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

• Published in: The depositional record Vol. 8; no. 2; pp. 436 - 456
• Main Authors: Spychala, Yvonne T., Ramaaker, Thymen A. B., Eggenhuisen, Joris T., Grundvåg, Sten‐Andreas, Pohl, Florian, Wróblewska, Sara
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01.06.2022; Wiley
• Subjects: Basins; flow processes; Geofag: 450; Geosciences: 450; Grain size; grain‐size counting; Matematikk og Naturvitenskap: 400; Mathematics and natural science: 400; palaeo‐reconstruction; Particulate organic carbon; Sediments; Stratigraphy; thin sections; Trends; turbidites; Turbidity; Turbidity currents; VDP; Arctic region; Greenland
• ISSN: 2055-4877; 2055-4877
• DOI: 10.1002/dep2.167

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. We studied the distribution of grain sizes from the proximal to the distal area of one lobe as well as between lobe sub‐environments. A total of 66 photographed thin sections were manually counted to determine the grain‐size distribution of lobe axis, lobe off‐axis and lobe‐fringe deposits. These sub‐environments have statistically distinct and variable grain‐size distributions superimposed on an overall non‐linear fining trend from lobe axis to lobe fringe. Furthermore, the sub‐environments show different longitudinal grain‐size trends. Lobe axis and fringe settings show (weak) basinward fining trends whereas lobe off‐axis settings show no variation in grain‐size distribution with distance. An explanation for these trends is the interplay of capacity‐driven deposition from the decelerating flow, the grain‐size stratification of the flows and advection of the flow over the lobe.