In the Surat Basin of eastern Australia, the Lower Jurassic Precipice Sandstone and 2 Evergreen Formation are a highly prospective reservoir-seal pair for notional future carbon 3 capture and storage. However, the succession remains poorly constrained from a paleo-4 depositional standpoint and this has impacted the capacity to construct predictive reservoir 5 models. Here we integrate sedimentological, ichnological, and palynological data from ten cores 6 located across a large region of the northern and central basin to produce conceptual 7 depositional models.8 Our analysis shows that the Lower Jurassic Series consists of fifteen recurring sedimentary 9 facies that are arranged into six facies associations -braidplain, lower delta plain, subaqueous 10 delta, delta-influenced shoreface, tidally influenced shoreline, and restricted marine shoals. The 11 facies associations occur in the context of a large scale fluvio-deltaic system that developed 12 within the basin. These results are supported by ichnological indications of marine and brackish 13 water, and a coastal suite of palynomorphs including rare dinocysts, acritarchs, and copepod 14 fragments. The very low abundance of marine palynomorphs are confined to the upper portion 15 of the Evergreen Formation, and in combination with sedimentological and ichnological results
16suggest that marine influence increased through time.
The Northern Carnarvon Basin was situated on the southern margin of the Tethys Ocean during the Late Triassic. This major depocentre accumulated extensive deltaic and shallow marine strata at this time and these successions have allowed the investigation of the initial radiation of cyst-forming dinoflagellates in the Southern Hemisphere. Numerous petroleum exploration wells in the basin have penetrated the fluvially dominated Mungaroo Formation and shallow marine Brigadier Formation of Carnian-Norian and Rhaetian age respectively. Consequently, huge numbers of cuttings and sidewall core samples from these northwest prograding deltaic systems are available for study. Many of the dinoflagellate cysts from the Mungaroo and Brigadier formations have not been taxonomically formalised, including many forms that are used in open nomenclature within the oil and gas industry. This study formally documents these occasionally abundant and diverse dinoflagellate cyst assemblages with the aim of providing a consistent taxonomic framework for future work on the Triassic successions of the Northern Carnarvon Basin. This will aid the recognition of individual flooding events via their characteristic palynomorph signatures and help to build on significant recent advances in regional sequence stratigraphy. One new genus, 14 new dinoflagellate cyst species and one new subspecies are described from the most diverse Late Triassic dinoflagellate assemblage yet published. A further nine genera and 17 dinoflagellate 2 species are also recorded from the Carnian-Rhaetian R. nagelii, R. wigginsii, W. listeri, H. balmei, R. rhaetica and D. priscum dinoflagellate zones. The associations documented are significant biostratigraphically. It is postulated that high diversity Triassic dinoflagellate cyst associations were palaeoclimatically controlled, and were confined to the temperate and cool temperate palaeolatitudes.
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