Proximal to distal grain‐size distribution of basin‐floor lobes: A study from the Battfjellet Formation, Central Tertiary Basin, Svalbard

Yvonne T. Spychala,Sten‐Andreas Grundvåg,Joris T. Eggenhuisen,Florian Pohl,Sara Wróblewska,Thymen A. B. Ramaaker

doi:10.1002/dep2.167

Abstract

AbstractThe grain‐size distribution of sediment particles is an important aspect of the architecture of submarine fans and lobes. It governs depositional sand quality and reflects distribution of particulate organic carbon and pollutants. Documenting the grain‐size distribution of these deep‐marine sedimentary bodies can also offer us an insight into the flows that deposited them. Submarine lobes are commonly assumed to linearly fine from an apex, meaning there should be a proportional relationship between grain size and distance from the lobe apex. However, not much detailed quantitative work has been done to test this hypothesis. Exposure of a 5 km long dip‐section of basin‐floor lobes in Clinoform 12, Battfjellet Formation, Spitsbergen, enable the study of basinward grain‐size evolution in lobe deposits. Furthermore, the dataset allows testing if there are any documentable grain‐size differences between lobe sub‐environments. For this purpose, the palaeogeography of Clinoform 12 was reconstructed and the youngest lobe, which was exposed in all collected logs, chosen to be evaluated for its grain‐size trends. Photographed thin sections of 66 rock samples were analysed to obtain quantitative grain‐size distributions. The results show that fining of lobe deposits occurs predominantly in the most proximal and most distal parts of the lobe, while the intermediate lobe, which is dominated by lobe off‐axis deposits, is characterised by a relatively consistent grain‐size range. Lobe sub‐environments show statistically distinct grain‐size distributions from lobe axis to lobe fringe. An explanation for these trends is the interplay of capacity and competence‐driven deposition with the grain‐size stratification of the flows. The outcomes of this study help to better understand the proximal to distal evolution of turbidity currents and their depositional patterns. They also provide important insights in reservoir potential of basin‐floor fans at lobe scale.

Highlights

Grain-size distribution is one of the fundamental attributes of facies properties
Re- assigning individual samples to other sub-environments based on their microscopic grain-size distribution could be justified in practice, but would here generate the appearance of circularity: grain size correlates with facies association, outlying grain-s ize distributions are re-assigned to another facies association, and correlate to facies association
The basin-floor fans of the Battfjellet Formation in Svalbard that outcrop in a proximal to distal orientation create the rare opportunity to analyse the longitudinal evolution of these distal deposits from lobe axis to fringe over a distance of 5 km

Summary

Introduction

Grain-size distribution is one of the fundamental attributes of facies properties. It reflects transport history and depositional mechanisms of sedimentary deposits. The processes that control the grain-size distribution across submarine fans are poorly understood. The root of this poor understanding seems to stem at least in part from the paucity of documentation of quantitative grain-size distribution in natural submarine fan deposits (Bell et al, 2018; Fildani et al, 2018; Kane et al, 2017)

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