Sediment microfabric records mass sedimentation of colonial cyanobacteria and extensive syndepositional metazoan reworking in Pliocene sapropels
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2018
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Löhr, S.C.
Kennedy, M.J.
George, S.C.
Williamson, R.J.
Xu, H.
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The Depositional Record, 2018; 4(2):293-317
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Stefan C. Löhr, Martin J. Kennedy, Simon C. George, Robyn J. Williamson, Huiyuan Xu
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Abstract
The sapropel record of the eastern Mediterranean provides unique insight into the primary climatic, oceanographic, and biological drivers of organic carbon enrichment in marine sediments. The dominant source of organic matter, timing of oxygen depletion at the sea floor, and extent of metazoan reworking of these deposits remain unclear. These questions are addressed by combining microbeam imaging with bulk and molecular geochemical characterization of several Pliocene sapropels, revealing four microfacies which record distinct palaeoceanographic conditions, phytoplankton assemblages, and degrees of postdepositional reworking. The most organic‐rich, carbonate‐lean sapropel intervals consist of alternating 10–60‐μm‐thick organic and detrital mineral laminae. Petrographical features consistent with a pelagic origin, δ15N 50 μm organomineral aggregates, interpreted as marine snow, whereas carbonate microfossil‐rich intervals record periods of nitrogen fixation and moderately increased primary production by a diverse assemblage of calcareous, organic‐walled, and siliceous plankton. The results presented here further show that burrowing by microscopic meiofauna impacted most sapropels, extending into seemingly laminated intervals below obvious disruption from burrowing macrofauna, indicating that metazoans influence organic carbon burial in oxygen‐depleted settings even where physical displacement of sediment is not visible.
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© 2018 The Authors. The Depositional Record published by John Wiley & Sons Ltd on behalf of International Association of Sedimentologists. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.