Postglacial Marine Transgression Research Articles

Post-glacial sea-level changes around the Australian margin: a review

It has been known since Rhodes Fairbridge’s first attempt to establish a global pattern of Holocene sea-level change by combining evidence from Western Australia and from sites in the northern hemisphere that the details of sea-level history since the Last Glacial Maximum vary considerably across the globe. The Australian region is relatively stable tectonically and is situated in the ‘far-field’ of former ice sheets. It therefore preserves important records of post-glacial sea levels that are less complicated by neotectonics or glacio-isostatic adjustments. Accordingly, the relative sea-level record of this region is dominantly one of glacio-eustatic (ice equivalent) sea-level changes. The broader Australasian region has provided critical information on the nature of post-glacial sea level, including the termination of the Last Glacial Maximum when sea level was approximately 125m lower than present around 21,000–19,000 years BP, and insights into meltwater pulse 1A between 14,600 and 14,300cal.yrBP. Although most parts of the Australian continent reveals a high degree of tectonic stability, research conducted since the 1970s has shown that the timing and elevation of a Holocene highstand varies systematically around its margin. This is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice-melt, including a process known as ocean siphoning (i.e. glacio-hydro-isostatic adjustment processes).Several seminal studies in the early 1980s produced important data sets from the Australasian region that have provided a solid foundation for more recent palaeo-sea-level research. This review revisits these key studies emphasising their continuing influence on Quaternary research and incorporates relatively recent investigations to interpret the nature of post-glacial sea-level change around Australia. These include a synthesis of research from the Northern Territory, Queensland, New South Wales, South Australia and Western Australia. A focus of these more recent studies has been the re-examination of: (1) the accuracy and reliability of different proxy sea-level indicators; (2) the rate and nature of post-glacial sea-level rise; (3) the evidence for timing, elevation, and duration of mid-Holocene highstands; and, (4) the notion of mid- to late Holocene sea-level oscillations, and their basis.Based on this synthesis of previous research, it is clear that estimates of past sea-surface elevation are a function of eustatic factors as well as morphodynamics of individual sites, the wide variety of proxy sea-level indicators used, their wide geographical range, and their indicative meaning. Some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level, the inter-comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years. These issues need to be thoroughly understood before proxy sea-level indicators can be incorporated into credible reconstructions of relative sea-level change at individual locations. Many of the issues, which challenged sea-level researchers in the latter part of the twentieth century, remain contentious today. Divergent opinions remain about: (1) exactly when sea level attained present levels following the most recent post-glacial marine transgression (PMT); (2) the elevation that sea-level reached during the Holocene sea-level highstand; (3) whether sea-level fell smoothly from a metre or more above its present level following the PMT; (4) whether sea level remained at these highstand levels for a considerable period before falling to its present position; or (5) whether it underwent a series of moderate oscillations during the Holocene highstand.

Sea-level rise and sediment budget controlling the evolution of a transgressive barrier in southern Brazil

Abstract This paper presents an evolutionary model for a coastal barrier in the southernmost coastal sector of Brazil during the Holocene. The dataset is based on 15–20 m drill cores and ground-penetrating radar (GPR) records. The model barrier evolution has two main steps. The first step is the transgression of the barrier controlled by sea-level rise during the Postglacial Marine Transgression, which ended at approximately 6–5 cal ka. Radiocarbon dating indicates that the coastal plain began to be flooded by lagoonal waters between ∼10 and 6.7 cal ka. The second step comprises a barrier transgression controlled by a negative sediment budget of the beach system during the last 6–5 cal ka in a period of an overall slow sea-level fall of approximately 2 m. During the second step, the transgressive barrier migrated because of coastal erosion (the negative sediment budget) and the landward transference of sand by wind and lagoonal delta washout.

Palaeogeographic Changes at Lake Chokrak on the Kerch Peninsula, Ukraine, during the Mid‐ and Late‐Holocene

This project has reconstructed the palaeogeographic and environmental evolution of Lake Chokrak on the Kerch Peninsula, Ukraine, during the mid‐ and late‐Holocene. This record has been evaluated in association with a regional archaeological data set to explore human–environment interactions over this period. The results show major changes in the palaeogeographic setting of Lake Chokrak since the 3rd millennium B.C., when the postglacial marine transgression had started to fill the study area. Microfaunal analyses reveal the long persistence of an open marine embayment that only became separated from the Sea of Azov when a sand barrier developed during the late 2nd millennium B.C. When colonizing the Black Sea region after the 8th century B.C., the Greek settlers erected a fortification with a small settlement on a promontory that was by then a peninsula‐like headland extending into the lake. The colonists abandoned their settlement at the end of the 1st millennium B.C. when the depth of the surrounding lake decreased from 1.5 m to less than 1 m. Today, Lake Chokrak dries up completely during summer. A detailed relative sea level (RSL) curve for the northern coast of Kerch has been established. Sea level reached its highest position at the present day. Since the 3rd millennium B.C., sea level continuously rose, without any of the previously postulated regression/transgression cycles. The RSL curve indicates differential subsidence rates within short distances in relatively stable areas, exceeding 40 cm per 1000 years. © 2012 Wiley Periodicals, Inc.

An Early Pleistocene grounded ice sheet in the Central North Sea

Abstract Evidence is presented for an Early Pleistocene grounded ice sheet in the Central North Sea (CNS). Dated basal Quaternary deposits from UK well 30/13-2 Josephine coincide with the lowest iceberg ploughmarked horizon in a southern CNS depocentre. This horizon has been traced northwards into the central CNS where it is identified as the Crenulate reflection, which exhibits a series of deep, channel-like features, interpreted as subglacial meltwater channels. Further north, a seismic reflection at the same level is characterized by megascale lineations that are interpreted to be the result of erosion, deposition and deformation of sediment beneath an advancing ice sheet. An overlying seismic reflection is characterized by a well-developed channel system that is thought to have drained the retreating ice sheet prior to a post-glacial marine transgression. A southern CNS Early Pleistocene depocentre is shown to have become inactive sometime in the Early to Middle Pleistocene and was replaced by a developing depocentre in the central and northern CNS that remained active into the Late Pleistocene. Evidence for an Elsterian or older grounded ice sheet in UK Continental Shelf Quad 22 is presented in the form of glaciotectonic thrust features.

Postglacial (after 18 ka) deep-sea sedimentation along the Hikurangi subduction margin (New Zealand): Characterisation, timing and origin of turbidites

Recent sedimentation along the Hikurangi subduction margin off northeastern New Zealand is investigated using a series of piston cores collected between 2003 and 2008. The active Hikurangi Margin lies along the Pacific–Australia subduction plate boundary and contains a diverse range of geomorphologic settings. Slope basin stratigraphy is thick and complex, resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the Quaternary. Turbidites deposited since c. 18ka in the Poverty, Ruatoria and Matakaoa re-entrants are central to this study in that they provide a detailed record of the past climatic conditions and tectonic activity. Here, alternating hemipelagite, turbidite, debrite and tephra layers reflect distinctive depositional modes of marine sedimentation, turbidity current, debris flow and volcanic eruption, respectively. Turbidites dominate the record, ranging in lithofacies from muddy to sandy turbidites, and include some basal-reverse graded turbidites inferred to be derived from hyperpycnal flows. Stacked turbidites are common and indicate multiple gravity-flows over short time periods. The chronology of turbidites is determined by collating an extremely dense set of radiocarbon ages and dated tephra, which facilitate sedimentation rate calculation and identification of the origin of turbidites. Sedimentation rates range from 285cm/ka during late glacial time (18.5–17ka) to 15 to 109cm/ka during postglacial time (17–0ka). Turbidite deposition is controlled by: (1) the emplacement of slope avalanches reorganising sediment pathways; (2) the postglacial marine transgression leading to a five-fold reduction in sediment supply to the slope due to disconnection of river mouths from the shelf edge, and (3) the Holocene/Pleistocene boundary climate warming resulting in a drastic decrease in the average turbidite grain-size. Flood-induced turbidites are scarce: nine hyperpycnites are recognised since 18ka and the youngest is correlated to the largest ENSO-related storm event recorded onland (Lake Tutira). Other turbidites contain a benthic foraminiferal assemblage which is strictly reworked from the upper slope and which relates to large earthquakes over the last c. 7ka. They yield a shorter return time (270–430years) than the published coastal records for large earthquakes (c. 670years), but the offshore record is likely to be more complete. The deep-sea sedimentation along the New Zealand active margin illustrates the complex interaction of tectonic and climate in turbidite generation. Climate warming and glacio-eustatic fluctuations are well recorded at a millennial timescale (18ka), while tectonic deformation and earthquakes appear predominant in fostering turbidite production at a centennial timescale (270–430years).

Shelf habitat distribution as a legacy of Late Quaternary marine transgressions: A case study from a tropical carbonate province

The legacy of multiple marine transgressions is preserved in a complex morphology of ridges, mounds and reefs on the Carnarvon continental shelf, Western Australia. High-resolution multibeam sonar mapping, underwater photography and sampling across a 280 km 2 area seaward of the Ningaloo Coast World Heritage Area shows that these raised features provide hardground habitat for modern coral and sponge communities. Prominent among these features is a 20 m high and 15 km long shore-parallel ridge at 60 m water depth. This ridge preserves the largely unaltered form of a fringing reef and is interpreted as the predecessor to modern Ningaloo Reef. Landward of the drowned reef, the inner shelf is covered by hundreds of mounds (bommies) up to 5 m high and linear ridges up to 1.5 km long and 16 m high. The ridges are uniformly oriented to the north–northeast and several converge at their landward limit. On the basis of their shape and alignment, these ridges are interpreted as relict long-walled parabolic dunes. Their preservation is attributed to cementation of calcareous sands to form aeolianite, prior to the post-glacial marine transgression. Some dune ridges abut areas of reef that rise to sea level and are highly irregular in outline but maintain a broad shore-parallel trend. These are tentatively interpreted as Last Interglacial in age. The mid-shelf and outer shelf are mostly sediment covered with relatively low densities of epibenthic biota and have patches of low-profile ridges that may also be relict reef shorelines. An evolutionary model for the Carnarvon shelf is proposed that relates the formation of drowned fringing reefs and aeolian dunes to Late Quaternary eustatic sea level.

Evidence for the episodic “turn on” and “turn off” of turbid-zone coral reefs during the late Holocene sea-level highstand

Terrigenous sediment accumulation within nearshore marine environments is regarded as a major factor inhibiting carbonate production and coral reef accretion. While recent ecological and geological research into reef development under long-term terrigenous sediment influence questions the overly simplistic nature of such views, understanding of the time scales of reef initiation and growth and the morphodynamics of reef accretion in these settings remains limited. Here we present evidence to support recent suggestions that, once established, rapid reef accretion and progradation is possible, but that the restricted accommodation windows in which such reefs develop often result in short-lived (ephemeral) phases of reef building. Specifically, we describe two discrete periods of reef growth within one small (∼600 m wide) coastal embayment around a high island on the terrigenous sediment–dominated inner shelf of the central Great Barrier Reef, Australia. These reef-building phases occurred at either end of the Holocene sea-level highstand, the first during the late postglacial marine transgression and early highstand (∼6900–4500 calibrated (cal) yr B.P.), the second following the late Holocene regression and stillstand (∼1600 cal yr B.P. to present). An ∼3000 yr hiatus occurred between these events, probably as a function of subtle changes in sea level and associated shoreline morphodynamics.

A Record of Holocene Benthic Foraminifera in Vibrocore SG#279, Spencer Gulf, South Australia

Core SG#279 recovered 1.1 m of Holocene bioclastic sediment from northern Spencer Gulf, South Australia. Benthic foraminifera preserved in these sediments provide proxies for the postglacial marine transgression. Species that are characteristic of tidal dominated, coastal seagrass meadows, Cribrobulimina mixta + Nubecularia lucifuga + Peneroplis planatus + Discorbis dimidiatus decrease in numbers upcore confirming their potential to signify a rising sea. Massilina milletti, which favours the deeper waters of northern Spencer Gulf, increases in abundance upcore, thus also signifying the transgression. Quinqueloculina lamarckiana, which positively correlates with increasing water depth in northeastern Gulf St Vincent, similarly provides evidence of the transgression. Maximum water depth is indicated for the core sediments at 40 cm. Data based on the distributions and relative numbers of Elphidium crispum and Elphidium macelliforme were not in accord with those of the other proxy species. It is concluded that the Elphidium ratio is unreliable when applied to sediments deposited at depths of <15 m. Above 40 cm in the core, the distribution of M. milletti provides evidence of marine regression that has been attributed to hydroisostatic uplift of northern Spencer Gulf. The foraminifera provide no credible evidence of any late Holocene sea level rise.

Late Quaternary geomorphology of the Manawatu coastal plain, North Island, New Zealand

This review examines the geomorphological evolution of the Manawatu coastal plain from the Last Glacial Maximum through the Holocene post-glacial marine transgression (c. 7500 cal yr BP) until the present, providing a context within which to examine the extent to which the Holocene evolution of the lower Manawatu valley follows tripartite evolutionary models of incised-valley infill. During the last glaciation the Manawatu River incised a broad, deep valley, while tributaries within the catchment dissected relict marine terraces. This occurred concurrently with the formation of a parabolic dune field at Koputaroa, with sediment sourced from the bars of the Manawatu River. During the post-glacial marine transgression rising sea-levels inundated the incised-valley. At the culmination of the Holocene marine transgression, the Himatangi anticline and Poroutawhao High restricted oceanic influences in the proto-Manawatu estuary, which was partially infilled with estuarine sediment. Estuarine deposition was quickly succeeded by fluvial deposition and floodplain due to high volumes of fluvial sediment introduced by the Manawatu River. A lack of characteristic bay-head delta development may be explained by rapid infill and consequent sediment bypass.

Cottons Breccia of King Island, Tasmania: Glacial or non-glacial, Cryogenian or Ediacaran?

The Cottons Breccia of King Island, Tasmania, is a 100-m-thick carbonate-clast diamictite traditionally interpreted as the product of a Cryogenian or Ediacaran glaciation. It was recently reinterpreted as a mass-flow deposit, unrelated to glaciation, within an active rift basin. We reaffirm the glacial–periglacial interpretation on the basis of sedimentary facies, internal facies relations, clast lithology and isotopic composition, clast fabric analysis, and consistent stratigraphic position beneath a typical post-glacial cap dolostone. The Cumberland Creek Dolostone closely resembles basal Ediacaran cap dolostones world-wide in terms of colour, texture, sedimentary structures and isotopic characteristics. Because it was deposited above storm wave-base, differences in δ13C between closely adjacent sections suggest diachronous deposition during post-glacial marine transgression of a basin with steep local topography. This is compatible with an active rift basin in which glacigenic diamictites of the end-Cryogenian (Marinoan) pan-glacial episode were lodged.

Post-glacial sediment dynamics in the Irish Sea and sediment wave morphology: Data–model comparisons

The irregular seafloor of the narrow Irish Sea on the NW European Shelf has been documented over several decades. From recently collected swath bathymetry data, very large trochoidal, nearly symmetrical sediment waves are observed in many parts of the Irish Sea and appear similar to those described from other continental shelf seas in North America that were covered by glacigenic sediments during the Last Glacial Maximum. Swath multibeam and single beam bathymetry data, backscatter intensity, shallow seismic imagery, video footage and sediment cores from the Irish Sea high sediment waves have been integrated to identify their genesis with reference to present and past hydrodynamic variability. From cross-sectional profiles over asymmetrical sediment waves in the Irish Sea the direction of asymmetry is used to map residual bed stress directions and associated bedload transport paths. Irish Sea peak bed stress vectors were generated using a two-dimensional palaeo-tidal model for the NW European shelf seas and compare well with the observations. Tidally induced bed stresses are modelled to have increased between 7–10 ka BP, to be nearly symmetrical in magnitude and to have reversed in dominant direction on a millennial scale. These environmental conditions during the post-glacial marine transgression are suggested here to help comprehend the construction of the very large sediment waves, with local variations due to differences in sediment grain size, sediment supply, water depth and intensified currents due to seafloor slopes. Model parameterisation using an open ocean boundary with time-dependent tidal changes and the implementation of high-resolution bathymetric information will improve future models of small-scale bed shear stress patterns and improve the predictive value of such modelling efforts.

Stabilisation of intertidal cobbles and gravels by Goniastrea aspera: an analogue for substrate colonisation during marine transgressions?

There is a widespread perception that coral larvae require stable (lithified) rock substrates to settle during reef initiation, and that these substrates are typically carbonate. However, reef core data show that reef establishment can also occur directly above a wide range of unlithified, non-carbonate sediment substrates, including relict alluvial sands and gravels. The mechanisms by which these lithic substrates are colonised and stabilised are not, however, well documented. Here, we describe such processes from an intertidal setting on the inner-shelf of the Great Barrier Reef, in a setting directly analogous to that which would have existed around many inner-shelf high islands during the post-glacial marine transgression when mid-Holocene reef initiation was taking place.

Preservation of a Late Glacial terrestrial and Holocene estuarine record on the margins of Kaipara Harbour, Northland, New Zealand

Subtidal to intertidal deposits from the margins of Kaipara Harbour in Northland preserve a c. 23 000 year incomplete sedimentary record of the transition from terrestrial to estuarine conditions. Cores are used to reconstruct the depositional setting for this transition, interpreted as a succession from dune and freshwater wetland to shallow estuarine environments. The fossil pollen record provides a proxy of Last Glacial Maximum and Late Glacial vegetation for the area. Stability of the Pleistocene dune landscape during the postglacial marine transgression is interpreted on the basis of strong dominance of tall forest taxa (Dacrydium) in the pollen record and soil development in dune sands, with preservation aided by location along the estuary margin. During the Holocene, reworking of the buried dune and wetland sediments has only reached to a depth of 1.5 m below the modern tidal flat. As such, the site provides a rare example of good preservation of Pleistocene deposits at the coast, where extensive reworking and loss of record are more typical.

Litho- and biofacies analysis of postglacial marine mud using CT-Scanning

Marine silty clay deposited during the Late-Wisconsinian postglacial marine transgression of eastern Québec (Goldthwait Sea) is ubiquitous in the sedimentary column of intertidal zones of the St-Lawrence Estuary. This mud is very compact and limits the penetration of organisms composing the modern Macoma balthica community. In order to describe the characteristics of intertidal sediments containing Goldthwait Sea mud, axial tomography (CT-Scan) is used. CT-Scan is a non-destructive method that can be used to describe sediment characteristics (grain size, mineralogy, primary and secondary sedimentary structures, fabric, shape and roundness, bedding contact), and to obtain high resolution, 3D representations of structures within sediment cores. Based on differences in the densities of analysed materials, the different lithologies, lithofacies, and organisms within the core can be discriminated, and a quantification of the volume occupied by the different components of the material can be made. Here, CT-Scan images provide information on the distribution, orientation and interweaving of thanatocœnosis shell beds that alternate with massive or faintly laminated postglacial marine mud beds, as well as on ichnofacies characteristics. In addition, we show 3D images of bioturbation structures within the recent sediment layer, which is distinguished from the underlying Goldthwait Sea mud. When coupled with conventional sedimentary (grain size statistics) and radiochronological ( 14C) analyses, these data provide information which is valuable for identifying depositional processes within sedimentary environments.

Vegetation change following mid-Holocene marine transgression of the Torres Strait shelf: a record from the island of Mua, northern Australia

The pollen and sedimentary record from a coastal backdune swamp on the island of Mua, Torres Strait, Australia, is presented. A 4.55 m core collected from the swamp centre provides a record of vegetation and landscape change spanning the postglacial marine transgression to present. Prior to 6000 radiocarbon years before present (yr BP) results show mangrove vegetation encroaching on the core site, periodically displacing non-mangrove taxa until the establishment of an extensive mangrove forest between 6000 yr BP and 3000 yr BP. Within the mangrove community a transition from lower-tidal Rhizophora forest to an upper-intertidal Ceriops community is evident. This is followed by the development of the current herbaceous freshwater swamp in the late Holocene. The dryland vegetation record is dominated by sclerophyll and rainforest elements with strongest forest representation occurring around the mid Holocene before a decline in tree density and the establishment of open woodlands in the late Holocene. The data suggest vegetation change accompanied marine transgression and a humid mid-Holocene climate, before stabilization of sea levels and the initiation of dominant on-shore catchment processes, signalling drier climatic conditions and possible human activity.

Barite-bearing cap dolostones of the Taoudéni Basin, northwest Africa: Sedimentary and isotopic evidence for methane seepage after a Neoproterozoic glaciation

The Taoudéni Basin of the West African craton contains one of the few genuine terrestrial records of a Neoproterozoic ice age. In the Adrar region of Mauritania, an extensive permafrost landscape, lithified moraines (tillites) and striated pavements are draped by a thin, generally <5-m thick dolostone, which is lithologically and isotopically similar to other basal Ediacaran cap dolostones worldwide. In Adrar, the cap carbonate unit exhibits a complex depositional history with significant lateral facies variation related to the irregular post-glacial, topographic relief and the complex interplay between glacioeustasy and isostatic rebound. The Adrar cap carbonate package consists of one or two dolostone units, with an intervening siliciclastic package of up to 40 m thickness, and a laterally extensive, thin limestone bed that disconformably overlies the uppermost dolostone. The cap dolostone comprises mechanically laminated beds that are disrupted by fitted-brecciation, sheet cracking, tepee formation, karstic dissolution and chaotic vein networks of silica, calcite and barite. The overlying thin bed of limestone breccia comprises volcaniclastic and detrital debris and authigenic barite crystals, cemented and commonly replaced by marine calcite. The close association between relative sea-level changes, glacier retreat and cap dolostone deposition across the Taoudéni Basin implies that cap dolostones formed largely over a period of ∼10 4 years, the maximum interval over which isostatic rebound is likely to operate. Barite has been reported from identical stratigraphic levels overlying terrestrial glacial deposits throughout NW Africa and formed locally during fluid mixing on, and in cavities beneath the seafloor during late stages of the post-glacial marine transgression. Samples of barite were collected from two distant localities in the Taoudéni Basin, in Mauritania and Mali. 87Sr/ 86Sr ratios exhibit an unusually narrow range for barite that closely matches contemporaneous seawater 87Sr/ 86Sr (0.7077–8). Barite δ 34S values range widely between 20‰ and 45‰ CDT, which indicates that sulphate derived from seawater and was subsequently modified by microbially mediated sulphate reduction. The consistent stratigraphic level and irregular distribution of barite deposits are consistent with a sedimentary exhalative origin for the barite, whereby Ba-rich fluids from shallow locations within the rock pile interacted with sulphate-bearing seawater; a hydrothermal origin for these fluids can be excluded. Isotopic constraints and the association of barite with terrestrial glacial deposits across the West African craton suggest that methane seepage from underlying permafrost may be one possible mechanism for Ba sequestration. The occurrence of seafloor barite precipitates at the contact between cap dolostones and overlying post-glacial limestones worldwide implies that changes in ocean composition, in particular increases in the sulphate content of ambient seawater provided an overriding control on barite mineralisation.

Holocene stratigraphic and morphological evolution of the Wandandian Creek delta, St Georges Basin, New South Wales

Subaerial exposure beside the Wandandian Creek channel during the last glacial maximum led to the development of red and orange mottling and, in some areas, produced a palaeosol over the Pleistocene land surface. Incision of the palaeo-Wandandian Creek, during the Late Pleistocene, formed a relatively deep steep-sided channel partially infilled with medium-grained fluvial sand. This palaeovalley became drowned as the post-glacial marine transgression impounded the western portion of St Georges Basin and the basal prodelta/lagoonal mud facies was deposited from ca 7 ka. The Wandandian Creek delta prograded down the palaeovalley and reached the study area ∼3500 – 4000 years ago with the deposition of delta-front sandy silt and the overlying prograded sand facies. The subaerial portion of the delta is characterised by well-developed floodplains, levees, mouth bars and backswamps. Dredging in Wandandian Creek and land clearing for rural and urban development have had little long-term effect on the growth and morphology of Wandandian Creek delta.

Foraminiferal record of the postglacial (Holocene) marine transgression and subsequent regression, northern Spencer Gulf, South Australia

Core SG120 recovered 3.65 m of Quaternary sediment from a northern, shallow-water environment of Spencer Gulf, a marine embayment into the southern continental margin of Australia. Previous investigations had revealed that the upper interval 0 – 148 cm is Holocene marine bioclastic sediment, and that the lower Late Pleistocene interval 250 – 365 cm, with its carbonate palaeosol, had a similar marine origin. However, the age and origin of the interval 148 – 250 cm remained subject to ambiguous interpretation. Re-examination of core SG120, employing detailed foraminiferal analysis, has revealed that this middle unit records the earliest sedimentation associated with the postglacial marine transgression into the northern gulf. These basal Holocene sediments, which incorporated broken, corroded and carbonate-encrusted tests from the underlying palaeosol, together with tests of more pristine appearance, were deposited in a shallow-water, seagrass sandflat environment similar to those in coastal settings of the modern gulf. The lithological change at 148 cm has therefore been reinterpreted as a facies change related to increasing water depth. Radiocarbon analyses of fossil molluscs support this interpretation and reveal that marine transgression, at the site of SG120, was initiated prior to 8600 y cal BP. Selected species of foraminifers (Nubecularia lucifuga, Massilina milletti, Peneroplis planatus, Discorbis dimidiatus, Elphidium crispum and E. macelliforme) together reveal a consistent record of the final stages of the transgression with maximum water depth indicated at a core depth of 90 cm. Subsequent regression, which has been attributed to the combined effects of hydroisostatic uplift and sediment aggradation, is equally recorded by the foraminiferal assemblages.

Postglacial Vegetation, Climate History and Land-Sea Interaction at Island Lake, Baie des Chaleurs, New Brunswick, as Documented by Palynological Analysis*

This study demonstrates that lakes located near the coast, close to large bodies of water, can document sea-level fluctuations and the subtle sea-land interaction that governs coastal areas. At Island Lake, located close to the head of Baie des Chaleurs, northern New Brunswick, the postglacial marine transgression corresponds with a reversal from a cold and dry herb and shrub tundra environment to open pioneer forest that was warmer and wetter. Successive incursions of poplar/aspen and spruce were succeeded by boreal forest dominated by spruce, alder and birch. A forest dominated by alder and fir, indicators of wetter and even colder local conditions followed. Paleoclimatic reconstruction inferred from pollen stratigraphy indicates that an early warming period culminating ca. 9450 BP, was followed by a period when temperatures remained cool. At the same time, the annual precipitation rose sharply, suggesting increased availability of moisture in this area. This is interpreted as a cooling effect due to the proximity to a large body of water to the study site and is attributed to the marine transgression into Baie des Chaleurs following the discharge of glacial lakes Agassiz and Barlow-Ojibway into the Great Lakes and Goldthwait Sea and the isostatic adjustment of the landmass. The cooling effect was recorded by a vegetation change from ca. 9450 to 8100 BP. Within that period, from ca. 8500 to ca. 8400 BP, the vegetation did not record the effect of the proximity to the sea. This period is postulated to be a period of low water levels in the Baie. Recovery to the regional climate norm occurred after 8100 BP when the climate was warmer than today. Since then the climate gradually cooled.

The geomorphological evolution of a wave-dominated barrier estuary: Burrill Lake, New South Wales, Australia

The geomorphological evolution of the Holocene wave-dominated barrier estuary at Burrill Lake on the New South Wales coast, Australia, has been investigated using a combination of seismic stratigraphy and lithostratigraphic analysis of vibracores collected from the back-barrier estuarine environment. A combination of radiocarbon and aspartic acid racemisation-derived ages obtained on Holocene fossil molluscs, and the thermoluminescent signal in remnant the Last Interglacial barrier provides the chronological framework for this investigation. Results from this paper show that the barrier estuary occupies a relatively narrow (< 1.5 km wide) and shallow (< 40 m deep) incised bedrock valley formed during sea-level lowstands. Late Pleistocene sedimentary successions and remnants of the Last Interglacial barrier have been preserved within the incised valley axis and at the mouth of the incised valley. These sediments, deposited during the Last Interglacial sea-level highstand, were partially removed during the last glacial maximum. Overlying the antecedent Late Pleistocene landsurface is a near basin-wide basal marine sand deposited in response to rising sea level associated with the most recent post-glacial marine transgression, which inundated the shallow incised valley ca. 7800 years ago. More open marine conditions, with a diverse assemblage of estuarine and marine mollusc species, persisted until ca. 4500 years ago when the emerging Holocene barrier resulted in the development of a low-energy back-barrier lagoonal environment. A Late Holocene 1–2 m regression of sea level ca. 3000 years ago further restricted oceanic circulation, increased the rate of fluvial bay-head delta progradation and the extension of the back-barrier central basin mud facies. The model of barrier estuary evolution developed for Burrill Lake is consistent with recent research conducted in Lake Illawarra and St. Georges Basin and can be applied to other estuaries that have formed in relatively shallow and narrow incised bedrock valleys on tectonically stable, wave-dominated coastlines.