CONODONT BIOSTRATIGRAPHY AND FACIES ANALYSIS OF GIVETIAN ROCKS IN THE SPANISH CENTRAL PYRENEES

Combination of conodont biostratigraphy and microfacies studies in several sections from the same sedimentary basin possibilities the accurate correlation of rock units, the precise arrangement of the depositional events recorded in these rocks and the evaluation of whether they were related to local conditions or due to global sea-level fluctuations. Significant advances in refining the Pyrenean Givetian conodont zonation and its comparison with the standard one have been made in the last decade. All 10 conodont zones have been recognized by means of their index taxa. Four facies (A, B, D and E) and seven subfacies (C1, C2, C3, F1, F2, G1 and G2), which correlate with the Standard Microfacies of Wilson SMF1-3, 5 and 12 with some variants, are recognized and temporally arranged in the Givetian sequence from the Spanish Central Pyrenees. Wackestone and/or packstone dominates but grainstone are also common; mudstone are restricted to the Upper Givetian of Renanué section. Within the bioclastic components the dacryoconarids dominate. Oncoidal rudstone are restricted to one Middle Givetian section. Carbonate sedimentation dominates, but some siliciclastic input is recorded in the Middle and Upper Givetian. The facies correspond to an outer carbonate platform that comprises from the proximal platform to the deep basin. In the Lower Givetian, facies with turbiditic deposits from deep environments dominate. Two settings are identified: intrabasinal swell and toe-of-slope. During the Middle Givetian there is an ample spectrum of environments as reflection of sea-level fluctuations. In general, the environment changed from toe-of-slope at the rhenanus/varcus Zone to middle parts of talus during the ansatus Zone that locally, due to small storms, moved back to the toe-of-slope. At the end of the ansatus Zone and during the semialternans/latifossatus Zone a shallowing trend (proximal platform) developed in the westernmost section while deeper environments ruled the eastern sections. During the Upper GIvetian deep environments prevailed. On the whole, a regressive trend is inferred for the Lower and Middle Givetian rocks that is followed by a transgresive tendency, which started earlier in the eastern part of the Pyrenean Basin.