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

Fluvial aggradation and incision are often linked to Quaternary climate cycles, but it usually remains unclear whether variations in runoff or sediment supply or both drive channel response to climate variability. Here we quantify sediment supply with paleo-denudation rates and provide geochronological constraints on aggradation and incision from the Sfakia and Elafonisi alluvial-fan sequences in Crete, Greece. We report seven optically stimulated luminescence (OSL)and ten radiocarbon ages, eight 10Be,and eight 36Cl denudation rates from modern channeland terrace sediments. For five samples, 10Be and 36Cl were measured on the same sample by measuring 10Be on chert and 36Cl on calcite. Results indicate relatively steady denudation rates throughout the past 80kyr, but the aggradation and incision history indicates a link with climate shifts. 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,followed by incision during MIS 1. Nearby climate and vegetation records show that MIS 2, 4, and 6 stadials were characterized by cold and dry climates with sparse vegetation, whereas forest cover and more humid 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 runoff; conversely, incision occurred during relatively warm and wet stages due to increased runoff. In this landscape, past hydroclimate variations outcompeted changes in sediment supply as the primary driver of alluvial deposition and incision

Paleoseismology of the southern Panamint Valley fault: Implications for regional earthquake occurrence and seismic hazard in southern California

Paleoseismologic data from the southern Panamint Valley fault (PVF) reveal evidence of at least four surface ruptures during late Holocene time (0.33-0.48 ka, 0.9-3.0 ka, 3.3-3.6 ka, and >4.1 ka). These paleo-earthquake ages indicate that the southern PVF has ruptured at least once and possibly twice during the ongoing (≤1.5 ka) seismic cluster in the Mojave section of the eastern California shear zone (ECSZ). The most recent event (MRE) on the PVF is also similar in age to the 1872 Owens Valley earthquake and the geomorphically youthful MRE on the Death Valley fault. The timing of the three oldest events at our site shows that the PVF ruptured at least once and possibly thrice during the well-defined 2-5 ka seismic lull in the Mojave section of the ECSZ. Interestingly, the 3.3-3.6 ka age of Event 3 overlaps with the 3.3-3.8 ka age of the penultimate (i.e., pre-1872) rupture on the central Owens Valley fault. These new PVF data support the notion that earthquake occurrence in the ECSZ may be spatially and temporally complex, with earthquake clusters occurring in different regions at different times. Coulomb failure function modeling of the Panamint Valley and Garlock faults reveals significant stress interactions between these two faults that may influence future earthquake occurrence. Specifically, our models suggest a possible rupture sequence whereby an event on the southern Panamint Valley fault can lead to the potential triggering of an event on the Garlock fault, which in turn could trigger the Mojave section of the San Andreas Fault. Key Points Four surface ruptures during late Holocene on the Panamint Valley faultData support notion that earthquake occurrences in the ECSZ are complexCFF modeling of the Garlock and Panamint Valley fault