Palaeoenvironmental control on distribution of crinoids in the Bathonian (Middle Jurassic) of England and France

Bulk sampling of a number of different marine and marginal marine lithofacies in the British Bathonian has allowed us to assess the palaeoenvironmental distribution of crinoids for the first time. Although remains are largely fragmentary, many species have been identified by comparison with articulated specimens from elsewhere, whilst the large and unbiased sample sizes allowed assessment of relative proportions of different taxa. Results indicate that distribution of crinoids well corresponds to particular facies. Ossicles of Chariocrinus and Balanocrinus dominate in deeper-water and lower-energy facies,with the former extending further into shallower-water facies than the latter. Isocrinus dominates in shallower water carbonate facies, accompanied by rarer comatulids, and was also present in the more marine parts of lagoons. Pentacrinites remains are abundant in very high-energy oolite shoal lithofacies. The presence of millericrinids within one, partly allochthonous lithofacies suggests the presence of an otherwise unknown hard substrate from which they have been transported. These results are compared to crinoid assemblages from other Mesozoic localities, and it is evident that the same morphological ad-aptations are present within crinoids from similar lithofacies throughout the Jurassic and Early Cretaceous

Oceanic response to Pliensbachian and Toarcian magmatic events: Implications from an organic-rich basinal succession in the NW Tethys

The Bächental bituminous marls (Bächentaler Bitumenmergel) belonging to the Sachrang Member of the Lower Jurassic Middle Allgäu Formation were investigated using a multidisciplinary approach to determine environmental controls on the formation of organic-rich deposits in a semi-restricted basin of the NW Tethys during the Early Jurassic. The marls are subdivided into three units on the basis of mineralogical composition, source-rock parameters, redox conditions, salinity variations, and diagenetic processes. Redox proxies (e.g., pristane/phytane ratio; aryl isoprenoids; bioturbation; ternary plot of iron, total organic carbon, and sulphur) indicate varying suboxic to euxinic conditions during deposition of the Bächental section. Redox variations were mainly controlled by sea-level fluctuations with the tectonically complex bathymetry of the Bächental basin determining watermass exchange with the Tethys Ocean. Accordingly, strongest anoxia and highest total organic carbon content (up to 13%) occur in the middle part of the profile (upper tenuicostatum and lower falciferum zones), coincident with an increase in surface-water productivity during a period of relative sea-level lowstand that induced salinity stratification in a stagnant basin setting. This level corresponds to the time interval of the lower Toarcian oceanic anoxic event (T-OAE). However, the absence of the widely observed lower Toarcian negative carbon isotope excursion in the study section questions its unrestricted use as a global chemostratigraphic marker. Stratigraphic correlation of the thermally immature Bächental bituminous marls with the Posidonia Shale of SW Germany on the basis of C27/C29 sterane ratio profiles and ammonite data suggests that deposition of organic matter-rich sediments in isolated basins in the Alpine realm commenced earlier (late Pliensbachian margaritatus Zone) than in regionally proximal epicontinental seas (early Toarcian tenuicostatum Zone). The late Pliensbachian onset of reducing conditions in the Bächental basin coincided with an influx of volcaniclastic detritus that was possibly connected to complex rifting processes of the Alpine Tethys and with a globally observed eruption-induced extinction event. The level of maximum organic matter accumulation in the Bächental basin corresponds to the main eruptive phase of the Karoo-Ferrar large igneous province (LIP), confirming its massive impact on global climate and oceanic conditions during the Early Jurassic. The Bächental marl succession is thus a record of the complex interaction of global (i.e., LIP) and local (e.g., redox and salinity variations, basin morphology) factors that caused reducing conditions and organic matter enrichment in the Bächental basin. These developments resulted in highly inhomogeneous environmental conditions in semi-restricted basins of the NW Tethyan domain during late Pliensbachian and early Toarcian time

Eficiência técnica da atividade leiteira em Minas Gerais: uma aplicação de regressão quantílica Technical efficiency of milk production in Minas Gerais: an application of quantile regression

O objetivo principal neste estudo foi analisar a influência de variáveis técnicas e econômicas sobre os índices de eficiência técnica de produtores de leite de Minas Gerais ao longo de pontos distintos da distribuição dos índices de eficiência utilizando-se a técnica de regressão quantílica. Os índices de eficiência técnica foram estimados com base em um modelo de fronteira estocástica utilizando-se dados de 875 produtores de leite do estado de Minas Gerais coletados no ano de 2005. Os principais resultados revelaram, na fronteira de produção, que possivelmente está havendo utilização extensiva do fator terra. De modo geral, a variável percentual de vacas em lactação foi a mais relevante na explicação da eficiência técnica em todos os quantis estudados, enquanto o percentual de mão-de-obra familiar utilizado foi importante para explicar apenas os menores níveis de eficiência. Além disso, foi encontrada diferença significativa entre os coeficientes estimados dos quantis em estudo, o que mostra que as variáveis explicativas não têm o mesmo impacto no aumento da eficiência em todos os pontos da distribuição.<br>The objective of this study was to evaluate the influence of technical and economic variables on the indices of technical efficiency of milk from Minas Gerais throughout distinct points of distribution of the efficiency indices by the technique of quantile regression. The technical efficiency indices were estimated based on a stochastic frontier model, using data from 875 milk producers in Minas Gerais state, Brazil, collected in 2005. The main results from production frontier showed the extensive use of the land factor. Overall, the variable percentage of lactating cows was the more relevant in explaining technical efficiency in all analyzed quantiles, whereas the percentage of household labor was important to explain only the lower levels of efficiency. Moreover, significant differences between the estimated coefficients of the quantiles were found in the study, which showed that the explanatory variables do not have the same impactation on increasing the efficiency at all points of distribution