The Ordovician is an important period in Earth’s history with exceptionally high sea levels that facilitated the Great Ordovician Biodiversification Event. This crucial biological event is regarded as the second most significant evolutionary event in the history of Paleozoic life, after the Cambrian radiation. The present study integrates palynological, petrographic, molecular and stable isotopic (δ13C of biomarkers) analyses of cores from five boreholes that intersected the Goldwyer Formation, Canning Basin, Western Australia, to determine depositional environments and microbial diversity within a Middle Ordovician epicontinental, tropical sea. A major transgression was detected in the laminated shales of the lower Goldwyer Formation (Units 1+2) which were deposited in anoxic bottom waters, as confirmed by low (<1) Pristane/Phytane ratios, and elevated dibenzothiophene and gammacerane indices. A second, less extensive, flooding event is recorded by shallow marine sediments of the upper Goldwyer Formation (Unit 4). Cores of these sediments, from two wells (Solanum-1 and Santalum-1A) are bioturbated and biomarkers indicate relatively oxygenated conditions, as well as the presence of methanotrophic bacteria, as determined from the high 3-methylhopane indices. Typical Ordovician marine organisms including acritarchs, chitinozoans, conodonts and graptolites were present in the lower and upper Goldwyer Formation, whereas the enigmatic organism Gloeocapsomorpha prisca (G. prisca) was only detected in Unit 4. The presence of G. prisca was based on microfossils and specific biosignatures presenting an odd-over-even predominance in the C15 to C19 n-alkane range. Cryptospores were identified in Unit 4 in the Theia-1 well and are most likely derived from bryophytes, making this is the oldest record of land plants in Australian Middle Ordovician strata. Biomarkers in some samples from Unit 4 that also support derivation from terrestrial organic matter include retene, benzonaphthofurans and δ13C-depleted mid-chain n-alkanes. This research contributes to understanding Ordovician marine environments from a molecular perspective since few biomarker studies have been undertaken on age-equivalent sections. Furthermore, the identification of the oldest cryptospores in Australia and their corresponding terrestrial biomarkers contributes to understanding the geographical evolution of early land plants.

Presentation for the Exploring for the Future Roadshow presentation about the Kidson Sub-basin seismic survey, Waukarlycarly-1 stratigraphic well, in addition to the Centralian Super Basin well correlation study.

Geoscience Australia currently uses two commercial petroleum system modelling software packages, PetroMod https://www.software.slb.com/products/petromod and Zetaware http://www.zetaware.com, to undertake burial and thermal history modelling on wells in Australian sedimentary basins. From the integration of geological (age-based sedimentary packages, uplift and erosional events), petrophysical (porosity, permeability, and thermal conductivity) and thermal (downhole temperature, heat flow, vitrinite reflectance, and Tmax) input data, to name the most significant, a best-fit model of the time-temperature history is generated. Since the transformation of sedimentary organic matter (kerogen) into petroleum (oil and gas) is a chemical reaction, it is governed by chemical kinetics i.e. time and temperature (in the geological setting pressure is of secondary importance). Thus, the use of chemical kinetics associated with a formation-specific, immature potential source rock (where available) from the basin of interest is considered a better practical approach rather than relying on software kinetic defaults, which are generally based on the chemical kinetics determined experimentally on Northern Hemisphere organic matter types. As part of the Australian source rock and fluids atlas project being undertaken by the Energy Systems Group’s Exploring for the Future (EFTF) program, compositional kinetics (1-, 2-, 4- and 14-component (phase) kinetics) were undertaken by GeoS4, Germany. The phase kinetics approach is outlined in Appendix 1. This report provides the compositional kinetics for potential source rocks from the Ordovician Goldwyer (Dapingian–Darriwilian) Formation and the Bongabinni (Sandbian) Formation, Carribuddy Group, Canning Basin, Western Australia.

The Middle Ordovician Stairway Sandstone consists of a succession of siliciclastic shallow marine sediments, stratigraphically positioned between the dark organic-rich siltstones of the Horn Valley Siltstone, and the regressive siltstones and shales of the overlying Stokes Siltstone, in the Amadeus Basin. The Stairway Sandstone is notable for containing early arandaspid fish fossils, and is a prospective reservoir for Larapinta Petroleum System hydrocarbons. The unit has not been directly dated, but a field sample from the uppermost Stairway Sandstone has yielded an abundant and well-preserved fauna, including micro-vertebrate and conodont fossils that enable correlation to high resolution international conodont biozonation schemes.

<div>Scientific studies undertaken on core from the Barnicarndy 1 well drilled in 2019 in the onshore Canning Basin in Western Australia as part of the Exploring for the Future program have shown that the well penetrated a thick section of the early Ordovician Nambeet Formation which contains abundant fossils reflective of deposition in an open marine environment. Although the calcareous shales are organically poor (average total organic carbon content 0.17 wt%) processing of 42 drill core samples recovered a plethora of acid-resistant, organic-walled microfossils. Seven core samples with the highest organic content were analysed for their molecular (biomarker) fossils and stable isotopic composition to provide insights into the type of organic matter preserved, and the redox conditions of the sediments during deposition.</div><div><br></div>This Abstract was submitted/presented to the 2022 Australian Organic Geochemistry Conference 27-29 November (https://events.csiro.au/Events/2022/October/5/Australian-Organic-Geochemistry-Conference)

Laboratory results for fluid inclusion gas analysis in GA's Isotope and Organic Geochemistry Laboratory under GSWA Approval G004119