TY - CONF

T1 - Holocene RSL variation on southwestern Disko Island (Greenland)

T2 - AGU Fall meeting 2016

AU - Emerich Souza, Priscila

AU - Nielsen, Lars

AU - Kroon, Aart

AU - Murray, Andrew Sean

AU - Sohbati, Reza

AU - Clemmensen, Lars B

PY - 2016

Y1 - 2016

N2 - We investigate RSL variations during the Holocene in Lakse Bugt by assessing topography, internal structure, and luminescence ages of fossil beach ridges and the modern beach. Lakse Bugt (Bay) lies on the southwestern coast of Disko Island in a mesotidal regime and a mild wave climate. Beach ridges are widespread over the marine terrace, extending from ~40 above sea level (m asl). The most recent ridges terminate either at the beach or at the coastal sandy cliffs ~8 m asl immediately behind the modern beach. These ridges are covered mainly by rounded boulders; the terrain surfaces of the swales have clearly been deformed by freezing and thawing processes, in contrast to those of the ridge crests, which are relatively smooth.High-resolution reflection GPR data and high resolution topographical data were collected along cross-shore transects using a shielded 250 MHz antennae system and a DGPS system, respectively. Sediment samples were collected along these transects from holes ~0.5 m deep using lightproof plastic tubes, and dated using standard optically stimulated luminescence (OSL) techniques on sand-sized quartz grains.Beach profiles show that current berms lie much above the high tide range, and therefore they must have been formed under conditions more energetic than usual. Additionally, the low-tide level is well-marked by a sharp transition of sediment grain size: cobbles occur on the upper shoreface, whereas the foreshore is sandy. Seaward down-lap reflection points were identified in the internal structure of all beach ridges. Radar reflections are strongly scattered at or just below the down-lap points, indicating the transition to a deeper layer with coarser material. Therefore, we suggest that in this location the radar down-lap points correspond to low-tide level at the time of deposition.Preliminary luminescence dating for samples collected ~9 m asl indicates that they were deposited in the late Holocene (4 to 2 ka ago); based on ridge separation, this suggests an accretion rate for these beach-ridges of ~8m/ka.

AB - We investigate RSL variations during the Holocene in Lakse Bugt by assessing topography, internal structure, and luminescence ages of fossil beach ridges and the modern beach. Lakse Bugt (Bay) lies on the southwestern coast of Disko Island in a mesotidal regime and a mild wave climate. Beach ridges are widespread over the marine terrace, extending from ~40 above sea level (m asl). The most recent ridges terminate either at the beach or at the coastal sandy cliffs ~8 m asl immediately behind the modern beach. These ridges are covered mainly by rounded boulders; the terrain surfaces of the swales have clearly been deformed by freezing and thawing processes, in contrast to those of the ridge crests, which are relatively smooth.High-resolution reflection GPR data and high resolution topographical data were collected along cross-shore transects using a shielded 250 MHz antennae system and a DGPS system, respectively. Sediment samples were collected along these transects from holes ~0.5 m deep using lightproof plastic tubes, and dated using standard optically stimulated luminescence (OSL) techniques on sand-sized quartz grains.Beach profiles show that current berms lie much above the high tide range, and therefore they must have been formed under conditions more energetic than usual. Additionally, the low-tide level is well-marked by a sharp transition of sediment grain size: cobbles occur on the upper shoreface, whereas the foreshore is sandy. Seaward down-lap reflection points were identified in the internal structure of all beach ridges. Radar reflections are strongly scattered at or just below the down-lap points, indicating the transition to a deeper layer with coarser material. Therefore, we suggest that in this location the radar down-lap points correspond to low-tide level at the time of deposition.Preliminary luminescence dating for samples collected ~9 m asl indicates that they were deposited in the late Holocene (4 to 2 ka ago); based on ridge separation, this suggests an accretion rate for these beach-ridges of ~8m/ka.

M3 - Poster

Y2 - 12 December 2016 through 16 December 2016

ER -