Early Jurassic palaeoenvironments in the Surat Basin, Australia - marine incursion into eastern Gondwana

Interpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two‐dimensional and three‐dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third‐order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub‐basins, with rivers flowing in different orientations in each sub‐basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas

A focus on the sedimentology of transgressions in interior seaways: utilising modern and outcrop analogues to interpret the subsurface Cretaceous Murta Formation, Eromanga Basin, Australia

Comprehension of the character and stratigraphic architecture of sedimentary rocks in the subsurface is derived from the observation of modern depositional processes on the surface of the Earth and field-based studies of similar depositional systems exposed in outcrop. In Australia’s Eromanga Basin, the Murta Formation is a substantial hydrocarbon reservoir; however it does not outcrop, data from wells are sparse and the depositional setting has previously been interpreted to be both continental lacustrine and marginal marine. Through extensive field and laboratory work, both for the Murta Formation and depositional analogues, this study investigates and discusses the sedimentology, stratigraphy and provenance of the Murta Formation in the Eromanga Basin. Murta Formation sediments were deposited in the Lower Cretaceous during the Berriasian to Valanginian, a key time of increased variation in global eustacy, continental breakup, climate change and just after a catastrophic mass extinction event at the Jurassic-Cretaceous boundary. Core investigations reveal that the Murta Formation is primarily composed of fine sands and muds, often arranged in coarsening up parasequences that become increasingly sand-dominated up section. The Murta Formation thickens over the Patchawarra and Poolowanna troughs, suggesting a basin depocentre in this area. Two basin-wide transgressive-regressive events are interpreted to have occurred and these most likely correspond with marine incursion in the Upper Murta Formation as the Eromanga Basin transitioned from continental lacustrine to marginal marine conditions. Zircon data indicate that sediments are sourced from mature cratons and younger volcanic provinces. This implies that the potential for unexplored reservoir presence on the western side of the basin is substantial, as mature, clean sands in were most likely deposited there in proximal deltaic environments. This project was motivated by research questions arising from the discovery of the Cuisinier Field, which unexpectedly yielded hydrocarbons in a new facies type within the Murta Formation. Sands within the Cuisinier system most likely represent a delta system deposited during a basin-wide marine regression and transgression event. As data for the Murta Formation are sparse, fluvial terminations in low accommodation basins are not widely-studied and marine transgressions in epicontinental seaways tend to be complex, analogue studies were also conducted. Lake Yamma Yamma in central Australia was investigated as it includes a substantial area of fluvial termination deposits at the main lake inlet, and has a similarly low-gradient basin setting to that of the Murta Formation. The geomorphology and sedimentology of deposits at the Lake Yamma Yamma site were described in detail, and controls on deposition interpreted. Based on this analogue study and literature review, ideas around the theme of fluvial termination deposits in a low gradient basin setting were applied to interpretation of the Murta Formation. The Dakota Formation, deposited at the initiation of the Cretaceous Western Interior Seaway, in Colorado, USA, was considered in detail at a specific outcrop locality and used as an analogue for the Murta Formation because it comprises a net transgressive system preserving internal transgressive and regressive cycles. Overall, the transgression was complex and piecewise. The size and shape of the deltaic features are similar to those observed in core in the Murta Formation, so thus provide a useful indicator for likely facies arrangements, as well as reservoir connectivity and geometries in the Murta Formation. These new studies of deposits in modern and outcrop localities, in combination with published literature, allowed an improved facies model to be developed for the Murta Formation. They also provide new insights into previously unstudied deposits, and contribute to aspects of research focus that are presently understudied. Lake Yamma Yamma has not previously been the focus of any papers despite being the largest playa lake in Queensland, Australia, and containing a substantial dryland terminal fluvial deposit, features often interpreted in the ancient record but not well studied in modern environments. As a part of this research, a new classification scheme to aid in the description and interpretation of dryland fluvial termination deposits is proposed. Although the Dakota Formation has been the focus of previous studies, the particular locality studied in this thesis has not been described in detail or assigned a comprehensive stratigraphic framework. As well as providing a detailed description of the sedimentology and a stratigraphic framework for the study area, this study also contributes new detrital zircon ages, which enabled an improved understanding of regional paleogeography. Furthermore, deposits preserved as a result of transgressions of epicontinental seas are not well understood and with no observable modern analogues, the detailed process-based understanding contributed by this study is very important in understanding similar deposits in the subsurface. In addition to contributing new perspectives on the Murta Formation of the Eromanga Basin, dryland fluvial termination deposits and the Dakota Formation of the Western Interior Seaway, the results of this thesis will provide a useful resource for the interpretation of similar systems in the geologic record.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, Australian School of Petroleum, 201

Widespread nearshore and shallow marine deposition within the Lower Jurassic Precipice Sandstone and Evergreen Formation in the Surat Basin, Australia

In the Surat Basin of eastern Australia, the Lower Jurassic Precipice Sandstone and Evergreen Formation are a highly prospective reservoir-seal pair for notional future carbon capture and storage. However, the succession remains poorly constrained from a paleodepositional standpoint and this has impacted the capacity to construct predictive reservoir models. Here we integrate sedimentological, ichnological, and palynological data from ten cores located across a large region of the northern and central basin to produce conceptual depositional models for the interval. Our analysis shows that the Lower Jurassic Series consists of fifteen recurring sedimentary facies that are arranged into six facies associations – braidplain, lower delta plain, subaqueous delta, delta-influenced shoreface, tidally-influenced shoreline, and restricted marine shoals. The facies associations occur in the context of large scale fluvio-deltaic systems that occupied the basin. These results are supported by ichnological indications of marine and brackish-water, a coastal suite of palynomorphs, and marine palynomorphs including rare dinocysts, acritarchs, and copepod fragments. The very low abundance of marine palynomorphs are confined to the upper portion of the Evergreen Formation, and in combination with the sedimentology and ichnology suggest that marine influence increased through time as the basin was filled. The elucidation of marine-influenced deposition contravenes all but the most recent facies interpretations of the Precipice Sandstone and Evergreen Formation, and suggests that the paleogeography of the Mesozoic of eastern Australia needs to be reconsidered. Importantly, the nearshore and shallow marine depositional affinity has important implications for the size, orientation, and distribution of geobodies when building geologically-realistic static reservoir models for dynamic flow simulation

Challenges of Gondwanan marine-nonmarine correlations - a palynological perspective

Marine-nonmarine correlations of the Permian of Laurussia are recently addressed using integrated sedimentological-palaeontological-geochemical signatures aiming to refine existing correlation schemes. However, for Gondwana such efforts are still in an early stage, with first studies on single localities and within distinct basins. Palynology is seen to be the key discipline to tackle this challenge and recent efforts to use climatic signatures recorded in palynomorph assemblages for cross-basin and interbasinal correlations of Karoo-aged basins in southern Africa are very promising. Their near continuous basin fill from the Pennsylvanian to the Early Jurassic captures the most prominent climate change in the Phanerozoic. Postglacial coal-bearing successions of Permian and Triassic age in the Main Karoo Basin of South Africa enable detailed studies of changing vegetation on land. Marine black shales capture changes in paleoceanographic conditions as reflected in marine phytoplankton assemblages and changing terrestrial input of pollen grains and spores, enabling precise correlation of terrestrial coals and marine shales. Ongoing research aims to establish the use of climate signals recorded in terrestrial and marine palynofacies for correlation on a Gondwana-wide, interregional scale

Controls on the geometry, stratigraphic distribution and quality of coals of Middle to Upper Jurassic strata in eastern Australia

The Middle to Upper Jurassic Walloon Coal Measures of eastern Australia host petroleum resources mostly in the form of coal bed methane. The coals accumulated at a high-latitude (>75°S) during a greenhouse epoch and occur in regionally extensive fluviolacustrine successions. Previous studies have described the spatial relationship of facies using a variety of (and sometimes ambiguously defined) stratigraphic frameworks. This was complicated by the absence of marker beds or published radiometric dates. The coal beds are thin and laterally discontinuous and their origin, which has been poorly understood, has implications for consistent stratigraphic correlations. Improved correlation techniques and an understanding of the controls on coal bed geometry should allow better prediction of: 1) the location and architecture of prospective reservoirs, and 2) gas drainage patterns around individual wells. This study aims to address these questions by building upon pre-existing notions on the evolution of eastern Australia during the Middle to Late Jurassic using an integrated approach with new sedimentologic and palynologic data, combined with precise U-Pb dating of volcanic sediments and basin subsidence studies. Zircon from twenty-eight tuffs in 12 wells across the Surat and Clarence- Moreton Basins were dated using the high-precision chemical abrasion thermal ionization mass spectrometry (CA-TIMS) technique to within an error margin of ±40 ka. In addition, two volcanogenic sandstones from one well that intersected the Birkhead Formation in the Eromanga Basin were dated using the same methodology to within ±50 ka. On a 1237 km transect, five regional datums 75°S), the coals originated from peats that accumulated in mires that experienced a warm temperate climate. Rapid and frequent climate change in the polar region may have limited the window of opportunity for thick, widespread coals to develop. New sedimentological and palynological data from the Surat Basin substantially revises interpretations of the environments of deposition. Sedimentary facies and spore-pollen assemblages confirm deposition in a predominately fluviolacustrine setting. However, the identification of tidally-influenced facies, acritarchs and dinoflagellate cysts (a first for Jurassic-aged strata in the basin) indicate periods of brackish water conditions. Marine incursions may have come from the north and the east during time of high eustatic sea-level during the Jurassic. Palaeogeographic reconstructions over 13 Ma reveal extensive fluviolacustrine systems draining from an eroding orogenic belt into proximal estuarine complexes. Allocyclic controls revealed by incised valleys and the deposition of transgressive estuarine facies strongly suggests the accumulation of coal (peat) was unlikely to be coeval with clastic sedimentation because of frequent changes in base level. This study illustrates that a multidisciplinary approach (notably the acquisition of precise U-Pb dates from volcanic sediments and the recognition of subtle indicators of marine influences) can be used to elucidate complex continental successions over large geographic areas. These type of studies will help in the search for subtle oil and gas reservoirs and better calculation of resource and reserve numbers. They may also be of use in better understanding sedimentary mineral resources and groundwater aquifer systems.Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 201

Miosporas y algas chlorococcales de la formación Los Rastros, Triásico medio a superior del centro-oeste de Argentina

El estudio de los niveles lacustres de la Formación Los Rastros (Triásico Medio a Superior) en la sección de Río Gualo (provincia de La Rioja), incluye una interesante palinoflora compuesta por miosporas y algas Chlorococcales. Entre las miosporas abundan los granos de polen de Corystospermales, con presencia subordinada de inaperturados, disacados diploxilonoides, esporas, monocolpados, monosacados y polen estriado. En el fitoplancton se destaca Botryococcus, pero también se observa Plaesiodictyon, que es una forma probablemente relacionada con las Hydrodictyaceae. Datos geológicos y variaciones en el contenido fitoplanctológico señalan que el sistema lacustre probablemente evolucionó desde un cuerpo de agua dulce y condiciones eutróficas, a un ambiente de carácter oligotrófico hacia la parte media y superior de la sección de Río Gualo. Así mismo, se enmienda el género Variapollenites a fin de ampliar su diagnosis original.Lacustrine strata of the Los Rastros Formation (Middle to Upper Triassic) at Río Gualo section (La Rioja province), yield a distinctive palynological assemblage of miospores and chlorococcalean algae. The miospore association is characterized by a relative abundance of corystosperm pollen grains with subordinate inaperturates, diploxylonoid disaccates, spores, monocolpates, monosaccates and striate pollen grains. The phytoplankton are mostly represented by Botryococcus but also by Plaesiodictyon, a form probably related to the Hydrodictyaceae. Geological data and variations in phytoplankton content indicate that the lacustrine system probably evolved from a stretcht of freshwater with eutrophic conditions, into a body with oligotrophic conditions through the middle and upper part of the Río Gualo section. The genus Variapollenites is emended in order to amplify its original diagnosis.Fil: Ottone, Eduardo Guillermo. Universidad de Buenos Aires; ArgentinaFil: Mancuso, Adriana Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Resano, Magdalena. Universidad de Buenos Aires; Argentin

Investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid-Cretaceous vertebrate fossil-localities in the Winton Formation, Queensland, Australia

The Winton Formation of central Queensland is recognized as a quintessential source of mid-Cretaceous terrestrial faunas and floras in Australia. However, sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited. The intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved Winton Formation in the Eromanga Basin, including Isisford, Lark Quarry, and Bladensburg National Park. Twenty-three facies and six repeated facies associations were documented, indicating a mosaic of marginal marine to inland alluvial depositional environments. These developed synchronously with the final regression of the Eromanga Seaway from central Australia during the late Albian-early Turonian. Investigations of regional- and local-scale structural features and outcrop, core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin. Significant palaeoenvironmental differences exist between the lower and upper portions of the preserved Winton Formation, warranting informal subdivisions; a lower tidally influenced fluvial-deltaic member and an upper inland alluvial member. This work further demonstrates that the Isisford fauna is part of the lower member of the preserved Winton Formation; whereas, fossil localities around Winton, including Lark Quarry and Bladensburg National Park, are part of the upper member of the Winton Formation. These results permit a more meaningful framework for both regional and global comparisons of the Winton flora and fauna

The sedimentary evolution of Permian to Cretaceous basins in Queensland, Australia: insights from lithostratigraphy, U–Pb zircon geochronology, sedimentary facies, and provenance analysis

Christopher Todd investigated the geology of Permian to Cretaceous rocks of the Galilee and Eromanga basins in Queensland. He provides constraints on stratigraphy, depositional environments, and ages of the strata, paying close attention to the poorly-studied Jurassic. Results help to characterise the economic hydrocarbon and groundwater systems within these basins