tephra SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O total Ref Hekla 4 Tephra 75.57 0.11 13.36 1.81 0.13 0.03 1.38 4.49 2.79 99.67 969 Hekla 4 Tephra 74.66 0.11 13.47 2.08 0.10 0.06 1.23 4.58 2.78 99.08 969 Hekla 4 Tephra 74.39 0.16 13.13 1.87 0.12 0.03 1.23 4.30 2.76 97.99 969 Hekla 4 Tephra 74.26 0.09 13.27 1.82 0.07 0.03 1.32 3.82 2.83 97.52 969 Hekla 4 Tephra 73.81 0.10 13.37 1.95 0.11 0.04 1.38 4.62 2.76 98.15 969 Hekla 4 Tephra 73.74 0.11 12.91 1.78 0.06 0.07 1.26 4.41 2.85 97.19 969 Hekla 4 Tephra 73.21 0.07 13.20 1.79 0.15 0.03 1.28 4.78 2.95 97.46 969 Hekla 4 Tephra 72.96 0.12 13.10 1.97 0.11 0.02 1.27 4.78 2.90 97.23 969 Hekla 4 Tephra 72.82 0.10 13.07 1.90 0.11 0.05 1.20 4.60 2.86 96.72 969 Hekla 4 Tephra 72.78 0.06 13.39 1.94 0.13 0.01 1.42 4.62 2.84 97.19 969 ------------------------------------------------------------------------ 969: Boygle, J.E. (1994) Tephra in lake sediments: An unambiguous geochronological marker? PhD. Thesis, University of Edinburgh, Edinburgh,