Fossil Charophytes Research Articles

The bulbils of Palaeonitella cranii (Charales, Charophyceae) revisited, with notes on other inflated cells of this alga that are not bulbils

Palaeonitella cranii is a charophyte alga (Charophyceae) from the Lower Devonian Rhynie chert of Scotland that consists of an axis of alternating internodes and nodes, with whorls of branchlets arising from the nodes. Conspicuous spherical to ovoid structures believed by most to be the bulbils of P. cranii are often found together with the axes and branchlets; however, they have so far only been insufficiently studied. Here, we revisit the bulbils, along with the rhizoids on which they were formed, based on new material from the Rhynie and Windyfield chert sites. The bulbils are up to 540 μm in diameter and occur singly or in groups on rhizoid nodes. A small node recognizable at the apical end in some specimens is evidence that the bulbils are modified branch rhizoids. There is also evidence of lower-order branch rhizoids extending from the apical node, as well as for sprouting. Palaeonitella cranii thrived in shallow pools and outflow channels of the Rhynie geothermal wetland. The bulbils might have enabled the plant to persist if photosynthesis was limited and to regenerate if the thallus was destroyed, but they might also have served as dispersal units. Other significantly inflated cells, which are not bulbils, may occur in both axes and branchlets of P. cranii, but are generally rare. Some of these cell alterations may be due to parasites. This study complements our understanding of P. cranii, the only fossil charophyte known from both above- and below-ground parts of the thallus, and from reproductive structures.

Charophytes from the Cretaceous–Palaeogene transition in the Jhilmili intertrappean beds of Central India

The Jhilmili intertrappean beds (Chhindwara District, Madhya Pradesh) of Central India are studied from a palaeoenvironmental, palaeoecological, and palaeobiogeographical perspective using fossil charophytes. These beds have yielded a diverse charophyte assemblage, consisting of Platychara perlata, Platychara raoi, Platychara sahnii, Peckichara cf. varians, Nemegtichara cf. grambasti, and Chara sp. 1. These charophytes were recovered from a 60 cm thick clayey and nodular limestone unit that is underlain by claystone and overlain by laminated claystones deposited on fluvial floodplains. This charophyte assemblage suggests a Late Cretaceous–Early Danian age, which agrees with the previous dating carried out using freshwater to brackish water ostracods and planktic foraminifera found in the same beds, together with dasycladalean and halimedacean chlorophytes. The Jhilmili intertrappean charophyte assemblage resembles those found in other infra‐and intertrappean sections of western, central, and southern India. The charophyte assemblage indicates that during the Cretaceous–Palaeogene timespan the Indian subcontinent mainly experienced interchange with Laurasia (China, Europe, and North America) but also with Gondwana (North Africa and South America). In the opposite sense, Laurasian species might have dispersed to India by means of a sweepstakes route across the Kohistan–Dras volcanic arcs.

Charophyte communities in Barremian Iberian wetlands

A combined micropalaeontological, taphonomical and sedimentological study was carried out in the non-marine Barremian of the Maestrat Basin (E Iberian Chain) to elucidate the palaeoecology of Barremian charophytes. Understanding the palaeoecology of fossil charophytes is of prime importance for the accurate application of charophyte biozonations, since most species used as biostratigraphic markers and/or biozone index species are restricted to facies formed in a particular environment. Five charophyte biocoenoses were distinguished. (1) Charophyte association from freshwater alkaline lakes receiving low clastic input, mainly composed of Atopochara trivolvis var. triquetra, Clavator harrisii, Ascidiella stellata, and A. triquetra. The thalli known as Munieria grambastii, corresponding to Clavator utricles, were extremely abundant in the shallowest facies of the lake margins, and Hemiclavator-rich populations were also locally dominant. (2) An association characteristic of freshwater alkaline lakes with high clastic input was mainly composed of Echinochara lazarii, Globator maillardii var. trochiliscoides, A. trivolvis var. triquetra, C. harrisii, Hemiclavator neimongolensis var. neimongolensis, and locally also Clavator calcitrapus. (3) Monospecific populations of Porochara maestratica thrived in brackish settings with little clastic influence, whereas (4) monospecific E. lazarii populations thrived in clastic-influenced brackish settings. (5) A charophyte association grew in lakes that developed in mudflat to floodplain environments and was mainly constituted by E. lazarii, A. trivolvis var. triquetra, and C. harrisii var. harrisii and var. reyi. Accordingly, the palaeoenvironmental conditions inferred indicate that most of the charophyte species were controlled by (i) bathymetry, (ii) clastic content in the sedimentary environment and (iii) salinity. The stratigraphic succession studied shows an upwards increase in clastic content from the base to the top, which is associated with the more humid period recorded along the margins of the Tethys and the Boreal realm during the early Barremian–early late Barremian. In consequence, those species restricted to clastic-poor settings are constrained to the lower part of the section, whereas those taxa that were able to thrive in clastic-rich settings persisted throughout the entire section. This observation establishes a link between the changes observed in the charophyte floras recognized and the environmental changes that occurred during the Barremian in western Europe.

New charophyte assemblage from middle Miocene lacustrine deposits of Moneva (Ebro Basin, Spain)

Two new fossil charophyte species from middle Miocene lacustrine deposits of Moneva (Ebro Basin, NE Spain) are described and illustrated. Sphaerochara miocenica nov. sp. is represented by medium sized gyrogonites with a characteristic spheroidal shape and ornamented with numerous small and regularly spaced tubercles arranged along the spiral cells. Several specimens show an unusual carbonate encrusted layer that covers completely or partially the gyrogonite. Psilochara monevaensis nov. sp. is characterized by large gyrogonites, with typical prolate shape and protruding apical poles. A second population of S. miocenica nov. sp. from a distant early upper Miocene lacustrine basin located in the Middle East (Bekaa Valley, Lebanon), identified in a previous study as Sphaerochara sp., is described and illustrated here, allowing the comparison of these distant populations. Ecologically, the associated fauna and facies from both localities suggest that these taxa grew in very shallow athalassic lakes. Interestingly, S. miocenica nov. sp. having a wide geographic distribution in peri-Mediterranean lakes with variable salinity, may become a fossil guide for the Miocene, providing at the same time important palaeoecological information.

Charophyte flora from the Miocene of Zahle (Beeka Valley, Lebanon). Biostratigraphic, palaeoenvironmental and palaeobiogeographical implications

Neogene lacustrine deposits in Zahle, western margin of the Bekaa Valley (Lebanon), are studied from a biostratigraphic and paleoenvironmental point of view using fossil charophytes. These sediments contain a well-preserved charophyte assemblage described and illustrated here for the first time including the taxa: Nitellopsis (Tectochara) merianiiGrambast & Soulié-Märsche, 1972, Lychnothamnus barbatus var. antiquusSoulié-Märsche, 1989, Chara aff. microceraGrambast & Paul, 1965 and Chara sp. Nitellopsis (T.) merianii has been reported in several European and Asiatic localities ranging in age from Late Eocene to Pliocene, L. barbatus var. antiquus has been found in several European Miocene localities in Europe and Turkey, while Chara aff. microcera has been documented from a large number of west European localities ranging in age from Early Oligocene to Early Miocene. Based on these data, we inferred that the basal part of the lacustrine deposits of Zahle is lower Miocene in age which is consistent with isotopic results obtained from basalts located northern, laterally and above the lacustrine sequence of Zahle. The palaeoenvironmental characteristics at the base of these deposits are inferred by comparing of the occurrence of N. (T.) merianii and L. barbatus var. antiquus with the ecological requirements of their nearest living relatives (Nitellopsis obtusa and Lychnothamnus barbatus). This suggests that the Bekaa Valley was occupied by a permanent, shallow oligotrophic freshwater lake during the Miocene. This study also provides valuable data about the palaeogeographic distribution of Neogene charophyte from Lebanon and the Middle East region.

A new charophyte flora from the Upper Triassic of Skåne (Sweden) and implications on biostratigraphy, taphonomy and the palaeoenvironment

The record of fossil charophytes from Sweden was previously restricted to the Ladinian-earliest Carnian Falsterbo Formation. Here, we present a charophyte assemblage from the Upper Triassic Kågeröd Formation exposed at the Bälteberga Gorge (Skåne, southern Sweden) from the perspectives of taxonomy, taphonomy, palaeoecology and biostratigraphy. The microfossils originate from an interval of reddish sandy mudstone and are represented by rare fossil thalli, calcium carbonate encrustations of thalli and numerous calcified fructifications, called gyrogonites. The assemblage is relatively diverse, comprising six species belonging to four genera of the family Porocharaceae (Auerbachichara cf. rhaetica, Porochara sp., Stellatochara germanica, Stellatochara aff. subsphaerica, Stenochara aff. donetziana, Stenochara aff. kisielevskyi). Both the sedimentological context and the preservation of the charophyte remains point to an autochthonous origin for the charophyte-bearing strata. An autochthonous origin together with the habitat of modern charophytes, infer that the charophyte interval was deposited in shallow ephemeral pond or lake in a terrestrial setting. Their occurrence is also indicative of low amount of nutrients and the numerous thalli encrustations suggest a rather alkaline water composition. Some of the described species (Auerbachichara cf. rhaetica and Stellatochara aff. subsphaerica) are useful for biostratigraphical correlations which attributes the assemblage to the Auerbachichara rhaetica Range zone (sensu Bilan, 1991) in the proposed Germanic Triassic charophyte zonation. This range zone is assigned to a latest Carnian to late Norian age, strengthened by an interlayering with rocks containing a characteristic assemblage of palynomorphs (Corollina meyeriana subzone a and b) in the Upper Triassic of the Polish part of the Germanic Basin. The findings of the first Triassic thalli further strengthen the suggestion that the early Mesozoic fossil record of charophytes is not solely composed of oospores and gyrogonites. A better understanding of vegetative fossil remains (silicified thalli and encrustations) of charophytes may provide important future palaeoecological implications and links between recent and extinct forms. Our findings also provide evidence that charophyte occurrences in the Kågeröd Formation are strictly controlled by palaeoenvironmental factors.

Charophyte flora from the Brian Head Formation, southwestern Utah, and its biostratigraphic implications

The age of Cenozoic non-marine rocks exposed in southwestern Utah is controversial because they generally have discontinuous exposures, marked lateral facies changes, post-depositional diagenetic alteration, and scarce fossils. A well-preserved fossil charophyte assemblage is described here from the variegated unit of the Paleogene Brian Head Formation, along the western margin of the Sevier Plateau (Casto Canyon quadrangle). The charophyte assemblage is composed of three species previously documented in the European and Asiatic continents: Sphaerochara aff. major Riveline 1986, Hornichara aff. lagenalis (Straub 1952) Huang and Xu 1978, and Harrisichara tuberculata Grambast 1958. The biostratigraphic ranges of these three species suggest a relative age of late Eocene (Priabonian)-early Oligocene (Rupelian) for the base of Brian Head Formation. These results are consistent with recent isotopic studies undertaken in the underlying conglomerate at Boat Mesa and the overlying volcaniclastic unit of the Brian Head Formation which are both late Eocene in age. Hence, in agreement with this isotopic data, the charophyte flora from the Brian Head is late Eocene in age. Moreover, this study provides valuable data about the paleogeographic distribution of biostratigraphic-key species of the European Paleogene that have been reported, for the first time, in North America.

Gyrogonites and oospores, complementary viewpoints to improve the study of the charophytes (Charales)

Charophytes (Charales) are multicellular algae growing in fresh- to hypersaline waters and recorded as fossils by their oospores (formed by resistant organic walls) and gyrogonites (formed by intracellular calcification of the spiral cells surrounding the oospore). Preservation of oospores is mostly restricted to Late Pleistocene–Holocene sediments, whereas calcareous gyrogonites provide the fossil record of charophytes since the Late Silurian (425 Ma) and constitute the only link between living and fossil charophytes. Oospores and gyrogonites represent successive developmental stages occurring after fertilisation of the oogonia; however, gyrogonites do not develop in the extant genera Nitella and Tolypella section Tolypella of Tribe Nitelleae, and in most species of the subgenus Charopsis. For Tribe Chareae and Sphaerochara (Tolypella section Rothia), gyrogonites display more useful characters than the oospores, allowing easy identification of the extant genera Nitellopsis, Lychnothamnus, Lamprothamnium, Sphaerochara and Chara subgenus Chara. Determination to species level, and in particular the study of plastic species, needs a statistical approach. Extant oospores/gyrogonites can be used as modern analogues to infer palaeohydrological conditions and record past biodiversity. The ecological requirements of the living species provide important information for the restoration/conservation of wetlands and their management, and contribute to the reconstruction of Quaternary palaeoenvironments. The aim of the present paper is to highlight the importance of the gyrogonite, especially when studying extant charophytes, the application of both gyrogonites and oospores to palaeoenvironmental reconstructions, and to provide an accurate terminology and determination criteria for their study.

Lower Cretaceous charophytes from the Serrania de Cuenca, Iberian chain: Taxonomy, biostratigraphy and palaeoecology

The assemblages of fossil charophyte fructifications from the La Huérguina Formation at the La Huérguina stratotype and the Las Hoyas section, along with some other samples from isolated outcrops are composed of Atopochara trivolvis var. triquetra, Globator maillardii var. trochiliscoides, Globator maillardii var. biutricularis var. nov., Clavator harrisii var. reyi, Ascidiella cruciata and Mesochara harrisii. Some reworked utricles of Ascidiella iberica var. iberica were also found. The in situ assemblage belongs to the Cruciata-Paucibracteatus Biozone, which is Late Barremian–Early Aptian in age. These results confirm that the entire deposition of the La Huérguina Formation took place within this biozone and not earlier, as previously thought. The top of the unit can be limited to the uppermost Barremian with biostratigraphic data from ostracods. Globator maillardii var. biutricularis var. nov. is defined as the end form for the Globator lineage according to present knowledge. It is characterised by its unique utricle morphology, showing a basal ring representing a second, external utricular layer. This layer shows a primitive structure, reminiscent of G. maillardii var. mutabilis, in contrast to the internal utricle, which is more derived and similar to G. maillardii var. trochiliscoides. In comparison with other non-marine formations of the same age in the Iberian Chain and in Europe, the charophyte assemblages from the La Huérguina Formation appear to be relatively poor and monotonous, suggesting that some of the species found elsewhere never reached this part of the basin owing to the brief development of non-marine facies there. The main differences in composition between the samples studied are indicative of the palaeoecological conditions. Atopochara trivolvis triquetra was found to be dominant in shallow lacustrine facies and Globator maillardii var. trochiliscoides and var. biutricularis are associated with temporary lakes from a well-drained palustrine area. Clavator harrisii and Mesochara harrisii thrived on floodplains whereas Ascidiella cruciata grew in palustrine environments with significant edaphic activity.

Stratigraphy and biostratigraphy (charophytes) of the marine-terrestrial transition in the Upper Eocene of the NE Ebro Basin (Catalonia, Spain)

The onset of endorheic sedimentation in the Ebro Basin is a prominent feature of the basin’s evolution and has recently been characterized as a rapid event occurring in the Early Priabonian. In the north-eastern part of the basin this event coincides with the deposition of the Artes Formation (Fm.), mainly built up by red beds of alluvial origin. The marine-continental boundary has been poorly studied up to now in the so-called Llucanes area, and what was previously thought to be the base of the Artes Fm. is actually a transitional unit, which we define as the Sant Boi Formation, which covers the underlying marine Milany Depositional Sequence and passes laterally to the Terminal Complex, extending over 15km along the eastern margin of the Ebro Basin. The Sant Boi Fm. is formed by up to 15-20m of alternating siltstones and lutite, grading upwards to brackish and lacustrine marls and lignite, and represents deposition in a brackish to freshwater floodplain. It is characterized biostratigraphically by the fossil charophyte assemblage Harrisichara lineata, Harrisichara vasiformis-tuberculata and Nodosochara jorbae, from the middle part of the Priabonian. In contrast, the overlying red beds of the Artes Fm. are characterized by assemblages containing Harrisichara tuberculata, Nodosochara jorbae and Lychnothamnus longus from the Late Priabonian. These results are largely consistent with recent magnetostratigraphic studies performed south of the studied area, and have enabled us to refine the stratigraphy of the marine-continental transition in the north-eastern Ebro Basin.

A CHARACEAN THALLUS WITH ATTACHED GYROGONITES AND ASSOCIATED FOSSIL CHAROPHYTES FROM THE MAASTRICHTIAN OF THE EASTERN PYRENEES (CATALONIA, SPAIN)(1).

The new species Clavatoraxis microcharophorus is described from the Lower Maastrichtian of the Eastern Pyrenees (Catalonia, Spain). Microchara sp. gyrogonites were found in anatomical connection with this thallus, attached to bract-cell rosettes and coated by a structural tunica, formed by an expanded bract cell. This is a feature unknown in extant characeans, which only display lime incrustations similar to tunicae in extremely alkaline and well-illuminated environments. This is the first time that a complete fossil characean is described. The attribution of characean vegetative remains to the genus Clavatoraxis shows that this genus is not exclusive of clavatoraceans as previously thought. The taphonomic study of C. microcharophorus sp. nov. and associated fossil charophytes, along with sedimentological and microfacies analyses, has enabled us to characterize the habitat of this species in the Maastrichtian lake of Vallcebre. They grew forming meadows, and their remains were deposited in the poorly oxygenated lake bottom, where they were well preserved. A number of other characeans and porocharaceans were living in shallower belts. This was the case for Peckichara sp. and Munieria grambasti in the freshwater lacustrine meadows. Another species, Feistiella malladae, was found parautochthonous in brackish lakes.

Découverte de charophytes de l’Albien dans la Formation Kebar (Tunisie centrale) : implications paléoécologiques et paléobiogéographiques

In Tunisia, in the platform domain, the Aptian-Albian transition is associated with a major stratigraphic gap not precisely dated, which is related to the subaerial exposure of the Aptian Orbata platform. Locally, in central Tunisia (Jebel Kebar), this gap is substituted by the sedimentary records of the Kebar Formation. This formation provided a rich association of fossil charophytes, formed by Atopochara trivolvis trivolvis, Clavator harrisii zavialensis and Sphaerochara verticillata which allows attributing it to the late Aptian–early Albian interval (most probably early Albian). In addition, a new variety, Sphaerochara verticillata var. kebariensis, is described. The charophyte assemblage shows significant biogeographic affinities with a coeval flora found in the Iberian Peninsula. The Kebar Formation was previously regarded as exclusively nonmarine, but the presence of the assemblage of charophytes and associated ostracods described rather indicates a fluctuation between margino-littoral (lagoonal) and continental environments.

Discovery of Fossil Charophytes from the Late Triassic Xujiahe Formation and Early Jurassic Lower Yimen Formation, Sichuan Province, and Its Significance

This paper describes the fossil charophytes collected from the Late Triassic Xujiahe Formation in Dazu and Early Jurassic Lower Yimen Formation in Xichang, Sichuan Province, and their significance. Up to now, papers dealing with fossil charophytes of the Late Triassic, especially of the Early Jurassic, have been rarely published. The description of the two new species of Porochara, P. dazuensis and P. xichangensis, and their fossil assemblage not only provides an important basis for classification and correlation of red beds in southwestern China but reveals for the first time the features of the charophyte flora of the Late Triassic-Early Jurassic in the area, thus offering valuable data for the establishment of Triassic and Jurassic charophyte fossil zones in China.

Charophytes, indicators for low salinity phases in North African sebkhet

Among water plants of lakes and ponds, the charophytes are useful for palaeolimnology because they provide autochthonous fossils in the form of their calcified fructifications, termed gyrogonites. Particular species of the Characeae are adapted to brackish water and serve as a modern analogue to infer the salinity of salt lake sediments. Here we focus on Lamprothamnium papulosum whose significance in terms of palaeo-salinity is reviewed with particular attention to the ecological requirements for calcification. New data describe the finding of L. papulosum from Holocene sediments at Sebkha Mellala, Algeria. Previous Quaternary records of this species from North Africa (Mauritania, Libya (Fezzan), Sudan, Mali and Morocco) are discussed in terms of their significance for palaeolimnology. The present paper highlights the potential of fossil charophyte gyrogonites as indicators of former low salinity phases in present-day hypersaline environments.

Palaeogene Charophytes of the Balearic Islands (Spain)

Fossil charophytes were recorded in two different stratigraphic units from the non- marine Palaeogene of the Balearic Islands. In the Peguera Limestone Fm. of Mallorca the charophyte flora is characterised by two assemblages. The first contains Raskyella peckii subsp. meridionale, Harrisichara caeciliana and Maedleriella mangenoti, from the Bartonian and Lutetian; whilst the second is characterised by Harrisichara vasiformistuberculata and Nitellopsis (Tectochara) aemula, Middle Priabonian in age. The Cala Blanca Detrital Fm. has yielded Lychnothamnus stockmansii and Sphaerochara inconspicua in Menorca whilst in Mallorca it contains Lychnothamnus praelangeri, L. langeri and Sphaerochara hirmeri. This flora is Late Priabonian and Oligocene in age. These results suggest that the beginning of Paleogene non-marine deposition was diachronic in Mallorca. In terms of biogeography, the Eocene charophytes of Mallorca show affinity with North-African floras. The presence of the Eocene African subspecies Raskyella peckii meridionale in Mallorca enables the biogeographic boundary between this form and the European subspecies R. peckii peckii to be drawn at about 32o N latitude in the Iberian Plate.

Equilibrium and disequilibrium stable isotope effects in modern charophyte calcites: implications for palaeoenvironmental studies

Stable isotopes in fossil charophyte calcite may record palaeoenvironmental information but at present, very little is known about isotopic records in modern Chara stem encrustations or gyrogonites. This problem is addressed with isotopic data from present-day Chara from a wide spread of freshwater environments in Britain and Ireland. δ 13C values of stem encrustations from low water flow environments (lakes, ponds, ditches) are more positive than their coexisting gyrogonite values, by between 0.6 and 3.0‰, reflecting microenvironmental metabolic effects caused by photosynthesis. In stronger water flows, where dissolved inorganic carbon is well mixed, stem encrustation δ 13C values are close to equilibrium. δ 18O values in Chara stem encrustations are not equilibrium values, being typically offset to isotopically lighter compositions by about 1.5‰ relative to equilibrium by kinetic effects during rapid calcification. Gyrogonite δ 18O values are less negative than coexisting stem encrustation values by between 0.7 and 1.7‰. There is no clear evidence that gyrogonite δ 18O or δ 13C values are influenced by extensive disequilibrium but the data are difficult to interpret further without new experimental studies. Isotopic records in fossil lacustrine Chara marls (mainly stem encrustation calcites) should be interpreted with caution. Environmental records, essentially of relative changes in late summer water temperature or hydrology may be preserved, but these are unlikely to represent true equilibrium values. Gyrogonite calcification probably happens on a timescale of weeks, such that isotopic data represent ‘snapshots’ of the environmental conditions at the time of calcification. The timing of calcification in Chara may itself be variable depending on environment and temperature; it is a major unknown that currently hinders interpretation of isotopic data.

Biogeography of living and fossil Nitellopsis (Charophyta) in relationship to new finds from Morocco

AbstractAim To document the distribution of two closely related macrophyte species, the fossil Nitellopsis (Tectochara) merianii (A. Braun ex Unger) Grambast & Soulié‐Märsche and Nitellopsis obtusa (Desvaux) J. Groves, the single living species of genus Nitellopsis and to draw the relationships between first finds of N. merianii in North Africa and previously known records.Location South part of the High Atlas Range, Aït Kandoula basin, Morocco.Methods New finds of fossil charophyte gyrogonites were determined and illustrated. Using a large bibliographic database of both fossil and extant charophytes, we depict the biogeographical distribution N. merianii and N. obtusa and summarize the ecological requirements of N. obtusa as a modern analogue.Results The Aït Kandoula deposits, dated by magnetostratigraphy and vertebrate fossils to Upper Miocene, provided the first fossil populations of N. merianii in Africa. The distribution patterns of the Tertiary N. merianii and the living N. obtusa superimpose on a large area that extends from Spain to East Asia and characterize them as typically Eurasian taxa indicative for permanent, relatively cold and deep freshwater lakes. During the Quaternary, similar palaeolakes in the Sahara were colonized by N. obtusa.Main conclusions The presence of the Eurasian species N. merianii in North Africa is the result of dispersal by migratory waterbirds and attests to N–S migration occurring during the Upper Miocene (10–5 Myr ago). Gyrogonites imported from Southern Europe could germinate and fulfil their life cycle so as to form a new seed bank of gyrogonites because they had been deposited in a suitable environment consisting of a freshwater mountain lake.

Epiphytic Overgrowth of Charophyte Thalli by Stromatolite-like Structures and Fungi in the Lower Cretaceous of the Iberian Ranges (Spain)

The Lower Cretaceous (113 million years old) lacustrine deposits of Las Hoyas(Iberian Ranges, Cuenca, Spain) yield an epiphytic assemblage formed by thecharophyte species Clavatoraxis diaz-romeraliiMartín-Closas & Diéguez overgrown by a muddy, laminatedstromatolite-like structure. Fossil charophyte thalli coated with biogeniclaminations were previously unknown from the fossil record. Within thisstromatolite-like structure, filaments are found which correspond to thalli ofanother charophyte, Palaeonitella vermicularisMartín-Closas & Diéguez, and to septate hyphae of fungi(Ascomycetes). The distribution pattern of the biogenic lamination and itsselective growth only on the strongest thalli ofClavatoraxis diaz-romeralii suggests that it occurredwhen these macrophytes were still alive, standing upright on the lake bottom.From this point of view the stromatolite-like structures are reminiscent ofextant overgrowths of charophyte thalli by epiphytic, filamentouscyanobacteria, eucaryotic algae and fungi. These assemblages appear to developafter eutrophication of nutrient-poor environments, which are more suitablefor charophyte growth.

Stable carbon and oxygen isotopic compositions of recent charophyte oosporangia and water from Malham Tarn, U.K.: palaeontological implications

Charophyte oosporangia and water samples from a highly calcareous lake were measured for stable carbon and oxygen isotopic composition. The time period over which the oosporangia calcify is short, thus any biochemical relationship between the water and oosporangia"s calcite represents only one ‘time window’ (late Summer in Malham Tam). This important temporal restraint must also apply to interpretations of all fossil material measured. The δ18Oc of the charophyte oosporangia is deduced to be in equilibrium with the δ18Oω of the water for a given temperature. The δ13 Cc of the charophyte oosporangia was approximately 2.5 per mil lower than the δ13CDIC in the water we measured. With the release Of CO2 with phosphoric acid from the charophyte oosporangia, there was no significant difference in the δ18Oc values obtained, regardless of whether or not the carbonate was separated from the organic center, however δ13Cc values were marginally lower for carbonate plus organic center measurements. Our results indicate that fossil charophyte gyrogonites can be used to elucidate the geochemistry of the ancient water body in which they lived.

A review of the nonmarine Cretaceous-Tertiary transition in China

The nonmarine Cretaceous-Tertiary transition has been well-documented only in North America. Several potential nonmarine Cretaceous-Tertiary sites exist in China and are reviewed here, although as yet they have not yet been evaluated in detail. These sites are found in Hubei, Hunan, Jiangsu, Xinjiang, Qinghai-Gansu, Sichuan-Guizhou, Shanxi and Heilongjiang provinces. They are identified using fossil charophytes, palynomorphs, ostracods, conchostracans and vertebrates. The supposed Cretaceous-Tertiary boundary site in Nanxiong (Guangdong province) is shown probably to have a significant hiatus at the boundary.