Late Cenozoic uplift of the Amanos Mountains and incision of the Middle Ceyhan river gorge, southern Turkey; Ar–Ar dating of the Düziçi basalt

Using the Ar–Ar technique, we have obtained the first numerical dates for the Pleistocene volcanism along the valley of the River Ceyhan in the Düziçi area of southern Turkey, in the western foothills of the Amanos Mountains. Our six dates indicate a single abrupt episode of volcanism at  270 ka. We have identified a staircase of 7 fluvial terraces, at altitudes of up to  230 m above the present level of the Ceyhan. Using the disposition of the basalt as an age constraint, we assign these terraces to cold-climate stages between marine oxygen isotope stages 16 and 2, indicating rates of fluvial incision, equated to surface uplift, that increase upstream through the western foothills of this mountain range at between 0.25 and 0.4 mm a^− 1. Extrapolation of these uplift rates into the axis of the range suggests that the entire  2300 m of present-day relief has developed since the Mid-Pliocene, a view that we confirm using numerical modelling. Since  3.7 Ma the Amanos Mountains have formed a transpressive stepover along the northern part of the Dead Sea Fault Zone, where crustal shortening is required by the geometry. Using a physics-based technique, we have modelled the overall isostatic response to the combination of processes occurring, including crustal thickening caused by the shortening, erosion caused by orographic precipitation, and the resulting outward flow of mobile lower-crustal material, in order to predict the resulting history of surface uplift. This modelling suggests that the effective viscosity of the lower crust in this region is in the range  1–2 × 10¹⁹ Pa s, consistent with a Moho temperature of  590 ± 10 °C, the latter value being in agreement with heat flow data. This modelling shows that the nature of the active crustal deformation is now understood, to first order at least, in this key locality within the boundary zone between the African and Arabian plates, the structure and geomorphology of which have been fundamentally misunderstood in the past.     

Tectonic geomorphology of the Triglav Lakes Valley (easternmost Southern Alps, NW Slovenia)

We present a study on the impact of litho-structural setting and neotectonic activity on meso- and macro-scale relief production in Alpine areas. The topography of the high alpine Triglav Lakes Valley, NW Slovenia, was studied by means of detailed mapping and stratigraphic study of the valley. The Triglav Lakes Valley is characterised by a generally asymmetric transverse (E–W) profile: a very steep eastern slope, a relatively flat valley and a relatively gentle western slope. On the transverse profile the valley floor is essentially flat, gently dipping towards the east. In the longitudinal cross-section, however, the valley floor is marked by sharply-defined fault blocks extending in a W–E to NW–SE direction. Additionally, the highest block (elevations  2100 m) is in the northern part of the valley, the lowest (elevations  1600 m) in the southern part of the valley. Our research shows that the Triglav Lakes Valley directly represents the topographic expression of Paleogene–Neogene thrusting and faulting, having recorded the following geomorphologic evolutionary stages: 1. an Oligocene to early Miocene W-vergent thrusting phase, with steep W-facing slopes of the eastern part of the valley directly representing the thrusting front; and 2. a Neogene-to-present strike–slip faulting in NNE–SSW direction with two bifurcating right-lateral strike–slip systems. We show that the Triglav Lakes Valley almost perfectly mimics the wedge-shaped damage zone located between these faults.     

Preliminary slip rate estimates for the Düzce segment of the North Anatolian Fault Zone from offset geomorphic markers

New estimates on the Quaternary slip rate of the active transform margin of North Anatolia are provided. We investigated the area struck by a Mw 7.1 earthquake on the 12th of November 1999 that ruptured the Düzce Fault segment of the North Anatolian Fault. In order to analyze the spectacular tectonically driven cumulative landforms and the drainage pattern settings, we carried out a 1:25,000-scale geological and geomorphological mapping along the fault trace. We reconstruct and describe, as offset geomorphic markers, right-hand stream deflections and fluvial terraces inset into alluvial fan deposits. Radiocarbon dating indicates that  100 m stream deflections were built up by the last  7000 yrs of fault activity. Conversely, two documented and correlated Late Pleistocene fluvial terraces are horizontally offset by  300 and  900 m, respectively. These were dated by means of Optically Stimulated Luminescence (OSL) to  21 ka BP and 60 ka BP. Assuming a constant rate of deformation for the Düzce Fault, ages and related offsets translate to consistent slip rates that yield an average slip rate of 15.0 ± 3.2 mm/yr for the last 60 ka. Thus, the Düzce Fault importantly contributes to the North Anatolian margin deformation, suggesting a present-day partitioning of displacement rates with the Mudurnu Fault to the south and confirming its important role in the seismic hazard of the area.     

Late Pleistocene tectonic-geomorphological development within a passive margin — The Cariatá trough, northeastern Brazil

Studies on the geomorphological evolution of the South American passive margin have been based on the pediplanation model, which predicts that its morphology is a response to regional uniform uplift and concomitant development of erosion surfaces. We combined remote sensing, geological mapping, lithostratigraphic and facies analyses, and luminescence dating in the Cariatá trough, northeastern Brazil, in order to determine how brittle tectonics and climate influenced colluviation and the shaping of local landforms in the Quaternary. Our work indicates that Cariatá is an asymmetrical trough  40 km long,  25 km wide, 250–550 m deep, and delimited by ENE–WSW-trending faults to the north and south. We recognized an ENE–WSW-oriented compression related to a strike-slip faulting regime, which corresponds to the present-day stress field in the region. This faulting event led to the deposition of colluvial fans, shed from adjacent uplifted crustal blocks, in a tectonically controlled depression. The colluvial succession is  45 m thick and presents two facies assemblages that filled the southern and, in particular, the northern borders of the trough: non-cohesive debrisflow and mudflow deposits. Optically stimulated luminescence dates of the sedimentary infill yielded ages at 224–128 ka and 45–28 ka, dominated by debrisflow and mudflow deposits, respectively. These ages may be over-estimated due to poor bleaching of colluvium, but they and our field data suggest that the margins of the trough were tectonically uplifted and eroded twice in the Late Pleistocene. The spasmodic colluvial accretion reflects the occurrence of high-magnitude, low-recurrence episodes probably associated with climate shifts in a semi-arid hillslope system. It follows that the present-day low-lying piedmont in which the Cariatá trough occurs is a juxtaposition of surfaces of various ages. This trough may have counterparts across the region. These conclusions do not corroborate the application of the cyclical pediplanation hypothesis in the area.     

Geomorphological evidence for the Late Holocene evolution and the Holocene lake level maximum of the Aral Sea

During the Holocene the Aral Sea underwent various transgressive and regressive phases of different magnitudes. However, previous work has not yet fully clarified the evolution and chronology of the individual phases. Research presented here throws light on the evolution of the Aral Sea during the past  2000 years. It includes field surveys, tachymetric and DGPS-derived altitude measurements, analysis of sediments from two areas of the northern and southern Aral Basin (Tastubek Bay and Karaumbet Bay), and their correlation with GIS-based lake area models. Geomorphological and sedimentological evidence from the study areas shows a transgression of the Aral Sea around 200 AD, ending at a lake level maximum of 54 to 55 m. After a medieval regression, the lake reached this level again between the late 16th and early 19th century AD. The digital elevation model SRTM-3 was used to estimate a lake size of 72,400 km² for the lake level maximum.Elevated palaeoshorelines, specifically at 72–73 m, are completely absent in the study areas. Local remains of escarpments at elevations of 66 m and 73 m are due to resistant Miocene caprock and are therefore not interpretable as shoreline features.     

Mid–late Holocene hydrological changes in the Mahi River, arid western India

This paper attempts to quantify contemporary and palaeo-discharges and changes in the hydrologic regime through the mid–late Holocene in the alluvial reach of the arid Mahi River basin in western India. The occurrence of terraces and pointbars high above active river levels and change in the width/depth ratio can be regarded as geomorphic responses to changes in discharge. Discharge estimates are made based on the channel dimensions and established empirical relations for the three types of channels: mid–late Holocene, historic (the channel that deposited extensive pointbars above the present-day average flow level) and the present ones. The bankfull discharge of the mid–late Holocene channel was  55 000 m³ s^− 1 and that of the historic channel was  9500 m³ s^− 1, some  25 times and  5 times greater than that of the present river (2000 m³ s^− 1), respectively. Since the mid–late Holocene, the channel form has changed from wide, large-amplitude meanders to smaller meanders, and decreases in the width/depth ratio, unit stream power and the bed shear stresses have occurred. It can be inferred that there has been a trend of decreasing precipitation since the mid–late Holocene.     

Using fluvial terraces to determine Holocene coastal erosion and Late Pleistocene uplift rates: An example from northwestern Hawke Bay, New Zealand

In order to make robust predictions of future coastal processes and hazards, historical rates of coastal processes such as coastal erosion need to be put into a long-term (Holocene) context. In this study a methodology is proposed that uses fluvial terraces to construct longitudinal profiles which can be projected offshore to infer paleo-coastline positions. From these positions, an average Holocene coastal erosion rate can be calculated. This study also shows how constraints can be placed on sea level changes and Late Pleistocene uplift rates using fluvial terraces, and by assuming the latter has been constant since  55–37 ka, these constraints feedback into the coastal erosion rate calculations. For the northwestern Hawke Bay (North Island, New Zealand) coastline, Late Pleistocene uplift rates of 0.6 ± 0.2, 0.6 ± 0.2, and − 0.1 ± 0.1 (i.e., stable or subsiding) mm/yr have been determined for the Waikari, Mohaka, and Waihua River mouths, respectively. These rates are consistent with previous interpretations of subsidence to the northeast and uplift being the result of regional, subduction-related processes. A Holocene coastal erosion rate of 0.5 ± 0.1 m/yr was determined for the Waikari River mouth, which is at the higher end of the calculated historical ( 1880–1980) rates (0.02–0.5 m/yr). If this difference is significant, then two possible reasons for this difference are: (i) the historical rate is affected by events such as the 1931 Napier earthquake, and (ii) the Holocene rate is the average of a steadily declining rate over the last 7.3 ka.     

Flux and fate of Yangtze River sediment delivered to the East China Sea

Numerous cores and dating show the Yangtze River has accumulated about 1.16 × 10¹² t sediment in its delta plain and proximal subaqueous delta during Holocene. High-resolution seismic profiling and coring in the southern East China Sea during 2003 and 2004 cruises has revealed an elongated ( 800 km) distal subaqueous mud wedge extending from the Yangtze River mouth southward off the Zhejiang and Fujian coasts into the Taiwan Strait. Overlying what appears to be a transgressive sand layer, this distal clinoform thins offshore, from  40 m thickness between the 20 and 30 m water depth to < 1–2 m between 60 and 90 m water depth, corresponding to an across shelf distance of less than 100 km. Total volume of this distal mud wedge is about 4.5 × 10¹¹ m³, equivalent to  5.4 × 10¹¹ t of sediment. Most of the sediment in this mud wedge comes from the Yangtze River, with some input presumably coming from local smaller rivers. Thus, the total Yangtze-derived sediments accumulated in its deltaic system and East China Sea inner shelf have amounted to about 1.7 × 10¹² t. Preliminary analyses suggest this longshore and across-shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid-Holocene highstand, and after re-intensification of the Chinese longshore current system. Sedimentation accumulation apparently increased around 2000 yrs BP, reflecting the evolution of the Yangtze estuary and increased land erosion due to human activities, such as farming and deforestation. The southward-flowing China Coastal Current, the northward-flowing Taiwan Warm Current, and the Kuroshio Current appear to have played critical roles in transporting and trapping most of Yangtze-derived materials in the inner shelf, and hence preventing the sediment escape into the deep ocean.     

Tectonic geomorphology and hydrocarbon induced topography of the Mid-Channel Anticline, Santa Barbara Basin, California

The geomorphology of the western sector of the Mid-Channel Anticline (MCA), Santa Barbara, southern California suggests the actively growing fold is laterally propagating to the west. The presence of fold scarps and cross faults that segment the structure suggests that buried faults that are producing the folding are present at shallow depths. The summit area of the anticline at the Last Glacial Maximum (22 to 19 ka) was probably a small late Pleistocene island. Evidence for presence of the island includes what appears to be terrestrial erosion and is supported by assumption of sea level change and rates of uplift and subsidence.Pockmarks and domes ranging in diameter from  10 to 100 m, and several meters deep are present along the crest and flanks of the MCA. These features appear to be the result of hydrocarbon emission. Their formation has significantly modified the surface features, producing simple to complex erosional and/or constructional topography. A large pockmark near the anticline crest dated by two calibrated AMS radiocarbon dates of 25.3 and 36.9 ka continues to emit hydrocarbon gases. We term the topography produced by hydrocarbon emission as Hydrocarbon Induced Topography (HIT).     

Rates of fluvial bedrock incision within an actively uplifting orogen: Central Karakoram Mountains, northern Pakistan

Terrestrial cosmogenic nuclide (TCN) ¹⁰Be surface exposure ages for strath terraces along the Braldu River in the Central Karakoram Mountains range from 0.8 to 11 ka. This indicates that strath terrace formation began to occur rapidly upon deglaciation of the Braldu valley at  11 ka. Fluvial incision rates for the Braldu River based on the TCN ages for strath terraces range from 2 to 29 mm/a. The fluvial incision rates for the central gorged section of the Braldu River are an order of magnitude greater than those for the upper and lower reaches. This difference is reflected in the modern stream gradient and valley morphology. The higher incision rates in the gorged central reach of the Braldu River likely reflect differential uplift above the Main Karakoram Thrust that has resulted in the presence of a knickpoint and more rapid fluvial incision. The postglacial fluvial incision rate (2–3 mm/a) for the upper and lower reaches are of the same order of magnitude as the exhumation rates estimated from previously published thermochronological data for the Baltoro granite in the upper catchment region and for the adjacent Himalayan regions.     

Spatial variability of soil hydrophobicity after wildfires in Montana and Colorado

Increases in runoff and erosion after wildfires are often attributed to the development of hydrophobic soils. The potential for increased overland flow depends on the spatial contiguity of the hydrophobicity as well as its overall strength, but there is limited information on the spatial variability of soil hydrophobicity. We conducted spatially intensive hydrophobicity measurements in 225 m² and 1 m² plots in forested areas of Montana and Colorado burned at moderate to high severity, and in unburned control plots. Both the burned and unburned 225 m² plots contained 10–23 hydrophobic soil patches in which hydrophobicity was strongest at the surface and declined rapidly with depth. The hydrophobic patches were closer together and up to 3 times larger in the burned plots. Consequently, 19% to 76% of the burned plots were hydrophobic compared to just 11% of the unburned plots. In five of the six burned plots, the patches were not laterally connected, suggesting that in most cases Hortonian overland flow generated from hydrophobic patches will infiltrate near its point of origin. The 1 m² plots were smaller than most of the hydrophobic patches, so they did not capture the spatial characteristics of soil hydrophobicity. Characterization of the spatial variability of soil hydrophobicity should be based on measurements conducted at  1 m intervals across areas of > 100 m². Due to the patchiness of soil hydrophobicity at the 10⁰ to 10¹ meter scale, overland flow measurements in small ( 1 m²) plots may overestimate the magnitude and variability of runoff from burned catchments.     

A frost “buzzsaw” mechanism for erosion of the eastern Southern Alps, New Zealand

In the Southern Alps, New Zealand, large gradients in precipitation (< 1 to 12 m year^− 1) and rock uplift (< 1 to 10 mm year^− 1) produce distinct post-glacial geomorphic domains in which landslide-driven sediment production dominates in the wet, rapid-uplift western region, and rockfall controls erosion in the drier, low-uplift eastern region. Because the western region accounts for < 25% of the active orogen, the dynamics of erosion in the extensive eastern region are of equal importance in estimating the relative balance of uplift and erosion across the Southern Alps. Here, we assess the efficacy of frost cracking as the primary rockfall mechanism in the eastern Southern Alps using air photo and topographic analysis of scree slopes, cosmogenic radionuclide dating of headwalls, paleo-climate data, and a numerical model of headwall temperature. Currently, active scree slopes occur at a relatively uniform mean elevation ( 1450 m) and their distribution is independent of hillslope aspect and rock type, consistent with the notion that frost cracking (which is maximized between − 3 and − 8 °C) may control rockfall erosion. Headwall erosion rates of 0.3 to 0.9 mm year^− 1, measured using in-situ ¹⁰Be and ²⁶Al in the Cragieburn Range, confirm that rockfall erosion is active in the late Holocene at rates that roughly balance rock uplift. Models of the predicted depth of frost activity are consistent with the scale of fractures and scree blocks in our field sites. Also, vegetated, paleo-scree slopes are ubiquitous at elevations lower than active scree slopes, consistent with the notion that lower temperatures during the last glacial advance induced pervasive rockfall erosion due to frost cracking. Our modeling suggests temporally-averaged peak frost cracking intensity occurs at 2300 m a.s.l., the approximate elevation of the highest peaks in the central Southern Alps, suggesting that the height of these peaks may be limited by a “frost buzzsaw.”     

Sediment source changes over the last 250 years in a dry-tropical catchment, central Queensland, Australia

Rivers draining to the Great Barrier Reef are receiving increased attention with the realisation that European land use changes over the last  150 years may have increased river sediment yields, and that these may have adversely affected the reef environment. Mitigation of the effects associated with such changes is only possible if information on the spatial provenance and dominant types of erosion is known. To date, very few field-based studies have attempted to provide this information. This study uses fallout radionuclide (¹³⁷Cs and ²¹⁰Pb_ex) and geochemical tracing of river bed and floodplain sediments to examine sources over the last  250 years for Theresa Creek, a subcatchment of the Fitzroy River basin, central Queensland, Australia. A Monte Carlo style mixing model is used to predict the relative contribution of both the spatial (geological) sources and erosion types. The results indicate that sheetwash and rill erosion from cultivated basaltic land and channel erosion from non-basaltic parts of the catchment are currently contributing most sediment to the river system. Evidence indicates that the dominant form of channel erosion is gully headcut and sidewall erosion. Sheetwash and rill erosion from uncultivated land (i.e., grazed pasture/woodland) is a comparatively minor contributor of sediment to the river network. Analysis of the spatial provenance of floodplain core sediments, in conjunction with optical dating and ¹³⁷Cs depth profile data, suggests that a phase of channel erosion was initiated in the late nineteenth century. With the development of land underlain by basalt in the mid-twentieth century the dominant source of erosion shifted to cultivated land, although improvements in land management practices have probably resulted in a decrease in sediment yield from cultivated areas in the later half of the twentieth century. On a basin-wide scale, because of the limited spatial extent of cultivation, channel sources are likely to be the largest contributor of sediment to the Fitzroy River. Accordingly, catchment management measures focused on reducing sediment delivery to the Great Barrier Reef should focus primarily on decreasing erosion from channel sources.     

Geomorphic inferences from regolith thickness, chemical denudation and CRN erosion rates near the glacial limit, Boulder Creek catchment and vicinity, Colorado

Granitic regolith, developed in the Boulder Creek catchment and adjacent areas, records a history of deep weathering, some of which may predate Quaternary time. Field and well-log measurements of weathering, chemical denudation and rates of erosion derived from ¹⁰Be cosmogenic radionuclide (CRN) data help to quantify rates of landscape change in the post-orogenic Rocky Mountains. The density of oxidized, fractured bedrock ranges from 2.7 to about 2.2 g cm^− 3, saprolite and grus have densities between 2.0 and 1.8 g cm^− 3, and 30 soil samples averaged 1.6 ± 0.2 g cm^− 3. Highly weathered regolith in 540 wells averages 3.3 m thick, mean depth to bedrock in 1661 wells is 7 m, and the weathered thickness exceeds 10 m in relatively large local areas east of the late Pleistocene glacial limit. Thickness of regolith shows no simple relationship to rock type or structure, local slope, or distance from channels. Catchments in the vicinity of the Boulder Creek have an average CRN erosion rate of 2.2 ± 0.7 cm kyr^− 1 for the past 10,000 to 40,000 yr. Annual losses of cations and SiO₂ vary from about 2 to 5 g m^− 2 over a runoff range of 10 to nearly 160 cm.Using measured rates in simple box models shows that if a substantial fraction of void space is created by volume expansion in the weathering rock materials, 7 m of weathered rock materials could form in as little as 230 kyr. If density loss results mainly from chemical denudation and some volume expansion, however, the same weathering profile would take > 1340 kyr to form. Rates of erosion measured by CRN could be balanced by the rate of soil formation from saprolite if the annual solute loss from soil is 2.0 g m^− 2 and 70% of the density decrease from saprolite to grus and soil results from strain. Saprolite, however, forms from oxidized bedrock at a far slower rate and rates of saprolite formation cannot balance soil and grus losses to erosion. The zone of thick weathered regolith is likely an eroding relict landscape. The undulating surface marked by relatively low relief and tors is not literally a topographic surface of Eocene, Oligocene or Miocene age unless it was covered with deposits that were removed in Pliocene or Quaternary time.     

Late Holocene upper bounds of flood magnitudes and twentieth century large floods in the ungauged, hyperarid alluvial Nahal Arava, Israel

The impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided Nahal Arava, southern Israel, was documented as part of developing tools to (a) identify recent large floods, (b) determine these flood's respective magnitudes in alluvial ungauged streams, and (c) determine long-term upper bounds to flood stages and magnitudes. Along most of its course Nahal Paran, a major tributary that impacts the morphology, floods and sediments of Nahal Arava at the study reach, is a coarse-gravel, braided ephemeral stream. Downstream of the Arava–Paran confluence, aeolian and fluvial sand delivered from eastern Arava valley alters the channel morphology. The sand has accreted up to 2.5 m above the distinct current channels, facilitating the recording of large floods. This sand enhances the establishment of denser riparian vegetation (mainly Tamarix nilotica and Haloxylon persicum) that interacts with floods and affects stream morphology. A temporal association was found between specific floods recorded upstream and tree-ring ages of re-growth of flood-damaged tamarix trees (‘Sigafoos trees’) in the past 30 years. This association can be utilized for developing a twentieth century flood chronology in hyperarid ungauged basins in the region. The minimum magnitude of the largest flood that covered the entire channel width, estimated from flood deposits, is approximately 1700–1800 m³s^− 1. This is a larger magnitude than the largest gauged flood of 1150 m³s^− 1 that occurred in 1970 about 30 km upstream in Nahal Paran. Our estimation agrees with flood magnitude estimated from the regional envelope curve of the largest floods. Based on Holocene alluvial stratigraphy and OSL dating in the study reach we also conclude that flood stages did not reach the late Holocene ( 2.2 ka) surface and therefore we estimate a non-exceedance upper bound of  2000 m³s^− 1 flood magnitudes for Nahal Arava during that interval. This study indicates that in unfavorable areas the combination of hydrology, fluvial morphology and botanic evidence can increase our understanding of ungauged basins and give information crucial for hydrology planning.     

Combining cosmogenic nuclides and major elements from moraine soil profiles to improve weathering rate estimates

Previous studies of chemical weathering rates for soil developed on glacial moraines generally assumed little or no physical erosion of the soil surface. In this study, we investigate the influence of physical erosion on soil profile weathering rate calculations. The calculation of chemical weathering rates is based on the assumption that soil profiles represent the integrated amount of weathering since the time of moraine deposition. The weathering rate of a surface subjected to denudation is the sum of the weathering loss from the existing soil profile added to the weathering loss in the material removed by denudation, divided by the deposition age. In this study, the amount of weathered material removed since moraine deposition is calculated using the denudation rate estimated from cosmogenic nuclide data and the deposition age of the moraine. Weathering rates accounting for denudation since moraine deposition are compared to weathering rates based on the assumption of no physical erosion and on the assumption of steady-state denudation for the Type Pinedale moraine ( 21 ka) and the Bull Lake-age moraine ( 140 ka) in the Fremont Lake Area (Wind River Mountains, Wyoming, USA). The total weathering rates accounting for denudation are 8.15 ± 1.05 g_(oxide) m^− 2 y^− 1 for the Type Pinedale moraine and 4.78 ± 0.89 g_(oxide) m^− 2 y^− 1 for the Bull Lake-age moraine, which are  2 to 4 times higher, respectively, than weathering rates based on the assumption of no physical erosion. The weathering rates based on denudation since moraine deposition are comparable or smaller than weathering rates assuming steady-state denudation. We find the assumption of steady-state denudation is not valid in depositional landscapes with young deposition ages or slow denudation rates. The decrease in weathering rates over time between the Type Pinedale and Bull Lake-age soils that is observed in the case of no physical erosion is decreased when the influence of denudation on the total weathering rates is taken into account. Fresh unweathered material with high reactive mineral surface area is continuously provided to the surface layer by denudation diminishing the effect of decreasing weathering rate over time.     

Gigantic low-gradient landslides in the northern periphery of the Crimean Mountains (Ukraine)

Large-scale, low-gradient ancient landslides estimated at 5.4–18.9 km² in area and  0.2–1.2 km³ in volume have been studied in the northern hilly periphery of the Crimean Mountains (Ukraine). They originated on slopes along wide water gaps of rivers (Belbek, Kacha, Alma and Biyuk–Karasu) crossing the cuestas of the northern foothills. The slopes generally consist of slightly northward tilting Miocene (mainly Sarmatian) limestones overlying weak, clay-rich Lower Neogene–Palaeogene substratum with a significant content of smectite. Although the region is characterised by the least active contemporary morphodynamics within the Crimean Mountains, the landslides which were studied are of the same size or even larger than various types of landslides occupying active geomorphic domains of the highest mountain range in the southernmost part of the peninsula. The landslides are generally a spreading type, but the sliding mechanics were probably very complex, involving toppling, rotational slides, gravitational folding and translational block slides. All the landslides which were studied are located in the vicinity of regional faults and three of them have headscarps aligned along faults. A common feature is also a location close (within several km) to the Mesozoic suture zone which is the most important tectonic feature in the northern periphery of the Crimean Orogene. This suture was formerly classified as aseismic; however, evidence of strong, low-frequency palaeoearthquakes was collected during the last decade within both the Mesozoic suture and the low-lying northern part of the Crimean Peninsula. Radiocarbon dating of deposits associated with the landslides has revealed at least two phases of increased landslide-activity during the Late Glacial chronozone and Holocene epoch. The main landslide phase presumably took place at some time between the Late Glacial and Atlantic chronozones. Minor reactivation of landslide toes occurred during the Subatlantic chronozone and some of them have been active up to recent times. The first major landslide phase was possibly triggered by an earthquake, whereas late Holocene activity can be attributed both to seismic and hydroclimatic factors.     

Ultra-high rates of loess sedimentation at Zhengzhou since Stage 7: Implication for the Yellow River erosion of the Sanmen Gorge

The Mangshan loess plateau is located 25 km to the west of Zhengzhou on the south bank of the Yellow River. Here the river flows out through the Sanmen Gorge releasing most of its suspended load following a dramatic decrease in gradient. The stratigraphy of the Mangshan loess deposits, consisting of a number of loess and palaeosol sequences, was established following magnetostratigraphic studies and measurements of magnetic susceptibility and grain size distribution. The Bruhnes/Matuyama boundary was found at the depth of about 130 m, indicating that this sequence at Mangshan resembles what is observed elsewhere in the Loess Plateau.The upper part of the Mangshan loess displays extremely high sedimentation rates ( 50 m³ per 1000 years), lower susceptibility values and coarser grain-size distribution, unlike the lower part of the profile and other sections in the Loess Plateau. This striking change indicates that the upper Mangshan loess had a different sediment source, different from the deserts that act as a common source for most of the loess deposits in central China. This sediment source is believed to be the proximal Yellow River floodplain, and the ancient alluvial fan lying at the eastern end of the Sanmen Gorge. The age estimation of the formation of the alluvial fan, based on Mangshan loess, suggests that the Yellow River may have eroded the Sanmen Gorge at approximately MIS 7.     

Using basin thermal history to evaluate the role of Miocene–Pliocene flat‐slab subduction in the southern Central Andes (27° S–30° S)

Studies in both modern and ancient Cordilleran‐type orogenic systems suggest that processes associated with flat‐slab subduction control the geological and thermal history of the upper plate; however, these effects prove difficult to deconvolve from processes associated with normal subduction in an active orogenic system. We present new geochronological and thermochronological data from four depositional areas in the western Sierras Pampeanas above the Central Andean flat‐slab subduction zone between 27° S and 30° S evaluating the spatial and temporal thermal conditions of the Miocene–Pliocene foreland basin. Our results show that a relatively high late Miocene–early Pliocene geothermal gradient of 25–35 °C km⁻¹ was typical of this region. The absence of along‐strike geothermal heterogeneities, as would be expected in the case of migrating flat‐slab subduction, suggests that either the response of the upper plate to refrigeration may be delayed by several millions of years or that subduction occurred normally throughout this region through the late Miocene. Exhumation of the foreland basin occurred nearly synchronously along strike from 27 to 30° S between ca. 7 Ma and 4 Ma. We propose that coincident flat‐slab subduction facilitated this wide‐spread exhumation event. Flexural modelling coupled with geohistory analysis show that dynamic subsidence and/or uplift associated with flat‐slab subduction is not required to explain the unique deep and narrow geometry of the foreland basin in the region implying that dynamic processes were a minor component in the creation of accommodation space during Miocene–Pliocene deposition.