Texas State University




Radiocarbon assays from select archaeological-geoarchaeological research projects within Texas river basins were compiled and recalibrated using the same calibration curve (i.e., INTCAL09). Chronometric data from investigations within the Nueces, San Antonio, Colorado, Brazos, and Trinity River basins were uniformly calibrated to construct a consistent chronological framework. Once calibrated, the analogous chronometric data were then used to compare drainage basins, paleoenvironmental data, and cultural chronologies across Texas and the region. These comparisons revealed four periods (Synchronous Events I–IV) in the Holocene that occurred simultaneously within all of the examined drainage basins. Synchronous Event I dating to 8,750–8,250 cal yr BP (~6800–6300 BC), Synchronous Event II dating to 7,000–6,250 cal yr BP (~5050–4300 BC), and Synchronous Event III 5,250–5,000 cal yr BP (~3300–3050 BC) are apparent periods of instability. While Synchronous Event IV occurs at 1,000–750 cal yr BP (~AD 950–1200) represents a period of stability. These events may be attributed to previously identified widespread climatic changes and seemingly coincide with several transitions in the archaeological record.

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