Investigations on the Peach 4 Debrite, a Late Pleistocene Mass Movement on the Northwest British Continental Margin

Abstract

The Peach 4 debrite is the most recent in a series of large scale Pleistocene MTDs within the Barra fan on the northwest British continental margin. Geophysical data indicate that Peach 4 was formed through a combination of blocky and muddy debris flows and affects an area of~700 km 2 . BGS core sample 56 -10 36, located directly over the Peach 4 debrite, provides a minimum age of 14.68 ka cal BP for the last major failure. An upwards fining turbidite sequence in BGS core sample 56 -10 239 is associated with increased As and S concentrations, indicators of diagenetic pyrite which forms under anoxic conditions. It is proposed that As and S concentrations may provide a method of distinguishing between contourite and turbidite sedimentation, though further research is required.Keywords: Submarine mass movement, submarine landslide, mass transport deposit, debrite, debris flow, turbidite, Barra fan, British ice sheet, arsenic, sulphur, pyrite. Regional setting and sedimentation on the Barra fanThe Peach 4 debrite is located on the northwest British continental margin within the Barra fan. Sedimentation on the fan is governed by a combination of down-slope and across-slope mechanisms. The primary across slope process is driven by contouritic current circulation, resulting in contourite deposits such as the Barra Fan Drift. This deposit consists of sediment waves with a length of~3 km and height of 15-30 m, smaller local contourite deposits are also located on the Barra Fan (Knutz et al. 2002). The largest down-slope sedimentation feature on the Barra Fan is the Peach debris flow complex, the location of which is shown on Figure 1a. Holmes et al. (1998) mapped the complex, which covers an area of~1600 km 2 , identified four major units of Pleistocene age: debrite 1 (823 km 3 ), debrite 2 (673 km 3 ), debrite 3 (199 km 3 ) and debrite 4 (135 km 3 ). Using the age/depth profile of Knutz et al. (2001), Maslin et al. (2004 estimated the age of the three most recent debrites: 2, 3 and 4 as 36.5, 21 and 10.5 ka cal BP respectively; this most recent date we revise below. This paper first investigates the morphology and timing of the Peach 4 debrite and then analyses the sedimentology and geochemistry of a sediment core from the boundary of the major failure in order to try and understand the recent sedimentation processes.

True Volumes of Slope Failure Estimated From a Quaternary Mass‐Transport Deposit in the Northern South China Sea

“…Considering that the two previous cases (the Storegga Slide and the study area) have similar turbidite rates, and other slope failures (volume > 1,000 km 3 ) located in deepwater regions with gentle slope gradients are similar to the northern South China Sea, the turbidite rates calculated in this work can be used as a reference to large slope failures. A large amount of turbidites (e.g., 1,890-5,292 km 3 for Makran Accretionary Complex) would therefore be expected in large-scale slope failures (see Table S2 for the possible turbidite contents of large-scale slope failures [imaged volume ≥ 1,000 km 3 ]; Armandita et al, 2015;Burg et al, 2008;Calvès et al, 2015;Chaytor et al, 2010;Collot et al, 2001;Denne et al, 2013;Dingle, 1977Dingle, , 1980Frey-Martinez et al, 2005;Gee et al, 2006;Haflidason et al, 2004;Hjelstuen et al, 2007;Lamarche et al, 2008;Lee et al, 2004;Leslie & Mann, 2016;Mosher et al, 2012;Niemi et al, 2000;Owen et al, 2010;Piper et al, 1997;Popenoe et al, 1993;Torelli et al, 1997;Trincardi & Argnani, 1990;Vanneste et al, 2006;Wynn et al, 2000). It is worth to note that there are still some uncertainties about the volume estimates for turbidites in the study area.…”

Sediment failures within the Peach Slide (Barra Fan, NE Atlantic Ocean) and relation to the history of the British-Irish Ice Sheet

“…Due to the location of 56/-10/36 within the area bounded by the prominent landslide scarp it would be expected that this core would provide a minimum age for the emplacement of Peach 4 (Owen et al, 2010). However, on analysing the data more closely it seems that the core does not match the nearby seismic data, which indicates a hard seabed as opposed to the soft material sampled by the core.…”

“…This paper builds on extensive previous work on the Peach Slide and includes a reanalysis of seismic and other geophysical data (see Owen et al, 2015) as well as new foraminiferal δ 18 O, particle size sedimentology and 14 C dates from a core in the Peach Slide headwall area (using methods presented by Owen et al, 2010;Owen, 2013). These new data are combined with key previous work in the area (Armishaw et al, 1998;Armishaw et al, 2000;Holmes et al, 1998;Knutz et al, 2002;Kroon et al, 2000) and recent studies on the growth, extent and deglaciation of the British-Irish Ice Sheet (BIIS) (Clark et al, 2012;Dove et al, 2015;Hughes et al, 2016;Small et al, 2017) to provide an updated geological model for sedimentation on the Barra Fan.…”

Extreme wave events in Ireland: 14 680 BP–2012

“…There are two historical submarine mass movement events of particular interest: the first occurred in the Barra Fan, offshore north-west of Ireland (Owen et al, 2010), and the second in the Porcupine Basin, offshore south-west of Ireland (Huvenne et al, 2002). Both of these locations are indicated in Fig.…”

“…Holmes et al (1998) suggest that four large-scale submarine landslides make up the Peach Slide. Owen et al (2010) sampled and analysed cores from the area. They concluded that the Peach 4 debrite, the most recent in a series of large-scale mass transport deposits, has a minimum age of 14 680 yr BP, was formed through a combination of blocky and muddy debris flows and affects an area of 700 km 2 .…”