A single Dras‐Kohistan‐Ladakh arc revealed by volcaniclastic records

Tectonic interpretations of arc remnants in the Himalayan orogen remain uncertain, despite their important implications for the overall convergence history between India and Eurasia. Provenance results from deep‐water volcaniclastic rocks of the Indus Suture Zone in Ladakh provide new constraints on the Mesozoic tectonic evolution of the Dras and Kohistan‐Ladakh arcs. Detrital zircon (DZ) U‐Pb ages and whole‐rock geochemistry of the fault‐bounded Upper Cretaceous Nindam and Paleocene Jurutze formations present age patterns and compositions that are consistent with those of the Dras and Kohistan‐Ladakh arcs, respectively. The combination of DZs of the Nindam and Jurutze formations with the igneous zircons of the Dras and Kohistan‐Ladakh arcs shows similar age distributions that support a Late Jurassic to Paleocene tectonic connection between all these units. We argue that the secular trends in geochemical composition of DZs and volcaniclastic material are consistent with the magmatic evolution of one convergent margin, which shifted from a primitive to a mature stage during the Late Cretaceous. The recognition of a single Dras‐Kohistan‐Ladakh arc sets the stage for reevaluating competing scenarios of the Mesozoic evolution of the India–Eurasia convergent system. We find that the most likely scenario is that of a Jurassic arc formed above a south‐dipping intraoceanic subduction zone and accreted to Eurasia during the Early Cretaceous, after which it evolved above a north‐dipping subduction zone

Editorial: Tibetan Plateau uplift and environmental impacts: new progress and perspectives

No abstract available

Controls on Erosion in the Western Tarin Basin: Implications for the Uplift of Northwest Tibet and the Parmir

We present here bulk sediment major element chemistry, Nd and Sr isotope ratios, and detrital apatite fission-track (AFT) and U-Pb zircon ages to characterize the provenance of the southwestern Taklimakan Desert (northwest China) and the three major rivers draining this region. We establish the spatial and temporal controls on erosion and sediment transport in the modern Tibetan rain shadow. The Hotan River drains the North Kunlun block and is characterized by zircon populations at 160–230 Ma and 370–520 Ma. The Yarkand River shares these grains with the Hotan, but also has a very prominent zircon population at 40–160 Ma, which is common in Karakoram basement, indicating heavy sediment flux from these ranges to that drainage. This implies a strong control on erosion by topographic steepness and precipitation mediated through glaciation. Our zircon data confirm earlier studies that indicated that the Taklimakan sand is derived from both the Kunlun and Pamir Mountains. AFT ages are younger in the Hotan River than in the Kashgar River, which drains the Pamir, and in both are younger than in the Transhimalaya and parts of the western edge of the Tibetan Plateau. Exhumation is estimated at ∼1000 m/m.y. in the North Kunlun and ∼500 m/m.y. in the eastern Pamir, which have been exhuming more slowly than the western ranges in the recent past. Holocene aggradation terracing was dated using quartz optically stimulated luminescence methods and is mostly associated with times of fluctuating climate after 4 ka, with phases of valley filling dated at 2.6, 1.4, and 0.4 ka. The heights and volumes of the terraces show that sediment storage in the mountains is not a significant buffer to sediment transport, in contrast to the more monsoonal Indus system directly to the south. South of the Mazatag Ridge a significant eolian deposit accumulated ∼500 yr ago, but this has been deflated in more recent times. Comparison of the modern river data with those previously measured from Cenozoic foreland sedimentary rocks shows that no sediment similar to that of the modern Yarkand River is seen in the geologic record, which is inferred to be younger than 11 Ma, and probably much less. Uplift of the North Kunlun had started by ca. 17 Ma, somewhat after that of the Pamir and Songpan Garze of northwestern Tibet, dated to before 24 Ma. Sediment from the Kunlun reached the foreland basin between 14 and 11 Ma. North Kunlun exhumation accelerated before 3.7 Ma, likely linked to faster rock uplift

Shaping landscapes and industry: linking historic watermill locations to bedrock river knickpoints

Watermills have been an essential source of mechanical power for over two millennia. Their careful siting often took into account local hydrology, topography, and economic demand, attesting to the important place they held in premodern and early modern societies. This paper highlights the significance of Paul Bishop's work on mills over the last 20 years, which revealed that numerous historical watermills along Scottish rivers were closely located near overly steep stretches of river to maximize waterpower and minimize cost. Termed ‘knickpoints’, many of these steep erosional features formed thousands of years ago during and after melting of the British–Irish Ice Sheet. Post-glacial isostatic rebound caused rivers to erode into bedrock at rates set by river catchment size and sediment availability. Although bedrock knickpoints along the Scottish coast are relatively stable over human timescales (<103 years), knickpoints generated by milling in England have been invoked as potential hazards due to their potential to migrate over similar timescales. Bishop's observations on the colocation of knickpoints and watermills encouraged a more comprehensive investigation of the relationship between natural and human systems over the last 250 years and invited re-evaluation of prevailing narratives for the history of water technology and patterns of water-powered industrialization in Britain

Eccentricity-paced monsoon variability on the northeastern Tibetan Plateau in the Late Oligocene high CO 2 world

Constraining monsoon variability and dynamics in the warm unipolar icehouse world of the Late Oligocene can provide important clues to future climate responses to global warming. Here, we present a ~4-thousand year (ka) resolution rubidium-to-strontium ratio and magnetic susceptibility records between 28.1 and 24.1 million years ago from a distal alluvial sedimentary sequence in the Lanzhou Basin (China) on the northeastern Tibetan Plateau margin. These Asian monsoon precipitation records exhibit prominent short (~110-ka) and long (405-ka) eccentricity cycles throughout the Late Oligocene, with a weak expression of obliquity (41-ka) and precession (19-ka and 23-ka) cycles. We conclude that a combination of eccentricity-modulated low-latitude summer insolation and glacial-interglacial Antarctic Ice Sheet fluctuations drove the eccentricity-paced precipitation variability on the northeastern Tibetan Plateau in the Late Oligocene high CO2 world by governing regional temperatures, water vapor loading in the western Pacific and Indian Oceans, and the Asian monsoon intensity and displacement

Quantifying episodic erosion and transient storage on the western margin of the Tibetan Plateau, upper Indus River

Transient storage and erosion of valley-fills, or sediment buffering, is a fundamental but poorly quantified process that may significantly bias fluvial sediment budgets and marine archives used for paleoclimatic and tectonic reconstructions. Prolific sediment buffering is now recognized to occur within the mountainous upper Indus River and is quantified here for the first time using OSL dating, petrography, detrital zircon U-Pb geochronology, and morphometric analysis to define the timing, provenance, and volumes of prominent valley-fills. This study finds that climatically-modulated sediment buffering occurs over 103–104 yr timescales and results in biases in sediment compositions and volumes. Increased sediment storage coincides with strong phases of Summer Monsoon and Winter Westerlies precipitation over the Late Pleistocene (32–25 ka) and mid-Holocene (~8–6 ka), followed by incision and erosion with monsoon weakening. Glacial erosion and periglacial frost-cracking drive sediment production and monsoonal precipitation mediates sediment evacuation, in contrast to the arid Transhimalaya and monsoonal frontal Himalaya. Plateau interior basins, although volumetrically large, lack transport capacity and are consequently isolated from the modern Indus River drainage. Marginal plateau basins that both efficiently produce and evacuate sediment may regulate the overall compositions and volumes of exported sediment from the Himalayan rain shadow

Orbital- and millennial-scale Asian winter monsoon variability across the Pliocene–Pleistocene glacial intensification

Intensification of northern hemisphere glaciation (iNHG), ~2.7 million years ago (Ma), led to establishment of the Pleistocene to present-day bipolar icehouse state. Here we document evolution of orbital- and millennial-scale Asian winter monsoon (AWM) variability across the iNHG using a palaeomagnetically dated centennial-resolution grain size record between 3.6 and 1.9 Ma from a previously undescribed loess-palaeosol/red clay section on the central Chinese Loess Plateau. We find that the late Pliocene–early Pleistocene AWM was characterized by combined 41-kyr and ~100-kyr cycles, in response to ice volume and atmospheric CO2 forcing. Northern hemisphere ice sheet expansion, which was accompanied by an atmospheric CO2 concentration decline, substantially increased glacial AWM intensity and its orbitally oscillating amplitudes across the iNHG. Superposed on orbital variability, we find that millennial AWM intensity fluctuations persisted during both the warmer (higher-CO2) late Pliocene and colder (lower-CO2) early Pleistocene, in response to both external astronomical forcing and internal climate dynamics

Northern hemisphere ice sheet expansion intensified Asian aridification and the winter monsoon across the mid-Pleistocene transition

The mid-Pleistocene transition 1.25 to 0.6 million years ago marked a major shift in global climate periodicity from 41,000 to around 100,000 years without a concomitant orbital forcing shift. Here, we investigate Asian climate dynamics associated with two extreme glacial loess coarsening events at the onset and middle of the mid-Pleistocene transition by combining new and existing grain size and magnetic susceptibility records from the Chinese Loess Plateau spanning the last 1.6 million years with general circulation model simulations. We find that the two extreme glacial events reflect exceptionally enhanced Asian aridification and winter monsoon activity. They coincided with notable Northern Hemisphere glacial ice sheet expansion at 1.25 and 0.9 million years ago when the 100,000-year periodicity initiated and intensified, respectively. Our results indicate that these anomalously dry and windy Asian glacials were probably driven by an amplified terrestrial climate response to the coincident Northern Hemisphere ice sheet expansion

Monsoon controls on sediment generation and transport: Mass budget and provenance constraints from the Indus River catchment, delta and submarine fan over tectonic and multimillennial timescales

How well do deep-sea sedimentary archives track erosion in upland sources, driven by climatic change or tectonic forcing? Located on the western edge of South Asian monsoon influence, the Indus River system is particularly sensitive to variations in monsoon rainfall and thus provides a unique opportunity to estimate the nature of sedimentary signal propagation (i.e., recognizable pulses of sediment) through a large river basin under different climatic conditions. In this review we examine the impact that changing monsoon rainfall has had on NW Himalayan landscapes and its foreland since the middle Miocene. Rates of erosion are linked to summer monsoon rains over tectonic timescales but patterns of erosion are more explicitly linked to tectonically-driven rock uplift. Positive feedback between rock uplift and orographic precipitation drives increased erosion and transport from the Lesser Himalaya since the Miocene. After 2 Ma, erosion increasingly shifts to the Inner Lesser Himalaya. As defined multiproxy evidence, strong monsoon rainfall intervals broadly result in increased erosion and faster sediment transport together with increased chemical weathering, although the latter is further linked with global temperature and to the magnitude of sediment recycling within the routing system. We estimate that during the Holocene, most sediment (67–89% of the total ~6000 km3 or 16.3 x 1012 t) delivered to the ocean was sourced either from direct bedrock erosion through channel incision linked to higher discharge or from remobilized, recycled glacial sediment initially deposited during the Last Glacial Maximum (LGM). Post-LGM sediment is primarily stored within the delta plain and shelf clinoform systems. Over the last 14 kyr, average mass delivery rates (936–1404 Mt/y) are much higher than pre-damming estimates (pre-1940s; 250–300 Mt/y). To reconcile observations with pre-damming estimates, high sediment supply rates, probably during strong monsoon intervals over the early Holocene, are required. Long-term rates were high (182-273 Mt/y) during a middle Miocene strong monsoon interval. Quaternary Indus submarine fan sedimentation is limited to sea-level lowstands, at which times shelf and delta sediment is eroded and reworked into deep water. As a result, and for at least the past 2–3 m.y., most sediment delivered to the Indus submarine fan was initially eroded from bedrock during strong summer monsoon intervals but deposited into the fan under weak monsoon intervals. During the most recent sea level lowstand, only ~24% of sediment deposited in the fan was derived from synchronous onshore bedrock erosion, with the remaining accounted for by recycled terrace, floodplain, and shelf clinoform system sediment. Variations in monsoon intensity over the last glacial cycle strongly impact the locus of onshore erosion, with increased relative Himalayan bedrock erosion during times of strong, wet monsoon intervals and increased Karakoram bedrock erosion during drier glacial intervals