Paleo‐denudation rates suggest variations in runoff drove aggradation during last glacial cycle, Crete, Greece

Abstract

The impact of Quaternary climate cycles on denudation rates and fluvial aggradation and incision is debated, especially in non-glaciated regions. Here we present paleo-denudation rates and geochronological constraints on aggradation and incision from the Sfakia and Elafonisi alluvialfan sequences on Crete, Greece. We report seven optically stimulated luminescence (OSL), ten radiocarbon ages, and eight 10 Be and eight 36 Cl denudation rates from modern and terrace sediments. For five samples, 10 Be and 36 Cl were measured on the same sample by measuring 10 Be on cherts and 36 Cl on calcite. Results indicate relatively steady denudation rates throughout the past 80kyr, but the aggradation and incision history indicate a link with shifts in climate. At the Elafonisi fan, we identify four periods of aggradation coinciding with Marine Isotope Stages (MIS) 2, 4, 5a/b, and likely 6, and three periods of incision coinciding with MIS 1, 3, and likely 5e. At the Sfakia fan, rapid aggradation occurred during MIS 2 and 4, analogous to aggradation periods at the Elafonisi fan system, followed by up to 50 m of incision during MIS 1. Nearby climate and vegetation records show that MIS 2, 4, and 6 were characterized by cold and dry climates with sparse vegetation, whereas forest cover and wet conditions prevailed during MIS 1, 3, and 5. Our data thus suggest that past changes in climate had little effect on landscape-wide denudation rates, but exerted a strong control on the aggradation-incision behaviour of alluvial channels on Crete. During glacial stages, we attribute aggradation to hillslope sediment release promoted by reduced vegetation cover and decreased river sediment transport capacity; conversely, incision occurred during relatively warm and wet stages due to increased river transport capacity. We conclude that, in this landscape, past hydroclimate variations outcompeted changes in sediment supply as the primary driver of alluvial deposition and incision.

Integrated uplift, subsidence, erosion and deposition in a tightly coupled source‐to‐sink system, Pagliara basin, northeastern Sicily, Italy

“…We first use our luminescence‐constrained age model to describe the deposition and then uplift of the clastic sequence preserved in the footwall of a major normal fault embedded in a deforming forearc. Our data aligns with some recent studies that shows that rates of sediment accumulation are not dependent on changes in the rate of erosion during glacial–interglacial climate change (Ott et al., 2022). The age model allows us to then integrate the sedimentologic data with an inversion of the fluvial topography (Gallen, 2018; Goren et al., 2014; Pavano & Gallen, 2021; Pazzaglia & Fisher, 2022) that links uplift and erosion in the source to subsidence and deposition in the sink, and the construction of the sedimentary architecture of the Pagliara delta complex.…”

“…Although our TCN data are not dense enough to resolve whether erosion has been unsteady over several glacial cycles (e.g. Ott et al, 2022), given the short 10 Be integration time as erosion rates approach 1.3 mm/yr of just a few millennia, catchment-scale hillslope soil production and landslide frequency must be relatively uniform and steady even as climate changes. In any event, the unsteady trapping of sediment at the mouth of the paleo-Pagliara River and resulting rapid shallowing of sediment transport slope favoured autogenic processes, leading the temporarily lateral switching and repeat stacking of prodelta and deep-water depositional environment (PD c facies).…”