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Geomorphological and structural patterns of the scarp‑related steep dry valleys in limestone ridges: A case study from South Carpathians, Romania

Caractéristiques géomorphologiques et structurales des vallées sèches profondes associées aux escarpements calcaires : une étude de cas dans les Carpates Méridionales, Roumanie
Laura Tîrlă, Ionuț Mirea et Iuliana Vijulie
p. 399-408

Résumés

Le recul d'un escarpement est un processus naturel normal qui contrôle l'évolution du paysage des structures monoclinales ou tabulaires. Le versant calcaire, de regard N‑O, du Massif Vânturarița‑Buila, une chaîne de montagnes située dans les Carpates Méridionales, est fortement incisé par des vallées profondes et sèches, parallèles entre elles et perpendiculaires à la direction de la crête de la montagne. Nous avons effectué une analyse morphométrique et structurale de ces éléments afin d'estimer le contrôle géomorphologique sur l'évolution régressive de l'escarpement et ses relations avec la tectonique. L'analyse des profils longitudinaux permet de définir la plupart des paramètres morphométriques pertinents. La pente moyenne varie habituellement entre 35° et 50°, mais dépasse souvent 60°. Les longueurs reflètent la variabilité de l'épaisseur de la roche calcaire exposée et les changements des valeurs de pente expriment le contrôle structural de la stratification qui explique le caractère abrupt de la morphologie. La distribution spatiale et le développement des vallées sèches encaissées (type 'cheminée') et le processus de retrait de l'escarpement sont contrôlés par des linéaments tectoniques. Nous avons effectué une analyse comparative de l’orientation des fractures extensionnelles, des failles décrochantes dextres, des failles majeures et des vallées sèches escarpées. Les résultats montrent une orientation préférentielle le long de l’axe NO‑SE et NE‑SO. La variabilité de taille et de morphologie des secteurs escarpés en forme d'amphithéâtre dépend de l'épaisseur de la roche calcaire de couverture. Le long de quelques-unes des vallées sèches (type 'cheminée') ont été trouvés des spéléothèmes formés dans des grottes de type "fissure", exposées lors du recul de l'escarpement. Cette étude montre que l'analyse combinée, géomorphologique et structurale, des vallées sèches encaissées de montagnes calcaires peut fournir des informations utiles sur l’évolution et la morphologie de l’abrupt régressif sur lequel elles se développent.

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Notes de la rédaction

Article soumis le 28 juillet 2016, reçu sous sa forme révisée le 10 octobre 2016 et définitivement accepté le 15 novembre 2016.

Texte intégral

This study was financially sustained by the IFA‑CEA project no. C4‑08/2014‑2016, 'Climate change teleconnections between Western and Eastern Europe based on speleothem records of the Last Interglacial in France and Romania (FREem)'. The authors are grateful to M. Stoica from the University of Bucharest for great support during the field work and constructive discussions on the tectonic evolution of the study area. V. Drăgușin is acknowledged for improving suggestions and English proofing, I. Șandric for providing a part of the materials, L. Faur and A.L. Cercleux for French proofing. We thank P.G. Salvador from the University of Lille for assistance during the editorial process, C. Ek from the ULG‑Liège University and an anonymous reviewer for constructive remarks which helped us to improve the paper content.

1. Introduction

1Scarp retreat is a typical geomorphological process which develops in sedimentary bedded structures, driving the evolution of landscape by continuously consuming the area of the steep outcrop (Schmidt, 2004). It is known as the slope‑parallel recession of a resistant caprock that terminates any elevated, plateau‑like landform. Although largely approached by studies based on the evolution of escarpments in arid environments (Howard and Selby, 1994; Gutiérrez et al., 1998; Gutiérrez, 2012), the mechanisms which drive the scarp retreat process of homoclinal limestone ridges in temperate mid‑latitudes are quite similar (King, 1975). By observing the longitudinal morphology of a retreating scarp, two essential components are distinguished: prominent ridges or slope fragments usually subjected to slumping, and a number of steep dry valleys dissecting the scarp, tightly connected to the presence of fractures and faults. The steep dry valleys result from the common acting of various weathering and gravitational processes particularly developed on limestone. Since the limestone behavior to weathering processes (including chemical weathering by dissolution) is unique among the various rock types, the dry valleys carved in such bedrock exhibit a particular evolution and morphology.

2Preliminary studies on the Vânturarița‑Buila Massif in the South Carpathians, Romania have previously reported the presence of numerous steep, short valleys dissecting the retreating scarp (Călin, 1988; Badea et al., 1998; Tîrlă, 2012). In the Romanian karst literature these minor landforms are called “hornuri” (not to be confused with the English term “horn”, which means “a prominent sharp peak usually shaped by glacial processes” (Embleton and King, 1968). In karst terminology, the term “dry valley” is accepted for this type of landform, considering that “not all valley forms on limestone are necessarily the result of fluvial erosion and slope wash” (Sweeting, 1972).

3The specific morphological patterns of the small dry valleys in Piatra Craiului Massif were described in detail by Constantinescu (1997, 2009). He defined the “horn” as a 1st order elemental valley in the Horton‑Strahler classification system, very short (50‑100 m), narrow (5‑10 m) and steep (average slope > 60°). However, these values should not be fully considered, as in reality there are numerous exceptions in the natural environment. The “chimney”‑type, concave‑up linear landforms dissecting the NW‑facing scarp of the Vânturarița‑Buila Massif were hereafter referred to as steep dry valleys (SDVs).

4The spatial distribution of steep dry valleys in limestone ridges or massifs reflects a specific stage in their evolution. Apart from the interaction of tectonic and gravitational processes and forms, karstification has a significant contribution. The presence of speleothems (terrestrial archives of paleoenvironmental information) is related to the arrangement of joints and faults network, hence – to tectonics. The SDVs develop along these tectonic features during the scarp slope retreat and expose the gradually unearthed speleothems.

5The main purpose of this paper is to study the morphometry and development of steep dry valleys in relation to structural patterns given by tectonic fractures and faults in a retreating limestone scarp. We also outlined the importance of SDVs in providing supplemental environmental information compared to other mountain areas, especially in the Carpathians. Orientation‑based structural analysis shows the relations between spatial distribution of SDVs, fractures and faults. Geomorphological analysis of SDVs longitudinal profiles revealed an interesting correlation between the limestone caprock thickness – inferred from SDVs ground lengths – and the arc radius of the amphitheater‑shaped scarp they dissect.

2. Geological setting

6The Vânturarița‑Buila Massif is a sub‑unit of the Căpățânii Mountains, located in the central part of Southern Carpathians (Romania) (fig. 1‑2). It is a massive SE‑dipping hogback, a limestone‑capped ridge with a dominant NE‑SW direction given by the initial setting of the Getic Nappe over the Danubian basement unit. Geology consists in a thick overthrust sheet of metamorphic rocks of the Median Dacides basement (Getide terranes) in the South Carpathians (Săndulescu, 1984; Balintoni, 1997). Dominant rocks in the Getic Nappe outcropping beneath the major escarpment include paragneiss, amphibolite and eclogite stripes (Oncescu, 1965; Iancu et al., 1998). A 250‑300 m thick layer of massive reef limestone of Kimmeridgian‑Tithonian age from the sedimentary cover of the Getic Nappe lies upon it (Mutihac and Mutihac, 2010). It outcrops only in the south‑eastern part of Căpățânii Mountains because of a local tectonic uplift of the basement and forms the prominent ridge of the Vânturarița‑Buila Massif. Limestone sequences in the Vânturarița‑Buila Massif are remnants of the Getic Carbonate Platform, which occurs throughout the South Carpathian Domain (Patrulius, 1976). The entire mountain front is composed of tectonic compartments separated by NW‑SE oriented strike‑slip and dip‑slip faults. A major NE‑SW segmented fault separates the Vânturarița‑Buila Massif in the Getic Domain from the molassic Olănești Hillocks in the Dacian Basin.

7The steep dry valleys incised into the limestone caprock are closely related to scarp retreat process. Most of them are located on the NW‑facingmajor scarp; other valleys developed on the prominent opposite scarps in “Curmătura Builei” (Buila Pass); and very few are fault‑related, dissecting the major fault scarps on the SE‑facing slope.

Fig. 1 − Geographic setting of the Vânturarița‑Buila Massif.
Fig. 1 − Situation géographique de Massif Vânturarița‑Buila.

Fig. 1 − Geographic setting of the Vânturarița‑Buila Massif.Fig. 1 − Situation géographique de Massif Vânturarița‑Buila.

A. In the Căpățânii Mountains and B. In the Romanian Carpathians. C. The digital elevation model was created on the basis of EU‑DEM (GMES RDA Project, Copernicus Programme), with a 25‑meter resolution.
A. Dans les montagnes Căpățânii B. Dans les Carpates roumaines. C. Le modèle numérique de terrain (MNT) a été réalisé sur la base du projet EU‑DEM (Projet GMES RDA, Programme Copernic de l'Union Européenne ‑ 2015), avec une résolution de 25 m.

Fig. 2 − Basic geology of the area and distribution of the scarp‑related steep dry valleys (modified after Lupu et al., 1978).
Fig. 2 − Géologie simplifiée de la zone d'étude et distribution des vallées sèches escarpées formées par retrait de l'escarpement (modifié d’après Lupu et al., 1978).

Fig. 2 − Basic geology of the area and distribution of the scarp‑related steep dry valleys (modified after Lupu et al., 1978).  Fig. 2 − Géologie simplifiée de la zone d'étude et distribution des vallées sèches escarpées formées par retrait de l'escarpement (modifié d’après Lupu et al., 1978).

3. Materials and methods

8The inventory, mapping, morphometric analysis and relationship with tectonics of the scarp‑incised dry valleys were based on field research and DEM analysis. Orthorectified aerial imagery was used to identify and extract the valleys, as well as to comparetheir resulted lengths to field measurements. The total number of dry valleys found was 58, although only 47 are located on scarps and therefore considered in this analysis. They were numbered V1 to V47. The geological map at a scale of 1:50,000 provided several major NW‑SE‑ and NE‑SW‑oriented faults and fractures which helped sketching the main tectonic framework of the massif. A number of 300 faults and fractures were identified and manually extracted from the aerial imagery. As well, the major faults documented on the geological map at the scale of 1:50,000 (Lupu et al., 1978) served as tectonic landmarks. Orientations of fractures, faults and steep valleys were calculated using the EasyCalculate 10 tool in ArcMap (Tchoukanski, 2010). Rose diagrams were constructed in order to perform a comparative structural, orientation‑based analysis on the two datasets ‑ steep valleys and tectonic structures ‑ and observe the relations between joint and fracture systems and valleys formation.

9We identified the linear patterns of the steep valleys using the longitudinal profiles extracted from a medium‑resolution DEM, created by interpolating elevation values of contour lines from the 1:25,000‑scale topographic map. We calculated the following morphometric parameters of the linear valleys: maximum and minimum elevation, elevation range (ΔH), length, average and maximum slope, maximum slope length, and azimuth. Field measurements were applied on 8 prominent valleys grouped on the north‑western slopes of the Albu, Buila and Vânturarița mounts. The statistical analysis shows the role of median in outlining the particular morphometry of each group (tab. 1). During field research, a GPS device (eTrex Vista® Hcx by Garmin) and a Freiberg geological compass were used. Field geomorphological mapping of the ridge‑top was systematically carried in order to identify related karst landforms (sinkholes, potholes, crevice‑type caves) and deposits (speleothems).

Tab. 1 − Synthetic statistical data on the morphometry of steep dry valleys in the Vânturarița‑Buila Massif.
Tab. 1 − Données statistiques synthétiques de la morphométrie des SDVs dans le massif de Vânturarița‑Buila.

Tab. 1 − Synthetic statistical data on the morphometry of steep dry valleys in the Vânturarița‑Buila Massif.  Tab. 1 − Données statistiques synthétiques de la morphométrie des SDVs dans le massif de Vânturarița‑Buila.

The values represent the median of each morphometric parameter.
Les valeurs représentent la moyenne de chaque paramètre morphométrique.

4. Results and discussions

4.1. Morphometry of the steep dry valleys

10The major NW‑facing limestone scarp and the small opposite fault‑related scarps in central area of the massif (Buila Pass) are dissected by a total number of 47 steep dry valleys. These minor landforms indicate the most retreated sections of the limestone scarps. We synthesized data by grouping the SDVs according to their spatial distribution and calculating the median values of the key morphometric parameters (tab. 1).

11The highest elevations are reached in Mt. Vânturarița (1789 to 1872 m), and the lowest in Mt. Stogșoare (925 to 1127 m). To the northern extremity, Mt. Stogu (1494 m) stands as an insular remnant of the carbonate platform. Here, elevations of the dry valleys range between 1228 m and 1350 m. The difference in elevation (ΔH) between the top and the base of a steep dry valley developed in caprock is especially suggestive about the exposed caprock thickness in that section. Its role will be further discussed in this paper in relation to tectonic control over the scarp retreat process. Most values of ΔH range between 50 and 170 m, with extremes around 10 m and 200 m. Several patterns are observed in their distribution. Moderate differences, hardly exceeding 100 m, were found in Mt. Vânturarița, the highest area of the massif. Very high values occur in Mt. Stogșoare, a tectonic block which stands at the lowest elevations (950‑1150 m): over 200 m in elevation range.

12Directly related to vertical difference, the longest SDVs occur in the Stogșoare area (~150 to ~270 m), deeply incised by the Cheia River, and in Mt. Buila‑Albu (~230 m). The latter developed in the limestone caprock. By comparison, the steep dry valleys in Mt. Vânturarița are surprisingly short (~100 to ~140 m) regardless of the fact that it reaches the highest elevations in the entire massif. Similar to the elevation difference, the length of SDVs is directly proportional to the thickness of exposed Jurassic limestone caprock. It varies according to the tectonic pattern of the landform: the uplifted metamorphic blocks are thinly capped by the bedded limestone, whereas the subsided blocks bear a thicker stack of carbonate rocks.

13Slope is an essential morphometric parameter of the SDVs and is commonly high, according to the parallel‑retreat character of limestone caprock. The valleys are steep, with average slope ranging between 35° and 50°. The 'Hornurile Popii' tectonic‑karst corridors in Mt. Piatra are atypical dry valleys. Their development might be due to some parallel reverse faults probably inherited since the Late Cretaceous tectogenesis (Iancu et al., 2005). Tectonic relaxation related to post-Sarmatian extensional events, and then controlled by the scarp retreat process, has moved the fault walls off from each other and the deep dry valleys formed. Maximum slope usually exceeds 40° and even 60°, except for the tectonic‑karst corridorsin Mt. Piatra, with 25°‑30°. The azimuth pattern was included in the structural analysis, in relation to tectonic features.

14The morphometric patterns of the SDVs were graphically illustrated on the longitudinal profiles (fig. 3). All the profiles were scale‑fit for an easier interpretation and grouped according to their spatial development across the NW‑facing main scarp and the two opposite‑facing minor scarps in Buila Pass.

Fig. 3 − Longitudinal profiles of the steep dry valleys.
Fig. 3 − Profils longitudinaux des vallées sèches (type en 'cheminée').

Fig. 3 − Longitudinal profiles of the steep dry valleys.  Fig. 3 − Profils longitudinaux des vallées sèches (type en 'cheminée').

A‑E. Location of the main groups of dry valleys; F. Convergent dry valleys in Mt. Stogu (1494 m a.s.l.); G. The highest dry valleys, in Mt. Vânturarița (1875 m a.s.l.); H. The longest and steepest dry valleys in Mt. Buila, V22‑V26; I. V23 and V24 expose the most abundant and interesting unearthed speleothems in the Vânturarița‑Buila Massif; J. Gentle‑inclined, fault‑related “Hornurile Popii” corridors in Mt. Piatra. Shaded areas : knickpoints and benches.
A‑E. Localisation des principaux groupes de vallées sèches ; F. Vallées sèches convergentes dans le Mont Stogu (1494 m) ; G. Vallées sèches les plus élevées dans la Montagne Vânturarița (1875 m) ; H. Les longues vallées sèches et escarpées du Mont Buila V22‑V26 ; I. V23 et V24 comprennent les plus abondants et intéressants spéléothèmes (exhumés) dans le Massif Vânturarița‑Buila ; J. Couloirs « Hornurile Popii » dans le Mont Piatra, en pente douce, formés le long de failles. Les zones ombrées (en gris) : les points d'inflexion et les surfaces structurales.

15Most of dry valleys developed on the NW‑facing limestone caprock have uniform, steep longitudinal profiles, not depicting any significant breaks. Scarp knickpoints and benches appear to be restricted only to V22‑V24 steep dry valleys, on the western flank of Mt. Buila. Here, the landscape has recorded an important stage of the scarp retreat process. Parallel slices detach from the caprock along very deep, arcuate tensile fractures (the “D” scarp sector in Figure 4). Right under the mountaintop, an immense slice has lowered by 2 to 5 meters triggered by gravitational forces and subsequent partial collapse, resulting in a ridge‑top depression associated with double opposite ridges – a structural complex of gravitational origin known as “sackung” (Gutiérrez‑Santolalla et al., 2005). Here we will shortly point out only the implications this sackung complex has on the SDVs differentiate geomorphology.

Fig. 4 − Correlation between the orientations of major faults (in grey), tensile fractures and minor faults (in black) and steep dry valleys (in red).
Fig. 4 − Corrélation entre la direction des failles principales (gris), les linéaments tectoniques (noir) et l’orientation des vallées sèches escarpées (rouge).

Fig. 4 − Correlation between the orientations of major faults (in grey), tensile fractures and minor faults (in black) and steep dry valleys (in red).Fig. 4 − Corrélation entre la direction des failles principales (gris), les linéaments tectoniques (noir) et l’orientation des vallées sèches escarpées (rouge).

16V22, V23 and V24 are parallel, side‑by‑side steep dry valleys formed at the western edge of the ridge‑top depression on Mount Buila. The collapse origin of this depression is also supported by the subsurface morphology and surface discontinuities found in the upper sector of the steep dry valleys. Crevice‑type caves or gull caves with typically unstable breakdown morphology have developed deep down under the depression. The entrance in the Collapsed Cave (cadastral number 2044/7; Emil Racoviță Institute of Speleology, 2016), the largest crevice‑type cave in Mt. Buila, is located at the upper end of V23, at 1817 m a.s.l. (value obtained by GPS measurement).

17The cliff‑and‑bench topography of the three steep dry valleys (V22, V23, and V24) is controlled by gravitational processes. The similar knickpoints and benches identified at 1750‑1760 m on the longitudinal profiles of V22 and V24 indicate the depth of collapse deformations, ~70‑80 meters. In case of V23 (which is different because it formed on the exposed caprock of collapsed slice, at the western edge of ridge‑top depression), the knickpoints and bench at 1790‑1810 m point out the development of another step at ~30 meters below the bottom of depression. A direct relationship exists between the underground morphology of collapse caves and geomorphology of SDVs revealed by longitudinal profiles.

18Overall, correlation of all the analyzed longitudinal profiles of the steep dry valleys provides geomorphological information of the entire limestone scarp.

4.2. Precision assessment by field survey

19In order to calibrate the data obtained by DEM processing, 8 of the most representative dry valleys were sampled. All of them are located on the retreating scarp. Azimuth and slope field measurements were tested on each of them and the values were compared to those extracted from the DEM in Global Mapper application (tab. 2).

Tab. 2 − Comparative DEM‑ and field‑based measurements on the morphometric patterns of steep valleys (all values are given in degrees).
Tab. 2 − Comparaison entre les mesures extraites du MNT et celles mesurées sur le terrain concernant les types morphométriques des vallées abruptes (toutes les valeurs sont en degré).

Tab. 2 − Comparative DEM‑ and field‑based measurements on the morphometric patterns of steep valleys (all values are given in degrees).Tab. 2 − Comparaison entre les mesures extraites du MNT et celles mesurées sur le terrain concernant les types morphométriques des vallées abruptes (toutes les valeurs sont en degré).

20The differences between values (ΔA, ΔS) represents data precision (up to ± 2° for azimuth and up to ± 7.6° for slope) and are rather caused by application errors, largely given the low field accessibility and the complex morphology of the scarp slope, to which adds the obstruction caused by the natural vegetation abundance. Data accuracy is higher for the azimuth values, considering that orientations extracted both from the topographic map and the orthorectified images are more accurate than those measured directly in the field. For slope and longitudinal profiles extracted from the DEM, the accuracy is somewhat problematic because of its medium resolution. However, the accuracy assessment showed that the method is qualitatively superior to field measurements.

4.3. Relation between the steep dry valleys and the tectonic‑structural patterns

21The development of most SDVs was favored by the tectonic features, such as tensile fractures and strike‑slip faults, which were already documented in the Vânturarița‑Buila Massif (Tîrlă and Vijulie, 2013). One could notice that where a fault or tension fracture intersects the scarp, SDVs occur. The degree of fracturing in a scarp is highly significant to its retreat rate; hence fracturing largely determines its resistance to erosion (Gutiérrez, 2012).

22Clayton's statement that “[...] every fault line is the locus of a dry valley and their formation by frost and snow action is a possibility” perfectly applies to SDVs in the Vânturarița‑Buila Massif. He also affirms that “disintegration of limestones by frost is particularly accelerated along fault and joint‑lines” (Clayton, 1966). In geomorphological sense, the process develops along the scarp‑related steep valleys, where rocks are loosened by freeze‑thaw action.

23An orientation‑based structural analysis involved two datasets linked to tectonic (faults and fractures) and geomorphic features (steep dry valleys) in the Vânturarița‑Buila Massif (fig. 4). N1‑3 represents the total number of features analyzed. The bin size is 10 degrees, and the dashed arcs correspond to amphitheater‑shaped scarp sections lettered A‑E. One could notice at first glance that the tectonic network is well organized into an orthogonal pattern. Reverse faults, tension fractures and joints are preferrably NE‑SW oriented, and dextral strike‑slip faults run perpendicularly on a NW‑SE direction.

24Although the anisotropic properties of the SDVs’ spatial distribution are influenced by fault and joint orientations, they depend on the morphology of the retreating scarp. Several individual amphitheater‑shaped headwalls can be observed on the map in Figure 4. They are outlined by dashed half‑circles between the Piatra and Vânturarița peaks. Rounded shapes are typical for slopes undermined by combined groundwater sapping and mass wasting processes (Howard, 1995; Laity, 2008). Individual drainage systems form at the caprock basis of the Vânturarița‑Buila Massif, where springs emerge. The limestone caprock lacks an organized drainage network, though infiltration water is consistent. But we consider that the greatest influence is of tectonics, and less of other mechanisms. The Vânturarița‑Buila Massif is 'cut' into quasi‑parallel slices by transversal dextral strike‑slip faults (fig. 2), denser to the north of Buila Pass, in Mt. Albu, Buila and Vânturarița, and sparser to the south, in Mt. Piatra. The scarp has an amphitheater shape where the strike‑slip faults are denser, but this shape is loosened where faults are remote to one another. Then, freeze‑thaw action and mass wasting complete and polish the rounded‑shaped scarp.

25Thus, regardless or slightly dependant of the obvious tectonic control, the amphitheater‑shape typical for a retreating scarp induces the rounded arrangement in SDVs spatial distribution. A remarkable pattern was observed in the arcs size. The long‑dashed arcs outlining the rounded‑shaped scarp in Mt. Albu and Mt. Vânturarița have a radius of ca 0.45‑0.5 km. A larger, ~0.65 km‑sized arc radius, is prefigured in Mt. Buila by the tension fracture system (the short‑dashed arc). Instead, to the south‑west, the minor opposite‑facing scarps in Buila Pass describe smaller arcs, with radiuses of 0.26 to 0.38 km (fig. 4). We presume that variations in size of the amphitheater‑shaped scarps are related to the base of the scarp undermined by seepage water sub‑sapping and mass wasting. In other words, the scarp’s height is directly proportional to the amphitheater‑shape size. For example, amphitheaters in the Colorado Plateau range from several hundreds of meters, where they are shaped into a specific rock layer, to tens of kilometers in size, comparable to the outstanding thickness of various sedimentary layers. Only to verify our assumption, we sampled five amphitheater‑shaped scarps from the Colorado Plateau and included them into our analysis. Four scarps (named Colorado‑1 to Colorado‑4 in Table 3) have smaller arc radiuses (< 1 km), are cut into the lower Tapeats Sandstone (Karlstrom et al., 2012) and represent the steepheads of elemental valleys. The fifth scarp (Colorado‑5) cuts the middle sedimentary sequence of the Colorado Plateau (i.e. the Temple Butte, Redwall and Surprise Canyon formations) and has an arc radius of 2.7 km. The pattern also applies to submarine landforms; a 55‑km amphitheater‑shaped scarp was crowned on the northern insular slope of Puerto Rico, from a water depth of 3000 m to 6700 m, after a giant submarine slope failure (Schwab et al., 1991). We synthesized all data in Table 3. The related graph depicts a remarkable correlation between the size of arc radius corresponding to amphitheater‑shaped scarps and the caprock thickness (fig. 5). A detailed analysis of more sampled scarps developed in caprocks of various thicknesses and resistance is useful for strengthening this assertion.

Tab. 3 − Variability of exposed caprock thickness and the arc radiuses of scarp sectors at different scales in the Vânturarița‑Buila Massif, Colorado Plateau and continental slope of Puerto Rico.
Tab. 3 − Variabilité de l’épaisseur de l’abrupt et du rayon des arcs de cercle circonscrits aux secteurs escarpés en forme d’amphithéâtre, mesurée à différentes échelles dans le Massif Vânturarița‑Buila, le plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.

Tab. 3 − Variability of exposed caprock thickness and the arc radiuses of scarp sectors at different scales in the Vânturarița‑Buila Massif, Colorado Plateau and continental slope of Puerto Rico.Tab. 3 − Variabilité de l’épaisseur de l’abrupt et du rayon des arcs de cercle circonscrits aux secteurs escarpés en forme d’amphithéâtre, mesurée à différentes échelles dans le Massif Vânturarița‑Buila, le plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.

Fig. 5 − Correlation graph between the caprock thickness and the arc radiuses corresponding to amphitheater‑shaped scarps in Vânturarița‑Buila Massif, Colorado Plateau and the submerged slope failure in Puerto Rico.
Fig. 5 − Graphes de corrélation entre la hauteur de l’abrupt et les rayons des cercles circonscrits aux secteurs d’abrupt en forme d’amphithéâtre du Massif Vânturarița‑Buila, le Plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.

Fig. 5 − Correlation graph between the caprock thickness and the arc radiuses corresponding to amphitheater‑shaped scarps in Vânturarița‑Buila Massif, Colorado Plateau and the submerged slope failure in Puerto Rico.  Fig. 5 − Graphes de corrélation entre la hauteur de l’abrupt et les rayons des cercles circonscrits aux secteurs d’abrupt en forme d’amphithéâtre du Massif Vânturarița‑Buila, le Plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.

A. Of each sample; B. Of all data. In case of Vânturarița‑Buila Massif, the exposed caprock thickness was inferred from the medians of SDVs lengths.
A. Données des unités géographiques ; B. Toutes les données. Dans le cas du Massif Vânturarița‑Buila, la hauteur de l’abrupt (épaisseur du toit de la formation rocheuse) a été obtenue à partir des valeurs médianes de la longueur des vallées sèches abruptes.

26The elevation range (ΔH) between the basis and the top of SDVs (tab. 1) is therefore relevant to estimate the size of amphitheater‑shaped scarp. It also indicates the thickness of the outcropping limestone caprock, ranging between ~50 m in Buila Pass and 107‑136 m in Mt. Albu, Buila and Vânturarița. We can observe that the median values in Buila Pass (56 m in Mt. Piatra NE‑facing scarp, and 86 m in Mt. Albu SW‑facing scarp) are almost half of the ones in the central part of the massif (tab. 3, fig. 5).

4.4. Geomorphic implications of steep dry valleys on the scarp retrogressive evolution

27Limestone provides an advantage in addition to other types of rocks: the presence of speleothems as terrestrial proxies, climatic and tectonic archives containing information on the landscape evolution. In limestone ridges, steep dry valleys develop on the retreating scarp preferentially where crevice‑type caves or relict karstification levels intersect the topographic surface, becoming exposed. This is explained by the fact that they formed under the control of strike‑slip faults and tension fractures, which provided the pathways for water infiltration and circulation into the rock mass. Initially, small sinkholes and potholes occur and develop on the ridge top; then, as the scarp retreats, these open into the linear steep dry valleys. Further, weathering and mass movements continue to shape the slope profile. As scree covers a part of the 'horn' base, this becomes inactive and the SDV continues to develop only on the caprock outcrop, simultaneously with the slope retreat. Fluvial processes gradually remove the scree, given the trend of achieving equilibrium of the slope profile.

28According to Necea et al. (2005), a tectonic rebound occurred during the Late Pleistocene until present‑day. The Carpathians uplift resulted in the reactivation of ancient faults. In the mountain environment we discuss, gravitation and karstification combined have enlarged some of the inherited longitudinal faults and opened new cracks which they modeled, resulting crevice‑type caves or gull‑caves. These usually occur within the first 0.5 km from the scarp margin (Farrant et al., 2014). This type of cave is common in the Vânturarița‑Buila Massif, where low thickness of limestone caprock and high structural dip inhibited the development of large karst systems. The bedded structure of limestone has favored the development of a stepped crevice to the size of a cave – a crevice‑type cave, very similar to the model advanced by Margielewski and Urban (2003).

29Consistent radiating fibrous aragonite and calcite layers grew on the fault walls in Mt. Albu and Mt. Buila, a phenomenon favored only by extension. In some cases, the amount of horizontal extension is given by calcite layers thickness. Uncommonly abundant and well‑developed speleothems were found at the top of V24 steep valley in Mount Buila, at 1810 to 1820 m a.s.l. Since there is not any (allochthonous) river nearby, karstification has most probably developed in a tensile crevice system deep inside the limestone bedrock throughout the Pleistocene, under stable environmental conditions. As the mountain uplifted, speleothems were progressively exhumed and unearthed by weathering, long after their growing has ceased. Certain results can be achieved during future research from U‑series dating and isotopic analyses. In this study, we established a correlation between the spatial development of the steep dry valleys and the presence and abundance of these calcite deposits.

30Tectonics controls the scarp retreat by major and minor mass movements. Minor mass movements consist in small rockfalls, scree transport and deposition along the steep valleys. Instead, the DSGSDs (deep seated gravitational slope deformations) are major mass movements which occur in response to disturbance of slope equilibrium (Margielewski and Urban, 2003). They are the main processes controlling the scarp retreat. The tension cracks that precede the formation of head‑scarp are scarp‑parallel and very deep; when they open and widen, the 'crevice‑type caves' form. The DSGSDs in Mount Buila host a great variety of exposed and underground landforms: ’chimney’‑type, steep dry valleys with abundant speleothems and giant aragonite‑to‑calcite deposits on the fracture walls, collapse 'crevice'‑type caves, sackung and sackung features (uphill‑facing scarps), etc.

31The karstifiable nature of limestone bedrock is a plus advantage to observing underground morphology; typical karst processes and speleothem formation turns simple crevices into real caves. In limestone ridges, scarp retreat is a process by which the access to environmental archives stored by the tectonic lineaments network is provided through SDVs development, which retreat jointly with the scarp.

5. Conclusions

32Knowledge on the general and detailed morphology of a retreating scarp is practical for further research on its geomorphological, paleotectonic and paleoclimatic landscape evolution during the Quaternary.

33Morphometric data of the steep dry valleys in the Vânturarița‑Buila Massif (South Carpathians) provide information about the geomorphic processes involved in scarp retreat. Faults and tensile fractures control the spatial distribution and morphology of the steep dry valleys developed on the exposed caprock. These valleys reflect a certain evolution stage of tectonic‑karst landforms related to the normal scarp retreat process. The cliff‑and‑bench topography of several SDVs in Mount Buila is determined by gravitational processes (especially collapses) that act upon the limestone caprock and control its retrogressive evolution, particularly dynamic in this part of the massif.

34The major transversal strike‑slip faults which separate the tectonic blocks direct the amphitheater‑shape of the retreating scarp. An obvious correlation between the thickness of exposed bedded strata on the NW‑facing steep slope and the circumference of amphitheater‑shaped scarp sections was observed in the central area of the massif.

35The spatial distribution and morphology of the steep dry valleys developed on a retreating limestone scarp is closely related to its normal evolution. At the same time, geomorphological analysis of SDVs can reveal specific patterns of the scarp retreat process in its various stages of evolution.

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Bibliographie

Badea L., Niculescu G., Roată S., Călin D., Ploaie G. (1998) − Masivul Vânturarița‑Buila. Caracterizare geomorfologică. Buletinul Geografic, 2, 3‑36.

Balintoni I. (1997) − Geotectonica terenurilor metamorfice din România. Editura Carpatica, Cluj‑Napoca, 178 p.

Călin D. (1988) − Masivul Vânturariţa‑Buila. Observaţii geomorfologice. Studii şi Cercetări de Geofizică, Geologie şi Geografie (Geografie), XXXV, 91‑96.

Clayton K.M. (1966) − The origin of the landforms of the Malham area. Field Studies, 2, 359‑384.

Constantinescu T. (1997) − Le karst de Piatra Craiului (2). L'exokarst. Travaux de lʼInstitut de Spéologie "Émile Racovitza", XXXVI, 207‑223.

Constantinescu T. (2009) − Masivul Piatra Craiului : Studiu geomorfologic. Editura Universitară, București, 163 p.

Embleton C., King C.A. (1968) − Glacial and Periglacial Geomorphology. St. Martin's Press, New York, 608 p.

Emil Racoviță Institute of Speleology (2016) Karst Cadaster of Romania. Archives of the Romanian Academy, Bucharest (unpublished material).

Farrant A.R., Noble S.R., Barron A.J.M., Self C.A., Grebby S.R. (2014) − Speleothem U‑series constraints on scarp retreat rates and landscape evolution: an example from the Severn valley and Cotswold Hills gull‑caves, UK. Journal of the Geological Society, 172 (1), 63‑76.
DOI:
10.1144/jgs2014-028

Gutiérrez M. (2012) − Geomorphology. CRC Press, Boca Raton (FL), 1014 p.

Gutiérrez M., Sancho C., Arauzo T. (1998) − Scarp retreat rates in semiarid environments from talus flatirons (Ebro Basin, NE Spain). Geomorphology, 25 (1‑2), 111‑121.
DOI:
10.1016/S0169-555X(98)00034-8

Gutiérrez‑Santolalla F., Acosta E., Ríos S., Guerrero J., Lucha P. (2005) – Geomorphology and geochronology off sackung features (uphill‑facing scarps) in the Central Spanish Pyrenees. Geomorphology, 69, 298‑314.
DOI:
10.1016/j.geomorph.2005.01.012

Howard A.D. (1995) − Simulation modeling and statistical classification of escarpment planforms. Geomorphology, 12 (3), 187‑214.
DOI:
10.1016/0169-555X(95)00004-O

Howard A.D., Selby M.J. (1994) − Rock Slopes. In Parsons A.J., Abrahams A.D. (Eds.): Geomorphology of Desert Environments. Chapman & Hall, London, 123‑172.
DOI:
10.1007/978-94-015-8254-4_7

Iancu V., Mărunțiu M., Johan V., Ledru P. (1998) − High‑grade metamorphic rocks in the pre‑Alpine nappe stack of the Getic‑Supragetic basement (Median Dacides, South Carpathians, Romania). Mineralogy and Petrology, 63, 173‑198.
DOI:
10.1007/BF01164150

Iancu V., Berza T., Seghedi A., Gheuca I., Hann H.‑P. (2005) − Alpine polyphase tectono‑metamorphic evolution of the South Carpathians: A new overview. Tectonophysics, 410, 337‑365.
DOI:
10.1016/j.tecto.2004.12.038

Karlstrom K.E., Timmons J.M., Crossey L.J. (2012) – Introduction to Grand Canyon geology. In Timmons J.M., Karlstrom K.E. (Eds.): Grand Canyon Geology: Two Billion Years of Earth’s History. Special Paper 489, The Geological Society of America, Boulder, 1‑6.

King L.C. (1975) − Bornhardt landforms and what they teach. Zeitschrift für Geomorphologie, 19, 299‑318.

Laity J.J. (2008) − Deserts and Desert Environments. Wiley‑Blackwell, Chichester, 360 p.

Lupu M., Popescu B., Szasz L., Hann H.P., Gheucă I., Dumitrică P., Popescu G. (1978) − Geological map 126a ‑ Vânturarița sheet (L‑35‑97‑A), scale 1:50,000.

Margielewski W., Urban J. (2003) − Crevice‑type caves as initial forms of rock landslide development in the Flysch Carpathians. Geomorphology, 54 (3‑4), 325‑338.
DOI:
10.1016/S0169-555X(02)00375-6

Mutihac V., Mutihac G. (2010) − The geology of Romania within the Central‑East‑European geostructural context. Editura Didactică și Pedagogică, Bucharest, 690 p.

Necea D., Fielitz W., Mațenco L. (2005) − Late Pliocene–Quaternary tectonics in the frontal part of the SE Carpathians: Insights from tectonic geomorphology. Tectonophysics, 410, 137‑156.
DOI:
10.1016/j.tecto.2005.05.047

Oncescu N. (1965) − Geologia României. Editura Tehnică, București, 534 p.

Patrulius D. (1976) – Upper Jurassic‑Lower Cretaceous carbonate rocks in the eastern part of the Getic carbonate platform and the adjacent flysch troughs. In Patrulius D., Drăgănescu A., Baltres A., Popescu B. & Rădan S. (Eds.): Carbonate rocks and evaporites guidebook. Institute of Geology and Geophysics, Bucharest, 71‑82.

Săndulescu M. (1984) − Geotectonica României. Editura Tehnică, București, 334 p.

Schmidt K.H. (2004) − Caprock. In Goudie A.S. (Ed.): Encyclopedia of Geomorphology (Vol. I). Routledge, London/New York, 116‑118.

Schwab W.C., Danforth W.W., Scanlon K.M., Masson D.G. (1991) – A giant submarine slope failure on the northern insular slope of Puerto Rico. Marine Geology, 96, 237‑246.
DOI:
10.1016/0025-3227(91)90149-X

Sweeting M.M. (1972) − Karst Landforms. Macmillan/Columbia University Press, London/New York, 378 p.

Tchoukanski I. (2010) − EasyCalculate 10. ET Spatial Techniques, Pretoria. Retrieved from http://www.ian‑ko.com/free/EC10/EC10_main.htm.

Tîrlă L. (2012) − Bazinul hidrografic Olănești: Studiu de geomorfologie. Editura Universității din București, București, 381 p.

Tîrlă L., Vijulie I. (2013) − Structural‑tectonic controls and geomorphology of the karst corridors in alpine limestone ridges: Southern Carpathians, Romania. Geomorphology, 197, 123‑136.
DOI : 10.1016/j.geomorph.2013.05.003

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Annexe

Version française abrégée

Le recul d'un escarpement dans les structures sédimentaires tabulaires ou monoclinales est un processus d'évolution du paysage dans lequel les couches de roches dures du toit sont continuellement affectées par les processus géomorphologiques (Schmidt, 2004). Cette dynamique implique certaines caractéristiques des formes de relief développées à partir de l'escarpement. À travers cette étude, nous avons analysé les relations entre les faits géomorphologiques et les éléments tectono‑structuraux organisant les vallées sèches associées aux processus de recul des escarpements calcaires dans la partie centrale du Massif de Vânturarița‑Buila (Carpates Méridionales). Des vallées karstiques sèches et encaissées, de type ”cheminée”, ont déjà été étudiées par ailleurs dans le massif calcaire de Piatra Craiului, selon un angle d'approche sensiblement différent (Constantinescu, 1997, 2009).

Le Massif de Vânturarița‑Buila est un témoin de la Plateforme Carbonatée Gétique, datée du Jurassique supérieur ‑ Crétacé inférieur. Les calcaires ont une épaisseur de 250‑300 m et sont disposées en discordance sur la base métamorphique du domaine gétique. La structure générale est monoclinale. 47 vallées karstiques de type élémentaire ”cheminée” (SDVs), numérotés V1 à V47, ont été inventoriées et analysées sur les escarpements calcaires situés dans la partie Nord‑Ouest du Massif de Vânturarița‑Buila.

Les données morphométriques ont été obtenues à l'aide de profils longitudinaux issus d'un modèle numérique du terrain (MNT) et ont fait l'objet d'une analyse statistique sommaire. La relation des vallées avec le système de failles et de fractures a été abordée à partir d'une analyse de leur orientation, réalisée à partir d'ortho‑photographies à haute résolution (0,5 m). Les valeurs des azimuts ont été obtenues avec l'application EasyCalculate10 d’ArcMap et traitées avec le logiciel Grapher pour obtenir les roses d’orientation. Certaines caractéristiques de la morphologie de l'escarpement calcaire ont été corrélées avec la morphométrie, l'orientation et la concentration des vallées sèches encaissées. La cartographie géomorphologique a été le support principal permettant d'établir des corrélations spatiales entre la distribution des vallées sèches et des autres reliefs karstiques (dolines, nids de poule, grottes de fissures) ou des formations telles que les spéléothèmes.

La morphométrie des vallées sèches donne les résultats suivants : leur longueur est comprise entre 100 et 140 m (vallées courtes) et 150‑270 m (vallées longues) ; la différence d'altitude (ΔH) est comprise entre 50 et 170 m ; les vallées sont pentues, la pente moyenne étant généralement comprise entre 35° et 50°, à quelques exceptions près ; les pentes maximales sont comprises entre 40° et 64°. La différence d'altitude et la longueur des vallées sont des paramètres qui reflètent directement la variation d'épaisseur de la couche calcaire exposée de l'escarpement et modelée par les processus entrainant son recul.

L'analyse des profils longitudinaux des vallées souligne leurs particularités morphométriques et les relations spatiales entre eux. Les profils sont relativement uniformes, sans discontinuités importantes. Seules trois des vallées ouvertes dans l’escarpement du Mont Buila (V22‑V24) présentent une topographie étagée entre 1750 et 1810 m d'altitude, avec des replats et des points d'inflexion. Nous pensons qu'ils sont liés à la présence d'affaissements d'origine struturale (sackung) donnant des formes de relief de type "ridge‑top depression" et "crevice‑type caves" ou grottes de type "fissure" (Gutiérrez‑Santolalla et al., 2005), des blocs de rochers effondrés, etc. La plus grande grotte de type "fissure" du Mont Buila est la Collapsed Cave (numéro cadastral 2044/7), qui est situé en tête de la vallée V23, à 1817 m. La topographie étagée est contrôlée par des processus gravitationnels, indiquant la profondeur des déformations causées par des effondrements internes. Le lien entre la morphologie de la grotte effondrée et les vallées sèches encaissées et situées dans son voisinage immédiat est établi.

Le développement des SVDs est contrôlé par la tectonique, la majorité étant formée le long des fractures de distension ou des failles de décrochage dextre. Les résultats de l'analyse structurale montrent clairement un regroupement des fractures de distension selon une orientation parallèle avec l’abrupt, ~NE‑SO, et en fonction de la faille de décrochage dextre en un système orienté perpendiculairement, ~NO‑SE. Dans le cas des vallées sèches encaissées, l’orientation le long des fractures et des failles est influencée par la morphologie générale de l'escarpement ‑ une série de petits amphithéâtres de circonférence différente ‑ dans lequel sont regroupées les vallées karstiques encaissées. Nous avons trouvé que la circonférence de l'amphithéâtre est directement proportionnelle à la hauteur de l'escarpement et l'épaisseur de la masse calcaire exposée, obtenue par le calcul de la longueur des vallées. Nous avons comparé la situation de Vânturarița et d'autres escarpements semi‑circulaires formés dans des conditions différentes (Plateau du Colorado et de Puerto Rico). Les résultats (fig. 5) indiquent une corrélation très forte entre les deux paramètres, avec un coefficient de corrélation général de ~0,9. Il atteint même 0,98‑0,99 quand l'étude des escarpements ne s'applique qu'à chacune des zones d'étude prises isolément. Des études plus détaillées sont nécessaires pour conforter notre argumentation, mais nos investigations amènent à penser que ces analyses sont suffisantes.

Dans les grottes de type "fissure", sur les escarpements de faille, et dans les fractures riches en gisements de minéraux récents, se sont développés des spéléothèmes. Ils sont exposés en surface en raison de processus gravitationnels, en particulier dans les vallées sèches. Les spéléothèmes constituent des archives de l'environnement terrestre qui peuvent fournir des informations précieuses sur l'évolution géomorphologique récente du Massif de Vânturarița‑Buila.

Dans l'ensemble, l'analyse géomorphologique des vallées sèches encaissées, à laquelle sont intégrés les paramètres morphométriques et les profils longitudinaux, fournit des informations sur le développement spatial et la configuration du versant calcaire escarpé façonné par le processus de recul. La connaissance approfondie de ces processus et des formes associées peut aider à la reconstruction de paléoenvironnements quaternaires corrélatifs de l'évolution de l'escarpement mais aussi de l'ensemble du massif.

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Table des illustrations

Titre Fig. 1 − Geographic setting of the Vânturarița‑Buila Massif.Fig. 1 − Situation géographique de Massif Vânturarița‑Buila.
Légende A. In the Căpățânii Mountains and B. In the Romanian Carpathians. C. The digital elevation model was created on the basis of EU‑DEM (GMES RDA Project, Copernicus Programme), with a 25‑meter resolution. A. Dans les montagnes Căpățânii B. Dans les Carpates roumaines. C. Le modèle numérique de terrain (MNT) a été réalisé sur la base du projet EU‑DEM (Projet GMES RDA, Programme Copernic de l'Union Européenne ‑ 2015), avec une résolution de 25 m.
URL http://geomorphologie.revues.org/docannexe/image/11528/img-1.jpg
Fichier image/jpeg, 3,3M
Titre Fig. 2 − Basic geology of the area and distribution of the scarp‑related steep dry valleys (modified after Lupu et al., 1978). Fig. 2 − Géologie simplifiée de la zone d'étude et distribution des vallées sèches escarpées formées par retrait de l'escarpement (modifié d’après Lupu et al., 1978).
URL http://geomorphologie.revues.org/docannexe/image/11528/img-2.jpg
Fichier image/jpeg, 4,3M
Titre Tab. 1 − Synthetic statistical data on the morphometry of steep dry valleys in the Vânturarița‑Buila Massif. Tab. 1 − Données statistiques synthétiques de la morphométrie des SDVs dans le massif de Vânturarița‑Buila.
Légende The values represent the median of each morphometric parameter.Les valeurs représentent la moyenne de chaque paramètre morphométrique.
URL http://geomorphologie.revues.org/docannexe/image/11528/img-3.jpg
Fichier image/jpeg, 272k
Titre Fig. 3 − Longitudinal profiles of the steep dry valleys. Fig. 3 − Profils longitudinaux des vallées sèches (type en 'cheminée').
Légende A‑E. Location of the main groups of dry valleys; F. Convergent dry valleys in Mt. Stogu (1494 m a.s.l.); G. The highest dry valleys, in Mt. Vânturarița (1875 m a.s.l.); H. The longest and steepest dry valleys in Mt. Buila, V22‑V26; I. V23 and V24 expose the most abundant and interesting unearthed speleothems in the Vânturarița‑Buila Massif; J. Gentle‑inclined, fault‑related “Hornurile Popii” corridors in Mt. Piatra. Shaded areas : knickpoints and benches.A‑E. Localisation des principaux groupes de vallées sèches ; F. Vallées sèches convergentes dans le Mont Stogu (1494 m) ; G. Vallées sèches les plus élevées dans la Montagne Vânturarița (1875 m) ; H. Les longues vallées sèches et escarpées du Mont Buila V22‑V26 ; I. V23 et V24 comprennent les plus abondants et intéressants spéléothèmes (exhumés) dans le Massif Vânturarița‑Buila ; J. Couloirs « Hornurile Popii » dans le Mont Piatra, en pente douce, formés le long de failles. Les zones ombrées (en gris) : les points d'inflexion et les surfaces structurales.
URL http://geomorphologie.revues.org/docannexe/image/11528/img-4.jpg
Fichier image/jpeg, 4,4M
Titre Fig. 4 − Correlation between the orientations of major faults (in grey), tensile fractures and minor faults (in black) and steep dry valleys (in red).Fig. 4 − Corrélation entre la direction des failles principales (gris), les linéaments tectoniques (noir) et l’orientation des vallées sèches escarpées (rouge).
URL http://geomorphologie.revues.org/docannexe/image/11528/img-5.jpg
Fichier image/jpeg, 4,1M
Titre Tab. 2 − Comparative DEM‑ and field‑based measurements on the morphometric patterns of steep valleys (all values are given in degrees).Tab. 2 − Comparaison entre les mesures extraites du MNT et celles mesurées sur le terrain concernant les types morphométriques des vallées abruptes (toutes les valeurs sont en degré).
URL http://geomorphologie.revues.org/docannexe/image/11528/img-6.jpg
Fichier image/jpeg, 216k
Titre Tab. 3 − Variability of exposed caprock thickness and the arc radiuses of scarp sectors at different scales in the Vânturarița‑Buila Massif, Colorado Plateau and continental slope of Puerto Rico.Tab. 3 − Variabilité de l’épaisseur de l’abrupt et du rayon des arcs de cercle circonscrits aux secteurs escarpés en forme d’amphithéâtre, mesurée à différentes échelles dans le Massif Vânturarița‑Buila, le plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.
URL http://geomorphologie.revues.org/docannexe/image/11528/img-7.jpg
Fichier image/jpeg, 184k
Titre Fig. 5 − Correlation graph between the caprock thickness and the arc radiuses corresponding to amphitheater‑shaped scarps in Vânturarița‑Buila Massif, Colorado Plateau and the submerged slope failure in Puerto Rico. Fig. 5 − Graphes de corrélation entre la hauteur de l’abrupt et les rayons des cercles circonscrits aux secteurs d’abrupt en forme d’amphithéâtre du Massif Vânturarița‑Buila, le Plateau du Colorado et le glissement immergé de la pente continentale de l'île de Puerto Rico.
Légende A. Of each sample; B. Of all data. In case of Vânturarița‑Buila Massif, the exposed caprock thickness was inferred from the medians of SDVs lengths. A. Données des unités géographiques ; B. Toutes les données. Dans le cas du Massif Vânturarița‑Buila, la hauteur de l’abrupt (épaisseur du toit de la formation rocheuse) a été obtenue à partir des valeurs médianes de la longueur des vallées sèches abruptes.
URL http://geomorphologie.revues.org/docannexe/image/11528/img-8.jpg
Fichier image/jpeg, 2,7M
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Laura Tîrlă, Ionuț Mirea et Iuliana Vijulie, « Geomorphological and structural patterns of the scarp‑related steep dry valleys in limestone ridges: A case study from South Carpathians, Romania », Géomorphologie : relief, processus, environnement, vol. 22 - n°4 | 2016, 399-408.

Référence électronique

Laura Tîrlă, Ionuț Mirea et Iuliana Vijulie, « Geomorphological and structural patterns of the scarp‑related steep dry valleys in limestone ridges: A case study from South Carpathians, Romania », Géomorphologie : relief, processus, environnement [En ligne], vol. 22 - n°4 | 2016, mis en ligne le 09 janvier 2017, consulté le 23 février 2017. URL : http://geomorphologie.revues.org/11528 ; DOI : 10.4000/geomorphologie.11528

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Auteurs

Laura Tîrlă

Department of Regional Geography and Environment, Faculty of Geography – Bucharest University – Bălcescu Bd. 1, 010041, Bucharest, Romania (tirla@geo.unibuc.ro). Tel: +40 724 693 615

Ionuț Mirea

‘Emil Racoviță’ Institute of Speleology, Romanian Academy – Frumoasă St. 31, 010986, Bucharest, Romania (ionut.cornel.mirea@gmail.com).

Iuliana Vijulie

Department of Regional Geography and Environment, Faculty of Geography – Bucharest University – Bălcescu Bd. 1, 010041, Bucharest, Romania (iuliana.vijulie@g.unibuc.ro).

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