Development of a precise and accurate age–depth model based on 40Ar/39Ar dating of volcanic material in the ANDRILL (1B) drill core, Southern McMurdo Sound, Antarctica

High precision 40Ar/39Ar dates on a variety of volcanic materials from the AND-1B drill core provide pinning points for defining the chronostratigraphy for the core. The volcanic materials dated include 1) felsic and basaltic tephra, 2) interior of a ~ 3 m thick intermediate submarine lava flow, and 3) felsic and basaltic volcanic clasts. In the upper 600 m of the core, two felsic tephra, two basaltic tephra and the intermediate laval flow yield precise and depositional ages, with further maximum age constraints from volcanic clasts. Below 600 m in the core, tephric intervals are significantly altered and maximum age constraints only are available from volcanic clasts. The ages for eight stratigraphic intervals are 1) 17.17–17.18 mbsf, basaltic clast (maximum depositional age 0.310 ± 0.039 Ma, all errors quoted at 2σ), 2) 52.80–52.82 mbsf, three basaltic clasts (maximum depositional age 0.726 ± 0.052 Ma), 3) 85.27–85.87 mbsf felsic tephra (1.014 ± 0.008 Ma), 4) ~ 112–145 mbsf sequence of basaltic tephra (1.633 ± 0.057 to 1.683 ± 0.055 Ma), 5) 480.97–481.96 mbsf pumice-rich mudstone (4.800 ± 0.076 Ma), 6) 646.30–649.34 mbsf intermediate lava flow (6.48 ± 0.13 Ma), 7) 822.78 mbsf kaersutite phenocrysts from volcanic clasts (maximum depositional age 8.53 ± 0.53 Ma) and 8) ~ 1280 mbsf, three volcanic clasts (maximum depositional age 13.57 ± 0.13 Ma). Minimum average sediment accumulation rates or 102 and 87 m/Ma for the upper and lower 650 m of core, respectively were calculated using the 40Ar/39Ar analyses. The volcanic material recovered from AND-1B also reveals a general northward progression of volcanism in Southern McMurdo Sound.