Mesozoic radiolarian biochronology - current status and future directions

摘要

Mesozoic radiolarian biochronologic scales have been developed since the 1970s and most of them reached their present day status in the 1990s. The degree of temporal resolution, on average, corresponds to substage level and is suf?cient to provide a meaningful framework for general geological studies. The great majority of zonal schemes were elaborated in low-latitude sections but are applicable in high latitudes as well because an adequate number of species occur worldwide. This paper presents a short historical review and a synthesis of currently used zonations developed in North America, Europe and Asia. The advantages and the shortcomings of the existing zonations are discussed. As a general rule, the zonations including a high number of taxa in each zone have a much greater applicability for global correlations than those de?ned exclusively with marker taxa. In the forthcoming years, particular studies will focus on zonal division of under-explored time intervals and on improved calibration to chronostratigraphy. Two joint objectives for future research are brie?y introduced. The ?rst objective, achievable in a relatively short time, is to compile a composite Mesozoic zonation that would provide a single reference standard for radiolarian dating at a global scale. The second objective is to re?ne the radiolarian zonal schemes, which, in certain intervals, have already attained the resolution comparable to that of the standard ammonite zones. To increase the degree of precision and accuracy to this level through the entire Mesozoic is a long-term goal that requires additional high-resolution sampling and emphasis on detailed documentation of evolutionary ?rst and last appearances in different phylogenetic lineages.