ACTA GEOLOGICA HISPANICA, t. 18 (1983), n." 314, pags. 217-233
Quaternary Glacial Geology of Alta Ribagorqa Basin (Central Southern Pyrenees)
by J. M. VILAPLANA
Dpt. de Geomorfologia i Tectoliica. Facultat de Geologia. Universitat de BarcelonaGran Vía, 585. 08007 Barcelona.
ABSTRACT RESUM
This paper is an abstract of the doctoral thesis presented by Aquest article 6s un resum de la tesi doctoral que presenta the autor at the University of Barcelona on September 1983. It I'autor a la Universitat de Barcelona el setembre de 1983. Es constitutes a regional study about the Quatemary Glacial Geol- tracta d'un estudi regional sobre I'evolució quatemaria de les ogy in the Ribagorca high valleys. It is the first work in relation Altes Valls de la Ribagorca que té com apbjectiu principal la re- to the geomorphology, sedimentology and stratigraphy of the construcció del glacialisme quatemari. Es el primer treball que glacial and related deposits in this zone of the Pyrenees. Several tracta, de manera monografica, els aspectes geomorfologics, sedi- formations of quatemary deposits have been studied in detail mentologics i estratigrafics, del's diposits quatemaris de les valls (mainly in Llauset Valley and in Taüll area); and the local qua- de la Noguera Ribagorcana i de la Noguera de Tor. Les princi- temary stratigraphy is established and finally a correlation with pal~formacions sedimentaries d'origen glacial han estat estu- some previously studied areas in the Pyrenees is attemped. diades amb especial detall (principalment les de la Vall de Llau- set i les del sector de Taüll). En aquest article hom presenta una estratigrafia dels diposits quatemaris, a nivel1 de conca hidrogra- fica, a partir de la qual s'estableix una correlacio amb les dades estratigrafiques i cronologiques més recentment obtingudes en el vessant Nord del Pirineu.
RESUMEN INTRODUCTION Este artículo es un resumen de la tesis doctoral que el autor presentó en la Universidad de Barcelona en Septiembre de 1983. 'The Alta Ribagorca Basin is drained by two Consiste en un estudio regional que trata de la evolución cuater- main valleys: the Noguera Ribagorqana Valley and nana de los Altos Valles de la Ribagorpa, el cual tiene como the Boí Valley which is named Noguera de Tor. principal objetivo la reconstrucción del glaciarismo cuatemano. Both valleys come from the Northem sector of the Es el primer trabajo que trata, de manera monográfica, la geo- Alta Ribagorqa, where the highest peaks are found, morfología, la sedimentología y la estratigrafia de los depósitos cuatemarios de los valles de la Noguera Ribagorcana y de la No- some of them above or very close to 3000 meters guera de Tor. Las principales formaciones sedimentarias de ori- a.s.1. gen glacial han sido estudiadas con especial interés (pnncipal- The highest sector is constituted by Hercinian mente las del Valle de Llauset y las del sector de Taüll). En este granites, the Palaeozoic rocks (limestones, schists, artículo se elabora una estratigrafia de los depósitos cuatemarios a nivel de cuenca, a partir de la cual se establece una correlación shales and quartzites) crop out towards the South. con los datos estratigraficos y cronológicos más recientes de la Al1 of these materials are in contact with the Meso- vertiente Norte del Pirineo. zoic rocks near Pont de Suert area. During the Quatemary, those valleys were oc- of recent Quatemary is found in the present lacus- cupied by important valley glaciers, which hd a trine sedimentation in the majority of lakes located length of more than 30 kilometers. These glaciers in the upper parts of the valleys. played an important geomorphologic and sedimen- tary role, both, in the covered areas and in the mar- ginal zones. Djuring the maximum of the glacial ex- Fluvial terraces tension, the fiont of Noguera 'Ribagorcana Glacier went as far as South of Vilal1e:r (940 meters a.s.1.); The existence and preservation of fluvial ter- the Boi Glacier (Noguera de Tor glacier), which races in these valleys is determined by severa1 fac- had a not miich bigger alimenitation basin went as tors. The valley morphology (narrow valleys and far as South of Llesp (890 meten a.s.1.). steep slopes) makes dificult the sitting up of allu- The glacial landforms are ciommon in the upper vial plains, which are only present in zones of val- parts of the basin; the glacial deposits are such ley widening. It must be also considered that the in- common than the erosion fonns in the lower parts tense dynamics on the slopes has degraded most of of the basin. the terraces. The relief is characterized by important glacial The better remains of fluvial terraces are found cirques in the valley heads, carved in granitic areas. in Pont de Suert area and in the confluence of Boí Al1 these cirques have overdeepened basins (often and Noguera Ribagorcana Valleys (Figure 1). in staggered progression) psesently occupied by Five levels of fluvials terraces between 3 and small lakes (some of them veiy close to 100 meters 200 meters above the present river level are distin- in depth). There are importzint extensions of pol- guished; their relative heights are indicates in Fig- ished and striated rocks at t'he bottom of the cir- ure 3. These fluvial deposits are mainly constitued ques. by gravels, pebbles and some boulders -often with The valleys have steep slopes, with a U-shaped imbricated disposition- and saridy matrix. There profile (specially where a crystalline bedrock exists, are some interestratified beds arid lenses of sand. and where the greatest accutnulation of glacial ice The clast lithology is mainly grariodioritic however -in quantitjr and time- was produced). There are schists are also present. The clast shape is rounded two big overdeepened basins at the backside of im- and subrounded, but in some cases, typical glacial portant roc:k thresholds in the studied valleys. shapes (faceted, elongated) are also present, which These basins are produced by glacial erosion of the indicates the glaciofluvial origin of these deposits. bedrock in the zones of greatest accumulation of glacial ice: - The Bono basin (Nogiuera Ribagor~anaVal- Ti11 and related deposits ley), about 5 km length and 0.8 km width, present- ly occupied by an alluvia.1 plain. A maximum In such nanow and deep valley of the Alta Ri- depth of 213 meters is calculated for the bedrock bagorca region we can group tills and related de- (Paleozoic basement). posits according to their position. On the bottom - The Barruera Basin (;a similar model in the valley position we find two great families of depos- Boí Valley), where the palaeozoic basement is its: ice-terminal ti11 complexes and glaciofluvial found at l!j0 meters under the alluvial plain. deposits which are filling the overdeepened basins. On the slopes, quite high with reference to the present river level, we find ice-lateral ti11 QUATERNARY DEPOSITS complexes.
The most important deposits are of glacial ori- gin (Upper Pleistocene age), and they are represen- -Ice-terminal ti11 complexes ted by some ti11 types and related sediments: glacio- lacustrine 'and glaciofluviall deposits, and some pe- They don7 ocup much extension, and the few riglacial deposits on the slopes. outcrops that exist are not good. These deposits are There are some fluvial terraces near Pont de mainly represented by end moraines (Figure 1). Suert, sorne of them related with the glacial depos- The glacial deposits called tenninal morainic com- its of the upper zones. The lower terraces are ge- plex were firtsly quoted, in the Pyrenees, by Penck nerally aittributed to a Postglacial period (Goron, (1 88 1). Later others quatemarists tried to locate the 194 1 and Sole, 195 1). A good sedimentary record terminal complexes of differerit valleys in order to ALTA RIBAGORCA BASlN - Central Southern Pyrenees -
p
---\ *--.- -v.*- -HósPitoi'~;" de Viella p',py - 1 \-.>., i '., '4 , I -, ' +------.-- ,' a, , . ob O 4
--,- --,
'\ .-..-. t '.,
, \, \, : .--A -y--- , -,1 .--.\4 b ;' 0, $"-\-.*-- ,-. ; \\ ' o-' 1, 2; ', .'> '\ ?-- F--..T-' 3 f : o' --,- $;e--.-- ' ',-ec, ,',l. ;Vilaller + ; '%--, ;,( -U .,?A ', '. -,c.-- -. ,' ,\, S, 2 ;* -.'--.. 'b .,; 'r,: .,--., '. '-. g,'Llesp '.: ; , l r L-- .. .- .-, , e.: '. ' ,-. ', ,., / \I> > :' *l \ ,-.' L s. :,' -.A- T. -.- \-., ,,' -, I .S, 4 . ,I 3, ' , __e' > 1 --' \, -->- +*.,-,---'' El Pont de Suert :
Embossoment 1,. d'Escales O 5 km
Figure 1. Alta Ribagorca Basin. This map show the studied area and its situation in the Pyrenees Mountains and also the location of the most important sedimentan formations indicated in the text. Ice-terminal ti11 corn~lexes:l. Grilló; 2. Sant Antoni fsee Fie. 3): 3. Se- minari de Vilaller (see Fig. 4); 4. Barranc de Besiberri. Bottom-vallev deposits. 5. Overdeepened basin of Bono; 6. Overdeepened basin of Barruera (see Fig. 5); Ice-lateral ti11 complexes: 7.Llestui (see Fig. 6); 8. Taüll (see Fig. 7).
21 9
I delimite the extensión of the quaternary glaciers. similar to the «mud tilb) defined by The bigest extension of the quaternary valley- Schlüchter (1977) in the Alps. glaciers and iihe smaller wid1.h of the Marginal The ice-terminal ti11 complex of Seminari de Vi- Ranges in the northen slope of the Pyrenees al- laller shows the best preserved original morphology lowed the glalciers to reach as far as the Aquitaine of terminal morainic ridge. At the bottom of the Basin where riumerous end moraines are found (in deposit there is a ti11 with a grey silty-clay consoli- french called qc(va1lum morainiques»). We can men- dated matrix and with striated and subrounded tion the terwilinal morainic complexes of Aurudy clasts. The upper part is less corisolidated and a Buzy (Ossau Valley) and Lsurdes (Pau Valley), beige silty-sand matrix is present. From field obser- both of them very close to 400 m. a.s.1. vations, and according to the model proposed by The terminal morainic coríuplexes in the south- Boulton and Eyles (1979) for the formation of ern slope of the Pyrenees are very different to the dump-moraines, an interpretative schema of this northern one:s. The main differences are the alti- ice-terminal ti11 complex is elaborate in Figure 4. metric situation, the position of the deposits, the The Barranc de Besiberri deposits, at the upper preservation grade; and even in some cases their ex- part of the Noguera Ribagorqana Valley are re- istence can be called in question. Penck (1 88 1) had mains of two end moraines at 1.530 m. a.s.1. de- already emphasized the lesser extension of the qua- graded by fluvial erosion. The deposit is mainly ternary glaciers in the southein slope of the Pyren- constitued by a supraglacial till. ees, he placed the end moraines about 1000 m. a.s.1. on average, while in the northen slope were placed at 570 m. a.s.1. Al1 the authors, from Penck -Bottom-valley deposits (1881) to the most recent ones (Marti et al., 1978) have pointed out that not any glacier of the south- A great number of small lakes exist in the high ern slope reached the Ebro! Basin, not even the part of Alta Ribagorqa Basin, above 2000 m. They small intrarnontane basins (excepting the Querol have been formed by glacial erosion and located Glacier at Puigcerda, Cerdelnya). This fact made mainly in the bottom cirques an,d also on the bot- dificult the formation of terminal morainic com- tom valley. The sedimentary fi11 of these basins plexes, but 'through they werca formed, the torrential should contain stratigraphic information since de- water streaias during the retraction of the quater- glaciation to the present time. Lake Llauset repre- nary glaciiers and during the Postglacial pe- sents one of the most important of these ! ;; and riod, destroyed most of the terminal morainic de- its lacustrine filling deposits are studied in an spe- posits. cific article in this review (Vilaplana et al., 1'984). These cleposits are const.itued by morainic ma- The two bigest basins are found in bottom- terial in thiz Alta Ribagorqa Basin, but they are not valley situation in the lower part of two main val- much extended and the morphology is badly pre- leys (Bono and Barruera located at 1000 m. a.s.1.). served. In the Noguera Ribagorqa Valley there are The deposits that fill these basins have been stu- three localities with till deposits in relation to ter- died by Vilaplana and Casas (1983). The conven minal moraines, from soutll to north: Sant Antoni tional suriicial studies was complement with vertical till, SemifiLari de Vilaller till and Barranc de Besi- electrical soundings in order to determine the depth berri till. In the Boí Valley there is only most exter- of the paleozoic bedrock and the character of the nal one: C:rilló ti11 (Figure 1). Some of these depos- quaternary filling. The analysis of the resistivity its were already quoted by severa1 authors (Ober- data suggests that the Bono and Barruera depressions maier, 1921; Frodin, 1927; García Sainz, 1935 and are overdeepened basins 200 m and 150 m depth Mey, 1968). The most externa1 end moraines (Sant respectively. We have distiriguished three dif- Antoni arid Grilló) are very eroded and only a part erent lithofacies of quatemary deposits (Fig. 5): of the deposit is preserved. 1 prefer cal1 these depo- sits by the term ice-termiiizal ti11 complex, because a) Bottom deposits, with Xow electrieal resisti- from the sedimentological point of view it is more vity (from 80 to 200 0hms.m); interpeted as realistic. In most cases frontal morainic morpho- muddy sediments deposited in lacustrine envi- logy don't exist because the erosion destroyed it. ronement. Ti11 is always present and in some terminal com- b) Intermediate deposits. with medium electri- plexes it is related with glaciofluvial and / or gla- cal resistivity (from 300 to 800 0hms.m); inter- ciolacustrine deposits. It consists in a basa1 ti11 with preted as diamict with a large fine matrix of flu- an high contents of clayey matrix (> 50%) and it is violacustrine origin. Figure 2. Cieological map of Alta Ribagorca region (Southem Central Pyrenees), from ZWART (1972). 1. Quatemary deposits; 2. Oligo- cene; 3. Upper Cretaceous; 4. Jurassic and lower Cretaceous; 5. Permo-Triassic; 6. Posthercynian Carboniferous; 7. Prehercynian Carboniferous; 8. Devonian; 9. Silurian; 10. Cambro-Ordovician; 1 1. Silicified homfels; 12. Granodiorite of Maladeta Massif. I - Composite section oí' Noe,wera Ribagorcana
Ribagorcana Fluvial t>~-racesin Pont dc Suert area 45 River
20
O m
Krmit.~d1, Sr . ~Avitoiii W-E 1 #il,l.* 1 t
Figure 3. Trarisversal cross-section of Noguera Ribagorcana Valley near Sant Antoni Church (see location in Fig. i). l. Ice-terminal till complex of St. Antoni; 2. Fluvial telrraces: recent alluvions (To); terrace +3m (TI);terrace +20m (Tz); 3. Carboniferous bedrock.
c) Top deposits, with high electrical resitivity supraglacial till, both in relation to lacustrine, flu- (from 1500- 1700 0hrris.m); corresponding to vial or slope deposits. One of the best examples is the alluvial sands, gravels and boulders which the Llestui complex in the Llauset Valley, a tribu- crop out in the present alluvial plain. tary of the Noguera Ribagorcana River. A glacial tongue 10 km long, flowed through that valley du- This results suggest that both overdeepened de- ring the last Quaternary Glaciation, to join on to pressions (Bono and Barruera) were eroded by the the main glacier of the Noguera Ribagorqana. At Ribagorqana and Tor Glaciers respectively, during this time, the ice-lateral ti11 co,mplex with glaciola- the maxirnum glacial phasle. And during the retreat custrine deposits of Llestui was formed on the left of the valley glaciers both overdeepened basins were margin of the Llauset Glacier by obstruction of a filled by glaciolacustrine deposits. small fluviotorrencial basin. These deposits are re- ported by Serrat et al. (1983) as one of the best examples of ice-marginal lacustrine sedimentation -Ice-lateral ti11 complexes in the Southern Pyrenees. From these autors, the great amount of sedimentary material without hia- This 'type of deposits ;are constituted by lateral tus in this marginal lake, indicates a large period of moraines with subglacial 1511 sometimes covered by glacial-stabilization. This sedimentary complex was studied in detail by Vilaplana (1983 a) from both Glacial deposits in Taüll Valley sedimentological and stratigraphical point of view (Fig. 6). There is a clear influence of the late- Taüll Valley is located in the Noguera de Tor ral expansion'of the glacier wich prograded in the River Basin also named Boi Valley and it is consti- lake. The supraglacial ti11 shows a geometry like a tuted by Sant Martí River (which springs near Port dump moraine, but in lateral position, that indi- de Rus 2622 meters a.s.1.) and its tributary, Gine- cates a glacial lateral advance. The rhythmite (la- brell Creek (which comes from port d'Ertra 2460 minated muds) sediments alternate with levels of meters a.s.1.). Taüll Valley is bounded by Sant Ni- diamicts produced by mass movements from the colau Valley to the North and Durro Valley to the lateral moraine into the lake. There is also a South (Fig. 1). progressive incorporation of lacustine mud in the The bedrock is constituted by palaeozoic rocks, subglacial ti11 matrix. mainly the Cambro-Ordovician Serie, formed by In relation to the stratigraphy,,we atribute these shales and sandstones with some conglomerates, deposits to the stabilization phase after the maxi- quartzites and quartz-veins. There are silurian mum of the last Quaternary Glaciation, (Vilaplana, coal-shales both in Ginebrell Valley and Sant Martí 1983). All the radiocarbon dates samples give an Valley head. A granodioritic band crops out in the age of 34.000 years B.P. (Fig. 6). From the first par- Pessó Peak area. . tial data of the palynological stratigraphy carried Sant Martí and Ginebrell Valleys have a typical out by A. Esteban & Vilaplana, (1984), and the glacial morphology with numerous cirques at the correlation with the lacustrine deposits of Biscaye upper parts. There are basal ti11 accumulations at (Lourdes), in the Northen slope of the' Pyrenees, the bottom of the cirques (Coma del Port de Rus). studied by M. Mardones (1982), an age between These basal tills are partially covered by rock- 65.000 and 3 1.500 years B.P. is proposed for this glacier moraines. formation (See Figure 12). There is a considerable basin-shaped widening
N-S Sant 1 Arc del Seminari Mani& ?
1 1 Ice - Flow Direction
Figure 4. Ice-terminal ti11 complex of Seminari de Vilaller in the Noguera Ribagorcana Valley (see location in Fig. 1). a) Longitiidinal cross-section. b) Reconstruction of the Ice-terminal sedimentation from a model proposed by BOULTON and EYLES (1979). lkíaximum glacial depos- its (St. Antoni deposition). Gfl: Sant Mamés glaciofluvial deposits; Sb: Subglacial lee-side till. Postmaximum glacial deposits (Semin- ari de Vilaller deposition); Gf: Glaciofluvial deposits; Sp: Supraglacial till; Lod: Lodgement till, Glacial retreat deposits; L: Lacustrine deposits; F: Fluvial deposits. in the confluence of Ginebrell and Sant Martí val- posits. Another subglacial ti11 is (with an erosive leys, where ain important quantity of sediments contact) above the fluviolacustrine deposits. On top (mainly of glacial origin) are faund. of this last ti11 there are glacioflu.via1 gravels and During thi: maximum glacial phase in the Qua- sands. ternary, this bjasin was the confluence point of three We interpret this alternance as a typical ice- valley-glaciens: the great Tor Glacier and the two marginal environment between Ginebrell and Sant small glacien; (Sant Martí and Ginebrell) foming Martí Glaciers, whose advances and retreats are the Taüll Glacier (see Fig. 9). marked by the alternance of tills with glaciofluvial During thie last Quaternaly glacial maximum, and glaciolacustrine sediments. the greatest glacier extension was produced. After the maximunn phase both Sanit Martí and Ginebrell Glaciers were disconnected from the Tor Glacier, -Ice-lateral ti11 complex of Taüll wich obstructed the Taüll Valley drainage. The main consecluence of this prolonged obstruction It is a clayey matrix ti11 with a. clear lateral mo- was a sedimi~ntaryoveraccuniulation in Taüll Ba- rainic ridge morphology, located 200 m above sin. Taüll village (See figure 7). Alluvial cone deposits and o1;her kind of slope deposits are in contact with glacial deposits. The major part of the glacial -Mulleres de:posits deposit is constitued by a lodgement till; in the up- per part there is a supraglacial flow till. Both mor- 80 meteirs thickness of quaternary deposits is phology, clast lithology and fabric allow us to as- calculated using geoelectricali studies in the south- sure that it was deposited as a lateral moraine from ern part of this basin (Ginebrell area). There is a the Tor Glacier which eiitcred in Taüll Valley predominance of tills in surface, but the vertical upon Taüll Glacier. profiles carlied out in the scarce outcrops and the geophysical studies of electrical resistivities, allow us to differenciate severa1 litkiofacies. -Local glacial chronology The vertical profiles (Fig. 8) show a subglacial ti11 at the bottom, covered Iby fluviolacustrine de- The different glacial phases that we can inter-
.'iW N€ '~I~c*ticc<€VI::-od 1200,
1060. ,, ,, Lllndw d. rw*,
"O. 1040. q mo.
9?3 m920-
b-'50._-?m !m(2a 3/L_j 4m ,!;T gsí:
Figure 5. Longitudinal geoelectrical profile of Barruera overdeepened basin. 1. Dam; 2. Top deposits, with resi,stivities between 1600 and 1700 Ohm,.m; 3. Intermediate ideposits, with resistivities between 525 and 800 Ohm-m; 4. Bottom dcpasits. with resistivjty of 80 Ohm-m; 5. Paleozoic bedrock; 6. Location of vertical electrical sounding.
224 pret both from sediments and landforms are: QUATERNARY STRATIGRAPHY AND GLA- - A maximum glacial extension phase followed CIAL CHRONOLOGY IN THE ALTA RIBA- by an important stability phase of the great glaciers GORCA BASIN (Le. Tor Glacier). During the stability phase there was an important sedimentation, mainly in margi- A stratigraphy of quatemary deposits of Alta nal environments. Also during this phase, the small Ribagorca region is established taking into account glaciers (Sant Martí and Ginebrell Glaciers) had se- and correlating the different sedimentary com- vera1 advances and retreats (two of them well plexes studied by Vilaplana (1983 a). marked), conditioning the alternance of ti11 layers with fluviolacustrine levels deposited in an ice- marginal environement. Pleistocene previous to the Last Pyrenean Glatia- After the stability phase, the gradual but final tion. retreat of al1 the glaciers to the cirque areas was produced. The almost totality of glacial quaternary depos- Finally, we detect a last glacial pulsation show- its in the Alta Ribagorca are attributed to a last ing special characteristics and restricted to some and important glatiation. There are only two sedi- cirques (those above 2200 m and northem orient- mentary formations of earlier age -presently difi- ed). This last phase which produced rock glaciers in cult to determine it precisely- a high terrace and a the Pyrenees Mountains is called Tardiglacial (Ser- colluvial deposit. rat,1979). In Taüll area this phase is represented The first one is the fluvial terrace leve1 T, by rock glacier moraines in Coma de Port de Rus (180-200 m above the present river level) of the (Sant Martí Cirque). Noguera Ribagorqana River, in Pont de Suert area
Ssctim 1 conl. 1 Section ü 5 LITHOLOGV !
GRAlN SIZE
i : iutiln (clay ond sil¡)
S' : fine aand
S" : modium sond
S"'" cooree sond 9 : QrOrcIs and pebbles b : bo~ldars
CONTACTS COLOUR
- BrCilCnOl 340üO . .. WWu deformed LI- 3045 zoq...'.' , :. ;; . . INTERNAL S7iUCTURES . Situation of the vertical sectiwis - poralle! Iominotior deforred iamination
...-n ripple
chonnel - flome slructure (pelili: njection) O preudo-lodule
drop~ton~'~
vergent lold lvergencefhe Nor!h)directeon fram
Figure 6. Stratigraphical sections of Llestui.
-- ~ Figure 7. Map of quaternary depoisits of Taüll and Durro Valleys (both tributaries of Noguera de Tor Valley). l. Glacial deposits; 2. Gla- ciofluvial deposits; 3. Glaciolacuistrine deposits; 4. Rock glacier moraines; 5. Recent lake deposits; 6. Alluvial deposits; 7. Alluvial cone deposits; 8. Periglacial slope deposits; 9. Debns cone; 10. Land-slide deposits: 1 l. Land-slide scar.
(Fig. 3). \Ve have two objective criteria to atribute pyrenean terraces and he attributed Günz age to these dep~ositsto an old glaciation: the glaciofluvial the higer terrasses located between 90 and 120 m. characterlstics of the deposit and its altimetric posi- a.r.1. Solé Sabarís (1951) ratified the same interpre- tion. In relation to the age of the T, level, we can tation. According to other authors who worked in try to ust: the altimetric stratigraphic criteria pro- Puigcerda area (South-eastern Pyrenees) taking into posed by the classical authors in the Pyrenees. Go- account both weathering and altimetric criteria ron (1 94 11) established a slratigraphy for the fluvial (Chevalier, 1906; Panzer, 1932; Boissevain, 1934 LEGEND --Mulleres profiles (-3Scar, landslide -height a.s.l.: 1700m Terrace siape -1ong. : O0 51' 18"
Marainic ridge -lat. : 42O 30'29" + Alluviai fan INTERNAL BEDDING STRUCTURES '\-, Talweg parallel lamination CZI] Wacial deposits deformed laminatlon cross Iamlnation m Morainic baulders COLOUR parailel beddtng cross bedding-deltaic toresets m Glacio-fluvial terrace be~qe blue synsedimentcry normal foults Lacustrine deposits black Channel grey Fluvial deposits CONTACTS achre Abrupt Erasianal m Peat TRANSPORT DlRECTlON I I =Martí profile m Gdilluclion deposits 4 polaeocurrent direction m Scree ( transport direction , from clast lithaloqy m Paleozaic bedrock
III
Riu dr GiinstM
Figure 8. Quatemary deposits of the Taüll area: vertical sections.
and Nussbaum, 1946), the terrace T, ought to h,ave by the lateral moraine of Artiga (Bono area), clearly a pre-Mindel age. According to the stratigraphy atributable to the last glaciation (Vilaplana, 1983). proposed by Serrat (1980) in the Ter Basin (South- Two things must be considered in relation to the eastern Pyrenees) the correlation with the T, ter- age of this deposit: The existence of the morai- race give also a pre-Mindel age. In spite of my re- nic matenal included in the slope deposit which at- servations to use the alpine stratigraphical termino- tests an anterior glaciation (which might corre- logy for the pyrenean glaciations, before the estab- spond to the glaciation indicated by T, terrace); lishment of a good correlation between the pyre- and the age of the colluvion which is earlier to the nean valleys, 1 prefer say that the age of the T, ter- position of the lateral moraine of 1'Artiga (last gla- race is atributable to an old pyrenean glaciation. cial maximum; see Fig. 12). As an hypothesis, we Without present data is impossible to establish ex- can think that this deposit is the consequence of an actly if it correspond to the Middle or Lower Pleis- important slope erosion between two glacial pe- tocene. riods. The other old deposit is a colluvial formation In any case, these are the only sedimentary re- constitued by periglacial slope material and which cords found in these valleys related to glacial pe- includes reworked morainic matenal. It is covered riod earlier to the last one and, by now, they do not Figure 9. Gi.acial extension during the last glacial maximum (Phase 1) in the Alta Ribagorca Pasin. 1. Glacial basin boundary; 2. Water streams; 3. Obstruction lake; 4. Height point; 5. Ice flow; 6. Glacial transfluence; 7. Bedrock; 8. Glacier.
give any inforrnation witlh reference to the exten- established; and it is also correlated with thc crono- sion and characteristics oil this or these old quater- stratigraphy and the glacial chronology proposed nary glaeiations. by Mardones (1982) and by Mardones and Jalut (1983) in Lourdes area (Northen slope of the Pyr- enees). The synthesis is given in the figure 12. Last Pyrenean Glaciation Three great phases have been differentiated wi- thin the last glaciation in the Alta Ribagorca Basin. During the Upper P1e:istocene a very important glaciarisation occurred in the Alta Ribagorca Basin. This glaciation had an innportant extension (Figure Glacial Maximum Phase 9) and clestroyed almost al1 the remains of the ear- lier glaciations. The maximum expansion of the valley-glaciers A stratigraphy of the different Late Pleistocene (Fig. 9) took place, followed by a prolonged stabili- sedimeritary units of the Alta Ribagorca Basin is zation of them. During this phase the great excava- ALTA RIBAGORCA BASIN
-Central Southern Pyrenees -
,r ) I ', >-' I L. -+' :'- -..A- , * , -. -, , ., 1, I ,., c C ' -- - - . " --" E, Pont ,e ~Gi .- . S-- ,_.._fl---,,- I .- ,__----.\r,-- Embassament 1,. 5 km Figure 10. Glacial extension during the second phase (Phase 11 Postmaximum) of the last Pyrenean Glaciation in the alta Ribagorca Ba- sin. ALTA RIBAGORCA BASIN -Central Southern Pyrenees - Figure l. l. Glacial extension tlunng the third phase (Phase 111 Final) of the last Pyrenean Glatiation in the lblita Ribagorea Basin. tion both in the cirques and valleys was produced -Postmaximum Phase by the glaciers. Important overdeepened basins were formed at the bottom of the main valleys -1000 m. The second phase of the last glaciation was also a.s.1.- (Bono and Barruera). These erosive processes characterized by valley-glaciers, though lesser ex- were conditioned by both the important rock thresh- tensives than those during the maximum phase (Fi- olds and the confluence of severa1 glacial tongues gure 10). The erosive and sedimentary capacities (ice-overaccumulation). The sedimentation on the are very lower with reference to the first phase. The bottom of the valleys and cirques was not much main sedimentary unit of this phase is represented important. The main deposition took place in the by the Seminari de Vilaller ice-terminal ti11 com- ice-marginal zones: ice-terminal ti11 complexes plex in the Noguera Ribagorcana Valley. No abso- (Sant Antoni ti11 and Grilló till) and ice-lateral ti11 lute dates have been established for this deposit, if a complexes (Llestui formation and Taüll moraine). correlation with the stadial X of Mountain glaciers During this phase of ice-marginal deposition, it (Mardones, 1982 and Mardones & Jalut, 1983) is must be emphasized the setting up of lacustrine en- accepted, it would be placed between 25000 and vironments due to the destruction of the tributary 14820 years B.P. (see fig. 12). valleys by the main glaciers (Serrat et al., 1983). From both the absolute dates carried out in the Llestui formation and the correlation with the strat- -Final Phase igraphy proposed at Lourdes (Mardones, 1982 and Mardones & Jalut, 1983), the phase of maximum It was the last phase of the last quaternary gla- extension was between 70000 and 50000 years BP ciation, restricted with referente to the other two and the later stabilization lasted until 3 1.900 years phases (Figure 11). The glacial tongues were BP (see fig. 12). I SOUTHERN P Y R E NT E S 1 NORTHEN PYRENEES 1 Alto Ribaqor~o Bosin VILA APLANA,^^^^) Biscaye-Lourdes (MARDONES,1982) ICHRONOSTRATIGRADWGLAC;AL CHRGNOSTAATIGRAPHY GLACIAL PHASES SEDIMENTARY UNITS 4C RADIOCARBON DATES eoftd &mi% UNLT S PHPSES 4 7 Fnnt de Susrt Terroce Ti I SO1en''uer 'ir'ue Barso'' Recen1 mominic iidps* 1 HOLOCENE POSTGLACIAL Basibarri silque -1 FO~~O- lnterglocial 4 IiCn Recant Iocustrinc deporitr in botlom oiqus loket CI- 5420?13OBP 1 i E ; P 1 BP - Sfadial ll! Rack Glocier moroiner TARDIGLACIAL ' .oieiertadioi 2t TARDI- lop 12620?160 8P 12780 ~p Botiarn cirque moroinar +- 1 - 13250 BP , Intriuslodiol 20 LOKC ~lauitf PHASE III Pont de Suert Terroce T~ urt 1 1 Las1 Ice- termino1 trll camplsi ul Bc. Beribarri 1 ~tadlel11 m 1 = Advonce I 1 liilereltcdicil 1 PIO 1 15000 BP . I W Pon1 ds Svart Terrese T2 z z PHACE I, + - 20930 ? 310 BP 1 u W Stod~ol 1 I Z U *lemediG>C l O _I LO"fOt "ni, i O I- Postmalimum ice - terminal ti11 camplax 01 seminari 1 24000 BP 2 a Advance W de viloller 1 l~ourde~interestodid 1 a - 1 I rr~ns~tion U. e 1 31900 BP Pon1 de Suert Tcrroca T3 r->34000BP 1 a Glacial r.Llariui - O 1 dzLourder Stodiol i g W ~ce-lo~rottiti compiixar i-Senc' '4, l- siabilizalion , .Aciipo E a S O , .Eiill .; U0 1 38400 BP E E -1 l.Toüll - I 0 Birceye Intetartoaioi suE: I ,e 1 45000 OP + Pon1 de Suert Tiriaca T4 2 E Glacial t O - 0 Sant Antani LOSI GloCiol SO 50000-70000 BP o Expansion Ice-termino1 till Complaisr ' W O Maiimum P- ,,Id ,,Id I I U I ,\ ,\ I MIDDLE OH EARLYI?) INTERGLACIAL Colluvial deposit of Bc. Arlipa PLEISTOCENE GLACIAL Pwt de Eueft Terrace T5 Figure 12. Quatemary stratigraphy and glacial chronology of Alta Ribagorca Basin and its correlation with the glacial chronolog! of Lourdes area (Pyrenees Mountains). shorter than 18 kilometers in leghth at the main and Western Pyrenees, the small cirque-glaciers valleys, while only cirque glaciers ocupied the which caused these deposits were place$ during his- small valley-lneads. During this phase of small ero- torical times. Concretly, Martí et al., (1978) quoted sive capacity, tills were deposited on te bottom of a cold pulsation between the XVII-XIX centuries, some cirques, and the terminal moraine of the Ri- and correlated it with the little-Ice-Age in the Alps. bagorcana Glacier was deposited in the Barranc de At present, there are no glaciers in the Alta Ri- Besiberri. Diiring the glacial retreat of phase 2 and bagorca Basin. The only present evidences of gla- during this last phase, the in-filling of the lakes at cial dynamics are found in the nearby Maladeta the overdeepened basins (Bono and Barniera) ac- Massif (NW of the studied area) where five small cording to the correlation witl~the stratigraphy pro- cirque-glaciers occur with a total area of 2.6 square posed by Mardones (1982) and Mardones & Jalut kilometers. (Serrat et al., 1980). (1983), this last phase, of brief duration, would be placed between 14820 and 13000 years B.P. ACKNOWLEDGEMENTS 1 wish to thank the following Institutions and people for ma- Once the pleistocene glaciers retreated, a cold king possible the present work with their support and their acti- and dry piilsation was pro~duced.This pulsation ve collaboration. was definedl by Serrat (1929) at the Eastem Pyren- Servei Geologic de Catalunya (Dpt. Obres Publiques i Políti- ca Territorial de la Generalitat de Catalunya). ClRlT de la Ge- ees as Tarcliglacial episode; this phase was placed neralitat de Catalunya. ENHER (National Hydropower Compa- at the Pyrenees between 13000 and 10000 years ns). B.P. Mardones (1982) dated this cold phase at Bis- Dr. Christian Schlüchter (ETH - Zürich). Dr. David Sernt caye between 11200 and 1Ci860 years B.P. Jalut et (Dpt. Geomorfologia i Tectonica-Univ. Barcelona). Josepa Bni (Dpt. Geografia-Univ. Barcelona). Jaume Bordonau (Dpt. Geo- al. (1983) dated this cold, dry and brief phase at morfologia i Tectonica-Univ. Barcelona). Dr. Juan R. Vidal Ro- Freychinecle (Ariege Pyrenees) a little earlier than maní (Laboratorio Xeoloxico de Laxe). Dr. Jacques Evin (Labo- 1 1200 years B.P. ratoire de Radiocarbone; Univ. Claude Bemard-Lyon 1). The Pleistocene period in the Alta Ribagorca ended with this Tardiglacial phase, and the Holo- cene or Postglacial period started. Holocene Period REFERENCES The nlost complete stratigraphy of the Holo- cene has to be searched in 'the high lakes, at the up- ALIMEN, M.; SOLÉ SABAR~S,L.; VJRGILI, C. 1957. «Com- per part of the valleys and the bottom-cirques. In paraison des formations glaciaires des versants N et S des Py- fact, some of these lakes already started their sed- rénées)). Res. Com. Veme Conpis INQU, Madrid- Barcelona. entary record during the final part of the Last Pleis- BOISSEVAIN, H. 1934. uEtude géologique et géomorphologi- tocene Glaciation. que d'une partie de la haute vallée tiu Sege». Bttll. Suc. Hist. The rnost important example of these lakes is Nat. Toulouse. T. LXVI, p. 32-1701.27 fig. 1 mapa Toulouse. Llauset L,ake which is being studied from sedimen- BOULTON and EYLES, N. 19'79. «Sedimentation by valley gla- ciers; a model and genetic classiffcation». In: Schlüchter, Ch., tological and stratigraphical view-points. The first ed., «Moraines and varvew, A.A. Balkema, Rotterdam, p. results of'this study are presented in a paper within 11-23. this review (Vilaplana, Schlüchter & Verdaguer, BRU, J., MARTÍ, C., SERRAT, D. and VILAPLANA, J.M. 1984). 1983. ~Symposiumand field trip on glacial pleistocene depo- With reference to the glacial dynamics in the sits in Southem Pyrenees: Excursion guiden. INQUA Comis- sion on Genesis and Lithology of Quatemary deposits. Uni- Alta Ritbagorca basin duiring the Holocene, it can versitat de Barcelona and Instituto de Estudios Pirenaicos. 53 be said that there are evidences of glacial dynamics P. at the iipper parts of tl~emountains. There are CHEVALIER, M. 1906. «Sur les glaciers pléistocknes dans les well-preserved morainic ridges containing very vallées d'Andorre et dans les hautes vallées espagnoles envi- ronnantes». C.R.Acad. Sciences, t. 142, p. 662-910. Pans. fresh materials at the uppermost zones (between DALLONI, M. 1930. «Etude géologique des Pyrénéea Catala- 2.600 ai~d3.000 m. a.s.l,.). Acording to severa1 ob- nes» Ann. Fas. Soc. Marseille. T.XXVI, Fasc. 111, 1 vol. 373 servations carried out in other basins of the Central p., 65 fig., 12 lam., 1 mapa. Argel. DREIMANIS, Aleksis. 1976. «Tills: Their origin and proper- OBERMAIER, H. 192 1. «Die Eiszeitiliche Verglerscherung Spa- ties)). In R. Legget, editor: «Glacial tilb). Special publication nien)). Peternanss Geogr. Mitt. t. 67, p. 158-162, Gotha. n." 12 of the Roya1 Soc. oJ'Canada, p. 1 1-49. PANZER, W. 1932. «Die eiszcitilichen Endmoranen von Puig- ESTEBAN, A. & VILAPLANA, J.M. 1984. «Premiers résultats cerda (Ostpyrenaen))). Zeitschr. J: Glets-cheik. Berlin. Tra- d'analyses polliniques dans des sediments et tourbieres du duccio de LI. Solé «Geleres quatemiries dels Pirineus)). Bassin de la Noguera Ribagorcana (Pyrénees Centrales, Llei- Butll. C.E.C., t. XLIV, pp. 153-162, 1 fig. Barcelona (1934). da)». Com. Symposium: Modifications de I'environement a la PENCK, A. 188 1. «Die Eiszeit in der Pyrenaenu. Erdk. Leipzig. fln du Pleistocene et pendant I'HolocPne dans le bassin Mé- Trad. Francesa per L.B. «La piriode glaciaire dans les Pyre- diterranéen Occidental. INQUA- Stra. Subc. Sept- 1983 nées)). B.S.M.N. t. XIX, p. 105-200. Toulouse (1885). Toulouse. SCHLÜCHTER, Ch. 1977. ((Grundmorane versus Schlammora- FONTBOTÉ, J.M.; SOLÉ SABARÍS, L., ALIMEN, H. 1957. ne -two types of lodgement tlll in the Alpine Fareland of «Livret guide de I'excursion N. PYRENEES)). INQUA, vZme Switzerland)).Boreas, vol. 6, p. 18 1-188. Oslo. Com. Inter. 107 pp. Madrid-Barcelona. SERRAT, D. 1979. «Rock glacier morainic deposits in the Eas- FRODIN, J. 1927. «GLaciala Fomer i Pyrenennan. Meddelan- tern Pyrenees)). In: SCHLUCHTER, Ch. ed.: ((Morainesand den Fran Lunds Universitets Geograflska Institution. Ser. C., verves. Origin, genesis, classif?cation». p. 93-100, A.A. Bal- n.O 26, 156 p. Lund. kema, Rotterdam. GARCIA SAINZ, 1935. «Morfología glaciar y preglaciar de la SERRAT, D. (coordinador) & EQUIPOS de Geomorfologia Al- región de la Nogueran (C. Cinca-Segre). Bull. Soc. Geogr. Na- pina (Fac. Geografia y Geología de Barcelona) 1980. «Cata- cional, n.O 54 TLXXV, p. 64-1 lO..Madrid. logo de los glaciares de la Península Ibérica (1979))).j\rort.s de GORON, L. 1941. «Le rble des glatiations quatemaires dans le Geografia Física: 3 p. 35-55, Dpt. de Geografia, Universitat modelé des vallées maitresses des Pré-Pyrénées ariégeoises et de Barcelona. garonnaises et de leur avant-pays)). Edit. Privat, 400 p., 56 SERRAT, D.; VILAPLANA, J.M. and MARTÍ, C. 1983. fig. 15 1am. phot. 6 lam. Toulouse. «Some depositional models of glaciolacustnne environment JALUT, G.; DELIBRIAS, G.; DAGNAC, S.; MARDONES, M. in Southem Pyreneesn. in: EVENSOK et al. Editors: Tflls & BOUHOURS, M. 1982. «A palaeoecological approach to and related deposits, p. 132-144. A.A. Balkema, Rotterdam. S the last 2 1.O00 years in the Pyrenees: the peat bog of Freychi- SOLE SABARIS, L. 1951. Los Pirir~eos.El medio y el hombre. nede (alt. 1350 m, Ariege South of France)» Palaeogeograp- Biblioteca española de Cult. General. t. 8,627 p. Barcelona. hy, ~laeoclimatology,Palaeoecology, vól. 40. p. 32 1-359. TAILLEFER, F. 1957. ((Glaciaire Pyrénéen. Versant Nord et MARDONES, M. 1982. «Le Pleistocene Supérieur et 1'Holoce- versant Sud». Rev. Géog. Pyr. rt Sud-Ouest. t. XXVIII. p. ne du piémont de Lvurdes: Le gisement de Biscaye. (Hautes 22 1-224,8 fig. Toulouse. Pyrénées, France))). Etude palynologique, These de 3.cmcCy- TOMAS QUEVEDO, S. 1979. ((Diatomeas de las aguas epicon- cle, 96 p., Universitb de Toulouse. tinentales de España: Géneros Cymbella y Gornphonerna, MARDONES, M. & JALUT, G. 1983. «La tourbiere de Biscaye Dpt. Ecologia Univ. de Barcelona. Tesi Llicenciatura (inedi- (Alt. 409 m, Hautes Pyrenées): Approche paleoécologique ta). des demieres 45000 années)). Pollen et Spores, Vol. XXV, n." VILAPLANA, J.M. 198 1. «El método de estudio del glaciarismo 2, p. 163-212. cuatemario en el Pirineo y sus posibles aplicaciones en las MARTI BONO, C.E.; SERRAT CONGOST D.; GONZALEZ, Sierras Galaico-Portuguesas)). Cuad. Lab. Xeol. de Laxe, n.O M.C. 1978. «Los fenómenos glaciares de la vertiente meri- 2, vol. 1, p. 275-288.0. Castro. dional de los Pirineos)). ((Mediofísico, desarrollo regional y VILAPLANA, J.M. 1983 a. ((Estudi del glaciarisme qziaternari geogrdfíco, V. Col. Geogr., Granada 1877 p. 67. 73. Univer. de les altes valls de la Ribagorga)). Tesi Doctoral, Departa- Granada. ment de Geomorfologia i Tectonica. Facultat de Geologia. MARTI 1 RIBA, J. 1980. «Morfologia glacial i periglacial de la Universitat de Barcelona, 322 p., 1 annex amb 10 map. Ribera de Sant Nicolau. (Alta Ribagorca). Iniciació a I'estudi VILAPLANA, J.M. 1983 b. ((Sobre la Geomorfologia de la Vall de la dinamica actual)). Tesi de Llicenciatura. Departament de Llauseb. Revista d'lnvestigacions Geológiques. Vol. 36. de.Geografia. Universitat de Barcelona. (inedita). VILAPLANA, J.M. & SERRAT, D. 1979. «Els diposits d'origen MARTI 1 RIBA, J. 1981. ((Estudio del glaciarismo cuatemario glacial de la cubeta de la Massana-OrdinolAndorra: llur sig- de un sector del Alt Ribagorcm. Notes de Geografía Fisica, nificació paleogeograficm. Acta Geol. Hisp. Vol. XIV home- 5, p. 33-47, Dpt. de Geografia. Barcelona, Juny 1981. natge al Dr. Ll. Solé Sabaris, p. 433-440, Barcelona, 1982. MARTINEZ DE PISÓN, E. y ANTÓN BURGOS, J. 1981. VILAPLANA, J.M. & CASAS, A. 1983. «Las cubetas de so- ((Repertorio bibliográfico sobre morfología glaciar de la Pe- breexcavación glacial de Bono y de Barruera (Alta Ribagor- nínsula Ibérica)). Cuadernos de Invest. Geogr., Fasc. 1,2, ca: Pirineo Central))). Cuadernos de Lab. Xeol. de Laxe. n." T VII, p. 3-49, Mayo-Diciembre 198 1. 6, p. 283-309. O Castro. MEY, P.H.W. 1968. «The geology of the Upper Ribagorzana VILAPLANA, J.M. SCHLUCHTER, Ch. & VERDAGUER, A. and Baliera Valleys, Central Pyrenees, Spain)). Leidse Geol. 1983. «Sedimentological and Stratigraphical approach to la- Mededel. 41- p. 153-220. Leiden. custrine Late Pleistocene environement of Lake Llauset MEY, P.H.W. 1968. «The geology of the Upper Ribagorzana (Southem Pyrenees).)) Acta Geológica Hispanica: 3-4, vol. and Tor Valleys, Central Pyrenees, Spainn. Leidse Geol. Me- 18. dedel. 41- p. 229-292. Leiden. ZWART, H.J. 1972. «Geological Map of the Pyrenees)) 1: NUSSBAUM, F. 1946. ((Orographische und morphologische 200.000, Leiden, Geological Institut of Leiden University. Untersuchungen ir der ostlichen Pyrenaen)). Jahresb. Geogr. Gess. Ben., Bd XXXV-XXXVI, 345 p., 94 fig., 4 lam. fot. Bema.