Tablelands are typical reliefs in many cratons of the world, particularly in the eastern portion of South America. Until recently, tablelands have been interpreted as resulting from initial ...superficial fluvial erosion that segmented wide plateaus and subsequent slope retreat that decreased plateau areas into smaller mesas and buttes. Based on morphological observations and isotopic measurements in sandstone caves in Brazil, we present an alternative scenario in which such sandstone landscapes may result from karst processes. This study relies on cosmogenic nuclide pair concentrations (10Be and 26Al) measured in river-borne, modern fluvial sediments, suggesting that these fluvial sediments may have actually undergone complex exposure-burial histories. Collapse of cave ceilings and associated karst processes in sandstones may thus represent an initial step responsible for the morphogenesis of the regional tablelands landscape. The widespread occurrence of similar karst geoforms in tablelands in several areas in eastern/northern South America suggests that this model may have a general implication.
•The morphogenesis of the tablelands landscape can have relation with karst geoforms.•The tablelands can be formed by surface and subsurface fluvial processes.•River sediments in Eastern Amazonian show a complex burial exposure history.
Quantifying the permeability in karst aquifers often is imprecise and difficult to interpret. Therefore, it is possible to notice the increase and decrease of permeability values related to the known ...triple porosity within the karstic system. This work analyzed small- and well-scale data from a tubular well situated in a Brazilian Neoproterozoic karst aquifer to show the scale effect and relationships between fractures/channels flow zones and regional tectonic structures of the area. At the micro-scale, 3D micro-Ct images of tubular well core samples and thin sections were used to analyze the aquifer matrix and micro-fractures. In well-scale, data from high-resolution acoustic geophysical logging, borehole video, and drilling reports helped to analyze fractures and channels. Multi-scale lineament mapping with geophysical logging aided to correlate the major tectonic structures in the area to the existing flow zones. The result showed an increase of eleven orders of magnitude in values of permeability and transmissivity from micro- to well-scale, indicating the scale effect, explained by the low permeability of the matrix and the influence of fractures and channels in flow zones in the aquifer. The groundwater flow can be linked regionally to the presence of tectonic structures associated with the anticlinal fold present in the study area, diabase dike intrusions, and the Cenozoic transcurrence. The use of high-resolution methods makes possible the distinction between matrix, fractures, and channels in the calculation of hydraulic parameters allowing a better understanding of the influence of each structure in the groundwater flow.
The karstification process causes mineral dissolution and mechanical removal of carbonate rocks, creating multiscale secondary porosity that greatly affects the development of karst reservoirs. The ...carbonate rock weathering is mainly nucleated from fractures and bedding planes and spreads out for large areas, forming a ghost-rock karst system divided by different weathering intensities. Locally, where the hydrodynamic conditions are high total removal of the weathered rock lead to the rise of the cave network and eventually the collapse or subsidence of dolines and other karst landforms. This case study presents the use of 2D and 3D GPR data to map karst levels and features in depth of a karst system in the semiarid region of NE Brazil. Synthetic GPR data and direct observation on doline crack walls support the division of karst units into ghost-rock, alterite, and residual soil zones, marked by low-amplitude reflections, and fresh to slightly weathered bedrock, indicated by vertical high-amplitude GPR zones. High-resolution aerial images and digital elevation model provide the surface geometry and distribution of karst landforms, controlled by an orthogonal weathering/fracture system identified in the GPR profiles and time slices. In addition, the karst system was vertically divided into four zones and the area of occurrence of karst units in each zone was estimated. Pore space was then calculated for each zone, assuming porosities to the filling material. We analyzed the estimated pore space distribution compared with a gas-bearing karst reservoir in China.
Al-Coeffiah karst terrain is located in Benghazi plain which is a part of Al-Jabal Al-Akhdar anticlinorium, northeast Libya. The exposed stratigraphic sequence of the area is largely represented by ...the Middle Miocene limestone rocks of Benghazi Formation. The area is affected by abundant karstic features such as caves and giant dolines with many subsurface voids and canal networks which extends for several kilometers. This research is based on field observations combined with analysis of high-resolution satellite imagery of Al-Coeffiah karst terrain. The main aim is to assess potential geohazards provided by the karst features, including (i) rock failure, (ii) groundwater pollution, and (iii) geochemical processes. The potential geohazards have been found to lies in the large caves at shallow depths such as Al-Jebah, Habibi, Merisi, and Boukarmah doline-caves. In addition, there is a greater geohazard in fractured karst terrains which are created by dolines in soft sediments. Chemical and bacteriological analyses indicate that the groundwater pollution in Al-Coeffiah area and its surrounding regions is considered as one of the most serious problems largely due to the seepage of sewage water through karst phenomena particularly during the last 10 years.
Karst plateaus often have a complex geological and geomorphological history. It is widely accepted that their development requires a long period of karst denudation. This study reconstructs the ...palaeodrainage network of a karst plateau, analyses its properties and establishes its geomorphological significance. The main purpose of this research was to deepen our understanding of a key stage in the evolution of karst plateaus — the transition from a fluvial land surface to one dominated by karst surface processes. The study was conducted on a large part of the Una–Korana plateau, the largest plateau in the Dinaric karst. The majority of the plateau is made of carbonate rocks of Triassic, Jurassic and Cretaceous age that set the conditions for the development of the karst. We have reconstructed the palaeodrainage network based on 1:25,000 topographic maps with 10m contours. The transition of the surface drainage network to the underground karst drainage network is still in progress, so, depending on the degree of karstification, the drainage network was divided into three categories: active, dry and relict. It was found that 90.5% of the pre-existing drainage network has undergone some degree of karstification. The active surface drainage network gradually shifted to a dry network, then to a relict network. The surface drainage network is gradually replaced by a dense network of dolines. Today, the flat and karstified inter-fluvial area is drained underground towards the main watercourses and these drain the entire region over the surface towards the Pannonian basin. This is the largest known karst palaeodrainage network in the Dinaric karst that has been reconstructed in this way.
•The palaeodrainage network on a karst plateau of the Dinarides was reconstructed•Reconstructed drainage network consists of active, dry and relict valleys.•The relict valleys dominate with 78% of the total length.•Drainage network has similar parameters as the network in non-karst areas.•Doline density is the highest in the area of relict valleys.
The morphology of collapse dolines varies according to their maturity and effectiveness of the removal of collapsed material. In addition, the variable balance between various geomorphic processes ...due to local geologic, hydrologic and climatic settings results in a diverse morphology of collapse dolines and dynamics of their morphogenesis. A single generalised proposed sequence of collapse dolines morphogenesis has therefore limited value and more detailed study is needed in terrains which differ in terms of geology, hydrology and/or climate. There is a particularly well exposed karst in Stockyard Gully National Park in the southwestern coastal part of Western Australia, formed in Quaternary aeolianites, consisting of a dense field of collapse dolines up to 100 m in diameter and on average 10 m deep. Extensive field work combined with available data of local rock stratigraphy and a comparison to collapse dolines worldwide revealed that the principal processes of collapse doline formation in Stockyard Gully National Park are similar to processes responsible for collapse doline formation worldwide (i.e., collapses above underground chambers and removal of the collapsed material). However, rock characteristics in the area influence their morphometry due to the mechanical weakness of aeolianite compared to well-cemented limestones, and a surface calcrete layer with stronger mechanical resistance than underlying aeolianite. Consequently, we propose a new 4-stage multiphase breakdown sequence of collapse doline morphogenesis in aeolianites, divided into cave dome, calcrete caprock dome, young collapse doline, and mature collapse doline. Calcrete caprock dome is stabilised by the uppermost well cemented calcrete and represents a distinctive phase just before the final breakdown to form an actual collapse doline.
•Mechanically resistant layer of calcrete influence collapse doline formation.•4-stage sequence of collapse dolines formation in aeolianites is introduced.•Mature collapsed dolines in study area formed between 100 and 3 ka.
The plasma membrane (PM) is subjected to multiple mechanical forces, and it must adapt and respond to them. PM invaginations named caveolae, with a specific protein and lipid composition, play a ...crucial role in this mechanosensing and mechanotransduction process. They respond to PM tension changes by flattening, contributing to the buffering of high-range increases in mechanical tension, while novel structures termed dolines, sharing Caveolin1 as the main component, gradually respond to low and medium forces. Caveolae are associated with different types of cytoskeletal filaments, which regulate membrane tension and also initiate multiple mechanotransduction pathways. Caveolar components sense the mechanical properties of the substrate and orchestrate responses that modify the extracellular matrix (ECM) according to these stimuli. They perform this function through both physical remodeling of ECM, where the actin cytoskeleton is a central player, and via the chemical alteration of the ECM composition by exosome deposition. Here, we review mechanotransduction regulation mediated by caveolae and caveolar components, focusing on how mechanical cues are transmitted through the cellular cytoskeleton and how caveolae respond and remodel the ECM.
Matarsko podolje, in SW Slovenia, is a karstic surface with many dolines, which appear between the flysch-composed Brkini hills in the NE and Mt. Slavnik in the SW. We have analyzed dolines to find ...the morphometric parameters of the depth, area, volume, and circularity index and also calculated the doline density and pitting index. All parameters were also calculated separately for individual lithological units to explain the variations of the calculated values among these groups. Morphometry was performed in GIS environment on a 1 × 1 m digital elevation model with bare earth obtained by lidar. The results show a high density of dolines (94 dolines/km
2
) and also a high pitting index (
R
p
= 8.27) compared to other studies. There are some significant differences between the measured values in individual lithologies, as the depths, areas, and volumes are largest in dolomitic beds (other beds include various types of limestones and carbonate breccia). The median values of depth, area, and volume are 2.98 m, 541 m
2
, and 690 m
3
. The circularity index is also lowest in dolomite beds and Kozina limestones; however, the differences are not so pronounced as for areas and volumes. Dolines’ longer axes are parallel to the directions of major structural elements; however, more detailed mapping should be done to confirm the influence of faults and fracture zones on the doline geometry.
Carbonates are the main components of Iberian Quaternary lake sediments. In this review we summarize the main processes controlling carbonate deposition in extant Iberian lakes located in Mesozoic ...and Tertiary carbonate-dominated regions and formed through karstic activity during the Late Quaternary. The lakes, relatively small (1ha to 118ha) and relatively shallow (Zmax=11 to 40m) provide examples of the large variability of sedimentary facies, depositional environments, and carbonate sources. Hydrology is dominated by groundwater inflow except those directly connected to the fluvial drainage. Nine lakes have been selected for this review and the main facies in palustrine, littoral and profundal environments described and interpreted.
Clastic carbonates occur in all Iberian lakes due to the carbonate composition of the bedrocks, surface formations and soils of the watersheds. Low temperatures and dilute meteoric waters seem responsible for the low carbonate content of sediments in high elevation lakes in the glaciated terrains in the Pyrenees and the Cantabrian Mountains. Clastic carbonates are dominant in small karst lakes with functional inlets where sediment infill is dominated by fining upward sequences deposited during flood events. Re-working of littoral carbonates is common in shallow environments and during low lake level stages. In most lakes, endogenic carbonate production occurs in two settings: i) littoral platforms dominated by Chara and charophyte meadows and ii) epilimnetic zone as biologically-mediated calcite precipitates. Continuous preservation of varves since the Mid-Holocene only occurs in one of the deeper lakes(Montcortès Lake, up to 30m) where calcite laminae textures (massive, fining upward and coarsening upward) reflect seasonal changes in limnological conditions. However, varves have been formed and preserved in most of the lakes during short periods associated with increased water depth and more frequent meromictic conditions.
Most Iberian lakes are in a mature stage and karstic processes are not very active. An outstanding example of a lake with intense karstic activity is Banyoles Lake where increased spring discharge after long rainy periods causes large remobilization and re-suspension of the sediments accumulated in the deepest areas, leading to the deposition of thick homogeneous layers (homogeinites).
The Iberian karst lake sequences underline the large variability of facies, carbonate sources, and depositional environments in small lake systems. They illustrate how lake types evolve through the existence of a lake basin at centennial or even smaller time scales. Hydrology is the paramount control on facies and depositional environment patterns distribution and lake evolution and, consequently, a lake classification is proposed based on hydrology and sediment input. A correct interpretation of carbonate sources and depositional history is a key for using lake sequences as archives of past global changes.
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•Large facies, sources and environments variability in small lake systems•Lake types evolve at centennial or even smaller time scales.•Hydrology is a main control on facies and environment distribution and evolution.•We propose a lake classification based on hydrology and sediment input.
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