Chert intervals in DSDP and ODP sites (Table 1)

Radiolarian cherts in the Tethyan realm of Jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates. However, the widespread occurrence of cherts in the Eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones. In a new survey of the global spatio-temporal distribution of Cenozoic cherts in Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sediment cores, we found that cherts occur most frequently in the Paleocene and early Eocene, with a peak in occurrences at ~50 Ma that is coincident with the time of highest bottom water temperatures of the early Eocene climatic optimum (EECO) when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity. Cherts occur less commonly during the subsequent Eocene global cooling trend. Primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation. This timing of peak Eocene chert occurrence, which is supported by detailed stratigraphic correlations, contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and/or volcanism in a supposedly sluggish ocean of the EECO, followed during the subsequent middle Eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification, with the formation of chert as a result of biosilica transformation during diagenesis. Instead, we suggest that basin-basin fractionation by deep-sea circulation could have raised the concentration of EECO dissolved silica especially in the North Atlantic, where an alternative mode of silica burial involving widespread direct precipitation and/or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling-deficient conditions of the EECO. Cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones.

¡Me engañaste, me mentiste! La embajada persa a Atenas (Ar. Ach. 61-124) y sus implicaturas frente al público

Atendiendo a la relación establecida entre la comedia y los ámbitos político- legales que la circundan, se ha podido instituir un vínculo entre la ficción cómica y la realidad política de la Atenas clásica que se percibe fundamentalmente en las primeras comedias de Aristófanes. Dentro de Acarnienses podremos entonces determinar un nuevo punto de análisis si consideramos que en las breves declamaciones del persa se cifra uno de los recursos más notorios de la diplomacia estatal: la manipulación ante la asamblea del discurso de los embajadores de una nación por parte de la voz autorizada de la pólis receptora (Ammendola: 2001-2002). Será nuestro propósito abordar un costado diverso de esta escena definiendo su peso específico, aparentemente secundario, en la trama total de la obra. De ese modo nos interesará detectar la verdadera trascendencia del comportamiento del embajador persa respecto de los ciudadanos atenienses representados en la persona del viejo Diceópolis