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Origin of biancane and calanchi in East Aliano, southern Italy
Geomorphology 77 (2006) 142 – 152 www.elsevier.com/locate/geomorph
Origin of biancane and calanchi in East Aliano, southern Italy Jamshid Farifteh ⁎, Rob Soeters Department of Earth System Analysis, International Institute for Geo-Information Science and Earth Observation (ITC), The Netherlands Received 19 May 2005; received in revised form 22 December 2005; accepted 23 December 2005 Available online 8 February 2006
Abstract Areas underlain by Plio-Pleistocene marine mudstone in south Italy are severely affected by denudation processes and have been transformed into badlands with two well defined types of landform: biancane and calanchi. In this paper, factors that contributed to the development of the Aliano badlands and particularly to the geneses of biancane and calanchi have been studied, based on aerospace data; field observations on geomorphic processes and geological structure; laboratory measurements of soil and bedrock samples; and morphometric analysis. Several maps and spatial data were prepared to describe factors which are thought to be related with landform formations, such as lineament distribution, elevation, slope, and pipe distribution. Morphometric characteristics of biancane and calanchi (steepness and slope length), dominant active processes, and the dip/orientation of beddings, joints, and fault planes were investigated, and 71 samples of soils and bedrock were taken to characterise their properties. The results of the analyses of the soil/bedrock samples show no significant differences in their properties between biancane and calanchi. Field observations do not support the idea that biancane are the final product of calanchi development, but support the hypothesis that biancane and calanchi are formed under different terrain conditions related to structural patterns and denudation processes of highly erodible materials. The origin of biancane is associated with highly dissected surfaces along a reticular system of small joints. In contrast, calanchi are formed on steep wall-like slopes along larger lineaments where the rate of incision into the slopes surpasses the denudation of the densely vegetated back-slope. © 2006 Elsevier B.V. All rights reserved. Keywords: Badlands; Biancane; Calanchi; Erosion; Structural control; South Italy
1. Introduction Badlands are a common landscape in south Italy, particularly in the Plio-Pleistocene sedimentary basins with weakly consolidated sequences of marine mudstone. Development of these badlands, like many other badlands in the world, can be related to physicochemical properties of surface material, climatic conditions, deforestation and intensive denudation processes ⁎ Corresponding author. Tel.: +31 053 4874227; fax: +31 053 4874336. E-mail address: [email protected] (J. Farifteh). 0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2005.12.012
(Bryan and Yair, 1982). Alexander (1982) described erosion in Italian badlands and associated it with lithology of fine clastic sediments, such as clays, claysilt, marls and poorly cemented sands with an appreciable amount of fines. Several authors have emphasized the importance of the physicochemical properties of the soil in badland erosion, particularly of clayey sediments (Bryan and Yair, 1982; Imeson and Verstraten, 1988). The Aliano badlands in south Italy show two spectacular types of landform: biancane and calanchi. Biancane are characterized as small conical domes (either symmetrical or asymmetrical) dissected by micro-rills and micro-pipes with disordered micro-relief
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(Torri and Bryan, 1997) and often with a vegetation cap. Calanchi are a denudation landform consisting of highly dissected bare and steep slopes (Alexander, 1982) with a parallel to sub-parallel closely spaced network of gullies. The spatial distribution of biancane and calanchi presents a complex pattern, which may reflect even minor differences in geomorphic processes, material properties, structural patterns and morphometric aspects. The genesis of these landforms has been the focus of a scientific debate for more than two decades. Vittorini (1977) explained the origin of calanchi and biancane as related to the granulometric composition, clay mineralogy and the sedimentary environment. Alexander (1982, 1989) argued that cohesive sediments with a high exchangeable sodium percentage are very susceptible to the formation of biancane, whereas the formation of calanchi is related to characteristics of sediments, climatic conditions and geomorphic processes, such as mass movement. According to Moretti and Rodolfi (2000) the genesis and evolution of calanchi landscape in the Atri area of Italy were caused by interaction of environmental components such as highly erodible soils and substrata, intensity of storms causing linear erosion and shallow slides, agricultural practices and tectonic activity. Battaglia et al. (2002) concluded that the formation of biancane and calanchi were due to differences in surface material: biancane tends to form in very fine sediments (silty clays) with a very high clay content (65–70%), whereas calanchi develops in relatively coarser sediments (e.g., sandy clay silts) with a notable sand proportion (6–18%). They also indicated that both landforms may develop in sediments of intermediate grain size and there is no particular trend in the mineralogy of clays which could be correlated with landform development, while pore water composition seems to have a major effect. Torri and Bryan (1997) concluded that the key process in biancane development should be related to the high erodibility of Pliocene marine mudstone. The genetic processes differentiating calanchi and biancane have thus been studied extensively with most focus on the properties of surface materials and the influence of topography, climatic factors, erosion and tectonics (Vittorini, 1977; Alexander, 1989; Torri et al., 1994; Calzolari and Ungaro, 1998; Moretti and Rodolfi, 2000). However, the relations of landform development with the stage of geomorphological evolution, geological setting and denudation processes have not received sufficient attention. In this study, factors including geological setting, material properties and terrain conditions are examined
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to better interpret the origin of biancane and calanchi in the Aliano badlands. Our detailed study on these landforms has provided an explanation for their origin, casting doubt on the previous simple explanations based on material properties in conjunction with climate conditions. 2. Study area The study area is located to the east of Aliano in south Italy, between 40°16′N and 40°21′N, and 16°14′E and 16°20′E (Fig. 1). It is characterised by hot dry summers and mild winters with high intensity rainfall. The area belongs to the Sant'Arcangelo basin, a piggyback basin of the Upper Tertiary age (Hippolyte et al., 1991; Pieri et al., 1994), which was later affected by transcurrent faulting to form a pull-apart depression (Turco et al., 1990). Tectonic activity has strongly influenced basin evolution (Bonini and Sani, 2000) and had large impacts on landform development in the area. The basin is filled with terrigenous to shallow marine successions of the Upper Pliocene to Lower Pleistocene, with four major sedimentary cycles (Caldara et al., 1988). The eastern part of the basin, which includes the study area, is characterised by sediments pertaining to a deltaic system with different phases of progradation and recession. It consists of Lower Pleistocene prodelta clays and muds, sands of a forebed sequence and a coastal environment. The sequence stratigraphy and the structures of the basin have been extensively studied (Vezzani, 1967; Lentini, 1979; Casero et al., 1988; Caldara et al., 1988; Carbone et al., 1991; Catalano et al., 1993; Hippolyte et al., 1994; Pieri et al., 1994; Zavala and Mutti, 1996; Monaco et al., 1998; Gianoa et al., 2000; Cello et al., 2003).
Fig. 1. Location of the study area.
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The structural pattern of the basin resulted from the Neogene subduction of the Apulian continental margin, which also affected the region in general (Casero et al., 1988). Tectonic disturbances and removal of younger deposits including accumulation glacis (Verstappen, 1983) produced a complex pattern of lineaments in the area. Accumulation glacis is referred to in the geological map as terraces (Lentini and Vezzani, 1974), and according to Verstappen (1983) the terraces are considered to be of the Lower to Middle Quaternary. The joint system in the area has mainly developed as a result of the tectonic activities during the synsedimentary deformation of the St. Arcangelo basin (Caldara et al., 1988; Hippolyte et al., 1991) and by the overloading of younger deposits (Verstappen, 1983). The NE/SW and NW/SE joint orientations (Fig. 2) are clearly reflected in the patterns of drainage and morphology, particularly in the northern study area where more sandy layers are intercalated in the sequence (Farifteh and Soeters, 1999). The orientations of joint planes measured at 116 points in the field also show two main populations: 55° to 85° and 330° to 10° from north. Gray-blue marly clay formation covers a considerable part of the study area where both biancane and calanchi are formed (Fig. 3). The clay is folded, with dominant dip of 20° to 25° and strike direction of 315° to 360° from north, and is heavily jointed (Farifteh, 1994). The overall geomorphological development of the area resulted from periodic intensive erosion that began in the Late Pleistocene and continued during the Holocene, as a consequence of tectonic movements, climatic changes and related sea level fluctuations (Verstappen, 1983). The oldest landform in the study
area is an accumulation glacis, which once occupied the whole area of the current badlands. One of the remnants of this glacis is a planation surface capped by gravel deposits on the top of Mt. Serra d'Oro (381 m), one of the highest points in the study area (Fig. 3a). The extension of this glacis can also be inferred from small remnants of gravel deposits at several places on other hilltops at corresponding heights. The field evidence such as remnants of paleosol on the top of biancane, valley infill deposits, formation of recent micropediment in the biancane area, and deposition of recent material in the main valley are indications of various periods of incision and deposition. The gentle undulating surface in Alianello with smooth convex hilltops and shallow valleys (Fig. 3a) reflects a period of incision. Weakly developed calcretes occur on this surface, suggesting a climate with at least one pronounced dry period alternated with a wetter season during which carbonate was mobilised. Triangular facets occur along the border between the deeply incised Fosso degli Embrici and the parallel valleys to the north (Fig. 3a), confirming the influence of the major fault. The close spacing of the parallel valleys reflects the distribution of major joints. Extensive non-concentrated erosion favoured the development of micro-pediments in the dissected uplands and larger valley pediments, most of which are still preserved. Dissection of the infill of the main valleys (e.g., Fosso degli Embrici) reaches locally up to 30 m, and in the parallel valleys the current streambed is located on the mudstone bedrock. The renewed head-ward gully erosion from the valleys is often initiated from tunnels and pipes, which collapse when they grow beyond certain dimensions (usually several meters in diameter) to form gullies. The
Fig. 2. Rose diagram and frequency histogram of lineament orientation, based on enlarged aerial photo (scale 1:8000) field verification.
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Fig. 3. (a) Perspective view of the study area based on digital elevation model superimposed by SPOT panchromatic image. (b) Geological map of a selected area. (c) Landform and lineament map of the selected area.
tunnelling is basically controlled by joints in the mudstone, as can be observed from the correlation between lineaments/joints and the distribution of pipes
(Farifteh and Soeters, 1999). Currently, increased nonconcentrated slope processes on the recently denudated slopes generate large amount of sediments.
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3. Materials and methods Our study was based on the interpretation of aerial photos and SPOT panchromatic images, and subsequent verification of the results in the field. All the data were integrated in a GIS environment to support statistical analyses and the final development of a conceptual model which describes geomorphological genesis and landforms formation in the study area. As a preliminary step, several inventory maps (lithology, landforms, lineaments, process, dominant surface processes, elevation, slope, land cover, and pipe distribution), highlighting the factors thought to be related to landform formation, were prepared. Representative sub-areas with both biancane and calanchi, or those mainly with either biancane or calanchi, were selected for soil sampling and field topographic measurements. In the field, the slope length and slope steepness of 127 calanchi and 265 biancane were measured. The dominant geomorphic processes on calanchi and biancane as well as areas between biancane (interbiancane areas) were recorded in the field at each observation point using a checklist. The dip and orientation of joints and stratification in marly clay bedrock were measured at 222 points. The bedrock was also sampled at 20 sites at a depth of 0–20 cm. To characterise soil properties, 51 soil samples were collected from several types of locations such as biancane flanks, calanchi slopes, the top of biancane, micro-pediments in inter-biancane areas and valleys filled with deposits. The soil samples were collected
Table 1 Descriptive statistics of field-measured slope steepness and length of biancane and calanchi Summary statistics
Biancane
Calanchi
Slope (°)
Length (m)
Slope (°)
Length (m)
Minimum Mean Median Maximum Std. dev. S.E. mean Skewness Kurtosis CV% Number of measurements
20.7 38.9 39.6 54.0 5.20 0.32 0.22 0.74 0.13 n = 265
2.7 7.2 6.7 19.7 2.6 0.16 1.05 2.02 0.35
35.1 45.0 45.0 58.5 4.58 0.41 0.41 0.00 0.10 n = 127
10.5 20.6 19.0 51.0 7.3 0.65 1.11 1.44 0.35
Std. dev. = standard deviation, S.E. mean = standard error of the mean, CV = coefficient of variation (std. dev./mean).
from a depth of 0–20 cm, but for the recent deposits in main valleys, sampling was also performed at depths of 40–60 cm and 80–100 cm. The samples were analysed for grain sizes, Atterberg limits, pH, electrical conductivity (EC), CaCO3 contents, organic matter contents, cation exchange capacity (CEC), water-dispersible clay contents (WDC) and mineral composition. The analyses were performed at the International Soil Reference and Information Centre, the Netherlands, based on procedures described by Van Reeuwijk (1993). Statistical analyses (e.g., ANOVA) were used to quantitatively compare the two landforms in terms of morphometry and material composition. The spatial data derived from the aerial photos together with the
Fig. 4. Biancane types: (a) without a top cover, (b) with paleosol and vegetation cap and (c) with only paleosol cap.
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Fig. 5. Frequency distribution of length (a) and slope (b) of biancane and calanchi.
field and laboratory data were used to model the formation and evolution of biancane and calanchi. 4. Results 4.1. Spatial distribution of biancane and calanchi Overlaying the distribution map of biancane and calanchi on the geological and lineament maps shows that these landforms occur only on the gray-blue marly clay where joints and lineaments densely occur (Fig. 3a, b). Based on the presence and abundance of these landforms, the study area can be divided into four major landscape types (Fig. 3c): (1) the area mainly with calanchi in the northern and northwestern study area; (2) the area with both calanchi and biancane in the northern
part of the Fosso Degli Embrici valley; (3) the areas mainly with biancane in several places in the study area such as the northeastern and central parts of the badlands; and (4) the areas without calanchi and biancane in several zones where the bedrock is sandstone or conglomerate as well as where the grayblue marly clay is covered by dense vegetation. 4.2. Geomorphological characteristics of biancane and calanchi Biancane in the study area are mostly formed on slopes where the landscape is highly dissected by rills, gullies and collapsed pipes. Tops of biancane are occasionally covered with paleosol (Fig. 4) with a thickness of 0.6–1.0 m, consisting of highly weathered
Fig. 6. Example of calanchi. (a) Bare face-slope with closely spaced parallel network of gullies. (b) Back-slope of the calanchi covered with dense vegetation.
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J. Farifteh, R. Soeters / Geomorphology 77 (2006) 142–152 Table 3 Results of chemical analysis for samples taken from biancane and calanchi
and leached clays or silty soil similar to sediment recently accumulated at the foot of biancane. A paleosurface through the tops of these biancane can be reconstructed. Biancane close to the main valley are considered to have formed at an early stage of the dissection of the paleosurface. They are lower than younger biancane distant from the main valley, and do not have the soil cap on the top. Biancane have slope lengths of 2.7 to 19.7 m, with an average of 7.2 m, and slopes of ca. 20° to 50° (Table 1 and Fig. 5). A combination of the average slope length and a slope of 40° corresponds to a biancane height of 6 to 7 m. The locations of calanchi are mainly controlled by joints and faults. Calanchi are characterised by a dense parallel system of fluting gullies with narrow and sharp pillars (Fig. 6a). The back-slopes of calanchi are covered by dense vegetation (Fig. 6b), which slows down backward erosion of the front-slopes and thus their steepness is maintained. The slope angle of calanchi varies between ca. 35° to 60°, and slope lengths range from 10.5 to 51.0 m (Table 1 and Fig. 5). About 67% of the observed calanchi have slope lengths between 10 and 22 m in which 41% have a length of 14 to 20 m.
Sample no.
pHs ECe (mS/cm) BSP (%) Na (mmolc/l) Ca (mmolc/l) Mg (mmolc/l) K (mmolc/l) SAR (mmolc/l) PAR (mmolc/l) ESP (%)
Biancane
Calanchi
5b
6b
9b
2c
3c
5c
8.1 16.0 83.0 198.3 20.6 23.0 4.3 43.0 0.9 38.0
8.8 8.8 97.0 93.9 4.0 3.6 1.1 48.0 0.6 41.0
8.6 7.0 110.0 69.6 2.2 3.2 0.8 42.0 0.5 38.0
8.8 18.0 70.0 219.6 14.3 15.3 3.4 57.0 0.9 45.0
8.6 9.2 100.0 93.0 5.0 3.3 1.5 46.0 0.7 40.0
8.5 8.0 87.0 80.0 4.4 4.6 1.4 38.0 0.7 35.0
pHs = pH reading of saturated soil paste. ECe = electrical conductivity of saturation extract. BSP = base saturation percentage, SAR = sodium adsorption ratio of saturated extract. PAR = potassium adsorption ratio of saturated extract. ESP = exchangeable sodium percentage.
soluble salts, and are very dispersive due to excess exchangeable sodium. The X-ray diffraction results (Table 4) show a relatively large quantity of smectite, indicating that both biancane and calanchi are formed on expandable clay, which agrees with the high cation exchange capacity (CEC) and the values of Atterberg limits. Similarly to previous results (Torri and Bryan, 1997; Phillips and Robinson, 1998; Moretti and Rodolfi, 2000), the soil analyses confirm the susceptibility of the gray-blue marly clay to erosion. One-way ANOVA applied to data in Tables 1 and 2 showed no significant (p N 0.05) differences in material properties between biancane and calanchi. Granulometric analysis also showed no clear differentiation between the samples taken from both landforms (Fig. 7), which corroborates the results obtained by Alexander (1982), but contradicts those of Battaglia et al. (2002) who suggest that biancane are mainly formed on silty clay
4.3. Material properties Tables 2–4 show the results of the laboratory analyses on the soil samples taken from biancane and calanchi. Summary statistics of several physical soil properties are given in Table 2. The particle size distribution data shows that biancane and calanchi are mainly composed of very fine materials (silty clay). Table 3 shows that pH values were higher than 8.0 and the exchangeable sodium percentages (ESP) are higher than 15 for all the samples, indicating that they are alkaline soils. They also contain a high concentration of
Table 2 Summary statistic of soil properties calculated for samples collected from biancane and calanchi landforms Summary statistics
Biancane
Calanchi
Sands (%)
Silts (%)
Clays (%)
L.L.
P.L.
P.I.
Sands (%)
Silts (%)
Clays (%)
L.L.
P.L.
P.I.
Minimum Maximum Mean Media Std. dev. S.E. mean Skewness Kurtosis CV%
0.7 3.3 1.58 1.4 0.93 0.33 0.68 − 0.71 0.59
48.3 57.8 51.7 50.95 3.44 1.22 0.72 − 0.81 0.07
40.2 51.0 46.7 47.5 3.86 1.37 −0.59 0.99 0.08
45.0 52.0 48.6 48.5 2.56 0.90 −0.04 −1.40 0.05
20.4 23.1 22.2 22.3 0.77 0.26 − 1.36 1.45 0.04
24.0 30.0 26.9 26.5 2.23 0.79 0.17 −1.49 0.08
0.30 3.90 1.32 0.60 1.32 0.44 1.10 − 0.36 1.0
45.7 56.4 50.9 50.0 3.35 1.12 0.42 − 0.60 0.07
40.5 53.7 47.8 49.0 3.99 1.33 − 0.48 − 0.48 0.08
42.0 53.0 47.4 48.0 3.94 1.31 0.04 − 0.86 0.08
20.1 23.7 21.7 21.7 1.26 0.42 0.32 − 1.02 0.05
21.0 30.0 25.9 26 2.9 0.96 − 0.41 − 0.62 0.11
N = 9, L.L. = liquid limit, P.L. = plastic limit and P.I. = plasticity index, std. dev. = standard deviation, S.E. mean = standard error of the mean, CV = coefficient of variation (std. dev./mean).
tr–+
ILL SME tr.
tr–+
ILL SME tr.
tr–+
ILL SME tr.
4.4. Geomorphic processes
ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. Quartz
ILL SME tr.
Mixed layer clays are classified based on the ordering scheme: regular and random. tr. = race, +–++ = estimate of relative abundance, * = well crystallised, ILL = illite, SME = smectite.
ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr.
ILL SME tr.
tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+
tr–+ tr–+ tr–+
Chlorite Mixed layer clay Regular Random Components
149
and clayey silt while calanchi are on clayey silt and silty sand.
ILL SME tr.
tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+
tr–+
tr–+
+ + + + + + + Smectite Low charge High charge
Mica/illite
+
+
+ + +
+
+
+– ++ tr–+
+– ++ tr–+
+
+– ++ tr–+
+
tr–+
+– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++
+– ++
+
++
+– ++ +– ++ +– ++
11c 10c
++ ++ ++
7c 6c
+– ++ +– ++ ++
5c 4c
++ ++
3c 2c
+– ++ +– ++ ++
1c 9b
+– ++ +– ++ ++
8b 7b
++ ++
+– ++ +– ++ +– ++ +– ++ +– ++ +– ++
6b 5b 4b 3b 2b 1b
+– ++ +– ++ Kaolinite*
Calanchi Biancane Sample no.
Table 4 X-ray diffraction of biancane and calanchi samples
++
8c
9c
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Field observations of active denudation processes on biancane and calanchi as well as areas between biancane (inter-biancane areas) are given in Table 5. The denudation processes in the biancane areas can be divided into two categories. The active processes on biancane flanks are sheet wash, small-scale riling and piping (Torri et al., 1994) and slumping, which are comparable to processes acting on the interfluves of the calanchi slopes (Table 5). The sediment produced by erosion of biancane slopes forms micro-pediments at their foot. These micro-pediments are rather irregular in height, as they are controlled by local factors such as base levels for gullies, collapsed pipes and tunnels. The active processes in the inter-biancane area (Table 5 and Fig. 8) are rilling, gullying, piping and deposition of silty clays (with a thickness of a few cm to 1.5 m). The inter-biancane area is mainly composed of micropediments, and dominated by local gullies as well as partly collapsed tunnels or pipes. Rilling, gullying and slumping are the most common processes operating on the calanchi slopes (Table 5). They occurred in all observed calanchi slopes and have a major impact in the development of calanchi. Other processes, such as sheet wash, microrilling and micro-piping are active on the interfluves. Small landslides can often be observed at gully heads, where calanchi slopes meet gentle back-slopes covered with silty soils provided by ploughing, weathering and leaching. These landslides produce debris flows, resulting in the deposition of flow-lobes on much gentler foot-slopes (micro-pediments) at the base of the gullies. 5. Discussion and landform development models 5.1. Factors affecting distribution of biancane and calanchi Geomorphological, geological, pedological and land cover data for the study area indicate complex relationships among lithology, geological structure, vegetation and denudation processes. However, the interpretation of the data also provides some inferences about landform development in the study area. The geological setting which has an extensive joint system due to tectonic disturbances, facilitated terrain
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Fig. 7. Cumulative curves of particle size distribution of samples taken from biancane (black dotted lines) and calanchi (red solid lines). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
dissection by erosion. The structurally controlled strike ridges were developed and less erosion has been taking place along apparent dip slopes because of less converged water flow, while the higher rates of erosion on the other side of the slopes maintain steep slopes. Consequently, the structural setting accounts for a dense vegetation cover on the back-slopes but a very sparse cover on the face-slopes. Micro-climate may also affect vegetation density, since south-facing slopes may react differently from north-facing slopes due to higher insolation. Anthropogenic factors such as deforestation and overgrazing are among the factors that also affect vegetation density and erosion intensity (Kayser, 1964; Verstappen, 1983). Overall, the differences in vegetation density seem to play a major role in determining geomorphic processes in the study area. Material properties such as high erodibility and dispersibility of gray-blue marly clay eased gullying and piping erosion, and consequently had a large impact on the formation of biancane and calanchi and in turn the development of the Aliano badland. The physical and chemical analyses of the soil/bedrock samples did not show significant differences in material properties between biancane and calanchi, although in many publications the origin of the two landforms has been related to granulometric composition, clay mineralogy and the sedimentation environment (Vittorini, 1977; Alexander, 1982, 1989; Battaglia et al., 2002).
As noted before, both biancane and calanchi are only formed on the gray-blue marly clay. In the areas mainly with calanchi, the clay is overlain by the Aliano sand or conglomerates, which have protective effects like dense vegetation cover and therefore prevent further linear erosion. These areas as well as the areas with both calanchi and biancane are characterised by several major lineaments (Fig. 3c). This correlation suggests a strong influence of geological structure on the formation of calanchi. The areas mainly with biancane are not underlain by the Aliano sand or conglomerate and away from major lineaments, but are associated with reticular joint systems (Fig. 3c). In summary, it is not variation in the properties of soil/bedrock material but the structural patterns in bedrock and the existence of cap vegetations or rocks which have strongly controlled the distribution of biancane and calanchi. 5.2. Model of biancane formation Based on the results of our investigation, a model of biancane/calanchi formation is proposed. The initiation of biancane appears to be associated with reticular joint systems along which a network of rills formed. Then an interconnected network of gullies and collapsed pipes were formed due to strong erosion, generating block-like small hills with vegetated tops and bare flanks. During periods of weak erosion,
Table 5 Observed denudation process active on biancane, calanchi and inter-biancane areas Landforms
Total Number of observations of dominant processes number of Sheet wash Micro-rilling Rilling Rill/piping Piping/tunnelling Gullying Shallow slumping Slumping observations
Biancane 170 Inter-biancane area 75 Calanchi 127
170 75 127
170 0 0
170 75 127
151 71 58
0 25 0
0 39 127
87 0 0
0 0 127
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Fig. 8. Biancane with micro-pediments and inter-biancane area with dense vegetation cover.
small-scale riling, piping and slumping were active on the flanks of each blocky hill, reducing the size of the hills and rounding their shape. Such processes ultimately provided small conical domes or pinnacles known as biancane. By this time, the inter-biancane areas were stabilised because of lower topographic gradients and less concentrated surface flow, inducing deposition and providing an improved vegetation cover. At the same time, micro-pediments were formed at the foot of the domes or pinnacles. The water table in the parent material, which is mainly controlled by joint distribution and topographic relief, provided the base level of erosion and affected the height of biancane. 5.3. Model of calanchi formation Calanchi formed on steep straight face-slopes, mainly controlled by lineaments along deeply incised valleys where the rate of incision is much higher than the lowering of the densely vegetated backslopes. The face-slopes controlled by lineaments have the topography of long straight walls with a small variation in height. Therefore, erosion on the face-slopes was not concentrated in a few places, and formed a system of closely spaced small parallel gullies and interfluves with small pillars. Shallow mudslides from gully heads also contributed to erosion. The processes on the face-slopes seem to be in dynamic equilibrium, resulting in parallel slope retreat and conservation of calanchi topography. The vegetation cover on the back-slopes prevents linear erosion and thus plays a major role in maintaining calanchi. Calanchi can be destroyed if rapid erosion occurs on the back-slopes or strong linear erosion occurs on a certain part of the face slope. Therefore, some
researchers thought that the development of calanchi leads to the genesis of biancane. However our model of the biancane formation noted above indicates that biancane in the study area cannot be regarded as a product from calanchi. 6. Conclusions Biancane and calanchi in the Aliano badlands were both formed on highly dispersible mudstone but under different structural controls and denudation processes. Biancane are mostly initiated on slopes where the surface has been highly dissected along a reticular system of joints. The erosional remnants of the areas between the joints represent biancane. Biancane are not the final product of calanchi development, even though occasionally a dissected calanchi may ultimately form biancane. Calanchi are located along major lineaments and are generated by rapid fluvial erosion where the rate of incision below the face-slope surpasses the erosion on the densely vegetated backslope. Calanchi are maintained by the parallel retreat of the face-slope under a condition of dynamic equilibrium. Laboratory analysis of soil/bedrock samples taken from biancane and calanchi showed no significant differences, casting doubt on previous studies which attributed the differences between the two landforms to material differences. Acknowledgements Many thanks are due to Professor T. Oguchi, Dr. F. Corsi, Professor H. Th. Verstappen and Dr. M. Yemfack for their constructive comments to improve the manuscript. The laboratory analysis performed by the International Soil Reference and Information Centre is also gratefully acknowledged.
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References Alexander, D.E., 1982. Difference between calanchi and biancane badlands in Italy. In: Bryan, R.B., Yair, A. (Eds.), Badlands Geomorphology and Piping. Geo Books, Norwich, pp. 71–87. Alexander, D.E., 1989. Calanchi-accelerated erosion in Italy. Geography 65 (2), 95–100. Battaglia, S., Leoni, L., Satori, F., 2002. Mineralogical and grain size composition of clays developing calanchi and biancane erosional landforms. Geomorphology 49, 153–170. Bonini, M., Sani, F., 2000. Pliocene–Quaternary transpressional evolution of the Anzi-Calvello and Northern S. Arcangelo basins (Basilicata, Southern Apennines, Italy) as a consequence of deepseated fault reactivation. Marine and Petroleum Geology 17, 909–927. Bryan, R.B., Yair, A. (Eds.), 1982. Badland Geomorphology and Piping. Geo Books, Norwich, pp. 1–22. Caldara, M., Loiacono, F., Morlotti, E., Pieri, P., Sabato, L., 1988. I depositi Pliopeistocenici della parte nord del Bacino di S. Arcangelo (Appennino Lucano): Caratteri geologici e Paleoambientali. Memorie della Societa Geologica Italiana 41, 391–410. Calzolari, C., Ungaro, F., 1998. Geomorphic features of a badland (biancane) area (Central Italy): characterisation, distribution and quantitative spatial analysis. Catena 31, 237–256. Carbone, S., Catalano, S., Lazzari, S., Lentini, F., Monaco, C., 1991. Presentazione della carta geologica del bacino del fiume Agri (Basilicata). Memorie della Societa Geologica Italiana 47, 129–143. Casero, P., Roure, F., Endignoux, L., Moretti, I., Muller, C., Sage, L., Vially, R., 1988. Neogene geodynamic evolution of the Southern Apennines. Memorie della Societa Geologica Italiana 41, 109–120. Catalano, S., Monaco, C., Tortorici, L., Tansi, C., 1993. Pleistocene strike-slip tectonics in the Lucanian Apennine (Southern Italy). Tectonics 12, 656–665. Cello, G., Tondi, G., Micarelli, E., Mattioni, L., 2003. Active tectonics and earthquake sources in the epicentral area of the 1857 Basilicata earthquake (southern Italy). Journal of Geodynamics 36, 37–50. Farifteh, J., 1994. A model for the geomorphological development of an area in east of Alianello (Basilicata, Southern Italy). MSc thesis, International Institute for Geo-Information Science and Earth Observation (ITC). Enschede, The Netherlands. Farifteh, J., Soeters, R., 1999. Factors underlying piping in the Basilicata region, southern Italy. Geomorphology 26, 239–251. Gianoa, I.S., Maschioa, L., Alessiob, M., Ferrantia, L., 2000. Radiocarbon dating of active faulting in the Agri high valley, southern Italy. Journal of Geodynamics 29, 371–386. Hippolyte, J.C., Angelier, J., Roure, F., Muller, C.R., 1991. Geometric et mecanisme de formation d'un bassin “Piggyback”: le bassin de Sant'Arcangelo (Italie meridionale). Comptes Rendus de l'Académie des Sciences. Paris 312 (II), 1373–1378.
Hippolyte, J.C., Angelier, J., Roure, F., Casero, P., 1994. Piggyback basin development and thrust belt evolution: structural and palaeostress analyses of Plio-Quaternary basins in the Southern Apennines. Journal of Structural Geology 16, 159–173. Imeson, A.C., Verstraten, J.M., 1988. Rills on badland slope: a physicochemically controlled phenomenon. Geomorphic processes in Environments with strong seasonal contrasts, Vol I: Hillslope processes. Catena. Supplement 12, 139–150. Kayser, B., 1964. Recherches sur les sols et l' erosion en Italie meridionale. Luncanie. Paris, 127. Lentini, F., 1979. Le Unita' Sicilidi della val d'Agri (Appennino Lucano). Geologica Romana 18, 215–224. Lentini, F., Vezzani, L., 1974. Note illustrative del Foglio 506 S. Arcangelo. V. di 46, I.R.P.I., Cosenza. Monaco, C., Tortorici, L., Paltrinieri, W., 1998. Structural evolution of the Lucanian Apennines, southern Italy. Journal of Structural Geology 20, 617–638. Moretti, S., Rodolfi, G., 2000. A typical “calanchi” landscape on the Eastern Apennine margin (Atri, Central Italy): geomorphological features and evolution. Catena 40, 217–228. Phillips, C.P., Robinson, D.A., 1998. The impact of land use on the erodibility of dispersive clay soils in central and southern Italy. Soil Use and Management 14, 155–161. Pieri, P., Sabato, L., Loiacono, F., Marino, M., 1994. Il bacino di piggyback di Sant'Arcangelo: evoluzione tettonico-sedimentaria. Bollettino della Societa Geologica Italiana 113, 465–481. Torri, D., Bryan, R.B., 1997. Micropiping processes and biancane evolution in Southeast Tuscany, Italy. Geomorphology 20 (3–4), 219–235. Torri, D., Colica, A., Rockwell, D., 1994. Preliminary study of the erosion mechanisms in biancane badland (Tuscany, Italy). Catena 23, 281–294. Turco, E., Maresca, R., Cappadona, P., 1990. La tettonica pliopleistocenica del confine calabro-lucano: modello cinematico. Memorie della Societa Geologica Italiana 45, 519–529. Van Reeuwijk, L.P., 1993. Procedures for Soil Analysis. International Soil Reference and Information Centre (ISRIC), Wageningen, The Netherlands. Verstappen, H.Th., 1983. Geomorphology of the Agri valley, Southern Italy. ITC Journal 4, 291–301. Vezzani, L., 1967. Il bacino plio-pleistocenico di S. Arcangelo (Lucania). Atti dell'Accademia Gioenia di Scienze Naturali in Catania S6. Supplemento di scienze geologiche 18, 207–227. Vittorini, S., 1977. Some observations about origin and role of two kinds of erosions on clays; calanchi and biancane. Bollettino della Società Geografica Italiana Roma-Ser. X 25–54. Zavala, C., Mutti, E., 1996. Stratigraphy of the Plio-Pleistocene Sant'Arcangelo Basin Basilicata, Italy. Atti Riunione Gruppo Sedimentologia del C.N.R., Catania, pp. 279–282 (10–14 Oct.).
Origin of biancane and calanchi in East Aliano, southern Italy Jamshid Farifteh ⁎, Rob Soeters Department of Earth System Analysis, International Institute for Geo-Information Science and Earth Observation (ITC), The Netherlands Received 19 May 2005; received in revised form 22 December 2005; accepted 23 December 2005 Available online 8 February 2006
Abstract Areas underlain by Plio-Pleistocene marine mudstone in south Italy are severely affected by denudation processes and have been transformed into badlands with two well defined types of landform: biancane and calanchi. In this paper, factors that contributed to the development of the Aliano badlands and particularly to the geneses of biancane and calanchi have been studied, based on aerospace data; field observations on geomorphic processes and geological structure; laboratory measurements of soil and bedrock samples; and morphometric analysis. Several maps and spatial data were prepared to describe factors which are thought to be related with landform formations, such as lineament distribution, elevation, slope, and pipe distribution. Morphometric characteristics of biancane and calanchi (steepness and slope length), dominant active processes, and the dip/orientation of beddings, joints, and fault planes were investigated, and 71 samples of soils and bedrock were taken to characterise their properties. The results of the analyses of the soil/bedrock samples show no significant differences in their properties between biancane and calanchi. Field observations do not support the idea that biancane are the final product of calanchi development, but support the hypothesis that biancane and calanchi are formed under different terrain conditions related to structural patterns and denudation processes of highly erodible materials. The origin of biancane is associated with highly dissected surfaces along a reticular system of small joints. In contrast, calanchi are formed on steep wall-like slopes along larger lineaments where the rate of incision into the slopes surpasses the denudation of the densely vegetated back-slope. © 2006 Elsevier B.V. All rights reserved. Keywords: Badlands; Biancane; Calanchi; Erosion; Structural control; South Italy
1. Introduction Badlands are a common landscape in south Italy, particularly in the Plio-Pleistocene sedimentary basins with weakly consolidated sequences of marine mudstone. Development of these badlands, like many other badlands in the world, can be related to physicochemical properties of surface material, climatic conditions, deforestation and intensive denudation processes ⁎ Corresponding author. Tel.: +31 053 4874227; fax: +31 053 4874336. E-mail address: [email protected] (J. Farifteh). 0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2005.12.012
(Bryan and Yair, 1982). Alexander (1982) described erosion in Italian badlands and associated it with lithology of fine clastic sediments, such as clays, claysilt, marls and poorly cemented sands with an appreciable amount of fines. Several authors have emphasized the importance of the physicochemical properties of the soil in badland erosion, particularly of clayey sediments (Bryan and Yair, 1982; Imeson and Verstraten, 1988). The Aliano badlands in south Italy show two spectacular types of landform: biancane and calanchi. Biancane are characterized as small conical domes (either symmetrical or asymmetrical) dissected by micro-rills and micro-pipes with disordered micro-relief
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(Torri and Bryan, 1997) and often with a vegetation cap. Calanchi are a denudation landform consisting of highly dissected bare and steep slopes (Alexander, 1982) with a parallel to sub-parallel closely spaced network of gullies. The spatial distribution of biancane and calanchi presents a complex pattern, which may reflect even minor differences in geomorphic processes, material properties, structural patterns and morphometric aspects. The genesis of these landforms has been the focus of a scientific debate for more than two decades. Vittorini (1977) explained the origin of calanchi and biancane as related to the granulometric composition, clay mineralogy and the sedimentary environment. Alexander (1982, 1989) argued that cohesive sediments with a high exchangeable sodium percentage are very susceptible to the formation of biancane, whereas the formation of calanchi is related to characteristics of sediments, climatic conditions and geomorphic processes, such as mass movement. According to Moretti and Rodolfi (2000) the genesis and evolution of calanchi landscape in the Atri area of Italy were caused by interaction of environmental components such as highly erodible soils and substrata, intensity of storms causing linear erosion and shallow slides, agricultural practices and tectonic activity. Battaglia et al. (2002) concluded that the formation of biancane and calanchi were due to differences in surface material: biancane tends to form in very fine sediments (silty clays) with a very high clay content (65–70%), whereas calanchi develops in relatively coarser sediments (e.g., sandy clay silts) with a notable sand proportion (6–18%). They also indicated that both landforms may develop in sediments of intermediate grain size and there is no particular trend in the mineralogy of clays which could be correlated with landform development, while pore water composition seems to have a major effect. Torri and Bryan (1997) concluded that the key process in biancane development should be related to the high erodibility of Pliocene marine mudstone. The genetic processes differentiating calanchi and biancane have thus been studied extensively with most focus on the properties of surface materials and the influence of topography, climatic factors, erosion and tectonics (Vittorini, 1977; Alexander, 1989; Torri et al., 1994; Calzolari and Ungaro, 1998; Moretti and Rodolfi, 2000). However, the relations of landform development with the stage of geomorphological evolution, geological setting and denudation processes have not received sufficient attention. In this study, factors including geological setting, material properties and terrain conditions are examined
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to better interpret the origin of biancane and calanchi in the Aliano badlands. Our detailed study on these landforms has provided an explanation for their origin, casting doubt on the previous simple explanations based on material properties in conjunction with climate conditions. 2. Study area The study area is located to the east of Aliano in south Italy, between 40°16′N and 40°21′N, and 16°14′E and 16°20′E (Fig. 1). It is characterised by hot dry summers and mild winters with high intensity rainfall. The area belongs to the Sant'Arcangelo basin, a piggyback basin of the Upper Tertiary age (Hippolyte et al., 1991; Pieri et al., 1994), which was later affected by transcurrent faulting to form a pull-apart depression (Turco et al., 1990). Tectonic activity has strongly influenced basin evolution (Bonini and Sani, 2000) and had large impacts on landform development in the area. The basin is filled with terrigenous to shallow marine successions of the Upper Pliocene to Lower Pleistocene, with four major sedimentary cycles (Caldara et al., 1988). The eastern part of the basin, which includes the study area, is characterised by sediments pertaining to a deltaic system with different phases of progradation and recession. It consists of Lower Pleistocene prodelta clays and muds, sands of a forebed sequence and a coastal environment. The sequence stratigraphy and the structures of the basin have been extensively studied (Vezzani, 1967; Lentini, 1979; Casero et al., 1988; Caldara et al., 1988; Carbone et al., 1991; Catalano et al., 1993; Hippolyte et al., 1994; Pieri et al., 1994; Zavala and Mutti, 1996; Monaco et al., 1998; Gianoa et al., 2000; Cello et al., 2003).
Fig. 1. Location of the study area.
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The structural pattern of the basin resulted from the Neogene subduction of the Apulian continental margin, which also affected the region in general (Casero et al., 1988). Tectonic disturbances and removal of younger deposits including accumulation glacis (Verstappen, 1983) produced a complex pattern of lineaments in the area. Accumulation glacis is referred to in the geological map as terraces (Lentini and Vezzani, 1974), and according to Verstappen (1983) the terraces are considered to be of the Lower to Middle Quaternary. The joint system in the area has mainly developed as a result of the tectonic activities during the synsedimentary deformation of the St. Arcangelo basin (Caldara et al., 1988; Hippolyte et al., 1991) and by the overloading of younger deposits (Verstappen, 1983). The NE/SW and NW/SE joint orientations (Fig. 2) are clearly reflected in the patterns of drainage and morphology, particularly in the northern study area where more sandy layers are intercalated in the sequence (Farifteh and Soeters, 1999). The orientations of joint planes measured at 116 points in the field also show two main populations: 55° to 85° and 330° to 10° from north. Gray-blue marly clay formation covers a considerable part of the study area where both biancane and calanchi are formed (Fig. 3). The clay is folded, with dominant dip of 20° to 25° and strike direction of 315° to 360° from north, and is heavily jointed (Farifteh, 1994). The overall geomorphological development of the area resulted from periodic intensive erosion that began in the Late Pleistocene and continued during the Holocene, as a consequence of tectonic movements, climatic changes and related sea level fluctuations (Verstappen, 1983). The oldest landform in the study
area is an accumulation glacis, which once occupied the whole area of the current badlands. One of the remnants of this glacis is a planation surface capped by gravel deposits on the top of Mt. Serra d'Oro (381 m), one of the highest points in the study area (Fig. 3a). The extension of this glacis can also be inferred from small remnants of gravel deposits at several places on other hilltops at corresponding heights. The field evidence such as remnants of paleosol on the top of biancane, valley infill deposits, formation of recent micropediment in the biancane area, and deposition of recent material in the main valley are indications of various periods of incision and deposition. The gentle undulating surface in Alianello with smooth convex hilltops and shallow valleys (Fig. 3a) reflects a period of incision. Weakly developed calcretes occur on this surface, suggesting a climate with at least one pronounced dry period alternated with a wetter season during which carbonate was mobilised. Triangular facets occur along the border between the deeply incised Fosso degli Embrici and the parallel valleys to the north (Fig. 3a), confirming the influence of the major fault. The close spacing of the parallel valleys reflects the distribution of major joints. Extensive non-concentrated erosion favoured the development of micro-pediments in the dissected uplands and larger valley pediments, most of which are still preserved. Dissection of the infill of the main valleys (e.g., Fosso degli Embrici) reaches locally up to 30 m, and in the parallel valleys the current streambed is located on the mudstone bedrock. The renewed head-ward gully erosion from the valleys is often initiated from tunnels and pipes, which collapse when they grow beyond certain dimensions (usually several meters in diameter) to form gullies. The
Fig. 2. Rose diagram and frequency histogram of lineament orientation, based on enlarged aerial photo (scale 1:8000) field verification.
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Fig. 3. (a) Perspective view of the study area based on digital elevation model superimposed by SPOT panchromatic image. (b) Geological map of a selected area. (c) Landform and lineament map of the selected area.
tunnelling is basically controlled by joints in the mudstone, as can be observed from the correlation between lineaments/joints and the distribution of pipes
(Farifteh and Soeters, 1999). Currently, increased nonconcentrated slope processes on the recently denudated slopes generate large amount of sediments.
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3. Materials and methods Our study was based on the interpretation of aerial photos and SPOT panchromatic images, and subsequent verification of the results in the field. All the data were integrated in a GIS environment to support statistical analyses and the final development of a conceptual model which describes geomorphological genesis and landforms formation in the study area. As a preliminary step, several inventory maps (lithology, landforms, lineaments, process, dominant surface processes, elevation, slope, land cover, and pipe distribution), highlighting the factors thought to be related to landform formation, were prepared. Representative sub-areas with both biancane and calanchi, or those mainly with either biancane or calanchi, were selected for soil sampling and field topographic measurements. In the field, the slope length and slope steepness of 127 calanchi and 265 biancane were measured. The dominant geomorphic processes on calanchi and biancane as well as areas between biancane (interbiancane areas) were recorded in the field at each observation point using a checklist. The dip and orientation of joints and stratification in marly clay bedrock were measured at 222 points. The bedrock was also sampled at 20 sites at a depth of 0–20 cm. To characterise soil properties, 51 soil samples were collected from several types of locations such as biancane flanks, calanchi slopes, the top of biancane, micro-pediments in inter-biancane areas and valleys filled with deposits. The soil samples were collected
Table 1 Descriptive statistics of field-measured slope steepness and length of biancane and calanchi Summary statistics
Biancane
Calanchi
Slope (°)
Length (m)
Slope (°)
Length (m)
Minimum Mean Median Maximum Std. dev. S.E. mean Skewness Kurtosis CV% Number of measurements
20.7 38.9 39.6 54.0 5.20 0.32 0.22 0.74 0.13 n = 265
2.7 7.2 6.7 19.7 2.6 0.16 1.05 2.02 0.35
35.1 45.0 45.0 58.5 4.58 0.41 0.41 0.00 0.10 n = 127
10.5 20.6 19.0 51.0 7.3 0.65 1.11 1.44 0.35
Std. dev. = standard deviation, S.E. mean = standard error of the mean, CV = coefficient of variation (std. dev./mean).
from a depth of 0–20 cm, but for the recent deposits in main valleys, sampling was also performed at depths of 40–60 cm and 80–100 cm. The samples were analysed for grain sizes, Atterberg limits, pH, electrical conductivity (EC), CaCO3 contents, organic matter contents, cation exchange capacity (CEC), water-dispersible clay contents (WDC) and mineral composition. The analyses were performed at the International Soil Reference and Information Centre, the Netherlands, based on procedures described by Van Reeuwijk (1993). Statistical analyses (e.g., ANOVA) were used to quantitatively compare the two landforms in terms of morphometry and material composition. The spatial data derived from the aerial photos together with the
Fig. 4. Biancane types: (a) without a top cover, (b) with paleosol and vegetation cap and (c) with only paleosol cap.
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Fig. 5. Frequency distribution of length (a) and slope (b) of biancane and calanchi.
field and laboratory data were used to model the formation and evolution of biancane and calanchi. 4. Results 4.1. Spatial distribution of biancane and calanchi Overlaying the distribution map of biancane and calanchi on the geological and lineament maps shows that these landforms occur only on the gray-blue marly clay where joints and lineaments densely occur (Fig. 3a, b). Based on the presence and abundance of these landforms, the study area can be divided into four major landscape types (Fig. 3c): (1) the area mainly with calanchi in the northern and northwestern study area; (2) the area with both calanchi and biancane in the northern
part of the Fosso Degli Embrici valley; (3) the areas mainly with biancane in several places in the study area such as the northeastern and central parts of the badlands; and (4) the areas without calanchi and biancane in several zones where the bedrock is sandstone or conglomerate as well as where the grayblue marly clay is covered by dense vegetation. 4.2. Geomorphological characteristics of biancane and calanchi Biancane in the study area are mostly formed on slopes where the landscape is highly dissected by rills, gullies and collapsed pipes. Tops of biancane are occasionally covered with paleosol (Fig. 4) with a thickness of 0.6–1.0 m, consisting of highly weathered
Fig. 6. Example of calanchi. (a) Bare face-slope with closely spaced parallel network of gullies. (b) Back-slope of the calanchi covered with dense vegetation.
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and leached clays or silty soil similar to sediment recently accumulated at the foot of biancane. A paleosurface through the tops of these biancane can be reconstructed. Biancane close to the main valley are considered to have formed at an early stage of the dissection of the paleosurface. They are lower than younger biancane distant from the main valley, and do not have the soil cap on the top. Biancane have slope lengths of 2.7 to 19.7 m, with an average of 7.2 m, and slopes of ca. 20° to 50° (Table 1 and Fig. 5). A combination of the average slope length and a slope of 40° corresponds to a biancane height of 6 to 7 m. The locations of calanchi are mainly controlled by joints and faults. Calanchi are characterised by a dense parallel system of fluting gullies with narrow and sharp pillars (Fig. 6a). The back-slopes of calanchi are covered by dense vegetation (Fig. 6b), which slows down backward erosion of the front-slopes and thus their steepness is maintained. The slope angle of calanchi varies between ca. 35° to 60°, and slope lengths range from 10.5 to 51.0 m (Table 1 and Fig. 5). About 67% of the observed calanchi have slope lengths between 10 and 22 m in which 41% have a length of 14 to 20 m.
Sample no.
pHs ECe (mS/cm) BSP (%) Na (mmolc/l) Ca (mmolc/l) Mg (mmolc/l) K (mmolc/l) SAR (mmolc/l) PAR (mmolc/l) ESP (%)
Biancane
Calanchi
5b
6b
9b
2c
3c
5c
8.1 16.0 83.0 198.3 20.6 23.0 4.3 43.0 0.9 38.0
8.8 8.8 97.0 93.9 4.0 3.6 1.1 48.0 0.6 41.0
8.6 7.0 110.0 69.6 2.2 3.2 0.8 42.0 0.5 38.0
8.8 18.0 70.0 219.6 14.3 15.3 3.4 57.0 0.9 45.0
8.6 9.2 100.0 93.0 5.0 3.3 1.5 46.0 0.7 40.0
8.5 8.0 87.0 80.0 4.4 4.6 1.4 38.0 0.7 35.0
pHs = pH reading of saturated soil paste. ECe = electrical conductivity of saturation extract. BSP = base saturation percentage, SAR = sodium adsorption ratio of saturated extract. PAR = potassium adsorption ratio of saturated extract. ESP = exchangeable sodium percentage.
soluble salts, and are very dispersive due to excess exchangeable sodium. The X-ray diffraction results (Table 4) show a relatively large quantity of smectite, indicating that both biancane and calanchi are formed on expandable clay, which agrees with the high cation exchange capacity (CEC) and the values of Atterberg limits. Similarly to previous results (Torri and Bryan, 1997; Phillips and Robinson, 1998; Moretti and Rodolfi, 2000), the soil analyses confirm the susceptibility of the gray-blue marly clay to erosion. One-way ANOVA applied to data in Tables 1 and 2 showed no significant (p N 0.05) differences in material properties between biancane and calanchi. Granulometric analysis also showed no clear differentiation between the samples taken from both landforms (Fig. 7), which corroborates the results obtained by Alexander (1982), but contradicts those of Battaglia et al. (2002) who suggest that biancane are mainly formed on silty clay
4.3. Material properties Tables 2–4 show the results of the laboratory analyses on the soil samples taken from biancane and calanchi. Summary statistics of several physical soil properties are given in Table 2. The particle size distribution data shows that biancane and calanchi are mainly composed of very fine materials (silty clay). Table 3 shows that pH values were higher than 8.0 and the exchangeable sodium percentages (ESP) are higher than 15 for all the samples, indicating that they are alkaline soils. They also contain a high concentration of
Table 2 Summary statistic of soil properties calculated for samples collected from biancane and calanchi landforms Summary statistics
Biancane
Calanchi
Sands (%)
Silts (%)
Clays (%)
L.L.
P.L.
P.I.
Sands (%)
Silts (%)
Clays (%)
L.L.
P.L.
P.I.
Minimum Maximum Mean Media Std. dev. S.E. mean Skewness Kurtosis CV%
0.7 3.3 1.58 1.4 0.93 0.33 0.68 − 0.71 0.59
48.3 57.8 51.7 50.95 3.44 1.22 0.72 − 0.81 0.07
40.2 51.0 46.7 47.5 3.86 1.37 −0.59 0.99 0.08
45.0 52.0 48.6 48.5 2.56 0.90 −0.04 −1.40 0.05
20.4 23.1 22.2 22.3 0.77 0.26 − 1.36 1.45 0.04
24.0 30.0 26.9 26.5 2.23 0.79 0.17 −1.49 0.08
0.30 3.90 1.32 0.60 1.32 0.44 1.10 − 0.36 1.0
45.7 56.4 50.9 50.0 3.35 1.12 0.42 − 0.60 0.07
40.5 53.7 47.8 49.0 3.99 1.33 − 0.48 − 0.48 0.08
42.0 53.0 47.4 48.0 3.94 1.31 0.04 − 0.86 0.08
20.1 23.7 21.7 21.7 1.26 0.42 0.32 − 1.02 0.05
21.0 30.0 25.9 26 2.9 0.96 − 0.41 − 0.62 0.11
N = 9, L.L. = liquid limit, P.L. = plastic limit and P.I. = plasticity index, std. dev. = standard deviation, S.E. mean = standard error of the mean, CV = coefficient of variation (std. dev./mean).
tr–+
ILL SME tr.
tr–+
ILL SME tr.
tr–+
ILL SME tr.
4.4. Geomorphic processes
ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. Quartz
ILL SME tr.
Mixed layer clays are classified based on the ordering scheme: regular and random. tr. = race, +–++ = estimate of relative abundance, * = well crystallised, ILL = illite, SME = smectite.
ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr. ILL SME tr.
ILL SME tr.
tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+
tr–+ tr–+ tr–+
Chlorite Mixed layer clay Regular Random Components
149
and clayey silt while calanchi are on clayey silt and silty sand.
ILL SME tr.
tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+ tr–+
tr–+
tr–+
+ + + + + + + Smectite Low charge High charge
Mica/illite
+
+
+ + +
+
+
+– ++ tr–+
+– ++ tr–+
+
+– ++ tr–+
+
tr–+
+– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++ +– ++
+– ++
+
++
+– ++ +– ++ +– ++
11c 10c
++ ++ ++
7c 6c
+– ++ +– ++ ++
5c 4c
++ ++
3c 2c
+– ++ +– ++ ++
1c 9b
+– ++ +– ++ ++
8b 7b
++ ++
+– ++ +– ++ +– ++ +– ++ +– ++ +– ++
6b 5b 4b 3b 2b 1b
+– ++ +– ++ Kaolinite*
Calanchi Biancane Sample no.
Table 4 X-ray diffraction of biancane and calanchi samples
++
8c
9c
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Field observations of active denudation processes on biancane and calanchi as well as areas between biancane (inter-biancane areas) are given in Table 5. The denudation processes in the biancane areas can be divided into two categories. The active processes on biancane flanks are sheet wash, small-scale riling and piping (Torri et al., 1994) and slumping, which are comparable to processes acting on the interfluves of the calanchi slopes (Table 5). The sediment produced by erosion of biancane slopes forms micro-pediments at their foot. These micro-pediments are rather irregular in height, as they are controlled by local factors such as base levels for gullies, collapsed pipes and tunnels. The active processes in the inter-biancane area (Table 5 and Fig. 8) are rilling, gullying, piping and deposition of silty clays (with a thickness of a few cm to 1.5 m). The inter-biancane area is mainly composed of micropediments, and dominated by local gullies as well as partly collapsed tunnels or pipes. Rilling, gullying and slumping are the most common processes operating on the calanchi slopes (Table 5). They occurred in all observed calanchi slopes and have a major impact in the development of calanchi. Other processes, such as sheet wash, microrilling and micro-piping are active on the interfluves. Small landslides can often be observed at gully heads, where calanchi slopes meet gentle back-slopes covered with silty soils provided by ploughing, weathering and leaching. These landslides produce debris flows, resulting in the deposition of flow-lobes on much gentler foot-slopes (micro-pediments) at the base of the gullies. 5. Discussion and landform development models 5.1. Factors affecting distribution of biancane and calanchi Geomorphological, geological, pedological and land cover data for the study area indicate complex relationships among lithology, geological structure, vegetation and denudation processes. However, the interpretation of the data also provides some inferences about landform development in the study area. The geological setting which has an extensive joint system due to tectonic disturbances, facilitated terrain
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Fig. 7. Cumulative curves of particle size distribution of samples taken from biancane (black dotted lines) and calanchi (red solid lines). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
dissection by erosion. The structurally controlled strike ridges were developed and less erosion has been taking place along apparent dip slopes because of less converged water flow, while the higher rates of erosion on the other side of the slopes maintain steep slopes. Consequently, the structural setting accounts for a dense vegetation cover on the back-slopes but a very sparse cover on the face-slopes. Micro-climate may also affect vegetation density, since south-facing slopes may react differently from north-facing slopes due to higher insolation. Anthropogenic factors such as deforestation and overgrazing are among the factors that also affect vegetation density and erosion intensity (Kayser, 1964; Verstappen, 1983). Overall, the differences in vegetation density seem to play a major role in determining geomorphic processes in the study area. Material properties such as high erodibility and dispersibility of gray-blue marly clay eased gullying and piping erosion, and consequently had a large impact on the formation of biancane and calanchi and in turn the development of the Aliano badland. The physical and chemical analyses of the soil/bedrock samples did not show significant differences in material properties between biancane and calanchi, although in many publications the origin of the two landforms has been related to granulometric composition, clay mineralogy and the sedimentation environment (Vittorini, 1977; Alexander, 1982, 1989; Battaglia et al., 2002).
As noted before, both biancane and calanchi are only formed on the gray-blue marly clay. In the areas mainly with calanchi, the clay is overlain by the Aliano sand or conglomerates, which have protective effects like dense vegetation cover and therefore prevent further linear erosion. These areas as well as the areas with both calanchi and biancane are characterised by several major lineaments (Fig. 3c). This correlation suggests a strong influence of geological structure on the formation of calanchi. The areas mainly with biancane are not underlain by the Aliano sand or conglomerate and away from major lineaments, but are associated with reticular joint systems (Fig. 3c). In summary, it is not variation in the properties of soil/bedrock material but the structural patterns in bedrock and the existence of cap vegetations or rocks which have strongly controlled the distribution of biancane and calanchi. 5.2. Model of biancane formation Based on the results of our investigation, a model of biancane/calanchi formation is proposed. The initiation of biancane appears to be associated with reticular joint systems along which a network of rills formed. Then an interconnected network of gullies and collapsed pipes were formed due to strong erosion, generating block-like small hills with vegetated tops and bare flanks. During periods of weak erosion,
Table 5 Observed denudation process active on biancane, calanchi and inter-biancane areas Landforms
Total Number of observations of dominant processes number of Sheet wash Micro-rilling Rilling Rill/piping Piping/tunnelling Gullying Shallow slumping Slumping observations
Biancane 170 Inter-biancane area 75 Calanchi 127
170 75 127
170 0 0
170 75 127
151 71 58
0 25 0
0 39 127
87 0 0
0 0 127
J. Farifteh, R. Soeters / Geomorphology 77 (2006) 142–152
151
Fig. 8. Biancane with micro-pediments and inter-biancane area with dense vegetation cover.
small-scale riling, piping and slumping were active on the flanks of each blocky hill, reducing the size of the hills and rounding their shape. Such processes ultimately provided small conical domes or pinnacles known as biancane. By this time, the inter-biancane areas were stabilised because of lower topographic gradients and less concentrated surface flow, inducing deposition and providing an improved vegetation cover. At the same time, micro-pediments were formed at the foot of the domes or pinnacles. The water table in the parent material, which is mainly controlled by joint distribution and topographic relief, provided the base level of erosion and affected the height of biancane. 5.3. Model of calanchi formation Calanchi formed on steep straight face-slopes, mainly controlled by lineaments along deeply incised valleys where the rate of incision is much higher than the lowering of the densely vegetated backslopes. The face-slopes controlled by lineaments have the topography of long straight walls with a small variation in height. Therefore, erosion on the face-slopes was not concentrated in a few places, and formed a system of closely spaced small parallel gullies and interfluves with small pillars. Shallow mudslides from gully heads also contributed to erosion. The processes on the face-slopes seem to be in dynamic equilibrium, resulting in parallel slope retreat and conservation of calanchi topography. The vegetation cover on the back-slopes prevents linear erosion and thus plays a major role in maintaining calanchi. Calanchi can be destroyed if rapid erosion occurs on the back-slopes or strong linear erosion occurs on a certain part of the face slope. Therefore, some
researchers thought that the development of calanchi leads to the genesis of biancane. However our model of the biancane formation noted above indicates that biancane in the study area cannot be regarded as a product from calanchi. 6. Conclusions Biancane and calanchi in the Aliano badlands were both formed on highly dispersible mudstone but under different structural controls and denudation processes. Biancane are mostly initiated on slopes where the surface has been highly dissected along a reticular system of joints. The erosional remnants of the areas between the joints represent biancane. Biancane are not the final product of calanchi development, even though occasionally a dissected calanchi may ultimately form biancane. Calanchi are located along major lineaments and are generated by rapid fluvial erosion where the rate of incision below the face-slope surpasses the erosion on the densely vegetated backslope. Calanchi are maintained by the parallel retreat of the face-slope under a condition of dynamic equilibrium. Laboratory analysis of soil/bedrock samples taken from biancane and calanchi showed no significant differences, casting doubt on previous studies which attributed the differences between the two landforms to material differences. Acknowledgements Many thanks are due to Professor T. Oguchi, Dr. F. Corsi, Professor H. Th. Verstappen and Dr. M. Yemfack for their constructive comments to improve the manuscript. The laboratory analysis performed by the International Soil Reference and Information Centre is also gratefully acknowledged.
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