T1 Terrace Research Articles

Response of terrace deposit thickness to climate change and tectonic deformation: An example of the Liyuan River in the Northeast Tibetan Plateau

AbstractThe relationships between tectonics, climate and sedimentation are important for understanding landscape evolution. In order to elucidate these relationships, we conducted a detailed survey of the thickness of terrace deposits and the altitude of terrace surfaces along the Liyuan River valley, in the Northeast (NE) Tibetan Plateau. We have dated the formation ages of terraces T3 and T4 to 42 ± 3.2 and 93.7 ± 7.5 ka, respectively, using optically stimulated luminescence (OSL) method. By compiling the deposit thickness of terraces, palaeoclimate records and local tectonism, we found that variations in precipitation account for the temporal differences in thickness/rates of sediment deposition in terraces T4 and T3. However, the spatial distribution of terrace deposit thickness was determined by tectonism, including faulting and folding, which changed the local base level. In order to maintain a foreland‐ward‐dipping gradient, the Liyuan River adjusts its sedimentary processes via spatially differentiated aggradation.

The late Quaternary mountain-front terrace sequences along the Langshan Mountains: Implications for the evolution of the western Hetao Graben

As the extensional boundary between Langshan Mountains and the Hetao Basin, the vertical displacement of the Langshan Piedmont Fault (LPF) forms the typical basin and range landform and controls the uplift of the Langshan Mountains and the deposition of the Hetao Basin. Based on the 10Be concentrations for the quartz gravel samples collected from two different mountain-front terrace sequences, we can calculate that the exposure ages for T3, T2 and T1 terraces on the northern site of the LPF (Site 1) are ~136 ka, ~72 ka and ~29ka, and the exposure ages for T3, T2 and T1 terraces on the southern site of the LPF (Site 2) are ~96 ka, ~65 ka and ~45 ka, respectively. Furthermore, the vertical slip rates are ~0.33 mm/a since about late Pleistocene, ~0.21 mm/a since ~72 ka, ~0.17 mm/a since ~29 ka for the northern part of the LPF, and ~0.61 mm/a since about late Pleistocene, ~0.74 mm/a since ~65 ka, ~0.27 mm/a since ~45 ka for the southern part. The vertical slip for different part and different periods of the LPF shows different rates. In addition, the decrease of the vertical slip rates since late Pleistocene suggest that the activity of the LPF is becoming weak.

USING OF AIRBORNE LIDAR ALTIMETRY AND SEMI-AUTOMATED GIS TOOLS FOR IDENTIFICATION AND MAPPING OF FLUVIAL TERRACES IN THE AUGŠDAUGAVA SPILLWAY VALLEY

River terraces are one of the typical and widespread Quaternary fluvial landforms in Latvia. Until recently, distinguishing and mapping of these features have required extensive field surveys. However, the availability of high resolution digital elevation models (DEM) derived from airborne laser altimetry and application of modern geographic information systems (GIS) provides sufficient background to resolve these tasks. In this study, we apply an integrated methodology based on using of remote sensing, i.e. laser scanning or Light Detection and Ranging (LiDAR) data and combining of semi-automated TerEx tools for the detection of fluvial terraces in DEM. The empirical tests performed using the tools in the study area reveal that the application of TerEx gives the reliable results. However, presence of minor landforms which increase the topographical roughness of the surface directly influence the quality of extracted data, thus leading to the necessity of additional manual editing. The obtained data indicate that the terrace sequence in the Augšdaugava spillway valley consists of eight different terrace levels – T1 to T8. Only terraces T1 and T2 are easily recognizable in the study area, whereas the upper terraces do not have explicit edges.

The Late Quaternary slip-rate of the Kichera Fault (North Baikal Rift) from morphotectonic, paleoseismological and cosmogenic 10Be analyses

Late Quaternary slip rates characterize the seismic potential of an active fault in terms of estimating the average expected recurrence period for rupturing episodes. Along the Baikal Rift faults the slip rate distributions are poorly understood. This study provides morphotectonic and paleoseismological analyses of the Kichera Fault that stretches within the North Baikal Rift over a length of 100 km. Exposure ages of key displaced terraces of the Neruchanda River from in-situ produced cosmogenic 10Be depth profiles show that the highest terrace T5 is older than 315 ka, intermediate terrace T3 was abandoned 100.0 ± 30 ka ago and the lowest terrace T1 is as old as 48.3 ± 19.9 ka. These exposure ages, coupled with terrace elevation from the actual Neruchanda River bed, allow us to estimate the incision rates for the corresponding time periods which are 0.1 (maximum), 0.16 ± 0.05 and 0.19 ± 0.08 mm yr−1, respectively. Using the cumulated amplitudes of the terrace displacement, we estimate the vertical slip rates along the Kichera Fault are 0.42 ± 0.13 and 0.19 ± 0.08 mm yr−1 over the last ~100 ka and ~48.3 ka, respectively. Paleoseismological studies including morphomertic analyses of the tectonic scarp and trenching across the fault allowed estimating the age (5.4 ka) and minimum magnitude (6.8) of the last Kichera Fault rupture. Using the estimates of short- and long-term slip rates, we propose mean recurrence intervals of 5.3 and 2.4 ka, respectively. The last interval is shorter than the time since the last earthquake, indicating that the future event could be of greater magnitude to maintain the long-term average slip rate.

Quaternary landscape evolution of patagonia at the Chilean Triple Junction: Climate and tectonic forcings

Glacial and fluvial landforms record the recent history of the Earth surface and have the potential to provide information about uplift and climate changes during Quaternary times. Patagonia hosts uniquely well-preserved moraine deposits, along with outwash and fluvial terraces. This offers the possibility of determining the timing of glacier advances since the Great Patagonian Glaciation (ca. 1.2 Ma) and allows us to investigate landscape response to climate and tectonic forcing.In this study, we present twenty-eight new in situ 10Be exposure ages for glacial deposits, outwash sediments, and fluvial terraces at the latitude of the Chile Triple Junction (∼46°30′S). We combine this database with a detailed mapping and a morphological analysis of the Deseado River terrace system. The glacial and outwash deposits document at least five major glacial advances in the Lago Buenos Aires valley before the deposition of the Moreno system during Marine Isotope Stage (MIS) 8. Key advances occurred during MIS 12 and MIS 16. Further ice expansions that resulted in Telken V and VI/VII outwash surfaces date to 780 ka and ca. 1.2 Ma respectively. Overall, our data show the difficulty of dating pre-LGM glacial deposits using surface exposure methods and reinforce the idea that outwash surfaces are better targets to determine the age of glacial sequences in the region.The Deseado River terrace system yields stratigraphically consistent ages that range from 1167 to 447 ka, which indicate that these terraces formed during Pleistocene times. Our analysis suggests that terraces T3, T7 and T8 may have been formed during cold stages, close to the glacial-interglacial transitions. We also calculated incision rates that reveal a strong initial pulse, from ca. 1200 to 900 ka, which was followed by significantly weaker river incision pulses.Finally, our geomorphological analysis confirms that the oldest fluvial terraces of the Deseado River system exhibit a NE-SW tilting through a broad area, next to the Atlantic Ocean. This was previously interpreted as the surface response to a long-wavelength dynamic uplift, a phenomenon that should be reassigned to the early Pleistocene.

Springs of Pasighat, a valuable resource for the community: A hydrogeological study carried out using geoelectrical resistivity technique

Many springs occur in and around Pasighat. Eight major springs of the area were considered for the study. These springs are Dimple type, Fault dam type, and a combination of Fault dam and Border type. The highest discharge is 263.23 L/sec and the lowest is 1.91 L/sec. The aquifers are terrace deposits that comprise of unsorted boulders, cobbles and pebbles in sandy matrix and the springs occur at the base of different terrace levels. Due to the scarcity of dug wells or deep tube wells, subsurface investigations were done using vertical electric sounding (VES). VES data generated at six locations show H-type situation. The aquifers are at shallow depth, unconfined, and have good hydrogeological prospects. At the T2 terrace, volume of water stored is 42,14,512.5 m3 and the combined discharge of springs is 38,257.92 m3/day. These springs are recharged by precipitation and influent streams. Springs of the study area are aligned along the Himalayan Frontal Thrust (HFT) and its splays, and they have a major role in the evolution of these springs. The springs were formed due to topographic breaks and less permeable collapsed debris. Local people use spring water for the household, irrigation, laundry, and fisheries.

Luminescence Chronology of the Yellow River Terraces in the Heiyukou Area, China, and Its Implication for the Uplift Rate of the Ordos Plateau

Abstract The precise chronology of the fluvial terraces of the Yellow River in China is essential to understand its geomorphological evolution history. More terrace ages are needed for the correlation of the terraces along the river and the construction of the longitudinal profile. In this study, seven terraces (T1–T7) in the Heiyukou area of the Jinshaan Canyon of the river were identified and were sampled for optical dating. The reliability of the ages was evaluated on the bases of bleachability, comparison of optical ages on fine and coarse grains, stratigraphic consistency of OSL ages, age distribution and geomorphological setting. The results show that the paired T2 terrace was formed at 72 ± 3 ka, and the T4, T5 strath terraces were dated to 108 ± 4 and >141 ± 4 ka, respectively. The ages for the samples from T6 and T7 were significantly underestimated, and the ‘infinitely old’ pre-Quaternary Red-Clay sample on the T7 terrace was dated to 134 ± 6 ka. The long-term river incision rates were calculated to be <0.36, 0.34 and 0.18 mm/a for at least the past 141, 108 and 72 ka, respectively, which also reflect the uplift rates of the Ordos plateau. The implication for dating terrace deposits is that terraces should be systemically sampled and dated using both fine and coarse grain fractions. The reliability of the ages obtained for high terraces should be evaluated using a relative chronology of dated samples on a case-by-case basis, if no independent numerical age controls are available.

Features of terraces and the incision rate along the lower reaches of the Yarlung Zangbo River east of Namche Barwa: Constraints on tectonic uplift

Abstract Along the lower reaches of the Yarlung Zangbo River, scattered alluvium sections appear on T1 and T2 terraces. The alluvial deposits on the T1 terrace in Linduo and Ximogou and the T2 terrace in Guoguotang are composed principally of coarse-grained sand particles and rock fragments, with no observable fine-grained components. The T1 terrace alluvium section is dominated by clay and silt and occurs near the town of Dexing, and optically stimulated luminescence dating of sample from this site revealed an age of 18.2 kyear, which indicates that the incision rate of the Yarlung Zangbo River has been 4.7 mm/year since the formation of this section. On the basis of the component characteristics of terraces in Motuo County, the provenance for the terraces is probably related to the breaking of the palaeo-dammed lakes in the middle reaches of the Yarlung Zangbo River. A 430 m elevation difference still exists between the study area and the local base level downstream of the Yalung Zangbo River (Assam Plain), although this river has a strong incision capability (4.7 mm/year), which suggests that tectonic uplift remains very intense east of the Namche Barwa syntaxis.

The Late Quaternary dip–slip characteristics of the left-lateral strike-slip Yuanmou fault, the southwestern margin of the north–south seismic belt of China

The North–South Seismic Belt distributed along the eastern margin of the Tibetan Plateau is a regional-scale seismically active zone. The Yuanmou Fault, located at the junction of the North–South Seismic Belt and the Central Yunnan Sub-Block, is an important boundary of earthquakes distribution and topography. Therefore, the studying of the Late Quaternary activity of the Yuanmou Fault is of great significance to understand the regional geodynamic mechanism and its efforts on the regional tectonic activities, seismic distribution and future risk. Based on field observations and analysis of earthquake geology and tectonic geomorphology and the dating results of Quaternary chronology, together with the previous studies, revealed that: (1) the fluvial terrace T1 was cut by the Yuanmou fault on the northern section of Jiangbian, and the most recent earthquake event happened about 7 ka B.P. age on the Jiangbian–Luochuan segment. (2) Based on the offset measurement and dating results of deformed terraces, the horizontal and vertical average slip rate of the Yuanmou fault were determined to be ~ 1.0 mm/year and ~ 0.1 mm/year, respectively. (3) Moreover, the latest activity time of the southern segment of the Yuanmou Fault is late Pleistocene, indicating the segmentation between the northern and southern segments of the Yuanmou Fault. (4) The differential activity intensity and activity ways of the Yuanmou Fault on different segments is probably associated with the change of local stress. Therefore, these findings concerning with seismic activities and activity segmentation of the Yuanmou Fault reveal the complexity of the regional dynamic mechanisms and provide a new insight for exploring regional differences in the tectonic deformation mechanisms of the southeastern margin of the Tibetan Plateau during the Late Cenozoic.

Late Quaternary activity characteristics of the strike-slip Dongbielieke Fault in West Junggar, China

The Dongbielieke Fault, an active fault that originated during the Holocene, is located at a key position in the West Junggar orogenic belt. The total length of NE-striking the fault is 120 km. Since the Late Quaternary, continuous activity on the Dongbielieke Fault has caused clear left-lateral dislocations at all morphological units along it, and a continuous linear steep ridge has formed on the eastern side of the Tacheng Basin. Using high-resolution UAV images and differential GPS to depict and measure the strike-slip dislocations at each river terrace level, it was found that the maximum left-lateral dislocations in the T5, T4, and T2 terraces are 30.7 m, 12.0 m, and 8.7 m, respectively. In addition, based on the geomorphic ages from optically stimulated luminescence analyses, we have limited the sliding rate of different terraces on the Dongbielieke Fault. The average left-lateral strike-slip rate since the late Quaternary of the Dongbielieke Fault is 0.91 ± 0.18 mm/a. Combining the GPS rates for North Tianshan with those for the Tacheng Basin, it is believed that the three large NE-trending strike-slip faults (Daerbute, Tuoli, and Dongbielieke faults) absorb a large amount of residual deformation in the area. This would allow the faults to maintain a higher left-lateral slip rate. In summary, analysis of surface faulting, Quaternary geology, seismicity, and measurements of Holocene morphology suggests that the Dongbielieke Fault is an active strike-slip fault with high seismic risk. However, it is unlikely that this fault could generate an earthquake of magnitude greater than 7.5. Our data do not allow for discussion of a more complex seismic cycle.

Surface rupture geomorphology and vertical slip rates constrained by terraces along the Wulashan piedmont fault in the Hetao Basin, China

The Wulashan piedmont fault is a typical normal fault in the northern Ordos Block and has exhibited intense activity since the Late Pleistocene. It is located among the Ordos Block, Alashan Block, Yanshan Block and North China Block and between the NE expansion of the Tibetan Plateau and the subduction of the Pacific Plate. This area is important as a key location to study the remote effects of the Tibetan Plateau NE expansion. Historical M 8 earthquakes in 7 BCE and 849 CE occurred near this fault and thus the fault poses a potential earthquake threat but has received little research attention. We observed the surface ruptures, measured the heights of terraces created by fault offsets, excavated trenches and used optically stimulated luminescence (OSL) dating of samples to study the late Quaternary fault activity. This study shows that the fault is divided into three segments. Three levels of terraces were produced by movement on the fault. The T1 terrace formed at approximately 10 ka, the T2 terrace formed between 30 and 40 ka, and the T3 terrace formed between 40 and 50 ka. Based on the average terrace heights along the fault, we calculate that the vertical fault slip rates have been approximately 1.12–1.34 mm/a in the Holocene and 2.2–2.28 mm/a since 50 ka. Our analysis shows that the Daqingshan piedmont fault has the highest vertical slip rate, the Wulashan piedmont fault has an intermediate slip rate and the Sertengshan piedmont fault has the lowest vertical slip rate. The area between the Wulashan and Daqingshan piedmont faults readily accumulates seismic stress and represents a potential future earthquake site. Trenches provide visible evidence of vertical rupture and slip movement in subsurface profiles, revealing six events on the Gongmiaozi segment since 25 ka and 14 events on the Baotou segment since 120 ka. The analysis shows that the Ordos peripheral fault system formed due to the subduction of the Pacific Plate. The northward expansion of the Tibetan Plateau and the movement of the Ordos Block have caused fault activity in the northern part of the Hetao Basin since the Late Pleistocene. The modern tectonic stress field and the upwelling of asthenospheric material east of the Hetao fault zone have resulted in an increase in the slip rate on the Hetao fault zone from west to east.

Determining the Age of Terrace Formation Using Luminescence Dating—A Case of the Yellow River Terraces in the Baode Area, China

Dating fluvial terraces has long been a challenge for geologists and geomorphologists, because terrace straths and treads are not usually directly dated. In this study, the formation ages of the Yellow River terraces in the Baode area in China were determined by dating fluvial deposits overlying bedrock straths using optically stimulated luminescence (OSL) dating techniques. Seven terraces (from the lowest terrace T1 to the highest terrace T7) in the study area were recognized, and they are characterized by thick fluvial terrace deposits overlaid by loess sediments. Twenty-five samples from nine terrace sections were dated to about 2–200 ka. The OSL ages (120–190 ka) of the fluvial samples from higher terraces (T3–T6) seem to be reliable based on their luminescence properties and stratigraphic consistency, but the geomorphologic and stratigraphic evidence show that these ages should be underestimated, because they are generally similar to those of the samples from the lower terrace (T2). The formation ages of the terrace straths and treads for the T1 terrace were deduced to be about 44 ka and 36 ka, respectively, based on the deposition rates of the fluvial terrace deposits, and the T2 terrace has the same strath and tread formation age of about 135 ka. The incision rate was calculated to be about 0.35 mm/ka for the past 135 ka, and the uplift rate pattern suggests that the Ordos Plateau behaves as a rigid block. Based on our previous investigations on the Yellow River terraces and the results in this study, we consider that the formation ages of terrace straths and treads calculated using deposition rates of terrace fluvial sediments can overcome problems associated with age underestimation or overestimation of strath or fill terraces based on the single age of one fluvial terrace sample. The implication is that, for accurate dating of terrace formation, terrace sections should be systematically sampled and dated.

Evolution of the Upper Yellow River as Revealed by Changes in Heavy-Mineral and Geochemical (REE) Signatures of Fluvial Terraces (Lanzhou, China)

Despite decades of study, the factors that controlled the formation and evolution of theupper reaches of the Yellow River, including uplift of the northeastern Tibetan Plateau, Pliocene-Pleistocene climate change, and autogenetic processes are still poorly constrained. The stratigraphicrecord of such paleogeographic evolution is recorded in the sequence of nine terraces formed duringprogressive incision of the Yellow River in the last 1.7 Ma. This article investigates in detail forsediment provenance in terraces of the Lanzhou area, based on heavy-mineral and geochemical(REE) signatures. Two main provenance changes are identified, pointing each to a majorpaleogeographic reorganization coupled with expansion of the upper Yellow River catchment andenhanced sediment fluxes. The first change took place between the deposition of terrace T9 (formedaround 1.7 Ma) and terrace T8 (formed around 1.5 Ma), when rapid fluvial incision point to tectoniccontrol and active uplift of northeastern Tibetan Plateau. The second change took place betweendeposition of terrace T4 (formed around 0.86 Ma) and terrace T3 (formed around 0.14 Ma), duringa period of low incision rates and notably enhanced sediment fluxes as a response to enhanced EastAsian Summer Monsoon and consequently increased precipitations, pointing instead chiefly toclimatic control.

Geomorphic changes along the Yiluo River influenced the emergence of the first urban center at the Erlitou Site, Central Plains of China

Geomorphological research at archaeological sites has shown that ancient environmental conditions have significant implications for understanding changes in archaeological site distribution and layout. The Luoyang Basin in Central China was a center for early urbanism including several large cities in antiquity, but the geomorphic environments that supported these ancient cities have remained uninvestigated. From 2006 to 2011, a field project was conducted in the Luoyang Basin in attempt to understand the relationship between environmental changes and the development of urbanism. Forty-nine profiles were sampled on the alluvial terraces of the Luoyang Basin to examine the geomorphological evolutionary history of the Yi River and Luo River. Our study indicates that the T1 Terrace formed around 7000 cal yr BP and provided a stable landform for Yangshao (7000-5000 yr BP) and Longshan (5000-3900 yr BP) settlements. However, massive floods around 4000-3800 yr BP destroyed some of these late Longshan settlements and caused the Luo River to change its course to southern part of the Luoyang Basin. Those floods significantly altered the landforms and laid a solid foundation for the succeeding development of the urban center at Erlitou.

Accurate determination of the Pleistocene uplift rate of the NE Japan forearc from the buried MIS 5e marine terrace shoreline angle

We used tephra and phytolith stratigraphy to refine Pleistocene marine terrace chronology, with reference to reported eustatic sea levels associated with the dated marine terraces, and estimated uplift rates along the northern part of the northeast (NE) Japan forearc (the overriding plate in the northeast Japan subduction zone) by using elevation measurements of the buried shoreline angle beneath well-dated marine terrace surfaces to derive more accurate paleo-sea levels. On the Kamikita Plain, northernmost Honshu Island, the T4 and T3 marine terraces were correlated to marine isotope stage (MIS) 5e and MIS 7c or 7e, respectively, by the stratigraphic positions of the tephras Toya (MIS 5d) and WP (MIS 7b). The T2 terrace surface, which had previously been assigned to MIS 7, is buried by loess correlated to MIS 8 by its phytolith assemblage; therefore, this terrace can be reasonably re-correlated to MIS 9. The reported optically stimulated luminescence ages for Middle Pleistocene terrace deposits tend to be younger than these refined terrace ages. We used the buried shoreline angle elevation, determined from the reconstructed profile of the marine terrace deposits and paleo-sea cliff, to refine the uplift rate of T4 since MIS 5e. The accurate rate thus determined, 0.18–0.26 m/ky, is slower than the rates initially inferred from the inner edge of T4, but faster than the reported rate (0.14–0.19 m/ky, as recalculated here) inferred from the assumed MIS 5e shoreline elevation. In addition, it is roughly compatible with the rate inferred by using the top of T2 lagoon deposits to determine the shoreline elevation during MIS 9. Therefore, during the last 300 ka, the uplift rate of the Kamikita Plain has been constant at about 0.2 m/ky. This Pleistocene uplift is probably attributable to a combination of moment release on the megathrust, isostatic uplift driven by crustal thickening, and reverse faulting of the upper crust.

Soil liquefaction in seasonally frozen ground during the 2016 Mw6.6 Akto earthquake

Soil liquefaction is a type of coseismic hydrological change triggered by earthquakes, and its occurrence results in major property damage and casualties. The dynamics of coseismic hydrological changes are not fully understood. In order to address this, we studied coseismic deformations such as liquefaction and ground fissures that occurred as a result of strong seismic activity during the 2016 Mw6.6 Akto earthquake, which took place in the interior of the Pamir Plateau in northwestern China. This paper presents a systematic survey of the frozen soil liquefaction and ground fissures caused by this earthquake. The majority of liquefaction sites near the Karaat River are located on the T1 terrace, in Bulake village, and are adjacent to the alluvial fan of the Kungai Mountain. We find that the liquefaction was caused by the original spring and coseismic ground fissure during the earthquake. Approximately 80% of the liquefaction sites are formed along the original spring in the epicenter. The maximum height of sand boils is 15 cm. The remaining 20% of the liquefaction sites are formed along the coseismic ground fissure. Our results suggest that the frozen soil layer impedes liquefied material in the lower unfrozen soil layer from reaching the surface, and the material formed from liquefaction is consequentially channeled through the primary fault and coseismic ground fissures. Liquefaction associated with the Akto earthquake demonstrates the importance of accounting for the possibility of a series of coseismic geological disasters, such as soil liquefaction and ground fissures, in areas with similar geology, altitude, and temperature.

Aspects of late Quaternary geomorphological development in the Khangai Mountains and the Gobi Altai Mountains (Mongolia)

The reconstruction of geomorphological processes as a result of environmental change is approached by investigating and dating some fluvial, aeolian and lacustrine archives at specific locations that form a N-S basin and range transect across the Khangai Mountains south to the eastern Gobi Altai mountains in Mongolia. Geomorphological processes varied a) spatially with different climatic conditions and vegetation cover in relation to different elevation and latitude and b) temporally due to climatic shifts during the late Quaternary. In total, 15 sections from three distinct sub-regions along that transect were dated by 22 OSL ages. The Khangai Mountain sub-region exhibits mainly late Glacial to Holocene aeolian silty to sandy cover sediments mainly in the upper catchment reaches (>1800 m a.s.l.). Sections in the northern and central Gobi represent river terraces and alluvial fans in basin areas as well as aeolian sediments in the mountains above 2200 m a.s.l. The oldest terrace surface found in this study (T2; NGa1) dates to the penultimate Glacial cycle. The T1 terrace surfaces, on the northern Khangai Mountain front and in the central Gobi sub-region yield a maximum accumulation during the global Last Glacial Maximum (gLGM) and late Glacial time. During the gLGM phase represents rather sheetflow dominated transport built the alluvial fans and in late Glacial times the sediments exhibit more debrisflow controlled accumulation. Incision, forming the T1-terrace edges is therefore, supposed for the Pleistocene-Holocene transition and subsequent early Holocene. The geomorphic evidence is interpreted as stronger fluvial morphodynamics induced by enhanced humidity under beginning interglacial conditions. These processes coincided with the development of aeolian mantles at higher altitudes in the Khangai and Gobi Altai mountains where higher temperatures and humidities supported the formation of a vegetation cover, that served as a dust trap at least since late Glacial times and reduced the sediment supply on the alluvial fans.

The caves of Sierra de Atapuerca and human use of the karst landscape during the Pleistocene (Burgos, Spain)

The Sierra de Atapuerca karst is an interesting inactive multilevel cave system, which is the result of the action of ancient base levels during the Plio-Pleistocene. It contains one of the most important prehistoric sites for the understanding of old settlements in Eurasia, and was listed by the UNESCO World Heritage Site in 2000. These caves were formed on the bases of sub-horizontal conduits with SN paleo-drainage, with the discharge zone located in the head of Pico river. The conduits are organized into three main levels that appear perched between 90 and 60 m above the current course of the Arlanzón River, coinciding with the base levels generated mainly by the fluvial terraces T2, T3 and T5. Incision of the water table released the upper ducts from the action of water while the lower levels were being developed in the phreatic zone. The vadose caves would have been used by wildlife and hominids for more than 1.2 Ma, preserving the important archaeo-paleontological records of the Early and Middle Pleistocene.

Pleistocene geodynamic evolution of the Arlanzón valley: implications for the formation of the endokarst system and the open air archaeological sites of the Sierra de Atapuerca (Burgos, España)

The Arlanzón river is located in the NE Duero Depression (Castilian Plateau of northern Spain), where it drains the anticlinal ridge of the Sierra de Atapuerca, where a rich record of karstic and open air Palaeolithic archaeological sites are located, spanning the last 1.22 Ma. The geomorphological sequence of this valley is composed of fourteen fluvial terraces from T1 (+92-100 m), to level T14 (+2-3 m), ranging from the Early Pleistocene to the Holocene and mainly related to cold MIS. Available chronological data and terrace relative heights extracted from LiDAR data, have allowed the reconstruction of the downcutting phases of the valley, which show an acceleration of the incision rates throughout the Quaternary, probably related to tectonic uplift. In the Sierra de Atapuerca multilevel endokarst system, three sub-horizontal cave levels appear spatially and chronologically related to the Arlanzón fluvial terraces T2 (+82-91 m), T3 (+70-78 m) and T4 (+60-67 m)/T5 (+50-58 m). The association between fluvial terrace base levels and sub-horizontal phreatic caves suggests a relatively short period of time for the formation of these phreatic passages when compared to karstic vadose entrenchments related to the low incision rates of the Arlanzón river (< 0.038-0.045 m/ka). In the valley, the incision of 0.061 m/ka caused the progressive exhumation of a neogene limestone layer containing flint, which erosion and successive re-sedimentation phases by alluvial and colluvial processes on the valley slopes during the Middle and Upper Pleistocene caused many wide captation areas of raw material, which were exploited by the Neanderthals during MIS 3 and 4.

Identifying the source of fluvial terrace deposits using XRF scanning and Canonical Discriminant Analysis: A case study of the Chihshang terraces, eastern Taiwan

The source of fluvial deposits in terraces provides important information about the catchment fluvial processes and landform evolution. In this study, we propose a novel approach that combines high-resolution Itrax-XRF scanning and Canonical Discriminant Analysis (CDA) to identify the source of fine-grained fluvial terrace deposits. We apply this approach to a group of terraces that are located on the hanging wall of the Chihshang Fault in eastern Taiwan with two possible sources, the Coastal Range on the east and the Central Range on the west. Our results of standard samples from the two potential sources show distinct ranges of canonical variables, which provided a better separation ability than individual chemical elements. We then tested the possibility of using this approach by applying it to several samples with known sediment sources and obtain positive results. Applying this same approach to the fine-grained sediments in Chihshang terraces indicates that they are mostly composed of Coastal Range material but also contain some inputs from the Central Range. In two lowest terraces T1 and T2, the fine-grained deposits show significant Central Range component. For terrace T4, the results show less Central Range input and a trend of decreasing Central Range influences up section. The Coastal Range material becomes dominant in the two highest terraces T7 and T10. Sediments in terrace T5 appear to have been potentially altered by post-deposition chemical alteration processes and are not included in the analysis. Our results show that the change in source material in the terraces deposits was relatively gradual rather than the sharp changes suggested by the composition of the gravels and conglomerates. We suggest that this change in sources is related to the change in dominant fluvial processes that controlled by the tectonic activity.