Adjustment of a drainage network to capture induced base-level change: an example from the Sorbas Basin, SE Spain

Geomorphology 34 Ž2000. 271–289 www.elsevier.nlrlocatergeomorph

Adjustment of a drainage network to capture induced base-level change: an example from the Sorbas Basin, SE Spain Anne E. Mather ) Department of Geographical Sciences, UniÕersity of Plymouth, Drake Circus, Plymouth, DeÕon, PL4 8AA, UK Received 24 March 1999; received in revised form 27 December 1999; accepted 22 January 2000

Abstract Quaternary catchments in the south of the Sorbas Basin, SE Spain have been affected by two regionally significant river captures. The river captures were triggered by changes in regional gradients associated with sustained Quaternary uplift in the region of 160 m May1. The first capture occurred in the early Pleistocene and re-routed 15% of the original Sorbas Basin drainage into the Carboneras Basin to the south. The second occurred in the late Pleistocene and re-routed 73% of the original Sorbas Basin drainage to the east. This latter capture had dramatic consequences for base-level in the Sorbas Basin master drainage. Local base-level was lowered by 90 m at the capture site, 50 m at 7 km upstream and 25 m at 13 km upstream of the site. The base-level change instigated a complex re-organisation of the drainage networks in systems tributary to the master drainage over the ensuing period Žsome 100 ka.. After the capture, drainage systems closer to the capture site experienced a tenfold increase in incision rates over most of their network. Those located some 13 km upstream of the capture site experienced a fivefold increase in incision, although in this instance, the changes do not appear to have propagated to the headwater regions of the drainage nets. The sensitivity of individual catchments was largely governed by geological controls Žstructure and lithology.. The detailed network evolution in the most sensitive areas can be traced by reconstructing former drainage pathways using abandoned drainage cols and the alignment and degree of incision of the drainage networks. Three main stages of evolution can be identified which record the progressive spread of base-level changes from the master drainage. These are Stage 1 Žpre-capture.: original south-to-north consequent drainage; Stage 2 Žearly stage, post capture.: aggressive subsequent southwest-to-northeast and east–west drainage developed along structural lineaments first in the east of the area ŽStage 2a., and later in the west of the area ŽStage 2b.; and Stage 3 Žlate stage, post capture.: obsequent drainage developing on the topography of the Stage 2 drainage. All stages of the network evolution are associated with drainage re-routing as a function of river capture at a variety of scales. The results highlight the complex response of the fluvial system, and the very different geomorphological histories of adjacent catchments, emphasising the need for regional approaches for examining long-term changes in fluvial systems. q 2000 Elsevier Science B.V. All rights reserved. Keywords: base-level; river capture; drainage evolution; tectonics; SE Spain

1. Introduction )

Fax: q44-1752-233054. E-mail address: [email protected] ŽA.E. Mather..

Fluvial systems in areas of active tectonics are subjected to major shifts in behaviour in response to

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deformation. The response of an individual fluvial system will be dependent on Ža. the balance between magnitude and frequency of the tectonic activity compared to the available stream power and Žb. the sensitivity of the fluvial system to change, dependent on climate, geology and proximity to internal geomorphic thresholds. Responses to change are usually complex and both spatially and temporally variable as a function of the balance between these factors locally within a catchment. Most studies examining the response of a fluvial system to tectonics focus on systems where the balance between the scale of tectonic activity, the energy of the fluvial system, and the antecedent conditions of the drainage network combine to deflect the fluvial system Žsee for example, Alexander and Leeder, 1987; Jolley et al., 1990; Mulder and Burbank, 1993.. Particularly in areas undergoing epeirogenic uplift, however, river capture has been demonstrated to be the key modifier of the fluvial environment ŽHarvey and Wells, 1987; Harvey et al., 1995; Mather 1991, 1993a; Mather and Harvey, 1995; Calvache and Viseras, 1997.. River capture often has dramatic effects upon the affected drainage networks. River capture can lead to Ž1. reorganisation of drainage networks through beheading and diversion ŽBishop, 1995.; Ž2. the evolution of differing landscape configurations in adjacent river systems ŽTeeuw, 1991.; Ž3. variations in meander morphology ŽDeshaies and Weisrock, 1995.; Ž4. re-routing of sediment supply, effecting changes in sediment budgets ŽDingle and Hendey, 1984; Clayton, 1994.; Ž5. changes in river biota ŽWaters et al., 1994; Gollman et al., 1997; Hurwood and Hughes, 1998.; and Ž6. changes in local and regional base-levels ŽHarvey et al, 1995.. This paper examines the latter of the above scenarios — the impact of base-level changes associated with a river capture event in the Sorbas Basin, SE Spain. The river capture occurred within the late Pleistocene Žca. 100 ka, Harvey et al, 1995. and was principally driven by differential uplift. Resulting base-level changes in the affected area reached a maximum of ca. 90 m at the point of capture ŽHarvey et al, 1995.. Some 9 km upstream of this capture point base-level changes were restricted to ca. 45 m ŽHarvey et al, 1995.. It is the impact of this change on three drainage systems tributary to the main river which will be investigated. The study area covers

approximately 25 km2 . The complex evolution of the drainage networks since the base-level change will be traced using a combination of evidence from the geological record ŽPliorPleistocene sediments. and geomorphological record Ždrainage alignments, degree of incision, and capture cols..

2. Regional geology The Sorbas Basin is defined by the Sierra de los FilabresrBedar to the north and Sierra Alhamillar Cabrera in the south ŽFig. 1.. The east and west margins of the basin are poorly defined topographic highs. The Sierras are composed of Mesozoic and older basement rocks which can be broadly divided into the Nevado Filabride and Alpujarride nappes ŽFig. 1; Egeler and Simon, 1969; Garcıa-Hernandez ´ ´ et al., 1980; Sanz de Galdeano, 1990.. The Sorbas Basin is one of a series of east–west sedimentary basins developed in the Trans-Alboran shear zone ŽLarouziere ´ et al., 1988., a zone dominated by left-lateral movement within the internal zone of the Betics. The faulting helps define the Neogene Basins, generating localised variations in compression and extension directions over the period of basin evolution ŽKeller et al., 1995.. Within the Sorbas Basin, during the Quaternary, compression has been dominantly north–south, with associated east–west extension ŽMather and Westhead, 1993.. Within the Sorbas Basin, the maximum deformation during the PliorPleistocene occurred at the southern basin margin ŽMather and Westhead, 1993., where sediments of that age are tilted at 708 ŽMather, 1991; Mather and Stokes, 1996. and dragged into NNErSSW fault zones which have affected river terrace sediments of late Pleistocene age within the central basin ŽMather et al., 1991; Kelly and Black, 1996.. Uplift rates for this part of the basin have been calculated at 160 m May 1 over the PliorPleistocene ŽMather, 1991.. Rates were calculated using the current elevation of the last Žlower Pliocene. marine incursion into the region, and corrected for sea level fluctuation ŽMather, 1991.. Seismicity is still active with regular small magnitude events of less than four, and major earthquakes Žwith intensities of X on the Mercalli Scale. recorded in the historic record ŽWWW, 2000..

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273

Fig. 1. Regional setting of the study area Žmodified from Mather and Stokes, 1996..

The basin sedimentary fill ranges from Seravallian to Pliocene in age, and was dominated by ma-

rine conditions until the late Messinianrearly Pliocene ŽWeijermars, 1991., and then by terrestrial

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sedimentation during the Pliocene and early Pleistocene. Following the Pliocene, continued uplift stimulated incision of the drainage networks, as documented by Mather Ž1991, 1993a,b., Mather and Harvey Ž1995., Harvey et al. Ž1995. and Stokes Ž1997..

3. Geology of the selected catchments The area which forms the focus of this study is dominated by the catchment areas of three south-tonorth draining fluvial systems. These are, from west-

to-east, the Rambla de Mocatan, ´ Barranco Infierno, and Barranco de Hueli ŽFig. 2.. The Rambla de Mocatan ´ catchment is dominated by weak lithologies Ž PliorPleistocene conglomerates and sands, Messinian marls, and some carbonate, Fig. 2.. The Barranco Infierno shows a greater variety of lithologies, including some gypsum in the lower reaches. The Barranco de Hueli is dominated by the most resistant lithologies Žgypsum and some carbonates.. The structure within the study area is dominated by a NW–SE steeprreverse fault which forms a prominent topography bounding the northern outcrop of the PliorPleistocene sediments ŽFig. 2.. Other

Fig. 2. Geology of the study catchments.

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major structural lineaments include a set of NE–SW faults ŽFig. 2. which form part of a large left lateral NNW–SSE lineament which cuts through the basin ŽFig. 1. and is clearly visible on satellite imagery ŽMOPT Instituto Geografico Nacional, 1992.. Dip of ´ the local sediments is generally to the north, but is modified locally by both post-depositional faulting and by syn-sedimentary folding ŽMather and Westhead, 1993., producing complex local dip and strike patterns ŽFig. 2..

4. Early evolution of the drainage network (plio r pleistocene) The early evolution of the drainage networks in the Sorbas Basin has been documented by Mather Ž1991, 1993a,b, 1999. and Mather and Harvey Ž1995.. It is recorded in the final phase of basin fill, the Cariatiz Formation ŽMoras Member. and Gochar Formation ŽMather, 1991; Mather and Harvey, 1995..

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The fluvial systems, which are mainly represented by first generation conglomerates, have been distinguished using a combination of sedimentology and provenance ŽFig. 3.. In general terms, consequent drainage was centripetal towards the basin centre, comprising three fluvial systems from the basin margins and a fourth which axially drained the basin from west-to-east before exiting into the Carboneras Basin in the south where it fed a small PliorPleistocene marine fan-delta ŽMather, 1993b.. In the south of the Sorbas Basin, the original drainage network outlined above was substantially modified by two major river capture events. The earliest occurred in the early Pleistocene and isolated the study area from its former mountain source Ž1 on Fig. 1; Mather, 1993a.. The capture succeeded in re-routing 15% of the original Sorbas Basin drainage into the Carboneras Basin to the south. The second occurred in the later Pleistocene Žca. 100 ka; Harvey et al., 1995; 2 on Fig. 2. and re-routed 73% of the original Sorbas Basin drainage from the Carboneras Basin in the south to the Vera Basin in the east.

Fig. 3. PliorPleistocene fluvial systems of the Sorbas Basin Žmodified from Mather 1991..

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The study area examined in this paper is located in the south of the Sorbas Basin ŽFig. 1., where the modern drainage is incised into the PliorPleistocene sediments of the south-to-north draining Mocatan ´ System ŽMather, 1991; Mather and Harvey, 1995.. These sediments are sourced from the metacarbonates of the Alpujarride basement of the Sierra Alhamilla, and uplifted Tortonian sandstones ŽMather, 1993a.. The presence of the metacarbonates confirms continuity of the drainage between the Sierra Al-

hamilla in the south, where Alpujarride basement is exposed, and the PliorPleistocene drainage systems in the study area. This Mocatan ´ System drained into the west-to-east draining axial system ŽLos Lobos System of Mather, 1991; Mather and Harvey, 1995.. The sediments were isolated from their original headwater source areas by a major river capture during the early Pleistocene by the west-to-east draining Rambla Lucainena ŽFig. 1.. This was an aggressive subsequent drainage which headcut paral-

Fig. 4. Schematic cross-section showing the impact of the Rambla de Lucainena capture on the study area ŽPliocene represents Mocatan ´ System, Gochar Formation. Ža. before capture by the Rambla de Lucainena: south-to-north study area drainages still connected to Sierra Alhamilla source, and Žb. after capture by the Rambla de Lucainena: south-to-north study area drainages isolated from the Sierra Alhamilla by the valley of the Rambla Lucainena. Sketch is some 6 km across.

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lel to the mountain front, along the weaker lithologies of the Tortonian sands and marls ŽFigs. 1 and 4; Mather, 1993a; Mather and Harvey, 1995.. The modern Rambla de Mocatan ´ river system now drains from the Risco de Sanchez ridge ŽFig. 4., starting some 3 km basinward from the mountain front. The top of the PliorPleistocene fill is truncated by an erosional geomorphic surface on which a mature calcrete is developed ŽStage V–VI, after Machette, 1985.. This surface grades into the uppermost river terrace sequence of the axial Sorbas Basin drainage Žterrace A of Harvey et al., 1995.. The modern drainage network developed in response to incision of the main end-Pliocene river systems as observed in many of the sedimentary basins in the region ŽMather, 1991; Mather and Harvey; 1995; Viseras, 1991; Stokes, 1997; Stokes and Mather, 2000; Calvache and Viseras, 1997.. The incision is recorded by a well-developed suite of river terraces ŽHarvey and Wells, 1987; Harvey et al., 1995.. The drainage outlet for the Sorbas Basin continued through the topographic low between the Sierras Alhamilla and Cabrera until the late Pleistocene. This is documented by three levels of river terraces ŽA, oldest, to C of Harvey and Wells, 1987.. Sometime between terrace C Žca. 100 ka, Harvey et al., 1995. and terrace D, an aggressive subsequent drainage, the Rio Aguas, headcut from the Vera Basin located to the east, along the strike of weak Messinian marls and re-routed the master drainage of the Sorbas Basin out to the east ŽFig. 1.. This capture ŽAguasrFeos capture of Harvey and Wells, 1987. had profound implications for the lowering of baselevel in the Sorbas Basin ŽHarvey et al., 1995.. At the point of capture Ž2 on Fig. 1. the base-level has been lowered some 90 m since the capture event Ži.e. post terrace C, ca. 100 ka, Harvey et al., 1995.. The study area is located upstream of the AguasrFeos capture site. As the capture-induced erosion progressed up through the Sorbas Basin, its magnitude became less, reaching about 45 m of vertical incision at Sorbas since the late Pleistocene ŽHarvey et al., 1995.. Beyond Sorbas transmission of the later stages of the base-level change to the west is inhibited by nick points reflecting lithological changes in the main river bed Žthe river system drops 20 m over 1 km.. Within the study area, the catchments had already been erosionally detached from

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their source areas by the Rambla Lucainena in the late Pleistocene. Thus, headwater controls such as variation in water and sediment discharge were largely removed and the study area became dominated by the base-level changes in the axial basin drainage Žthe Rio Aguas.. This part of the evolution is recorded in the geomorphology of the study area via features such as the drainage network alignment, degree of incision, and the positioning of numerous capture cols. These data are described below and used to reconstruct the evolution of the drainage through the Quaternary.

5. Strategy A detailed drainage map was constructed using the contour crenulations and blue line network from

Fig. 5. Drainage networks in the study area.

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Fig. 6. Detail of 1–2 and 2a–b captures at the watershed of the Rambla Mocatan ´ and Barranco Infierno catchments. Stage 2a relates to the Barranco Infierno and Stage 2b to the Rambla Mocatan. ´ For location see Fig. 5.

the 1:25 000 Mapa Topografico Nacional de Espana ´ ˜ series Ž1031-I and 1031-III. supplemented with detail from 1:30 000 black and white aerial pho-

tographs. Observations on known PliorPleistocene Žbased on work on the Gochar Formation by Mather, 1991, 1993a. and modern drainage alignments were then used to determine significant modifications in the drainage network. Within the modern topography, 27 potential capture cols were identified ŽFig. 5.. The capture cols were distinguished from simple erosional lows between drainage divides using a combination of Ža. their positioning and alignment within the drainage network Žsee for example Fig. 6.; Žb. the presence of well developed pedogenic carbonate accumulation ŽStage III–IV, after Machette, 1985. in the base of the oldest and highest cols indicating long term stability; and Žc. dramatic truncation of the cols by incision Žup to 60 m. of oblique drainage alignments. The relative positioning of the cols within the catchments and their elevation above mean sea level was calculated using 1:25 000 and 1:10 000 topographic maps. The above data facilitated the division of the network into three basic drainage stages: ŽStage 1. original consequent drainage; ŽStage 2. aggressive subsequent drainage;

Fig. 7. Plots of the capture cols and regression line for 1–2 cols in a north–south transect through the study area. Horizontal axis given as Eastings Žm. from 1:25 000 topographic map. Altitude is in m.a.s.l.

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and ŽStage 3. obsequent drainage. The relative spatial positioning of the cols within the drainage network, combined with their relative altitude could then be used to allocate a relative temporal position within the drainage network Že.g. 1–2 col: an original consequent captured by an aggressive subsequent; 2–3 col: an aggressive subsequent captured by an obsequent.. These data were then plotted along

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a south-to-north axis Žapproximately parallel to the central axis of the catchment areas. for two of the main catchments ŽBarranco Infierno and Rambla Mocatan, ´ Fig. 7.. Regression lines were fitted to the data sets to give an indication of the overall catchment gradient ŽFig. 7.. Insufficient data were available to develop such a plot for the Barranco de Hueli.

Fig. 8. Plots of the relative PliorPleistocene surface, 1–2 cols regression line and modern drainage profile in a north–south transect through Ža. the Barranco Infierno and Žb. the Rambla Mocatan. ´ Horizontal axis given as Eastings Žm. from 1:25 000 topographic map.

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6. The Quaternary drainage network configuration Using the strategy outlined above, three basic elements to the drainage network can be recognised ŽFig. 5.. Stage 1. Original consequents: rivers orientated S–N or SSW–NNE, paralleling the dominant drainage directions recorded in the PliorPleistocene sediments ŽMather, 1991, 1993a.. Stage 2. Aggressive subsequents: rivers orientated oblique to the consequent drainage Žfrom E–W to WSW–ENE.. Typically these exploit structural weaknesses such as fault alignments Žcontrast Figs. 2 and 5.. Stage 2 can be further subdivided into a more incised network in the east ŽStage 2a. which is truncated by later Stage 2b drainage in the west ŽFig. 6.. Stage 3. Obsequents: gully networks orientated oblique to Stage 2 above, typically with a N–S orientation. Within the above framework, the following cols can be identified: 1–2 Cols: original consequent drainage cols isolated by pirating aggressive subsequent drainage. These are typically elevated between 575 and 425 m, depending on their relative position within the catchment ŽFigs. 7 and 8.. The cols are typically floored by well developed pedogenic calcretes ŽStage III–IV after Machette, 1985. and inset some 12–80 m below the PliorPleistocene geomorphic surface depending upon their location within the catchment ŽFig. 8.. 2a–2b Cols: early aggressive subsequent drainage in the east ŽStage 2a. captured by later aggressive subsequents in the west ŽStage 2b; Figs. 6 and 7.. 2–3 Cols: aggressive subsequent cols isolated by pirating obsequent drainage. These are typically elevated around 450 m, depending on their relative position within the catchment ŽFig. 7. and inset some 75 m below the PliorPleistocene geomorphic surface ŽFigs. 7 and 8.. 7. The study catchments 7.1. Barranco de Hueli The Barranco de Hueli, some 5.5 km above the AguasrFeos capture site, has a relatively lower

drainage density than the other two catchments ŽFig. 5. and is dominated by deeply incised Ž70 m deep. canyons. The long profile is very similar to the Barranco Infierno, with a sharp nick point at about 5 km from its source ŽFig. 9. where it passes over a collapsed cave system within gypsum. Evidence of capture modification is present but limited ŽFig. 5.. 7.2. Barranco Infierno The Barranco Infierno catchment is some 7 km above the AguasrFeos capture site and demonstrates the most significant modification by river capture ŽFig. 5.. A plot of the 1–2 Žoldest. cols for the catchment indicates a catchment gradient for Stage 1 drainage of around 0.405 ŽFig. 7., inset some 40 m below the PliorPleistocene geomorphic surface ŽFig. 8.. Most river sections form incised canyons through the stronger lithologies Žcarbonate and gypsum., although aggressive subsequent drainage has created small areas of badlands in the weaker PliorPleistocene sands and gravels ŽFig. 5.. The modern river profile shows a pronounced nick point at about 5.5 km from source ŽFig. 9. associated with an active cave system in gypsum. The modern cave system consists of two main levels joined by a pitch of 30 m, and associated with one main fossil gallery ŽSO010 Plans 3 and 4, Catalogo General de Cavidades ´ del Karst de Yesos de Sorbas, Almeria.. The current base-level difference between the Barranco Infierno above and below the cave system is some 40 m, most of which is taken up in the main 30 m pitch. 7.3. Rambla Mocatan ´ The Rambla Mocatan ´ is some 13 km above the AguasrFeos capture site and has undergone significant modification by river capture ŽFig. 5.. A plot of the 1–2 Žoldest. cols for the catchment indicates a catchment gradient around 0.341, ŽFig. 7., inset some 35 m below the PliorPleistocene geomorphic surface ŽFig. 8.. The modern river profile is broadly parallel to the other two catchments in its mid-sections, but is dramatically steeper in its headwater reaches ŽFig. 9.. As a function of the predominance of weaker lithologies in this catchment, the most prolific and laterally most extensive valleys and associated badlands are found in this catchment ŽFig. 5.. The badland areas are dominated by complex

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Fig. 9. Long profiles for the three main catchment areas drawn from 1:25 000 topographic map.

piping ŽSpivey, 1997; Alexander et al, 1999.. Locally, the piping forms an extensive subsurface drainage network, with vertical drops of 15 m and horizontal galleries, which can be 2 m or more in height. This extensive erosion post-dates agricultural terracing in the study area, and is actively developed into newly developed agricultural tracks. It is clear from ŽFigs. 5, 7 and 8. that of the three catchments studied, most of the drainage re-organisation through river capture has occurred in the Rambla Mocatan ´ and Barranco Infierno. As a function of the narrow nature of many of the valleys in these two catchments and active erosion, few terraces are preserved. What is clearly in evidence, however, is the development of an extensive flat-bottomed valley fill some 4 m thick. The age of this is unclear. It is not associated with any well-developed soil profiles, but predates the agricultural terracing.

8. The Quaternary drainage network evolution Combining both the geological and geomorphological information, it is possible to reconstruct the

sequential development of the fluvial drainage and associated landforms, and ascertain the key controls on the landscape over the Quaternary Žsee Fig. 10 and Table 1 for summaries.. The oldest Ž1–2. cols located within the catchment area would appear to relate to the earliest stages of Pleistocene drainage evolution, prior to the AguasrFeos capture Ži.e. terraces A to C of Harvey and Wells, 1987; Harvey et al., 1995.. This can be inferred from a number of lines of evidence. Firstly, the degree of incision into the PliorPleistocene geomorphic surface associated with the 1–2 cols Ži.e. the Stage 1 drainage. is broadly similar between the Mocatan ´ and Infierno catchments. It is only the post Stage 1 drainage that shows the dramatic differences in incision between these sites ŽFigs. 7–9.. Secondly, if the general trend line for the cols Ži.e. Stage 1 catchment. is extended to the main axial drainage Ž600 on the horizontal axes of Fig. 8., the surface would lie above or at the terrace C level Žpre-capture terrace. of Harvey and Wells Ž1987. and Harvey et al. Ž1995.. In the case of the Barranco Infierno, the catchment associated with the Stage 1 drainage would lie at an elevation of approximately 410 q ry 30 m.

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Top terrace C for the axial drainage occupies a surface at about 380 m at this point ŽHarvey et al., 1995.. In the case of the Rambla de Mocatan, ´ the projected Stage 1 catchment would occupy a level of 430 q ry 20 m, placing it at a similar level to the top C terrace of the axial drainage in this part of the basin Ž430 m, Harvey et al., 1995.. It would therefore seem logical that the Stage 1 drainage, recorded in the preserved 1–2 cols, relates to the early and middle Pleistocene evolution of the drainage system, i.e. the development of terraces A–C ŽHarvey et al., 1995.. This type of age is also hinted at by the mature calcretes developed within some of the 1–2 drainage cols. 8.1. Stage 1. Pre-capture scenario (early and middle Pleistocene) The Barranco Infierno and Rambla Mocatan ´ show broadly similar evolutions up until the incision which post dates terrace C in the basin centre. Both catchments incised a similar amount Žsome 40 m. into the PliorPleistocene surface ŽFig. 8.. The early drainage associated with these two catchments and the Barranco de Hueli were dominated by N–S and NNE– SSW orientated original consequent drainage ŽFig. 10a.. 8.2. Stage 2. Early post-capture drainage (post 100 ka) Within a relatively short-time period, the consequent drainage of Stage 1 was truncated by the development of aggressive subsequent drainage of Stage 2. This lead to the preservation of the early ŽStage 1. drainage network in the form of the 1–2 cols ŽFigs. 5, 7 and 8.. Taking into account the fact that the Stage 1 drainage had incised down to approximate terrace C levels prior to modification,

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Stage 2 would appear to post date terrace C, and thus could be related to the base-level changes instigated in the axial drainage by the AguasrFeos river capture. Stage 2 can be further subdivided into a relatively earlier Stage 2a drainage in the east and a later, cross-cutting Stage 2b in the west. This is suggested by two lines of evidence: Ž1. Stage 2a drainage cols of the Barranco Infierno system are themselves truncated and captured by Stage 2b drainage cols of the Rambla Mocatan ´ ŽFig. 6. and Ž2. that unlike the Barranco Infierno catchment to the east, the lower level of the Mocatan ´ Stage 1 catchment falls slightly lower than comparable terrace C levels, implying that incision occurred for longer. The most severe modifications to the catchments post Stage 1 drainage development occurred in the east where the base-level changes were at a maximum. Taking the lower level of the Stage 1 drainage Žthus making figures comparable with the base-level changes estimated by Harvey et al., 1995; taken from the base of the C terrace. some 50 m of incision occurred post the AguasrFeos capture ŽFig. 8a.. In the west, the post capture incision was restricted to some 25 m ŽFig. 8b.. Thus it would appear that the development of the major subsequent drainage occurred first in the east ŽFig. 10b. and then progressed further west ŽFig. 10c.. Thus, assuming that the PliorPleistocene surface is 1.6 Ma, and that the lower level of the Stage 1 drainage corresponds to terrace C Žca. 100 ka, Harvey et al., 1995., we can estimate the rate of change of incision associated with the base-level changes in the Rio Aguas master drainage. The data would suggest that 7 km upstream of the capture site incision rates increased tenfold in tributary catchments whilst 13 km upstream of the capture site the incision increased fivefold, post the AguasrFeos capture. It would also appear that the effects of the base-level changes in the more westerly catchments did not propagate to the headwater regions of the drainage networks ŽFig. 9.. Not all the

Fig. 10. Quaternary development of the drainage Ža. Stage 1, early and middle Pleistocene drainage Žbefore AguasrFeos capture.; Žb. development of Stage 2a late Pleistocene drainage as AguasrFeos base-level changes are felt in the east of study area; Žc. progressive development of Stage 2b late PleistocenerHolocene drainage as AguasrFeos base-level changes are felt in the west of study area; Žd. the Stage 3 modern drainage network configuration. For a fuller discussion of these changes, see text. Numbers indicate Ž1. Barranco de Hueli; Ž2. Barranco Infierno; and Ž3. Rambla Mocatan. ´

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Table 1 Summary of the spatial and temporal evolution of the Quaternary drainage systems in the study area Sorbas Basin terrace equivalent ŽHarvey and Wells, 1987.

Main control

Response

Area affected

Features developed

Stage 1: early–mid Pleistocene

A–C

Ø previous topography Ø uplift

Ø maintenance of Stage 1 consequent drainage

all

Ø S–N and SSW–NNE drainage

Ø base-level changes in master drainage in east of area

Ø tenfold increase in incision rates of tributaries, headward erosion and development of Stage 2a aggressive subsequent drainage Ø capture of Stage 1 consequent drainage by Stage 2a drainage

east

Ø E–W and WSW–ENE drainage

east

Ø 1–2 cols developed

Ø fivefold increase in incision rates of tributaries, headward erosion and development of Stage 2b aggressive subsequent drainage Ø capture of Stage 1 consequent drainage and Stage 2a aggressive subsequent drainage by Stage 2b aggressive subsequent drainage Ø local base-levels developed, erosion restricted

west

Ø E–W and WSW–ENE drainage

west

Ø 1–2 cols and 2a–2b cols developed

central

Ø erosion and sediment supply

Ø Stage 3 badland and gully development Žobsequent drainage. Ø capture of Stage 2 aggressive subsequent drainage by Stage 3 obsequent drainage Ø aggradation

Ø aspect and geology Ø human activity

Ø expansion of badlands via piping, gullying and capture

Aguasr Feos riÕer capture Stage 2a: late upper D Pleistocene

Stage 2b: late Pleistocener Holocene

lower D

Ø base-level changes in master drainage in west of area

Ø expansion of karst drainage in gypsum Stage 3: Holocene

Stage 3: recent

E

Ø lithology and structure

east

central

Ø badlands and north–south gully development Ø 2–3 cols developed

all

Ø flat valley fills

central

Ø badlands and north–south gullying, piping and capture

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Relative timing

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post-capture evolution of the catchments was dominated by incision, however. The development of a valley fill some 4 m thick in the Stage 2 drainages suggests a period of catchment-wide aggradation. This valley fill may well correspond to the aggradational E terraces Žradiocarbon dated at 2310 q 80ry 90; Harvey and Wells, 1987. found elsewhere in the region. 8.3. Stage 3. Later post-capture drainage Stage 3 obsequent drainage is most clearly developed in the Barranco de Mocatan ´ catchment, developing 2–3 cols ŽFig. 5.. This in part must reflect the more sensitive nature of this catchment to any baselevel changes, as the catchment is developed on weakly consolidated silts, sands and gravels. This has led to rapid lateral expansion of the drainage network and the development of the relatively wide valley associated with the drainage networks of the Rambla Mocatan. ´ In the Barrancos Infierno and Hueli in the east, the sensitivity of the catchments is greatly inhibited by the presence of gypsum and carbonates.

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These lithologies restricted the lateral development of many of the valleys, resulting in narrow, incised canyons. In addition, the gypsum is associated with both active and collapsed karst systems which have isolated the upper reaches of these systems Ži.e. above ca. 5 km from source, Fig. 9. from the impacts of base-level changes in the Rio Aguas. Above the nick points associated with these systems ŽFig. 9., the river systems have been buffered from the last 30 m of incision of the Rio Aguas ŽFig. 9.. With continued incision into the weak lithologies, the Stage 3 gullies developed the badland landscape visible today. These gullies and associated piping are today leading to additional re-routing of water and sediment within the badland network via micro-piracy ŽFig. 11.. In some instances, this appears to be aspect controlled, with more active gully development on south-facing slopes ŽFig. 11., driving the pirating gully systems. Sub-surface piping has also re-routed Stage 2b drainages. The positioning of the pipe and gully systems appears to be closely aligned with joints within the Gochar Formation sediments ŽSpivey, 1997. which have developed as a combination of tectonic stresses ŽMather and Westhead 1993.

Fig. 11. Stages 1–3 drainage in the Rambla de Mocatan ´ area of the study site. North is to the right of the image. Arrows indicate direction of drainage. Note imminent capture of Stage 2b drainage by Stage 3, south facing gully. Also note flat-bottomed valley fill of some Žpiped. Stage 2b drainages. Stage 3 gully face is cut into slopes some 20 m in height.

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and Pleistocene landslide activity Žcurrently under investigation..

9. Discussion The development of the system is clearly influenced by several key factors intrinsic and extrinsic to the study area Žsee Table 1.. 9.1. Intrinsic controls Intrinsic controls include the geology of the catchment. The strike of both structural lineaments and bedding ŽFig. 2. has influenced the development of Stage 2 aggressive subsequent streams and Stage 3 obsequent gullies. Local dominance of sand and silt lithologies has encouraged the development of extensive badland areas ŽFig. 5.. In addition, the geology has controlled the relative sensitivity of the Barrancos Infierno and Hueli. In both cases, the gypsum served to buffer the areas upstream of the cave systems from the later continued incision of the Rio Aguas. The Barranco de Hueli was the least sensitive to change, due to the dominance of gypsum and carbonates in the catchment area inhibiting the lateral development of the drainage network. The geology is thus important in governing the sensitivity of the local regions of the catchments to extrinsic controls such as climate and tectonics. 9.2. Extrinsic controls: tectonics The development of drainage over the Quaternary is at a time scale sufficient to reflect long-term controls such as tectonics. Uplift in excess of 160 m May1 has been affecting the region throughout the Quaternary ŽMather, 1991., together with both compressional and strike-slip faulting ŽMather and Westhead, 1993.. This uplift has affected regional gradients, which stimulated many river captures ŽHarvey and Wells, 1987; Mather, 1999; Mather and Harvey, 1995.. Notably the AguasrFeos capture in the late Pleistocene ŽHarvey and Wells, 1987. accelerated incision, lowering base-level by 90 m at the capture point ŽHarvey et al., 1995., and some 25 m at the study site located some 13 km upstream of the

capture point. This base-level change has been significant in stimulating a progressive east-to-west reactivation of erosion in the Rio Aguas master drainage and its tributaries ŽFig. 10.. Transmission of the base-level changes west of Sorbas would have been inhibited in the later stages by nick points developed in more resistant lithologies. 9.3. Extrinsic controls: climate Climate over the course of the PliorPleistocene has undergone many fluctuations related to European glacials and interglacials ŽHarvey et al., 1995.. This has stimulated alternating trends in aggradation and degradation within the catchments, depending on the net increaserdecrease in effective run off and sediment supply. In general, aggradation has been associated with European glacials when the local climate was cold, dry and stormy. The more arid climate would have led to less vegetational stabilisation of slopes and thus accentuated erosion. The major incision was associated with milder, more humid European interglacials linked with increased vegetation cover and associated slope stability ŽAmor and Florschutz, 1964; Butzer, 1964; Sabelberg, 1977; Rhodenburg and Sabelberg, 1980; Harvey, 1987; Harvey et al., 1995.. Thus, regional climatic change may have driven some of the general incisionraggradation trends seen within the Sorbas Basin and study area. The fine-grained valley fills found within the study area may well reflect increased sediment supply associated with enhanced human activity in the Holocene. This was thought to be responsible for similar sedimentation Žterrace E. seen elsewhere in the Province and dated as Holocene ŽHarvey and Wells, 1987; Harvey et al., 1995.. 9.4. Extrinsic controls: anthropogenic influences Human influence is apparent within the region on both an historic and recent basis. Within the Mocatan ´ catchment, agricultural terraces are prolific and cut by Stage 3 gully systems. Much of the early terracing in this area reflects the expansion of agriculture associated with Moorish occupation of Spain in the Eleventh Century A.D. ŽSutton, 1999.. If the old stone terraces here are Moorish, this would suggest

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that much of the badland expansion has occurred within the last 1000 years. The agricultural terracing, once abandoned, may have locally stimulated degradation by affecting local geomorphological and hydrological conditions Že.g. local slope and hydraulic gradients and infiltration rates., as observed in adjacent areas ŽSpivey, 1997.. Active expansion of agricultural terraces over the last decade and the creation of service tracks has dramatically affected the landscape in the catchment. Compaction of surfaces, removal of vegetation, foreshortening of gully systems, and oversteepening of slopes from cut and fill terrace development have all exacerbated problems with slope stability. This has accentuated pipe and gully development with tracks being destroyed by piping within a year of construction. Clearly, the large Žbasinal. scale modifier of the fluvial environment has been river capture driven by regional tectonics and their impact on regional gradients. This has instigated major scale base-level changes, which have affected erosion patterns within the study area. On the smaller Žcatchment. scale, the change in base-level, combined with varied sensitivities of the geology associated with the study area, have led to a very complicated reorganisation of the drainage net. The end product of the complex drainage reorganisation is a series of adjacent valleys which each have very different geomorphological histories which can only be understood when placed in the wider context of the drainage network development.

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The main extrinsic controls on the drainage evolution in the study area have been Ž1. the regional tectonics which have stimulated river capture which has led to Ž2. erosional detachment of the source areas of the original consequent drainages in the early Pleistocene, removing the influence of upstream controls such as fluctuations in sediment and water discharge to the drainage system and thus led to the dominance of Ž3. base-level changes bought about by the incision of the Rio Aguas master drainage following the AguasrFeos capture which acted as the main stimulus for incision assisted by Ž4. the climate which regionally controlled sediment supply and effective run-off and thus may have helped to drive rates of aggradationrdegradation within the study area. The study clearly demonstrates the complexities in drainage development that can occur in the longterm record, in this case principally driven by baselevel changes. These base-level changes varied spatially, and induced a tenfold increase in erosion rates in the east of the study area, but only a fivefold increase some 6 km further upstream. Each valley demonstrates a markedly different history of evolution as a function of the dramatic and complex responses of the drainage network to the base-level change. The study emphasises how the local drainage development is only understandable in the context of the regional picture.

Acknowledgements 10. Conclusions Controls intrinsic to the study area have played an important role in governing the sensitivity of the drainage networks to external changes. This sensitivity varies with the geological characteristics of the study area: Ž1. structural Žstrike, fault, and jointing. controls on drainage alignment; Ž2. lithological controls on the erodibility of the sediments and thus the rate of drainage net expansion and badland development; and Ž3. geological controls on the development of subsurface drainage. Where the subsurface drainage has developed, it has served to buffer upstream areas from continuing downstream base-level changes.

The author would like to thank Tim Absolom from the Cartographic Unit, University of Plymouth for drafting the figures, Lindy Walsh of Cortijo Urra for supporting the field work, and Adrian Harvey, Martin Stokes, Roy Alexander, Cesar Viseras, and Larry Mayer for reviewing various versions of the manuscript.

References Alexander, J., Leeder, M.R., 1987. Active tectonic control on alluvial architecture. In: Etheridge, F., Flores, G., Harvey, R.M. ŽEds.., Recent Developments in Fluvial Sedimentology.

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Society of Economic Paleontologists and Mineralogists, Special Publication 39, pp. 243–252. Alexander, R., Spivey, D.B., Faulkner, H., Willshaw, K., 1999. Badland morphology and geoecology, Mocatan ´ System: processes and patterns. In: Mather, A.E., Stokes, M. ŽEds.., BSRGrBGRG SE Spain Field Meeting Guide Book. University of Plymouth, pp. 134–151. Amor, J.M., Florschutz, F., 1964. Results of the preliminary palynological investigation of samples from a 50 m boring in southern Spain. Boletin de la Real Sociedad Espanola de Historia Natural ŽGeologia. 62, 251–255. Bishop, P., 1995. Drainage rearrangement by river capture, beheading and diversion. Progress in Physical Geography 19, 449–473. Butzer, K.W., 1964. Climatic-geomorphologic interpretation of Pleistocene sediments in the Eurafrican sub-tropics. In: Howell, F.C., Bouliere, F. ŽEds.., African Ecology and Human Evolution. Methuen, London, pp. 1–25. Calvache, M., Viseras, C., 1997. Long-term control mechanisms of stream piracy processes in southeast Spain. Earth Surface Processes and Landforms 22, 93–105. Clayton, C.J., 1994. A rock volume accumulation curve for the late Ordovician–Silurian Welsh basin. Geological Magazine 131 Ž4., 539–544. Deshaies, M., Weisrock, A., 1995. Amplitude of incised Quaternary meanders and river-basins area in north-eastern France — palaeogeographic implications. Geodinamica Acta 8 Ž1., 33–55. Dingle, R.V., Hendey, Q.B., 1984. Late Mesozoic and Tertiary sediment supply to the eastern Cape Basin ŽSE Atlantic. and palaeo-drainage systems in southwestern Africa. Marine Geology 56, 13–26. Egeler, C.G., Simon, O.J., 1969. Orogenic evolution of the Betic zone ŽBetic Cordilleras, Spain. with emphasis on nappe structure. Geologie en Mijnbouw 48, 296–305. Garcıa-Hernandez, M., Lopez-Garrido, A.C., Rivas, P., Sanz De ´ ´ ´ Galdeano, C., Vera, J.A., 1980. Mesozoic palaeogeographic evolution of the external zones of the Betic Cordillera. Geologie en Minjnbouw 59, 155–168. Gollmann, G., Bouvet, Y., Karakousis, Y., Triantaphyllidis, C., 1997. Genetic variability in Chondrostoma from Austrian, French and Greek rivers ŽTeleostei, Cyprinidae.. Journal of Zoological Systematics and Evolutionary Research 35, 165– 169. Harvey, A.M., 1987. Patterns of Quaternary aggradational and dissectional landform development in the Almeria region, southeast Spain: a dry-region tectonically-active landscape. Die Erde 118, 193–215. Harvey, A.M., Miller, S.Y., Wells, S.G., 1995. Quaternary soil and river terrace sequences in the AguasrFeos river systems: Sorbas Basin, southeast Spain. In: Lewin, J., Macklin, M.G., Woodward, J.C. ŽEds.., Mediterranean Quaternary River Environments. Balkema, Rotterdam, pp. 263–281. Harvey, A.M., Wells, S.G., 1987. Response of Quaternary fluvial systems to differential epeirogenic uplift: Aguas and Feos river systems, southeast Spain. Geology 15, 689–693. Hurwood, D.A., Hughes, J.M., 1998. Phylogeography of the

freshwater fish, Mogurnda adspersa, in streams of northeastern Queensland, Australia: evidence for altered drainage patterns. Molecular Ecology 7, 1507–1517. Jolley, E.J., Turner, P., Williams, G.D., Hartley, A.J., Flint, S., 1990. Sedimentological response of an alluvial system to Neogene thrust tectonics, Atacama Desert, northern Chile. Journal of the Geological Society ŽLondon. 147, 785–794. Keller, J.V.A., Hall, S.H., Dart, C.J., McClay, K.R., 1995. The geometry and evolution of a transpressional strike-slip system: the Carboneras fault, SE Spain. Journal of the Geological Society ŽLondon. 152, 339–351. Kelly, M., Black, S., 1996. Uranium–thorium dating of calcretes at Urra. In: Mather, A.E., Stokes, M. ŽEds.., 2nd Cortijo Urra Field Meeting, SE Spain: Field Guide. University of Plymouth, p. 71. De Larouziere, ´ F.D., Bolze, J., Bordet, P., Hernandez, J., Montenat, C., Ott d’Estevou, P., 1988. The Betic segment of the lithospheric Trans-Alboran shear zone during the late Miocene. Tectonophysics 152, 41–52. Machette, M.N., 1985. Calcic soils of the southwestern United States. In: Weide, D.L. ŽEd.., Soils and Quaternary geology of the southwestern United States. Geological Society of America Special Paper 203, pp. 115–122. Mather, A.E., 1991, Cenozoic drainage evolution of the Sorbas Basin SE Spain, Unpublished PhD Thesis, University of Liverpool, 276 pp. Mather, A.E., 1993a. Basin inversion: some consequences for drainage evolution and alluvial architecture. Sedimentology 40, 1069–1089. Mather, A.E., 1993b. Evolution of a Pliocene fan delta: links between the Sorbas and Carboneras Basins, SE Spain. Tectonic Controls and Signatures in Sedimentary Successions. In: Frostick, L., Steele, R. ŽEds.., IAS Special Publication 20, pp. 277–290. Mather, A.E., 1999. Alluvial fans: a case study from the Sorbas Basin, southeast Spain. In: Jones, A.P., Tucker, M.E., Hart, J.K. ŽEds.., The Description and Analysis of Quaternary Stratigraphic Field Sections. Technical Guide 7 Quaternary Research Association, London, pp. 77–110. Mather, A.E., Harvey, A.M., 1995. Controls on drainage evolution in the Sorbas Basin, southeast Spain. In: Lewin, J., Macklin, M.G., Woodward, J. ŽEds.., Mediterranean Quaternary River Environments Balkema, Rotterdam, pp. 65–76. Mather, A.E., Harvey, A.M., Brenchley, P.J., 1991. Halokinetic deformation of Quaternary river terraces in the Sorbas Basin, southeast Spain. Zeitschrift fuer Geomorphologie 82, 87–97. Mather, A.E., Stokes, M., 1996. Impact of deformation on PliorPleistocene fanrfluvial systems in the Sorbas and Vera Basins, SE Spain. In: Mather, A.E., Stokes, M. ŽEds.., 2nd Cortijo Urra Field Meeting, SE Spain: Field Guide. University of Plymouth, pp. 58–70. Mather, A.E., Westhead, R.K., 1993. PliorQuaternary strain of the Sorbas Basin, SE Spain: evidence from sediment deformation structures. Quaternary Proceedings 3, 57–65. ´ MOPT Instituto Geografico Nacional, 1992, Aguilas Ortoimagen ´ Espacial, 1:100 000. Mulder, T.J., Burbank, D.W., 1993. The impact of incipient uplift

A.E. Matherr Geomorphology 34 (2000) 271–289 on patterns of fluvial deposition: an example from the salt range, In: Marzo, M., Puidefabregas, C. ŽEds.., Northwest Himalayan Foreland, Pakistan. Alluvial Sedimentation. IAS Special Publication 17, pp. 521–539. Rhodenburg, H., Sabelberg, U., 1980. Northwest Sahara margin: terrestrial stratigraphy of the Upper Quaternary and some palaeoclimatic implications. In: Van Sinderen Bakker, E.M. Sr., Coetsee, J.A. ŽEds.., Palaeoecology of Africa and the Surrounding Islands 12, pp. 267–276. Sabelberg, U., 1977. The Stratigraphic record of late Quaternary accumulation series in southwest Morocco and its consequences concerning the pluvial hypothesis. Catena 4, 204–215. Sanz de Galdeano, C., 1990. Geologic evolution of the Betic Cordilleras in the Western Mediterranean Miocene to the present. Tectonophysics 172, 107–119. Spivey, D., 1997, Scale, process and badland development in Almeria Province, PhD Thesis, University of Liverpool, 267 pp. Stokes, M., 1997, PliorPleistocene drainage evolution of the Vera Basin, SE Spain, PhD Thesis, University of Plymouth, 390 pp. Stokes, M., Mather, A.E., 2000, Tectonically induced base-level

289

changes of PliorPleistocene alluvial fan deposits, Vera Basin, SE Spain. Journal of the Geological Society ŽLondon.. Sutton, K., 1999. The Qanat irrigation system of the Campo de Tabernas, Almeria. In: Mather, A.M., Stokes, M. ŽEds.., 3rd Cortijo Urra Field Meeting, SE Spain: Field Guide. University of Plymouth, pp. 152–156. Teeuw, R.M., 1991. Comparative-studies of adjacent drainage basins in Sierra-Leone — some insights into tropical landscape evolution. Zeitschrift fuer Geomorphologie 35 Ž3., 257– 267. Viseras, C., 1991. Estratigrafia y sedimentologia del relleno aluvial de la cuenca de Guadix, PhD Thesis, University of Granada, 327 pp. Waters, J.M., Lintermans, M., White, R.W.G., 1994. Mitochondrial-DNA variation suggests river capture as a source of variance in gadopsis – bispinosus Ž pisces, gadopsidae.. Journal of Fish Biology 44, 549–551. Weijermars, R., 1991. Geology and tectonics of the Betic Zone, SE Spain. Earth Science Reviews 31, 153–236. WWW, 2000, Andalusian Institute of Geophysics, University of Granada Website http:rrwww.ugr.esriagreq – iageng.html.