Latest Toarcian-earliest Bajocian (Jurassic) Grammoceratinae (Hildoceratidae,Ammonitina) of the western Tethys: Their palaeobiogeographic and phylogenetic significance

Grammoceratinae (Hildoceratidae, Ammonitina) abound in the Toarcian strata of many western Tethyan localities, especially the Subbetic and Lusitanian basins (of southern Spain and central western Portugal, respectively). They decline through the Aalenian and disappear by the lowermost Bajocian. The genera Asthenoceras, Vacekia (subgenera Vacekia and Nadorites) and Fontannesia are traditionally considered as the last Grammoceratinae, with species of Osperleioceras occurring in the uppermost Toarcian. Grammoceratinae are common in the eastern Pacific, especially Oregon and Alaska where Asthenoceras is abundant. They also occur in the eastern Tethys (Thailand). Although studies of Toarcian to early Bajocian Subbetic and Lusitanian grammoceratins already exist, new material from these and other palaeogeographic areas (England, Portugal and Spain) is revised here. A new genus, Linaresites nov. gen. (for Fontannesia montillanensis Linares and Sandoval) and two new species (Vacekia striata Henriques, and Asthenoceras taverai Sandoval) are described. Another form, “Asthenoceras” sp. A is described and let in open nomenclature. Temporal analysis of Aalenian to early Bajocian Grammoceratinae demonstrates a progressively more evolute morphology through time, sometimes coupled with size reduction. Palaeogeographic evidence suggests that during the early Middle Jurassic, western Tethys and eastern Pacific were temporarily well connected, possibly through the Hispanic Corridor, as demonstrated by the similarity between Tethyan and eastern Pacific Grammoceratinae.     

Calcareous nannofossil changes during the late Callovian–early Oxfordian cooling phase

Calcareous nannofossil quantitative and biostratigraphic analyses integrated with carbon and oxygen stable isotopes were carried out on the core ANDRA (Agence Nationale pour la gestion des Déchets Radio-Actifs—FRANCE) HTM 102 across the Callovian/Oxfordian boundary drilled at Cirfontaines-en-Ornois, Départment de Haute-Marne, eastern France. Calcareous nannofossil assemblages at the Callovian–Oxfordian transition are dominated by the genus Watznaueria. An increase in abundance of Biscutum spp. and A-group, which consists of Axopodorhabdus spp. (A. atavus, A. rahla, and A. cylindratus), Podorhabdus grassei, Octopodorhabdus decussatus, Hexapodorhabdus cuvillieri (family Axopodorhabdaceae), and Triscutum spp., correlates with a significant positive excursion in δ¹⁸O suggesting that these groups were probably adapted to cooler surface waters. A positive increase in δ¹³C values is coupled with high abundances of eutrophic taxa such as Zeughrabdotus erectus, Biscutum spp., and small-sized Watznaueria britannica, and a decrease in abundance of the big and oligotrophic taxa Schizosphaerella punctulata and Watznaueria manivitae. Climate cooling across the Callovian/Oxfordian boundary probably triggered a breakdown in stratification of surface waters leading to more intense nutrient recycling and higher primary productivity that favoured the shift in abundance of small-sized eutrophic taxa in the East Paris Basin.     

The upper Shemshak Formation (Toarcian–Aalenian) of the Eastern Alborz (Iran): Biota and palaeoenvironments during a transgressive–regressive cycle

The siliciclastic, up to 4,000 m thick Upper Triassic–Bajocian Shemshak Formation is widespread across the Iran Plate, especially in the Alborz Mountains of northern Iran. In contrast to its lower, generally non-marine part, the upper part is marine. Based on the Tazareh section of the eastern Alborz, an integrated analysis of this marine interval is presented. The 1,700 m thick marine sedimentary succession records a gradual deepening from inner to mid and outer shelf environments from the Middle Toarcian to early Late Aalenian. During the Late Aalenian–Early Bajocian, the trend was reversed and infilling of the basin by a large delta system occurred. This general facies development reflects a nearly symmetrical transgressive–regressive (T–R) megacycle, terminated by the inter-regional mid-Cimmerian tectonic event. A renewed transgression in the early Late Bajocian initiated a subsequent sedimentary megacycle. The bioturbated mid and outer shelf sediments contain a low to moderately diverse benthic fauna dominated by deep burrowing bivalves, often preserved in the growth position. A hierarchy of four orders of sedimentary cycles can be recognized (parasequences, parasequence sets, unconformity-bounded third-order depositional sequences, and the 13 ma long second-order T–R megacycle). A regional correlation with the Jajarm area (200 km to the east) shows a very similar temporal facies pattern of the upper Shemshak Formation. The eastern Alborz T–R cycle is completely out-of-phase with other (eustatic) sea-level curves, suggesting regional tectonic control. Rough estimates of subsidence rates give an average value of 126 m/ma. However, much higher values for the Aalenian (230 m/ma), particularly the Late Aalenian (700 m/ma), indicate a distinct increase in subsidence rate towards the Early Bajocian mid-Cimmerian tectonic event. These high subsidence rates suggest that the sediments of the Shemshak Formation of the eastern Alborz formed in a (young) rift basin.     

Thin-shelled bivalve buildup of the lower Bajocian,South Iberian paleomargin: development of opportunists after oceanic perturbations

An exceptional buildup of thin-shelled bivalves (3.5 m thick and more than 12 m long), apparently the largest in the literature, is reported from the External Subbetic (Betic Cordillera, southern Spain). Calcareous nannofossils indicate the NJT8 biozone (late Aalenian) below the buildup and the NJT9 biozone (early Bajocian) at the base of the buildup. The thin-shelled bivalves, commonly referred to as filaments, are Bositra-like forms, an opportunistic bivalve that flourished under stressed conditions. Geochemical proxies (carbon isotopes, P_org and Ba_bio, and Cr/Al, V/Al and Ni/Co ratios) indicate that the marine environment was subjected to changes in oxygenation and trophic conditions, which, under the optimum states, promoted extremely high rates of production of the thin-shelled bivalves. The large buildup accumulated on the sea-floor under favorable hydrodynamic conditions and local topography. The significance of these depositional characteristics in relation to the previous literature is discussed.     

Fossil plant evidence for Early and Middle Jurassic paleoenvironmental changes in Lanzhou area, Northwest China

Estimating the paleoclimate changes through CO₂ levels has become a promising area of geological research. This paper focuses on analysis of fossil Ginkgo in continuous sedimentary series in northwestern China using plant anatomy and organic geochemistry approaches. The CO₂ variation curve during Early and Middle Jurassic is reconstructed based on the stomatal ratio method, which is consistent with the estimated results of GEOCARB III. In comparison with the carbon isotopic composition measured from the fossil leaves of Ginkgo, we suggest that the stomata-based CO₂ concentrations for the Jurassic are generally consistent with the predictions of the geochemical model, ranging from 1000 to 1600 ppmv. Measurements of carbon isotope values demonstrate that the water use efficiency of the fossil Ginkgo in a “green house” world is higher than that of the living Ginkgo. Investigations of physiological responses of plants to the increasing CO₂ level at the present and in the future should help demonstrate this effect. The cause of the carbon isotopic shift at the boundary between Aalenian and Bajocian for the Yaojie Basin is unclear and therefore needs further investigation.     

Global radiolarian zonation for the Pliensbachian, Toarcian and Aalenian

Jurassic radiolarians from 220 samples in Queen Charlotte Islands, B.C., Williston Lake, B.C., east-central Oregon, Baja California Sur, southern Spain, Austria, Slovenia, Turkey, Oman, Japan and Argentina were studied in order to construct global zonation for the Pliensbachian, Toarcian and Aalenian stages. Well-preserved faunas from continuous stratigraphic sections in Queen Charlotte Islands provide the most detailed record for this time interval, and all collections are tied to North American ammonite zones or assemblages. Collections from nearly all other areas lack independent dating except for early Toarcian carbon-isotope dating in Slovenia and late Aalenian ammonites in Spain.A database of 197 widely distributed updated taxonomic species was used to construct a Unitary Association (UA) zonation for the interval. A global sequence of 41 UAs was obtained for the top of the Sinemurian to the base of the Bajocian. The first and the last UAs represent the Late Sinemurian and the Early Bajocian respectively. The remaining 39 UAs were merged into nine zones (four Early Pliensbachian, one Late Pliensbachian, one Early Toarcian, one Middle-Late Toarcian, and two Aalenian) according to prominent radiolarian faunal breaks and ammonite data. The new zones are the Canutus tipperi - Katroma clara Zone (latest Sinemurian/earliest Pliensbachian); Zartus mostleri - Pseudoristola megaglobosa, Hsuum mulleri - Trillus elkhornensis and Gigi fustis - Lantus sixi zones (Early Pliensbachian); Eucyrtidiellum nagaiae - Praeparvicingula tlellensis Zone (Late Pliensbachian); Napora relica - Eucyrtidiellum disparile Zone (Early Toarcian); Elodium pessagnoi - Hexasaturnalis hexagonus Zone (Middle and Late Toarcian); Higumastra transversa - Napora nipponica Zone (early Aalenian); and Mirifusus proavus - Transhsuum hisuikyoense Zone (late Aalenian). These zones can be correlated worldwide and link previously established UA zonations for the Hettangian-Sinemurian and the Middle to Upper Jurassic. The new zonation allows high-resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of Jurassic radiolarians.     

Calcareous nannofossils of the Cenomanian/Turonian boundary interval from the Boreal Realm (Wunstorf,northwest Germany)

The Cenomanian/Turonian boundary interval (CTBI) is marked by an intense climatic warming presumably caused by large magmatic eruptions. This warming was characterised by one of the most prominent Mesozoic perturbations of the carbon cycle, the Oceanic Anoxic Event 2 (OAE2), which is marked by a well pronounced positive carbon isotope excursion (CIE). Sediments of the OAE2-interval often consist of organic rich black shales suggesting widespread bottom water anoxia during the CTBI. This study focuses on calcareous nannofossils from the CTBI of a European section (Wunstorf Core; northwest Germany). A total of 105 samples were examined for calcareous nannofossils using the settling technique. Eight bioevents (last occurrences: Corollithion kennedyi, Lithraphidites acutus; first occurrences: Rotelapillus biarcus, Corollithion exiguum, Eprolithus octopetalus, Eprolithus eptapetalus, Quadrum gartneri, Eiffellithus eximius) have been recognised throughout the middle Cenomanian to middle Turonian interval. With the exception of eleven samples preservation is moderate to good. Calcareous nannofossils are abundant (mean 2.0 billion specimens/g sediment) and highly diverse (mean 58 species/sample). Assemblages are dominated by Watznaueria spp. (32.3%), Prediscosphaera spp. (13.4%), Zeugrhabdotus spp. (11.2%) and Biscutum spp. (10.5%). Pre-OAE2 and also post-OAE2 nannofossil assemblages show high abundances of Biscutum spp. (～ 20%) indicative for stable mesotrophic conditions. The assemblages of the OAE2 itself are marked by high values for Watznaueria spp. and low frequencies of Biscutum spp. making oligotrophic conditions during the OAE2 likely. High absolute abundances of organic walled dinoflagellates and the occurrence of frequent stress tolerant nannofossil genera like Retecapsa spp. in the organic rich intervals suggest, however, a deposition of black shales enhanced by high primary productivity. Thus dinoflagellates and calcareous nannofossils are interpreted to reflect different seasonal signals during the time of black shale deposition. Short-term high fertile seasons allowed the blooming of the organic walled dinoflagellates whereas calcareous nannofossils dominated the longer oligotrophic seasons. The black shale deposition was supported by the formation of large amounts of organic matter during fertile seasons as well as by surface water stagnation during oligotrophic seasons.     

Zooplankton induced decrease in inorganic phosphorus uptake by plankton in an oligotrophic lake

Experiments conducted on samples collected from a large oligotrophic lake revealed the following: (1) excretion rates of PO _inf4 ^sup3– by single Daphnia thorata were below detection (5 pmol animal^–1 min^–1) in 20 ml of oligotrophic lake water over a period of 10 min, (2) experimental addition of D. thorata to 20 ml aliquots of lake water decreased community-wide microbial uptake of PO _inf4 ^sup3– on two occasions (as measured by ³²PO _inf4 ^sup3– incorporation), and (3) the presence of D. thorata increased uptake by organisms smaller than 1µm, and decreased uptake by large phytoplankton. The specific mechanism for these responses remains unclear, but the results imply that when phytoplankton larger than 1µm encounter cm scale patches of water recently occupied by Daphnia they may experience decreased PO _inf4 ^sup3– availability rather than elevated concentrations of PO _inf4 ^sup3– caused by excretion. We show that ³²P uptake experiments using natural plankton assemblages can be influenced by the presence or absence of large zooplankton, and that neither grazing, turbulence, nor PO _inf4 ^sup3– excretion can account for this influence.     

Xylulose fermentation by Saccharomyces cerevisiae and xylose-fermenting yeast strains

Xylulose fermentation by four strains of Saccharomyces cerevisiae and two strains of xylose-fermenting yeasts, Pichia stipitis CBS 6054 and Candida shehatae NJ 23, was compared using a mineral medium at a cell concentration of 10 g (dry weight)/l. When xylulose was the sole carbon source and fermentation was anaerobic, S. cerevisiae ATCC 24860 and CBS 8066 showed a substrate consumption rate of 0.035 g g cells^–1 h^–1 compared with 0.833 g g cells^–1 h^–1 for glucose. Bakers' yeast and S. cerevisiae isolate 3 consumed xylulose at a much lower rate although they fermented glucose as rapidly as the ATCC and the CBS strains. While P. stipitis CBS 6054 consumed both xylulose and glucose very slowly under anaerobic conditions, C. shehatae NJ 23 fermented xylulose at a rate of 0.345 g g cells^–1 h^–1, compared with 0.575 g g cells^–1 h^–1 for glucose. For all six strains, the addition of glucose to the xylulose medium did not enhance the consumption of xylulose, but increased the cell biomass concentrations. When fermentation was performed under oxygen-limited conditions, less xylulose was consumed by S. cerevisiae ATCC 24860 and C. shehatae NJ 23, and 50%–65% of the assimilated carbon could not be accounted for in the products determined.     

Abundance and distribution of pelagic rotifers in a cold,deep oligotrophic alpine lake (Königssee)

Rotifer community structure of the oligotrophic, alpine lake KGnigssee was investigated from October 1982 to October 1983. Twenty different species were found, including several cold-stenothermal and oligotrophic species. Polyarthra vulgaris/dolichoptera, Kellicottia longispina and Keratella cochlearis were the most abundant species throughout the year, comprising 90% of the total rotifer community (2.8 × 10⁶ individuals m^–2, maximum). The remainder of the rotifer community was represented by as many as eight species which occured for a short time in summer and autumn. The rotifer community was limited to the upper 50 m (85–100%) in which most (60–80%) of the rotifers preferred the trophogenic layer (0–20 m). Species-specific depth preferences were observed. Rotifer abundance and distribution are discussed in terms of the specific environmental conditions in Königssee. The rotifer community of Konigssee is compared to that of Lake Constance in its former oligotrophic state.