In situ calcite U–Pb geochronology of carbonate and clastic sedimentary rocks from the Canning Basin, Western Australia

Abstract

Abstract In sedimentary basins, the determination of the absolute timing of deposition and diagenetic events is a challenging yet critical parameter necessary in the reconstruction of paleo-fluid evolution and burial histories. Here we demonstrate the practical application of in situ calcite U–Pb geochronology on core samples from the Olympic 1 well in the Canning Basin of Western Australia. Using quantitative mineralogy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analytical techniques, we obtained an authigenic calcite U–Pb age of 469.7 ± 4.3 Ma for limestone in the Samphire Marsh Member of the Lower Ordovician Nambeet Formation. This precise depositional age can be independently verified using zircon thermal ionisation mass spectrometry U–Pb ages of 479.4 to 470.2 Ma determined on adjacent volcanic ash beds. Further geochronology studies on calcite cements from the Lower Ordovician Fly Flat Member sandstone from the Nambeet Formation returned a U–Pb age of 365.3 ± 5.8 Ma. This is the first study to place absolute age constraints on the diagenetic event that occluded the intergranular space in a sandstone reservoir. The calcite cementation age suggests that impairment of reservoir quality in the Fly Flat Member sandstone occurred in the Late Devonian, much earlier than major petroleum charge events in the Canning Basin. The calcite U–Pb geochronometer, when combined with complementary quantitative mineralogical analysis, can build direct temporal constraints on the depositional and diagenetic processes in both carbonate and clastic sedimentary rocks in basins worldwide. Key Points The integration of automated scanning electron microscopy/energy-dispersive X‐ray spectrometry quantitative mineralogical analysis with LA-ICP-MS analysis enables more reliable and efficient i n situ calcite U–Pb dating. An accurate age of 469.7 ± 4.3 Ma is obtained for carbonate sedimentation in the Samphire Marsh Member of the Lower Ordovician Nambeet Formation in the Canning Basin. The calcite cementation age of 365.3 ± 5.8 Ma provides an absolute time constraint on pore-occluding lithification of the Fly Flat Member sandstone reservoir in the Canning Basin. I n situ calcite U–Pb dating can place precise temporal constraints on sediment deposition and paragenetic sequence in sedimentary basins.