FORTY YEARS OF GSSPS—A CRITICAL APPRAISAL

The use of boundary stratotypes to define chronostratigraphic units began in the 1960s, and, in the 1980s, these were called GSSPs (global stratotype sections and points). The first GSSP, defining the base of the Devonian System, was established in 1977. Now, approximately two-thirds of the Phanerozoic GSSPs (64 of 99 in 2011) have been ratified by the International Commission on Stratigraphy (ICS). However, this apparent progress toward precise definition of a Phanerozoic chronostratigraphic timescale is underlain by multiple problems that call into question the GSSP method. Most glaring among these problems is that many of the ratified GSSPs (particularly for the Paleozoic) are already being redefined largely because they are uncorrelateable, so the ICS chronostratigraphic scale is unstable and replete with false precision. Two nonscientific issues underpin the GSSP method: (1) many of its practitioners believe that once defined, a GSSP cannot be changed, and (2) the process of identifying, defining and ratifying a GSSP is mired in politics decided by the votes of small groups of specialists. In addition, many GSSPs have been questionably defined by arbitrarily chosen species-evolutionary events in supposed chronomorphoclines of microfossils. This produces GSSP criteria that often cannot be replicated and, because they are microfossil based, are invisible on outcrop and thus of no use to mappers and other geoscientists who are not among the handful of micropaleontologists who established the boundary criterion. Furthermore, some GSSPs have even been defined on non-unique criteria, such as magnetostratigraphic or chemostratigraphic events, that cannot be identified without resort to paleontological criteria. Indeed, the problems of the GSSP method are best underscored by considering how little research funding is devoted to it. The fact is that the politics and some of the practices of the GSSP method have convinced many that the process is non-scientific, so it is not considered worthy of support. By abandoning the GSSP method and refocusing the development of a chronostratigraphic timescale on identifying significant and broadly correlateable biochronological events to define time boundaries, an improved timescale is already possible for much of the Phanerozoic.