Mid‐Holocene Development of Mangrove Communities Featuring Rhizophoraceae and Geomorphic Change in the Richmond River Estuary,New South Wales,Australia

This paper describes the hitherto unreported occurrence of mid‐Holocene mangrove deposits in the Richmond River estuary, southeastern Australia, thereby providing evidence for changes in the distribution and composition of mangrove communities within a subtropical estuarine system during the Holocene. Stratigraphic, radiocarbon and palynological evidence indicates that widespread development of mangrove communities took place in the upstream reaches of the Richmond River estuary during the period 7000 to 6000 years BP. These communities maintained their habitat through substrate aggradation under the conditions of a moderate sea‐level rise, in contrast to other estuaries within the region, which generally experienced the submergence of intertidal substrates. Mangrove species belonging to the family Rhizophoraceae, most likely Bruguiera gymnorrhiza and Rhizophora stylosa, dominated these communities, in strong contrast to contemporary communities, which are dominated by Avicennia marina. Moreover, these mid‐Holocene communities were located a considerable distance upstream of the contemporary occurrences of Rhizophoraceae species within the estuary. The changes in the spatial distribution and composition of mangrove communities parallel the large‐scale evolution of the estuary driven by sea‐level variation. Shallow, buried Pleistocene terraces probably contributed to the regionally unique aggradational response of the mangrove communities and their substrates to a sea‐level rise during mid‐Holocene times.     

The Significance of Coastal Processes for Management of the River Murray Estuary

The tidal prism in the River Murray estuary has been reduced by over 85 percent since completion of the barrages in 1940 and regulation has diminished the rate and size of river flows through the estuary. Reduced fluvial flushing has emphasised the dominance of coastal processes at the river mouth. These are expressed in the accretion and stabilisation of a flood-tidal delta, the migration of the mouth, the erosion of Sir Richard Peninsula and the accumulation of new flood-tidal deltaic deposits. Inconclusive studies relating river flow to mouth migration indicate the importance of coastal processes such as littoral drift, tidal flux and sea state, particularly at times of low river flow, in explaining the position and morphology of the mouth. Previous management strategies have failed to consider coastal processes adequately.     

Geographical Influences on Settlement-Location Choices by Initial Colonizers: a Case Study of the Fiji Islands

From 3200 to 2850 cal BP (1250–900 BCE), the Lapita people of the Bismarck Archipelago (Papua New Guinea) undertook voyages eastward that led to their colonization of the eastern outer Solomon Islands, Vanuatu, New Caledonia, Fiji, Tonga and Samoa. The earliest (Lapita) settlements in Fiji were along the Rove Peninsula in southwest Viti Levu Island. At the time of colonization, sea level was 1.5 m higher than today. The Rove Peninsula was then a smaller island off the coast of larger Viti Levu, with a broad, fringing reef along its windward coasts, which was probably the main attraction for Lapita colonizers. As elsewhere during Lapita times in the western tropical Pacific Islands, settlement choice for the initial colonizers of the Fiji Islands was at one level driven by site access, at another by the presence of broad, fringing coral reefs suitable for marine foraging. The earliest settlement along the Rove Peninsula was at Bourewa, occupied first in 3050 cal BP (1100 BCE), where people lived in houses on stilt platforms built along the axis of a subtidal sand barrier; on one side was a broad coral reef, on the other a partly-enclosed tidal inlet. There is no evidence that the Bourewa settlers practised horticulture or agriculture at this time, their subsistence being predominantly marine foraging. After some 300 years of following this subsistence strategy, the inhabitants of Bourewa responded to sea-level fall and the arrival of cultivars (of taro and yam) by including horticulture. As sea level fell further, a total of 550 mm during the Lapita era, the tidal inlet dried up and marine-food resources diminished to a point where the natural environment of the Rove Peninsula could no longer sustain its Lapita inhabitants. All Lapita sites in the area were abandoned about 2500 cal BP (550 BCE), at the same time as the Lapita culture, marked by the end of dentate-pottery manufacture, came to an end in Fiji.     

Formation of beach‐ridge plains: an appreciation of the contribution by Jack L. Davies

A robust debate among coastal geomorphologists as to the processes by which beach‐ridge plains around Australia have formed was initiated by a former President of the Institute of Australian Geographers. This review gives special consideration to the work of Jack L. Davies, whose academic contributions to coastal geomorphology in Australia have not always been appropriately acknowledged when explaining how similar plains have evolved elsewhere in the world. Davies recognised that relatively steep storm waves caused erosion (cut) on beaches, whereas less steep long‐period swell waves returned sand (fill). He considered the beach berm to be the nucleus on which a beach ridge formed, which could subsequently develop into a foredune, in contrast to cobble ridges that were deposited during storms. Offshore conditions regulate supply of sand to the shoreline, partly through effects on wave refraction, with higher rates of supply where the nearshore is shallow. It was apparent to Davies that the elevation of successive ridges might, but not necessarily, provide evidence of past changes of sea level, despite adornment by variable amounts of windblown dune sand. Morphodynamic understanding of long‐term coastal evolution, based on radiocarbon dating chronologies, has demonstrated that Australian coastal plains formed over the past ~6,000 years when sea level has been close to its present level, in contrast to several documented locations in the northern hemisphere where the sea has been rising for the past few millennia. Particularly insightful were observations by Davies that ridge formation could be influenced by a range of factors including changes in sea level, storminess, or sediment supply. These factors acting singly or in combination seem likely to change in the future. Understanding such responses remains a high priority and can be addressed by new technologies, such as light detection and ranging, optically stimulated luminescence dating, ground‐penetrating radar, and computer simulation.     

Estuarine Beach Morphology in Microtidal Middle Harbour,Sydney

Microtidal Middle Harbour, Sydney, contains a range of estuarine beach morphologies from steep reflective beachfaces to wide low‐tide terraces. The most exposed beaches are morphologically similar to lowest‐energy open‐ocean beaches; however, the remainder of the profiles cannot be adequately explained by established beach morphodynamic models. Estuarine beach morphology in Middle Harbour appears to be primarily influenced by storm events. Deep‐water ocean waves rework profiles in the lower part of estuary. For beaches protected from these waves, tidal fluctuations are the main determinant of beach profile. Locally‐generated wind waves are only a significant energy contributor where the fetch is large enough; however, this only occurs on two beaches where low‐tide terraces are formed.     

The possible role of humans in the early stages of machair evolution: palaeoenvironmental investigations in the Outer Hebrides,Scotland

Low altitude sandy plains (machair) are a distinctive feature of the Atlantic coasts of the Scottish Outer Hebrides. They formed as a result of shoreward movement of sediment consequent upon a rise in Holocene sea levels. During the long period over which machair has been forming, the earliest date proposed for their human occupation is the Neolithic. The natural origins of the machair are not disputed, but examination of deposits at sites in the islands of Benbecula and Grimsay encourages us to advance a possible anthropogenic role in the process of machair development, and also to suggest that human involvement may date from the Mesolithic period (pre-5000 BP [ca. 5730 cal BP]), a time for which archaeological evidence is lacking from the Outer Hebrides. The presence of charcoal might suggest that burning of the vegetation cover of the machair was an additional factor to the supposedly dominant marine and aeolian processes in sand mobility. Removal of shrub vegetation may also have left sand surfaces open to deflation. There remains a difficulty in separating natural from human causes in investigations of long-term coastal evolution.     

MIDDLE HOLOCENE PERIODICITIES IN RAINFALL INFERRED FROM OXYGEN AND CARBON ISOTOPIC FLUCTUATIONS IN PREHISTORIC TROPICAL ESTUARINE MOLLUSC SHELLS

Stable oxygen and carbon isotopic ratios in modern and archaeological estuarine mollusc shells, Polymesoda radiata, change in accordance with seasonal salinity fluctuations in the Acapetahua estuary located on the Pacific coast of southern Mexico. This region receives ?3000 mm of precipitation annually, most during a wet season between April and October. The changing flux of fresh water and organic detritus into the estuary causes large changes in the oxygen and carbon isotopic composition of the estuarine waters and in the carbonate precipitated by P. radiata. Oxygen isotopic ratios in the shells of molluscs collected by late Archaic period populations (5000–4000 BP) in this region indicate that patterns of rainfall were similar to today. Modern shells, however, exhibit much more negative carbon isotopic values than observed in prehistoric shells. This change may be associated with the input of modern fertilizers into the estuary.     

Diatom-inferred salinity changes in relation to Holocene sea-level fluctuations in estuarine environments of Argentina

Espinosa, M.A., Hassan, G.S. & Isla, F.I., September 2012. Diatom-inferred salinity changes in relation to Holocene sea-level fluctuations in estuarine environments of Argentina. Alcheringa 36, 377–391. ISSN 0311-5518.

The analysis of diatoms from three sedimentary sequences in the Quequén Grande River basin (Buenos Aires province, Argentina) has allowed the reconstruction of local and regional palaeosalinity changes in relation to Holocene sea level fluctuations. An established diatom-based salinity transfer function is used in combination with autecological methods to reveal a maximum sea level between ca 7000 and 6000 ¹⁴C years BP. This marine influence was recorded in deposits exposed 2 km and 12 km upstream, but not 32 km from the mouth. The fossil diatom assemblages are characteristic of an estuarine lagoon with maximum inferred salinities of 15‰. When the Holocene transgression began to flood the former valley (ca 7000 ¹⁴C years BP), brackish lagoons evolved into estuarine settings in the lower valley, but shallow freshwater ponds with salinities <4‰ persisted at 32 km from the mouth.     

The Chenier Plain,a Genetic Type of Accumulative Coastland

The chenier plain of southwestern Louisiana is described on the basis of the American literature and a personal visit. It is suggested that this is a distinctive type of accumulative coastland characterized by the alternation of marsh and beach ridges and formed by the pulsating influx of stream-borne and marine sediment and the alternating predominance of longshore and onshore transportation of sediment. The chenier plain of Louisiana is found to have analogs in the Guiana coast and in the Myzeqeja plain of Albania as well as in ancient, buried chenier deposits.     

Morphology and Significance of Transverse Ridges (De Geer Moraines) Adjacent to the Moray Firth,NE Scotland

Abstract

High-resolution NEXTMap digital surface models and aerial photographs are used to map suites of transverse ridges at Tarbat Ness and to the west of Elgin, along the margins of the Moray Firth in northeast Scotland. Based on their morphology, configuration and location, interpret these landforms as De Geer moraines which formed at or near former grounding line positions of the Moray Firth palaeo-ice stream. The Tarbat Ness De Geer moraines almost certainly formed at a marine margin. Reaching altitudes of 55 m above present OD, these landforms may provide one of the highest geomorphological indicators for former relative sea level in mainland Britain. Evidence from surrounding landforms and sediments suggest that the ridges formed between c. 15 000–18 000 cal yrs BP, indicating that a significant fall in relative sea level may have taken place prior to an ice margin re-advance in the Moray Firth, known as the Ardersier Oscillation.     

Absolute chronology of fluvial events in the Upper Dnieper River system and its palaeogeographic implications

A set of 121 radiocarbon and OSL dates has been compiled from the Upper Dnieper River and tributary valleys, Western European Russia. Each date was attributed according to geomorphic/sedimentological events and classes of fluvial activity. Summed probability density functions for each class were used to establish phases of increasing and reducing fluvial activity. The oldest detected reduction of fluvial activity was probably due to glacial damming at LGM. Within the Holocene three palaeohydrological epochs of millennial-scale were found: (1) high activity at 12,000–8,000 cal BP marked by large river palaeochannels; (2) low activity at 8,000–3,000 cal BP marked by formation of zonal-type soils on -floodplains; short episodes of high floods occurred between 6,500—4,400 cal BP; (3) contrasting hydrological oscillations since 3,000 cal BP with periods of high floods between 3,000–2,300 (2,000) and 900–100 cal BP separated by long interval of low floods 2,300 (2,000)-900 cal BP when floodplains were not inundated — zonal-type soils were developing and permanent settlements existed on floodplains. In the last millennium, four centennial-scale intervals were found: high flooding intervals are mid-11–mid-15^th century and mid-17–mid-20^th century. Intervals of flood activity similar to the present-day were: mid-15–mid-17^th century and since mid-19^th century till present. In the context of palaeohydrological changes, discussed are selected palaeogeographic issues such as: position of the glacial boundary at LGM, role of changing amounts of river runoff in the Black Sea level changes, floodplain occupation by Early Medieval population.     

Holocene hyrax dung deposits in the afroalpine belt of the Bale Mountains (Ethiopia) and their palaeoclimatic implication

Abstract

The results of pollen analysis and radiocarbon dating are presented for two hyrax dung deposits from rock shelters found in the Afroalpine zone of the Bale Mountains (South-Central Ethiopia). Deposits accumulated from about 15,000 to 1500 (cal) years BP and from 7000 (cal) years BP till nowadays, respectively. Pollen spectra of the initial stages of deposit development (up to 15,000 (cal) years BP) correlate with unfavourable conditions in the Late Glacial Maximum. The African Humid Period (AHP) (15,000–5000 (cal) years BP) is registered in this palaeoecological record as well as the Younger Dryas event (about 12,500 (cal) years BP). Upward shift of Afromontane forest belt and expansion of ericoid communities at high altitudes were characteristic of the Pleistocene/Holocene transition (about 10,000 (cal) years BP). The AHP which continues around 10,000 (cal) years BP after Younger Dryas, was interrupted by a dry episode around 8200 (cal) years BP. Principal aridisation trend during the last 5000 years was observed. Presumably the first traces of human activities in this area can be shown for up about 2500 (cal) years BP.     

A 6000 Year‐old Fossil Dugong from Botany Bay: Inferences about Changes in Sydney's Climate,Sea Levels and Waterways

The excavation in the 1890s of a skeleton of the warm‐water marine mammal Dugong dugon, associated with Aboriginal artefacts, from a Botany Bay salt marsh, marked the beginning of speculation about climate and sea level change in Australia over the period of human occupation. The dugong bones have recently been dated, giving a conventional ¹⁴C age of 5520±70 years BP, which is consistent with three older ¹⁴C dates for a layer of buried trees that underlies much of the north Botany sediments. The carefully drawn cross‐sections of depositional strata produced by the original discoverers allow further interpretation of the pattern of Holocene sea‐level fluctuations in the Sydney region. Layers of estuarine sediment, such as the one containing the dugong skeleton, are inter‐bedded with peat layers containing in situ roots and stumps, suggesting that the site alternated between sub‐aerial exposure and submergence throughout the Holocene. The presence of the dugong is suggestive of warmer conditions, and its inland location indicates a more extensive Botany Bay in the recent past. This is in agreement with other work from southern New South Wales describing both warm‐water marine species and higher sea levels several thousand years ago.

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Archaeological sedimentology of overbank silt deposits on the floodplain of the Ohio river near Louisville,Kentucky

The surface of the floodplain of the Ohio River about 20km southwest of Louisville, Kentucky, is a series of linear ridges and swales that are subparallel to the channel of the river, which here is relatively straight and flows southward. Numerous prehistoric occupational sites are located on these ridges. The sediments that underlie the ridges, which were examined in four archaeological excavations as deep as 8 m, are predominantly sandy silt and silty fine to very fine sand and appear to be mainly the product of overbank deposition from suspended load. Abundant cultural material and occupational sites dating as early as 10,000 years BP are found in the sediments at depths as great as 6·5 m. The fine sediments of the floodplain are underlain by sand and gravel.The context of the cultural materials and the stratigraphy and morphology of the deposits indicate that the ridged deposits began as linear riverside sand and gravel bars. These were succeeded upward by fine-grained overbank deposits in which the ridged morphology was maintained because the overbank silt and fine sand were deposited as prograding elongate bars at high water. As the floodplain ridge built upward, the sedimentation rate decreased and the sand content of the sediments diminished, and as the river channel occasionally shifted, the ridged deposits were built in successive subparallel sequences.Two archaeological consequences are implicit in this depositional model of orderly growth of the floodplain. First, available archaeological data from floodplain segments along other parts of the river should confirm the model; and second, the model should make it possible to search the floodplains of the Ohio River for stratified sites of any desired age.     

The charophyte Lamprothamnium succinctum as an environmental indicator: a Holocene example from Tom Thumbs Lagoon,eastern Australia

The palaeobiota from a middle to late Holocene succession in Tom Thumbs Lagoon, N.S.W., Australia, reflects a range of environmental conditions caused by sea-level changes and active estuarine sedimentation. At the base of the succession (～ ?0.4 m AHD) a thin bed, containing molluscs dated at 6.7 ka B.P. by radiocarbon and amino acid racemisation, and foraminifers is indicative of open estuarine conditions. From +0.35 m AHD towards the top of the sequence the charophyte Lamprothamnium succinctum occurs in subrecent deposits. This species is characterised here by statistical measurements, and new characters are described and illustrated. The charophytes record a drop in sea level and the establishment of a lower salinity artificial wetland. The investigation has also established that decalcification in charophytes can be related to acidification produced by the release of organic acids, aggravated after 1928 by anthropogenic pollution.     

BREACHING OF A BEACH RIDGE AND THE FORMATION OF BEACH CUSPS

The development of beach cusps was observed on Mont-St-Pierre beach on the southern shore of the St Lawrence estuary on the Gaspé peninsula, in July 1979. Local observations and sediment analyses showed that the cusp material originated from a beach ridge located in the upper part of the tidal area. The initial stage in the formation of cusps was the breaching of this beach ridge by the swash. Material transported by the swash and backwash formed the cusp horns. No cusps were observed to develop on the western part of the beach where the beach ridge was not breached by the swash.
Le développement des croissants de plage a été observé sur la plage de Mont-St-Pierre, la céte méridionale de l'estuaire du Saint-Laurent, sur peninsule de la Gaspésie, en juillet 1979. Les observations faites sur l'aire de recherche et les analyses skdimentaires ont révélé que les matériaux des croissants de plage étaient essentiellement originaires d'une crtte de plage qui se trouvait dans la partie supérieure de la zone de rnarée. La formation des croissants de plage a commencé par la rupture de la crtte de plage que les bas-fonds avaient causées. Ces matkriaux transportés par les bas-fonds et les bas-fonds revenants ont produit les parties pointues des croissants. Aucun croissant de plage ne s'était produit dans la région ouest de la plage ou les bas-fonds n'ebrkchaient pas la crtte de plage.     

Historical signature of Roman mining activities in the Bidasoa estuary (Basque Country,northern Spain): an integrated micropalaeontological,geochemical and archaeological approach

This work presents an integrated micropalaeontological (foraminiferal content), geochemical (Pb, Zn, Cu, Ni, Cr, and Al, Pb isotope ratios, radiocarbon dating) and archaeological approach to the environmental impact caused by Roman mining in the Bidasoa estuary (northern Spain). Sediments collected in the ancient Roman port of Irun represent a typical infilling sequence, reflecting a progressive isolation from the estuarine environment. They exhibit elevated contents of Pb, clearly higher than those recommended nowadays for acceptable sediment quality. Isotope composition confirms exploitation of local galenas as the main source for this metal. Results from a borehole (25 m long) reveal that Pb pollution extended also to the adjacent estuarine area. The beginning of Roman mining activities is recorded by a marked increase in Pb concentrations. However, the maximum value appears later in time (after 660 cal AD). Although this enrichment could be related to the reworking upstreams of previously polluted materials, recently obtained archaeological data suggest that episodes of historically non-documented mining activities could have taken place in the surrounding area after Roman times.     

Holocene Elevated Sea Levels on the North Coast of Vietnam

We present evidence of elevated Holocene sea levels on the north coast of Vietnam, comprising radiocarbon dating of raised coastal geomorphological and palaeobiological features at localities on the margins of the Bac Bo (Red River) Plain. This evidence indicates that by ca. 5500 cal yr B.P. mid‐tide lay approximately 5.4 m above national datum, that is 3.25 m above present local mid‐tide. By c. 3500 cal yr B.P., sea level was lowering and, by ca. 2000 cal yr B.P., mid‐tide lay at or above 1.5 m above present local mid‐tide. It is not yet possible to infer patterns of sea‐level fluctuation other than an overall lowering of elevation, although the separation of the raised and modern erosion notches does suggest two dominant mid to late Holocene periods of erosion — probably periods of sea‐level still‐stand or relatively slow sea‐level change. The intervening period of relatively rapid sea‐level change and associated reduced erosion probably dates to after ca. 2000 cal yr B.P..     

The Geology of Deep Sea Mineral Resources

Abstract

Mineral resources are only economically attractive when they have been concentrated by nature. New theories of the evolution of the oceans are guidelines for prospecting. In the central Red Sea, tectonic and volcanic proce e favour the enrichment of metalliferous muds with copper and zinc as valuable metals, and similar muds may eventually be found on mid-oceanic ridges. The discovery of manganese nodules with a high economic content of copper, nickel and cobalt has up to now been restricted to areas of formerly or recently high productivity and to the deep central parts of the oceans. Oil and gas occur only in thick sediment series. They are mostly connected with continental margins or marginal basins as the oceans' central areas are too young and too distant from land, and therefore have not received a large enough deposit of terrigenous material.     

Age and sedimentological features of fluvial series in the Toruń Basin and the Drwęca Valley (Poland)

The deposits of the Toruń Basin are dominated by a few-metre thick sand series which fill up buried valley-like depressions. In many cases they underlie the Weichselian till which builds up the ice marginal streamway (pradolina) terraces or they are exposed at the basin slopes. As the results of the geological and sedimentological studies, as well as of the dating of the deposits at the sites in the Toruń Basin indicate, the deposits include two fluvial series accumulated before the advancement of the Leszno Phase ice sheet, i.e. in Middle Weichselian and at the beginning of Late Weichselian. The oldest fluvial series connected with the Saalian Glaciation was found at the mouth section of the Drwęca Valley. The fluvial system of the Toruń Basin during Middle Weichselian and at the beginning of Late Weichselian developed in two phases of the sand-bed braided river. During the first one the river channel were dominated by large mid-riverbed sandbars, while during the second phase the water flow was smaller and, as a result, low transverse sandbars and two-dimensional dunes developed. Other active river channel also showed low-energy flows, more intensive meandering than in the case of the braided rivers, as well as sandy side-bars. Analysis of the rounding and frosting of the quartz grains indicate that the studied series of the Weichselian sandy deposits represent alluvia of a river which were fed from two diverse sources. The first one might have represented the alluvia of a warm river which transformed its load, while the other one might have mainly carried the underlying Quaternary deposits.