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Sea level controls on buried geomorphology within the Swan River estuary during the Late Quaternary

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A high-resolution seismic survey was carried out across the metropolitan reach of the Swan River (Perth, Western Australia) to investigate its Late Quaternary sub-surficial geomorphology. Shallow imaging data, integrated with sediment cores, pre-existing literature (including dating) and LiDAR images, revealed three main units, forming a complex system of buried paleochannels, which developed during the Late Quaternary glacial sea level lowstands, and infilled during interglacial highstands. The deepest unit was interpreted as comprising estuarine to fluvial sediments of the Perth Formation, deposited during the Last Interglacial (~130-80 thousand years before present) in a wide paleo-valley that cut the basement. The sedimentary sequence of the overlaying middle unit belongs to the Swan River Formation, which consists of heterogenic fluvial to lacustrine sediments, deposited during the Last Glacial lowstand (~80-18 thousand years before present). The shallowest unit comprises Holocene fluvial and estuarine sediments, up to ten-thousand-year-old. This research represents the first environmental high-resolution acoustic investigation of the Swan River estuary. The findings have improved the understanding of the Late Quaternary Swan River development, providing a useful tool for modelling river onset and evolution, following sea level transgressions.
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ASEG Extended Abstracts
ISSN: 2202-0586 (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/texg19
Sea level controls on buried geomorphology
within the Swan River estuary during the Late
Quaternary
Giada Bufarale, Mick O’Leary & Alexandra Stevens
To cite this article: Giada Bufarale, Mick O’Leary & Alexandra Stevens (2019) Sea level controls
on buried geomorphology within the Swan River estuary during the Late Quaternary, ASEG
Extended Abstracts, 2019:1, 1-3, DOI: 10.1080/22020586.2019.12073056
To link to this article: https://doi.org/10.1080/22020586.2019.12073056
Published online: 11 Nov 2019.
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AEGC 2019: From Data to DiscoveryPerth, Australia 1
Sea level controls on buried geomorphology within the Swan River
estuary during the Late Quaternary
Giada Bufarale* Mick O’Leary Alexandra Stevens
Curtin University UWA / Curtin University Curtin University
Bentley, WA 6102 35 Stirling Hwy, Crawley, WA 6009 Bentley, WA 6102
giada.bufarale@gmail.com mick.oleary@uwa.edu.au m.a.stevens@curtin.edu.au
INTRODUCTION
Late Pleistocene and Holocene Epochs (spanning from ~130 ky
to present) have been distinguished by several orbitally-driven
changes in sea level. This period captured the peak of the Last
Interglacial (Marine Isotope Stage MIS 5e; 127 to 116 ky) with
sea levels between 3 and 6 metres above present. The stage
between 110 ky and 80 ky saw sea level oscillating between -
10 and -30 metres below present (MIS 5d, c, b and a). After 40
ky, global cooling saw sea levels fall to around -125 m at the
Last Glacial Maximum (LGM), which peaked around 18 ky
years BP. The global deglaciation, following the LGM, was
characterised by rapidly rising sea levels reaching near present
elevations around 7 ky BP (see Bufarale et al., 2017 for full list
of references).
This study aimed to construct a more detailed picture of Late
Quaternary sequence stratigraphy and sedimentary architecture
of the metropolitan Swan River (Perth, Western Australia), to
better understand how changing sea level driven fluctuations
(base level) have influenced the evolution of the estuary
throughout this period.
METHOD AND RESULTS
Approximately 30 km of high-resolution shallow seismic
profiles were collected using a boomer-sub bottom profiler
system along the Swan River estuary, between the Narrows
Bridge and Blackwall Reach (Figure 1, top). Survey lines were
devised to capture a range of substrate architectures and
geometries, to a maximum depth of 40 m below the riverbed.
The processed acoustic profiles revealed a complex system of
paleochannels where three main unconformities (R1, R2 and
R3) bound as many seismic units (U1, U2, U3), over the
acoustic basement (Figure 1, bottom).
Integrating these data with sediment borehole analyses, LiDAR
(Light Detection and Ranging) images and the available
literature of the geology and chrono-stratigraphy of the area, it
was possible to determine the development of these units
(Figure 2).
Since no dating has been undertaken for this research, the
following interpretation was performed using pre-existing
literature, including Wallace and Kimber (1989); Kendrick et
al. (1991); Gozzard (2007); Brooke (2010) and Mathew (2010).
Results and Discussion
The deepest unit (U3) is interpreted as the Perth Formation,
which consists of ~20 m thick interbedded, fluvial to estuarine
sediments that were deposited in a large paleo-valley that
incised into the underlying acoustic basement (bedrock: Tamala
Limestone and Kings Park Formation). This period spans ~130-
80 thousand years before present (BP) in the Last Interglacial
(correlating this formation to the sediments dated by Murray-
Wallace and Kimber (1989) and Kendrick et al. (1991)).
The Perth Formation is overlain by a ~27 m thick unit (U2),
composed of heterogenic fluvial to lacustrine sediments,
belonging to the Swan River Formation (Gozzard, 2007).
Similar to U3, U2 also infills channels incised in older deposits
and reflects the hydrogeological conditions linked with sea
level changes during the Last Glacial lowstand.
SUMMARY
A high-resolution seismic survey was carried out across
the metropolitan reach of the Swan River (Perth, Western
Australia) to investigate its Late Quaternary sub-surficial
geomorphology. Shallow imaging data, integrated with
sediment cores, pre-existing literature (including dating)
and LiDAR images, revealed three main units, forming a
complex system of buried paleochannels, which developed
during the Late Quaternary glacial sea level lowstands, and
infilled during interglacial highstands.
The deepest unit was interpreted as comprising estuarine
to fluvial sediments of the Perth Formation, deposited
during the Last Interglacial (~130-80 thousand years
before present) in a wide paleo-valley that cut the
basement.
The sedimentary sequence of the overlaying middle unit
belongs to the Swan River Formation, which consists of
heterogenic fluvial to lacustrine sediments, deposited
during the Last Glacial lowstand (~80-18 thousand years
before present).
The shallowest unit comprises Holocene fluvial and
estuarine sediments, up to ten-thousand-year-old.
This research represents the first environmental high-
resolution acoustic investigation of the Swan River
estuary. The findings have improved the understanding of
the Late Quaternary Swan River development, providing a
useful tool for modelling river onset and evolution,
following sea level transgressions.
Key words: sea level fluctuations, high-resolution seismic
stratigraphy, Swan River paleochannels, Late Quaternary.
Swan River geomorphology Bufarale, O’Leary and Stevens
AEGC 2019: From Data to Discovery Perth, Australia 2
Holocene (last ~10 ky) fluvial and estuarine deposits form the
shallowest unit (U1). These sediments are up to 14 m thick and
have a highly variable internal structure, ranging from layered
to chaotic deposits. The Holocene sediments are also found
filling paleochannels and blanketing the pre-existing
topography.
Figure 1. Top: Locality map showing the study area.
Seismic survey track plot is marked, in yellow. Bottom:
Intersecting seismic cross section showing the buried
geology described in the text. Length of profile 1: ~ 1000 m;
length of profile 2: ~650 m.
CONCLUSIONS
This research describes new insights resulting from the first
environmental high-resolution seismic investigation in the
metropolitan reach of the Swan River estuary.
The data indicated that sea level-driven changes in base level
and the influence this latter had on fluvial sediment dynamics
played a major role in controlling the development of the Swan
River during the Late Quaternary. Throughout this geological
time, paleochannels developed in glacial low sea level stands,
and have been filled by sediments, during interglacial
highstands. Pre-existing topography has shaped and influenced
successive morphological features, as well.
A fuller account of this work can be found in Bufarale et al.
(2017).
Figure 2. Top: Sea level curve in the past 250 ky. Odd
numbers refer to Interglacial Marine Isotope Stages (MIS)
and even numbers indicate the Glacial MIS. Modified after
Lisiecki and Raymo (2005); Berger (2008) and Saqab and
Bourget (2015). Bottom: Schematic cross-section showing
the evolution of the morpho-stratigraphy in the
metropolitan reach of the Swan River through the Late
Quaternary (approximately from Perth CBD to South
Perth), based on seismic profiles and Gozzard (2007).
Horizontal axis: ~ 3 km, orientation N-S; vertical axis:
depth/elevation values are in metres, referred to the present
sea level. Orange lines represent the width of active valley.
A) During the Last Glacial period, a deep inset valley cut
the pre-existing Kings Park Formation and Perth
Formation, during a low sea level stand. B) Changes in sea
level caused by fluctuations in the climate during the last
50-70 ky of this Glacial period resulted in an alternation of
erosion and deposition during which the paleochannel was
filled with the variegate sediments of the Swan River
Formation. C) Last Glacial Maximum (MIS 2, ~ 18 ky BP).
As the sea level reached its lowest point, the most recent
paleochannel was cut and successively (D) infilled with
fluvial deposits through the Holocene interglacial
conditions.
ACKNOWLEDGEMENTS
The original form of this research study was carried out as part
of a PhD thesis at Curtin University (2014-2018), undertaken
by G. Bufarale. The views and material contained in this
presentation are those of the first author and co-authors and not
those of her current employer. The first author would like to
thank the contribution of the Australian Government Research
Training Program Scholarship in financially supporting this
research; Professor Lindsay Collins and Dr Mick O’Leary for
their supervision; and the Swan River Trust for approving the
survey and providing the vessel support for marine operation.
Swan River geomorphology Bufarale, O’Leary and Stevens
AEGC 2019: From Data to Discovery Perth, Australia 3
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Brooke, B., Creasey, J. and Sexton, M., 2010. Broad-scale
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Sea level controls on paleochannel development within the
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Gozzard, J.R., 2007. The Guildford Formation re-evaluated,
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Kendrick, G.W., Wyrwoll, K.-H., Szabo, B.J., 1991. Pliocene
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Mathew, G.V., 2010. Analysis and interpretation of ground and
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... The coastal zone channel morphological changes are preserved as paleochannels in the sedimentary record and provide evidence of paleo-coastline position. Correlation among the morphology of coastal zone paleochannels and sea level changes has been well documented in previous studies (Colman and Mixon, 1988;Fan et al., 1990;Koss et al., 1994;Donoghue and White, 1995;Sloss et al., 2005;Weschenfelder et al., 2010;Ishihara et al., 2012;Bae et al., 2018;Bufarale et al., 2019). ...
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Analysis and interpretation of ground and building movements due to EPB tunnelling
  • G V Mathew
Mathew, G.V., 2010. Analysis and interpretation of ground and building movements due to EPB tunnelling. PhD Thesis, University of Western Australia.