TY - JOUR

T1 - Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway

AU - Grundvåg, Sten‐Andreas

AU - Helland‐Hansen, William

AU - Johannessen, Erik P.

AU - Eggenhuisen, Joris

AU - Pohl, Florian

AU - Spychala, Yvonne

N1 - Funding Information: The project received funding from the Research Council of Norway (grant number 228107). YS, JTE, and FP received funding from the Netherlands Organization for Scientific Research (grant number 864.13.006). We are grateful for the financial support from Equinor (former Statoil) during our fieldwork campaigns in 2009 and 2010. JE, FP and YS, are grateful for financial support from Equinor, Shell and ExxonMobil during our fieldwork in 2017. David Kosowski and Silje Smith-Johnsen are thanked for precious assistance during past fieldwork campaigns. Elliot Broze is acknowledged for great companionship in the field and for valuable contributions to this project during his thesis work at Hyrnestabben. We endorse Stig Henningsen for his safe boat operations and good evening company onboard. We are also grateful for the invaluable logistical support from Sara Cohen at UNIS. Finally, we are grateful for detailed journal reviews and constructive feedback by Ronald Steel, Mattia Marini and Roberto Tinterri.

PY - 2023/11/27

Y1 - 2023/11/27

N2 - Flood-generated hyperpycnal flows are dense, sediment-laden, turbulent flows that can form long-lived, bottom-hugging turbidity currents, which undoubtedly transport large volumes of fine-grained sediments into the ocean. However, their ability in transferring sand into deep-water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi-steady hyperpycnal flows; (ii) turbidites deposited by waning, surge-type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick-bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant-rich hybrid event beds and associated climbing ripple cross-laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf-edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone-filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand-laden discharges readily generated quasi-steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant-rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi-faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single-peaked floods.

AB - Flood-generated hyperpycnal flows are dense, sediment-laden, turbulent flows that can form long-lived, bottom-hugging turbidity currents, which undoubtedly transport large volumes of fine-grained sediments into the ocean. However, their ability in transferring sand into deep-water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi-steady hyperpycnal flows; (ii) turbidites deposited by waning, surge-type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick-bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant-rich hybrid event beds and associated climbing ripple cross-laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf-edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone-filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand-laden discharges readily generated quasi-steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant-rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi-faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single-peaked floods.

KW - Clinoforms

KW - Svalbard

KW - hybrid event beds

KW - quasi-steady hyperpycnal turbidity currents

KW - sediment gravity flows

KW - submarine lobes

UR - http://www.scopus.com/inward/record.url?scp=85168271954&partnerID=8YFLogxK

U2 - 10.1111/sed.13105

DO - 10.1111/sed.13105

M3 - Article

VL - 70

SP - 2057

EP - 2107

JO - SEDIMENTOLOGY

JF - SEDIMENTOLOGY

SN - 0037-0746

IS - 7

ER -