2012 GSA Annual Meeting in Charlotte
Paper No. 248-3
Presentation Time: 9:00 AM-6:00 PM

CHANGES IN THE SILICATE WEATHERING INTENSITY ON PANGEA: AN ESTIMATE FROM THE EARLY MESOZOIC DEEP-SEA SEQUENCE IN JAPAN

IKEDA, Masayuki, Ehime University, Matsuyama, 7900802, Japan, m.ikeda0415@gmail.com, TADA, Ryuji, Department of Earth and Planetary Science, The University of Tokyo, Tokyo, and OLSEN, Paul E., Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964-1000

Silicate weathering is one of the most important regulators of the Earth system dynamics through nutrient supply and consumption of atmospheric CO2. However, its changes in the geologic past using geologic records have been controversial due to the lack of appropriate method to quantitatively measure the past global silicate weathering intensity. One way for its reconstruction would be an estimation of the pelagic biogenic silica burial rate, because silicate weathering and pelagic biogenic silica burial are the major source and major sink of dissolved silica in the present ocean, respectively (e.g. Treguer et al., 1995). During the Mesozoic, the pelagic bedded chert is the potential major sink of biogenic silica in the ocean. We therefore first estimate the biogenic silica burial rate for the Inuyama bedded chert in Japan based on the major elements chemical analysis of individual chert and shale beds on the continuous sequence with bed-by-bed resolution. The rhythmically alternation of chert and shale beds were reflected by the precession cycle (Ikeda et al., 2010). By using the chert-shale couplet as time scale, we reconstructed the variation in the biogenic silica burial rate for the Inuyama bedded chert from the Early Triassic to Early Jurassic. Together with paleogeographic distribution of bedded chert compiled from previous studies, the biogenic silica burial rate in the low latitude Panthalassa ocean in the form of bedded chert was several times higher than the biogenic silica burial rate in the modern global ocean (DeMaster, 2002). This result suggests that bedded chert was the major sink of dissolved silica in the ocean at least during the early Mesozoic. Therefore, the variations in the biogenic silica burial rate for bedded chert should be proportional to the variations in the dissolved silica input to the ocean in time-scales longer than its residence time in the ocean (15 kyr; e.g. Treguer et al., 1995). The high biogenic silica period is correlated with high lake level period in the equatorial Pangea based on the correlation between the bedded chert and the Newark Supergroup, where lake level and the silicate weathering intensity would be affected by precipitation. This result further supports the idea that biogenic silica burial rate for bedded chert was the potential measure forsilicate weathering intensity.

2012 GSA Annual Meeting in Charlotte
General Information for this Meeting
Session No. 248--Booth# 248
Terrestrial Proxies of Paleoclimate and Paleoenvironment in Deep Time (Posters)
Charlotte Convention Center: Hall B
9:00 AM-6:00 PM, Wednesday, 7 November 2012

Geological Society of America Abstracts with Programs, Vol. 44, No. 7, p. 584

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