We analyzed the synchrony and diachrony of commonly used Neogene biostratigraphic events from data published in the Initial Reports of the Deep Sea Drilling Project (DSDP) and in the Proceedings of the Ocean Drilling Program (ODP). On the basis of the combined biostratigraphic and magnetostratigraphic evidence, new Neogene age models were constructed for 35 globally distributed DSDP and ODP holes. Biostratigraphic events from the four major plankton groups (calcareous nannofossils, diatoms, planktonic foraminifera, and radiolarians) were compiled from DSDP and ODP reports. After the elimination of possible sources of error such as stratigraphic hiatuses and reworking of specimens, 124 biostratigraphic events that occurred in at least four holes were analyzed in detail: for each event a biochronologic age estimate was derived by projection of the depth of the event onto the line of correlation of each hole, and from these a global mean age for each event was calculated, together with its standard deviation.

Average standard deviations for event ages by fossil group are: calcareous nannofossil first appearance datums (FADs): 0.57 m.y. (21 events), calcareous nannofossil last appearance datums (LADs): 0.60 m.y. (25 events), diatom FADs: 0.57 m.y. (7 events), diatom LADs: 0.85 m.y. (14 events), planktonic foraminifera FADs: 0.88 m.y. (22 events), foraminifera LADs: 0.68 m.y. (16 events), radiolarian FADs: 0.30 m.y. (9 events), radiolarian LADs: 0.31 m.y. (10 events). Since the average sample spacing in the sites used for this analysis is only 0.185 m.y., we have examined the data for true patterns of diachrony and for other biases. Diachrony is more frequent among cosmopolitan than among endemic taxa, thus there is a general trade-off between the obtainable age precision and the geographic extent of a bioevent. Precision of age calibrations also decreases with increasing age. Although some of these features may be due to investigator bias, they appear in part to be real phenomena, and thus could also provide opportunities for further exploration of important paleobiological processes, such as change in environmental gradients through time, evolutionary adaptation of species populations and migration due to water mass changes. ¿ American Geophysical Union 1994