The floral study and the observed vegetational changes during Miocene regarding the palaeoenvironmental evolution of the Messara-Gavdos area in Crete
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Ζηδιανάκης, Ιωάννης
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Abstract
Based on macro-remains, three fossil plant assemblages are described from the Miocene of the Messara Basin (southern Crete) and the adjacent Gavdos Island. The palaeoflora of Kassanoi, which is the oldest (Messara Basin, Viannos Fm, Serravallian), is mainly documented by leaf imprints, including a fern, a conifer (Tetraclinis cf. salicornioides) and 24 angiosperms. The assemblage is dominated by Daphnogene polymorpha, Myrica lignitum, Podocarpium podocarpum and Salix cf. angusta. Well documented are further Berchemia multinervis, Decodon gibbosus, Fraxinus sp., Populus populina and Ulmus cf. plurinervia.
The plant record from Pitsidia (Messara Basin, Ambelouzos Fm, Lower Tortonian) comprises thousands of specimens. The plant material is preserved as imprints often covered by an inorganic encrustation (replica). One alga, 2 ferns, at least 5 conifers and more than 45 woody angiosperms have been identified. Dominant species are Myrica lignitum and Pinus pitsidiensis sp. nov. documented by vegetative and reproductive organs. Leaves of deciduous oaks (Q. pseudocastanea and Q. cf. kubinyii) and Daphogene polymorpha as well as twigs of Taxodium dubium are also fairly common. Several further taxa are represented by both vegetative and fertile (fruits/infructescences) organ remains such as Liquidambar europaea, Podocarpium podocarpum, Acer and Ulmus (ZIDIANAKIS et al., 2017). Other well documented taxa are ”Pteris” oeningensis, two- and five-needled pines as well as the woody dicots Acer integrilobum, A. tricuspidatum, Carya sp., Fagus gussonii, Mimosites sp., Populus populina, Quercus mediterranea and Ulmus cf. plurinervia.
A unique mass-occurrence of Myrica and Pinus characterises the flora of Pitsidia (ZIDIANAKIS et al., 2014). Myrica remains include leaves, fruits and male catkins. The leaves have been assigned to Myrica lignitum (UNGER) SAPORTA, the fruits, sometimes even attached to their infructescence axis, to M. ceriferiformis KOWNAS, and the male catkins to M. cf. goeppertii. Taphonomic evidence indicates that the different plant organs derived from a single species of Myrica. The fruit size, the unbranched male catkins and mainly the fused filaments into a staminal column in the male flower, point towards the sect. Cerophora (sensu CHEVALIER) of the subgen. Morella (ZIDIANAKIS et al., 2015). This reveals a closer affinity to the American, African and Macaronesian species of Myrica than to Asian ones.
Pinus pitsidiensis sp. nov. includes dwarf and long shoots, isolated needles, fascicle bracts and probably pollen cones, winged seeds and isolated scales of male cones. Based on the number of needles per fascicle, the persistence of the basal sheath, the distribution of stoma rows and resin ducts in the needles an assignment to sect. Pinus, subgen. Pinus is proposed for this species (ZIDIANAKIS et al., 2016).
From the palaeoflora of Metochia which is the youngest (Gavdos Island, Metochia Fm, middle Tortonian) (MANTZOUKA et al., 2015), further taxa are reported, among them are a five-needled pine, Quercus mediterranea, and cf. Ziziphus paradisiaca. Remarkable is the leaf remain of a palm (Sabalites sp.).
The age estimation of the plant-bearing sediments was possible according to previous studies and is based on bio-stratigraphy (Pitsidia, Metochia, and Kassanoi) (e.g. MEULENKAMP et al., 1979; ANTONARAKOU, 2001; ZACHARIASSE et al., 2011), on Sr-isotope stratigraphy (Pitsidia) (KRÖGER, 2004) and magneto- and cyclo-stratigraphy (Metochia) (HILGEN et al., 1995; KRIJGSMAN et al., 1995).
In Pitsidia excavation, a square grid was established in order to record the collected specimens three- dimensionally. The enumeration of the flora has been attempted and the lateral and vertical distribution of the material within the fossiliferous deposits is pictured. Damages on Pitsidia plant material due to biostratonomic and diagenetic processes have been examined. Judging from the frequency of the after-shedding damages, the material underwent severe mechanical stress probably due to transportation.
The studied floras share only a few elements. Differences in composition may be attributed to differences in environmental and mainly depositional settings. Additionally, these floras are compared to the further Neogene record of Crete and the Greek peninsula as well as to the modern flora of the area.
Also, plant/arthropod interactions were analysed to assess further palaeo-synecological signals. The spectrum of traces in Pitsidia comprises external foliage feeding, piercing and sucking, galling, mining and oviposition as main types of leaf damages.
The plant material is evaluated systematically-taxonomically. Vegetation assessment is attempted both empirically-sociologically and by the Integrated Plant Record (IPR) vegetation analysis. The climate is estimated based on the Coexistence Approach (CA). The reconstructed vegetation models are thoroughly presented and discussed in the context of the palaeoenvironmental history of the Messara-Gavdos area. According to the IPR vegetation analysis, the plant assemblages of Pitsidia and Kassanoi were classified to the zonal subtropical, subhumid sclerophyllous or microphyllous forest (ShSF). A mixed mesophytic broad-leaved forest with a small proportion of thermophilic elements resulted for Metochia. The palaeoclimatic datasets from the floras of Pitsidia and Metochia reveal a warm temperate to subtropical climate (13.5 to 18.5 oC for the mean annual temperature and approx. 850–1600 mm for the mean annual precipitation), with a weak seasonal drought that did not coincide with the warmest period of the year. Thus, a Cfa-type sensu KÖPPEN-GEIGER system can be referred for the Messara-Gavdos area.
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Keywords
Miocene, Plant fossils, Flora, Vegetation, Messara (Crete), Gavdos, Environment