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Late Devonian facies variety in Iran: volcanism as a possible trigger of the environmental perturbation near the Frasnian-Famennian boundary

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Mahmudy Gharaie M. H. , Matsumoto R. , Kakuwa Y. , Milroy P. G.

Geological Quarterly

2004

tom Vol. 48, No 4

323-332

Upper Devonian successions surrounding the Frasnian-Famennian (F-F) boundary in Iran consist of mixed carbonate/silisiclastic deposits. The successions are characterized by conspicuous ferruginous limestones, clay-rich units, black shales, and mafic volcanic rocks that provide important insights into palaeoenvironmental conditions during this interval of Earth’s history. An increase of kaolinite/illite ratio in clays associated with the F-F boundary suggests that increased chemical weathering was facilitated by warm and humid climatic conditions. Distinctive ferruginous-oolite deposits overlying the crucial Frasnian-Famennian boundary interval indicate a high supply rate of Fe-bearing clay originated during enhanced weathering under such climatic conditions. Black shales associated with the F-F boundary are interpreted to be the result of a high primary productivity caused by an increased influx of land-derived nutrients and regional volcanic activity. Widespread rift-related, basaltic activity along eastern Laurussia and northern Gondwana during the mid-Late Devonian is believed to have contribution to this global warming surrounding the F-F boundary.

The choristoderan reptile Monjurosuchus from the Early Cretaceous of Japan

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Matsumoto R. , Evans S. E. , Manabe M.

Acta Palaeontologica Polonica

2007

tom 52

nr 2

The choristoderan reptile Monjurosuchus is described from the Lower Cretaceous Tetori Group of Japan on the basis of an associated specimen from the Kuwajima Formation, Ishikawa Prefecture, and more fragmentary remains from the contemporaneous Okurodani Formation, Gifu Prefecture. This is the first report of Monjurosuchus from Japan, but a long−necked choristodere, Shokawa, has already been recorded from these deposits. Monjurosuchus was first described from the Lower Cretaceous Jehol Biota of China, although it has only recently been recognised as a choristodere. As reconstructed, the Japanese Monjurosuchus differs from the type species, Monjurosuchus splendens, in the structure of the postorbital region, reduction of the quadratojugal, a slender parietal with a deep groove along the interparietal suture, and elongation of the jugal. As in M. splendens, the lower temporal fenestrae are closed. A cladistic analysis was performed in order to place Japanese and Chinese taxa, including the incompletely described Chinese long−necked Hyphalosaurus lingyanensis, into choristoderan phylogeny. The results support the monophyly of Neochoristodera and of a Sino−Japanese clade of long necked choristoderes. The placement of the European Tertiary Lazarussuchus remains problematic, but the analysis supports its placement within Choristodera rather than on the stem. The identification of Monjurosuchus from Japan provides an additional link between the fossil assemblages of the Tetori Group and those of the slightly younger Jehol Biota of China.