Pyritized radiolarians and siliceous sponges from oxygen-restricted deposits (Lower Toarcian,Jurassic)

In Lower Toarcian marls and marly limestone deposits from the South Iberia Paleomargin (Fuente Vidriera section, Betic Cordillera, southern Spain), siliceous skeletons of radiolarian and spicules of hexactinellid sponges are preserved in pyrite. The original siliceous skeletons (hydrated amorphous silica) were dissolved and totally replaced by pyrite. The radiolarians are locally very well preserved as independent remains or fused to pyrite framboids, in some cases distorted by the pyrite framboid growth. Pyritization of the remains and decay of the organic matter of these organisms by sulphate-reducing bacteria favored the early pyritization at the same time that silica dissolved. Pyrite formation was associated with organic matter decay through sulphate reduction; the amorphous silica skeleton acts either as a nucleation substrate or induces precipitation of pyrite precursors during biogenic silica dissolution. The organic matter may also help to stabilize colloids that are important for framboid precipitation. Pyritization occurred soon after the death of the organism, taking place in the upper sediment column just below the sediment–water interface, at the redox boundary where oxygen-bearing and hydrogen sulphide-bearing waters are in contact. The size of pyritized radiolaria (>40 μm) and the mean size of pyrite framboids (6.3–7.1 μm) are compatible with pyritization within the sediment–water interface under dysoxic conditions. The presence of trace fossils and benthic foraminifera exclude anoxic and euxinic conditions during the early Toarcian in this setting.     

Influence of different occupations with possible mutagenic effects on reproduction and level of induced chromosomal aberrations in peripheral blood.

In a group of 200 dysfertile couples (400 persons), the possible role of different occupations in failures of reproduction was assessed. These couples were examined from different points of view, classical genetic examination (pedigree, kayrotype, etc.) included. The suspected genotoxic effects in the personal history were checked also by testing the level of induced chromosomal aberrations. A significantly increased level of induced chromosomal aberrations was detected in 37 persons, i.e., 9.3% of the whole group under study. The average level of induced aberration in these subjects was 6.8%, as opposed to the control group (fertile and dysfertile persons without any unusual exposure to mutagens) with a mean of 1.58% aberrant cells in peripheral blood. Most of the occupations with demonstrated genotoxic effects involve daily contact with chemicals of different types. In some persons also intensive therapy in the recent past had genotoxic effects.     

Slope breccias colonized by bivalves and serpulids during the Middle Jurassic (Subbetic,SE Spain)

The Middle Jurassic of the Intermediate Domain, in the northern Subbetic (External zones of the Betic Cordillera, SE, Spain), reveals the transition from hemipelagic limestones (Baños Formation) to overlying shallow-water oolitic limestones (Jabalcuz Formation). Near La Guardia (Jaén), the basal part of the succession that records this transition comprises clast-supported calcareous breccias 24 m thick. Transverse sections reveal a fan shape close to a normal fault. The upper parts of some breccia beds were colonized by bivalve patches that locally evolve to bivalve-serpulid bioherms. The bioherms are massive, with low relief and a metre-scale lenticular shape. Two main parts have been differentiated: a bivalve bioherm and a serpulid bioherm. The bivalve bioherm consists of densely packed mytiloids in life position with secondary serpulids, where the matrix is a grainstone of bioclasts, peloids, and ooids. Laterally, there are accumulations of reworked bivalves. The serpulid bioherm is made up of serpulid aggregates in a bioclast wackestone. On an unstable slope with abundant breccias, bioherm development took place in favourable periods of low sedimentation rate. The pioneer colonisers of the sea-bottom were mytiloid bivalves in relatively high-energy waters. Shell comissures were aligned parallel to the dip of the slope as an adaptation to feeding from the plankton and seston inputs associated with palaeocurrents. The intercalation of reworked bivalve beds likely indicates brief periods of higher-energy storm events. The serpulid bloom in the upper part of the buildups was probably related to a stage of low-energy conditions (as evidenced by the delicacy of these structures), which is congruent with the wackestone texture. The relief provided by the bivalves favoured the development of the serpulid bioherm phase in an elevated and advantageous position for suspension-feeding. The dense packing in these bioherms offered clear advantages in this unstable palaeoenvironment: (1) dense populations are less susceptible than isolated individuals to overgrowth by other sessile organisms or predator attacks; and (2) the interconnection among individuals enhances stability and resistance against high-energy events, and increases the growth potential of future generations. The interruption of bioherm growth was probably related to the deposition of new breccia beds and reworked oolitic limestones.     

Estimation of lipase activity by the diffusion plate method

A diffusion plate method for the assay of the activity of lipases in large series of samples was worked out. When using this method the maximum deviation was found to be ±3.8%.     

Tooth Size Variation in Assemblages of Tremacyllus (Hegetotheriidae,Notoungulata): Insights into Geographical Gradients,Systematics, and Sexual Dimorphism

Tooth size variation within fossil assemblages can be associated with intra- or interspecific variation, functional, developmental, and geographical factors, and/or sexual dimorphism. Understanding these sources of variation is necessary to develop diagnoses for fossil mammals, where teeth are usually the most frequent remains. Tremacyllus (Ameghino, 1891) (Hegetotheriidae, Notoungulata) is a genus of small-sized herbivorous mammals abundant in late Miocene to Pliocene outcrops of southern South America. Its simplified, euhypsodont dentition and size variability have hampered systematics studies and led, for instance, to an overestimation of the number of species. I analyzed tooth size variations within assemblages of Tremacyllus in a quantitative framework to test three hypotheses: (1) magnitudes of size variation are different among tooth loci and assemblages; (2) tooth size follows a geographical pattern within the analyzed sample (Bergmann’s rule), but is also associated with taxonomy; and (3) there is a correlation between size variation and sexual dimorphism reflected in distinguishable subgroups. Results indicate that patterns of variation might be associated with eruption time and/or functional position. Northwestern forms are larger than southwestern-Pampean ones, not conforming to Bergmann’s rule but revealing a strong influence of latitude. Size differences between assemblages agree with dental features that distinguish T. incipiens and T. impressus, allowing expanded species diagnoses. Two size subgroups might reflect sexual dimorphism in the absence of biostratigraphic or morphological differences between them. This interpretation indicates that northwestern specimens referred to T. diminutus should be referred to T. incipiens.