The Bight Basin: a tale of three deltaic megasequences
Ingine Strømsøyen A B , Edwin Schomacker A , Bo Søderstrøm A and Bärbel M. T. Waagan AA Equinor ASA, PO Box 3, 1330 Fornebu, Norway.
B Corresponding author. Email: inks@equinor.com
The APPEA Journal 59(2) 952-957 https://doi.org/10.1071/AJ18213
Accepted: 19 March 2019 Published: 17 June 2019
Abstract
The Bight Basin developed during the Jurassic and Cretaceous in response to repeated periods of extension and thermal cooling leading up to, and following, the onset of seafloor spreading between present-day Australia and Antarctica. The bulk of the resulting sedimentary basin fill includes up to 15 km of Middle Jurassic–recent sediments comprising three deltaic megasequences: White Pointer, Tiger and Hammerhead. High quality seismic 3D data have enabled detailed mapping of the megasequences, evaluation of the nature of infill and assessment of implications for hydrocarbon prospectivity. The Cenomanian White Pointer Megasequence succeeds a period of widespread mudstone deposition in the basin. Growth fault and complex styles of deposition are a function of the high accumulation rates. The growth faulting gradually ceased towards the top of the megasequence allowing for the delta to advance into the basin. Renewed tectonic activity during accumulation of the Turonian–Santonian Tiger Megasequence led to formation of the Outer High trend in the basin. Basal transgressive mudstones during early Tiger deposition are succeeded by a set of progradational–retrogradational units. The base of the Santonian–Maastrichtian Hammerhead Megasequence records widespread subaerial erosion and formation of incised valleys depicting a distinct drop in relative sea level most likely in response to the start of the Australian and Antarctic breakup. This event is followed by a widespread regional flooding event, before the Hammerhead delta built out, first in a highly progradational and subsequently in a more aggradational style. At the end of the sequence, the delta steps back due to decreasing sediment input. Detailed seismic stratigraphic mapping has improved the understanding of the gross depositional environment developed throughout the three megasequences, and importantly also helped identification of the main reservoir fairways and their distribution through time.
Keywords: Ceduna Sub-basin, delta environments, Hammerhead Megasequence, Outer High, seismic facies mapping, shore-face, slope channels, Tiger Megasequence, White Pointer Megasequence.
Ingine Kristin Strømsøyen is a Principal Geologist in Equinor. She received a BSc and MSc from the Department of Earth Science at the University of Bergen in Petroleum Geology/Sedimentology. She joined Statoil (Equinor) in 2005, where she has mainly worked in Exploration. She has experience from working regional scale to prospect evaluation projects around the world; from pre-salt Brazil, Onshore US and Norwegian Continental Shelf and has, since 2014, worked on several projects in Australasia. |
Edwin Schomacker received his PhD in Petroleum Geology in 2008 from the University of Oslo. His research focused on geological reservoir characterisation, forcing factor responses and application of depositional trends in sequence stratigraphic analysis. He joined StatoilHydro (now Equinor) in 2008 where he has worked as a geologist and project leader in regional, access and maturation projects of the exploration division; including areas such as the Caribbean, South America, East Africa, Myanmar and Australia. His current position is project leader for the Halten exploration project of the Norwegian Sea, Norway. |
Bo Söderström graduated with a Master of Petroleum Exploration in 1982 at the University of Gothenburg, Sweden. He then started in the oil industry as an explorationist working for Svenska Petroleum Exploration in Stockholm. In 1985 he joined Norsk Hydro in Norway, which in 2007 merged with Statoil and is now Equinor ASA. His current position is Specialist Geophysics in Equinor’s International Offshore organisation. |
Bärbel M. Traub Waagan finished her PhD in Geophysics at the University of Edinburgh in 2005. She worked as a researcher for Sintef Petroleum Research in Trondheim, Norway, for three years. In 2008 she joined StatoilHydro in Oslo working in the Seismic Imaging and Processing Department and later as exploration geophysicist. She works currently with Equinor ASA in Exploration International Offshore. She is a member of the EAGE and SEG. |
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