Quaternary pyroclastics from Santorini/Greece and their significance for the Mediterranean palaeoclimate WALTER L. FRIEDRICH, HANS PICHLER and SIEGFRIED KUSSMAUL Friedrich, W. L., Pichler. H. & Kussmaul, S.: Quaternary pyroclastics from Santorini/Greece and their DGF significance for the Mediterranean palaeoclimate. Bull. geol. Soc. Denmark, vol. 26, pp. 27-39. Copen­ hagen, August 1st 1977. Radiocarbon data from four different horizons of the Santorini volcanic pile show that an unusually long period of volcanic inactivity of about 15,000 yr preceded the late-Minoan outburst. Three different plant-bearing palaeosols of about 37,000 yr, 18,000 yr and 13,000 yr B.P. can be correlated with interstadials in eastern Macedonia, deep-sea cores from the Mediterranean and interstadials from the northern hemisphere. Fossil plants from the Fira palaeosol, Santorini (~ 37,000 yr B.P.) indicate that the climatic conditions at that time were nearly the same as at present. A similar flora with a correspon­ ding age of about 37,000 yr B.P. also existed on Lipari/Eolian islands, suggesting that this warm period in the Weichselian was widely developed in the Mediterranean area. Walter L. Friedrich, Laboratoriet for Palaeontologi og Stratigrafi, Geologisk Institut, Aarhus Universi­ tet, DK-8000 Aarhus, Denmark. Hans Pichler, Mineralogisch-Petrographisches Institut der Universitåt, Wilhelmstrasse 56, D-74 Tubingen, Federal Republic of Germany. Siegfried Kussmaul, Escuela de Geologia, Ciudad Universitaria "Rodrigo Facio", Apto. 35, San José, Costa Rica. December I7th, 1976. Dedicated to Prof. M. Schwarzbach on the occasion of his 70th birthday. The Santorini archipelago, which is part of the important from the archaeological point of view, Cycladian Volcanic Arc (fig. 1), is situated in the is still being excavated near Akrotiri in the sou­ southern Aegean Sea and consists of the older thern part of Thera (Marinatos 1968-1974). The ring-islands Thera, Therasia and Aspronisi to­ pottery from the excavations near Akrotiri be­ gether with the younger Kameni islets (fig. 2). longs stylistically to the late-Minoan la period The ring-islands are remnants of a single circu­ which according to Marinatos (1971: 410) is asc­ lar island, called Stronghyli, which was inhabi­ ribed a life of 50 years between 1,550 and 1,500 ted by the Minoan population. In the late-Mi­ B.C. Based on this, the age of the initial eruption noan time, after an interval of about 15,000 yr of was proposed to about 1,520 B.C. (Marinatos volcanic inactivity on Stronghyli, paroxysmal 1968: 56). eruptions occurred which culminated in the col­ Two radiocarbon ages from carbonized trees lapse of the central part of the old island. Thus found underneath the late-Minoan pumice (Bo) the Santorini caldera, comprising an area of from the quarries near the town of Fira about 7 about 83 km2, was formed. The eruptions produ­ km from the excavations are published which ced a thick pumice layer, reaching a thickness of might indicate the starting point of the late-Mi­ up to 60 m south of the town of Fira, called the noan eruption: 1) A piece of bark from a tree Upper Pumice Series (or Bo, abbreviated from found together with human teeth and bones and the German term "oberer Bimsstein"; Neumann fragments of painted pottery gave a conventional van Padang 1936). This striking top layer on the radiocarbon date of 1,420+100 yr B.C. (= ring-islands consists of air-fall pumice and base 3,370±10O yr B.P.) (Galanopoulos 1958). 2) A surge deposits, overlain by thick pyroclastic trunk of a small carbonized tree still standing flows (Pichler & Kussmaul 1972; Pichler 1973; upright gave a conventional radiocarbon age of Gunther & Pichler 1973). The Upper Pumice Se­ 1,456±43 yr B.C. (5568 halflife) (= 3,406±43 yr ries buried both an old soil horizon (fig. 2) and B.P.) (Marinatos 1968: 56). Both radiocarbon late-Minoan settlements on Therasia (Fouqué ages are in excellent agreement with the ab­ 1969) and Thera. Such a settlement, not only ove-mentioned date based on ceramic findings, 28 Friedrich et al.: Quaternary pyroclastics from Greece 7? ...AE GIN A '"•!*>. \J10 METHANA POROS >XvX*. t» PATMOS •» •x'x'x'x"'*'" ^ • • • • • • • •*•*•*•*• f^l •• • • • • "•"•*•*•*•*• t»«/4 <S ^ ••v.vX'Xv/X*. C\ /Il •'• • • • • »^Ha •HT» • • • < ANTIMILOS -Xif. c3A ,/X^ ^f •••••••• > «> ••X*:*x£i«fcv. /*i ^ '•W.V.V.V.V.Rl fr3tt&:<<&k-:<K..M .. .vx^x^wx-x^v^v^w •.W.V.V.V.V.V. SANTORINI .-.•.•.-.•.•.•.•.•.•VX'^A-,. WvXv..-.-.'.-.".^ N I S Y %R O.*.--w»I* S •rXvX"» ! * a a a a a a a a a a a a a » a «. a. a a a a a • a a a a a • a a * a *"-."-"- -aa".. •-"-"*•»" * ~ »•-•-^*_"-1 • •••••••-- *_• • • • • «*«• ••••••• • ••••••• 1> • • • • • • • • • •SOifTi < • • • • 1 •••••••••••••••••••• • « • • • • •»•••• • • • • -••"•••••••••••••••••••• aBaA*aa**a*aaA»aaBaA*A C* a* _ •* a* •* • A •* »• a _ •» • • • • 50 100 Km -36° L -i > 1 24 2.6 " I H^. /. Geographic position of the Santorini islands in the Cycladian Volcanic Arc (dotted zone). Cenozoic volcanic areas are figured in black. but if the two radiocarbon dates are calibrated the cores collected during the Albatros cruises after the tree ring curve of Clark (1975) ages of with the Upper Pumice Series on Santorini. La­ l,730±^gyrB.C.(forconv. l,420±100yrB.C.) ter on this correlation was confirmed by Ninko- and l,780±}5g yr B.C. (for conv. 1,456+43 yr vich & Heezen (1965,1967), Keller & Ninkovich B.C.) result. This might indicate that the two (1972), Ryan (1972), etc. radiocarbon samples taken from the quarries near The stratigraphic sequence underlying the Mi­ the town of Fira may represent a violent earth­ noan palaeosol in the central part of Thera island quake event preceding the late-Minoan pumice is characterized by at least 21 alternating pyro- eruption. clastic strata (fig. 4, table 1) which are treated in Since 1939 this late-Minoan outburst of the the following chapter. This sequence rests on the Thera volcano is widely considered to have so-called Middle Pumice Series (or Bm, from caused the decline of the Minoan civilization "mittlerer Bimsstein"; Gunther (1972). Below (Marinatos 1939, 1968-1974; Galanopoulos 1971; that layer a conspicuous sequence of whitish pu­ van Bemmelen 1971; and many others). Recent mice and ash deposits with an average thickness investigations on Crete with respect to that prob­ of up to 80 m is developed (fig. 3). In the profile lem have given rise to serious doubts to the south of the town of Fira this Lower Pumice validity of this theory (Pichler & Schiering, in Series (or Bu, from "unterer Bimsstein"; Pa- press). dang 1936) overlies some lava flows of quartz-la- Ash of this late-Minoan eruption has also been tiandesitic composition. Most of the strata of found in many Quaternary deep-sea cores of the that section, from sea-level up to the top (220 m), eastern Mediterranean. Mellis (1954) was the including the Upper Pumice Series, are products first to correlate the "Upper Tephra Layer" in of the Thera volcano, which was the main volca- Bulletin of the Geological Society of Denmark, vol. 26 1977 29 1 7,9 70 ±1 70 18,050+340 12,950 ±756 THERASIA / 3,370 ±100 3,509 + 44 3 6.70 0 1V|5 >3 7,0 0 0 4 4,5 00 ±5,25 0 1 7,700+170 1 8,165±210 1 8.880 + 230 3 km Fig. 2. Radiocarbon dates of Santorini volcanics: location and Aspronisi which are almost entirely covered by the Upper Pu- ages (cf. table 2). The site of the section (fig. 3) is also shown. mice Series. The post-Minoan Kameni islands are figured in Dotted areas mark the ring-islands Thera, Therasia and black. nic centre on Santorini. A detailed description of Pyroclastic Stratigraphy the volcanic history of the Santorini group was given by Pichler et al. (1972); the stratigraphy The upper part of the pyroclastic sequence of the and petrology of the Lower, Middle and Upper Thera volcano between the Middle (Bm) and Pumice Series are described by Gunther (1972) Upper Pumice Series (Bo) is excellently exposed and Gunther & Pichler (1973). New radiocarbon at the base of the pumice quarries south of the data concerning the upper part of the Thera vol­ town of Fira. The sequence consists of at least cano sequence has been recently published 21 strata with a total thickness of about 35 m, for (Pichler & Friedrich 1976). the most part comprising dark ashes, cinders, 30 Friedrich et al.: Quaternary pyroclastics from Greece Bo li . : ft "Wtrn Bm -~ BuJ ..J.«,'\P :',—-.'' "•""-»>?' "S*'yr?. - ••••.-..."-: ^c^ 'iBBwr-* - - -••••'- ESF •'. <#;v;%iL; • F/g. J. 7"/ie caldera walls south of the pumice quarries of FU ralThera island, Santorini. The sequence corresponds to the schematic section in fig. 4. Bu = Lower, Bu = Middle, Bo = Upper Pumice Series. scoriae, pumice, bombs, xenolithic lapilli, Generally the plant remains are very badly blocks and lahar deposits (fig. 4). Many of these preserved. In the plant horizons of strata 7 and strata can be subdivided into numerous small 13 several moulds of Chamaerops trees were beds and horizons. Some of the layers are deeply found (figs. 7, 8) indicating that the palms grew weathered and decomposed to palaeosols, some in situ and reached a height of about 2-3 m with a of which contain moulds of roots and thin stems stem thickness of 30-40 cm. The leaves of Olea of trees and bushes. and Pistacia, however, have been transported Remains of former vegetation have been found by water, and mostly isolated leaves and small in 11 horizons. Four of the strata are rich in plant branches can be found.