Formal subdivision of the Quaternary System/Period: Present status and future directions

The Quaternary System/Period and Pleistocene Series/Epoch were defined in 2009 by the Global boundary Stratotype Section and Point (GSSP) for the Gelasian Stage/Age (2.58 Ma), which aligns with Marine Isotope Stage (MIS) 103 and approximates the Gauss-Matuyama Chron boundary, contrary to earlier reports. The Vrica GSSP (1.80 Ma) was repurposed in 2011 to define the Calabrian Stage, effectively completing the Lower Pleistocene Subseries/Subepoch. The candidate for the Middle Pleistocene Subseries (and proposed Chibanian Stage) GSSP (similar to 774 ka) is the Chiba section, Japan. It aligns with MIS 19 and approximates the Matuyama-Brunhes Chron boundary (similar to 773 ka). The Upper Pleistocene Subseries, with a base traditionally marked by the onset of the Last Interglacial, is not yet defined by GSSP. The Holocene Series/Epoch was formally defined in 2008 by a GSSP in the NGRIP2 Greenland ice core with an age of 11,700 yr b2k (before 2000 CE) and in 2018 was subdivided, using climatic events at 8.2 and 4.2 ka, into the Greenlandian, Northgrippian and Meghalayan stages/ages and their corresponding Lower/Early, Middle, Upper/Late subseries/subepochs. The Northgrippian GSSP (8236 yr b2k) is defined in the NGRIP1 Greenland ice core, and the Meghalayan GSSP (4250 yr b2k) in a speleothem from Meghalaya, India. This subdivision formally introduces the rank of subseries/subepoch, and incorporates by far the briefest of all stages into the geological time scale. Using ice cores and a speleothem for GSSPs is unique to the Holocene. The presently undefined term Anthropocene is already used extensively and, like Holocene subdivisional terms, its functionality will be enhanced by formal definition. The Anthropocene should not be confused with anthropogenic: it reflects a tipping point in the Earth System response to the marked intensification of human impacts, not simply the fact of human impact. The geological Anthropocene, as currently envisioned, would start in the mid-twentieth century, holding the rank of series, and terminating the Holocene but not interfering with its subdivision other than to terminate the Meghalayan Stage.