Ichthyolith

Abstract: To improve the resolution of ichthyolith stratigraphy in the Pacific Neogene and Oligocene, 12 new taxa are described, and their ranges are determined in Giant Piston Core 3 and in 104 samples dated by means of calcareous microfossils. These new ichthyoliths increase by one-third the number of reliable ichthyolith stratigraphic events for the sequences studied. The stratigraphic utilization of these microfossils is improved by adaptation of a scheme which assesses the relative reliability of earliest and latest occurrence data in correlated sequences. This procedure allows for less subjective decisions regarding the stratigraphic dependability of individual forms and provides a basis for choosing between conflicting correlation lines.

Abstract: Seventy meters of Cenozoic and Mesozoic pelagic clay cored at DSDP Sites 595 and 596 provide the basis for a preliminary analysis of ichthyolith biostratigraphy in the southwest Pacific. A most likely order of the more reliable ichthyolith events is compared with a synthesis of ichthyolith biostratigraphy in the North Pacific and with dated composite ranges. The resultant preliminary ichthyolith stratigraphy suggests that the Cenozoic is represented by the upper 20 m at Site 596 and 16 to 22 m at Site 595. Mixing of taxa precludes a clear recognition of the Cretaceous/Tertiary boundary at Site 595. The occurrence of 13 newly described subtypes is recorded in Mesozoic sediments at Sites 595 and 596. These new subtypes and previously described Mesozoic forms may be useful for recognizing Mesozoic subdivisions when their occurrences in sequences dated by other microfossils are investigated.