Search

The evolution of arc‐continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc‐continent collision, we studied the biostratigraphy and provenance of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas‐Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc‐continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward. Plain Language Summary: The Palawan microcontinental block is a continental fragment separated from the South China margin along with the seafloor spreading of the South China Sea (SCS). It finally collided with the Cagayan Ridge volcanic arc because of southward subduction of the Proto‐SCS. Therefore, precisely constraining the evolution of arc‐continent collision could help us to understand its association with the ending of the SCS spreading. To constrain the evolution of arc‐continent collision, we determined the depositional age and source of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Our results shows that the Isugod Basin sediments were deposited during the Late Miocene (11.5–5.6 Ma) following local gravitational collapse of the Palawan orogenic wedge driven by uplift and oversteepening. Isugod Basin sediments were eroded from both the orogenic wedge and obducted forearc ophiolite that were uplifted and exposed subaerially, indicating collision began before ∼11.5 Ma. As the onset of collision could be constrained to ∼18 Ma, we propose a significant uplift pulse in the hinterland of the wedge began at 13.4–11.5 Ma in the late stage of collision. This further indicates that arc‐continent collision in Palawan did not stop although compression derived from spreading of the SCS had ceased at 16–15 Ma. Key Points: Sediments in the Isugod Basin were deposited at 11.5–5.6 Ma following local gravitational collapse of the Palawan wedge driven by upliftThe Isugod Basin sediments were supplied by erosion of the Palawan wedge and obducted forearc ophiolite exposed subaerially since ∼11.5 MaOnset of Palawan arc‐continent collision at ∼18 Ma followed by a significant uplift pulse in the Palawan wedge beginning within 13.4–11.5 Ma [ABSTRACT FROM AUTHOR]

Airborne mineral dust is sensitive to climatic changes, but its response to orbital forcing is still not fully understood. Here, we present a reconstruction of dust input to the Subarctic Pacific Ocean covering the past 190 kyr. The dust composition record is indicative of source moisture conditions, which were dominated by precessional variations. In contrast, the dust flux record is dominated by obliquity variations and displays an out‐of‐phase relationship with a dust record from the mid‐latitude North Pacific Ocean. Climate model simulations suggest precession likely drove changes in the aridity and extent of dust source regions. Additionally, the obliquity variations in dust flux can be explained by meridional shifts in the North Pacific westerly jet, driven by changes in the meridional atmospheric temperature gradient. Overall, our findings suggest that North Pacific dust input was primarily modulated by orbital‐controlled source aridity and the strength and position of the westerly winds. Plain Language Summary: Glacial‐interglacial climate variations can affect dust transport to the ocean, but the controls on past dust fluxes to the North Pacific Ocean remain poorly constrained. This region is important because fertilization of phytoplankton growth by dust‐borne iron may have contributed to lower glacial atmospheric CO2, and dust records could also constrain the past dynamics of the North Pacific westerly winds. Here, we highlight the dominance of obliquity cycles in modulating latitudinal shifts of the westerly winds and, in turn, dust inputs. In contrast, precession regulates the aridity of the dust source regions, which determines both dust emission rates and composition. Such orbital‐scale fluctuations in the dust flux could influence ocean‐atmosphere interactions in the middle and high northern latitudes, with implications for global atmospheric circulation and ocean carbon storage. Key Points: Moisture availability in Asian dust source regions to the North Pacific Ocean were controlled by precessionNorth Pacific dust flux reveals dominant obliquity variations, but is out‐of‐phase at different latitudesThe westerlies in the Northern Hemisphere were primarily modulated by obliquity cycles in the late Pleistocene [ABSTRACT FROM AUTHOR]

Tectonic subsidence on rifted, passive continental margins are largely controlled by patterns of extension and the nature of strain partitioning in the lithosphere. The Sunda Shelf, adjacent to the SW South China Sea, is characterized by deep basins linked to regional Cenozoic extension associated with propagating seafloor spreading caused by slab pull from the south. Analysis of seismic reflection profiles and drilled sections crossing the Nam Con Son and Cuu Long basins highlight Oligocene extension, with most of the thinning concentrated in the ductile mid-lower crust. Upper crustal extension was modest and ductile flow is inferred to be directed northwestwards, towards the oceanic crust. Basin inversion occurred in the Mid Miocene, associated with the collision of the Dangerous Grounds Block and Borneo. Subsequent accelerated tectonic subsidence exceeded predictions from uniform extension models assumed to relate to extensional collapse after inversion. We correlate this to a period of faster erosion onshore driven by strong monsoon rains in Indochina and Peninsular Thailand at that time. Erosion of the onshore basement, inducing rock uplift and coupled with loading of the basins offshore, drives ductile mid-lower crustal flow, likely to the northeast under Indochina, and/or to the west where Plio-Pleistocene subsidence of the shelf is very slow. Significant sediment delivery from the Mekong River into the Cuu Long Basin began in the Late Miocene and migrated seawards as the basin filled. Mass balancing suggests that the basins of this part of the Sunda Shelf are filled through erosion of bedrock sources around the Gulf of Thailand. There is no need for sediment delivery from a major river draining the Tibetan Plateau to account for the deposited volumes. [ABSTRACT FROM AUTHOR]

Sedimentary deposits from the northern South China Sea (SCS) can provide important constraints on past changes in ocean currents and the East Asian summer monsoon (EASM) in this region. However, the interpretation of such records spanning the last deglaciation is complicated because sea‐level change may also have influenced the depositional processes and patterns. Here, we present new records of grain size, clay mineralogy, and magnetic mineralogy spanning the past 24 kyr from both shallow and deep‐water sediment cores in the northern SCS. Our multi‐proxy comparison among multiple cores helps constrain the influence of sea‐level change, providing confidence in interpreting the regional climate‐forced signals. After accounting for the influence of sea‐level change, we find that these multi‐proxy records reflect a combination of changes in (a) the strength of the North Pacific Intermediate Water inflow, (b) the EASM strength, and (c) the Kuroshio Current extent. Overall, this study provides new insights into the roles of varying terrestrial weathering and oceanographic processes in controlling the depositional record on the northern SCS margin in response to climate and sea‐level fluctuations. Plain Language Summary: Sediments in the South China Sea (SCS) provide important records of past changes in the ocean circulation and atmospheric patterns in the Pacific Ocean. However, the interpretation of sedimentary archives from this region in terms of changes in the ocean currents or the climate‐driven sediment supply can be challenging because of the potential influence of global sea‐level fluctuations. In order to better constrain these multiple controls on the sedimentary regime of the northern SCS, we present new mineralogical records from sediment cores collected from both shallow‐ and deep‐water sites. After assessing the effects of sea‐level change, we find that the clay mineral assemblage in shallow sites from the northern SCS can generally be used to reconstruct the evolution of the East Asian summer monsoon. In deep‐water sites, the clay mineralogy instead reflects changes in the relative abundance of sediment supplied from Taiwan compared to Luzon, revealing an enhanced inflow of the Kuroshio Current during the mid‐late Holocene. Furthermore, millennial‐scale variability in the North Pacific Intermediate Water inflow can be traced using changes in magnetic mineralogy and the inflow appears to have been stronger at the end of the last ice age. Key Points: Sedimentary records from shallow and deep‐water sites have differing sensitivities to changes in ocean currents and the East Asian monsoonClay mineralogy in shallow sites reflects sea‐level change, while deep‐water records respond to incursion of the Kuroshio CurrentMagnetic grain‐size indicates stronger deep currents during Heinrich Stadial 1, associated with the North Pacific Intermediate Water [ABSTRACT FROM AUTHOR]

Testing models that link climate and solid Earth tectonics in mountain belts requires independent erosional, structural and climatic histories. Two well‐preserved stratigraphic sections of the Himalayan foreland basin are exposed in NW India. The Jawalamukhi (13–5 Ma) and Joginder Nagar sections (21–13 Ma) are dated by magnetostratigraphy and span a period of significant climate change and tectonic evolution. We combine sediment geochemistry, detrital zircon U–Pb dating and apatite fission track analyses to reconstruct changes in the patterns of erosion and exhumation in this area from the Early Miocene to Pliocene. The provenance of the foreland sediments reflects a mixture of Tethyan and Greater Himalayan sources from 21 to 11 Ma, with influx from the Inner Lesser Himalaya starting after 11 Ma, and a strong increase in Crystalline Inner Lesser Himalayan erosion after 8 Ma. This distinct shift in provenance most likely reflects exhumation of the Kullu‐Rampur Window, as well as the northward motion of the Jawalamukhi section towards the Himalayas, drainage reorganization in the foreland, and/or tectonically driven drainage capture in the mountains. Prior to 10.5 Ma sediment came from a large river whose sources were Greater Himalaya and Haimanta dominated, likely a palaeo‐Sutlej, while after 8 Ma the source river was dominated by a more local drainage. Our work is consistent with Nd isotope and mica Ar‐Ar constraints from the same sections that demonstrate initial Inner Lesser Himalayan unroofing in this region from 11 Ma, earlier than the 2 Ma implied from the marine record and during a period of summer monsoon weakening when fission track data indicate very rapid cooling and erosion of the Lesser Himalaya sources from no later than 10 Ma. Tectonically driven rock uplift coupled with southerly migration of the maximum rainfall belt during a time of drying, may have focused erosion over the Lesser Himalayan Duplex and created the Kullu‐Rampur Window. [ABSTRACT FROM AUTHOR]

Despite the importance of the westerlies to the global climate system, we still know little about their long‐term evolution and possible orographic controls during the late Cenozoic because of the lack of sedimentary records with precise chronological control. Eolian deposition in the North Pacific preserved past information about the westerlies, the major wind system delivering Asian dust to the Pacific. A continuous, high‐resolution eolian flux record since 23 Ma was reconstructed from sediments at Deep Sea Drilling Project Site 296 in the North Pacific. Combined with dust flux at Ocean Drilling Program Site 1208, variations in their difference indicated a northwards shift of the westerlies during 23‒9 Ma and a relatively stable state since then. We suggest that Tibetan uplift since the early Miocene began to drive the poleward shift of the westerlies until 9 Ma, after which the westerlies remained relatively stable over Asia on million‐year timescales. Plain Language Summary: The Northern Hemisphere Westerly wind is a significant component of planetary‐scale atmospheric circulation and has a large impact on regional and global climate change. Although numerous modern observations and orbital time‐scale studies of the Westerly wind have been conducted, we still know little about its evolution on million‐year time‐scales, which may modulate the overall amplitude of short‐term variations. Eolian deposition in the North Pacific has preserved precious information about the westerlies in the past. A continuous and high resolution eolian flux record dating from 23 Ma was reconstructed from sediments at Deep Sea Drilling Project Site 296 in the Northwest Pacific. Combined with dust records at Ocean Drilling Program Site 1208 to the east, we constrain how the path and strength of the Northern Hemisphere Westerlies have changed since the early Miocene. The two eolian records indicate a northwards shift of the westerlies between 23 and 9 Ma and a relatively stable state since then. We suggest that stepwise uplift of the Tibetan Plateau since at least the early Miocene began to drive the northwards shift of the Northern Hemisphere Westerlies until about 9 Ma, after which the westerlies remained relatively stable over Asia‐North Pacific on million‐year timescales. Key Points: We reconstruct the eolian flux record in the North Pacific since 23 Ma at high resolutionThe Northern Hemisphere Westerlies shifted northward between 23 and 9 Ma and have remained relatively stable since thenTibetan uplift drove the northward shift of Northern Hemisphere Westerlies in the early late Miocene [ABSTRACT FROM AUTHOR]

Sediment transport through the Mississippi River affects the lives and economies of millions of people along its course, so that understanding the controls on this process is of scientific and societal importance. Detrital U‐Pb geochronology, supported by grain size and major element data, can be a robust tool for constraining sediment provenance in clastic sedimentary systems that has been applied to the Mississippi. However, sediment storage and reworking can complicate interpretation, and this can be further exacerbated by anthropogenic alteration via the construction of levees, dams, locks and river diversion projects. In this study, we date zircons from the modern Mississippi River and compare them to previously acquired data to illustrate the difference between samples taken from the same catchment in order to better understand the downstream propagation of the modern detrital zircon signal. The modern Mississippi River and tributary systems show distinct similarities and are comparable between studies when samples are not too far separated (<100 km). We estimate that the Arkansas River is more important than previously proposed, at least in terms of sand supply, supplying 7%–11% of the total load. The largest supplier of sediment to the Mississippi is the Missouri River (33%–43%), which derives much of its sediment from sedimentary rocks in the foredeep deposited during the Sevier and Laramide events. Anthropogenic alteration of the modern river system can be seen in the downstream propagation of a Red River cut‐off signal following construction of the "River Control Structure", implying slow zircon transport rates (<2.8 km/year). Differences in the degree of recycling caused by sampling locations and low numbers of grains introduce significant uncertainties to mixing calculations. [ABSTRACT FROM AUTHOR]

The Indus Fan, located in the Arabian Sea, contains the bulk of the sediment eroded from the Western Himalaya and Karakoram. Scientific drilling in the Laxmi Basin by the International Ocean Discovery Program recovered a discontinuous erosional record for the Indus River drainage dating back to at least 9.8 Ma, and with a single sample from 15.6 Ma. We dated detrital zircon grains by U‐Pb geochronology to reconstruct how erosion patterns changed through time. Long‐term increases in detrital zircon U‐Pb components of 750–1,200 and 1,500–2,300 Ma record increasing preferential erosion of the Himalaya relative to the Karakoram between 8.3–7.0 and 5.9–5.7 Ma. The average contribution of Karakoram‐derived sediment to the Indus Fan fell from 70% of the total at 8.3–7.0 Ma to 35% between 5.9 and 5.7 Ma. An increase in the contribution of 1,500–2,300 Ma zircons starting between 2.5 and 1.6 Ma indicates significant unroofing of the Inner Lesser Himalaya (ILH) by that time. The trend in zircon age spectra is consistent with bulk sediment Nd isotope data. The initial change in spatial erosion patterns at 7.0–5.9 Ma occurred during a time of drying climate in the foreland. The increase in ILH erosion postdated the onset of dry‐wet glacial‐interglacial cycles suggesting some role for climate control. However, erosion driven by rising topography in response to formation of the ILH thrust duplex, especially during the Pliocene, also played an important role, while the influence of the Nanga Parbat Massif to the total sediment flux was modest. Plain Language Summary: Mountain belts are constructed by tectonic forces from within the solid Earth modulated by surface processes. The Himalaya represents the type example of such interactions, where the growth of the mountains and the Asian monsoon interact. Sediments from the Arabian Sea allow the long‐term erosion patterns of the NW Himalaya to be reconstructed. We use the crystallization age of zircon sand grains in sediment dating back to 15.6 Ma to see how the erosion has changed in response to the evolving climate. There is a trend toward more erosion from the Himalaya and less from the Karakoram starting around 8.3–7.0 Ma, which was a time of transition toward a drier climate in the NW Himalaya. Furthermore, we see a sharp increase in erosion from the Inner Lesser Himalaya starting between 2.5 and 1.6 Ma. This was caused by the formation of a thrust duplex pushing up these ranges, which in turn focused orographic precipitation. The timing of this exposure is much younger than understood from studies of sedimentary rocks in the foreland basin onshore. Our study highlights the role that tectonics plays in controlling what parts of the mountain belt are subject to the fastest erosion. Key Points: Geochronologic analyses show increased relative erosion from the Himalaya compared to the Karakoram between 8.3–7.0 Ma and 5.9–5.7 MaChanging patterns of erosion correlate with climatic drying at ∼7.7–5.9 Ma and relate to solid Earth tectonic forces building topographyErosion from the Inner Lesser Himalaya increased between 2.5 and 1.6 Ma on a regional scale [ABSTRACT FROM AUTHOR]

Cenozoic surface uplift of Tibetan Plateau has driven the birth and reorganization of large river systems in Asia. The development of the Yangtze River, closely linked to plateau uplift, has important implications for the regional tectonic-geomorphology processes, but is still under debate. The key scientific question is whether the Upper Yangtze (upper Jinshajiang) once flowed southeast to the South China Sea. In this study, we carried out provenance analysis on Paleogene sedimentary rocks in the Jianchuan Basin, composed of the Baoxiangsi, Jinsichang, and Shuanghe formations. We compared them with similar deposits in other regional basins, as well as with potential sources. Heavy-mineral and geochemical data show that sediments from the Jinsichang formation are more mature compared with those from the Shuanghe and Baoxiangsi formations. The Jinsichang formation represents the products of a large fluvial system, whereas the Baoxiangsi formation is mainly dominated by local sources. The Shuanghe formation contains material from both distant sources and locally eroded materials. Detrital zircon U-Pb age patterns from the Jianchuan Basin are similar to those in sediments in the Gonjo, Simao, and Chuxiong basins, and show great similarity with the modern Jinshajiang River. Statistical analysis of the zircon ages suggests that the Songpan-Ganzi terrane was the primary source for all sediments, while the Yangtze Craton and northern Qiangtang terrane constitute secondary sources. Taken together these data confirm that a paleo-Jinshajiang flowed south toward to the South China Sea from the SE Tibetan Plateau in the late Eocene, constraining the age of formation of the First Bend. [ABSTRACT FROM AUTHOR]

Uplift and erosion of the Himalayas and Tibetan Plateau have resulted in the deposition of some of the largest sedimentary masses on Earth. Chemical weathering of these materials has been invoked as a primary driver of long‐term global cooling because weathering of silicate material consumes atmospheric CO2. We here combine geochemical data from scientific drill sites in the Arabian and South China Seas, together with sediment mass flux budgets, to estimate changes in chemical weathering fluxes for the Indus, Mekong, and Pearl river systems. The rate of CO2 consumption decreased by 50% between ∼16 and 5.3 Ma, especially in the Indus system, as onshore erosion slowed and provenance shifted away from mafic arc units in the suture zone. Falling chemical weathering fluxes during a period of global cooling refutes the idea that Himalaya–Tibetan Plateau uplift drove Neogene global cooling. Plain Language Summary: The cause of long‐term cooling of the Earth since ∼50 million years ago has been a source of controversy. It has been proposed that initiation of the uplift of the Himalayas and Tibetan Plateau caused faster erosion. Chemical weathering of this eroded material is thought to have driven a reduction in greenhouse gas CO2, allowing the planet to cool. In this study, we make the first regional budget of chemical weathering from this area and demonstrate that this mechanism was not effective enough to be the main control of the long‐term global climate. This implies that other mechanisms, such as organic carbon burial, or erosion in other locations, such as New Guinea, Indonesia, and the Philippines, were more important. Key Points: Sediment deposited by Pearl, Mekong, and Indus Rivers has become less altered since the middle MioceneTotal chemical weathering fluxes from these river basins decreased by 50% since 16 MaHimalaya‐Tibetan uplift and erosion is not driving global cooling since 16 Ma [ABSTRACT FROM AUTHOR]

The Himalayan and Tibetan highlands (mountains), with high rates of physical erosion, are extreme settings for earth surface processes, generating one of the largest recent terrigenous detritus and organic carbon discharges to the ocean. However, their significance with respect to the global carbon and climate cycles during the Quaternary is still unclear, especially in quantitative terms. Here, we present comprehensive records of continental erosion and weathering, terrestrial supply, marine productivity, and organic carbon burial in the distal Arabian Sea, Bay of Bengal, and southern South China Sea since ∼700 ka over orbital timescales. These records exhibit periodicities corresponding to sea level and Indian summer monsoon intensity changes. During glacial periods, the enhanced highland surface erosion and activation of deep‐sea channels significantly increased inputs of terrigenous detritus, nutrients, and organic carbon into the Arabian Sea and Bay of Bengal, whereas strengthened continental shelf surface weathering and organic matter preservation occurred in the South China Sea. Conclusively, our integrative proxies in the study area demonstrate, for the first time, pronounced glacial burial pulses of organic carbon (∼1.12 × 1012 mol/yr), dominantly originating from the highland surface erosion and marine productivity. Together with the increased silicate weathering on the exposed tropical continental shelves and in the tropical volcanic arcs, the enhanced burial flux of organic carbon in the tropical marginal seas, therefore, highlights the large contributions that tropical regions can make within the glacial‐interglacial carbon inventory of the ocean and atmosphere and thus cause significant negative feedback on the global climate. Plain Language Summary: Anthropogenic emissions of the greenhouse gas CO2 are significantly changing the global climate and environment, resulting in a warmer state for which there is no historical analog. Marine records hold valuable lessons for the future of our warming world, as marine sediments are an important reservoir of the global organic carbon and then modulate release of CO2 into the atmosphere. Currently, the major river systems originating from the Himalaya and Tibetan Plateau discharge ∼25% of the global fluvial sediment flux to the ocean, acting as an important source of continental organic carbon at tectonic and current timescales. Our integrative mineralogical‐geochemical study demonstrates the enhanced highland (mountain) erosion and activation of deep‐sea channels, increased supplies of the produced materials, strengthened marine productivity, and effective preservation of organic carbon in the deep Arabian Sea and Bay of Bengal during cold periods. In contrast, strengthened chemical decomposition of silicates on the exposed continental shelf was coeval with increased organic carbon storage in the deep South China Sea. The study area contributed ∼1/4 of the current global marine burial flux of organic carbon during sea‐level lowstands and thus represents a key precedent for understanding increasingly severe global warming. Key Points: A first integrative study of Quaternary inputs of Himalayan and Tibetan erosion and weathering products in distal marginal seas is presentedIncreased highland erosion and terrestrial organic matter burial in the deep Arabian Sea and Bay of Bengal occurred during glacial periodsEnhanced continental shelf weathering and terrigenous organic carbon flux in the abyssal South China Sea appeared during sea‐level lowstands [ABSTRACT FROM AUTHOR]

We test the hypothesis of a major Paleogene river draining the SE Tibetan Plateau and the central modern Yangtze Basin that then flowed south to the South China Sea. We test this model using U‐Pb dated detrital zircon grains preserved in Paleogene sedimentary rocks in northern Vietnam and SW China. We applied a series of statistical tests to compare the U‐Pb age spectra of the rocks in order to highlight differences and similarities between them and with potential source bedrocks. Monte Carlo mixing models imply that erosion was dominantly derived from the Indochina and Songpan‐Garzê Blocks and to a lesser extent the Yangtze Craton. Some of the zircon populations indicate local erosion and sedimentation, but others show close similarity both within northern Vietnam, as well as more widely in the Eocene Jianchuan, Paleocene‐Oligocene Simao, and Oligocene‐Miocene Yuanjiang basins of China. The presence of younger (<200 Ma) zircons from the Qamdo Block of Tibet is less easily explicable in terms of recycling by erosion of older sedimentary rocks and implies a regional drainage linking SE Tibet and the South China Sea in the Late Eocene‐Oligocene. Detrital zircons from offshore in the South China Sea showed initial local erosion, but with a connection to a river stretching to SE Tibet in the Late Oligocene. A change from regional to local sources in the Early Miocene in the Yuanjiang Basin indicates the timing of disruption of the old drainage driven by regional plateau uplift. Plain Language Summary: The unusual geometries of rivers in SW China and SE Tibet, especially the sharp bend in the Yangtze River, suggest that the modern rivers are the product of disruption of an older drainage that used to supply sediment from Tibet to the South China Sea in the Paleogene. In this work we measured the age of the zircon sand grains in sedimentary rocks stretching across the region but especially in newly redated sediments from northern Vietnam. The ages of these crystals are diagnostic of different source areas. We see similarities between these age patterns in SW China, as well as in similar aged rocks in Vietnam and extending into the offshore in the Late Oligocene. The zircon ages change radically before the Late Miocene (~10 Ma), implying that the rivers were close to their present state by that time. The regional similarities are supportive of the idea that a major river existed in this region prior to around 35 Ma. This was disrupted by the uplift of the Tibetan Plateau, which caused a retilting of Asia toward the east and the break‐up of the old drainage pattern, creating the modern Yangtze and Red Rivers. Key Points: A major river drained from Tibet to the South China Sea in the Eocene‐OligoceneThe old drainage was disrupted by uplift of Tibetan Plateau and motion on the Red River‐Ailao Shan FaultDrainage reorganization likely occurred in the Late Oligocene‐Early Miocene [ABSTRACT FROM AUTHOR]

We present a multiproxy record of Sr‐Nd isotopes and major and trace elements for clay‐sized (<2 μm) siliciclastic sediment fractions from the International Ocean Discovery Program Site U1456 in the eastern Arabian Sea to extract reliable chemical indicators not influenced by the grain‐size effect, quantitatively estimate detrital provenance, and constrain silicate weathering/erosion in response to the Indian summer monsoon over orbital timescales. A provenance analysis of fine‐grained siliciclastic sediments indicates a two end‐member mixture from the Indus River (20–90%) and rivers draining the Deccan Traps (10–80%). A prominent increase in terrigenous input from the Indus River occurred at ~0.5 Ma, probably resulting from an intensive erosional event in the Himalayan region. Moreover, αAlK at Site U1456, which is calculated as Al/K ratio of the study sample versus Al/K ratio of the upper continental crust, can be generally used to reflect the chemical weathering intensity in the source regions. During most interglacial and even certain glacial periods, the Indian summer monsoon reinforcement is closely coupled with enhanced continental chemical weathering and physical erosion. Wavelet and spectral analyses of the αAlK record display strong 125‐, 35‐, 29‐, and 23‐kyr periodicities since 1.2 Ma with significant ~100‐kyr cycles established at the end of the Mid‐Pleistocene Transition (~0.7 Ma), suggesting forcing mechanisms linked with both Northern and Southern Hemispheric processes. Significant fluctuations observed in silicate weathering/erosion during ~1.2–0.7 Ma indicate an enhancement of the Indian summer monsoon with increased variability in association with the Mid‐Pleistocene Transition. Key Points: Indus River and Deccan Traps supplied fine‐grained sediments to the eastern Arabian Sea since 1.2 MaThe Indian summer monsoon reinforcement can trigger strong chemical weathering and rapid continental erosion over orbital timescalesαAlK records indicate significant changes in the Indian summer monsoon in association with the Mid‐Pleistocene Transition [ABSTRACT FROM AUTHOR]

Systematic variation in elemental and Sr‐Nd isotopic compositions of the clay‐sized (<2 μm) siliciclastic fraction from the International Ocean Discovery Program (IODP) Site U1456 (Laxmi Basin) provides valuable insights into dynamic changes in continental weathering intensity in the western Himalayas and sediment inputs from the Indus River and Deccan Traps to the eastern Arabian Sea. Long‐term, high‐resolution proxy records from the sediment core reveal that the main sources (i.e., Indus River and Deccan Trap basalts) of the fine‐grained detrital sediments have significantly changed with Indian summer monsoon variation over the studied time interval. During two depositional periods (3.8–3.3 and 2.7–1.2 Ma) corresponding to a weak Indian summer monsoon, the Indus River contributed fine‐grained sediments with high K/Al, high 87Sr/86Sr, and low εNd to the study site. Between 3.3 and 2.7 Ma and between 1.2 and 0 Ma, deposition in the eastern Arabian Sea was governed by large inputs of Deccan Trap‐derived basaltic sediments, characterized by high Mg/Al and Fe/Al, low 87Sr/86Sr and chemical index of alteration values, and high εNd values, associated with a change to a stronger Indian summer monsoon driving stronger chemical weathering. Synchronous changes in the geochemical proxies since 3.8 Ma highlight that variations in the inputs of siliciclastic sediments and Indian summer monsoon development are closely coupled. Plain Language Summary: The Indian summer monsoon is an extremely important part of the Earth's climate system. Weathering and erosion of sediments are deeply affected by monsoon rainfall. Since 3.8 Ma, the geochemical records suggest that the clay‐sized siliciclastic fractions at Site U1456 were mainly derived from the Indus River when the Indian summer monsoon was generally weak. In contrast, the siliciclastic sediment supply from the Deccan Traps increased when the monsoon intensified. In particular, we propose that chemical weathering intensities can be tracked using K/Al ratios and chemical index alteration and the smectite/(illite + chlorite) in the fine fraction of marine sediments from the eastern Arabian Sea since 3.8 Ma. Conducting research in the region is of great importance for understanding past and present climatic conditions. Key Points: The silicate weathering intensity in the western Himalayan flood plains has primarily been controlled by the monsoon climate since 3.8 MaThe Indus River and Deccan Traps are the two dominant provenances for clay‐sized sediments in the eastern Arabian SeaSummer monsoon intensity has dominated the input from the Indus River and Deccan Traps to the eastern Arabian Sea [ABSTRACT FROM AUTHOR]

The East China Sea Shelf has an unusually wide and low gradient shelf, supplied from sediment‐charged rivers and large river delta systems, with bottom currents sweeping the sea floor and located in the path of strong typhoons. Sediment gravity flow deposits, including four hybrid event beds and a high density turbidite, are identified in a core from the mid‐shelf of the East China Sea. The hybrid event beds typically comprise three or two internal divisions from the base to the top: (i) H1, H3 and H5; or (ii) H3 and H5. Radiocarbon ages of the hybrid event beds were in the range of 3821 to 8526 yr bp. Based on correlation with surrounding cores, the hybrid events may have happened at any time between 1930 yr bp and 3890 yr bp. The δ13C values in hybrid event beds together with bathymetry data suggest local erosion on the shelf. The average δ13C value for the H1 division is similar to the H3 division in the hybrid event beds, implying that the organic matter in the H1 and H3 divisions may come from the same source area. Cross‐plots of upper continental crust normalized rare earth elements in the five units reveal that the sediment source of the four hybrid event beds and the turbidite was ultimately primarily from Korean rivers. Partial transformation from a moderate‐strength debris flow with the additional role of erosional bulking can explain occurrences of hybrid event beds on the East China Sea Shelf. The data indicate that hybrid sediment gravity flow deposits were sourced from intra‐shelf failures and subsequently transformed and deposited as hybrid event beds. The study shows that hybrid sediment gravity flows and turbidity currents may not necessarily indicate proximity to a major fluvial or deltaic system and that intra‐shelf sedimentation can be a sediment source. It is unlikely that the debris flows and turbidity currents were triggered by a hyperpycnal flow or tsunami, because both can carry continental and/or coastal signals which have not been recognized in the core. Typhoons are the probable triggering mechanism. [ABSTRACT FROM AUTHOR]

Use of deep‐water sediments in submarine fans to reconstruct changing erosion onshore is based on the premise of relatively simple transport between source and sink. However, debate continues regarding the degree of sediment buffering and recycling in the sediment transport process. In this study, we investigate the origin of sediment in the Indus Submarine Canyon since the Last Glacial Maximum (LGM; ~20 ka) using zircon U‐Pb dates. Zircon grains in the submarine canyon are resolvably different from those at the river mouth, at least before 6.6 ka, implying a disconnection between the river mouth and the canyon up to that time. Sand may be stored near the river mouth as sea level rose, while finer‐grained sediment was directly transferred into deeper water. Since 1 ka the upper canyon has shown big and rapid provenance changes, most notably a sharp increase in erosion from Nanga Parbat, whose influence is minor in the modern river. Such rapid changes imply a lack of buffering in the recent past. The modern river contrasts with sediments in the canyon in terms of its zircon U‐Pb age populations and may be influenced by significant anthropogenic impact on the terrestrial drainage basin, especially damming. [ABSTRACT FROM AUTHOR]

Point bars formed by meandering river systems are an important class of sedimentary deposit and are of significant economic interest as hydrocarbon reservoirs. Standard point‐bar models of how the internal sedimentology varies are based on the structure of small‐scale systems with little information about the largest complexes and how these might differ. Here a very large point bar (>25·0 m thick and 7·5 × 13·0 km across) on the Mississippi River (USA) was examined. The lithology and grain‐size characteristics at different parts of the point bar were determined by using a combination of coring and electrical conductivity logging. The data confirm that there is a general fining up‐section along most parts of the point bar, with a well‐defined transition from massive medium‐grained sands below about 9 to 11 m depth up into interbedded silts and fine–medium sand sediment (inclined heterolithic strata). There is also a poorly defined increase in sorting quality at the transition level. Massive medium sands are especially common in the region of the channel bend apex and regions upstream of that point. Downstream of the meander apex, there is much less evidence for fining up‐section. Finer sediment accumulated more readily after the establishment of a compound bar in the later stages of construction, at the terminal apex and in the bar tail. This work implies that the best reservoir sands are likely to be located in the centre of the point bar, deposited in a simple bar system. Reservoir quality decreases towards the bar edge. The early‐stage channel plug is largely composed of coarsening‐upward cycles of silt to clay and is dominated by clay and clayey silt material with poor reservoir characteristics. [ABSTRACT FROM AUTHOR]

The thick Silurian siliciclastic sedimentary rocks in the Qin‐Fang region contrasting with their absence in surrounding regions have long been an enigma for the early Paleozoic geology of South China. Here we employ detrital zircon U‐Pb geochronology and Lu‐Hf isotope analysis of Cambrian to Devonian samples from the Qin‐Fang and adjacent regions to trace sedimentary provenance and to further constrain its tectonic setting. The similar age spectra of the Cambrian samples from both sides of the Qin‐Fang region imply that they should be derived from a common source(s), arguing against the presence of a Cambrian ocean in the Qin‐Fang region. However, the U‐Pb age patterns of these Cambrian samples, as well as from Silurian and Ordovician sandstones both from within and outside the Qin‐Fang region, differ significantly from those of a middle Devonian sample from the Qin‐Fang region, and Ordovician to upper Triassic samples from the Indochina Block. These results, in conjunction with regional geological information, indicate that the Yunkai Mountain, which is located adjacent to the Qin‐Fang region, must have been emerged above sea level in the middle Devonian. Meanwhile, it can also imply that the Qin‐Fang region should be a part of South China rather than being a segment of the Indochina Block. A two‐stage evolutionary history of the Qin‐Fang region is proposed, (1) an intracontinental basin mainly filled by materials eroded from east Gondwana and/or eastern Cathaysia Block during the early Paleozoic and (2) a foreland basin in the Yunkai Mountain region at least since the middle Devonian. Plain Language Summary: Whether there was an ocean existed in the Qin‐Fang region, southern South China and what is its plate tectonic affiliation have long been an enigma for the early Paleozoic geology of South China. This study can tell us that the Qin‐Fang region, without an ocean developed during the early Paleozoic, is a part of South China rather than being a segment of the Indochina Block. Sediments in the Qin‐Fang region were mainly sourced from east Gondwana and/or eastern Cathaysia Block during the Silurian, and then transformed to receive massive materials from the Yunkai Domain since the middle Devonian. Key Points: The Cambrian sandstone samples in and on both sides of the Qin‐Fang region share a common source(s)The Yunkai Domain emerged from the sea in the middle DevonianThe Qin‐Fang region is part of South China rather than the Indochina Block and has undergone two stages of evolution [ABSTRACT FROM AUTHOR]

The Sr and Nd isotopic compositions of siliciclastic sediments and the Nd isotopic compositions of planktonic foraminifera are investigated in sediment trap samples collected in 2015 at water depths of 500 and 2,800 m to (1) track the seasonal changes in the sources and transport patterns of siliciclastic sediments to Benham Rise, (2) constrain the Nd isotopic compositions of the planktonic foraminifera throughout the water column, and (3) assess the influences of lithogenic inputs on the Nd isotopic compositions of the water masses. We demonstrate that volcanic matter and eolian dust are derived primarily from Luzon Island and the Ordos Desert, respectively. In addition, we show that reduced precipitation over Luzon Island and the weakened East Asian winter monsoon intensity result in mass fluxes from Luzon Island and the eastern Asian deserts to the sea, respectively, that are weaker in the winter than in the spring. Furthermore, the εNd values of the foraminifera collected at a water depth of 500 m change slightly in 2015, suggesting negligible impacts of lithogenic Nd inputs characterized by significant seasonal flux variations. In contrast, the εNd values of the planktonic foraminifera collected at a water depth of 2,800 m are systematically more radiogenic and appear to display seasonal variability. Such results suggest the rapid modification of εNd values during the settling of planktonic foraminifera by the precipitation of Mn coatings derived from water masses at deposition depths, with greater contributions of colder water masses originating from the volcanic Luzon Island margin during the winter. Plain Language Summary: Based on the first report of Sr‐Nd isotopic compositions of siliciclastic sediments and Nd isotopic compositions of planktonic foraminifera in sediment trap samples collected from the western Philippine Sea in 2015 at water depths of 500 and 2,800 m together with the relevant current information, we try to recover the potential linkages between the East Asian winter monsoon strength, the East Asian summer monsoon (precipitation) intensity, and the siliciclastic sediment source‐to‐sink processes as well as the influences of lithogenic inputs on the Nd isotopic compositions of the water masses at the northern margin of the western Pacific Warm Pool in different seasons of 2015. On the one hand, we quantitatively estimate the eolian dust sources to the study area. On the other hand, we find the rapid changes in planktonic foraminiferal εNd values during settling in the western Philippine Sea. Such results are critical for effectively interpreting the siliciclastic sediment source‐to‐sink processes and marine circulation as well as the behind controlling mechanisms at low latitudes during the geological past. Key Points: The eolian dust sources to the western Philippine Sea are determined and quantifiedThe impacts of the East Asian monsoon on the siliciclastic fluxes to the Benham Rise are characterizedRapid changes in planktonic foraminiferal εNd values occur during settling in the ocean [ABSTRACT FROM AUTHOR]

The formation of the Pamir salient and the Tashkorgan‐Yarkand River is highly debated with the ages ranging from pre‐Cenozoic to late Miocene. One approach to resolve these issues is to draw support from the sedimentary record in the surrounding basins. A volcaniclastic sequence, which divides into Lower and Upper Members, was identified in the southwestern Tarim Basin. The Lower Member was transported by dilute streamflows, which likely flowed during or soon after eruptions, while the Upper Member was formed by a syneruptive volcanic debris flow. Chronological, petrologic, and geochemical data consistently indicate that the sequence was derived from the Central Pamir at ~11 Ma. The ~11 Ma emplacement of the volcaniclastic sequence provides unique constraints for the evolution of the Tashkorgan‐Yarkand River and the Pamir salient. Provenance data indicate a multistage evolutionary history of the Tashkorgan‐Yarkand River. The paleo‐Tashkorgan River was initially formed in the piedmont of the Pamir marginal range before ~15 Ma. This river cut back into the Tashkorgan region at ~15 Ma, after which it has eroded the Central Pamir by ~11 Ma. The N‐S trending upper reaches of the Tashkorgan River and the Yarkand River were established after ~11 Ma. The emplacement of the volcanic debris flow, together with regional deformation evidence, indicates limited strike‐slip motion between Pamir and the Tarim at least since ~11 Ma, which refutes hundreds of kilometers offset between the Pamir and the Tarim after this time and supports an earlier indention of the Pamir salient. Key Points: An ~11‐Ma syneruptive volcanic debris flow was identified within the Xiyu Formation in the Pamir‐West Kunlun foreland basinThe Tashkorgan River was established before ~15 Ma, while the Yarkand River was developed after ~11 MaNo large‐scale offset between the Pamir and the Tarim occurred after ~11 Ma [ABSTRACT FROM AUTHOR]

Abstract: The mode and tempo of Cenozoic fluvial input into the South China Sea by Asian rivers were strongly controlled by tectonically induced topographic changes and landscape development that resulted in repeated river captures and reversals. New Nd isotope and U‐Pb detrital zircon data from clastic sedimentary sequences in the northern South China Sea display secular variations reflecting significant changes in the compositions of fluvial sediment as well as changes in source rocks. The oldest, Eocene‐Oligocene (before ∼25 Ma) clastic rocks of the South China Sea contain sediments with ɛNd values of −5 to −7.5 and detrital zircons of Cretaceous, Jurassic, and Permo‐Triassic, all derived from southern Cathaysia. The Oligocene‐Middle Miocene (∼25–11 Ma) sediments in the South China Sea strata display ɛNd values of −12 to −14 and Archean, Proterozoic, and Paleozoic detrital zircons, suggesting northern Cathaysia and/or the Yangtze Blocks as their provenance. The headward expansion of the Pearl River and reversal of the Middle Yangtze River correlates with the opening of the South China Sea and growth of the eastern Tibetan Plateau at ∼25 Ma. Further uplift of the eastern Tibetan Plateau and the Wuyi‐Nanling Mountains in SE China around 11 Ma reshaped the landscape and caused another phase of erosion—pattern adjustment and drainage—divide migration in East Asia, leading to the establishment of the modern fluvial systems of the Pearl, Minjiang, and Lower Yangtze Rivers. [ABSTRACT FROM AUTHOR]

High-resolution multiproxy records, including clay minerals and Sr-Nd-Pb isotopes of the clay-sized silicate fraction of sediments from IODP Site U1429 in the northern Okinawa Trough, provide reliable evidence for distinct control mechanism on fine-grained sediments input from the Yellow River and the southern Japanese Islands to the northern Okinawa Trough since 34 ka BP. Provenance analysis indicates that the sediments were mainly derived from the Yellow River and the island of Kyushu. Since the last glacial, clay-sized sediments transported from the Yellow River to the study site were strongly influenced by sea-level fluctuation. During low sea-level stage (∼34-14 ka BP), the paleo-Yellow River mouth was positioned closer to the northern Okinawa Trough, favoring large fluvial discharge or even direct input of detrital sediments, which resulted about four times more flux of clay-sized sediments supply to the study area as during the relatively high sea-level stage (∼14-0 ka BP). The input of Kyushu-derived clay-sized sediments to the study site was mainly controlled by the Kuroshio Current and Tsushima Warm Current intensity, with increased input in phase with weakened Kuroshio Current/Tsushima Warm Current. Our study suggests that the Kuroshio Current was very likely flowed into the Okinawa Trough and thus influenced the fine-grained sediment transport in the area throughout the last glacial and deglacial. During ∼34-11 ka BP, the Kyushu clay-sized sediment input was mainly controlled by the Kuroshio Current. Since ∼11 ka BP, the occurrence of Tsushima Warm Current became important in influencing the Kyushu fine-grained sediment input to the northern Okinawa Trough. [ABSTRACT FROM AUTHOR]

The timing of the establishment of the Yangtze River, whether prior to the early Miocene (~24 Ma) or more recently (~2 Ma), has been a point of much debate. Here we applied detrital zircon U-Pb dating to Miocene sedimentary rocks from Taiwan and to estuary sands from modern rivers in SE China to trace sediment provenance and to further constrain the evolution of the Yangtze River. Detrital zircon U-Pb ages from Miocene sandstones of the Western Foothills show similar age spectra to Miocene and modern sediments in the Yangtze River drainage and some similarity to the Minjiang River sediments. However, they differ significantly from ages in some sandstones from the Hengchun Peninsula accretionary prism and from the estuary sands of the Jiulongjiang River. This information, together with petrographic and sedimentary facies analysis, argues that the Jiulongjiang and Minjiang Rivers were major sources to some Hengchun Peninsula turbidites (~12 Ma), while synchronous sedimentation in the Western Foothills was supplied from the Yangtze, Minjiang (or similar river), and possibly even the Yellow River. These sediments were transported southward/eastward via rivers or channels to the marginal sedimentary basins now inverted in the Western Foothills in Taiwan. The Yangtze River must have been established prior to the middle Miocene. [ABSTRACT FROM AUTHOR]

The Song Gianh is a small-sized (~3500 km2), monsoon-dominated river in northern central Vietnam that can be used to understand how topography and climate control continental erosion. We present major element concentrations, together with Sr and Nd isotopic compositions, of siliciclastic bulk sediments to define sediment provenance and chemical weathering intensity. These data indicate preferential sediment generation in the steep, wetter upper reaches of the Song Gianh. In contrast, detrital zircon U-Pb ages argue for significant flux from the drier, northern Rao Tro tributary. We propose that this mismatch represents disequilibrium in basin erosion patterns driven by changing monsoon strength and the onset of agriculture across the region. Detrital apatite fission track and 10Be data from modern sediment support slowing of regional bedrock exhumation rates through the Cenozoic. If the Song Gianh is representative of coastal Vietnam then the coastal mountains may have produced around 132 000-158 000 km3 of the sediment now preserved in the Song Hong-Yinggehai Basin (17-21% of the total), the primary depocenter of the Red River. This flux does not negate the need for drainage capture in the Red River to explain the large Cenozoic sediment volumes in that basin but does partly account for the discrepancy between preserved and eroded sediment volumes. OSL ages from terraces cluster in the Early Holocene (7.4-8.5 ka), Pre-Industrial (550-320 year BP) and in the recent past ( ca. 150 year BP). The older terraces reflect high sediment production driven by a strong monsoon, whereas the younger are the product of anthropogenic impact on the landscape caused by farming. Modern river sediment is consistently more weathered than terrace sediment consistent with reworking of old weathered soils by agricultural disruption. [ABSTRACT FROM AUTHOR]

The North Sakhalin Basin in the western Sea of Okhotsk has been the main site of sedimentation from the Amur River since the Early Miocene. In this article, we present regional seismic reflection data and a Neogene- Recent sediment budget to constrain the evolution of the basin and its sedimentary fill, and consider the implications for sediment flux from the Amur River, in particular testing models of continental-scale Neogene drainage capture. The Amur-derived basin-fill history can be divided into five distinct stages: the first Amur-derived sediments (>21-16.5 Ma) were deposited during a period of transtension along the Sakhalin- Hokkaido Shear Zone, with moderately high sediment flux to the basin (71 Mt year−1). The second stage sequence (16.5-10.4 Ma) was deposited following the cessation of transtension, and was characterised by a significant reduction in sediment flux (24 Mt year−1) and widespread retrogradation of deltaic sediments. The third (10.4-5.3 Ma) and fourth (5.3-2.5 Ma) stages were characterised by progradation of deltaic sediments and an associated increase in sediment flux (48-60 Mt year−1) to the basin. Significant uplift associated with regional transpression started during this time in southeastern Sakhalin, but the north-eastward propagating strain did not reach the NE shelf of Sakhalin until the Pleistocene (<2.5 Ma). This uplift event, still ongoing today, resulted in recycling of older deltaic sediments from the island of Sakhalin, and contributed to a substantially increased total sediment flux to the adjacent basinal areas (165 Mt year−1). Adjusted rates to discount these local erosional products (117 Mt year−1) imply an Amur catchment-wide increase in denudation rates during the Late Pliocene- Pleistocene; however, this was likely a result of global climatic and eustatic effects, combined with tectonic processes within the Amur catchment and possibly a smaller drainage capture event by the Sungari tributary, rather than continental-scale drainage capture involving the entire upper Amur catchment. [ABSTRACT FROM AUTHOR]

The transport of sediment from the mouth of the Indus River on to the deep-water submarine fan is complicated by temporary storage within large clinoforms on the shelf on either side of the submarine canyon, where most of the sedimentation since the start of the Holocene has occurred. In contrast, shelf edge clinoform deltas represent the products of forced regression and not the progradation of highstand clinoforms as far as the shelf edge. Clinoform sediments have a mixed provenance that involves significant reworking of older sediment deposited during or before the last glacial maximum. Recent sedimentation in the canyon head has been very rapid in the last few centuries ( ca. 10 cm year−1), but has been starved of sand probably because of 20th century damming. Sandy layers appear to represent annual monsoonal floods with a particularly large flood every 50-70 years. This canyon head sediment is also reworked by currents flowing along the canyon axis before being deposited deeper into the canyon. The last sandy sediment to reach the mid-canyon ( ca. 1300 m depth) was transported around 7000 year BP at a time of rising sea-levels, and might reflect reworking by the transgression, or local slumping from the walls of the canyon. Dating of the uppermost in a series of terraces in the mid-canyon area suggests that the canyon may have been partly filled and emptied of sediment at least three times since ca. 50 ka. We conclude from the Holocene record that sediment flux to the deep-water fan experiences major buffering, reworking and recycling both on the shelf and within the submarine canyon prior to its deposition, so that turbidite sands in the deep Arabian Sea cannot be used to correlate with climatic or tectonic events onshore over timescales of 103-105 years. [ABSTRACT FROM AUTHOR]

Subsidence in foreland basins is modulated by the size of the flexural load, the elastic thickness of the foreland lithosphere, the nature of the sedimentary fill, and the rate of convergence. Basal 'forebulge unconformities' are well known from these basins, but here we focus on a major unconformity in the Himalayan foreland, which removed much of the Oligocene-lower Miocene. This is a critical time in the Himalaya because it spans the period of initial rapid exhumation of high-grade metamorphic rocks and the start of motion on the Main Central Thrust. We show that the synchronous timing of unconformity and rapid Greater Himalayan exhumation may be explained by the same trigger, enhanced erosion. We estimate that accelerating erosion between 24 and 20 Ma would have removed ∼1.5 km more rock from the Greater Himalaya than would have been the case had erosion remained at the slower Paleogene rates. During this time erosion must have temporarily exceeded rock uplift rates. By transferring rock from the Himalaya to the Indian Ocean the load is reduced and the Indian Plate is flexed less, so that the depth of the foreland basin shallows to a new equilibrium state. We use a flexural model to estimate that erosional unloading could have caused uplift of 400-500 m of the basin at the range front, extending 70-150 km into the basin. Intensification of the Asian summer monsoon around the Oligo-Miocene boundary (∼24 Ma) is the most likely trigger of the stronger erosion. Similar unconformities are seen at 15-16 Ma and in the Pleistocene also, linked to faster erosion at these times. [ABSTRACT FROM AUTHOR]

India-Asia collision has resulted in the largest orogenic event on Earth since at least 500 Ma, and this has had a profound influence on the drainage patterns of Asia, on the Asian monsoon climate, on global oceanography, as well as on faunal extinctions. Despite this importance, understanding of the Paleogene evolution of this system is limited. U-Pb and Lu-Hf isotopic analyses of detrital zircons from the clastic sedimentary rocks of the Indus Molasse, located within the Indus Suture of the Ladakh Himalaya, India, show that most have Mesozoic-Cenozoic ages and juvenile Hf isotopic compositions. This suggests that the main source of these sediments is the Transhimalayan batholith, with minor flux from the Lhasa-Karakoram terrane and Indian plate. The lower Indus Molasse (Chogdo Formation) is inferred to have been deposited at 60-49 Ma, whereas the upper Choksti Formation was deposited later than 45-41 Ma and contains a greater contribution from the Lhasa terrane. The Transhimalayan batholith was eroded throughout Indus Molasse sedimentation, but increasing exhumation of Lhasa-Karakoram terrane indicates its progressive uplift after initial collision, and requires formation of a paleo-Indus River shortly after collision. [ABSTRACT FROM AUTHOR]

The Indus River is the only major drainage in the western Himalaya and delivers a long geological record of continental erosion to the Arabian Sea, which may be deciphered and used to reconstruct orogenic growth if the modern bedload can be related to the mountains. In this study we collected thermochronologic data from river sediment collected near the modern delta. U-Pb ages of zircons spanning 3 Gyr show that only ∼5% of the eroding crust has been generated since India-Asia collision. The Greater Himalaya are the major source of zircons, with additional contributions from the Karakoram and Lesser Himalaya. The 39Ar/40Ar dating of muscovites gives ages that cluster between 10 and 25 Ma, differing from those recorded in the Bengal Fan. Biotite ages are generally younger, ranging 0-15 Ma. Modern average exhumation rates are estimated at ∼0.6 km/m.y. or less, and have slowed progressively since the early Miocene (∼20 Ma), although fission track (FT) dating of apatites may indicate a recent moderate acceleration in rates since the Pliocene (∼1.0 km/m.y.) driven by climate change. The 39Ar/40Ar and FT techniques emphasize the dominance of high topography in controlling the erosional flux to the ocean. Localized regions of tectonically driven, very rapid exhumation (e.g., Nanga Parbat, S. Karakoram metamorphic domes) do not dominate the erosional record. [ABSTRACT FROM AUTHOR]

Subsidence of Lima Basin, part of the Peruvian forearc, is controlled by tectonic erosion by the subducting Nazca plate. Multichannel seismic reflection data coupled with age and paleowater depth constraints derived from Ocean Drilling Program (ODP) coring now allow the rates of erosion to be reconstructed through time. In trenchward locations the forearc has experienced limited recent relative uplift (700-850 m) likely due to preferential basal erosion under the center of Lima Basin. Long-term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench. Since 47 Ma (Eocene) up to 148 km of the plate margin have been lost at an average rate of up to 3.1 km myr−1. Appoximately 110 km of that total appears to be lost since 11 Ma, implying much faster average rates of trench retreat (10 km myr−1) since collision of the Nazca Ridge with the Lima Basin at 11 Ma. Although there is no clear subsidence event at ODP Site 679 during the time at which Nazca Ridge was subducting beneath this part of the forearc (4-11 Ma), the more trenchward ODP Sites 682 and 688 show significant deepening after 11 Ma indicating that subduction of the ridge accelerates tectonic erosion. Long-term rates of crustal erosion in the region of Lima Basin are greater than estimates of regional arc magmatic productivity, implying that such margins are net sinks of continental crust. [ABSTRACT FROM AUTHOR]

Abstract The Dras 1 Volcanic Formation of the Ladakh Himalaya, India, represents the eastern, upper crustal equivalent of the lower crustal gabbros and mantle peridotites of the Kohistan Arc exposed in Pakistan. Together these form a Cretaceous intraoceanic arc now located within the Indus Suture zone between India and Eurasia. During the Late Cretaceous, the Dras–Kohistan Arc, which was located above a north-dipping subduction zone, collided with the south-facing active margin of Eurasia, resulting in a switch from oceanic to continental arc volcanism. In the present study we analyzed samples from the pre-collisional Dras 1 Volcanic Formation and the postcollisional Kardung Volcanic Formation for a suite of trace elements and Nd isotopes. The Kardung Volcanic Formation shows more pronounced light rare earth element enrichment, higher Th/La and lower ℇNd values compared with the Dras 1 Volcanic Formation. These differences are consistent with an increase in the reworking of the continental crust by sediment subduction through the arc after collision. As little as 20% of the Nd in the Dras 1 Volcanic Formation might be provided by sources such as the Karakoram, while approximately 45% of the Nd in the Kardung Volcanic Formation is from this source. However, even before collision, the Dras–Kohistan Arc shows geochemical evidence for more continental sediment contamination than is seen in modern western Pacific arcs, implying its relative proximity to the Eurasian landmass. Comparison of the lava chemistry in the Dras–Kohistan Arc with that in the forearc turbidites suggests that these sediments are partially postcollisional, Jurutze Formation and not all pre-collisional Nindam Formation. Thus, the Dras–Eurasia collision can be dated as Turonian–Santonian (83.5–93.5 Ma), older than it was previously considered to be, but consistent with radiometric ages from Kohistan. [ABSTRACT FROM AUTHOR]