This work focuses on the study of collapse dolines, which are the most expressive collapse structures in carbonate rocks, and their relations with preexisting and syn-collapse fractures. The study ...area has two fracture sets that were formed before folding, early N-S/E-W- and late NE-SW/NW-SE-striking sets, which concentrate most of the dissolution in the region and allow the formation of the dolines. We define subsidence rings as the circular and ellipsoidal concentric zones around collapse structures, which are subjected to subsidence due to major collapses and represent locations where new fractures are formed. In these subsidence rings, the downfaulted topography plunges towards the doline center and reaches more than 10 m in relation to unaffected areas away from dolines. The topographic data indicate that the mean radius of the combined rings is ~twice the radius of the collapse, which corresponds to the closed depression due to failure and downfall of blocks. The subsidence process enlarges, links preexisting fractures, and forms a new set of semicircular concentric opening mode fractures, here named collapse fractures. Increases in the apertures and densities of these fractures occur towards the dolines, which increases fracture porosity around collapse structures. Fractures are reactivated as normal faults close to the main collapse at the doline edge. This increase in fracture intensity could represent an indicator of permo-porous quality improvement in these areas. Further, this fracturing increases structural instability, raising the risk of accidents in areas built on soluble carbonate rocks, since the affected area may be much larger than previously predicted. Subsidence rings around collapse dolines could merge with other rings from neighboring collapse structures and potentially increase porosity and permeability, as well as linking areas in carbonate reservoirs.
•Subsidence rings are highly fractured zones around dolines prone to collapse.•Gravity-induced, semicircular open-mode collapse fractures occur in the rings.•Collapse fractures reactivate and reopen preexisting background fracture sets.•The total subsidence ring width is ~ twice the radius of the related doline.•Subsidence rings coalesce and form highly fractured areas around collapse structures.
The carbonate-dominated, mid-Cretaceous to early Cenozoic stratigraphy of north Kuwait exhibits seismic evidence for karstification at multiple stratigraphic levels. Seismic coherence and attribute ...data sculptured across mapped stratigraphic horizons, isochrons and cross-sections reveal a complex distribution of karstic geomorphology. Seismic facies have been rationalized into seismic facies associations (SFA) - SFA-1: small-scale dolines, sinkholes and polygonal channels, SFA-2: large-scale dissolution pipes and coalesced pipes, SFA-3: karst-modified faults and collapse zones, SFA-4: large fluvial channels and karst-related tributaries and SFA-5: massive undifferentiated karst. Karstification shows a strong link to the underlying structural framework, with intense karstification and partial collapse associated with transtensional/transpressional fault systems, and the common alignment of karst-related features along individual fault segments.
Karstification is particularly focused across the top of the Campanian Hartha Formation, where it is manifested by small-scale dolines, sinkholes, and polygonal channels. Below, the Campanian to Santonian Mutriba Formation displays a complex array of large-scale dissolution pipes and coalesced pipes, which, together with karst-modified faults and collapse zones, penetrate several hundred meters into the underlying stratigraphy. Above the Hartha Formation, the top of the Maastrichtian Tayarat Formation is dissected by fluvial channels which drained the relative upland of the Dhabi Plateau situated in the south of the study area. Cross-sections showing local thickening of early Cenozoic Rus Formation stratigraphy suggest differential subsidence and superstratal sag linked to Paleocene collapse of the underlying karstified Cretaceous fault systems.
Evidence for surface processes such as fluvial incisions suggest emergence and a dominance of epigene karstification in the latest Cretaceous (Hartha and Tayarat Formations). This suggests relative sea-level fall and emergence, probably linked to foreland deformation adjacent to the Zagros margin. A prominent structural control on karst distribution, together with seismically resolvable pipes that transcend entire carbonate formations for 100's of meters, also suggests that surface terrains were overprinted and enhanced in a burial environment. This was probably by hypogenic fluid, driven by large-scale basin circulation related to Late Cretaceous/early Cenozoic foreland deformation.
•There is widespread seismic evidence for formation scale karstification in the Cretaceous stratigraphy of North Kuwait.•Despite important carbonate reservoirs, seismic evidence for karstification is hitherto unreported in the literature.•Seismic karst suggests both epigene and hypogene processes - the latter have recieved lttle attention in Middle East carbonate reservoirs.•The 3D distribution of karst can be related to the broad evolution of the Arabian Plate margin.
Numerous karst dolines have been formed along the Croatian coast and many have been submerged during the Late Glacial and Holocene sea level rise. The coastal area of Cres Island in the Northern ...Adriatic is a typical example of this geomorphological setting, where transitional forms from subaerial to submerged dolines are present. Once dolines are formed they can accumulate soil, water and sediments due to their morphology. Sediments are an especially valuable source of environmental data. This paper presents the results of the study of foraminiferal assemblages and sediment geochemistry, supplemented with grain-size and mineralogical data, from the marine ponds developed in the karst dolines on Cres Island. Obtained data is correlated with the sediment core record from submerged dolines in the present-day embayments along the coastal zone of Cres Island. In total, 3 sediment cores were collected in the marine ponds Marinska, Arcij and Podbrajde, while 2 longer sediment cores have been extracted from the Jaz and Sonte embayments. The Marinska, Arcij and Podbrajde marine ponds have distinct geochemical and mineralogical sediment compositions, with monospecific foraminiferal assemblages and generally differ from each other. The common characteristics are their high N and P concentrations and the algal origin of organic matter. Agglutinated foraminiferal taxa (Haplophragmoides canariensis and Trochammina inflata), typical for intertidal environments, are abundant in the brackish-water Marinska pond, while stress-tolerant species Ammonia tepida has been identified in the Arcij marine pond. Environmental conditions in the Podbrajde marine pond did not facilitate the development of a rich foraminiferal fauna. Results from the present-day marine ponds enabled recognition of similar environments in the sediment cores collected in the Jaz and Sonte embayments that were progressively inundated during the Holocene sea level rise. A palaeo-marine pond existed in the Sonte embayment until 6610 cal BP, when the sea flooded the investigated area. A marine pond in the Jaz embayment was formed at 711 cal BP. Low-diversity foraminiferal assemblages in these palaeo-ponds are similar to those recognized in the present-day Arcij marine pond on Cres Island. However, differences in the geochemical composition of palaeo-marine ponds, in comparison to the present-day ponds, exist. They might be attributed to climate variability oVer time and Variations in the geological setting of each environment. High Mo concentrations and abundant organic matter content are the main sediment characteristics of the recognized palaeo-marine ponds in the Jaz and Sonte embayments.
The Messinian Salinity Crisis (5.97–5.33 Ma) is one of the most dramatic sea level change events in the global geological record. During this event, marine connection between the Atlantic Ocean and ...the Mediterranean Sea was restricted, and episodically blocked. While division of the Messinian Salinity Crisis to three major stages is well established and accepted, the scale of sea level change at each stage is still debated. The magnitudes of the Mediterranean fluctuations throughout the Messinian Salinity Crisis have implications for contemporary connectivity between the eastern and western Mediterranean basins.
During the third stage of the Messinian Salinity Crisis, commonly known as the Lago Mare, Mediterranean Sea level fluctuated repeatedly. Lago Mare drawdowns in the eastern Mediterranean were estimated earlier to vary between <200 m and all the way down to the abyssal basin. Here we assemble morphological, lithological and stratigraphic evidence for Lago Mare levels across the Israeli margin. We differentiate between low-stands of various scales and durations to constrain the magnitude of discrete Lago Mare drawdowns. Since the rates of syn-Messinian isostatic rebounds in response to water column removal are ambiguous, drawdown magnitudes are estimated here as a range and not as an absolute value.
We propose that during the Lago Mare, ravinement along a continuously regressing-transgressing coastline abraded the upper continental margin offshore Israel. The Mediterranean regressed to a depth of 380–550 m below present-day mean sea level, and the eroded strata were evacuated downslope and deposited basinward of this depth as wedge-shape clastic complexes. During relatively short intervals, sea level receded to altitudes ~100 m below the erosional surface. These sea level recessions exposed a pronounced inflection in the slope gradient to sub-aerial processes, generating knickpoints and headward migration of incising gullies. These gullies developed later into channels, conduits for sediment bypass. Fan-deltas were deposited off these channels outlets.
A major sea level fall towards the end of the Messinian Salinity Crisis reached 630–900 m below present-day mean sea level. Streams incised into the exposed tops of the clastic wedges and fan-deltas. Additionally, meteoric water dissolved evaporites within the clastic complexes and formed sinkholes and dolines. During this interval the Mediterranean Sea level fell to below the depth of the Sicily Sill, which separated the eastern and western Mediterranean basins. This finding reinforces previously proposed paradigms, which suggested that the Messinian Salinity Crisis was terminated by spillover events from the Atlantic Ocean to the western Mediterranean basin, and consequently from the western to the eastern basin.
•Successive falling and rising sea levels shaped the morphology and stratigraphy of the Levant margin during the Lago Mare stage.•Ravinement along the shifting coastline abraded the upper margin down to a depth of 365–535 m bmsl.•During the late Lago Mare stage sea level receded to 615–885 m bmsl.•Towards the end of the Messinian salinity Crisis, the eastern and western Mediterranean basins were not connected.
So far reported unstable correlations between environmental settings and doline geometry require a revision of doline delineating methods and morphometric analyses that follows from such input data. ...We examine the reliability of the most accessible data sources for doline delineation, namely basic topographic maps at a scale of 1:5,000 and ortho-rectified aerial photographs (digital orthophotos) of 0.5 m resolution. Their reliability has been quantified in the Dinaric karst (Krk Island, NE Adriatic Sea). The adequacy of most commonly used morphometric parameters (viz. elongation and circularity) and their variations applied in previous studies are mathematically verified and practically tested. The simulation of an individual method behaviour performed on polygons with increasing circularity and elongation demonstrated their ranges of validity. The efficiency of a particular method was verified by the application to the real dataset of dolines. The optimal variation of an individual parameter (circularity = Pcc/Pd; elongation = of the best fitting ellipse) is identified and suggested for use in order to provide uniform results and increase the comparability of future morphometric analyses. Asymmetry (the distance between the centroid of doline ground plan and the centroid of the largest inscribed circle) as an additional parameter for describing doline ground plans has been developed and is proposed for further use.
Al Jabal Al Akhdar anticlinorium, NE Libya, has the most extensive and diversified karstic features
.
Collapse dolines are among the most prominent karst phenomena with many of them developed during ...the Holocene. This research uses field observations and numerical modelling to understand the geometry and formation mechanisms of these dolines. Detailed measurements of 66 collapse dolines including locations, elevations and dimensions (diameters and depths) are documented herein. The dolines have diameters ranging from several meters to tens of meters, while their depths vary from few meters to over a hundred meters. Some giant dolines can be classified as “Tiankengs”. The dolines have average diameter of 55 m and height/depth of 60 m. There is a strong linear correlation between dolines areas and volumes with a determination coefficient (
R
2
) of 0.88. When 65 collapse dolines in China are added to the dataset for comparison, the correlation becomes
R
2
= 0.83. This geometric similarity may suggest an analogous mechanism of their development. This research reveals that these dolines developed from the enlargement of fractures and bedding planes, forming various sizes of cavities in the sub-surface through chemical weathering. The subsequent collapse of the roof of these enlarged voids was most likely influenced by local stress fields around them, leading to extensive extension and shear fractures. Numerical models suggest that the local stress field favoured rupture and fracture propagation, once tensile and shear stresses exceed the tensile and shear strengths of the host rocks, thus causing the breakdown and the formation of collapsed dolines.
This paper reviews the current state of knowledge about environmental changes at the MIS 3/2 transition in the northern Alps and their foreland, covering the time frame from 35 to 25 ka. Lake and ...peat deposits, cave sediments, loess and glacial deposits are presented and the response of their biotic and abiotic proxies to climate change is discussed. During late MIS 3, interstadial conditions, albeit weak, occurred at c. 36–32 ka. At climatically favourable sites, small patches of trees (mainly Pinus and some Betula) existed together with some shrubs. The environmental conditions during late MIS 3 are also reflected by a boreal brown soil horizon, a cambisol called Lohne soil, found in many loess sequences. Subsequently, the environmental conditions became harsher as shown by the proxy data. From c. 30 ka onwards the absence of pedogenesis sensu stricto and the plant assemblages point to an Arctic climate in the northern Alpine foreland. Accentuating, glaciers advanced beyond the northern limit of the Alps around the MIS 3/2 boundary and reached their maximum extent in the foreland at about 25 ka.
Pleistocene detrital deposits in the central Ebro Basin frequently show deformation features due mainly to karstification in the underlying Neogene evaporites. In 123 cases, estimation of parameters ...of shape and minimum volume of materials involved was accomplished. Six of them were analysed in more detail to establish the main processes involved in their genesis and the succession of events. All the deformation features in the selected sites are synsedimentary. To achieve the objectives, intense fieldwork was made applying methods of sedimentology and structural geology. Usually, a complex evolutionary pattern was observed, with evidences of dissolution, sagging, collapse, gravity flow, suffosion, and plastic flow. In a schematic way, three main situations, independent of the age of the analysed deposits, can be distinguished: (a) slow subsidence, (b) collapse, and (c) temporal overlapping of both processes. In the first 2 scenarios, basins with smooth or abrupt borders, respectively, were generated on the land surface. In the third one, slow subsidence was followed by a collapse, located in the area of maximum flexure. These patterns are also observed in present‐day dolines. Comparison of direct and indirect parameters between paleodolines and present‐day dolines indicates a bigger size of the latter, probably caused by the different conditions of observation. This study helps to know the possibilities in the evolution of mantled karst features, to estimate the volume of material affected by karstification and to improve the knowledge of present‐day dolines behaviour. Consequently, study of paleodolines must be considered to achieve a better urban planning in active karstic areas.
Understanding how fractures influence fluid flow in carbonate rocks is essential to understanding karst evolution, oil reservoirs, and aquifer exploitation. The present study investigates karst ...fracture geometry at the surface and subsurface in the Irecê Basin, a Neoproterozoic epicontinental cratonic basin in the São Francisco Craton, Brazil. We used an Unmanned Aerial Vehicle (UAV) to map both fractures in three outcrops and valley geometries, Light Detection And Ranging (LiDAR) to map 3500 m of cave conduits, and Electrical Resistivity Tomography (ERT) to identify karst zones between 90 and 110 m deep. Our results indicate that the Brejões Karst System is comprised of dissolution and collapse features such as caves, dolines, pavements, and karst valley. The quantitative analysis of subseismic fractures (<50 m long) identified 4398 fractures in Outcrop A, 2458 in Outcrop B, 4374 in Outcrop C, and 7172 in 18 cross-sections of the Brejões Cave. These fractures form a corridor with four main sets striking N–S, NNE–SSW, NW–SE, and E–W, where the fracture system is essential to cave connectivity, permeability, and development. The highest frequency of fractures coincides with the main cave axes, where the intersection of the fracture/fault are sites prone to dissolution. The ERT profiles indicated a high density of geophysical anomalies that correspond to enlarged fractures in the epikarstic zone that extend between the surface and approximately 30 m deep. The cave infill impacts the cave characterization and leads to underestimating cave dimensions. This study may contribute to an underestimation of the role played by subseismic scale fractures in karst evolution in gently deformed settings.
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•The karst comprises river valley, cave, dolines and enlarged fractures.•Four sets of subseismic fractures (<50 m long) control the karst system.•Karstification enhanced fluid flow within a fracture corridor.•We used ground-based LiDAR in subseismic-scale reservoir analog.•We integrated digital outcrop of cave with Electrical Resistivity Tomography.
Dolines, or closed karst depressions, are the most characteristic feature of karst landscapes. The two main types of doline are those formed by the removal of material by solution and those formed by ...the geological processes of collapse or suffosion. Solution dolines are most frequently found in carbonate karst in high relief karst massifs. Various algorithms can be used to identify and delineate dolines in high-resolution digital elevation models (DEM) where the lower size limit is determined by the resolution of the DEM, i.e., the size of the cell or the DEM pixel in terrain units. The work presented here addresses the size distribution of dolines, which is a significant component of the geomorphometric analysis of dolines. On the basis of experimental results, various authors have advocated the lognormal or the power distribution as the best fit to experimental data. A power distribution is consistent with a fractal structure implying the fractal nature of the sizes of dolines which, in turn, may reflect a relationship between size and the structural controls of fracture networks and the fractal fragmentation of the terrain. This paper presents case studies of four karst landscapes that are representative of karst massifs in Spain. Two of these are located in the Pyrenees in the north of Spain and two are located in the Betic mountains in the south of Spain. In all four cases, a lognormal distribution provides a bad fit while a power law distribution provides a good fit in three cases and in the fourth case provides a good fit for dolines that have a diameter greater than 50 m.
•The paper presents an analysis of the size-distribution of dolines in four high relief karsts.•In the four cases studied, the lognormal distribution does not fit the experimental data.•In three of the four cases, the power law provides a good fit to the data.•In the remaining case the power law is a good model for dolines larger than 50 m.•The power law implies the fractal character of the sizes of dolines.
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