Double alignments of ammonoid aptychi from the Lower Cretaceous of Southeast France: Result of a post-mortem transport or bromalites?

A new preservation of aptychi is described from the Valanginian limestone−marl alternations of the Vergol section (Drôme), located in the Vocontian Basin (SE France). Aptychi are arranged into two parallel rows which are generally 50 mm in length and separated by 4 mm. The alignments are very often made by entire aptychi (around 10 mm in length), oriented following their harmonic margin. Aptychi show the outside of valve to the viewer: they are convex−up. This fossilization of aptychi is successively interpreted as the result of post−mortem transport by bottom currents (taphonomicresedimentation process) or the residues (bromalites: fossilized regurgitation, gastric and intestinal contents, excrement) from the digestive tract of an ammonoid−eater (biological processes). Both the parallel rows of aptychi are more likely interpreted as a coprolite (fossil faeces) and they could be considered as both halves (hemi−cylindrical in shape) of the same cylindrical coprolite which would have been separated in two parts (following the long axis) just after the animal defecated. Considering this hypothesis, a discussion is proposed on the hypothetical ammonoid−eater responsible for them

Biostratigraphy, carbon isotope and sequence stratigraphy of South Tethyan Valanginian successions in the Essaouira-Agadir Basin (Morocco)

A detailed stratigraphic analysis was carried out on Valanginian deposits of six Moroccan sections of the Essaouira-Agadir Basin (EAB, South Tethyan margin) in order to characterize the Weissert Event and propose correlations with the North Tethyan margin (southeeast France Basin). The studied successions consist of alternating marlstone and limestone beds with sandy intercalations, and are well exposed and relatively rich in ammonites. Ammonite biostratigraphy and sequence stratigraphy were established for all successions, whereas calcareous nannofossil and carbon stable isotope analyses were performed for two and five sections, respectively. For each succession, an accurate ammonite zonal scheme allows to recognize the standard zonation established for the Mediterranean Province. A calcareous nannofossil zonation is provided for Zalidou and Aït Hamouch, considered as reference sections. The detailed biozonations allowed to ascribe an accurate age for most of the sedimentary discontinuities and depositional sequences identified in the EAB. Eastewest and northesouth transects are established for the Valanginian depositional system. Despite some stratigraphic gaps, the Valanginian carbon isotope excursion (CIE) was recognized in most of the studied sections. The Moroccan successions are correlated with those of reference sections of southeeast France i.e., the Vocontian Basin (Vergol-La Charce) and Provence Platform (Carajuan), using bio-sequence-chemo-stratigraphy. These inter-basin correlations allowed to evidence major 'mid-Valanginian' and upper Valanginian eustatic regressions; the possible role of tectonics and glacio-eustacy is also discussed

Biostratigraphy, carbon isotope and sequence stratigraphy of South Tethyan Valanginian successions in the Essaouira-Agadir Basin (Morocco)

A detailed stratigraphic analysis was carried out on Valanginian deposits of six Moroccan sections of the Essaouira-Agadir Basin (EAB, South Tethyan margin) in order to characterize the Weissert Event and propose correlations with the North Tethyan margin (southeeast France Basin). The studied successions consist of alternating marlstone and limestone beds with sandy intercalations, and are well exposed and relatively rich in ammonites. Ammonite biostratigraphy and sequence stratigraphy were established for all successions, whereas calcareous nannofossil and carbon stable isotope analyses were performed for two and five sections, respectively. For each succession, an accurate ammonite zonal scheme allows to recognize the standard zonation established for the Mediterranean Province. A calcareous nannofossil zonation is provided for Zalidou and Aït Hamouch, considered as reference sections. The detailed biozonations allowed to ascribe an accurate age for most of the sedimentary discontinuities and depositional sequences identified in the EAB. Eastewest and northesouth transects are established for the Valanginian depositional system. Despite some stratigraphic gaps, the Valanginian carbon isotope excursion (CIE) was recognized in most of the studied sections. The Moroccan successions are correlated with those of reference sections of southeeast France i.e., the Vocontian Basin (Vergol-La Charce) and Provence Platform (Carajuan), using bio-sequence-chemo-stratigraphy. These inter-basin correlations allowed to evidence major 'mid-Valanginian' and upper Valanginian eustatic regressions; the possible role of tectonics and glacio-eustacy is also discussed

Palaeotemperatures, polar ice-volume, and isotope stratigraphy (Mg/Ca, delta 18O, delta 13C, 87Sr/86Sr) : the Early Cretaceous (Berriasian, Valanginian, Hauterivian)

Temporal trends through Early Cretaceous time of δ13C, δ18O, Mg/Ca, and 87Sr/86Sr in calcite, and δ18O in seawater, are discussed using belemnites from SE France and SE Spain. Both positive and negative excursions in δ13Cc are seen in the Berriasian–Hauterivian interval, but none appear to be connected to Paraná–Etendeka volcanism and none can be tied convincingly to changes in sea level. Negative excursions to − 2‰ in δ13Cc occur in the Upper Berriasian and in the Lower Valanginian. Small positive excursions in δ13Cc occur in the uppermost Valanginian (upper C. furcillata Zone) and uppermost Hauterivian (B. balearis/P. ohmi Zones). A major positive excursion in δ13Cc in the Valanginian rises to + 1.5‰ through the upper K. biassalense Subzone (upper B. campylotoxus ammonite Zone of the Lower Valanginian), which correlates to Chron M11An.1n., and continues through the S. verrucosum Zone (Upper Valanginian). Extrapolation from carbon-isotope correlations of the onset of this excursion shows that the base of the Hauterivian (F.A. of Acanthodiscus ammonite genus) coincides with the base of Chron M10n and has a numerical age of 133.9 Ma. In Berriasian, Lower Valanginian and Upper Hauterivian belemnites, δ18Oc is mostly negative (around − 0.3‰, three-point mean) but becomes positive (up to + 0.4‰, three-point mean) in the Upper Valanginian and Lower Hauterivian before returning to negative values in the Upper Hauterivian. The transition from negative to positive values, through the S. verrucosum Zone, is accompanied by a 30% decrease in Mg/Ca in belemnite calcite, confirming that the trend in δ18Oc represents mostly cooling. The trend of δ18Osw, computed from Mg/Ca and δ18Oc, lags trends in Ca/Mg and δ18Oc and becomes around 0.8‰ more positive through the Upper Valanginian and Lower Hauterivian in response, we postulate, to the formation of substantial amounts of polar ice after a period of global cooling. By Late Hauterivian times, temperature proxies (δ18Oc and Mg/Ca) show substantial warming had occurred and δ18Osw had returned to less positive values, presumably as a result of waning ice-volume. Sea level lowstands of up to 90 m, reported to occur in the Late Berriasian and Early Valanginian, are not recorded in our δ18Oc or Mg/Ca data, so they were either not real or were tectonic in origin. Values of 87Sr/86Sr in seawater rose monotonically by 0.000294 through Berriasian, Valanginian and Hauterivian time, except in Late Valanginian time, when a plateau in 87Sr/86Sr occurred. Through extrapolation, the value of 87Sr/86Sr is estimated to be 0.707180 ± 0.000010 at the base of the Berriasian and 0.707474 ± 0.000010 at the base of the Barremian; it is fixed by regression analysis to be 0.707294 ± 0.000005 at the base of the Valanginian and 0.707383 ± 0.000005 at the base of the Hauterivian

RisaAligner software for aligning fluorescence data between Agilent 2100 Bioanalyzer chips : application to soil microbial community analysis

Ribosomal Intergenic Spacer Analysis (RISA) is a high-resolution and highly reproducible fingerprinting technique for discriminating between microbial communities. The community profiles can be visualized using the Agilent 2100 Bioanalyzer. Comparison between fingerprints relies upon precise estimation of all amplified DNA fragment lengths; however, size standard computation can vary between gel runs. For complex samples such as soil microbial communities, discrimination by fragment size is not always sufficient. In such cases, the comparison of whole fluorescence data as a function of time (electrophoregrams) is more appropriate. When electrophoregrams [fluorescence = f (time)] are used, and more than one chip is involved, electrophoregram comparisons are challenging due to experimental variations between chips and the lack of correction by the Agilent software in such situations. Here we present RisaAligner software for analyzing and comparing electrophoregrams from Agilent chips using a nonlinear ladder-alignment algorithm. We demonstrate the robustness and substantial improvement of data analysis by analyzing soil microbial profiles obtained with Agilent DNA 1000 and High Sensitivity chips