The use of microstructures for discriminating turbiditic and hemipelagic muds and mudstones

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 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.

Greenalite Nanoparticles in Alkaline Vent Plumes as Templates for the Origin of Life

“…2C, 2D). The distribution and orientation of the greenalite particles closely resemble the texture of freshly deposited muds (Bennett et al, 1981(Bennett et al, , 1991Kase et al, 2016) and frozen clay slurries (Deirieh et al, 2018), which commonly comprise 5-20% mud and 80-95% water. The microfabric of the greenalite-chert bands indicates that some of the ferrous silicate particles settled from suspension as colloidal flocs (Rasmussen et al, 2019a).…”

Evidence for anoxic shallow oceans at 2.45 Ga: Implications for the rise of oxygenic photosynthesis

“…Their random orientation and uniform distribution are identical to the fabric of greenalite in deeper-water BIFs (Rasmussen et al, 2015a(Rasmussen et al, , 2017. This fabric closely resembles the texture of clay slurries (Deirieh et al, 2018) and modern marine muds (Bennett et al, 1981;Kase et al, 2016), supporting a depositional origin for the greenalite particles (Rasmussen et al, 2019). The preservation of depositional textures in parts of the chert implies that early diagenetic silica cementation "froze" the original fabric of the chemical muds, minimizing the effects of diagenesis, burial-related compaction, and metamorphism.…”

Poroelastic Modeling of a Heterogeneous Geologic Medium: A Case Study from Kanto Basin in Japan

“…Semiconsolidated mudstone units from the Kazusa Group rocks were devoid of depositional structures, showing rather homogeneous hydraulic properties spatially in contrast to weakly consolidated sandstone units that showed vertical gradation with gradual variation in hydraulic properties (Hirayama and Nakajima 1977). Mudstone units were mainly composed of silt-sized grains with around 25 to 30 weight percent of clay-sized particles (Kase et al 2016) whereas sandstone units composed of around 3 to 17 volume percent of fine-grained particles (Ito 2008).…”