T1 Terrace Research Articles

Late Quaternary right-lateral slip rate along the Tangyuan segment of the Yilan–Yitong Fault Zone on the NE China Plain

The slip rate of strike-slip active faults is crucial for fault rupture behavior analysis and seismic hazard assessment. Although many segments of the Yilan–Yitong Fault Zone (YYFZ) in NE China have been strongly deformed since the late Quaternary, little progress has been made on its slip rate. With the help of high-resolution satellite images, detailed field investigations, seismic reflections, and Quaternary chronological dating, we mainly studied the late Quaternary right-slip rate of the YYFZ. Field investigations revealed an ∼15 km long by ∼1–2 m high-surface scarp belt extending along the Tangyuan graben interior, with a series of sag ponds and small parallel bulges. Research has revealed that the most recent paleoearthquake (∼M 7.0) occurred between 2,800± 600 a BP and 1,700 ± 200 a BP, with evidence of coseismic surface rupture. The T2 terrace abandonment age of the Heijin River is approximately 55.13 ± 1.78 ka (OSL), and the maximum cumulative right-lateral offset may reach 110 ± 5 m. Thus, the maximum right-slip rate of the Tangyuan segment of the YYFZ since the late Quaternary is constrained to 1–2 mm/a according to the upper terrace model. This study suggests that the presence of a new fault in the basin interior merits more attention when assessing the influential surface range and earthquake potential along the YYFZ, and the features of “low tectonic loading rate, activity migration in space, and clustering in time separated by ten thousand years of seismic quiescence” observed along the YYFZ are highly important for earthquake model construction and tectonic deformation studies in stable continental regions (SCRs).

Glacier dam evolution and knickpoint migration in the Yarlung Tsangpo Gorge, eastern Himalayas, since the last glacial period

The repeated cut-and-fill process induced by the late Quaternary glacial damming and catastrophic outburst events in the Yarlung Tsangpo Gorge (YTG) in the eastern Himalaya may reflect the interaction between rock uplift, climate change and river incision in the southeastern Tibetan Plateau. Here we provide the detailed reconstruction of the cut-and-fill history recorded at the entrance of the YTG, based on geomorphological, sedimentological and chronological analyses. The results reveal a catastrophic glacial-dam breach during the last deglaciation (∼18 ka), and the outburst flood eroded a ∼30–45 km long valley floor filled with glacial diamicton and glaciofluvial deposits, which was later further incised to form terrace T2 with a height of ∼350 m. The second dam failure occurred at ∼5 ka, producing a spillway, forming terrace T1 with a height of ∼100 m. The vertical incision and horizontal migration rate of the knickpoint at the glacier dams were estimated as 0.02 m/yr, and 2.5 m/yr since the last deglaciation, based on the age of the terraces and distance of the knickpoints. We consider the glacial dams to be effective in impeding headward river erosion during glacial periods. This, along with rapid river headward erosion during the last interglacial period, results in two knickpoints on the longitudinal profile due to the differences in erosion resistance. The fluvial reaches corresponding to the repeated cut-and-fill processes are confined to the center of the Namche Barwa massif, suggesting that rapid rock uplift counteracted fluvial headward erosion and maintained the stability of the bedrock knickpoint. Therefore, in comparison to glacial dams, tectonic uplift is the most important component in plateau margin stabilization.

Combining geomorphological and kinematic models to analyze tectonic deformation rates: A case study of the Bayin anticline in the eastern Tian Shan Mountains

Quantitatively characterizing the geometry, kinematics, and deformation rate of fold-thrust belts in intermontane basins is the key to understanding strain partitioning within the Tian Shan range. This work focuses on the Bayin anticline in the Youludusi Basin, a typical intermontane basin located within the eastern Tian Shan. The Kaidu River cuts through the Bayin anticline and has developed three levels of terraces (T1–T3) across the structure. By using cosmogenic nuclide and optically stimulated luminescence dating methods, the formation ages of terraces T1 and T3 are constrained to 11.54 ± 0.55 ka and 42 + 7.0/−7.1 ka, respectively. When applying a listric thrust fault model to the Bayin anticline and using terraces as references, the vertical displacements are estimated to be 16.45 + 6.46/−3.19 m (T1), 32.08 + 12.85/−6.19 m (T2), and 95.93 + 38.94/−18.6 m (T3), and the shortening amounts are 10.56 + 8.33/−5.04 m (T1), 20.46 + 16.68/−9.64 m (T2), and 61.24 + 50.22/−28.93 m (T3). Based on this listric thrust fault model and terrace T1–T3 ages, the rate of fault slip controlling the growth of the Bayin anticline is determined to be 1.6 ± 1.0 mm/yr, and the crustal shortening rate of the anticline is 1.0 + 0.7/−0.6 mm/yr. The estimated crustal shortening deformation of the Bayin anticline accounts for ∼12 % of the total deformation in the Youludusi Basin. In terms of the entire orogenic belt, the crustal shortening absorbed in the southern, central, and northern parts accounts for 24 %–56 %, 46 %–71 %, and 19 %–74 %, respectively, of the total strain across the eastern Tian Shan. Therefore, we believe that the Eastern Tianshan undergoes uniform deformation.

Evolutionary model and palaeoenvironmental interpretation of the La Codera archaeological complex (Ebro Basin, NE Spain)

La Codera archaeological site is one of the most important settlements from the 1st Iron Age in the Ebro valley, dated between ca. 800 795 and ca. 460 cal. BC. The archaeological area also includes other later settlements. We analyzed the geomorphological context of the area by conducting a geoarchaeological survey and sampling. We also completed the evolutionary framework of the settlement, including paleoenvironmental information. Four slope stages (S1–S4) were identified, some of them related to fluvial terraces. Stages S4 and S3 are two old residual slopes dated to the Pleistocene, without evidence of human occupation. Older features related to human occupations are charcoals dated to Chalcolithic times from T2 terraces of La Codera stream. Slope S2 contains archaeological remains from the 1st Iron and Bronze Ages. Therefore, La Codera and its slopes were occupied during the Bronze Age, before Iron Age settlements. Slope S2 formation corresponds to the stable environmental stage known as the Iron Age Cold Epoch, or 2.8 Bond Event, also identified in many areas of the Ebro Depression. This period was followed by an erosive stage after the Roman Epoch (possibly during the 1.4 Bond Event). Later, a new slope (S1) formed, together with a new terrace (T1). This slope includes walls and ceramics from Iberian, Roman, and Medieval times toward the northeast of the settlement. These features make it possible to infer that this last accumulation formed during the cold stages of the LIA.

Study on the late quaternary activity of the Jinyang-Ningnan segment of the Lianfeng fault zone

The Lianfeng fault zone is located at the junction of the Daliangshan subblock and the South China block and is the southern boundary of the Daliangshan subblock. It is a very active tectonic area, which is of great significance to understanding its seismogenic environment. However, there are relatively little existing data on its activity and the timing of its latest activity. In the Jinyang-Ningnan segment of the Lianfeng fault zone along the Jinsha River, remote sensing image interpretation, field geologic surveys, high-precision drone measurements, and sample dating indicate that the river terraces T1 (the lowest, 15–40 m above the local river level) and T2 (60–90 m above the local river level) developed in the mid-Holocene and late Pleistocene. This indicates that the Jinsha River basin has been strongly downcutting since the Late Pleistocene. The fault profiles are mainly exposed in the T1 and T2 terraces of the Jinsha River. Based on this information in combination with the fault characteristics of the sedimentary profile and stratigraphic dating, it is believed that the Lianfeng fault zone was active at least along the Jinyang-Ningnan segment, with the latest activity occurring no earlier than the early to mid-Holocene.

Paleo-lake evolution influenced by tectonic processes and climate changes in the Hetao Basin during the late Quaternary

Exploration of paleo-lake evolution is crucial for the understanding of climatic and tectonic roles in earth surface. Previous studies mainly focused on the climatic effect on river-lake transitions and lake evolutions through lacustrine deposits, but with limited consideration of tectonic drivers, especially for the tectonic rift lakes in the Hetao area.Based on the analyses of lacustrine and fluvial piedmont terraces and a 400-m core from the northern Hetao Basin, along with the optically stimulated luminescence and detrital zircon U-Pb dating, we adopted an integrated “tectonics-climate-surface processes” approach to explore the climatic and tectonic effects on the lake evolution of the Hetao rift basin. Results show that lacustrine deposition on the piedmont terrace T1 (60–47 ka), underlying the T3 fluvial (80–60 ka), has an erosion contact with pluvial deposits at 55 ka, implying the paleo-lake formation at ∼ 80–60 ka and shrinkage at ∼ 55–47 ka. Lake formation was forced by basin depression under the tensile stress of tectonic movement, and was recharged by the Yellow River due to obstruction of the outlet at Tuoketuo caused by uplift.Lake shrinkage was due to the combined effect of basin lifting and warm-wet climate conditions that promoted outflow. A substantial decrease in the erosion base level and rapid water drainage induced by river cutting caused erosion of lacustrine deposits in the basin. The limited sedimentary space of the lake basin in early MIS 2 should be considered a factor in lake disappearance in addition to the dry climate. This study highlights that tectonic effects may be more important than climatic effects in the evolution of rift lakes near the young fold mountain belts.

Electron spin resonance and optically stimulated luminescence chronology of the Sanggan River terraces in the Nihewan Basin, North China

The chronology study of river terraces is important to reconstruct the history of regional climate change and tectonic uplift. Due to greater signal dose saturation levels, electron spin resonance (ESR) dating became as a potentially powerful tools for the chronology of Middle Pleistocene terraces. In this study, two profiles of terrace fluvial sediments from the Sanggan River Canyon were dated using quartz Ti–Li center ESR method. The ESR dating results show that the terraces T3 to T6 were formed at 125 ± 16 ka, 181 ± 20 ka, 315 ± 31 ka and 379 ± 44 ka, respectively. T1 and T2 were formed at 7 ± 0.3 ka and 43 ± 4 ka respectively obtained from optically stimulated luminescence (OSL) dating. These are among the first numerical ages obtained for such high terraces in the Nihewan Basin. The present work contributes to establish the chronological framework of the Late Middle Pleistocene and Holocene terraces of the Sanggan river and to improve the Quaternary stratigraphy of the Nihewan Basin.

Electron Spin Resonance Dating of the Quaternary Fluvial Terrace System of the Upper Han River, Central China

The geomorphology of the upper Han River, which is located in the southern Qinling Mountains (central China) and within the northern subtropical monsoon climate zone, contains abundant information on tectonic and climatic changes. Many Paleolithic sites are preserved in the Quaternary terraces in this region, making it an ideal area for studying both geomorphology and ancient human activity. However, owing to limitations in dating methods, the formation ages of the higher terraces T3–T5 of the upper Han River remain unclear. We collected 11 samples of sediment from the higher Quaternary terraces of Wufeng, Qingqu and the Yunyang Basin for electron spin resonance (ESR) dating of quartz grains. Results show that the formation ages of terraces T3, T4 and T5 are 422–401 ka, 627–621 ka and 1129–1099 ka, respectively. Integrating this information with the timings of documented climatic transitions and the history of regional uplift, we propose that the upper Han River terraces formed in response to the combined effects of climatic transition and tectonic uplift.

Revised age and stratigraphy of the classic Homo erectus-bearing succession at Trinil (Java, Indonesia)

Obtaining accurate age control for fossils found on Java (Indonesia) has been and remains challenging due to geochronologic and stratigraphic uncertainties. In the 1890s, Dubois excavated numerous faunal fossils—including the first remains of Homo erectus—in sediments exposed along the Solo River at Trinil. Since then, various, and often contradictory age estimates have been proposed for the Trinil site and its fossils. However, the age of the fossil-bearing layers and the fossil assemblage remains inconclusive. This study constructs a chronostratigraphic framework for the Trinil site by documenting new stratigraphic sections and test pits, and by applying 40Ar/39Ar, paleomagnetic, and luminescence (pIRIR290) dating methods. Our study identifies two distinct, highly fossiliferous channel fills at the Trinil site. The stratigraphically lower Bone-Bearing Channel 1 (BBC-1) dates to 830–773 ka, while Bone-Bearing Channel 2 (BBC-2) is substantially younger with a maximum age of 450 ± 110 ka and an inferred minimum age of 430 ± 50 ka. Furthermore, significantly younger T2 terrace deposits are present at similar low elevations as BBC-1 and BBC-2. Our results demonstrate the presence of Early and Middle Pleistocene, and potentially even late Middle to Late Pleistocene fossiliferous sediments within the historical excavation area, suggesting that Dubois excavated fossils from at least three highly fossiliferous units with different ages. Moreover, evidence for reworking suggests that material found in the fossil-rich strata may originate from older deposits, introducing an additional source of temporal heterogeneity in the Trinil fossil assemblage. This challenges the current assumption that the Trinil H.K. fauna –which includes Homo erectus-is a homogeneous biostratigraphic unit. Furthermore, this scenario might explain why the Trinil skullcap collected by Dubois is tentatively grouped with Homo erectus fossils from Early Pleistocene sediments at Sangiran, while Trinil Femur I shares affinities with hominin fossils of Late Pleistocene age.

Deciphering the role of late Quaternary sea level fluctuations in controlling the sedimentation in the Brahmaputra Plains

Continent-continent collision between Eurasian and the Indian plate during the Cenozoic period lead to the formation of the Himalayan Mountain chain and the development of the Indus-Ganga-Brahmaputra foreland basin to the south. Complex climate-tectonic interactions in this orogenic belt are responsible for the rapid erosion and filling of the Indus-Ganga-Brahmaputra foreland basin with the eroded materials. This study based on geomorphic mapping, lithofacies analysis, and geochemical (Strontium-Neodymium i.e., SrNd analysis) provenance characterization, as well as optically stimulated luminescence (OSL) ages, provides a dated sedimentation framework for the western Assam lowland areas. The dated relict fan surface lies ~40 m above mean sea level (msl), is incised and forms a regional valley terrace T1 composed of meandering channel deposits. Modern braided rivers flow on the T0 surface. The findings suggest that the alluvial fan is composed of three distinct lithofacies associations and aggraded during 27 to 3 ka. The bottom-most gravelly-sandy facies indicates progradation of the fan during the last glacial maximum (LGM), owing to the increased gradient of the Himalaya bound rivers. The middle facies is a sheet flood deposit which formed during the Latest Pleostocene-early Holocene period with rising sea level and increasing precipitation. During the Mid-Late Holocene, the uppermost facies is deposited as rivers lost their gradient in response to high sea level stand, resulting in inland sedimentation within muddy meandering channels. Our analysis found that falling sea level during the late Holocene was associated with greater precipitation and allowed the river to incise, to form gullies over the fan surface and form the valley terrace T1. The SrNd isotope fingerprints have been used to identify varying fan sediment sources in the Himalaya's southern front (i.e., Lesser and Higher Himalaya) as a function of changing monsoon conditions.

Revision of TD1 and TD2 stratigraphic sequence of Gran Dolina cave (Sierra de Atapuerca, Spain)

Gran Dolina is a cavity infilled by at least 25 m of Pleistocene sediments divided into 12 lithostratigraphic units and 19 sedimentary facies. These sedimentary facies have been divided into allochthonous facies, defined as sediment inputs from the outside, and autochthonous facies, defined as sediments generated within the karst; but this division has been challenged in recent works. In this study, TD1 and TD2 units of Gran Dolina have been detailed studied and the use of autochthonous facies has been assessed. For that purpose, we have studied the stratigraphic excavation profile, combining field observation with laboratory sedimentary analysis (sieving, laser diffraction, and XRD) to characterize the texture and structure of the sediments. Based on these studies, a total of 8 sedimentary facies have been identified. Consequently, TD1 unit has been separated into two sub-units and 13 layers, while the TD2 unit has been divided into three sub-units. The facies associations indicate a succession of phreatic and vadose phases that would define together epiphreatic conditions inside the cave, related to the transition between Arlanzón valley terraces T3 and T4. Interior facies (and entrance facies for allochthonous facies) is proposed to define Gran Dolina's sediments since the facies analyses indicate transport by underground flows.

Evolution of fluvial landscapes since the late Pleistocene at the Wangchenggang site of the Ying River Basin, Central China: Implications for the development and change of prehistoric settlements

AbstractReconstructing the evolution of fluvial landscapes is vital to our understanding of how and why early settlements used or abandoned locations in dynamic alluvial settings, especially places such as China's Central Plains where alluvial landforms have dominated since at least the late Pleistocene era. The Wangchenggang (WCG) site on the upper reaches of the Ying River is considered to be the legendary capital of the Great Yu who, according to historical documents, heroically tamed the big floods and founded the first dynasty of Xia. However, evolution of the alluvial landscape of the Holocene Ying River and its influence on the long‐term settlement change at the WCG site remains unclear. We present a detailed reconstruction of long‐term landscape evolution and settlement change at the site, based on the results of our geoarchaeological investigation, and published paleoclimate and archaeobotanical data. The results show that the region experienced an episode of extensive alluvial accretion in the late Pleistocene. From the end of the late Pleistocene to the early Holocene, the Ying River began to incise the alluvial plain, leading to the formation of the oldest terrace (T3). The middle and late Holocene in the Ying River valleys saw two episodes of alluvial aggradation between 7.7–5.4 ka B.P. (before present) and 4.5–3.8 ka B.P., respectively. Each of these events was followed by an alluvial incision, resulting in the formation of new alluvial terraces. During the historical periods, the youngest terrace T1 was formed. These cyclic changes in the regional fluvial landscape profoundly impacted the location and expansion of prehistoric settlements. During the Peiligang period (9.0–7.0 ka B.P.), the early stages of alluvial aggregation resulted in wide and shallow channels along the rivers. Early humans who relied on gathering and hunting for food chose to establish small settlements along such riverine environments. As alluvial aggradation continued in the Yangshao period (7.0–5.0 ka B.P.), they moved to a higher place, away from the rivers in the southwest, and flourished on high alluvial grounds. When a secondary terrace formed after the Longshan period (5.0–4.0 ka B.P.), people moved eastward again to build an early city on the T2 terraces and T3 terraces of the Ying River. When the water levels rose toward the terrace surfaces, they began to build moats and practiced mixed millet–rice farming. During the Eastern Zhou Dynasty (770–4256 B.C.), when the river started to down cut on a large scale, humans responded by building settlements on the lower and flat plains in the east.

Luminescence chronology of the Sankosh river terraces in the Assam- Bhutan foothills of the Himalayas: Implications to climate and tectonics

Himalaya is an active fold and thrust belt formed due to continent-continent collision between the Eurasian and Indian plates. It comprises a 3000 km long chain of mountains that span ∼1000 km across, with major boundary thrusts viz., Main Central Thrust (MCT), Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). MFT is marked as mountain front and is the most active thrust; however, evidence of tectonic activity along MCT and MBT also exists. Tectonic activity along MFT created uplifted terraces which now serve as geomorphic archives of past tectonic events. The present study focussed on a glacial-fed river Sankosh that originates in northern Bhutan, and crosses MCT, MBT and MFT before joining the Brahmaputra River in Assam. Due to tectonic uplift, the river shows a deflection at MFT, incising and thus forming four levels of strath terraces. Luminescence chronology, geomorphic studies and analysis of satellite images suggest four levels of terraces T4 (highest level, 195 m asl), T3, T2 and T1 (lowest level, 120 m asl). The quartz was found insensitive for luminescence dating, and thus fading corrected Infra-Red Stimulated Luminescence (IRSL) ages on feldspar minerals were measured that provided ages of 143-77 ka (T4), 65-36 ka (T2) and 35-14 ka (T1), respectively. The T3 terrace was present only on the right bank of the river and could not be accessed. These ages accord with other studies at the Chalsa and Malbazar, North Bengal (west of the study area) and this regional disposition of similar ages suggest that these formed during glacial-interglacial periods. The strath terraces indicate a time-averaged tectonic uplift with a 0.5 mm/year rate over the past 150 ka.

Optical Dating of Quartz Grains From the Minjiang Fluvial Terraces in the Sonpan Area on the Eastern Margin of the Tibetan Plateau

The fluvial terraces along the banks of the Minjiang River are very important for understanding the tectonic activities of the eastern margin of the Tibetan Plateau and have been widely investigated. However, the reliability of the ages previously reported for the terraces needs further evaluation. In this study, the Minjiang River terraces in the Sonpan area from Hongqiaoguan to the Songpan town were investigated and dated using optically stimulated luminescence (OSL) techniques on quartz grains. Seven strath terraces (T1–T7) were recognized based on the exposures of fluvial sediment and the elevation of bedrock strath, and two of them have been reported by previous studies. The terrace deposits and overlying loess were sampled for OSL dating. The samples exhibited a large scatter in De, even for loess samples, which could be attributed to poor bleaching at deposition. However, the OSL ages obtained using the minimum age model were underestimated, and those obtained using the central age model are considered relatively reliable based on stratigraphic and geomorphological consistency and the comparison of the ages between stratigraphically parallel samples. The results show that the loess samples overlying fluvial terrace sediments were deposited later than terrace formation and their OSL ages cannot represent the terrace formation ages. The T1, T3, T4, T5, and T6 terraces were dated to 13.5 ± 0.6, 29.0 ± 1.7, 48.0 ± 3.3, 44.3 ± 5.2 and 63.8 ± 4.7 ka, respectively. The T4 and T5 terraces may be the same terrace with a weighted mean age of 46.9 ± 2.8 ka. The ages of the T2 and T7 terraces were inferred to be ∼20 and ∼80 ka, respectively, based on the relationship between strath ages and elevations of the other terraces. The mean bedrock river incision rates were calculated to be 1.2 ± 0.1 mm/a for the time period of 64 ka for the T6 terrace—14 ka for the T1 terrace, and 0.15 mm/a for the past 14 ka.

Remotely sensed time series of rapid terrace formation: Laguna del Viedma valley (Patagonia)

The Patagonian Andes were affected by a range of geophysical drivers of landscape incision during the Last Glacial Interglacial Transition and Early Holocene. Deciphering drivers of river system response during this period is complex, and magnitudes and timescales of landscape change are poorly constrained. Herein, a remotely sensed time series of modern terrace formation is investigated from the Laguna del Viedma valley as a modern analogue of Late Quaternary landscape evolution in Patagonia. The aim of the research was to constrain the timing of terrace formation following lake level fall of the Laguna del Viedma over a 35 year period from 1985-2019. The objectives were to: 1) use satellite imagery from 1985-2019 to document glacier and lake changes in the study area; 2) map landforms of the Laguna del Viedma valley; and 3) analyse terrace elevations. In total seven terrace surfaces were distinguished, with the oldest four pre-dating the ALOS PALSAR DEM (February 2000) used. Landform evidence shows the highest, and vegetated, T1 terrace surface (+40-75 m) grades to the highest lake level and was likely the elevation of the valley floor during Holocene neoglacials. Viedma glacier recession then led to a phase of lake regressions/transgressions with an overall trend of lake level fall. The DEM shows ~20 m incision from the 1985 floodplain level (T3) to the T4 level floodplain by 2000. This constrains a minimum rate of incision of 1.33 m/yr, however, the satellite time series demonstrates rapid T3 terrace formation, with evidence for mass movements contributing to lateral terrace erosion by 1986. The implications of the data are discussed within the context of the Late Quaternary palaeohydrology of Patagonia where lake level falls of 10s to 100s of metres occurred within many large river systems of the Patagonian Andes from 42-52⁰ S. The data herein demonstrate that base level falls from sudden lake drainage events were likely a major driver of rapid landscape change in Patagonia during deglaciation.

10Be dating of the Kuitun River terraces in the northern Chinese Tian Shan foreland: Insights into fluvial evolution and tectonic shortening pattern

Characterizing active deformation of a piedmont structure is particularly helpful for understanding the dynamics of deformation of its adjacent active orogenic belt. This work focuses on fluvial geomorphology of the Kuitun River, which flows northwards out of the high mountains and perpendicularly cuts the E-W-striking Dushanzi anticline, a structure of the outermost fold-and-thrust belt in the northern Chinese Tian Shan foreland. Four episodes of alluvial fan development (fans F1–F4, sequentially younger in abandonment age) were identified. Based on the fluvial geomorphological framework constructed by these four alluvial fans, six terraces (terraces T1–T6, sequentially increasing height above the riverbed) were then defined. The topographic analyses and 10Be dating of these alluvial landforms show that the Kuitun River originally flowed northwestwards before at least 80 ka. Subsequent rock uplift caused by fold growth could have resulted in an eastward deflection, after which the river began to flow northeastwards to construct fan F2. At ~67 ka, accumulation of fan F2 ended, and the Kuitun River deflected westwards to flow northwards and began to construct fan F3. The final stabilization of the Kuitun River channel occurred at ~13 ka due to intense river incision forced by climate change, when the river began to incise a 200-m deep canyon and form a flight of strath terraces flanking the valley. By using geomorphic surfaces as the references, the Late Pleistocene and Holocene shortening rates of the Dushanzi anticline were estimated to be 0.71 + 0.17/−0.16 mm/yr (over the past ~67 kyr) and 1.6 + 0.39/−0.37 mm/yr (over the past 13 kyr), respectively. When combined with the long-term shortening rate of ~0.44 mm/yr since initiation of fold growth, it is inferred that the Dushanzi anticline likely experienced an acceleration of deformation during the late Quaternary. With respect to the entire orogenic belt, both fluvial geomorphic records and GPS surveys indicate that most of N-S crustal shortening (likely >70%) across the Tian Shan has been absorbed in the piedmonts of the range, a typical active orogenic belt in the interior of Asia.

Luminescence dating of a megaflood event on a terrace of the Jinsha River, China

The numerical dating of megaflood sediments is a worldwide challenge, a fact that has impeded a full understanding of Late Quaternary dam-outburst flood processes that occurred along the river courses of the Tibetan Plateau. Optically stimulated luminescence (OSL) dating has been widely used on such sediments. Due to their short transportation distances prior to deposition, the OSL signals of megaflood sediments are often partially bleached, resulting in age overestimations. Here, we report on a comparison of OSL ages obtained using both quartz (4–11 μm FG; 90–125, 180–250 μm CG) and K-feldspar (180–250 μm CG) extracted from sediments taken from the Binghong-Bingnong Neolithic-Bronze Age site on the second Jinshan River terrace (T2), in Yunnan Province, southwestern China. Contrary to previous experience suggesting that CG fractions are usually better bleached than FG fractions prior to deposition, our results showed that the OSL ages for the FG quartz fraction were generally younger than those for the CG fraction. This would suggest that the two fractions may have come from different sources, and may have been subject to different geomorphological processes prior to deposition. FG quartz fractions may be suitable to define the maximum age of sediments located in alpine gorge regions. CG quartz fractions can be used by applying the minimum age model (MAM) to select relatively well-bleached grains yielded ages close to the ‘true’ burial ages of the sediments. The results showed that the post-IR IRSL225 ages of single grain K-feldspar were overestimated by > 3 ka, suggesting K-feldspar may not be suitable dating material for megaflood sediments <30 ka. The OSL dates suggest that the T2 terrace was formed ∼8.4 ka, that aeolian sediments were deposited during ∼2.6–1.5 ka, and that the megaflood event occurred after ∼1.5 ka.

Significance of fluvial landform evolution and river reorganization in settlement development over the past 50 ka: A case study of Baodun site on Chengdu Plain, SW China

The Baodun archaeological site, which is representative of Baodun Culture (4.5–3.6 cal. ka BP), is a well-known walled site covering large areas of the Chengdu Plain (CDP), which is located in the upper reaches of the Yangtze River. The CDP is a low-lying sedimentary basin that is one of the cradles of Chinese civilization and was formed by many rivers originating from the northeastern part of the Qinghai–Tibetan Plateau. Geological and hydrological characteristics have strongly influenced the development of ancient cultures on the CDP. However, their relationship has not been validated. Based on field investigations, ground surveys, microgeomorphological discrimination, grain-size measurements, tree species identification, and the analysis of fluvial deposits, including age dating, height measurement, and observations of gravel layers, we investigated the effects of geomorphology and river channel migration on the evolution of the Baodun site. The results showed that three grades of terraces developed at the Baodun site region during the past ~50 ka BP, which had important impacts on the regional evolution of geomorphology and river systems. The chronology constrains the ages of terraces T1, T2, and T3 to ~7, ~22, and ~48 ka, respectively; T2 and T3 were closely related to tectonic activity, whereas T1 was related to climate variation. Similar to the modern river system, ancient waterflow primarily originated from the northwest; however, it mixed with water from other directions in the past. We attribute the construction of the Baodun site to the persistently outcropped terraces and the attraction of more stable rivers, which provided space and resources for the Baodun people. The evolution of the river system influenced the safety of the Baodun site, and flooding was the main factor leading to its decline and abandonment. The stability of the terrace and sedimentary environments and the decreased precipitation were important factors influencing the large-scale habitation of archaeological sites on the CDP during the middle and late Holocene.

Geomorphological and sedimentary records of Late Quaternary activities of Qiaojia-Jinyang segment of Lianfeng fault zone, Southwest China

Lianfeng fault zone (LFZ) in Southwest China has great significance for understanding the seismogenic environment, but its nature and latest active age is still poor constrained up to now. The Qiaojia-Jinyang segment (QJS) of LFZ intersects with Jinsha River; so the well-developed river terraces provide a potential spatio-temporal constrains for recent faulting of QJS. Based on investigation of the terrace deposits along river, this paper makes a detailed logging and dating of the faulting and liquefaction of QJS. Combined previous data, the spatio-temporal sequence of the Late-Quaternary river terraces in the area was redetermined. It is considered that the river terraces T1 (lowest) and T2 at QJS (~ 10–20 m and 60–70 m, respectively, above the local river level) are roughly developed in the Middle Holocene and the Late Pleistocene, indicating that the valley along QJS was strongly undercut since the Late Pleistocene. Based on the analysis of the morphological characteristics, spatial distribution, material composition and intersecting relationship between the sand veins and the layers, the strong ground motions is preliminarily detected, which indicates the strong seismic activity of the during the Quaternary. Combined with the faulting characteristics and the dating data of strata within the profiles of terrace deposits, it is considered that the LFZ is active at least at QJS, and the latest active time is not earlier than the Early-Middle Holocene. These findings provide a clear geological evidences for the seismicity assessment at LFZ, and help to the understanding of regional tectonic environment and the prevention of earthquake disasters.

Incision and aggradation phases of the Amazon River in central-eastern Amazonia during the late Neogene and Quaternary

The development of the Amazon River as a transcontinental drainage has been narrated in terms of the sedimentary record in western Amazonia and in marine offshore areas. However, little is known about the landscape changes in central-eastern Amazonia, which is considered a former water divide prior to the establishment of the Amazon as a transcontinental drainage. In this study, we carried out geomorphological and sedimentary facies analyses of fluvial deposits associated with the Amazon River in central-eastern Amazonia. Additionally, extended range luminescence ages and sediment provenance data are used to help to improve the chronostratigraphic framework of the study area. Erosive scarps bound the Amazon River valley in the study area, where higher elevation upland terrains (locally called ‘terra firme’) are sustained by older and resistant bauxitic-lateritic paleosols that cap the Cretaceous sandstone bedrock. Two abandoned fluvial terraces (T3 and T2), representing lower elevation terra firme, and the active floodplain (T1), collectively record the incision and aggradation phases of the Amazon River in a NE-SW oriented valley since the Late Miocene. The T3 is intensely dissected and has weathered deposits with surface elevations between 30 and 50 m above sea level (a.s.l.). These deposits are composed of gravel with boulders, coarse sand, and locally grey mud rich in organic matter. Quartz thermally-transferred optically stimulated luminescence (TT-OSL) dating allows us to determine the oldest Quaternary ages reported for fluvial terraces associated with the Amazon River. Depositional ages for the T3 deposits range from 944 ka to 2.3 Ma. The T2 deposits form a flat area with surface elevations between 25 and 30 m a.s.l. These deposits comprise fine to medium sand interbedded with mud and locally coarse sand and mud alternations forming inclined heterolithic stratification. Feldspar post-infrared infrared (pIRIR290) luminescence ages indicate an incision and aggradation phase leading to deposition of the T2 from 557 to 140 ka. The T1 represents the active floodplain with a surface elevation lower than 25 m a.s.l. These deposits are composed of moderately to well-sorted silty fine sand and greyish mud. OSL sensitivity measurements suggest that deposits from all terraces are formed by a mixture of Andean and shield-cratonic sediments, which are similar to the sediments transported by the modern Amazon River. The fractures in the Paleozoic to Cretaceous bedrock that comprises the higher elevation terrain incised by the Amazon River in central-eastern Amazonia lead to differential fluvial erosion, shaping the current NE-SW and NW-SE valley orientation. The T3 and T2 terraces record the progressive incision of the Amazon River valley since the Late Miocene, leading to poor preservation of fluvial deposits in comparison with western Amazonia. Here in central-eastern Amazonia, fluvial activity has been locked into a narrow fluvial valley in comparison with a wide area in western Amazonia. The stratigraphic scenario with a limited accommodation space favoured the recycling of terraces within the Amazon River valley. The restricted distribution of deposits associated with the Amazon River in central-eastern Amazonia is attributed to the uplift behaviour and high erosional resistance of the Paleozoic and Mesozoic bedrock forming a high elevation plateau. During the Pleistocene, the T3, T2 and T1 deposits record at least three main phases of incision, which promoted the abandonment of floodplains and formation of new lowland terra firme areas.