Intracontinental endorheic basins are key elements of source-to-sink systems as they preserve sediments eroded from the surrounding
catchments. Drainage reorganization in such a basin in response to changing boundary conditions has strong implications on the
sediment routing system and on landscape evolution. The Ebro and Duero basins represent two foreland basins, which developed in
response to the growth of surrounding compressional orogens, the Pyrenees and the Cantabrian mountains to the north, the Iberian
Ranges to the south, and the Catalan Coastal Range to the east. They were once connected as endorheic basins in the early
Oligocene. By the end of the Miocene, new post-orogenic conditions led to the current setting in which the Ebro and Duero basins are
flowing in opposite directions, towards the Mediterranean Sea and the Atlantic Ocean. Although these two hydrographic basins recorded
a similar history, they are characterized by very different morphologic features. The Ebro basin is highly excavated, whereas relicts
of the endorheic stage are very well preserved in the Duero basin. The contrasting morphological preservation of the endorheic stage
represents an ideal natural laboratory to study the drivers (internal and/or external) of post-orogenic drainage divide mobility, drainage
network, and landscape evolution. To that aim, we use field and map observations and we apply the
Landscapes subjected to contrasted erosion rates between adjacent drainage basins show a migration of their drainage divide toward the
area of lower erosion rates (Bonnet, 2009; Willett et al., 2014). This is the case for mountain ranges characterized by gradients in
precipitation rates due to orography, once landscapes are in a transient state and are not adjusted to precipitation differences
(Bonnet, 2009). It also occurs when drainage was reorganized in response to capture (Yanites et al., 2013; Willett et al., 2014). River
capture actually drives a drop in the spatial position of drainage divide (Prince et al., 2011) but also produces a wave of erosion in
the captured reach (Yanites et al., 2013) that may impact divide position. Historically, migration of divides has been inferred by
changes in the provenance of sediments stored in sedimentary basins (e.g., Kuhlemann et al., 2001). It is however a process that is
generally very difficult to document in erosional landscapes. Recent developments have provided models and analytical approaches to
identify divide migration in the landscape (Bonnet, 2009; Castelltort et al., 2012; Willett et al., 2014; Whipple et al., 2017). Among
them the recently developed
The Ebro and Duero drainage basins in the northern Iberian Peninsula show geological and geomorphological evidence of very contrasted
erosional histories during the Neogene. They initially recorded a long endorheic stage from the early Oligocene to the late Miocene
(Riba et al., 1983; Garcia-Castellanos et al., 2003). Since then, both basins opened toward the Atlantic Ocean (Duero) or the
Mediterranean Sea (Ebro). The Ebro basin's opening is reflected in the landscape by evidence of river incision (Garcia-Castellanos
et al., 2003), whereas the Duero basin does not show significant incision in its upstream part as a large relict of its endorheic
morphology is preserved (Antón et al., 2012). The Duero River long profile actually shows a pronounced knickpoint (knickzone)
defining an upstream domain of high mean elevation (
Simplified geological map of the study area.
Topographic map of the study area with all the rivers considered in this study. The red lines represent drainage divides between main hydrographic basins.
Zoom of the geological map of the Iberian Range showing the location of the Jalón River tributaries. The river long profiles of these streams and the location of knickpoints are shown to the left.
The Ebro and Duero basins represent two hydrographic basins located in the northern part of the Iberian Peninsula (Fig. 1). The bedrock of the Ebro and Duero drainage basins mainly consists of Cenozoic deposits, and Mesozoic and Paleozoic rocks in their headwaters (Fig. 2). They once formed a unique flexural foreland basin during the Cenozoic controlled by the surrounding mountain belts: the Pyrenees and the Cantabrian mountains to the north (Pulgar et al., 1999), the Iberian and Central ranges to the south (Guimerà et al., 2004; De Vicente et al., 2007), and the Catalan Coastal Range (CCR) to the east (López-Blanco et al., 2000; Salas et al., 2001), during collision between Iberia and Europe since the Late Cretaceous.
From the Late Cretaceous, the Ebro and Duero basins were essentially filled by clastic deposits, and opened toward the Atlantic Ocean
in the Bay of Biscay (Alonso-Zarza et al., 2002). During the late Eocene–early Oligocene, the uplift in the Western Pyrenees
(Puigdefàbregas et al., 1992) led to the closure of the Ebro and Duero basins as attested by the Ebro basin continentalization
dated at
The Iberian Range (Figs. 2 and 4) is a double vergent fold-and-thrust belt resulting from Late Cretaceous inversion of Late Jurassic–Early Cretaceous rift basins during Iberia–Europe convergence (Salas et al., 2001; Guimerà et al., 2004; Martín-Chivelet et al., 2002). It is divided into two NW–SE-directed branches, the Aragonese and the Castilian branches, separated by the Tertiary Almazán subbasin (Bond, 1996). The Almazán subbasin has been connected to the Duero basin since the early Miocene (Alonso-Zarza et al., 2002).
The Iberian Range is essentially made of marine carbonates and continental clastic sediments ranging from late Permian to Albian, overlying a Hercynian basement. The Cameros subbasin to the NW represents a Late Jurassic–Early Cretaceous trough almost exclusively filled by continental siliciclastic deposits (Martín-Chivelet et al., 2002 and references therein; Del Rio et al., 2009). Shortening in the Iberian Range occurred from the Late Cretaceous to the early Miocene, along inherited Hercynian NW–SE structures (Gutiérrez-Elorza and Gracia, 1997; Guimerà et al., 2004; Gutiérrez-Elorza et al., 2002). The opening of the Calatayud basin in the Aragonese branch occurred during the Early Miocene in response to right-lateral transpression on the southern margin of the Iberian Range (Daroca area) (Colomer and Santanach, 1988). It is followed during the Pliocene and the Pleistocene by pulses of extension-reactivating faults in the Calatayud basin and the formation of grabens such as the Daroca, Munébrega, Gallocanta, and Jiloca grabens (Fig. 4; Colomer and Santanach, 1988; Gutiérrez-Elorza et al., 2002; Capote et al., 2002). This is also outlined by the occurrence of late Pliocene to Early Pleistocene breccias and glacis levels in the Daroca and Jiloca grabens (Gracia, 1992, 1993a; Gracia and Cuchi, 1993; Gutiérrez-Santolalla et al., 1996). These Neogene troughs are filled by continental deposits and pediments, up to the Quaternary (Fig. 4). The Neogene tectonic pulses in the Iberian are interrupted by periods of quiescence during which erosion surfaces developed (Gutiérrez-Elorza and Gracia, 1997).
Deformation and uplift of the Iberian Range and Cameros basin resulted in the development of a new drainage divide between the Duero and Ebro basins and in the isolation of the Almazán subbasin (Alonso-Zarza et al., 2002). In contrast, the connection between the Duero and Ebro basins has not been affected by significant deformation and uplift in the proto-Rioja trough (Mikes, 2010).
The Rioja trough (Figs. 2 and 5) recorded important subsidence, especially during the Cenozoic (
Climate exerts a major control on valley incision, sediment discharge, and on the evolution of drainage networks (Willet, 1999; Garcia-Castellanos, 2006; Bonnet, 2009; Whipple, 2009; Whitfield and Harvey, 2012; Stange et al., 2014). The mean annual precipitation map for the northern Iberian Peninsula (Hijmans et al., 2005) shows a similar pattern for both the Ebro and Duero basins as they record very low precipitation, associated with global subarid conditions, with the exception of the Cameros basin, which records a slightly higher precipitation rate (Fig. 6). There is a strong contrast to the north, toward the Mediterranean Sea and the most elevated areas in the Cantabrian and Pyrenean belts, where precipitation drastically increases.
The paleoclimatic evolution from the Late Cretaceous to the Neogene is linked with both the effects of surrounding mountain uplift,
and with the latitudinal variation drift of Iberia from 30
Glaciers are considered a very efficient erosion tool in a continental environment. They are likely to influence drainage divide
migration (Brocklehurst and Whipple, 2002). There is large evidence of glacier development, especially for the Late Pleistocene in the
Pyrenees (Delmas et al., 2009; Nivière et al., 2016; García-Ruiz et al., 2016), in the Cantabrian belt (Serrano et al., 2013,
2016; García-Ruiz et al., 2016), and in the Central Range (Palacios et al., 2011, 2012; García-Ruiz et al., 2016). However,
although numerous moraines have been mapped throughout the Iberian Range (Ortigosa, 1994; García-Ruiz et al., 1998; Pellicer and
Echeverría, 2004), there is no evidence of U-shaped valleys and because of the lack of very highly elevated massifs (
The easternmost part of the Duero River is opposed to the Ebro tributaries that are the Jalón, Huecha, Queiles, Alama, Cidacos, Iregua, and Najerilla rivers, whereas the Arlanzón and Pisuerga rivers (Duero tributaries) are opposed to the Najerilla, Tirón, Oca, and Rudrón rivers, and to the westernmost part of the Ebro River (Fig. 3). The northeastern part of the Duero basin (the easternmost Duero River, the Arlanzón and Pisuerga rivers) mainly consists of broad flat valleys characterized by low incision depth and low-gradient streams with concave longitudinal profiles (Antón et al., 2012, 2014). By contrast, the western part of the Ebro basin is characterized by more incised valleys, especially in the Cantabrian and in the Cameros–Iberian Range domains, with more complex longitudinal profiles (knickpoints, remnants of highly elevated surfaces). Previous studies (Gutiérrez-Santolalla et al., 1996; Pineda, 1997; Mikes, 2010) have already shown that the Jalón and Homino rivers, which belong to the Ebro basin, have recently captured parts of the Duero basin in the Iberian Range and in the Rioja trough, respectively. Such evolution has been recorded by the occurrence of geomorphological markers as wind gaps and elbows of captures, as well as by the presence of knickpoints and/or remnants of highly elevated surfaces in river long profiles. To highlight this dynamic evolution, we performed a morphometric analysis of rivers all around the divide separating the Ebro basin from the Duero basin, with particular attention given to the Aragonese branch of the Iberian Range (Fig. 4) and to the Rioja trough (Fig. 5), where captures have already been described.
The studied basins were digitally mapped using high-resolution (
Neogene tectonics in the Iberian range controlled the uplift of topographic ranges and the formation of several basins whose connection with the Ebro or the Duero has occasionally changed through time. Today, the western part of the Almazán subbasin (Figs. 2 and 4) belongs to the Duero catchment, its eastern part being drained by the Ebro drainage network and especially by the Jalón River and its tributaries (Fig. 4). Gutiérrez-Santolalla et al. (1996) proposed that the Jalón River captured this domain after cutting into the Mesozoic and Neogene strata and the two Paleozoic ridges of the Aragonese branch of the Iberian Range. They used chronostratigraphic evidence to build a relative chronology of capture events in the Jalón area. First, the incision of the northern Paleozoic ridge and capture of the Calatayud basin by the Jalón River is attributed to a post-Messinian age. The Jiloca River, the easternmost main Jalón tributary, is then thought to capture the Daroca graben area to the east during the late Pliocene–Early Pleistocene. This is followed from the Early to Late Pleistocene by the capture of the Jiloca graben to the southeast and finally by the capture of the Munébrega graben to the southwest, by the Jalón River (Gutierrez-Santolalla et al., 1996), toward the easternmost part of the Almazán subbasin.
The Jalón River and tributaries show knickpoints in their longitudinal profiles (Fig. 4), at locations that are consistent with the
events of captures proposed by Gutiérrez-Santolalla et al. (1996), suggesting that these captures are actually witnessed by
knickpoints. The capture of the Jiloca graben corresponds to a major knickpoint in the Jiloca River profile that appears very smoothed,
and that is followed by an upstream
According to Gutiérrez-Santolalla et al. (1996), the Jalón River reached the southern Paleozoic ridge of the Aragonese branch, to the southwest of the Calatayud basin, and captured the Munébrega graben and the Almazán subbasin (also characterized by a pronounced knickpoint) during the Pleistocene–Holocene, slightly after the capture of the Jiloca graben by the Jiloca River. This is coherent with morphological analysis of longitudinal profiles, as the major knickpoint related to the capture of the Jiloca graben appears very smoothed, whereas knickpoints observed in the west are sharper, suggesting they are younger. However we cannot rule out some local influence of the lithology on the shape of these knickpoints.
Finally, the Piedra River (Jalón tributary) long profile shows major sharp knickpoints and two successive
In the Rioja trough area, the position of the Ebro–Duero divide is partly controlled by the Bureba anticline. It consists of folded Middle Cretaceous to early Miocene series, covered by undeformed middle Miocene to Holocene deposits (Fig. 5). The anticline is orientated E–W to the west and NE–SW to the east. The western part of the Rioja trough to the west of the NE–SW-directed branch of the Bureba anticline (Fig. 5) used to be drained toward the Duero basin since the Oligocene (Pineda, 1997; Mikes, 2010). The westward migration of the divide to its current location is thought to have occurred in several steps of captures as shown by the occurrence of remnants of escarpments during the late Miocene–Pliocene (Mikes, 2010). Once the eastern branch of the Bureba anticline has been incised, the Ebro tributaries captured the western part of the Rioja trough, up to the E–W branch of the Bureba anticline to the southwest, from the late Miocene to the Pliocene. The western part of the anticline forms a topographic ridge that is incised by the Jordan River (Fig. 5) in a place where the divide between the Ebro and Duero river networks is located to the north of the ridge. To the east of this location, however, the topographic ridge formed by the Bureba anticline controls the current location of the main drainage divide (Fig. 5). Here, the ridge exhibits several wind gaps, located on the northward prolongation of the Hoz, Rioseras, and Nava Solo rivers (Figs. 5 and 7). Further east, the Diablo River does not incise the ridge and its headwater is located in the core of the eastern branch of the Bureba anticline, the Fuente Valley (Fig. 5). These last streams are tributaries of the Ubierna River, which is a tributary of the Arlanzón River and so, of the Duero River. To the north, the Ebro River system is represented, from west to east, by the Homino River (a tributary of the Oca River) and its four tributaries, the Molina, the Fuente Monte, the Zorica, and the San Pedro rivers (Figs. 5 and 7). All these streams are outlined by Late Pleistocene to Holocene alluvial series that are deposited at the bottom of their respective valleys. Valleys from the Duero side appear larger than those from the Ebro side, which are significantly more incised.
The Jordan River's headwater is located north of the ridge formed by the Bureba anticline. We can continuously follow its valley
deposits northward along a broadly gentle slope, up to the locality of Cornégula (Fig. 5). However, the current course of the Jordan
River is cut
To the southeast, the headwater of the Hoz River is located to the south of a wind gap cut into the Bureba ridge (Fig. 7c). To the north, in the exact prolongation of the Hoz River, the Molina River shows a bend similar to the elbow of capture previously described for the Homino River (Fig. 7) and there is a minor knickpoint located on this elbow, according to the extracted river long profile. Thus, it is likely that the Molina River used to represent the former upper reach of the Hoz River, in a period when the Ebro–Duero divide was located northward, before being captured by the Ebro network.
To the east, the Rioseras and the Nava Solo rivers also have their headwaters located to the south of wind gaps in the Bureba ridge (Fig. 7). Similarly, in their exact prolongations, the Fuente Monte and the Zorica rivers show important elbows of capture with minor knickpoints. They may also represent former upper reaches of Duero streams that have been captured by the Ebro network (Figs. 5, 7 and 8).
Further east, the headwater of the Diablo River is located on the depression represented by the core of the eastern branch of the Bureba anticline, the Fuente valley. In its prolongation to the northeast, the San Pedro River incises the northeastern termination of the anticline from the north before entering the valley, leading to a southward retreat of the divide (Fig. 5). Capture is again evidenced by important incision contrast between the Ebro and Duero systems and by sharp knickpoints on the upper reach of the San Pedro River long profile when crossing the Santonian dolomites (Fig. 8). According to this whole set of observations, and in agreement with previous findings of Pineda (1997) and Mikes (2010), we propose that the western part of the Rioja trough in the Bureba area has been recently captured by the Ebro drainage network, leading to a sequence of southwestward retreat of the main drainage divide toward the Duero basin (Fig. 7e).
A similar capture pattern can be observed further west in the continuity of the Bureba anticline (Fig. 5). The San Anton River shows a well-defined elbow of capture accompanied by a smoothed knickpoint (See Fig. S1 in the Supplement) at its junction with the Rudrón River (Ebro tributary). The river course is highly incised toward the east, along the northern flank of the WNW–ESE anticline, almost connecting to the upper reach of the Ubierna River. Valley deposits are also observed in the continuity of the Ubierna valley, the former route of which is suggested by a wind gap (Fig. 5). However, this domain is no longer connected to its network as it is now wandered from the north by the Nava River, a tributary of the Moradillo River, which is a tributary of the Rudrón River. This domain clearly records captures leading to divide migration toward the Duero, also in favor of the Ebro basin.
Mean annual precipitation map for the study area (data from Hijmans et al., 2005).
River long profiles for all the streams described in the Bureba area showing evidence of river capture. Colors are given to rivers that are linked in these capture processes.
We used all observations that support divide migration in the Iberian Range and Rioja trough to estimate a paleo-position of the
drainage divide between the Duero and Ebro drainage basins (Fig. 9). For this purpose, we considered the location of major
knickpoints
along the rivers where fluvial captures are defined. Both the Ebro River and several tributaries show highly elevated
Incision in the Ebro basin leads to the capture of new drainage areas, whereas the Duero basin recorded important loss of its own
surface. The present-day drainage area of the Cenozoic Duero basin, upstream of the major knickzone observed to the west in the Iberian
Massif, is
Topographic map showing the location of all the knickpoints and low-relief surfaces that may be associated with river capture. The black dashed line represents a possible paleodrainage divide between the Ebro and Duero basins. The area between this dashed line and the present-day location of the divide in red may have belonged to the Duero basin before being captured by the Ebro basin.
Duero River long profile (black line) and difference in the specific stream power of the river (grey) calculated by considering the paleo and present-day position of its divide. Positive values suggest a significant diminution of the incision capacity of the Duero River, particularly along the knickzone of its longitudinal profile. Details on calculation are available in the Supplement (Sect. S1).
Topographic map with
The comparison of the shape of longitudinal profiles of rivers across divide is a way to infer
disequilibrium between rivers and the potential migration of their divide that has been proposed recently (Willett et al., 2014). The
When using the
We used the
There is a strong contrast in
To sum up,
The oldest capture evidence in our study area corresponds to the incision of the northern part of the Iberian Range by the Jalón River
and by the capture of the Calatayud basin, attributed to the post-Messinian (Gutiérrez-Santolalla et al., 1996). We propose, based
on morphological evidence (Fig. 4) and in agreement with stratigraphic data (Gutiérrez-Santolalla et al., 1996), that the Jalón
river system captured the Jiloca graben to the east since the Early Pleistocene, before progressively capturing the Almazán subbasin
toward the west in the Holocene (Gutiérrez-Santolalla et al., 1996). From
Thus, there is a good correlation between
The pursuit of such a long-term capture trend may be driven by tectonic and/or climatic forcing (Willett, 1999; Montgomery et al., 2001; Sobel et al., 2003; Sobel and Strecker, 2003; Bonnet, 2009; Whipple, 2009; Castelltort et al., 2012; Kirby and Whipple, 2012; Goren et al., 2015; Van der Beek et al., 2016). However, such a long-term trend in drainage reorganization may also occur in tectonically quiescent domains, independent of external forcing (Prince et al., 2011). Here, the Iberian Range and the Cameros basin recorded extension pulses from the late Miocene to the Early Pleistocene, responsible for the formation of several grabens as previously described (Gutiérrez-Santolalla et al., 1996; Capote et al., 2002). Extension events are also recorded during the Holocene; nevertheless, the youngest erosion surface of late Pliocene–Early Pleistocene age observed in our study area shows no tectonic-related deformation and reworking, suggesting that tectonic activity is reduced here (Gutiérrez-Elorza and Gracia, 1997). This is also consistent with the relative scarcity of seismic activity observed in our study area, compared, for instance, to the Pyrenees, or to the Betics (Herraiz et al., 2000; Lacan and Ortuño, 2012). We consequently propose that local tectonic activity is not the main driver of the capture histories documented here, as most capture events postdate the cessation of tectonic activity and occur during periods of quiescence (Gutiérrez-Santolalla et al., 1996).
The Cameros Massif is characterized by relatively high mean annual precipitation up to
A striking morphological feature for river capture in our study area is the important contrast in the incision pattern (e.g., Fig. 1b) from one side of the divide to the other. This suggests that the incision capacity of the river network is the main driver for capture and divide migration. Both tectonic and climatic forcing does not appear to control drainage reorganization between the Ebro and Duero basins.
The opening of the Ebro basin toward the Mediterranean Sea during the late Miocene led to widespread excavation (Garcia-Castellanos
et al., 2003; Garcia-Castellanos and Larrasoaña, 2015), favored by more humid and seasonal climatic conditions (Calvo et al., 1993;
Alonso-Zarza and Calvo, 2000). By contrast, incision related to the opening of the Duero basin toward the Atlantic Ocean is
concentrated to the west in the Iberian Massif, characterized by a large-scale knickzone (150
Our stream power analysis along the Duero River (Fig. 10) shows that the difference in drainage area of the Duero inferred from our paleo-divide map (Fig. 9) induces a noticeable decrease in stream power values of the Duero in the vicinity of the knickzone. This stream power is a minimum estimate because calculation does not take into account possible captures and divide migration in other areas along the Duero basin divide, nor the full history of the divide migration through time and the related ongoing decrease in water discharge as documented in laboratory-scale landscape experiments (Bonnet, 2009). Some contrasts of incision are also observed in the Iberian Range along the southern border of the Duero, and in the Cantabrian domain to the north. Both show more important incision than in the Duero basin, suggesting potential river captures and divide migration at the expense of the Duero basin, increasing the total of lost drainage area. Even if it gives a minimal estimate, our stream power analysis suggests that drainage area reduction may have limited the erosion in the Duero basin. This provides an explanation for the preservation of the lithologic barrier to the west, along the main knickzone of the Duero considered as an intermediate, local base level (Antón et al., 2012).We propose that the reduction of the Duero drainage area caused by captures and incision in the Ebro basin is responsible for a significant decrease in the incision capacity in the Duero basin. We infer that the ongoing drainage network growth in the Ebro basin may be responsible for the current preservation of large morphological relicts of the endorheic stage in the Duero basin.
The opening of the Ebro basin toward the Mediterranean Sea resulted in a drastic base level drop. This results in the establishment of
an upstream-migrating incision wave that propagates to every tributary of the Ebro network, responsible for knickpoint migration
(Schumm et al., 1987; Whipple and Tucker, 1999; Yanites et al., 2013) and for drainage reorganization and divide migration. The
In this paper we present a morphometric analysis of the landscape along the divide between the Ebro and Duero drainage basins located in the northern part of the Iberian Peninsula. This area shows abundant evidence of river captures by the Ebro drainage network resulting in a long-lasting migration of their divide toward the Duero basin. Although these two basins record a similar geological history, with a long endorheic stage during Oligocene and Miocene times, they show a very contrasted incision and preservation state of their original endorheic morphology. Since the late Miocene, the Ebro basin has been opened to the Mediterranean Sea and recorded important erosion. In contrast, the Duero has been opened to the Atlantic Ocean since the late Miocene–Early Pliocene but its longitudinal profile exhibits a pronounced knickpoint, which delimits an upstream domain of low relief and limited incision, likely representing a relict of its endorheic topography. We propose that this contrast of incision is the main driver of the migration of divide that we document. The morphological analysis of rivers across the divide highlights areas where geomorphic disequilibrium is still ongoing, which suggests that the Ebro–Duero divide is currently mobile. The quantification of the decrease in the drainage area of the Duero based on the reconstruction of a paleo-position of the Ebro–Duero divide shows that the divide migration results in a significant lowering of the stream power of the Duero River, particularly along its knickzone. We suggest that divide migration induces a decrease in the incision capacity of the Duero River, thus favoring the preservation of large relicts of the endorheic morphology in the upstream part of this basin.
No data sets were used in this article.
AV undertook morphometric modeling and interpretation, and wrote the paper. SB and FM contributed to the interpretation and the writing.
The authors declare that they have no conflict of interest.
This study was funded by the OROGEN project, a TOTAL-BRGM-CNRS consortium. We thank the two reviewers and associated editor Veerle Vanacker for very useful and constructive comments that greatly helped us to clarify and improve this paper. Edited by: Veerle Vanacker Reviewed by: two anonymous referees