Colin V. Murray-Wallace

Holocene sea-level change on the southeast coast of Australia: a review

A revised Holocene sea-level curve for the southeast coast of New South Wales, Australia, is presented based on a review of previously published geochronological results for fossil molluscs, organic-rich mud, mangrove roots and fixed biological indicators. It is supplemented by new radiocarbon and amino acid racemization-derived ages on fossil molluscs from transgressive sandsheet facies in back-barrier settings within shallow incised valleys along the southern coast of New South Wales. This data base has been limited to fossils with accurate descriptions of their facies associations and stratigraphic relationships to present mean sea level. Results show that sea level during the Holocene marine transgression rose to between −15 and −11 m at 9400—9000 cal. yr BP. Sea level then rose to approximately −5 m by 8500 cal. yr BP and to approximately −3.5 m between 8300 and 8000 cal. yr BP inundating shallow incised valleys resulting in the deposition of shell-rich transgressive sandsheets within shallow incised bedrock valleys. Present sea level was attained between 7900 and 7700 cal. yr BP, approximately 700—900 years earlier than previously proposed. Sea level continued to rise to between +1 and +1.5 m between 7700 and 7400 cal. yr BP, followed by a sea-level highstand that lasted until about 2000 cal. yr BP followed by a gradual fall to present. A series of minor negative and positive oscillations in relative sea level during the late-Holocene sea-level highstand appear to be superimposed over the general sea-level trend. However, the precise nature of the oscillations are difficult to quantify because of problems associated with accurately determining palaeotidal and wave regimes, climatic conditions and the antecedent morphology of the shallow marine environments during the mid Holocene.

Aminostratigraphy of Quaternary coastal sequences in southern Australia — An overview

Abstract Since the early 1980s, amino acid racemisation reactions have been applied to the dating of Quaternary coastal deposits in Australia. Sequences of Middle Pleistocene age or younger have received the greatest attention. Amino acid racemisation has been applied as a relative and numeric dating method, as well as for identifying remanie fossils and in delineating the spatial distribution of some fossil mollusc species. The method has also been used to verify the radiocarbon ages of fossil molluscs from interstadial sediments. It has also been used in studies of coastal neotectonics and in comparisons with other dating methods (e.g. electron spin resonance and thermoluminescence). The most reliable results are from replicate analyses of the hinge region of well-preserved and diagenetically unmodified fossil bivalve molluscs from deeply buried situations (i.e. > 1 m). Molluscs have been dated from a range of sites around the southern Australian coastline and include specimens of Plio-Pleistocene age, and from Middle Pleistocene (Oxygen Isotope Stage 7; ca. 220 ka BP), Late Pleistocene (Substage 5e; ca. 125 ka BP), interstadial (Stage 3; 45 to 30 ka BP), last glacial (Stage 2; ca. 18 ka BP) and Holocene sequences. Amino acid racemisation dating of the Australian Quaternary coastal record has: (1) confirmed the widespread occurrence of last interglacial coastal strata and allowed their correlation with sequences of equivalent age from the northern hemisphere; (2) identified strata of penultimate interglacial age; and (3) confirmed the interstadial age of marine strata (Stage 3) in Gulf St Vincent, South Australia. Aminostratigraphic studies of the southern Australian Quaternary coastal record also indicate that sea-levels during the penultimate interglacial (Stage 7) may have been higher than otherwise predicted on the basis of the oxygen isotope record.

Late Quaternary sea-level highstands in the Tasman Sea: evidence from Lord Howe Island

Abstract Lord Howe Island, situated 600 km east of Australia, provides a unique opportunity to evaluate Late Quaternary highstands of sea level in the Tasman Sea. The mid-ocean island, which is the site of the southernmost coral reef, is composed of basalts of late Tertiary age, and calcarenites derived from bioclastic reefal carbonates. Both erosional and depositional evidence of Late Quaternary highstands of sea level is preserved. Uranium-series disequilibrium dating of coral clasts from a calcarenite beach facies at Neds Beach on the northeast of the island yielded a mean age of 136,000 yr B.P. Thermoluminescence dating of the quartz sand fraction from the same deposit, using fine-grained and coarse-grained methods, yielded ages of 138,000 and 116,000 yr B.P., respectively. These ages are interpreted to indicate that this beach unit, within which fossil bones and eggs of the extinct horned turtle, Meiolania , are found, formed during the Last Interglacial when the sea was 2–4 m above present. Benches and platforms developed on Tertiary basalt and on Late Pleistocene calcarenite on the more sheltered lagoonal shore on the west of the island indicate a sea level up to 1.5 m higher than present during the Holocene. Cemented boulder conglomerates (ca. 3000 yr B.P.) at North Head, and emergent mollusc-rich carbonate muds (ca. 900 yr B.P.) within an embayment fill at Old Settlement Beach, further support this interpretation. These palaeo-sea-level data from the Tasman Sea support previous estimates of the height of the Last Interglacial sea surface relative to eastern Australia, and supplement a growing body of evidence for a higher sea level in the region during the mid to late Holocene.

Facies architecture of a last interglacial barrier: a model for Quaternary barrier development from the Coorong to Mount Gambier Coastal Plain, southeastern Australia

Abstract The last interglacial Woakwine Range, a linear, barrier shoreline complex of temperate bioclastic carbonate origin, in the southeast of South Australia, occurs essentially uninterrupted over a distance of 300 km and up to 10 km inland from the present coastline. Mapping of the internal facies architecture of the barrier as revealed in McCourts Cutting southeast of Robe, reveals the presence of transgressive and regressive facies associated with the last interglacial maximum (Oxygen Isotope Substage 5e), as well as an older aeolianite within the core of the barrier, correlated herein with Oxygen Isotope Stage 7. Amino acid racemisation and thermoluminescence dating indicate that volumetrically, the majority of the Woakwine Range is of last interglacial age. The bulk of the barrier structure comprises aeolian facies in the form of landward-migrating coastal dunes. The internal facies appear to record the culmination of the post-Stage 6 marine transgression at the onset of Substage 5e, and possibly the termination of Substage 5e based on the shallow seaward dip of the discontinuity between regressive littoral and sublittoral facies.

LATE QUATERNARY PALEOSEALEVELS AND PALEOENVIRONMENTS INFERRED FROM FORAMINIFERA, NORTHERN SPENCER GULF, SOUTH AUSTRALIA

Spencer Gulf is an elongate marine embayment extending northwards ca. 300 km inland into southern continental Australia to the apex at Port Augusta, with a narrow estuarine extension northwards. Since the post-glacial sealevel maximum, prograding coastal sedimentation has been effective through the trapping and binding actions of seagrasses, mangroves and cyanobacterial mats, and a well-defined zonation of subtidal, intertidal and supratidal sedimentary facies is characteristic of the northern gulf. Mollusks and foraminifera are prolific, especially within seagrass meadows, and their abundant remains, entire and comminuted, form bioclastic carbonate sediments. Distinctive assemblages of foraminifera are associated with the various estuarine and marine environments. The hypersaline estuary north of Port Augusta is characterized by the textulariids Ammobaculites barwonensis and Trochammina inflata, the latter most common where mangroves are present. Two species of Triloculina, T. inflata and T. oblonga are the only common miliolids, while the rotaliids are represented by Ammonia beccarii, Elphidium articulatum and Nonion depressulus. South of Port Augusta, in euryhaline intertidal waters, Trochammina inflata, A. beccarii and E. articulatum are commonly associated. The shallow subtidal Posidonia seagrass meadows support an abundant fauna which is dominated by three species, Nubecularia lucifuga, Peneroplis planatus and Discorbis dimidiatus. These species continue into the deeper waters, ca. 20 m, where they are subordinate to Quinqueloculina lamarckiana, Massilina milletti, Elphidium crispum and E. macelliforme. A vibrocore from 20 m water depth in Northern Spencer Gulf recovered 4 m of late Quaternary fossiliferous sediment. Amino acid racemization (AAR) and radio-carbon ages derived from fossil mollusks revealed four chronostratigraphic packages of sediment: 400–360 cm, penultimate interglacial, oxygen isotope stage 7; 360–240 cm, last interglacial, oxygen isotope substage 5e; 240–180 cm, interstadial, oxygen isotope stage 3; and 180 cm to the top of the core, postglacial, oxygen isotope stage 1. Species of foraminifera within the core are mostly also living in the modern gulf, thus the preserved assemblages permit plausible interpretations of paleoenvironments and paleosealevels. Large numbers of Q. lamarckiana and M. milletti in the substage 5e interval indicate that the last interglacial sealevel in southern Australia was only slightly higher than that of today. N. lucifuga is abundant in the stage 3 sediment, thus paleowaterdepth at the core site was ca. ≤2 m. This evidence further supports interstadial paleosealevels above −30 m, as previously determined for Gulf St Vincent. Basal sediments of the postglacial interval preserve a monospecific assemblage of Miliolinella labiosa which signifies an estuarine setting having many of the characteristics of a saline lake. Maximum Holocene sealevel is signified by the acme of M. milletti at 90 cm. Subsequent local hydroisostatic relative fall of sealevel is shown by changes up-core from 90 cm in both the general foraminiferal record, for example by declining numbers of M. milletti, and also by reduced numbers of E. macelliforme compared with those of E. crispum.

Holocene Sea Level Fluctuations and the Sedimentary Evolution of a Barrier Estuary: Lake Illawarra, New South Wales, Australia

Abstract Lithostratigraphy of the Holocene Lake Illawarra barrier estuary on the New South Wales coast, Australia, adds details to previous models of barrier estuary evolution. Establishment of a detailed chronology, with the use of 121 aspartic acid–derived ages and six radiocarbon ages, has allowed the definition of a five-stage geomorphic model for the infill of the barrier estuary. A broad incised valley formed during the sea level lowstand represents the initial stage. Stage two is represented by a basal transgressive marine sand sheet deposited in response to rising sea levels associated with the last postglacial marine transgression, which inundated the shallow incised valley ca. 8000–7500 years ago. This feature is not present in the deeper and narrower incised valleys used to establish previous barrier estuary models. The more open marine conditions, with a diverse assemblage of estuarine and marine mollusc species, persisted until ca. 5000 years ago when the barrier started to become emergent and resulted in the development of a low-energy back-barrier lagoonal environment (stage 3). A late Holocene regression (1–2 m) of sea level between 3200–2500 years ago (stage 4) further restricted oceanic circulation and increased the rate of fluvial bay-head delta progradation. The final stage has seen a rapid extension of the fluvial deltas and increased rates of lagoonal sedimentation during the past 200 years as a result of land clearing for agriculture and urban and industrial development. This five-stage evolutionary model of barrier estuary evolution developed for Lake Illawarra can be applied to other shallow estuaries on tectonically stable, wave-dominated coastlines.

A pleistocene origin for shore platforms along the Northern Illawarra Coast, New South Wales

SUMMARY This paper examines the composition, structure and age of clastic deposits situated behind shore platforms at Austinmer and Coledale on the northern Illawarra coast, New South Wales. Our results support earlier chronological evidence of a Pleistocene history for shore platforms along the Illawarra coast. The size and fabric of sediments within these deposits indicate rapid, high‐energy deposition of bedrock eroded from platforms adjacent to the deposits. The elevations of the deposits above the modern shoreline suggest higher sea levels or higher wave energy gradients than presently occurs across these platforms. Dating of sediments within these deposits using 14C, AAR and TL techniques indicates Late Pleistocene and Late Holocene erosion of the shore platforms. Platform development was initiated before the Last Interglacial as correlative sediments lie atop relict platform surfaces landward of the modern platforms.

Aminostratigraphy and electron spin resonance dating of Quaternary coastal neotectonism in Tasmania and the Bass Strait islands

Tasmania and the Bass Strait islands (King and Flinders) preserve a widespread but fragmentary Quaternary coastal record. Quaternary coastal sediments occur in a range of morphostratigraphic settings, typically contain well‐preserved and diverse molluscan fossil assemblages of shallow water origin, and provide evidence for varying degrees of neotectonic uplift over contrasting temporal and spatial scales. Holocene and Late Pleistocene (last interglacial) coastal strata occur most extensively in this region, as revealed by amino acid racemization, electron spin resonance and radiocarbon dating. Radiocarbon dates for marine molluscs from Holocene coastal strata range between 790 to 7120 a and relate specifically to the interval since the culmination of the post‐glacial marine transgression. Holocene coastal sediments in this region do not provide convincing evidence for a higher sea level during the last 7000 years. The last interglacial coastal sediments in Tasmania represent the highest topographic occurr...

Ancestral Murray River on the Lacepede Shelf, southern Australia: Late Quaternary migrations of a major river outlet and strandline development

The Murray River drains the 1.06 × 106 km2 Murray–Darling Basin and discharges into the sea at the Murray mouth in southeast South Australia. The outlet faces the 180 km-wide Lacepede Shelf and forms part of a wave-dominated beach barrier/lagoon complex, the largest of its type on the Australian coast. Global glacial cycles during the Pleistocene produced lowered sea-levels and exposure of much of the Lacepede Shelf, with the paleoshoreline advancing out to the present edge of the continental shelf during glacial maxima. Mapping and sediment sampling of the Lacepede Shelf in 2006 and 2007 allowed the ancient course of the Murray River on the shelf to be traced and studied for the first time, revealing a 200 km-long system of ancient infilled channels and lagoons. The main system of anastomosing Pleistocene channels begins southeast of the present Murray mouth, off Lakes Alexandrina and Albert, runs southward initially but then veers west-southwest across the central Lacepede Shelf before heading southwest directly south of central Kangaroo Island, and splaying into the head of Sprigg Canyon at the shelf edge. The Last Glacial Maximum channel starts near the current Murray mouth and forms part of this channel system. An earlier channel system ran a more direct, shorter 150 km south-southwest path from off Lakes Alexandrina and Albert to the shelf edge. The Lacepede Shelf is founded on a platform of gently folded, shallow-marine Miocene carbonates. The top of the platform is a prominent regional flat-lying erosional unconformity with local karstic relief in the order of 10 m. Unconsolidated sediment cover (?Pliocene–Quaternary) is mostly relatively thin or absent. However, a depocentre (Lacepede Basin), commonly 6–10 m thick, underlies the central Lacepede Shelf and that part of the shelf directly south of Lakes Alexandrina and Albert. This basin comprises estuarine, lagoonal/lacustrine and fluvial facies of the paleo Murray River, including channel-fill and point-bar deposits. Sediment drifts and residual paleo dunefields are common components of the young sediments on the shelf. A Holocene yellow/red fine quartz sand less than a metre thick, likely to have formed from reworked Last Glacial Maximum eolian sheets/dunes as well as lagoonal/lacustrine sediments, is the predominant sediment type at the surface of the central and northern Lacepede Basin. Paleochannels or paleovalleys of the Murray River incised into the Miocene carbonate platform are typically 10–20 m deep, 450–1000 m wide and contain up to 25 m of sedimentary fill and cover.

Origin of the Late Neogene Roe Plains and their calcarenite veneer: implications for sedimentology and tectonics in the Great Australian Bight

The Roe Calcarenite, a 2 – 3 m-thick, soft, quartzose molluscan sand of grainstone to rudstone texture, is a critical unit for deciphering the geodynamic and sea-level history of the southern Australian continental margin. Biostratigraphic and Sr-isotope analysis of molluscs and brachiopods confirms that the unit is Late Pliocene. Amino acid racemisation analyses indicate a minimum age of Early Pleistocene. The general depositional environment was a shallow illuminated shoreface to the inner shelf with the seafloor probably covered by seagrass, much like the modern seafloor offshore the Roe Plains today, but perhaps somewhat warmer. The calcarenite lies on an interpreted marine erosion surface cut into Upper Oligocene to Middle Miocene Eucla Group cool-water carbonates. Such planation, which affected all of the inner shelf, took place throughout the Early Pliocene due to the combination of uplift via basin inversion and eustatic highstand. The process, which led to ∼85 km of cliff retreat in ∼3 million years, is interpreted to be a variant on the shaved shelf process operating on the shelf today. The Roe Calcarenite is envisaged as the last of many calcarenites deposited during small-scale highstands that were eroded during subsequent transgressions. It is preserved because the Roe Plains were uplifted immediately after deposition, part of a widespread Plio-Pleistocene boundary tectonic event. It has been continuously exposed since uplift and subject to arid-zone pedogenic diagenesis. This succession is a relatively quiescent example of uplift, erosion and deposition related to basin inversion. It was much less intense than coeval events further east in the St Vincent, Otway and Gippsland Basins. Together, these Late Neogene tectonic-sedimentary packages illustrate the spectrum of stratigraphic successions that might be expected from basin inversion along an otherwise passive continental margin.