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1

Ammonite assemblage and age of the hydrocarbon seep La Elina, Neuquén Basin, Argentina

Parent Horacio, Kaim Andrzej, Garrido Alberto C.

Annales Societatis Geologorum Poloniae

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2023

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Vol. 93, No. 4

353--361

EN

The ancient hydrocarbon seep deposits at the La Elina Ranch, Neuquén Basin, northern Patagonia, Argentina, are the only Mesozoic seep site in South America yielding metazoan fossils. Apart from benthic mollusc shells and worm tubes, they yielded a number of nektonic ammonoids. Four species of ammonoids were identified: Hildaitoides retrocostatus, Hammatoceras ex gr. insigne, Calliphylloceras cf. nilssoni, and Phylloceras sp. The occurrences of three species (H. ex gr. insigne, C. cf. nilssoni, and Phylloceras sp.) probably are fortuitous, while H. retrocostatus might have actually thrived in, or around the seep, as indicated by numerous well-preserved juveniles, in addition to some adult specimens. The bathymetric estimates indicate a depth not greater than 200 m, while the benthic molluscs, typical of hydrocarbon seeps, indicate a much greater depth. It is hypothesized that the deep-water taxa might have occurred in a shallower setting, owing to rising anoxia and/or strong input of continental waters from the eastern and/or southeastern deltaic system. The ammonite assemblage indicates that the seep at La Elina is (Andean) Middle Toarcian, probably Chilensis Zone, in age.

2

Cephalopod fauna and stratigraphy of the Adnet type red deposits of the Krížna unit in the Western Tatra Mountains, Poland

Myczyński R., Jach R.

Annales Societatis Geologorum Poloniae

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2009

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Vol. 79, No 1

27-39

EN

The Lower Jurassic Adnet type red limestones and marlstones (Kliny Limestone Member, Huciska Limestone Formation) of the Krížna unit in the Tatra Mountains comprise cephalopod fauna represented by ammonites, belemnites and rarely by nautiloids. Ammonites belong to the families Phyloceratidae, Lytoceratidae, Hildoceratidae and Dactylioceratidae and indicate Early Toarcian Serpentinum Zone, Middle Toarcian Bifrons Zone (most probably Sublevisoni and Bifrons Subzones) and Late Toarcian Pseudoradiosa Zone. Hence, the age of Adnet type deposits may be estimated as Early Toarcian-Late Toarcian. Relatively moderate diversity of ammonite assemblage is noticed. Ammonites and nautiloids are preserved mainly as internal moulds, only some specimens display preserved calcified shells. Part of this macrofauna has resedimented character. Studied ammonite assemblage is closely related to that of the Mediterranean Province.

3

Towards an ammonite subzonation of the Toarcian in Bulgaria

Metodiev L.

Volumina Jurassica

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2006

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Vol. 4, no. 1

186-188

EN

A scheme of 9 ammonite zones and 16 subzones for the Toarcian of the Balkan Mts. is given. It is an amplification of the standard put forward by Sapunov (1968) for the Toarcian in Bulgaria. The subzones and some zones are newly proposed. They are still in working phase and need refinement. This zonal (subzonal) set is enhanced by range chart of the ammonite genera found in Bulgaria and juxtaposed to the scheme of Elmi et al. (1997) (Fig. 1). Tenuicostatum Zone (Crosbeyi and Semicelatum subzones). The zone corresponds to the range of Dactylioceras (Orthodactylites). Protogrammoceras and Tiltoniceras are also available. The subzones are defined by the ranges of D. (O.) clevelandicum and D. (O.) crosbeyi as well as D. (O.) tenuicostatum and D. (O.) semicelatum. Falciferum Zone (Serpentinum and Falciferum subzones). The zone embraces the ranges of Harpoceras and Hildaites. The former were recently found to come out upwards outside the zone. The ranges of H. serpentinum and Hildaites define the Serpentinum Subzone. The advent of the zonal index and the mass-incoming of Hildoceras fix the Falciferum Subzone. Bifrons Zone (Lusitanicum, Bifrons and Semipolitum subzones). The subzones accepted herein are based on the successive ranges of the species of Hildoceras. Associates of Dactylioceratidae are also present, though too sporadically. Haugia and Phymatoceras arise at the top of the zone, which ends at the last occurrence of Hildoceras. Variabilis Zone. The zone was formerly placed in the Lower Toarcian, while here it is laid in the Upper Toarcian. The zone comprises the latest Dactylioceratidae, Chartronia and Denckmannia. It is limited at the top by the advent of Pseudogrammoceras and Podagrosites. Haugia ammonites are rare and of less biostratigraphical value than in NW Europe. Two subzones could be used: Collina spp. and Chartronia- Denckmannia spp. Thouarsense Zone (Bingmanni, Thouarsense and Fascigerum subzones). The zone as here understood is narrower than in the older scheme. It is defined in terms of its subzones, being composed of species of Pseudogrammoceras, Grammoceras and Esericeras. The top is taken at the extinction of Grammoceras and Esericeras. Fallaciosum Zone. Owing to the particular abundance of its index, it is used as separate zone. The extinction of Pseudogrammoceras and Podagrosites and the advent of Phlyseogrammoceras and Pseudolillia trace the upper limit. Dispansum Zone. No authentic record caused it wasn’t be into the standard. It is now clearly discernible by species of Phlyseogrammoceras, Hammatoceras, Hudlestonia and Pseudolillia. Pseudoradiosa Zone (Levesquei and Pseudoradiosa subzones). It is instead of the older Levesquei and Moorei zones as being framed throughout by finely ribbed Dumortieria. These are ruling in the Pseudoradiosa Subzone. Coarsely ribbed species are dominant in the Levesquei Subzone. Aalensis Zone (Mactra and Aalensis subzones). A succession of finely ribbed and more evolute Pleydellia and P. (Cotteswoldia) (Mactra Subzone) followed by P. (Walkericeras) and finely ribbed but less evolute Pleydellia (Aalensis Subzone) defines the zone. First Pseudammatoceras, Bredyia and Czernyeiceras appear at the top.

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Toarcian-Aalenian ammonite faunas from the western Middle Atlas (Morocco): controls of their distribution

El Hammichi F., Benshili K., Elmi S.

Volumina Jurassica

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2006

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Vol. 4, no. 1

169-169

EN

The SW part of the Moroccan Middle Atlas represents an area where the ammonite faunas are often abundant either in outer bioclastic and ferruginous beds or in outer distal platform marly limestones (Mibladéne Fm. and Al Yabés Fm.). Sedimentary discontinuities are frequently marked by condensed (bioclastic, ferruginous and encrusted limestones). The biostratigraphy is based on the distribution of 120 species, 46 genera and 7 families. The ammonite succession fits well with the West Tethyan standards. However, there are noticeable differences between the faunal communities of the diverse sectors (“subbasins”) of the studied region. This differentiation is largely due to a palaeostructural partitioning provoked by extensional tectonic movements that strengthen or lessen the eustatic variations. The faunas are largely cosmopolitan at the exception of those of the Gradata and Bonarellii zones having a strong South-Tethyan character with Collina, Collinites, Telodactylites and Furloceras to the lack of Haugia, Brodieia, Grammoceras, Esericeras and Hudlestonia. The main qualitative turnover occurs at the beginning of the Gradata Zone and it is followed by a near complete segregation of faunal assemblages. This well known scenario is complicated by local to regional conditions linked both to environments, tectonics and, perhaps, climates. For example, Phylloceratina are rare, but Lytoceratina can be abundant, although these two groups present great variations in proportion of their occurrence to the entire fauna (37% in the condensed sections; 22% in the expanded successions). These data must be compared with the percentages of Phylloceratina and Lytoceratina in other Tethyan localities: 20% on the neritic seamounts of Sicily and of the Southern Alps; 30% on their borders; 70% in small and strongly subsiding subbasins (umbilicus) as well as at some levels of the Djebel Nador ammonitico rosso (Western Algeria) Hammatoceratids of the Aalensis and Opalinum zones are strongly similar to those of Sicily and Southern Alps. Presence of involute and acute Pseudaptetoceras klimakomphalum (Vacek) and P. christianae (Elmi & Mouterde) documents the seaways between the Alpine Tethys and the peri-Atlantic basins (Portugal).

5

The Pliensbachian/Toarcian boundary in Canada: ammonite succession and correlations

Macchioni F., Palfy J., Smith P.

Volumina Jurassica

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2006

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Vol. 4, no. 1

182-182

EN

The Pliensbachian-Toarcian transition in North America is best typified by the Queen Charlotte Island ammonite succession where 3 assemblages are recognized, all of which include representatives of Lioceratoides, Protogrammoceras and Tiltoniceras. The lower assemblage also includes Fanninoceras, Amaltheus and Arieticeras, and is placed in the Pliensbachian (Carlottense Zone). The upper assemblage also includes the first occurrences of Dactylioceras and is placed in the Toarcian (Kanense Zone). The correlation of the intermediate assemblage is uncertain and it was initially placed in the Pliensbachian because it occurred beneath Dactylioceras and above Amaltheus. However, Pleuroceras that characterizes the northwest European uppermost Pliensbachian does not occur in British Columbia and it is also questionable whether the incoming of the genus Dactylioceras can be used as a means of correlation with the basal Toarcian (Tenuicostatum Zone) of northwest Europe. Consequently, it has been difficult to confidently correlate the Pliensbachian-Toarcian transition as defined in North America with the boundary as defined in northwest Europe. Light is being shed on this problem by recent work on faunas from the Laberge Group in the Yukon Territory and the Spatsizi Formation (Hazelton Group) in northcentral British Columbia. As has often been noted, Canadian sequences show stronger affinities with Mediterranean successions rather than the Boreal successions of northwest Europe. In addition to representatives of Fontanelliceras, Neolioceratoides, Canavaria, Bouleiceras and Tauromeniceras, there are several new occurrences of Dactylioceras. The Tethyan Dactylioceras cf. simplex occurs low in the Kanense Zone and suggests a correlation with the D. simplex horizon of the basal Polymorphum Zone in the Mediterranean area, which predates the basal Tenuicostatum Zone of NW Europe.

6

The Early Toarcian environmental event

Coe A., Cohen A., Kemp D., Pearce Ch., Caswell B., Skelton P.

Volumina Jurassica

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2006

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Vol. 4, no. 1

155-156

EN

A pronounced negative carbon-isotope excursion in marine organic matter, marine carbonate and terrestrial plant material during the Early Toarcian indicates a major and sudden perturbation to the global carbon cycle, which has been previously ascribed to the release of a large volume of methane from marine methane hydrates (Hesselbo et al. 2000, Cohen et al. 2004). Associated features of this event include evidence for a 400-800% increase in global chemical weathering rate (Cohen et al. 2004), a major increase in seawater temperatures, increased global organic carbon burial, a crisis in the primary producers and mass extinctions. We have characterized the precise structure of the carbon-isotope excursion at high resolution using analyses of bulk organic carbon from organic-rich mudrocks from Yorkshire, UK (Kemp et al. 2005). Our data record 3 separate, abrupt negative shifts of up to 3 per mil each. We interpret this stepwise excursion pattern as unambiguous evidence for 3 separate pulses of methane release from methane hydrates. Evidence from other recently published papers on this event in which the above interpretation has been questioned will be discussed. We have also obtained high-resolution calcium carbonate, sulphur and total organic carbon concentration data from the same section. These data have been analysed using spectral analysis and reveal cycles that we ascribe to astronomical precession. The stratigraphic phase relationship between the cyclostratigraphy and the 3 pulses of methane release also permits a direct causal link to be made between methane hydrate dissociation and astronomical climate forcing (Kemp et al. 2005). Our new cyclostratigraphy allows us to constrain accurately the duration of different parts of the environmental perturbation, including the onset and recovery periods. New Mo-isotope data that we have produced suggest that rapid changes in the redox state of the oceans occurred on very short (thousand year) timescales during the Early Toarcian. These changes in redox are directly linked in time to the three abrupt carbon isotope shifts. We are currently completing high-resolution palaeontological studies through this interval in order to better characterize the associated mass extinction event and to understand the life habits of the marine fauna that characterize the crisis interval.

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Stratigraphic distribution of brachiopods in the Lower Jurassic – Middle Jurassic transition of the Lusitanian Basin (Portugal) and a proposal of biozonation

Andrade B., Joral F., Henriques M.

Volumina Jurassica

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2006

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Vol. 4, no. 1

143-143

EN

A detailed revision of the brachiopods of the Lower-Middle Jurassic transition in the Lusitanian Basin (Andrade 2006) has enabled the establishment of the stratigraphical distribution of this fauna. More than 2,000 specimens were collected at 11 sections throughout the basin, including the Bajocian GSSP in Murtinheira (Cabo Mondego). In all, 24 species, belonging to 14 genera, have been recognized along a stratigraphical interval that includes the Upper Toarcian, the Aalenian, and the Lower Bajocian. The Toarcian associations are characterized by species also recorded in neighbouring basins, such as Stroudithyris stephanoides, Sphaeroidothyris vari, Pseudogibbirhynchia bothenhamptonensis and Soaresirhynchia renzi; as well as species endemic to the Lusitanian Basin, such as Choffatirhynchia alcariensis, Nannirhynchia delgadoi, N. cotteri, Praemonticlarella conimbriguensis, Neozeilleria duartei and Pamirorhynchia(?) jorali. This mixed palaeobiogeographical character persists in the Aalenian, in which the associations include, together with widely distributed species such as Neozeilleria anglica, Pseudogibbirhynchia mutans or Lophrothyris withingtonensis, other species known in neighbouring basins, such as Sphaeroidothyris uretae and Neozeilleria sharpei, and other species recorded only in the basin, such as Soaresirhynchia minor, S. murtinheirensis and Sphaeroidothyris henriquesae. In the Lower Bajocian, excluding Loboidothyris perovalis, only endemic species are present (belonging mainly to endemic genera), such as Lusitanina bituminis, Stroudithyris choffati, Lusothyris atlantica and Mondegia limica. The interpretation of these distributions also enables to propose a brachiopod based biozonation for the studied interval. Three zones have been erected: 1. the Renzi Zone, for the Upper Toarcian, with two subzones: Renzi and Duartei; 2. the Anglica Zone, that ranges from the Aalensis Biochronozone of the Toarcian to the base of the Bajocian. It has been subdivided in 3 subzones: Nuskae, Anglica and Uretae; 3. the Choffati Zone, which comprises the main part of the Discites, Laeviuscula and Sauzei biochronozones, with two subzones: Bituminis and Limica; 4. this proposal of biozonation can be correlated with other established in neighbouring basins, such as the Iberian Range in Spain or the French Basins.

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Sequence stratigraphy and depositional setting of the Pliensbachian and Toarcian marly limestones in the Lusitanian Basin, Portugal

Duarte L.

Volumina Jurassica

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2006

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Vol. 4, no. 1

157-158

EN

The Pliensbachian and Toarcian series in the Lusitanian Basin (Portugal) are generally dominated by hemipelagic deposits, represented by marl/limestone alternations that are very rich in nektonic and benthic fauna. These sediments are included in the following four formations: Vale das Fontes, Lemede, S. Giăo and, partially, Póvoa da Lomba. The weak lateral facies variation, generally observed at the basin scale, suggests that these sediments were deposited in an epicontinental extensional basin on a homoclinal carbonate ramp controlled by eustatic fluctuations and regional tectonics. Considering the Late Triassic – Late Callovian large cycle, the sediments correspond to the maximum transgressive facies which can be widely observed throughout the succession. A detailed studied of several stratigraphic sections in terms of sedimentological, geochemical and paleontological analysis shows that the Pliensbachian-Toarcian series is subdivided into two second-order sequences (SP and ST). The Pliensbachian succession shows a typical second-order transgressive/regressive sequence, with a dominant marly deposition at the base and a calcareous dominant facies at the top. The basal discontinuity of the SP is particularly well observed in the western part of the basin, dating roughly from the Sinemurian/Pliensbachian boundary. The series shows a large transgressive phase, ending in the middle-upper part of the Margaritatus Zone (around Subnodosus/Gibbosus subzones boundary) associated with an organic-rich deposition verified at the basin scale. During the Spinatum Zone the sedimentation returned to a calcareous regime very rich in benthic macrofauna. The upper discontinuity of the SP observed in the whole basin dates from the lowermost Polymorphum Zone (intra-Mirable Subzone). The base of ST (Polymorphum Zone) corresponds to an abrupt flooding event, through a generalised marly accumulation in the whole basin. However, around the Polymorphum-Levisoni interval, an important tectonic activity occurred, responsible for a great sedimentary change with special facies features in some positions of the basin. The dominance of marl observed at the top of the Levisoni Zone marks the maximum peak transgression of the Toarcian second-order sequence, showing some evidence of pelagic deposition, with thin-shelled bivalve-rich (Bositra sp.) horizons. The Upper Toarcian – Lower Aalenian succession shows a regressive trend, ending ST with an upward increase of calcareous and bioclastic content, including ahermatipic corals in the eastern sectors. The upper discontinuity dates from the Opalinum Zone and shows different sedimentary records across the basin. ST it is subdivided into four third-order depositional sequences (St1 to St4), each bounded by regional discontinuities, recognized over most parts of the Lusitanian Basin.

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Recent data on the ostracod fauna from the Lower and Middle Toarcian of Peniche, Portugal

Pinto S., Cabral M., Duarte L.

Volumina Jurassica

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2006

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Vol. 4, no. 1

204-205

EN

At Peniche region, western Portugal, a rather continuous marly limestone succession ranging in age from the Sinemurian to the earliest Aalenian crops out. The ostracod fauna from a 74 m thick packet within this succession has been studied, encompassing deposits that range from the topmost Pliensbachian (topmost Spinatum Biozone) to the Middle Toarcian (Polymorphum, Levisoni, Bifrons and basal Gradata biozones). The studied levels belong to Lemede (2 m) and Cabo Carvoeiro Formations. From the 47 samples collected in the marly layers, a single one is azoic. Sample numbers and bed subdivision are according to biozonation in Duarte (1995), which considers 5 packets: topmost Spinatum, Polymorphum, Levisoni, Levisoni+Bifrons, Bifrons+basal Gradata. The systematic study of the ostracods has been undertaken, and some palaeoecological aspects have also been addressed, namely hydrodynamics (carapace/valve ratio), bathymetry and oxygenation, based on marker genera/groups. Around 8000 individuals were obtained (1 individual =1 carapace or 1 valve), which are commonly badly preserved. At least 58 species belonging to 22 genera have been identified until now. The top of Spinatum Biozone displays both high diversity (8-15 species/sample) and abundance (222-402 individuals/sample) of ostracods. The dominant species are from the genus Ogmoconcha, Ogmoconchella and Liasina, associated with Polycope, Paracypris, Ledahia, among others. The Polymorphum Biozone shows high diversity (3-22 species/sample) and variable abundance (1-150 individuals/sample). The genera Ogmoconcha, Ogmoconchella and Liasina still dominate and, from the first levels of the biozone, heavily ornamented species of Kinkelinella are present; the genus Isobythocypris occurs for the first time. In Levisoni Biozone, the ostracod diversity (1-4 species/sample) and abundance (1-150 individuals/ sample) are low, in contrast with previous biozones. Ogmoconcha and Ogmoconchella disappear, and the genus Cytherella appears for the first time, becoming dominant together with Liasina in the first levels of the biozone. In the upper part, Kinkelinella dominates and at the top Bairdiacypris and Cytheroptheron occur for the first time. Levisoni+Bifrons shows that ostracod diversity is moderate (5-11 species/sample) and abundance is high (60-310 individuals/sample). Species from the genera Bairdiacypris and Kinkelinella dominate, Cytherella and Patellacythere are common. Bifrons+basal Gradata shows higher diversity (3-18 species/sample) than previous unit and variable abundance (16-468 individuals/sample). Bairdiacypris, Cytherella and Kinkelinella dominate, and Macrocypris and Trachycythere(?) occur for the first time. All of the recognized species have been found in formations of a similar age in Western Europe, and are benthic marine species, except the genus Polycope (pelagic). Most of the species indicates a deep marine setting, with variable oxygenation levels, from normal to low (predominance of Metacopina and Cytherella), for the all section. The water energy was also variable, being stronger at the topmost Spinatum and Polymorphum biozones, within which ostracod valves are dominant, and lower at the Levisoni and Levisoni+Bifrons biozones, within which ostracod carapaces clearly dominate.

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Pliensbachian/Toarcian boundary: the proposed GSSP of Peniche (Portugal)

Elmi S.

Volumina Jurassica

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2006

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Vol. 4, no. 1

5-16

EN

The Peniche section (Portugal) is cosidered as a potential stratotype (GSSP) for the Pliensbachian- Toarcian boundary and it is analysed on the background of the available data on the ammonite successions from other Tethyan and NW European areas.

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Pliensbachian – lowermost Toarcian chemostratigraphy (elemental and TOC) of the Peniche section (Lusitanian Basin, Portugal)

Veiga de Oliveira L., Duarte L., Rodrigues R.

Volumina Jurassica

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2006

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Vol. 4, no. 1

217-218

EN

In Portugal, the Peniche section constitutes one of the most continuous series of Lower Jurassic. This study is based on a detailed chemostratigraphic analysis of the Pliensbachian - lowermost Toarcian marly limestones, belonging to the Vale das Fontes, Lemede and Cabo Carvoeiro formations. 196 samples of limestones and marls were analyzed in terms of minor and major elements (Fig. 1). Total organic carbon (TOC) was determined in 233 samples. Besides the stratigraphic distribution of these geochemical parameters, the aim of this work is to perform a discussion about biogenic influx and aluminosilicate phasefluxes. The Al concentrations are a good indicator of detrital flux and good correlations between them signify aluminosilicate affiliation. In Peniche, K (0.98), Si (0.96) and Ti (0.98) show, in all section, excellent correlation with Al2O3. Mg (0.82), Ba (0.80), Cr (0.78), Li (0.80), Na (0.74), Sc (0.80), V (0.81) and Zr (0.86) correlate well with Al2O3 but other secondary factors, beyond the detrital flux, affect the resultant concentrations. The Pearson's coefficients between Al2O3 and CaO is strongly negative (-0.98), suggesting divergent behaviours for this elements. Al2O3 and Fe2O3 correlate moderately (0.61). However, the correlation coefficients calculated for each stratigraphic unit show variable values. Lemede Formation and the Members Marls and Limestones with Uptonia and Pentacrinus (MLUP), Lumpy Marls and Limestones (LML), to the Vale das Fontes Formation, and CC1, to the Cabo Carvoeiro Formation, show high correlation coefficients between Al2O3 and Fe2O3 (0.87, 0.91, 0.88 and 0.97, respectively). On the other hand, the Member CC2 has moderate correlation (0.67) and the Member Marls and Limestones with Bituminous Shales (MLBF) has weak correlation (0.20). These variations suggest that the elemental inputs change during the Pliensbachian - lowermost Toarcian, in the Peniche area. Ba enrichment is considered an indicator of high flux of biogenic material and high surface-water productivity. But, in the studied section, correlation between Al2O3 and Ba is high (0.80) and Ba lacks any correlation with TOC (0.17). Thus, in the Peniche region, the distribution of Ba is dominated by the original detrital flux and transported to the basin, mainly, as a constituent of clays. The mainly TOC values in the Pliensbachian - lowermost Toarcian of the Peniche section are below 2. But the MLBF (Ibex to Margaritatus zones) represents a high TOC interval with concentrations up to 15%, correlated with the 2nd order flooding interval, well know in the Lusitanian Basin.

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Micropalaeontologic, geochemical and cyclostratigraphic approach for the timing of the Early Toarcian Oceanic Anoxic Event in the Paris Basin (GPF-Sancerre borehole)

Clemence M., Huret E., Bartolini A., Galbrun B., Gardin S., Hinnov L., Beaumont V.

Volumina Jurassica

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2006

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Vol. 4, no. 1

154-155

EN

The marine sedimentary record of the Toarcian exhibits evidence for a perturbation of the global carbon cycle associated with high burial of organic matter, known as the Early Toarcian Oceanic Anoxic Event (OAE). It is accompanied by climate warming, elevated rates of marine faunal extinction and short-lived, strong negative isotope excursion in both oceanic and terrestrial reservoirs. The timing and the pattern of the negative shift in 13C are critical for understanding the possible mechanism of this isotopic event, and the nature and the origin of the Early Toarcian OAE. To improve our understanding of the palaeoenvironmental background of the Early Toarcian OAE, we have investigated the sedimentary record of the GPF-Sancerre borehole from the southern Paris Basin (Cher, France) by integrating geochemical analyses (13Corg, TOC and CaCO3) with synecological analyses of benthic foraminifers and calcareous nannofossils; and assessing the duration of the 13C excursion by cyclostratigraphic analysis using magnetic susceptibility (MS) and CaCO3 data. Our results indicate progressive environmental deterioration from Domerian/Toarcian to a paroxysm coincident with the Early Toarcian OAE (highest TOC values and negative excursion of 13Corg). This deterioration is marked by a high fertility period that precedes anoxic conditions. The OAE coincides with a major crisis in the benthos and with a decrease of calcareous nannofossils. Following this major dysoxic episode, the water column is characterized by a succession of alternating suboxic and stagnation phases that correlates well with positive values of 13Corg. These results attest of a highly perturbed environment, characterized by the presence of opportunist species both in the benthos and nannoplankton communities. To quantify the timing of these events, high resolution cyclostratigraphic analysis is applied to MS and CaCO3 data (sampling interval – 2 cm). Cycles of ca. 0.5, 1 and 2.5 m are observed. The calculation of cycle frequency ratios matches that of the Milankovitch orbital cycles. The duration of the negative isotope excursion can be estimated by counting cycles to 120,000š40,000 yrs. The diminution of cycle thicknesses at the Domerian/Toarcian boundary (353-358 m interval) reflects a decrease of sedimentation rate. We interpreted this result as an evidence for a potentially condensed level. This multi proxies approach is innovative and promising to better understand the water column dynamic during the OAE (nannofossil and foraminifer association), shows that the OAE is a multiphase event (beginnings, acme and recovery) and estimates brief events (<200,000 yrs), follows the sedimentation rate evolution and highlights potential hiatuses (condensed zones).

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Calcareous nannofossils biostratigraphy and oxygen isotope composition of belemnites: Pliensbachian – lowermost Toarcian of Peniche (Lusitanian Basin, Portugal)

Veiga de Oliveira L., Duarte L., Rodrigues R., Perilli N.

Volumina Jurassica

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2006

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Vol. 4, no. 1

219-219

EN

The Lusitanian Basin is located in the western Iberian margin, opened during the Triassic.The Lower Jurassic is particularly well represented at Peniche, which exhibits a continuous seriesof carbonate sediments, more than 450 m thick and aged between Sinemurian and Toarcian.In lithostratigraphic terms it corresponds to the Agua de Madeiros, Vale das Fontes, Lemede and CaboCarvoeiro formations. In this study, 145 m thick section (from the Jamesoni to the Levisoni ammonite zones),was analyzed in terms of calcareous nannofossils biostratigraphy and oxygen isotopes of belemnite rostra.The nannofossil biozones NJ4a, NJ4b, NJ5a (Pliensbachian; upper part of Jamesoni to Spinatumammonite zones), NJ5b (uppermost Pliensbachian - lowermost Toarcian; upper part of Spinatumto Levisoni ammonite zones) and NJ6 (lowermost Toarcian; upper part of Levisoni ammonite Zone) wereidentified based on proposed NW European schema and correlated with ammonite zones. Additionally,the secondary biostratigraphic events were registered which will be useful to refine the nannofossilsbiozonation: the first occurrences (FO) of Biscutum grande and B. finchii were found in the upper part ofthe NJ4a biozone (lower part of Margaritatus ammonite Zone); the FO of Lotharingius frodoi wasidentified at the same stratigraphical level as L. hauffii; the FO of L. sigillatus was found in the upper partof the NJ5a biozone (Spinatum Zone); the first common occurrence (FCO) of Calyculus spp. was recognizedin the NJ5b base, near the Pliensbachian/Toarcian boundary; the FO of Carinolithus spp. was identifiedwithin NJ5b biozone, correlated with the lower part of the Levisoni ammonite Zone and below the extinctionlevels of Calcivascularis jansae and B. grande which are other nannofossil secondary events.The oxygen-isotope profile of the Peniche section seems to reflect primary signals and can be usedto interpret the sea water paleotemperatures variations. In the Early Pliensbachian the temperature showsa gradual cooling trend (NJ3 and the lower part of the NJ4a; Jamesoni ammonite Zone). Afterward,there is a warm period (NJ4a and NJ4b; Jamesoni to lower part of Spinatum ammonite Zone) correlatedwith high TOC values interval (up to 15%), suggesting a relative sea level rise and concomitant high surfacewaterproductivity. In fact, the Margaritatus ammonite Zone corresponds, in the Lusitanian Basin,to 2nd-order flooding interval. In the Late Pliensbachian and Early Toarcian (NJ5a and lowermost partof NJ5b; Spinatum to Polymorphum ammonite zones), the isotopic values show slight variations.However, they suggest a small cooling trend in the upper part of Spinatum ammonite Zone and a warmtendency in the lower part of Polymorphum ammonite Zone.

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Ammonoidea Toarcian biohorizons in the Basque-Cantabrian Basin (N Spain): a correlation between the Iberian Range and the Mediterranean Province standard scale

Goy A., Martinez G., Ureta S.

Volumina Jurassica

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2006

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Vol. 4, no. 1

166-167

EN

In the Basque-Cantabrian Basin several detailed biostratigraphical studies in Toarcian sediments have been carried out, and all the zones and the most subzones from the NW European Province standard scale have been characterized. Recent investigations allow us to complete the reference scale and define 35 successive ammonoidea biohorizons that can be identified in the whole basin with rare exceptions. Biohorizons have been established with similar criteria to those suggested by Page (1995), and when possible, the evolution of a particular taxonomic group has been taken into account. The use of taxa with an important record overlap in the basin has been avoided. • Tenuicostatum Zone (1 – simplex, 2 – mirabile, 3 – crosbeyi, 4 – tenuicostatum, 5 – semicelatum). Successive species of Dactylioceras with reference sections in Camino (1, 2, 3, 5) and San Miguel de Aguayo (4). • Serpentinus Zone (6 – elegantulum, 7 – exaratum, 8 – elegans, 9 – pseudoserpentinus, 10 – douvillei). Species of Harpoceratinae (Eleganticeras, Cleviceras, Harpoceras) and Hildoceratinae (Orthildaites) with reference sections in Tudanca (6, 7, 8, 9) and San Andrés (10). • Bifrons Zone (11 – sublevisoni, 12 – tethysi, 13 – lusitanicum, 14 – apertum, 15 – bifrons, 16 – semipolitum). Successive species of Hildoceras with reference section in San Andrés. • Variabilis Zone (17 – variabilis, 18 – illustris, 19 – phillipsi, 20 – vitiosa). Species of Haugia with reference section in San Andrés. • Thouarsense Zone (21 – “Grammoceras”, 22 – “Essericeras”, 23 – fallaciosum). The presence of discontinuities in numerous sections and the poor and casual record of Grammoceras and Essericeras, challenging the establishment of the lowers biohorizons in this Zone. Their reference sections are Cillamayor (21, 22) and Castillo Pedroso (23). • Dispansum Zone (24 – cappuccinum, 25 – pachu, 26 – gruneri). The firsts two are successive species of Hammatoceras and the third one is a Gruneria species with a extensive record in the basin. All of them have the reference section in Cillamayor. • Pseudoradiosa Zone (27 – levesquei, 28 – munieri, 29 – pseudoradiosa, 30 – tectiforme). Successive species of Dumortieria and Paradumortieria with reference section in Cillamayor. • Aalensis Zone (31 – mactra, 32 – subcompta, 33 – aalensis/fluitans, 34 – falcifer, 35 – buckmani). Successive species of Pleydellia with reference section in San Andrés. This succession of biohorizons has numerous similarities with the one for the Iberian Range and considerable differences with sucessions from regions further south in the Iberian Peninsula. Moreover, the presence of the same taxa as other W. Tethys regions, where detailed biozonations have been made, enable the establishment of a precise correlation between the Basque-Cantabrian Basin and the Mediterranean Province, for some particular intervals and specifically for the base of Tenuicostatum/ Polymorphum Serpentinus/Levisoni, Bifrons, Dispansum/Speciosum and Aalensis zones. The discontinuous records of Collina gemma and Dumortieria meneghinii provide difficulties in correlation between Variabilis/Gradata, and Pseudoradiosa/Meneghinii zones, respectively. The present knowledge on the Basque-Cantabrian Basin doesn’t allow the precise correlation of the base of Thouarense/Bonarelli Zones.

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First record of Jurassic (Toarcian - Bajocian) ammonites from the northern Lut Block, east-central Iran

Seyed-Emami K., Fürsich F. T., Wilmsen M., Schairer G., Majidifard M. R.

Acta Geologica Polonica

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2004

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Vol. 54, no. 1

77--94

EN

A very thick and lithologically rather unusual marine sedimentary succession is described from the Kuh-e-Shisui area, northwestern Lut Block (east-central Iran). It contains a low diversity ammonite fauna comprising the families Dactylioceratidae, Hildoceratidae, Graphoceratidae, Hammatoceratidae, and Sonniniidae, which are concetrated in several levels, indicating the Lower-Lower Middle Toarcian, Upper Toarcian, Aalenian, and Lower Bajocian. The ammonite fauna, consisting of 21 taxa, descibed for the first time from the Lut Block, corresponds to that of the Badamu Formation of the Kerman-Ravar region (southern Tabas Block, to the west of the Lut Block), but is far less diverse. An exception is the occurrence of Lower Toarcian Harpoceratinae and Hildoceratinae, which hitherto have not been recorded from east-central Iran. The ammonite fauna is closely related to that of northwestern Europe.