Tertiary basins of Spain the stratigraphic record of crustal kinematics EDITED B Y PETER F. FRIEND Department of Earth Sciences, Unzversity of Cambridge A N D CRISTINO J. DABRIO Madrid, Spain CAMBRIDGE UNWERSITY PRESS 40 West 20th street, N & Y & ~ , NY 1 0 0 1 1 4 2 1 1 ~ ~ ~ ~ 10 Stamford Road, Oakleigh, Melbourne 3166, Australia 0 Cambridge University Press 1996 First published 1996 Printed in Great Britain at the University Press, Cambridge A catalogue recordfor this book is availablefrom the Brilish Library Library of Congress calnloguing ixpubliealion data Tertiary basins of Spain : the stratigraphic record of crustal kinematics / edited by Peter F. Friend and Cristina J. Dabrio. p, m. - (World and regional geology series) Includes bibliographical references. SBN 0 521 46171 5 I. Geology, Stratigraphic - Tertiary. 2. Geology, Structural - Spain. 3. Basins (Geology)-Spain. I. Friend, P.F. 11. Dabrio, Cristino 1. 111. Series. QE691.T465 1995 551.7'8'0946 - dc20 94-21724 CIP ISBN 0 521 46171 5 hardback Contents Lisr of conrriburors ix Prefnce P.F. FRlENDand C.J. D A B R I O xiii Dedication 10 Professor Oriol Riba I Arderiu c. P u l ~ o ~ r i ~ n ~ G a s xv Memorial, Etienne Moissenef 1941-1994 P. awaoblu, N. MolssENET and o. R ~ A nvii P A R T G G E N E R A L GI. Tertiary stages and ages, and some distinctive stratigraphic approaches 3 P.F. FRIEND G 2 Cenozoic latitudes, positions and topography of the Iberian Peninsula 6 A.G. SMITH G3. Tertiary tectonic framework of the Iberian Peninsula 9 C.M. SAN2 D E FALDEANO G4. Deep crustal expression of Tertiary basins in Spain 15 E. B A N D A G 5 Oil and gas resources of the Tertiary basins of Spain 20 F. MELENDEZ-HE VIA^^^ E. A L V A R E Z DE B U E K G O G6. Mineral resources of the Tertiary deposits of Spain 26 M A . c a n c i a D E L CUR*, C.J. D A B R L O ~ ~ ~ S, o n o h i a ~ z P A R T E EAST El. Geological setting of the Tertiary basins of Northeast Spain 43 P. AN AD ON^^^ E. R O C A E2. The lithos~here of the Valencia Troueh: a brief review 49 M. TORN^ E3. , De~ositionai seauences in the Gulf of Valencia Tertiary basin 55 W. M A R T ~ N E z D E L O L M O E4. Neogene basins in the Eastern Iberian Range 68 P. A N A D ~ N and E. MOlsSENET E5. The Tertiary of the Iberian margin of the Ebro basin: sequence stratigraphy 77 I. V I L L E N A . G. PARDO. A . PEREZ. A. ~ ~ R o z a n d A. , ~, GONZLLEZ E6. Tertiarv of the Iberian marein of the Ebro basin: paleogeography and tectonic control 83 I. VILLENA, a. PARDO, A. PBREZ, A. ~ ~ R o z a n d A. GONZLLEZ E 7 Stratigraphy of Paleogene deposits in the SE margin of the Catalan basin (St. Feliu de CodinesSt. Llorenc del Munt sector, NE Ebro basin) 89 J. CAPDEYILA, E. MAESTRO-MAIDEU, E. RE MAC HA^^ J. S E R R A ROIG EX. Onshore Neogene record in NE Spain: Vall&PenedBs and El Camp half-grabens (NW Mediterranean) L. CABREKAand F. C A L V E T E9. The Paleogene basin of the Eastern Pyrenees J.M. COSTA, E. M A E S T R O - M A I D E U ~ ~ ~ CH. BETZLER E l 0 The Neogene Cerdanya and Seu d'Urgell intramontane basins (Eastern Pyrenees) E. R O C A El l . Eocene-Oligocene thrusting and basin configuration in the eastern and central Pyrenees (Spain) J. v ~ n c i s and D.W. B U R B A N K E12. The Late Eocene - Early Oligocene deposits of the NE Ebro basin, west of the Segre River E. M A E S T R O - M A I D E U ~ ~ ~ I. s m n a R O I G E13. Chronoloav of Eocene foreland basin evolution along the .. western oblique margin of the South-Central Pyrenees P. BENTHAMand D.W. B U R B A N K E14. Evolution of the Jaca piggyback basin and emergence of the External Sierra, southern Pyrenees P.J. HOGANand D.W. B U R B A N K E15. Long-lived fluvial palaeavalleys sited on structural lineaments in the Tertiary of the Spanish Pyrenees s . ~ , V I N C E N T and r. ELLIOTT E16. Evolution of the central part of the northern Ebro basin margin, as indicated by its Tertiary fluvial sedimentary infill P.F. FRIEND, M.J. LLOYD, R. MCELROY, I. TURNER, A. V A N G E L D E R and S.J. V I N C E N T E17 The Rioja Area (westernmost Ebra basin): a ramp valley with neighbouring piggybacks M.J. J U R A D D ~ ~ ~ o. R I B A P A R T W W E S T Wl . The Duero Basin: a general overview 1.1. SANTISTEBAN, R. MEDIAVILLA, A. MART~N-SERRANO and C.J. o a e n l o W2. Alpine tectonic framework of south-western Duero basin 1.1. SANTISTEBAN, R. MEDIA VILLA^^^ a. ~ a n r i N - S E R R A N O W3. South-western Duero and Ciudad Rodriga basins: infill and dissection of a Tertiary basin J . L . SANTISTEBAN, A. M A R T ~ N - S E R R A N O , R. M E D I A Y I L L A and C.J. DABnlo W4. Tectono-sedimentary evolution of the Alrnazin basin, NE Spain I. BOND ill ... v111 Contents W 5 Tertiary basins and Alpine tectonics in the Cantabrian Mountains (NW Spain) I.L. ALONSO, J .A. PULGAR, I.C. GARC~A-RAMOSand P. B A R B A W6. Lacustrine Neogene systems of the Duero Basin: evolution and controls R. MEDIAVILLA, c l . DABRIO, A. M A R T I N - S E R ~ A N O and 1.1. S A N T I S T E B A N W7. North-weslern Cainoroic record: present knowledge and the correlation problem a. MART~N-SERRANO, R . M E D I A V I L L A and 1.1. S A N T I S T E B A N W8. Onshore Cenozaic strike-slip basins in NW Spain L. C A B R E R A , B. F E R R I ~ , A. s ~ E Z , P.F . S A N T A N A C H ~ ~ ~ J. B A C E L A R W 9 Tertiary of Central System basins A. MARTIN-SERRANO, J.I. SANTLSTEBAN and R. M E D I A V I L L A P A R T C C E N T R E C l . Structure and Tertiary evolution of the Madrid basin G. D E YICENTE, I.M. GONZ~LEZ-CASADO, A. MUROZ- MARTIN, J. GlNERatld M A . RODR~GUEZ-PASCUA C2. Neogene tectono-sedimentary review of the Madrid basin G. D E VLCENTE, I . E . CALVO and A. MUAOZ-MART~N C3. Sedimentary evolution of lake systems through the Miacene of the Madrid Basin: paleoclimatic and paleohydrological constraints I.P. CALVO, A.M. ALONSO Z A R Z A , M A . G A R C ~ A D E L CuRa, S. O R D ~ A E Z , I.P. RGDR~GUEZ-ARANDA and M E . SANZ-MONTERO C4. Palmmorphologic features of an intru-Vallesiao paleokarst, Tertiary Madrid Basin: significance of paleokarstic surfaces in continental basin analysis I .C. CAFJAVERAS, I.P. CALVO, M. HOYOSand S. O n o h r j ~ z CS. Tectono-sedimentary analysis of the Loranca Basin (Upper Oiigocene-Miocene. Central Spain): a 'nan-sequenced' . foreland basin J . J . G ~ M E z FERNINDEZ, M. D ~ A Z - M O L L N I ~ I ~ ~ A . L E N D ~ N E Z C 6 Paleoecology and paleoclimatology of micromammal faunas liiom Upper Oligocene - Lower Miocene sediments in the Loranca Basin, Province of Cuenca, Spain n . DAAMS, M.A. A L V A R E Z SIERRA, A I . vaN DER MEULEN and P. PELIEL-CAMPOMANES C 7 Fluvial fans of the Loranca Basin, Late Oligocene - Early Miocene, central Spain M. D ~ A Z - M O L L N A ~ ~ ~ A. T O R T O S A C8. Saline deposits associated with fluvial fans. Late Oligocene - 214 Early Miocene, Loranca Basin, Central Spain 308 I. ARRlBASand M. DiAZ-MOLINA C 9 Shallow carbonate lacustrim depositional controls during the Late Oligacene - Early Miocene in the Loranca Basin 228 (Cuenca Province, central Spain) 313 M.E. ARRIBAS, R. asa and M. D~AZ-MOLINA 237 P A R T S S O U T H S1. The Betic Neogene basins: introduction 321 . 247 CH. M O N T E N A T S2. Neogene palaeogeography of the Betic Cordillera: an - . - . . attempt at reconstructmn 323 C.M. S A N Z DE G A L O E A N O ~ ~ I. n o o ~ i o u ~ z - F E R N A N D E Z S3. Depositional model of the Guadalquivir - Gulf of CBdir Tertiary basin 330 C. RlAzAand W. M A R T ~ N E Z D E L OLMG S 4 Late Neogene depositional sequences in the foreland basin of Guadaiquivir (SW Spain) F.,. SIERRO, 1.4. G O N Z ~ L E Z DELOADO, C.,. DABRIO, I.A. r ~ o n ~ s a n d r. C I V I S SS. Miocene basins of the eastern Prebetic Zone: some tectano- sedimentary aspects CH. MONTENAT, P. OTT D'ESTEVOUand L. P IERSON D 'AUTREY S 6 Stratigraphic architecture of the Neogene basins in the central sector of the Betic Cordillera (Spain): tectonic control and base-level changes I. F E R N ~ N D E Z . I. SORlAand C. VISERAS allocyclic and autocyclic processes on the resultant stratigra~hic organizat~on ~ ~ 1. FERN~NDEZ, C. VlSERASand I. S O R l A S 8 Late Neogene basins evolving in the Eastern Betic transcurrent fault zone: an illustrated review CH. M O N T E N A T ~ ~ ~ P, OTT D'ESTEVOU S9. Tectonic signals in the Messinian stratigraphy of the Sorbas basin (Almeria, SE Spain) J .M. M A R T ~ N ~ ~ ~ ].C, BRAGA S10 Basinwide interpretation of seismic data in the Alborin Sea c. DOCHERTY and E. B A N D A W6 Lacustrine Neogene systems of the Duero Basin: evolution and controls R. MEDIAVILLA, C.J. DABRIO, A. M A R T ~ N - S E R R A N O A N D J.I. SANTISTEBAN Abstract Vertical aggradation of Neogene fluvial and lacustrine deposits occurred until the Late Neogene in central and northem areas of the Duero Basin, coeval with river incision in the south- westerncorner ofthe basin. The whole basin became exorheicin the Latest Neogene. We have differentiated five tectonosedimentary units (TSUs) of basinal extent, bounded by unconfonnities or breaks in the sedimentary record. Deposits in each TSU consist of alluvial-fan deposits in areas close to the active northern and eastern margins, and fluvial deposits along the western margin. These systems converged in the lower, subsiding areas of the basin occupied by carbonate-evaporite lacustrine systems. Tectonics and climate controlled sedimentation. The main faults active from the Neogene to the Present reflect Late Hercynian basement fractures that were re-activated during the Alpine Oro- geny, both fracturing blocks and modifying landscapes, and creat- ing or modifying the areas of subsidence. Analysis of climatic variations during the Miocene shows that deposition of saline materials occurred in dry TSUs (1, 2) and, particularly, in humid TSUs (3. 4). Climate does not seem to have been a determining . . factor for the formation of evaporites. However, it was a very important factor in determining both the amount of water that reached the basin and, eventually, also the extent of the lacustrine systems. Introduction By the end of Oligocene times, the northern and southern margins of the Duero Basin experienced final compressional stresses and were uplifted by reverse faults above the Paleogene deposits of the basin (Barba, pers. commun., 1992; see also Chapter W2). During the Neogene, sedimentation took place in an exten- sional regime, with major vertical movements, which continue at present. Gentle subsidence in the south-western margin during the Neo- gene favoured the headward erosion ofthe Atlantic fluvial network that began to he defined in Uppermost OligoceneEarly Neogene timeslhlartin-Serrano, 1991; see also Chapter W3). Coeval to river incision at this side of the basin, high subsidence rates in thecentral Fig. 1. Tectonic map of the Duero Basin (fmm Baena et d., in press) and composite cross section of the central zone. 1: Fractures; 2: faults with indication af the sinking block; 3: overthrust; 4: fracture (supposed); 5: river; 6: strike and dip. and northern areas of the basin (Fig. 1)caused vertical aggradation of Neogene fluvial and lacustrine deposits until the end of the Neogene when the whole basin became exorheic. We have differen- tiated five tectonosedimentary units (TSU, sensu Megias, 1982 and Pardo er al., 1989) of basinalextent separated by unconformitiesor breaks in the sedimentary record (Figs. 2 and 3). Ingeneral, each of these TSUsconsists of alluvial-fan deposits in areas close to the active north and east margins, and fluvial deposits along the west margin. At that time, Paleogene arkoses formed the southern margin along the Honruhia-Pradales Range, which con- stituted a relatively passive area as suggested by the scarce develop- ment of alluvial deposits. All these systems converge in the lower, subsiding areas of the basin (Fig. 2) occupied by the carbonate-evaporite lacustrine systems studied in this paper. There is an abundant literature concerning these deposits (e.g. Hernbndez-Pacheco, 1915; Royo Ghmez, 1926; San Miguel de la Camara, 1946; Garcia del Cura, 1974; Ordoiiezetal., 1980;Ordo1iezetal., 1981;PorteroetaI., 1982; W6 Lacustrine Neogene systems of the Duero Basin 229 As a whole, lacustrine sediments onlap Paleogene sediments in the southern margin (Fig. 5) and Mesozoic deposits of the Canta- brian Range in the north (Fig. 4B). Deposits of TSU 1 form an expansive and shallowing-upwards sequence topped by a major kantification profile (Pineda & Arce, in press). The deposition of TSU I records an important tectonic reactivation (basal unconfor- mity) and the progressive infill of the basin under a delayed m ; M ~ S ~ Y ~ & ~ & ; , q m N ~ ~ E N E ~ L A C U S T ~ ~ N E ~ ISOBATH MAP diastrophic regime. BASE OFTERTIARY m iGNE0USRa;KS 0 CEN0201C EERSSDWU m ~ g ~ ' ~ a ~ ~ ~ A E r TSU 2 L: LEON V V A W W L l D SSALAMANCA L:LUK)RA \ This rests disconfonnably upon TSU I and covers the l m greatest area (Figs. 3,4B and 4C). It crops out in the central Duero UUU] ""a,e,,,*,y Basin with a maximum thickness of 60 m. Plio-Quaternay Near the margins of the basin, TSU 2 consists of coarse-grained D , Upper Miocene siliciclastic sediments (conglomerate, sand, mud) of alluvial-fan ' *7:r 1 , , B!? /;).I / ~ower-middle Miocene and ~roximal fluvial svsteis flowing from sourceareas located to U - vaieogene the north, north-east andeast. Thesedeposits fineouttomoredistal Pre-Tenialy subsraturn fluvial systems in the south. In the Valladolid-Palencia area, the siliciclastic sediments change to lacustrine limestones, dolostones / semons and marls. Probably, these were formed in shallow lakes sur- J folds rounded by paludal or swampy fringes (Fig. 8B). In the pattern / fauns suggested, fluvial systems flowed to topographically lower areas supposed to lie somewhere to the west of the central areas. However, there are no lacustrine Neogene deposits in these areas and we suggest that these fluvial systems drained outside the basin. The vertical stacking of the siliciclastic sediments is explained by a high rate of subsidence in the basin (Fig. 6). Deposits of TSU 2 represent the progradation of fluvial over Fig. 2. Lacustrine Neagene deposits in the Duera Basin. A to F refer to cross- sections shown on Fig. 4. Armenteros, 1986; Mediavilla & Dabrio, 1986, 1988, 1989a. l989b; Corrochano & Armenteros, 1989; Pineda, in press; Pineda & Arce, in press; Mediavilla&Picart, in press; Piles & Picart, in press; Lopez Olmedo & Enrile, in press; Nestares & Wouters, in press). TSU 1 This reaches a maximum visible thickness of 50 m to the northofthestudy area(Fig. 3). Hereit dips to thesouth-west. Near the Cantabrian and Iberian ranges it consists of alluvial gravels, sands and alluvial muds that rest unconfonnahly upon Mesozoic and Paleogene deposits (Pineda & Arce, in press), (Fig. 4A). These coarse-grained sediments change to lacustrine carbonates and evaporites towards the south-west and north-east. Lacustrine sediments crop out diswntinuously in a NE-SW fringe parallel to the Pisuerga and Arlanz6n river valleys. Maxi- mum thicknesses are measured east of these rivers whereevaporitic deposits (dolostones, microlenticular gypsum and gypsarenites) are best represented. There are also paludal fringes with carbonate sedimentation in positions laterally equivalent to these saline lakes (Fig. RA). ~ - lacustrine facies with a coarsening-upwards trend that is thought to record tectonic movements in both the source areas and the basin. Mediavilla & Dabrio (1989) and Pineda & Arce, (in press) showed that NNW-SSE and WNW-ESE faults affected the sediments of TSU 2 along the northern margin (Fig. 4D). In the central areas there are fractures with block tilting, and also layers with palaeo- seismites (Baena er al., in press). The fractures observed at the surface are not really important, but they reflect the reactivation of the older, deeper Pisuerga scissors fault that lowered the NW block to the north-east and the SE block to the south-west, as demon- strated by careful thickness measurements. In the central areas ofthe basin the unit is topped by dark layers of clay and limestone, interpreted as Ruvio-paludal deposits. In other places these layers are paleosoils (Portero & del Olmo, 1982a, h, c; Mediavilla & Dabrio, 1986). These sediments form a con- tinuous layer, of regional extent, considered as a marker level that indicates a sedimentary hiatus. TSU 3 This unit rests unconformably upon TSU 2, and it onlaps the Mesozoic and Paleogene deposits of the northern and southern margins respectively (Figs. 4D and 5). The thickness is 2545 m; the maximum thicknesses occur NE and SW ofthe Pisuerga River (Fig. 7). To the north-east there is a zone of subsidence with two maxima 230 R. Mediavilla et a1 TECTONISM 0 TECTONISM? FOLDING - FLATTENINGSURFACE E EXORHEIC Fig. 3. Sbatigraphic framework of the Neogene depositsofthe Duero Basin, climatic and tectonie variations. Climatic curve after Lopez Mariinez et d. (1%). Classic denominations: A, Facies DueAas(Pomer0 & Del Olmo, 1982); B, Tierra de Campos; C, Cuestas (Hernandez Pscheco, 1915); D, Piramo I; E,Pirrmo 2 (San Miguel de la Cimara, 1946). B, Sedimentary record, tectonic events and mammal sites in the Duero Basin. TSU -teetonosedimentary units. W6 Lacustrine Neogene systems of the Due ro Basin 23 1 A B NE SSW NNE 1050 TSU 2 TSU 2 TSU 2 CRETACEOUS (m) C N NE D NEOGENE SW CRETACEOUS 300 (Arenas de Utrillas Fm] NW E 900 SE -- - - TSU 2 - - 780 -~ - (m) * TSU 4 - - Fig. 4. Geologiccross-wtiom to show lateral relationships and ehangesoffaeies and thickness in the Neogene TSU of the Duera Basin. Location of sections indicated in Fig. 2. A, B, C a d D: after Pineda (in press); E: after Pav6n et al., (in press); F: after L6pez Olmedn er al., (in press). local base level base level ........ A episodes of veacal aggradatian Fig. 6. Coeval di-tion and vertical aggradation during the deposition of TSU 2 in central and sonth-western Duero Basin. Fig. 5. Onlsp of Nwgene TSUs upon the Paleogene substrshlm in the area of Vallsdolid and Portillo. Modified from Portem and Del Olmo (1982), and Del Olmo and Portero (1982). R. Mediavilla et a1 Fie. 7. Correlation Panel for Neoeene demits in central Duero Basin. Same key as Figure 8 with the addition o f VL: Valbuena; VI: ViUsiimena: VA: . - Valdeolmillos; VE: Valdezste;H: Hontoria;F: Fombellido; T: T6rtolesdeEsgoeva; PD: PeAdbade Duero; PE: Pebafiel; CA: Csstrillo deDuero. (+) maximum thickness (subsidence) and (-) minimum thicknss (subsidence) for lacustrine deposits. Location of sections indicated in palaeogeographic maps (compare with Fig. 1 for scale). (Fig. 4E). To the south-east, the areas of maximum subsidence coincide with the E-W direction of the Duero River. TSU 3 records one of the events of major lacustrine expansion and displacement of the fluvial systems towards the north-east border and towards the west. The lacustrine systems include several subenvironments. In the shallow marginal areas (Figs. 4Fand 7)sand to mud units related to the development of alluvial systems alternate with episodes of organic clays or paludal fossiliferous limestones. Towards the central areas, far away from alluvial influence, chemical sedimentation increased. Faciesassociationsaremainiy of the carbonate-vaporite type (limestones, dolostones, primary microlenticular gypsum or gypsarenites with ripple cross-lamina- tion). In some places there are also lenticular sand and mud bodies of deltaic origin. The areal distribution of subenvironments (Fig. 8C, D) is gov- erned by: 1. the existence of topographically lower, more strongly subsiding, areas controlled by fractures, which became depo- centres; and 2. the supply of fresh water and siliciclastic sediments from source areas located to the north-west, north-east and south-east. The deposits of TSU 3 generally form a shallowing-upwards sequence that reflects the expandingcharacter of this unit (carbon- a t ~ v a p o r i t e deposits increasingly dominate upwards). This sequence records basin infill with a decreasing diastrophic regime. The top of the unit is marked by a change in the sedimentary polarity, a displacement of the areas of maximum subsidence and depocentres (Fig. 7). and progradation of carbonate marginal lacustrine facies towards the central areas of lakes and widespread pedogenesis. The paleosol formation does not necessarily imply an anomalous event. Periodic desiccation could have been a common feature. We assume that it was a basin-wide feature because of two facts: its occurrence in all the measured stratigraphic sections (despite the diversity of sedimentary environments involved), and the signifi- cant change in physical and chemical conditions of the basin, W6 Lacustrine Neogene systems of the Duero Basin 233 environmental distributionand sedimentary processes detectedjust above this layer. Accordingly, we consider that this pedogenic episode indicates an extensive sedimentary discontinuity. TSU 4 The thickness of TSU 4 is 35 to 55 m (Fig. 3) with the maximum located some distance to the south-east of the areas with thickest TSU 3 (Fig. 7). TSU 4 is a complex unit composed of three sedimentary cycles each recording a progradation of alluvial upon lacustrine deposits, later expansion of lacustrine facies and final progradation ofcarbonatemarginal faciesto thecentral parts of the lacustrine areas. The facies architecture in the first two cycles is similar to TSU 3, although there was a shift of depocentres between these units, producing variations in the areal distribution of sedimentary environments (Fig. 8D). As in TSU 3, the facies pattern was controlled by: I . location of fresh water and sediment supply that, by the end of the second, upper cycle, prevented the deposition of evaporitic facies; and 2. the existence of fault-related, subsiding areas that became depocentres. The third cycle shows a similar pattern hut there was no deposition of evaporites due to dilution of the lacustrine waters. At the top of this cycle, and in stratigraphic positions equivalent to the development of the lacustrine systems, there are fluvial systems, that drain to the west. The proximity of these systems to the south- western zones of the basin - which were the first to be captured by the exorheic Atlantic fluvial network - suggests that perhaps they were the first Neogene fluvial systems to be captured (Figs. 8E and 9). However, it is difficult to verify the equivalence of these isolated (encased) deposits or to confirm that they belong to the third cycle, because of the lack of connection of outcrops due to erosion. The prograding character of the alluvial deposits inside each cycle, particularly in the two younger cycles, has been explained by successive tectonic reactivations (tectonic uplifts) of the basin margins (Portero et al., 1982, in press; Garcia del Cura, 1974; Pineda & Arce, in press). However, Pincda & Arce (in press) indicate that in the margins and neighbouring areas there is no evidence of deformation due to these tectonic movements. On the other hand, the sedimentary characteristics of fluvial deposits, even in locations close to the margins, indicate deposition by high- sinuosity fluvial systems in low-gradient zones (Pineda & Arce, in press; Armenteros, 1986). Moreover, the transition from alluvial to lacustrine facies is gradual (Fig. 3). All these features lead us to conclude that the progradations of the fluvial systems resulted from oscillations of base level, perhaps related to 'pulses' of subsidence in the centre of the basin due to fluctuations of the rate of subsidence. The unconformable nature of the lower boundary (unconformity recorded as a shift of depocentres with respect to those of the underlying TSU 3) and theupper boundary (unconformity due to a tectonic phase with faulting and folding related to adaptation to subsurface fractures) of this rock unit indicates that these three cycles form a single TSU. TSU 5 This unit rests discordantly upon TSU 4 but in positions topographically lower than it. It is represented by alluvial-fan deposits (gravels) in the northern and southern borders, whereas in central areas, where it is located E of the Pisnerga River, it consists of 5 to 15 m of fluvial conglomerates changing vertically to floodplain muds, pedogenic crusts and paludal carbonates. This TSU was previously interpreted as parl of the basin infill (Mediavilla & Dabrio, 1989). but recent research (Mediavilla et al., in press) has related it to basin emptying as the first terrace of this area. Controls of sedimentation Tectonics The main faults active from the Neogene to the Present reflect Late Hercynian basement fractures that were reactivated, faulting the surface, modifying landscapes, and creating and modi- fying the previously established areas of suhsidence. The Neogene sedimentary record of the Duero Basin illustrates the relationships of tectonics and sedimentation. Tectonics controlled the sedimentation of all TSUs in different ways in the various areas, as recordedin the unitsdescrihed. Increaseofactivity in the margins (TSU 2) produced retraction of lacustrine environ- ments, whereas decreasing activity favoured expansion of lacus- trine deposits (TSUs 1,2,4). Duringdeposition ofunit TSU4 there was a hybrid pattern with progradation of fluvial systems and expansion of lacustrine deposits. This was a result of accelerated diastrophicactivity in the central areas (subsidence) that promoted progradation of alluvial systems but decreasing activity in the margins that allowed expansion units and covering of marginal areas. Tectonics also influenced sedimentation by modifying paleogeo- graphies, creating and moving the low areas that focused the drainage pattern. These modifications of the geometry of the basin, and of the areas of sediment and fresh-water supply produced a diversity of facies patterns in the sedimentary record of the basin. Climate Evaporites are one of the most popular criteria used in interior basins as climatic indicators. Analysis ofclimaticvariationsduring the Miocene (Fig. 3) shows that deposition of saline materials occurred both in dry periods (TSUs 1.2) and humid periods (TSUs 3,4). It is noteworthy that maximum development occurred particularly in humid periods. According to this, it seems clear that climate was not a determining factor for the generation of evaporites. In our opinion, the disap- pearance of saline lakes cannot be related to a particular climatic evolution because, in the Duero Basin, the end of evaporite deposition coincided with a climatic trend to more arid conditions (TSU4). However, climate wasaveryimportant factor determining theamount ofwater that reached the basin and, eventually, also the 234 R. Mediavilla c1 a1 Fig.8. PalaeogeographicmapsfortheNeogeneTSU in IheDuero Basin. SymbolspsinFig. 7. The areaswith alluvial fansin exorheieregimearemspped with the present morphology in plan. (L f!j) a1e~awol6uos m auasoaled rJ auo~satu!l~auo~solop B (adA~ he) p104 J unsdA6 u!Sld pOOlj tine8 / I swalsk ~nnli o!aqJopua suej la!Anlle