ROCK-LANDFORM-SOIL RELATIONSHIP FOR GEOMORPHOPEDOLOGICAL CHARACTERIZATION IN THE REGION OF LAVRA VELHA, OCCIDENTAL CHAPADA DIAMANTINA, BAHIA RELAÇÃO ROCHA-RELEVO-SOLO PARA CARACTERIZAÇÃO GEOMORFOPEDOLÓGICA NA REGIÃO DE LAVRA VELHA, CHAPADA DIAMANTINA OCIDENTAL, BAHIA

The Lavra Velha region is situated on the western edge of the Chapada Diamantina and comprised of a crystalline basement and a metasedimentary cover that corresponds to the Ibitiara Granitoid and the Espinhaço Supergroup, respectively. The Chapada Diamantina is internationally recognized for mineral production and tourism, and because of that it has become a constant target for novel research that aims at characterizing its main geological and physiographic aspects. The present work aims at pointing out geomorphopedological associations of the Lavra Velha region by analyzing the interdependence between rock, landform and soil. To this end, geology, geomorphology and pedology data were obtained from literature, remote sensing Informações sobre o Artigo Recebido (Received): 17/08/2019 Aceito (Accepted): 14/01/2020


Introduction
The analysis of the rock-landform-soil association is essential for the study of landscape evolution. According to Torrado et al. (2005), the pedogenetic processes are controlled by the dynamics of several factors, among which stand out are climate, geomorphology, and geology. The climate infl uences soil development, both through the availability of water that acts as a weathering agent and a chemical leaching of minerals, as well as by temperature which works as a catalyst for chemical reactions leading to degradation of rocks. The landform directly infl uences the pedogenetic evolution, since it controls the amount of water infi ltrated through the terrain, and consequently, the speed of the chemical reactions that promote rock weathering (CURI & FRANZMEIER, 1984). Typically, soils that come from quartz-rich rocks tend to present medium to coarse texture and acidic pH (MEDEIROS et al., 2013). In contrast, soils resulting from the decomposition of basic/ultrabasic rocks tend to be clayey and alkaline (TORRADO et al., 2006).
Research focused on the understanding of the rock--landform-soil relationship and its infl uence on several types of natural phenomena have been developed throughout the world since the 1960s (e.g. TROEH, 1964;LEPSCH et al., 1977;TRICART & KILLIAN, 1979;THOMAS et al., 1999;CASTRO & SALOMÃO, 2000;LACERDA et al., 2008). However, surveys involving these three landscape components simultaneously in association with litho-structural variables are still limited. Despite this, the geomorphopedological characterization, in which there is a soil-landform-rock analysis associated with litho-structural elements, has been approached as an important mechanism to understand the landscape evolution and soil distribution, as shown in the works conducted by Villela et al. (2013) and Villela et al. (2015).
In the Brazilian regions where research is focused on the integrated analysis of landscape components,

Palavras-chave:
Relação Relevo-Rocha-Solo; Região de Lavra Velha; Chapada Diamantina Ocidental. data and fi eld expeditions. In the studied area, we recognized metasedimentary and crystalline rocks, on which fl at to gently undulating landforms beside crests and cliff s developed. Oxisols occur on fl at to gently undulating landforms while Entisols, Inceptisols and rock outcrops appear in the aligned crests, cliff s and undulating hills. Alfi sols predominate in undulating hills associated with mafi c rocks. Features of the landscape show landforms resembling the Appalachian geomorphological model as fi rst described by William Morris Davis, and they suggest landform evolution by geochemical and mechanical erosion under a strong litho-structural control. The geomorphopedological associations allowed the understanding of the relationship between the major elements of the physical environment from Lavra Velha region and, consequently, a predictive model of the rock-landform-soil distribution that can be useful for geomorphopedological mapping of the western edge of the Chapada Diamantina.
Therefore, this study is focused mainly on the recognition of rock-landform-soil association and its correlation with litho-structural factors for the geomorphopedological characterization of the Lavra Velha region. This region is located on the occidental portion of the Chapada Diamantina in Brazil and has an increased level of mineral and tourism activities. The result is a precursor model archetype for integrated modeling of the geomorphopedological setting in this physiographic domain.

Study Area
The study area is situated north of Ibitiara, in the mid-west of the state of Bahia, Brazil ( Figure 1). It corresponds to a quadrant of 150 km 2 , between latitudes 12° 29' 20" and 12° 37' 05" S, and 42° 18' 59" and longitudes 42° 10' 22" W. Starting from Salvador, the state capital, access to the area can be achieved by land via highways BR-324, BR-116 and BR-242. The landform of the region is represented by the Sertanejo Pediplain made up of elongated, parallel ridges running in a north-south direction, belonging to the Espinhaço Supergroup of Pre-Cambrian age (Ribeiro, 1974). The predominant vegetation is the open arboreal caatinga, without palms. The climate is semi-arid, hot and dry, corresponding to the BSh climate in the Koppen (1936) classifi cation. The annual average temperature is 26.5 °C and the average annual rainfall is only 746 mm, with higher rainfall volumes from October to April. where the study area is (box outlines area shown in B and C). C) Focus on the study area (the green background is part of the city of Ibitiara).

Materials and Methods
Aiming at delineating the geomorphopedological units, we gathered information such as geology, geomorphology, pedology, drainage, hypsometry, slope and topography from the specialized literature, along with offi ce and fi eld data. Studies conducted by Tricart & Killian (1979), Castro & Salomão (2000), Lacerda et al. (2008), and Villela et al. (2013Villela et al. ( , 2015 were considered in order to approach the morphopedological setting and, consequently, to make the fi nal geomorphopedological map. Steps and diff erent sources of data will be presented as follows. Geological data was obtained from the research developed by the Geological Survey of Brazil for the Ibitiara-Rio das Contas Project (2005), as well as the geological mapping conducted by Campos (2013) and Carlin et al. (2018). In addition, a fi eld expedition was undertaken to describe outcrops and collect rock samples from the region.
The techniques used by Nascimento et al. (2018) were followed for the geomorphological mapping due to the satisfactory outcome achieved by their approach in an area with a similar geomorphological setting of the study site. The cartographic base included topographic maps from the SEI on the scale of 1:100,000, and Digital Elevation Models (DEM) from the PALSAR sensor aboard the ALOS satellite, with the spatial resolution of 12.5 meters. This data was adjusted to assist in the elaboration of hypsometry, slope declivity, slope aspect, geology, pedology and geomorphology maps. These maps were overlapped and used for understanding rock-landform-soil relationships. The digitization and elaboration of the cartographic base, as well as the models presented in this work, were done in the Georeferenced Information Processing Laboratory (LAPIG) of the University of Campinas (IG/UNICAMP).
The survey, characterization, and spatialization of soils relied on the research developed by Ribeiro (1974) in the city of Ibitiara, as well as data from the Brazilian Agricultural Research Corporation (EM-BRAPA, 2001), and the Bahia Environment and Water Resources Institute (INEMA, 2014). Moreover, a fi eld expedition was carried out to recognize and describe morphological attributes of soil profi les. In the present study, laboratory analyses were not performed to get physical and chemical attributes of the soil. In the fi eld the soil was classifi ed up to the second level and additional attributes can be found in the sources mentioned previously.
Geomorphopedological units were determined based on the maps previously mentioned, mainly on the geological, geomorphological and pedological maps, which were integrated by overlaying their records. Geomorphopedological units were diff ered from each other mostly through the rock-landscape--soil combination.

Geology
The study area consists of rocks corresponding to Granitoid Ibitiara, Espinhaço Supergroup and intrusive mafi c rocks as shown in the geological map ( Figure 2).
In the study area, the main rocky outcrops occur as blocks ( Figure 3A), along structurally aligned hills, mainly in the northern end of the Ibitiara anticline. The granitoid is fi ne to medium grained, hololeucocratic, and vary from granitic to granodioritic composition. The most mineral constituents are quartz, altered plagioclase, altered K-feldspar (orthoclase), as well as muscovite, tourmaline, chlorite, hematite, magnetite and epidote. In general, these rocks are foliated, following the NNW-SSE regional trend, with infl ections to NNE-SSW and a high angle of dip.
The Espinhaço Supergroup encompasses rocks of the Rio dos Remédios Group, represented by Lagoa de Dentro and Ouricuri do Ouro tectosequences and by metasedimentary rocks of the Paraguaçu Group.
According to Guimarães et al. (2005), the formations of the Lagoa de Dentro and Ouricuri do Ouro corresponds to tectosequences of metasediments with interdigitated lateral contact. In the surveyed region, the best rocky expositions of the Lagoa de Dentro/Ouricuri do Ouro tectosequences are located at the top of undulating hills, as well as at the top of the Mangabeira ridge and some roadcuts. Outcrops are mainly in blocks or fl agstone and are comprised mostly metasandstones and polimitic metaconglomerate with rounded pebbles and boulders related to basement rocks, as well as lithic metasandstones, metarkoses and metagraywackes (Figura 3B).
The Paraguaçu Group is represented by rocks of low metamorphism and deformation degree from the Mangabeira Formation, composed of metasandstones, impure metachert, and metasiltstone, and from the Araçuaí Formation, composed mainly of metagraywacke (GUIMARÃES et al., 2005). In the investigation area, those rocks are exposed mainly on the top of hills and escarpments of the Boqueirão de Fogo ridge. The outcrops occur as both blocks and fl agstones and are comprised mainly of metasandstones ( Figure 3C).
Mafi c rocks are intrusive into the rocks mentioned above, mostly in the form of dykes and sills. In general, they consist of gray to green isotropic gabbros with thick plagioclase crystals ( Figure 3D). In the study area, the elevation ranges from 850 meters to 1,150 meters. Most area is represented by fl at landform and gently undulating hills surrounded by elongated, narrow and steep slope ridges. The drainage patterns consist mainly of trellis and rectangular, varying according to the litho-structural control. The geomorphological compartmentalization of the area encompasses three large units (Figure 4).  Unit I is comprised of parallel and aligned ridges and escarpments with steep slopes (> 45%) and low drainage density ( Figure 5A). Unit II consists of undulating hills with slope top-bottom roughness less steep than Unit I (8%< slope < 45%). In general, the geomorphic features show convex or rounded top hills and medium to high drainage density ( Figure 5B). Unit III encompasses a fl at landform to gently undulating hills with predominantly rounded tops and medium to high drainage density ( Figure 5C). In this unit, locally, rocky outcrops and relict features of rounded to fl at hills top at higher altitudes arise ( Figure 5D). The Oxisols ( Figure 7A, B, C) are deeper than 200 cm and shows little diff erentiation into horizons. They occupy 50% of the study area and consist generally of moderate A horizon with yellow-brown colors, and porous B horizon with sandy clay to clayey sand textures and colors ranging from yellow, red-yellow and red (variations 10R; 10YR; 7.5YR; 5YR and 2,5 YR in the Munsell color chart).
Concerning the Alfi sols ( Figure 7D), they are shallow and occupy only 1% of the study area. In general, they present an A horizon often marked by a cover with rock fragments of diff erent sizes that characterize desert paving or surface stoniness. The B horizon is textural type with reddish colors (5YR and 2.5 YR in the Munsell color chart). In addition, cracks can be observed in this horizon in function of the presence of 2:1 clay mineral.
Entisols is dominantly litholic and occurs constantly associated with Inceptisols and rock outcrops ( Figure 7E and F). Because of this characteristic, we have chosen to group spatially these two soil orders. The Entisols are shallow, with moderate A horizon developed directly on C horizon. The texture is mainly sandy-loam and, occasionally, stony. It diff ers from the Inceptisols because of the absence of B horizon. Thus, the set (Entisols and Inceptisols) occupies 49% of the study area, in which the main profi le exposures occur in the Boqueirão do Fogo, Mangabeira and Lavra Velha ridges.  The geomorphopedological model established for the region of interest is a consequence of the integrated analysis of geological, geomorphological and pedological data along with structural meanings obtained from laboratory and fi eld works. Therefore, these units are not only a function of combined and overlapped rock-landform-soil data (morphopedological elements), but also of litho-structural factors in accordance with the work conducted by Villela et al. (2015). From this analysis, fi ve main geomorphopedological units were defi ned (Figure 8). Units I and II consist of Oxisols, which are associated mostly with gently undulating hills and fl at landform present in open valleys. Locally, undulating hills may occur. While Unit I is supported by crystalline rocks corresponding to the Ibitiara Granitoid, Unit II is composed of metasedimentary rocks of the Ouricuri do Ouro and Lagoa de Dentro formations beside metasedimentary rocks of the Paraguaçu Group.
Unit III is composed of Alfi sols associated to un-dulating hills. It mainly occurs at the bottom of slopes developed on the Ibitiara Granitoid and the Paragaçu Group, in which mafi c intrusion occur. On this unit, there is often pebbles and boulders from gabbroic rocks in diff erent stages of decomposition. Units IV and V correspond to Entisols and Inceptisols associated with rock outcrops, which occur at parallel and aligned crests, and cliff s. The Unit IV is maintained by crystalline rocks related to the Ibitiara Granitoid, whilst Unit V is supported by metasandstones and metaconglomerates of the Ouricuri do Ouro and Lagoa de Dentro formations, as well as by metasandstones of the Paraguaçu Group.

Rock-Landform Relationship and Pedogenetic Implication
The Entisols and Inceptisols, developed on more pronounced landforms (slope> 45%), are located at the highest topographic levels (950m< altimetry> 1150m). Hence, the topography seems to have strong infl uence on the pedogenetic evolution of those soil types in the Lavra Velha region by controlling weathering agents and development of weathered materials. This is because areas with a steep slope infl uence water infi ltration, thus the soils are predisposed to less intense leaching and to become shallow. Therefore, by this mechanism, those soil types were possibly developed toward the top of the Lavra Velha, Boqueirão and Mantiqueira ridges. This perspective is agreed with in the work carried out by Benites et al. (2007). These authors also reported Entisols and Inceptisols associated with rock outcrops toward the top of the Espinhaço mountain range, whose development is a function mainly of topography and lithology.
Regarding bedrock infl uences on Entisol and Inceptisol formation, the presence of muscovite/sericite on soil profi les developed on granitoid; quartz and clay minerals on soil profi les developed on rocks from the Espinhaço Group; and along with rock fragments from the lithology right under the soil profi le, indicates incipient pedogenic processes which depend largely on primary minerals composition and their transformation into secondary minerals.
The Alfi sols are associated with undulated landforms (8%< slope < 45%) in the sectors of altitudes which range from 900m to 1000m mostly. The occurrence of this soil order and litholic Entisols are quite common in these landforms in the northeast of Brazil (AGBENIN & TIESSEN, 1995). In the study area, the main occurrences of Alfi sols are associated with mafi c rocks intruded into the Ibitiara Granitoid and metasandstones of the Paraguaçu Group. The development of these soils seems to be infl uenced not only by the strong rock-landform relationship, but also by the composition of the parent material. The landform controls surface weathering agents while mafi c rocks are the main sources of raw material for soils' development. The mineralogy of those rocks, composed of calcium feldspar and ferromagnesian silicates, once transformed into secondary minerals, generated soils with 5YR and 2.5YR shades and high activity clay. This result is consistent with the work conducted by Ribeiro (1974) in Ibitiara that describes similar soils developed on mafi c rocks.
The yellow, red-yellow and red Oxisols are formed in the fl at and gently undulating landforms, at topographic levels that rarely exceed 950m and slopes often less than 20% steep. These landforms favor the infi ltration of water and make the action of weathering agents more eff ective with more intense weathering down in the soil profi le and close to bedrocks, including the formation of deeper soil. The development of these soils occurs on both metasedimentary and crystalline substrates. In the crystalline substrate, the Oxisols tend to be predominantly red-yellow or red, perhaps due to the abundant presence of hematite resulting from the hydrothermal alteration that aff ects the Granitoid Ibitiara, which were reported by Campos (2013) and Carlin (2018). On the other hand, when these soils are developed on rocks of the Espinhaço Supergroup, they are predominantly yellowish Oxisols, indicating the presence of goethite and smaller proportions or absence of hematite. This interpretation is based on Fontes (1991) and Resend (1976), who reported that goethite and hematite are not only the main Fe forms present in Brazilian Oxisols, but also the reason for their yellow and red colors.

Structural Setting of Landscape and Soil Distribution
The confi guration of the landscape and the distribution of the soils of the Lavra Velha region seem to be strongly conditioned by litho-structural factors.
The drainage and the landform patterns developed in the old folded and exhumed geological setting, when associated with local and regional sections, along with litho-structural components, reveal the controls exerted by the compressive tectonic that aff ected the area reported by Guimarães et al. (2005), and in line with Campos (2013). The landscape shows a parallel and aligned ridge-and-valley landform displayed as a well typical Appalachian-style folded relief as mentioned in De Barros et al. (2019). Figure 9 (A, B and C) shows schematic and simplifi ed block diagrams, adapted from Suertegaray (2003), in which are illustrated a generic evolution of a folded landform from the Appalachian landscape.
The geological setting, of which the Lavra Velha region is included, was aff ected in varying degrees by NNW-SSE-trending shear zones and by dissimilar folding developed during the Brasiliano orogeny (GUI-MARÃES et al., 2005;CRUZ & ALKIMIN, 2006). As a result, in the late proterozoic, the landscape was marked by a setting of anticline and syncline folds. De Vries & Benthem (2013) and Cawood & Bond (2019) report that during compressive structural events, the development of a series of fracture families (longitudinal and transverse joints) is common in the closeness of the anticline hinge. Hence, those joint fractures would facilitate the ingress of weathering agents, such as water and plant roots and, consequently, eff ect landform evolution, as stated in the works conducted by Graham et al. (1994) and Oilier & Pain (1996). From this perspective, at the end of the Brasiliano orogeny, the Lavra Velha region would be aff ected by weathering more intensively near the anticline hinges because of the deformational structures that would increase the permo-porosity of the rocks in these areas. The weathering and geochemical erosion could be also heightened due to paleoclimate oscillation over geological time, which would contribute to the deeper soil formation (RIBEIRO, 1974), as well as to the collapse of anticlinal hinge areas.
In this respect, the confi guration of the Lavra Velha landscape region would be pronounced by ridges, represented mostly by limb portions or perhaps synclines, and valleys, represented mainly by anticlines, along a NNW--SSE direction as indicators of the litho-structural control.
From the perspective of analyzing the landscape confi guration, it becomes easier to understand patterns of soil distribution in the Lavra Velha region. The more developed soils are in the lower area of the terrain, which among others include the fold hinge zone of the Ibitiara Granitoid anticline. These areas, as mentioned previously, was probably more susceptible to the geochemical erosion that led to the collapse of the mineral structures present in the original rocks and, as a result, the lowering of the land-surface together with the development of deeper soils. This perception is in accordance with works conducted by Hill (1995), Oilier & Pain, (1996, and Frazier & Graham (2000). These previous studies showed the diff erential weathering of fractured rocks, and consequently, the infl uence of fractures on pedogenic processes in addition to their role in the transformation of bedrocks into soils.
Relative to less developed soils, these are distributed in areas with sharp landforms that refl ect the structural crests aligned to the axis of the anticlinal fold, beside the shear zones. These soils also occur at the top of residual geological bodies that were shaped by old planation surfaces and thus recording diff erential erosion processes. These landforms are often found in Brazilian semi-arid regions, and they represent portions of the substrate resistant to the processes of pediplanation and pedogenesis in the northeastern region (DOS SANTOS et al., 2010). Lowering of the land-surface, mainly around the fold hinge. Rocky bodies may outcrop and remain as relict landforms; (C) Ridge and valley topography formed as result of the dissected landforms. Stages A, B and C are based on the Appalachian-style folded landform as described by Suertegaray (2003).

Conclusion
The rock-landform-soil relationship associated with litho-structural attributes allowed the defi nition of the main geomorphopedological units in the Lavra Velha region. The fi ve mapped units are composed of Entisols, Inceptisols, Alfi sols and Oxisols maintained by landforms and rocks associated with the Ibitiara Granitoid, the Espinhaço Supergroup and the mafi c intrusions.
The structural landscape framework resembles the Appalachian-style folded landform as initially proposed by William Morris Davis and illustrated later by Suertegaray (2003).
Landscape setting controls the development and distribution of soils, in which deep soils (Oxisols) are associated with fl at and gently undulating landforms, which denotes sectors intensively aff ected by deformational structures. On the other hand, shallow soils (Entisols and Inceptisols) are associated with higher altitude terrain that correspond mostly to parallel and aligned ridges.
The distribution of Alfi sols is mainly associated with lithology. These soils are developed from intrusive mafi c rocks.
Other sectors in the western region of the Chapada Diamantina does not present mapping of the rock--landform-soil association. Thereby, the geomorphopedological model proposed in this work can be used for the prediction and individualization of similar units in other portions of this physiographic domain, in order to assist in technical and scientifi c studies. Higher altitude areas are favorable for the identifi cation and mapping of lithologies and deformational structures, while areas associated with the lower landforms present the best exposures of soil profi les that could be useful to pedological and pedogeochemical surveys.