Characterisation of two fluvio-lacustrine loessoid deposits on the island of Gran Canaria, Canary Islands

ARTICLE IN PRESS

Quaternary International 196 (2009) 36–43

Characterisation of two fluvio-lacustrine loessoid deposits on the island of Gran Canaria, Canary Islands I. Mene´ndez, L. Cabrera, I. Sa´nchez-Pe´rez, J. Mangas, I. Alonso Departamento de Fı´sica, Universidad de Las Palmas de Gran Canaria, Campus de Tafira 35017, Las Palmas de Gran Canaria, Canary Islands, Spain Available online 27 June 2008

Abstract The Canary Islands are close to the largest desert in the world, the Sahara, and as a result, the influence of air-transported dust in the area is of great significance. The present analysis consists of a study of two deposits in the NE and NW, respectively, of the island of Gran Canaria, considered as fluvio-lacustrine loessoids. They exhibit the characteristics of aeolian deposits, re-worked by fluvial processes, at the mouth of gullies, and later edaphized. In the NW profile (Ga´ldar), formed from 400 ka to present, there are four different levels with abundant manganese stains over each and separated by dense calcrete laminations. This sequence may be associated with cyclical processes of deposits in humid conditions, and drying (Mn mobility), plus the formation of arid soil (carbonate precipitation). The formation of the Galdar profile took place between the Upper Pliocene and the Upper Pleistocene–Holocene. The NE profile (Jina´mar) reveals a similar cyclic profile. The Jina´mar fluvio-loess deposit was formed between the Upper Pliocene and the Upper Pleistocene (1.96–0.1 Ma). The high percentage of the silt fraction (60–90%) and the high percentage of quartz, a mineral which is totally imported from the Sahara Desert, are the main arguments in favour of the definition of these loess-like deposits. r 2008 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction Large silt deposits found in contemporary landscapes tend to be alluvial or aeolian. However, the aeolian deposits of loess contain particles that are the result of weathering and pedological processes (Smalley and Rogers, 1997) and are transported by rivers and re-deposited on alluvial fans, in wadis and terminal basins (Yaalon, 1987). These particles are then transported to floodplains (Assallay et al., 1998). Loess deposits need various specific requisites in order to form. These include the following: a large supply of silt-size particles over a period of tens to hundreds of thousands of years, and the existence of an adequate dust trap (Pye, 1995). In addition, the generation of loess deposits requires a threshold of an aeolian rate of deposition of 0.5 mm a 1 (Pye and Sherwin, 1999). When this ratio is not reached, the deposits are called loessoids. Obruchev (1945) makes a distinction between primary and secondary loess, which are either defined as redeposited loess or as originated by other non-aeolian Corresponding author.

E-mail address: [email protected] (I. Mene´ndez).

processes. In the latter category, he included the loess reworked by colluvial or fluvial processes (Pye, 1995). In addition, the edaphization of the aeolian deposits is commonly considered to be a necessary premise for definition of a loess formation (Pecsi, 1990). Consequently, a loess is a complex deposit, mainly aeolian, but with a weathering and fluvial past, and an edaphic future. Due to the complexity of the genesis and definition of loess, and the breadth of the terminology, various authors have opted for the diplomatic term of ‘‘loess-like’’ (Derbyshire, 1995; Nemecz et al., 2000; Hesse and McTainsh, 2003; Jefferson et al., 2003; Danukalova and Eremeev, 2006) or loessoids (Pye and Sherwin, 1999). Much attention has been given, over the last few years, to loess forming under hot climatic conditions, largely disconnected from the classical glacial silt sources, such as deserts. The origin of silt is, in the main, a result of a desert environment: there is aeolian abrasion and attrition, salt precipitation, isolation and frost weathering (McTainsh, 1987; Smalley, 1990; Pye, 1995; Assallay et al., 1998; Smith et al., 2002). Alternatively, these landforms and associated deposits may be the result of other varied atmospheric conditions, much wetter in this case (Bu¨del,

1040-6182/$ - see front matter r 2008 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2008.05.011

ARTICLE IN PRESS I. Mene´ndez et al. / Quaternary International 196 (2009) 36–43

1963; Smith et al., 2002). The loess mineralogy profile depends upon the regional geology, although the percentage of quartz is dominant (45–55%), with a marked presence of remains of feldspar, carbonates, heavy minerals, clay minerals and volcanic glass shards (Pye, 1995). The aim of the present study is to analyse two loessoid deposits, by grain size and mineralogy. These two loessoid deposits are edaphized, mouth-gully deposits. One of these is to be found in the NE of Gran Canaria, and the other in the NW. This is the first study of loess-like deposits on this island. 2. Regional context The island of Gran Canaria is, more or less, at the centre of the Canary Islands (Fig. 1). The island has a roughly circular topology, with a diameter of around 45 km, and an area of 1560 km2. The highest point (1949 m, at Pico de Las Nieves) is close to the centre of the island, and gives rise to a dense radial network of strongly incised gullies. Totally 56% of the island’s surface has an average slope of between 151 and 301 (Sa´nchez et al., 1995). The climatic differences from the North (temperate and humid) to the South (warm and dry) are produced by the Trade Winds (N-NE component) and the topographical influence, as is indicated by the mainly wet and cloudy conditions on the Northern slopes of Gran Canaria. The topography also gives rise to an altitudinal gradient in climatic conditions: arid–semiarid coastal areas (o250 mm a 1), temperate in mid-elevation areas (250–800 mm a 1), and humid and cold conditions for the summit areas (4800 mm a 1, Marzol, 1988). The average humidity and the annual rainfall increase according to altitude. In addition, the result of the island’s proximity to the West Saharan Desert allows the predominance of Saharan winds (30% of the year, over a 5-year period, Sancho et al., 1992), which transport abundant aeolian dust. The Trade Winds prevail over the rest of the year, blowing from N-NE (Dorta et al., 2002).

37

Tropical storm conditions, coming from the W-SW, are rare occurrences and are highly related to heavy rainfall (Marzol, 1988). From a geological perspective, the first sub-aerial volcanism on the island of Gran Canaria occurred in the Miocene (14.5–14.1 Ma), and was characterised by extrusion of immense volumes of alkali basalts, corresponding to the shield stage in the layering of the island volcanic edifice. Later, the episode of alkali volcanism took place between 14.1 and 7.0 Ma, creating more differentiated, silica-undersaturated rocks (tephrites, phonolite–tephrites, phonolites, trachytes, and rhyolites). This was followed by a hiatus in volcanic activity, between 7.0 and 5.5 Ma, giving rise to erosion and the deposition of the sedimentary sequence of the Las Palmas Detritic Formation. Finally, a stage of volcanic rejuvenation from 5.5 Ma to present gave rise to differentiated basaltic rocks (Barcells et al., 1992; Carracedo et al., 2002; Vera, 2004). The catchment area of the Ga´ldar deposit consists of a ravine some 35.63-km2 long, with a volume of 2.3 km3, a thalweg length of 17.379 km, maximum elevation of 1.111 km and maximum incision of 245 m on alkali basalt lavas. The catchment area of the Jinamar deposit is a ravine some 70.62-km2 long, with a volume of 8.47 km3, a thalweg length of 21.298 km, maximum elevation of 1.634 km and maximum incision of 422 m on ignimbrite and alkali basalt lavas (Mene´ndez et al., 2008). The sub-saturated silica nature of the alkaline volcanic rocks in the Canary Islands, characteristic of an oceanic intra-plate island, precludes the presence of quartz in the paragenesis of the materials in the Canary Islands. Any quartz particles found in any natural deposits on these islands must have been exported. The generation of loess areas is nowadays accepted in this peri-desert, and several authors have already defined ‘‘desert’’ loess in the Easternmost islands within the Canary Archipelago (Coude´-Gaussen, 1987, on Fuerteventura Island; Wright, 2001 and Zo¨ller et al., 2003; for the island

Fig. 1. The location of the studied fluvio-lacustrine loess profiles on the island of Gran Canaria.

ARTICLE IN PRESS 38

I. Mene´ndez et al. / Quaternary International 196 (2009) 36–43

of Lanzarote) but has not, as yet, been ascribed to the island of Gran Canaria. Potentially, the Saharan dust is the main source of loess-like deposits in the Canary Islands. The mineralogical reference for the Saharan dust compositions reveals great abundance of quartz, with low quantities of clays, feldspars, calcite, and halite (Kiefert and McTainsh, 1996; Goudie and Middleton, 2001). Nevertheless, airborne dust from the island of Gran Canaria is mainly quartz (ca. 40%) with lesser amounts of Mg-calcite, calcite, feldspars, dolomite, magnetite, aragonite, halite, and very scarce quantities of illite, kaolinite–chlorite, and palygorskite (Menendez et al., 2007).

fine-sifted matter. This situation should have favoured the formation of a lacustrine system (Fig. 1). The outcrop is 160 m a.s.l. The substrate of the Galdar profile consists of a basaltic conglomerate, created by the surrounding rift platform lava, and dating from 2.5 Ma (Upper Pliocene, Guillou et al., 2004). The age of the volcanic cone of Galdar is Middle Pleistocene, and the lacustrine loessoid deposits in Galdar are defined as Holocene (Barcells et al., 1990). However, all the deposits may be older (Upper Pleistocene), since the Upper Pleistocene period was only dated using geomorphological criteria. In the Galdar profile, from the bottom to the top, there are four differentiated levels, separated by dense calcrete laminations (Figs. 2 and 3). There is

3. Material and methods Two outcrops, one in the N-NE part of the island (the Jina´mar deposit) and the other in the NNW area (the Ga´ldar deposit), were selected for analysis. Stratigraphic columns were constructed, and a sample of each differentiated level was collected for the analysis of texture and mineralogy. No shells were found in any layer that allowed for amino-acid chronology and the extreme light exposure, by night, of the outcrops, due to their urban context, discouraged the use of any luminescence technique. The grain size fractions in the soil samples were dry sieved from 1 to 4 + (2–0.063 mm) at 0.5 + intervals. Additionally, the grain size analyses of samples of the silt and clay fractions were carried out with a Coulter LS100 laser diffractometer. The mineralogical study used a PHILIPS-Binary Scan X-ray Diffractometer (XRD), and a Cu-diffracted-beam source. The measurement conditions were 5–801 2y. Profile analyses and phase identification were carried out manually, and contrasted with two automated analysis programs (DIFFRACPlus SEARCH, Brukers, and Xpowder software, Martin, 2004). The quantitative mineralogical composition was determined by dividing the diffractogram peak areas by the following reflectivity power factors (Martı´n-Pozas, 1975): 0.1 for illite; palygorskite, and kaolinite; 1.5 for quartz and feldspars; 1.0 for calcite, calcite-Mg, dolomite and halite; and 1.5 for magnetite. All of these values were normalized to 100%, assuming only the presence of crystalline phases. The disaggregating compounds (H2O2 or Na4P2O7) were not applied to any samples. A 15-min ultrasonic bath was used to destroy the soil aggregates, in detriment of the aeolian aggregates present in the samples (Matthews, 1991; Mason et al., 2003).

Fig. 2. An image of the Galdar outcrop, differentiated by levels. Legend: G: Galdar plot; J: Jinamar plot; numbers indicated levels from bottom (1) to the top of the profile (4); a–c are lateral changes; 0 and 00 are nonloessoids levels.

4. Results 4.1. Galdar deposit The formation of the Galdar deposit seems to have been associated with the construction of a volcanic cone close to the mouth of the gully, thereby presenting an impediment to the fluvial network, and the subsequent accumulation of

Fig. 3. Stratigraphic sections of Galdar and Jinamar profiles. Key: G: Galdar plot; J: Jinamar plot; numbers indicate levels from bottom (1) to the top of the profile (4); a–c are lateral changes; 0 and 00 are non-loessoid levels.

ARTICLE IN PRESS I. Mene´ndez et al. / Quaternary International 196 (2009) 36–43

J00 J4

100

J3 J2b J2a J1

80

J0

60

G4

100

G3 G2b G2a

80

G1 60

40

40

20

20

% 0

39

% 0 gravel

sand

silt

gravel

clay

sand

silt

clay

Fig. 4. The grain-size distribution of the selected profile levels, obtained by sieving. Key: G: Galdar plot; J: Jinamar plot; numbers indicate levels from bottom (1) to the top of the profile (4); a–c represent the lateral changes; 0 and 00 are non-loessoid levels.

also an abundance of Mn stains on each and every level. The age range formation of the Galdar profile is between the Upper Pliocene and the Upper Pleistocene– Holocene. The silt fraction predominates in all levels (from 64% to 92%; Fig. 4). The grain-silt size distributions over the different levels in the Galdar profile are polymodal, with a clear downward trend from the modal size of the top two levels (2–3 mm) with respect to the lower levels (25–40 mm; Table 1; Fig. 5). High proportions of quartz are found in the silt fraction over all the various levels (57–97%; Table 1, Fig. 6), with a more marked presence on the lower levels, followed by feldspars. It is interesting to note the absence of carbonates in the matrix under analysis, as opposed to carbonate concretions in the crevices. 4.2. Jinamar deposit The Jinamar deposit forms a North terrace, ca. 40 m asl, at the mouth of the gully of Telde (Fig. 1). The substrate profile is at the pyroclastic basaltic level, which is the lower limit of the fluvio-lacustrine loessoid deposit (J0; Figs. 3 and 7). This pyroclastic level corresponds to the rift platform lavas of the Telde gully, dating back to 1.96 Ma (the Upper Pliocene; Barcells et al., 1990). This situation is favourable for the formation of a lacustrine system. Upwards, the pyroclastic deposit reveals four different levels, separated by carbonate laminations (less dense than those at the Galdar profile) with the development of Mn stains. At the top of the profile, there is an altered pyroclastic mantle (J00), dating to the Jinamar Volcano episode (the Upper Pleistocene; Barcells et al., 1990). Thereafter, the Jinamar fluvio-lacustrine loessoid deposit formed between these various volcanic events:

Table 1 The quartz content and the polymodal sizes of the samples obtained over the different levels of the profiles of Galdar and Jinamar Level

Q (%)

1st mode (mm)

2nd mode (mm)

3rd mode (mm)

4th mode (mm)

G4 G3 G2b G2a G1

97 78 89 73 57

2 3 30 25 40

5 6 21 19 24

21 24 10 11 10

– – 4 4 4

J4 J3 J2b J2a J1

97 69 7 1 24

40 40 6 15 2

21 9 1 32 5

2 4 32 1 21

– – – – –

from the Upper Pliocene to the Upper Pleistocene age (1.96 0.01 Ma). The profile shows a clear textural differentiation between the fluvio-lacustrine loessoid deposit, the basal deposit, the lateral change, and the surface material. The basal material is weathered lappili with a major sand fraction (58%; Fig. 4) and low silt concentration (7%). The lateral change level is clearly sandy (86%): a massive, thick deposit with signals of edaphization, with cutans and carbonate precipitation in nodules and fissures. The surface deposit is a weathered pyroclastic mantle, predominantly gravel (45%) with minor quantities of silt (14%; Fig. 4). The grain-silt size distributions over the various different levels of the Jinamar profile are polymodal, with a marked counter-trend towards an increased main size mode from the bottom (J1: 2 mm) to the upper three levels (J2 4: 15–40 mm; Table 1; Fig. 5). The mineralogical composition of the silty fraction is mainly quartz at the top and the

ARTICLE IN PRESS I. Mene´ndez et al. / Quaternary International 196 (2009) 36–43

40

bottom of the non-silty levels, and the upper loessoid levels; but carbonate predominates at the lower loessoid levels (Table 1; Fig. 6). 6

Primary modal size (16-32 µm) of Sun et al., 2002

%

Jinamar Silt J4 J3 J2b J2a J1

4

2

0 0,1

1 6

G4

µm 100

Primary modal size (16-32 µm) of Sun et al., 2002

%

Galdar Silt

10

Fig. 7. Jinamar profile.

4

G3

5. Discussion

G2b 2

G2a G1

0 0,1

1

10

µm 100

Fig. 5. Silt size distribution for the Galdar and Jinamar samples, analysed using a Coulter LS100 laser diffractometer. Key: G: Galdar plot; J: Jinamar plot; numbers indicate levels from bottom (1) to top of the profile (4); a–c are lateral changes; 0 and 00 are non-loessoid levels. The arrows mark the tendency of the modal size, increasing by depth in Jinamar Silt, and vice versa in Galdar Silt.

Silt Fraction

Q

Feldspars

Calcite

Calcite Mg

J00 J4 J3 J2a J2b J1 J0 0

10

20

Silt Fraction

30

40

50

Q

60

70

80

90

100 %

80

90

100 %

Feldspars

G1 G2a G2b G3 G4 0

10

20

30

40

50

60

70

Fig. 6. The mineralogy of the Galdar and Jinamar samples by main particle size (the silt fraction) using X-ray Diffractometer (XRD) analysis. Key: G: Galdar plot; J: Jinamar plot; numbers indicate levels from bottom (1) to the top of the profile (4); a–c are lateral changes; 0 and 00 are nonloessoid levels.

The aeolian dust deposition, as estimated by Prospero (1996; in Table 2a, p. 142) for the Canary Islands, is 16 g m 2 a 1. Direct measurements, on the island of Gran Canaria, carried out by Menendez et al. (2007) produced a range of 79–17 g m 2 a 1, obtained over plots at different altitudes, from 0 to 950 m a.s.l., respectively. If the apparent mean dust density is approximated to 1 g cm 3, and supposing that 50% of the accumulated dust in the soil is finally stabilized (Cattle et al., 2002), then the net accumulation rate for soil on Gran Canaria would be around 0.02–0.01 mm a 1. These values are lower than the threshold accumulation rate for loess formation of 0.5 mm a 1 as defined by Pye and Sherwin (1999). Considering a constant accumulation rate over time on the island, the possible aeolian deposits on the island of Gran Canaria should be called loessoids or loess-like, rather than loess. Values of 0.01–0.02 mm a 1 are consistent with the thickness of both profiles, as the Galdar profile (3-m thick) would have required 150–300 ka to develop, and the Jinamar profile (4-m thick), 200–400 ka. In both cases, the time interval is small enough to fit into the proposed dates for the formation of these deposits considering only the aeolian factor. Nevertheless, these fluvio-lacustrine deposits may represent periodic cleaning and re-concentration of the aeolian deposit, reflected in its mineralogy and texture. Saharan dust input should have been occurring in the Canary Archipelago ever since the Saharan region acquired its desert character. According to Giraudi (2005), this has occurred over at least 80 ka. The lowest frequency of haze conditions would correspond to wet-glacial phases (less than 20% for the interval 14.8–5.5 ka; De Menocal et al., 2000). The calculated Saharan dust input values on Gran Canaria Island could decrease during wetter times in the

ARTICLE IN PRESS I. Mene´ndez et al. / Quaternary International 196 (2009) 36–43

past. On the contrary, in glacial–interglacial transitions, when the wind strength was intensified, the Canary area received higher dust input (Moreno et al., 2001). Considering only the aeolian factor, the existence of a progression in the mean size distribution in loessoid levels, decreasing for Galdar, and increasing for the Jinamar profile, might suggest a progressive change in the distance of the main source of loessoids, in the degree of edaphization (Memezc et al., 2000), or changes in the palaeoclimatic conditions. Coarser fractions would indicate greater intensity in the wind conditions, enhancing the African Monsoon in the North Canary Basin (Moreno et al., 2001). The Galdar deposit would reflect progressive wetter conditions in its deposition time and vice versa for the Jinamar deposit. In addition, the increase in the modal size of the silt fraction gives rise to a higher percentage in the silt fraction over all the samples (Figs. 4 and 5). This would appear to indicate that the ages of both deposits are not totally correlated. The Jinamar deposit was fossilized by Holocene lava, and the top Galdar deposit may or may not be earlier. Nevertheless, these are the only estimations that need to be confirmed with more specific dates for each level. The mean size of around 5 mm is defined as typical for the Fuerteventura peri-Saharan loess (Coude´-Gaussen, 1991). Nevertheless, larger clasts may come from the Sahara, as observed by Middleton et al. (2001) who noted the presence of fine sand (462.5 mm) the sources of which appeared to be at distances in excess of 1000 km from the final destination, with no clearly defined mode of transport. This would not appear to concur with the traditional model of wind transport. However, if this was possible for sedimentary materials from the North Pacific Ocean, it should also be taken into consideration for the Canary Islands, where the distance is one order of magnitude lower (100 km). In fact, the Canary Islands may be considered to be adjacent to the Sahara desert, a source providing both coarse and fine aeolian populations, much as occurs in the loess areas of North-Western China (Pye and Zhou, 1989; Sun et al., 2002). Loess generally has a bimodal grain size (Nemecz et al., 2000; Donghuai et al., 2004). The typical loess defined by Sun et al. (2002) spans a range of sizes from 0 to 25 mm, with a primary modal size of 16–32 mm and a long tail on the fine side. This is the case of J4, J3, G2 and G1 levels. However, the curves for grain-size distribution in the Gran Canaria aeolian dust samples are polymodal, centring around 1.5–2 mm (clays), 6–8 mm (very fine-fine silts), 22–35 mm (coarse silt), and 62–130 mm (very fine sands; Fig. 4 in Menendez et al., 2007). If we assume that the aeolian inputs are at the origin of these loessoids, this might be an explanation for the polymodal trend in loessoid levels. Again, the lacustrine origin of the deposits studied may also justify the finer modal sizes and the polymodal behaviour, with the resultant typical re-worked loess, distributed over three or four modal sizes (Sun et al., 2002; Table 1).

41

In the Galdar profile, there are four differentiated levels, from the bottom to the top, separated by dense calcrete laminations. There is also abundance of Mn stains at every level. This sequence may indicate waterlogging (Rahmatullah et al., 1990; McDaniel and Buol, 1991; Retallack et al., 2002), reflecting near-ephemeral lacustrine situations. The autochthonous sediments generated in the catchments might correspond to volcanic matter (mainly alkali basalts and phonolites), in other words, feldspar, feldespatoids, magnetite, olivine, clinopyroxene, amphibolites and zeolites, among others. On the contrary, the samples of the Galdar and the Jinamar deposits that were analysed, with the exception of the feldspar and magnetite, which may also be allochthonous, either did not contain these minerals at all or were merely in minimal amounts. The silica subsaturated nature of rocks in the Canary Islands precludes the presence of quartz in the paragenesis of the rocks. The resultant high percentage of the silt fraction (between 60% and 90%; Fig. 4) and the high quartz content of these deposits (a mineral that is totally exported; Fig. 6) are the two major and decisive arguments in favour of the definition of these deposits as re-worked loess or loessoids. 6. Conclusions The results of geomorphological, mineralogical, and textural analysis support the definition of the studied outcrops of Galdar and Jinamar as fluvial-lacustrine loessoid deposits. The estimated deposition rates of aeolian dust measured in this Island fall below the threshold value of loess formation. The resulting high percentage of the silt fraction (between 60% and 90%) and the high quartz content of these deposits (a mineral which is totally exported) are the two main arguments in favour of the definition of these deposits as re-worked loess, in other words, fluvial-lacustrine loessoids. Acknowledgements This work is part of the R+D Project ‘‘Remolinos ocea´nicos y deposicio´n atmosfe´rica: influencia sobre los flujos de partı´culas y remineralizacio´n en la columna de agua’’ (CTM2004-06842-C03-01/MAR) financed by the EU Regional Development programme, FEDER, and the Spanish Secretary of State for Science and Technology. Our thanks also to Dr. Margaret Hart Robertson and to John H. Roberts, for the revision of the English used in this text. References Assallay, A.M., Rogers, C.D.F., Smalley, I.J., Jefferson, I.F., 1998. Silt: 2–62 mm, 9–4 +. Earth-Science Reviews 45, 61–88. Barcells, R., Barrera, J.L., Ruiz, M.T., 1990. Mapa Geolo´gico de Espan˜a escala 1:25.000 1a edicio´n (MAGNA). Hoja de Arucas (1101-III-VI; % 83-81; 83-82). ITGE. Serv. Pub. Mo. Industria, Madrid.

ARTICLE IN PRESS 42

I. Mene´ndez et al. / Quaternary International 196 (2009) 36–43

Barcells, R., Barrera, J.L., Gomez-Sainz, J.A., 1992. Mapa Geolo´gico de Espan˜a escala 1:100.000 1a edicio´n (MAGNA). Isla de Gran Canaria (21-21/21-22). ITGE. Serv.% Pub. Mo. Industria, Madrid. Bu¨del, J., 1963. Klima-genetische geomorphologie. Geographische Rundschau 14, 161–187. Carracedo, J.C., Pe´rez Torrado, F.J., Ancochea, E., Meco, J., Herna´n, F., Cubas, C.R., Casillas, R., Rodrı´guez Bardiola, E., Ahijado, A., 2002. Cenozoic volcanism II: the Canary Islands. In: Gibbons, W., Moreno, T. (Eds.), The Geology of Spain. The Geological Society, London, pp. 439–472. Cattle, S.R., McTainsh, G.H., Wagner, S., 2002. Aeolian dust contributions to soil of the Namoi Valley, Northern NSW Australia. Catena 47, 245–264. Coude´-Gaussen, G., 1987. The peri-Saharan loess: sedimentological characterisation and paleoclimatic significance. GeoJournal 15, 177–183. Coude´-Gaussen, G., 1991. Les Poussie`res Sahariennes. John Libbery Eurotext, Montagne, 485pp. Danukalova, G.A., Eremeev, A.A., 2006. Quaternary loess-like deposits of the Southern Urals. Quaternary International 152–153, 42–47. De Menocal, P., Ortiz, J., Guilderson, T., Adkins, J., Sarnthein, M., Baker, L., Yarusinsky, M., 2000. Abrupt onset and termination of the African Humid Period: a rapid climate responses to gradual isolation forcing. Quaternary Science Reviews 19, 347–361. Derbyshire, E., 1995. Aeolian sediments in the Quaternary record: an introduction. Quaternary Science Reviews 14, 641–643. Donghuai, S., Bloemendal, J., Rea, D.K., Zhisheng, A., Vandernberghe, J., Huayu, L., Ruixia, S., Tungsheng, L., 2004. Bimodal grain-size distribution of Chinese Loess, and its paleoclimatic implications. Catena 55, 325–340. Dorta, P., Gelado, M.D., Cardona, P., Collado, C., Criado, C., Herna´ndez, J.J., Mendoza, S., Siruela, V., Torres, M.E., Curbelo, D., Lo´pez, P., Rodrı´guez, E., 2002. Algunas consideraciones sobre la importancia del polvo de origen sahariano en el clima del archipie´lago canario y su aporte a las aguas superficiales ocea´nicas: el episodio de abril de 2002’’. Publicaciones de la AEC, El agua y el clima., Palma de Mallorca, pp. 13–24. Giraudi, C., 2005. Eolian sand in peridesert northwestern Libya and implications for Late Pleistocene and Holocene Sahara expansions. Palaeogeography, Palaeoecology, Palaeoclimatology 218, 161–173. Goudie, A.S., Middleton, N.J., 2001. Saharan dust storms: nature and consequences. Earth-Science Reviews 56, 179–204. Guillou, H., Pe´rez-Torrado, F.J., Hansen, A.R., Carracedo, J.C., Gimeno, D., 2004. The Plio-Quaternary volcanic evolution of Gran Canaria based on new K-Ar ages and magnetostratigraphy. Journal of Volcanology and Geothermal Research 135, 221–246. Hesse, P.P., McTainsh, G.M., 2003. Australian dust deposits: modern processes and the Quaternary record. Quaternary Science Reviews 22, 2007–2035. Jefferson, I.F., Evstatiev, D., Karastanev, D., Mavalyanova, N.G., Smalley, I.J., 2003. Engineering geology of loess and loess-like deposits: a commentary on the Russian literature. Engineering Geology 68, 333–351. Kiefert, L., McTainsh, G.H., 1996. Oxygen isotope abundance in the quartz fraction of aeolian dust: implications for soil and ocean sediment formation in the Australasian region. Australian Journal of Soil Research 34 (4), 467–473. Martı´n-Pozas, J.M., 1975. Ana´lisis cuantitativo de fases cristalinas por DRX, en Difraccio´n de muestras policristalinas. In: Saja, J.A. (Ed.), Me´todo de Debye-Scherrer. I.C.E. Universidad de Valladolid, Valladolid, Spain. Marzol, M.V., 1988. La lluvia, un recurso natural para Canarias, Servicio de publicaciones de la Caja General de Ahorros de Canarias, no. 130 (investigacio´n 32), Las Palmas de Gran Canaria, Gran Canaria. Mason, J.A., Jacobs, P.M., Greene, R.S.B., Nettleton, W.D., 2003. Sedimentary aggregates in the Peoria Loess of Nebraska, USA. Catena 53, 377–397.

Matthews, M.D., 1991. The effect of pretreatment on size analyses. In: Syvitski, J.P.M. (Ed.), Principles, Methods and Application of Particle Size Analyses, pp. 34–42. McDaniel, P.A., Buol, S.W., 1991. Manganese distributions in acid soils of the North Carolina piedmont. Soil Science Society of American Journal 55, 152–158. McTainsh, G., 1987. Desert loess in Northern Nigeria. Zeitschrift fu¨r Geomorphologie 31, 145–165. Menendez, I., Dı´az-Herna´ndez, J.L., Mangas, J., Alonso, I., Sa´nchez-Soto, P.J., 2007. Airborne dust accumulation and soil development in the North-East sector of Gran Canaria (Canary Islands, Spain). Journal of Arid Environment 71, 57–81. Mene´ndez, I., Silva, P.G., Martı´n-Betancor, M., Pe´rez-Torrado, F.J., Guillou, H., Scaillet, S., 2008. Fluvial dissection, isostatic uplift and geomorphological evolution of volcanic islands (Gran Canaria, Canary Islands, Spain). Geomorphology (accepted manuscript). Middleton, N.J., Betzer, P.R., Bull, P.A., 2001. Long-range transport of ‘‘giant’’ Aeolian quartz grains: linkage with discrete sedimentary sources and implications for protective particle transfer. Marine Geology 177, 411–417. Moreno, A., Targarona, J., Henderiks, J., Canals, M., Freudenthal, T., Meggers, H., 2001. Orbital forcing of dust supply in the North Canary Basin over the last 250 kyrs. Quaternary Science Reviews 20, 1327–1339. Nemecz, E., Pecsi, M., Zsuzsa Hartya´ni, Z., Horvath, T., 2000. The origin of the silt size quartz grains and minerals in loess. Quaternary International 68–71, 199–208. Obruchev, V.A., 1945. Loess types and their origin. American Journal of Science 243, 256–262. Pecsi, M., 1990. Loess is not just the accumulation of dust. Quaternary International 7–8, 1–21. Prospero, J.M., 1996. Saharan dust transport over the North Atlantic Ocean and Mediterranean: an overview. In: Guerzoni, S., Chester, R. (Eds.), The Impact of Desert Dust Across the Mediterranean. Kluwer Academic Publishers, Netherlands, pp. 133–151. Pye, K., 1995. The nature, origin and accumulation of loess. Quaternary Science Reviews 14, 653–667. Pye, K., Sherwin, D., 1999. Loess. In: Goudie, A.S., Livingstone, I., Stokes, S. (Eds.), Aeolian Environments, Sediments and Landforms. Wiley, West Sussex, England. Pye, K., Zhou, L.P., 1989. Late Pleistocene and Holoence aeolian dust deposition in North China and the Northwest Pacific Ocean. Palaeogeography, Palaeoclimatology, Palaeoecology 73, 11–23. Rahmatullah, Dixon, J.B., Golden, D.C., 1990. Manganese containing nodules in two calcareous rice soils of Pakistan. In: Douglas, L.A. (Ed.), Soil Micromorphology: A Basic and Applied Science. Elsevier, Amsterdam, pp. 387–394. Retallack, G.J., Tanaka, S., Tate, T., 2002. Late Miocene advent of tall grassland paleosols in Oregon. Palaeogeography, Palaeoclimatology, Palaeoecology 183, 329–354. Sa´nchez, J., Rı´os, C., Pe´rez-Chaco´n, E., Sua´rez, C., 1995. Cartografı´a Potencial del Medio Natural de Gran Canaria, Cabildo Insular de Gran Canaria and Universidad de Valencia (Eds.), Universidad de Las Palmas de Gran Canaria (Mapas y Memoria). Sancho, P., de la Cruz, I., Dı´az, A., Martin, F., Herna´ndez, F., Valero, F., Albarran, A., 1992. A five years climatology of back trajectories from the Izan˜a bascline station, Tenerife, The Canary Islands. Atmospheric Environment 26 (6), 1081–1096. Smalley, I.J., 1990. Possible formation mechanisms for the modal coarsesilt quartz particles in loess. Quaternary International 7–8, 23–27. Smalley, I.J., Rogers, C.D.F., 1997. L.S. Berg and the soil theory of loess formation. In: Yaalon, D.H., Berkowicz, S. (Eds.), History of Soil Science: International Perspectives. Advances in Geological Ecology, vol. 29. Catena Verlag, Reiskirchen, pp. 377–391. Smith, B.J., Wright, J.S., Whalley, W.B., 2002. Sources of non-glacial, loess-size quartz silt and the origins of ‘‘desert loess’’. Earth-Science Reviews 59, 1–26. Sun, D., Bloemendal, J., Rea, D.K., Vandenberghe, J., Jiang, F., An, Z., Su, R., 2002. Grain-size distribution function of polymodal sediments

ARTICLE IN PRESS I. Mene´ndez et al. / Quaternary International 196 (2009) 36–43 in hydraulic and aeolian environments, and numerical partitioning of the sedimentary components. Sedimentary Geology 152, 263–277. Vera, J.A., 2004. Geologı´a de Espan˜a. Sociedad Geolo´gica de Espan˜aInstituto Geolo´gico y Minero Espan˜ol, Madrid. Wright, J., 2001. Making loess-sized quartz silt: data form laboratory simulations and implications for sediment transport pathways and the

43

formation of ‘‘desert’’ loess deposits associated with the Sahara. Quaternary International 76–77, 7–19. Yaalon, D.H., 1987. Saharan dust and desert loess: effect on surrounding soils. Journal of African Earth Sciences 6 (4), 569–571. Zo¨ller, L., Suchodoletz, H.v., Ku¨ster, N., 2003. Geoarchaeological and chronometrical evidence of early human occupation of Lanzarote (Canary Islands). Quaternary Science Reviews 22, 1299–1307.