Abrupt mortality of marine invertebrates at the Younger Dryas-Holocene transition in a shallow inlet of the Goldthwait Sea

The late Pleistocene–early Holocene transition period was characterized by rapid environmental change. Here, we investigate the impact of these changes on the marine invertebrates living in a shallow inlet of the post-glacial Goldthwait Sea. The site is located near Baie-Comeau (QC, Canada), where a number of remarkably well-preserved shell deposits are found along the Rivière aux Anglais Valley on the north shore of the St. Lawrence maritime estuary. Seven phyla of marine invertebrates with a minimum of 25 species or taxa were inventoried in a shell deposit, dominated by a community of Hiatella arctica with Mytilus edulis and barnacles composing the subcommunity. The majority of taxa identified in the shell deposit are boreal and sub-Arctic species; however, temperate species that exist today in the St. Lawrence maritime estuary have not been found. Based on marine invertebrate diversity and δ18O(CaCO3) of Mytilus edulis, the water in the shallow inlet of the Goldthwait Sea must have been cold and saline. The range of AMS 14C ages from 15 Mytilus edulis, constrained to 10,900 and 10,690 cal. yr BP, and exceptional state of preservation of adult and juvenile molluscan specimens suggest the abrupt mortality of entire invertebrate communities due to changing hydrodynamic conditions that included the combined effect of freshwater discharge from the receding Laurentide Ice Sheet and rapid isostatic uplift.

The Moyjil site, south-west Victoria, Australia: chronology

An unusual shell deposit at Moyjil (Point Ritchie), Warrnambool, in western Victoria, has previously been dated at 67±10 ka and has features suggesting a human origin. If human, the site would be one of Australia’s oldest, justifying a redetermination of age using amino acid racemisation (AAR) dating of Lunella undulata (syn. Turbo undulatus) opercula (the dominant shellfish present) and optically stimulated luminescence (OSL) of the host calcarenite. AAR dating of the shell bed and four Last Interglacial (LIG) beach deposits at Moyjil and Goose Lagoon, 30 km to the west, confirmed a LIG age. OSL analysis of the host sand revealed a complex mixing history, with a significant fraction (47%) of grains giving an early LIG age (120–125 ka) using a three-component mixing model. Shell deposition following the LIG sea-level maximum at 120–125 ka is consistent with stratigraphic evidence. A sand layer immediately below the shell deposit gave an age of ~240 ka (i.e. MIS 7) and appears to have been a source of older sand incorporated into the shell deposit. Younger ages (~60–80 ka) are due to bioturbation before calcrete finally sealed the deposit. Uranium/thorium methods were not applicable to L. undulata opercula or an otolith of the fish Argyrosomus hololepidotus because they failed to act as closed systems. A U–Th age of 103 ka for a calcrete sheet within the 240 ka sand indicates a later period of carbonate deposition. Calcium carbonate dripstone from a LIG wave-cut notch gave a U–Th age of 11–14 ka suggesting sediment cover created a cave-like environment at the notch at this time. The three dating techniques have collectively built a chronology spanning the periods before and after deposition of the shell bed, which occurred just after the LIG sea-level maximum (120–125 ka).

The Moyjil site, south-west Victoria, Australia: prologue — of people, birds, shell and fire

Moyjil (also known as Point Ritchie) is the site of an unusual shell deposit in south-west Victoria showing many characteristics of a midden. Earlier research established an age of 60 ka or older for the shell deposit but could not establish whether humans or animals such as seabirds were responsible for its formation. This paper, the first of six in this special issue, summarises the most recent phase (~10 years) of investigations. The site’s age is now fixed as Last Interglacial and following the stage MIS 5e sea-level maximum (i.e. younger than 120–125 ka). Fragmentation and the limited size distribution of the dominant marine shellfish (Lunella undulata syn. Turbo undulatus) confirm the site as a midden. There is also evidence for fire (charcoal and discoloured and fractured stones) and two hearth-like features, one of which has been archaeologically excavated. None of the evidence collected is able to conclusively demonstrate a human versus animal origin for the site. Significantly, a human origin remains to be disproved. These papers provide the basis for a new phase of research into the possible cultural status of the Moyjil site.

The Moyjil site, south-west Victoria, Australia: stratigraphic and geomorphic context

Shelly deposits at Moyjil (Point Ritchie, Warrnambool), Victoria, together with ages determined from a variety of techniques, have long excited interest in the possibility of a preserved early human influence in far south-eastern Australia. This paper presents a detailed analysis of the stratigraphy of the host Bridgewater Formation (Pleistocene) at Moyjil and provides the context to the shelly deposits, evidence of fire and geochronological sampling. We have identified five superposed calcarenite–palaeosol units in the Bridgewater Formation, together with two prominent erosional surfaces that may have hosted intensive human activity. Part of the sequence is overlain by the Tower Hill Tuff, previously dated as 35 ka. Coastal marine erosion during the Last Interglacial highstand created a horizontal surface on which deposits of stones and shells subsequently accumulated. Parts of the erosional surface and some of the stones are blackened, perhaps by fire. The main shell deposit was formed by probable mass flow, and additional shelly remains are dispersed in the calcareous sand that buried the surface.

The Moyjil site, south-west Victoria, Australia: shells as evidence of the deposit’s origin

Characteristics of marine shellfish and other species found in a Last Interglacial (LIG) shell deposit at Point Ritchie (Moyjil) at Warrnambool in south-western Victoria have been compared to those from modern and LIG natural beach deposits, Holocene Aboriginal middens and modern Pacific Gull (Larus pacificus) middens. The research was aimed at determining whether properties such as shell speciation, size or taphonomy could identify the mechanism responsible for formation of the Moyjil deposit. Marine species found in the Moyjil deposit resemble those found in both Aboriginal and Pacific Gull middens and are non-discriminatory for the two types. Taphonomic properties such as wear and breakage pattern of opercula of the dominant species, Lunella undulata (syn. Turbo undulatus), are non-diagnostic because of post-depositional erosion and transport effects in the available specimens. The size of L. undulata opercula show clear bias toward larger individuals, in common with Aboriginal and seabird middens, when compared to natural shell deposits. Statistical analysis (ANOVA) of the size distributions shows a greater similarity of the Moyjil deposit to the two seabird middens than the two Aboriginal middens. Small individuals (operculum L. undulata as well as smaller shellfish species are absent from the seabird middens studied, but they are present in Aboriginal middens and in the Moyjil deposit. Overall, we conclude that shell properties alone are not sufficient to distinguish which predator collected the shellfish occurring in the deposit.

Present knowledge of the non-marine invertebrate fauna of the Outer Hebrides

SynopsisThe Outer Hebrides, because of their apparent isolation, attracted zoologists in the past who looked for new species and subspecies and some sought to explain the origin of the invertebrate fauna by exotic land connections in preglacial times. These expectations were largely unfulfilled and the speculations are unsupported by geologists or geomorphologists. The non-marine invertebrate fauna is examined from published records, museum collections and special field surveys and the lists total over 2500 species, of which approximately one-third are of general occurrence in the Outer Hebrides. Three species of mites are new to the British fauna and over 700 species, mainly insects, are additions to the Hebridean fauna. The fauna is impoverished compared with the mainland and this may be due to climate and the lack of variety of habitats and the low structure of the vegetative cover. Upland species occur on the moors and some descend to sea level, possibly on account of the low mean temperature in summer. Species with a north western distribution occur in the Odonata, Hemiptera, Lepidoptera, Hymenoptera and Diptera. Species with a discontinuous distribution are discussed and it is suggested that some reached the islands by natural means and others by human agency and there is no evidence of refugia for a glacial relict fauna. Examples are given of insects with a south western distribution arriving by sea in driftwood and five amphiatlantic species, including a freshwater sponge, which may have been brought by migrating birds, a wrack-fly, two strand-line beetles and a mite, which may have been distributed by the Gulf Stream and the North Atlantic Drift.There are no endemic species, but a few so-called subspecies of insects may be restricted to the Outer Hebrides. Changes in the fauna are traceable in a stratified Flandrian shell deposit in Harris, where two species have become extinct, and some insects have also become extinct in St Kilda during the last century. Some of the most conspicuous land snails have arrived in historic times and the most rapid coloniser has been a brackish-water snail which has spread throughout the islands since 1933.

A Late Pleistocene Marine Shell Deposit at Shippegan, New Brunswick

Twenty species of marine invertebrate shells from a gravelly sand deposit close to the present shore at Shippegan, New Brunswick, were identified and shown to be typical of a shallow-water association formed soon after glacial retreat. One specimen yielded a radiocarbon date of 12 600 ± 400 yr. This evidence strengthens previous conclusions on the date of Pleistocene deglaciation and on postglacial sea-level changes in this area.