Climbing‐ripple successions in turbidite systems: depositional environments, sedimentation rates and accumulation times

Abstract

setting where flows were expanding due to loss of confinement or a decrease in slope gradient. The resultant reduction in flow thickness, Reynolds number, shear stress, and capacity promoted suspension fallout and thus CRCL formation. CRCL in the New Zealand study area was deposited both outside of and within channels at an inferred break in slope, where flows were decelerating and expanding. In the South Africa study area, CRCL was deposited due to a loss of flow confinement. In the Magnolia study area, an abrupt decrease in gradient near a basin sill caused flow deceleration and CRCL deposition in off-axis settings. Sedimentation rate and accumulation time were calculated for 44 CRCL sedimentation units from the three areas using TDURE, a mathematical model developed by Baas et al. (2000). For T c divisions and T bc beds averaging 26 and 37 cm thick, respectively, average CRCL and whole bed sedimentation rates were 0.15 and 0.26 mm/s and average accumulation times were 27 and 35 minutes, respectively. In some instances, distinct stratigraphic trends of sedimentation rate give insight into the evolution of the depositional environment.CRCL in the three study areas is developed in very fine-to fine-grained sand, suggesting a grain size dependence on turbidite CRCL formation. Indeed, the calculated sedimentation rates correlate well with the rate of sedimentation due to hindered settling of very fine-and fine-grained sand-water suspensions at concentrations of up to 20% and 2.5%, respectively. For coarser grains, hindered settling rates at all concentrations are much too high to form CRCL, resulting in the formation of massive/structureless S 3 or T a divisions.3

Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

“…High angle of climb, with stoss-side preservation indicates high rates of aggradation (e.g., Allen, 1970;Jobe et al, 2012; Brooks et al | Evolution of a stepped slope profile GEOSPHERE | Volume 14 | Number 4 2014a, 2014b), commonly associated with non-uniformity in flows and accompanying decrease in velocity and/or flow height, possibly linked to an abrupt decrease in gradient or loss of confinement (e.g., Jobe et al, 2012;Morris et al, 2014aMorris et al, , 2014b, driving deposition through a reduction in flow capacity (e.g., Kneller and Branney, 1995). The presence of heterolithic foresets indicates deposition from mud-rich flows (Baas et al, 2016).…”

“…Normally graded siltstone beds suggest deposition from dilute turbidity currents, with the finer sediment residual within the flow after deposition of the coarser fraction of sediment load (Stow and Bowen, 1980;Jobe et al, 2012). Climbing-ripple lamination forms through late-stage tractional modification by flows, with high-sediment fall-out rates (Lowe, 1988).…”

“…Climbing-ripple lamination forms through late-stage tractional modification by flows, with high-sediment fall-out rates (Lowe, 1988). Low angle of climb suggests higher migration component and lower rates of suspended load fallout and aggradation than in structured sandstone (Allen, 1970;Jobe et al, 2012). Localized deformation and folding indicates slumping of material and/or significant dewatering.…”

Depositional architecture of sand-attached and sand-detached channel-lobe transition zones on an exhumed stepped slope mapped over a 2500 km2 area

“…Despite technological advances in subsurface imaging, the detailed analysis of exhumed deepwater systems at outcrop is still essential (Mutti and Normark, 1987) to provide information on sedimentary processes (e.g., Chapin et al, 1994;Pickering and Corregidor, 2005;Jobe et al, 2012), the stacking patterns and geometry of subseismic elements (e.g., Beauboeuf et al, 2000;Abreu et al, 2003;Schwarz and Arnott, 2007;Kane et al, 2007;Prélat et al, 2009), and the intrinsic controls on the anatomy of deepwater systems (e.g., Mutti 1985;Hodgson and Haughton, 2004;Moody et al, 2012;Burgreen and Graham, 2014). However, outcrops used as analogs are commonly isolated two-dimensional exposures, or have limited across-strike or downdip correlation potential, meaning that their paleogeographic context within the regional depositional architecture of a deepwater system is uncertain.…”

Sedimentary record of the younger saalian ice margin stagnation in eastern poland: development of a regular pattern of glaciolacustrine kames

“…Form when the slope gradient decreases. Characteristic for low-density turbidity currents in narrow grain-size range (Jobe et al 2012) …”