Geochemistry of Sub-Depositional Environments in Estuarine Sediments: Development of an Approach to Predict Palaeo-Environments from Holocene Cores

Dahiru D Muhammed,Richard H Worden,Luke J Wooldridge,Joshua Griffiths,Robert A Duller,Naboth Simon,James E P Utley,Iris T E Verhagen

doi:10.3390/geosciences12010023

Dahiru D Muhammed, Richard H Worden + Show 6 more

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https://doi.org/10.3390/geosciences12010023

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Abstract

In the quest to use modern analogues to understand clay mineral distribution patterns to better predict clay mineral occurrence in ancient and deeply buried sandstones, it has been necessary to define palaeo sub-environments from cores through modern sediment successions. Holocene cores from Ravenglass in the NW of England, United Kingdom, contained metre-thick successions of massive sand that could not be unequivocally interpreted in terms of palaeo sub-environments using conventional descriptive logging facies analysis. We have therefore explored the use of geochemical data from portable X-ray fluorescence analyses, from whole-sediment samples, to develop a tool to uniquely define the palaeo sub-environment based on geochemical data. This work was carried out through mapping and defining sub-depositional environments in the Ravenglass Estuary and collecting 497 surface samples for analysis. Using R statistical software, we produced a classification tree based on surface geochemical data from Ravenglass that can take compositional data for any sediment sample from the core or the surface and define the sub-depositional environment. The classification tree allowed us to geochemically define ten out of eleven of the sub-depositional environments from the Ravenglass Estuary surface sediments. We applied the classification tree to a core drilled through the Holocene succession at Ravenglass, which allowed us to identify the dominant paleo sub-depositional environments. A texturally featureless (massive) metre-thick succession, that had defied interpretation based on core description, was successfully related to a palaeo sub-depositional environment using the geochemical classification approach. Calibrated geochemical classification models may prove to be widely applicable to the interpretation of sub-depositional environments from other marginal marine environments and even from ancient and deeply buried estuarine sandstones.

Highlights

Reservoir quality studies in the petroleum industry have led to improved production strategies for oil and gas fields [1]
This study addressed the following research questions: 1. What elements are dominant within the surface sediment in the Ravenglass Estuary? 2
If Al and K were largely controlled by K-feldspar distribution, the highest concentrations of these elements would be in the coarser sedimentary sub-depositional environments

Summary

Introduction

Reservoir quality studies in the petroleum industry have led to improved production strategies for oil and gas fields [1]. Reservoir quality prediction in ancient estuarine and mixed fluvial–marine clastic sediments presents a challenge [8]. These problems are compounded by the presence of multiple sediment sources (variable hinterland geology as well as sediment sourced from the sea), the spatial and temporal variability in sediment transport related to the interaction of tidal and riverine processes, and the susceptibility of these environments to evolve as a result of relative sea-level change [7]. Geochemical approaches offer a practical way to effectively characterise and interpret estuarine and mixed fluvial–marine sediments, which may be linked to reservoir quality analysis of ancient and deeply buried strata because sediment geochemistry influences the mineral processes during diagenetic transformations [9]

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