Depositional architecture and evolution of progradationally stacked lobe complexes in the Eocene Central Basin of Spitsbergen

Abstract

The down-dip portion of submarine fans comprises terminal lobes that consist of various gravity flow deposits, including turbidites and debrites. Within lobe complexes, lobe deposition commonly takes place in topographic lows created between previous lobes, resulting in an architecture characterized by compensational stacking. However, in some deep water turbidite systems, compensational stacking is less prominent and progradation dominates over aggradation and lateral stacking. Combined outcrop and subsurface data from the Eocene Central Basin of Spitsbergen provide a rare example of submarine fans that comprise progradationally stacked lobes and lobe complexes. Evidence for progradation includes basinward offset stacking of successive lobe complexes, a vertical change from distal to proximal lobe environments as recorded by an upward increase in bed amalgamation, and coarsening and thickening upward trends within the lobes. Slope clinoforms occur immediately above the lobe complexes, suggesting that a shelfslope system prograded across the basin in concert with deposition of the lobe complexes. Erosive channels are present in proximal axial lobe settings, whereas shallow channels, scours and terminal lobes dominate further basinward. Terminal lobes are classified as amalgamated, non-amalgamated or thin-bedded, consistent with turbidite deposition in lobe axis, offaxis and fringe settings, respectively. Co-genetic turbidite-debrite beds, interpreted as being deposited from hybrid sediment gravity flows which consisted of both turbulent and laminar flow phases, occur frequently in lobe off-axis to fringe settings, and are rare and poorly developed in channels and axial lobe environments. This indicates bypass of the laminar flow phase in proximal settings, and deposition in relative distal unconfined settings. Palaeocurrent data indicate sediment dispersal mainly towards the east, and is consistent with slope and lobe complex progradation perpendicular to the NNW-SSE trending basin margin.

Distal turbidite fan/lobe succession of the Late Oligocene Zuberec Fm. – architecture and hierarchy (Central Western Carpathians, Orava–Podhale basin)

“…Therefore some of our interpretations are only prediction based on a comparison with published model of submarine fan lobes [e.g. [9][10][11]25].…”

“…The meso-to large scale boundaries between each lobe system or lobe complex are generally identified by distinct mudstone intervals which show large lateral continuity (ranging kilometers) indicate starvation of clastic sediment to the deeper part of the basin, probably related with relative sea-level rise [9,11,99].…”

“…The bed thickening-and/or coarsening-up packages of lobes were considered to reflect progradation [e.g. 11,13,[17][18][19][20]. However, vertical patterns in bed thickness may also correspond to compensational cycles as a result of the smoothing of the depositional topography associated with lobe abandonment and switching [9,10,[21][22][23][24][25].…”

“…[6][7][8][9][10][11]. A key outcrop-derived characteristic of submarine fan deposits is the presence of systematic vertical patterns in bed thickness and grain size distribution.…”

Tertiary deep-marine reservoirs of the North Sea region: an introduction

“…Stacking and connectivity in lobe-dominated reservoirs are not as well understood, as highlighted by the uncertainty range inherent in the architecture and connectivity of the lobe-dominated Fram and Arran reservoirs (Collins et al 2015;Jones et al 2015). Conceptual models are emerging with which to identify the nature of reservoir-quality variation and sand-body stacking in these settings (Prélat et al 2009;Grundvåg et al 2014), and their potential impact (Amy et al 2013), but further quantitative calibration from outcrops, particularly in relation to the impact of seafloor bathymetry (cf. Gervais et al 2006), is needed.…”