Oligocene plant assemblage from Rębiszów, Lower Silesia: First “volcanic flora” from Poland

RAFAŁ KOWALSKI, GRZEGORZ WOROBIEC, ELŻBIETA WOROBIEC, and KATARZYNA KRAJEWSKA

Kowalski, R., Worobiec, G., Worobiec, E., and Krajewska, K. 2020. Oligocene plant assemblage from Rębiszów, Lower Silesia: First “volcanic flora” from Poland. Acta Palaeontologica Polonica 65 (2): 273–290.

Fossil plant macroremains preserved in laminated diatomites from Łysa Góra near Rębiszów, Lower Silesia, have been documented for the first time. The fossil assemblage consists mostly of leaves, but fruits, seeds and sporadic flowers also occur. Forty-three identified taxa represent nineteen plant families: Aceraceae, Berberidaceae, Betulaceae, Cornaceae, Cupressaceae, Elaeocarpaceae, Ericaceae, Fagaceae, Lauraceae, ?Leguminosae, ?Meliaceae, Magnoliaceae, Pinaceae, Rhamnaceae, Rosaceae, Salicaceae, Tilioideae, Ulmaceae, Vitaceae, and one incertae sedis. The prevalence of entire margined leaves, mostly represented by Majanthemophyllum basinerve and Daphnogene cinnamomifolia, and a significant presence of Calocedrus suleticensis and Liriodendron haueri, are characteristic features of the Rębiszów flora. The composition of the plant assemblage points to a mesophytic forest with some riparian elements and suggests favourable, warm climatic conditions. Radiometrically dated basalts overlying fossiliferous layers and composition of palynoflora suggest at least Chattian (late Oligocene) age. The lithology and floristic composition link the Rębiszów flora with the so-called volcanic floras of the Nerchau-Flörsheim or Kleinsaubernitz floristic complex (Oligocene) from Germany and Czech Republic with Suletice-Berand flora being especially close.

Key words: Acrogymnospermae, Angiospermae, sporomorphs, volcanic floras, diatomites, Paleogene, Poland.

Rafał Kowalski [rafal.kowalski@mz.pan.pl] and Katarzyna Krajewska (passed away 2011), Museum of the Earth in Warsaw, Polish Academy of Sciences, Al. Na Skarpie 27, 00-488 Warsaw, Poland.

Grzegorz Worobiec [g.worobiec@botany.pl] and Elżbieta Worobiec [e.worobiec@botany.pl], W. Szafer Institute of ­Botany, Polish Academy of Sciences, ul. Lubicz 46, 31-512 Kraków, Poland.

Received 8 October 2019, accepted 9 January 2020, available online 16 April 2020.

Copyright © 2020 R. Kowalski et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

Localities where the late Paleogene plant remains occur are quite common in Central Europe, but fossil plant assemblages which were formed in connection with volcanic activity, so-called volcanic floras (Kvaček and Walther 1998), are rare. These floras, however, have particular relevance for our knowledge of Central European Paleogene vegetation. The importance of these type of floras is due to the fact that they represent zonal, upland vegetation and, often, they can be radiometrically dated. They also frequently provide exceptionally well preserved macro- and microfossils, both of plants and animals. The Oligocene volcanic floras are connected with distribution of the Central European Tertiary intraplate volcanic province (Birkenmajer et al. 2011) and have been documented so far from Germany and Czech Republic. Lower Silesia (SW Poland) belongs to the north-eastern part of this volcanic province as a part of the Bohemo-Silesian volcanic belt though Paleogene fossil macrofloras have not yet been reported from this area.

The fossil plant remains documented here were discovered at Łysa Góra (Urwista), located in the western part of Lower Silesia, ca. 2 km south of Rębiszów village (Fig. 1) by Stanisław Dyjor in 1979. The first attempts to investigate this fossil flora were undertaken much later, in the early 2000s by Katarzyna Krajewska. Krajewska and Dyjor planned a comprehensive collaborative paper about fossil flora from Rębiszów. Unfortunately, their untimely death thwarted this plan.

Considering the uniqueness of the Rębiszów flora among other Cenozoic floras from Poland, and its significance to knowledge of the Oligocene volcanic floras of Central Europe, we decided to continue the investigations of Krajewska and Dyjor. This paper also commemorates Katarzyna Krajewska as a paleobotanist as well as the efforts she made in studying this flora.

Some data on the site location and local geology presented in the Geological settings originate from a draft by Stanisław Dyjor given in a letter to Katarzyna Krajewska dated March 14, 2006. However, we also present an alternative view on the general geology of this locality based on more recent studies on the geology of the Rębiszów locality. The taxonomic composition within the assemblage was preliminarily recognised by Krajewska and prepared in the form of a list of indicated specimens. She investigated some of the remains in consultation with Zlatko Kvaček in 2004.

In preparation of the present treatment, we carefully reexamined (RK and GW) the whole collection to evaluate the taxonomic determinations made by Krajewska. Most of the carpological remains in the collection that remained unrecognised or unnoticed by Krajewska were studied during the preparation of this paper. Preliminary palynological analysis of the deposits containing the macroremains was conducted by Aleksandra Kohlman-Adamska and Maria Ziembińska-Tworzydło (unpublished material), but while preparing this report new and detailed palynological investigations were made (EW) to supplement the preliminary results.

This paper briefly documents current knowledge on the Łysa Góra fossil assemblage, including palynological analysis, interpretation of the vegetation and paleoclimate, and comparison with other European assemblages of the same age and age determination. In recognition of the work already done on this collection we decided to include Katarzyna Krajewska posthumously as a co-author of this paper.

Institutional abbreviation.—KRAM-P: Palaeobotanical col­lections of W. Szafer Institute of Botany, Polish Academy of Sciences, Kraków, Poland.

Geological settings

Volcanic vents in the Rębiszów area are connected with the Rębiszów fault zone, where a tectonic contact with the gneisses and granitic gneisses of the Izera complex and the Neoproterozoic Stara Kamienica mica schist can be observed (Birkenmajer et al. 2011).

According to Birkenmajer et al. (2011), volcanic activity in Lower Silesia began in the Rupelian (early Oligocene) and continued with variable intensity to Zanclean (early Pliocene). One of the latest radiometric datings suggests that volcanic activity in the Rębiszów area took place in the late Oligocene. Dates obtained from ankaratrites exposed in the Łysa Góra quarry are of ca. 25.3±1.0 Ma, and those exposed in Grudza quarry, ca. 4 km East of the Rębiszów village, are of ca. 26.0±1.0 Ma (Birkenmajer et al. 2011).

According to Stanisław Dyjor (unpublished material, a letter to Katarzyna Krajewska, 14.03.2006), the layers with plant remains which he found were exposed somewhere in or near the “lower quarry”. Despite the imprecise localisation, we are almost certain that the “lower quarry” could equate to an abandoned quarry that is located within a hill called “Łysa Góra” (Fig. 1). Unfortunately, despite two excursions to search this area, we were unable to find the exact position of the site where the fossils were collected. Below, we summarise the interpretation of the local geological settings left by Stanisław Dyjor. According to him, some of the basaltic vents or lava flows in the Rębiszów area are covered with small patches of various Cenozoic sedimentary rocks, which were deposited in a small lake. The lake probably formed after the stream was restricted by lava flow. Layers with plant remains are a part of a sedimentary series that originally filled the paleovalley, although much of their northern part was eroded in the Pleistocene. Sedimentary series were deposited between the lava flow on the southern margin and gneisses on the northern erosional margin of the valley, and consisted mostly of loamy sand and gravel with tuff and tuffite intercalations in the lower part, and diatomite with fossil flora in the upper part of the profile. Mass development of diatoms was probably induced by silica-rich water. The high-silica content probably resulted from percolation of waters through silica-rich volcanic rocks.

We have, however, considerable doubts about the above presented interpretation. The chronological order proposed by Stanisław Dyjor (unpublished material) is in contradiction with the technical report on the geological setting of the basalt resources in Rębiszów, which we had the opportunity to see during our visit to the main office of Pri Bazalt S.A. mining company and information provided by Adamczyk (2008). Both of the mentioned sources clearly state that sedimentary rocks with fossiliferous layers found in the study area are overlain by basalt. According to Adamczyk (2008), Cenozoic sedimentary series in the Rębiszów area were preserved only due to the protective basalt layer. This alternative interpretation suggests that sedimentary rocks are older than the basalts, in this case providing the upper age limit of the Rębiszów fossil flora.

During an excursion (31.07.2019) to an abandoned quarry located on the Urwista and Odarte Skały hills, RK and Olaf Tietz and Joerg Büchner (both Senckenberg Museum of Natural History, Görlitz, Germany) discovered three new sites where sedimentary sequences are exposed. According to Olaf Tietz and Joerg Büchner (personal communication 2019), the lithological characteristics and position of the sedimentary sequences in relation to the overlying basalts suggest that these deposits may represent maar lake infill rather than the infill of a lake formed by the damming of a river by a lava flow.

Thus, the fossil plant assemblage from Rębiszow represents a so-called volcanic flora sensu Walther (2005), which is similar to the Oligocene floras from Northern Bohemia, Czechia and Upper Lusatia, Germany (Akhmetiev et al. 2009). These assemblages were usually preserved in diatomaceous deposits of maar crater lakes, such as late Oligocene fossil flora from Kleinsaubernitz (Walther 1999, 2005).

The genesis and lithology of the deposits with a plant assemblage from Rębiszów (diatomaceous sediments in a volcanogenic lake) are also similar to the late Eocene Florissant fossil beds from Colorado, USA, yielding the renowned plant and animal fossil Lagerstätte (Meyer et al. 2004).

Material and methods

Fossil leaves from Rębiszów are mostly impressions, although sometimes traces of coalified tissues are preserved, especially in the case of fruits or cones. Considering the state of preservation, leaf remains usually lacking cuticles were identified based only on their macromorphology. The studied fossil material (almost 600 rock samples) are housed in the W. Szafer Institute of Botany, Polish Academy of Sciences, Kraków (KRAM-P 128/1–595). The studied fossil material from Rębiszów is probably the only such material obtained from the Łysa Góra (Urwista) locality. To our knowledge, no more material can be collected from the locality discovered by Stanisław Dyjor because the fossiliferous layer is no longer accessible.

Two samples from the sediments containing plant macroremains were used for the palynological study. They were prepared in the laboratory of the W. Szafer Institute of Botany PAS, using HCl, KOH, and HF (Moore et al. 1991). Ten slides were studied and in each sample more than 1000 sporomorphs (pollen grains and spores), as well as all co-occurring non-pollen palynomorphs, were counted.

Results

Plant macroremains assemblage.—We recognised 43 taxa among the plant macroremains from Rębiszów, but 36 are illustrated in this paper (Figs. 2–8, Table 1). Most numerous are angiosperm remains, but gymnosperms also represent a significant group. In respect of the systematic diversity the flowering plants also prevail and are represented by 19 families, including Aceraceae (Figs. 3D, 4F), Berberidaceae (Fig. 4G, K), Betulaceae (Figs. 3A, F, 4I, 5A, 7B), Corna­ceae, Elaeocarpaceae (Fig. 6E), Ericaceae, Fagaceae (Fig. 6A–C, F–H), Lauraceae (Fig. 4A–E), ?Leguminosae (Fig. 4J), ?Meliaceae (Fig. 7A, E), Magnoliaceae (Fig. 3C), Rhamnaceae (Fig. 5B), Rosaceae (Figs. 7D, 8B), Sali­caceae (Fig. 6D), Tilioideae (Fig. 3E), Ulmaceae (Fig. 3B), and Vitaceae (Fig. 5E, G). Conifers are represented by Cup­res­saceae: Calocedrus suleticensis (Brabenec, 1909) Kvaček, 1999 (Fig. 2A), Cunninghamia cf. miocenica Ettingshausen, 1872 (Fig. 2C), Cryptomeria cf. rhenana Kilpper, 1968 (Fig. 2D1, D2) and Pinaceae: Tsuga cf. moenana Kirchheimer, 1935 (Fig. 4H) and Tsuga sp. (Fig. 2B).

The plant assemblage is dominated by entire-margined leaves, which significantly overweigh toothed leaves, representing ca. 80% of the whole leaf assemblage. Among those, the most common species is Majanthemophyllum basinerve (Rossmässler, 1840) Knobloch and Kvaček, 1996 (ca. 46% of all leaves), which is a taxon of uncertain affinity. Representatives of Lauraceae (ca. 22% of all leaves) and Fagaceae (ca. 11% of all leaves) are less abundant in the Rębiszów flora. Among Lauraceae, the most common is Daphnogene cinnamomifolia (Brongniart, 1822) Unger, 1851 (ca. 96%), but the form D. lanceolata sensu Kvaček and Walther (1995) prevails over the form D. cinnamomifolia. Fagaceae are represented by Eotrigonobalanus furcinervis (Rossmässler, 1840) Walther and Kvaček, 1989, Trigono­bala­no­psis exacantha (Mai, 1970) Kvaček and Walther, 1988, cf. Trigonobalanopsis rhamnoides (Rossmaessler, 1840) Walther and Kvaček, 1988, cf. “Quercus” bavarica Kno­bloch and Kvaček, 2004, and Quer­cus sp. or Casta­nopsis sp.

The most common among toothed leaves are Alnus cf. gaudinii (Heer, 1856) Knobloch and Kvaček, 1976 and Alnus sp. (ca. 65%). Aside from leaf remains, Alnus Miller, 1754 is also represented by infructescence of A. kefersteinii (Goeppert, 1838) Unger, 1845. A very common element of the Rębiszów assemblage are fruits of Liriodendron haueri Ettingshausen, 1869 (more than 53 specimens). Characteristic but less common is Craigia bronnii (Unger, 1845) Kvaček, Bůžek, and Manchester, 1991 (ca. 11 specimens). Elements such as Ulmus sp., Ostrya atlantidis Unger, 1850, Mahonia sp., Dombeyopsis lobata Unger, 1850, Acer sp., Carpinus sp. vel Ostrya sp., Sloanea artocarpites (Ettingshausen, 1869) Kvaček and Hably, 2001, Populus cf. zaddachii Heer, 1859, cf. Rosa lignitum Heer, 1869, cf. Leguminosites sp. (or cf. Rhodomyrtophyllum sp.), and Vitis sp. or Ampelopsis sp. (arranged according to the number of specimens, see also Table 1) are sparse.

Palynoflora.—Palynological analysis revealed rich and well-preserved palynoflora. A total of 88 fossil-species were identified, including 19 species of spores, 15 species of pollen grains of gymnosperms, and 54 species of angiosperms. Palaeotropical and palaeotropical/warm-temperate elements dominate the spore-pollen spectra (Table 2).

Among gymnosperms, the most common are pollen grains of Cupressaceae (fossil-genera Inaperturopollenites Pflug and Thomson, 1953 and Sequoiapollenites Thiergart, 1958), Tsuga (Endlicher) Carrière, 1855 (mainly fossil-­species Zonalapollenites verrucatus Krutzsch, 1971) and bisaccate Pinaceae. Angiosperms are dominated by pollen grains of Fagaceae, including small tricolporate grains: Cupuli­feroipollenites oviformis (Potonié, 1934) Potonié, 1951, C. pusillus (Potonié, 1934) Potonié, 1951, Fusus­polle­nites fusus (Potonié, 1931) Kedves, 1978), Tricolporo­polle­nites villensis (Thomson, 1950) Thomson and Pflug, 1953, T. dolium (Potonié, 1931) Thomson and Pflug, 1953, Quer­coidites microhenricii (Potonié, 1931) Potonié, Thom­son, and Thiergart, 1950, Q. henricii (Potonié, 1931) Potonié, Thomson, and Thiergart, 1950, and a few specimens of Fagus­pollenites Raatz, 1937. The pollen of Betulaceae: mainly Alnipollenites verus (Potonié, 1931) Potonié, 1931 and Carpinipites carpinoides (Pflug, 1953) Nagy, 1985); Cyrillaceae/Clethraceae: mainly Cyrillaceaepollenites exactus (Potonié, 1931) Potonié, 1960); Fabaceae: Tricolporopolle­nites fallax (Potonié, 1934) Krutzsch, 1960, T. liblarensis (Thomson, 1950) Hochuli, 1978, and T. quisqualis (Potonié, 1934) Krutzsch, 1954); Hamamelidaceae: Tricolporopollenites staresedloensis Krutzsch and Pacltová, 1969); Juglandaceae; Mastixiaceae: Cornaceaepollis satzveyensis (Pflug, 1953) Ziembińska-Tworzydło, 1994; Sapotaceae and Vitaceae are also common. In addition, pollen grains of the families Aquifoliaceae: Ilexpollenites margaritatus (Potonié, 1931) Thiergart, 1938; Ericaceae; Meliaceae; Nyssaceae: Nyssapollenites contor­tus (Pflug and Thomson, 1953) Nagy, 1985; Oleaceae; Sali­caceae; Tilioideae: mainly Intratriporopollenites insculptus Mai, 1961; Sapindaceae: Aceripollenites Nagy, 1969; Ulma­ceae, and others are present.

Cryptogams are represented mainly by ferns from the families Lygodiaceae, Osmundaceae, Pteridaceae, Schi­zae­aceae, and others, plus a few spores of Lycopodiaceae and Selaginellaceae. Among non-pollen palynomorphs, fresh­water algae (Botryococcus Kützing, 1849 and zygospores of Zygnemataceae) are present. Spores of fungi are almost absent. In addition, some leaf-spines of plants with submerged leaves (Alismataceae, Hydrocharitaceae vel Ceratophyllum Linnaeus, 1754) and probably a fragment of a microsporangium of Salvinia Séguier, 1754, were encountered.

Discussion

Taphonomy and vegetation reconstruction.—In view of the lithology of the fossiliferous layer and preservation of the plant remains, as well as composition of the plant assemblage, we can interprete the sedimentary environment as calm, and most probably related to a small water body (maar lake?). This is confirmed by the presence of Botryococcus algae and zygospores of Zygnemataceae (Spirogyra Link, 1820, and Mougeotia Agardh, 1824). Extant representatives of Zygnemataceae occur in shallow, stagnant waters, which warm up easily, and these algae produce resting cells (e.g., zygospores) that enable them to survive through unfavourable growth conditions, e.g., desiccation (Worobiec 2014 and literature cited therein). The presence of leaf-spines of plants with submerged leaves also points to the occurrence of submerged (entirely under water) aquatic plants, such as Hydrocharitaceae or Ceratophyllum commonly found in ponds, marshes, and quiet streams. Remains of the water fern Salvinia are another example of floating aquatics growing in standing waters.

Well-preserved leaves and sparse flowers suggest that the plant remains were carried by wind and water only over a short distance and originated from vegetation surrounding the basin (see e.g., Ferguson 1985).

Based on the floristic composition of the Rębiszów fossil assemblage we can distinguish three types of vegetation. The vast majority of the fossil remains represents plants of the mesophytic forest around the sedimentary basin. The angiosperm elements of this vegetation are as follows (arranged according to frequency): Majanthemophyllum basinerve (Rossmässler, 1840) Knobloch and Kvaček, 1996, Daphnogene cinnamomifolia (Brongniart, 1822) Unger, 1851, Liriodendron haueri Ettingshausen, 1869; Fagaceae (Trigonobalanopsis cf. “Quercus” bavarica), Craigia bron­nii (Unger, 1845) Kvaček, Bůžek, and Manchester, 1991, Sloanea artocarpites (Ettingshausen, 1869) Kvaček and Hably, 2001, Ostrya sp., Acer sp. div, Mahonia sp., cf. Lau­ro­phyllum acutimontanum Mai, 1963, cf. Leguminosites sp. or cf. Rhodomyrtophyllum sp., and cf. Rosa lignitum Heer, 1869. Conifers, especially Calocedrus Kurz, 1873, but also Cunninghamia Brown, 1826, Cryptomeria Don, 1838, and Tsuga (Endlicher, 1847) Carrière, 1855, were also important components of the Oligocene vegetation of Rębiszów. The tree layer of that mesophytic forest can probably be subdivided into the upper (canopy) and lower tree layer (understory). Based on their modern habits, we can infer that the upper canopy was composed of Cunninghamia, Crypto­meria, Liriodendron Linnaeus, 1753, Fagaceae, and Sloanea Linnaeus, 1753, whereas in the understory, trees and shrubs such as Calocedrus, Daphnogene Unger, 1850, Craigia Smith and Evans, 1921, Ostrya Scopoli, 1760, Acer Linnaeus, 1753, Laurophyllum Goeppert, 1853, Maho­nia Nuttall, 1818, and probably Rosa Linnaeus, 1753 may have occurred. Lianas are modestly represented by a single leaf of Vitis Linnaeus, 1753 or Ampelopsis Michaux, 1803 and one seed impression of Ampelopsis cf. rotundata Chandler, 1925. Some authors suggest that Majanthemo­phyllum Weber, 1852, which is a dominant element in the Rębiszów fossil assemblage, could be a climber (Walther 1999), but this assumption lacks conclusive evidence. Paly­no­logical analysis supports the results obtained from the investigations of plant macroremains. Many fossil taxa from the spore-pollen assemblage have their counterparts in macroremains. In addition, based on the palynoflora, several elements could be added or some details could be provided. For example, we could add to the list of taxa: Fagus Linnaeus, 1753, Mastixiaceae, and Sapotaceae. Fossil macroremains of the herbaceous layer have not been found. Similarly, palynological analysis shows almost exclusively pollen of trees and shrubs. On the other hand, various spores of cryptogams, including ferns and lycopods, have been recorded. These cryptogams could be elements of the forests’ herbaceous layer, or it is probable that they grew on the lake margin.

Riparian taxa were probably confined on the shore of the water body and were not so abundant. The main component among the riparian taxa was probably Alnus Miller, 1754, presumably accompanied by Craigia, Ulmus Linnaeus, 1753, Acer, Populus Linnaeus, 1753, and Vitis vel Ampelopsis. Palynological analysis also revealed the presence of Carya Nuttall, 1818, Fraxinus Linnaeus, 1753, Pterocarya Kunth, 1824, and Salix Linnaeus, 1753. Presumably, also Daphno­gene cinnamomifolia may have played a part, as it was suggested that it might tolerate riparian conditions (Kvaček and Walther 1998). On the other hand, according to Mai and Walther (1991) Populus zaddachii Heer, 1859 might be a component of a mesophytic forest as well. Species typical for swamp communities were not found among the macroremains from Rębiszów. However, as in both palynological samples taken from Rębiszów, pollen grains of Taxodium/Glyptostrobus type prevail, and we could not exclude the presence of swamp communities in the vicinity. The absence of swamp plant macroremains in this fossil assemblage reflect the absence or scarcity of temporarily inundated areas around the basin. Besides, this could also be related with the fact that volcanic floras typically represent the mesophytic climax vegetation (Walther 2005; Akhmetiev et al. 2009). Thus, the results of palynological analysis increased our knowledge on the diversity of plant communities occurring in the Rębiszów area during the Oligocene.

Moreover, the experience derived from the autecology of modern relatives of fossil plants shows that many extant species thrive in a relatively wide range of habitats (Reed 1988). Therefore, we believe that the majority of those species found in Rębiszów were not confined to one particular vegetation type (compare Worobiec and Szynkiewicz 2016), but we could contend that, generally, it was of mixed mesophytic forest type.

Palaeoclimate.—The composition of the assemblage of plant macroremains from Rębiszów, especially the presence of representatives of genera Calocedrus Kurz, 1873, Craigia Smith and Evans, 1921, Cunninghamia R. Brown, 1826, Daphnogene Unger, 1850, Laurophyllum Goeppert, 1853, Sloanea Linnaeus, 1753, and Trigonobalanopsis Kva­ček and Walther, 1988 points to subtropical (sensu Belda et al. 2014) climatic conditions in this part of the Oligocene in Lower Silesia. Recent counterparts of Rębiszów vegetation could be found in the Mixed Mesophytic Forests of China (Wang 1961).

Composition of spore-pollen spectra (domination of pa­laeo­tropical and palaeotropical/warm-temperate elements) also points to warm, subtropical climatic conditions.

Comparison between the Rębiszów flora and Central Euro­pean Oligocene floras and age evaluation.—Taxo­no­mic composition clearly links the Rębiszów flora with the late Paleogene, so-called volcanic floras from the neighboring regions of the Czech Republic and SE Germany (Kvaček and Walther 2001, 2004; Walther 2005; Akhmetiev et al. 2009). With only 43 taxa, it is relatively poorly diversified in relation to other coeval fossil floras. Comparing the composition of the Rębiszów flora and some Oligocene floras from Kundratice, Seifhennersdorf, Markvartice, Suletice-Ber­and, and Kleinsaubernitz, several common elements can be indicated: Daphnogene cinnamomifolia forma lanceolata Kvaček and Walther, 1995, D. cinna­momi­folia forma cinnamomifolia Kvaček and Walther, 1995, Laurophyllum acutimontanum Mai, 1963, Craigia bronnii (Unger, 1845) Kva­ček, Bůžek, and Manchester, 1991, Sloanea artocarpites (Ettingshausen, 1869) Kvaček and Hably, 2001 (Kvaček and Walther 2001). Also, Rosa lignitum Heer, 1869, Populus zaddachii Heer, 1859, and Liriodendron haueri Ettings­hausen, 1869 quite often occur in those floras. However, Mahonia Nuttall, 1818 is relatively sparse and has been documented only in some sites, including early Oligocene of Bechlejovice (Kvaček and Walther 2004) and late Oligocene of Suletice-Berand (Kvaček and Walther 1995). One of the characteristic features of the Rębiszów flora is an abundance of Calocedrus suleticensis (Brabenec, 1909) Kvaček, 1999, which has been reported so far only from the late Oligocene of Matrý, near Sebuzín (Kvaček et al. 2018) and the early Oligocene of Holý Kluk (Radoń et al. 2006) both Czechia, the early Miocene of Kymi, Greece (Kvaček 1999), the early Oligocene of Eger-Kiseged, Hungary (Kvaček and Hably 1998), and the late Oligocene of Suletice-Berand (Kvaček and Walther 1995). The occurrence of C. suleticensis is rather important. According to Kvaček and Walther (1998, 2001), it starts to appear in early/late Oligocene floras of the Nerchau-Flörsheim floristic complex. The domination of Majanthemophyllum basinerve (Rossmässler, 1840) Knobloch and Kvaček, 1996 in Rębiszów is unique in comparison to other Oligocene volcanic floras. Majanthemo­phyllum basinerve is only sparsely reported from Europe, it is known from the late Eocene (Staré Sedlo; Knobloch et al. 1996), and can provide only a little help in determining the age of the Rębiszów flora.

Considering the comparison mentioned above, the Rębiszów flora shows the closest relations only with some Oligocene floras. The high proportion of the laurophyllous element, and especially the presence of Calocedrus suleticensis, links the Rębiszów flora with early/late Oligocene floras of the Nerchau-Flörsheim floristic complex (especially Suletice) (Bůžek et al. 1976; Kvaček and Walther 1995, 1998, 2001). On the other hand, Majanthemophyllum basinerve has not been reported in floras of the Nerchau-Flörsheim floristic complex.

The composition of the Rębiszów palynoflora also clearly points to its Oligocene age. Crucial for the stratigraphic position of the studied flora is the presence of indicative taxa, such as Boehlensipollis hohli Krutzsch, 1962 (recorded in our samples and in the previous unpublished results by Kohlman-Adamska and Ziembińska-Tworzydło) and Cupa­nieidites eucalyptoides Krutzsch, 1962 (unpublished results reported by Kohlman-Adamska and Ziembińska-Tworzydło, announced here with permission of the authors). The ranges of these taxa are confined to the Rupelian–Eochattian (Krutzsch et al. 1992) or the Rupelian–early Chattian (Gra­bowska and Słodkowska 2003). The Rupelian has relatively rich palynological documentation due to the presence of lignites of the 5th Czempiń group of seams in the Polish Lowlands (Słodkowska 2004; Kasiński and Słodkowska 2016). In contrast, the Chattian palynofloras are very rare (Grabowska and Piwocki 1975). The Rębiszów spore-pollen assemblage is generally similar to the palynofloras from the 5th Czempiń seam (Kasiński and Słodkowska 2016). Nevertheless, the lack of some “older” taxa (for example Aglaoreidia cyclops Erdtman, 1960, and Cicatricosisporites dorogensis Potonié and Gelletich, 1933), and the presence of some “new” elements (for example Faguspollenites Raatz, 1937) rather point to the early Chattian age of the Rębiszów assemblage.

The Rębiszów flora is the first volcanic flora found in Poland and second Oligocene macroflora known from Poland. The Oligocene macroremain assemblage found in the marine Jasło limestone at Sobniów, southern Poland, consists of only 36 specimens of plant macroremains, including a few leaves (or leaflets) of dicotyledons (?Palaeo­carya sp., Laurophyllum princeps (Heer, 1856) Krausel and Weyland, 1951, Theaceae, and Leguminosae (“Leguminosentypus”) type sensu Berger (1955), monocotyledons, and predominat marine algae remains (Zastawniak and Worobiec 1997). The assemblage from Sobniów (marine deep water limestone deposits), however, represents a sedimentary environment completely different to the Rębiszów flora (shallow, freshwater lake). The Rębiszów flora is definitely richer, better preserved and accompanied by rich palynoflora. The fact that the fossil assemblage from Rębiszów represents the easternmost locality among the known Oligocene volcanic floras of Central Europe makes this site unique and of great value, and complements our knowledge of the Oligocene floras of this part of Europe.

Conclusions

The fossil plant assemblage form Rębiszów is the second Oligocene macroflora known from Poland. The Oligocene age of the deposits from this site is confirmed by the radiometrically dated basalts covering fossiliferous layers (ca. 25 Ma) and the presence of pollen Boehlensipollis hohli that constrains the possible age to the Rupelian–Chattian. The lithology, preservation of the plant remains, and the composition of the plant assemblage suggest that the sedimentary environment was calm, and most probably took place in a small and shallow, arguably maar lake. Based on the floristic composition three types of vegetation could be deduced from the Rębiszów flora. Most of the fossil remains represent plants of the mesophytic forest surrounding the sedimentary basin. Riparian vegetation was probably confined to the lake shore. Species typical for swamp communities were not found among macroremains. However, in palynological samples pollen grains of Taxodium/Glyptostrobus were found, suggesting the presence of swamp communities probably in a distant neighborhood. The composition of the assemblage of plant macroremains and spore-pollen spectra point to subtropical climatic conditions. Recent counterparts of Rębiszów vegetation could be found in Mixed Mesophytic Forests of China.

In light of the sedimentary environment and floristic composition, it is clear that the Rębiszów flora corresponds to so-called volcanic floras of the early/late Oligocene. Among them, it is closest to floras of the Nerchau-Flör­sheim or Kleinsaubernitz floristic complex. When considering the lithology, preservation and floristic composition, Rębiszów shows a close similarity to the early/late Oligocene fossil plant locality, Suletice-Berand (Kvaček and Walther 1995). The Rębiszów flora is the first volcanic flora found in Poland. A conclusive explanation of the position of the basalts in relation to the fossiliferous layers, sedimentary environment of deposits and detailed analysis of the palaeoclimate requires further studies of the Rębiszów floras. Considering the state of preservation of the plant remains and sedimentary environment of the newly found sites described and noted here, they may be productive for additional discoveries of well-preserved plant and animal fossils.

Acknowledgements

We thank Paweł Raczyński (University of Wrocław, Poland) who helped to arrange and participated in a first excursion to “Stary Łom” quarry in May, 2019. We also thank Izabela Sawicka (Pri Bazalt S.A. quarry manager, Rębiszów, Poland) for granting admission and friendly reception during our fieldwork. Special thanks are due to Steven Manchester (Florida Museum of Natural History, Gainesville, USA) and Torsten Utescher (University of Bonn, Bonn, Germany) for their helpful comments to the manuscript. This work was supported by the W. Szafer Institute of Botany, Polish Academy of Sciences, Kraków, Poland through the statutory funds (GW, EW).

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Acta Palaeontol. Pol. 65 (2): 273–290, 2020

https://doi.org/10.4202/app.00686.2019