The Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System), at Flodigarry, Staffin Bay, Isle of Skye, Scotland, UK

Following voting by the Kimmeridgian Working Group, the International Subcommission on Jurassic Stratigraphy and the International Commission on Stratigraphy, the Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System) was ratified by the executive of the International Union of Geological Sciences. The boundary is placed in the upper part of Bed 35 of the Staffin Shale Formation, 1.25±0.01 m below the base of Bed 36 in block F6 in the foreshore at Flodigarry, Staffin Bay, Isle of Skye, Scotland. The coordinates for the middle part of the two adjacent sections (sections F6N and F6S) are 57°39'39.5''N, 6°14'43.9''W and 57°39'40.5''N, 6°14'45''W; UK National Grid Scheme NG 4687 7139 and NG 4687 7142±5 m. This stratigraphic point coincides with the appearance over a short stratigraphic interval of several new ammonite taxa that delineate the base of the Subboreal ammonite Baylei Zone, the base of the Densicostata Subzone marked by the base of the flodigarriensis horizon, and, independently, the base of the Boreal ammonite Bauhini Zone. The main advantages of this locality are: the presence of a dual ammonite zonation marked by two extensively studied, well-preserved and very abundant groups of ammonites, and their preservation within a continuous section of ~120 m of open marine, fossiliferous, thermally immature mudrocks with no evidence of condensation or stratigraphic gaps. Dinoflagellate cysts, magnetostratigraphy and stable isotope data from the same section provide secondary markers. The stratigraphic point is located 0.17–0.65 m below the boundary interval between the dinoflagellate cyst zones DSJ 26 and DSJ 27 (equivalent to the boundary between subzones c and d of the Scriniodinium crystallinum (=Scr) Zone). The point is located 0.02–0.24 m above the base of reversed magnetozone F3r. This magnetozone probably correlates with marine magnetic anomaly M26r but may correlate to the younger anomaly M25r. The point coin cides with a well-marked broad minimum in δ13C values and a calculated low Sr-isotope value of 0.70687. The section has yielded nannofossils that show that the potential last occurrence of Octopodorhabdus decussatus that marks the lower part of the NJ15 zone occurs about 1.09 m below the boundary. The thermal immaturity and unweathered nature of the strata in the Flodigarry section has permitted a direct Re-Os radio-isotopic age of 154.1±2.2 Ma to be obtained from the mudrocks 0.05 m below the Kimmeridgian GSSP. Sequence stratigraphic analysis indicates that the GSSP lies within the lower part of a highstand system tract. The corresponding stratigraphic level in the Submediterranean-Mediterranean successions is close to the boundary between the Hypselum and Bimammatum ammonite zones. The change in ammonite groups noted at this level provides biostratigraphic markers for further global correlation

New Lower Kimmeridgian ataxioceratin ammonite from the eastern Iberian Chain, Spain: Systematic, biogeographic and biostratigraphic relevance

New ammonites collected bed−by−bed from the upper part of Ataxioceras hypselocyclum Chronozone deposits in the eastern Iberian Chain are described as Geyericeras gen. nov. The new genus includes micro− and macroconchiate Ataxioceratinae of small size, with moderate to loose coiling and subpolyplocoid ribs, a character crucial for its identification. Key points for the comparative identification of Geyericeras gen. nov. are: (i) microconchiate Geyericeras show morphological convergence with evolute specimens of the stratigraphically older genus Schneidia [m]; (ii) contemporary Ataxioceratinae genera such as Ardescia [m, M] and Lithacosphinctes [m, M] did not develop subpolyplocoid ribbing; (iii) smoothing of sculpture combined with short primary ribs are not realized in Geyericeras gen. nov. [M] and can be therefore used to separate the new genus from Ataxioceras [M]; and (iv) smaller shells, and weaker and less dense ribbing with no parabolic structures differentiate Geyericeras gen. nov. [m, M] from Parataxioceras [m, M], as well as the type of subpolyplocoid ribs seen among microconchiate specimens of these two genera. The new species Geyericeras aragoniense sp. nov. is the index and guide fossil for identification of a biohorizon occurring below the first occurrence of the genus Crussoliceras in the eastern Iberian Chain.This research is a contribution to the IGCP project 506 and has been supported by Projects BTE2005−01316 and CGL2008−3007, and the EMMI Group RNM178 J.A., Spain

Testing carbonate chemostratigraphy across differentiated ancient shallow-platform environments (Early Kimmeridgian, S Iberia)

Shallow-platform settings with marked differences in paleoplatform bottom physiography influence the degree of connection with oceanic waters and overall circulation patterns, even when sharing the same palaeoclimatic conditions. Two Kimmeridgian shallow-marine settings have been explored to test the sensitivity and reliability of carbonate chemostratigraphy to detect such differences. An integrated overview of the obtained elemental trends depicted four major facies, shared along specific stratigraphic intervals of both depositional records. Diagenesis obliterated original geochemical signals only throughout the siliciclastics-rich interval, corresponding to the most landward setting. For the remaining facies, elemental features could be attributed to the differential action of forcing mechanisms operating along the south-Iberian paleomargin during Kimmeridgian times. The highest degree of continental influence can be recognized by a strong relationship between Fe and Mn for the most proximal setting, which fades out along the mixed carbonate-fine siliciclastic rhythmic deposition in more open settings. A characteristic geochemical signature of progressively more positive d13C values and significantly higher Sr content is identified for the interval dominated by biogenic sponge buildups.This research was supported by Projects CGL2008-05251-E and CGL2012-39835 (MINECO) and the Research Group RNM-178, Junta de Andalucía, Spain. R. Coimbra is currently supported by the Post- Doctoral Fellowship SFRH/BPD/92376/2013 (Fundação para a Ciência e a Tecnologia, Portugal) and the research units GeoBiotec - UID/GEO/04035/2013 and MARE- UID/MAR/04292/2013

TAPHONOMIC TOOLS TO EVALUATE SEDIMENTATION RATES AND STRATIGRAPHIC COMPLETENESS IN ROSSO AMMONITICO FACIES (EPIOCEANIC TETHYAN JURASSIC)

A combined multidisciplinary approach has been applied to calculate minimum values of the stratigraphic completeness and, secondarily, sedimentation rates in 9.2 m thick Rosso Ammonitico facies from central Apennines (Italy) and 11 m thick deposits of the same facies in Southern Spain. Middle - Upper Toarcian expanded sedimentation in Valdorbia section (Umbria-Marche Apennines) and extremely condensed Oxfordian-Tithonian sedimentation at Puerto Escaño section (External Subbetic) have been investigated using combined taphonomic, ichnologic and sedimentologic data and analyses. At Valdorbia, infaunal tiering is largely preserved and 27 horizons of infaunal-tiering truncation and casting reveal strong erosional activity forced by tempestite/turbidite events. Therefore, microstratigraphic gaps could be evaluated without biostratigraphic control. In this expanded section, 13 horizons of firm- and hardgrounds have been recorded showing simple or gradational tiering. Conversely, in the condensed Puerto Escaño section, taphonomic analysis reveals 25 horizons of bioclasts truncation (mainly in ammonites), and 56 horizons of firm-hardgrounds intensively bioturbated. In Valdorbia rather than in Puerto Escaño section, the evaluation of flattening in burrows and spherical bioclasts reveal a measurable mechanical compaction and dissolution. In addition, Rosso Ammonitico at Valdorbia section favoured the calculation of decompaction coefficients (nd) for each lithology easier than in Puerto Escaño section. In condensed and essentially hiatal Rosso Ammonitico, mottled deposits due to intense bioturbation dominate and tiering cannot be recognizable. This fact is accentuated by usual overprinting of elementary depositional events, which in turn hampered the accurate calculation of missing deposits. Therefore, in condensed Rosso Ammonitico the latter was only available in terms of minimal missing-record trough the analysis of truncated bioclasts.&nbsp

INTEGRATED STRATIGRAPHY FROM THE CONTRADA FORNAZZO SECTION, MONTE INICI, WESTERN SICILY, ITALY: PROPOSED G.S.S.P. FOR THE BASAL BOUNDARY OF THE TITHONIAN STAGE

This paper deals with a definition of the lower boundary stratotype of the Tithonian Stage in the Upper Jurassic succession of Monte Inici, Western Sicily. The upper member of the Rosso Ammonitico Fm. is 27 m thick and shows a typical nodular-calcareous lithofacies; its lower beds have been sampled for biostratigraphic and paleomagnetic purposes. Though the succession is affected by high stratigraphic condensation, the resulting hiatuses have been shown to be below biochronological resolution and thus do not hinder any biostratigraphic definition. The biostratigraphic analysis has been based on the rich ammonite assemblages in which the common genus Hybonoticeras is the index-key for characterizing the Kimmeridgian-Tithonian boundary. Four ammonite biozones have been identified; the basal Tithonian one is defined by the assemblage of Hybonoticeras gr. hybonotum and Haploceras staszycii. The recorded calcareous nannofossil bioevents allow recognition of the V. stradneri and C. mexicana Zones, whose boundary is located a little below the identified Tithonian lower boundary. The paleomagnetic record shows normal polarity in the S. darwini/V. albertinum Zone and mainly reverse polarity in the H. beckeri and H. hybonotum Zones, with three minor normal polarity intervals; the lower boundary of the Tithonian falls in the oldest of these intervals. The integrated multidisciplinary stratigraphic information gathered from the Contrada Fornazzo section defines the lower boundary of the H. hybonotum Zone at the base of Bed 110, and supplies elements of chrono-correlation sufficient to regard this section as a possible G.S.S.P. of the Tithonian Stage

Concentraciones fosilíferas del Kimmeridgiano Superior en Mazapil, Zacatecas, México: Tafonomía e interpretación paleoambiental

Este último proyecto (Proyecto CGL2012-39835) y el Posgrado de Ciencias de la Tierra, UNAM; facilitaron la realización de una estancia de investigación de la primera autora en la Facultad de Ciencias de la Universidad de Granada. Se reconocen las aportaciones de los revisores, Sara Alicia Quiroz Barroso y Miguel Agustín Téllez Duarte. Se agradece a Marco Antonio Argáez Martínez su apoyo en campo, elaboración de láminas delgadas y superficies pulidas.Como aproximación preliminar al estudio detallado de concentraciones fosilíferas en el Jurásico Superior de México, se analizan las registradas en una sucesión de 410 cm de espesor de la Formación La Caja, perteneciente al Kimmeridgiano tardío, la cual aflora en el Cañón de San Matías. Mazapil, Zacatecas. Las observaciones litoestratigráficas, sedimentológicas, paleontológicas, bioestratigráficas y tafonómicas se realizaron estrato a estrato con resolución centimétrica. El estudio taxonómico y bioestratigráfico se centró en las asociaciones de macroinvertebrados, esencialmente ammonites. El análisis tafonómico se realizó sobre 1175 restos cuya composición responde a la de comunidades neríticas (ammonites 53 %, aptychi 27 %, bivalvos 18 % y gasterópodos 2 %) que se depositaron en profundidades menores que las de implosión para las carcasas de ammonites. En ámbito de plataforma sin evidencias de relieves pronunciados, se interpreta un contexto eco- sedimentario de baja energía (floatstone-wackestone de bioclastos y wackestone de radiolarios; existen parches locales de packstone), con depósito de limolitas incipiente e irregularmente calcáreas asociadas a un ambiente de plataforma sin evidencias de relieves pronunciados. Son características la ausencia de superficies de erosión expresivas, deslizamientos sinsedimentarios, aportes exóticos, y estructuras sedimentarias inequívocamente relacionadas con oleaje, así como el predominio de laminaciones paralelas y/o suavemente oblicuas. Las condiciones ecológicas incluyeron fondos disaeróbicos-poikiloaeróbicos con escaso registro de bentos in situ, y ferruginización frecuente relacionada con concentraciones de materia orgánica, así como inestabilidades en la columna de agua que afectarían a las comunidades de organismos pelágicos y bentónicos generando incrementos en la exportación de restos al fondo. Las concentraciones fosilíferas registradas son más expresivas hacia la base y techo de los estratos, son discontinuas y su configuración macroscópica responde a la de pavimentos y capas de conchas (shell beds). Se interpretan como eventitas distales resultantes de procesos con energía efectiva variable (huracanes, tormentas, corrientes de fondo ligadas a tormentas, aventamientos), cuya incidencia alcanzó sectores proximales de la plataforma externa en torno al nivel de base de tormentas. Secuencias de redepósito incompletas se relacionan con eventos de mayor energía efectiva y sobreimposición de horizontes. El patrón de la secuencia de redepósito tipo responde a eventos energéticos, disipación progresiva pero rápida de la energía, y retorno a condiciones eco-sedimentarias normales para el sector según el registro estratigráfico. La dinámica eco-sedimentaria propuesta para la sucesión estudiada en el perfil Cañón de San Matías responde a rupturas de equilibrio ambiental con periodos de recurrencia de rango inferior al de la resolución bioestratigráfica en ámbito de plataforma, sin evidencias de relieves próximos, ni de la existencia de ruptura de plataforma ni talud continental en el área, durante el intervalo estudiado del Kimmeridgiano tardío.A 410 cm thick succession of late Kimmeridgian deposits belonging to the La Caja Fm. has been analyzed in the San Matias Canyon as preliminary approach to the study of fossil concentrations in the Upper Jurassic of Mexico. Lithostratigraphic, sedimentologic, taxonomic, biostratigraphic and taphonomic observations based on a bed-by-bed sampling with centimeter scale resolution. Taxonomic and biostratigraphic analyses focused on macroinvertebrate assemblages, mainly ammonites. The taphonomic analysis applied to 1175 fossil remains of neritic communities (ammonites 53 %, aptychi 27 %, bivalves 18 % and gastropods 2 %), accumulated in depths lesser than those estimated for implosion of ammonite carcasses. Within a shelf-area without evidence of high-irregular seabeds, an eco-sedimentary context of low energy agrees with depositional conditions resulting in lithofacies of floatstone-wackestone of bioclasts and wackestone of radiolaria, together with local patches of packstone and the intercalation of calcareous siltstone. In addition, low energy conditions are in accordance with the absence of expressive erosion surfaces, synsedimentary sliding, exotic clasts, and sedimentary structures typically related to wave action, as well as with the common occurrence of parallel and/or subtle oblique laminations. Ecological conditions included disaerobic-poikiloaerobic seabeds with rare record of benthos in situ, common ferruginization related to organic matter-rich sediments, and water column instabilities affecting pelagic and benthic communities resulting in increased accumulation of skeletals remains on the seabed. The recorded fossiliferous concentrations are more evident to the bottom and top surfaces of beds, they are discontinuous, and their macroscopic biofabric corresponds to pavements and shell beds. These fossil-rich horizons are interpreted as distal eventites resulting from turbulence events of variable effective energy (hurricanes, storms, storm-forced bottom currents, and winnowing), the influence of which reached proximal sectors of the outer shelf at depths close to the storm wave base. Incomplete sequences related to reworking are interpreted as resulting from events of higher-than-background effective energy and over-imposition of depositional horizons. The pattern of the type sequence of re-deposition related to the succession of higher-than-background energy events, progressive but rapid dissipation of energy, and the return to background eco-sedimentary conditions. The eco-sedimentary dynamics proposed for the succession analyzed at the San Matias Canyon, Mazapil, Zacatecas, indicates pulses of paleoenvironmental instability within a neritic shelf, and with recurrence periods shorter than the range of biostratigraphic resolution. No evidence of high-irregular seabeds has been found in the surrounding area nor the occurrence of the shelf-break and slope in the area during the investigated stratigraphic interval of late Kimmeridgian age.Esta investigación fue apoyada por los proyectos UNAM-DGAPA-PAPIIT IN105311-3, IN102016, y el Proyecto CGL2012-39835 del Ministerio de Industria Economía y Competitividad (MINECO), España

Historia del conocimiento de los Ammonites del Jurásico de España: l. los tiempos de José Torrubia (1754)

The first published Jurassic Ammonites from Spain in the Aparato para la Historia Natural Española of José Torrubia (1754) is described here with plates depicting some Ammonite fossils atributed by Torrubia to «cornu ammonis». An evaluarían of the knowledge of Torrubia about the contemporaneus pa/aeontologicalliterature and the controversies about the petrifications is made

Foraminiferal assemblages as palaeoenvironmental bioindicators in Late Jurassic epicontinental platforms: relation with trophic conditions

Foraminiferal assemblages from the neritic environment reveal the palaeoecological impact of nutrient types in relation to shore distance and sedimentary setting. Comparatively proximal siliciclastic settings from the Boreal Domain (Brora section, Eastern Scotland) were dominated by inner−shelf primary production in the water column or in sea bottom, while in relatively seawards mixed carbonate−siliciclastic settings from the Western Tethys (Prebetic, Southern Spain), nutrients mainly derived from the inner−shelf source. In both settings, benthic foraminiferal assemblages increased in diversity and proportion of epifauna from eutrophic to oligotrophic conditions. The proximal setting example (Brora Brick Clay Mb.) corresponds to Callovian offshore shelf deposits with a high primary productivity, bottom accumulation of organic matter, and a reduced sedimentation rate for siliciclastics. Eutrophic conditions favoured some infaunal foraminifera. Lately, inner shelf to shoreface transition areas (Fascally Siltstone Mb.), show higher sedimentation rates and turbidity, reducing euphotic−zone range depths and primary production, and then deposits with a lower organic matter content (high−mesotrophic conditions). This determined less agglutinated infaunal foraminifera content and increasing calcitic and aragonitic epifauna, and calcitic opportunists (i.e., Lenticulina). The comparatively distal setting of the Oxfordian example (Prebetic) corresponds to: (i) outer−shelf areas with lower nutrient input (relative oligotrophy) and organic matter accumulation on comparatively firmer substrates (lumpy lithofacies group) showing dominance of calcitic epifaunal foraminifera, and (ii) mid−shelf areas with a higher sedimentation rate and nutrient influx (low−mesotrophic conditions) favouring potentially deep infaunal foraminifers in comparatively unconsolidated and nutrient−rich substrates controlled by instable redox boundary (marl−limestone rhythmite lithofacies).This research was carried out with the financial support of projects CGL2005−06636−C0201 and CGL2005−01316/BTE, and University of Oslo, Norway−Statoil cooperation. M.R. holds a Juan de la Cierva grant from the Ministry of Science and Technology of Spain