context, much of the focus has been on palaeovalleys as these are discrete bodies of sediment that can be described and understood in three dimensions. In some areas, palaeovalleys cutting down into earlier sedimentary rocks provide most of the sedimentary record for the Late Ordovician (e.g., Arabian Shield area: Vaslet, 1990; Douillet et al., 2012), whereas in other areas a substantive ‘interfluve’ record is preserved (e.g., southern Libya: Ghienne et al., 2007; 60 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

FIGURE 3.9 Distribution of palaeovalleys around the NW part of the Arabian Shield area after Aoudeh and Al-Hajri (1995).

Le Heron et al., 2010). The majority of small (i.e., a few hundred metres deep, few kilometre wide, tens of kilometre long) palaeovalleys are interpreted as tunnel valleys (e.g., Deschamps et al., 2013; Clerc et al., 2013; Ravier et al., 2015), i.e., incisions that were cut by meltwater under the confining pressure of the overlying ice sheet (Van der Vegt et al., 2012). With particular consideration for the large cross-shelf trough systems produced by palaeo-ice streams, Ghienne et al. (2007) developed simple predictive models explaining that the stratigraphy of former ice-stream pathways and interstream areas show distinct differences (Fig. 3.11). The palaeo-ice stream pathways appear to range 50À200 km wide, and up to 1000 km long; the smaller tunnel valleys occur both within the palaeo-ice stream pathways and in the interstream areas (Le Heron and Craig, 2008). In some regions, the tunnel valley incisions are almost completely isolated features cutting into preglacial strata, and any record of glacial deposits between them is almost entirely lacking (such as in Saudi Arabia). The reason for this is speculative but tentatively linked to diminished accommodation space in the Arabian Shield area, but more widely available in southern Libya forming the incision of the palaeovalleys. Some of the palaeovalleys coincide with pre-existing faults that crosscut the basement (Ghienne et al., 2003), whereas others appear to show no clear relationship to basement faults (Deschamps et al., 2013). This simple observation implies that whereas the presence of faults provided good conditions for palaeovalley excavation, structural weaknesses were not a prerequisite. Furthermore, in Morocco, petrographic analysis of sandstones and the observation that some palaeovalleys are underlain by suites of soft-sediment injectites whereas others are not, leads to a lively debate on the controls of tunnel valley genesis (Ravier et al., 2015)(Box 3.1). 3.3 THE SEDIMENTARY RECORD 61

FIGURE 3.10 Glacial phenomena from the Sarah Formation of NW Saudi Arabia. (A) Soft-sediment striated surface overlain by a siltstone horizon, thereby illustrating its intraformational nature. (B) Striated surface with some considerable (m-scale) topography. (C) Detail of part of the striated surface shown in (B). Note the large groove and ridge, testifying to its generation in unconsolidated sand. (D) Small extensional faults, typically associated with deformed intervals below striated surfaces. (E) Large granite boulder, representing part of a boulder pavement. (F) Detail of the boulder shown in (E). Note the striae running vertically through the photo. All photos: D.P. Le Heron. FIGURE 3.11 Simple models showing the difference in stratigraphic architectures of glacial deposits formed within (A) ice- stream pathways and (B) in interstream areas. From Ghienne, J.-F., Le Heron, D.P., Moreau, J., Deynoux, M., 2007. The Late Ordovician glacial sedimentary system of the West Gondwana platform. In: Hambrey, M.J., Cristofferson, P., Glasser, N., Hubbard, B. (Eds.), Glacial Sedimentary Environments: Processes and Products: Special Publication, International Association of Sedimentologists, vol. 39, pp. 295À319.

BOX 3.1 TUNNEL VALLEYS AND MELTWATER CHANNELS The occurrence of incisions several hundred metres deep, up to several kilometre wide, and up to several tens of kilometre in length has long been known since these structures were beautifully mapped by Beuf et al. (1971) in the Tassi N’Ajjer region. Given the occurrence of striated surfaces at the base of some of these, coupled with intense intrastratal deformation in others, the consensus is that these were cut through the action of subglacial meltwaters beneath an overriding ice sheet (hence the term tunnel valleys). Understanding the precise process of incisionÀwhether through a steady state, continuous, or catastrophic processÀhas remained problematic largely due to the absence of suitable modern analogues (see Van der Vegt et al., 2012, for a review). A new wave of investigations, conducted in southern Morocco (Clerc et al., 2013; Ravier et al., 2014), sheds new light on the problem. These are summarized in this box. The image (from Ravier et al., 2014) schematically shows the relationship between preglacial paralic strataÀrepresenting the substrate of a tunnel valley in MoroccoÀand the basal glacial infill of that valley. To the right, an inventory of deformation structures is shown, and their interpreted relationship to porewater pressure variations in 13 phases of development is indicated. Heightened porewater pressures, associated with hydrofracturing and brecciation, promote tunnel valley development. The preglacial strata are ideally configured to do this, owing to the layer cake intercalation of aquifers and aquitard horizons. Deposition and deformation of sediments occurred simultaneously within the valley once it had begun to form. A porewater pressure control clearly has applicability in Morocco, but regions where tunnel valleys cut into thick sandstone successions (such as in Mauritania: Ghienne and Deynoux, 1998) may still require an additional mechanism! (Continued ) 3.3 THE SEDIMENTARY RECORD 63

BOX 3.1 TUNNEL VALLEYS AND MELTWATER CHANNELS (CONTINUED) 64 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

3.3.6 THE INFLUENCE OF SEA LEVEL CHANGES ON GLACIATED SHELF ARCHITECTURE The application of sequence stratigraphic methodologies to Late Ordovician glacial successions is difficult, but considerable progress was made by Ghienne et al. (2007). In that paper, schematic stratigraphic architectures were shown during glacial advance, at an ice maximum, and during glacial retreat (Fig. 3.11). In a sequence stratigraphic framework, the sequence boundary was placed at the glacial erosion surface. This simple solution does not appear to be without its problems. In particular, owing to the very sandy nature of the deposits, there was confusion in the first few years of this century regarding where a glacial erosion surface or sequence boundary should be placed. The crux of the problem is that with a few exceptions (e.g., Denis et al., 2010), Hirnantian ice sheets appeared to advance over unconsolidated sediments. As they did so, soft- sediment striated surfaces were formed, with examples from Morocco (Le Heron, 2007; Le Heron et al., 2007; Loi et al., 2010; Clerc et al., 2013), Algeria (Beuf et al., 1971; Deschamps et al., 2013), Libya (Sutcliffe et al., 2000; Deynoux and Ghienne, 2004; Le Heron et al., 2005, 2010), Turkey (Monod et al., 2003), Jordan (Powell et al., 1994; Turner et al., 2005), Saudi Arabia (Vaslet, 1990; Clark-Lowes, 2005), and South Africa (Blignault and Theron, 2010)all clearly documented. The effects of advancing and overriding ice hence affected many tens to hundreds of metres of unconsolidated sediment (Le Heron et al., 2005; Blignault and Theron, 2010). The development of soft-striated sediments consequently occurred at multiple stratigraphic levels, akin to a sliding deck of cards over a table top (Sutcliffe et al., 2000). Hence, identifica- tion of the true sequence boundary (recording the ice sheetÀsediment interface) rather than a ‘quasi-unconformity’ produced through soft-sediment deformation is a very difficult, and seldom entirely objective, process (Box 3.2).

BOX 3.2 STRIATED GLACIAL SURFACES AND THEIR MODE OF FORMATION Considerable controversy once surrounded the true nature of soft-sediment striated surfaces in Late Ordovician rocks of Gondwana. It was determined that many grooved sandstone surfaces were crosscut by fluidization structures, and that in some places, stacked occurrences of striated surfaces repeated over a few metres of stratigraphy. These observations led Sutcliffe et al. (2000) to propose that they formed simultaneously in soft sediment, like a shearing deck of cards, an idea further developed by Deynoux and Ghienne (2004) who independently came to the same conclusions. Le Heron et al. (2005) developed this idea further, recognizing two types of striated surfaces: the stratigraphically repeated examples and the stratigraphically isolated examples. The stacked examples were attributed to freezing fronts moving up and down through a subglacial aquifer (i.e., they formed under cold-based conditions), whereas the stratigraphic isolation of others suggested to those workers that origin at the iceÀbed interface (sliding, warm-bed conditions) was the only plausible explanation. Denis et al. (2007, 2010) undertook detailed investigations of the Hirnantian-age Felar Felar Formation in the Djado Basin, northern Niger. Their 2010 paper, summarized here as models focusing on the typology of structures developed on subglacial pavements, effectively proposed the inverse hypothesis to Le Heron et al. (2005) whereby rigid bed conditionsÀsupported by an abundance of extensional microfaults, and grain crushing (as revealed through micromorphological study)Àwere associated with stratigraphically isolated examples. Source: Diagrams from Denis et al. (2010). (Continued ) 3.3 THE SEDIMENTARY RECORD 65

BOX 3.2 STRIATED GLACIAL SURFACES AND THEIR MODE OF FORMATION (CONTINUED)

(Continued ) BOX 3.2 STRIATED GLACIAL SURFACES AND THEIR MODE OF FORMATION (CONTINUED) 3.3 THE SEDIMENTARY RECORD 67

3.3.7 TYPICAL LITHOFACIES ASSEMBLAGES? As noted earlier, spectacular palaeovalley fill successions are characteristic of large areas of the glaciated shelf areas of Gondwana. The lateral and vertical complexity of lithofacies is notable, though some generalizations can be made. Sheet sandstones are recognized from across the central part of North Africa. These include the examples of the Algerian (Beuf et al., 1971; Hirst et al., 2002; Hirst, 2012) and Libyan (Girard et al., 2012a,b, 2015) Tassili N’Ajjers, together with examples from both the western (Jabal Eghei: Le Heron et al., 2015) and eastern (Jabal Azbah: Le Heron et al., 2010) flanks of Al Kufrah Basin near the Egyptian border. Together, these rocks of a broadly similar facies assemblage span a highly disconnected outcrop belt over 1000 km from west to east. The typical occurrence of climbing dune cross-stratification (Ghienne et al., 2010a)in many of these outcrops may imply that large swathes of the outcrop belts were deposited under supercritical conditions (Girard et al., 2015). These conditions are compatible with the idea that sustained flows, possibly resulting from meltwater outburst events, may be responsible for these as well as the tunnel valleys. Thus, the simple idea of meltwater dominance in this regional sedimentary system, coupled with the comparatively low accommodation space available in a broad, extensive shelf, explains both the complexity of the stratigraphy and the difficulty of generalizing a typical facies assemblage. It may be argued that the terminal phase of the glaciation has a common signature across many parts of North Africa and the Middle East. In an early pan-Gondwana attempt to devise a process- based model for these rocks, Sutcliffe et al. (2000) suggested a simple twofold glaciation. In their model, it was posited that the glacial cycles were possibly orchestrated by CrollÀMilankovitch cycles and that a regional crustal rebound event signalled the end of glaciation. Their proposed rebound deposits were identified as very coarse-grained to granular sandstones with abundant bioturbation, resting on a regional (and locally angular) unconformity. A very different interpretation was raised for these deposits by Moreau (2011) from SW Libya who showed that the bioturbated sandstones represented part of a palaeovalley fill. A common interpretation of environmental amelioration following peak glaciation is recognized. A substantial residual topography was left on the North African shelf following the glacial maximum. Aside from the interpretation of glacial landforms with a substantial present-day topography (e.g., mega-scale glacial lineations: Moreau et al., 2005; Moreau and Ghienne, 2016), the strongest evidence for this topography is biostratigraphic. For example, Aeronian shales drap- ing the Hirnantian glacial deposits on the southern Gargaf Arch, Libya, are consistent with pro- gressive flooding of a topography and diachroneity in the earliest, postglacial transgressive deposits (Lu¨ning et al., 2000). Given the regional considerations, it seems likely that much of this regional topography was related to the complexity of the incision network (as demonstrated by Moreau, 2011). A clear departure from this regional theme is in the western part of Al Kufrah Basin, Libya, where a thin, carbonate-rich interval at the top of the Mamuniyat glacial deposits is succeeded by shales with dropstones and a further striated pavement possibly recording a late- stage glacial advance (Le Heron et al., 2013). Based on stratophenetic arguments, the occurrence of Monograptus kufraensis sp. Nov in the shales may indicate either latest Hirnantian or an early Rhuddanian age (Page et al., 2013). 68 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

3.4 CONCLUSIONS This chapter has highlighted the various occurrences of Early Palaeozoic glacial deposits, concluding that most (though not all) are Hirnantian in age, and that an excellent archive is preserved in the North Africa and Middle East area. Owing to the intensity of research in this region over the last 20 years or so, models explaining the complexity of the stratigraphic record (i.e., whether an area lies within the inner, middle, or outer glaciated shelf: Ghienne et al., 2007), plus palaeogeographic models which map the location of both palaeo-ice streams at the glacial maximum plus grounding lines during retreat, are available. These models are being constantly refined and modified at the local scale, but it is emphasized that the significant data gaps in areas where the strata are missing are simply impossible to overcome in some areas. An area ripple for future investiga- tion and research concerns the geometry and extent of ice sheets in the Arabian peninsula, for which a detailed map has never been attempted.

REFERENCES

Abed, A.M., Makhlouf, I.M., Amireh, B.S., Khalil, B., 1993. Upper ordovician glacial deposits in Jordan. Episodes 16, 316À328. Allen, P.A., 2007. The Huqf Supergroup of Oman: basin development and context for Neoproterozoic glaciation. Earth-Sci. Rev. 84, 139À185. Available from: http://dx.doi.org/10.1016/j.earscirev.2007.06.005. Aoudeh, S.M., Al-Hajri, S.A., 1995. Regional distribution and chronostratigraphy of the Qusaiba Member of the Qalibah Formation in the Nafud Basin, northwestern Saudi Arabia. In: Al-Husseini, M.I. (Ed.), Geo ‘94, The Middle East Petroleum Geosciences (1). Gulf PetroLink, Manama, Bahrain, pp. 143À154. Armstrong, H.A., Turner, B.R., Makhlouf, I.M., Weedon, G.P., Williams, M., Al Smadi, A., et al., 2005. Origin, sequence stratigraphy and depositional environment of an upper Ordovician (Hirnantian) deglacial black shale, Jordan. Palaeogeogr. Palaeoclimatol. Palaeoecol. 220, 273À289. Available from: http://dx.doi. org/10.1016/j.palaeo.2005.01.007. Bernardez,´ E., Gutierrez-Marco,´ J.C., Hacar, Y.M., 2006. Sedimentos Glaciomarinos del Ordov´ıcico Terminal en la Zona Cantabrica´ (NO de Espan˜a). Geogaceta 40, 239À242. Berry, B.N., Finney, S.C., 2001. The Queenston sedimentary complex; a link with late Ordovician glaciation? (abs.). Abstr. Programs-Geol. Soc. Am. 33, 215. Beuf, S., Biju-Duval, B., de Charpal, O., Rognon, P., Gariel, O., Bennacef, A., 1971. Les Gre`sdu Palaeozoı¨que inferieur´ au Sahara. Editions Technip, Paris, 464 pp. Blignault, H.J., Theron, J.N., 2010. Reconstruction of the Ordovician Pakhuis ice sheet, South Africa. S. Afr. J. Geol. 113, 335À360. Brenchley, P.J., Storch,ˇ P., 1989. Environmental changes in The Hirnantian (Upper Ordovician) of The Prague Basin, Czechoslovakia. Geol. J. 24, 165À181. Brenchley, P.J., Marshall, J.D., Carden, G.A., Robertson, D.B.R., Long, D.G.F., Meidla, T., et al., 1994. Bathymetric and isotopic evidence for a short-lived Late Ordovician Glaciation in a Greenhouse Period. Geology 22, 295À298, doi:10.1130/0091-7613(1994)022 , 0295:BAIEFA . 2.3.CO. Clark-Lowes, D.D., 2005. Arabian glacial deposits: recognition of palaeovalleys within the Upper Ordovician Sarah Formation, Al Qasim district, Saudi Arabia. Proc. Geol. Assoc. 116, 331À347, doi:10.1016/S0016- 7878(05)80051-3. REFERENCES 69

Clerc, S., Buoncristiani, J.F., Guiraud, M., Vennin, E., Desaubliaux, G., Portier, E., 2013. Subglacial to proglacial depositional environments in an Ordovician glacial tunnel valley, Alnif, Morocco. Palaeogeogr. Palaeoclimatol. Palaeoecol. 370, 127À144. Available from: http://dx.doi.org/10.1016/j.palaeo.2012.12.002. Couto, H., Knight, J., Lourenc¸o, A., 2013. Late Ordovician ice-marginal processes and sea-level change from the north Gondwana platform: evidence from the Valongo Anticline (northern Portugal). Palaeogeogr. Palaeoclimatol. Palaeoecol. 375, 1À15. Available from: http://dx.doi.org/10.1016/j.palaeo.2013.02.006. de la Puente, G.S., Rubinstein, C.V., 2013. Ordovician chitinozoans and marine phytoplankton of the Central Andean Basin, northwestern Argentina: a biostratigraphic and palaeobiogeographic approach. Rev. Palaeobot. Palynol. 198, 14À26. Available from: http://dx.doi.org/10.1016/j.revpalbo.2012.03.007. Delabroye, A., Vecoli, M., 2010. The end-Ordovician glaciation and the Hirnantian Stage: a global review and questions about Late Ordovician event stratigraphy. Earth-Sci. Rev. 98, 269À282. Available from: http:// dx.doi.org/10.1016/j.earscirev.2009.10.010. Denis, M., Buoncristiani, J.-F., Konate,´ M., Guiraud, M., 2007a. The origin and glaciodynamic significance of sandstone ridge networks from the Hirnantian glaciation of the Djado Basin (Niger). Sedimentology. 54 (6), 1225À1243. Denis, M., Buoncristiani, J.-F., Konate,´ M., Ghienne, J.-F., Guiraud, M., 2007b. Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger). Geodin. Acta. 20 (3), 177À195. Denis, M., Guiraud, M., Konate,´ M., Buoncristiani, J.F., 2010. Subglacial deformation and water-pressure cycles as a key for understanding ice stream dynamics: evidence from the Late Ordovician succession of the Djado Basin (Niger). Int. J. Earth Sci. 99, 1399À1425. Available from: http://dx.doi.org/10.1007/s00531-009-0455-z. Deschamps, R., Eschard, R., Rousse,´ S., 2013. Architecture of Late Ordovician glacial valleys in the Tassili N’Ajjer area (Algeria). Sediment. Geol. 289, 124À147. Available from: http://dx.doi.org/10.1016/j.sedgeo.2013.02.012. Deynoux, M., Ghienne, J.-F., 2004. Late Ordovician glacial pavements revisited: a reappraisal of the origin of striated surfaces. Terra Nova 17 (5), 488À491. D´ıaz-Mart´ınez, E., Grahn, Y., 2007. Early Silurian glaciation along the western margin of Gondwana (Peru, Bolivia and northern Argentina): palaeogeographic and geodynamic setting. Palaeogeogr. Palaeoclimatol. Palaeoecol. 245, 62À81. Available from: http://dx.doi.org/10.1016/j.palaeo.2006.02.018. Douillet, G., Ghienne, J.-F., Geraud,´ Y., Abueladas, A., Diraison, M., Al-Zoubi, A., 2012. Late Ordovician tunnel valleys in southern Jordan. In: Huuse, M., Redfern, J., Le Heron, D.P., Dixon, R.J., Moscariello, A., Craig, J. (Eds.) Glaciogenic Reservoirs and Hydrocarbon Systems. The Geological Society, London, pp. 275À292. Available from: http://dx.doi.org/10.1144/SP368.4. Fortuin, A.R., 1984. Late Ordovician glaciomarine deposits Orea Shale in the Sierra De Albarracin Spain. Palaeogeogr. Palaeoclimatol. Palaeoecol. 48, 245À261. Ghavidel-syooki, M., A´ lvaro, J.J., Popov, L., Pour, M.G., Ehsani, M.H., Suyarkova, A., 2011. Stratigraphic evidence for the hirnantian (latest ordovician) glaciation in the zagros mountains, Iran. Palaeogeogr. Palaeoclimatol. Palaeoecol. 307, 1À16. Available from: http://dx.doi.org/10.1016/j.palaeo.2011.04.011. Ghienne, J.-F., 2003. Late Ordovician sedimentary environments, glacial cycles, and post-glacial transgression in the Taoudeni Basin, West Africa. Palaeogeogr. Palaeoclimatol. Palaeoecol. 189, 117À145. Ghienne, J.F., Deynoux, M., 1998. Large-scale channel fill structures in Late Ordovician glacial deposits in Mauritania, western Sahara. Sediment. Geol. 119, 141À159. Ghienne, J.-F., Deynoux, M., Manatschal, G., Rubino, J.-L., 2003. Palaeovalleys and fault-controlled depocen- tres in the Late-Ordovician glacial record of the Murzuq Basin (central Libya). C. R. Geosci. 335, 1091À1100. Available from: http://dx.doi.org/10.1016/j.crte.2003.09.010. Ghienne, J.-F., Le Heron, D.P., Moreau, J., Deynoux, M., 2007. The Late Ordovician glacial sedimentary system of the West Gondwana platform. In: Hambrey, M.J., Cristofferson, P., Glasser, N., Hubbard, B. (Eds.), Glacial Sedimentary Environments: Processes and Products: Special Publication, 39. International Association of Sedimentologists, pp. 295À319. 70 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

Ghienne, J.F., Girard, F., Moreau, J., Rubino, J.L., 2010a. Late Ordovician climbing-dune cross-stratification: a signature of outburst floods in proglacial outwash environments?. Sedimentology 57, 1175À1198. Available from: http://dx.doi.org/10.1111/j.1365-3091.2009.01142.x. Ghienne, J.F., Monod, O., Kozlu, H., Dean, W.T., 2010b. Cambrian-Ordovician depositional sequences in the Middle East: a perspective from Turkey. Earth-Sci. Rev. 1010, 101À146. Ghienne, J.F., Moreau, J., Degermann, L., Rubino, J.-L., 2013. Lower Palaeozoic unconformities in an intracratonic plat-form setting: glacial erosion versus tectonics in the eastern Murzuq Basin (southern Libya). Int. J. Earth Sci. 102, 455À482. Girard, F., Ghienne, J.F., Rubino, J.-L., 2012a. Occurrence of hyperpycnal flows and hybrid event beds related to glacial outburst events in a Late Ordovician proglacial delta (Murzuq Basin, SW Libya). J. Sediment. Res. 82, 688À708. Girard, F., Ghienne, J.F., Rubino, J.-L., 2012b. Channelized sandstone bodies (“cordons”) in the Tassili N’Ajjer (Algeria & Libya): snapshots of a Late Ordovician proglacial outwash plain. In: Huuse, M., Redfern, J., Le Heron, D.P., Dixon, R.J., Moscariello, A., Craig, J. (Eds.), Glaciogenic Reservoirs and Hydrocarbon Systems. Geol. Soc. London Spec. Publ., 368, pp. 355À380. Girard et al., 2015. Girard, F., Ghienne, J.F., Du Bernard, X., Rubino, J.-L., 2015. Sedimentary imprints of former ice-sheet margins: insights from an end-Ordovician archive (SW Libya). EarthÀSci. Rev. 148, 259À289. Grahn, Y., 1991. The Ordovician-Devonian biostratigraphy of Brazil. An. Acad. Bras. Cienc. Resumo Comun. 94. Grahn, Y., Caputo, M.V., 1992. Early Silurian glaciations in Brazil. Palaeogeogr. Palaeoclimatol. Palaeoecol. 99, 9À15, doi:10.1016/0031-0182(92)90003-N. Grahn, Y., Paris, F., 1992. Age and correlation of the Trombetas Group, Amazonas Basin, Brazil. Rev. Micropalaeontol 35, 20À32. Grahn, Y., Gutierrez,´ P.R., 2001. Silurian and Middle Devonian Chitinozoa from the Zapla and Santa Barbara´ Ranges, Tarija Basin, northwestern Argentina. Ameghiniana 38, 35À50. Gray, Y., Colbath, G.K., Faria, A., BoucoL, A.J., Rohr, D.M., 1985. Silurian age fossils from the Palaeozoic Paranfi Basin, southern Brazil. Geology 13, 521À525. Gutierrez-Marco,´ J.C., Ghienne, J.F., Bernardez,´ E., Hacar, M.P., 2010. Did the late Ordovician African ice sheet reach Europe? Geology 38, 279À282. Available from: http://dx.doi.org/10.1130/G30430.1. Hambrey, M., 1985. The Late OrdovicianÀEarly Silurian glacial period. Palaeogeogr. Palaeoclimatol. Palaeoecol. 51, 273À289. Hambrey, M.J., Harland, W.B., 1981. Earth’s pre-Pleistocene glacial record. Cambridge University Press, London, 1022 p. Hirst, J.P.P., 2012. Ordovician proglacial sediments in Algeria: insights into the controls on hydrocarbon reservoirs in the In Amenas field, Illizi Basin. In: Huuse, M., Redfern, J., Le Heron, D.P., Dixon, R.J., Moscariello, A., Craig, J. (Eds.), Glaciogenic Reservoirs and Hydrocarbon Systems. Geol. Soc. London Spec. Publ. 368, 319À354. Hirst, J.P.P., Benbakir, A., Payne, D.F., Westlake, I.R., 2002. Tunnel valleys and density flow processes in the upper Ordovician glacial succession, Illizi Basin, Algeria: influence on reservoir quality. J. Pet. Geol. 25, 297À324. Huuse, M., Redfern, J., Le Heron, D.P., Dixon, R.J., Moscariello, A., Craig, J., 2012. Glaciogenic Reservoirs and Petroleum Systems. Geol. Soc. Lond. Spec. Publ. 368, 1À28. Kump, L.R., Arthur, M.A., Patzkowsky, M.E., Gibbs, M.T., Pinkus, D.S., Sheehan, P.M., 1999. A weathering hypothesis for glaciation at high atmospheric pCO2 during the Late Ordovician. Palaeogeogr. Palaeoclimatol. Palaeoecol. 152, 173À187, doi:10.1016/S0031-0182(99)00046-2. Le Heriss´ e,´ A., Molyneux, S.G., Miller, M.A., 2015. Review of Palaeobotany and Palynology Late Ordovician to early Silurian acritarchs from the Qusaiba-1 shallow core hole, central Saudi Arabia. Rev. Palaeobot. Palynol. 212, 22À59. Available from: http://dx.doi.org/10.1016/j.revpalbo.2014.08.016. Le Heron, D.P., 2007. Late Ordovician glacial record of the Anti Atlas, Morocco. Sediment. Geol. 201, 93À110. REFERENCES 71

Le Heron, D.P., Meinhold, G., Elgadry, M., Abutarruma, Y., Boote, D., 2015. Early Palaeozoic evolution of Libya: perspectives from Jabal Eghei with implications for hydrocarbon exploration in Al Kufrah Basin. Basin Res. 27 (1), 60À83. Le Heron, D.P., 2016. The Hirnantian glacial landsystem of the Sahara: a meltwater-dominated system. In: Dowdeswell, J.A., Canals, M., Jakobssen, M., Todd, B.J., Dowdeswell, E.K., Hogan, K.A. (Eds.), Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient. Geological Society, London, Memoirs. Le Heron, D.P., Craig, J., 2008. First-order reconstructions of a Late Ordovician Saharan ice sheet. J. Geol. Soc. Lond. 165, 19À29. Available from: http://dx.doi.org/10.1144/0016-76492007-002. Le Heron, D.P., Dowdeswell, J.A., 2009. Calculating ice volumes and ice flux to constrain the dimensions of a 440 Ma North African ice sheet. J. Geol. Soc. Lond. 166, 277À281. Available from: http://dx.doi.org/ 10.1144/0016-76492008-087. Le Heron, D.P., Howard, J.P., 2010. Evidence for Late Ordovician glaciation of Al Kufrah Basin, Libya. J. Afr. Earth Sci. 58, 354À364. Le Heron, D.P., Sutcliffe, O., Bourgig, K., Craig, J., Visentin, C., Whittington, R., 2004. Sedimentary architecture of Upper Ordovician tunnel valleys, Gargaf Arch, Libya: implications for the genesis of a hydrocarbon reservoir. GeoArabia 9, 137À160. Le Heron, D.P., Sutcliffe, O.E., Whittington, R.J., Craig, J., 2005. The origins of glacially-related soft-sediment deformation structures in Upper Ordovician glaciogenic rocks: implication for ice sheet dynamics. Palaeogeogr. Palaeoclimatol. Palaeoecol. 218, 75À103. Le Heron, D.P., Ghienne, J.F., El Houicha, M., Khoukhi, Y., Rubino, J.L., 2007. Maximum extent of ice sheets in Morocco during the Late Ordovician glaciation. Palaeogeogr. Palaeoclimatol. Palaeoecol. 245, 200À226. Available from: http://dx.doi.org/10.1016/j.palaeo.2006.02.031. Le Heron, D.P., Craig, J., Etienne, J.L., 2009. Ancient glaciations and hydrocarbon accumulations in North Africa and the Middle East. Earth-Sci. Rev. 93, 47À76. Le Heron, D.P., Armstrong, H.A., Wilson, C., Howard, J.P., Gindre, L., 2010. Glaciation and deglaciation of the Libyan Desert: the Late Ordovician record. Sediment. Geol. 223, 100À125. Available from: http://dx. doi.org/10.1016/j.sedgeo.2009.11.002. Le Heron, D.P., Meinhold, G., Bergig, K., 2013. Neoproterozoic-Devonian stratigraphic evolution of the eastern Murzuq Basin, Libya: a tale of tilting in the central Sahara. Basin Res. 25, 52À73. Le Heron, D.P., Meinhold, G., Elgadry, M., Abutarruma, Y., Boote, D., 2015. Early Palaeozoic evolution of Libya: perspectives from Jabal Eghei with implications for hydrocarbon exploration in Al Kufrah Basin. Basin Res. 27, 1À24. Available from: http://dx.doi.org/10.1111/bre.12057. Loi, A., Ghienne, J.F., Dabard, M.P., Paris, F., Botquelen, A., Christ, N., et al., 2010. The Late Ordovician glacio-eustatic record from a high-latitude storm-dominated shelf succession: the Bou Ingarf section (Anti- Atlas, Southern Morocco). Palaeogeogr. Palaeoclimatol. Palaeoecol. 296, 332À358. Available from: http:// dx.doi.org/10.1016/j.palaeo.2010.01.018. Lu¨ning, S., Craig, J., Loydell, D.K., Storch,ˇ P., Fitches, B., 2000. Lower Silurian ‘hot shales’ in North Africa and Arabia: regional distribution and depositional model. Earth Sci. Rev. 49 (1À4), 121À200. McGillivray, J.G., Husseini, M.I., 1992. The Palaeozoic petroleum geology of central Arabia. Am. Assoc. Petrol. Geol. Bull. 76 (10), 1473À1490. Meinhold, G., Morton, A.C., Avigad, D., 2013. New insights into peri-Gondwana palaeogeography and the Gondwana super-fan system from detrital zircon UÀPb ages. Gondwana Res. 23, 661À665. Melvin, J., 2015. Lithostratigraphy and depositional history of Upper Ordovician and lowermost Silurian sediments recovered from the Qusaiba-1 shallow core hole, Qasim region, central Saudi Arabia. Rev. Palaeobot. Palynol. 212, 3À21. Available from: http://dx.doi.org/10.1016/j.revpalbo.2014.08.014. Monaldi, C.R., Boso, M.A., Fernandez,´ J.C., 1986. Estratigraf´ıa del Ordov´ıcico de la Sierra de Zapla, Pcia. Jujuy. Rev. Assoc. Geol. Argentina 41, 62À69. 72 CHAPTER 3 THE EARLY PALAEOZOIC GLACIAL DEPOSITS OF GONDWANA

Monod, O., Kozlu, H., Ghienne, J.F., Dean, W.T., Gu¨nay, Y., Le Heriss´ e,´ A., et al., 2003. Late Ordovician glaciation in southern Turkey. Terra Nov 15, 249À257. Available from: http://dx.doi.org/10.1046/j.1365- 3121.2003.00495.x. Moreau, J., 2011. The Late Ordovician deglaciation sequence of the SW Murzuq Basin (Libya). Basin Res. 23, 449À477. Moreau, J., Ghienne, J.-F., 2016. Cross-shelf trough and ice-stream lineations in the 440 Ma Late Ordovician rocks of northern Africa mapped from high-resolution satellite imagery. In: Dowdeswell, J.A., Canals, M., Jakobssen, M., Todd, B.J., Dowdeswell, E.K., Hogan, K.A. (Eds.), Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient. Geological Society, London, Memoirs. Moreau, J., Ghienne, J.-F., Le Heron, D.P., Rubino, J.-L., Deynoux, M., 2005. 440 Ma ice stream in North Africa. Geology 33, 753À756. Available from: http://dx.doi.org/10.1130/G21782.1. Page, A.A., Meinhold, G., Le Heron, D.P., Elgadry, M., 2013. Normalograptus kufraensis, a new species of graptolite from the western margin of the Kufra Basin, Libya. Geol. Mag. 150, 743À755. Paris, F., Verniers, J., Miller, M.A., Al-Hajri, S., Melvin, J., Wellman, C.H., 2015. Late OrdovicianÀearliest Silurian chitinozoans from the Qusaiba-1 core hole (North Central Saudi Arabia) and their relation to the Hirnantian glaciation. Rev. Palaeobot. Palynol. 212, 60À84. Available from: http://dx.doi.org/10.1016/j. revpalbo.2014.10.005. Powell, J.H., Moh’d, B.K., Masri, A., 1994. Late Ordovician—Early Silurian glaciofluvial deposits preserved in palaeovalleys in South Jordan. Sediment. Geol. 89, 303À314, doi:10.1016/0037-0738(94)90099-X. Ravier, E., Buoncristiani, J.-F., Guiraud, M., Menzies, J., Clerc, S., Goupy, B., Portier, E., 2014. Porewater pressure control on subglacial soft sediment remobilization and tunnel valley formation: a case study from the Alnif tunnel valley (Morocco). Sediment. Geol. 304, 71À95. Ravier, E., Buoncristiani, J.-F., Menzies, J., Guiraud, M., Clerc, S., Portier, E., 2015. Does porewater or meltwater control tunnel valley genesis? Case studies from the Hirnantian of Morocco. Palaeogeogr. Palaeoclimatol. Palaeoecol. 418, 359À376. Raymo, M.E., Ruddiman, W.F., 1992. Tectonic forcing of late Cenozoic climate. Nature 359, 117À122. Robardet, M., Dore,´ F., 1988. The Late Ordovician Diamictic Formations from SW Europe: N Gondwana Glaciomarine Deposits. Palaeogeogr. Palaeoclimatol. Palaeoecol. 66, 19À31. Rubinstein, C.V., de la Puente, G.S., 2008. Bioestratigraf´ıa del Palaeozoico Inferior en las Sierras Subandinas, provincia de Jujuy. In: Coira, B., Zappettini, E.O. (Eds.), 17 Congreso Geolo´gico Argentino: Geolog´ıa y Recursos Naturales de Jujuy, Relatorio, pp. 128À133. Scotese, C.R., Boucot, A.J., McKerrow, W.S., 1999. Gondwanan palaeogeography and palaeoclimatology. J. Afr. Earth Sci. 28, 99À114, doi:10.1016/S0899-5362(98)00084-0. Senalp, M., Al-Laboun, A., 2000. New evidence on the late Ordovician glaciation in central Saudi Arabia. Saudi Aramco J. Technol. 11À40. Smith, A.G., 1997. Estimates of the Earth’s spin (geographic) axis relative to Gondwana from glacial sediments and palaeomagnetism. Earth-Sci. Rev 42, 161À179, doi:10.1016/S0012-8252(96)00047-5. Smith, A.G., Pickering, K.T., 2003. Oceanic gateways as a critical factor to initiate icehouse Earth. J. Geol. Soc. Lond. 160, 337À340. Available from: http://dx.doi.org/10.1144/0016-764902-115. Storch,ˇ P., 1990. Upper Ordovician—lower Silurian sequences of the Bohemian Massif, central Europe. Geol. Mag. 127, 225À239. Available from: http://dx.doi.org/10.1017/S0016756800014503. Sutcliffe, O.E., Dowdeswell, J.A., Whittington, R.J., Theron, J.N., Craig, J., 2000. Calibrating the Late Ordovician glaciation and mass extinction by the eccentricity cycles of the Earth’s orbit. Geology 23, 967À970. Torsvik, T.H., Cocks, L.R.M., 2009. The Lower Palaeozoic palaeogeographical evolution of the northeastern and eastern peri-Gondwanan margin from Turkey to New Zealand. In: Bassett, M.G. (Ed.), Early Palaeozoic Peri-Gondwana Terranes: New Insights From Tectonics and Biogeography. Geological Society, London, pp. 3À21. Available from: http://dx.doi.org/10.1144/SP325.2. REFERENCES 73

Turner, B.R., Makhlouf, I.M., Armstrong, H.A., 2005. Late Ordovician (Ashgillian) glacial deposits in southern Jordan. Sediment. Geol. 181, 73À91. Available from: http://dx.doi.org/10.1016/j.sedgeo.2005.08.004. Van der Vegt, P., Janszen, A., Moscariello, A., 2012. Tunnel valleys: current knowledge and future perspectives. In: Huuse, M., Redfern, J., Le Heron, D.P., Dixon, R.J., Moscariello, A., Craig, J. (Eds.), Glaciogenic Reservoirs and Hydrocarbon Systems. Geological Society, London, pp. 75À97. Available from: http://dx.doi.org/10.1144/SP368.13. Van Staden, A., Zimmermann, U., Chemale Jr., F., Gutzmer, J., Germs, G.J.B., 2010. Correlation of Ordovician diamictites from Argentina and South Africa using detrital zircon dating. J. Geol. Soc. 167, 217À220, London. Vaslet, D., 1987. Early Palaeozoic glacial deposits in Saudi Arabia, a lithostratigraphic revision. Technical Record of Saudi Arabian Directorate General forMineral Resources, BRGM-TR-07-1. Vaslet, D., 1990. Upper Ordovician glacial deposits in Saudi Arabia. Episodes 13, 147À161. Young, G.M., Minter, W.E.L., Theron, J.N., 2004. Geochemistry and palaeogeography of upper Ordovician glaciogenic sedimentary rocks in the Table Mountain Group, South Africa. Palaeogeogr. Palaeoclimatol. Palaeoecol. 214, 323À345. Available from: http://dx.doi.org/10.1016/j.palaeo.2004.07.029.