Rock coast inheritance: an example from Galicia,northwestern Spain

A shore platform on the western coast of Galicia in northwestern Spain has been inherited from interglacial stages when sea level was similar to today. The wide, gently sloping intertidal platform is backed in places by supratidal rock ledges, and in other places by a steeper and narrower supratidal ramp. The gradient of the intertidal platform is consistent with the relationship between platform gradient and tidal range, but the slope of the ramp is much too high. The abandoned and degraded sea cliff is grass-covered along most of this coast, and the ledges and the ramp, which extend up to several metres above the highest tides, are covered by lichen and, in places, by salt-tolerant plants. Radiocarbon-dated sediments in the cliff, which range up to 36 000 years in age, lie on top of an ancient beach deposit. The former beach, remnants of which are found in situ on the ramp and rock ledges, as well as two caves that are filled with the dated sediments, are probably last interglacial in age. The morphological and sedimentary evidence suggests that the supratidal ramp and ledges were also formed during the last interglacial stage, whereas the wider intertidal platform is probably the product of several older interglacials, when sea level was generally similar to today. A general model is proposed for the inheritance of shore platforms in macro- and microtidal environments. Copyright © 1999 John Wiley & Sons, Ltd.     

Clast abrasion of a rock shore platform on the Atlantic coast of Ireland

The abrasion of coastal rock platforms by individual or clusters of clasts during transport has not been quantitatively assessed. We present a study which identifies the types of abrasion and quantifies erosion due to the transport of clasts during three storms in February and March 2016. We explore relationships between platform roughness, determined by the fractal dimension (D) of the topographic profiles, geomorphic controls and the type and frequency of abrasion feature observed. Clast transport experiments were undertaken in conjunction with the measurement of wave energy to assess transport dynamics under summer and winter (non‐storm) conditions. Platform abrasion occurred extensively during the storms. We identify two types of clast abrasion trails: simple and complex. In addition, we find two forms of erosion occur on these trails: Scratch marks and Percussion marks. An estimated 13.6 m² of the platform surface was eroded by clast abrasion on simple abrasion trails during the three storms. We attribute approximately two thirds of this to scratch‐type abrasion. The total volume of material removed by abrasion was 67 808 cm³. Despite the larger surface area affected by scratch marks, we find that the volume of material removed through percussion impact was almost seven times greater. We also find that the type and frequency of abrasion features is strongly influenced by the effect of platform morphometry on transport mode, with impact‐type abrasion dominating areas of higher platform roughness. Results of the clast transport experiments indicate that abrasion occurs under non‐storm wave energy conditions with observable geomorphological effects. We suggest that abrasion by clasts is an important component of platform erosion on high energy Atlantic coastlines, particularly over longer timescales, and that the morphogenetic link between the cliff and the platform is important in this context as the sediment supplied by the cliff is used to abrade the platform. © 2018 John Wiley & Sons, Ltd.     

甘肃北山地区晚第四纪构造变形特征及演化趋势

通过对甘肃北山地区ETM影像的细致分析和初步野外考察,对北山地区晚第四纪以来断裂活动时代和运动性质进行了研究。结合附近地区天山构造带、青藏高原北部边缘断裂的演化过程和区域构造应力场状态,对北山地区晚第四纪以来变形机制和演化趋势进行了研究。认为北山地区现今构造格局是在印度板块与欧亚板块相碰撞形成的北东向挤压构造应力场的作用下,重新激活东西向的晚古生代、中生代断裂,并产生北东向新生断裂而形成。晚第四纪以来,北山地区构造变形以南北向缩短为主,伴随有东西向伸展。随着印度板块的向北运移,北山地区的构造变形将进一步增强,即南北向缩短和东西向的扩展将进一步增强。     

Late Holocene tsunami traces on the western and southern coastlines of the Peloponnesus (Greece)

Greece, in particular the western and southern parts close to the subduction zone of the Hellenic Trench, experiences strong earthquakes and subsequent tsunamis. Nevertheless, field evidence of tsunamis from the late Holocene is extremely rare. Our research along the coastlines of the western and southern Peloponnesus resulted in new findings of tsunami impacts in the form of clusters and ridges of large boulders and thick tsunamigenic sand layers encountered in vibracores. Many boulders contained attached marine organisms, which prove that they were transported from the foreshore environment against gravity by extreme wave events. The attached organisms, which have been dated by ¹⁴C-AMS, suggest that historical tsunami events of great energy occurred around 1300 cal AD. A wood fragment found at the base of tsunami deposits in a vibracore from Cape Punta was dated to ~ 250 cal AD.     

Evolution of the ductile shear zone of the Paishanlou gold deposits,western Liaoning,China

The combination of field surveys with analysis of microstructure of tectonite and Electron Backscatter Diffraction (EBSD) on quartz fabric indicated that three periods of ductile shear events developed in the Paishanlou gold deposits and the E-W and NE-striking ductile shear zones were formed during each event. The E-W-striking ductile shear zone, accompanied by compressional and dextral shear slip, was shear-cut by the NE-striking shear zones, accompanied by compressional-sinistral shear slip and sinistral-normal shear slip, successively. An E-W-striking ductile shear zone developed at a deeper tectonic level and at middle- to high-temperatures, accompanied by abundant microstructures, including microlayering between a polycrystal quartz belt and mica, and quartz deformation was depended on cylinder (10-10) 〈a〉 or 〈c〉 glide. The development of an E-W-striking shear zone can be seen as a tectonic pattern in the region of the Paishanlou gold deposits of the collision between the Mongolian tectonic belt and the North Archean Craton from Suolun to the Linxi suture zone during the Indosinian. The NE-striking ductile shear zone developed approximately 160 Ma during the early Yianshanian at middle to shallow tectonic levels and at middle- to low-temperatures, accompanied by typical microstructures, including polycrystal quartz aggregation and quartz subgrain rotation recrystallization, etc., and quartz deformation was depended on prismatic (1011) 〈a〉 glide. The last ductile shear event around the NE-striking shear zone developed at low temperatures and shallow tectonic levels, yielding to a pre-existing NE-striking shear zone, accompanied by abundant microstructures, including low-temperature quartz grain boundary migration and bulging recrystallization. The last ductile shear movement may be related to lithosphere thinning and the destruction of the North China Craton from approximately 130-120 Ma, and this shear event resulted directly in the mineralization in the Paishanlou region.     

Development of the SAR TT-OSL procedure for dating Middle Pleistocene dune and shallow marine deposits along the southern Cape coast of South Africa

Optically stimulated luminescence (OSL) dating is now commonly used to estimate the depositional age of Quaternary landforms along the southern Cape coast of South Africa. Due to the early onset of dose saturation in the quartz-rich sediments from this region, determining the age of deposits much older than the last three glacio-eustatic sea-level high stands has been a challenge. In this study, we explored the feasibility of using the thermally-transferred OSL (TT-OSL) dating method to obtain ages for aeolian and shallow marine deposits at three different localities that hold promise to further illuminate the long and complex Late Quaternary sea-level history of this region. The bleachability and behaviour of both the recuperated OSL (ReOSL) and the basic-transferred OSL (BT-OSL) signals were investigated, and used as independent chronometers to infer (a) the degree of bleaching of the sediments and (b) the stability of the ReOSL signal for dating of older samples. We examined the sensitivity of both signals to varying preheat temperatures and further developed the single-aliquot regenerative-dose procedure for TT-OSL dating of our samples. To verify our procedures, and to understand some of the underlying mechanisms responsible for the problems we observed, modern analogues and known-age Marine Isotope Sub-stage (MIS) 5e samples from the same localities were also measured. The Middle Pleistocene deposits investigated in this study produced statistically consistent ReOSL and BT-OSL ages compatible with sea-level high stands during Marine Isotope Stage 11. This result is of considerable significance, as it may yield new insights into maximum sea-level heights during this period, which is widely considered an appropriate analogue for future environmental conditions.     

Multi-method pIRIR dating of sedimentary sequences at the southern edge of the Gurbantunggut Desert,NW China and its palaeoenvironmental implications

The Gurbantunggut Desert is the second-largest desert in China, located in the westerly-dominated region of north-western China. Previous understanding of palaeoclimate of this desert was mostly based on lake and loess records from the Junggar Basin and Tian Shan Mountains, whilst direct dating of sedimentary records from the desert was very limited. This study applies high-resolution post-infrared infrared stimulated luminescence (pIRIR) dating to three sedimentary profiles at the southern edge of the Gurbantunggut Desert, which contain aeolian sand and water-lain sediments, recording palaeoenvironmental changes at the desert margin since the Last Glacial Maximum (LGM). Different pIRIR dating procedures were applied for samples with different ages. For Holocene-aged samples, a single-aliquot regenerative-dose (SAR) pIRIR procedure based on a three-stepped pIRIR measurement at 110 °C, 140 °C and 170 °C was used, and a standard growth curve (SGC) procedure yields an equivalent dose (D_e) similar to that of the full-SAR procedure; thus, is applicable for accelerating D_e measurement. For samples much older than the Holocene, a multi-aliquot regenerative-dose (MAR) pIRIR procedure based on a three-stepped pIRIR measurement at 150 °C, 200 °C and 250 °C was found to be the optimal dating procedure, because a SAR procedure would yield underestimated ages due to uncorrected initial sensitivity change. pIRIR dating results of the investigated profiles reveal a substantial sand accumulation during the LGM, an intensification of aeolian deposition at ∼12 ka and a wetter depositional environment at ∼10–8 ka. A rapid fluvial deposition is dated at ∼20–19 ka, corresponding to the deglaciation period. The sedimentary records from the desert margin show some correlation with lake and loess records in the same region and suggest a complex response of the desert environment to different climatic factors.     

OSL and radiocarbon dating of a core from the Bohai Sea in China and implication for Late Quaternary transgression pattern

The Bohai Sea is a semi-enclosed continental shelf sea in northern China. Three transgression layers have been identified from the Late Quaternary strata in the western Bohai Sea and the coastal regions, which provide critical information on Late Quaternary sea-level fluctuations and landscape development. The three transgression layers were previously assigned to Marine Isotope Stage (MIS) 1 (transgression 1, T1), MIS 3 (T2) and MIS 5 (T3), respectively, mainly based on ¹⁴C dating. However, this chronological framework aroused an enigma that the regional sea level in MIS 3 was even higher than that of MIS 5, conflicting with the context of global sea-level pattern. In order to clarify this issue, here quartz optically stimulated luminescence (OSL) dating (four samples) was used to constrain the T2 chronology of borehole TJC-1 from the western Bohai Sea. Radiocarbon samples (eight) of peaty sediments were also measured for reference and comparison. All the four OSL samples showed saturation ages of >80 ka, suggesting that the T2 layer should have formed at least in MIS 5, instead of in MIS 3. Radiocarbon ages in T2 should have been severely underestimated, with a saturation age range of 22–30 cal ka BP, similar to all the previous published radiocarbon ages. The renewed OSL chronological framework for Late Quaternary transgressions in the western Bohai Sea is in better compliance with the history of global sea-level change.     

The chronology and long term dynamics of a low energy river system: the Kelvin Valley,central Scotland

The long term (Holocene) channel and floodplain dynamics of a low gradient, low energy, fine grained aggradational fluvial system within a formerly glaciated landscape in central Scotland, the Kelvin Valley, are described from a series of sediment stratigraphic transects and 12 ¹⁴C assays in a headwater reach between Kirkintilloch and Kilsyth. The ¹⁴C assays and dated archaeological sites on the floodplain together suggest that the River Kelvin ceased to aggrade more than 2000 years ago, probably much more, so the 4–6 m of channel and floodplain deposits are almost entirely of early to mid‐Holocene age. The Kelvin Valley is characterized, despite its low flow characteristics, by a highly variable floodplain architecture, in which some transects suggest long term channel stability and strong partitioning of floodplain sedimentation and others indicate high channel mobility. This variation makes the application of general models of fluvial evolution difficult. Copyright © 2007 John Wiley & Sons, Ltd.     

10,000 Years of explosive eruptions of Merapi Volcano, Central Java: archaeological and modern implications

Stratigraphy and radiocarbon dating of pyroclastic deposits at Merapi Volcano, Central Java, reveals 10,000 years of explosive eruptions. Highlights include:(1) Construction of an Old Merapi stratovolcano to the height of the present cone or slightly higher. Our oldest age for an explosive eruption is 9630±60 ¹⁴C y B.P.; construction of Old Merapi certainly began earlier.(2) Collapse(s) of Old Merapi that left a somma rim high on its eastern slope and sent one or more debris avalanche(s) down its southern and western flanks. Impoundment of Kali Progo to form an early Lake Borobudur at 3400 ¹⁴C y B.P. hints at a possible early collapse of Merapi. The latest somma-forming collapse occurred 1900 ¹⁴C y B.P. The current cone, New Merapi, began to grow soon thereafter.(3) Several large and many small Buddhist and Hindu temples were constructed in Central Java between 732 and 900 A.D. (roughly, 1400–1000 ¹⁴C y B.P.). Explosive Merapi eruptions occurred before, during and after temple construction. Some temples were destroyed and (or) buried soon after their construction, and we suspect that this destruction contributed to an abrupt shift of power and organized society to East Java in 928 A.D. Other temples sites, though, were occupied by “caretakers” for several centuries longer.(4) A partial collapse of New Merapi occurred <1130±50 ¹⁴C y B.P. Eruptions 700–800 ¹⁴C y B.P. (12–14th century A.D.) deposited ash on the floors of (still-occupied?) Candi Sambisari and Candi Kedulan. We speculate but cannot prove that these eruptions were triggered by (the same?) partial collapse of New Merapi, and that the eruptions, in turn, ended “caretaker” occupation at Candi Sambisari and Candi Kedulan. A new or raised Lake Borobudur also existed during part or all of the 12–14th centuries, probably impounded by deposits from Merapi.(5) Relatively benign lava-dome extrusion and dome-collapse pyroclastic flows have dominated activity of the 20th century, but explosive eruptions much larger than any of this century have occurred many times during Merapi's history, most recently during the 19th century.Are the relatively small eruptions of the 20th century a new style of open-vent, less hazardous activity that will persist for the foreseeable future? Or, alternatively, are they merely low-level “background” activity that could be interrupted upon relatively short notice by much larger explosive eruptions? The geologic record suggests the latter, which would place several hundred thousand people at risk. We know of no reliable method to forecast when an explosive eruption will interrupt the present interval of low-level activity. This conclusion has important implications for hazard evaluation.     

Multi‐method (14C, 36Cl, 234U/230Th) age bracketing of the Tschirgant rock avalanche (Eastern Alps): implications for absolute dating of catastrophic mass‐wasting

Correct and precise age determination of prehistorical catastrophic rock‐slope failures prerequisites any hypotheses relating this type of mass wasting to past climatic regimes or palaeo‐seismic records. Despite good exposure, easy accessibility and a long tradition of absolute dating, the age of the 230 million m³ carbonate‐lithic Tschirgant rock avalanche event of the Eastern Alps (Austria) still is relatively poorly constrained. We herein review the age of mass‐wasting based on a total of 17 absolute ages produced with three different methods (¹⁴C, ³⁶Cl, ²³⁴U/²³⁰Th). Chlorine‐36 (³⁶Cl) cosmogenic surface exposure dating of five boulders of the rock avalanche deposit indicates a mean event age of 3.06 ± 0.62 ka. Uranium‐234/thorium‐230 (²³⁴U/²³⁰Th) dating of soda‐straw stalactites formed in microcaves beneath boulders indicate mean precipitation ages of three individual soda straws at 3.20 ± 0.26 ka, 3.04 ± 0.10 ka and 2.81 ± 0.15 ka; notwithstanding potential internal errors, these ages provide an ‘older‐than’ (ante quam) proxy for mass‐wasting. Based on radiocarbon ages (nine sites) only, it was previously suggested that the present rock avalanche deposit represents two successive failures (3.75 ± 0.19 ka bp , 3.15 ± 0.19 ka bp ). There is, however, no evidence for two events neither in surface outcrops nor in LiDAR derived imagery and drill logs. The temporal distribution of all absolute ages (¹⁴C, ³⁶Cl, ²³⁴U/²³⁰Th) also does not necessarily indicate two successive events but suggest that a single catastrophic mass‐wasting took place between 3.4 and 2.4 ka bp . Taking into account the maximum age boundary given by reinterpreted radiocarbon datings and the minimum U/Th‐ages of calcite precipitations within the rock avalanche deposits, a most probable event age of 3.01 ± 0.10 ka bp can be proposed. Our results underscore the difficulty to accurately date catastrophic rock slope failures, but also the potential to increase the accuracy of age determination by combining methods. Copyright © 2016 John Wiley & Sons, Ltd.     

On the interest of using the multiple center approach in ESR dating of optically bleached quartz grains: Some examples from the Early Pleistocene terraces of the Alcanadre River (Ebro basin,Spain)

The present work reports the first numerical ages obtained for the two highest fluvial terraces (Qt1 and Qt2) of the Alcanadre River system (Northeastern Spain) representing the earliest remnants of Quaternary morphosedimentary fluvial activity in the Ebro basin. ESR dating method was applied to optically bleached quartz grains and both the Al and Ti centers were measured, in accordance with the Multiple Center approach. The results are overall in good agreement with the existing preliminary chronostratigraphic framework and our interpretation indicate that terraces Qt1 and Qt2 have an ESR age of 1276 ± 104 ka and 817 ± 68 ka, respectively. These data provide some chronological insights on the beginning of the fluvial sedimentary processes in a scenario of incision maintained over Quaternary in the Ebro Basin. These are among the first numerical ages obtained for such high terraces in the Iberian Peninsula.Our results demonstrate the interest of using the Multiple Center approach in ESR dating of quartz, since the two centers provide complementary information, i.e. an independent dose control. The overall apparent consistency between the ESR age estimates and the existing preliminary chronostratigraphic framework may be considered as an empirical evidence that the Ti–Li center may actually work for Early Pleistocene deposits, whereas the Ti–H center shows some clear limitations instead. Finally, these results demonstrate the interest of using ESR method to date Early Pleistocene fluvial terraces that are usually beyond the time range covered by the OSL dating method.     

Aeolization on the Atlantic coast of Galicia (NW Spain) from the end of the last glacial period to the present day: Chronology,origin and evolution of coastal dunes linked to sea-level oscillations

The Atlantic coast of Galicia (NW Spain) is a high-energy environment where shingle beaches are currently developing. These coarser sediments alternate with sandy deposits which are also considered as beaches typical of a low-energy environment. The physical association of both types of sediment with contrasted sedimentary significance raises problems of interpretation. The study of four outcrops of fossil aeolianites on this coast has allowed us to reconstruct their evolution from the end of the Upper Pleistocene to the present day. Their chronology, estimated by optically stimulated luminescence between 35 and 14 ky at the end of the last glaciation (MIS2), coincides with a local sea level 120 m below the present one. This implies a coastline shifted several kilometres from its current location and the subaerial exposure of a wide strip of the continental shelf covered by sands. The wind blew sand to form dunes towards the continent, covering the coastal areas, which then emerged with no other limitation than the active river channels. Sea-level rise during the Holocene transgression has progressively swamped these aeolian deposits, leaving only flooded dunes, relict coastal dunes and climbing dunes on cliffs up to 180 m high. The aeolian process continued as long as there was a sandy source area to erode, although accretion finished when the sea reached its current level (Late Holocene). Since then, the wind turned from accretion to erosion of the dunes and sand beaches. This erosion exposes the older shingle beaches (probably of Eemian age) buried under the aeolian sands, as well as old, submerged forest remains and megalithic monuments. The destruction of sand beaches and dunes currently observed along the Galician coast is linked, according to most researchers, to anthropogenic global warming. However, their management should consider these evolutive issues.     

Block removal and step backwearing as erosion processes on rock shore platforms: a preliminary case study of the chalk shore platforms of south‐east England

Shore platforms frequently exhibit steps or risers facing seaward, landwards or obliquely across‐shore. A combination of soft copy photogrammetry, ortho‐rectification, geo referencing and field measurement of step height are linked in a GIS environment to measure step retreat on chalk shore platforms at sample sites in the south of England over two periods, 1973–2001, 2001–2007. The methods used allow for the identification, delineation and measurement of historic change at high spatial resolution. The results suggest that while erosion of chalk shore platforms by step backwearing is highly variable, it appears to be of similar magnitude to surface downwearing of the same platforms measured by micro‐erosion meters (MEMs) and laser scanning, in a range equivalent to 0·0006 – 0·0050 m y^?1 of surface downwearing. This equates to annual chalk volume loss from the platforms, by the two erosion processes combined, of between 0·0012 m³ m^?2 and 0·0100 m³ m^?2. Results from the more recent years' data suggests that step retreat has variability in both space and time which does not relate solely to climatic variability. The results must be viewed with caution until much larger numbers of measurements have been made of both downwearing and step erosion at higher spatial and temporal resolution. Copyright © 2010 John Wiley & Sons, Ltd.     

Temporal variations in magma composition at Merapi Volcano (Central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity

Merapi Volcano (Central Java, Indonesia) has been frequently active during Middle to Late Holocene time producing basalts and basaltic andesites of medium-K composition in earlier stages of activity and high-K magmas from 1900 ¹⁴C yr BP to the present. Radiocarbon dating of pyroclastic deposits indicates an almost continuous activity with periods of high eruption rates alternating with shorter time spans of distinctly reduced eruptive frequency since the first appearance of high-K volcanic rocks. Geochemical data of 28 well-dated, prehistoric pyroclastic flows of the Merapi high-K series indicate systematic cyclic variations. These medium-term compositional variations result from a complex interplay of several magmatic processes, which ultimately control the periodicity and frequency of eruptions at Merapi. Low eruption rates and the absence of new influxes of primitive magma from depth allow the generation of basaltic andesite magma (56–57 wt% SiO₂) in a small-volume magma reservoir through fractional crystallisation from parental mafic magma (52–53 wt% SiO₂) in periods of low eruptive frequency. Magmas of intermediate composition erupted during these stages provide evidence for periodic withdrawal of magma from a steadily fractionating magma chamber. Subsequent periods are characterised by high eruption rates that coincide with shifts of whole-rock compositions from basaltic andesite to basalt. This compositional variation is interpreted to originate from influxes of primitive magma into a continuously active magma chamber, triggering the eruption of evolved magma after periods of low eruptive frequency. Batches of primitive magma eventually mix with residual magma in the magmatic reservoir to decrease whole-rock SiO₂ contents. Supply of primitive magma at Merapi appears to be sufficiently frequent that andesites or more differentiated rock types were not generated during the past 2000 years of activity. Cyclic variations also occurred during the recent eruptive period since AD 1883. The most recent eruptive episode of Merapi is characterised by essentially uniform magma compositions that may imply the existence of a continuously active magma reservoir, maintained in a quasi-steady state by magma recharge. The whole-rock compositions at the upper limit of the total SiO₂ range of the Merapi suite could also indicate the beginning of another period of high eruption rates and shifts towards more mafic compositions.     

Interrogating the time and processes of development of the Las Liebres rock glacier,central Chilean Andes,using a numerical flow model

The Las Liebres rock glacier is a large (~2.2 km long) Andean rock glacier whose internal composition and kinematics are known from previous studies. We investigate its development by posing and testing the following null hypothesis: the rock glacier has developed from a constant supply of debris and ground ice in periglacial conditions and resulting creep of the ice‐rock mixture. A rheological model was formulated based on recent advances in the study of ice‐rock mixture rheology, and calibrated on the known surface velocities and internal composition of the rock glacier. We show that the rock glacier viscosity is inversely related to both water and debris fractions, in agreement with recent field and theoretical studies of ice‐rock mixture rheology. Taking into account the possible variations in water fraction, the model was used to estimate the time spans of development (0.91–7.11 ka), rates of rock wall retreat (0.44–4.18 mm/a), and rates of ground ice formation (0.004–0.026 m/a) for the rock glacier. These results support the null hypothesis of a periglacial origin of the Las Liebres rock glacier. Copyright © 2016 John Wiley & Sons, Ltd.     

Detailed paleoseismic history of the Hinagu fault zone revealed by the high-density radiocarbon dating and trenching survey across a surface rupture of the 2016 Kumamoto earthquake,Kyushu, Japan

The NE-trending Hinagu fault zone, length 81 km, is one of the major active faults in Kyushu, Japan. From north to south, it is divided into three segments based on geomorphic features and paleoseismic behavior: the Takano-Shirahata, Hinagu, and Yatsushiro Sea segments. The 2016 Kumamoto earthquake produced a 6-km-long surface rupture with a dextral strike-slip displacement on the northern part of the Takano-Shirahata segment. Surface rupture, a faint east-side-up flexure with a vertical offset of less than 8 cm, was observed near the middle of the Takano-Shirahata segment. To examine past surface-rupturing earthquakes on the Takano-Shirahata segment, including rupture frequency and timing, we conducted a paleoseismic study with boring and trenching at Yamaide. A trench across the surface rupture exposed multiple fault strands associated with multiple surface-rupturing events that deformed several strata of fine-grained sediments. By structural and stratigraphic interpretation, high-density radiocarbon dating and tephra analysis, and Bayesian modeling, we constrained the timing of seven events, Events 1–7, to 0.84–1.25, 1.31–7.06, 9.99–11.0, 10.8–12.1, 12.0–13.0, 14.2–15.1, and before 14.8 kcal BP. Slip during Events 1–6 was obviously larger than the 2016 slip. The estimated average recurrence interval was about 2596–2860 years, but the interval between Events 2 and 3 was much longer than other intervals. Moreover, the vertical throw associated with Event 2 was larger than that of other events. This implies that the Takano-Shirahata segment has a period with rare larger earthquakes and a period with frequent smaller earthquakes. Some events might have produced ruptures on both the Takano-Shirahata and the northern part of the Hinagu segments simultaneously or in a short time. The variety of recurrence intervals suggests that the seismic activity has been affected by one or both activities of the Futagawa fault zone and the Hinagu segment.     

Growth by extension,and reworking,of a south‐western Kalahari linear dune

Optically stimulated luminescence (OSL) dating studies of linear (longitudinal) dunes have been used extensively to elucidate late Quaternary environments and climates in arid or formerly arid regions, yet understanding of the development of such dunes is incomplete. In particular, conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally, the degree to which they rework their own sediment during accumulation and whether they form primarily by extension, as opposed to lateral sand movement from adjacent interdunes. This study focuses on this last point, although the importance of the other controversies is discussed in context. A simple linear dune in the south‐western Kalahari, which has a prominent termination on a pan (playa) surface, provides an opportunity to directly test hypotheses of dune extension. Chronostratigraphy along a ~600 m transect along the crest of the dune, constrained by 42 OSL ages, reveals that the dune grew by extension on occasions in the late Pleistocene and early Holocene, but has also been subject to reworking along its length, which has continued until recent times. Dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation, whereas reworking is largely independent of conditions throughout the last ~18 ka, and may represent seasonal fluctuations in the position of the dune crest. The relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change. Copyright © 2011 John Wiley & Sons, Ltd.     

Lavini di Marco (Trentino,Italy): 36Cl exposure dating of a polyphase rock avalanche

The Lavini di Marco rock avalanche deposit (“Marocca di Marco”) is located along the left side of the middle Adige Valley, south of the town of Rovereto (NE Italy). The deposit is estimated to have a volume of ∼2 × 10⁸ m³ and cover an area of ∼6.8 km². It comprises Jurassic Calcari Grigi limestones that detached from the western slope of Mt. Zugna Torta. The Lavini di Marco is composed of at least two different rock avalanche bodies, the main deposit known as Lavini di Marco (the principal) and the much smaller Costa Stenda deposit. Costa Stenda deposits overlie Lavini di Marco deposits. Samples for ³⁶Cl exposure dating were collected from boulders within the deposits, from sliding plane bedrock and from the bedrock wall at the head scarp. Exposure ages range from 800 ± 210 to 21310 ± 1000 years. The latter age stands as a notable outlier suggesting that that Costa Stenda boulder was exposed for a considerable amount of time in the pre-slide bedrock. Lavini di Marco and Costa Stenda boulder ages are 2600 ± 200, 2700 ± 200, 3100 ± 300, 3300 ± 300, 3400 ± 300, 4400 ± 290, 5300 ± 300, and 5400 ± 300 years. The latter three are Costa Stenda boulders which we also interpret to contain inherited nuclide concentrations. The five remaining boulder ages cluster around 3000 years. We calculate a mean age for the Lavini di Marco and Costa Stenda rockslides of 3000 ± 400 years. Within the uncertainties of our data the two slides were simultaneous. For the bedrock sliding plane we obtained significantly younger ages, 1600 ± 100 and 1400 ± 100 years, and for the head scarp 800 ± 200 years. The sliding plane ages record small-scale reactivation which seems to overlap in time with a catastrophic flood event of the Adige River in Verona, as reported in the Fulda Annales, in 883 AD. Only the single age of 800 ± 210 years suggests activity at Lavini di Marco coincident with the well-known Verona earthquake (1117 AD).