Departamento Geología

Use of rock tablet method to measure rock weathering and landscape denudation

2021-01-01T00:00:00Z

[EN]Rock weathering is a key component of the rock cycle that transforms rocks in sediments, soils and/or dissolves minerals to ions, and plays an important role in landforms development and landscape evolution. The quantification of weathering is often challenging due to the impact of measuring techniques on the rock itself and/or the assumptions required to perform the calculations. Among different methods used to quantify rock weathering, rock tablet method is one of the most widely used. The rock tablet method consists of cutting rock samples in a shape that allows precise calculation of their volume and surface. These rock pieces, often named tablets when they are flat, are dried, precisely weighed and exposed to the natural environment for certain amount of time. After retrieval, the same laboratory procedure is repeated, and from the weight loss, the weathering rate is calculated. When the density of the rock is known and it is reasonable to assume that the lost material is removed from the ground surface, the weight loss can be used to calculate denudation rates. This is the case in karst regions, where rock tablets are one of the most commonly used methods to calculate denudation. This simple and versatile method requires only a limited amount of laboratory equipment to be implemented which makes it very popular. However, experimental design, preparation of samples and calculations are not homogeneous among researchers, sometimes making the results of this method challenging to be evaluated and compared. In this paper we describe the rock tablet method, include its historical overview, review the most significant studies that have used this technique, highlight its limitations, introduce correction factors to minimize some of those limitations, and provide good practice recommendations to help other researchers to obtain comparable results around the world.

ISODRIP, a model to transfer the δ18O signal of precipitation to drip water — Implementation of the model for Eagle Cave (central Spain)

2021-01-01T00:00:00Z

[EN]The isotope signature of cave waters provides an excellent opportunity to better understand the recharge in karst regions and the complexity of drainage systems in the vadose zone. We have developed a cave isotope hydrological model (ISODRIP) that requires entering basic hydrometeorological information and a precipitation δ18O record to simulate the discharge and δ18O signals of different drip sites. The model includes four different modules to simulate various flow route regimes: continuous and discontinuous drips under diffuse or preferential flows. We use precipitation and cave water δ18O records that were obtained in Eagle Cave (central Spain) during a 5-year period to test our model and to better understand the dynamics of karst aquifers. Eagle Cave waters do not record evaporation. The δ18O signals do not have seasonality, although they record intra-annual and inter-annual variability. Additionally, cave water δ18O signal falls within the range of the annual average weighted isotope composition of precipitation. Well-mixed cave waters, that characterize diffuse flows, record 1‰ δ18O variability, whereas partially-mixed waters, that flow along preferential drainage routes, have up to 3‰ δ18O variability. The results suggest that precipitation takes on average 15 months to reach the cave through the diffuse flow network, whereas under preferential flow the transit time is highly variable depending on the previous condition of the system. ISODRIP includes a soil layer above the vadose zone that controls large recharge events, together with direct recharge components that bypass the soil layer enabling at least some recharge all year round. Thus, the simulations reproduce the observed lack of seasonal bias in the cave water δ18O composition in relation to the average weighted isotope composition of precipitation. This research highlights the importance of understanding recharge dynamics and the configuration of particular drips sites to properly interpret speleothem δ18O records.

Temperature as a tracer of hydrological dynamics in an anchialine cave system with a submarine spring

2018-01-01T00:00:00Z

[EN]Although temperature is a nonconservative tracer, it often provides useful information to understand hydrological processes. This study explores the potential of temperature to characterize the hydrological dynamics of a submarine spring and its coastal karst aquifer in Krka Estuary (Croatia). The estuary is well stratified and its water column has a clear thermocline. A network of loggers was designed to monitor the temperature along vertical profiles in the estuary and the coastal aquifer, taking advantage of an anchialine cave that enabled access to the subterranean estuary. The location of the thermocline in the groundwater, which defines the upper boundary of the saline intrusion, depends on (1) the recharge of the aquifer via infiltration of precipitation, (2) the evolution of the thermocline in the estuary, and (3) the tidal oscillations. The sources of water flowing though the anchialine cave were identified: brackish water from the estuary above the thermocline, saline water from the estuary below the thermocline, and freshwater from infiltrated precipitation. A conceptual model is described that characterizes the hydrological dynamics of this coastal aquifer and its interactions with the estuary. Thus, at least for some hydrological settings, temperature is a valid tracer to characterize the main hydrological processes. The measurement of temperature is inexpensive compared to other (conservative) tracers. Therefore, for those hydrological settings that have water masses with distinct temperatures, the use of temperature as a tracer to establish conceptual models of the hydrological dynamics is encouraged.

Plasticity, Mineralogy, and WRB Classification of Some Typical Clay Soils along the Two Major Rivers in Croatia

2020-01-01T00:00:00Z

[EN]Quantification of soil plasticity is usually based on Atterberg limits or indices, which are then used for engineering and agricultural purposes on clay soils. Because these limits/indices are seldom analyzed during routine soil surveys, they are sometimes estimated from available soil properties using pedotransfer functions (PTFs). Main aim of this study was to test if two robust PTFs, previously created by other authors for other soils/areas, may be used for predicting plasticity of typical clay soils on fluvial deposits in Croatia. We analyzed mineralogy, plasticity, and related physicochemical properties of four representative soil profiles along Sava and Drava, two longest Croatian rivers. Particle size distribution patterns pointed to more uniform sedimentation along Sava, compared to Drava. Also, more clay was found within Sava profiles. Soil texture was finer farther away from the sources of both rivers. Soil cation exchange capacity (CEC) was almost fully positively correlated to clay content. On the other hand, Corg content showed no correlation to CEC. This is attributed to the significant presence of smectite across all studied soils. Clay was recognized as the main factor influencing soil plasticity. When compared to the measured values, the predicted values of plasticity index and liquid limit were heavily underestimated. Hence, region-specific PTFs should be developed for more accurate prediction of plasticity in these soils. According to the WRB-2015, the soils were classified as Eutric Reductigleyic Stagnic Gleysols (Clayic, Humic, Protovertic). Because soils were not dry during field description, shrink-swell cracks were not prominent, and therefore soils were not classified as Vertisols. We suggest that field criteria for classification of Vertisols should not depend on actual soil moisture. Instead, plastic limits/ indices could be used.

Long-term denudation rate of karstic North Dalmatian Plain (Croatia) calculated from 36Cl cosmogenic nuclides

2022-01-01T00:00:00Z

[EN]The development of a karst landscape results from complex interactions between lithology, climate, hydrology, soil, vegetation and tectonics. Weathering and erosion of carbonate rocks leads to denudation of karst landscapes. As dissolution of carbonate rocks is often considered to be the main process governing carbonate weathering, other processes are often overlooked. Here we present research done in the North Dalmatian Plain, a carbonate erosive surface located in the Dinaric karst region. Although the study site is composed of two different carbonate lithologies having different weathering style, there is no evident lithological impact on the topography of the erosive surface. Analyses of 36Cl concentration were performed in ten proximal bedrock samples from both lithologies and resulted in long-term denudation rates ranging from 14.7 to 22.8 m/Ma. Since no statistical significance was found between samples from different lithologies (all samples belong to a single normal population) and they have the same geomorphological context and climate features, variable denudation rates are attributed to local (sample specific) differences. In the study site there are no large outstanding rock residuals or patches with deep soil profiles. Thus, to maintain the levelled erosive surface, local differential denudation rates have to vary with time. We hypothesize that lichens and pedogenic carbonates have a significant role in modulating local differences in denudation rates. Our study shows that even at outcrop scale those differences can be significant, and the study of sample populations is preferred to single or limited number of analyses. Thus, the longterm denudation rate of the North Dalmatian Plain, including its local variability is 18.91±0.81 m/Ma. Despite classical studies on karst terrains assume that dissolution is the main process responsible for development of these landscapes, our research highlights the importance of physical weathering in combination with dissolution of carbonates as main controls on the denudation of karst landscapes.

Investigation of short-term denudation rates using the rock tablet method in Northern Velebit National Park (Croatia)

2024-01-01T00:00:00Z

[EN]The formation of karst landscapes is the result of a series of processes, whereby rock weathering and denudation play important roles. Soluble carbonate rocks are chemically weathered (dissolved) on the surface or under soil cover resulting in the formation of different karst morphologies and controlling surface denudation. The Dinaric karst area is the type-site for numerous karst features and phenomena, but studies on carbonate weathering in this region are still scarce, especially in the mountainous regions. To better understand the formation of Dinaric karst mountainous landscapes, we studied denudation rates at the northern part of Velebit Mountain using the rock tablet method. Denudation was measured using rock tablets consisting of local lithologies and “standard rock tablets” exposed to the natural environment at the surface, but also buried in the soil. Furthermore, rock tablets were placed in three different settings (open slope, small clearing, bottom of a doline) to evaluate the local factors impacting the denudation rate. The results of this study showed that the denudation rate is highly dependent on local factors and lithology, and that local rock tablets from different lithologies should be used to determine the actual denudation rate.

Thermal impact of Heinrich stadials in cave temperature and speleothem oxygen isotope records

2020-01-01T00:00:00Z

[EN]During each Heinrich stadial (HS), temperatures in southern Europe typically dropped several degrees during several hundred to few thousand years. We have developed a one-dimensional thermal conduction model that transfers the typical surface temperature anomaly of a HS to a series of hypothetical underlying caves. The results show that with increasing depth, the thermal anomaly is attenuated, the lag time increases, and the signal structure experiences larger modifications. The model suggests that in most cases, it is not acceptable to assume a synchronous thermal variability and similar average temperature values between the surface atmosphere and the cave interior at millennial timescales. We also simulated the thermal impact of the modeled HS on speleothem δ18O records. The outputs of most model scenarios suggest that temperature changes associated with the HS produce δ18O anomalies capable of contributing significantly or even decisively to the speleothem isotope variability. Therefore, despite controls other than temperature often being considered more important when interpreting Pleistocene speleothem δ18O records in temperate climates, this research suggests that temperature is expected to be one of the major controls of δ18O values in most cave sites outside the tropics and should be included as a significant parameter affecting Pleistocene speleothem δ18O records.

Characterization of soil drainage dynamics on karst terrains by developing a site-specific reservoir cascade scheme hydrological model with preferential flows

2022-01-01T00:00:00Z

[EN]Models provide quantitative solutions that enable better understanding of karst soils hydrology. A location in central Spain was selected to implement a 1-D hydrological model that uses a reservoir cascade scheme (RCS) approach to simulate soil water content (SWC) at daily resolution. The model simulates SWC for six soil layers and includes additional modules to reproduce preferential flow regime. The soil profile in the model is 0.5 m deep, developed in silt loam soil on top of dolomite marbles. Three different configurations of the model were considered. Configuration 1 considers a basic RCS module, whereas other configurations include preferential flows. Thus, Configuration 2 considers RCS module together with a continuous preferential flow module, where 1 to 5% of available SWC from each layer is drained every day along preferential pathways. Configuration 3 contains a discontinuous preferential flow module in addition to previous modules. The discontinuous preferential flow is only activated during rainfall events occurring after long dry periods. Simulated SWC values are compared with measured SWC values, so model parameters are iteratively adjusted to optimize the model results. The model produces the best simulations implementing the Configuration 3, when matrix flow and two preferential flow regimes are considered. The model shows that preferential flows significantly contribute to recharge and should not be neglected in soil hydrological models and recharge estimations in karst areas.

Characterisation of pedogenic carbonates in Calcocambisol at a location within the Dinaric part of Croatia

2025-01-01T00:00:00Z

[EN]Pedogenic carbonates are secondary carbonate deposits and are a constitutional part of many soils. We analysed a 95 cm deep Calcocambisol soil profile at a location in the Dinaric part of Croatia. Here, pedogenic carbonates are more abundant in the deeper part of the profile (>23 cm), and their amount and size increase with depth corresponding to soil properties along the profile. These pedogenic carbonates are spherical to irregular in shape and can be classified as nodules. Microscopical analysis of these nodules shows that dissolution and re-precipitation of carbonate take place in situ, without considerable movement through the soil profile. The growth of the nodules starts from multiple centres of nucleation, and their internal structure is a result of spatial and temporal environmental conditions in the soil matrix during carbonate precipitation. The inclusion of noncarbonate particles and preservation of the original soil structure confirm the replacive nature of nodule growth. Furthermore, the internal structure of nodules reveals multiple stages of calcite precipitation, indicating seasonal or event-based precipitation of carbonate.

Investigations of short-term denudation rates on the North Dalmatian Plain (Croatia)

2026-01-01T00:00:00Z

[EN]Studies of denudation rates in carbonate areas are an important step to understand rates of karst landscape development. Weathering of carbonate rocks is an essential process in soil formation and has a significant role in the global CO2 budget. We studied short-term weathering and denudation rates at a location in the Dinaric karst using the rock tablet method while monitoring surficial and soil environmental parameters. We exposed “standard” rock tablets and those from local lithologies to the natural environment at the surface and buried them at two depths (20 and 50 cm) in the soil profile. Our results show that the average actual denudation rate measured at this site is 2.28 μm/a (for rock tablets exposed at the surface and buried in the soil). Furthermore, this rate is higher at the surface (2.95 μm/a) than those recorded in the soil (1.46 μm/a and 1.99 μm/a at 20 and 50 cm depth, respectively) and is dominated by physical weathering processes driven by diurnal temperature cycles. On the other hand, weathering of rock tablets buried in the soil profile is dominated by chemical weathering processes strongly dependent on the availability of CO2 in the soil, resulting in higher denudation rates deeper in the soil profile. Furthermore, the denudation rate strongly depends on lithology; thus, local lithologies should be used to obtain actual denudation rates.

Laminated tufa sediments formed from overflow karst springs: Controls on their deposition and carbon-oxygen isotope records

2017-01-01T00:00:00Z

[EN]Tufa sediments are freshwater carbonates that precipitate in karst regions after degassing of carbon dioxide from groundwater in contact with the atmosphere. When laminated, these carbonates can provide high-resolution records for the study of climate, hydrological and environmental conditions at the time of their precipitation. The formation of these carbonates directly depends on the hydrological regime, and in karst regions discontinuous discharges are often recorded. This study investigates the record of recent laminated tufa sediments precipitated downstream overflow springs in Trabaque Canyon (central Spain). The hydrological dynamics of the karst system were monitored for over three years and a stable isotope record was obtained from laminated tufa carbonates precipitated from an overflow spring. Additionally, a hydrological model of overflow springs was generated and a tufa δ18O record under constrained parameters was simulated. Temperature is the dominant control of the variation in tufa δ13C and δ18O values within each lamina, although when comparing different laminae, δ13CDIC and δ18O of river water are also major controls. The positive correlation between tufa δ13C values and water temperature is caused by the fractionation occurred by carbon dioxide degassing due to the thermal dependence of carbon dioxide solubility. Additionally, the system recorded a temperature-independent degassing process caused by the large gradient between groundwater and atmospheric carbon dioxide that is limited to the proximity of the spring. This study cautions on the risk of assuming continuous deposition when studying laminated tufa sediments and highlights the potential of their stable isotope records to provide hydrological information of their aquifers during the past.

Basic Properties of Calcocambisol from a Location on North Dalmatian Plain

2021-01-01T00:00:00Z

[EN]Calcocambisol is the most dominant soil type developed on Dinaric karst. It is formed by pedogenic processes acting on carbonate rocks, which include weathering, accumulation of insoluble residue, organic matter, and allogenic material and braunification. Further development of Calcocambisol includes leaching of clay from upper soil horizons and secondary accumulation in lower horizons. Calcocambisols are exclusively developed on carbonate rocks characterised by diverse relief forms resulting in variable soil depth over short distances and consequently different phases of soil development. Thus, the goal of this study was to analyse morphological, physical, and chemical properties of Calcocambisols in different stages of development from a location within the Krka National Park. Results of soil analysis showed similarities in morphological properties, soil field and air capacity, density and SOC content. On the other hand, differences in properties included different carbonate content and pH values of topsoil and difference in particle size distribution. These differences can be attributed to irregular rocky surface which plays important role in allogenic particles distribution and water percolation. Increased leaching of clay particles to deeper horizons results in diversification of Bt (argic) horizon, indicating more advanced stage of soil development towards Luvisol formation.

Parent material as a key determinant of soil properties in southern part of National park Krka, Croatia

2021-01-01T00:00:00Z

[EN]Parent material is an important factor in soil formation, especially in soils formed in Mediterranean region dominated by calcareous sedimentary rocks. Their basic properties (mineralogical composition, coherence, and permeability for water) influence the resistance to weathering and type of weathering products, its amount, particle size distribution, as well as the intensity of hysicochemical transformations within the original rock residue. Thus, the aim of this study was to investigate the impact of parent material on soil properties in southern part of Krka National Park, Croatia. Weathering of carbonate parent material (limestones, dolomites, conglomerates, marls) along with other soil forming factors was the base for soil development in this area. Thus, Calcocambisols and Terra rossa, typical and ilimerized are the most widespread soil types, while Calcomelanosols, Colluvium and Rendzinas are as well represented, but in much lesser extent. Soil depth, presence of coarse fragments and carbonate content in these soils vary considerably depending on parent material, although factors such as relief, vegetation and anthropogenic impact cannot be neglected. In general, shallow soils (< 35 cm) were formed on limestones and conglomerates, while medium deep soils (35-70 cm) were formed on marly substrates. The content of coarse fragments of variable size in soils (fine gravel 2-6 mm to boulders 60-200 cm) is related to different weathering processes of parent material. The presence of carbonate nodules on soil surface and within soil profile also indicates pedogenetic processes related to different types of carbonate parent material.

Morphometrical Features of the Vis Island

2013-01-01T00:00:00Z

[EN]The object of this study are hillslopes of the Vis island. The slopes can be defined as relief surfaces determined by geographical position, slope inclination (related with horizontal surface) and slope aspect. Recent slope shapes can be defined as result of series of natural and anthropogenic factors during relief genesis and evolution. It is possible to correlate slope characteristics with geological structure and other natural geographic features (climate, soils, vegetation etc.) using geomorphometrical analysis. The main aims of this study are: a) analysis of morphometrical relief indicators (hypsometry, slope inclination and slope aspect), b) analysis of relationships between morphometrical indicators, and c) analysis of relatioships between morphometrical parameters, structural and lithological features, in order to gain more detailed understanding of exogeomorphological and morphostructural features of the investigated area. The final intention is to assess extent and intensity of dominant geomorphological processes. Special attention was given to detailed geomorphometrical analysis of morphostructures of Vis island in GIS environment based on DMR. Applied geomorphometrical relief analysis included use of different methods for precise calculation of numerical relief parameters of investigated area, which enabled mutual comparison of specified parameters and comparison with maps of tectonic units and lithology. The aim of this approach is more exact analysis and interpretation of morphometrical relief parameters as indicators of characteristics of endogenous and exogenous processes in the investigated area.

Some Basic Indices of Horizontal Landscape Structure of the Southern Part of Vis Island, Croatia

2013-01-01T00:00:00Z

[EN]This research is based on application of landscape metrics in GIS environment for determination of the basic features of horizontal landscape structure of the southern part of Vis island, Croatia. Landscape elements (or geocomplex types) are determined based on their abiotic (lithological and geomorphological features) and biotic elements (natural vegetation cover). Anthropogenic impact during historical-geographic development (agriculturally cultivated land and urbanized areas) are also considered. By means of GIS tools, the three layers of abiotic and biotic parameters were overlayed (lithology, slope inclinations and types of vegetation cover) and 2556 basic units (geocomplexes) were obtained. Generalization of this basic units by criterion of similarity enabled extraction of 132 types of geocomplexes. This types represent generalised homogenous spatial units which were basis for all further analyses. In the next phase, landscape metrics has been applied in order to determine basic characteristics of horizontal landscape structure: total area of each geocomplex type (including minor elements or basic geocomplexes included in each type), frequency, average areas of individual geocomplexes within types and spatial variability index. The main goals of the research are precise determination of abiotic and biotic features of landscape elements, their spatial structure and interrelationships, classification, typology and determination of existence of specific dominant/stable and vulnerable/labile geocomplex types. The results should serve as methodological framework for evaluation of the current state and future development trends of landscape elements of the researched area. They can be applied in planning and preserving landscape of the southern part of Vis island, and other areas as well.

Vertical landscape structure of the southern part of Vis Island, Croatia

2012-01-01T00:00:00Z

[EN]The paper presents some basic features of vertical landscape structure of the southern part of Vis Island, Croatia. Its aim is the determination of geocomplex types with a certain degree of stability and resistance to external influences, and confirmation or rejection of hypothesis that with the application of appropriate methods, the spatial relation between geocomplex types as well as the identification of specific dominant/stable and vulnerable/labile geocom-plex types can be precisely determined. The results should serve as the basis for estimation of current status and future trends in the development of geocomplex types as well as the environmental changes.