|Development of palaeoenvironment and fossil ecosystems in the Oligocene volcanic area (Doupov Mts., Czech Republic)
Radek Mikuláš, Jaromír Ulrych, Eva Kadlecová, (?Oldřich Fejfar), Vladimír Cajz
Introduction (iniciální forma R. Mikuláš)
Previous work (iniciální forma R. Mikuláš)
Geologic settings of the south-eastern part of the Doupov Mts. (iniciální forma V Cajz)
3A Methods of investigation (NOVĚ)!
The Dětaň site
a. rocks underlying the volcanoclastic sequence (R. Mikuláš)
b. tuffs and tuffites (R. Mikuláš)
volcanoclastics with quartz admixture (V. Cajz)
volcanoclastics with biogenic admixture (R. Mikuláš)
5. Stratigraphy and dating (R. Mikuláš, J. Ulrych)
Geochemistry (J. Ulrych)
geochemical characteristic of the volcanic rocks (J. Ulrych)
alteration of the volcanic rocks (J. Ulrych)
vertebrate fauna (E. Kadlecová, ?O. Fejfar)
invertebrate fauna (E. Kadlecová, ?O. Fejfar)
flora (R. Mikuláš)
bioturbation and ichnolofossils (R. Mikuláš)
Environments, factors of ecologic stress and ecosystems (iniciální forma R. Mikuláš)
pre-volcanic development (iniciální forma R. Mikuláš)
subaerial environments on tuffitic substrates (iniciální forma R. Mikuláš)
fluviatile environments (iniciální forma R. Mikuláš)
pyroclastic flows (iniciální forma R. Mikuláš)
Discussion (iniciální forma R. Mikuláš)
Conclusions (iniciální forma R. Mikuláš)
Vladimír Cajz – GLÚ AV,
Vladislav Rapprich - ČGS
The studied site (fig. 01 – lokalizace – VláďaR?) is situated at the same SE margin of the Doupovské hory Mts. (DH). This mountain range represents one of large volcanic complexes developed inside the Ohře/Eger Gaben, i.e. the SW-NE trending tectono-volcanic zone which belongs to European Cenozoic Rift System (Dezes et al. 2004).
DH volcanic complex
The DH complex covers an area of approx. 30–40 km in diameter and maximum inferred present-day thickness of volcanic products reaches 500 m. As DH complex has been subjected to intensive post-Miocene erosion processes, the erosion preserved large amount of superficial products here. These ones much prevail over intrusives and necks. The volcanic feeders have not been detected in detail for the whole DH complex yet. Based on air-borne magnetometry, several areas with larger concentration of magmatic production were identified and greater number of vents is expected than the only central vent (Šalanský 2004). The time dispersal of DH volcanic activity (38–22 Ma) has been allocated using only several existing radiometric data, nevertheless it corresponds with the main volcanic episode of the Ohře/Eger Gaben (cit Ulrych?). There were described two basic and different stages of DH volcanic activity based on new survey using volcanologic criteria (Hradecký 1997):
1) The older volcanism of uppermost Eocene to lower Oligocene age is represented by Plinian to Strombolian activity. The Plinian eruptions produced air-fall tuffs and pyroclastic flows (ignimbrites), whereas the Stombolian ones produced fall-out tephra – the lava production was minimal. Both types of explosive activity constituted up to 100 m thick set of pyroclastic and epiclastic material. The most complete and thickest sequences of this older activity are preserved and exposed on E and SE foothills of DH. The Plinian vents are presumably concentrated in the central area where the main crater is supposed, and the Strombolian ones are scattered over larger area of recent DH complex. The pyroclastics were partly resedimented in probable lake environment at the distal areas – the oldest tuffs were mostly deposited as subaquatic fall-outs and very often reworked as epiclastics. This type of volcaniclastic material contains well investigated paleontological remnants (Fejfar 1987).
2) The younger volcanic sequence of upper Oligocene to lowermost Miocene age forms predominantly effusive complex. Only sometimes subordinate tuffs are developed, as results of Strombolian and Hawaiian eruptions. Basaltic lavas of prevailing olivine-free types cover the largest area of the complex. The lavas are often of vesicular structure and brecciated in terrestrial conditions (aa facies – Rapprich, 2003). A greater number of vents, spread over the present mountain range and not significantly centralized, produced the lavas. Several other smaller vents produced of Strombolian and Hawaiian pyroclastics.
The recognition of autoclastic breccias led into redefinition of former “tuffs” between lava flows and thus to reassessment of volcanic activity type. The existence of many vents of presumable lava production and more complex evolution of several more-less independent sources/vents with numerous adventive craters, diffused on a large territory, does not correspond with the idea of one central volcano. This is supported by magnetometric results. Similarly, recognition of pyroclastic flows, as well as existence of co-ignimbritic ash-falls exhibit quite different activity of the first stage. Moreover, the dynamics of the volcanic activity is documented by presence of lahar accumulations (Rubín 1983; Hradecký 1997). Therefore, the recent knowledge of DH volcanism dismisses the former idea of stratovolcano (Zartner 1938 and others) and shows much more complicated setting of the complex.
Volcanic products of Dětaň area
The volcanics at Dětaň site, the previous kaolin and bentonite pit, overlie the Upper Carboniferous continental sandstones and arcoses. Fig. 02 (detailní mapa) shows results of new detailed survey in close surroundings of studied site. Preserved volcanic products basically reflect both main stages of the DH complex – the lower volcaniclastics are overlain by tephritic lava(s). But the detailed study of the area surrounding the location brought new data resulting in more complicated volcanic evolution (see bellow).
At the top of the kaolinised arcoses, irregular lenses of white quartzose sandstones to quartzites up to 80 cm thick are developed. They can represent the remnant of pre-volcanic quarzite-crust or ignimbrite deposition-related quarzitization (analogy with Dlouhý vrch Hill in the České středohoří Mts. – Malý et al., in print). Mainly pyroclastic sequence of about 40 metres in thickness overlies the sedimentary material. As the profile through this sequence, given here, is taken not only from the studied site and is pasted together from drilling data (Váňa ed. 1997 and references therein), from several other small outcrops in the vicinity and also from unpublished documentation of Hradecký, it gives more complex view on volcanic activity of this area. The sequence consists of several lithologic/genetic different deposits (Fig. 03 – cdr profil) divided into eight sets (A-H). More than 90 individual layers of volcaniclastics (Mikuláš et al. 2002) were distinguished at the studied site. General inclination of volcaniclastic sequence (110/5) indicates volcanic center(s) situated WNW of this site, closer to DH central area, whereas the base of present lava flows(s), leniently/softly dipping to NW/WNW indicates opposite direction of lava movement.
The lowermost volcanogenic layer (set A) is not accessible anymore. According to older documentations this layer consists of about 3 m thick greyish-brown not bedded ash with charcoal debris and argilized lithics. This is the layer of famous vertebrate fossils of Dětaň (e.g.: Fejfar 1987). The rock is non-lithified to weakly consolidated and non-laminated.
First accesible rock type at the studied site is represented by up to 4 m thick layer of well bedded grey tuffs with abundant rock fragments of mostly densely vesiculated basalts or basaltic scorias (up to 1 cm) which contain small phlogopites (set B; corresponding to layers 1-12 of Mikuláš et al. 2002). The scorias show dark grey to reddish colours. Isolated clinopyroxene crystals of 2 mm in diameter are also present in the tuff.
On the southern slope of the Ostružinový vrch hill, S of the studied quarry, there is present reddish hyaloclastic breccia of basaltic lava (set C), thick up to 1m. This rock type is missing at the studied site but the layer No.13 yields signs of facial relationship to this breccia.
Intercalations of red fine-grained tuffs with rare phlogopite and grey medium-grained tuffs rich in phlogopite alternate periodically and form about 10 m thick succession (set D; corresponding to layers 14-36 of Mikuláš et al. 2002). Individual layers do not show internal bedding or lamination. The size of phlogopite crystals in grey tuffs reaches up to 3 mm. This succession is crowned with bank/layer of medium-grained compacted grey tuff rich in phlogopite (part Da; most probably layers 37-42).
Similar alternation of red fine-grained and grey medium-grained tuffs continues in higher part of the sequence with total thickness of about 7 m (set E; corresponding to layers 43-64 of Mikuláš et al. 2002). The red intercalations become scarcer upward in the outcrop.
The following set started with about 4 m thick sequence of grey ash layers which enclose scarce lithics, crystals of clinopyroxenes (2 cm in diameter) and fragments of calcified wood up to 5 cm (set F; corresponding to layers 65-72 of Mikuláš et al. 2002).
Similar set continues with 4 m thick sequence of alternating layers of yellowish-ginger fine-grained laminated fall-out tuffs, light-coloured lapilli tuffs with phlogopite and yellowish green argilized ashes (set G; corresponding to layers 73-83 of Mikuláš et al. 2002). Sometimes, positive grading inside individual layers can be detected.
The volcanic sequence exposed in the studied site is terminated with 5-6 m of coarse- and medium-grained tuffs (set H; corresponding to layer 84 and following upwards). These tuffs are yellow at the base, yellowish-green in the central part and violet in upper part. Lithics and phlogopites (up to 1 cm) are abundant at the basis of this deposit. Suggestion of positive grading is present. Similar pyroclastic flow deposit is exposed in former quarry at the Ostružinový vrch Hill (Vrbička quarry), underlying tephritic lava(s). This deposit contains one complete tree trunk (limonitized and several metres in length), which is oriented NE-SW (234° the root system).
Tephritic lava flows
The Vrbička quarry, currently used as a communal-waste depository, and also another quarry N of the site (now recultivated), used compact tephritic rock for crushed stone production. Two terrestrial lava flows separated by coarse-grained autoclastic breccia were present. The thickness of lower lava (I) exceeded 5 m. Upper lava flow consisted of basal breccia (J) 1-4 m thick and compact facies with thickness of approximately 6 m (K). Nowadays, only one lava flow can be detected near the studied site, best preserved at Vrbička quarry and its SW vicinity. It represents remnant of the lower flow. The upper one was completely quarried out. The lava is developed from aphyric to slightly porphyric type with clinopyroxenes up to 2 mm large, possibly due to cooling conditions. The jointing changes upward from irregular blocky one through horizontal platy one up to subvertical columns with average diameter of 30-40 cm. Axes of columns, somewhat diverged from vertical orientation, are visible on a hill (525 a.s.l.), SW from the quarry. It can represent possible edge of the former lava flow.
Interpretation of volcanic activity
At the beginning of volcanic activity, the shallow lake to water stream environment is expected, based on the character of kaolin-rich sands overlying the Upper Carboniferous continental arcoses and possibly originating from them by rewashing in pre-volcanic period. The initial production of pyroclastic material – not more accessible set A with mammal bones – is difficult to determine now. The scattered distribution of individual bones fits to flow deposition, either to pyroclastic- or to epiclastic- (lahar) one, as well. Presence of charcoal debris shows better the pyroclastic flow genesis. Thus, the Plinian explosion in faraway area and deposition of pyroclastic flow(s) into water environ is supposed. The bone and charcoal content of the pyroclastic flow implies the idea of its moving through then vegetation killing individuals living there. Local transition of pyroclastic flow into lahar due to wet environment may not be excluded.
The overlying set of pyro- and auto- to epiclastics was produced mainly as Strombolian fall-out tephra from relatively proximal vent(s). Only set C – hyaloclastic breccia and possibly layer No. 13 – is a result of lava production associated with Strombolian activity and its interaction with water saturated environs. The post-genetic redepositional process was frequent during this development. The entire Strombolian volcanism (B-E) was buried by Plinian ash and lapilli flow- and fall- pyroclastic set (F-H). At some places, several depositional units of pyroclastic flows can be distinguished. In this case, thickness of individual depositional units varies around 15-20 cm (F). These units used to be accompanied by co-ignibritic ash falls, very fine-grained ash on the top of individual unit. The distance of Plinian centres can be documented by evolution of very thin units of individual pyroclastic flows and also by a layer of only ash-fall deposition (G). The overlying pyroclastic flows (H) are slightly different in lithology but their thickness is similar. Only the last pyroclastic flow (uppermost one of H) reaches thickness over 1 m and contains less mechanically destroyed wood. It can result either from much larger explosion, or from more proximal centre. The latter possibility is supported by orientation of the tree trunk and also by the lithological change (H vs. F). This may imply potential re-location of Plinian activity centres. More distant explosive centre(s) decreased activity (F,G) and new centre(s) with increasing activity developed closer to the studied site (H). The last preserved volcanic event is represented by Strombolian to Hawaiian terrestrial lava production (I-K) from proximal centre, situated most probably at opposite side than all foregoing Plinian volcanism. Its location is not clear enough, but the nearest vent of Kružínský vrch Hill cannot be excluded. The comparison of feeders’ location of lower Strombolian tuffs and upper lavas needs more data.
There exist two geochronological data from the studied site. Fejfar (1987) introduced the K-Ar age (37.7 Ma) measured on altered dark (Fe-Mg) mica. The sample was taken most probably from Strombolian tuffs overlying the lowermost fossiliferous pyroclastic flow. The tefritic lava from Vrbička quarry (uppermost preserved volcanic event) was processed by the same method (Mikuláš et al. 2002) and resulted at 32.6 ± 1.5 Ma. The data of mineral and whole rock analysis are not comparable well and moreover, the mica determination may not be exact due to its alteration. Nevertheless, both data assign the Dětaň site products to the lower volcanic sequence of uppermost Eocene to lower Oligocene age.
Dezes P., Schmid S.M. and Ziegler P.A. (2004): Evolution of the European Cenozoic Rift System: interaction of the Alpine and Pyrenean orogens with their foreland lithosphere. – Tectonophysics, 389, 1-33.
Fejfar O. (1987): A Lower Oligocene mammalian fauna from Dětan and Dvérce (NW Bohemia, Czechoslovakia). – Münchner Geowiss. Abh., A, 10, 253-264.
Hradecký P. (1997): The Doupov Mountains. In Vrána S. and Štědrá V. (Eds.): Geological model of western Bohemia related to the KTB borehole in Germany. – Sbor. geol. Věd, Geol., 47, 125-127.
Malý K.D., Cajz V., Adamovič J. and Zachariáš J. (in print): Silicification of quartz arenites overlain by volcaniclastic deposits – an alternative to silcrete formation. – Geologica Carpathica
Mikuláš R., Fejfar O., Ulrych J., Žigová A., Kadlecová E. and Cajz V. (2002): A study of the locality Dětaň (Oligocene, Doupov Mts. volcanite complex, Czech Republic): collection of field data and starting points for interpretation. – Geolines, 15, 91-97.
Rapprich V. (2003): Succession of lava flows of Úhošť Hill in relation to the history of magma reservoir. – Geolines 16, 88-89.
Rubín J. (1983): A lahar at the Doupovské hory Mts. foothills? (in Czech). - Sbor. Čs. geograf. Spol., 88, 259-260.
Váňa T. ed. (1997): Final report – Active admixtures for concrete, Timex Zdice (in Czech). – MS Geofond, Praha. (FZ 6582)
Šalanský K. (2004): Neovolcanics of the Czech Republic and their geophysical manifestations. – Czech Geol. Survey Spec. Pap. 17.
Ulrych J ???
Zartner R.W. (1938): Geologie des Duppauer Gebirges – Nördlicher Hälfte. – Abh. Deutsch. Ges. Wiss. Künste Prag, Math.-Wiss. Abt., 2, 1-129.
5. Stratigraphy and dating
The Doupovské hory Complex (DHC) represents the largest preserved Cenozoic volcanic complex in the Bohemian Massif. The present-day volume of surficial volcanic products is about 123 km2, areal extent c. 594 km2 and inferred present-day maximum thickness of volcanic products of about 400–500 m (Zartner 1938) and 500 m (Shrbený 1995). Unimodal olivine-free to olivine-poor nephelinite – tephrite – trachybasalt (often strongly analcimized) volcanic rock series associated with the DHC. An adequate theralite – monzodiorite – essexite hypabysal association was uncovered in the central part of the Doupovské hory Mts. (Ulrych et al. 1999). The isotopic composition of 87Sr/86Sr (0.703394 – 0.70438) and 143Nd/144Nd (0.512740 – 0.512845) of the primitive mafic volcanic rock of the DHC correspond to that presented for the Cenozoic volcanics of the Bohemian Massif: 87Sr/86Sr (0.7032 – 0.7037) and 143Nd/144Nd (0.51278 – 0.51288) (Wilson et al. 1994, Vokurka 1999?). On the basis of trace element compositions (Shrbený 1982, Wilson et al. 1994) and isotopic compositions (for citation see above) for primitive mafic rocks from the DHC the source of magmas is a sublithospheric HIMU mantle plume.
Despite the large continuous volcanic area the radiogenic data of volcanic products are rare (Ulrych et al. 1999). Only K-Ar data of unaltered massive rocks (not of altered phlogopite phenocrysts from breccias!) can be supposed as relevant (Kopecký 1987, Ulrych et al. 2003, Mikuláš et al. 2003). A review of Cenozoic volcanism of the Bohemian Massif (Ulrych et al. 1999) reveals the range of 22 to 28 Ma. New data of Mikuláš et al. (2003) shift the volcanic history of the DHC to the age of 32.6 Ma and partly approximate it to the problematic age of 37.7 Ma measured on “unaltered phlogopite” phenocrysts from tuff of the “Basal Formation” (Fejfar 1987). The thickness of the “Basal Formation” is of about 150 m (Cílek 1965), 50 m or more (Kopecký 1991) and newly 70 m (Hradecký and Raprich 2002). Based on the new Mikuláš et al. (2003) K-Ar data the volcanic activity of the DHC lasted minimum in the range 33 to 22 Ma through the whole Oligocene (Rupelian to Chattian) to the lowermost Miocene (Aquitanian). It corresponds to the volcanic maximum of the Cenozoic volcanism of the Bohemian Massif (32 to 20 Ma – Ulrych et al. 1999) and the main phase (28–20 Ma) of the Central European Volcanic Province (Lippolt 1982). These results are in agreement with geological position (including boreholes data) of tuffs (Pětipsy Basin) and basaltic flows (Radonice – Vilémov area) in the eastern part of the Doupovské hory Mts. both underlying the paleontologicaly documented Miocene coal sediments (Zartner 1938). The same author, however, supposed that the main part of the volcanic products corresponding to the prevailing “Second Effusive Phase” is associated with the Miocene volcanic activities, however, the minor “First Explosive Phase” is of the Late Oligocene age.
The Dětaň locality discovered an undated basaltic tuff (and tuffite) volcanosedimentary profile overlain by tephrite flow in the near Vrbička locality (32.6 Ma – Mikuláš at al. 2003). However, the altered (?) glassy leucitite lava flow covering the volcanosedimentary sequence in the near locality Dvérce was dated as 25.1 Ma old (Kopecký 1987). The geological position in distal parts of the DHC and results of the K-Ar dating rank the Dětaň tuffs (and tuffites) to the “First Explosive Phase” of Zartner (1938) (uppermost Oligocene), newly volcanologically defined by Hradecký (1997) as the “Volcanic Period characteristic by the Plinian explosion”.
According to Kopecký (1963) the older “biotite-bearing tuffs” and “younger “pyroxene-bearing tuffs” can be distinguished in the tuffs of the “Basal Tuff Formation” of the eastern margin of the Doupovské hory Mts. Transition from the volcanic tuffs characterized by the OH-bearing phases to the “water-free” phases commonly reflects the lowering of the water content in the parental magma.
3A. METHODS OF INVESTIGATION
Geochemical study of a set of volcanic rock samples was performed in laboratories of the Institute of Rock Structure and Mechanics, AS CR, Praha (Analyst: J. Švec) by wet way. Additional trace-element determinations were performed in the Nuclear Physics Institute AS CR, Praha-Řež by Instrumental Neutron Activation Analysis (Analyst: Z. Řanda). The precision of INAA determinations varies around 5% as checked by a series of duplicate analyses and it is well comparable with data published by Řanda et al. (1970). Accuracy of the individual element determinations was tested against the rock standard B-1. Absorbed molecular water in secondary minerals of the rock samples was removed by heating of all samples to 105 oC for 4 hours before analysing.
6.1 Geochemical characteristic of the volcanic rocks
A set of ten characteristic samples of volcaniclastic rocks (tuffs) was taken from the Dětáň profile (see Fig. 2) together with additional sample of massive volcanic rocks (lava) from the near locality Dvérce. The choice of representative samples covers both different stratigraphical position and petrographical character of volcaniclastic materials. Sampling sites of volcaniclastic rocks are presented in Fig. 2?. The detailed geological and lithological information on all rock samples is presented in Table 1. Chemical analyses of the tuffs including trace element contents are given together with characteristic geochemical ratios in Table 2.
Tuffs of the Dětaň profile reveal broad range of composition in particular of SiO2 contents but uniform alkali contents. High H2O+ and H2O– and CO2 contents are characteristic of the all tuff samples. The rocks plotted in the TAS diagram (Fig. 4 – Le Maitre ed. 2002) show a linear SiO2 controlled trend from foidite to picritic basalt, basalt, basaltic andesite and andesite. Rock samples can be classified into three groups:
1. foidite (No. 32) – picrobasalt (No. 27) – basalt (No. 1, 3) group (Mg# 49–58) reveals prevalently volcanic composition with non-frequent clastic admixture, but characterized by the highest carbonate contents (CO2 = 8.1–10.7 wt%) and chemical index of alteration CIA (Nesbitt and Young 1982) (61–79).
2. basalt (Nos. 70, 79, 13) group (Mg# 42–62), reveals a transitional composition between the first and third groups; the lowest alkali contents are characteristic CIA (52–74).
3. volcanosedimentary rocks of “andesite” (Nos. 56, 53) to “basaltic andesite” (No. 83) composition (group) Mg# (46–50) reveal a volcanic composition substantial affected by clastic admixture of quartz and more rare feldspars CIA (68–70).
For discriminative geochemical characteristics and classification of altered volcaniclastic rocks are appropriate discrimination diagrams of Winchester and Floyd (1977) based on immobile elements as Ti, Zr and Y which are insensitive to processes of alteration (see Fig. 5).
The special chemical characteristic shows a black tuff sample No. MN sampled from a basin-like depression in upper part of the volcanosedimentary sequence. Dark colour of the tuff is caused by a cryptocrystalline manganese pigment with higher Ba and Fe contents (Fig. 6?). The content of organic matter is low (< 1 vol.%).
Irrespectively of the clastic admixture all samples ale substantially altered. Alkali contents (Na2O + K2O wt%) reveal a relatively narrow range (see Fig. 4 – data after recalculation of analyses on the water-free basis). The alkali content is commonly uniformly lowered by alteration of all samples. Only one sample of the studied tuffs (No. 1) plots into the field (including parts of foidite, basanite – tephrite, trachyandesite, picrobasalt and basalt fields in TAS diagram) of massive volcanics of the DHC (see Fig. 4 based on 111 chemical analyses of Shrbený 1998).
Values of Mg# in the whole set of tuffs varies unsubstantially (42–62) and their average value (52) corresponds to that of the overlying tephrite flow (51). The similar results follow from the study of the CIA chemical index of alteration sensu Nesbitt and Young (1982). Variation of the set reveals value of 52–79 and average value (67). Slightly altered tephrite reveals value of 38. The minimum values about 30 present Nesbitt and Young (1982) for fresh basalt in Guyana. The data and characteristic ratios on the tuffs presented in Table 2 reveal variations associated with the grade of alteration and admixture of clastic xenolithic materials: K/Rb (130–250), Rb/Sr (0.10–0.36), Th/U (1.4–5.5), Zr/Hf (26–55), REE (176–400 ppm), Eu/Eu* (0.58–0.60), La/Yb (20–35). Geochemical characteristic of the tephrite lava are practically identical with those of tuffs. Partly higher REE contents in altered samples of tuffs are associated with partly concentrating of REE (Th, U?) by sorption mechanism in clay minerals during the argillitization process, see altered clinopyroxenite sill Těšnov, Bohemia (Ulrych et al. 1996). The LaN/YbN values (20-35) are mostly uniform with substantial predominance of LREE characteristic for products of alkaline volcanism.
The geochemical characteristics are comparable with pyroclastic lavas of the Benue Trough, Nigeria (Amajor and Ofoegbu 1988) representing the initial phase of continental rifting.
The matrix of all tuff (and tuffites ?) samples is formed predominately by clay minerals. Results of the XRD analyses indicate differences in modal phase composition in different size-fractions:
– the 0.01 – 0.05 mm fraction is dominated by smectite (20–90 vol%, aver. 50 vol%) over illite (0–60 vol%), kaolinite (0–15 vol%) and rare chlorite, whereas
– the clay fraction (< 0.001 mm) is characterized by the more substantial domination of the smectite (30–100 vol%, aver 70 vol%) over illite (0–40 vol%) and kaolinite (0–10 vol%).
Quartz (5–20 vol% in 0.01–0.05 fraction and 0–30 vol% in < 0.001 mm fraction), carbonates (prevalently calcite), Fe-oxyhydroxides and cryptocrystalline Mn-oxyhydroxides occur in most samples. The clastic material is prevalently represented by anhedral to subrounded grains of quartz (up to 0.5 mm in size) and altered alkali feldspars and plagioclases (max. 5 vol% – illitized and kaolinized) from the basement “kaolinized” Carboniferous arkoses. Some volcanic particles reminding by shape probably to drops of volcanic glass are transformed to smectite, too. Conspicuous dark brown (small crystals) to more altered bronze-coloured in marginal parts (large crystals) originally phlogopite flakes (0.05 – 10 mm in size) form up to 15 vol%; in clay fraction up to 25 vol%. They occur selectively in some beds only.
The XRD study of original phlogopites reveals presence of a phlogopite-vermiculite-kaolinite mixed-layer structure (analyst K. Melka). As the transformation is associated with a substantial lowering of K2O content (4–6 wt% Analyst: A. Langrová) the “phlogopites” in tuffs and breccias are unwelcome to K-Ar dating. Similar transformed phlogopite phenocrysts described Melka et al. (2000) from the phlogopite-bearing tuff from Oleška near Doupov in the Doupovské hory Mts. They are strongly inhomogeneous. Individual flakes not only mutually differ, but also each flake is composed of several mineral phases like hydrobiotite, phlogopite, smectite, vermiculite and kaolinite. They continuously transit into each other.
The volcaniclastic rocks of the Doupovské hory Mts. were geochemically studied by Adamová (1998). Their chemical composition in Winchester and Floyd (1977) diagram corresponds to alkali basalt, basanite-nephelinite, tephrite, and to lesser extent trachybasalt, trachyandesite and trachyte (Adamová 1998). Ulrych et al. (2001) published geochemical data on Cenozoic tuffs from the České středohoří Mts. However, these volcaniclastics are substantially less altered in comparison to that from Dětaň and their chemical composition is very near to composition of an adequate lavas of the effusive formations (Cajz et al. 1999). They plot mostly into the fields of massive rocks of effusions of the České středohoří Mts. (cf. Fig. 4).
“Pyroclastic beds” in the Doupovské hory Mts. are prevalently montmorillonized (Zartner 1938, Cílek 1965, Fajfar and Kvaček 1993). Cílek (1965) stressed also the crystallization of aragonite associated with the lowering of temperature of solutions (200–30 oC) and rising of pH (> 7). He associated it with the last stadium of transformation of the tuff material tending to the generation of bentonite. All signs indicate a substantial hydrothermal transformation of pyroclastic (and massive) volcanic material of “pyroclastic beds”.
The primitive mantle-normalized multi-element variation diagram in Fig. 7 shows moderate enrichment in incompatible element for altered basaltic tuffs. The same characteristic follows from the chondrite C1-normalized REE patterns in Fig. 8. The patterns of tuffs and massive tephrite are very similar. The chemical characteristic of the tuffs and massive rock is similar to composition of tuffs and lavas from the České středohoří Mts. (Ulrych et al. 2001). The K and Sr negative peaks of the field of the Dětaň tuffs are similar to that of the field of the basanite rocks of the České středohoří Mts. (cf. Ulrych et al. 2001). Depletion of the volcanic products in K is probably associated with the presence of residual K-rich phase (phlogopite?) in the mantle source. The negative peak for Sr is more intensive in tuffs in comparison to massive tephrite. It is associated with transformation of andesitic plagioclases. The transported Sr was prevalently fixed in carbonates (cf. Cílek 1965).
The omnipresent Eu anomaly has a uniform value of 0.6 (tuffs and lava). It can be explained by development of cumulate rocks (with Ca-rich plagioclases?) preceding crystallization both tuffs and massive lavas. The similar Eu anomaly (0.85) was recognized in trachybazaltic rocks of the České středohoří Mts. (Ulrych et al. (2001), too.
6.2 Alteration of the volcanic rocks
The CIA index sensu Nesbitt and Young (1982) of the volcaniclastites from Dětaň ranges from 52 to 79. Foidites (Group 1) have prevalently the highest values and high CO2 contents. The lowest values correspond to the rocks of the Group 3 with clastic admixture of quartz. CIA of all samples (52–79) plots within the range of mild alteration processes sensu Nesbitt and Young (1982). The CIA data are comparable with those published by Ulrych et al. (2001) on tuffs from the České středohoří Mts. with the most characteristic range of 40–75. CIA value (38) of the slightly altered tephrite (No. X) from the lava flow is similar to an average CIA value (31) of slightly altered rocks of lava flows from the České středohoří Mts. (Ulrych et al. 2001).
Adamová M. 1998. Geology of the Doupovské hory Mts. region. Minerčalogy and geochemistry of volcaniclastic rocks. Manuscript, Archive of the Czech Geological Survey, Praha (in Czech).
Amajor L.C., Ofoegbu C.O. 1968. Intra-continental-plate alkaline basaltic volcanism, Uturu, Southern Benue Trough, Nigeria. Acta Universitatis Carolinae, Geologica 1968, 1: 233–242.
Cílek V. 1965. Bentonite deposits at the eastern foothil of the Doupovské hory Mts. Acta Universitatis Carolinae, Geologica 1965, 1: 203–226. (in Czech with German and Russian Summary).
Fejfar, Kvaček Z. 1993.
Hradecký P. 1997. The Doupov Mountains. In Geological Model of western Bohemia related to the KTB borehole in Germany, Vrána S., Štědrá V. (eds.). Sborník geologických Věd, Geologie 47: 125–127.
Hradecký P., Rapprich V. 2002. Doupovské hory Mts. – New geological data. Hibsch 2002 Symposium. Excursion Guide. Abstracts. Czech Geological Survey, Prague.
Kopecký L. 1963: Tertiary Volcanism 154–182. In Explanation to the Synoptical Geological Map Teplice M–33–XIV and Chabařovice M–33–VIII. Central Geological Survey in Publishing House of the Czechoslovak Academy of Sciences, Praha. (in Czech)
Kopecký L. 1991. Western Bohemia In Ulrych J., Kopecký L., Kropáček V. Guide to Post-Symposium Excursion: Neoidic Volcanism of the Bohemian Massif. Symposium on Central European Alkaline Volcanic Rocks, Praha 1991, Charles University, Praha, 58 pp. (in Czech).
Kopecký L. 1987. Young volcanism pf the Bohemian Massif (a structural-geological and volcanological study) I. Geologie a hydrometalurgie Uranu 11, 3: 30–67.
Le Maitre R.W. ed. 2002. Igneous Rocks. A Classification and Glossary of Terms. IUGS, Cambridge University Press, Cambridge.
Lippolt H.J. 1962. K/Ar age determinations and the correlation of Tertiary volcanic activity in central Europe. Geologisches Jahrbuch D 52: 113–135.
Melka K., Adamová M.. Haladová I. 2000. Mixed-layer crystal structures of the hydrobiotite type in tuffs of the Doupovské hory Mts. region. Scripta Facultatis Scientiarium Naturalium Universitatis Masarykianae Brunensis, Geology 28–29, 7–18.
Mikuláš R., Fejfar O., Ulrych J., Žigová A., Kadlecová E., Cajz V. 2003. A study of the Dětaň locality (Oligocene, Doupovské hory Mts. Volcanic Complex, Czech Republic): collection of field data and starting points for interpretation. Geolines 15, 61–101.
Nesbitt H.W., Young G.M. 1982. Early Proterozoic climates and plate motions inferred from a major element chemistry of lutites. Nature 299: 715–717.
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Shrbený O. 1982. Chemistry of alkaline volcanic rocks of the Doupovské hory Mts., Bohemia. Časopis pro Mineralogii a Geologii 27: 139–159.
Shrbený O. 1995. Chemical composition of young volcanites of the Czech Republic. Czech Geological Survey Special Papers 4: 1–54.
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Zartner W.R. 1938. Geologie des Duppauer Gebirges. I. Nördliche Hälfte. Abhandlungen der Deutschen Gesellschaft der Wissenschaft und Künste in Prag. Mathematisch-Naturwissenschftliche Abteilung, 2. Band, 129 pp.
Gastropoda: (in the secondary casts only) Patula (Anguispira) friči ?Klika
Patula densestriata Klika.
Strobilus elasmodonta Reuss.
Acme (Acicula) sp.
Fauna from the locality Dětaň
1. Fauna list from the research in 1987 year by Fejfar
Marsupialia: Amphiperatherium sp.
Insectivora:cf. Paratalpa sp.
cf. Neurogymnurus sp.
Rodentia: Suevosciurus ehingensis Dehm
Plesispermophilus cf. atavus Schmidt-Kittler & Vianey-Liaud
Bransatoglis cf. micio (Misonne)
Eomys cf. zitteli Schlosser
cf. Parasminthus sp.
Paracricetodon cf. dehmi Hrubesch
Eucricetodon cf. murinus (Schlosser)
Pseudocricetodon montalbanensis Thaler
Artiodactyla: Gelocus laubei Schlosser
Bachitherium cf. curtum Filhol
Lophiomeryx mouchelini Brunet & Sudre
Propalaeochoerus cf. paronae Piaz
Entelodon antiquum Repelin
Antracotherium cf. monsvialense Zigno
Elomeryx crispus Gervais
Perissodactyla: Ronzotherium cf. filholi Osborn
Carnivora: Cephalogale sp.
Pseudocyonopsis cf. antiquus Ginsburg
Deltatheridia: Hyaenodon sp.
Other vertebrates: Geochelone (giant turtle)
small forms of reptilian.
1. Fauna list from the research in 1999 - 2001 year by Mikuláš, Fejfar, Kadlecová, Zigová:
Bransatoglis cf. micio (Misonne)
Paracricetodon cf. dehmi Hrubesch
Eucricetodon cf. murinus (Schlosser)
Other vertebrates: amphibians
Nově nalezená fauna z Dětaně (Doupovské hory). I. Část: Gliridae and Cricetidae (Rodentia, Mammalia).
The new founded Fauna from the Dětaň locality (Doupovské hory Mts.). Part I: Gliridae and Cricetidae (Rodentia, Mammalia).
O. Fejfar (Př.F.UK, Albertov 6, Praha 2, 128 43)
E. Kadlecová (Geologický ústav AV ČR, Rozvojová 135, Praha 6 – Lysolaje, 165 02)
Výzkum byl hrazen z prostředků grantu GAČR 205/00/1000 - Multidisciplinary research of locality Dětaň in Tertiary of Doupov Mts. – an integration of palaeontology and pedology.
We found during year 2000 thin lenses with rich fossil content. From this new deposit small fossil mammals (Bransatoglis sp., Gliravus sp., Paracricetodon cf. dehmi Hrubesch and Eucricetodon cf. murinus (Schlosser), gastropods and amphibians fauna were determined. This fauna attests age of this locality to the Lower Oligocene (mammal biozone MP 21).
keywords: lower Oligocene, Gliridae, Cricitidae, Czech republic, taxonomy, stratigraphy, Dětaň,
The locality is situated in the closed large kaolin pit in southeastern margin of Doupovské hory Mts.
V letech 2000 - 2001 byl nově prováděn paleontologický výzkum na lokalitě Dětaň na jihovýchodním okraji stratovulkánu Doupovské hory. Již dříve zde byla nalezena a popsána fauna drobných a větších savců (Fejfar, 1987; Fejfar & Kvaček, 1993)na jejichž základě byla lokalita datována do spodního oligocénu (savčí biozóny MP 21).
Systematic part (Taxonomy)
Order: RODENTIA Bowdich, 1821
Superfamily: Gliroidea Thomas, 1897
The Dormice (Gliridae) are a monophyletic family that is represented by only eight genera and some fourteen – fifteen species in the extant fauna. The geograhical range of the fossil and extant species of Gliridae is limited to Europe, Asia and Africa. The oldest record is known from Europe: Eogliravus wildi Hartenberger, 1971, Mas de Gimel, France, MP 10, Early Eocene. The diversification of the Gliridae began in the Early Eocene, continued during the Oligocene and culminated in the Early Miocene of Europe. The classification of the Gliridae based on the morphology of the molars (cheek teeth). We continue to use Gliridae Thomas, 1897 instead of Myoxidae Gray, 1821 trusting that this will contribute to the stability of nomenclature. The subdivision of the Gliridae follows the classification of Daams & de Bruijn (1995).
Family: GLIRIDAE Thomas, 1897
Subfamily: Gliravinae Schaub, 1958
Genus: Gliravus Stehlin & Schaub, 1951 (= Glamys Vianey-Liaud, 1989)
Type species: Gliravus majori Stehlin & Schaub, 1951
Gliravus daamsi Bosma & de Bruijn, 1982
Subfamily: Bransatoglirinae Daams & de Bruijn, 1995
Genus: Bransatoglis Hugueney, 1967 (= Paraglis Baudelot, 1970 = Oligodyromys Bahlo, 1975)
Type species: Bransatoglis concavidens Hugueney, 1967
Bransatoglis bahloi Bosma & de Bruijn, 1982
Bransatoglis cf. micio (Misonne, 1957)
Superfamily: Muroidea (Illiger, 1811)
Family: CRICETIDAE Rochebrune, 1863
The Cricetidae are the most important elements of the fauna from Dětaň for biostratigraphy. They are recorded in the last and in the new microfauna too.
Subfamily: Paracricetodontinae Mein & Freudenthal, 1971
Tribe: Paracricetodontini Mein & Freudenthal, 1971
Genus: Paracricetodon Schaub, 1925
Type species: Paracricetodon
Paracricetodon cf. dehmi Hrubesch,
Tribe: Eucricetodontini Mein & Freudenthal, 1971
Genus: Eucricetodon Thaler, 1966
Type species: Eucricetodon
Eucricetodon cf. murinus (Schlosser, )
bIOSTRATIGRAPHY AND pALAEOECOLOGY ASPECTS
The biostratigraphical position of the finds from Dětaň is given by the occurence of the several genera of cricetids: Eucricetodon and Paracricetodon, they are represented in bouth faunas – from the lastand from the new, and Pseudocricetodon , which is occured only in the last fauna.
Bosma, A.A. & H. de Bruijn 1979-82. Eocene and Oligocene Gliridae (Rodentia, Mammalia) from the Isle of Wight, England. Part I. The Gliravus priscus - Gliravus fordi lineage, Part II. Gliravus minor n.sp., Gliravus daamsi n.sp., and Bransatoglis bahloi n.sp. [2 parts]. – Proc. Kon. Ned. Akad. Wet., Amsterdam, B, 82, 85, 367 - 384, 365 – 371. Amsterdam.
Fejfar, O., 1987 – A Lower Oligocene mammalian fauna from Dětaň and Dvérce NW Bohemia, Czechoslovakia. – Münchner Geowiss. Abh. (A), 10, 253 – 264, München.
Fejfar, O. & Kvaček Z., 1993 - Excursion Nr. 3. Tertiary basins in Northwest Bohemia. - Pal„ont. Ges., 63. Tagung Prag, 1-35, 20 Fig., Prag.
Hugueney, M., 1967 – Les Gliridés (Mammalia, Rodentia) de lˇOligocene´supérieur de Coderet – Branssat (Allier). – C. R. somm. Soc. Géol. France 3, 91 – 92.
Hugueney, M., 1969 – Les Rongeurs (Mammalia) de l´Oligocene supérieur de Coderet – Branssat (Allier). – Doc. Lab. Géol. , Lyon, 34, 1 – 227.
List of Tables
Table 1 Complete stratigraphic column….. with special respect to detailed analysed samples.
Table 2 Chemical analyses of volcanic rocks from Dětaň (1-79) and Vrbička (X).
List of Figures
Fig. 1 Geological sketch of the Doupovské hory Mts. and adjacent areas
Fig. 2 Complete section of volcaniclastic rocks….. Plate 1
Fig. 3 Special photos of…. Plate 2
Fig. 4 Volcanic rocks of the Dětaň locality in the TAS diagram (Le Maitre ed. 2002).
Fig. 5 Volcanic rocks of the Dětaň locality in the discrimination diagram of inchester and Floyd 1977).
Fig. 6 Energy dispersive spectrum of sample MN from Dětaň collected with the DX-4 system and Philips 9400.
Fig. 7 PM-normalized multi-element variation diagram for volcanic rocks from Dětaň. Tuff –field with vertical hatching, heavy line – tephrite flow.
Fig. 8 C1 chondrite-normalized REE pattern for volcanic rocks from Dětaň. Tuff –field with vertical hatching, heavy line – tephrite flow.