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Long gaps in regional radiocarbon sequences are often considered evidence for occupation hiatuses, but they might also be a product of stochastic processes of occupation and limited numbers of dates. Here we show that, if radiocarbon dates over a span of time are distributed as a Poisson random variable (such that any point in that span has an equal probability of being dated), the gaps between dates will approximate a negative exponential distribution, with many short gaps and a few long ones. Long gaps between dates are to be expected under these conditions, even in the absence of true occupation hiatuses. This exponential distribution of gap lengths is robust even when the uniform probability assumption is relaxed, though true hiatuses have a distinctive, if subtle, signature. We use this model to assess the regional radiocarbon sequence from Qinghai Lake basin, western China, which shows two long possible occupation hiatuses during the period 12,500–4200 14 C BP. [ABSTRACT FROM AUTHOR]

Abstract: Dating and geomorphology of shoreline features in the Qinghai Lake basin of northwestern China suggest that, contrary to previous interpretations, the lake likely did not reach levels 66–140 m above modern within the past ∼90,000 yr. Maximum highstands of ∼20–66 m above modern probably date to Marine Isotope Stage (MIS) 5. MIS 3 highstands are undated and uncertain but may have been at or below post-glacial highs. The lake probably reached ∼3202–3206 m (+8–12 m) during the early Holocene but stayed below ∼3202 m after ∼8.4 ka. This shoreline history implies significantly different hydrologic balances in the Qinghai Lake basin before ∼90 ka and after ∼45 ka, possibly the result of a more expansive Asian monsoon in MIS 5. [Copyright &y& Elsevier]

Abstract: Qinghai Lake, located on the northeastern Qinghai–Tibet Plateau (Qing-Zang Gaoyuan), is China''s largest extant closed-basin lake. Its position relative to major Asian climate systems makes it sensitive to global climate change. The lake has been the subject of numerous paleoenvironmental investigations including dating of shoreline features around the lake basin. Here we report new age estimates of shoreline features, geomorphic exposures and archaeological sites that contribute to the development of a lake-level history for Qinghai Lake and a landscape model of the Qinghai Lake Basin. Lake highstands above 3230m (∼36m above the modern lake level) appear to date to late MIS 5, ∼70–110ka. The lake has had much more modest highstands since then: no evidence of MIS 3 lake stands higher than modern were found, and early Holocene highstands are no more than ∼12m above modern. If the age of highstands greater than 3230m is confirmed through future work, then the Qinghai Lake Basin hydrologic balance prior to ∼70ka was dramatically different than after that time, including during the Holocene. A simple hydrologic balance model provides insights into the combination of precipitation, evaporation, and runoff generation needed to sustain the lake at 3260m, the highest shoreline observed. A range of factors may explain the difference, primarily the relative strength of the East Asian monsoon. The basin was apparently subject to extensive alluviation during MIS 3, interrupted by widespread erosion and development of cryogenic features before and during the last glacial maximum (LGM). Loess that presently drapes much of the lower basin landscape began to be deposited after the LGM, ∼16–18ka. The landscape model outlined here has implications for archaeological visibility of early human occupation of the Qinghai–Tibet Plateau. [Copyright &y& Elsevier]