The Indus is the only major river in the western Himalaya and its sedimentary flux into the Indus... more The Indus is the only major river in the western Himalaya and its sedimentary flux into the Indus Fan might be expected to contain an erosional record of the growth of high topography since India-Asia collision. Interpretation of regional seismic profiles across the shelf and continental slope suggests sedimentation rates peaking in the Middle Miocene (11-16 Ma), then falling to the present day. This variability does not correlate with apparent monsoon intensification at 8.5 Ma or with Late Miocene to Recent exhumation in the ...
New bulk sediment Sr and Nd isotopes, coupled with U-Pb dating of detrital zircon grains from sed... more New bulk sediment Sr and Nd isotopes, coupled with U-Pb dating of detrital zircon grains from sediment cored by International Ocean Discovery Program in the Arabian Sea, allow reconstruction of erosion in the Indus catchment since ca. 17 Ma. Increasing Nd values from 17 to 9.5 Ma imply relatively more erosion from the Karakoram/Kohistan, likely linked to slip on the Karakoram Fault and compression in the Southern and Eastern Karakoram. Long-term decreasing Nd values after 5.7 Ma correlate with increasing relative abundance of >300 Ma zircon grains that are most common in Himalayan bedrocks, precluding large-scale drainage capture as the cause of decreasing Nd values in the submarine fan. Although the initial increase in Lesser Himalayan derived 1500–2300 Ma zircons after 7.0 Ma is consistent with earlier records from the foreland basin the much greater rise after 1.9 Ma, shortly after a fall in Nd values after 3.4 Ma, has not previously been recognized and suggests that widespread unroofing of the Crystalline Lesser Himalaya and to a lesser extent Nanga Parbat did not occur until after 3.4 Ma. No simple links can be made between erosion and the development of the South Asian Monsoon, implying a largely tectonic control to Lesser Himalayan unroofing.
In the latest Paleocene an abrupt shift to more negative delta13C values has been documented at n... more In the latest Paleocene an abrupt shift to more negative delta13C values has been documented at numerous marine and terrestrial sites [Bralower et al., 1997; Cramer et al., 1999; Kaiho et al., 1996; Kennett and Stott, 1991; Koch et al., 1992; Stott et al., 1996; Thomas and Shackleton, 1996; Zachos et al., 1993]. This carbon isotope event (CIE) is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4°-6°C [Kennett and Stott, 1991] and more moderate warming in the subtropics [Thomas et al., 1999]. Here we report 187Os/188Os isotope records from the North Atlantic and Indian Oceans which demonstrate a >10% increase in the 187Os/188Os ratio of seawater coincident with the late Paleocene CIE. This excursion to higher 187Os/188Os ratios is consistent with a global increase in weathering rates. The inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate, which acts to stabilize Earth's climate [Walker et al., 1981]. Estimates of the duration of late Paleocene CIE [Bains et al., 1999; Bralower et al., 1997; Norris and Röhl, 1999; Röhl et al., 2000] in conjunction with the Os isotope data imply that intensified chemical weathering in response to warm, humid climates can occur on timescales of 104-105years. This interpretation requires that the late Palcocene thermal maximum Os isotope excursion be produced mainly by increased Os flux to the ocean rather than a transient excursion to higher 187Os/188Os ratios in river runoff. Although we argue that the former is more likely than the latter, we cannot rule out significant changes in the 187Os/188Os ratio of rivers.
... The decrease in grain size in Cretaceous-Paleogene boundary deposits from the slope to the Be... more ... The decrease in grain size in Cretaceous-Paleogene boundary deposits from the slope to the Bermuda Rise ... in the depth of the CCD at the end of the Cretaceous are clearly ... ACOUSTIC EVIDENCE FOR THE DISTRIBUTION OF CRETACEOUS-PALEOGENE MASS WASTING. ...
Highly magnesian lavas characterised by strong light rare earth element depletion are a feature o... more Highly magnesian lavas characterised by strong light rare earth element depletion are a feature of Theistareykir and the Reykjanes Peninsula of Iceland, which are marginal to the proposed axis of the mantle plume. These lavas define positive covariations between whole rock osmium and olivine oxygen isotope ratios (187Os/188Os= 0.1269–0.1369; δ18Oolivine= 4.2–5.7‰) that extend the array defined by Hawaiian samples to more unradiogenic Os isotope ratios and lower δ18O. The Os–O variation is difficult to explain ...
The Indus is the only major river in the western Himalaya and its sedimentary flux into the Indus... more The Indus is the only major river in the western Himalaya and its sedimentary flux into the Indus Fan might be expected to contain an erosional record of the growth of high topography since India-Asia collision. Interpretation of regional seismic profiles across the shelf and continental slope suggests sedimentation rates peaking in the Middle Miocene (11-16 Ma), then falling to the present day. This variability does not correlate with apparent monsoon intensification at 8.5 Ma or with Late Miocene to Recent exhumation in the ...
New bulk sediment Sr and Nd isotopes, coupled with U-Pb dating of detrital zircon grains from sed... more New bulk sediment Sr and Nd isotopes, coupled with U-Pb dating of detrital zircon grains from sediment cored by International Ocean Discovery Program in the Arabian Sea, allow reconstruction of erosion in the Indus catchment since ca. 17 Ma. Increasing Nd values from 17 to 9.5 Ma imply relatively more erosion from the Karakoram/Kohistan, likely linked to slip on the Karakoram Fault and compression in the Southern and Eastern Karakoram. Long-term decreasing Nd values after 5.7 Ma correlate with increasing relative abundance of >300 Ma zircon grains that are most common in Himalayan bedrocks, precluding large-scale drainage capture as the cause of decreasing Nd values in the submarine fan. Although the initial increase in Lesser Himalayan derived 1500–2300 Ma zircons after 7.0 Ma is consistent with earlier records from the foreland basin the much greater rise after 1.9 Ma, shortly after a fall in Nd values after 3.4 Ma, has not previously been recognized and suggests that widespread unroofing of the Crystalline Lesser Himalaya and to a lesser extent Nanga Parbat did not occur until after 3.4 Ma. No simple links can be made between erosion and the development of the South Asian Monsoon, implying a largely tectonic control to Lesser Himalayan unroofing.
In the latest Paleocene an abrupt shift to more negative delta13C values has been documented at n... more In the latest Paleocene an abrupt shift to more negative delta13C values has been documented at numerous marine and terrestrial sites [Bralower et al., 1997; Cramer et al., 1999; Kaiho et al., 1996; Kennett and Stott, 1991; Koch et al., 1992; Stott et al., 1996; Thomas and Shackleton, 1996; Zachos et al., 1993]. This carbon isotope event (CIE) is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4°-6°C [Kennett and Stott, 1991] and more moderate warming in the subtropics [Thomas et al., 1999]. Here we report 187Os/188Os isotope records from the North Atlantic and Indian Oceans which demonstrate a >10% increase in the 187Os/188Os ratio of seawater coincident with the late Paleocene CIE. This excursion to higher 187Os/188Os ratios is consistent with a global increase in weathering rates. The inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate, which acts to stabilize Earth's climate [Walker et al., 1981]. Estimates of the duration of late Paleocene CIE [Bains et al., 1999; Bralower et al., 1997; Norris and Röhl, 1999; Röhl et al., 2000] in conjunction with the Os isotope data imply that intensified chemical weathering in response to warm, humid climates can occur on timescales of 104-105years. This interpretation requires that the late Palcocene thermal maximum Os isotope excursion be produced mainly by increased Os flux to the ocean rather than a transient excursion to higher 187Os/188Os ratios in river runoff. Although we argue that the former is more likely than the latter, we cannot rule out significant changes in the 187Os/188Os ratio of rivers.
... The decrease in grain size in Cretaceous-Paleogene boundary deposits from the slope to the Be... more ... The decrease in grain size in Cretaceous-Paleogene boundary deposits from the slope to the Bermuda Rise ... in the depth of the CCD at the end of the Cretaceous are clearly ... ACOUSTIC EVIDENCE FOR THE DISTRIBUTION OF CRETACEOUS-PALEOGENE MASS WASTING. ...
Highly magnesian lavas characterised by strong light rare earth element depletion are a feature o... more Highly magnesian lavas characterised by strong light rare earth element depletion are a feature of Theistareykir and the Reykjanes Peninsula of Iceland, which are marginal to the proposed axis of the mantle plume. These lavas define positive covariations between whole rock osmium and olivine oxygen isotope ratios (187Os/188Os= 0.1269–0.1369; δ18Oolivine= 4.2–5.7‰) that extend the array defined by Hawaiian samples to more unradiogenic Os isotope ratios and lower δ18O. The Os–O variation is difficult to explain ...
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