Fossil Plants from Weichselian Interstadials, Santorini

The upper part of the caldera walls of the ring-islands Thera and Therasia of the Santorini volcanic group are characterised by three striking pumice series: The Lower, the Middle, and the Upper Pumice Series. The age of the Upper Pumice Series is fixed by archeological findings (Marinatos 1968, 56) to around 1500 B.C., while the ages of the Middle and Lower Series are not yet known, but must be older than 37,000 years (Pichler & Friedrich 1976). The Upper Pumice Series cover most of the old ring-islands and late Minoan LM IB settlements which are still being excavated (Marinatos 1968 - 1974).

The geology of the Santorini volcanic group has been studied in recent years especially by Pichler and his co-workers Kussmaul, Günther, Schneider, and many others (for references, see Pichler et al. 1972 and Pichler & Friedrich 1976) . In 1976 Pichler & Kussmaul published a geological map of Santorini. In connection with this geological mapping the author joined this project in order to work on the fossil plants from this area.

The first report of fossil plants from Santorini was given by Lacroix in 1896. He collected plant material from quarries near the town of Fira on Thera together with the French volcanologist Fouqué. Knowledge about the existence of fossil plants from Santorini must be much older than indicated by this publication and Lacroix and Fouqué heard about the plant fossils from the monks of the island. Plant fossils from this locality in the neigbourhood of Fira must have been known at least since the time when the pumice and the underlying ashes were used for building purposes. The Lacroix locality was at Katophira, 15 meters below the end of the lava-flow upon which the town of Fira is built. This is near the site where later collections were made by Schuster (1936) and the present author.

Plant remains occur in several strata between the Middle and the Upper Pumice Series on Thera and Therasia. They are found in palaeosols which were formed during periods of long volcanic quiescence when the vegetation could become re-established in the areas which were devastated during periods of volcanic activity.

The traces of former vegetation are found as imprints of leaves, occasionally also of fruits and seeds, tree moulds and very rarely also charcoal. The latter allows absolute dating after the radiocarbon method. Based on radiocarbon data from charcoal of trees and shrubs three different palaeosols of Weichselian age from Thera and Therasia were dated and named: The Fira palaeosol (ca. 37,000 yr. B.P.), the Akrotiri/Millo palaeosol (ca. 18,000 yr. B.P.), and the Therasia palaeosol (ca. 13,000 yr. B.P.) (Friedrich et al 1977).

The uppermost part of the Therasia palaeosol corresponds to late Minoan time. The palaeosol in which late Minoan houses occur is spread all over Thera and Therasia. This so-called Minoan palaeosol is overlain by the Upper Pumice Series which was produced around 3300 B.P.

The content of fossils and their preservation in the palaeosols differ greatly since the quality of the outcrops generally is very poor. Fresh sections of the Fira palaeosol only occur in the pumice quarries south of the town Fira on Thera.

From this locality the following plant fossils were found: Chamaerops, Phoenix, Pistacia, Olea, and Tamarix, partly already reported by Schuster (1936) and Lacroix (1896). They indicate climatic conditions in the Mediterranean as today, since all these genera still exist among Mediterranean flora (Friedrich et al. 1977). Concerning the Akrotiri/Millo palaeosol, which is overlain by ignimbrite sheets on Thera and Therasia, moulds of smaller trees containing charcoal were observed. On the Akrotiri peninsula ten tree moulds with charcoal occurred in the lowermost part of the ignimbrite. They had diameters of 5 - 7 cm. From the Therasia palaeosol only charcoal remains are reported (Günther & Pichler 1973).

The radiocarbon data obtained from the different palaeosols from Santorini are shown in fig. 1.

The radiocarbon dated palaeosols from Santorini represent periods when trees or shrubs grew on the volcanic island. From a detailed study of a pyroclastic section at the pumice quarries near the town Fira, which spans the radiocarbon dated time interval from about 37,000 B.P. to 3300 years B.P., traces of trees were only found in four horizons (excluding the Minoan palaeosol). Moulds of roots were observed in 11 horizons which, based on their general appearance, might be from herbs.

Thus the impression of a vegetational change from trees to minor plants, which has been repeated several times, seems likely. The most probable explanation of such a change is that the vegetation was destroyed several times by volcanic activity, and that the observed plant-bearing horizons represent only the beginning stages of the re-establishing vegetation. But this change could also be due to variations in the climate. The period indicated by the radiocarbon dates ranges from the middle part of the Würm or Weichselian glaciations to the Holocene. Several climatic changes occurred in this period in the Mediterranean as indicated by pollen diagrams from Syria (Niklewski 1970), Iraq (Zeist 1969), Italy (Frank 1969), and Spain (Flors chütz 1971) as already stated by Wijmstra (1972).

The palynological study of the first 30 m of a 120 m deep peat section in Macedonia, Greece by Wijmstra (1969) showed that in the stadial phases within the Weichselian an open Artemisia Chenopodiaceae steppe existed in that area; during interstadials the vegetation changed into shrub steppe phases in which pine and oak were present. Climatic changes were also evidenced from micropaleontological studies of deep-sea cores from the Mediterranean (Blanc-Vernet 1972) and many other places in the northern hemisphere indicating climatic fluctuations in the Weichselian. It is therefore very probable that the Fira, Akrotiri/Millo, and Therasia palaeosols from Santorini represent interstadials with trees in the Weichselian, while during the stadials only herbs (steppe?) grew on Santorini.

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