Dust accumulation and loess formation under the oceanic 207 Hungarian Geographical Bulletin 59 (2) (2010) pp. 207–230. Dust accumulation and loess formation under the oceanic semiarid climate of Tenerife, Canary Islands Éva Kis and Ferenc Schweitzer1 Abstract Sediments formed by mixing dust of Saharan origin with local weathered pyroclastic rocks were investigated using granulometric analyses for environmental reconstruction. For this purpose traditional sedimentological parameters were applied together with indices such as FG (fi neness grade) and Kd (degree of weathering). It could be established that surface deposits are loess or loess-like sediments reworked by colluvial processes. It was also concluded that soils formed on alkalic basalt lava are semipedolites i.e. sediments that have undergone pedogenesis of limited extent, whereas on the phonolite genuine paleosols formed. The stratifi cation of sediments show half-year variation instead of an- nual one due to the alternating dry and wet seasons (parent material being transported by north-eastern and Sahara trade winds). With the exception of the soil developed on the phonolite lava all the deposits studied are younger than 1 Ma. Keywords: Saharan dust, pyroclastic rocks, grain size analysis, sedimentological indices, trade winds Introduction In the section at Bandas del Sur, on the south-eastern part of Tenerife (photos 1 and 2), Canary Islands (Figure 1) loess-like deposits and sediments aff ected by pedogenesis were investigated using grain size parameters. Based on the parameter values this method is aimed to characterize these deposits and to identify the environmental conditions that prevailed during their formation. The deposits have developed on volcanic pyroclastic rocks as a result of the weathering of the latt er and a concurrent admixture of the falling dust of African origin. Dust accumulation and formation of loess-like deposits is going on even nowadays (Photo 3). Nevertheless this so-called African dust is not uniform either; partly it was blown out from sand deserts of Sahara and from the western areas of Atlas Mountains, partly derives from “perisaharan loess” of Africa. On the Western Canary Islands airborne material of sand 1 Geographical Research Institute, Hungarian Academy of Sciences, H-1112 Budapest, Budaörsi út 45. E-mail: kisse@helka.iif.hu, schweitf@mtafk i.hu 208 Photo 1. The island of Tenerife, with the highest peak of the stratovolcano (Pico del Teide, 3718 m). (htt p://upload.wikimedia.org/wikipedia/commons/8/8c/Tenerife_LANDSAT-Canary_Islands.png) Photo 2. Volcanic rocks and sediments building up Tenerife (Photo by Schweitzer, F.) 209 Photo 3. Satellite image showing African dust blown towards the Canary Islands (htt p://earthobservatory.nasa.gov/IOTD/view.php?id=1169) Fig. 1. The Canary Islands hot spot. Carracedo, J.C. et al. 2002. htt p://www.mantleplumes.org/Canary.html 210 dunes and loessial sediments redeposited from the Eastern Canary Islands (Lanzarote, Fuerteventura) to Tenerife or Gran Canaria, sometimes reworked several times was also added. The climate on Tenerife is oceanic semiarid, thus periodicity i.e. alter- nating dry and humid half-years are refl ected by the stratifi cation of geologi- cal sequences. Half-year periods stem from the diff erences in warming of the ocean and land and expressed by dry trade winds of north-eastern direction in summer and humid trade winds blowing from the Sahara in winter. Half- year periods of deposition are manifest on Canary Islands similar to China, where they are the consequence of summer and winter monsoons due to dif- ferences of warming. Von Suchodoletz, H. et al. (2009) described and analysed reddish clays and loess-like yellowish sediments on the Isle of Lanzarote. He identi- fi ed paleosols, loessial colluvial layers and sediments/colluvia with traces of pedogenesis. Fluvio-lacustric loessial sediment was described on Gran Canaria by Menéndez, I. et al. (2009). Fluvial action was responsible here for the redeposi- tion of sediments. In his opinion calcareous sheets were formed in the humid seasons, whereas desiccation and formation of “dry” soils (with carbonate precipitation) characterized the arid phases. The method applied A unifi ed method of comparative grain size analysis has been elaborated for the analysis of Quaternary sediments and there were laid foundations of an exact characterization and comparability of these deposits by the classifi cation of loess regions. This method was tested in Hungary and applied exclusively by our research team for the investigation into Quaternary deposits (loess and loess-like sequences). Through the evaluation of the results an opportunity has opened to acquire much more information in a rapid way about the history of evolution of the studied area: palaeoenvironmental conditions during the deposition of the loess material; changes taking place in the geographical environment; climate fl uctuations during the past 2 million years, including the ice ages; warming maxima and cooling minima of temperature during the Quaternary; diff erences between the profi les of various loess regions based on the above research methods. – – – – – 211 Values of each parameter (index) as environmental indicator are gained by the application of analogous methods, so they are to be considered a highly correct and reliable source for a comparative analysis of profi les within a given region and between diff erent regions, and for drawing conclusions on their pal- aeogeography. Quaternary sediments are characterized using the above method and an att empt is made to draw conclusions about changes of the dynamics of rate of sedimentation and to establish local correlation between horizons with similar characteristics. Traditional sedimentological parameters (So, K, Sk, Md) were ap- plied together with two indices introduced in Hungary recently: FG (fi neness grade) and Kd (degree of weathering), and with CaCO3 content and percentage share of clay, silt, loess and sand fractions. The role of parameters as environmental indicators could be established. Their values point to changes in granulometry and in turn can also be instru- mental in demarcation of basic lithological units and identifi cation of phases of sedimentation and gaps in the process. Variations can be recognized inside seem- ingly homogeneous horizons as diff erences might be detected as well between layers of apparently identical genesis in order to make comparisons, correlations, to draw conclusions about palaeogeography of the given region. Table 1 contains two new indices. Fineness grade (FG) serves for an exact separation of horizons from each other, reconstruction of palaeotopography. Increasing or decreasing values of FG are indicative about the source area of the parent material of loess, about wind direction and velocity during transport. Kd index can be used to determine the degree of weathering, to point out extreme warming and cooling events. Traditional parameters provide additional informa- tion such as sorting (So) on the origin of the sediment material, kurtosis (K) is instructive for the sharp separation between loess and sand, asymmetry (Sk) gives orientation to separate between regions of accumulation and denudation. Of the newly adopted indices fi neness grade shows maximum values in soils and minima in sands. Knowing these values soil horizons become recognizable while those fi ner than the average represent young loesses and considerably fi ner ones indicate old loesses. Minimum values indicate sands, while somewhat higher ones represent silt interbeddings. FG values are used for an exact denomination of sediments, delimitation of the boundary of layers, their trend to increase or decrease refer to grain size to refi ne or coarsen so it can be used for distinguishing between old and young loesses, revealing alterations within paleosols, correlation between loess and paleosol horizons. Kd index is represented by minimum values in soils and maxima in loesses (and by fi gures slightly above minimum in sands). Apart from being useful for the identifi cation and demarcation of sediments, its maxima is suitable for pointing out extreme cooling within loess sequences (their exact depth can be identifi ed within a given loess layer) and minimum values refer to warming maxima inside 212 soils (exact depth within the soil horizon). Sorting (So) has its peaks of maximum in soils, minima in sands and average values are typical of loesses. According to Trask, P.D. (1932) So index values less than around 2.5 represent poorly sorted sediments, normal sorting is around 3 and well sorted deposits are above 4.5. In the sequences the highest figures repre- sent loess sand, stratified sand, clays and incipient soils. Minimum values ap- pear in unstratified sand, fi ne grained sand loess and in young loess. By this classi- fi cation most of the deposits are poorly or normally sorted sediment. Sk indicates asymme- try of sediments. They allow to distinguish between sands and loess on the one hand and clays and silt on the other, and to separate areas of accumulation from those of denudation. Using this pa- rameter more phases of sedi- mentation can be identifi ed than using other methods. Kurtosis (K) values are low in soils, with mini- mum peaks in sands and medium fi gures in loesses. Its extremes indicate mixing loess with soil, referring to boundaries of loess and soils sharply. Ta bl e 1 . V al ue s o f F G , K d, M d, So , K a nd S k in th e s ec tio n at B an da s d el Su r D en om in at io n FG (fi ne ne ss gr ad e) K d (d eg re e of w ea th er in g) M d m m (m ed ia n) So (s or tin g) K (k ur to si s) S k (a sy m m et ry ) Pa leo so l ( fo rm ed o n ph on ol ite la va ) 73 .1 2– 85 .8 4 1. 14 –1 .1 7 0. 01 6– 0. 02 3 3. 16 –3 .7 2 0. 15 –0 .2 3 0. 24 –0 .2 7 Se di m en t ( fo rm ed o n al ka li ba sa lt) a f- fe ct ed b y pe do ge ne si s 64 .2 8– 70 .2 3 1. 74 –1 .8 3 0. 04 1– 0. 14 0 6. 73 –6 .8 4 0. 46 –0 .5 1 0. 81 –1 .3 7 Lo es s se di m en t ( fo rm ed o n a se qu en ce aff e ct ed b y pe do ge ne si s) 56 .2 1– 64 .8 9 1. 12 –4 .4 9 0. 02 3– 0. 05 7 2. 26 –3 .1 5 0. 23 –0 .2 8 0. 12 –0 .1 8 Lo es s- lik e d ep os it I ( on w ea th er ed p um ic e st on e as p ar en t r oc k) 58 .0 9– 60 .0 2 2. 45 –4 .4 7 0. 02 7– 0. 18 7 5. 66 –5 .8 2 0. 36 –0 .3 8 0. 42 –0 .4 7 Lo es s- lik e d ep os it II (o n w ea th er ed la pi lli as p ar en t r oc k, w ith a n ad m ix tu re o f Sa ha ra n du st ) 60 .0 2– 62 .4 0 2. 72 –3 .1 5 0. 02 7– 0. 02 8 2. 59 –2 .7 8 0. 39 –0 .4 2 0. 17 –0 .2 2 0. 41 –0 .4 9 Lo es s- lik e d ep os it III (o n w ea th er ed b re cc ia as p ar en t r oc k, w ith a n ad m ix tu re o f Sa ha ra n du st ) 57 .1 3– 63 .0 9 2. 49 –3 .3 3 0. 02 7– 0. 08 5 1. 37 –1 .4 8 0. 36 –0 .4 3 0. 32 –0 .5 7 Se di m en t ( fo rm ed o n up pe r a lk al i b as al t) aff e ct ed b y pe do ge ne si s 63 .3 2– 71 .1 4 1. 68 –1 .7 3 0. 04 –0 .0 6 6. 01 –6 .1 1 0. 49 –0 .5 5 0. 34 –0 .3 8 213 Geographical sett ing Canary Islands are situated between 27 37’ and 29 23’ of northern latitude and 13 20’ és 18 16’ of western longitude. The largest isles are Tenerife, Fuerteventura, Gran Canaria, Lanzarote, La Palma, Gomera and Hierro (Figure 1) and there are numerous islets. The archipelago is located along the margin of the African lito- sphere plate. Tenerife is in the central part of Canary Islands (photos 1 and 2), 300 km off the coasts of mainland Africa. It is ca 97 km long, and 16 to 48 km wide. Pico del Teide is the highest mountain on Tenerife (“snow covered mountain”) and on the islands, raising to 3,718 m. Origin of the islands The latest results of investigations confi rm basalt rocks becoming younger from the west to the east. Figures of absolute dating seem to fi t in the theory by Hess, P.C. (1992) based on Schmincke, H.-U. (1976) that the islands emerged from the plate formed by sea-fl oor spreading from the Mid-Atlantic Ridge. Along the boundary of continental/oceanic plates sediments have accumu- lated in a thickness of ca 10 km, and “oceanized” subsequently. There is a consider- able diff erence between the age of oceanic crust (ca 180 Ma, Jurassic) and that of the majority of the volcanites (ca 20 Ma, Miocene). Transversal faults run perpendicu- lar to the ridge and might continue on the continental plate. Canary volcanism is presumably the continuation of the fault running from South Atlas. The emergence of the islands is due to the Canary hotspot, associated with convection upwelling of melted rock from great depth of the mantle (intraplate volcanism). According to Viñuela, J.M. (htt p://www.mantleplumes.org/Canary.html) Canary Islands formed at the margin of Jurassic oceanic plate and of African continental plate. Material of the mountain chain on the rise originated from the upper mantle and sett led in a vertical sequence. The fi rst alkali magmatic activity of this hotspot started with the emer- gence of the isle of Fuerteventura in Upper Cretaceous (~70 Ma), and contin- ued with submarine volcanism through Eocene and Oligocene (~39 Ma) into surface volcanism in Miocene (~20.6 Ma). The development of submarine and surface volcanism associated with hotspots include the following phases (Walker, G.P.L. 1990). Submarine volcanism Volcanism on the Canary Islands has included submarine stages and emergent stages. The latt er are shield building stage, declining stage, erosional stage, and 214 rejuvenated stage. Four isles: Fuerteventura, Lanzarote, Gran Canaria and Tenerife are currently in the stage of rejuvenation, La Gomera is in erosional stage, La Palma and El Hierro are in declining stage. It is widely accepted that the material of oceanic “hotspot” volcanism is molten rock upwelling from the mantle. The age of volcanism on the Canary Islands (Carracedo, J.C. et al. 2002): Fuerteventura 20.6 Ma (rejuvenated stage), Lanzarote 15.5 Ma (re- juvenated stage), Tenerife 11.6 Ma (rejuvenated stage), Gran Canaria 14.5 Ma (rejuvenated stage), La Gomera 12.0 Ma (erosional stage), El Hierro 1.12 Ma (shield building stage) és La Palma 1.77 (shield building stage). Surface volcanism According to Ancochea, E. et al. (1990) surface volcanism on the Canary Is- lands can be classed into four main groups: 1. “old basalt sequence” (11.6–3.3 Ma), presumably separated volcanic ensembles: Teno in the north-west, Anaga in the north-east, and Roque del Conde in the south, have K/Ar age of Late Miocene and Early Pliocene; 2. interruption of volcanic activity until 1.9 Ma with the dissection of the initial structure of the central Cañadas Volcano, emergence of Cañada sequence I and II as a result of trachyte, phonolite and basalt extrusions between 1.89 and 0.13 Ma; 3. minor eruptions of basalt from 0.9 Ma to historic times, minor basaltic eruptions on the ridge between Cañadas és Anaga stretching in south-west–north-east direction; 4. emergence of the caldera and disappearance of part of Cañadas Volcano between 0.17 and 0.13 Ma; subsequent building up of a volcano with the centre at Teide–Pico Viejo (basalt, trachyte, phonolite). According to the actually accepted geochronological data in the vi- cinity of Cañadas, i.e. within the study area, four pyroclastic phases could be distinguished during the past 2 million years: 1. San Juan de la Rambla phase (~2 Ma) towards North Tenerife (Ancochea, E. et al. 1990); 2. Adeje phase (1.5–1.8 Ma); 3. Las Amérocas phase (1.1–0.9 Ma) with all the pyroclastic clays between La Bentrana and Arico ignimbrites; 4. Bandas del Sur phase (0.7–0.15 Ma) in the south-east of Tenerife. Relief Landforms on the Canary Islands are characterized by heterogeneity within a small area. Surface features are the result of volcanism, wind and fl uvial erosion and marine abrasion. The main rocks to build up the islands are the basalts, phonolites and rhyolites. Volcanism is still active on Tenerife, Lanzarote and La Palma. The most typical landforms of volcanic origin are the cones with 215 calderas of diff erent size, the lava fi elds and basaltic plateaus. A basic type of valleys is represented by deeply cut barrancos running partly on a radial pat- tern. Also there are wide troughs (walles) and trench-like valleys dissected by a dense network of gullies. Sea coasts are mostly high. In the west of the island 100 m high coasts are not exceptions. In contrast, low coasts are infrequent, they rather occur in the south. The most ancient regions on Tenerife are the mountains of Teno, Anaga and (partly) those of Adeje–Lorenzo. There are walls built of basalt with a length of several hundred metres. Due to heavy rainfalls and a long erosional period lasting since the Tertiary barrancos are the most characteristic landforms. The considerable relief intensity between Teide peak and the sea coast strengthens the impact of erosion. Mountains of Anaga In the lack of plateaus, volcanic cones and walls of craters several elongated ridges stretching northwards and southwards were formed by barrancos cut- ting in deeply. Part of them resembles alpine relief. Teide and Las Cañadas Pico de Teide elevates to 3717 m, over timber line and is visible from all over the Canary Islands. In winter time the summit remains snow covered for weeks. This is a regular cone of a stratovolcano descending northward abrupt- ly. On its south-western side Pico Viejo rises to 3,102 m. Pico de Teide is half- circled at 20 km length by a curious piedmont called Las Cañadas del Teide. The landscape is dominated by extensive lava fi elds. At Bandas del Sur erosional gaps could be recognized which sepa- rate three cycles of landform evolution (Bryan, S.E. et al. 1998; Brown, R.J. et al. 2003). Altogether they make up 15 pyroclastic units (paleosols, other sediments, erosional gaps and “fallout” deposits originated from volcanic ash clouds). The ignimbrite of Arico is a product of Plinian eruptions of limited scale composed of falling dust and ash fl ows. The former deposited within a small area. The material of deposited pyroclastic fl ows can easily be separated. In this area no lava fl ows occur, only pyroclastic sediments can be found. The latt er are of phonolite or trachyphonolite (Rodehorst, U. et al. 1998) and origi- nate from the volcano Las Cañadas, active for 3.3 million years (Bryan, S.E. et al. 1998). The ignimbrite of Arico is labelled as “welded” one by Fritsch, K. 216 and Reiss, W. (1868). It was them who recognized that this type of ignimbrites unites the features of tuff s and lava fl ows. The ignimbrite was also investi- gated by Schmincke, H.-U. and Swanson, D.A. (1967), Ridley, W.I. (1971) and Alonso, J.J. et al. (1988). This viewpoint was opposed by Brown, J.R. et al. (2003). The studied section In the exposure (Photo 4, Figure 2) soils formed on phonolites and alkalic basalt, loess interbeddings, and loess-like deposits formed by the mixture of weath- ered pyroclastic matt er with an admixture of dust from Sahara were studied in the south-eastern part of Tenerife, in the surroundings of Arico. The oldest deposit is the lowermost phonolite with an age of 3.3–2 Ma (Martí, J. et al. 1994), followed upward by Arico ignimbrite: by K/Ar dating it is 0.65±0.03 Ma (Ancochea, E. et al. 1999) and by 40Ar/39Ar: 0.61±0.09 (Bryan, S.E. et al. 1998). The oldest ignimbrite in the environs is La Brentana with 40Ar/39Ar: 1.44±0.12 Ma and isochron age: 1.50±0.17 Ma (Alonso, J.J. 1989). Most of the layers in the section goes back to Bandas del Sur phase (0.7–0.15 Ma) and are associated with pyroclastic processes of Las Cañadas volcano (Huertas, M.J. et al. 2002). Photo 4. The studied section in the environs of Bandas del Sur (Photo by Kis, É. ) 217 In the lower- most part of the sec- tion the phonolite lava of Las Cañadas volcano is found dat- ed 3.5–2 Ma (Martí, J. et al. 1994, Photo 4, Figure 2). There is an erosional hiatus above it overlain by a pale- osol (Photo 5), which is separated from the superimposing layer formed on alkalic ba- salt undergoing double soil formation by two tuff horizons (photos 6 and 7, one of them is a phonolite pumice lapilli). Upwards the profi le there is a loess horizon (Photo 8). Fur ther up above the loess and a layer with the traces of pedogenesis the fi rst loess-like sediment sequence contain two well-sorted ash lay- ers and two weath- ered pumice horizons originated from fallout deposits (i.e. from ash clouds) with an ad- mixture of Sahara dust (Photo 9). There is a strong erosional hiatus above this layer. Parent material of the second loess-like sediment sequence with yellowish sandy colour is lapilli. Its characteristic fea- ture is the occurrence of light green pumice rock pieces that could reach 40 cm Fig. 2. The section at Bandas del Sur (Schweitzer, F. and Kis, É. 2010) 8,0 m CaCO3 7,0 6,0 5,0 4,0 3,0 2,0 1,0 0 Soil developed on alkalic basalt lava Phonolite pumice rock and ignimbrite Soil developed on alkalic basalt lava Loess-like deposit Soil developed on alkalic basalt lava Loess-like deposit Loess-like deposit CaCO3 Loess Soil developed on alkalic basalt lava (upper part) CaCO3 Soil developed on alkalic basalt lava Phonolite lava 0,57 Ma 0,65 Ma 2-3,5 Ma Soil developed on alkalic basalt lava (lower part) 218 Photo 5. The lowermost soil developed on phonolite (Photo by Poór, I.) Photo 6. Soil developed on alkalic basalt lava (Photo by Poór, I.) 219 Photo 7. Upper soil with the underlying tuff and breccia (Photo by Schweitzer, F.) Photo 8. Loess-like deposit upon alkalic basalt aff ected by pedogenesis (Photo by Poór, I.) 220 in size. The smaller they are the more they are zeolitized. There are voids i.e. places of large pumices having fallen out. This layer of zeolitized lapilli has been eroded intensely by the overlying breccia. Here at the boundary of two phases of sedimentation a long gap can be recognized (Photo 10). The third loess-like sediment sequence starts with breccia composed by black and green pumice stones above layers containing water (Photo 9: sedi- ments over lapilli). Upon this ash layer there is an embryonic soil developed on a pyroclastic fl ow. Further up a layer containing pumice follows and an embryonic soil developed on a pyroclastic fl ow can be detected that is overlain by two ash layers, with a thickness of ca 30 cm each (photos 8 and 9). Photo 9. Loess-like deposit formed by weathering of pumice rock and its mixing with Saharan dust above the lower double soil (Photo by Schweitzer, F.) 221 Climate The climate on the Canary Islands is determined by their position within the strip separating North- and South Atlantic with temperate and tropical climate, respectively and where the Sahara and the longitudinal Atlantic cli- matic zone meet. Decisive role belongs to three types of air currents: 1. oceanic tropical, 2. oceanic polar and 3. Saharan continental. The climate is rhythmic with alternating half-year periods (summer and winter half-years). Oceanic tropical climate dominates the summer half-year, whereas Sahara and oceanic polar prevail in the winter one. North-west off the island is situated the area of high pressure all year long (Azores high/anticyclon). Its position is varied during the year but basically remains within the Azores–Madeira–Canary strip. In the summer this Azores high is predominant with north-estern trade winds. In the winter however its position and strength change and oceanic polar or humid tropical air masses intrude and the latt er cause intense rain- falls. If Azores high moves eastbound the Canary Islands would fall under the infl uence of African continental climate. Climate on the islands shows periodicity, under the infl uence of mon- soon. In the dry summer half-year Azores high dominates up to 30° of northern Photo 10. Loess-like deposit formed by weathering of lapilli and its mixing with Saharan dust in the lower part of the photo (Photo by Kis, É.) 222 latitude with north-eastern trade winds of a 90–95% frequency. Trade winds generally are dry and do not bring rains. However, they do to the islands, because they take up moisture over the ocean and near-surface air is lift ed upwards by mountains which in turn condense water vapour in the rising and cooling air, and clouding over starts. During the humid winter half-year polar oceanic or humid tropical air masses might invade. At this time mon- soon is less signifi cant and winds blowing from the Sahara and transporting humid subtropical air masses turn northward along the western margin of the African continent (Ortiz, J.E. et al. 2006 based on Nicolson, S.E. 1996 and Moreno, A. et al. 2001). Half-year climate periods similar to the Canary Islands can be identi- fi ed in China as well (summer and winter Asian monsoon). Consequently, in both areas, e.g. on the Loess Plateau too stratifi cation of sediments displays half-year variations. Climate change, the amount of dust transported from Africa and the character of transport bear importance in our case because dust as parent material of loess and loess-like deposits at Tenerife have been blown out (and still are) by north-eastern trade winds, polar oceanic and continental Saharan winds. Dust blown out from the Sahara can reach places several thousand kilometres away, e.g. coral reefs of the Caribbean (Photo 11). Saharan dust ac- cumulates on the oceanic fl oor and it is detectable in deep cores. Part of the deposited dust might be redeposited repeatedly, because due to the sea level subsidence during the glacial epochs it appears on the surface of the shelf surrounding the isles. This is why we should have some idea about the past sea level oscillations. Dust transport In the summer Saharan dust is transported by north-eastern trade winds (Photo 11) and in winter this is done by the Saharan air masses. In the summer the northern portion of Saharan air masses fl ows north of the Canary Island at a height of 1,500–5,500 m. The material is moving horizontally in the lower part of the troposphere towards the islands (Koopmann, B. 1981; Bozzano, G. et al. 2002). Eventually dust is deposited upon dry or wet surface (Criado, C. and Dorta, P. 2003; Menéndez, I. et al. 2007). In winter dust is transported at 0–1500 m height during Calima event. Calima winds are continental African trade winds (harmatt an) defl ecting Atlantic cyclons westward, to Canary Is- lands (Criado, C. and Dorta, P. 2003). As dust is being deposited both on the ocean fl oor and land surface, particles sedimented over three years in deep sea were studied at European 223 Station for Time-series in the Ocean, off Canary Island. By Neuer, S. et al. 1997 sedimentation has a highly seasonal character, its maximum falls to late winter, early spring. Most of the particles consist of basalt, various minerals and carbonates and a large amount of organic matt er. Minerals make up eo- lian deposits of African origin. Comparing sediment at depths of 1 and 3 km it was found that the amount of sedimented particles increases gradually with depth. Annual deposition of organic carbon was 0.6 gm-2 at 1 km and raised up to 0.8 gm-2 at 3 km depth. On the Canary Islands in the warm and wet time intervals marine ter- races and fossil soils (with warm fauna) developed, whereas in dry intervals calcareous crusts and poligonal evaporite soils and eolian deposits (including dunes) (Petit, J.R. et al. 1999) formed. Of the sediment studied those having undergone pedogenesis formed in humid periods and loess and loess-like sediments formed during dry intervals. Photo 11. North-eastern trade winds transporting Saharan dust (htt p://www.phys.unsw. edu.au/~jbailey/planets/dust.html) 224 Sea level oscillations and the age of marine terraces Dating of terraces is a serious challenge for researchers as the islands are situ- ated in a highly tectonic area with a sizeable annual uplift . Zazo, C. et al. (2003) compared the highest sea levels during interglacials and interstadials with ma- rine isotope stages (OIS 5a [5c, 5e, 7, 11 or older]). During OIS 5e (135–117 ka) three sea level maxima occurred. At the highest of them sediments contained the so called Senegal Fauna. The rate of uplift was 0.011 mm/yr, which suggests 2 m sea level rising during OIS 5e. Terrace formation was triggered by intense tectonic movement. Most of the terraces emerged in the Middle and Late Pleis- tocene. Strombus bubonius warm fauna found in a layer of Cladocora caespitosa coral has OIS 7 age; Hillaire-Marcel, C. et al. 1986; Goy, J.L. et al. 1986; Zazo, C. and Goy, J.L. 1989; Chappell, J. and Shackleton, N.J. 1986 established 15 m rise in sea level, whereas Roy, P.S. and Boyd, R. (1996) came to 2–4 m in stable South Australia. This oscillation was determined by Hearty, P.J. and Kindler, P. (1995) in 2.5 m (OIS 7a) and ≤ 0 m (OIS 7c) on the Bahamas. The following warm faunas of high sea level stages dated OIS 9 or OIS 11. OIS 11 was the longest (420–360 ka) and warmest interglacial over the past Photo 12. Traces of sea level oscillations in the northern part of the Mountains of Anaga (Photo by Schweitzer, F.) 225 half of a million years (Droxler, A.W. and Farrell, J.W. 2000). Its warm fauna was described in Chile (Ortlieb, L. et al., 1996). During this interval sea level rising presumably was 17 m in South Australia with tectonic stability (Murray- Wallace, C.V. et al. 2001) and on the Bahamas (Hearty, P.J. et al. 1999) On Tenerife (Igueste, 97–13 m a.s.l.) warm marine fauna (Strombus bubonius) is dated OIS 5e (Zazo, C. et al., 2003, change in sea level: 0 m). In the Mountains of Anaga the fossil sea coast has an age of OIS 5e (≈130 ka), at Igueste de San Andrés OIS 5e (~131 ka). On the Canary Islands Strombus bubonius was dated last interglacial i.e. OIS 5e (Meco, J. et al. 2002). Talavera, F.G. et al. 1989; Zazo, C. et al. 2003 describe fossil coasts as of OIS 5 age and indicate sea level rise of 1–2 m (e.g. Poque de las Bodegas). The degree of uplift (sea level curve compared with present-day val- ues): El Medano 1.5 m, North Anaga 10.5 m (Photo 12, OIS 5e), Igueste de San Andrés 2.8 m, Playa de Gordejuela 18.5 m (540–690 ka), Montana Pelada 35 m, <778 ka. Results In the sections studied and their surroundings there were investigated sedi- ments formed by a mixture of weathered surface pyroclastic deposits with Saharan dust. The analyses were aimed to determine the character of these sediments and the circumstances of their formation. For sediment analysis (Table 1, Photo 3, Figure 3) a new method was applied by our research team with the involvement of the values of sedimentological parameters for the indication of environmental conditions for the fi rst time in Europe. With the applied method of environmental evaluation loessial materi- als and layers aff ected by pedogenesis were identifi ed in the studied surround- ings, hitherto largely neglected by researchers. Similar loessial sediments had not been described on Tenerife. There were determined parameter values for the sediments identifi ed as weathered pyroclastic surface deposits formed in the course of colluvial processes and subsequently mixed with Saharan dust. Environmental conditions, past cli- mate change and character of sea level oscillations had also been studied. Along with the traditional parameter values fi neness grade (FG) were determined used so far only in American and German literature, and Kd, applied by Chinese researchers. This way the deposits on Tenerife became characterized and new denominations for the layers were introduced. Of the other isles fl uvio-lacustric deposits have been identifi ed on Gran Canaria and colluvial loess on Lanzarote. Parameter values were used to characterize: a paleosol developed upon phonolite lava dated 2–3.5 Ma, the overlying ignimbrite sequence, upward 226 C L A Y S IL T S A N D c o a rs e -g ra in e d c o a rs e m e d iu m - g ra in e d % % 1 0 0 1 0 0 9 0 9 0 8 0 8 0 7 0 7 0 6 0 6 0 5 0 5 0 4 0 4 0 3 0 3 0 2 0 2 0 1 0 1 0 0 0 3 3 0 .0 0 0 2 0 .0 0 0 2 0 .0 0 1 0 .0 0 1 0 .0 0 2 0 .0 0 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 4 4 5 5 6 6 7 7 8 8 9 9 0 .0 1 0 .0 1 0 .0 2 0 .0 2 3 3 4 4 0 .0 5 0 .0 5 6 6 7 7 8 8 9 9 0 .1 0 .1 0 .2 0 .2 3 3 4 4 0 .5 0 .5 6 6 7 7 8 8 9 9 1 .0 1 .0 2 .0 2 .0 m m m m fi n e 11 22 55 66 33 77 44 fi n e c o a rs e fi n e - g ra in e d ti n y - g ra in e d Fi g. 3 . G ra in si ze cu rv e of th e se ct io n at B an da s d el S ur o n th e ba si c o f n in e se di m en t s iz e cl as se s ( K is , É ., Sc hw ei tz er , F . a nd d i G lé ri a, M . 2 01 0) 227 sediments aff ected by pedogenesis upon alkalic basalt lava, a series of sedi- ments formed upon parent rock formed on three ignimbrites and cover sedi- ments containing two alkalic basalt lavas aff ected by pedogenesis with tuff and breccia interbeddings. Apart from the soil and sediments there is a loess horizon superimpos- ing the deposit aff ected by pedogenesis over the lowermost alkalic basalt and three loessifi ed sediments on weathered surfaces with an admixture of Saharan dust. Sediment upon pumice stone as its parent material above the loess was described as the fi rst loessifi ed layer, that overlying lapilli as the second and the sediment aff ected by pedogenesis situated upon breccia parent rock as the third deposit. 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