Clay‐coat diversity in marginal marine sediments

Abstract

The specific mineralogy of clay grain coats controls the ability of the coat to inhibit quartz cementation in sandstones during prolonged burial and heating. How and why clay-coat mineralogy varies across marginal marine systems is poorly understood, even though these eogenetic phenomena strongly influence subsequent mesodiagenesis and reservoir quality. The novel development of the ability to predict the distribution of clay-coat mineralogy would represent an important development for sandstone reservoir quality prediction. In marginal marine sediments, clay minerals occur as grain-coats, floccules, mud intraclasts, clay-rich rock fragments or as dispersed material. However, the relationships between clay mineralogy, the amount of clay, and its distribution is poorly understood. This study focused on the Ravenglass Estuary, UK. The key aim was to develop and apply a novel methodology utilising scanning electron microscopeenergy dispersive spectrometry, for the first time, on grain coats in modern sediments, to differentiate the clay-coat mineral signature from that of the bulk sediment, and reveal the distribution of clay minerals across marginal marine sediments. The study showed that marginal marine sediments principally have their clay mineral assemblage present as clay-coats on sand grains. These clay-coats have a mixed clay mineralogy and are spatially heterogeneous across the range of marginal-marine depositional environments. The study further showed that clay-coat mineralogy is governed initially by the hydrologically-controlled segregation of the clay minerals within inner estuarine depositional environments, and subsequently by the selective abrasive removal of specific clay mineral types during reworking and transport into the outer estuary and the marine environment. The highest relative abundance of grain-coating chlorite was in sand-flat and tidal-bar depositional environments. The availability of an analogue data set, and an understanding of the controlling processes of clay-coat mineralogy, offer crucial steps in building a predictive capability for clay-coat derived elevated reservoir quality in deeply buried sandstones.

Stratigraphy and sedimentary evolution of a modern macro‐tidal incised valley: An analogue for reservoir facies and architecture

“…According to Zaitlin et al (1994), the deposits have formed a single, simple-fill in that most of the deposits correspond to one cycle of sea-level fall and rise during the Holocene (Lloyd et al, 2013). The Ravenglass incised valley is a relatively small, modern day macro-tidal estuary with a multitributary system that has undergone extensive interpretation of the surface and shallow subsurface sediment (Griffiths et al, 2018;Wooldridge et al, 2018Wooldridge et al, , 2019. Here, the study will examine the complete sedimentary in-fill of the Ravenglass valley, produce detailed facies descriptions and create high resolution correlations linking shoreline migration to style of sedimentation.…”

Automated Classification of Estuarine Sub‐Depositional Environment Using Sediment Texture

“…The surface sediments of the Ravenglass Estuary have been extensively studied, with geomorphologically distinct sub‐depositional environments identified using key diagnostic features, such as bedforms, sedimentary structures, sediment texture, and bioturbation traces (i.e., lithofacies and ichnofacies) (Daneshvar & Worden, 2018; Griffiths et al., 2018, 2019a, 2019b; Muhammed et al., 2022; Simon et al., 2021; Wooldridge et al., 2017a, 2017b, 2018, 2019a). Modern sub‐depositional environments in the Ravenglass Estuary have been defined (Figure 1b) and include gravel beds (De1), tidal flats (mud flats (De2), mixed flats (De3), sand flats (De4)), tidal bars (De5), tidal inlet (De6), backshore (De7), foreshore (De8), pro‐ebb delta (De9), and saltmarsh (De10) (Griffiths et al., 2018; Simon et al., 2021; Wooldridge et al., 2017b).…”

Automated mineralogy (SEM-EDS) approach to sandstone reservoir quality and diagenesis

“…Porosity relates to the volume of fluid in a given volume of rock and permeability relates to rate of movement of that fluid under a given pressure gradient. This contribution focusses upon the application of Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) techniques to sandstone reservoirs in the subsurface although SEM-EDS can be used for the study of carbonate and other reservoirs as well as unconsolidated sand (Wooldridge et al, 2019). The first part of the paper summarises primary and diagenetic controls on sandstone reservoir quality.…”