|mhorn||Дата: Monday, 12.09.2011, 15:59 | Сообщение # 1|
|Dera G., Neige P., Dommergues J.-L., Brayard A (2011) Ammonite paleobiogeography during the Pliensbachian–Toarcian crisis (Early Jurassic) reﬂecting paleoclimate, eustasy, and extinctions // Global and Planetary Change. Vol.78. P.92–105. |
The Pliensbachian–Toarcian crisis (Early Jurassic) is one of the major Mesozoic paleoecological disturbances when ca. 20% of marine and continental families went extinct. Contemporaneously, profound paleobiogeographical changes occurred inmost oceanic domains including a disruption of ammonite provincialismduring the Early Toarcian. Here, we quantitatively reappraise the structure and evolution of paleobiogeographical patterns displayed by ammonite faunas before, during, and after the biological crisis, over a time-interval including 13 biochronozones. The high-resolution study presented here involves the use of hierarchical Cluster Analyses, non-metric Multi-Dimensional Scaling methods, and Bootstrap Spanning Network approaches that we apply to a large database including 772 ammonite species from 16 northwestern Tethyan and Arctic basins. Our results conﬁrm a robust faunal dichotomy between Euro-Boreal and Mediterranean areas throughout the Pliensbachian, with the ﬁrst emergence of an Arctic biome during the cooling regressive event of the SpinatumZone.Whatever its complexity, Pliensbachian provincialismcould be directly linked to paleogeographical barriers and to latitudinal paleoclimatic and paleoecological contrasts. During the Early Toarcian, this pattern was progressively lost, with northward expansions of Mediterranean ammonites during the TenuicostatumZone, followed by a strong interprovincialmixing during the Falciferum Zone. This faunal homogenization results from the combination of several parameters including a major sea-level rise facilitating basinal connections, a global warming event stretching the spatial range limits of southern taxa, and a mass extinction preferentially removing endemic species. Ammonite provincialism, although slightly different, was progressively re-established during the cooling regressive trend of the Middle Toarcian. These results therefore suggest a paramount inﬂuence of paleoclimatic, eustatic, and extinction constraints on the paleobiogeography of Early Jurassic ammonites, even if some threshold effects or independent biological factors may sporadically complicate the patterns.
Thanks to G. Dera for this pdf!
Middle Jurassic - Lower Cretaceous ammonites & aptychi