Abstract

Measurements of 44Ca/42Ca and 143Nd/144Nd isotope ratios in carbonate fluorapatite (CFA) through the Aptian–Eocene section of the Negev (Israel), together with quantified rates of P and Ca accumulation and bulk sedimentation, permit an examination of the relationships of these five factors to Tethyan phosphogenesis. The data provide an Aptian–Eocene (ca. 70 Ma) record of the Ca isotope composition of 35 CFA samples (24 of which were also analyzed for Nd isotopes), representing 11 time-stratigraphic phosphate horizons within the sequence. The δ44Ca values are significantly lower in the Aptian–Albian samples (δ44Ca = −0.11‰ to −0.06‰) than in the Campanian–Eocene samples (δ44Ca = +0.22‰ to +0.42‰), whereas the εNd(T) values increase from continental crust like in the Aptian–Albian [εNd(T) = −10.9] to more radiogenic, Pacific-like [εNd(T) = −6.6 to −6.1] in the Campanian. Both peaks of δ44Ca and εNd(T) in the Campanian coincide with the peak of Tethyan phosphogenesis in the Negev, which is marked by a sharp increase of P accumulation rates (from <200 μmol·cm−2·k.y.−1 in pre-Campanian time to ∼1700 μmol·cm−2·k.y.−1 in the Campanian) and a decrease in rates of Ca accumulation and bulk sedimentation. The coincident increases of δ44Ca and εNd(T) values and P accumulation rates in the Negev area during the Campanian suggest that they are related in this time interval and were induced by the global Late Cretaceous sea- level rise and increasing circumequatorial Tethyan flow.

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