TY - JOUR

T1 - An Optical luminescence chronology for late Pleistocene aeolian activity in the Colombian and Venezuelan Llanos

AU - Carr, Andrew

AU - Armitage, Simon

AU - Berrio, Juan-Carlos

AU - Bilbao, Bibiana

AU - Boom, Arnoud

PY - 2016/3

Y1 - 2016/3

N2 - The lowland savannas (Llanos) of Colombia and Venezuela are covered by extensive aeolian landforms forwhich little chronological information exists. We present the first optically stimulated luminescence (OSL) age constraints for dunes in the Llanos Orientales of lowland Colombia and new ages for dunes in the Venezuelan Llanos. The sampled dunes are fully vegetated and show evidence of post-depositional erosion. Ages range from4.5±0.4 to 66±4 ka, with themajority dating to 27–10 ka (Marine Isotope Stage 2). Some dunes accumulated quickly during the last glacial maximum, althoughmostwere active 16–10 ka. Accretion largely ceased after 10 ka. All dunes are elongated downwind from rivers, parallel with dry season winds, and are interpreted assource-bordering features. As they are presently isolated from fluvial sediments by gallery forest it is proposed that activity was associated with a more prolonged dry season, which restricted gallery forest, leading to greatersediment availability on river shorelines. Such variability in dry season duration was potentially mediated by the mean latitude of the ITCZ. The cessation of most dune accretion after ca. 10 ka suggests reduced seasonality and a more northerly ITCZ position, consistent with evidence from the Cariaco Basin.

AB - The lowland savannas (Llanos) of Colombia and Venezuela are covered by extensive aeolian landforms forwhich little chronological information exists. We present the first optically stimulated luminescence (OSL) age constraints for dunes in the Llanos Orientales of lowland Colombia and new ages for dunes in the Venezuelan Llanos. The sampled dunes are fully vegetated and show evidence of post-depositional erosion. Ages range from4.5±0.4 to 66±4 ka, with themajority dating to 27–10 ka (Marine Isotope Stage 2). Some dunes accumulated quickly during the last glacial maximum, althoughmostwere active 16–10 ka. Accretion largely ceased after 10 ka. All dunes are elongated downwind from rivers, parallel with dry season winds, and are interpreted assource-bordering features. As they are presently isolated from fluvial sediments by gallery forest it is proposed that activity was associated with a more prolonged dry season, which restricted gallery forest, leading to greatersediment availability on river shorelines. Such variability in dry season duration was potentially mediated by the mean latitude of the ITCZ. The cessation of most dune accretion after ca. 10 ka suggests reduced seasonality and a more northerly ITCZ position, consistent with evidence from the Cariaco Basin.

KW - OSL dating

KW - source-bordering dunes

KW - Neotropics

KW - Savanna

KW - Chemical weathering

KW - Orinoco River

U2 - 10.1016/j.yqres.2015.12.009

DO - 10.1016/j.yqres.2015.12.009

M3 - Article

VL - 85

SP - 299

EP - 312

JO - Quaternary Research

JF - Quaternary Research

SN - 0033-5894

IS - 2

ER -