A Bayesian approach to integrating radiometric dating and varve measurements in intermittently indistinct sediment

Annually laminated lake sediment can track paleoenvironmental change at high resolution where alternative archives are often not available. However, information about the chronology is often affected by indistinct and intermittent laminations. Traditional chronology building struggles with these kinds of laminations, typically failing to adequately estimate uncertainty or discarding the information recorded in the laminations entirely, despite their potential to improve chronologies. We present an approach that overcomes the challenge of indistinct or intermediate laminations and other obstacles by using a quantitative lamination quality index combined with a multi-core, multi-observer Bayesian lamination sedimentation model that quantifies realistic under-and over-counting uncertainties while integrating information from radiometric measurements (210Pb, 137Cs, and C) into the chronology. We demonstrate this approach on sediment of indistinct and intermittently laminated sequences from alpine Columbine Lake, Colorado. The integrated model indicates 3137 (95g% highest probability density range: 2753-3375) varve years with a cumulative posterior distribution of counting uncertainties of-13g% to +7g%, indicative of systematic observer under-counting. Our novel approach provides a realistic constraint on sedimentation rates and quantifies uncertainty in the varve chronology by quantifying over-and under-counting uncertainties related to observer bias as well as the quality and variability of the sediment appearance. The approach permits the construction of a chronology and sedimentation rates for sites with intermittent or indistinct laminations, which are likely more prevalent than sequences with distinct laminations, especially when considering non-lacustrine sequences, and thus expands the possibilities of reconstructing past environmental change with high resolution.