Two charophytes-Platychara perlala (Peck & Reker) Grambast and Nemegtichara grambosti sp. nov- are described and illustrated from the Deccan Intertrappean beds near Rangapur, district Rangareddi, Andhra Pradesh. The genus Nemegtichara Karczewska & Ziembinska-Tworzydlo, first described from the Palaeogene "White Beds" of the Nemegt Basin in Mongolia and also known from the Cretaceous- Middle Eocene of China is being recorded for the first time from India. The age and palaeobiogeographic implications of the assemblage are also discussed.
The late Palaeocene carbon isotope excursion (C.I.E.) is often regarded as the best means of correlating marine and continental deposits. The few isotopic studies carried out in continental environments were based on pedogenic carbonate [Koch et al., 1992], or on organic matter. Sinha [1997] took up this subject starting from the outcrops on the coast of the English Channel at Varangeville, where marine sequences biostratigraphically constrain the isotopic excursion. His work documents a negative delta 13 C org excursion value approximately -27 per mil PDB. The present work points out that it is necessary to study more complete sections than those studied by Sinha. A section named Phare d'Ailly has been sampled in detail (figs. 1, 2, 3). In this section, for which detailed analysis of sedimentology, palaeontology and organic matter facies establish the continental nature of the palaeoenvironment, isotopic analysis of organic matter reveals a very negative delta 13 C org excursion value approximately -30 per mil PDB. The P/E interval synthesized in figure 2 shows three main groups, the stratigraphy of which is strongly constrained between the calcareous nannofossil Zones NP8 and NP11. The marine Thanetian facies belong to Zones NP8 and NP9. Above, the "Sparnacian" (Mont Bernon Group) is divided into 5 units referred to as SP. Unit SP2 is attributed to the Peckichara disermas Charozone, equivalent to Zone NP9. For unit SP4, an indirect correlation with Zone NP10 may be deduced. The upper part of the Varangeville Formation is known for its nannofossil association attributed to Zone NP11. We may conclude from these observations that the sparnacian sediments are synchronous with NP9-10 Zones and that they are effectively located in the time interval of the delta 13 C excursion. The SP1 and SP2 sediments were analysed for carbonate content, grain size distribution, clay mineralogy and total organic content (T.O.C.), using standard laboratory methods (fig. 3). An optical specification of the organic matter has been obtained from semiquantitative analysis of the organic matter facies. The survey of macro- and microfossils has supplied complementary supports for isotopic analysis (seed, wood and charcoal). The isotopic measurements were carried out on the bulk sediment and on complementary supports with a mass spectrometer in continuous flow delta + (Finnigan Mat). The measurement precision is better than 0.1 per mil and the reproducibility is about 0.15 per mil. Washing residues provide Gasteropoda, Bivalvia, Ostracoda, Characea, as well as fruits and seeds, microcodiums and otolith. All the palaeontological data illustrate a continental biota of a pure lacustrine environment, quiet and shallow, in a hot and humid climate. The organic matter facies analysis confirms the absence of any marine influence and documents a palaeoenvironment of lakes and ponds having an anoxic floor. Thus the carbon of the organic matter is considered to be continental and their isotopic variations linked to those of the atmospheric carbon.
In this study, we test the potentiality of using dasycladales and charophytes, calcareous shallow-marine and non-marine algae respectively as palaeoclimatic recorders. These algae mineralize their carbonate during short periods in summer. Throughout the Palaeogene, we compare the 18 O variation of these two taxa to identify a possible common factor influencing their isotopic composition, i.e. temperatures variations, from a local environmental signal. We sampled and isotopically analyzed eight species of charophytes and seven species of dasycladales from 23 formations ranging from the Palaeocene to the Oligocene series of the Paris Basin. By comparing the 18 O of these two groups living in different environment with that of shallow-marine mollusks from a previous study, we show that temperature variations are the main factor influencing their 18 O compositions and that local environmental effects does not screen the global thermal signal. Maximum annual palaeotemperatures are calculated from the 18 O of the dasycladales and indicate by comparison with the data from mollusks previously analyzed that dasycladales species used probably mineralized their carbonate in equilibrium with seawater. Dasycladales recorded the global climatic events already known for the Palaeogene, with high temperatures reached during the Early Eocene and Middle Eocene climatic optimums and relative cooling intervals during the Lutetian, the Priabonian and the Rupelian. Charophyte gyrogonites also recorded temperature variations in their 18 O compositions but reconstituting reliable temperature values in non-marine environments is not directly possible and requires constraining 18 O of local continental water using other proxies. These promising results show that carbonates mineralized from algae constitute a reliable support for palaeoclimatic information and should be more widely used in the fossil record.
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