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Brackish and marine ostracode assemblages from the Sinemurian of western Portugal, with description of new species
Abstract
Sinemurian ostracodes from the Lusitanian Basin (western Portugal, Iberian Peninsula) were studied using twelve samples from the marl-limestone succession of the Coimbra Formation at S. Pedro de Moel, north of Lisbon. The detailed taxonomical study identified 11 genera and 14 species, among which 3 are new species: Phraterfabanella boomeri Cabral and Colin n. sp., Klieana? coimbraensis Cabral and Colin n. sp. and "Klinglerella" roselinae Cabral and Colin n. sp. The recognized ostracode species are particularly similar to those described from the uppermostHettangian-Sinemurian offshore Southwest Ireland (Fastnet Basin) and France (Normandy, Central France and Quercy). Overall, the assemblages include four brackish species (one clearly dominant) and ten marine species. The paleoecological analysis of the assemblages allowed a detailed paleoenvironmental reconstruction, reflecting frequent variations from brackish to restricted marine to slightly more open marine settings, which is supported by sedimentological and other paleontological data.
... In this region, the Coimbra Fm is visible on both flanks of a fractured km-scale syncline exposed along the coastline ( Figure 1B). At the Praia Velha Beach, located to the north of the S. Pedro de Moel Village and at the northern cropping out edge of the syncline, the base of the Coimbra Fm is highly fractured and folded, in a succession dipping towards the west [see Azerêdo et al., 2010, Cabral et al., 2015, Dommergues et al., 2004, Duarte et al., 2014b. In the southern part of the syncline, at the Polvoeira Beach, the uppermost part of the Coimbra Fm is continuous [Figures 1B and 2; see also Duarte et al., 2012, 2014b and includes the transition to the overlying Água de Madeiros Fm [Duarte et al., , 2012[Duarte et al., , 2014a. ...
... According to the ammonite record [see Dommergues et al., 2004, Duarte et al., 2014b, the Coimbra Fm in this region is dated from the lower to upper Sinemurian. Previous studies in this region have also focused on ostracod assemblages [Cabral et al., 2013[Cabral et al., , 2015, organic and petrographic geochemistry [Brito et al., 2017, Poças Ribeiro et al., 2013 and gamma-ray analysis [Sêco et al., 2018]. ...
... It is demonstrable that the characteristic Sinemurian shallow-water and relatively high-energy carbonate deposition in the area [see also Azerêdo et al., 2010, Cabral et al., 2015 was interrupted by brief episodes of deposition under lower energy conditions, favouring the accumulation of argillaceous sediments and preservation of organic matter, sometimes with high concentrations of S and pyrite. Organic matter accumulation probably resulted from increased productivity and poorly oxygenated bottom water conditions that had their climax in UA and UF; the latter is the thickest black shale interval in the studied succession, with organic rich facies devoid of benthic macrofauna and ichnofossils ( Figures 3A, 3C,D, 4C and 5). ...
An integrated stratigraphic analysis of the Coimbra Formation was performed in the S. Pedro de Moel outcrops of the Lusitanian Basin (Portugal). This unit is dated from the lower–upper (Oxynotum Chronozone) Sinemurian and is subdivided into eight informal subunits. Except for its base, consisting of dolostones and microbialites, much of the succession consists of bioclastic and bioturbated micritic centimetric–decimetric limestones (sometimes rich in benthic macrofauna) alternating with millimetric–centimetric marly layers, all deposited in shallow-water carbonate ramp environments. Organic-rich sediments occur throughout, with total organic carbon reaching up to 12 wt%. At a broader scale, the Coimbra Formation is transgressive and part of a long-lasting 2nd-order transgressive–regressive facies cycle ending around the Sinemurian–Pliensbachian boundary. The vertical variation of $\delta ^{13}\mathrm{C}$ determined in bulk carbonate is characterized by relatively normal marine values ($0$–$2.5‰$); however, several negative shifts are associated with the organic-rich sediments, with a maximum amplitude of ${\sim }8‰$ in the Obtusum Chronozone. These shifts in bulk carbonate $\delta ^{13}\mathrm{C}$ are interpreted to be of diagenetic origin and, therefore, of local significance. However, it cannot be discarded that a regional/global signal is imprinted on the observed trends.
... In this region, the Coimbra Fm is visible on both flanks of a fractured km-scale syncline exposed along the coastline ( Figure 1B). At the Praia Velha Beach, located to the north of the S. Pedro de Moel Village and at the northern cropping out edge of the syncline, the base of the Coimbra Fm is highly fractured and folded, in a succession dipping towards the west [see Azerêdo et al., 2010, Cabral et al., 2015, Dommergues et al., 2004, Duarte et al., 2014b. In the southern part of the syncline, at the Polvoeira Beach, the uppermost part of the Coimbra Fm is continuous [Figures 1B and 2; see also Duarte et al., 2012, 2014b and includes the transition to the overlying Água de Madeiros Fm [Duarte et al., , 2012[Duarte et al., , 2014a. ...
... According to the ammonite record [see Dommergues et al., 2004, Duarte et al., 2014b, the Coimbra Fm in this region is dated from the lower to upper Sinemurian. Previous studies in this region have also focused on ostracod assemblages [Cabral et al., 2013[Cabral et al., , 2015, organic and petrographic geochemistry [Brito et al., 2017, Poças Ribeiro et al., 2013 and gamma-ray analysis [Sêco et al., 2018]. ...
... It is demonstrable that the characteristic Sinemurian shallow-water and relatively high-energy carbonate deposition in the area [see also Azerêdo et al., 2010, Cabral et al., 2015 was interrupted by brief episodes of deposition under lower energy conditions, favouring the accumulation of argillaceous sediments and preservation of organic matter, sometimes with high concentrations of S and pyrite. Organic matter accumulation probably resulted from increased productivity and poorly oxygenated bottom water conditions that had their climax in UA and UF; the latter is the thickest black shale interval in the studied succession, with organic rich facies devoid of benthic macrofauna and ichnofossils ( Figures 3A, 3C,D, 4C and 5). ...
... In this western part of the basin, the succession shows a continuous evolution from dolomitic limestones (unit A) with stromatolites (unit B) to organic marly deposits with ammonites (Unit F) and bioclastic limestones with brachiopods (Unit H), particularly enriched in bivalves (abundance and diversity), Rhizocorallium and Thalassinoides. Besides the microbial buildups, ostracod fauna recorded in units C and D indicates a great restriction of sedimentation, suggesting somewhat brackish conditions Cabral et al. 2015). The occurrence of ammonoids of the genus Ptycharietites (Dommergues et al. 2004 towards the top of Unit D makes it possible to date terms D to F of the Coimbra Fm as Obtusum Chronozone. ...
... Organic-rich and black shale facies were deposited In the Asturian and in the Basque-Cantabrian basins during three intervals, two of them during the early Pliensbachian (Jamesoni and Ibex chronozones) and the third one during the Late Pliensbachian Margaritatus Chronozone (Fig. 4.2a,b;Suárez-Ruiz 1987;Braga et al. 1988; Suárez-Ruiz and Prado 1995; Borrego et al. 1996); Quesada et al. 1996Quesada et al. , 1997Gómez et al. 2016a, b), which represents the source rocks of the Ayoluengo oil field (Quesada et al. 1996(Quesada et al. , 1997. These organic-rich levels are also present in the Lusitanian Basin of western Iberia 2014a, b, c;Silva 2013;Silva and Duarte 2015), suggesting some communication between the northern and western Iberian basins at that time. ...
... Locally, the succession displays diverse and abundant tiny benthonic macrofauna (mainly composed of oystreids, crinoids and brachiopods), ammonites and belemnites. The benthonic fauna is practically absent in black shale levels, whose elemental geochemistry reflects isolated periods of suboxicanoxic to intermittent euxinic conditions (Silva and Duarte 2015). ...
During the Late Triassic-Middle Jurassic interval Iberia acted as a passive margin, where extensional or transtensional faulting, linked to the propagation of the Central Atlantic and the opening of the Ligurian Tethys, generated a NW and NE trending fault system that conditioned facies and thickness distribution. These faults also favored the implantation of mantle plumes and associated volcanism, giving rise to the evolution from a magma-poor passive margin, during the latest Triassic to the Pliensbachian, to a magma-rich passive margin, which developed from the Pliensbachian to the Bajocian. Progressive extensional faulting, that propagated from east to west reached a climax during the Toarcian, probably related to the onset of sea-floor spreading in the northern part of the Central Atlantic.
... This oldest carbonate formation of the Lusitanian Basin has been studied for the present work only at S. Pedro de Moel (SPM) region and lithostratigraphic chart (Duarte and Soares, 2002;Azerêdo et al., 2003;Azerêdo, 2007;Kullberg et al., 2013;Rocha, 2014a, 2014b) where it is possible to define one of its most complete successions (Azerêdo et al., 2010;Duarte et al., 2014a) (Figs. 1 and 2). According to the lithostratigraphic chart of Duarte et al. (2014a) were studied the units A, F and H. Unit A is comprised of limestones deposited in a brackish environment at the base and dolostones intercalated with marls deposited in a restricted marine environment at the top (Azerêdo et al., 2010;Cabral et al., 2015). Unit F is represented by the most expressive record of black shales of the Coimbra Formation, in a succession particularly enriched in nektonic fauna (ammonites) (Duarte et al., 2014a). ...
... There are also illustrated their hopanes/ steranes (H/S) ratios. Cabral et al., 2015), which explains (Moldowan et al., 1985) the low values of the hopanes/steranes ratio (H/S; Fig. 9AeD and Tables 3 and 5 There are also illustrated their d 13 C data. (Azerêdo et al., 2010;Paredes et al., 2013;Duarte et al., 2013Duarte et al., , 2014aPoças Ribeiro et al., 2013;Cabral et al., 2015). ...
... Cabral et al., 2015), which explains (Moldowan et al., 1985) the low values of the hopanes/steranes ratio (H/S; Fig. 9AeD and Tables 3 and 5 There are also illustrated their d 13 C data. (Azerêdo et al., 2010;Paredes et al., 2013;Duarte et al., 2013Duarte et al., , 2014aPoças Ribeiro et al., 2013;Cabral et al., 2015). In the sample of Unit A, the highest values of the d 13 C (Fig. 8AeC and Table 5), C24 tetracyclic terpane/C23 tricyclic terpane ratio (-24/:23, Fig. 8AeC and Table 5), gammacerane/C30 ab hopane (G/30, Fig. 8AeC and Table 5) and C32/C31 ab hopanes (31/31, Fig. 8AeC and Table 5) and ...
Seeking to identify the oils groups accumulated in the Jurassic of the Lusitanian Basin and the source rock of each group, stable carbon isotope and gas chromatography coupled with mass spectrometry analyses were performed in oils and oil shows from the main discoveries, and on representative organic extracts from the potential source rocks, selected based on previous works and data obtained by total organic carbon and Rock-Eval pyrolysis techniques. The geochemical comparison between the oils, and between the oils and the organic extracts, allowed the identification of three oil groups, whose differences depend on their source rocks: oils generated at the Coimbra Formation (lower-upper Sinemurian) and accumulated in the same formation and in the Água de Madeiros Formation (upper Sinemurian-lower Pliensbachian) in the northern sector of the basin; oils originated from the top of the Cabaços Formation (middle Oxfordian) and accumulated in the Montejunto (middle-upper Oxfordian) and Abadia (lower-upper Kimmeridgian) formations, in the central and southern sectors of the basin; and oil generated and accumulated at the base of the Montejunto Formation in the central sector of the basin. The geochemical correlations between the oils and the organic extracts allowed the identification of the source rocks of the different accumulations of the Jurassic succession, allowing further guidance to the petroleum exploration in the Lusitanian Basin.
... The Lusitanian Basin of central western Portugal is an important Mesozoic depocentre, and the calcareous microfossil biostratigraphy of the Lower Jurassic succession has been well studied recently (e.g., Perilli and Duarte, 2006;Oliveira et al., 2007b;Pinto, 2008;Reggiani et al., 2010;Henriques and Canales, 2013;Mattioli et al., 2013;Cabral et al., 2014Cabral et al., , 2015Henriques et al., 2014;Ferreira et al., 2015;Rita et al., 2016). By contrast, the Jurassic palynology of this significant sedimentary basin has received relatively little attention. ...
... The Lower and Middle Jurassic series of the Lusitanian Basin are characterised by well developed marl and limestones alternations (Azerêdo et al.,3003), occasionally cyclic, and abundant and diverse nektonic, planktonic and benthic organisms (e.g. Henriques 1995;Fernández-López et al. 2006, 2009aOliveira et al., 2007a,b;Henriques 2008, 2013;Sandoval et al. 2012;Mattioli et al., 2013;Comas-Rengifo et al., 2013Figueiredo et al., 2014;Henriques et al., 2014;Cabral et al., 2011Cabral et al., , 2013Cabral et al., , 2014Cabral et al., , 2015Ferreira et al., 2015;Andrade et al. 2016;Rita et al., 2016;Correia et al., 2017a,b). The lithostratigraphy of the Lower and Middle ...
The biostratigraphy of the Lusitanian Basin is based mainly on macrofossils and microfossils (foraminifera, nannofossils and ostracods). Compared to these works, palynological studies are scarce in the Lusitanian Basin. Dinoflagellate cysts are a powerful biostratigraphical and paleoenvironmental tool and, their study may be a major contribution for the Lusitanian Basin background. In this project, the Lower and Middle Jurassic of the Lusitanian Basin was investigated for palynological and palaeoenvironmental analyses. Eight sections were sampled: São Pedro de Moel, Brenha, Peniche, Fonte Coberta, Maria Pares, Vale das Fontes, São Gião e Cabo Mondego; 358 samples of marls and marly limestones were studied in detail.
The palynological response to the Toarcian Oceanic Anoxic Event (T-OAE) was examined in the Lower Jurassic sections of Maria Pares, Vale das Fontes and Peniche. A low diversity dinoflagellate cyst flora, typical of the Sub-Boreal Realm, was recovered from the Emaciaticeras emaciatum and Dactylioceras polymorphum ammonite biozones (ABs). Prior to the T-OAE, dinoflagellates thrived in the Lusitanian Basin. The Hildaites levisoni AB represents the T-OAE and the overlying strata, and is characterised by a profound reduction in dinoflagellate cyst relative abundances, causing the extinction of Luehndea spinosa and disappearance of Nannoceratopsis spp. This dinoflagellate cyst “blackout” reflects significant environmental stress, such as marine anoxia, elevated temperatures and reduced salinity, with the former two probably being most important.
A comprehensive investigation of the Early and Middle Jurassic stratigraphical palynology of the Lusitanian Basin was undertaken and a palynostratigraphical chart is proposed based, especially, in dinoflagellate cysts. The Sinemurian material examined in São Pedro de Moel was barren of dinoflagellate cysts, however the Pliensbachian and Toarcian successions are characterised by relatively low diversities, but biostratigraphically significant. Luehndea spinosa dominates the uppermost Pliensbachian–lowermost Toarcian, and is an index species. The Luehndea spinosa and Mendicodinium microscabratum dinoflagellate cyst biozones were defined, both of which are subdivided into two dinoflagellate cyst subbiozones. The Middle Jurassic samples of São Gião and Cabo Mondego successions are correlated to ammonite biozones spanning Pleydellia aalensis to Zigzagiceras zigzag. The Cabo Mondego section largely yielded relatively abundant palynomorph associations. By contrast, the São Gião outcrop, which only includes the Toarcian–Aalenian transition, produced sparse assemblages. The uppermost Toarcian to lowermost Bajocian is characterised by a low diversity dinoflagellate cyst association. Above this (Witchellia laeviuscula AB) is a markedly more diverse assemblage. The trend of increasing dinoflagellate cyst diversity continued at the Bajocian–Bathonian transition. The acritarchs, prasinophytes, pollen and spores observed in this study are typical of Jurassic assemblages worldwide.
The palynostratigraphical scheme proposed in this project may be used in future hydrocarbon investigation of the Lusitanian Basin. The fluorescence colour of palynomorphs and spore-pollen colours (TAI) analyses, suggest that most of the Lower and Middle Jurassic sediments of the Lusitanian Basin are within the mature phase for oil generation. This work is presented as a significant contribution to the Lusitanian Basin background, especially for biostratigraphy.
... Polycopsis species in Kozur (1970), Bunza and Kozur (1971), Kozur et al. (2000) are therefore re-attributed to Polycope. We follow for instance Boomer (1991), Cabral et al. (2015) in considering Klinglerella Anderson, 1964 as a junior synonym of Ektyphocythere Bate, 1963. ...
The Triassic was a turning in the history of biodiversity: bracketed by two major biotic crises, characterised by major biotic, climatic and tectonic events, it saw the transition from the Palaeozoic to the Modern evolutionary faunas. Herein, we propose the first synthetic analysis of the diversity of marine and brackish-water ostracods over the entire Triassic, in the light of palaeoecological, palaeoenvironmental and palaeogeographical contexts. Although general diversity trends witnessed poor ostracod communities during most of the Early Triassic after the end-Permian crisis, the roots of their Triassic taxonomic rediversification were visible as early as the Di- enerian. The explosive diversification of the Spathian and Anisian was followed by a high-diversity plateau up to the brink of the end-Triassic extinction. A “morphological phylogeny” proposes that all Permian and Triassic ornate Bairdiidae derived from Petasobairdia in the Kungurian, with the emergence of the Ceratobairdia-lineage and Abrobairdia-lineage. While they are generally the “poor cousin” of trophic chain analyses, traces of typical Mesozoic drilling predation on Late Triassic ostracods unexpectedly document the increase in the efficiency of predators drilling abilities through the Triassic. Finally, the palaeogeographical distribution of ostracods was very dynamic during this interval, with distinct peri-palaeo-tethyan and peri-neotethyan biotas in the Early Triassic, followed by a dispersal and thus a relative homogenisation from the Anisian onwards.
... Italy.-Jurassic: Topotypes of Phraterfabanella tridentinensisWhatley and Boomer in Boomer et al., 2001, from Rotzo Member, Calcari Grigi Formation, Trento Platform, Venetian Prealps.Portugal.-Jurassic: Topotype of Phraterfabanella boo meriCabral and Colin, 2015, from Coimbra Formation, Praia da Concha, marl facies. ...
Sieve-type normal pore canals (StPC) occur commonly in living and fossil cytheroid ostracods but their biological function(s) and evolutionary history are poorly known. The new genus Minyocythere and its four species: Minyocythere macroporosa sp. nov., M. angulata sp. nov., M. maculosa, and M. tuberculata from the Middle Jurassic have StPC prominently developed, display a range of normal pore canals, and provide a context for review of the geological record and palaeobiological potential of these structures, and their application as a taxonomic tool compared with classical approaches. The related Cretaceous genus Dolocythere is reviewed and Dolocythere amphistiela sp. nov. described. The significance of StPC for comparative morphology, systematics, palaeobiology and environmental interpretation are discussed. The range of normal pore canals observed, including StPC, is greater than previously described and several types can occur on one animal implying different life functions. The potential of normal pore canals especially StPC for systematic use is established although good preservation is essential. The functional significance of normal pore canals and their setae must be verified with living material before their evolutionary history can be deduced and their application to palaeoenvironmental interpretation and modern environmental monitoring enhanced.
... Several works on the microfossil biostratigraphy of the Lower Jurassic successions of this basin have been recently published (e.g. Mattioli et al., 2013;Cabral et al., 2014Cabral et al., , 2015Henriques and Canales, 2013;Henriques et al., 2014;Ferreira et al., 2015;Rita et al., 2016). However, the study of Jurassic dinoflagellate cysts has received relatively little attention. ...
... The Lusitanian Basin of central western Portugal is an important Mesozoic depocentre, and the calcareous microfossil biostratigra- phy of the Lower Jurassic succession has been well studied recently (Perilli and Duarte, 2006;Oliveira et al., 2007a;Pinto, 2008;Reggiani et al., 2010;Henriques and Canales, 2013;Mattioli et al., 2013;Cabral et al., 2014Cabral et al., , 2015Henriques et al., 2014;Ferreira et al., 2015;Rita et al., 2016). By contrast, the Jurassic palynology of this sedimentary basin has received relatively little attention. ...
A comprehensive investigation of the Early Jurassic stratigraphical palynology of the Lusitanian Basin in western Portugal was undertaken, with most emphasis placed on dinoflagellate cysts. A total of 214 samples from an upper Sinemurian to upper Toarcian composite section based on six successions were examined. The Sinemurian material examined was barren of dinoflagellate cysts; however, the Pliensbachian and Toarcian successions are characterised by relatively low diversities where Luehndea spinosa, Mancodinium semitabulatum, Mendicodinium microscabratum, Nannoceratopsis gracilis, Nannoceratopsis senex, and Scriniocassis priscus are relatively common and biostratigraphically significant. Luehndea spinosa dominates the lowermost Toarcian (Dactylioceras polymorphum ammonite Biozone), and is an index species. At the base of the Hildaites levisoni ammonite Biozone, the effects of the Toarcian-Oceanic Anoxic Event (T-OAE) caused Luehndea spinosa to become extinct. At the same time, dinoflagellate cyst abundance and diversity markedly decreased. After the T-OAE, during the middle and late Toarcian, phytoplankton recovery was prolonged and slow in the Lusitanian Basin. The Luehndea spinosa and Mendicodinium microscabratum dinoflagellate cyst biozones are defined, both of which are subdivided into two dinoflagellate cyst subbiozones.
... The Lusitanian Basin of central western Portugal is an important Mesozoic depocentre, and the calcareous microfossil biostratigraphy of the Lower Jurassic succession has been well studied recently (Perilli and Duarte, 2006;Oliveira et al., 2007a;Pinto, 2008;Reggiani et al., 2010;Henriques and Canales, 2013;Mattioli et al., 2013;Cabral et al., 2014Cabral et al., , 2015Henriques et al., 2014;Ferreira et al., 2015;Rita et al., 2016). By contrast, the Jurassic palynology of this sedimentary basin has received relatively little attention. ...
... The Lusitanian Basin of central western Portugal is an important Mesozoic depocentre, and the calcareous microfossil biostratigraphy of the Lower Jurassic succession has been well studied recently (Perilli and Duarte, 2006;Oliveira et al., 2007a;Pinto, 2008;Reggiani et al., 2010;Henriques and Canales, 2013;Mattioli et al., 2013;Cabral et al., 2014Cabral et al., , 2015Henriques et al., 2014;Ferreira et al., 2015;Rita et al., 2016). By contrast, the Jurassic palynology of this sedimentary basin has received relatively little attention. ...
A comprehensive investigation of the Early Jurassic stratigraphical palynology of the Lusitanian Basin in western Portugal was undertaken, with most emphasis placed on dinoflagellate cysts. A total of 214 samples, from an upper Sinemurian to upper Toarcian composite section based on six successions, were examined. The Sinemurian material examined was barren of dinoflagellate cysts, however the Pliensbachian and Toarcian successions are characterised by relatively low diversities. Luehndea spinosa, Mancodinium semitabulatum, Mendicodinium microscabratum, Nannoceratopsis gracilis, Nannoceratopsis senex and Scriniocassis priscus were relatively common, and are biostratigraphically significant. Luehndea spinosa dominates the lowermost Toarcian (Dactylioceras polymorphum ammonite Biozone), and is an index species. At the base of Hildaites levisoni ammonite Biozone, the effects of the Toarcian-Oceanic Anoxic Event (T-OAE) caused Luehndea spinosa to become extinct. At the same time, dinoflagellate cyst abundance and diversity markedly decreased. After the T-OAE, during the middle and late Toarcian, phytoplankton recovery was prolonged and slow in the Lusitanian Basin. The Luehndea spinosa and Mendicodinium microscabratum dinoflagellate cyst biozones were defined, both of which are subdivided into two dinoflagellate cyst subbiozones.
... Alguns dos trabalhos mais recentes focalizam-se nas regiões de S. Pedro de Moel e de Peniche sobre as caraterísticas sedimentológicas, litostratigráficas e biostratigráficas da formação de Coimbra e da Formação de Água de Madeiros (Duarte et al., 2008) -com particular atenção para a caraterização geoquímica e petrográfica do conteúdo em matéria orgânica Correia et al., 2012Correia et al., , 2013Poças Ribeiro et al., 2013;Mendonça Filho et al., 2013;Silva et al. 2013Silva et al. , 2015, na análise paleontológica e paleoecológica da macrofauna bentónica (Paredes et al., 2013a(Paredes et al., , b, 2014, no estudo de detalhe da sucessão de amonoides (Dommergues et al., 2004(Dommergues et al., , 2010Comas-Rengifo et al., 2013;Duarte et al., 2014a), na análise biostratigráfica, taxonómica e paleoecológica da fauna de ostracodos (Loureiro et al., 2011(Loureiro et al., , 2013Cabral et al., 2013Cabral et al., , 2015, e também na caraterização biostratigráfica dos nanofósseis calcários do Sinemuriano Superior (Mattioli et al., 2013). Azerêdo et al. (2010) preocupam-se em caraterizar e interpretar de um ponto de vista paleoambiental cúpulas estromatolíticas que ocorrem na formação de Coimbra da região de S. Pedro de Moel. ...
A formal lithostratigraphic framework is proposed for the
Lower Jurassic dolomitic-limestone succession of Lusitanian Basin,
cropping out in the Coimbra-Penela region (western-central Portugal). In
this proximal domain of the basin, the Coimbra Formation (Early to Late
Sinemurian) and the S. Miguel Formation (Late Sinemurian to Early
Pliensbachian) were defined and characterized in according with the
normative imposed by the International Stratigraphic Guide. In turn, the
Coimbra Formation is subdivided into two members: the Vila Seca
Member, at the base, and the Casa do Sal Member, at the top. The
proposed units locally reach a combined total thickness of ca. 110 m. The
available biostratigraphic references of ammonites and of benthic fauna,
by comparison with the profiles from the distal domain (S. Pedro de Moel
and Peniche), allow the interpretation of an original regional correlative
framework.
Keywords: Coimbra Formation, S. Miguel Formation, lithostratigraphy,
Sinemurian-Early Pliensbachian, Lusitanian Basin.
... Alguns dos trabalhos mais recentes focalizam-se nas regiões de S. Pedro de Moel e de Peniche sobre as caraterísticas sedimentológicas, litostratigráficas e biostratigráficas da formação de Coimbra e da Formação de Água de Madeiros (Duarte et al., 2008) -com particular atenção para a caraterização geoquímica e petrográfica do conteúdo em matéria orgânica Correia et al., 2012Correia et al., , 2013Poças Ribeiro et al., 2013;Mendonça Filho et al., 2013;Silva et al. 2013Silva et al. , 2015, na análise paleontológica e paleoecológica da macrofauna bentónica (Paredes et al., 2013a(Paredes et al., , b, 2014, no estudo de detalhe da sucessão de amonoides (Dommergues et al., 2004(Dommergues et al., , 2010Comas-Rengifo et al., 2013;Duarte et al., 2014a), na análise biostratigráfica, taxonómica e paleoecológica da fauna de ostracodos (Loureiro et al., 2011(Loureiro et al., , 2013Cabral et al., 2013Cabral et al., , 2015, e também na caraterização biostratigráfica dos nanofósseis calcários do Sinemuriano Superior (Mattioli et al., 2013). Azerêdo et al. (2010) preocupam-se em caraterizar e interpretar de um ponto de vista paleoambiental cúpulas estromatolíticas que ocorrem na formação de Coimbra da região de S. Pedro de Moel. ...
A formal lithostratigraphic framework is proposed for the Lower Jurassic dolomitic-limestone succession of Lusitanian Basin, cropping out in the Coimbra-Penela region (western-central Portugal). In this proximal domain of the basin, the Coimbra Formation (Early to Late Sinemurian) and the S. Miguel Formation (Late Sinemurian to Early Pliensbachian) were defined and characterized in according with the normative imposed by the International Stratigraphic Guide. In turn, the Coimbra Formation is subdivided into two members: the Vila Seca Member, at the base, and the Casa do Sal Member, at the top. The proposed units locally reach a combined total thickness of ca. 110 m. The available biostratigraphic references of ammonites and of benthic fauna, by comparison with the profiles from the distal domain (S. Pedro de Moel and Peniche), allow the interpretation of an original regional correlative framework.
The stratigraphical occurrence of ostracod assemblages of the uppermost Pliensbachian (emaciatum Biozone) and Lower–Middle Toarcian (polymorphum, levisoni and bifrons biozones) at Peniche, western Portugal, is reported, an interval that encompasses the Toarcian Global Boundary Stratotype Section and Point (GSSP) and the Toarcian Oceanic Anoxic Event as represented by a Carbon Isotope Excursion (CIE). The broad pattern of ostracod faunal turnover and replacement in the Peniche GSSP section before, during and after the CIE, including “survivor” and “Lazarus” species, and the stepwise extinction of metacopine ostracods is similar to that described from elsewhere in Western Europe. Assemblage composition is closest to material described from the Fastnet Basin, offshore SW Ireland, and the Mochras Farm Borehole, Wales, Great Britain. The δ13C record at Peniche and Mochras Farm facilitates a very refined comparison of ranges of species in common between the two sites. The species Bairdia paramolesta sp. nov. and Kinkelinella ventrocarinata sp. nov. are described.
This paper reports the deposition of a collection of type and figured material in the Senckenberg Museum, Frankfurt-am-Main. It has proved necessary to make certain taxonomic revisions that have come to light in recent years concerning the paper by Damotte, Cabral & Berthou (1990) on the Aptian of Portugal. Original names are cited below.
This paper studies the very first Lusitanian ammonites. These late Sinemurian (Obtusum Zone) forms are found in two distinctly marly layers within the mainly calcareous "Coimbra Beds s.s." which crop out north of São Pedro de Muel (Portugal). These ammonites are endemic taxa belonging to the groups Ptycharietites ptychogenos (Pompeckj) and Ptycharietites muellense nov. sp. They exhibit such highly derived morphologies that they cannot be likened to any other genus of the related Asteroceratinae subfamily. Paedomorphic spreading of smooth, involute, platycone morphologies is a very unusual process within the Asteroceratinae in particular and within the Arietitidae in general. Until now the groups of P. ptychogenos (Pompeckj) and of P. muellense nov. sp. have only been reported in the northern part of the Lusitanian basin and do not seem to have any palaeogeographical affinities with the adjacent NW European or Tethyan faunas. The first appearance of the genus Ptycharietites in the Lusitanian basin was a sudden event. It could be interpreted as a punctuated evolutionary event or as a faunal ingression from some undetermined origin. In fact, as the Lusitanian basin has the only onshore outcrops for the whole Central North Atlantic area, origination in one or more undocumented neighbouring offshore basins is the more plausible hypothesis.
The aim of this study was to understand the ostracod distribution in the Upper Sinemurian-lowermost Pliensbachian of S. Pedro de Moel region (top of the Coimbra and Água de Madeiros formations) and Peniche (Polvoeira Member of the Água de Madeiros Formation). At S. Pedro de Moel 39 samples were studied; 4099 ostracods were found and distributed into 32 taxa. The most common are Ogmoconchella celticensis Ainsworth, 1989 and Polycope cf. cerasia Blake, 1876. The ostracods reveal an increasing water depth, from brackish to slightly marine at the bottom to open marine at the top, where no benthic forms were recovered. At Peniche, 10 samples were studied, all of which had poorly preserved ostracods, in a total of 753 individuals distributed into 22 taxa. The most abundant are Liasina cf. lanceolata Apostolescu, 1959 and Ektyphocythere aff. sinemuriana (Ainsworth, 1989). The depositional environment of the Peniche succession would have been more dynamic and oxygenated than the one from S. Pedro de Moel region.
The detailed study of the ammonite succession (more than 800 specimens) observed in two expanded sections (Polvoeira and Água de Madeiros), located in the S. Pedro de Moel area (Lusitanian Basin), has allowed characterizing the Oxynotum and Raricostatum chronozones of the Upper Sinemurian. The Oxynotum Chronozone (Oxynotum Subchronozone) is recognized by the occurrence of the genera Oxynoticeras, Bifericeras, Cheltonia and Plesechioceras and the Raricostatum Chronozone (Raricostatum, Macdonnelli y Aplanatum subchronozones) by the record of several typical taxa of the standard zonation, pertaining to the genera Echioceras, Leptechioceras y Paltechioceras gr. tardecrescens. Based on the occurrence of Gemmellaroceras (G. aff. aenigmaticum) and the first record of Apoderoceras subtriangulare, the Sinemurian-Pliensbachian boundary is formally defined for the first time in the Lusitanian Basin.
The stratigraphical distribution of Upper Sinemurian brachiopods at S. Pedro de Moel and Peniche (Lusitanian Basin) is presented here. They are represented by 9 families, 11 genera and 21 recognized species, spanning from the Oxynotum to the lower part of Aplanatum subchronozones at S. Pedro de Moel and from the upper part of Aplanatum to lower part of Taylori subchronozones in the Peniche area. The most common families are Rhynchonellidae (39%), Tetrarhynchiidae (28%) and Zeilleriidae (16%). The highest abundance and diversity of brachiopods is recognized in the Oxynotum Subchronozone at S. Pedro de Moel. A rapid decrease in brachiopods is observed until the lower part of the Aplanatum Subchronozone, interpreted as the result of specific local conditions, most probably related to a deepening episode and/or oxygen depleted conditions. Shallower water conditions are inferred by the represented associations at Peniche. Most of the recorded taxa are related with the NW European Province.
Recebido em 15/01/2013 / Aceite em 10/05/2013 Disponível online em Junho de 2013 / Publicado em Junho de 2013 Abstract: Two sections of the Lusitanian Basin (Portugal), S. Pedro de Moel and Peniche, have been studied in detail for calcareous nannofossil biostratigraphy. This study allowed us to detect thirty-six bioevents, both first and last occurrences, in the exceptionally continuous interval comprised between the Late Sinemurian and the Early Toarcian, representing more than 10 Ma time span. Calcareous nannofossil events were compared to the available ammonite zones. The new biostratigraphic data acquired in the Lusitanian Basin permit a re-evaluation of available nannofossil stratigraphy for the time interval considered and the proposal of a new stratigraphic scheme. Nannofossil biostratigraphy permits the effective dating of Lower Jurassic major paleoceanographic events. Resumo: Duas secções da Bacia Lusitânica, concretamente S. Pedro de Moel e Peniche, foram estudadas em detalhe com vista a uma análise biostratigráfica dos nanofósseis calcários. Este estudo permitiu definer 36 bioeventos, tanto de primeiras como últimas ocorrências, num intervalo excepcionalmente contínuo, compreendido entre o Sinemuriano superior e o Toarciano inferior, representando mais de 10 Ma. Os eventos dos nanofósseis calcários foram comparados com a biozonação de amonites disponível. Estes novos dados biostratigráficos obtidos na Bacia Lusitânica permitem uma reavaliação da informação estratigráfica dos nanofósseis calcários para o referido intervalo de tempo e propor um novo quadro biostratigráfico. A biostratigrafia dos nanofósseis permite uma datação precisa dos maiores eventos paleoceanográficos ocorridos durante o Jurássico Inferior. Palavras-chave: Nanofósseis calcários, Biostratigrafia, Jurássico Inferior, Bacia Lusitânica.
The occurrence and abundance of ostracods found in 98 subdivisions (Faunicycles) of late Jurassic to early Cretaceous age in the English Purbeck and Wealden are summarised. Most of the taxa found are illustrated from holotype or other material and details of their ranges and abundance given in relation to each faunicycle. The characters of the ostracod assemblages and zones are described. Three new species (Cypridea brendae, C. hispida and Eoparacypris edmundsi); also two new subspecies (Cypridea setimpelota and C. tuberculata dorsiclavara) are described and figured. A lectotype for Palaeocytheridea pellucida is selected and figured.
Resumo: Estudaram-se, no que respeita os ostracodos, doze amostras margosas recolhidas na série calcária da região de S. Pedro de Moel, aflorante nas arribas das contínuas Praia Velha e Praia da Concha (Formação de Coimbra, Sinemuriano inferior a superior). A fauna identificada é escassa e mal conservada na base, tornando-se progressivamente mais abundante (alguns níveis com mais de 2000 exemplares), diversificada e melhor preservada para o topo; é bastante parecida com a descrita noutras regiões da Europa, em níveis da mesma idade ou muito próxima, nomeadamente no offshore da Bacia de Fastnet, SO da Irlanda e em França, apresentando porém algumas espécies novas. Nos cortes estudados os ostracodos indicam variação de fácies, de ambiente marinho de pequena profundidade, geralmente restrito, a ambiente mais aberto, ou mesmo a salobro. Abstract: Twelve samples from the marly levels of the limestone succession from São Pedro de Moel region, exposed along the coastline of the Praia Velha and Praia da Concha (Coimbra Formation, Lower to Upper Sinemurian), were studied as regards to ostracods. The recognized fauna is relatively scarce and very poorly preserved at the base, then it gradually becomes more abundant and diversified upwards, being also better preserved; in some levels, more than 2.000 specimens were collected. The fauna is very similar to those described in other European regions, in levels of the same age or relatively close, namely in the Fastnet Basin, offshore SW Ireland and in France, though exhibiting several new species. In the studied sections, the ostracods suggest variable facies, reflecting either a shallow marine environment, usually restricted, or a more open to brackish one.
This work provides detailed information of outcrop gamma-ray logging from the Sinemurian-Pliensbachian organic-rich units (Agua de Madeiros and Vale das Fontes formations) of the Lusitanian Basin, which are recognized as one of the most important potential oil source rocks interval of Portugal. The study included total and spectral gamma-ray measurements in outcrop and laboratory, Total Organic Carbon (TOC) content and whole-rock mineralogical characterization by X-ray diffraction, carried out in the two most important outcrop areas of the Western Lusitanian Basin (S. Pedro de Moel and Peniche). The outcrop data was compared with subsurface information. The results show high variability of the gamma radiation (26 to 210 cps) and radioactive elements associated with the lithological, mineralogical and geochemical differences. The TOC data yielded the organic matter enrichment of both formations, where the highest values are observed in the Agua de Madeiros Formation (maximum=20.4%). The highest U concentration (11 ppm) is consistent with the highest Total Organic Carbon peak mainly supported by the precipitation of authigenic U (10 ppm). The majority of the analysed samples show an obvious authigenic U enrichment, especially in the Agua de Madeiros Formation where it represents the main component of the total U content. A highly significant U/TOC correlation (r up to 0.87) with a low ratio (0.3-0.7 ppm/wt.% TOC) was obtained, confirming that U content can be used as a proxy for organic richness in the studied depositional system. The gamma-ray tool was also useful in the identification of 2nd order Transgressive-Regressive facies cycles (and maximum flooding surfaces) and in the correlation between outcrop and subsurface data.
The ostracode genus Fossocytheridea Swain and Brown 1964 is emended herein. A summary of the diagnostic characters include: (1) a median sulcus, (2) a tripartite antimerodont hinge with distinct heart-shaped terminal elements, (3) distinct sexual dimor-phism; (4) a narrow inner margin that has 20-28 straight radial pore canals, and (5) variability in the external carapace (pore shape, pore density, and patterns of reticulation) that bears close resemblance to Cyprideis. Two new species are described from southwest Utah (U.S.A): Fossocytheridea mosbyense sp. nov. and Fossocytheridea kirklandi sp. nov. and 21 taxa previously assigned to Fabanella, Sarlatina, Ovocytheridea, Dolocytheridea, Antibythocypris, and Cytheridea are assigned to the emended genus. Fossocytheridea resem-bles Cyprideis with respect to both shell morphology and ecology since it occurs in association with euryhaline biota in coal-bearing strata. Expansion of marginal marine environments during the highest sea level of the Mesozoic saw Fossocytheridea successfully mi-grate and dominate restricted coastal environments. Since this expansion, the prominent characters of Fossocytheridea have been pre-served in descendent genera belonging to the tribe Cyprideidini Kollmann 1960 that are preserved to this day in Cyprideis.
Micropalaeontological investigation of one of a number of black shale horizons within the carbonate platform sediments of the Calcari Grigi Formation (Trento Platform, NE Italy) has yielded the first recorded oligohaline, early Jurassic, ostracod assemblage. The shale is dated as late Sinemurian on the basis of large benthic foraminiferal biostratigraphy in the sediments above and below. The shale is devoid of foraminifera and ammonites, which supports a non-marine context. Three previously unknown ostracod species are identified, however, the assemblage is dominated (>95%) by a single taxon which is erected as a new genus and species (Phraterfabanella tridentinensis Whatley and Boomer gen. et sp. nov.) which further supports the interpretation of a “stressed” environment. The two remaining ostracod taxa are assigned to Klieana and Limnocythere both considered to represent non-marine or very low salinity conditions. This new genus includes probable members from the Rhaetian of Hungary and France as well as from the Liassic of France. The new genus is shown to be one of the earliest representatives of the Cytherideidae, a family which survives to the present and includes the modern pandemic, euryhaline species Cyprideis torosa.The discovery of such an assemblage within an otherwise marine sequence indicates temporary, physical isolation from marine influence. Sedimentological, faunal and geochemical evidence suggests that the organic rich shale may indicate high organic carbon supply via continental runoff in this tropical palaeogeographical setting. Resulting dysaerobia within the sediment would have created a particularly stressed environment.
The paleoecology of limnic ostracodes is reviewd in the context of the evolution of their environment. In order to understand why there is a rich ostracode fossil record we examine data such as the quantitative and qualitative distribution of living ostracode species and ostracode assemblages (ways of describing and limitations). Importance of biological and physico-chemical factors for the local accumulation of high numbers of ostracodes and diversified assemblages is emphasized. We discuss the limits of extrapolations of information from ecology to paleocology. We stress how paleontological knowledge can be applied to neontological studies. The possibility of using Holocene ostracodes as indicators of morphometric changes of lakes, temperature, salinity, eutrophication and as a criterion of meromictic conditions is demonstrated.Relationships between ostracodes and the chemical environment and particularly the morphological response of the carapace are considered: e.g., diversity and qualitative composition of assemblages and chemical stability, types of carapace mineralization and ornamentation and chemistry of bottom waters. These ideas, developed from studies on Recent material, are tested for limnic Cenozoic faunas.In the Mesozoic, the main questions arising from the study of nonmarine ostracodes deal with the possible evaluation of paleosalinities in marginal lagoonal environments (Purbeck-Wealden) and with evaluation of depth and hydrochemical and paleoclimatological regime in truly lacustrine intracratonic basins.Some peculiarities of Paleozoic nonmarine ostracode assemblages are described. The paleoecological cause of changes in diversity of several ostracode groups in the Carboniferous and Permian is emphasized.
The upper Sinemurian to Pliensbachian series of the Lusitanian Basin (Portugal) correspond to marly limestone sediments rich in benthic and nektonic macrofauna. This sedimentary record includes several intervals of organicrich facies, which are particularly well developed in the western sectors of the basin. They correspond to grey and dark marls locally showing strong lamination (black shale type) and are recognized as one of the most important potential oil source rocks. This study shows the vertical and lateral distribution of these organic-rich intervals, supported by over 550 total organic carbon (TOC) determinations. The results presented reveal two important intervals, with several black shale occurrences, in the Oxynotum(?)–Raricostatum (Polvoeira Member of Água de Madeiros Formation) and at the top of the Ibex-upper part of Margaritatus zones (top of the Vale das Fontes Formation), showing in the distal (western) sectors up to 22% and 15% TOC, respectively. TOC values decrease progressively towards the proximal sectors, the youngest organic-rich interval being the most expressive at the basin scale. This lateral TOC distribution, the facies stacking patterns and the decrease observed in benthic macrofauna confirm that these intervals are related to 2nd-order transgressive phases. 2nd-order regressive phases, developed during the uppermost Raricostatum and Spinatum zones respectively, show lower TOC values. TOC distribution combined with other stratigraphic and sedimentological parameters enabled seven facies maps to be created for the time interval studied. At the regional scale, this study shows for the first time the good similarity between the upper Sinemurian-Pliensbachian sedimentary successions of the Lusitanian and Basque- Cantabrian basins.
This work synthesizes all of the observations since the late nineteenth century of the highly endemic Late Sinemurian (Obtusum Chronozone) ammonite faunas of the Lusitanian Basin. It is based mainly on recent abundant collections from the Penedo da Saudade section near São Pedro de Muel (Leiria, Portugal). This rich material (some eight species and four genera), collected bed by bed, allows us to propose an initial biostratigraphic, palaeobiogeographic, evolutionary and taxonomic synthesis of these mostly endemic faunas. The genus Epophioceroides n. gen. is new and three new species are identifi ed: Epophioceroides apertus n. gen. n. sp., Ptycharietites (Subgen. indet. A) asteroceroides n. sp. and Ptycharietites (Ptycharietites) heterogenus n. sp. So far they have been found at São Pedro de Muel only. The only non-endemic ammonite, Asteroceras sp. indet., collected from the base of the fossiliferous sequence, suggests an age in the Obtusum Chronozone for the subsequent taxa. Most probably faunas belong to the Stellare Subchronozone but taxa from the highest fossiliferous levels may also belong to the Denotatus Subchronozone. The newly collected material requires the morphological range of the genus Ptycharietites to be extended to include late forms that become either clearly evolute (subserpenticone) such as Ptycharietites (Pompeckioceras) cf. onchocephalus or clearly involute (suboxycone) such as Ptycharietites (? Subgen. indet. B) sp. indet. A. In terms of ontogeny, paedomorphosis – a rare “size-based” heterochronic process among the Asteroceratinae subfamily – is shown to be of major importance throughout the evolution of the genus Ptycharietites. In palaeobiogeographic terms all endemic Late Sinemurian (Obtusum Chronozone) ammonite faunas (Ptycharietites and Epophioceroides n. gen.) of the Lusitanian Basin remain poorly understood. While they suggest marked isolation of the Lusitanian Basin and perhaps also constraining environmental conditions during the Obtusum Chronozone, there is nothing to indicate whether other basins of the “Iberia-Newfoundland” conjugate margins experienced the same endemic trend. Nor is it clear whether the Late Sinemurian endemic faunas are closely related to NW European or to W Tethyan (Mediterranean) faunas. However, the earliest ammonite collected from the São Pedro de Muel section (i. e., Asteroceras sp. indet., bed 500b) suggests a possible NW European affi nity.
The Triassic-Jurassic boundary in the North Celtic Sea and Fastnet Basins is difficult to recognize because of variable poor recovery of short-ranging palynomorphs and ostracod taxa. There are no clear lithological breaks coinciding with the system boundary. Micropalaeontological and palynological analysis of ditch-cutting samples from 10 wells has allowed a composite workable biostratigraphy to be established, based on range tops and abundances of selected taxa. Petrophysical log interpretation has been used to identify lithological units by comparison with those described from the British onshore. Four associations of ostracod and palynomorph taxa have been identified. These have been used to recognize the Hettangian and Rhaetian stages, and to distinguish lowermost Sinemurian-uppermost Hettangian and lowermost Hettangian-upper Thaetian intervals. Correlation of the proposed succession with micropalaeontological and stratigraphical successions of the Triassic-Jurassic stages of onshore Britain and Europe is discussed. -Authors
Rhaetian, Hettangian and Sinemurian Ostracoda from the Fastnet Basin, offshore southwest Ireland are described. Twenty-one genera representing forty-one species; thirteen of which are new, were recovered from 247 productive samples. The resulting biostratigraphy and palaeoecology are discussed with reference to other selected areas. -Author
The Lower Jurassic sequence and ostracods from 36 borings within the Danish Embayment are analysed and described.Hettangian, Sinemurian and Pliensbachian are demonstrated on the basis of extensive ostracod faunas, whilst only weak indications of Aalenian have been found.The following ostracod zones are defined as a basis for a biostratigraphical subdivision of the Lower Jurassic series in the Danish Embayment:The Ogmoconchella adenticulata - Nanacythere (Nanacythere) simplex Zone (Upper Pliensbachian).The Ogmoconchella danica Zone (Upper Sinemurian and Lower Pliensbachian).The Gramannella apostolescui - Kinkelinella (Klinglerella ) foveolata Subzone (Lower Pliensbachian).The Progonoidea reticulata Subzone (lowest Upper Sinemurian, Lias Beta-1a).The Cristacythere betzi - C. crassireticulata Zone (upper Lower Sinemurian).The Ogmoconchella aspinata Zone (Hettangian and lower Lower Sinemurian).The chronostratigraphical subdivision of the Lower Jurassic sequence in the Danish Embayment is presented, based upon the ostracod faunas described here and upon previous investigations of sediments, foraminifera and megafossils.The conditions prevailing in the basin are discussed, with descriptions of the sedimentary and faunal developments, and an evaluation of the relationships with other parts of the Northwest European area.124 ostracod species are described; 23 are described as new, whilst 30 species which cannot be referred to any known species are described with open nomenclature owing to limited or badly preserved material. The remaining 71 species have all been described previously and are more or less well-known. The 124 species fall into 27 genera or subgenera, of which 2 genera (Pseudomacrocy pris and Cristacythere) and 1 subgenus (Nanacythere (Goniocythere)) are established as new.A subdivision is made of the described Lower Jurassic "Procytheridea". The genus Klinglerella Anderson, 1964 is placed as a subgenus under Kinkelinella Martin, 1960. Pleurifera Gramann, 1962 and Progonoidea Gramann, 1962 are regarded as independent genera placed together with Kinkelinella and the new genus Cristacythere.The family Healdiidae is regarded as being represented by only three genera in the Lower Jurassic: Ogmoconcha, Ogmoconchella and Pseudohealdia. The Ontogenetic development of the muscle scar area in Ogmoconchella is shown to be a development from a simple muscle scar of the Pseudohealdia-type to a typical Ogmoconchella-scar.ree genera in the Lower Jurassic: Ogmoconcha, Ogmoconchella and Pseudohea!dia. The Ontogenetic development of the muscle scar area in Ogmoconchella is shown to be a development from a simple muscle scar of the Pseudohea/dia-type to a typical Ogmoconchella-scar.
The North-Lusitanian Subbasin has sustained a complex evolution which can be divided into five main stages: 1. Liassic Distension leading to the differentiation of the Arunca-Montemor lineament; 2. Lower Liassic Rifting with development of endemic ammonite-faunas (Upper Sinemurian); 3. Differential Subsidence (Middle Liassic to Lower Aalenian): eustatic changes were complicated by a strong acceleration of the differential subsidence; 4. Progradation of a carbonate platform Middle Aalenian to Lower Callovian); 4. The closure of the subbasin began during the Middle Callovian and was followed by emersion. There is an abridged English version. -English summary
The Lower Jurassic in the Lusitanian Basin (Portugal) is mainly represented by hemipelagic carbonated deposits rich in organic matter (OM). In this study, supported by a high-resolution stratigraphic and sedimentological framework, the analysis of the OM content of the Coimbra and Água de Madeiros formations in the reference outcrop sections of S. Pedro de Moel and Peniche is presented. This is a multidisciplinary approach to the study of 31 samples in these series, supported by organic petrography [palynofacies, spore coloration index (SCI) and random vitrinite reflectance (%Rr)] and organic geochemistry [total organic carbon (TOC) and biomarkers].The palynofacies analysis provides evidence that the OM is mainly composed of particles belonging to the amorphous organic matter (AOM) group. The phytoclasts correspond mostly to the non-opaque (translucent) subgroup, generally degraded and oxidized, with significant representation in some stratigraphic levels of the Coimbra Formation and the Polvoeira Member at Peniche. The palynomorphs are mainly composed of Classopollis pollen grains, zygospores, Acritarchs and Prasinophyte phycomata. The TOC data confirm that most samples are OM-rich, with some stratigraphic horizons of the Coimbra Formation reaching 8.8 wt.%. The predominance of marine OM was confirmed by the Pr/nC17 and Ph/nC18 ratios. The Pr/Fi and homohopane ratios (C35/C34) indicate that some stratigraphic horizons were deposited under dysoxic-anoxic conditions. Despite the organic-rich nature of these two units, the random vitrinite reflectance (%Rr = 0.45), the spore coloration index (3.0–4 0) and the presence of ββ hopanes suggest that these rocks, in terms of OM maturity, are thermally immature.
It is hypothesized that carbon and nitrogen isotopic compositions (delta C-13 and delta N-15) of fossil wood fragments will provide useful information regarding conditions prior, during, and after deposition. Eleven fossil wood samples were collected from the Sinemurian-lowermost Pliensbachian marly hemipelagic deposits of the Agua de Madeiros Formation at S. Pedro de Moel (Lusitanian Basin, Portugal), and analyzed using optical and geochemical methods to confidently determine their use in palaeoenvironmental studies. Organic petrography observations show that the fossil wood samples contain a wide variety of particles mostly related to the phytoclast group, but also include resin impregnations, palynomorphs, and/or marine amorphous organic matter. A significant positive correlation between total carbon content and delta C-13 is observed (defined by 8 out of 11 samples), and most samples have high delta N-15. These data suggest that isotopic compositions of the studied samples were severely affected by sedimentary and diagenetic processes (biological or related to early diagenesis and coalification). It is evident that various processes of alteration either acted on different samples of the studied stratigraphic interval, or occurred with different magnitudes. It is considered that future stable isotopic studies on fossil wood should involve detailed screening as presented in this study, to ensure a proper understanding of the biological (mostly biodegradation) or diagenetic processes affecting samples and their impact on the determined chemical proprieties.
In the Lusitanian Basin (central-western Portugal), the Lower Jurassic carbonate-dominated succession is thought to have significant source rock potential. One of the most important units is the Água de Madeiros Formation (Upper Sinemurian – lowermost Pliensbachian) which is composed of alternating organic-rich marls and limestones including black shale horizons. This paper is based on a study of this formation at its type locality at S. Pedro de Moel in western Portugal. Data includes Total Organic Carbon (TOC) measurements, palynofacies analyses and results of Rock-Eval pyrolysis presented within a high-resolution lithostratigraphic framework.
TOC contents were measured in some 200 samples from the Água de Madeiros Formation covering a stratigraphic interval of 58 m, and vary widely up to a maximum of about 22 wt %. Kerogen assemblages are dominated by marine amorphous organic matter with varying contributions by phytoclasts and palynomorphs. A majority of the 85 samples analyzed by Rock-Eval pyrolysis have S2 values above 10 mg HC/g rock, reaching a maximum of 78 mg HC/g rock. These high S2 values are correlative with maximum values of the Hydrogen Index which averages 355 mg HC/g TOC (maximum of 637 mg HC/g TOC). However in spite of these indicators of source-rock potential, the Água de Madeiros Formation in the study area is thermally immature or very early mature, as indicated by Tmax values below 437 °C and average vitrinite reflectance values of 0.43 % Ro.
Well-preserved dome-shaped carbonate stromatolites occur in the lowermost part of the Sinemurian of the Lusitanian Basin (Portugal), at S. Pedro de Moel region (W of the basin). Deposition in the region took place on a westward-dipping carbonate ramp. The stromatolitic mounds are not found anywhere else in the Sinemurian of the basin and therefore are regarded as specific bioevents. In contrast to marginal-marine stromatolitic crusts, subtidal carbonate mounds other than sponge-mounds have been seldom reported in the Lower Jurassic, in particular in the Sinemurian, either from Europe or North-Africa. Therefore, the case documented here contributes to enhance the knowledge on stromatolites of this age in the Peri-Tethyan and Proto-Atlantic regions. The depositional setting of the studied succession is interpreted as a mainly low-energy, restricted marine one, punctuated by higher-energy episodes and, locally, subjected to more open marine influence. The existence of a topographic high and detached shoals at a more distal location of the ramp is likely, considering regional seismic evidence, the record in offshore (to the W) wells of peloidal/ooid wacke-packstones with detrital quartz and occurrence of a few ooid grainstones in the studied section. The inferred positive relief would act as a physical constraint that, coupled with the low-gradient of the ramp, defined an embayment-like environment in which the prevailing ecological conditions must have been, for the part of the succession bearing the stromatolites, unfavorable for many benthic organisms, favoring the microbial community. The upper part of the succession suggests stepwise environmental openness to more marine influence alternating with frequent environmental restriction.
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A. C., 2013. Ostracodos do Sinemuriano superior da região de S.
Pedro de Moel e de Peniche: relação com o contexto sedimentar.
Comunicações Geológicas, 100 (Especial I): 49–54.
48, h = 0.28. 9 Male right valve, external view; L = 0.60, h = 0.30. 10 Male left valve, external view; L = 0.59, h = 0.32. 11 Male carapace, dorsal view; L = 0.58, h = 0 Sample PCR-251. 12 Male carapace, right view; L = 0.56, h = 0.33. 13 Female carapace, right view
- Ektyphocythere Retia
Ektyphocythere retia (Ainsworth 1989). Sample
PCR-253.
8 Female carapace, right view; L = 0.48, h = 0.28.
9 Male right valve, external view; L = 0.60, h = 0.30.
10 Male left valve, external view; L = 0.59, h = 0.32.
11 Male carapace, dorsal view; L = 0.58, h = 0.30.
12-16. Ektyphocythere sinemiurana (Ainsworth 1989). Sample
PCR-251.
12 Male carapace, right view; L = 0.56, h = 0.33.
13 Female carapace, right view; L = 0.51, h = 0.31.
14 Male carapace, left view; L = 0.56, h = 0.30.
15 Female carapace, ventral view; L = 0.50, h = 0.30.
16 Male carapace, dorsal view; L = 0.57, h = 0.33.