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.     

Mississippian monumentality in the Yazoo Basin: recent investigations at the Carson site (22CO505), northwestern Mississippi

Investigations at the Carson site (22CO505), located in Coahoma County, Mississippi, have uncovered data on the development of a large Mississippian mound center dating to the period from A.D. 1200 through European contact. Recent sediment coring, excavation, artifact analyses, and radiocarbon and optically stimulated luminescence (OSL) dating shed light on earthworks and household structures at Carson, and on Mississippian culture in the Yazoo Basin more generally. Sediment coring demonstrates a laterally transgressing Mississippi River system deposited coarse sandy ridges and clay-filled swales underneath a surface horizon comprised of variously coarse to medium-fine sediment originating from generalized overbank flooding. In some instances, flood-borne sediments were found on mound flanks, indicating that at times river-based flooding may have interrupted mound construction. Sediment coring and trench excavation also demonstrate that Carson’s Mound D was built in four stages, with Stages II and III comprising the major stages of earth moving. Excavations on the mound summit reveal evidence of several superimposed structures that were burned in place and likely used for the production of stone, shell, and wooden craft items, perhaps related to Mississippi Ideational Interaction Sphere (MIIS) paraphernalia. Here we describe recent investigations at Carson and present preliminary findings; forthcoming publications will emphasize strategies of power, monumentality, craft production, and Mississippian exchange systems.     

Stratigraphy and geochronology of La Playa archaeological site,Sonora, Mexico

La Playa archaeological site in northern Sonora, Mexico contains a long record of human activity that includes the Paleoindian period (terminal Pleistocene) and much of the Holocene. The size and complexity of La Playa has discouraged a systematic characterization of its stratigraphy and geochronology, a deficiency we redress in the study. We distinguished seven stratigraphic units ranging in age from >44,570 to 400 cal yr B.P. using ¹⁴C dates from charcoal and terrestrial gastropods found mostly in archaeological features. All of the buried (in situ) cultural remains are contained in Units B (4690–1580 cal yr B.P.) and C (1010–400 cal yr B.P.) and represent overbank deposition from the nearby Rio Boquillas. Occupation at the site peaks in Units B₄ and B₅, corresponding to the Cienega phase (2800–1800 cal yr B.P.) of the Early Agricultural period. This period coincides with the growth of early agricultural villages in the region and is marked at La Playa by thousands of archaeological features including roasting pits, human burials, and extensive canal irrigation systems. The presence of semi-aquatic and aquatic snails demonstrates that water was present year round in the canal systems constructed during this period. Stable and radiometric isotopic evidence suggests that early agriculturalists diverted ground water over several kilometers from the nearby Rio Boquillas. The extensive Cienega phase occupation ended after about 1700 cal yr B.P. with deep erosion of the site, an event also visible in alluvial records in southern Arizona that marked the end of the Early Agricultural period and significant changes in settlement organization in the region.     

Mobilization of ore fluids during Alpine metamorphism: evidence from hydrothermal veins in the Variscan basement of Western Carpathians,Slovakia

Hydrothermal polymetallic veins of the Gemeric unit of the Western Carpathians are oriented coherently with the foliation of their low‐grade Variscan basement host. Early siderite precipitated from homogeneous NaCl‐KCl‐CaCl₂‐H₂O brines with minor CO₂, while immiscible gas–brine mixtures are indicative of the superimposed barite, quartz–tourmaline and quartz–sulphide stages. The high‐salinity aqueous fluid (18–35 wt%) found in all mineralization stages corresponds to formation water modified by interaction with crystalline basement rocks at temperatures between 140 and 300°C. High brominity (around 1000 ppm in average) resulted from evaporation and anhydrite precipitation in a Permo‐Triassic marine basin, and from secondary enrichment by dissolution of organic matter in the marine sediments at diagenetic temperatures. Sulphate depletion reflects thermogenic reduction during infiltration of the formation waters into the Variscan crystalline basement. Crystallization temperatures of the siderite fill (140–300°C) and oxygen isotope ratios of the parental fluids (4–10‰) increase towards the centre of the Gemeric cleavage fan, probably as a consequence of decreasing water/rock ratios in rock‐buffered hydrothermal systems operating during the initial stages of vein evolution. In contrast, buoyant gas–water mixtures, variable salinities and strongly fluctuating P–T parameters in the successive mineralization stages reflect transition from a closed to an open hydrothermal system and mixing of fluids from various sources. Depths of burial were 6–14 km (1.7–4.4 kbar, in a predominantly lithostatic fluid regime) during the siderite and barite sub‐stages of the north‐Gemeric veins, and up to 16 km (1.6–4.5 kbar, in a hydrostatic to lithostatic fluid regime) in the quartz–tourmaline stage of the south‐Gemeric veins. The fluid pressure decreased down to approximately 0.6 kbar during crystallization of sulphides. U‐Pb‐Th, ⁴⁰Ar/³⁹Ar and K/Ar geochronology applied to hydrothermal muscovite–phengite and monazite, as well as cleavage phyllosilicates in the adjacent basement rocks and deformed Permian conglomerates corroborated the opening of hydrothermal veins during Lower Cretaceous thrusting and their rejuvenation during Late Cretaceous sinistral transpressive shearing and extension.     

Paleochannel Studies in Archaeology: The Case of The Vychegda River,Northeastern European Russia

Geological and geomorphological settings are often taken into account when choosing strategy in archaeological studies. In the Vychegda River valley (Archangelsk Province, Komi Republic), at the end of the Late Pleistocene and in the Holocene, lateral channel migrations were the dominant process of riverine landscape changes and hence directly influenced human occupation of the valley. Therefore, to assess the physical settings of archaeological sites we employed paleochannel analysis, a geomorphological technique aimed at reconstructing river channel transformations in the historical and geological past. The potential application of paleochannel analysis in archaeology includes designing archaeological surveys and predicting destructive river actions at archaeological sites located in river valleys.     

X-ray microtomographic imaging of charcoal

We assess the potential of X-ray microtomography as a tool for the non-destructive, three-dimensional examination of the internal structure of charcoal. Microtomographic analysis of a series of charcoals produced by the experimental pyrolysis of pine wood at temperatures from 300 and 600 °C in nitrogen only and in nitrogen mixed with 2% oxygen indicates that, despite substantial shrinkage, observed porosity, pore size and pore connectivity are all increased by pyrolysis and also by chemical oxidation. Analysis of a number of altered and unaltered archaeological and geological charcoals has demonstrated the capacity of the technique to identify and map the distribution of authigenic mineral contamination within charcoal fragments. The results are of significance to radiocarbon dating in that they provide insights into the mechanisms by which charcoal can be contaminated by extraneous carbon in the natural environment.     

Approaches to marsupial biochronology in Australia and New Guinea

Mammal (marsupial) palaeontology is useful for the correlation of non-marine strata of Australia and New Guinea. The geochronological framework constructed from marsupial data is based substantially in stage-of-evolution biochronology, which is not subject to the formal guidance of a code, or regulation by an authority. Instead, it has evolved through an informal consensus of usage. Principles and practices of stage-of-evolution biochronology and its historical development are reviewed from an Australian perspective. Amongst more recent developments in the discipline are the establishment of the first marsupial biostratigraphy for the continent, covering the Etadunna Formation of the Lake Eyre Basin (Woodburne et al., 1993), and the introduction of novel terminology to express marsupial succession in the Carl Creek Limestone of northwestern Queensland (Archer et al., 1989). The merits of the various approaches to biochronology are examined: stage-of-evolution biochronology has provided, and will continue to contribute to, a correlation framework for a continent with a sparse mammal record not generally amenable to biostratigraphic resolution. Terminology proposed by Archer et al. (1989) is shown to be unsatisfactory.