Peter D Clift | University College London (original) (raw)

Books by Peter D Clift

Geological Society, London, Special Publications , 2024

Scientific drilling provides extended records of continental environmental conditions during the ... more Scientific drilling provides extended records of continental environmental conditions during the Neogene in Asia and northern Australia. Spectral data allows reconstruction of the environment using abundances of hematite and goethite. Hematite formation is favoured by dry or seasonal conditions. Hemipelagic sites show the most regular records. Monsoon strengthening started in the Early Miocene and peaked at 17–20 Ma in the Bay of Bengal and at 10–15 Ma in southern China before weakening after ~12 Ma and ~10 Ma respectively. The Indus dried after ~8 Ma and again after 3 Ma, while eolian sediment sources to the Sea of Japan show increased aridity after 5 Ma and 3 Ma. The Mekong indicates increasing aridity after 6 Ma, similar to Eastern Australia. In contrast, NW Australia shows a trend towards wetter conditions after 8 Ma, a humid period at 4–6 Ma, followed by drying. There is a link between drying and vegetation in the Mekong and Pearl River basins, as well as Eastern Australia. Monsoon strengthening is linked to topographic uplift in the Himalaya, together with Tethyan gateway closure. Long term drying is likely driven by global cooling since the Middle Miocene.

Papers by Peter D Clift

Journal of the Geological Society, 2024

Arc-continent collision is a fundamental stage in the plate-tectonic cycle that allows the contin... more 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 CO 2 from the atmosphere compared with Himalayan drainages.

Geology, 2005

The Jurassic Talkeetna volcanic arc of south-central Alaska is an oceanic island arc that formed ... more The Jurassic Talkeetna volcanic arc of south-central Alaska is an oceanic island arc that formed far from the North American margin. Geochronological, geochemical, and structural data indicate that the arc formed above a north-dipping subduction zone after ca. 201 Ma. Magmatism migrated northward into the region of the Talkeetna Mountains ca. 180 Ma. We interpret this magmatism as the product of removal of the original forearc while the arc was active, mainly by tectonic erosion. Rapid exhumation of the arc after ca. 160 Ma coincided with the sedimentation of the coarse clastic Naknek Formation. This exhumation event is interpreted to reflect collision of the Talkeetna arc with either the active margin of North America or the Wrangellia composite terrane to the north along a second north-dipping subduction zone. The juxtaposition of accreted trench sedimentary rocks (Chugach terrane) against the base of the Talkeetna arc sequence requires a change from a state of tectonic erosion to accretion, probably during the Late Jurassic (before 150 Ma), and definitely before the Early Cretaceous (ca. 125 Ma). The change from erosion to accretion probably reflects increasing sediment flux to the trench due to collision ca. 160 Ma.

EGU General Assembly Conference Abstracts, Apr 1, 2012

Abstract In this study we have examined the changes in a number of commonly used proxies for chem... more Abstract In this study we have examined the changes in a number of commonly used proxies for chemical weathering intensity in the northern South China Sea at ODP Site 1144 and in the delta of the Pearl River. Sediment at ODP Site 1144 is dominantly eroded from Taiwan and shows a sharp increase in the state of weathering of sediment deposited after 12 ka, reaching a peak at 10 ka and then decreasing to a lower background level after~ 7 ka. The higher hematite/goethite values suggest more arid weathering despite the monsoon ...

AGU Fall Meeting Abstracts, Dec 1, 2008

Abstract Much of the sediment eroded from eastern Tibet has been preserved in the Song Hong-Yingg... more Abstract Much of the sediment eroded from eastern Tibet has been preserved in the Song Hong-Yinggehai (SH-Y) and Qiongdongnan (Qi) sedimentary basins of the NW South China Sea which together form one of the largest sedimentary basins in SE Asia. Sediments preserved in these basins can be used to reconstruct erosion and in turn constrain the timing of regional tectonism and plateau uplift as well as for the history of intensification of the Asia Monsoon. Here we present some new results of the SH-Y and Qi Basins based on ...

EGS - AGU - EUG Joint Assembly, Apr 1, 2003

Abstract Subduction plate boundaries, at which tectonic erosion removes material from the overrid... more Abstract Subduction plate boundaries, at which tectonic erosion removes material from the overriding plate, account for 57% of the total length of the global subduction system and are favored where convergence rates exceed 7 cm/yr and where the sedimentary cover is less than 1 km. Accretion conversely preferentially occurs in regions of slow convergence (&amp;amp;amp;amp;lt; 8.5 cm/yr) and/or trench sediment thicknesses&amp;amp;amp;amp;gt; 1 km. The slope gradients and taper angle of accretionary plate margins correlates with plate convergence rates, while erosive margin ...

Journal of Asian Earth Sciences, Jun 1, 2019

Multiproxy records from Core MD06-3054 in the western Philippine Sea and published results from t... more Multiproxy records from Core MD06-3054 in the western Philippine Sea and published results from the nearby Core MD06-3052, which are both located at the northern margin of the Western Pacific Warm Pool (WPWP), provide precise reconstructions and evidence for the potential controls on continental erosion and weathering intensities in Luzon. These data also constrain sediment source-to-sink processes in the sea since 27 ka at the millennial scale. We demonstrate that the siliciclastic fraction is derived from Luzon volcanic rocks and eolian dust from mainland Asia. Stronger physical erosion and chemical weathering generally occurred during the last glaciation, Heinrich Event 1, the Younger Dryas, and the period from 10.3 to 11.3 ka. In contrast, the Bølling-Allerød was characterized by weaker physical erosion and chemical weathering. During the last glaciation, Heinrich Event 1, and the Younger Dryas, the lower sea level led to enhanced erosion and weathering of the exposed shelf sediments. In contrast, the weaker physical erosion and chemical weathering that occurred during the Bølling-Allerød and the Holocene, except after 2.1 ka, are closely correlated with the higher sea level. The stronger physical erosion and chemical weathering at 10.3-11.3 ka may be derived from the reworking of older sediments during the time of a strengthening summer monsoon. Furthermore, enhanced human activity since 2.1 ka has become the dominant control on erosion in Luzon. Rapid weathering changes in the WPWP during the last deglaciation highlight the high variability in local controls at low latitudes during these periods and the potential influence of controls at high latitudes.

Geological Society of America eBooks, 2007

Six samples collected from pre-, syn-, and post-Talkeetna arc units in southcentral Alaska were d... more Six samples collected from pre-, syn-, and post-Talkeetna arc units in southcentral Alaska were dated using single-grain zircon LA-MC-ICP-MS geochronology to assess the age of arc volcanism and the presence and age of any inherited components in the arc. The oldest dated sample comes from a volcanic breccia at the base of the Talkeetna Formation on the Alaska Peninsula and indicates that initial arc volcanism began by 207 ? 5 Ma. A sedimentary rock overlying the volcanic section in the Talkeetna Mountains has a maximum depositional age of 467 Ma. This is in agreement with biochronologic ages for the top of the Talkeetna Formation, suggesting that the Talkeetna arc was active for ca. 40 m.y.

Journal of the Geological Society, May 1, 1997

Abstract Formation of a pronounced basement ridge along many transform continental margins has be... more Abstract Formation of a pronounced basement ridge along many transform continental margins has been attributed to a variety of processes during continental break-up, including transpressional crustal thickening, and thermal rejuvenation and igneous underplating during passage of a spreading ridge. ODP drill holes on the Côte d&amp;amp;amp;amp;amp;amp;amp;#x27;Ivoire-Ghana margin now provide the first opportunity to quantify the vertical motions along this type of margin. Apatite fission-track dating of detrital sands suggests that large amounts of erosion ...

Earth-Science Reviews, Sep 1, 2021

Abstract How well do deep-sea sedimentary archives track erosion in upland sources, driven by cli... more Abstract How well do deep-sea sedimentary archives track erosion in upland sources, driven by climatic change or tectonic forcing? Located on the western edge of South Asian monsoon influence, the Indus River system is particularly sensitive to variations in monsoon rainfall and thus provides a unique opportunity to estimate the nature of sedimentary signal propagation (i.e., recognizable pulses of sediment) through a large river basin under different climatic conditions. In this review we examine the impact that changing monsoon rainfall has had on NW Himalayan landscapes and its foreland since the middle Miocene. Rates of erosion are linked to summer monsoon rains over tectonic timescales but patterns of erosion are more explicitly linked to tectonically-driven rock uplift. Positive feedback between rock uplift and orographic precipitation drives increased erosion and transport from the Lesser Himalaya since the Miocene. After 2 Ma, erosion increasingly shifts to the Inner Lesser Himalaya. As defined multiproxy evidence, strong monsoon rainfall intervals broadly result in increased erosion and faster sediment transport together with increased chemical weathering, although the latter is further linked with global temperature and to the magnitude of sediment recycling within the routing system. We estimate that during the Holocene, most sediment (67–89% of the total ~6000 km3 or 16.3 x 1012 t) delivered to the ocean was sourced either from direct bedrock erosion through channel incision linked to higher discharge or from remobilized, recycled glacial sediment initially deposited during the Last Glacial Maximum (LGM). Post-LGM sediment is primarily stored within the delta plain and shelf clinoform systems. Over the last 14 kyr, average mass delivery rates (936–1404 Mt/y) are much higher than pre-damming estimates (pre-1940s; 250–300 Mt/y). To reconcile observations with pre-damming estimates, high sediment supply rates, probably during strong monsoon intervals over the early Holocene, are required. Long-term rates were high (182273 Mt/y) during a middle Miocene strong monsoon interval. Quaternary Indus submarine fan sedimentation is limited to sea level lowstands, at which times shelf and delta sediment is eroded and reworked into deep water. As a result, and for at least the past 2–3 m.y., most sediment delivered to the Indus submarine fan was initially eroded from bedrock during strong summer monsoon intervals but deposited into the fan under weak monsoon intervals. During the most recent sea level lowstand, only ~24% of sediment deposited in the fan was derived from synchronous onshore bedrock erosion, with the remaining accounted for by recycled terrace, floodplain and shelf clinoform system sediment. Variations in monsoon intensity over the last glacial cycle strongly impact the locus of onshore erosion, with increased relative Himalayan bedrock erosion during times of strong, wet monsoon intervals and increased Karakoram bedrock erosion during drier glacial intervals.

Geological Society, London, Special Publications, 2010

We reconstruct past changes in the East Asian summer monsoon over the last 20 Ma using samples fr... more 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.

Nature Geoscience, Dec 1, 2008

What was the objective of the work? The work built on several earlier projects which hinted that ... more What was the objective of the work? The work built on several earlier projects which hinted that the evolution of the Asian monsoon and the Himalaya were closely linked. We had some clues that climate affects the location of faults in the modern mountains from earlier investigations of active tectonics, but it was not clear whether this relationship extended further back in time. Thus, we decided to reconstruct continental weathering in southern China and Tibet, the source region of the rivers that drain to the South China Sea, using sediment cores from the Pearl River system.

Chemical Geology, Oct 1, 2012

We analyzed sediment from Ocean Drilling Program (ODP) Site 1144 in the northern South China Sea ... more We analyzed sediment from Ocean Drilling Program (ODP) Site 1144 in the northern South China Sea to examine the weathering response of SE Asia to the strengthening of the East Asian Monsoon (EAM) since 14 ka. Our high-resolution record highlights the decoupling between continental chemical weathering, physical erosion and summer monsoon intensity. Mass accumulation rates, Ti/Ca, K/Rb, hematite/goethite and 87 Sr/ 86 Sr show sharp excursions from 11 to 8 ka, peaking at 10 ka. Clay minerals show a shorter-lived response with a higher kaolinite/(illite+ chlorite) ratio at 10.7-9.5 ka. However, not all proxies show a clear response to environmental changes. Magnetic susceptibility rises sharply between 12 and 11 ka. Grain-size becomes finer from 14 to 10 ka and then coarsens until~7 ka, but is probably controlled by bottom current flow and sealevel. Sr and Nd isotopes show that material is dominantly eroded from Taiwan with a lesser flux from Luzon, while clay mineralogy suggests that the primary sources during the Early Holocene were reworked via the shelf in the Taiwan Strait, rather than directly from Taiwan. Erosion was enhanced during monsoon strengthening and caused reworking of chemically weathered Pleistocene sediment largely from the now flooded Taiwan Strait, which was transgressed by~8 ka, cutting off supply to the deep-water slope. None of the proxies shows an erosional response lasting until~6 ka, when speleothem oxygen isotope records indicate the start of monsoon weakening. Although more weathered sediments were deposited from 11 to 8 ka when the monsoon was strong these are reworked and represent more weathering during the last glacial maximum (LGM) when the summer monsoon was weaker but the shelves were exposed.

EGU General Assembly Conference Abstracts, Apr 1, 2016

Geological Society, London, Special Publications , 2024

Journal of the Geological Society, 2024

Geology, 2005

EGU General Assembly Conference Abstracts, Apr 1, 2012

AGU Fall Meeting Abstracts, Dec 1, 2008

EGS - AGU - EUG Joint Assembly, Apr 1, 2003

Journal of Asian Earth Sciences, Jun 1, 2019

Geological Society of America eBooks, 2007

Journal of the Geological Society, May 1, 1997

Earth-Science Reviews, Sep 1, 2021

Geological Society, London, Special Publications, 2010

Nature Geoscience, Dec 1, 2008

Chemical Geology, Oct 1, 2012

EGU General Assembly Conference Abstracts, Apr 1, 2016

Geological Magazine, 2020

Potential interactions between the solid Earth and the climate system have long been recognized b... more Potential interactions between the solid Earth and the climate system have long been recognized by geoscientists. Such links have been the subject of both modelling and observational studies that have attempted to assess the degree and nature of any coupling. The uplift of high mountains and the closure of ocean gateways disrupt circulation patterns in the atmosphere and oceans, and thereby affect the transfer of heat from low latitudes to the poles (Borrelli et al. 2014; Korte et al. 2015; Tada et al. 2016). It has been suggested that uplift of mountains also causes long-term cooling as a result of increased chemical weathering of silicate minerals that draws down concentrations of CO 2 , a greenhouse gas, in the atmosphere (Raymo & Ruddiman 1992). Rapid sedimentation may further sequester organic carbon in major depocentres where it remains, at least until it is subducted or uplifted in a new phase of orogeny (Galy et al. 2007). In turn, the atmosphere and hydrosphere influence the solid Earth, largely through the action of surface processes that cause erosion and exhumation and consequentially help to define the structure of mountain belts (Koons et al. 2003; Sinclair et al. 2005; Whipple 2009). No system is believed to typify these interactions better than the Asian monsoon and the building of the Himalaya, Tibetan Plateau and associated ranges (Prell & Kutzbach 1992; Molnar et al. 1993; Clift & Webb 2019). This special issue of Geological Magazine is designed to showcase results of research undertaken after International Ocean Discovery Program (IODP) Expedition 355 in the spring of 2015 (Pandey et al. 2016c). This research effort involved deep coring of the sediments deposited in the Laxmi Basin of the eastern Arabian Sea by the research vessel JOIDES Resolution. The objective was to recover a record of evolving erosion, weathering and continental climate linked to the Indus Basin, as well as the oceanography of the Arabian Sea, which has long been recognized to be closely linked to the intensity of the South Asian monsoon (Kroon et al. 1991; Prell et al. 1992). A secondary objective was to better understand the tectonics of the Laxmi Basin itself and assess its role in the opening of the Indian Ocean. While some results have been published elsewhere, this special issue represents the biggest single collection of work completed by the science party, exploiting the unprecedented long-duration sedimentary records that are required to examine how climate and tectonics may have co-varied in the western Himalayas since the start of the India-Asia collision, likely at c. 60-50 Ma (Najman et al. 2010; DeCelles et al. 2014; Wu et al. 2014). The emplacement of a large mass-transport complex (MTC) into the Laxmi Basin during late Miocene time (Calvès et al. 2015; Dailey et al. 2020) means that much of the earlier history remains unknown either because of erosion by the MTC, or because of drilling difficulties caused by the rocks within the MTC (Pandey et al. 2016a, b). Nonetheless, a record of evolving climate and erosion dating from c. 10.8 Ma to the present represents a major improvement in our understanding of evolving climate, erosion and tectonics in SW Asia. Coring was undertaken at two sites. Site U1456 is located in the middle of the Laxmi Basin, whereas Site U1457 is located on the western side of the basin adjacent to Laxmi Ridge; the latter was specifically positioned to recover samples from the igneous basement, which was successful (Pandey et al. 2016c). Reconstructions of the palaeoceanography in the western Indian Ocean represented some of the first and most important constraints on the varying intensity of the South Asian monsoon (Kroon et al. 1991; Prell et al. 1992). In the west, summer monsoon winds cause coastal upwelling of nutrient-rich deep water offshore Oman, resulting in blooms of plankton (Curry et al. 1992). A number of proxies have now been applied to the newly recovered sediment in order to understand how the palaeoceanography in the eastern Arabian Sea also varied. Satpathy et al. (2019) examined upper water column dynamics using an assemblage of records based on oxygen and carbon isotopic variations in foraminifers, as well as a Mg/Ca-based sea-surface temperature reconstruction. Their work indicates two discrete intervals of monsoon-related change in the upper water column at 2.7-1.85 Ma and 1.65-1.55 Ma. They suggest that the upper water column was more stratified between 2.7 and 1.85 Ma as a result of weak Asian monsoon circulation. The 1.65-1.55 Ma interval was instead related to strong winter monsoon winds.

Geophysical Research Letters, 2021

Uplift and erosion of the Himalayas and Tibetan Plateau have resulted in the deposition of some o... more 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.

Earth and Planetary Science Letters, 2022

Rapid uplift and exhumation is hypothesized to occur within focused zones of orogenic syntaxes wh... more Rapid uplift and exhumation is hypothesized to occur within focused zones of orogenic syntaxes which may dominate sediment flux from a mountain belt. The Namche Barwa-Gyala Peri Massif (NBGPM) in the Himalayan Eastern syntaxis is an example of such a high sediment production zone. Here we apply detrital zircon and rutile U-Pb dating to modern river sediments sampled up-and downstream of the Nanga Parbat-Haramosh Massif (NPHM) in the Western Himalayan syntaxis. Mass balancing of these data show that the total amount of sediment contributed to the trunk Indus from NPHM is relatively small, accounting for 9-10% of the total zircons reaching the Arabian Sea, and potentially much less when source fertility is taken into account. The sediment productivity of NPHM is high but likely less than half of that seen at NBGPM (30-56 Mt/yr vs. 72-211 Mt/yr). This discrepancy may be explicable by the drier climate, less prominent syntaxial knick-zone, and weaker spatial relationship between NPHM and the Indus River compared to its eastern twin. Our revised sediment flux estimate for NPHM implies regional modern exhumation rates of ∼3-5 mm/y, lower than estimated from the core massif since 1.7 Ma.

Scientific Drilling, 2022

The International Ocean Discovery Program (IODP) conducted a series of expeditions between 2013 a... more The International Ocean Discovery Program (IODP) conducted a series of expeditions between 2013 and 2016 that were designed to address the development of monsoon climate systems in Asia and Australia. Significant progress was made in recovering Neogene sections spanning the region from the Arabian Sea to the Sea of Japan and southward to western Australia. High recovery by advanced piston corer (APC) has provided a host of semi-continuous sections that have been used to examine monsoonal evolution. Use of the half-length APC was successful in sampling sand-rich sediment in Indian Ocean submarine fans. The records show that humidity and seasonality developed diachronously across the region, although most regions show drying since the middle Miocene and especially since ∼ 4 Ma, likely linked to global cooling. A transition from C 3 to C 4 vegetation often accompanied the drying but may be more linked to global cooling. Western Australia and possibly southern China diverge from the general trend in becoming wetter during the late Miocene, with the Australian monsoon being more affected by the Indonesian Throughflow, while the Asian monsoon is tied more to the rising Himalaya in South Asia and to the Tibetan Plateau in East Asia. The monsoon shows sensitivity to orbital forcing, with many regions having a weaker summer monsoon during times of northern hemispheric Glaciation. Stronger monsoons are associated with faster continental erosion but not weathering intensity, which either shows no trend or a decreasing strength since the middle Miocene in Asia. Marine productivity proxies and terrestrial chemi-Published by Copernicus Publications on behalf of the IODP and the ICDP.

Geological Society of America Bulletin, 2019

A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in v... more A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in volume all but one other known complex on passive margins worldwide. The complex, named the Nataraja Slide, was drilled by International Ocean Discovery Program (IODP) Expedition 355 in two locations where it is ~300 m (Site U1456) and ~200 m thick (Site U1457). The top of this mass-transport complex is defined by the presence of both reworked microfossil assemblages and deformation structures, such as folding and faulting. The deposit consists of two main phases of mass wasting, each consisting of smaller pulses, with generally fining-upward cycles, all emplaced just prior to 10.8 Ma based on biostratigraphy. The base of the deposit at each site is composed largely of matrix-supported carbonate breccia that is interpreted as the product of debris-flows. In the first phase, these breccias alternate with well-sorted calcarenites deposited from a high-energy current, coherent limestone blocks that are derived directly from the Indian continental margin, and a few clastic mudstone beds. In the second phase, at the top of the deposit, muddy turbidites dominate and become increasingly more siliciclastic. At Site U1456, where both phases are seen, a 20-m section of hemipelagic mudstone is present, overlain by a ~40-m-thick section of calcarenite and slumped interbedded mud and siltstone. Bulk sediment geochemistry, heavy- mineral analysis, clay mineralogy, isotope geochemistry, and detrital zircon U-Pb ages constrain the provenance of the clastic, muddy material to being reworked, Indus-derived sediment, with input from western Indian rivers (e.g., Narmada and Tapti Rivers), and some material from the Deccan Traps. The carbonate blocks found within the breccias are shallow-water limestones from the outer western Indian continental shelf, which was oversteepened from enhanced clastic sediment delivery during the mid-Miocene. The final emplacement of the material was likely related to seismicity as there are modern intraplate earthquakes close to the source of the slide. Although we hypothesize that this area is at low risk for future mass wasting events, it should be noted that other oversteepened continental margins around the world could be at risk for mass failure as large as the Nataraja Slide.

Geological Magazine, 2019

The late Miocene is a time of strong environmental change in SW Asia. Himalayan foreland stable i... more The late Miocene is a time of strong environmental change in SW Asia. Himalayan foreland stable isotope data show a shift in the dominant vegetation of the flood plains away from trees and shrubs towards more C4 grasslands at a time when oceanic upwelling increased along the Oman margin. We present integrated geochemical and colour spectral records from International Ocean Discovery Program Site U1456 in the eastern Arabian Sea to reconstruct changing chemical weathering and erosion, as well as relative humidity during this climatic transition. Increasing hematite/goethite ratios derived from spectral data are consistent with long-term drying after c. 7.7 Ma. Times of dry conditions are largely associated with weaker chemical alteration measured by K/Rb and reduced coarse clastic flux, constrained by Si/Al and Zr/Al. A temporary phase of increased humidity from 6.3 to 5.95 Ma shows a reversal to stronger weathering and erosion. Wetter conditions can result in both more and less alteration due to the nonlinear relationship between weathering rates, precipitation and sediment transport times. Trends in relative aridity do not follow existing palaeoceanographic records and are not apparently linked to changes in Tibetan or Himalayan elevation, but more closely correlate with global cooling. An apparent opposing trend in the humidity evolution in the Indus compared to southern China, as tracked by spectrally estimated hematite/goethite, likely reflects differences in the topography in the Indus compared to the Pearl River drainage basins, as well as the generally wetter climate in southern China.

Abstract. Climate exerted constraints on the growth and decline of past human societies but our k... more Abstract. Climate exerted constraints on the growth and decline of past human societies but our knowledge of temporal and spatial climatic patterns is often too restricted to address causal connections. At a global scale, the inter-hemispheric thermal balance provides an emergent framework for understanding regional Holocene climate variability. As the thermal balance adjusted to gradual changes in the seasonality of insolation, the Inter-Tropical Convergence Zone migrated southward accompanied by a weakening of the Indian summer monsoon. Superimposed on this trend, anomalies such as the Little Ice Age point to asymmetric changes in the extratropics of either hemisphere. Here we present a reconstruction of the Indian winter monsoon in the Arabian Sea for the last 6000 years based on paleobiological records in sediments from the continental margin of Pakistan at two levels of ecological complexity: sedimentary paleo-DNA reflecting water column environmental states and planktonic foraminifers sensitive to winter conditions. We show that strong winter monsoons between ca. 4,500 and 3,000 years ago occurred during an interval of weak interhemispheric temperature contrast, which we identify as the Early Neoglacial Anomaly (ENA), and were accompanied by changes in wind and precipitation patterns across the eastern Northern Hemisphere and Tropics. This coordinated climate reorganization may have helped trigger the metamorphosis of the urban Harappan civilization into a rural society through a push-pull migration from summer flood-deficient river valleys to the Himalayan piedmont plains with augmented winter rains. Finally, we speculate that time-transgressive landcover changes due to aridification of the Tropics may have led to a generalized instability of the global climate during ENA at the transition from the warmer Holocene Optimum to the cooler Neoglacial.

Citation: Giosan, L., Orsi, W. D., Coolen, M., Wuchter, C., Dunlea, A. G., Thirumalai, K., Munoz, S. E., Clift, P. D., Donnelly, J. P., Galy, V., and Fuller, D. Q.: Neoglacial Climate Anomalies and the Harappan Metamorphosis, Clim. Past Discuss., https://doi.org/10.5194/cp-2018-37, in review, 2018.

Chapman Conference on the Evolution of the Monsoon, Biosphere and Mountain Building in Cenozoic Asia , 2020

An international group of scientists met between January 5 and 9, 2020 at the AGU Headquarters in... more An international group of scientists met between January 5 and 9, 2020 at the AGU Headquarters in Washington, D.C. to review recent research in the monsoon and geology of Asia, highlighting new results from International Ocean Discovery Program (IODP) expeditions, recently drilled in key areas of the East Asian, Indian and Australian monsoon subsystems. This Chapman Conference brought together participants from marine geology, paleoceanography, paleoclimatology, atmospheric sciences, tectonics, geochemistry, climate modelling, and related fields. The aim was to build a broader, overarching regional perspective that would help establish connections between groups of researchers that might otherwise not come together. Participants discussed the emerging science from the new IODP drilling expeditions and compared results with erosional records and continental environmental data, as well as with the latest information on the evolving tectonics and uplift histories of the Himalayan mountain range and Tibetan Plateau. Discussions underlined the importance of integrating results into meaningful syntheses that also relate to current understanding of modern monsoon atmospheric dynamics. Finally, participants proposed ideas for future drilling in monsoonal regions and for developing multidisciplinary research strategies, based on the recently acquired experience in the region. Ultimately, these approaches should pave the way toward a synoptic understanding of the long-term evolution of the monsoon, its primary forcing mechanisms and the inter-linkages between regional subsystems.

Progress in Earth and Planetary Science, 2022

Although there is increasing evidence for wet, monsoonal conditions in Southeast Asia during the ... more Although there is increasing evidence for wet, monsoonal conditions in Southeast Asia during the late Eocene, it has not been clear when this environment became established. Cenozoic sedimentary sequences constrained by radiometrically dated igneous rocks from the Jianchuan Basin in the southeast flank of Tibetan Plateau now provide a section whose facies and climatic proxies determine this evolution. Semi-arid conditions had dominated the region since Paleocene controlled by the northern subtropical high pressure system, culminating in mid Eocene when desert dunes developed. From 36 Ma, the basin began to accumulate swamp sediments with coals, together with synchronous braided river deposits and diversified pollen assemblages, indicating significant increase in precipitation. This remarkable transition from dry to wet conditions precedes the Eocene/Oligocene boundary at 34 Ma, thus excluding general global cooling as the prime driver. We propose that uplift of Tibetan Plateau might have reached a threshold elevation by that time, operating through thermal and dynamic forcing, causing the inception or significant intensification of monsoonal rains to penetrate into this downwind locality.

Tectonophysics, 2020

Subduction erosion is a long-term, large-scale geological process that dominates the structural i... more Subduction erosion is a long-term, large-scale geological process that dominates the structural inventory of a large number of convergent margins. Along the Peruvian convergent margin, this process has controlled the structural deformation of the forearc as a consequence of spatio-temporal variations during the Cenozoic. However, the pace at which tectonic erosion occurred has not been linked to regional, subduction-related events. The aim of this study is to show that subduction erosion along the Central Peruvian convergent margin off Trujillo (7 ∘ S-9 ∘ S) was influenced by plate convergence variability since the Late Cretaceous. Drilling data, multi-channel seismic (MCS) data and subsidence analyses are used to investigate the long-term effect of subduction erosion on the tectonic evolution of the Peru margin. Our study shows that subduction erosion (1) did not occur between the Cretaceous and Early Eocene (110-56 Ma), (2) increased and fluctuated between the Eocene and Pliocene (56-5 Ma) with a maximum average trench retreat of 3 km.Myr −1 between the Middle Miocene and Late Miocene (20-5 Ma), and (3) has decreased since the Pliocene (5 Ma) (1 km.Myr −1 of average trench retreat). A remarkable finding is that shorter periods of faster subduction erosion coincide with or follow major plate reorganization events that were marked by changes in the velocity and direction of relative plate convergence as well as with well-known phases of Andean orogeny. Based on our analyses, we therefore conclude that convergence variability off Peru is a primary mechanism controlling the pace at which tectonic erosion occurred along the Trujillo Basin during the Cenozoic.

Geology, 2020

The First Bend on the Yangtze River, the point where the river ceases flowing towards the south a... more The First Bend on the Yangtze River, the point where the river ceases flowing towards the south and heads towards the NE has been one of the most strongly debated geomorphic features in Asia, because it holds the key to understanding the history of the Yangtze River and is linked to the tectonic uplift of SE Tibetan Plateau. Mid to Upper Eocene sedimentary rocks preserved in the Jianchuan Basin located immediately SW of the First Bend, demonstrate that a large river system, presumably the paleo-Jinshajiang River (the upper Yangtze), used to flow south through that region. Provenance analysis of sediments over the wider region, based mostly on U-Pb dating of detrital zircon grains, confirms that the once south-flowing paleo-Yangtze River originated in the Tibetan Plateau and flowed into the South China Sea. Uplift and inversion of the Jianchuan Basin, starting in or after the latest Eocene and associated with wider plateau uplift at that time, caused the river to be diverted towards the east where it was confined along tectonic lineaments associated with strike-slip faulting, giving birth to the First Bend and the modern Yangtze River.