Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The dolomite veins making up rhythmites common in burial dolomites are not cement infillings of supposed cavities, as in the prevailing view, but are instead displacive veins, veins that pushed aside the host dolostone as they grew. Evidence that the veins are displacive includes a) small transform-fault-like displacements that could not have taken place if the veins were passive cements, and b) stylolites in host rock that formed as the veins grew in order to compensate for the volume added by the veins. Each zebra vein consists of crystals that grow inward from both sides, and displaces its walls via the local induced stress generated by the crystal growth itself. The petrographic criterion used in recent literature to interpret zebra veins in dolomites as cements - namely, that euhedral crystals can grow only in a prior void - disregards evidence to the contrary. The idea that flat voids did form in dolostones is incompatible with the observed optical continuity between the saddle dolomite euhedra of a vein and the replacive dolomite crystals of the host. The induced stress is also the key to the self-organization of zebra veins: In a set of many incipient, randomly-spaced, parallel veins just starting to grow in a host dolostone, each vein’s induced stress prevents too-close neighbor veins from nucleating, or redissolves them by pressure-solution. The veins that survive this triage are those just outside their neighbors’s induced stress haloes, now forming a set of equidistant veins, as observed.

The upper Miocene Parilla Formation, Lorca Basin, Spain, provides an example of stacked high-frequency cycles of mixed carbonates and siliciclastics. Cycles developed on a steep carbonate ramp bordering an alluvialfan system. Three cycle variants are distinguished: siliciclastic-dominated cycles at the proximal part of the ramp, mid-ramp mixed carbonate – siliciclastic cycles, and carbonate-dominated cycles on the more distal parts of the ramp. The vertical thickness of these stacked simple sequences ranges from 0.7 up to 8 m. High-frequency changes in relative sea level resulted in a dynamic interplay between terrigenous sediment supply and carbonate production rates. During falling stage and lowstands, the alluvial system migrated basinwards and coarse-grained siliciclastics were deposited, whereas rising sea level and highstands provided optimal conditions for the production and accumulation of biogenic carbonates. Coral colonies up to 4 m thick provide a minimum measure of the magnitude of sea-level change involved in the development of the cycles. In contrast to previously documented simple carbonate sequences, this hybrid system of carbonates and siliciclastics preserves a more complete record of cyclic sea-level change, where terrigenous sediment supply compensated for the reduction in carbonate production during periods of falling and low sea level.

Exhumation in the Eromanga Basin of South Australia and Queensland has been quantified using the compaction methodology. The standard method of estimating exhumation using the sonic log has been modified and the adjusted sonic, the bulk density and neutron logs, have been used to estimate exhumation. Additionally the use of a single shale has not been adopted, and seven units, ranging in age from Cretaceous to Jurassic have been analysed. All units yield similar results; and burial at depth greater than currently observed is the most likely cause of overcompaction. The use of the adjusted sonic, bulk and neutron logs have been justified. This study has major implications for hydrocarbon exploration since predicted maturation of source rocks will be greater for any given geothermal history if exhumation is incorporated in maturation modelling.

The Early Mesozoic record of northern Gondwana was strongly influenced by sea level fluctuations during the opening of the Neotethys Sea. Detailed facies analysis of the Late Triassic / Early Jurassic Abu Shaybah Fm (Libya, western Mediterranean), and the Triassic Mukheiris Fm (Jordan, eastern Mediterranean) documents the transgressions and regressions that took place during the Neotethys opening. Both formations present similar facies and depositional environments, and are made up mainly by continental siliciclastic sequences and minor carbonate deposits. The facies arrangement in both zones indicates deposition in a tide-dominated environment as a part of a transgressive sequence, succeeded by a high-energy sandy fluvial deposition. In both regions the braided fluvial systems drained basinwards and impinged into the Neotethys Sea located to the north. The fluvial deposition of both formations ended abruptly due to renewed Neotethyan marine floodings that resulted in the development of carbonate shelf environments.

As a result of votes by the Subcommission on Carboniferous Stratigraphy [SCCS] that were ratified by the International Commission on Stratigraphy [ICS] and the International Union of Geological Sciences [IUGS] over the period 1999-2004, the official subdivision of the Carboniferous System has been substantially modified. For subsystems, the terms Mississippian and Pennsylvanian should be used in all regions of the world to replace the more ambiguous and more awkward terms Lower and Upper Carboniferous. Regional geographic names for series and stages may continue to be used in those regions in which they developed, specifically in Western Europe, the USA, and China. However, their global equivalents should be denoted equally, particularly as they become better correlated, in order to facilitate global correlation in future work. The SCCS also voted to standardize the scale of all regional units termed stages at rough equivalency with the global stages now recognized in the Carboniferous (which are similar in scale to those in the adjacent Devonian and Permian Systems). Therefore, the up to 26 subdivisions of the Tournaisian, Visean, Namurian, Westphalian and Stephanian of the regional western European classification should now be ranked and termed only as substages.

The Miranda do Douro orthogneiss was believed to be the oldest magmatic rock of the Central Iberian Zone, on the base of a U-Pb discordia upper intercept of 618 ± 9 Ma. Nevertheless, new ion-microprobe and LA-ICPMS U-Pb zircon dating revealed that the crystallization age was 483 ± 3 Ma. The orthogneiss also contains a 605 ± 13 Ma zircon population that indicates that the source-rock for the Ordovician magma was Pan-African. Moreover, a few ~3.17 Ga zircon grains were also recorded. These grains are the oldest found so far in Iberia, and its occurrence would suggest the involvement of an Archean crust in the Pan-African orogeny.

The new species Burlagonomegops alavensis (Araneae: Lagonomegopidae) is described from Lower Cretaceous (Aptian) amber from Álava (Basque Country), Spain. This is the first fossil spider to be described from this deposit and extends the known geological range of this family by approximately 15–20 Ma, from the previously oldest described lagonomegopid in Burmese amber. Given the broad geographic range of this family in the Cretaceous and their absence in Tertiary fossil resins, the global extinction of this family is enigmatic. In contrast to other spider families, it may be that the end-Cretaceous extinction event did have an effect on this strictly fossil family.

This study focuses on element behaviour during combustion in the Orhaneli thermal power plant (a 210 MW unit, Bursa-Turkey). A total of 51 samples, feed coals (FCs), fly ashes (FAs) and bottom ashes (BAs), which were systematically collected over an eight-week period, have been analysed for major, minor and trace elements (Al, Ca, Fe, K, Mg, Na, S, As, B, Ba, Be, Bi, Cd, Co, Cr, Cs, Cu, Ga, Ge, Hf, Hg, Li, Mn, Mo, Nb, Ni, P, Pb, Rb, Sb, Sc, Se, Sn, Sr, Ta, Th, Ti, Tl, U, V, W, Y, Zn, Zr and REEs). This study shows that FCs on an airdried basis have high moisture (av. 9%), high volatile matter (av. 33%), very high ash yield (av. 53%), relatively high sulfur content (av. 2.14%) and low gross calorific value (av. 1775 kcal/kg). Proximate analyses of combustion residues imply that BAs have higher contents of unburned carbonaceous matter than FAs. Mean values of trace element concentrations in FCs fall within the ranges of most world coals, except for Cr, Cs, Ni and U which occur in concentrations slightly higher than those determined for most of world coals. Some elements such as S, Hg, As, B, Bi, Cd, Cs, Ge, K, Pb, Rb, Sb, Se, Sn, Tl, and Zn are indicating enrichments in FAs. The remaining elements investigated in this study have no clear segregation between FAs and BAs. The mass balance calculations point to Ca content of feed coal controlling the partitioning of elements in this power plant, producing a high removal efficiency for highly volatile elements such as Hg, B and Se, and a high retention of As, Bi, Cd, Cs, Ge, Pb, Rb, Sb, Sn, Tl and Zn in FAs. However, the high enrichment in trace elements of FAs can increase the hazardous potential of this coal by-product.