SPONGE SPICULE ASSEMBLAGES FROM THE MIDDLE ORDOVICIAN OF PONÓN TREHUÉ, SOUTHERN MENDOZA, ARGENTINA

Sponge spicule assemblages are described fom residues of conodont samples from Ordovician strata in the Sierra Pintada, southern Mendoza Province, Argentina. Spicules have been recovered from the Arenigian allochthonous megaconglomerates and from autochthonous limestones and carbonates sandstones of the Ponón Trehue Formation. This formation is a elastic-carbonate sequence representing olistostromic and turbidite facies. Conodonts in this formation are Llandeillan in age. The spicules are calcified and moderately preserved. The material shows a low diversity. Poriferan taxa found in this formation include heteractinid spicules as well as hexactinellid hexactines and non-lithistid demospongiid triaene and oxeas with some doubt. Associations of exclusively heteractinid spicules are restricted to allochthonous blocks of the shallow carbonate platform of the San Juan Formation (Arenig). In the outer platform and slope, autochthonous calcarenites and dark limestones contain hexactine spicules. These spicules evidence the existence of sponges in the Ordovician of the Ponón Trehue area, as a part of the Precordillera terrane.

Biostratigraphy and microfacies of the pelagic carbonate formations in the Yavorets section (Tithonian–Berriasian), Western Balkan Mts, Bulgaria

Calpionellid study has provided new evidence of early and late Tithonian age of the top of the Gintsi Formation, and of late Tithonian and early Berriasian age of the Glozhene Formation in the Yavorets section (Western Balkan Mts, Bulgaria). The calpionellid Chitinoidella, Praetintinnopsella, Crassicollaria, and Calpionella zones have been documented in successive order. Three calcareous dinocyst zones – Colomisphaera tenuis, Colomisphaera fortis and Stomiosphaerina proxima, have been determined in this lower Tithonian to lower Berriasian interval. From the base upwards, the following microfacies have been recognized: Saccocoma (Gintsi Formation, lower and upper Tithonian), Globochaete alpina, and calpionellid (Glozhene Formation, upper Tithonian and lower Berriasian). The base of the Berriasian has been traced at the explosion of the uniformly shaped spherical variety of Calpionella alpina. Evolutionary lineages of species of the genus Calpionella are discussed, as well as the vertical distributions and abundance peaks of crassicollarians. The calpionellid zones described herein are correlated with coeval zonations from the Western, Central and Eastern Tethyan domains. The regional correlation with previously studied sections of Tithonian/Berriasian pelagic carbonates in the Western Balkan Mts revealed a transition to hemipelagic deposition of the limestone-marl succession of the Salash Formation and/or sandstone accumulation during the middle to late Berriasian (Elliptica and Simplex calpionellid subzones) due to unstable conditions of the sedimentary environment. From the west to the east in the Western Balkan Unit (i.e., from the Rosomač section in eastern Serbia to the Sarbenitsa, Bov and Yavorets sections in the Iskar River Valley area), there is a trend of slight progressive deepening of the basin. This is manifested in the occurrence of redeposited shallow-carbonate-platform microfossils in the west to greater thickenesses of the Gintsi and Glozhene formations and occurrence of sandstone channel deposits in the east.

BIOTIC AND ABIOTIC EVENTS IN A SHALLOW CARBONATE PLATFORM (UPPER CRETACEOUS, SOUTH PYRENEAN MARGIN)

A detailed sedimentological and paleontological study of the Late Santonian-Late Campanian carbonate platform deposits of the Serres Marginals area (South margin of the Pyrenean Basin) has been performed. Three depositional shallow carbonate sequences have been distinguished (CI, C2 and C3). Within the shallow platform sequences moderate energy subtidal to intertidal, high energy sand-shoal, protected lagoon and restricted lagoon to lacustrine fades have been identified.