Late Pleistocene foragers, c. 35,000-11,5000 years ago
The boundary between this chapter and the previous one is set by the sudden mudflow of wet guano and its rapid reworking, Lithofacies 3 and 3R (the 'pink and white silts' defined in Chapter 3), which engulfed much of the archaeological zone of the West Mouth, partially covering the interbedded Lithofacies 2 and 2C and the human-occupation record contained within them, including the Deep Skull. The most important lithofacies for determining the history of this period of time is Lithofacies 4, the 'brown silts with anthropogenic deposits' immediately overlying Lithofacies 3 and 3R. The oldest radiocarbon dates from Lithofacies 4 are from charcoal in the Harrisson Excavation Archive, originally obtained at 60-66 inches depth in Trench Y /E3, of 35,890±250 bp or 40,489-41,613 cal. BP (OxA-15163), and from charcoal we obtained from the pit-infill deposits overlying Lithofacies 3 in Section 2.1 (Fig. 3.29), of 33,790±330 bp or 37,431-39,550 cal. BP (OxA-11302) and 29,070±220 bp or 33,121-34,518 cal. BP (OxA-11303). The boundary between this chapter and the next is the global transition to the Holocene, the modern climatic era, now dated in Greenland ice cores to 11,702 calendar years before the year 2000 (Rasmussen et al. 2006) but for convenience here rounded to c. 11,500 cal. BP. Lithofacies 4 continued to accumulate into the Early Holocene (Chapter 3).