The use of microstructures for discriminating turbiditic and hemipelagic muds and mudstones |
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| Authors: | Yoshihiro Kase Makoto Ito Ken Ikehara Shigeru Takizawa |
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| Institution: | 1. Department of Earth Sciences, Graduate School of Science, Chiba University, Chiba, JapanPresent address: Geological Survey of Hokkaido, Hokkaido Research Organization, Nishi 12, Kita 19, Kita‐ku, Sapporo, Hokkaido 060‐0819, Japan.;2. Department of Earth Sciences, Graduate School of Science, Chiba University, Chiba, Japan;3. Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Ibaraki, Japan |
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| Abstract: | The microstructures of turbiditic and hemipelagic muds and mudstones were investigated using a scanning electron microscope to determine whether there are microstructural features that can differentiate turbiditic from hemipelagic sedimentary processes. Both types of muddy deposits are, in general, characterized by randomly‐oriented clay particles. However, turbiditic muds and mudstones also characteristically contain aggregates of ‘edge‐to‐face’ contacts between clay particles with long‐axis lengths of up to 30 μm. Based on observations of the clay fabric of the experimentally‐formed muds settled from previously agitated muddy fluids, these types of aggregates, hereafter referred to as ‘aggregates of clay particles’, are interpreted as having been formed by the collision of component flocs in turbulent fluids. Furthermore, some aggregates of clay particles have ‘face‐to‐face’ contacts between clay particles; this is similar to face‐to‐face aggregates characteristically developed in fluid‐mud deposits that are commonly recognized only in turbiditic mudstones, indicating the possibility of a final stage of deposition under highly‐dense conditions, such as temporary fluid muds. In conjunction with earlier proposed lithofacies‐based and ichnofacies‐based criteria, aggregates of clay particles should be useful for the differentiation of turbiditic and hemipelagic muddy deposits, particularly with limited volumes of non‐oriented samples from deep‐water successions. |
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| Keywords: | Deep‐water deposits flocs hemipelagites microstructures turbidites turbiditic muds |
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