Chapter 4 : molluscan remains from the valley cores

Abstract

Molluscs often have quite specific environmental requirements (Evans 1978, 82; Giusti et al. 1995; Schembri et al. 2018). Many species require only a few square metres of habitat, so they are excellent micro-habitat indicators. Their shells can be dispersed, for instance by running water, but generally, compared with other biotic materials used in palaeoecology (such as pollen grains or seeds), they do not disperse far from their life habitat and therefore provide important indications of local environments. Alkaline sediments, which are very common in the Maltese Islands, will preserve molluscan shells and other calcareous biogenic material over thousands of years. This makes the analysis of molluscan shells potentially a very important tool for the reconstruction of past environments in Malta. Geologists and archaeologists recognized the value of molluscs as palaeoenvironmental indicators as early the first quarter of the nineteenth century ad (Conybeare 1824; Preece 1998; Evans & O’Connor 2005, 41). Molluscan analysis is still, however, comparatively rare as a palaeoenvironmental tool, and for instance is less commonly used than pollen analysis (e.g. Preece 1998, 158; Fenech 2007). In the Maltese Islands, the application of the technique has been limited and there has been no comprehensive palaeoenvironmental study using molluscan analysis. Trechmann (1938), Giusti et al. (1995) and Hunt (1997) used the sporadic occurrence of land snails in Maltese Quaternary deposits as an indication that these had accumulated in open, exposed conditions. The highly cemented Quaternary deposits precluded anything other than the production of species lists by these authors. Pedley (1980) suggested a brackish depositional environment for the Pleistocene Fiddien Valley Tufa on molluscan evidence. Fenech (2007) and Marriner et al. (2012) analysed cores taken in Holocene estuarine deposits at Marsa and Burmarrad, respectively. These studies showed the progress of the Holocene marine transgression and the infilling of the estuaries, and Fenech (2007) also showed the persistence of open, exposed terrestrial environments in the catchment of the Marsa estuary over c. 7000 years. At the Neolithic Xagħra Brochtorff Circle (Schembri et al. 2009) and the Neolithic and later temple site at Tas-Silġ (Fenech & Schembri 2015), molluscan analysis demonstrated long histories of anthropogenic disturbance and sparse vegetation since the later Neolithic, but a considerable portion of these studies was done on shells recovered by troweling and dry sieving with a large fraction and therefore subject to a form of taphonomic bias caused by the exclusion of most very small taxa. Analysis of a cave fill near Victoria on Gozo, based on assemblages recovered by sieving, identified a phase of spectacular erosion caused by Classical period agricultural practices, followed by a more stable grazed landscape in the Medieval and post-Medieval periods (Hunt & Schembri 2018). Inevitably, the research done before the start of the FRAGSUS Project was very partial in coverage. The environmental history of the Maltese Islands was still largely unknown. [excerpt]