Anthropogenic trigger for Late Holocene soil erosion in the Jebel Toubkal, High Atlas, Morocco

W.J. Fletcher1* & P.D. Hughes1

1Quaternary Environments and Geoarchaeology, Geography, School of Environment, Education and Development, The University of Manchester, Manchester, M13 9PL, UK

*Corresponding author, will.fletcher@manchester.ac.uk

Abstract

The Assif n’Imserdane valley, located in the Jebel Toubkal area of the High Atlas, Morocco, is a highly dynamic geomorphological setting. The valley was glaciated during the Late Pleistocene, and subsequently experienced a catastrophic rock avalanche leading to the formation of one of the largest mass movement landforms in North Africa. Recent research (Hughes et al., GSA Bulletin 126: 1093-1104) has dated the formation of the rock avalanche to the mid-Holocene at 4.5 ± 0.5 ka. In this paper, we examine the sedimentological (organic matter content, magnetic susceptibility, particle size and XRF) and palaeoecological (pollen and spores, non-pollen palynomorphs (NPPs), microcharcoal and conifer tracheid fragments) record of a small infilled basin located adjacent to a Late Pleistocene moraine and close to the rock avalanche in the Arroumd sector. The deposits, primarily fine-grained and minerogenic with a low concentration of organic microfossils including pollen, coprophilous ascospores, wood and charcoal microfragments, are enriched in fine silts and ferrimagnetic minerals, consistent with erosional sources from surrounding slope soils. Three radiocarbon dates from the deposit indicate that the infill event occurred during the first millennium AD (after 430 - 640 AD). As such, the deposits point to a phase of slope instability and erosion that is not linked to either deglaciation processes or to the mid-Holocene rock avalanche. Instead, the nature and timing suggest that an anthropogenic trigger of degradation to the natural vegetation cover may be implicated, consistent with an increasing scale and intensity of pastoral activity in the southern High Atlas during the early Islamic period in Morocco. The record casts light on a previously undocumented phase of landscape instability in the dynamic setting of the Assif n’Imserdane valley, and highlights the potential for further exploration of small infilled basins in the High Atlas to illuminate the geoecological history of the region.

Keywords

High Atlas, pollen, non-pollen palynomorphs, microcharcoal, anthropogenic impact, soil erosion

1. Introduction

The Assif n’Imserdane in the Toubkal sector of the High Atlas, Morocco, represents a dynamic mountain landscape shaped by multiple forcing factors on Quaternary timescales. The understanding of the nature, timing and drivers of change in the High Atlas is a research priority, as for other Mediterranean and semi-arid mountain regions (Regato and Salmon, 2008; García-Ruiz, 2010). The Toubkal sector was the setting for some of the largest Pleistocene glaciers and ice fields in North Africa (Hughes et al., 2004; 2011; Hannah et al., 2016). The Assif n’Imserdane is also well-known as the location of one of North Africa’s largest mass movements and associated deposits, the Arroumd landform. Recent investigation employing cosmogenic isotope dating has demonstrated that the Arroumd rock avalanche events occurred during the mid-Holocene, ca. 4500 years ago (Hughes et al, 2014). Moraine features within the Assif n’Imserdane also yield similar mid-Holocene ages, despite corresponding altitudinally to Pleistocene moraine deposits in other locations of significantly greater antiquity, predating the Last Glacial Maximum (Hughes et al., 2004; 2011). The ages point to significant geomorphological modification of landsurfaces and landforms associated with the rock avalanche event and the inferred tectonic (earthquake) forcing.

To date, there are relatively few sedimentological or palaeoecological records from the High Atlas that can provide longer-term climatological or ecological context for the mid-Holocene Arroumd landslide. The most recent record is from Oukaimeden (2725 m, 31.2038°N, 7.8566°W; Figure 1) just 10 km to the northeast of Arroumd, where pollen, non-pollen palynomorph (NPP) and macrocharcoal data obtained from marsh and archaeological deposits span the last 4000 years (Ruiz et al., 2015). The study builds on pioneering work by Reille (1976). The composite pollen record derived from several clustered sites suggests increasing anthropic pressure through grazing and fire, against a backdrop of fluctuating hydrological conditions. Earlier studies have been limited by lack of dates, poor resolution and the limited length of the sediment record. For example, a pond at Tighaslant (2197 m a.s.l., 31.4368°N, 7.4688°W; Figure 1) just northwest of the Tizi n’Tichka (Bernard & Reille, 1987; Reille & Pons, 1992) provided one of the few pollen sequences for the High Atlas until the work of Ruiz et al. (2015). The Tighaslant record was from a short (<1 m) core at low resolution (18 samples) but appears to span from the early Holocene. In this (undated) record, human disturbance is thought to be responsible for decline of evergreen oak (Quercus ilex) in the pollen record. Bernard & Reille (1987) argue that this disturbance is likely to postdate the arrival of Arabs in Morocco. The general scarcity of lakes and bogs suitable for recovery of sub-fossil organic material poses a challenge for palaeoecological reconstruction in the High Atlas, and encourages the investigation of other terrestrial deposits that have not been previously considered, such as fluvial, alluvial, slope deposits and soils.

In this study, we present new findings regarding a minerogenic sedimentary deposit situated in a small basin located between the northern slope of the valley and a lateral moraine in the Assif n’Imserdane, in the Toubkal sector of the High Atlas (Figure 2). The unusual topographical setting and unique (within the context of the Assif n’Imserdane) occurrence of the deposit prompted further investigation, with the general aim of improving the understanding of landscape history in this sector of the High Atlas and elaborating the knowledge of drivers of Quaternary change in the region. In terms of the age of the deposit and drivers of change, we consider three hypotheses:

I. The deposit accumulated during the Pleistocene or early Holocene due to the creation of accommodation space by the emplacement of the bounding moraine (glacial and paraglacial drivers)

II. The deposit accumulated in response to geomorphological instability associated with the mid-Holocene Arroumd rock avalanche event ca. 4500 years ago (tectonic drivers)

III. The deposit is of more recent age and is associated with other, previously undocumented driver(s) of change in the area including anthropogenic impact (anthropogenic drivers).

Regarding the third hypothesis, it is noteworthy that palaeoecological records from other areas of Morocco point to an intensification of human impact on the landscape during the last 2000-1500 years (Cheddadi et al., 2015), but little information is available for the High Atlas territory. A key multiproxy study from marine core GeoB-6008 on the southern Moroccan continental margin (McGregor et al., 2009; Figure 1) also suggests the crossing a threshold in landscape stability between 650 and 850 AD, with enhanced signals of terrestrial erosion. However, the inferred processes of increased anthropogenic impact via livestock grazing pressure of this study have yet to be tested in the terrestrial source areas, namely ephemeral rivers of the southern High Atlas Mountains and the catchment of the Tensift River.

2. Study setting

The Assif n’Imserdane valley (Figure 2) is situated in the High Atlas, in the vicinity of the highest peak in North Africa, Jebel Toubkal (4167 masl). Precambrian intrusive and extrusive igneous rocks, including a wide range of lithologies, such as diorites, gabbros, basalts, andesites, and rhyolites form the mountains of the Toubkal sector (Delcaillau et al., 2010). The Assif n’Imserdane valley faces northwest and is bounded to the southeast by a fault-controlled rock wall reaching over 1500 m in height and culminating at the western ridge of Aksoual (3912 masl). The study site is a small basin (31.1290°N, 7.9082°W, 2125 masl) located approximately half-way between the northern watershed of the valley and the current stream channel (Figure 3a). The surface of the basin, measuring approximately 40 x 20 m is highly visible because the surface has been cleared of stones and has served until recently as a football pitch for the nearby village of Arroumd (Figure 3b). The minor summit of Souka (2525 m a.s.l.) and the slopes to the north of the basin are formed in intrusive igneous rocks, which extend as far as the Aït Souka river between Imlil and Tamatert (cf. Delcaillau et al. 2010, section 4.1.2) (Figure 2). To the south, the basin is dammed by a moraine consisting of a wide variety of Precambrian basalt-andesite boulders. These are sourced from the NW cliffs of Azrou n’Tamadôt at the head of the valley (see Figure 2). These cliffs are formed in a stack of extrusive Precambrian igneous rocks comprising various grades of extrusive igneous lithologies and dominated by basalt (Pouclet et al. 2007).

The High Atlas montane climate is characterized by large seasonal contrasts in temperature, moderate to high annual precipitation (mostly as snow), a short dry period in summer, strong winds and frequent storms (Ros et al., 2000). The means of the minima of the coldest month and maxima of the warmest month at Imlil (1765 masl) are estimated as -3.3°C and 30.6°C, respectively (http://en.climate-data.org/location/118970), and were measured as -10.5°C and 16°C, respectively, at the Toubkal refuge at 3200 masl (Ros et al., 2000). Annual precipitation in the Arroumd study area during the 1950s was recorded as 515 mm/yr at 1900 masl, and 837 mm/yr at 3200 masl

(Messerli, 1967). The surrounding slopes of the Assif n’Imserdane are covered by a low, degraded pasture and have no arboreal cover, in contrast to neighbouring valleys where an open cover of arborescent Juniperus thurifera exists at the same altitude, characteristic of the montane Mediterranean bioclimatic stage in the High Atlas.

3. Methods

3.1 Sedimentological analyses

The sedimentary infill of the deposit was surveyed using a narrow gouge auger, recording the total depth and characteristics of the sediment across the site. Due to the highly compacted nature of the sediments the gouge auger was also used to retrieve sediment samples in the field (Borehole A). An individual charcoal fragment was recovered from the base of the deposit in a second parallel drilling (Borehole B). Sediment samples from Borehole A spanning 5cm depth were cut from the interior section of the material in the auger, paying particular attention to cleaning away the outermost layer of sediment to avoid contamination. A series of six surface sediment samples were also collected in the immediate surroundings of the borehole, including one sample from the surface of the deposit, three from the flanking catchment slope, one from the adjacent moraine surface and one from the nearby Arroumd rock avalanche, with a view to exploring sediment source signatures. For the purpose of comparing source rock and sediment composition, three samples of outcropping intrusive igneous bedrock near the Arroumd basin study site were also collected. A reference set of eleven previously unpublished XRF analyses on extrusive volcanic lithologies from boulders near the upper rock walls of the valley is also presented here.

All sediment and soil samples were sealed in Ziploc bags, transported to The University of Manchester and stored at 4°C prior to analysis. Twenty subsamples from Borehole A (labelled AR1 - AR20) for sedimentological analysis were air dried and gently disaggregated in a mortar and pestle. Determination of organic matter content was made by drying at 105°C followed by loss-on-ignition (LOI) at 550°C (Dean, 1974). Magnetic susceptibility measurements were made in 10 cm3 pots using a Bartington Instruments MS2B sensor at low and high frequencies, permitting the calculation of mass specific susceptibility (LF) and the frequency dependent component of susceptibility (fd%) following Dearing (1999). Particle size measurements were undertaken on subsamples following heating in sodium pyrophosphate (4%) using a Malvern Mastersizer 2000 laser granulometer. Sub-samples for XRF analysis were measured on a Ritaku NEX-CG energy-dispersive x-ray fluorescence (ED-XRF) bench-top analyser. Values for key major elements of interest for characterisation of volcanic rock provenances (specifically Na, K, Si) are calculated on the basis of their occurrence in the form of oxides (Na2O, K2O, SiO2). Surface samples were screened at 2000 µm and 63 µm. LOI, LF and fd%, and particle size measurements were taken on the <2000 µm fraction. XRF analysis was performed on the fine (<63 µm) fraction, and additional LF, fd%, and particle size measurements were also taken on the fine fraction. Bedrock samples were crushed, milled and sieved (<63 µm) for XRF analysis. XRF measurements were made on pelletised samples for the surface and boulder samples requiring 12g of dry material, but only on compacted material for the borehole samples due to insufficient material for pellets. Borehole samples were packed into measurement rings with a mylar film base.

3.2 Organic microfossil analyses

Ten sub-samples, corresponding to every second sedimentological subsample, were processed for evaluation of the organic microfossil content of the sediments. A simplified dense-media separation preparation procedure avoiding strong oxidative stages (e.g. acetolysis) was followed, based on the protocol of Nakagawa et al. (1998). Dense media separation can be especially effective in the case of strongly minerogenic sediments (Allen et al., 2009). Indeed, an initial attempt following a standard pollen preparation protocol including HF treatment and acetolysis failed to produce usable residues. Lycopodium tablets were added to sediment sub-samples of 2 cm3, which were then treated with 7% HCl (20', 90°C), 10% KOH (5', 90°C), and multiple water washes (x20) to remove clays. Organic and inorganic fractions were then separated using sodium polytungstate (SPT) solution prepared to a specific density of 1.88 g/cc. The organic fraction was dehydrated in ethanol and mounted on microscope slides in a mobile medium (glycerol). Microscope slides were scanned at 400x magnification using a Nikon Eclipse 50i high-power binocular microscope, and counts of the following microfossils recorded: (a) pollen and spores of vascular plants, with reference to Reille (1992) and Beug (2004); (b) non-pollen palynomorphs (NPPs), principally fungal spores,q observing HdV- (Hugo de Vries Laboratory) codes for identifiable NPPs and with reference to several sources including van Geel and Aptroot (2002), van Geel et al. (2003), Cugny et al., (2010) van Geel et al. (2011), and Lopez-Vila et al. (2014); (c) softwood tracheid fragments, with reference to Richter et al. (2004) and Watson and Dallwitz (2008). Critical identifications and microphotographs were made at 1000x magnification. Due to a very low concentration of microfossils in the sediment, and in order to ensure comparable effort between samples, counts proceeded until reaching a target of at least 300-500 marker spores, on the principle that this can provide a reliable estimate of the absolute concentration of the detected microfossils (e.g. Etienne et al., 2014). Subsequently, an estimate of microcharcoal particle concentration was obtained by scanning the slides at 200x magnification until a total of 200 objects (microcharcoal and marker spores) was reached, following the approach of Finsinger and Tinner (2005). The separate scanning for microcharcoal allows for the condenser diaphragm and light source to remain fixed and constant between samples (whereas both are routinely altered to optimise viewing conditions for pollen and NPP identifications) assisting in the consistent classification of black, opaque, angular particles (Whitlock and Larsen, 2002). Due to the low achievable count sizes for pollen and spores (between 14 and 107, µ=57) and NPPs (between 10 and 230, µ=81), percentage frequencies are not calculated; rather, concentration diagrams are presented.

3.3 Radiocarbon dating

An individual charcoal fragment of sufficient size for dating was observed in the field and recovered from the base of the deposit (Borehole B, 224-234 cm). For Borehole A, subsamples of the core not used for sedimentological and microfossil analysis were dispersed in water and screened using 125 µm mesh to search for datable material. In general, little organic material was recovered in the screening process. A sample of fine, comminuted charcoal in the size range ca.125-250 µm was recovered from depth 140-147 cm within the Borehole A sequence. The two charcoal samples were dried at 40°C and sent to Beta Analytic for AMS radiocarbon determinations. Due to the lack of macrofossils, a sample of bulk sediment from Borehole A at depth 75-80cm was also submitted for AMS radiocarbon dating. This depth was selected with respect to the concentration of palynomorphs (pollen and NPPs) in the sediments. In light of the low organic content of the total sediment (<5% LOI) and absence of macrofossils, organic microfossils are considered to constitute

the main dating material for this sample, although these were not specifically isolated from the sediment matrix for dating.

4. Results

4.1 Sedimentological analyses

[FIGURE 4]

Gouge-auger survey indicates that the deposit is of variable depth between 150 cm and 240 cm, overlying an irregular stone surface. The deposit is defined along the western and southern edge by the boulder-rich moraine deposit, and tapers out towards the northern and western edges into colluvial material and thin, stony slope soils. The sediments are composed of yellowish brown (7.5 YR 5/4), massive, compacted silts, with silty-sands occurring towards the base of the deposit. Visual inspection of the sandy component in terms of colour and angularity suggests derivation of the material from outcropping diorite on the immediately adjacent hillslope. During the survey, fine charcoal flecks were noted in a band around 140-150 cm depth. The stratigraphical and sedimentological record for Borehole A is shown in Figure 4. Three stratigraphic units were noted in the field (A-I, A-II, A-III).

LOI values in Borehole A reflect the low organic matter content of the sediment (1.9-6.5 %, µ=4.5%), with typical values around 3-5 % in units A-I and A-III, and minimum values around 2% in A-II. Particle size analysis shows the predominance of unimodal, poorly sorted silts with mean grain size of 6.7 – 7.2 µm in A-I and A-III, and bimodal, very poorly sorted sandy silts with mean grain size ranging between 30 µm and 180 µm in A-II (Figure 4). Three modal grain size classes can be observed in the distribution curves: (1) a fine silt mode around 6-9 µm, dominating in units A-I and A-III, and secondary in unit A-II; (2) a coarse sand mode around 500 µm - 800 µm, dominating in unit A-II; (3) a coarse silt mode (30 µm - 50 µm) evident as a “shoulder” in the distribution curves, particularly for AI and AIII (Figure 5).

[FIGURE 5]

Mass-specific magnetic susceptibility (LF) values of 0.8 x 10-6 – 1.4 x 10-6 SI units are recorded, with highest values in A-I and A-III, and lowest values in A-II (Figure 4). The frequency-dependent component (fd%) ranges from 6 % to 8 %, also with highest values in A-I and A-III, and lowest values in A-II. A declining trend in both LF and fd% across A-III is observed. Both LF and fd% are positively correlated with the medium silt to clay particle size fractions, and show the strongest positive correlation with the fine silt fraction (R=0.734, p<0.001, R= 0.715, p<0.001, respectively).

[FIGURE 6]

XRF-based estimates of Na2O, K2O, SiO2 in the fine sediment fraction (<63 µm) are shown in Figure 6 and summarised in Table 1. In A-I and A-III, consistent values of K2O (3% - 3.5%) and SiO2 (52% - 58%) are observed, excluding the outlying uppermost sample. In A-II, values for K2O and SiO2 are reduced by up to 1.5% and 20%, respectively, while Na2O values are elevated by 0.5% relative to those in A-I and the immediately overlying sediments of A-III. A gradual increase in Na2O values from 1.5% - 2.5 % is observed in A-III. The extreme low Si values (<35%) for two of the borehole samples (AR16, AR1-

surface) may represent measurement noise due to small sample size for these samples and poor detection of the light Si element.

[TABLE 1]

[FIGURE 7]

The values for LOI and magnetic susceptibility (LF) are broadly similar for the borehole samples, the basin surface, and the catchment surface samples (Figure 7), with slightly lower values for these parameters in the surface samples. The frequency dependent component (fd%) is significantly lower in the surface samples than in the borehole samples (Mann-Whitney U = 47.5, p<0.001). The particle size distributions for the surface samples reveal similar modes to the borehole samples, but with a greater importance of the coarse mode (coarse sands) in the whole samples, and of the intermediate mode (coarse silts) within the fine (<63 µm) fraction (Figure 5). Only the sample taken from the basin surface displays a well-developed fine silt mode comparable to the borehole samples. Comparative Na2O, K2O, SiO2 data for the surface samples (Figure 6, Table 1) highlight strong overall similarities in composition between the borehole and surface sediment samples. In contrast, greater differences are observed between the borehole/surface and local bedrock samples, which are distinguished primarily by higher Na2O content (Table 1). Heterogeneous extrusive igneous lithologies are evident in the reference set of valley boulders.

4.2 Microfossil concentrations

To facilitate discussion of the microfossil record, three microfossil assemblage zones (MAZ-) are defined on the basis of the concentration values for pollen and spores, NPPs, softwood fragments and microcharcoal particles.

[FIGURE 8]

Concentration values for identifiable pollen and spores of vascular plants range between 125 and 3300 microfossils per cm3 (µ=1130), with highest values occurring in the upper part of the deposit (MAZ-3 (Figure 8). The preservation condition of the pollen and spores is variable, with many grains presenting indications of degradation (exine thinning, surface pitting, loss of ornamentation, etc.). A population of indeterminate degraded palynomorphs is recorded, corresponding to between 10 and 58% (µ=26%) of the total pollen and spore counts. Preservation is worse in MAZ-1 and MAZ-2, as indicated by higher percentages of degraded grains alongside lower overall concentration and diversity of morphotypes.

Among the identifiable pollen and spores, a small number of tree taxa are documented including widespread taxa such as Pinus and evergreen Quercus, as well as taxa indicative of long-distance pollen transport from lower altitudes (Argania, Olea, Phillyrea). Ephedra, a shrub taxon of dry, rocky terrain, is recorded in all samples. A modest diversity of herb taxa is documented, particularly in MAZ-1, with the strongest representation of Asteraceae, Caryophyllaceae, Chenopodiaceae and Plantago pollen, accompanied by occurrences of other dry ground and pasture taxa, such as Crassulaceae, Paronychia, Brassicaceae, Erodium and Helianthemum. Only rare occurrences of moisture-demanding taxa are recorded, notably Isoetes, a fern ally characteristic of flooded ground on minerogenic substrates, and Potamogeton, an aquatic plant of shallow and brackish water.

[FIGURE 9]

[TABLE 2]

Concentration values for NPPs (Figure 8) range between 210 and 7910 microfossils per cm3 (µ=2350), and show very similar patterns to vascular plant microfossils including highest values in MAZ-3. A range of coprophilous fungal types are documented (Figure 9), reaching maximum abundance and diversity in MAZ-3. These include Sporormiella, Sordariaceous spores including Sordaria, Podospora and Cercophora, as well as Delitschia and Trichodelitschia. Fungal types of more varied ecology but of likely coprophilous status (N’Douba et al., 2013) including Delitschia, Chaetomium, and Coniochaeta ligniaria are also well represented. A microfossil attributed to Diporotheca based on similarities to HdV-1245 (van Geel et al., 2011) shows affinities with Chaetomium and Coniochaeta ligniaria; it may possibly derive from host parasite relationships in soils, as suggested for Diporotheca rhizophila (Hillbrand et al., 2012). The related types Gelasinospora and Neurospora are also documented. These microfossils may serve as indicators of local fires as they are carbonicolous and occur on charred substrates (Van Geel and Aptroot, 2006); Gelasinospora may also be coprophilous, however (Lundqvist, 1972). Across MAZ-2 and MAZ-3, the progressive development of two groups of NPPs can be observed, with (i) a first group including Podospora, Delitschia, Chaetomium, Coniochaeta ligniaria and Neurospora giving way to (ii) a second group (including Sporormiella, Sordaria, Cercophora, Trichodelitschia, Gelasinospora and Valsaria). A small number of distinct NPP types that were not identifiable to previously published types are reported in Table 2.

The sediments contain abundant non-charred microscopic wood fragments, particularly towards the base of the deposit (MAZ-1). A subset of the fragments are moreover recognisable as tracheid fragments displaying uniseriate bordered pits of unambiguous softwood (conifer) origin, including examples of both early- and latewood growth (Figure 9-30,31). Concentration values for tracheid fragments presenting uniseriate bordered pits are shown in Figure 8, and range between 0 and 710 fragments per cm3 (µ=300). In rare cases, earlywood cross-fields are also detected, displaying two small pits per cross-field of Cupressoid type, and showing scalloped tori in the tracheid pits (Figure 9-32,33) characteristic of Juniperus thurifera (Watson and Dallwitz, 2008). Finally, concentration values for microcharcoal range between 210 and 8880 particles per cm3 (µ=2750), with peak values detected in the middle part of the deposit (MAZ-2).

4.3 Radiocarbon dating

[TABLE 3]

The two available dates on charcoal from the Arroumd deposit (Table 3) present a reversed set of ages, with a single charcoal fragment dated to 1520-1310 cal BP (2) recovered from the base of the deposit (Borehole B) and fine charcoal fragments dated to 2740-2490 cal BP (2) in Borehole A (140-147 cm). The bulk sediment determination (Borehole A, 75-80 cm) yields an age of 1225-1010 cal BP (2).

5. Discussion

5.1 Sediment sources and characteristics

The irregular basal profile of the deposit suggests that it overlies directly boulders of the lateral moraine ridge that runs along the northern flank of the Assif N’Imserdane. The low organic matter content of the silty sediment infill reflects the minerogenic characteristics of the deposit and low organic preservation, that may be linked to seasonal drying, sub-aerial oxidation and decomposition of organic matter. The LOI curve shows strong affinities with the concentration curves of wood fragments and microcharcoal. The compacted silty infill displays three modal sizes, with a fine silt mode (6-9 µm) dominating most of the sequence that suggests settling of fine particles in an aqueous environment. This mode is weakly developed in the surface samples and this contrast points to a selective enrichment of this fine sediment component within the basin. Overland flow in erosion-prone semi-arid environments has been shown to selectively transport the silt fraction (Parsons et al., 1991; Martinez-Mena et al., 2000), and a likely source for this material is soil derived particles transported by overland flow during seasonal snow melt and rainfall. Transport pathways for this process may include the shallow gullies and ephemeral channels draining towards the site from the E (Figure 3C). Selective fractionation along these transport pathways may also be implicated, with trapping of coarse material along the moraine margin above the basin area and subsequent concentration of fine material in the basin. The coarse sand mode (500 µm - 800 µm) which is well represented in the catchment samples, point to higher-energy transport conditions or highly localised erosion leading to input of coarse material to the basin. The intermediate coarse silt mode (~30-50 µm), present in the basin sediments and also well represented in the fine fraction of the soil samples, may reflect an aeolian component. This component may be locally sourced, for example from debris associated with the catastrophic rock avalanches (Hughes et al., 2014), or possibly of distant origin but subject to remobilisation within the local context. The modal size is characteristic of coarse aeolian dust as detected, for example, on the North West African margin between 17° and 33°N (cf. EM1, Holz et al., 2004). Overall, the contrasting particle size distributions of the Arroumd soil and borehole samples suggest preferential transport and redeposition of the fine silt component into the basin, leaving sandy and stony lag soils in the surrounding slopes.

The magnetic susceptibility of the borehole samples is within the range where terrigenous ferrimagnetic mineral concentrations dominate the signal (Dearing, 1999). The magnetic signal is strongly linked to the fine silt sediment fraction, as demonstrated by within sample correlations and by the overall higher magnetic susceptibility of fine-grained borehole sediments compared with the coarser surrounding catchment samples. The frequency dependent component, which has been linked to topsoil formation processes and also to land cover burning (Dearing et al., 1996, 1997), also appears relatively enriched in the borehole samples, with values of up to 8% indicating a significant contribution from superfine paramagnetic minerals in the semi-stable domain. These characteristics suggest that while the ferrimagnetic component may ultimately derive from volcanic bedrock sources in the valley, their abundance is not directly controlled by bedrock characteristics, but rather by weathering, soil formation and possibly burning processes. Highest fd% values are indeed associated here with highest concentrations of microcharcoals. The enhancement of magnetic properties in the borehole sediments also supports indications from particle size characteristics that erosion processes have led to a selective concentration of ferrimagnetic and paramagnetic minerals at the borehole location.

The concentrations of Na2O, K2O and SiO2 as estimated by XRF analysis for the Borehole A samples are generally consistent and close to those of fine surface sediments from hillslope surface material, the adjacent moraine and the rock avalanche (with the exception of samples in A-II, and the

uppermost borehole sample, AR1), supporting a local origin for the borehole sediments. The strongly homogeneous characteristics of the surface samples is noteworthy, and may be a legacy of the catastrophic mid-Holocene Arroumd rock avalanches (Hughes et al., 2014), which would have not only deposited the main boulder debris field (Figure 2), but also generated and spread enormous quantities of fine debris throughout the lower valley. This debris appears andesitic / trachy-andesitic in character (Figure 6), but may integrate a wider diversity of lithological material from within the valley. The compositional contrasts between the borehole/surface samples and the local intrusive bedrock suggests that the characteristics of the regolith in the Assif n’Imserdane may be strongly influenced by debris remobilisation associated with the rock avalanche. While sedimentological characteristics point to a local hillslope origin, the eroded material does not appear to derive principally from local bedrock, notwithstanding taphonomic (diagenetic, weathering and transport) processes that may alter the lithological source signature.

Units A-I and A-III appear to derive from a supply of well-mixed, fine-grained material from hillslope sediments with a significant avalanche dust component. In contrast, unit A-II includes coarse sandy material to the site associated with a shift to a more proximal sediment source and/or an increase in the energy of sediment transport. The exact source of the coarse grained material is not known, with possible contributions from bedrock outcrops and the Pleistocene moraine on the margin of the site. The relative elevation in Na2O values in A-II may point towards an input of locally-derived bedrock material which is relatively strongly enhanced in Na (Table 1). Similarly, the gradual increase in Na2O values throughout the unit A-III may also relate to a modest increase in bedrock-derived material despite the weak overall compositional similarity between the borehole and local bedrock material. However, the bounding moraine also represents a heterogeneous source of course material, potentially including the diversity of lithologies observed in boulders from upper parts of the valley (Figure 6).

5.2 Insights from organic microfossil content

The highly minerogenic and non-waterlogged Arroumd deposit does not represent an ideal site for palaeoecological investigation, due to low organic preservation and non-waterlogged status. Nevertheless, with careful application of a dense-media separation protocol, it was possible to extract small amounts of organic residues including a surprising and informative diversity of organic microfossils. It is essential to consider that the very low (and variable) concentration of pollen, spores and NPPs (1-2 orders of magnitude lower than typical lake sediments), the high percentages of degraded palynomorphs, and small achievable count sizes, all point to poor preservation conditions demanding extremely cautious interpretation of the microfossil record. Subaerial exposure, oxidation, wetting and drying cycles and bacterial attack in aerobic contexts can all contribute to the degradation and destruction of palynomorphs (Campbell, 1991; Carrión et al., 2009). Indeed, in this setting, it must be anticipated that biases in the microfossil assemblages will be present, including overrepresentation of robust palynomorphs, selective loss of delicate microfossils, and generally reduced abundance and diversity of microfossils. The abundance of Asteraceae types, for example, is fairly common in preservational environments, including soils and cave deposits (Havinga, 1984; Carrión, 1992). Furthermore, transport pathways for microfossils into the site may be varied (including atmospheric deposition, local gravity processes, and surface runoff) and may involve storage and remobilisation from soil organic matter.

The low concentration and achievable counts preclude detailed vegetation reconstruction. Broadly, the pollen spectra are consistent with a dry montane environment, with predominance of herbaceous types and aridity tolerant shrubs of rocky ground (Ephedra types). Low abundances of montane arboreal pollen (Pinus, Quercus evergreen type) reflect tree cover from neighbouring vegetation belts at lower altitudes (e.g. Figure 1). Occurrence of small amounts of arboreal pollen from lower altitudes and distant sources is a consistent feature of High Atlas surface pollen spectra (Bell and Fletcher, 2016), in this case shown particularly by the presence of the thermophilous Argania and Olea. Argania, for example, is endemic to arid lowlands of south-western Morocco (annual rainfall <400 mm/yr, elevation <1200m (Imoulan et al., 2010), and Olea is widespread but never at elevations exceeding 1700 masl (Ouazzani et al., 1996). Although not a local signal, the occurrence of Argania only in the upper samples of MAZ-3 may be linked to the increased economic importance and expansion of management practices in southwestern Morocco during the Middle Ages (Ruas et al., 2015). The richest pollen spectrum at Arroumd (AR4, MAZ-3) suggests an open, grazed vegetation at the site, including nitrophile (Plantago, Helianthemum), low-growing (Paronychia) and prickly (Eryngium) taxa, alongside other herbs (Asteraceae, Brassicaceae, Caryophyllaceae, Chenopodiaceae). Preservation biases notwithstanding, rare occurences of Isoetes, Cyperaceae, Potamogeton and fern (monolete and trilete) spores point to a seasonal to brackish humid freshwater environment (Ramdani et al., 2009), best expressed in MAZ-3.

The range and abundance of NPPs point to an important local presence of coprophilous Ascomycetes. Several taxa shown to be very reliable dung indicators and strongly linked to grazing pressure in the western Pyrenees (Cugny et al., 2010) including Sporormiella, Sordaria (including HdV types 55A and 55B), Podospora and Trichodelitschia are well represented in MAZ-3. Other likely coprophilous taxa that occur frequently in the deposit and for which possible source species are recognised components of the Moroccan coprophilous fungi (Richardson, 2004; N’Douba et al., 2013) include Chaetomium, Coniochaeta ligniaria, and Delitschia. The affinities between Gelasinospora and Sporormiella in MAZ-3 suggests it may reflect coprophilous species at this site. Neurospora, in contrast, is detected in association with the highest microcharcoal concentrations, coherent with a carbonicolous ecology (Van Geel and Aptroot, 2006). Overall, the strong representation of both certain and likely coprophilous fungi point to important grazing pressure at the site. As a seasonal waterbody, the basin is likely to have been a valuable resource for pastoral activities, and the basin surface itself is likely to have been grazed on a seasonal basis. The precise causes for the succession of two groups of ascomycetes across MAZ-2 and MAZ-3 are unknown. Both groups suggest a broadly coprophilous ecology, although the first group contains several taxa of varied ecology with possible carbonicolous and lignicolous associations while the second group includes the most reliable grazing indicators (following Cugny et al., 2010). The succession might relate to an increase in herbivore density and grazing pressure. Other factors to consider include a change in host material associated with different grazing animals, as well as preservation and taphonomical factors associated with local wetness and direct access to the lagoon surface (Raper and Bush, 2009; Parker and Williams, 2012).

Wood micro-fragments in MAZ-1 and, to a lesser extent MAZ-2, point to the local presence of trees, specifically conifers including Juniperus thurifera. The abundance of well-preserved softwood fragments in the otherwise almost sterile basal samples raises questions about the possible derivation and taphonomy of these microfossils. One possibility is that the fragments derive from naturally occurring woody litter below a woody vegetation cover. Alternatively, anthropogenic

disturbance may be implicated. For example, the practice of cutting branches from trees for firewood and leaving them to dry on the hillslopes, widespread across the Atlas, might contribute to an amplified soil component of micro-scale woody debris that can be mobilised by erosion. Similarly, felling and clearing for timber is known to produce a pulse of woody input to soils, particularly small branches and twigs (Abbott and Crossley, 1982). A final, and intriguing, agent of disturbance to be considered at this location is the atmospheric pressure wave(s) that would have accompanied the catastrophic rock avalanches of ca. 4500 cal BP. Air blasts caused by rock avalanches and rock avalanches are easily capable of uprooting and snapping trees, as observed in 2007 over a 500,000 m2 area at Cima Una in the eastern Alps (Viero et al., 2013). The destructive capacity of the Arroumd rock avalanche is intimated by its scale; at an estimated >60 x 106 m3 (Hughes et al., 2014), it was at least three orders of magnitude bigger than the Cima Una rockfall.

With wood fragment evidence for the presence of Juniperus thurifera, it is surprising that Cupressaceae pollen was not encountered in the samples. Several possibilities may be considered, namely (i) that Juniperus thurifera is a poor pollen producer that is underrepresented even where locally present (Bell and Fletcher, in press), (ii) that Cupressaceae pollen may not be well preserved in sub-optimal settings, and (iii) that disturbance factors (cutting, felling) mean that plants were either not pollinating or no longer alive at the time that the wood fragments were deposited in the basin.

The general progression from low to high concentration of all microfossil groups excluding softwood fragments may be driven by sedimentation rate effects (i.e. gradual deceleration of accumulation rates) or to preservation effects (i.e. a dry-to-wet transition favouring reduced rates of decomposition and decay. A combination of effects cannot be excluded. Taking into account the percentage of degraded pollen and spores (Figure 8), it appears that the lower part of the MAZ-1 (corresponding to sediment unit A-I) with both low total concentration and low degraded percentage may be dominated by rate effects (i.e. rapid deposition). In contrast, the upper part of the sequence may be dominated by preservation effects, showing a shift from low concentration, high degraded percentage (i.e. poor preservation) in MAZ-2 to relative high concentration, low degraded percentage (i.e. good preservation) in MAZ-3. This could be explained by fluctuations in moisture status, as detected at other small bogs in the High Atlas (Ruiz et al., 2015)

5.3 Age of the deposit

The available radiocarbon dates indicate a late Holocene timeframe for accumulation of the deposit. The reversal of ages presented by the dates on charcoal is most likely explained by reworking of the fine charcoal fragments from the environment yielding an age older than the time of sediment deposition for the upper sample. An alternative explanation, i.e. that the lower date is younger that the true age of sediment deposition due to contamination, is considered less likely since a single, relatively large fragment would be susceptible to mechanical breakage during storage, erosion, transport and redeposition processes. Taking into account the possibility of reworking of charcoal in the semi-arid environment (Scott, 2002), the charcoal dates provide a terminus post quem for the initiation of sediment infilling of 1520-1310 cal BP (430 - 640 AD). The bulk sediment age further supports a first millennium AD age for the deposit, and helps to constrain the timing of the base of MAZ-3 to 1225-1010 cal BP (725 – 940 AD). Although the exact composition of the dated material in this sample is unknown, the date is considered reliable thanks to the insights into the nature of the

organic content provided by the microfossil analyses of adjacent levels. Specifically, the high concentrations of relatively fragile pollen and NPPs, and low concentrations of more robust microcharcoal and wood fragments, suggest that problems of reworking of old material should be negligible.

5.4 Environmental implications

The combined information from sedimentological indicators and organic microfossils suggest a sequence of significant environmental changes around the site. The sequence begins with the initiation of sedimentation during the first millennium AD, postdating the youngest dated charcoal fragment (i.e. after 1520-1310 cal BP, or 430 - 640 AD). While it is conceivable that earlier depositional episodes may have occurred and the associated deposits were subsequently subject to erosion or deflation processes, no direct evidence for such episodes (e.g. unconformities, heterogeneity of basal sediments) was encountered during the survey of the site. Rather the emplacement of the moraine since at least the Pleistocene suggests that accommodation space at the moraine margin existed for many millennia prior to significant sediment accumulation, such that a trigger for this change must be considered. The abundance of softwood fragments suggests that this trigger may have been destruction of the local woody vegetation cover. Deforestation is one of the key historic triggers for soil erosion in Mediterranean mountain regions (García-Ruiz, 2010) and closely linked to enhanced erosion in semiarid areas. Pressure on forest resources in Morocco is intense, and indeed, the total absence of tree cover within the Assif n’Imserdane is striking, even in the context of neighbouring valleys. Although the possibility of forest destruction by rockfall air blast is intriguing, the timing does not appear coherent with the onset of sedimentation. Nevertheless, mechanistic linkages, for example by an enhanced woody debris soil store in the valley soils, or long-lasting impacts on the resilience of the local forest cover are possible.

The onset of sedimentation and deposition of hillslope-derived fine-grained minerogenic sediments (A-I) was followed by a pulse of localised erosion (A-II) transporting sands into the basin, associated with coprophilous fungal spores. This erosional event may therefore have been conditioned by the disturbance of the woody cover and exacerbated by the activity of grazing animals. As suggested by the concentration characteristics of microfossils, A-I and A-II may have been deposited in rapid succession, and may represent different facets of the same erosional sequence, i.e. the progressive erosion of upper surface sediments followed by bedrock-derived material. Intense, flashy rainfall events may be implicated in the transport of coarse-grained material (A-II) to the site.

A-III documents a return to fine-grained sedimentation from inferred hillslope sources. Peak microcharcoal abundances and presence of Neurospora (MAZ-2) along with highest fd% values point to significant burning in the landscape, possibly as a tool to improve the quality of pasture (Ruiz et al., 2015). A gradual enrichment in Na2O content suggests a progressive increase in bedrock derived sediment consistent with ongoing hillslope erosion. An enriched content of pollen and NPPs (MAZ-3) reveals a diverse suite of coprophilous fungal spores associated with significant grazing pressure around the site within an open pasture landscape from 1225-1010 cal BP (725 – 940 AD). Rare tree pollen derives from lower elevation and distant sources, but contributes to the picture of a wider anthropogenic landscape with developing Argania culture (Ruas et al., 2015). The enrichment in palynomorphs that provides these insights into the pastoral pressures in the Toubkal region may

also reflect more favourable preservation conditions associated with slightly wetter conditions at the site and the development of a shallow pond with Isoetes and Potamogeton.

Returning to the original hypotheses about the timing and drivers of change, the stratigraphical and geochronological information allow the first two hypotheses to be rejected. Although the moraine that bounds the deposit is likely to have been in place since the last glacial, and despite signals of geomorphological destabilisation of landforms associated with the series of catastrophic rock avalanches ca. 4500 years ago in response to an inferred earthquake, sedimentary infilling of the accommodation space did not commence until the Late Holocene. Glacial, paraglacial and tectonic drivers do not appear to be directly implicated as triggers of sediment transport into the study site, although a legacy of disturbance and dust generation of the rock avalanches may be implicated in the sensitivity of local soils to Late Holocene erosion. The third hypothesis, that the deposit is of more recent age and can be linked with other, previously undocumented driver(s) of change in the area is, however, corroborated. The Late Holocene timeframe for the onset of infilling and the sequence of environmental changes inferred from the sedimentology and organic microfossils point to anthropogenic drivers of change, specifically destruction of the local tree cover, burning and intensification of pastoral activities.

Although the limited geochronological data precludes the development of a detailed age-model for infilling, it is noteworthy that the data for initiation of infilling after 1520-1310 cal BP (430 - 640 AD) and increase in grazing indicators from 1225-1010 cal BP (725 – 940 AD) fit temporally with the inference of regional-scale terrestrial erosion in southern Morocco (McGregor et al., 2009). From marine core GeoB 6008-1, McGregor et al. (2009) report an abrupt increase in sedimentation rate, Fe intensity, and pollen flux between 650 and 850 AD, interpreted as multiple indicators of widespread erosion and fluvial transport of terrestrial material onto the continental shelf. The authors present a convincing picture of social and economic development at this time, including an expanding pastoral and agricultural base at the time of—and indeed shortly before—the extension of Arab rule and Islamisation of southern Morocco. The geographical location of the study area within the wider catchment of the Tensift river, and the indications of erosion, fire and grazing pressures suggests a non-coincidental connection with the findings from marine core GeoB 6008-1. The Assif n’Imserdane is located in the montane hinterland of the ancient Berber city of Aghmat (Figure 1), described by the Andalus geographer Al-Bakri as a flourishing city where 100 cattle and 1000 sheep were slaughtered in the weekly souk (in translation, 1965), and close to the later city of Marrakech, founded in 1060 AD. Trading promoted development of High Atlas villages such as nearby Tamatert (Figure 2) on the strategic routes across the High Atlas between Aghmat and Sijilmassa, the medieval centre of the trans-Saharan gold and slave trades (Lightfoot and Miller, 1996).

The processes leading to the infilling of the small back-moraine basin at Arroumd may be characteristic of changes in the wider landscapes of the southern High Atlas during the first millennium AD as reflected in the integrated marine record. At Oukaimeden (Ruiz et al., 2015), human activity is detected throughout the last 4000 years, but a significant increase in nitrophile vegetation and coprophilous spores point to a shift in grazing intensity after 947 ± 44 14C yr BP (930 – 750 cal BP, 1010-1210 AD). This increase in grazing intensity is similar to the changes observed in MAZ-3 at Arroumd from 1225-1010 cal BP (725 – 940 AD) onwards. On the basis of the available radiocarbon data, this shift may have occurred a few centuries earlier at Arroumd (median

difference 260yr, 2 range 130 – 400 yr). Further investigations will be required to confirm intraregional patterns of spatial and temporal variability, and to relate these patterns to the rich and complex social and cultural history of the region. Nevertheless, our findings help to confirm anthropogenic pressures of the historical era as a significant driver of environmental change in this sector of the High Atlas, along with glacial and tectonic forcing.

Finally, it is recognised that Late Holocene geomorphological changes in the High Atlas will have occurred in the context of a variable climate. This climatic context remains poorly documented at the regional scale. In comparison, more information is available for the Middle Atlas, where dendrochronological, lacustrine and speleothem records indicate significant Late Holocene hydrological changes, including an interval of high lake levels during the Classical era (2300 cal BP – 1700 cal BP, 350 BC – 250 AD) (Damnati et al., 2015) and humid conditions during the Little Ice Age (Esper et al., 2005; Wassenburg et al., 2013). These humid episodes bracket an interval of drier but also highly variable conditions evidenced in speleothem data (Wassenburg et al., 2013) and low lake-levels (Damnati et al., 2015). It is therefore possible that a shift to arid conditions after the Classical era may have promoted landscape instability at Arroumd, for example through increased flashiness of rainfall regime, reduced ground cover, reduced soil infiltration rates, etc. In the wider context, the onset of infilling in the Arroumd basin after 1520-1310 cal BP (430 - 640 AD) occurred in the context of aridification in southern Spain after the end of the Iberian-Roman Humid Period at 350 AD (Martín-Puertas et al., 2009) and in association with the onset of climate cooling in Eurasia associated with the so-called Late Antiquity Little Ice Age (LALIA, 540-660 AD) (Büntgen et al., 2016). A subsequent return to more humid conditions by 1225-1010 cal BP (725 – 940 AD may furthermore be evidenced in improved palynomorph preservation in the upper part of the deposit (MAZ-3).

However, as hydrological shifts are likely to have occurred throughout the Holocene, not least during several significant rapid climate change (RCC) intervals (e.g. Fletcher and Zielhofer, 2013), it appears likely that an anthropogenic trigger is required to explain this particular episode of erosion and infilling. Of course, synergistic interaction between anthropogenic pressures (cutting, burning and pastoralism) and arid conditions during the first millennium AD may be implied. For example, increased drought stress and unpredictability in moisture regime may have promoted extensification of pastoral activities, leading to a cascade of changes including soil compaction, fragmentation of the vegetation cover, enhanced runoff, nutrient losses, etc. that ultimately triggered irreversible erosion and ecosystem modification (van de Koppel et al., 2002; Asner et al., 2004). The exploration of such synergies represents a key future direction for landscape studies in the High Atlas and highlights the need for future development of independent regional palaeoclimate data.

6. Conclusions

The investigation of the sedimentary infill of a small, seasonally flooded basin in the Assif n’Imserdane valley provides new insights into the drivers of landscape change in the southern High Atlas. Stratigraphical and sedimentological indicators (LOI, magnetic susceptibility, particle size and XRF analyses) reveal a predominantly fine-grained, minerogenic lithology sourced from the surrounding hillslopes on volcanic substrates, with minor components of aeolian dust and locally-sourced coarse-grained material. Enhanced fine-fraction and magnetic properties (LF and fd%) point to selective concentration of soil-derived fine particles within the basin probably linked to overland flow occurring during seasonal snow melt. Organic microfossils (pollen and spores, NPPs,

microcharcoal and softwood tracheid fragments) suggest a sequence of environmental changes associated with erosional processes in the catchment, namely disturbance of the woody vegetation cover (MAZ-1), increases in burning (MAZ-2), and intensification of grazing pressure (MAZ-3). The initiation of sedimentation into the basin is shown to have occurred after 1520-1310 cal BP (430 - 640 AD), placing the sequence of events within the context of enhanced social and economic pressures on the rural landscapes of the southern High Atlas during the first millennium AD (McGregor et al., 2009; Ruiz et al., 2015). Comparison with hydrological records from the Middle Atlas suggests that sensitivity of the montane environment to anthropogenic disturbance may have been exacerbated by a transition towards drier climatic conditions at this time, but independent palaeoclimate data for the High Atlas specifically is needed to confirm the role of synergistic (human-climate) impacts.

The findings of the investigation highlight the challenges of palaeoenvironmental research on non-waterlogged deposits in semi-arid mountain landscapes, specifically limited organic material for radiocarbon dating, and interpretational challenges in settings with sub-optimal preservation of organic microfossils. Nevertheless, the findings also highlight the potential for “widening the palaeoecological net” to include a wider range geomorphological settings in the pursuit of new information on the geoecology of mountain regions. In this case, the study of NPPs within a multi-proxy approach provides new insights into the links between historical grazing pressure and landscape change. This technique is relatively under-utilised in the North African context (cf. Zapata et al., 2013) and has great potential to illuminate further the history of pastoral activities in the Atlas ranges.

Acknowledgements

The authors acknowledge financial support from a Royal Geographical Society Field Centre Grant and the Research Stimulation Fund of the School of Environment, Education and Development. The authors thank Dr Sarah Kneen for support in the borehole sampling, and acknowledge many fruitful and supportive discussions in the field area with our colleagues Dr John Nudds, Dr Peter Ryan and Professor Jamie Woodward (University of Manchester). We also thank John Moore and Jonathan Yarwood of the Physical Geography Laboratory for technical support. The helpful comments of two anonymous reviewers are gratefully acknowledged.

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List of Figures

1. Map of dominant vegetation cover of the southern High Atlas (redrawn from Emberger, 1939), showing the location of (a) Arroumd study area, and other sites mentioned in the text: (b) Oukaimeden (Reille, 1976; Ruiz et al., 2015); (c) Tighislant (Bernard and Reille, 1987); (d) marine core GeoB-6008 (McGregor et al., 2009).

2. Map showing the location and geomorphological context of the Assif n’Imserdane valley and the Arroumd infilled basin (Hughes et al., 2014).

3. Images showing the setting of the study location: (a) view looking NE showing the perched position of the deposit behind a Pleistocene lateral moraine on the northern flank of the Assif n’Imserdane above the Arroumd rock avalanche and the village of Arroumd (Source: P.D. Hughes); (b) view looking E across the studied basin, showing the position of the infilled basin between the adjacent hillslope and lateral moraine (Source: P.D. Hughes); (c) satellite image showing the location of the deposit, with erosion scars and ephemeral stream tracks visible on the adjacent hillslopes (Source: Google Earth. 31°07’44.13’’N and 7°54’29.54’’W. 01/08/2015). Arrow in (a) indicate the location of the study location in (a) and boreholes A and B in (b) and (c).

4. Stratigraphical data for Arroumd Boreholes A&B, with quantitative sedimentological data for Arroumd Borehole A.

5. Particle size distribution curves for Arroumd Borehole A and surface samples.6. Biplot of XRF data for Si and Na + K, estimated as mass percent of common oxides (SiO2 vs

Na2O + K2O) showing borehole samples, surface sediment samples from the catchment, and local bedrock (intrusive igneous) samples from the adjacent hillslope. Comparative data from eleven boulders (diverse extrusive igneous lithologies) from the upper areas of the Assif n’Imserdane valley also shown. For reference, TAS (Total Alkali Silica) classifications for intrusive (red labels) and extrusive (grey labels) igneous rocks are shown, following Middlemost (1994). Intrusive rock abbreviations: D, diorite; FG, foid gabbro; FMD, foid monzodiorite; FMS, foid monzosyenite; FS, foid syenite; G, granite; Ga, gabbro; GaD, gabbroic diorite; GD, granodiorite; M, monzonite; MD, monzodiorite; MG, monzogabbro; PG, peridote-gabbro; QM, quartz monzonite; S, syenite.

7. Dotplot comparison of individual values for sedimentological properties of Arroumd Borehole A and surface sediment samples.

8. Concentration diagram for organic microfossils for Arroumd Borehole A.9. Images of non-pollen palynomorphs (NPPs) and woody microfossils from Arroumd Borehole

A, Assif n’Imserdane valley, High Atlas, Morocco. Scale bars = 10µm: (1) Podospora sp. (HdV-368); (2) Sordaria (HdV-55a); (3) Sordaria (HdV-55b); (4) Coniochaeta ligniaria (HdV-172); (5) Chaetomium sp. (HdV-7A); (6) Coniochaeta xylariispora (HdV-6); (7) Sporormiella (HdV-113); (8) Sporormiella (HdV-113); (9) Cercophora sp. (partially broken) (HdV-112); (10) Gelasinospora sp. (HdV-1); (11) Diporotheca sp. (cf. HdV-1245); (12) Glomus sp. (HdV-1103); (13) hyphae fragment; (14) UoM-2; (15) HdV-83; (16) Trichodelitschia sp. (HdV-546); (17) UoM-3; (18) UoM-4; (19-21) conidia fragments; (22) UoM-1; (23) hyphal body; (24) fungal spore colony; (25) fungal spore tetrad; (26) hyphal bodies; (27) globose echinate microfossil (algae?), cf. HdV-495, cf. BRN-1 (Feeser and O’Connell, 2010); (28) hyphal bodies; (29) Argania pollen, equatorial view; (30) conifer tracheids with toroid pitting (latewood); (31) conifer tracheids with toroid pitting (earlywood); (32) wood fragment with radial cross-fields

and Cupressoid pitting; (33) wood fragment with Cupressoid pitting (highlighted) in the cross-fields and scalloped torus margins (arrow) consistent with Juniperus thurifera. See Table 3 for description of unidentified UoM types.

10.

Table 1. XRF summary statistics (mean, sd) for Na, K and Si, expressed as common oxides.

Na2O (%) K2O (%) SiO2 (%)Borehole A (n=20) 1.9 ± 0.4 2.9 ± 0.6 49.4 ± 10.6Surface samples (n=6) 1.8 ± 0.1 3.8 ± 0.4 57.8 ± 0.8Bedrock (n=3) 6.3 ± 0.6 2.5 ± 0.6 61.1 ± 6.6

Table 2. Description of NPP types at Arroumd not identifiable to previously documented types, labelled by temporary UoM (University of Manchester) identification code.

ID Description M.A.Z. Assemblage associations PhotographUoM-1 Spheroidal microfossil, two apertures (pores) situated on one side and

projecting in profile; smooth, thick walled and very strongly pigmented (dark brown); diameter 30-35 µm.

1 Gelasinopora (HdV-1) Figure 9-22

UoM-2 Tri-septate fungal spores; truncated end spores; thick septae, raised in profile and without constrictions or pores; smooth and pigmented (dark brown); length 30-40 µm, width 18-24 µm.

1,2,3 Chaetomium (HdV-7A), Coniochaeta ligniaria (HdV-172)

Figure 9-14

UoM-3 Crescent-shaped ascospore; without pores; smooth and lightly pigmented (yellow-brown); longest dimension <12 µm; similar to IBB-260 (Lopez-Vila et al., 2010), but smaller and broader.

1,3 Chaetomium (HdV-7A),Sporormiella (HdV-113)

Figure 9-17

UoM-4 Ascopore cluster (4 spores), cruciform tetrad arrangement; individual spores flattened along proximal face; spores smooth and pigmented (dark brown); longest axis of individual spores <20 µm. Possibly undivided clusters of HdV-6 (Coniochaeta cf. xylariispora).

3 Sporormiella (HdV-113), Sordaria (HdV-55A), Gelasinopora (HdV-1), Valsaria (HdV-263)

Figure 9-18

Table 3. Radiocarbon data from the Arroumd deposit.

Code Sample Depth (cm)

Material & Weight (g)

Conventional Radiocarbon Age

13C/12C (‰)

Calibrated Age (AD/BC), 2

Calibrated Age (AD/BC), median

Calibrated Age (BP), 2

Calibrated Age (BP), median

Beta-429039

Borehole A, 75-80

Bulk sediment, 2.217 g

1190 ± 30 BP -23.3 725-940 AD 830 AD 1225-1010 1120 BP

Beta-326757

Borelhole A, 140-147

Comminuted charcoal 0.00796 g

2520 ± 30 BP -23.2 790-540 BC 650 BC 2490-2740 2590 BP

Beta-302208

Borehole B, 223-224

Charcoal fragment, 0.1246 g

1500 ± 40 BP -21.8 430-640 AD 560 AD 1310-1520 1390 BP

Figure 1. Map of dominant vegetation cover of the southern High Atlas (redrawn from Emberger, 1939), showing the location of (a) Arroumd study area, and other sites mentioned in the text: (b) Oukaimeden (Reille, 1976; Ruiz et al., 2015); (c) Tighislant (Bernard and Reille, 1987); (d) marine core GeoB-6008 (McGregor et al., 2009).

Figure 2. Map showing the location and geomorphological context of the Assif n’Imserdane valley and the Arroumd infilled basin (Hughes et al., 2014).

Figure 3. Images showing the setting of the study location: (a) view looking NE showing the perched position of the deposit behind a Pleistocene lateral moraine on the northern flank of the Assif n’Imserdane above the Arroumd landslide and the village of Arroumd (Source: P.D. Hughes); (b) view looking E across the studied basin, showing the position of the infilled basin between the adjacent hillslope and lateral moraine (Source: P.D. Hughes); (c) satellite image showing the location of the deposit, with erosion scars and ephemeral stream tracks visible on the adjacent hillslopes (Source: Google Earth. 31°07’44.13’’N and 7°54’29.54’’W. 01/08/2015). Arrow in (a) indicate the location of the study location in (a) and boreholes A and B in (b) and (c).

Figure 4. Stratigraphical data for Arroumd Boreholes A&B, with quantitative sedimentological data for Arroumd Borehole A.

Figure 5. Particle size distribution curves for Arroumd Borehole A and surface samples.

Figure 6. Biplot of XRF data for Si and Na + K, estimated as mass percent of common oxides (SiO2 vs Na2O + K2O) showing borehole samples, surface sediment samples from the catchment, and local bedrock (intrusive igneous) samples from the adjacent hillslope. Comparative data from eleven boulders (diverse extrusive igneous lithologies) from the upper areas of the Assif n’Imserdane valley also shown. For reference, TAS (Total Alkali Silica) classifications for intrusive (red labels) and extrusive (grey labels) igneous rocks are shown, following Middlemost (1994). Intrusive rock abbreviations: D, diorite; FG, foid gabbro; FMD, foid monzodiorite; FMS, foid monzosyenite; FS, foid syenite; G, granite; Ga, gabbro; GaD, gabbroic diorite; GD, granodiorite; M, monzonite; MD, monzodiorite; MG, monzogabbro; PG, peridote-gabbro; QM, quartz monzonite; S, syenite.

Figure 7. Dotplot comparison of individual values for sedimentological properties of Arroumd Borehole A and surface sediment samples.

Figure 8. Concentration diagram for organic microfossils for Arroumd Borehole A.

Figure 9. Images of non-pollen palynomorphs (NPPs) and woody microfossils from Arroumd Borehole A, Assif n’Imserdane valley, High Atlas, Morocco. Scale bars = 10µm: (1) Podospora sp. (HdV-368); (2) Sordaria (HdV-55a); (3) Sordaria (HdV-55b); (4) Coniochaeta ligniaria (HdV-172); (5) Chaetomium sp. (HdV-7A); (6) Coniochaeta xylariispora (HdV-6); (7) Sporormiella (HdV-113); (8) Sporormiella (HdV-113); (9) Cercophora sp. (partially broken) (HdV-112); (10) Gelasinospora sp. (HdV-1); (11) Diporotheca sp. (cf. HdV-1245); (12) Glomus sp. (HdV-1103); (13) hyphae fragment; (14) UoM-2; (15) HdV-83; (16) Trichodelitschia sp. (HdV-546); (17) UoM-3; (18) UoM-4; (19-21) conidia fragments; (22) UoM-1; (23) hyphal body; (24) fungal spore colony; (25) fungal spore tetrad; (26) hyphal bodies; (27) globose echinate microfossil (algae?), cf. HdV-495, cf. BRN-1 (Feeser and O’Connell, 2010); (28) hyphal bodies; (29) Argania pollen, equatorial view; (30) conifer tracheids with toroid pitting (latewood); (31) conifer tracheids with toroid pitting (earlywood); (32) wood fragment with radial cross-fields and Cupressoid pitting; (33) wood fragment with Cupressoid pitting (highlighted) in the cross-fields and scalloped torus margins (arrow) consistent with Juniperus thurifera. See Table 3 for description of unidentified UoM types.