Quaternary International 93–94 (2002) 85–100
Climatic and human influence on river systems and glacier
fluctuations in southeast Spain since the Last Glacial Maximum
Lothar Schulte*
Department of Physical Geography and Institute of Geoecology, University of Barcelona, Baldiri Reixac s/n, E-08028 Barcelona, Spain
Abstract
The semi-desert environments of the Mediterranean region are most sensitive to climatic changes and human land exploitation.
This paper is focused on the Late Pleistocene and Holocene geomorphic evolution of southeast Spain, one of the driest regions in
Europe. Late Pleistocene and Holocene chronosequences of river terraces were established for the Antas and Aguas valleys,
respectively. The deposition of up to four fluvial terraces during isotope stage 2 points to important erosion and accumulation
processes at the end of Late Pleistocene in the Vera basin. In contrast to the stage 2 deposits, the Holocene terraces are composed of
point bar deposits accumulated by meandering rivers with less sediment discharge. According to the obtained 14C-dating and
extracted pottery fragments, Holocene terrace deposition occurred during the Atlantic period, early Middle Ages, Little Ice Age
(LIA) and the 20th century. The most outstanding site in southern Spain for studying Holocene glacier shifts (up to five endmoraines) is the Veleta cirque in Sierra Nevada, where the southernmost glacier of Europe persisted during the Little Ice Age. The
climate changes of the LIA probably are recorded by two glacier fluctuations, as indicated by 210Pb dating and historical data. The
reconstruction of the evolution of the Aguas and Antas valleys stress that the aggradations of the lower terraces is mostly climateinduced although during the last 500 years, human interference in the landscape (Christian conquest, mining boom of the 19th
century, etc.) may have played an important role to river dynamics. r 2002 Elsevier Science Ltd and INQUA. All rights reserved.
1. Introduction
Morphological processes are the result of specific
paleoenvironmental conditions and changes. The natural ‘‘archives’’ of these processes, including fluvial
terraces, travertines, slope deposits and paleosols, can
be interpreted by geomorphological, sedimentological,
pedological and chronostratigraphical methods. In the
context of a geoarchaeological survey of the Vera basin
by the EC Project AGUAS, geomorphological studies
on fluvial and slope deposits have been carried out in the
Aguas and Antas valleys. The aim of this paper is to
gain a better understanding of Late Pleistocene and
Holocene geomorphic evolution in one of the driest
regions in Europe. A crucial question is whether the
river dynamics in Mediterranean environments during
the last 6000 years have been dominated by climate
fluctuations or whether they have been conditioned by
human impact, or both. With regard to the shifts in
climate during the Holocene and the Little Ice Age
*Fax: +34-93-449-5748.
E-mail address: [email protected] (L. Schulte).
(LIA) in southern Spain, additional research was
focused on the glacier fluctuations in the Veleta cirque
in Sierra Nevada, unique during the Holocene glaciated
cirque of southern Spain.
Due to the covering of historical sites by thick alluvial
deposits (e.g. Olympia) the research of Holocene
Mediterranean geomorphic environments was focused
from the beginning on the sensitivity of fluvial processes
to the influence of human land-use. However, in his
pioneer studies of the Mediterranean valleys, Vita-Finzi
(1969) points out the importance of climate as a control
on river dynamics. Regional studies undertaken by
Bruckner
.
(1986) and Van Andel et al. (1990) show that
regional and local river dynamics are much more
complex than the stratigraphical subdivision of valley
floors in ‘‘older’’ and ‘‘younger fill’’ deposits as
proposed by Vita-Finzi (1969). More recent studies
from the Iberian peninsula (D!ıaz del Olmo and Borja
* Monne! et al., 1996;
Barrera, 1991; Schulte, 1995; Pena
Faust and D!ıaz del Olmo, 1997; Fuller et al., 1998;
Garc!ıa Mart!ınez et al., 1999) stress the accumulation of
several Holocene river terraces. However, the relationship between the depositional phases of the different
1040-6182/02/$ - see front matter r 2002 Elsevier Science Ltd and INQUA. All rights reserved.
PII: S 1 0 4 0 - 6 1 8 2 ( 0 2 ) 0 0 0 0 8 - 3
86
L. Schulte / Quaternary International 93–94 (2002) 85–100
river systems and the definition of a general fluvial
stratigraphy for the Mediterranean region is difficult to
establish.
2. Materials and methods
Late Pleistocene and Holocene fluvial terraces of the
Vera basin and glacial and periglacial landforms of the
Veleta cirque (Sierra Nevada) were mapped by aerial
photograph surveys and fieldwork (scale 1:25,000).
Sedimentological descriptions were carried out in fluvial
sediments and slope deposits. From several geological
sections, samples and artifacts were collected and their
magnetic susceptibility was measured. The chronology
of the river terrace sequences was determined from
geomorphologic and sedimentological criteria, 14C,
IRSL and U/Th radiometric dating as well as from
artifacts. In addition, 210Pb dating was undertaken in
flood deposits of the Aguas River (Vera basin) and in
lacustrine sediments of the Veleta cirque. 210Pb-ages
were calculated following the Constant Initial Concentration model (CIC; Binford, 1990). Soil description and
geochemical and micromorphological analysis were
carried out to assess late Quaternary soil development.
3. Site description
The Vera basin and the eastern Sorbas basin are
located at the eastern margin of the Betic ranges in
southeast Spain between 371020 N and 371200 N and
between 11480 W and 21090 W (Fig. 1). The landscape is
characterised by the sharp contrast between the 1300 m
high ranges with steep slopes and the mostly smoothshaped basins situated at altitudes between 0 and 400 m
a.s.l. The basins were formed as a result of Miocene
extension; interbedded marine marl, reef-limestone,
gypsum, calcareous sandstone, siltstone and conglomerate were also deposited. During the Pliocene, pediments and thick alluvial fans, were formed on the edges
of the basins. Climate changes, tectonics, river capture
and eustatic oscillations of the base level generated a
staircase of pediments, alluvial fans, and fluvial terraces.
The semi-desert steppe communities, characterised by
sparse vegetation cover, offer little protection against
erosion processes from thunderstorms (mainly in spring
and autumn). Today the total annual precipitation is
approximately 250 mm/yr and the mean annual temperature, 181C (Fig. 1). Three mayor river systems cross
the Vera basin from the west to the Mediterranean Sea
in the east: the Almanzora River in the north, the Antas
River in the centre and the Aguas River in the south
(Fig. 1). According to archaeological data, human
settlement and land-use are recorded in the Vera basin
since the Neolithic period. Chapman et al. (1998)
consider the Argaric (Bronze Age), Phoenician, late
Roman and Nazari (late Middle Ages) periods as well as
the 19th century as intervals of increased population
density.
The Veleta cirque is located in the central part of
Sierra Nevada (371040 N; 31220 W), 120 km west of the
Vera basin. The Sierra Nevada is the highest range of
the Iberian peninsula and belongs, like the Vera basin,
to the Betic system. The Veleta cirque, situated at an
altitude of between 3045 m (cirque bottom) and 3396 m
a.s.l. (Veleta peak), was covered during the Pleistocene
by the Veleta-Guarnon glacier measuring up to 5.4 km
in length. During the Little Ice Age the Veleta cirque
glacier was the southernmost glacier on the European
continent.
4. Results
4.1. The lower and valley floor terraces in the Aguas
catchment
The morphological studies of the lower and valley
floor terraces, including floodplain deposits of the Aguas
River, are focused on the upper and lower sections of
the river, as well as on its tributary, the Rambla Ancha.
The results of the fluvial evolution of the Rambla Ancha
are partially based on the papers published by French
and Passmore (1998) and Schulte et al. (2000). In the
upper Aguas River and in the Rambla Ancha catchment, the lower terraces can be subdivided into 4 fluvial
terraces (T4a–d in the Aguas and TI–TIV in the Rambla
Ancha), whereas in the lower Aguas River, only two
river terraces have been mapped. The channel deposits
show a sedimentological structure of braided gravel
river systems defined by the presence of horizontal- and
cross-bedded gravel and frequent boulders (Figs. 2 and
3)(see also Fig. 5).
A sequence of four lower terraces can be observed in
several sections located at +15 m (T4a), +11 m (T4b),
+8 m (T4c) and +6 m (T4d) above the riverbed in the
upper Aguas River between the village of Sorbas and the
gorge of the Miocene gypsum escarpment next to the El
Nacimiento area. (Fig. 2, site referred to as no. 1 in
Fig. 1; Schulte, 1998b). The difference in altitude
between the surface of the oldest terrace T4a and the
second one T4b is clear, whereas the escarpments
between the other terraces (T4b–d) are smoother. Few
differences have been detected regarding the altitude of
the base of the terraces which rest on folded Miocene
marls and Pleistocene fluvial and paludal deposits. The
folds and faults are related to Pleistocene halokinetic
deformation, as pointed out by Mather et al. (1991).
In the Rambla Ancha, a tributary of the lower Aguas
River, a section shows four lower terraces (TI to TIV)
located between +8 m and +4 m above the riverbed
L. Schulte / Quaternary International 93–94 (2002) 85–100
2°00' W
1°45' W
RA
2°15' W
87
O
GRE
Huercal-Overa
G
R
711
A
MA
M
AL
L
367
S
SIERRA
S
DE
BR
L
LO
ES
37°15'
N
An
ta
s
1.301
Monteagudo
766
Ra.
Hor
no
s
Mo
far
Alfaix
de
o
Rí
961
1
C
SIERR
37°00'
N
1.387
SIERRA
DE
AL
HA
MI
LL
Medi
S
S O R B A
terr
Ra
.
as
Agu
N
S I
B A
a
4
ane
Turre
Sorbas
S
Alm
an
zo
ra
O
a
A
Se
J
an
37°15'
N
A M
V E R A
F M
J
IE
I
10
RR
N
A
A
A
Río
A
á
Rí
o
Carboneras
Carboneras
N
0
2°15' W
2°00' W
37°00'
N
10 km
1°45' W
L. SCHULTE, 99
Neogene and
Quaternary basin fill
Fault
Watershed
Neogene volcanic rock
Syncline
Misfit river
Pennibetic basement
Escarpment
1
Iberian
Peninsula
Location of sections
Sierra
Nevada
Vera
basin
Fig. 1. Location of the study area. The geological cartography is based on the geological maps 1:50,000 (I.G.M.E.). Reconstruction of the
Pleistocene river captures and misfit rivers according to Mather et al. (1991) and Schulte (1995, 1998a, 2002).
(Fig. 3; referred to as no. 2 in Fig. 1). As in the upper
Aguas valley, the difference in altitude between the
surface of the oldest lower terrace and the other lower
terraces is considerable. IRSL dating of fine-grained
sands shows an age of 21,5007800 yr B.P. for the oldest
lower terrace TI of the Rambla Ancha and
16,70071600 yr B.P. for the third lower terrace TIII
(French and Passmore, 1998; Schulte et al., 2000).
The age of the lower Aguas terraces is more difficult
to determine. Radiocarbon dates made on pollen
concentrates extracted from coarse-sand layers of the
fluvial terraces in the upper Aguas valley yield ages of
9640760 (9029–8568 cal. yr B.C.; CAMS 59174=Ag786.2, Fig. 2) for terrace T4a and 8430760 yr B.P.
(7544–7368 cal. yr B.C.; CAMS 59175=Ag-789.2,
Fig. 2) for terrace T4c. These ages do not match the
data obtained from the Rambla Ancha. This could be
the result of subsequent infiltration of the pollen from
the surface of the mainly coarse-grained T4 terraces.
Therefore, the radiocarbon data probably represent
minimum ages of these deposits.
However, the maximum age of the T4 terraces is
defined by 12 U/Th ages on a thick travertine deposit,
located in the middle Aguas River near the village
of Alfaix at 25 m above the riverbed (Schulte, 2002).
The latest travertine formation at 54,70071800 yr B.P.
(U/Th) was followed by an important period of incision
of the Aguas River and by the accumulation of the
terraces of level T4 (+10 m). According to this
morphostratigraphical context, the lower terraces of
the Aguas River accumulated after 54,700 yr B.P.
The sedimentological characteristics of the T4 terraces, including bedding and the presence of coarse
gravel and blocks, are similar to the fluvial terrace T3,
dated with U/Th techniques between 167,50076800 and
148,30078300 yr B.P. (isotope stage 6), according to
Schulte (2002). Cumulic Haploxerolls with an organic
carbon content up to 1.8% represent the maximum soil
L. Schulte / Quaternary International 93–94 (2002) 85–100
88
Lower terrace sequence (T4b-d) in the upper Aguas valley next to the Barranco Aguarico mouth
SW
NE NW
150 m
T4a (+15 m)
Ag-789.2
m
a.s.l.
T4b
SE
110 m
Ag-786.2
T4b
m
a.s.l.
T4b
325
325
T4c
T4d
320
H
315
320
315
Aguas riverbed
Unconformity (12°)
Fault
Sand lenses
Boulder
Clay
Rounded gravel
Secondary carbonates
Not visible section
Subrounded - subangular gravel
Stratified sediments
Fluvial and paludal deposits, deformed
previously to terrace T4a accumulation
Sand
Sorted sediments
Silt
Skeletal gravels
Neogene marls
Ag-789.2
Sample site
Schulte, UB, 1999
Fig. 2. Lower terrace sequence (T4a–d) in the upper Aguas valley next to the mouth of the Barranco Aguarico (referred to as no. 1 in Fig. 1). The
limit between terrace T4b and T4c, which in this section is obscured by slope deposits and vegetation, can be clearly observed in outcrops near Sorbas
and east of Cortijo Urra. The section next to the Barranco Aguarico mouth was first studied by Mather et al. (1991). They do not distinguish different
lower terraces (T4a–d) as proposed by Schulte (1998b), but define this river deposits as one terrace unit (terrace D3) proposing a late ‘‘Wurmian’’
.
age.
Fluvial terrace
TIV
IRSL Dating
TIII
TII
16.7 ka +/- 1.6 ka
TI
21.5 ka +/- 0.8 ka
N
S
115 m
m
8
7
6
5
4
3
2
1
Ancha riverbed
0
A horizon
Boulder and stones
Colluvium
Not visibles section
Gravel
Silt
Agriculture terrace
Sand
Marl
Sample site
Cartography: SCHULTE & FISCHER ´99
Fig. 3. Lower terraces of the Rambla Ancha. IRSL-dating according to French and Passmore (1998) and Schulte et al. (2000) (referred to as no. 2 in
Fig. 1).
formation on the surfaces of the lower fluvial terraces
T4a–d. Unlike the Haploxeralfs of the +22 m terrace T3
(isotope stage 6), no illuviation (Bt) or calcic horizons
(Bk) were formed (Schulte and Julia" , 2001). Never-
theless, the Haploxerolls show a stronger pedogenesis
than the soils on the Holocene terraces. These sedimentological and pedological criteria and the higher altitude
of surface levels and terrace bases compared to the
L. Schulte / Quaternary International 93–94 (2002) 85–100
89
Holocene River Terrace Sequence of the Lower Aguas River, SE Spain
H1
Fluvial terrace
Approximate age
Early Middle Age
> 5.000 B.P.
Copper age
settlement
m above
riverbed Chalcolithic age
in the 70's
4
7th c.
Silt
1
Pottery sherds
0
River bed
70's,
>1993/94 A.D.
Today
1040 +/-40 yr BP (14C)
19th-20th c.
2
20th c.
H4b
430 +/-50 yr BP (14C)
3
Sand
H4a
Onset of the Little Ice Age
1902 +/-4 A.D.
(210Pb)
der
el
H3
H2
Nazari
(13th-15th c.)
0th-12th c.
Archaeological site
Chalcolithic
-1
Charcoal
Irrigation silts
>
Older than...
<
Younger than...
-2
-3
-4
Last glacial channel sediments
-5
Pb-210 dating site
Gravel
pits
L.SCHULTE, UB, 1999
Overbank deposits
Flood
control
dam
-6
Fig. 4. Synoptic Holocene River terrace sequence of the lower Aguas River.
Holocene river deposits may indicate a Last Glacial
Maximum (LGM) or Late Glacial age of the T4a–d
terraces.
A Holocene chronosequence of five river terraces (H1
to H4b) was established for the lower Aguas valley
(Fig. 4). In contrast to the stage 2 deposits, the Holocene
terraces are composed of well-stratified point bar
deposits with lesser coarse gravel content, and are
mostly free of boulders. The structure of the Holocene
fluvial deposits points to a meandering river regime with
lesser sediment discharge. The differences in altitude of
the Holocene terrace surfaces in the lower Aguas River
are very small (forming row terrace texture). As a result,
in some areas a morphological differentiation between
the terrace units is only possible by mapping the
paleomeanders using aerial photographs.
The oldest Holocene terrace H1 is predominantly
located at the floodplain rim at altitudes of between
4.5 and 4 m above the riverbed. A Chalcolithic site
(5000–4200 yr B.P.) was found next to the confluence of
the Rambla Mofar and the Aguas River (Chapman
et al., 1998) on the surface of terrace H1 indicating the
ante quem age of the fluvial deposit.
The surface of terrace H2 (from 3.5 to 2.5 m above the
riverbed) is approximately 1 m lower than terrace H1.
Near the La Loma de Faz ridge, a section shows channel
deposits covered by overbank sediments and irrigation
silt. Radiocarbon dating on microcarbon yields an age
of 1040740 yr B.P. (961–1034 cal. yr A.D.; CAMS
59178) for the channel deposits of terrace H2. The
fine-grained overbank deposits are much younger as
potsherds from the 17th and 19th centuries or later and
210
Pb-dating (190274 A.D. at 85 cm depth) indicate.
From the +2 m terrace of the Rambla Ancha, Passmore
(1997, personal communication) obtained a radiocarbon
age of 1340750 yr B.P. (656–756 yr cal. A.D.; Beta100600). A morphological correlation with the Aguas
terraces by longitudinal sections is difficult to establish.
Fig. 5 presents the sedimentological structure of the
Aguas Holocene terraces H3 (+2 m; referred to as no. 3
in Fig. 1), perfectly exposed in a gravel pit near Cortijo
El Navajo east of Turre. Three sedimentological units
were distinguished. The lower unit U1 consist of not
stratified but imbricated gravel and blocks, which were
accumulated by a braided gravel river during the Late
Pleistocene, as indicated by a maximum IRSL-age of
42,100 yr B.P. (Passmore, 1997, personal communication). In contrast, units U2 and U3 are composed of
sands and pebbles of point bar deposits resulting from
the lateral migration of the Aguas River. Charcoal
90
Section of the Holocene terrace H3, gravel pit near Cortijo El Navajo (29,5 m a.s.l.)
E
W
90 m
<42.100 yr B.P. (IRSL)1
430 +/- 50 yr B.P.
Lithology
Magnetic susceptibility
k(10-3SI)
0
0.5
1.0
29,5 m
a.s.l.
m
0
D
U3
2
?
U2
U1
B
4
A
6
C
8
8
Base of gravel pit
B
Silts
Mud balls
unded gravel
Clay
Charcoal
brounded - subangular gravel
Stratified sediments
Not visible section
Boulder
nd
Skeletal gravel
A
Magnetic susceptibility
profile
Shift of paleomeander
A
650
0
0.5
1.0
Sample site
L. SCHULTE, 99
Fig. 5. Section of the Holocene terrace H3 exposed in a gravel pit near Cortijo El Navajo (29.5 m) (referred to as no. 3 in Fig. 1). Unit U1=Late Pleistocene, unit U2 = Holocene, unit
U3=Holocene terrace H3. The magnetic susceptibility profile, measured in situ with a Magnetic Susceptibility Meter (Kapameter Model KT-5), shows considerable variations according to the
lithological/sedimentological changes. 1=IRSL dating provided by Dr. D. Passmore, University of Newcastle, UK.
L. Schulte / Quaternary International 93–94 (2002) 85–100
cm
0
Base of exploitation
L. Schulte / Quaternary International 93–94 (2002) 85–100
Pb activity profile of the H2 terrace flood deposits (Ag-711)
Lithology and soil horizons
Ages yr A.D.
0
0 cm
- 20
1998
1959 +/-2
1945 +/-2
- 40
- 60
- 20
0.4
- 60
Pb activity profile
210Pb activity (dpm/g)
k(10-3SI)
0.6 0.7
1
x-axe is logarithmic
10
0 cm
Vb
- 20
- 40
- 40
1939 +/-2
Va
0.2
0 cm
1981 +/-1
Vb
210
Magnetic susceptibility
Va
supported 210Pb
210
91
- 60
0.53 cm/a
av. 0.89 cm/a
2.9 cm/a
1933 +/-3
- 80
- 100
1902 +/-4
IV
- 80
- 80
- 100
IV
- 100
- 120
III
- 120
III
- 120
- 140
II
- 140
II
- 140
- 160
I
- 160
I
- 160
- 180
Gravel
Charcoal
A horizon
Sand
Pottery fragments 19th - 20th c.
Channel deposits
Silt
Pottery fragments younger
than 17th c.
- 200
Cartography: SCHULTE & FISCHER ´99
Fig. 6. Lead-210 activity profile, magnetic susceptibility and sedimentology of the overbank deposits of the fluvial terrace H2 (referred to as no. 4 in
Fig. 1).
fragments extracted from unit U3 were dated by
radiocarbon (AMS) with an age of 430750 yr B.P.
(1417–1611 cal. yr A.D.; Beta-100599). Nazari (Arabian)
pottery fragments found in the exposed gravel deposits
of Holocene terrace H3, downstream near Las Cuartillas, support the determination of this age.
The youngest terraces H4a (+1.5 m) are comprised of
small terrace remnants deposited along the modern
riverbed. This terrace dates to the 20th century as recent
artifacts indicate. The river sand and gravelbars of
terrace H4b correspond to the frequent flood events that
occurred in the Vera basin at the end of the 1940s. These
events are also recorded by the 128-year-precipitation
record of Murcia, 80 km northwest of the study
area. Precipitation data prior to 1953 from the Vera
basin is not available. The torrential rainstorms
also enhanced the accumulation of floodplain deposits.
Lead isotope dating (Fig. 6; referred to as no. 4 in
Fig. 1) has permitted the calculation of the sedimentation rate of the upper floodplain sediments of the terrace
H2 near La Loma de Faz. Between the 1930s and the
1950s, the sedimentation rate amounts to 2.9 cm/a
compared to an average of 0.89 cm/a between 1902
and 1998 (Fig. 6).
4.2. Slope erosion processes in the lower Aguas valley
Slope deposits can be a useful indicator for environmental changes. As in the case of river terraces, slope
deposits record erosion and pedologic processes related
to environmental conditions and changes, although they
may have a local significance. A section next to the
Chalcolithic site Las Pilas, located at the foot of the
northern slope of Sierra Cabrera, shows a sequence of
colluvia and intercalated incipient organic soils (buried
Entic Haploxerolls). These buried soils have reworked
epipedons and contain pottery fragments and silex due
to anthropogenic use. The lowest soil at a depth of
240 cm date to the Chalcolithic period, whereas the
soil at 120 cm corresponds to the Roman times.
Important erosion processes followed both soil formations. However, slope erosion ceased since the Nazari
period (13th to 15th centuries, late Arabian times),
probably due to the building of agricultural terraces.
92
L. Schulte / Quaternary International 93–94 (2002) 85–100
4.3. The lower and valley floor terraces in the Antas
catchment
The first studies on late Quaternary river dynamics in
the Vera basin were undertaken in the lower Antas
River by Schulte (1995). These preliminary studies will
be completed by new results reported in this paper.
The Late Pleistocene and Holocene terrace sequences
of the Antas River are less differentiated than the terrace
stratigraphy of the Aguas River. This can be explained
by the smaller river catchment (261 km2; Aguas catchment=539 km2) and the valley configuration. A section
next to Cortijo El Esparragal represents the bestpreserved exposure of the lower terraces of the Antas
valley. The T4a and T4b terraces at +7 m and +6 m
respectively, presumably from the Late Pleistocene,
cover older fluvial deposits as a result of terrace
intersection in the lower course of the river. Unfortunately, no radiometric dating was obtained from the
lower terraces T4a and T4b. Nevertheless, a Late
Pleistocene age for these terrace segments can be derived
from morphostratigraphical (height above Holocene
valley floor terraces and today’s riverbed), sedimentological (metre-diameter boulders, braided river deposits), and pedological findings (Haploxerolls formed on
T4a and T4b terrace surfaces). Defined fluvial deposits
dated from the Late Pleistocene were found near the
coastline. In the context of palynological studies,
! Cano (1997) dated the organic matter,
Pantaleon
derived from fluvial deposits at a depth of 24 m, 1 km
west from the Antas mouth, at 16,8607120 B.P. (14C).
These coarse-grained channel deposits were accumulated by the incised Antas River during the lower sea
level stand. U/Th dating from a travertine deposit
located next to the village of Antas (Schulte, 2002) yields
an age of 9300770 yr B.P. This travertine does not
provide evidence with respect to the accumulation of the
Holocene terraces, but indicates more humid environmental conditions in the aridity of southeast Spain at the
beginning of the Holocene (Schulte and Julia" , 2001).
The Holocene river-stratigraphy of the lower Antas
valley includes four Holocene terraces (H1, H2, H3a and
H3b) located at altitudes between 4.5 and 1 m above the
*
riverbed. South of Cortijo de Juan Nu! nez,
the channel
deposits of the oldest Holocene terrace H1 (+4.5 m) are
covered by 3.6 m-thick floodplain sediments and colluvia. In the lower part of the mostly fine-grained
floodplain deposits, two buried Entic Haploxerolls have
been preserved. The age of the fluvial terrace H1 is
difficult to determine. No pottery fragments have been
found in the fluvial sediments except in the uppermost
colluvium at the top of the terrace profile. This lack of
artifacts points to a deposition of the river terrace at a
time prior to the first Neolithic settlements in the Vera
basin (6000 yr B.P.). This chronological interpretation is
supported by pedological evidence. The pedogenesis of
the buried soils is similar to the early Holocene soil
formation in the Aguas valley, whereas the soils on the
younger Holocene terraces are less developed.
The connection of the morphological studies of the
Antas River with the geoarchaeological research of
coastline changes undertaken by Hoffmann (1988) may
provide information regarding the chronology of fluvial
terrace H1. Radiocarbon dating of the organic matter
recovered at 3.30 and 2.50 m depth from drill hole no. 26
(Hoffmann, 1988) near the coastline north of Puerto
Rey yields uncalibrated ages of 97707700 and
60307370 yr B.P. Morphological field studies and
survey of aerial photographs show that the drilling sites
belong to an ancient mouth of the Antas River. The
floodplain situated between this paleo-mouth and the
present course of the Antas River probably correlates
with Holocene terrace H1. However, sea level rise
during Versillian transgression and the corresponding
river response must be taken into account. Future
morphological studies should be focused on these
coastal morphodynamics.
The Holocene terrace H2 is located at 3 m above the
riverbed, and is formed by monotonous floodplain silt
2 m thick and gravel from the channel deposits. In the
upper channel deposits, pottery fragments from the 16th
century or later were found. Artifacts extracted from the
floodplain sediments date to the 20th century.
In several sections, terrace H3a (+1.5 m) shows
laminar sedimentation structure in its floodplain deposits. Glass fragments near the base of the overbank
deposits date to the end of the 19th century and the
beginning of the 20th century. Next to the confluence of
the Rambla Salvador and the Antas River, a 19th
century aqueduct caused excessive sedimentation (terrace H3a); the resulting backwater finally produced the
collapse of the aqueduct. The youngest terrace H3b (1 m
above the riverbed) was accumulated only along the last
4 km of the Antas River’s course and was formed from
the frequent rainstorms at the end of the 1940s. The shift
in the river’s course from several floods can be detected
by the detour of irrigation channels.
4.4. Holocene glacier fluctuations in Sierra Nevada as an
indicator for Holocene climatic changes
An interesting question of geomorphological research
in southeast Spain is the response of fluvial dynamics in
the lowlands and glacier fluctuations in high mountain
areas such as the Sierra Nevada to the climate changes.
The most outstanding site in southern Spain for
studying Holocene glacier shifts is the Veleta cirque,
where the southernmost glacier of Europe persisted
during the Little Ice Age. In the Guarnon valley and
Veleta cirque four end-moraines (M1, M2, M3 and M4),
located between 1600 and 2980 m a.s.l., resulted from
!
late Pleistocene glaciation. Gomez
Ortiz et al. (1996)
L. Schulte / Quaternary International 93–94 (2002) 85–100
93
Moraine segments of the Veleta Cirque (Sierra Nevada)
4
LG
M
N VA
LLE
Y
HM
1
2.993 m
NO
HM
3
G
UA
R
55 m
3.06
M
H
V
m
L
M
LG
E
E
3.133 m
T
A
C
IR
Q
U
E
Iberian
Peninsula
Sierra
Nevada
A
Aguas
and
d
Antas river
0
100
200 m
468
Fig. 7. Map of the Holocene moraines of the Veleta cirque in Sierra Nevada (Spain).
recognised a Late Glacial period moraine and three
different Holocene glacier advances in the Veleta cirque
(3050 m a.s.l.).
Based on detailed morphological mapping of the
Veleta cirque, an additional two more moraine units
were identified. Fig. 7 shows the location of the moraine
ridges. The outermost and highest moraine M4 is
!
assumed to be of Late Glacial age (Gomez
Ortiz et al.,
1996) although no radiometric dating was obtained.
Morphological evidence points to a pre-Holocene age.
The topographical configuration of the western lateral
moraine permits the reconstruction of the glacier’s
dimensions, which by far exceeds the ice mass of the
five younger (Holocene) glacier stands.
So far, only the age of the two youngest moraines
can be determined. The youngest moraine HM4b
(HM=Holocene moraine), located at an altitude of
3060 m, corresponds to the extent of the glacier in 1876,
as reported by Hellmann (1881) and represents the latest
glacier advance at the end of the Little Ice Age. The
approximate age of the second youngest moraine HM4a
can be estimated by 210Pb-dating undertaken in lacustrine sediments located between the glacier stillstands.
Fig. 8 shows the sedimentological structure and the
210
Pb-activity profile of the lacustrine sands and silts.
The sample taken from a depth of 7 cm revealed an age
of 190873 A.D. Extrapolation of 210Pb dates provide
only poor approximate ages, primarily due to the
possible presence of discontinuities as pointed out in
Fig. 8. However, the data indicate that the base of unit 4
could be between 200 and 250 years old. Both the
underlying lacustrine sediments (units 3 and 2) and
the till are older. According to these findings, moraine
HM4a represents an earlier advance of the glacier,
L. Schulte / Quaternary International 93–94 (2002) 85–100
94
Pb activity profile of section CV-1 (Veleta cirque, Sierra Nevada)
210
3.088 m
a.s.l.
Age yr A.D.
210Pb activity (dpm/g)
210
Pb-samples
1
10
100
supported 210Pb
0 cm
5
- 10
- 15
- 20
- 25
- 30
Boulder
Gravel
nd
Silt
Not visible section
Samples
Cartography: SCHULTE & FISCHER ´99
Fig. 8. 210Pb activity profile of lacustrine sediments located between the Holocene moraines HM4a and HM4b in the Veleta cirque (Sierra Nevada,
Spain) at 3088 m a.s.l. 1=Ground moraine. 2 to 4=Layered lacustrine silts with intercalated fine sand layers. See location of profile in Fig. 7.
probably at the beginning of the Little Ice Age. A much
earlier accumulation of the coarsely grained till (unit 1)
is not very plausible. This moraine has been altered very
little compared to the older Holocene moraines (HM1,
HM2 and HM3), which are rich in fine material.
5. Discussion: Late Pleistocene and Holocene
morphodynamics
According to the obtained findings, the evolution of
the valley floors of the Aguas and Antas rivers record
several important morphodynamic changes. The 6–9
late Quaternary fluvial terraces result from alternating
periods of river accumulation and incision. The absence
of faults in the lower and valley floor terraces (T4a to
T4d and H1 to H4b), indicates that neotectonics have
not played a decisive role in fluvial dynamics during the
last 23,000 years. Nevertheless, the youngest observed
tectonic deformation, which affected the travertine
deposit of Alfaix, dates after 54,700 yr B.P. (U/Th;
Schulte, 1998b, 2002). Therefore, the formation of the
fluvial terraces in the Aguas and Antas rivers has been
linked to other factors such as paleoenvironmental
changes, sea level oscillations, and human impact. In the
following paragraphs, we discuss the complex effects of
these factors, taking into consideration the geomorphological results from other regions of the Mediterranean.
5.1. The climatically controlled river terraces
5.1.1. Late Pleistocene fluvial dynamics
The assessment of human impact on morphological
processes since the Neolithic period requires a detailed
study of the Late Pleistocene and early Holocene
geomorphological contexts. This paper focuses on the
last 23,000 years. The chronostratigraphy in Fig. 9
shows the geomorphological evolution of the Vera and
eastern Sorbas basins, as well as that of the Sierra
Nevada.
River dynamics during isotope stage 2 were very
active, leading to the deposition of two to four fluvial
terraces in the Aguas, Antas and Rambla Ancha
catchments (Fig. 9; Schulte, 1998b; Schulte et al., 2000;
French and Passmore, 1998). The sediments of these
fluvial terraces reveal vertical deposition of braided river
systems with high transport capacity.
Chronological dating was obtained form the Rambla
Ancha catchment (Figs. 3 and 9). The oldest lower
terrace TI (21,5007800 yr B.P.) was formed during
the LGM (Heinrich event H2?), while the third lower
terrace TIII (16,70071600 yr B.P.) was accumulated
during the transition from the isotope minimum to the
Late Glacial period and correlates probably with
Heinrich event H1. The youngest member of the terrace
sequence was possibly deposited during the Late Glacial
period.
L. Schulte / Quaternary International 93–94 (2002) 85–100
Fig. 9. A Late Pleistocene and Holocene chronostratigraphy of the Vera basin, eastern Sorbas basin and Sierra Nevada. 1=U/Th dating undertaken by Dr. R. Juli"a, CSIC, Barcelona; 2=14C
dating financed by EC project ‘‘Aguas’’ (EV5V-CT94-0487); 3=IRSL dating financed by EC project ‘‘Aguas’’; 4=14C dating financed by DGICYT project PB96-0385; 5=14C dating
according to Hoffmann (1988); 6=14C age according to Dr. D. Passmore, University of Newcastle, UK (1997, personal communication), 14C dating financed by EC project ‘‘Aguas’’;
!
7=according to Pantaleon-Cano
(1997), 14C dating obtained from charcoal extracted from fluvial deposits drilled at a depth of 23 m next to the mouth of the Antas River.
95
96
L. Schulte / Quaternary International 93–94 (2002) 85–100
The terraces T4a–d of the Aguas River date
subsequent to the travertine formation around
54,70071700 yr B.P. (isotope stage 3). The validity of
the obtained radiocarbon data of 9640760 and
8430760 yr B.P., yielded from pollen samples, is
questionable in determining the age of the terraces T4a
and T4c. On the other hand, the sedimentological
distinction of the terraces T4a to T4d with respect to
the accurate Holocene-defined river terraces is obvious.
In this paper, a LGM and Late Glacial age for these
terraces is proposed according to the results obtained
from the Rambla Ancha.
No radiometric dates were obtained from the two
lower Antas River terraces T4a and T4b. Nevertheless,
altitudes pertaining to riverbed, sedimentological and
pedological data provide arguments for a Late Pleistocene age.
Braided and torrential river structures in the gravel
deposits of the lower terraces of the Aguas and Antas
rivers and Rambla Ancha catchment reflect violent
fluvial dynamics and increased sediment discharge.
These dynamics probably occurred during the Late
Pleistocene as a result of an irregular precipitation
pattern and a concentration of torrential rainstorms due
to the southward-shift of the westerlies (Ganopolski
et al., 1998). These, in turn, produced sparse vegetation
and increased the overland flow during high-magnitude
events. Pollen records from Padul (Pons and Reille,
1988) show taxa of artemisia-steppe vegetation during
the LGM and Late Glacial period (e.g. Younger Dryas).
In the Sierra Nevada, several end-moraines located at
!
different altitudes (Gomez
Ortiz et al., 1996; Fig. 9)
document the response of glacier dynamics to colder
climate conditions and the lowering of the equilibrium
line altitude (up to 1000 m) during the last glacial period
in the high mountain areas of southern Spain. The
periglacial boundary descended simultaneously. Periglacial deposits were detected in the Betic ranges at
altitudes of 1000 m, whereas in the lowlands no clear
periglacial indicators were found (Schulte et al., 2000).
Therefore, the late Pleistocene fluvial dynamics in the
lowlands of southeast Spain were not triggered by
periglacial processes.
5.1.2. Chronology of Late Pleistocene terraces in the
Mediterranean Iberian Peninsula
The discussion of fluvial terrace chronology of the
Late Pleistocene, and in particular, the last cold period
in the Iberian Peninsula, is controversial. Mather et al.
(1991) proposed that in the upper Aguas valley, the
terraces located at +38 m (terrace D1), +25 (terrace
D2) and +12 m (terrace D3) above riverbed correspond
to an early, middle and late ‘‘Wurmian’’
.
age. However,
even the most recent calcrete-based U/Th dating of this
terrace sequence, published by Kelly et al. (2000),
provides only very recent minimum ages (around
89707280 yr B.P.) for terrace deposition.
Since the 1990s, several studies based on radiometric
dating have been published, although the results differ
considerably. From fluvial deposits of the river systems
of the Valencia province and the Guadalope catchment
!
(Teruel province), Prozynska-Bordas
et al. (1992) and
Fuller et al. (1998) obtained TL and IRSL-ages from
115,000 to 14,000 yr B.P. covering the entire Late
Pleistocene period. Fluvial deposits dated by faunal
remains, and IRSL and U/Th as cold isotope stages 6
and 2, were reported from the Guadalquivir (Faust and
D!ıaz del Olmo, 1997), Guadalope (Fuller et al., 1998),
* Monne! et al., 1999) and Vera
Guadalaviar river (Pena
basin (Schulte, 1998b, 2002). Moreover, in the Guadalaviar valley (Teruel province, NE-Spain) at 1200 m
* Monne! et al. (1999) detected cold climate
altitude, Pena
indicators (e.g. stratified periglacial slope deposits),
which interfinger the +25 m terrace.
The results of this paper suggest that the braided river
terrace formation in the Vera basin during the Late
Pleistocene is the result of torrential morphodynamics
corresponding to the colder periods of isotope stage 2.
This process may be similar to the aggradation of the
braided Aguas river terrace T3 during isotope stage
6 between 167,50076800 and 148,30078300 yr B.P.
(U/Th; Schulte, 1998b, 2002). If this is so, the fluvial
environments of the basin can be associated with longterm global climate changes.
5.1.3. Early and middle Holocene fluvial dynamics
In contrast to the Late Pleistocene deposits, meandering river systems constructed the Holocene terraces.
The Holocene terraces H1 of the Aguas and Antas
rivers were formed prior to the Chacolithic period
(5000–4300 yr B.P.; Fig. 9) and probably correlate with
the middle Holocene terrace (8000–4000 yr B.P.) of the
Guadalquivir river in western Andalusia (Garc!ıa
Mart!ınez et al., 1999; Fig. 10). Fuller et al. (1998) report
periods of terrace aggradation from the Guadalope river
in NE Spain at 8000 yr B.P. and 6000–5000 yr B.P. using
14
C and IRSL dating techniques.
In the Basilicata, in southern Italy, Bruckner
.
(1986)
obtained a radiocarbon age of 72507140 yr B.P. from
the lowest unit of the oldest Holocene river terrace.
Fluvial terraces with a similar chronology are reported
from Greece (Van Andel et al., 1990) and Syria (Courty,
1994). The synchroneity of the terrace deposition in
these Mediterranean catchments points to a climate and/
or sea level control of the river environment. Regarding
the evolution of the Aguas and Antas rivers, control by
natural factors is supported by archaeological data
which shows that human occupation and land-use in the
Vera basin during the Neolithic period (6000–5000 yr
B.P.) were insignificant, and so the human influence on
river dynamics was negligible.
L. Schulte / Quaternary International 93–94 (2002) 85–100
97
Holocene river terrace sequences
SW Spain
SE Spain
(Guadalquivir river)
DÍAZ DEL OLMO & BORJA BARRERA, 1991
NE Spain
(Aguas river)
(Huerva river)
SCHULTE, 1998a, 2002
PEÑA MONNÉ et al., 1996
GARCIA MARTíNEZ et al., 1999
Age
Terrace Terrace
Th3
Th2
H4b
H4a
Middle Age
Roman times
4000-8000 BP, Middle Holocene
20th c.
20th c.
Terrace
Age
Age
20th c.
19th-20th c.
N0
Th1
H3
H2
Christian Conquest, LIA
(Early) Middle Age
N1
N2
Post Middle Age
Middle Age
TH2
TH1
H1
older than 5000 BP
N3
6000 BP - 5th c. AD
Fig. 10. Chronostratigraphy of river terrace sequences of southwest, southeast and northeast Spain.
Courty (1994) interprets the river accumulation in
Syria between 7000 and 5000 yr B.P. as the result of a
more humid climate. Soil and travertine formation
(9300770 yr B.P.; Fig. 9) in the Vera basin (Schulte and
Julia" , 2001) indicate more humid environments in
southeast Spain during the early Holocene, as shown
by the pollen records of Padul, Salines and Antas (Pons
! Cano,
and Reille, 1988; Burjachs et al., 1997; Pantaleon
1997). Enhanced pedogenesis was also detected by Faust
and D!ıaz del Olmo (1997) in southwest Spain. These
paleoecological records provide evidence that river
terrace aggradation also could have occurred during
periods with increased annual precipitation.
In the Mediterranean basin, the formation of the early
and middle Holocene terraces is often attributed to the
rise of sea level during the Versillian transgression.
However, longitudinal sections of the Pleistocene river
terraces (Schulte, 2002) and drilling near the coast of the
! Cano, 1997)
Vera basin (Hoffmann, 1988; Pantaleon
indicate that Pleistocene river incision occurred only in
the lowest 4 km of the Aguas and Antas courses. Sea
level rise does not appear to be the dominant factor
concerning Holocene river evolution in the Vera basin.
5.2. Fluvial terraces influenced by human action
The first anthropogenic influence on morphological or
pedological processes in the Vera basin dates to the
Chalcolithic period (5000 to 4300 yr B.P.). The lower
buried soil of the slope section of Las Pilas shows
disturbances related to land-use during the Copper Age.
The same section records important erosion and
accumulation processes subsequent to Chalcolithic
period and Roman times.
The post-Roman slope erosion probably correlates
with the early Middle Age terraces dated 1040740 yr
B.P. in the Aguas valley (Schulte, 1998b; Fig. 9) and
1350750 yr B.P. in the Rambla Ancha catchment (D.
Passmore, personal communication, 1997). The formation of these terraces could have been attributed to
climatic factors. Pollen profiles from the Almeria and
Alicante provinces indicate a maximum level of aridity
at the beginning of the Middle Ages (Burjachs et al.,
1997). Terrace aggradation caused by human impact
during the late Visigothic and early Arabian period is
questionable due to the low population density and
subsistence agriculture production in the Vera basin
(Chapman et al., 1998). The climatic origin of the
medieval terrace can also be deduced from the correlation of the fluvial stratigraphies of southwest and
northeast Spain and Italy, taking into consideration
the different historical context of each region. In
the Guadalquivir river terrace, deposition began during
the 10th century (Garc!ıa Mart!ınez et al., 1999) and in the
*
Huerva River it began during the 5th century (Pena
Monne! et al., 1996). Furthermore, Bruckner
.
(1986)
detected medieval fluvial activity and sediment aggradation in southern Italy.
During the Little Ice Age the river dynamics in the
Vera basin were very active, thus generating the H3
terrace of the Aguas River and the H2 terrace of the
Antas River. The H3 terrace of the Aguas River, dated
430750 yr B.P. by radiocarbon, corresponded to the
beginning of the LIA, whereas the Antas river terrace
H2 suggests a slightly later LIA fluctuation, as pottery
fragments indicate (Fig. 9). The geoarchaeological
research undertaken by Hoffmann (1988) shows important delta growth and seaward shift of the Andalusian coastline during the last 500 years. According to his
results, a bay which persisted during Roman times next
to the mouth of the Antas River, was infilled presumably during Modern times. River terrace accumulation also occurred during the Little Ice Age in the
Guadalentin, Fuente Librilla and Gebas basins (CalmelAvila, 2000), located 50 km to the northeast of the Vera
* Monne!
basin, in the Huerva valley (NE-Spain; Pena
et al., 1996) and Guadalope valley (NE-Spain; Fuller
et al., 1998).
The terrace accumulation in the Vera basin could be
linked to specific climatic conditions of the LIA as
traced by the following studies. Dendrochronological
studies of the Iberian Peninsula (Creus Novau et al.,
98
L. Schulte / Quaternary International 93–94 (2002) 85–100
1997) show increased variability of temperature and
precipitation during the 14th, 15th and 16th centuries.
The paleoclimatological research based on documentary
data carried out by Barriendos Vallve and Martin Vide
(1998) gives evidence of higher rainfall intensity at the
Spanish Mediterranean coast toward the end of the 16th
and 18th centuries and during the mid-19th century.
The existence of colder climate conditions during the
Little Ice Age in southeastern Spain is apparent in the
high mountain area of Sierra Nevada. In the Veleta
cirque, two frontal moraines of the LIA are preserved
(Figs. 7 and 9): an older moraine, formed probably
during an earlier climate shift of the LIA (Schulte,
2002), and a younger moraine, which corresponds to the
!
extension of the glacier in 1876 (Gomez
Ortiz et al.,
1996). Due to global warming since the end of the Little
Ice Age, the Veleta cirque glacier decreased dramatically
at the end of the 19th century and disappeared during
the first half of the 20th century as historical documents
and scientific descriptions confirm. The melting of the
glacier may also be linked to the decrease of annual
precipitation, which is registered by the yearly precipitation record (1902 to 1995) of the University of Granada
(Cartuja), located at the northern foot of the Sierra
Nevada (Rodr!ıguez et al., 1996). Today, only fossil ice
covered by debris remains in the Veleta cirque.
However, the H3 deposits of the Aguas River can also
be ascribed to human-induced slope destabilisation and
alluviation related to the ‘‘Christian Conquest’’. The
expulsion of the Muslims and the following landredistribution (‘‘Repartimiento’’) among the new Christian population in the 16th century brought about the
transformation of small to large-sized agriculture plots
in the lowlands of the basin and at the same time the
abandonment of irrigation systems located on the steep
slopes of Sierra Cabrera and Sierra Bedar (Chapman
et al., 1998). Slope instability and increased surface
runoff during torrential rainstorms may have caused
important erosion processes and have enhanced sediment supply in the river systems. These erosion
processes caused by human impact were reinforced by
the specific climatic conditions during the Little Ice Age.
The youngest fluvial terraces in Vera basin were
deposited at the end of the 19th century and during
the 20th century (Fig. 9). The accumulation of the older
one is partly interpreted as human-induced, resulting
from the important landscape degradation by mining in
Sierra de Bedar between 1846 and 1920. During the
mining boom, population density of the Vera basin
reached its highest peak in history (Chapman et al.,
1998). Agriculture terraces were built in the surrounding
ranges up to the highest areas to keep up with the food
demand. After closing the last mine in 1920, nearly all
agriculture terraces were abandoned. The subsequent
erosion processes are visible today. On the other hand,
historical climatologic studies undertaken by Barriendos
Vallve and Martin Vide (1998) indicate frequent floods
at the beginning of the century. Finally, torrential
rainstorms at the end of the 1940s formed the youngest
terrace of the Antas River. The increase of the
sedimentation rate of the floodplain deposits during
this decade was detected in the lower Aguas valley using
210
Pb-dating techniques.
6. Conclusions: climate or human controlled river
dynamics?
The Mediterranean subtropics are characterised by a
fragile ecosystem sensitive to natural and humaninduced environmental changes. In general, fluvial
systems respond to the modification of their catchments
caused by these environmental changes. The morphological studies undertaken on fluvial terraces and slope
deposits in the Aguas and Antas catchments as well as
on the glacier deposits of the Veleta cirque provide an
interesting data repository of geomorphic response to
the last 23,000 years of paleoenvironmental evolution in
southeast Spain, although the assessment of the
involved factors is complex. In the Aguas River and
Rambla Ancha it has been possible to differentiate
between cold climate stage fluvial terraces associated
with braided channel platforms and terraces deposited
by meandering channels during interglacial periods (e.g.
the Holocene) (Schulte, 1998b, 2002).
Based upon the braided river system deposits of the
lower terraces, we conclude that the fluvial terrace
sequence of the studied river systems is likely to reflect
marked changes in flood and sediment supply patterns,
and in particular, rare high-magnitude events. Obviously, some of these terraces can be associated with
long-term global climate changes, such as the cold stage
climates. Whereas in the Sierra Nevada glacier advances
were predominantly the result of temperature depression, in the lowlands torrential rainstorms and steppe
vegetation primarily controlled surface runoff and river
dynamics, as shown by pollen data (Pons and Reille,
1988). The influence of Pleistocene periglacial environments on the morphogenesis of the southeastern Iberian
Peninsula lowlands are negligible and are limited to
altitudes above 1000 m (Schulte et al., 2000). Overall,
during the LGM and the Late Glacial period, important
erosion and deposition processes occurred simultaneously in the Vera basin and in other Mediterranean
river systems (Faust and D!ıaz del Olmo, 1997; Fuller
* Monne" et al., 1999).
et al., 1998; Pena
The Holocene chronosequences of 5 and 4 river
terraces established for the Aguas and Antas valleys,
respectively, also show considerable fluviodynamic
changes in the valley floor during the last 10,000 years.
The oldest terraces, which correspond to the Atlantic
L. Schulte / Quaternary International 93–94 (2002) 85–100
period (?) and the Middle Ages, can be explained by
natural factors, above all by climate.
Regarding the Little Ice Age, two periods of terrace
accumulation in the Vera basin and glacier advances in
Sierra Nevada have been detected. Nevertheless, the
obtained data should be carefully interpreted due to
chronological uncertainties concerning the absolute ages
of the Antas terrace H2 and the glacier stillstand HM4a.
We do not have enough evidence to confirm if there
exists a synchronism between glacier advance and river
terrace aggradation in southeastern Spain.
Likewise, we should take into consideration that the
two fluviodynamic periods were detected in two
different river systems. The archaeological and historical
studies undertaken by Chapman et al. (1998) point out
that there was no significant chronological difference in
the periods of land-use between the river catchments.
The socio-economic changes of the 16th century affected
the environment of Sierra de Bedar in a similar way to
the Sierra Cabrera. Therefore, the possible slight
differences in chronology between terrace H3 of the
Aguas and H2 of the Antas rivers cannot be interpreted
as compelling evidence for a differentiated fluvial
response to human impact.
Nevertheless, we can assume that the climatically
induced erosion processes and sediment supply of rivers
at the beginning of the Little Ice Age were increased by
the human impact related to the abandonment of the
irrigation systems and agriculture terraces on the hill
slopes after the expulsion of the Muslim population.
Similarly, the mining activity between 1846 and 1920
could have played an important role in river environments and terrace formation from the end of the 19th
century to the beginning of the 20th century.
Channel shifting, terrace accumulation (terrace H3b
of the Antas River) and the increase of the rate of
sedimentation in the lower Aguas floodplain during the
1940s present a recent example of the decisive influence
of torrential rainstorms on river dynamics. This
observation will probably help us to understand the
terrace accumulation of the past.
Fig. 10 shows the Holocene chronostratigraphies of
three river systems located in southwest, southeast and
northeast Spain according to D!ıaz del Olmo and Borja
* Monne! et al. (1996), Garc!ıa
Barrera (1991), Pena
Mart!ınez et al. (1999), and Schulte (1998a, b, 2002).
Tentative correlation can be established regarding
the middle Holocene (Atlantic) and the Middle Age
terraces. In addition, in the two Mediterranean
catchments, the Aguas and Huerva river systems, terrace
formation occurred simultaneously during the Little Ice
Age.
Therefore, taking into consideration the late river
history in the Pleistocene, it can be concluded that the
formation of several of the terrace levels in the Vera
basin during the last 23,000 years was mainly linked
99
with major global climate changes. With regard to the
river dynamics of the last 500 years, human activities
may have played an important role, although it is still
difficult to define the influence of each factor. Future
research should focus on the chronological framework
of the river terrace stratigraphy. Furthermore, a higher
resolution of the database will help to clarify the
influence of minor climate fluctuations and the magnitude of human impact on the Mediterranean River
environments in southeast Spain.
7. Uncited references
Pirazolli, 1991; Wenzens, 1991.
Acknowledgements
These studies were financially supported by the
CIRIT (Grant FI/96-1.255), DGICYT (PB-CT940487) and the European Commission (AGUAS Project,
EV5V-CT94-0487 and PACE Project, ENV4-CT970492). 210Pb dating was carried out at the Palynological
Laboratory of the Department of Geography, University of California at Berkeley. Roger Byrne and Jae Kim
kindly introduced me to this dating technique. I wish to
! Julia" , Research Centre on Earth Science,
thank Ramon
Barcelona, for providing several U/Th dates, Robert
Risch and Montserrat Menasanch, Department of
Social Anthropology and Prehistory, Universitat Au"
tonoma
de Barcelona for their determination of the
artifacts, as well as Dave Passmore for the joint
geomorphological fieldwork and for supplying radiometric dating (IRSL) within the AGUAS Project. I
!
express my gratitude to Antonio Gomez,
Department of
Physical Geography, University of Barcelona and
Francesc Burjachs, Research Centre on Earth Science,
Barcelona, for their helpful suggestions. I also thank
Daniel Dresher, University of Barcelona, for proofreading the entire manuscript.
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