Toarcian

Jurassic belemnites represent promising proxies especially for palaeoecological and also palaeobiogeographical reconstructions. However, basic knowledge on taxonomic composition, biostratigraphy and diversity of Early Jurassic belemnites is still dramatically low, especially for France. The present study provides new data on belemnites from the southern part of the Northwest European Province. More than 700 specimens have been collected along the Tournadous section in the Causses Basin (Southern France); they represent ten genera and 30 species belonging to Hastitidae, Megateuthididae, Passaloteuthididae, and Salpingoteuthididae. Furthermore, numerous ammonites have been collected, allowing to establish a standard chronostratigraphical scheme of the studied section and thus to assign, for the first time, a precise chronostratigraphical distribution to the Early Jurassic belemnites of Southern France. The analysis of belemnite diversity and its variations along the section compared to the well-known fauna of the northern part of the Northwest European province (Germany and England) open interesting prospective for belemnites palaeobiogeography.

The magnetic parameters (magnetic susceptibility, isothermal remanent Magnetization at 1 tesla (IRM 1 T and IRM -300 mT), of 77 samples were analysed across the Toarcian marly limestone succession in the Rabaçal area (northern Lusitanian Basin), involving around 170 m of thickness. The S-300 ratios were also calculated. The series include the top of the Lemede, S Gião (subdivided into five members) and the Póvoa da Lomba formations, well controlled by ammonite biostratigraphy. The main objectives of this study are: 1) to present a stratigraphic record of the magnetic parameters of the studied marl-limestone succession, emphasizing the relations with lithostratigraphic units; 2) to characterise the magnetic record; and 3) to highlight the importance of this data in the palaeoenvironmental interpretations. The sampling was carried out in order to obtain a sample of 1 kg of the selected strata using diamagnetic material. In the Lab, the mass of the samples was determined by an electronic scale with an accuracy of 0.0001 g. The samples were measured on a magnetic susceptibility meter, Agico, Kappabridge KLY-4S model (Czech Republic), in the Petrophysics Laboratory, Department of Geosciences, Environment and Spatial Planning/Geology Centre, University of Porto. A magnetic field of 300 Am-1 was applied in the measurements. The samples were measured 3 times and an average value was then calculated. The IRM measurements were carried out using a high sensitivity Molspin Minispin magnetometer and the magnetic fields were imparted using a Molspin pulse magnetizer in the Department of Earth Sciences, University of Coimbra. This was done in order to obtain IRM values at 1 T, and -300 mT. The susceptibility values range between 1.38 and 12.43 E-08 m3kg-1 and the IRM 1T values range between 9.50 E-05 Am2 kg-1 and 6.88 E-01 Am2 kg-1. The obtained value reveal the following conclusions:1) some of the lower values are obtained in micritic limestones of the different formations and at different biostratigraphic positions; 2) the higher values are measured and calculated on marl samples, interpreted due to the terrigenous component; 3) some limestone beds show high values of magnetic susceptibility (between 5.69 and 12.43 E-08 m3kg-1) and IRM 1 T (76.10 E-05 and 6.88 E-01) clearly related to the presence of magnetite (S-300 between 0.82 and 0.84).

During the Early Toarcian there was a significant disruption in the short-term active carbon reservoir as revealed by carbon-isotope records, which show a broad positive shift that is interrupted by a large 5–7‰ negative excursion (δ13Corg). Carbon-isotope excursion co-occurs with the deposition of organic-rich shales in many areas. This perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia. The two leading hypotheses as to the cause of this event invoke either global or regional controls. Here we present carbon-isotope data from Haida Gwaii, British Columbia, Canada showing a significant perturbation within a temporally constrained Early Toarcian succession that was deposited in the northeastern paleo-Pacific Ocean. These data reinforce the concept that the short-term active carbon reservoir was affected globally, and assist with the correlation of ammonite zonal schemes between western North America and Europe. The δ13Corg data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7‰ (8.5‰ in δ13Cwood) in the Early Toarcian Kanense Zone. This negative excursion also coincides with increasing total organic carbon (TOC) from ~ 0.4% to ~ 1.2%. These data suggest that the Early Toarcian carbon-isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric).► We present new Early Toarcian carbon-isotope data from the northeastern paleo-Pacific Ocean. ► A negative CIE of 7‰ δ13Corg and 8.5‰ δ13Cwood average − 31‰ for 11 m in the Early Toarcian Kanense Zone. ► Negative CIE also coincides with increasing total organic carbon (TOC) from ~ 0.4% to 1.2%. ► Data show a global control mechanism and a correlation of ammonite zonal schemes.

A recent finding of Pleydellia buckmani Maubeuge, 1947 (Hildoceratoidea, Graphoceratidae, Dumortieriinae)  from  Monte  Nerone  (PU,  Italy)  is  here  reported  and  documented.  This graphoceratid is a marker of the Pleydellia buckmani Subzone (last subzone of the Pleydellia aalensis Biozone, uppermost Toarcian; see Cariou & Hantzpergue, 1997). Ammonites referred to this taxon are typical of late Toarcian successions from Luxembourg, Germany, France, Spain, Bulgary and Iran (Maubeuge, 1947; Rulleau et al., 2001; Schulbert, 2001; Weis et al., 2010; Di Cencio, 2014a) but are seldom reported in Italy. In fact, the taxon was signaled only once from the “condensed” succession of the Monte Nerone Area (Fosso del  Presale  section;  Cresta  et  al.,  1995)  and,  with  certainty,  it  was  reported  in  uppermost Toarcian sediments from Sicily (Pallini et al., 2004). The studied specimen was collected in well-bedded, hazelnut, nodular mudstone-wackestone strata (Calcari nodulari nocciola sensu Centamore et al., 1971) pertaining to the Bugarone Fm. (Jacobacci et al., 1974). P. buckmani is easily recognizable, differing from all other species of the genus in its several very fasciculated and sinuous ribs (Di Cencio, 2014b). The specimen here described sheds new light on the stratigraphy and biostratigraphy of the Monte Nerone
Area.  Several  aspects  of  the  Umbria-Marche  Domain  have  remained  still  unexplored,  and numerous  long-standing  problems  are  still  open  to  debate.  A  “renaissance”  of  ammonites studies can definitely play a fundamental role in this respect.

Centamore E., Chiocchini M., Deiana G., Micarelli A. & Pieruccini U. (1971) - Contributo alla conoscenza del Giurassico dell'Appennino umbro-marchigiano. Studi Geol. Camerti, 1: 7-89, 7 figg., 17 tabb., 45 tavv., 2 all.
Cresta S., Basilici G., Bussoletti A., Comas M.J., Elmi S., Fernandez-Lopez S., Ferretti A., Goy A., Henriques M.H., Kalin O., Jimenez A., Martinez  G.,  Sandoval  J.,  Ureta  S. &  Venturi  F.  (1995).  Relazione  sul Workshop  “Paleontologia  e  Biostratigrafia dei  sedimenti ammonitiferi  toarciano-bajociani  in  successioni  di  alto  morfostrutturale  dell‟Appennino  umbro-marchigiano:  l‟area  di  Monte Nerone. Correlazioni con altre regioni della Tetide occidentale” (Piobbico, 2-14 agosto 1993). Boll. Serv. Geol. It., 112: 129-139, 1 fig., 1 tav. 
Di Cencio A. (2014a). Species Schedules: a new idea for Fossils' Data Sheets. 9th International Symposium Cephalopods – Present and Past & 5th International Symposium Coleoid Cephalopods through Time, 4-14 September 2014, Zurich.
Di  Cencio  A.  (2014b).  The  systematic  and  taxonomic  revision  of  the  „Pleydellia-group‟  ammonites  from  the  Minette  ironstones  (Late Toarcian), southern Luxembourg. 9th International Symposium Cephalopods – Present and Past & 5th International Symposium Coleoid Cephalopods through Time, 4-14 September 2014, Zurich.
Jacobacci A., Centamore E., Chiocchini M., Malferrari N., Martelli G. & Micarelli A. (1974). Note illustrative della Carta Geologica d'Italia alla scala 1:50.000 Foglio 290, Cagli. Servizio Geologico d'Italia, 1-41, Roma.
Maubeuge P.L. (1947). Sur quelques ammonites de lì"Aalénien Ferrugineux" du Luxembourg et sur l'échelle stratigraphique de la formation ferrifère franco-belgo-luxemburgeoise. Inst. Grand Ducal de Luxembourg, Section Sci. natur., 17: 73-87, 2 pl. Luxembourg. 
Pallini G., Elmi S. & Gasparri F. (2003-04). Late Toarcian – late Aalenian ammonites assemblage from Mt. Magaggiaro (Western Sicily, Italy). Geologica Romana, 37: 1-66, 6 figg., 5 tabb., 16 tavv. 
Rulleau L., Elmi S. & Thevenard B. (2001). Géologie et Paléontologie des dépots ferrugineux du Toarcien et de l'Aalenien aux environs de Lyon. Docum. Lab. Géol. Lyon, 154: 1-153.
Schulbert C. (2001). Die Ammonitenfauna und Stratigraphie der Tongrube Mistelgau bei Bayreuth (Oberfranken). PhD Thesis: 1-183, 31pls.
Weis R., Mariotti N., Di Cencio A., Faber A., Fuchs D. & Guérin-Franiatte S. (2010). Cephalopods from the Jurassic „Minette‟ Ironstone Formation of Luxembourg and Lorraine (NE Paris Basin): an update. 8th International Symposium Cephalopods  – Present and Past, 30 August – 3 September, Dijon.