STRONTIUM ISOTOPE STRATIGRAPHY - POTENTIAL RESOLUTION AND EVENT CORRELATION

A new generation Sr-87/Sr-86 isotope curve for the Phanerozoic seawate r, based on a compilation of 3635 stratigraphically well defined and w ell preserved skeletal components, results in a substantially narrower band, with some discrepancies, if compared to the 'curve' of Burke et al. (1982), which is based mostly on whole-rock samples. The results obtained from low-Mg calcite shells (foraminifers, belemnites, brachio pods and oysters) are mostly superior to those from phosphatic skeleta l components, such as conodonts, even if the latter are exceptionally well preserved (CAI less than or equal to 1.5). At this stage, the Pha nerozoic data set based on fossils is patchy for the Cambrian, Upper O rdovician-Lower Devonian and Upper Carboniferous-Triassic intervals. T he major practical constraint that precludes delineation of an unequiv ocal Sr isotope curve for the Phanerozoic seawater is the uncertainty in the assignment of absolute ages to the samples. As a result the cur ve is in reality a band. This is a reflection of the limitations of bi ostratigraphy and geochronology that are inherited by any derivative c orrelation and dating technique, including isotope stratigraphy. II is therefore unlikely that, in the near future, the Sr isotope stratigra phy will surpass the resolution capability of biostratigraphy as a glo bal correlation tool. On the other hand, if complemented by lithostrat igraphy, it is potentially a valuable tool for correlation of sequence s on intrabasinal and regional scales. Taking into account the above l imitations, careful consideration must be given to assignment of highe r order isotope peaks to specific 'events' within a biozone and to the use of such events as a global correlation tool. (C) 1997 Elsevier Sc ience B.V.