5 drillcore samples of Early Cambrian Mount McDonnell Formation shallow marine mudstone intersected by SADME stratigraphic drillhole Investigator 2 on Kangaroo Island between 139 and 505 metres depth KB were analysed geochemically to determine their source rock richness and thermal maturity, as a validation check against the presumed geochemical artefacts of weathering and contamination of 17 surface samples of the same rock unit analysed previously. Although they proved to be no more organic-rich than the surface samples of the same lithofacies from adjacent coastal outcrops, three of the five cores examined have extract yields appreciably greater than the maximum outcrop value (viz. 64 ppm). Extractable organic matter is better preserved in the core samples, and its hydrocarbons (saturates and aromatics) display no evidence of contamination by younger, non-indigenous, organic matter. The core samples are uniformly organically lean (total organic carbon ~0.1%) and contain low concentrations of extractable organic matter (EOM < 280 ppm). Reliable maturity data were obtained for three samples from 139-344 metres depth in Investigator 2. GC-MS analysis of the two-ring and three-ring aromatic hydrocarbons revealed maturity levels (VRcalc ~1.1%) equivalent to the wet gas-condensate phase of petroleum generation from a rock containing Type II kerogen. Such source beds, now overmature, are present elsewhere within the Stansbury Basin (e.g. within the upper Heatherdale Shale on Fleurieu Peninsula). The excellent agreement between these maturities and those previously obtained from nearby outcrop samples of the Mount McDonnell Formation reinforces the conclusion that the Early Cambrian sequence, immediately north of the Cygnet-Snelling Fault on the southern margin of the Stansbury Basin, is still within the oil preservation window.