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

Abstract

The 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.

Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway

“…The successive shelf‐edges of these clinoforms have been mapped by previous studies (Plink‐Björklund et al ., 2001; Mellere et al ., 2002; Steel & Olsen, 2002; Grundvåg et al ., 2014b). The depositional architecture, internal organization and the established hierarchy of the lobe complexes builds largely on previous studies (Steel & Olsen, 2002; Crabaugh & Steel, 2004; Johannessen & Steel, 2005; Petter & Steel, 2006; Grundvåg et al ., 2014a; Spychala et al ., 2021). Thus, to provide stratigraphic context for the recognized bed types described later, a summary is given here.…”

“…The lowermost lobe complex (LC 9) has its up‐dip pinch‐out to the north‐west of Hyrnestabben on the neighbouring mountain of Storvola (i.e. Clinoform 12 of Steel & Olsen, 2002), thus extending basinward for a minimum distance of ca 6.5 km (Figs 2A and 6; Crabaugh & Steel, 2004; Petter & Steel, 2006; Spychala et al ., 2021). The most up‐dip segment of the two succeeding lobe complexes 10 and 11 are exposed in a north‐west/south‐east‐oriented outcrop section on Storvola which can be traced further across to Hyrnestabben where the outcrop transect gradually turns to the north‐east (Fig.…”

“…7B), which represent an important constituent of the distal lobe fringe bed type association (e.g. Spychala et al ., 2021). Many TB3 beds appear to transition up‐dip into TB2 beds, thus being part of a lateral continuum of bed type configurations.…”

“…Based on the stratigraphic distribution, relative proportion and abundance of bed types, as well as degree of bed amalgamation and overall sandstone content, four bed type associations are recognized, representing: (i) lobe axis ; (ii) lobe off‐axis ; (iii) lobe fringe ; and (iv) distal lobe fringe depositional sub‐environments (Fig. 12; see also Grundvåg et al ., 2014a and Spychala et al ., 2021). The four bed type associations stack to form recurrent thickening‐upward and sandying‐upward units, referred to as lobes , in accordance with previous studies (Figs 13 and 14; Crabaugh & Steel, 2004; Grundvåg et al ., 2014a; Spychala et al ., 2021).…”

“…2E; Plink‐Björklund & Steel, 2004; Petter & Steel, 2006). However, few, if any, of the previous studies of the clinoforms and the associated lobe complexes convincingly demonstrate the presence of sandy hyperpycnites on the basin floor (Crabaugh & Steel, 2004; Johannessen & Steel, 2005; Grundvåg et al ., 2014a; Spychala et al ., 2021). Here, sedimentological data from core and outcrops are combined to interpret flow processes and down‐slope flow transformations responsible for the documented bed type variability and distribution.…”