A proposed Global Boundary Stratotype Section and Point for the base of the Middle Ordovician Series： The Niquivil section, Precordillera of San Juan, Argentina

The Niquivil section, Argentine Precordillera, fulfills most of the requirements for a Global Stratotype Section and Point （GSSP） for the base of the Middle Ordovician Series. It has excellent conodont biostratigraphy in a continuous succession of uniform lithology, is readily accessible, and the critical interval is not tectonically affected. The position of the Lower/Middle Ordovician Series boundary in the Central Precordillera is placed at the middle part of the San Juan Formation, an open-platform carbonate unit. The Niquivil section is proposed as a GSSP for the base of the Middle Ordovician, which is marked by the FAD of the conodont Cooperignathus aranda （Cooper）. It occurs in level NCA, at the upper part of the Oepikodus evae Zone （overlapping uppermost records of O. evae in association with other guide species）; i.e., 100.15 m above the base of the reference section. The auxiliary Pena Sombria section from northern Precordillera records graptolites of the lower （but not lowest） Middle Ordovician in the Isograptus victoriae maximus Zone, few meters above the proposed boundary biohorizon. The range of C. aranda can be correlated with the I. victoriae lunatus Zone up to the lower part of the Undulograptus austrodentatus Zone in diverse sections of the world. C. aranda presents cosmopolitan distribution and occurs in virtually all environments. The proposed GSSP preserves a carbon-isotope record that provides an auxiliary marker of potential global application. Radiometric dating of K-bentonite samples, interbedded with carbonate strata yielding lower records of C. aranda, were recovered from the auxiliary Talacasto section in Central Precordillera （469.8 ±2.3 Ma, U-Pb SHRIMP dating）.

WEIGHTED INEQUALITIES AND APPLICATIONS TO BEST LOCAL APPROXIMATION IN LUXEMBURG NORM

In this paper we establish a result about uniformly equivalent norms and the convergence of best approximant pairs on the unitary ball for a family of weighted Luxemburg norms with normalized weight functions depending on ε, when ε→ 0. It is introduced a general concept of Pade approximant and we study its relation with the best local quasi-rational approximant. We characterize the limit of the error for polynomial approximation. We also obtain a new condition over a weight function in order to obtain inequalities in Lp norm, which play an important role in problems of weighted best local Lp approximation in several variables.

A UNIFIED APPROACH TO CERTAIN PROBLEMS OF BEST LOCAL APPROXIMATION

In this paper we study best local quasi-rational approximation and best local approximation from finite dimensional subspaces of vectorial functions of several variables.Our approach extends and unifies several problems concerning best local multi-point approximation in different norms.

Simultaneous Optimal Controls for Non-Stationary Stokes Systems

This paper deal with optimal control problems for a non-stationary Stokes system. We study a simultaneous distributed-boundary optimal control problem with distributed observation. We prove the existence and uniqueness of a simultaneous optimal control and we give the first order optimality condition for this problem. We also consider a distributed optimal control problem and a boundary optimal control problem and we obtain estimations between the simultaneous optimal control and the optimal controls of these last ones. Finally, some regularity results are presented.

The Farallon-Aluk ridge collision with South America:Implications for the geochemical changes of slab window magmas from fore- to back-arc

The collision of a divergent ocean ridge may evolve into two end cases： in the continuity of ocean-floor subduction, or in the detachment of the subducted plate. The northern Patagonia active plate margin has the unique situation that in Cenozoic time it has been subjected to two divergent ridge collisions, each one representing one of the end members. The Neogene Antarctica-Nazca divergent ridge collision evolved as a continuous ocean-floor subduction system, promoting a magmatic hiatus at the arc axis, the obduction of part of the ridge ocean-floor in the fore-arc, and basaltic volcanism in the back-arc. In contrast, the Paleogene Farallon-Aluk divergent ridge collision evolved into a transform margin, with the detachment and sinking of the Aluk plate and the development of a large slab window. As in the previous case, this collision promoted a magmatic hiatus at the arc axis, but the tectono-magmatic scenario changed to postorogenic synextensional volcanism that spread to the former fore-arc （basalt, andesite, rhyolite） and former back-arc （bimodal ignimbrite flare-up, basalt）. Geochemistry of this slab window synextensional volcanism shows more MORB-like basalts towards the former fore-arc, and MORB-OIB-Iike basalts towards the former back-arc. Instead, an isolated undeformable crustal block in the former back-arc, with an ＂epeirogenic＂ response to the slab window and extensional regime, was covered by OIB-type basalts after uplift. Major elements show that slab window basalts reach TiO2 values up to 3 wt%, as compared with the top value of 1.5 wt% of arc magmas. Besides, the MgO with respect to （FeOt ＋ A1203） ratio helps to distinguish slab window magma changes from the former fore-arc to the former back-arc and also with respect to the ＂epeirogenic＂ block. Higher contents of HFS elements such as Nb and Ta also help to distinguish this slab window from arc magmas and also, to distinguish slab window magma changes from the former fore-arc to the former back-arc and ＂epeirogenic＂ block settings. The isotope compositions of slab window magmatism show a disparate coeval array from MORB to crustal sources, interpreted as a consecluence of the lack of protracted storage and homogenization due to the extensional setting.

Changes in call properties of Boana pulchella (Anura, Hylidae) in response to different noise conditions

The increasing expansion of urban areas leads to the emergence of new noisy environments that can affect animal communication.Calls play a crucial role in the mating displays of anurans,and the negative impact of anthropogenic noise-induced auditory masking has been reported in several species.We investigated the acoustic variation in 96 males(n=971 calls)of the treefrog Boana pulchella across acoustically undis-turbed sites and different noise conditions,associated with urban areas(URBAN)and roads(ROAD),in Central Argentina.We analyzed the effect of anthropogenic noise conditions on 6 temporal(call duration[CD],intercall interval,first and second note duration,internote interval,and call rate)and 3 spectral(dominant frequency of first and second note,frequency difference between them)call properties.The effects of temperature and size on acoustical variables were controlled.We observed differences in all call attributes among the noise conditions,except for intercall interval.Males exposed to URBAN and ROAD exhibited significant changes in CD,dominant frequency of the second note,and fre-quency difference between them.URBAN males had longest internote interval,while ROAD individuals displayed increased first and second note duration and call rates.Interestingly,ROAD males exhibited immediate changes in call rate in direct response to passing heavy vehicles.Our study emphasizes the impact of anthropogenic noise on the acoustic characteristics of B.pulchella calls.Understanding how animals adapt to noisy environments is crucial in mitigating the adverse effects of urbanization on their communication systems.Future investigations should explore whether the observed call adjustments are effective in avoiding or mitigating the negative consequences of anthropogenic noise on reproductive success.