Van Tuyl et al. Pinnacle features at the base of isolated carbonate buildups marking point sources of fluid offshore Northwest Australia James Van Tuyl†, Tiago M. Alves, and Lesley Cherns 3D Seismic Laboratory, School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, CF10 3AT Cardiff, UK ABSTRACT of the North West Shelf after the early Oligo­ GEOLOGICAL SETTING cene (Rosleff­Soerensen et al., 2012; Belde We investigated pinnacle features at the et al., 2017; Rankey, 2017). To understand what Mesozoic–Cenozoic Evolution of base of late Oligocene–Miocene isolated controls carbonate growth on equatorial mar­ the Browse Basin carbonate buildups using three-dimensional gins, it is important to explain the onset of iso­ seismic and borehole data from the Browse lated carbonate buildup growth in the Browse The Browse Basin is an offshore sedimentary Basin, Northwest Australia. Brightened seis- Basin, and in similar carbonate sequences basin on Australia’s North West Shelf, a north­ mic reflections, dim spots, and other evidence in the Browse Basin. east­striking passive continental margin devel­ of fluid accumulation occur below most pin- Locally, Howarth and Alves (2016) mapped oped from the Late Jurassic to the present day nacle features. An important observation is clustered fluid­flow features above late Oligo­ (Fig. 1; Stephenson and Cadman, 1994; Rosleff-­ that all pinnacles generated topography on cene–Miocene karst systems and within iso­ Soerensen et al., 2012, 2016). Located on the successive late Oligocene–Miocene paleo- lated carbonate buildups. These fluid­flow fea­ southeast edge of the Timor Sea, the Browse seafloors, therefore forming preferential tures were interpreted as being associated with Basin exhibits a margin­parallel, landward­dip­ zones for the settlement of reef-building or- a salt diapir at depth, despite: (1) the absence ping half­graben geometry (Fig. 2; Struckmeyer ganisms by raising the paleo-seafloor into the of thick evaporites in great parts of the Browse et al., 1998; Rosleff­Soerensen et al., 2012). photic zone. Their height ranges from 31 m Basin, and (2) the presence of the shallow­water Jurassic continental rifting between Greater to 174 m, for a volume varying from 33 km3 Seringapatam Reef in the area interpreted by India and Western Australia (Veevers and Cot­ to 11,105 km3. Most of the pinnacles, how- Howarth and Alves (2016). While the latter au­ teril, 1978; Langhi and Borel, 2008; Rosleff ever, are less than 2000 km3 in volume and thors discussed fluid flow within (and above) ­Soerensen et al., 2012, 2016) generated north­ present heights of 61–80 m. As a result of the larger isolated carbonate buildups, they east­trending structures on the North West Shelf, this work, pinnacles are explained as the first did not address the potential significance of including in the Yampi, Leveque, Caswell, and patch reefs formed in association with mud migrating fluids on isolated carbonate buildup Barcoo subbasins (Fig. 1; Longley et al., 2002; volcanoes or methanogenic carbonates, and initiation and growth. Hence, there is still no Langhi and Borel, 2008; Rosleff­Soerensen et al., they are considered as precluding the growth complete under standing of what controlled the 2012, 2016; Howarth and Alves, 2016). Early of the larger isolated carbonate buildups. We distribution of isolated carbonate buildups in the Cretaceous subsidence and the deposition of a postulate that pinnacle features above fluid- Browse Basin, and the role migrating fluids may passive­margin sequence buried the rift­related flow conduits demonstrate a valid seep-reef have played during buildup evolution. topography (Fig. 2; Stephenson and Cadman, relationship, and we propose them to be re- In this paper, we document for the first time 1994; Struckmeyer et al., 1998; Langhi and fined diagnostic features for understanding the relationship between fluid flow and the Borel, 2008; Rosleff­Soerensen et al., 2012). fluid flow through geological time. growth of late Oligocene–Miocene isolated car­ Seafloor spreading in the Indian and Southern bonate buildups in the Browse Basin through Oceans caused northward migration of Aus­ INTRODUCTION the interpretation of the Poseidon three­dimen­ tralia from ~40°S in the Eocene–Oligocene to sional (3­D) seismic volume. This was done ~20°S at present (Apthorpe, 1988; McGowran Carbonate strata dominate the Miocene stra­ regardless of the presence of the Seringapatam et al., 2004; Rosleff­Soerensen et al., 2012). In tigraphy of the Browse Basin, Northwest Aus­ Reef in the study area, as it forms a prominent particular, late Oligocene–early Miocene colli­ tralia (Rosleff­Soerensen et al., 2012), and depo­ near­surface carbonate platform that is distinct sion between the Pacific and Australasian plates sition on other equatorial margins (Brouwer from the pinnacle features documented in this promoted counter clockwise rotation of the Aus­ and Schwander, 1987; Eberli and Ginsburg, paper. Therefore, we addressed the following tralian continent (Veevers and Powell, 1984). 1987; Grötsch and Mercadier, 1999; Wil­ research questions: This rotation generated subsidence and shallow son et al., 2000; Pomar, 2001; Fournier et al., (1) What is the origin of fluids and what struc­ extensional faulting in the outer North West 2005). Significantly, the Browse Basin records tures controlled fluid flow in the Browse Basin? Shelf (Stephenson and Cadman, 1994). Fault re­ a change from a carbonate ramp to a rimmed (2) What do pinnacle features observed at the activation (Harrowfield and Keep, 2005; Rosleff-­ platform during the Cenozoic, with regional base of isolated carbonate buildups reflect in Soerensen et al., 2012) and moderate tectonic in­ data documenting the contiguous growth of terms of geological processes? version in the Browse Basin (Keep et al., 2000). carbonate buildups in the shallowest parts (3) Was there an active seep­reef relationship The Cenozoic oceanography of the North in the Browse Basin during the late Oligocene West Shelf was closely controlled by the Indo­ †vantuylj@ cardiff .ac .uk and Miocene? nesian Throughflow (Fig. 1; McGowran et al., GSA Bulletin; September/October 2018; v. 130; no. 9/10; p. 1596–1614; https://doi .org /10 .1130 /B31838 .1 ; 14 figures; Data Repository item 2018098 ; published online 4 April 2018 . 1596 Geological Society of America Bulletin, v. 130, no. 9/10 © 2018 The Authors. Gold Open Access: This paper is published under the terms of the CC­BY license. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/130/9-10/1596/4316280/1596.pdf by guest on 24 September 2021 Pinnacle features marking point sources of fluid in carbonate buildups A E115° E135° B E121° E123° E125° 0° Poseidon-1 w Poseidon-2 Seringapatam Reef Figure 1C S11° Indonesia Throughflo Indonesian Brecknock-1 S5° Throughflow Seringapatam Indonesian Caswell Sub-Basin S13° Sub-Basin South Java Current S15° Leeuwin Current Barcoo Yampi Shelf Sub-Basin S15° Australia N Leveque Shelf N S25° 750 km 75 km Australia S17° C E122° E122.30° King Sound Major Paleozoic/Mesozoic fault Major fault Fig. 6B S13.30° Study area in Rosleff-Soerensen et al. (2016) Fig. Fig. 14A Cenozoic fault 5 Fig. 12C Fig. 6A Anticline Study area in this work g. 3D Fi Well Basin outline Fig. 12A Fig. 6C Fig. 12 Fig. B Fig. 3F Figure 1. (A) Location map of the Browse Basin showing the study area, ocean cur- Fi 13 g N Fig. 5C . rents, and their flow directions (arrows). (B) Enlarged location map of the seismic data Fig. 3E 2 Fig. 5B set and the Poseidon-1 and Poseidon-2 wells relative to the main structural elements of 25 km the Browse Basin. The figure also shows the location of Rosleff-Soerensen et al. (2016) S14° study and the Brecknock-1 well. (C) Location map showing the position of all cross sec- Cross-section tions and mapped horizons shown in this work. Data gap due to the presence of the modern Seringapatam Reef 1997; Gallagher et al., 2009; Kuhnt et al., 2004; reached maturity and started expelling hydro­ the Browse Basin represent an aggradational car­ Rosleff­Soerensen et al., 2012). The Indonesian carbons during the Miocene (Blevin et al., bonate shelf. The Miocene rimmed platform was Throughflow flooded the North West Shelf with 1998a; Grosjean et al., 2016). The Lower– drowned in the late Miocene and largely buried warm, low­salinity water, delivering Pacific Middle Jurassic Plover Formation (synrift) by Pliocene hemipelagic sediment (Rosleff-­ and Asian reef species (Collins, 2010; Rosleff­ forms the major sandstone reservoir in the Soerensen et al., 2012; Belde et al., 2017), Soerensen et al., 2012). Bathymetric controls Browse Basin. Postrift strata include Upper Ju­ whereas the modern­day Seringapatam Reef is on the Indonesian Seaway during Miocene con­ rassic organic­rich marine shales (Stephenson locally emergent (Fig. 2; ConocoPhillips, 2012). vergence between Australia and the Banda arc and Cadman, 1994; Rosleff­Soerensen et al., (McGowran et al., 1997) strengthened the Indo­ 2012; Grosjean et al., 2016), and interbedded Faults nesian Throughflow (Gallagher et al., 2009; Lower Cretaceous shales and carbonates with Rosleff­Soerensen et al., 2012) and are thought thin hydro carbon­bearing turbidites (Stephen­ The reactivation of Jurassic faults and re­ to have extended carbonate production up to son and Cadman, 1994). gional tectonic inversion that occurred after the 29°S, along Australia, by the Holocene (Zhu Argillaceous carbonates became prevalent in onset of subduction in the Timor Trough resulted et al., 1993). the Browse Basin during the Paleocene (Fig. 2; in highly variable deformation styles across the Apthorpe, 1988). An Eocene–early Oligocene Browse Basin (Harrowfield and Keep, 2005). Regional Stratigraphy and Associated carbonate ramp developed before a stratigraphic Small­scale normal faults crosscut late Oligo­ Petroleum System break recording uplift and erosion of the inner cene–Miocene strata in the eastern part of the shelf (Fig. 2; Stephenson and Cadman, 1994; study area, forming east­trending lineaments on The seismic­stratigraphic framework of the Howarth and Alves, 2016; Belde et al., 2017).