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 to have 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.This article is protected by copyright. All rights reserved.

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