Calpionellid zonation at the Jurassic/Cretaceous boundary within the ViglaLimestone Formation (Ionian Zone, western Greece) and carbon isotope analysis

The calpionellid standard zones, Crassicollaria, Calpionella and Calpionell opsis, identified in the Tithonian-Berriasian carbonate sequence at Paramyt hia (Ionian Zone, western Greece), have been subdivided into eight subzones : the Tithonian Crassicollaria Zone into the Crassicollaria intermedia and Crassicollaria brevis Subzones, the early Berriasian Calpionella Zone into the Calpionella alpina, Remaniella and Calpionella elliptica Subzones, and the late Berriasian Calpionellopsis Zone into the Calpionellopsis simplex, Calpionellopsis oblonga and Praecalpionellites murgeanui Subzones. On the b asis of this zonation the Jurassic/Cretaceous boundary (Tithonian/Berriassi an boundary) is equated to the lower boundary of the Calpionella alpina Sub zone. The carbon-stable isotope measurements performed on bulk samples from Paramythia indicated a decrease in delta(13)C values from the Tithonian to the Berriasian owing to (a) a decrease in transfer of organic matter into the sea caused by the lowering in Calcite Compensation Depth, (b) the prese nce of a deeper-water environment in the Ionian Basin and (c) a fall in the sea level and increased oxygenation of the water column. These changes, wh ich favoured the deposition of carbonates, led to a decrease in burial rate of the organic matter and to the fall in the carbon-stable isotope values. (C) 1999 Academic Press.