Os Isotope Record in a Cenozoic Deep-Sea Core: Its Relation to Global Tectonics and Climate

Turekian, Karl K.; Pegram, William J.

doi:10.1007/978-1-4615-5935-1_17

Cited by 20 publications

(20 citation statements)

References 18 publications

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“…In a higher-resolution Ocean Drilling Project sediment core (67), the spike of low Os isotope values at the KTB could be differentiated from a decrease due to Deccan volcanism that apparently started Ϸ0.5 Myr before the KTB, whereas sustained delivery of unradiogenic Os from weathering of Deccan was thought to contribute to relatively low Os isotope values for several million years after Deccan emplacement. A distinct decrease in Os isotope ratios was also found at Ϸ50-55 Ma in the slowly deposited deep-sea sediment core and attributed to weathering of Tethyan ophiolites that became exposed during the India-Eurasia collision (66). Alternatively, we suggest that this decrease in Os isotopes could be due to enhanced weathering of the Deccan Traps when this large province of continental basalts drifted into the equatorial humid belt at Ϸ55 Ma.…”

Section: Weathering Of Deccan Traps In Equatorial Humid Beltsupporting

confidence: 49%

Equatorial convergence of India and early Cenozoic climate trends

Kent

Muttoni

2008

Proc. Natl. Acad. Sci. U.S.A.

144

108

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India's northward flight and collision with Asia was a major driver of global tectonics in the Cenozoic and, we argue, of atmospheric CO 2 concentration (pCO2) and thus global climate. Subduction of Tethyan oceanic crust with a carpet of carbonate-rich pelagic sediments deposited during transit beneath the high-productivity equatorial belt resulted in a component flux of CO 2 delivery to the atmosphere capable to maintain high pCO 2 levels and warm climate conditions until the decarbonation factory shut down with the collision of Greater India with Asia at the Early Eocene climatic optimum at Ϸ50 Ma. At about this time, the India continent and the highly weatherable Deccan Traps drifted into the equatorial humid belt where uptake of CO 2 by efficient silicate weathering further perturbed the delicate equilibrium between CO 2 input to and removal from the atmosphere toward progressively lower pCO 2 levels, thus marking the onset of a cooling trend over the Middle and Late Eocene that some suggest triggered the rapid expansion of Antarctic ice sheets at around the Eocene-Oligocene boundary.CO2 ͉ Deccan ͉ Tethys ͉ Himalaya ͉ Eocene M odern-day glacial climate, characterized by polar ice at sea level, is the long-term cooling derivative of a Cretaceousearly Cenozoic world dominated by warm conditions and the general absence of ice sheets (1, 2). The zenith of global warmth in the Cenozoic (0-65 Ma) was reached at Ϸ50 Ma during the Early Eocene climatic optimum (EECO) as the culmination of a Late Paleocene-Early Eocene (Ϸ60-50 Ma) warming trend in oceanic bottom waters (3) (Fig. 1A). The EECO was characterized by the widespread occurrence of cherts (4) (Fig. 1B) and reflected in warm climate conditions at even extreme high latitudes (5, 6). A persistent cooling trend ensued over the Middle and Late Eocene that eventually plummeted into a glacial climate mode with the inception of major Antarctic ice sheets at Oi-1 near the Eocene-Oligocene boundary at Ϸ34 Ma (7). Changes in ocean circulation and heat transport related to the opening of Southern Ocean gateways (8) occurred well after the start of the cooling trend at Ϸ50 Ma and do not seem to adequately account for inception of Antarctic glaciation according to recent climate models (e.g., refs. 9 and 10). Instead, reduction in greenhouse gas concentrations is the more likely fundamental cause of Antarctic freezing and global cooling (10). This is supported by the occurrence of high (albeit highly scattered) pCO 2 estimated values of Ͼ1,000 ppm at around the EECO (e.g., 11, 12; see also ref. 13) and generally low (Ͻ500 ppm) pCO 2 estimated values after Oi-1 that followed a decline that more or less parallels the long-term temperature record (14, 15) (Fig. 1 A). However, what triggered the global cooling from the EECO to Oi-1 (and thus the cause of the long-term decrease in pCO 2 ) is unclear (16).The BLAG model (17, 18) postulates that long-term changes in pCO 2 and resulting climate were driven primarily by variations in mantle outgassing tied to global seafloor prod...

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Section: Weathering Of Deccan Traps In Equatorial Humid Beltsupporting

confidence: 49%

Equatorial convergence of India and early Cenozoic climate trends

Kent

Muttoni

2008

Proc. Natl. Acad. Sci. U.S.A.

144

108

View full text Add to dashboard Cite

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“…Recent studies show that the erosion of mountainous regions results in an increase in the rate of burial of organic carbon, which may be more important than silicate weathering as a sink for CO 2 (France-Lanord and Derry 1997; Derry and FranceLanord 1997). Turekian and Pegram (1997) suggested that increased weathering of black shales in the Himalayas since 7 Ma may have increased the delivery of phosphorus to the ocean, increasing productivity, and thus lowering atmospheric CO 2 . Kump and Arthur (1997) argued that during the Late Neogene, chemical weathering increased in the Himalayas but declined elsewhere, providing for a slow, even decline in atmospheric CO 2 .…”

Section: Variations In Atmospheric Greenhouse Gas Concentrationsmentioning

confidence: 98%

The Late Cenozoic uplift - climate change paradox

Hay

Söding

DeConto

et al. 2002

International Journal of Earth Sciences

117

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The geologic evidence for worldwide uplift of mountain ranges in the Neogene is ambiguous. Estimates of paleoelevation vary, according to whether they are based on the characteristics of fossil floras, on the masses and grain sizes of eroded sediments, or on calculations of increased thickness of the lithosphere as a result of faulting. Detrital erosion rates can be increased both by increased relief in the drainage basin and by a change to more seasonal rainfall patterns. The geologic record provides no clear answer to the question whether uplift caused the climatic deterioration of the Neogene or whether the changing climate affected the erosion system in such a way as to create an illusion of uplift. We suggest that the spread of C 4 plants in the Late Miocene may have altered both the erosion and climate systems. These changes are responsible for the apparent contradictions between data supporting uplift and those supporting high elevations in the past. A brief historical perspectiveLyell (1830) was impressed by the marked contrast between the conditions required for deposition of the Carboniferous coals as opposed to the present climate. Convinced that the climate of the British Isles had been different in the past, he proposed that the change reflected differences in the global latitudinal distribution of land and sea, arguing that with more extensive land areas in the polar regions, the earth would become cooler, and conversely, with more land in the equatorial regions, the earth would be warmer.

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“…Nutrient supply from land to the oceans may have been low as a result of the low topographic relief, combined with high sea levels and thus relatively small continental area. Together these factors could have caused low weathering and erosion rates as deduced from the strontium isotopic record of marine carbonates (Turekian and Pegram, 1997). By contrast, higher temperatures, possibly higher atmospheric pCOz, higher humidity at high latitudes, and lack of ice cover on the Antarctic continent may have worked in an opposite direction.…”

Section: Warm Deep-ocean Environmentsmentioning

confidence: 99%