Absolute time markers and age-depth model for the last 75 kyr of Lake Chala sediments

The 171 time markers include 162 14C ages on bulk organic matter or grass charcoal in sediment intervals of the composite Challacea (CH03, CH05) sequence (Blaauw et al., 2011), transferred to the DeepCHALLA (DCH) composite sequence using mm- or  cm-scale cross-correlation of visual lithostratigraphy (Baxter et al., 2023). The other nine time markers are six 210Pb-dated intervals from gravity core CH99-1G transferred to the CH05 and DCH sequences using 1-cm resolution magnetic-susceptibility profiles (Blaauw et al., 2011), the November 2016 (DCH) and March 2005 (CH05) sediment-water interfaces, and the YTT cryptotephra (Baxter et al., 2023). Lab codes stand for the Poznan Radiocarbon Laboratory (Poz-), the Chrono Centre at Queen’s University in Belfast (UBA-), the Isotope Physics Laboratory at the University of Groningen (GrA-), the Saint-Croix Watershed Research Station of the Science Museum of Minnesota (SMM), and the Cambridge Tephra Laboratory (CT-). ‘Offset’ refers to the old-carbon age offset of bulk organic 14C dates, modelled using 16 paired dates on bulk organic matter and grass charcoal and three sections allowing 14C wiggle-match dating using closely spaced bulk organic samples (Blaauw et al., 2011). The compound error on corrected 14C ages was calculated as SQRT ((Age Error)^2 + (Offset STD)^2). All dated intervals are represented by their DCH event-free depth in meter (mefd).