King Sound Research Articles

Seasonal use of a macrotidal estuary by the endangered dwarf sawfish, Pristis clavata

Abstract Sawfishes (Family: Pristidae) are one of the most imperilled fish families worldwide. There is an increasingly urgent need to better understand the biology, ecology, and population status of the five sawfish species to develop more effective conservation measures. The dwarf sawfish, Pristis clavata, is one of the least researched members of the pristids, with literature limited to analysing disparate datasets or collations of rare encounters in northern Australia. This study examined the spatial ecology of dwarf sawfish using targeted surveys and acoustic telemetry to determine its habitat use in a macrotidal estuary in northern Australia. Seventeen dwarf sawfish were tagged with acoustic transmitters and monitored in the Fitzroy River estuary and adjacent King Sound (Kimberley, Western Australia) between August 2015 and November 2017. Dwarf sawfish observed within the Fitzroy River estuary and King Sound were juveniles, ranging between 740 and 2,540 mm in total length. Catch per unit effort of dwarf sawfish in the late dry season was relatively high in the estuary, with the catch rate in 2015 being one of the highest reported for any sawfish species. Acoustic detections revealed a distinct seasonal pattern in the use of different parts of the estuary and King Sound, which was found to be driven by salinity. Dwarf sawfish predominately occupied a single large pool near the terminus of the tidal limit in the late dry season (August–November), before transitioning to regions in closer proximity to the river mouth or in King Sound in the wet and early dry seasons (December–July). Given the high abundance and residency of dwarf sawfish in the Fitzroy River estuary, this area is an important nursery for the species during the late dry season and should be formally recognized as a habitat protection area for the species.

Regional Assessment of the Conservation Status of Snubfin Dolphins (Orcaella heinsohni) in the Kimberley Region, Western Australia

Implementing conservation measures for data-limited species is a fundamental challenge for wildlife managers and policy-makers, and proves difficult for cryptic marine animals occurring in naturally low numbers across remote seascapes. There is currently scant information on the abundance and habitat preferences of Australian snubfin dolphins (Orcaella heinsohni) throughout much of their geographical range, and especially within the Kimberley region of northern Western Australia. Such knowledge gaps curtail rigorous threat assessments on both local and regional scales. To address this and assist future conservation listings, we built the first comprehensive catalog of snubfin dolphin sightings for the Kimberley. We used these data to estimate the species’ extent of occurrence (EOO) and area of occupancy (AOO) along the region’s 7,000 km coastline, following a simple Bootstrap bivariate kernel approach to combine datasets of varying quality and quantify uncertainty. Our catalog consists of 1,597 visual detections of snubfin dolphins made over a period of 17 years (2004–2020) and collated from multiple sources, including online biodiversity repositories, peer-reviewed scientific articles, citizen science programs, as well as dedicated marine wildlife surveys with local Indigenous communities and Ranger groups. Snubfin dolphins were consistently encountered in shallow waters (<21 m depth) close to (<15 km) freshwater inputs, with high detection rates in known hotspots (e.g., Roebuck Bay, Cygnet Bay) as well as in coastal habitats suspected to be suitable (e.g., Prince Regent River and surrounds, King Sound, Doubtful Bay, Napier Broome Bay and the upper Cambridge Gulf). Bootstrap estimates of EOO and AOO were 38,300 (95% CI: 25,451–42,437) km2 and 700 (656–736) km2 respectively, suggesting that snubfin dolphins in the Kimberley are likely Vulnerable under IUCN criteria B2 at a regional scale, in keeping with their global classification. Our study offers insights into the distribution of a vulnerable coastal cetacean species and demonstrates the value of integrating multiple data sources for informing conservation assessments in the face of uncertainty.

Evidence of Phytoplankton Light Acclimation to Periodic Turbulent Mixing Along a Tidally Dominated Tropical Coastline

AbstractOne of the largest tropical tidal ranges in the world occurs in King Sound, a semienclosed embayment in the tropical Kimberley region of Western Australia. Incubations of phytoplankton within King Sound displayed reduced photosynthetic efficiency, elevated maximum photosynthetic rates, and no measurable photoinhibition. A response typical of high light adapted phytoplankton despite decreased water clarity and low ambient nutrient concentrations in the estuary. This is in contrast with the adjacent shelf where phytoplankton, associated with a deep chlorophyll maximum, display high photosynthetic efficiency and strong light inhibition typical of low light adaptation. Remote sensing and numerical modeling suggest that spatial and temporal variations in tidal mixing drive changes in light variability and in photoacclimation. In King Sound phytoplankton experience the largest variations in light over short time scales where diatoms dominate since they can rapidly acclimate to water column light conditions by adjusting pigment within the cell. The photophysiological response of the phytoplankton in the Sound suggests that acclimation to alternate weak and strong mixing exposes them to cyclical changes in light intensity delaying the onset of photoinhibition, allowing higher maximum photosynthetic rates to be attained. These findings highlight the importance of a multifaceted approach to understanding the links between physics and photoacclimation strategies employed by phytoplankton to more accurately determine rates of depth‐integrated productivity in complex coastal areas.

Terrestrial Signature in Coral Ba/Ca, δ18O, and δ13C Records From a Macrotide‐Dominated Nearshore Reef Environment, Kimberley Region of Northwestern Australia

AbstractThe geochemistry preserved in massive scleractinian corals has long been used as proxies for river runoff, but its reliability in naturally extreme environment (i.e., strong hydrodynamics and intensive thermal stress) has not been tested yet. Using Porites coral collected from the macrotidal nearshore Kimberley region of northwestern Australia, we assess the impacts of river runoff and associated changes in this extreme environment using elemental (Ba/Ca) and isotopic (δ18O and δ13C) compositions at both near monthly and annual resolutions. On the monthly timescales, significant terrestrial signatures were noted in skeletal Ba/Ca, ∆δ18O, and to a lesser extent in δ13C time series, highlighting their linkage to runoff input of Fitzroy River. However, all the geochemical time series as well as the observational coastal sea surface salinity exhibited a consistent ~1‐ to 2‐month lag with river discharge, possibly a manifestation of the sluggish water and sediments exchange in King Sound which are likely induced by strong tidal forcing. On the annual timescales, Ba/Ca follows the variation in river discharge, while freshwater supplied by both runoff and rainfall all contributed to δ18O variations. In contrast, annual δ13C is mainly dominated by the 13C Suess effect, showing a gradually downward trend. Importantly, we find that δ18O and Ba/Ca records exhibit consistent and significant long‐term trends, with δ18O being decreasing and Ba/Ca being increasing, coupled with the increased Australian monsoon, indicating that strengthened monsoon precipitation has likely brought more freshwater and sediment loads to the nearshore Kimberley region.

A New Cowrie from the Estuaries of Northwestern Australia

A new species of cowrie in the genus Erronea (Ipserronea) is described from the muddy coastal estuaries of King Sound, Western Australia, at the mouth of the Fitzroy River. The new cowrie, here named Erronea (Ipserronea) garyi n. sp., is the smallest-known member of its subgenus and inhabits oyster and Pinna beds on intertidal mud flats adjacent to mangrove jungles and river inlets. This new mudflat-dwelling dwarf cowrie is the fifth-known species in the subgenus Ipserronea

Biophysical oceanography of tidally-extreme waters of the southern Kimberley coast, Western Australia

The continental shelf of the South Kimberley region of Western Australia is wide (~300 km) and interactions with the Indian Ocean culminate in extreme tides. This results in some of the largest tropical tides in the world (reaching 11 m on spring tide) measured in King Sound (KS), a large embayment which opens to the Indian Ocean. This remote area of Australia is very rich in natural resources and under increasing developmental pressures, but despite this the marine environment has been poorly studied. In Austral autumn (April/May) 2010, we examined phytoplankton biomass and production across four onshore-offshore transects from coastal waters (also within KS) to the 1000 m isobath, and their responses to physical and chemical environmental variables associated with tidal forces during a four week voyage aboard the RV Southern Surveyor. Using temperature and salinity relationships we found three distinct water masses; KS, Kimberley Shelf, and Kimberley Shelf break waters. The highest chlorophyll-a biomass in the study area was measured in a band along the 200 m isobath (27–46 mg Chl a m−2), and associated with greater concentrations of nutrients (332–392 mmol NO3- m−2, 650–823 mmol Si m−2, 21–39 mmol PO43- m−2). Phytoplankton biomass inside KS was dominated by large diatoms (as determined from accessory pigment analyses), shifting to a community largely comprised of picophytoplankton offshore. Rates of primary production (PP) on the shelf, via measurements of phytoplankton carbon (14C) uptake from photosynthesis versus irradiance incubations, decreased from coastal areas (222–560 mg C m−2 d−1) to offshore waters (45–78 mg C m−2 d−1). In KS, PP was highest (1692 mg C m−2 d−1) despite low standing stock nutrient concentrations (0.02–1.5 mmol NO3- m−2) and relatively high concentrations of suspended particulate material reducing light availability (Kd = 0.27 m−1).

Coastal Talitridae (Amphipoda: Talitroidea) from north-western Australia to Darwin with a revision of the genus Cochinorchestia Lowry & Peart, 2010.

Three species of coastal talitrids are reported from north-western Western Australia: Australorchestia tantabiddyensis sp. nov., from Tantabiddy Rockholes Cave, Cape Range National Park; Talorchestia dampieri sp. nov. from Roebuck Bay, Broome and Cygnet Bay, King Sound; and Tropicorchestia derbyensis gen. et sp. nov. from Derby, King Sound. Five species are reported from west of Darwin, Northern Territory: Cochinorchestia lindsayae sp. nov.; Cochinorchestia metcalfeae sp. nov.; Floresorchestia limicola (Haswell, 1880); Microrchestia ntensis sp. nov.; and Tropicorchestia glasbyi sp. nov. The genus Cochinorchestia Lowry & Peart, 2010 is revised: Orchestia notabilis of Griffiths, 1973 is assigned to the new species Cochinorchestia morrumbene sp. nov. from Mozambique; Orchestia sp. of Ledoyer, 1979 is assigned to the new species Cochinorchestia poka sp. nov. from Ambon, eastern Indonesia; and Orchestia notabilis of Ledoyer 1986 is assigned to the new species Cochinorchestia tulear sp. nov. from south-western Madagascar. Microrchestia sp. of Bussarawich 1985 appears to be an undescribed species of Cochinorchestia from Thailand. We introduce the term virgula dentata to describe the highly modified tip of antenna 2 in talitrid amphipods and propose a theory for the age and current distribution of the family.

Molecular phylogenetics and comparative anatomy of Kimberleytrachia Köhler, 2011 – a genus of land snail endemic to the coastal Kimberley, Western Australia with description of new taxa (Gastropoda, Camaenidae)

Kimberleytrachia Köhler, 2011 is a genus of camaenid land snail endemic to the Western Australian Kimberley region. It comprises twelve previously recognised species, all of which occur within the high precipitation zone along the north-western coast between the Admiralty Gulf and King Sound and within less than about 50 km distance from the coast. By evaluating the variation in shell and genital anatomy as well as the differentiation in the mitochondrial markers 16S and COI, we assess the monophyly of Kimberleytrachia with respect to other camaenid genera from north-western Australia. In addition, we newly describe six species (K. jacksonensis n. sp., K. leopardus n. sp., K. nelsonensis n. sp., K. serrata n. sp., K. setosa n. sp. and K. silvaepluvialis n. sp.) based on comparative morphology and mitochondrial DNA differentiation. We found that a rather smooth, weakly elevated shell and, in particular, the complex penial anatomy are key morphological characteristics of Kimberleytrachia. Its constituent species are differentiated by a combination of shell and genital features and their morphological disparity appears to be more pronounced when species occur in sympatry. While island species are usually narrowly endemic to one or a few islands, the mainland species have much larger distributional ranges. One new species from the Maret and Berthier Islands, Bonaparte Archipelago, is phylogenetically and morphologically so distinct from Kimberleytrachia that it is recognized as a new monotypic genus, Succochlea n. gen.

3D geological model for King Sound, Canning Basin, Western Australia using FALCON® high resolution airborne gravity gradiometry data

A 3D geological model for King Sound, in the offshore Canning Basin, Western Australia, was produced by interpretation of FALCON® high resolution airborne gravity gradiometry and magnetic data, aided by 2D gravity models, 2D seismic data and well logs. Pseudo-depth slices of the vertical gravity gradient (GDD) and magnetic data and interpreted seismic horizons were used to constrain the vertical distribution of sedimentary sequences, intrasedimentary intrusives and basement rocks. Basement depth was determined from the magnetic data using traditional profile-based automated magnetic depth estimation techniques with well control. The 3D model indicates an elevated, fault-bounded platform of Archaean to Proterozoic basement in the north. The platform is rimmed by Late Devonian and Early Carboniferous carbonate reefs and carbonate breccias and in the south, contemporaneous siliciclastic submarine fans and turbidite deposits occur in a deep marine environment. Density values derived from published literature and measured in wells at King Sound were assigned to units in the geological model. A forward model was calculated and compared to the observed GDD data. The assigned density values were then modified, within the expected range for each rock type, using property inversions until a good fit between the modelled and observed data was obtained. Models derived from potential field data can be beneficial for petroleum exploration in frontier basins worldwide, where only limited well and seismic data are available. The 3D geological model provides a good framework for use in designing future exploration programs in the area and it aids data visualisation and interpretation.

Research Centre for the History and Analysis of Recorded Music (CHARM) Sound Files Search and Discography (review)

Research Centre for the History and Analysis of Recorded Music (CHARM) Sound Files Search and Discography. King's College London, 2009. http://www.charm.rhul.ac.uk/index.html. (Accessed 20 May 2013). [Requires a Web browser, an Internet connection (Mozilla Firefox, Chrome, Internet Explorer 7, or Opera 10 or above recommended) and a media player (Winamp, Songbird, or VLC media player recommended).]IntroductionCHARM (Research Centre for the History and Analysis of Recorded Music) Sound Files Search is an online audio archive that provides access to almost 5,000 classical music files that were digitized from a collection of 78 rpm discs located at the King's Sound Archive at King's College London. Initiated in 2004, funding for the project was made possible thanks to a fiveyear grant from the UK-based Arts and Humanities Research Council (AHRC). Part of this funding was used to establish the CHARM Transfer Project in order to digitize, index, and archive the audio files online. The digitization project received additional funding in 2009 from Jisc (a UKbased charity that focuses on the intersections between higher education and digital technologies), which allowed digitization to continue, concentrating on recordings of British and Irish performers produced between 1900 and 1950. Although AHRC funding for the CHARM Transfer Project ran out in 2009, the CHARM Sound Files Search is still freely available online and hosted by Royal Holloway, University of London.1The CHARM Transfer Project was part of a much larger research center concentrating on the musicological study of classical music sound recording in the first half of the 1900s that brought together researchers of several prominent academic institutions including Royal Holloway, Uni - versity of London, King's College London, and the University of Sheffield. In addition to the online sound files, the CHARM Web site also presents a searchable discography, academic papers, and the findings of a series of research projects.Information pertaining to organizational structure and acknowledgments for the project are readily available on the site. Access to the entire CHARM Web site-including research findings, much of the metadata, and audio files-is freely available to anyone with an Internet connection. Supported by a mandate that CHARM would act as an advocate for the extension of fair dealing for sound recordings, the project aims to provide openly available data and files whenever possible. For sound files that were not in the public domain, CHARM attempted to negotiate the rights to provide online access.In 2009, CHARM researchers were awarded an additional five years of funding, but the project shifted focus to the musicological study of live performance as opposed to recorded performance. Although funding for the project has expired and additional development of the Sound File Search has ceased, the site remains online and open to the public.ContentThe recordings selected for inclusion in the Sound Files Search were digitized from the King's College London King's Sound Archive of over 145,000 78 rpm discs, representing a broad range of classical repertoire recorded and produced in the earlyto mid-1900s. Many of these recordings were acquired through donation from the BBC Gramophone Library and used in London and regional UK BBC studio broadcasts from the early 1900s to 1960s. For more information on the history and holdings of the King's Sound Archive, visit http://www.kcl.ac.uk/artshums/depts/music /research/proj/ksa/index.aspx (accessed 20 May 2013).The files chosen for the CHARM Transfer Project attempt to avoid duplication by excluding repertoire that is already available in CD or online reissues. The site provides clear justification for the scope of the Sound Files collection. Within the collection there are several notable strengths including almost 500 recorded Schubert songs. The site also includes several subcollections that hold unique and in some cases rare recordings of famous individuals in the classical music performing and broadcasting scenes of the early 1900s. …

Basin architecture from high-resolution gravity gradient, magnetic, and seismic data, King Sound, Canning Basin, Western Australia

An interpretation of geologic structure at King Sound in the Canning Basin was completed using airborne gravity gradient, magnetic, and seismic data. During the Late Devonian and Mississippian periods, the elevated part of the basement in the north was rimmed by carbonate reefs and redeposited carbonate debris, whereas in the south, siliciclastic submarine fans and turbidites were deposited along the margin of the basement in a deep-marine environment. Three principal lithologic units were identified from the vertical gravity gradient (GDD) in the basin: (1) the Fairfield Group carbonates of high density are interpreted to be the source of prominent positive gravity anomalies; (2) forereef debris and carbonate clastics reworked from carbonates higher up the slope or from the carbonate platform are interpreted to be the source of medium-density responses; and (3) turbidites, debris flows, and associated clastic basinal sequences of low density are interpreted to be the source of prominent negative gravity anomalies. Depth slices of GDD indicate the channelized nature of turbidite flows. In the lower section of the basin, intrasedimentary intrusives were identified from magnetic, GDD, seismic, and well data. Depth to magnetic basement calculation indicates that the surface of the Archean to Paleoproterozoic basement ranges from 3200 to 130 m (10,499–427 ft) below sea level. The northwest- and northeast-oriented south-dipping faults cut the basement and propagate upward into the sediments. A three-dimensional geologic model constructed for King Sound satisfies all known geologic constraints and is consistent with the gravity, magnetic, seismic, and well data.

Predicted response of coastal wetlands to climate changes: a Western Australian model

A review of the Western Australian coast systems shows a range of models of how coastal wetlands could respond to climate change because it spans climates from tropical humid, tropical arid, to near-temperate humid, faces various oceans that drive coastal processes and maintain coastal landforms and habitats, and adjoins a range of hinterland types that develop variable coastal habitats, runoff and rainfall. It thus provides a plethora of settings that latitudinally will respond differentially to any changes in air temperatures, evaporation, rainfall patterns, freshwater influx, wind regimes and storm activity, and derivative responses such as changes in sediment supply, maintenance of coastal forms, coastal groundwater and biota. A review and examples of coastal wetland response to climate changes are provided from Walpole–Nornalup Inlet Estuary, Leschenault Inlet Estuary, the Point Becher area and King Sound.

Life history notes of the critically endangered dwarf sawfish, Pristis clavata, Garman 1906 from the Kimberley region of Western Australia

The dwarf sawfish, Pristis clavata, was captured in marine waters of King Sound and estuarine waters of the Fitzroy, May and Robinson Rivers, in the Kimberley region of Western Australia. Observations of sexual maturity and annuli present on vertebrae suggest that the estuarine waters of at least the Fitzroy River act as a nursery for the species, where immature individuals may remain for at least 3 years. The capture of immature individuals in excess of 2,330 mm TL during the current study in addition to Peverell’s (Peverell in Environ Biol Fishes 73:391–402, 2005) record of a mature male measuring 3,060 mm TL implies that the species may attain far greater lengths than previously reported and that the common name may not be entirely appropriate. In contrast to the sympatric freshwater sawfish Pristis microdon, the number of rostral teeth of individual P. clavata can not be used to differentiate males from females, with both sexes possessing an average of 42 rostral teeth.

Freshwater Sawfish Pristis microdon Latham, 1794 (Chondrichthyes : Pristidae) in the Kimberley region of Western Australia

The Freshwater Sawfish Pristis microdon was captured in marine waters of King Sound, and estuarine and fresh waters of the Fitzroy and Robinson rivers, in the Kimberley region of Western Australia. In light of the IUCN listing of the species as critically endangered, non-destructive means, including tagging-recapture data and information from specimens found dead on the banks, were utilised. Observations of sexual maturity, annuli present on vertebrae, recaptures of tagged individuals and length-frequency data suggested that the freshwaters of the Fitzroy River are a nursery for this species where immature individuals (up to 2800 mm total length) remain for a maximum of four or five years. Morphology and counts of the number of rostral teeth indicated that, in most cases, the rostral tooth morphology can be used to differentiate male and female P. microdon and also are useful in distinguishing this species from the congeneric and sympatric Pristis clavata. Furthermore, differences in the relationship between rostrum length and total length between the sexes may provide an effective diagnostic tool for the collation of historical distribution and sex ratio data from rostrums held in private collections. Rostral tooth counts and length at age data also suggest that the synonymisation of P. microdon, Pristis zephyreus and Pristis perotteti is not warranted.

Classification of the Australian continental shelf based on predicted sediment threshold exceedance from tidal currents and swell waves

Estimates of significant wave height and period, together with tidal current speed over a semi-lunar cycle, were used to predict the area on the Australian continental shelf over which unconsolidated sediment was mobilised (threshold exceedance). These sediment-entraining processes were examined independently to quantify their relative importance on the continental shelf. Using observed grain size data, mobilisation from swell waves occurred on ∼31% and tidal currents on ∼41% of the continental shelf. Swell wave energy is sufficient to mobilise fine sand (0.1 mm diameter) to a water depth of 142 m on the Otway Shelf near the western entrance to Bass Strait. Tidal currents in King Sound (northwest shelf) are capable of mobilising large areas of medium sand (0.35 mm diameter) 100% of the time. Superimposing the distribution of threshold exceedance by wave and tidal currents indicates that there are areas on the shelf where either wave-induced or tidal currents dominate, some areas where waves and tides are of relatively equal importance and still other areas where neither is significant. We define six shelf regions of relative wave and tidal energy: zero (no-mobility); waves-only, wave-dominated, mixed, tide-dominated and tides-only. Our results provide a predictive, process-based understanding of the shelf sedimentary system that has applications to marine engineering projects and to regional studies of pollution dispersal and accumulation where significant shelf sediment mobilisation is a factor.

Dynamics of the turbidity maximum in King Sound, tropical Western Australia

King Sound is a 100-km-long embayment located in tropical northwestern Australia with a spring tidal range of 11 m. This is the second largest tide in the world after the Bay of Fundy in Canada. Intertidal areas cover about 800 km 2. The upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m −3. Field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998. The tide was a propagating wave, shoaling and dissipating by friction as it entered the sound. This mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb. An evaporation-driven salinity maximum zone was found in the upper reaches of the sound, and this was also where the turbidity maximum occurred. Tidal pumping by the tidal asymmetry and, possibly, the biological filter formed by muddy marine snow, trapped the fine sediment in the upper regions of King Sound. Wind-driven waves contributed significantly to entrainment of bottom fine sediment, possibly through wave pumping of the sediment and not wave-induced orbital velocities. Field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height.

THE GEOLOGY AND HYDROCARBON POTENTIAL OF THE EP 104 PERMIT, NORTHWEST CANNING BASIN, WESTERN AUSTRALIA

Current interpretations suggest the presence of five Devonian reef building cycles in EP 104 with a further two in the Ordovician, Nita, and Willara formations. The possible Devonian reefs occur in the NVorral, Lower and Upper Pillara, Virgin Hills, and Nullara carbonate cycles. Minor buildups may be present in the Fairfield and Laurel formations.The Upper Pillara reef complex was subaerially exposed and partly eroded for a period of 10 to 50 million years, following the Early Frasnian 'Tappers Inlet orogeny'. Large potential hydrocarbon reservoirs were created by the secondary mega-porosity formed during this period, and these were sealed by the regional Laurel transgression in the Early Carboniferous. This mode of porosity enhancement is applicable to all the potential reef cycles, as varying degrees of unconformity mark their upper boundaries, generally followed by onlap of sealing lithologies. The Upper Pillara cycle is considered the most prospective of the Devonian carbonate cycles which were the main targets in the first five wells.In response to the success of Home Energy Co. Ltd at Sundown, the last four wells in EP 104 have had Permo-Carboniferous objectives. This drilling resulted in the discovery in 1982 of the small Kora oilfield, believed to have been sourced from the Laurel Formation.The Black Rocks Prospect, in King Sound, is being considered for the first 1986 exploration well. This represents a return to Devonian Pillara reefs, the traditional primary targets in EP 104. As a bonus, drape, accentuated by late collapse of the reefal core, has localized multiple Permo-Carboniferous structural closures, coincident with reefal closure.By comparison with the highly productive Swan Hills and Rainbow-Keg River reefs in Canada the Pillara and Worral carbonate cycles in EP 104 must have considerable potential.

Long-term erosion of the tidal flats King Sound, north western Australia

King Sound in northwestern Australia, with a tropical semi-arid climate is situated in a macrotidal tide-dominated regime. The shores of King Sound are bordered by tidal flats that exhibit a considerable variation in geomorphology and stratigraphy. Erosion is the dominant geomorphic process forming the tidal flats today. Three types of erosion are important; these are sheet, cliff and tidal-creek erosion. Tidal-flat geomorphology at the local scale is an expression of which erosion type is dominant. The geomorphology at regional scale is largely an expression of the extent that erosion has gone to completion in removing Holocene, Pleistocene and bedrock stratigraphic units. Determination of erosion rates over the past few decades, extrapolation of these rates into the past, together with stratigraphic and diagenetic data point to a long-term erosional history for King Sound, King Sound itself appears to be formed largely as a result of long-term lateral erosion.

Sedimentology and the stratigraphic sequence of a tropical tidal flat, north-western Australia

King Sound, with its semiarid-tropical climate and large tides (11.5 m maximum), offers an opportunity to study unique mangrove-fringed tidal flats. Although much of the coastline is in an erosional phase there are local areas of deposition where the sedimentologic processes are active and stratigraphic sequences are developing. The tidal flats are zoned into several geomorphic/lithofacies units: (1) low tidal sand flats are underlain by megarippled sand and shelly sand; (2) mud/sand slopes encompass mid to low tidal levels and are underlain by mud/sand laminite and mud laminite; (3) mangal/mud flats, occurring between MSL and MHWS, harbour an abundant, diverse biota including mangroves, crustacea and molluscs; bioturbated mud is accumulating on these flats; (4) salt flats are the highest tidal unit and they are underlain by laminated and vesicular mud. The distribution of sediment types, sedimentary structures and biota across tidal flats is related ultimately to frequency of inundation and groundwater salinity. Physical processes dominate over biological in the frequently inundated, well-winnowed low tidal areas; upslope, sediments become finer and biogenic activity progressively becomes dominant, reaching a peak in the mangal. Thereafter to landward infrequent wetting and hypersalinity results in decrease in biota. With lateral progradation or vertical shoaling a stratigraphic sequence is generated that reflects the dynamic history of tidal flats. Laterally prograded sequences contain the four lithofacies in a stacked sheet-like array. Shoaled sequences are composed of three or four lithofacies and contain abundant erosional contacts, erosional products and shoal geometry bedforms within and between lithofacies. Regional tidal flat accretion appears to take place by an alternation of aceretion and erosion which results in laterally prograding sequences alternating with shoaling sequences.

Mangrove Zonation Along an Eroding Coastline in King Sound, North-Western Australia

Mangrove Zonation Along an Eroding Coastline in King Sound, North-Western Australia