Planation Research Articles

Structural inheritance, morphotectonics and Holocene activity of the Cucalón-Pancrudo extensional fault (Iberian Chain, Spain)

A large active extensional fault is characterized, which will contribute to improve seismic hazard assessment in an intraplate region of the Mediterranean domain whose seismic potential until today has been underestimated. The Cucalón-Pancrudo fault (CPF) is a NNW-SSE striking extensional fault that represents the negative (extensional) inversion of a previous, Late Variscan and Paleogene, transpressional fault. It is part of the Río Grío-Pancrudo fault zone, the largest active structure in the intraplate central-eastern Iberian Chain. This study focuses on characterizing the CPF structure, morphotectonics and paleoseismology. The fault offsets a well-known regional planation surface (lower level of the Fundamental Erosion Surface, FES3, 3.5 Ma), providing a basis for calculating the maximum fault throw (c. 280–300 m, including the contribution of a minor synthetic fault and a gentle accommodation monocline), and hence estimating the net slip (c. 305–325 m) and the long-term slip rate (0.09 mm/a). A trench dug in a Holocene fluvial terrace reveals an ensemble of listric, domino-style ruptures synthetic to the main fault. They were activated during at least two paleoseismic events (X, Z), 14.9 ± 1.4 ka and 6.9 ± 0.4 ka in age. An intermediate event (Y), dated to 11.0 ± 1.0 ka, as an uncertainty because the attribution of their ruptures to event Z cannot be ruled out. The total net slip accumulated during these events (1.15–1.25 m) provides an apparent short-term slip rate of 0.07–0.09 mm/a, very similar to the long-term slip rate. Nevertheless, it is very likely that the faults exposed in the surveyed trench do not represent a complete paleoseismic record. Therefore, the actual slip rate during Late Pleistocene-Holocene times could be significantly higher, approaching that reported for most of the recent extensional faults in the central Iberian Chain. The inclusion of CPF in the map of Active Faults of Iberia (QAFI database) will result in improving seismic hazard assessment in Spain.

СТЕПЕНЬ ВЛИЯНИЯ НЕОТЕКТОНИКИНА СЕЙСМИЧНОСТЬ АБИНСКОГО СЕГМЕНТА СЕВЕРО-ЗАПАДНОГО КАВКАЗА

Relief is one of the sources of information about neotectonic activity. Using structural-geomorphological analysis, it is possible to identify weak zones, which often reflect hidden low-amplitude faults and fracture zones under the surface of Quaternary deposits. Using structural-geomorphological analysis, planation surfaces were identified, displacement amplitudes along faults and the magnitude of neotectonic movements were determined for certain periods of time. The results obtained were compared with seismicity and the degree of inheritance was revealed. 3D computer geological modeling of the stress state also helps in identifying zones of increased neotectonic activity, as the most dangerous zones in terms of seismicity. The stress state and directions of the compression axes in the horizontal plane were calculated using the RMS Roxar software. Also, for a more detailed study of the latest geodynamics of the Abinsk segment, the frequencies of earthquakes and the amount of seismic energy released were analyzed, and frequency graphs were plotted. When comparing the growth deformations of neotectonic uplift structures and the values of the latest stress state with seismicity, their significant correlation was revealed.

Extensive palaeo-surfaces beneath the Evans–Rutford region of the West Antarctic Ice Sheet control modern and past ice flow

Abstract. The subglacial landscape of Antarctica records and influences the behaviour of its overlying ice sheet. However, in many places, the evolution of the landscape and its control on ice sheet behaviour have not been investigated in detail. Using recently released radio-echo sounding data, we investigate the subglacial landscape of the Evans–Rutford region of West Antarctica. Following quantitative analysis of the landscape morphology under ice-loaded and ice-unloaded conditions, we identify 10 flat surfaces distributed across the region. Across these 10 surfaces, we identify two distinct populations based on clustering of elevations, which potentially represent remnants of regionally coherent pre-glacial surfaces underlying the West Antarctic Ice Sheet (WAIS). The surfaces are bounded by deeply incised glacial troughs, some of which have potential tectonic controls. We assess two hypotheses for the evolution of the regional landscape: (1) passive-margin evolution associated with the break-up of the Gondwana supercontinent or (2) an extensive planation surface that may have been uplifted in association with either the West Antarctic Rift System or cessation of subduction at the base of the Antarctic Peninsula. We suggest that passive-margin evolution is the most likely of these two mechanisms, with the erosion of glacial troughs adjacent to, and incising, the flat surfaces likely having coincided with the growth of the WAIS. These flat surfaces also demonstrate similarities to other identified surfaces, indicating that a similar formational process may have been acting more widely around the Weddell Sea embayment. The subsequent fluctuations of ice flow, basal thermal regime, and erosion patterns of the WAIS are therefore controlled by the regional tectonic structures.

Drainage reorganization and divide migration driven by basin subsidence: An example from the Micang Shan, outskirts of eastern Tibet and its implications for Cenozoic evolution of the Yangtze River

AbstractThe Cenozoic India‐Asia collision has elevated the Tibetan Plateau and produced large strike‐slip faults in the interior and margins of the plateau, which profoundly influenced drainage reorganization and divide migration in Asia. Recent studies have revealed that the drainage divides between the major rivers in and around the Tibetan Plateau have been migrating for tens of millions of years, due to tectonic and/or climatic disturbance or river capture events. Drainage‐divide stability analysis can provide new, independent insights into the Cenozoic evolution of the river systems. In this study, we focus on the Hanzhong Basin and the adjacent Micang Shan (Shan means Mountain(s)) at the tail of the Qingchuan strike‐slip fault in the outskirts of eastern Tibet. We investigated the stability of the Micang Shan drainage divide, which separates the Han and Jialing rivers (two major tributaries of the Yangtze River), using two methods—χ‐plot and Gilbert metrics. The results show that most segments of the Micang Shan drainage divide are either moving south or stable. We further calculated the predicted stable divide location and identified the abandoned river channels and residual planation surfaces. Based on these analyses, we suggest that (1) the migration of the Micang Shan drainage divide is driven by the tectonic subsidence of the Hanzhong Basin; and (2) the upper reaches of the Han River flowed southward to the Sichuan Basin before basin subsidence. This study supports the hypothesis that the Palaeo‐Middle Yangtze River and its tributaries primarily flowed southward. Moreover, the flow direction of the Middle Yangtze River has been, and still is, transitioning from southward to eastward. The change in river network flow direction is driven by regional block tilting towards the east, surface deformation from strike‐slip faulting, regional extension east of the Tibetan Plateau and/or increased influence from the summer monsoon.

Numerical determination of pavement mean texture depths at different degrees of traffic polishing-induced wear

All existing digital image-based numerical mean texture depth (MTD) calculation methods are unable to achieve a consistent level of acceptable accuracy for MTD values calculated at different degrees of pavement polishing. To solve this problem, a novel procedure is proposed to determine MTD as a function of degree of polishing represented by a texture statistic ‘directional wear index’ DWI. First, a relationship is established between DWI and the elevation H eq that defines the equivalent top surface of MTD. H eq is derived from 3-D digital image based on the concept of planation surface. Through studying laboratory specimens and field pavements polished to different degrees, a well-defined relationship between DWI and H eq was established. Knowing H eq from the H eq–DWI relationship, MTD is calculated as the mean depth of the voids between H eq and the test surface. The digital image-based procedure is able to concurrently determine MTD and the surface's degree of polishing.

Plio-Pleistocene drainage reorganization in the middle Yellow River of China, revealed by provenance and paleocurrent analysis of fluvial sediments

Continental-scale drainage reorganization is generally understood to result from landform evolution forced by the coupling between tectonic activity and climate change, attracting worldwide attention. Planation surfaces and river terraces constitute the most direct geomorphological archives for integrating the history of river systems and for reconstructing processes of drainage reorganization based on provenance analysis of the fluvial sediments. The Middle Yellow River has incised into the Ordos Block, which was previously levelled by a planation surface, creating the Jinshaan Gorge and linking the Hetao Basin to the north and the Fenwei Basin to the south. Multiple lines of evidence, from terraces correlation, sedimentary characteristics, and fluvial provenance, suggest that the Middle Yellow River catchment was occupied by fluvio-lacustrine systems before drainage integration, accumulating a sedimentary sequence derived from surrounding Red Clay and bedrocks during the period between 8.3 and 3.7 Ma. The planation surface was uplifted subsequently, forcing reorganization of the fluvio-lacustrine systems. Their integration resulted in the formation of the Jinshaan Gorge prior to 1.2 Ma. Numerous terraces were created during incision by the Middle Yellow River from north to south along the gorge. Our data, obtained from zircon UPb dating and lithological composition of fluvial gravels, further points to a remarkable discrepancy in provenance between the fluvio-lacustrine systems overlying the planation surface and the terraces sequence formed by the integrated Middle Yellow River, confirming the drainage reorganization process constrained by the geomorphic records.

From landform inventories to landscape evolution? - Karst development in the Central Styrian Karst (Austria)

In the Central Styrian Karst (CSK, Styria, Austria) 1158 karst landforms were used to obtain a better understanding of the landscape evolution in this region. An automatically delineated doline inventory was combined with an existing cave inventory to investigate surface and subsurface karst landforms in relation to their elevation above the local base level at the transition zone between the Eastern Alps and the Pannonian Basin. The landform entities analysed consist of 51 % dolines and 49 % caves and are related to various stages of landform evolution and thus ages.The CSK was ice-free during glacial times and therefore allow for a much longer preservation of surface landforms compared to landforms that were reshaped during glaciations. Nevertheless, weathering and downwasting do re-shape and even may lead to the disappearance of surface landforms (i.e., dolines); however, subsurface landforms (i.e., caves), if accessible, might preserve information about older geomorphological stages.An old, a mature, and a young stage of landform evolution can be distinguished in the CSK and be related to planation surfaces preserved in the area, presumably older than five Ma. The chosen approach is likely applicable for other areas in the world too by implying karstification over million years' time scale.Besides those regional implications, there are local (neo-) tectonic inferences derived from the analyses that might explain some discrepancies in correlations of levels and planation surfaces, but requiring further more detailed investigations. The automatic doline delineation in the forested karst of the CSK made an area not yet mentioned in the literature become apparent.With an increasing availability of high-resolution digital elevation models, remote-sensed inventories of dolines (surface landforms) renew the question of dolines as diagnostic landforms for karstification. However, in the CSK it is revealed that an absence of dolines due to e.g., surface erosion does not indicate the absence of karstification. Therefore, landscape evolution should consider both surface (i.e., doline) and subsurface (i.e., cave) landforms.

Karst of Sterlitamak (BASHKIR) Shikhans and Their Surroundings in Southern Pre-Ural Area

Abstract—Shikhans, or lone mountains, is the local name for island mountains in the flat foothills of the Southern Urals. The shikhans are denudation remnants, sometimes with preserved residuals of Miocene-Pliocene planation surface on their tops, which allows estimating the total time of development of karst processes at least 5 million years. Despite more than 200 years of research on the shikhans, karst and its manifestations have received little attention to date. A map of karst in the shikhan territory was drawn up according to the standard methodology of karstological survey. Widespread and quite rare forms of carbonate karst of the shikhans and sulphate karst of their close vicinities were characterised. It was established that along with widespread and known in temperate latitudes karstic features, very rare corrosion wells are developed in the gypsum of the Kungurian Stage in the study area, forming karst fields with the highest density of karst forms known in the East European Plain. Gypsum caves at various stages of formation, as well as semi-blind karst-erosion gullies not typical for the lowland sulphate karst of the region were recorded. For the carbonate karst of the Shikhans in the limestones of the Sakmarian Stage, the highest location of karst caves in the foothills of the Southern Urals and the oldest (earky Middle Pleistocene) age of their foundation were established. The main peculiarity of distribution of both surface and underground karst-holes is a clearly expressed dependence of forms and frequency of their occurrence on the course of formation of relief elements in the Neogene-Quaternary time. The presence in a small area of two types of karst by composition of karst rocks with very rare karst forms predetermines the high scientific, practical and educational significance of the shikhans and their surroundings.

Topography and drainage system evolution in the ‘‘Volubilis basin’’ (South Rifain Ridges, Northern Morocco)

The Volubilis piggy-back basin, located at the front of the Rif belt, northern Morocco, is a subsided area, as a continuation of the deformational orogenic ridges, related to the present-day African and Eurasian convergence. For the first time, by morphotectonic studies, we analyzed the topographic evolution and drainage systems response. Our results proved the influence of active tectonics in the drainage network and topography of the Volubilis basin. The young phase is indicated by a less dissected planation surface comparing to the ridges, as well as by the ε-shaped hypsometric curve of the khoumane river. This latter drains the continuation of the basin and the eastern arc, where the tectonic activity is mostly concentrated. Based on swath analysis, the general trend of tilting was characterized and was attributed to the recent tectonic movement combined with folds growth of the ridges.

Quantifying the late Quaternary incision rate in the upper Jinsha River with dated fluvial terraces and transient tributary profiles

The region occupied by three parallel rivers on the southeastern edge of the Tibetan Plateau is a zone with dramatically fluctuating topography and a complex tectonic setting. Deeply incised river valleys have become an ideal place for scholars to study the coupling relationships among river erosion, climate change and regional uplift. The fluvial terraces preserved in the upper Jinsha River provide the basis for exploring the history of river erosion. Through field investigation and dating results of terraces, the short-term incision rates of the upper Jinsha River are determined to be 0.18–5.47 mm/yr. In addition, the palaeo-profiles, which were reconstructed using two analytical methods, show that there are two depth intervals for the incision in the Jinsha River, namely, 1200 ± 220 m and 340 ± 250 m. They correspond to two early planation surfaces of the river, and the long-term average incision rates of the upper Jinsha River are estimated to be 0.23–0.34 mm/yr. By analysing the relationship between fluvial terrace formation and climate change, combined with the formation history of the early planation surface, it is recognized that the main force driving incision in the upper reaches of the Jinsha River comes from regional uplift. Climate change causes a continuous alteration between river incision and sediment accumulation, and this transition is also perturbed by mass flow events.

A tropical soil (Lixisol) identified in the northernmost part of the Mediterranean (Istria, Croatia)

Terra rossa soils on the Istrian peninsula are generally considered polygenetic relict soils. They overlie and mark the youngest subaerial unconformity in the northwestern part of the Adriatic Carbonate Platform and are susceptible to erosional and redepositional processes. Terra rossa soils represent a valuable archive of information that can be used to understand present and past soil formation processes in the context of climate variability and landscape dynamics, especially in low-lying parts of the karst landscape where thicker deposits are typically found. We studied a 3 m thick terra rossa profile in a karst depression on the northernmost part of the southwestern Istrian planation surface and analysed the micromorphology, physical/chemical properties, geochemistry, bulk and clay mineralogy, and composition of heavy and light mineral fractions. The profile shows several signs of colluviation and polygenesis with clay distribution along the profile, clearly indicating lithic discontinuities. Kaolinisation, along with iron oxide formation, is the dominant process in the studied profile. Ferralitisation and lessivage processes were diagnosed throughout the profile, with intense clay translocation occurring despite the extremely stable soil microaggregates. In accordance with the WRB system, the profile is classified as Rhodic Lixisol (Clayic, Aric, Cutanic). This implies that some terra rossa soils, previously classified as e.g. Cambisols or Luvisols, might actually be Lixisols or other (sub-)tropical soils (e.g. Nitisols), in which relict properties are preserved in the present climate. The finding of a Lixisol in the study area indicates the old age of the surface of the karst depression and provides the first data on the burial history of the southwestern Istrian planation surface. We suggest the older Quaternary interglacials, the mid-Piacenzian Warm Period (Pliocene) and the Miocene Climatic Optimum as favourable periods for the formation of the studied soil.

RETRACTED: A tropical soil (Ferralsol) identified in the northernmost part of the Mediterranean (Istria, Croatia)

Terra rossa soils on the Istrian peninsula are generally considered polygenetic relict soils. They overlie and mark the youngest subaerial unconformity in the northwestern part of the Adriatic Carbonate Platform and are susceptible to erosional and redepositional processes. Terra rossa soils represent a valuable archive of information that can be used to understand present and past soil formation processes in the context of climate variability and landscape dynamics, especially in low-lying parts of the karst landscape where thicker deposits are typically found. We studied a 3 m thick terra rossa profile in a karst depression on the northernmost part of the southwestern Istrian planation surface and analysed the micromorphology, physical/chemical properties, geochemistry, bulk and clay mineralogy, and composition of heavy and light mineral fractions. The profile shows several signs of colluviation and polygenesis with clay distribution along the profile, clearly indicating lithic discontinuities. Kaolinization, along with iron oxide formation, is the dominant process in the studied profile. Ferralitization and lessivage processes were diagnosed throughout the profile, with intense clay translocation occurring despite the extremely stable soil microaggregates. In accordance with the WRB system, the profile is classified as Lixic Rhodic Ferralsol (Clayic, Aric). This implies that some terra rossa soils, previously classified as e.g. Cambisols or Luvisols, might actually be Ferralsols or other tropical soils (e.g. Lixisols), in which relict properties are preserved in the present climate. The finding of a Ferralsol in the study area indicates the old age of the surface of the karst depression and provides the first data on the burial history of the southwestern Istrian planation surface. We suggest the older Quaternary interglacials, the mid-Piacenzian Warm Period (Pliocene) and the Miocene Climatic Optimum as favourable periods for the formation of the studied soil.

Biomarker evidence for late Miocene temperature and moisture from the Alagu planation surface, NE Tibetan Plateau

The late Miocene climatic change is critical to understanding the interactions among late Cenozoic global cooling, tectonic activity and the Asian monsoon system evolution. However, paleoclimate reconstruction is restricted to qualitative descriptions, and quantitative work is rare, which limits further study. Here, we reconstruct the late Miocene temperature and hydroclimate changes based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) and magnetic susceptibility evidence in the Alagu planation surface in the northeastern Tibetan Plateau (NE TP), which is at the junction of the zones of westerly and monsoonal influences. The following preliminary conclusions have been drawn: the late Miocene temperatures exhibit a near-linear decreasing trend, mainly in response to global sustained cooling rather than tectonic activity; while the humidity shows an increasing trend opposite to that of temperature. We regard the possible reason for the opposite evolution of the late Miocene temperature and moisture of the Alagu planation surface as the weakening East Asian summer monsoon (EASM) caused by global cooling, leading to westward monsoonal moisture transport and thereby enhancing precipitation.

Old orogen – young topography: Evidence for relief rejuvenation in the Bohemian Massif

Abstract The Bohemian Massif is the relic of a major Paleozoic mountain range that is known to have exhumed and its surface levelled in the Permian, but its Neogene landscape evolution is largely unconstrained. The landscape is characterized by rolling hills and extended planation surfaces above an elevation of about 500 m. However, at lower elevations deeply incised gorges confined by steep hillslopes are abundant and contrast impressively with the low relief landscapes above. Rivers with a bimodal morphology (i.e. steep at lower elevations and gentle at higher elevations) drain either to the north into the Vltava (Moldau) River or to the south into the Danube River. Hence, a continental drainage divide runs through the Bohemian Massif. Here, we quantify spatial characteristics of the Bohemian Massif landforms by computing landscape metrics like steepness index or geophysical relief derived from digital elevation models. From this we infer temporal change of the landscape in the past and predict them for the future evolution of the region. We show that the landscape is characterized by out-of-equilibrium river profiles with knickpoints abundantly at elevations between 450 m and 550 m separating steep channel segments at lower elevations from less steep channels at higher elevations. Hypsometric maxima at or close above knickpoint elevations, along with high and low values in geophysical relief as indicator for the degree of fluvial landscape dissection downstream and upstream of major knickpoints, support the idea of landscape bimodality. Furthermore, we find a distinct drainage divide asymmetry, which causes the reorganization of the drainage network of the region. Across-divide gradients in channel steepness predict the northward migration of the Danube-Vltava drainage divide including growth and shrinkage of tributary catchments, thus controlling changes in the Central European drainage pattern. All aspects suggest that the region experienced relief rejuvenation during the last few million years. We suggest that this relief rejuvenation is related to the inversion of the Molasse basin with a long wavelength rock uplift pattern and low uplift rates. Vertical motion of crustal blocks at discrete faults may locally affect the uplift pattern. However, the contrasting bedrock properties between the sedimentary cover (Molasse sediments) and the crystalline basement (Bohemian Massif) cause substantial differences in erosion rate and are thus the superior control on the topographic variations of the entire region.

New evidence from heavy minerals and detrital zircons in Quaternary fluvial sediments for the evolution of the upper Yangtze River, South China

AbstractIn the Three Gorges and adjacent areas, there are three planation surfaces and five terraces along the Yangtze River that record the evolution history of the river system. Here, we used diagnostic heavy minerals, U-Pb geochronology, and trace elements of detrital zircons from one planation surface, two terraces, and a modern point bar to reconstruct the evolution history of the upper Yangtze River, specifically the Chuan River in the Sichuan Basin. The sediments in the lowest planation surface had different felsic source rocks derived from east of the Three Gorges, which indicated that before the disintegration of the lowest planation surface (0.75 Ma), there were two paleorivers: the westward-flowing paleo-Chuan River and eastward-flowing paleo-Yangtze River separated by the Huangling Dome. At 0.75–0.73 Ma, the dominant detrital zircons from the Sichuan Basin in the sediments of terrace T5 (the highest terrace) confirmed that the paleo-Yangtze River cut through the Three Gorges and captured the paleo-Chuan River, and the Daliang Mountains became the new drainage divide. Finally, the appearance of materials from the upper Jinsha River in terrace T2 indicated that the paleo-Yangtze River progressively captured the paleo-Jinsha River, and the modern upper Yangtze River formed before 0.05 Ma. These river capture events of the upper Yangtze River confirmed the Quaternary uplift of the SE Tibetan Plateau.

Distribution feature and development characteristics of geohazards in Wudu district, Gansu province, Northwest China

BackgroundThe study area located at southeast Gansu, China, has long been afflicted by the intense occurrence of geohazards. The study area is characterized by interleaving terrain of precipitous mountains and valley basins, abundant precipitation, and complicated geological setting. In this work, 1144 geohazards including 759 landslides, 281 debris flows, and 104 collapse were presented and their types were categorized in detail. Then, the distribution of geohazards were analyzed and the controlling role of hazard-inducing environment and triggering factors on geohazards were preliminary presented.ResultsIn this work, correlation analysis between geohazards and geological, topographical, and geomorphological context was conducted. Concave slopes with height smaller than 200 m and slope gradient between 21° and 40° is the favorable topographic feature for landslide occurrence and the predominant slope aspects of landslides are southwest, south, west, and southeast. Collapse generally occurs in slope with gradient larger than 45°. Valleys with valley gradient less than 400‰, valley height between 100 and 500 m, and watershed area of 1–10 km2 register the largest percentage and the most favorable slope gradient for the supply of solid source at the debris flow source area is 25°–45°. The preferable strata for geohazards (landslide, collapse and debris flow) are Middle and upper Pleistocene loess, Holocene diluvium, Silurian phyllite and slate, Neogene mudstone, and Devonian schist and gneiss, and most geohazards occurred in tectonic erosional middle altitude mountain, tectonic erosional high-middle altitude mountain, tectonic erosional-diluvial planation surface. In addition, the controlling role of triggering factors, i.e., precipitation, earthquake, and human engineering activity was discussed and described in this work.ConclusionGeohazards in the study area are synthetically controlled by the hazard-inducing environment and triggering factors. The complicated sliding-prone strata and steep topography resulted from strong tectonic movement provides a favorable basis for the development and formation of geohazards. Heavy rainfall, strong seismic motion, and human engineering activity are the main triggering factors for geohazard occurrence.

Improved numerical method for determination of pavement mean texture depth from 3-dimensional digital image

The conventional manual sand-patch method of mean texture depth (MTD) measurement is unsuitable for network level pavement condition monitoring. Relying on 2-D mean linear profile depth (MPD) to estimate 3-D MTD is also unsuitable because MTD-MPD regression relationship varies from one pavement mix type to another. This problem of network level MTD measurements and monitoring can be overcome if MTD could be numerically determined from 3-D digital laser images. All the numerical MTD determination methods proposed by researchers in recent years made a common invalid assumption that the MTD top surface was defined by the high texture peaks of the test surface. This study presents evidence to show that the top surface defining MTD actually lies below the highest peaks of the test surface. Next, applying the concept of planation surface, a novel numerical procedure is proposed to identify a reference surface for MTD calculation by means of a second-derivative plot of peak-height percentiles. The validity of the proposed method was verified experimentally with measured MTD values of both laboratory fabricated specimens and in-service pavements. For four different surface course materials, the errors in the predicted MTD values range from 0.20 to 7.31 %. The proposed method produced improved accuracy in MTD predictions compared with the existing methods which were based on incorrectly assumed MTD top surfaces.

Linking uplift, erosion, and sedimentation using landscape evolution models: Madagascar since the Late Cretaceous

SummaryWe present a study to estimate the large‐scale landscape history of a continental margin, by establishing a source‐to‐sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best‐fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.

Geomorphological evolution of the calcareous coastal cliffs in North Iberia (Asturias and Cantabria regions)

This paper presents an analysis of the main morphologies observed in the coastal cliffs of northern Spain (Asturias and Cantabria regions). The objective of this contribution is to establish a hypothesis on the origin and evolution of this rocky coast, as well as to present a detailed inventory, to characterise quantitatively and qualitatively singular morphologies and to highlight the geological heritage of this protected coast. The evolution process starts with the formation of an ancient coastal planation surface characterised by a flat morphology caused by regional mainly uplift and to relative sea level falls. Afterwards, wave erosion processes would have started eroding the cliff foot and simultaneously, karst activity produced some exokarst morphologies (sinkholes, karren, etc.) through stratification and fracturing network, while the underground drainage systems produced some caves and chasms. In the following step, corresponding to the last glaciation from the paleoclimatic point of view, sea level fall together with a deepening of the fluvial network caused the preservation of the existing caves and chasms and the generation of new ones at a lower level. On the other hand, dissolution processes on limestones created sinkholes in those areas characterised by alternating layers of limestones and marls, generating collapses. When the sea level reached the maximum height during the Holocene a new erosion cycle of the coastal cliffs began. As a consequence, new landforms and processes were produced, like bays, caves fillings, and intrusion of new sediments in small confined estuaries. In these areas, other types of morphologies associated with the last sea level rise can be observed, such as closed beaches, uncommon closed estuaries developed inside a sinkhole, blowholes produced by mixed wave action and widening of prevailing vertical pipes inside the limestones (including the second largest in the world), total or partial sedimentary filling of small confined estuaries, as well as a tombolo deposit. It is important to point out, that some sites described are included in the Spanish Inventory of Sites of Geological Interest (IELIG). Due to the evolution model here proposed, a portion of the coastal sector described are included in the Global Geosites Project.

Development and structure of karstification of the Dong Van Karst Plateau UNESCO Global Geopark, North Vietnam based on cave survey data

This paper presents a quantitative study of the relationship between the cave system and the tectonic and karst evolution of the Dong Van Karst Plateau based on analysis and statistics of geometric parameters and orientation of cave passages. The region is located in northern Vietnam and belongs to the extended part of the South China karst belt (Yunnan karst plateau), which is composed mainly of carbonate rocks. Cave classification based on cave conduits geometric parameters shows that caves developed mainly in the vadose zone (27 vadose branchwork caves, 10 mixed caves developed under the control of fault systems, and 12 water-table caves). The degree of correlation between cave levels and planation surfaces suggests that the development of horizontal cave passages is related to two levels of planation surfaces, including one at 1250–1450 masl (equivalent to cave level at 1350–1450 masl), and at 1000–1250 masl (corresponding to cave level at 1200–1250 masl). Additionally, cave passage orientation shows that the cave system formed and developed under the influence of tectonic activities in the Cenozoic. The dominant orientation trend is roughly in the East–West direction and occurred in the early phase (Eocene–Miocene). Next is a trend roughly North–South that occurred in the late phase (Pliocene–Quaternary). The last orientation trend follows the NW–SE direction due to the reactivation of paleo-fault systems in the same direction. Although there are limitations due to accessibility and the level of cave exploration, this research suggests that analysis and statistics of the geometric parameters and orientation of cave passages based on cave survey data can be one of the effective approaches used to identify the development and structure of karstification in the karst region.