Palaeoenvironmental significance of plant macrofossils from the Piànico Formation, Middle Pleistocene of Lombardy, North Italy

Quaternary International 204 (2009) 20–30

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Palaeoenvironmental significance of plant macrofossils from the Pia`nico Formation, Middle Pleistocene of Lombardy, North Italy Edoardo Martinetto* ` di Torino, Dipartimento Scienze della Terra, via Valperga Caluso 35, 10125 Torino, Italy Universita

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 27 December 2008

Compressed leaves and carpological assemblages from the Pia`nico Formation, which was deposited into the Pia`nico-Se`llere palaeolake, are newly studied, and the early 20th century leaf collection by Rytz is preliminarily revised. Despite the occurrence of two tephra layers, the dating of this Formation is still controversial: a long temperate period (Pia`nico-Se`llere Interglacial), corresponding to its lower BVC (‘‘Banco Varvato Carbonatico’’) member, would either correlate to OIS 11 or to OIS 19. The macrofloral record of the BVC member includes the locally extinct species Acer cappadocicum Gleditsch sensu lato, Pinus peuce Griseb., Prunus lusitanica L., Pyracantha coccinea M.J. Roemer, and Rhododendron ponticum L. var. sebinense (Sordelli) Sordelli. A number of other locally extinct species (Picea omorika (Pancic) Purkine, Rhamnus alaternus L., Tilia caucasica Rupr.) have not been figured and described in detail by the reporting authors, thus they should be confirmed by better documentation. From the biostratigraphic point of view the Pia`nico fossil flora does not display taxa typical for the Early Pleistocene (e.g. Carya, Liquidambar, and Eucommia), and a single fruit remain may putatively be assigned to the extinct species Potamogeton marginatus Dorofeev, which occurs from the Holsteinian to the Weichselian in Eastern Europe. Re-examination of the plant macrofossil record confirms that aquatic plants are absent from the leaf assemblages of the Pia`nico Formation and only very rarely occur as carpological remains (Najas marina L. and Potamogeton). The presence of lake-margin species suggests that patches of sedge and reed marshes bordered the lake at the beginning of BVC deposition, and later decreased or disappeared. On the low mountain slopes, steeply dipping into the lake, closed and prevalently deciduous woody vegetation was growing during the BVC deposition. Evergreen shrubs to small trees might well have grown as understorey in the deciduous woodlands (Buxus, Ilex) or in more open, drier rocky places (especially Pyracantha). The macrofossil evidence suggests that, unlike Picea abies (L.) Karsten, P. peuce and Abies cf. alba were not restricted to higher altitudinal belts. The occurrence of P. abies cones in the basal layers of the MLP (‘‘Membro di La Palazzina’’) member most probably indicates the settlement of spruce close to the lake-shore. This would be in agreement with the cooling-related contraction of broadleaved forests and the expansion of cool-adapted vegetation types to lower elevations, as indicated by palynological data of the upper part of the Pia`nico Formation. Ó 2008 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction The Pia`nico-Se`llere lacustrine deposits (Fig. 1) have long been known for their rich palaeobotanical content, and their compressed leaf assemblages have been described in several publications (e.g.: Fischer in Baltzer, 1896; Sordelli, 1896; Amsler, 1900; Patrini, 1921; Maffei, 1924; Rytz, 1925, 1953; EmmertStraubinger, 1991). On the basis of sedimentary facies, deposit distribution and basin palaeomorphology, Moscariello et al.

* Tel.: þ39 011 6705337; fax: þ39 011 6705339. E-mail address: [email protected] 1040-6182/$ – see front matter Ó 2008 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2008.11.014

(2000) considered that the Pia`nico-Se`llere sedimentation took place in a fairly deep, closed lake basin characterized by surrounding steep bedrock slopes. Geological and palaeobotanical studies of the 20th century led to the general consensus on a ‘‘Riss–Wu¨rm’’ age (i.e. around 120 ka) for the plant-rich layers of this succession (e.g. Lona and Venzo, 1956), but recently the dating of two volcanic ash (tephra) layers provided substantially older, though controversial, ages: around 800 ka (Pinti et al., 2001, 2007) and around 400 ka (Brauer et al., 2007a). Such controversy originated from the different approaches: direct K/Ar dating of one of these tephras (T21d) by Pinti et al. (2001), and tephrochronological approach, based on both tephras (T32 and T21d) by Brauer et al. (2007a,b).

E. Martinetto / Quaternary International 204 (2009) 20–30

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Fig. 1. Map of the outcrops of the Pia`nico-Sellere basin and synthetic stratigraphic logs of sections (2)–(9). The following sections yielded plant macrofossils studied in this paper: B) Beehive section; M) Main section; O) Oblique section; S) Sergio section; W) Wall section. Modified after Moscariello et al. (2000). BVC: ‘‘Banco Varvato Carbonatico’’; MLP: ‘‘Membro di La Palazzina’’; and SAB: ‘‘Sabbie e Argille Basali’’.

Pinti et al. (2007) heavily criticised Brauer et al.’s (2007a) approach and claimed that only the K/Ar date is reliable, which would be confirmed by the reverse palaeomagnetic polarity in the SAB unit, below the base of the Pia`nico Formation, assigned by them to the end of the Matuyama chron. Brauer et al. (2007b) did not reject this assignment, but suggested the presence of ‘‘a major hiatus between the interglacial deposits and the underlying SAB unit where reverse polarity has been measured’’. Also, recently studied fossil vertebrates (Sala, 2004) do not support an attribution to the last interglacial. Pollen analysis (Rossi, 2004) allowed the identification of three major temperate periods (namely ‘‘Pia`nico-Se`llere Interglacial, Clusone I interstadial, and Clusone II interstadial’’) alternating with stadial phases (Presolana I, Presolana II, and Presolana III). The forest dynamics during the temperate phases are marked by the abundance of ‘‘Quercetum elements’’ and Abies, while Pinus, Picea and steppe elements expand during stadial episodes. As a consequence of controversial dating, the longest temperate period (Pia`nico-Se`llere Interglacial), corresponding to the BVC member (Fig. 2), would either correlate to OIS 11 (Brauer et al., 2007b) or to OIS 19 (Pinti et al., 2007). Palaeobotanical accounts from the 19th and 20th century were published before an accurate assessment of the stratigraphic frame of the Pia`nico-Se`llere lacustrine deposits was available (Moscariello et al., 2000). Therefore, the related collections cannot be assigned to a precise litho- and chronostratigraphic interval. Lithologic descriptions indicate that most of the published palaeobotanical data may be referred to the BVC (‘‘Banco Varvato Carbonatico’’) member (Fig. 2) or, to a lesser extent, to the MLP (‘‘Membro di La Palazzina’’) member of the Pia`nico Formation. A list of taxa that were mentioned in previous studies is given in Table 1. This information is still important in order to assess local occurrence and frequency of particular taxa. However, there was a strong need for new macrofossil collections from particular layers in the stratigraphic succession, with precise correlation to pollen zones. For this reason, new plant macro/mesofossil investigations have been carried out since the year 2000. The aim of this contribution is to compare new results with the previously available palaeobotanical records and to draw some palaeoenvironmental conclusions within the frame of the palynological and stratigraphical records.

2. Material and methods The stratigraphic framework of the Pia`nico-Se`llere succession, as well as the names and location of the studied sections (Fig. 1), and units are based on Moscariello et al. (2000) and Rossi (2004). Compressed plant remains are abundant within thinly laminated lacustrine chalk (‘‘S’’ and ‘‘L’’ assemblages in Fig. 2), even if the highest concentrations are found within a few layers of resedimented, non-laminated chalk with chaotically dispersed plant parts (B4N and B4A assemblages in Fig. 2). The stratigraphic column published by Rossi (2004), which was used as a guide for sampling, is adopted in this paper. Another column, published by Brauer et al. (2007a), differs in slight details (see caption of Fig. 2). The traditional way to collect plant macrofossils from the Pia`nico Formation (Sordelli, 1896; Emmert-Straubinger, 1991) consisted of splitting blocks of sediments along the bedding planes. With such a method leaves and large winged fruits/seeds can be easily sampled, even today, in almost every portion and outcrop of the BVC member as well as in limited portions of the MLP unit. Recently, a modern stratigraphic framework for the Pia`nicoSe`llere succession has been presented (Moscariello et al., 2000). Using this framework, plant fossils were collected by the ‘‘Caffi’’ Natural Science Museum of Bergamo in a portion (ca. 1 m thick) of the ‘‘Beehive’’ section (Confortini et al., 2003) yielding about 300 mostly fragmentary leaf specimens (‘‘L’’-assemblage) studied by Leidi (2004) under the survey of the present author. A second sampling was undertaken during the preparation of the field guide for the INQUA-SEQS 2006 excursion, in a 50 cm-thick portion of the ‘‘Sergio’’ section, about 1.5 m above the t6 turbiditic layer (‘‘S’’assemblage: Fig. 2). Within this interval, a surface densely covered by iso-oriented needle-leaves of Taxus baccata L., associated with Buxus leaves, was detected (Fig. 3(4)); indeed, this is the result of a selective depositional mechanism. Other specimens were collected on bedding planes with scattered leaves of different shape and dimension (Fig. 3(7)). In the remaining portion of the Pia`nico-Se`llere succession, the stratigraphic position (Fig. 2) of relevant and easily identifiable plant macrofossils (cones, Buxus leaves) has been marked under the survey of C. Ravazzi, and will be used to draw palaeoenvironmental conclusions.

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Fig. 2. Synthetic stratigraphic section of the Pia`nico Formation, showing the position of plant macrofossil samples; modified after Rossi (2004). The right column shows the extension of three major temperate periods (Pia`nico-Se`llere Interglacial, Clusone I interstadial, and Clusone II interstadial) alternating with stadial phases (Presolana I, Presolana II, and Presolana III). The ‘‘L’’ assemblage was sampled in the ‘‘Beehive’’ section (Confortini et al., 2003), which corresponds to the ‘‘Deer’’ section of Brauer et al. (2007a). These authors described a tephra layer called T32 in their ‘‘Deer’’ section (¼Beehive.), laying 8.1 m above the T21b tephra, i.e about 0.3 m above the t 32 layer in this figure, which is faithfully reported from Rossi’s (2004) figure 1. Brauer et al. (2007a) did not state if their T32 should correspond to Rossi’s (2004) t 32, measured in the Snail section, or not.

E. Martinetto / Quaternary International 204 (2009) 20–30 Table 1 List of plant macrofossil taxa so-far reported for the Pianico-Se`llere lacustrine deposits, updated from Moscariello et al. (2000). Species

First reporting

Abies cf. alba Miller Abies pectinata DC. Acer cappadocicum Gleditsch

This paper Fischer in Baltzer (1896) Emmert-Straubinger, 1991 This paper Fischer in Baltzer (1896) Rytz, 1953 Fischer in Baltzer (1896) Sordelli, 1878 Amsler, 1900 Maffei, 1924 Amsler, 1900 Maffei, 1924 Maffei, 1924 Maffei, 1924 Maffei, 1924 Fischer in Baltzer (1896) Sordelli, 1873 Sordelli, 1878 This paper This paper Maffei, 1924 Rytz, 1953 Emmert-Straubinger, 1991 Maffei, 1924 Sordelli, 1873 This paper Fischer in Baltzer (1896) Amsler, 1900 Patrini, 1921 Fischer in Baltzer (1896) Sordelli in Bassani, 1886 Baltzer, 1893 Emmert-Straubinger, 1991 Patrini, 1921 This paper Emmert-Straubinger, 1991 Sordelli in Bassani, 1886 Maffei, 1924

Acer campestre L. Acer cf. insigne Boiss. et Buhs. Acer cf. monspessulanum L. Acer cf. obtusatum W.K. Acer laetum C.A. Meyer Acer lobelii (Mey.) Pax. Acer neapolitanum Ten. Acer obtusatum subsp. euobtusus Pax. Acer obtusatum Wall. Acer opalus Mill. ([Acer gr. opalus Mill.) Acer opalus Mill. var. elongatum Chabert. Acer peronai Schwerin (?) Acer pseudoplatanus L. Acer pseudoplatanus Linn. var. paucidentata Gaudin Acer sismondae C. Th. Gaudin Ajuga cf. reptans L. Alisma sp. Alnus glutinosa (L.) Gaertn. Alnus incana (L.) Moench. Amelanchier ovalis Medicus Andromeda polifolia L. Buxus sempervirens L. Carex gr. caespitosa L. Carpinus betulus L. Castanea cf. vesca Gaertn. Castanea latifolia Sordelli Castanea sativa Miller Castanea sp. Castanea sp. nov. Celtis australis L. Chara vulgaris L. Cladium mariscus (L.) Pohl. Cornus sanguinea L. Corylus avellana L. Crataegus ‘‘oxyacantha L.’’ ([Crataegus laevigata (Poir.) DC.) Crataegus pyracantha Medicus Cytisus alpinus L. Cytisus purpureus Scop. Erica cinerea L. Fragaria vesca L. Hedera helix L. Helleborus niger subsp. macranthus Freyn. Hypericum cf. androsaeum L. Hypericum perforatum L. Ilex aquifolium L. Laburnum alpinum (Miller) Berch. et Presl cf. Lonicera xylosteum L. Lycopus europaeus L. Magnolia sp. Micromeria thymifolia (Scop.) Fritsch Moheringia cf. trinervia (L.) Clairv. Najas marina L. Origanum vulgare L. Ostrya carpinifolia Scop. Phragmites communis Trin. Picea abies (L.) Karsten s.l. Picea excelsa (Lam.) Link Picea omorika (Pancic) Purkine Pinus cf. excelsa Wall. Pinus cf. peuce Griseb. Pinus excelsa Wall.

Amsler, 1900 Amsler, 1900 Emmert-Straubinger, 1991 This paper This paper Amsler, 1900 Amsler, 1900 This paper This paper Amsler, 1900 Rytz, 1953 This paper This paper Sordelli, 1873 This paper This paper Emmert-Straubinger, 1991 This paper Emmert-Straubinger, 1991 Maffei, 1924 This paper Amsler, 1900 Emmert-Straubinger, 1991 Amsler, 1900 Fischer in Baltzer (1896) Patrini, 1921 (continued on next page)

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Table 1 (continued ) Species

First reporting

Pinus excelsa Wall. var. peuce Gris. Pinus peuce Griseb Pinus sp. Pinus sp. nova Poaceae (Phragmites-type) Populus alba L. Populus nigra L. Populus nigra L. var pyramidalis Roz. Populus sp. Potamogeton cf. marginatus Dorofeev Prunus lusitanica L. Prunus spinosa L. (?) Pyracantha coccinea M.J. Roemer Quercus cf. petraea (Mattuscka) Liebl. Quercus cf. sessiliflora Salisb. Quercus Robur L. sessiliflora (Salisb.) Quercus sessiliflora Salisb. Rhamnus alaternus L.

Patrini, 1921 Maffei, 1924 Sordelli in Bassani, 1886 Baltzer, 1893 This paper Maffei, 1924 Patrini, 1921 Patrini, 1921 Amsler, 1900 This paper This paper Maffei, 1924 Rytz, 1953 This paper Amsler, 1900 Maffei, 1924 Rytz, 1953 Emmert-Straubinger, 1991 Rytz, 1953 Maffei, 1924 Amsler, 1900 Fischer in Baltzer, 1896 Sordelli, 1878 This paper

Rhamnus alpinus L. var. imeretina Rhamnus alpinus L. Rhamnus cf. alpinus L. Rhododendron ponticum L. Rhododendron sebinense n. sp. Rhododendron ponticum L. var. sebinense (Sordelli) Sordelli Rosa sp. Salix sp. Sambucus nigra L. Sorbus aria (L.) Crantz Taxus baccata L. Thalictrum minus L. Tilia caucasica Rupr. Tilia cordata Miller Tilia platyphyllos Scop. Tilia sp. Tilia tomentosa Moench. Ulmus campestris L. Ulmus glabra Hudson Verbascum blattaria L. Viburnum lantana L. Viola sp. Viscum album L. Viscum sp. Vitis sylvestris Gmelin Vitis vinifera L. Vitis vinifera L. ssp. sylvestris Gmelin

This paper Maffei, 1924 This paper Fischer in Baltzer, 1896 Sordelli, 1873 This paper Rytz, 1953 Rytz, 1953 Maffei, 1924 Amsler, 1900 Emmert-Straubinger, 1991 Sordelli, 1873 Emmert-Straubinger, 1991 This paper Fischer in Baltzer, 1896 This paper Emmert-Straubinger, 1991 Amsler, 1900 Emmert-Straubinger, 1991 Amsler, 1900 This paper

Confirmed taxa in bold type; the other names represent invalid synonyms or doubtful records.

Furthermore, a preliminary revision of about 300 leaf compressions or impressions, forming the ‘‘Rytz collection’’, has been carried out. These fossils, most probably sampled within the BVC member (abundant Buxus leaves, see below) in the period 1921–1934 (Rytz, 1925, 1953), are preserved on pieces of white laminated chalk from the Pia`nico-Se`llere basin, which were formerly housed at the Bern Botanical Institute (Switzerland). Original hand-written labels with names of plant taxa were found in several boxes, although in some cases they obviously did not correspond to the content. This permitted checking of the determination of most of the taxa previously reported by Rytz (1953). Leaves of the Pia`nico Formation have traditionally been identified by gross-morphological comparison to modern material. Emmert-Straubinger (1991) reported details of cuticle features of Hedera leaves from Pia`nico, and, based on these, suggested an affinity to Hedera helix L. rather than to Hedera colchica (K. Koch) K. Koch. More extensive cuticle investigations would be needed in

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Fig. 3. Examples of fossil leaves collected by splitting laminated sediment along bedding planes, ‘‘S’’ assemblage of the Sergio section (Figs. 2, 9 and 10 excepted). 1: Acer cappadocicum Gleditsch,  0.8; 2: Acer cappadocicum, as drawn by Sordelli (1896) (¼‘‘A. laetum’’)  0.6; 3: Acer cf. opalus,  0.7; 4: bedding plane covered by iso-oriented needles of T. baccata L.,  1.0; 5: Tilia sp.,  0.8; 6: Pyracantha coccinea M.J. Roemer,  1.0; 7: leaf of Hedera helix L. associated with a smaller elliptic leaf of Buxus sempervirens L. (above, right),  0.9; 8: cf. Lonicera xylosteum,  1.3; 9, 10: Rhododendron ponticum L. var. sebinense (Sordelli) Sordelli, as drawn by Sordelli (1896), fruit ( 1.3) and leaf ( 0.9); 11: Rhododendron ponticum L. var. sebinense (Sordelli) Sordelli,  0.8.

E. Martinetto / Quaternary International 204 (2009) 20–30

order to verify the occurrence of problematic (such as cf. Lonicera xylosteum: Fig. 3(8)) and locally extinct taxa. For the present study, plant remains obtained from bulk sediment samples were also analysed. Emmert-Straubinger (1991) affirmed having used such a method, but did not report detailed results. This method allows obtaining original palaeofloristic data based, for example, on small-sized seeds and fruits of herbaceous plants, which may not have a leaf or pollen record (see below). The carpological material was identified by comparison with the extensive reference collections of both recent and Pleistocene material stored at the Museum fu¨r Naturkunde in Berlin. Relevant literature was consulted to confirm the identifications, e.g. Velichkevich and Mamakova (2003) and Velichkevich and Zastawniak (2006). Field work was carried out in several sections of the Pia`nico-Se`llere basin in order to locate layers with suitable concentrations of terrestrial plant macrofossils. Two assemblages of this

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type (Fig. 4) were detected in turbidite layers, and the following bulk samples were collected: - B4N: Sergio section, turbiditic layer below the t0 layer in the BVC member, size 3 dm3; - B4A: Main section, at the top of slump no. 3 in the BVC member, size 0.8 dm3. Standard methods to dissolve/disaggregate clastic sediments (e.g., Martinetto, 1994; Basilici et al., 1997) did not work very well with the Pia`nico-Se`llere carbonates. Therefore, the sediments were treated in the following way: dry sediment was placed in a basin and reduced to blocks not larger than 30 cm3. A volume of 5% H2O2 comparable to the sediment’s one was added and left to react for 2 h. The dissolved sediment was filtered with a mesh size of 0.3 mm, and the residue left to dry for several days (heating

Fig. 4. Examples of carpological remains collected by sieving sediment samples (B4N, B4A). 1–3: Pyracantha coccinea M.J. Roemer, remain of a ‘‘berry’’ with 5 fruits, subapical view (1), fruit from the dorsal and ventral side (2), another fruit seen from both lateral sides (3), B4N; 4: Vitis vinifera L. ssp. sylvestris Gmelin, seed in dorsal and ventral view, B4A; 5: Pinus peuce Griseb., cone, B4N; 6: Rhododendron cf. ponticum L. var. sebinense (Sordelli) Sordelli, base of a fruit (capsule) seen from two sides, B4A; 7: Verbascum blattaria L., seed, B4A; 8: Potamogeton cf. marginatus Dorofeev, endocarp in lateral and dorsal view, B4N; 9–13: Sambucus nigra L., seeds showing size and shape variation, B4A; 14: Picea abies (L.) Karsten s. l., cone from the MLP member of the Oblique section. Thin scale bars ¼ 1 mm, thick ones ¼ 1 cm.

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avoided). All the cycle was repeated three times. After the last filtering the residue was dropped again in 5% H2O2 and, after a few minutes, the floating fraction (‘‘A’’), which is richer in fruits and seeds, was filtered separately from the sinking one (fraction ‘‘B’’), always with a final mesh size of 0.3 mm. The abundant plant remains deposited at the bottom of the basin were collected with a battery of sieves whose final mesh size was 0.8 mm (fraction ‘‘C’’). Most mesofossils sorted from the residue were still covered by a white carbonatic ‘‘dust’’ which hampered identification and photography; this was removed by immersion in acetic acid for several days. In sample B4A the three fractions ready for analysis (A–C) were examined separately in order to understand the differences in their content. 3. Results In the residues of bulk sediment samples plant remains definitely prevailed; the volume of fraction C (see above) was nearly 50 times larger than that of fraction B, and fraction A was nearly 1/3 of B. However, the most concentrated and diverse assemblage of small-sized fruits and seeds was present in A. Fraction B contained many coniferous needles and a few seeds, and carpological remains of three species have been exclusively found in B: Carex gr. caespitosa L., Thalictrum cf. flavum L., and Brassicaceae indet. The complete analysis of C was done only for the material larger than 3 mm. Sorting the material smaller than 3 mm is extremely timeconsuming and resulted in only one immature Tilia fruit and a Buxus endocarp in 1/10 of the whole material, apart from the common needles. The experience gained from extensive sampling in various Pliocene localities (Martinetto, 1994; Basilici et al., 1997) would suggest that the studied sediment samples, which are comparably small, only provided the most common components of the Pia`nico mega/mesofossil assemblages. Future work should be addressed to the collection of larger samples, even from the same layers (up to several hundred litres) in order to gather remains of rarer species. The palaeobotanical analysis of samples B4N and B4A permitted identification 26 and 23 taxa, respectively, mainly represented by fruit/seed remains. The assemblage of sample B4N (Table 4) testifies to the occurrence of 12 species of herbaceous angiosperms and 13 of woody plants. Some non-arboreal forms represent emergent freshwater macrophytes or wetland plants (Alisma, Carex, Cladium, and Phragmites-type), and just a few species belong to submerged forms (Najas, Potamogeton). Ajuga cf. reptans L., Micromeria thymifolia (Scop.) Fritsch, Hypericum cf. androsaeum L., Hypericum perforatum L. and Origanum vulagare L. can be interpreted as herbs growing in better-drained conditions, while the remaining taxa have broad ecological requirements. The most common arboreal forms are Abies cf. alba, Acer campestre L., Acer cf. opalus Miller, Acer ex sect. Platanoidea, Carpinus betulus L., Pinus, and Tilia spp. The most common shrub is Pyracantha coccinea M.J. Roemer. In sample B4A 11 species represent herbaceous angiosperms and 10 are woody plants. The main differences in comparison to B4N are the scarcity of Acer and Pyracantha remains, compensated by the abundant occurrence of Buxus. Herbs requiring well-drained conditions include two species not represented in B4N: Fragaria vesca L. and Moheringia cf. trinervia (L.) Clairv. Finally, two interesting woody forms occur with a few carpological remains in both samples: Sambucus nigra L. (Fig. 4(9–13)) and Vitis vinifera L. ssp. sylvestris Gmelin (Fig. 4(4)). Among the cones which were sampled from known stratigraphic positions, and later identified, three specimens belonged to Picea abies (L.) Karsten s. l. (50, 60 and 130 cm above the MLP base, Oblique and Wall sections), and five specimens to Pinus peuce Griseb. (BVC, about 6 m from the base in the Sergio section, and

Table 2 List of plant taxa forming the compression assemblage ‘‘S’’, Sergio section. F ¼ frequent; No. ¼ number of specimens. Species

Nr.

Part

Abies cf. alba Abies cf. alba Abies cf. alba Acer cf. campestre Acer cappadocicum Acer gr. opalus Acer sect. Platanoidea Alnus incana Buxus sempervirens Buxus sempervirens Carpinus betulus Carpinus betulus Corylus avellana Hedera cf. helix cf. Lonicera xylosteum Populus cf. nigra Pyracantha coccinea Quercus cf. petraea Rhododendron ponticum var. sebinense Rosa sp. Salix sp. Taxus baccata Tilia sp. (spp.?)

F 2 2 1 3 12 2 2 F 1 1 1 2 7 1 2 1 2 3 1 2 F 3

Leaf Scale Seed Leaf Leaf Leaf Fruit Leaf Leaf Fruit Fruit Leaf Leaf Leaf Leaf Leaf Leaf Leaf Leaf Leaf Leaf Leaf Leaf

MLP, respectively 30, 42, 146 and 167 cm above the base in the Wall section). In the ‘‘S’’ compression assemblage 17 taxa were identified on the basis of leaf remains (Table 2), and relatively few fruits and seeds were detected (two fruits of Acer sect. Platanoidea, two seeds and two cone scales of A. cf. alba, one fruit of Buxus sempervirens L. and C. betulus L.). Within the ‘‘L’’ leaf assemblage not more that 40 out of 300 fragmentary specimens were identified on a macromorphological basis, and they were assigned to the nine taxa reported in Table 3. 3.1. Notes on some locally extinct species The earliest works on the Pia`nico fossil flora, in particular by Sordelli (1878, 1896), reported the occurrence of exclusively fossil species: Neckera ossulana Sordelli, Acer sismondae Gaudin, Castanea latifolia Sordelli, and Rhododendron sebinense Sordelli. Such species were not confirmed by Emmert-Straubinger (1991), who only listed modern European entities. However, also this author confirmed, and even increased, the record of locally extinct plants in the Pia`nico fossil flora: Acer cappadocicum Gleditsch, Picea omorika (Pancic) Purkine, P. peuce Griseb., P. coccinea M.J. Roemer, Rhamnus alaternus L., Rhododendron ponticum L., Tilia caucasica Rupr. Three of these species (P. omorika, R. alaternus, and T. caucasica) should be better documented because their occurrence merely relies on a nominal citation by Rytz (1953) and

Table 3 List of plant taxa identified within the compression assemblage ‘‘L’’, Beehive section. No. ¼ number of specimens. F ¼ frequent. Species

Nr.

Part

Acer cappadocicum Acer gr. opalus Alnus sp. Carpinus betulus Hedera cf. helix Picea sp. Pyracantha coccinea Quercus cf. petraea Rhododendron ponticum var. sebinense

2 20 1 1 (2?) 3 1 1 (3?) 4 5

Leaf Leaf Leaf Leaf Leaf Shoot Leaf Leaf Leaf

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Emmert-Straubinger (1991). On the other hand, a solid macropalaeobotanical documentation testifies for the occurrence of the species reported below. 3.1.1. P. peuce Griseb. (Fig. 4(5)) This species is well documented by cones with unmistakable characters. Also the large ovoid seeds permit a reliable distinction from other European pines. A well-preserved cone specimen was found in the B4N sample (Fig. 4(5)); in B4A a seed occurred, and other cones have been collected in the field from four layers of the MLP member (see above). 3.1.2. A. cappadocicum Gleditsch (Fig. 3(1–2)) Leaf morphology is the most suitable character for a specific diagnosis of maples, and some fossil specimens recovered at Pia`nico-Se`llere, in both the ‘‘S’’ and ‘‘L’’ leaf assemblages, are characterized by 3- to 5-palmate leaves, with entire margin and attenuate lobe apex, which are typical for A. cappadocicum. Some authors consider the modern Turkish maple A. cappadocicum as a broader species, also including a subspecies endemic to southern Italy and the Balkan peninsula, which is treated as a distinct species (Acer lobelii Ten.) by most authors. Comparison with modern samples (Humboldt University Arboretum, Berlin; Hohenheim Bot. Garten, Stuttgart) showed that the fossil leaves are identical to those of A. cappadocicum. Leaves of A. lobelii differ for the irregular shape of lobes with few, irregularly spaced teeth. Even if they often show acute sinuses between lobes, as in the Pia`nico fossils, this same character has also been observed in A. cappadocicum at the Hohenheim Bot. Garten. A. cappadocicum and A. lobelii belong to section Platanoidea, and fruits with a morphology typical for such section are frequent in sample B4N. 3.1.3. P. coccinea M.J. Roemer (Fig. 3(6); Fig. 4(1)–(3)) Leaves of this species had already been reported by Amsler (1900) and Rytz (1953), and carpological remains found in B4N and B4A samples confirm the identification. In fact Pyracantha is distinguished from Cotoneaster by the ‘‘berry’’ with 5 stones (instead of 3), with woody and persistent style, attached to the apical part of the ventral side of the stone (in Cotoneaster attached to the median part). The B4N sample also yielded a few fruits (see Fig. 4(3)) resembling Pyracantha clactonensis (Reid and Chandler) Field, which has been recently confirmed as an extinct species by Bridgland et al. (2001) on the basis of biometric analyses of Middle Pleistocene fruit-stones from Barling, England. 3.1.4. Potamogeton cf. marginatus Dorofeev (Fig. 4(8)) The single endocarp from sample B4N is identical to abundant Pleistocene specimens from the interglacial of Grabschu¨tz, Germany (Mai, 1990a), assigned to the extinct P. marginatus Dorofeev. However, it is also extremely similar to some modern specimens of P. lucens, being just a little smaller, which could be the result of drying contraction of the mummified fossil. The low but distinct carina in the middle of the dorsal valve and the permanent style are differential characters against the similar Potamogeton  zizii W.D.J. Koch ex Roth and P. perfoliatus L. Unfortunately, a single specimen is unsuitable for a definite identification, so that more abundant material should be detected in the future. P. marginatus occurs in the Mikulino (Eemian) interglacial and the Weichselian (‘‘Wu¨rm’’) of Eastern Europe, as well as in the interglacial of Grabschu¨tz (Germany), which is tentatively correlated to the Holsteinian (Mai, 1990a). Therefore, from the biostratigraphic point of view, the occurrence of P. marginatus Dorofeev would suggest an Holsteinian to Weichseilian age. However, Mai (1990b) pointed out that similar endocarps, which

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can only be discriminated with abundant and well-preserved material, have been described from older sediments as P. dvinensis Velichkievich (Early Pleistocene) and P. sechmanicus Dorofeev (Pliocene). Even the living species P. lucens L. has been reported, though on the basis of questionable fruit remains, from Pliocene (Leschik, 1952; Szafer, 1954) and Early Pleistocene deposits (Baas, 1932). 3.1.5. R. ponticum L. var. sebinense (Sordelli) Sordelli (Fig. 3(9–11); Fig. 4(6)) The occurrence of leaves with morphological characters identical to the modern ones of R. ponticum has first been recognized by Sordelli (1878), and later accepted by other authors (Wettstein, 1888; Tralau, 1963). The Rytz collection contains about 15 leaves of this type, which have also been found in both the ‘‘L’’ and ‘‘S’’ leaf assemblages. Denk (2006) pointed out that the name R. ponticum var. sebinense should be used for these fossils, and also stated that it ‘‘is more similar to the modern eastern subsp. ponticum (Turkish and Caucasian populations) than to the western subsp. baeticum (Boissier and Reuter) Handel-Mazzetti’’ (Iberian populations). A single fragmentary fruit (capsule) of Rhododendron was found in sample B4A. Its morphology with thin receptacle and short calyx lobes excludes assignment to either R. ferrugineum L. (campanulate receptacle) or R. hirsutum L. (long, ciliate calyx lobes), whereas R. ponticum produces comparable fruits. Further characters, which agree with the R. ponticum-type (general shape, oblique axis), are shown by a complete capsule (external impression) still preserved in the Rytz collection, which is very similar to the specimen figured by Sordelli (1896, pl. 43, fig. 9)). Therefore, these fruits were produced by the same plant taxon as the leaves (R. ponticum var. sebinense).

4. Comparison with similar macrofloral assemblages A list of European Middle Pleistocene macroflora-bearing sites has been compiled by Mai (1983), who discussed the difficulty to draw general biostratigraphic conclusions, due to the large number of fossil sites, which are not reliably dated. However, he pointed out the relevance of extinct and ‘‘exotic’’ (locally extinct) elements for the characterization of different Middle Pleistocene interglacials. In samples B4N and B4A those extinct or ‘‘exotic’’ species which characterize the interglacial deposits of central and eastern Europe (e.g. Brasenia spp., Dulichium arundinaceum L., Potamogeton spp.: Mai, 1983; Velichkevich and Zastawniak, 2006) have not been detected (but see above for P. cf. marginatus). Only the few C. betulus nutlets in B4N could possibly have biostratigraphic relevance. In fact, their small nut-size is more characteristic of pre-Eemian populations (mainly Pliocene and Early Pleistocene), while the Eemian ones have statistically larger nuts (Jentys-Szaferowa, 1960, amended with personal observations). As for the ‘‘exotic’’ elements, there are no sites in Europe which share all the taxa occurring in the Pia`nico-Se`llere lacustrine deposits. The co-occurrence of Celtis australis L., B. sempervirens, and P. coccinea has been reported for the travertines of La Rouquette in France (Ambert et al., 1992), assigned to MIS 7 (Vernet et al., 2008), and for the Bilzingsleben II site1 in Germany. According to Mai (1983), in central Europe this association of taxa would suggest

1 Mallickl and Frankl (2002) stated that ‘‘In the present state the Bilzingsleben site cannot be accurately [radiometrically] dated and . previous dating attempts most likely suffered from altered samples as well. However, the site or even the diagenetic processes should be older than 300,000 yr because otherwise U-series activity ratios would not yield values equal or close to radioactive equilibrium’’.

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a warm interglacial phase in the Elsterian–Saalian interval. This argument cannot be applied to the fossil assemblages found south of the Alps, where the pollen floras show several peculiarities in the Middle Pleistocene (Follieri et al., 1988). In Italy there are just a few leaf assemblages which could serve as reference points: Oriolo, in the Emilia–Romagna region (Martinetto and Sami, 2001) – The site is dated around 800,000 a by a combination of magnetostratigraphy and mammal biochronology. The palaeoflora has a larger number of ‘‘exotic’’ elements (Acer aff. palmatum L., Carya, Gleditschia, Parrotia, Pterocarya, Tsuga, and Zelkova) in comparison to the Pia`nico flora, but shares with it A. cf. cappadocicum, P. cf. peuce, and P. coccinea. Riano Romano near Rome (Follieri, 1958; Mastrorilli, 1965) – According to Bonadonna and Bigazzi (1969) the site is radiometrically dated to around 300,000 a. The macroflora, rather similar to the Pia`nico one, mainly differs by the occurrence of the ‘‘exotic’’ Pterocarya and Zelkova. The single ‘‘exotic’’ taxon found in both assemblages is A. cf. cappadocicum. Re in the Vigezzo valley (northernmost Piedmont) – The site cannot be considered as reliably dated, even if assigned to the ‘‘Riss/ Wu¨rm’’ interglacial by Sidler and Hantke (1993). It yielded abundant leaf remains of arboreal plants still living in northern Italy (Sordelli, 1896; Gianotti, 1949;). The presence of the locally extinct B. sempervirens, ‘‘Castanea latifolia Sordelli’’, and R. ponticum suggests an affinity to Pia`nico. In conclusion, the presently available macrofloral documentation only allows stating that the Pia`nico comprehensive palaeoflora differs from the few analogous assemblages (Martinetto, 1999) known in the Early Pleistocene (incl. possible transition to the Middle Pleistocene at Oriolo: Martinetto and Sami, 2001) by the absence of really extinct taxa (possible exception: P. cf. marginatus Dorofeev) and the scarce number of locally extinct ones (e.g. lack of Carya, Liquidambar, Eucommia), which is also characteristic for the Middle Pleistocene flora of Riano Romano. The absence of extinct aquatic and wetland plants in a Middle Pleistocene carpofloral assemblage could be regarded as surprising in comparison to the central European record (Velichkevich and Mamakova, 2003). However, an identical situation has been reported, at comparable latitude, for an interglacial deposit (Holsteinian?) of southern France (Field et al., 2000). Furthermore, the carpological analyses carried out until now in the Pia`nico Formation are not sufficient for definitive considerations, so that further sampling would be needed to confirm the real absence of extinct plant taxa. 5. Palaeoenvironmental implications In both samples B4N and B4A, remains of mesic woody plants dominate quantitatively, as well as in all the known leaf assemblages from BVC, ‘‘S’’ in particular. These leaf and carpological remains were certainly produced by deciduous arboreal taxa (Acer, Carpinus, Quercus, Ulmus, and Tilia), associated to such evergreen elements as Ilex aquifolium, P. coccinea and the needle-leaved T. baccata. This kind of record suggests closed woody vegetation, prevalently deciduous, growing on the low mountain slopes, steeply dipping into the lake (Moscariello et al., 2000). Evergreen shrubs to small trees might well have grown as part of the understorey in the deciduous woodlands (Buxus, Ilex) or in more open, drier rocky places (especially Pyracantha). Possibly, B. sempervirens was rare around the lake at the beginning of the BVC deposition, as suggested by the absence of macroremains in B4N and low pollen percentage of Buxus at the bottom of BVC (Rossi, 2004). Already 2 m above the base in the Sergio section (Fig. 2), Buxus leaves become the most common fossils, which would suggest a certain abundance not far from the lake. Fruits/seeds of herbaceous plants are

very scarce in B4N, and they invariably belong to species which could grow in woodlands (Ajuga cf. reptans, F. vesca, Hypericum cf. androsaeum, Lamiaceae, Moehringia cf. trinervia, and Viola sp.). The present re-investigation confirms the conclusion by Emmert-Straubinger (1991) that aquatic plants are absent from the leaf assemblages of the Pia`nico-Se`llere laminated chalks (now placed in the BVC member) and very rare in the carpological ones (Najas marina and Potamogeton in B4N). Lake-margin species are represented in B4N by abundant Cladium mariscus and rare Alisma sp. fruits, as well as culms of cf. Phragmites. Such records suggest that patches of sedge and reed marsh occurred around the lake at the beginning of the BVC deposition, and later (layer t 19a: Fig. 2) decreased or disappeared. In fact, the B4A sample did not provide aquatic plants, and the wetland plants were only represented by a few fruits of Lycopus europaeus and Thalictrum minus. The macrofossil assemblages studied in the BVC member do not provide contrasting evidence for the altitudinal development of vegetation belts proposed on a palynological basis by Moscariello et al. (2000) and Rossi (2004). Yet, on the basis of actuopalaeontological observations (Spicer and Wolfe, 1987), the occurrence of a large and

Table 4 List of plant taxa gathered from two sediment bulk samples, respectively from the Sergio and Main sections. Species Abies cf. alba Abies cf. alba Abies cf. alba Acer campestre Acer gr. opalus Acer sect. Platanoidea Acer spp. Ajuga cf. reptans Alisma sp. Brassicaceae indet. Buxus sempervirens Buxus sempervirens Buxus sempervirens Buxus sempervirens Micromeria thymifolia Carex gr. caespitosa Carex spp. Carpinus betulus Cladium mariscus Cornus sanguinea Corylus avellana Carpolithes sp. Erica cinerea Fragaria vesca Hypericum cf. androsaeum Hypericum perforatum Ilex aquifolium Lycopus europaeus Moheringia cf. trinervia Najas marina Origanum vulgare Pinaceae indet. Pinus peuce Pinus peuce Poaceae (Phragmites-type) Potamogeton cf. marginatus Prunus lusitanica Pyracantha coccinea Pyracantha coccinea Rhododendron cf. ponticum Sambucus nigra Taxus baccata Thalictrum minus Tilia spp. Verbascum blattaria Viola sp. Vitis vinifera ssp. sylvestris

B4N 6 f 22 24 21 17 1 1

6 3 14 35 2 4

B4A

Part

7 12 f

Cone scale Seed Leaf Fruit Fruit Fruit Fruit Fruit Fruit Seed Leaf Fruit Endocarp Seeds Fruit Fruit Fruit Fruit Endocarp Endocarp Fruit Fruit Seed Fruit Seed Seed Seed Fruit Seed Seed Fruit Seed Seed Cone Stem Endocarp Endocarp Endocarp Berry Fruit Seed Seed Fruit Fruit Seed Seed Seed

3 1 2 1 27 12 34 8 1 1 6

2 1 1 4 1 2 5 6 16 3 20 12 1 2 1 1 31 14 1 3 18

1

1

2 1 4 ? 2 5 1 2 1

E. Martinetto / Quaternary International 204 (2009) 20–30

well-preserved P. peuce cone (sample B4N) and various A. cf. alba Miller remains (‘‘S’’ assemblage) would suggest that these conifers were not restricted to higher altitudinal belts, but occurred, at least with a few fertile individuals, not far from the lake-shore. On the other hand, P. abies (L.) Karsten, which is not recorded in the whole BVC macrofossil record, would be likely restricted to the upper altitudinal belts. The single macrofossil assemblage (‘‘L’’) from the MLP member does not differ significantly from the BVC ones, as it still contains thermophilous (P. coccinea) and locally extinct elements (A. cappadocicum, R. ponticum var. sebinense). The main difference is represented by the absence of Buxus, in fact isolated leaves have been observed all the way up to the upper part of the BVC, but never in MLP, including the ‘‘L’’ assemblage (in agreement with pollen records). Thus, it may be suggested that the vegetation of the Clusone II interstadial was much alike the one of the Pia`nico-Se`llere Interglacial phase, and only more detailed investigations could confirm if the absence of Buxus and the rare occurrence of Picea macrofossils (Table 4) reflect cooler palaeoclimatic conditions. In the basal layers of the MLP member, several cones of P. abies (Fig. 4(14)) were detected, which have not been found in the BVC member, and probably indicate the settlement of spruce close to the lake-shore, in agreement with the suggested contraction of the broadleaved forest and descent of vegetation belts downslope (Moscariello et al., 2000; Rossi, 2004), as a consequence of the cooling indicated by the pollen diagram at the base of MLP (Presolana I stadial). The data so-far obtained clearly indicate that the intensification of plant macrofossil investigations would be most useful to complete the picture of plant community change around the Pia`nico-Se`llere lake at the transition from the Pia`nico-Se`llere Interglacial phase (Rossi, 2004) to the Presolana I stadial and during the following stadial/interstadial transitions. Furthermore, the analysis of new palaeocarpological samples would most probably permit the detection of diagnostic biostratigraphic indicators (Velichkevich and Mamakova, 2003; Velichkevich and Zastawniak, 2006), which could eventually contribute to the solution of the controversy about the chronostratigraphic position of the Pia`nico-Se`llere Interglacial. Acknowledgments I thank Cesare Ravazzi for providing essential information regarding the Pia`nico succession and the stratigraphic context of various palaeobotanical samples; he has also prepared, together with Sabrina Rossi, the drawings of Figs. 1 and 2. I am much indebted to Dieter Hans Mai for the consistent help in the identification of carpological material and for facilitating my work in the reference collections of the Museum fu¨r Naturkunde in Berlin. I am also thankful to Barbara Leidi for the hard work carried out with the preparation of the ‘‘L’’ leaf assemblage, and to Brigitte Amman and Elisa Vescovi for their help in locating and studying the Rytz collection. Thomas Denk and an anonymous reviewer provided constructive and valuable improvements to the manuscript. A grant received from the Synthesys project in 2007 allowed me to compare directly the Pia`nico fruits and seeds with those of central European interglacials. References Ambert, P., Guendon, J.-L., Vaudour, J., Magnin, F., Roiron, P., Quinif, Y., Aguilar, J.-L., Marinval, P., 1992. Pale´oenvironnements au Ple´istoce`ne moyen dans la valle´e du Tarn: la formation travertineuse de la Rouquette (Creissels – Aveyron). Geobios 14, 133–139. Amsler, M., 1900. Flore interglaciaire de Pia`nico. Compte Rendu des travaux de la Societe´ Helve´tique de Sciencies Naturelles re´unie a` Thusis, 44–46.

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