<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)

A regional hydrocarbon prospectivity study was undertaken in the onshore Canning Basin in Western Australia as part of the Exploring for the Future (EFTF) program, an Australian Government initiative dedicated to driving investment in resource exploration. As part of this program, significant work has been carried out to deliver new pre-competitive data including new seismic acquisition, drilling of a stratigraphic well, and the geochemical analysis of geological samples recovered from exploration wells. A regional, 872 km long 2D seismic line (18GA-KB1) acquired in 2018 by Geoscience Australia (GA) and the Geological Survey of Western Australia (GSWA), images the Kidson Sub-basin of the Canning Basin. In order to provide a test of geological interpretations made from the Kidson seismic survey, a deep stratigraphic well, Barnicarndy 1, was drilled in 2019 in a partnership between Geoscience Australia (GA) and the Geological Survey of Western Australia (GSWA) in the Barnicarndy Graben, 67 km west of Telfer, in the southwest Canning Basin. Drilling recovered about 2100 m of continuous core from 580 mRT to the driller’s total depth (TD) of 2680.53 mRT. An extensive analytical program was carried out to characterise the lithology, age and depositional environment of these sediments. This data release presents organic geochemical analyses undertaken on rock extracts obtained from cores selected from the Barnicarndy 1 well. The molecular and stable isotope data carbon and hydrogen will be used to understand the type of organic matter being preserved, the depositional facies and thermal maturity of the Lower Ordovician sedimentary rocks penetrated in this well. This information provides complementary information to other datasets including organic petrological and palynological studies.

The Exploring for the Future (EFTF) program is an initiative by the Australian Government dedicated to boosting investment in resource exploration in Australia. Geoscience Australia’s EFTF Energy program is aimed at improving the understanding of the petroleum resource potential of Australia. A key to understanding resource potential and basin evolution is a reliable time frame to correlate rock units. This palynological reconnaissance study focusses on the acid-resistant organic-walled microfossils (or palynomorphs) recovered from 42 samples taken within the fully cored Lower Ordovician Nambeet Formation (1354.80–2435.04 mRT) in the Barnicarndy 1 stratigraphic well, located in the Barnicarndy Graben, Canning Basin. The lack of palynomorph recovery from the Barnicarndy Formation, Yapukarninjarra Formation, and Neoproterozoic Yeneena Basin, also intersected in this well, means that the age of those units remain undated using micropalaeontological methods. The purpose of this study is to assess the yield and preservation of recovered palynomorphs, and determine their utility for regional, and international, correlation of the Lower Ordovician sedimentary section. Although the total organic matter content of the sampled Lower Ordovician core is typically low (average ≤0.2 wt%), reflecting sediment deposition in an oxidising, open marine environment, a diverse suite of palynomorphs has been identified and includes: acritarchs (of probable algal origin); other algal microfossils (including green algae, or prasinophytes); probable cyanobacteria; cryptospores (derived from the earliest land plants); graptolites and chitinozoans (both from extinct marine groups); scolecodonts (detached elements of worm jaws); and organic-walled tubes, some of which are of either probable fungal or cyanobacterial origin. Digital images accompany this record and include examples of all of these aforementioned microfossils. Microfossil yield per sample is, mostly, low; and preservation ranges from poor, where specimens are either fragmentary and/or distorted by pyrite crystal growth, to good; and commonly both preservation states occur together within the same sample. As with the admixture of preservation states per sample, palynomorph colour, typically used as an indicator of thermal maturity of organic matter, commonly ranges from thermally mature (brown) to over mature (black), often within the same Lower Ordovician core sample. This is tempered by the fact that these observations are based, mostly, on oxidised kerogen preparations, but, the relative maturity indicators remain valid. The occurrence of acritarchs assigned to the Rhopaliophora pilata–R. palmata complex, together with Athabascaella playfordii, and Aryballomorpha grootaertii, allows correlation with assemblages previously recovered from the Nambeet Formation intersected in two petroleum exploration wells in the Canning Basin (Samphire Marsh 1, type section; and Acacia 2). These species also occur globally, with A. grootaertii recovered from sedimentary rocks in southern China and Canada that have been independently dated as Early Ordovician, late Tremadocian–early Floian (about 475–482 Ma). Conodont faunas from cores in Barnicarndy 1 record the same (late Tremadocian–early Floian) age, which enhances the utility of A. grootaertii for age dating. The dates also demonstrate that the Barnicarndy 1 well intersects some of the oldest Paleozoic sedimentary rocks in the Canning Basin. There are compositional differences between the palynological assemblages from the younger Samphire Marsh Member and underlying Fly Flat Member of the Nambeet Formation which, despite difficulties in sample processing, are genuine and reflect changes in the depositional environment. Most obvious is the record of Gloeocapsomorpha prisca and ?Eomerismopedia maureeniae, both of probable cyanobacterial affinity, with in situ occurrences in the Lower Ordovician Samphire Marsh Member. Earlier studies suggested that G. prisca was confined to younger (Middle) Ordovician palynological assemblages in the Canning Basin, and its common abundance was used as a biozone marker, but the occurrences reported here and in unpublished studies, have shown that this is no longer applicable. In younger Ordovician formations in the Canning Basin (notably the upper Goldwyer Formation), and globally, G. prisca is an important organism contributing to the hydrocarbon potential of Paleozoic marine source rocks. If present in greater abundance elsewhere in the basin, it could increase the petroleum prospectivity of the Nambeet Formation. A distinctively shaped acritarch, of probable algal origin, assigned to the genus Dactylofusa is restricted to an assemblage from the Fly Flat Member, and may be useful for future basinal biozone correlation. Most samples from the Samphire Marsh Member contain early land-plant spores, of probable bryophyte affinity, that sometimes occur together with irregularly-shaped spore clusters, likely derived from aeroterrestrial charophyte algae; both of which are collectively known as cryptospores. In addition, Grododowon orthagonalis, superficially similar to E. maureeniae and recorded in some samples from the Samphire Marsh Member, is also considered to be of charophyte algal origin. The cryptospores include the species Dyadospora murusattenuata, Tetraplanarisporites sp., and Laevolancis divellomedium. Collectively, these cryptospores are important as they herald the first emergence of plants onto wetlands during the Early Ordovician; and being of late Tremadocian–early Floian age, they are amongst the oldest land-plant spores known in Australia and globally. The record of cryptospores from Barnicarndy 1 enhances those recently reported from the Nambeet Formation in Samphire Marsh 1, and from the lower Goldwyer Formation in Theia 1. Locally, the cryptospore record demonstrates a supply of terrestrial material into the marine environment during deposition of the Samphire Marsh Member. Globally, records of these cryptospores contribute to the understanding of the evolution and geographic distribution of the earliest land flora. Inevitably, there are microfossils found in this study that could be described as new species, and a detailed systematic study of all fossil groups is recommended to realise their utility for zonal correlation and age dating. The palynological data presented here provide complementary information to the conodont age dating, organic petrological, and organic geochemical studies conducted on the Barnicarndy 1 core. Collectively, these studies contribute to a better understanding of the depositional history and hydrocarbon prospectivity of the Canning Basin.

This petroleum systems summary report provides a compilation of the current understanding of petroleum systems for the Canning Basin. The contents of this report are also available via the Geoscience Australia Portal at https://portal.ga.gov.au/, called The Petroleum Systems Summary Assessment Tool (Edwards et al., 2020). Three summaries have been developed as part of the Exploring for the Future (EFTF) program (Czarnota et al., 2020); the McArthur Basin, the Canning Basin, and a combined summary of the South Nicholson Basin and Isa Superbasin region. The petroleum systems summary reports aim to facilitate exploration by summarising key datasets related to conventional and unconventional hydrocarbon exploration, enabling a quick, high-level assessment of the hydrocarbon prospectivity of the region.