Stratal architecture and platform evolution of an early Frasnian syn‐tectonic carbonate platform, Canning Basin, Australia

Abstract

Facies architecture and platform evolution of an early Frasnian reef complex in the northern Canning Basin of north-western Australia were strongly controlled by syn-depositional faulting during a phase of basin extension. The margin-attached Hull platform developed on a fault block of Precambrian basement with accommodation largely generated by movement along the Mount Elma Fault Zone. Recognition of major subaerial exposure and flooding surfaces in the Hull platform (from outcrop and drillcore) has enabled comparison of facies associations within a temporal framework and led to identification of three stages of platform evolution. Stage 1 records initial ramp development on the hangingwall dip slope with predominantly deep subtidal conditions that prevented any cyclic facies arrangements. This stage is characterised by basal siliciclastic deposits and a major deepening-upward facies pattern that is capped by a sequence boundary towards the footwall (north-west) and a major flooding surface towards the hangingwall. Stage 2 reflects the bulk of platform aggradation, significant platform growth towards the hangingwall and the development of reef margins and cyclic facies arrangements. Thickening of this stage towards the hangingwall indicates that accommodation was generated by rotation of the fault block and overlying platform. Stage 3 records a major flooding and backstep of the platform margin. The Hull platform illustrates important elements of margin-attached carbonate platforms in a half-graben setting, including: (i) prominent, but limited, coarse siliciclastic input that does not have a major detrimental effect on carbonate production near the rift margin in arid to semi-arid settings; (ii) wedge-shaped accommodation created by syn-depositional rotation of fault blocks and tilting of the hangingwall dip slope, resulting in shallowwater facies and subaerial exposure up-dip of the rotational axis and deeper water facies down-dip; and (iii) evolution of a ramp to rimmed shelf, coincident with a sequence boundary-flooding surface, that is accelerated by tilting of the hangingwall dip slope during fault-block rotation.

Upper Devonian microvertebrates from the Canning Basin, Western Australia

“…This event occurs at the base of the MN 11 Zone and coincides with the absence of phoebodont taxa in the Canning Basin. Despite reported localised tectonic overprinting (Southgate et al 1993;George and Chow 2002;Chow et al 2013), evidence of a longer-term 2 nd order transgressive event is observable in these sections. The effect of these localised and global events may be highly influential in the faunal changes and extinctions seen in the basin (George and Chow 2002).…”

“…Within Australia this species is now recognised as ranging from MN 6-11 CZ and has been previously used to constrain a Frasnian age for the base of the Gneudna Formation type section in the Carnarvon Basin (Turner and Dring 1981;Trinajstic and George 2009). Within the Canning Basin A. seddoni has been used to confirm a Frasnian age for the Hull platform (Chow et al 2013). Although the increased range of A. seddoni, decreases the ability to obtain more finely resolved ages for strata, its confinement to the Frasnian still makes this species an important zone fossil.…”

“…Difficulty in correlating Frasnian and Famennian sections within the Lennard Shelf is partly due to a complex underlying topography on which the reef was established, as well as depositional heterogeneity (Playford et al 2009). Tectonic activity during the period of reef building (Chow et al 2013) and deformation following post-depositional exhumation have also added to a fragmentary Frasnian and Famennian record across the basin (Playford et al 2009). …”

“…However, as the co-occurring phoebodont teeth preserve the delicate lateral carinae and striations on the cusps, this explanation no longer seems likely for all scales. Another possibility for the absence of ornament is intraspecific variation, with both ornamented and non-ornamented scales present in shallow water facies at Hull Range (Chow et al 2013 fig. 3D).…”

Variations in architecture and cyclicity in fault-bounded carbonate platforms: Early Miocene Red Sea Rift, NW Saudi Arabia

“…This study explores whether in maritime rift basin carbonate platforms, seismically driven cycles may be responsible for the development of 5 th order depositional cycles, resulting from high-frequency syn-sedimentary fault activity that might generate a recurrent motif in carbonate deposition Benedictis et al, 2007;Hamon and Merzeraud, 2008;Chow et al, 2013). fluctuations were probably a moderately high-amplitude and high-rate phenomenon.…”