Fossils down under or finding fossils in boreholes

Dr Susan Parfrey (Australia) You may be familiar with collecting fossils from eroded rock surfaces, a riverbank, a road or rail cutting, a cliff face or a fresh cut surface such as a quarry. But there is another way fossils can be recovered – from boreholes. Boreholes have been drilled in Queensland for many years for exploration and to investigate the regional geology. Since Queensland is a relatively flat part of Australia, outcrops can be hard for geologists to find. Therefore, drilling offers a way of studying sub-surface geology that assists in the understanding of the stratigraphy of the State. Usually, drilling does not produce usable macrofossils. The process of drilling normally involves pushing a mud mixture down the borehole and over the bit, for cooling and lubrication. In this process, larger fossils are forced to the surface in the drilling mud and are broken into small pieces making them impossible to identify. However, microfossils can be recovered, as they are so small they are undamaged by the drilling process and are recovered at the surface to be identified and used in biostratigraphy (to date and correlate rocks). However, in Queensland, drilling was undertaken by the Geological Survey that retrieved lengths of core which provided access to deeply-buried strata and allowed recovery of both micro and macrofossils. Exploration companies also often retrieved short lengths of core at specific levels of interest, which sometimes contain fossils. Before a borehole is drilled, considerable geological mapping of the surface is undertaken. Only then … Read More

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