Improved methods for isolating and validating indigenous biomarkers in Precambrian rocks

Hydrocarbon biomarkers in highly mature Precambrian rocks have the potential to provide important information about the diversity ecology, and evolution of early life, but studying them presents special analytical challenges. Extractable hydrocarbons are present in Archean and most Paleoproterozoic sedimentary rocks in such trace concentration that even slight contamination from petroleum-derived materials in situ or during drilling, storage, sampling, handling and laboratory analysis would compromise the results and, thereby, any consequent inferences. Here we report protocols that we have developed for the analysis of cores from several recently completed deep-time scientific drilling initiatives. By paying special attention to cutting, cleaning, crushing and extraction, it is possible to significantly reduce laboratory blanks to acceptable levels. When these methods are utilized, meaningful variations in the patterns of biomarkers over stratigraphic and lithologic boundaries provide compelling evidence for syngeneity.     

Anurans from the Candeleros Formation (?Cenomanian-Turonian) of west-central Argentina: new evidence for pipoid evolution

The fluvio-lacustrine deposits of the ?Cenomanian-Turonian Candeleros Formation in the northwestern fringe of Patagonia have yielded numerous remains of vertebrates, including anurans. A new, partially articulated immature specimen of a small pipimorph pipoid from the upper part of this unit is described herein. Although incompletely preserved, the morphology and proportions of the skeleton are strongly reminiscent of corresponding elements of the holotype of Avitabatrachus uliana from the lower section of the same formation at a nearby locality, thus suggesting that these specimens might represent the same, or a closely related, taxon. The new specimen is a metamorphosing individual: it has a zygapophyseal articulation between the sacrum and the neural arch of a postsacral vertebra that bears conspicuous transverse processes, and four pairs of ribs. These traits are not present in the available material of A. uliana, but they might have occurred within the normal range of variation of a single species. Although the generic and specific allocation of the new material is uncertain, a parsimony analysis performed to clarify the relationships of A. uliana supports a phylogenetic placement of this taxon outside the crown Pipidae. The evidence provided by the Candeleros anurans confirms the presence of stem pipids in Patagonia in the early Late Cretaceous.     

Failure of masonry arches under impulse base motion

Recent seismic events have caused damage or collapse of invaluable historical buildings, further proving the vulnerability of unreinforced masonry (URM) structures to earthquakes. This study aims to understand failure of masonry arches—typical components of URM historic structures—subjected to horizontal ground acceleration impulses. An analytical model is developed to describe the dynamic behaviour of the arch and is used to predict the combinations of impulse magnitudes and durations which lead to its collapse. The model considers impact of the rigid blocks through several cycles of motion, illustrating that failure can occur at lower ground accelerations than previously believed. The resulting failure domains are of potential use for design and assessment purposes. Predictions of the analytical model are compared with results of numerical modelling by the distinct element method, and the good agreement between results validates the analytical model and at the same time confirms the potential of the distinct element framework as a method of evaluating complex URM structures under dynamic loading. Copyright © 2007 John Wiley & Sons, Ltd.     

Nutrients, sea level and tectonics: constrains for the facies architecture of a Miocene carbonate ramp in central Italy

ABSTRACT In the western part of the central Apennines, Lower–Middle Miocene carbonates were deposited on a tropical–subtropical carbonate ramp. They record two long-term cycles, the first of which is illustrated in this paper. Between 21 and 17.5 Ma, Miocene carbonates, paraconformably overlying the Cretaceous limestones, record a transgressive event during a time of global (2nd order) sea-level lowstand. It is postulated that this deviation is related to an increase in tectonic subsidence. Between 17.5 Ma and 16–15 Ma, with a progressive relative sea-level rise, the inner–middle ramp facies belt stepped back, whereas the bryozoan-dominated outer ramp facies belt stepped back but simultaneously prograded. This bloom of suspension-feeding organisms is interpreted to reflect an increased nutrient availability, hence a change from oligotrophic to eutrophic conditions. Strontium-isotope dates constrain correlation of the second phase with a eutrophic event possibly linked to the influence of the neighbouring Apenninic accretionary wedge and foredeep system.     

Infections and Inequalities

Anthrax. The word conjures images of germ warfare, which is pretty ridiculous when you discover that we're not really sure anthrax has ever been used in this fashion. Germ warfare is certainly not what came to mind when a six-year-old girl showed up in our clinic with half of her face puffed up like a balloon, her right eye swollen shut (Figure 1). We were in rural Haiti, where a very different sort of germ warfare is the rule. So what came to mind that day was the word epidemic, and sure enough a young woman from the same village was also diagnosed with cutaneous anthrax—called charbon in Haiti, "malignant pustule" in the older textbooks—on her right chest wall. Soon after their arrival, both were receiving intravenous penicillin; they would recover completely. Later that night, the clinic's medical staff held a meeting. Another anthrax case had been diagnosed a few days earlier, and the patient was from the same area. It seemed increasingly likely that we were dealing with an epidemic. By morning, we learned that a young man from the village had just died of charbon. Why? "Because he didn't have enough money to get here." It costs no more than four dollars to take a truck from their village to our clinic. It was an epidemic, all right, and it had already taken a life.     

Paleomagnetic constraints on the Plio–Pleistocene geodynamic evolution of the external central–northern Apennines (Italy)

We report on new paleomagnetic results obtained from 27 sites sampled in the Plio–Pleistocene sequences at the external front of the central–northern Apennines. Previous analyses of Miocene (Messinian) sediments indicated that the present shape of the northern Apenninic arc is due to the oroclinal bending of an originally straight belt oriented around N320° and that vertical axis rotations accompanied the migration of the thrust fronts toward the Adriatic foreland [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153–3166]. We tried to provide new paleomagnetic constraints for the timing and rates of the oroclinal bending process during the Pliocene and the Pleistocene. The results suggest that CCW rotations observed in the northern part of the studied area are possibly younger than 3 Ma. No regional rotation is recorded in the Pliocene and Pleistocene sediments from the southern part of the study area, analogously to the Messinian sediments of the ‘Acquasanta’ domain of Speranza et al. [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153–3166]. A local significant CCW rotation (23°±10°) is identified in the Early Pleistocene sediments that crop out along the Adriatic coast between Ascoli and Pescara, indicating differential motion of the thrust sheets. This rotation must be younger than 1.43 Ma.     

Geological constraints for earthquake faulting studies in the Colfiorito area (central Italy)

On September 26, 1997, at 00.33 h(GMT), a Mw 5.7 earthquake occurred in the axial zone of theUmbria-Marche Apennines of central Italy, in the Colfiorito basin area. At09.40 h (GMT), a M_w 6.0 earthquake again struck the area withinthe Colfiorito basin, a major intramontane basin filled with Quaternarycontinental deposits. The two main shocks, and the associated aftershockswere within a roughly NNW-SSE trending zone of largest damage (Imax10), in which ground deformation has been observed. Along this trend,Cello et al. (1997a) had mapped a few capable faults, showingtranstensional to pure extensional kinematics. Field inspection of themapped faults, carried out after the main shocks, revealed that some ofthem were locally reactivated (for lengths of several hundreds metres andsurface slip in the range of 2–8 cm) during the September 26, 1997earthquakes.     

Demographic variation in a desert shrub, Larrea tridentate, in response to a thinning treatment

We performed a perturbation experiment to determine the relative importance of intra-specific competition on the demographic performance of a population of creosotebush, Larrea tridentata. From 1992 to 1995, we followed 1000 individuals, half of which were in plots subjected to a thinning treatment, and the other half were in unmanipulated plots. We found no significant response to the thinning treatment for any of the traits studied. The strict interpretation of these results is that intra-specific competition is not important in this Larrea population.