The non-existing seas: Finding marine mollusks in island basins. Are they secure marine indicators

Περίληψη

Fossil marine molluscs are considered by geologists as indicators of marine presence into an area. Findings of marine molluscs spark theories of palaeogeographical evolution however the presence of marine molluscs into the soft surficial strata of an area is not always a safe indicator of marine presence. In two intermountain areas, Philippi and Vromolimnes basins, in northern Greece marine presence have been proposed after the discovery of marine molluscs. In this paper these areas are re-examined however recent data do not confirm the previous hypothesis of marine presence. In Philippi basin sediments containing marine molluscs were described as Intermediate Pleistocene Terrace. Investigation of these sediments showed that they are of anthropogenic origin containing among others marine molluscs as food litter. In Vromolimnes basin a Pleistocene marine invasion has been proposed after the discovery of few marine molluscs supported by the high salinity (soil and ground water) and the presence of halophyte vegetation. However, this hypothesis cannot be accepted since the mollusc fauna consists of only 4 mixed species; it includes marine but also fresh water shells which is impossible to naturally co-exist. The shells are possibly of anthropogenic origin because all molluscs are edible and commonly found in many prehistoric settlements. Discovery also of scattered pottery shards in the area further supports the human origin of the molluscs. For a long time and in many cases the possibility of the presence of molluscs due to human activity was generally underestimated by geologists resulting sometimes into erroneous interpretations of the findings. Overall; deciding the presence of marine environment on the basis of fossil molluscs found into recent surficial unconsolidated sediments should be treated with caution and in this work simple criteria are proposed for this.