Search

Arc–continent collision is a fundamental stage in the plate-tectonic cycle that allows the continental crust to grow and can influence global climate through chemical weathering. Collision between Australia and the oceanic North Coast Range–New Britain Arc began in the Middle Miocene, resulting in uplift of the modern New Guinea Highlands. The temporal evolution of this collision and its erosional and weathering impacts is reconstructed here using sedimentary archives from the Gulf of Papua. Sr and Nd isotopes show dominant erosion from igneous arc-ophiolite crust, accounting for c. 40–70% of the total flux in the Early Miocene, and rising to c. 80–90% at 8 Ma, before falling again to 72–83% by the present day. Greater erosion from Australia-derived units accelerated in the Pliocene, like the classic Taiwan collision but with greater erosion from arc rather than continental units. Chemical alteration of the sediment increased through time, especially since c. 5 Ma, consistent with increasing kaolinite indicative of more tropical weathering. Erosion was focused in the high topography where mafic arc units are preferentially exposed. Comparison of sediment with bedrock compositions implies that the source terrains have been more efficient at removing CO2 from the atmosphere compared with Himalayan drainages. Supplementary material: Details of analytical conditions, analytical results and compositions compiled from the GEOROC database are available at https://doi.org/10.6084/m9.figshare.c.7168147 [ABSTRACT FROM AUTHOR]

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. 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. 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 Sediments in the Isugod Basin were deposited at 11.5–5.6 Ma following local gravitational collapse of the Palawan wedge driven by uplift The Isugod Basin sediments were supplied by erosion of the Palawan wedge and obducted forearc ophiolite exposed subaerially since ∼11.5 Ma Onset 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

The Ganges River, one of the largest rivers on Earth, is a typical monsoonal and flood-controlled system but has low inter-annual peak discharge variability. The seasonal discharge can reach 70 000 m3 s−1 during the wet season but maintains a low base flow of 500–3000 m3 s−1 during the dry season. However, the constancy in peak discharge every year categorizes the lower Ganges River as a river with low inter-annual peak discharge variability. This paper examines the modern lower Ganges River by conducting a detailed process-oriented investigation of the main channel, channel margin and overbank deposits, supplemented by satellite image observation and comparison with other modern fluvial systems. The channel and braid bar deposits show a dominance of small-scale to medium-scale cross-sets, with a variety of accretion processes constructing braid bars. The braid bar and channel deposits are typical of facies models of rivers with low inter-annual peak discharge variance. In contrast, the channel flank deposits are dominated by planar lamination, massive sand and mud couplets, and some ripple cross-lamination, with very little cross-bedding. Characteristic channel margin deposits represent sediments that accumulated by high-speed flows, multiple-surge and rapidly depositing flows, rapid or regular waning flows and hyperconcentrated flows. The overbank deposits predominantly comprise current ripples with long, thin bedforms and soft sediment deformation structures, which record flow transformation on the muddy flat topography and the processes of an unstable river bank. Our study shows that the channel margin and floodplain deposits are entirely different from those of the braid bar and channel. The bedform distribution of the fluvial deposits here (main channel, channel margin and overbank) may be an important tool in the identification of similar seasonal rivers with low inter-annual peak discharge variance and in the interpretation of fluvial processes. Supplementary material: The sediment texture and the depositional age is available at: https://doi.org/10.6084/m9.figshare.c.5144403 [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. 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. 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 Moisture availability in Asian dust source regions to the North Pacific Ocean were controlled by precession North Pacific dust flux reveals dominant obliquity variations, but is out‐of‐phase at different latitudes The westerlies in the Northern Hemisphere were primarily modulated by obliquity cycles in the late Pleistocene

Although there is some evidence for an Eocene monsoon, the most important intensification of rainfall appears to start at c.24 Ma in the Early Miocene. Many palaeoceanographical proxies for monsoon intensity are linked to wind and do not correlate well with humidity of the continental climate over tectonic timescales. Rainfall peaked in the middle Miocene (c.15 Ma) with strong drying after 8 Ma. This timing does not correlate well with either initial uplift of the Tibetan Plateau or with the retreat of shallow seas from central Asia. The c.24 Ma onset of strengthening rainfall is associated with the initiation of rapid erosion and cooling of Himalayan metamorphic rocks. The progressive detachment of the subducting Indian lithosphere from the eastern and western syntaxes at c.25 Ma to the east-central Himalaya at c.13–11 Ma would have produced corresponding propagation of rising Himalayan topography following release of the weight of the detached slab. Rapid uplift of the Himalayan barrier, blocking moisture-laden winds, is considered the most likely trigger for a stronger summer monsoon in South Asia, which in turn allowed faster erosion and exhumation of the Greater Himalaya after 24 Ma.

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. 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

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 εNdvalues 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 εNdvalues 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 εNdvalues 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. 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 εNdvalues 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. 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 εNdvalues occur during settling in the ocean

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. 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. 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 Sedimentary records from shallow and deep‐water sites have differing sensitivities to changes in ocean currents and the East Asian monsoon Clay mineralogy in shallow sites reflects sea‐level change, while deep‐water records respond to incursion of the Kuroshio Current Magnetic grain‐size indicates stronger deep currents during Heinrich Stadial 1, associated with the North Pacific Intermediate Water

Documenting the origins of megadiverse (sub)tropical aquatic ecosystems is an important goal for studies of evolution and ecology. Nonetheless, the geological and ecological establishment of the modern Yangtze River remains poorly understood. Here, we reconstruct the geographic and ecological history of an endemic clade of East Asian fishes based on the mitochondrial phylogenomics analysis of Cyprinidae using 15 fossil calibrations. We estimate an ancestral condition of benthic spawning with demersal or adhesive eggs in southern East Asia before ∼23 Ma and a derived condition of riverine spawning with semi-buoyant eggs in the Yangtze by ∼18 Ma. These results imply the formation of Yangtze riverine ecosystems around the Oligocene-Miocene boundary in response to plateau uplift and monsoon strengthening. Some of these cyprinids reverted to benthic spawning with adhesive eggs by ∼15 Ma, a time of rising to peak net diversification rates, indicating the formation of potamo-lacustrine ecosystems by the mid-Miocene during a strong East Asian summer monsoon. Our study provides increased spatiotemporal resolution for the co-evolutionary histories of the Yangtze River and its biodiversity and highlights biological evidence concerning the geomorphological dynamics of the Yangtze River.

Sediment is delivered by the rivers of SE Asia to the South China Sea where it provides an archive of continental environmental conditions since the Eocene. Interpreting this archive is complicated because sediment may be derived from a number of unique sources and the rivers themselves have experienced headwater capture that also affects their composition. A number of methods exist to constrain provenance, but not all work well in this area. Anthropogenic impacts, most notably agriculture, mean that the modern rivers contain more weathered materials than they did up until about 3000 years ago. The rivers have also changed their bulk chemistry and clay mineralogy in response to climate change, so that these proxies, as well as Sr isotopes, are generally unreliable provenance indicators. Nd isotopes resolve influx from Luzon, but many other sources in SE Asia have similar values and clear resolution of end members can be difficult. Instead, thermochronology methods are best suited, especially apatite fission track, which shows more diversity in the sources than either U–Pb zircon or Ar/Ar muscovite dating. Nonetheless, even fission track is best used as part of a multiproxy approach if a robust quantitative budget is desired.

Reconstructing variations in the intensity of chemical weathering in river basins is crucial if we are to understand how climate change impacts environment and whether there are feedbacks between climate and weathering processes. Quantifying chemical weathering is, however, a complicated process, involving a number of competing proxies. We compare weathering records from the Pearl River delta of southern China and Ocean Drilling Program (ODP) Sites 1144 and 1146 on the northeastern slope of the South China Sea in order to test which proxies are the most widely applicable and robust. Comparison with speleothem rainfall records indicates that K/Al tracks precipitation variations most closely and out-performs the widely used Chemical Index of Alteration (CIA). Correlation of K/Al and kaolinite/illite indicates that this clay ratio is also an effective proxy of weathering intensity across all sites and timescales. Kaolinite/smectite, and to a lesser extent smectite/(illite+chlorite), are also indicative of weathering intensity, but show more scatter between sites that may be linked to provenance effects. Mg/Al is relatively immune to grain-size effects, but does not correlate well with other proxies. K/Rb is a reasonably reliable indicator of chemical weathering intensity and may be more sensitive than CIA or K/Al to weathering changes over short timescales and when weathering is not too intense. 87Sr/86Sr can be useful but can be influenced by both grain size and provenance effects. In general marine archives of fluvial sediment may record variations in weathering linked to climate, but these are increasingly signals of reworking going further offshore.

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. 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. 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 We reconstruct the eolian flux record in the North Pacific since 23 Ma at high resolution The Northern Hemisphere Westerlies shifted northward between 23 and 9 Ma and have remained relatively stable since then Tibetan uplift drove the northward shift of Northern Hemisphere Westerlies in the early late Miocene

The continental crust is the primary archive of geological history, and is host to most of our natural resources. Thus, the following remain critical questions in Earth Science, and provide an underlying theme to all of the contributions within this volume: when, how and where did the continental crust form? How did it differentiate and evolve through time? How has it has been preserved in the geological record? This introductory review provides a background to these themes, and provides an outline of the contributions contained within this volume.

This paper uses an extensive dataset from more than 200 samples to provide a comprehensive source-to-sink analysis of the Amur River and its delta in the Russian Far East. The majority of sand-sized sediment in the Amur River and its former delta comes from upstream of the Lesser Khingan Ridge, shown by uniformity of sediment composition in the lower 1700 km of the river. Stable mineral ratios, U–Pb age spectra and garnet geochemistry show little stratigraphic provenance-specific variation in the Neogene delta. This renders Miocene–Pliocene drainage capture models unlikely.The onset of uplift in the delta is marked by a decrease in the apatite–tourmaline index (ATi) in Upper Pliocene offshore well samples, caused by dissolution of apatite as sediments were uplifted and eroded onshore Sakhalin. These wells also show variable ATi and garnet–zircon index (GZi) values in Lower Miocene samples, which could potentially be used for stratigraphic correlation.A positive correlation between GZi values and distance from the river mouth is attributed to hydrodynamic sorting across the delta system. This has negative implications for the use of this stable mineral index and others of a similar hydraulic equivalence as regional correlation tools on a basin scale (>100 km).Supplementary material:Heavy mineral data, petrographic data, geochronometric data, sample locations available at www.geolsoc.org.uk/SUP18643.

Early Ordovician collision of the Lough Nafooey Arc (part of the Baie Verte Oceanic Tract) with the passive continental margin of Laurentia peaked at c. 475 Ma in Scotland and Ireland and was followed by subduction polarity reversal. We examined Upper Ordovician–Silurian sedimentary rocks from western Ireland to see whether collision was followed by renewed arc magmatism. Despite the scarcity of dated igneous intrusions between the Grampian (c. 470 Ma) and Acadian (c. 420 Ma) orogenies in Ireland, detrital zircons show a continuity of activity peaking at 480–440 Ma, implying no hiatus in regional magmatism. Differences in zircon U–Pb age spectra highlight the isolation of basins in the southern Killary Harbour area from those north of the South Mayo Trough. These latter rocks were largely derived by erosion from Moine and Upper Dalradian sources. By contrast, the Killary Harbour Basin shows a decreasing influence from the Dalradian after c. 436 Ma and an increasing influence of contemporaneous magmatic zircons. These were transported from sources along-strike from the present NE, probably at the southern end of the Scandian Mountains in SE Greenland. The western Irish basins formed as pull-apart basins in a forearc setting and are analogous to Cenozoic pull-apart basins in Sumatra. Supplementary material: U-Pb zircon analytical data is available at a decreasing influence from the Dalradian after c. 436 Ma and an increasing influence of contemporaneous https://doi.org/10.6084/m9.figshare.c.5209849 [ABSTRACT FROM AUTHOR]

Several palaeoclimate proxy records have been interpreted as representing the direct effects of Tibetan uplift on climate, and particularly the intensity of the Asian summer monsoon. However, there are other possible causes for the transitions and changes which have been observed, such as varying greenhouse gas concentrations, nodes or extremes in orbital forcing, and changing continental configurations. In this study we model the direct effects of Tibetan uplift on sea surface temperatures (SSTs), vegetation, and river discharge. We investigate whether these climatic effects of topographic uplift are likely to be detectable in proxy records, and also whether the proxies could be used to distinguish between different paradigms for the history of plateau uplift. We find that the SSTs in the western Pacific, South China Sea and Indian Ocean are generally insensitive to Tibetan uplift; however, vegetation in the region of the plateau itself, and river discharge from the Yangtze, Pearl, and in particular the Ganges/Brahmaputra, could provide a good test of our understanding of Tibetan uplift history.

The Song Hong-Yinggehai (SH-Y) and Qiongdongnan (Qi) basins together form one of the largest Cenozoic sedimentary basins in SE Asia. Here we present new records based on the analysis of seismic data, which we compare to geochemical data derived from cores from Ocean Drilling Program (ODP) Site 1148 in order to derive proxies for continental weathering and thus constrain summer monsoon intensity. The SH-Y Basin started opening during the Late Paleocene–Eocene. Two inversion phases are recognized to have occurred at c. 34 Ma and c. 15 Ma. The Qi Basin developed on the northern, rifted margin of South China Sea, within which a large canyon developed in a NE–SW direction. Geochemical and mineralogical data show that chemical weathering has gradually decreased in SE Asia after c. 25 Ma, whereas physical erosion became stronger, especially after c. 12 Ma. Summer monsoon intensification drove periods of faster erosion after 3–4 Ma and from 10–15 Ma, although the initial pulse of eroded sediment at 29.5–21 Ma was probably triggered by tectonic uplift because this precedes monsoon intensification at c. 22 Ma. Clay mineralogy indicates more physical erosion together with high sedimentation rates after c. 12 Ma suggesting a period of strong summer monsoon in the Mid-Miocene.

We reconstruct past changes in the East Asian summer monsoon over the last 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 of Leg 184 in the northern South China Sea based on the major (Al, Ca, Na, K, Ti, etc.) and trace element (Rb, Sr, and Ba) geochemistry of terrigenous sediments. This study and combined review suggests that the long-term evolution of the East Asian summer monsoon is similar to that of the Indian summer monsoon, but distinct from the East Asian winter monsoon. Generally, the Asian summer monsoon intensity has decreased gradually from its maximum in the Early Miocene. In contrast, the Asian winter monsoon shows a phased enhancement since 20 Ma BP. Moreover, our study shows that the long-term intensities of the Asian summer and winter monsoons may have different forcing factors. Specifically, the winter monsoon is strongly linked to phased uplift of Tibetan plateau and to Northern Hemispheric Glaciation. In contrast, global cooling since 20 Ma BP may have largely reduced the amount of water vapour held in the atmosphere and thus weakened the Asian summer monsoon.

The Indus Delta is constructed of sediment eroded from the western Himalaya and since 20 ka has been subjected to strong variations in monsoon intensity. Provenance changes rapidly at 12–8 ka, although bulk and heavy mineral content remains relatively unchanged. Bulk sediment analyses shows more negative Ndand higher 87Sr/86Sr values, peaking around 8–9 ka. Apatite fission track ages and biotite Ar–Ar ages show younger grains ages at 8–9 ka compared to at the Last Glacial Maximum (LGM). At the same time δ13C climbs from –23 to –20‰, suggestive of a shift from terrestrial to more marine organic carbon as Early Holocene sea level rose. U–Pb zircon ages suggest enhanced erosion of the Lesser Himalaya and a relative reduction in erosion from the Transhimalaya and Karakoram since the LGM. The shift in erosion to the south correlates with those regions now affected by the heaviest summer monsoon rains. The focused erosion along the southern edge of Tibet required by current tectonic models for the Greater Himalaya would be impossible to achieve without a strong summer monsoon. Our work supports the idea that although long-term monsoon strengthening is caused by uplift of the Tibetan Plateau, monsoon-driven erosion controls Himalayan tectonic evolution. SUPPLEMENTARY MATERIAL: A table of the population breakdown for zircons in sands and the predicted Nd isotope composition of sediments based on the zircons compared to the measured whole rock value is available at http://www.geolsoc.org.uk/SUP18412

Presents a study that examined the age and geochemical affinity of the Delaney Dome Formation in Connemara, Ireland and attempted to relocate it within the original geometry of the Grampian Orogeny in order to understand its original tectonic setting and its development. Description of the Dome; Age of the Dome formation; Eruption and emplacement of the Dome formation.

The influence of fluid flux on petrogenesis in the Tonga-Kermadec Arc was investigated using ion microprobe measurements of B/Be and boron isotope ratios (11B/10B) to document the source and relative volumes of the fluids released from the subducting oceanic plate. We analyzed young lavas from eight different islands along the Tonga-Kermadec Arc, as well as glass shards in volcanic sediments from Ocean Drilling Program (ODP) Site 840, which record the variations in the chemistry of Tonga magmatism since 7 Ma. B/Be is variable (5.8–122), in young Tonga-Kermadec Arc lavas. In contrast, glass shards from ∼3 to 4 Ma old volcanic sediments at Site 840 have the highest B/Be values yet reported for arc lavas (18–607). These values are too high to be related simply to a sediment influence on petrogenesis. Together with very high δ11B values (−11.6 to +37.5) for the same shards and lavas these data indicate that most of the B is derived from fluid escaped from the subducting altered Pacific oceanic crust, rather than from sediment. High δ11B values also reflect large degrees of isotopic fractionation in this cold fast subduction zone. Lower δ11B values noted in the Kermadec Arc (17 to −4.4) are related to the influence of sediment eroded from New Zealand and slower convergence. High fluid flux (B/Be) is synchronous in Tonga and the Marianas at 3 to 4 Ma and may be related to acceleration of the Pacific Plate just prior to this time.

Describes the accretion tectonics of the Neotethyan Ermioni Complex, Peloponessos, Greece. Imbrication of sulphide bodies, thrust slices of cherts and serpentinized within a tectonic stack; Distribution of basalts limestones and metalliferous sediments within the complex; Description of the processes involved in the assembly of Ermioni Complex.

AbstractThe Argolis Peninsula, southern Greece, is believed to form part of a Pelagonian microcontinent located between two oceanic basins, the Pindos to the west and theVardar to the east, in Triassic to Tertiary time. In eastern Argolis, two important units are exposed: (i) the Ermioni Limestones cropping out in the southwest; (ii) the Poros Formation, observed on an offshore island in the northeast, and on the adjacent mainland. Both these units comprise late Cretaceous (Aptian-Maastrichtian) pelagic limestones, calciturbidites, lenticular matrix- and clast-supported limestone conglomerates and slump sheets. However, the Poros Formation is distinguished from the Ermioni Limestones by the presence of bituminous micritic limestones and an increasing proportion of shale up sequence. These successions are deep-water slope carbonates that once formed the southeast-facing passive margin of the Pelagonian platform (Akros Limestone). Beyond this lay a late Cretaceous ocean basin in the Vardar Zone. This ocean was consumed in an easterly-dipping subduction zone in latest Cretaceous (?) to early Tertiary time, giving rise to an accretionary complex (Ermioni Complex). During early Tertiary (Palaeocene-Eocene) time the passive continental margin (Pelagonian Zone) collided with the trench and accretionary complex to the east. As the suture tightened, former lower-slope carbonates (Ermioni Limestones) were accreted to the base of the over-riding thrust sheets and emplaced onto the platform. Farther west, bituminous upper slope carbonates (Poros Formation) flexurally subsided and passed transitionally upwards into calcareous flysch and olistostromes in a foreland basin. These sediments were then overridden by the emplacing thrust stack and themselves underplated. Late-stage high-angle faulting then disrupted the tectonostratigraphy, in places juxtaposing relatively high and low structural levels of the complex.

Subsidence analysis of ODP/DSDP drill sites located on oceanic crust on the Southeast Greenland, Edoras Bank, and Vøring Plateau margins, as well as on the Iceland-Faeroe Ridge, shows that the subsidence of these areas does not follow the agerelationship of normal oceanic crust. By correcting for the effect of thickened oceanic crust in raising the level to which subsidence will occur and analyzing the rate of thermal subsidence, it is possible to provide maximum temperature estimates for the underlying asthenosphere through time by identifying periods of anomalous depth to basement. Isostatic models predict crustal thicknesses of 27 km under the Iceland-Faeoe Ridge, around 20 km at Edoras Bank and Southeast Greenland, and 16–17 km at the Vøring Plateau. Asthenospheric temperatures at the time of continental break-up range from 50°C to 100°C above normal mantle, which are insufficient to account for the crustal thicknesses if melting is purely a passive adiabatic process. Asthenospheric upwelling must thus have been more rapid than spreading following break-up. At Edoras Bank the thermal anomaly dissipated within 5 Myr of rifting, similar to that inferred from the eastern US margin, where no plume is considered to have affected the rifting process. The need to invoke thermal input from the Iceland Plume in generating the thickened crust at Edoras Bank, and possibly elsewhere in the Northeast Atlantic, is called into question. However, a 14–20 Myr anomaly, peaking at 12 Myr post-rift, in Southeast Greenland suggests that, although the plume did provide heat to this margin, its strongest influence post-dated break-up.

Crustal thickening caused by igneous underplating related to continental break-up in the northeast Atlantic has been invoked as the cause of the apparent lack of thermal subsidence seen in many Mesozoic basins in the northwest European area. In this study, we examine a set of commercial wells in the Rockall-Faeroe-Shetland region and calculate tectonic subsidence histories. The rate of post-rift basement subsidence during the Cretaceous-Cenozoic, determined from backstripping calculations, always implies a higher degree of extension than the total basement subsidence, assuming uniform extension. Furthermore, the size of this discrepancy increases northward along the Rockall Trough, and westwards in the northern North Sea towards Scotland. We interpret this depth anomaly to reflect the effect of igneous underplating, rethickening the crust following Mesozoic and Cenozoic extension. Late Paleocene extension is identified in subsidence reconstructions throughout the west of Britain area, and is greatest in the Rockall Trough. Assuming that the underplating is gabbroic in composition, the subsidence depth anomalies indicate a regional pattern of 2–3 km underplated between the Erris Trough and Porcupine Basin, increasing to 4–5 km in the West Lewis Basin and Hebrides Shelf area. In the Faeroe-Shetland Basin underplating is 1.0–1.5 km in the east, and increases to 4–5 km in the west. The data support the hypothesis of a major asthenospheric thermal anomaly centered under the Faeroes in the Paleocene. Dynamic uplift of the region is often difficult to identify but is locally seen to develop rapidly around 63 Ma, implying rapid emplacement of the mantle anomaly. The intrusion of gabbroic bodies to the base of the crust in the late Paleocene may have had an impact on the thermal maturation of petroleum source rocks in the region. However, thermal maturity indicators show smaller peak heatflows than predicted from simple thermal models, suggesting that underplating was a gradual process, achieved through the accretion of several small, rapidly cooled bodies.

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 CO2consumption 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. 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. 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 Sediment deposited by Pearl, Mekong, and Indus Rivers has become less altered since the middle Miocene Total chemical weathering fluxes from these river basins decreased by 50% since 16 Ma Himalaya‐Tibetan uplift and erosion is not driving global cooling since 16 Ma

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 × 1012mol/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. Anthropogenic emissions of the greenhouse gas CO2are 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 CO2into 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. 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 A first integrative study of Quaternary inputs of Himalayan and Tibetan erosion and weathering products in distal marginal seas is presented Increased highland erosion and terrestrial organic matter burial in the deep Arabian Sea and Bay of Bengal occurred during glacial periods Enhanced continental shelf weathering and terrigenous organic carbon flux in the abyssal South China Sea appeared during sea‐level lowstands

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, αAlKat 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 αAlKrecord 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. 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 timescalesαAlKrecords indicate significant changes in the Indian summer monsoon in association with the Mid‐Pleistocene Transition

No abstract

Collisions between oceanic island-arc terranes and passive continental margins are thought to have been important in the formation of continental crust throughout much of Earth's history. Magmatic evolution during this stage of the plate-tectonic cycle is evident in several areas of the Ordovician Grampian-Taconic orogen, as we demonstrate in the first detailed geochemical study of the Tyrone Igneous Complex, Ireland. New U-Pb zircon dating yields ages of 493 ± 2 Ma from a primitive mafic intrusion, indicating intra-oceanic subduction in Tremadoc time, and 475 ± 10 Ma from a light rare earth element (LREE)-enriched tonalite intrusion that incorporated Laurentian continental material by early Arenig time (Early Ordovician, Stage 2) during arc-continent collision. Notably, LREE enrichment in volcanism and silicic intrusions of the Tyrone Igneous Complex exceeds that of average Dalradian (Laurentian) continental material that would have been thrust under the colliding forearc and potentially recycled into arc magmatism. This implies that crystal fractionation, in addition to magmatic mixing and assimilation, was important to the formation of new crust in the Grampian-Taconic orogeny. Because similar super-enrichment of orogenic melts occurred elsewhere in the Caledonides in the British Isles and Newfoundland, the addition of new, highly enriched melt to this accreted arc terrane was apparently widespread spatially and temporally. Such super-enrichment of magmatism, especially if accompanied by loss of corresponding lower crustal residues, supports the theory that arc-continent collision plays an important role in altering bulk crustal composition toward typical values for ancient continental crust. [ABSTRACT FROM AUTHOR]