Abstract

The higher land plants (vascular plants) consistently register δ¹³C signatures from the atmosphere with a nearly constant offset during their life span^[1]. Because the phytoclasts in deposits are original from these higher plants, the organic δ¹³C signals measured in phytoclasts can reflect the atmospheric carbon-isotope signature the time of deposition^[2,3]. This study integrates the organic δ¹³C data sets, C/N ratio, and palynological analysis to explore the relationship between carbon isotopes, sedimentary facies, and inferred relative sea-level changes. In this study, negative δ¹³C excursions are coincident with the clay-rich strata and higher sea levels, whereas the positive shifts are related with sand-rich strata and relatively lower sea levels. Moreover, due to the relatively rapid atmospheric circulation (ca.10-40 years), the terrestrial carbon-isotope signals registered the δ¹³C signatures from atmosphere could represent the global carbon-isotope fluctuation^[4]. This inference is supported by plausible correlation of the positive and negative carbon-isotope excursions in our terrestrial organic matter to similar fluctuations recorded from oceanic carbonates globally^[5], where the strata are equivalent to the Middle Miocene Monterey Event in age^[6,7]. However, in strata of early Miocene age the correlations are much less convincing. In this study we explore a range of possible additional influences on phytoclast carbon-isotope composition with a view to strengthening the use of carbon-isotope stratigraphy as a tool for correlation between terrestrial and oceanic stratigraphy.

Reference

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