Correlations with the XRD data show

Correlations with the XRD data show that, with one exception (SR-17), yield and organic carbon can also be correlated directly with the abundance of carbonate (calcite) and inversely to the abundance of quartz plus feldspar (Fig. 9B–C). Accumulation and preservation of algal material in the lake sediments were probably favoured by a deepwater environment, with low dissolved oxygen and low rates of clastic input. Such an environment would have also favoured carbonatedeposition, leading to the correlations mentioned above. No particularcorrelation seems to be apparent between oil yield or organic carbon content and the overall proportion of clay minerals (Fig. 9D). Together with the inverse correlation with quartz plus feldspar mentioned above, this suggests that fine clays, but not coarser-grained quartz and feldspar particles, may have also accumulated in the deep lake environment along with the carbonate and the algal material.