Craig R. Sloss

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.

Onset of Mediterranean outflow into the North Atlantic

The when of Mediterranean water outflow The trickle of water that began to flow from the Mediterranean Sea into the Atlantic Ocean after the opening of the Strait of Gibraltar turned into a veritable flood by the end of the Pliocene 2 to 3 million years ago. It then began to influence large-scale ocean circulation in earnest. Hernández-Molina et al. describe marine sediment cores collected by an ocean drilling expedition (see the Perspective by Filippelli). The results reveal a detailed history of the timing of Mediterranean outflow water activity and show how the addition of that warm saline water to the cooler less-salty waters of the Atlantic was related to climate changes, deep ocean circulation, and plate tectonics. Science, this issue p. 1244; see also p. 1228 Mediterranean outflow water began to enter the Atlantic and influence global ocean circulation by the late Pliocene. [Also see Perspective by Filippelli] Sediments cored along the southwestern Iberian margin during Integrated Ocean Drilling Program Expedition 339 provide constraints on Mediterranean Outflow Water (MOW) circulation patterns from the Pliocene epoch to the present day. After the Strait of Gibraltar opened (5.33 million years ago), a limited volume of MOW entered the Atlantic. Depositional hiatuses indicate erosion by bottom currents related to higher volumes of MOW circulating into the North Atlantic, beginning in the late Pliocene. The hiatuses coincide with regional tectonic events and changes in global thermohaline circulation (THC). This suggests that MOW influenced Atlantic Meridional Overturning Circulation (AMOC), THC, and climatic shifts by contributing a component of warm, saline water to northern latitudes while in turn being influenced by plate tectonics.

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.

Aminostratigraphy of two Holocene wave-dominated barrier estuaries in southeastern Australia

Abstract An aminostratigraphy of Lake Illawarra and St Georges Basin, two wave-dominated barrier estuaries in southeastern Australia, has been derived on the basis of the extent of aspartic acid racemisation in the Holocene fossil molluscs Anadara trapezia and Notospisula trigonella. Relative ages were also assigned to Late Pleistocene fossil molluscs on the basis of the extent of racemisation of the slower racemising amino acids valine, leucine, and proline. Aminostratigraphy indicates that remnant Last Interglacial deposits within both incised valleys form a substrate over which Holocene estuarine sediments have been deposited and form a core for the Holocene barrier. Results from this study also indicate that the early geomorphological evolution of wave-dominated barrier estuaries formed in broad and relatively shallow, incised valleys is different from previously published models of Holocene barrier estuary evolution that explain successions in narrow, drowned valleys. Divergence from previous models is seen with the deposition of a near-basinwide shell-rich transgressive sandsheet deposited as rising sea levels breached remnants of Last Interglacial barriers during the most recent postglacial marine transgression (PMT; ca. 12,000–7000 Cal BP). Subsequent development of the estuaries follows the previously developed models with the Holocene barrier and central mud basin accumulating over the initial transgressive sandsheet. The aminostratigraphic framework derived from this study will serve as a geochronological template for future studies in wave-dominated barrier estuaries on the southeast coast of Australia.

An introduction to dating techniques: a guide for geomorphologists

This chapter provides researchers with a guide to some of the types of dating techniques that can be used in geomorphological investigations and issues that need to be addressed when using geochronological data, specifically issues relating to accuracy and precision. This chapter also introduces the ‘types’ of dating methods that are commonly used in geomorphological studies. This includes sidereal, isotopic, radiogenic, and chemical dating methods.

Holocene sea-level change and coastal landscape evolution in the southern Gulf of Carpentaria, Australia:

A revised Holocene sea-level history for the southern Gulf of Carpentaria is presented based on new data from the South Wellesley Archipelago and age recalibration of previous research. Results confirm that rising sea levels during the most recent post-glacial marine transgression breached the Arafura Sill ca. 11,700 cal. yr BP. Sea levels continued to rise to ca. –30 m by 10,000 cal. yr BP, leading to full marine conditions. By 7700 cal. yr BP, sea-level reached present mean sea-level (PMSL) and continued to rise to an elevation of between 1.5 m and 2 m above PMSL. Sea level remained ca. + 1.5 between 7000 and 4000 cal. yr BP, followed by rapid regression to within ± 0.5 m of PMSL by ca. 3500 cal. yr BP. When placed into a wider regional context results from this study show that coastal landscape evolution in the tropical north of Australia was not only dependent on sea-level change but also show a direct correlation with Holocene climate variability. Specifically, the formation and preservation of beach-rock deposits, intertidal successions, beach and chenier ridge systems hold valuable sea-level and Holocene climate proxies that can contribute to the growing research into lower latitude Holocene sea-level and climate histories.