THERE’S SOMETHING FISHY IN THE GREAT BASIN: A 15 KA PALEOHYDROLOGIC RECORD FROM FISH BONE ISOTOPES FROM THE PAISLEY CAVES, OREGON

Oxygen, carbon, and strontium isotope compositions of zooarchaeological materials can provide useful information about animal provenance and diet, yielding insight into past environmental conditions. Isotopes of fish remains in archaeological context have received relatively little study, despite excellent prospects for examining past aquatic habitats. The Paisley Caves archaeological site, located in southern Oregon, U.S.A., provides a unique opportunity to apply isotope analysis to fish remains to reconstruct the paleohydrology and paleoclimate of the northwest Great Basin. The site is located in the endorheic drainage basin of pluvial Lake Chewaucan, which fluctuated greatly in lake extent in response to climate change since the last deglaciation. Stratified sediments from the site are exceptionally well dated, continuously spanning the past 15 ka, and contain abundant sub-fossil fish bones. The fish assemblage is dominated (~99%) by fossils of the Order Cypriniformes, of which only the endemic Great Basin minnow species, tui chub (Siphateles bicolor), can be positively identified. The habitat tolerance of tui chub is wide, ranging from freshwater spring pools and streams to the highly evaporated, saline, alkaline lakes typical of endorheic drainage systems. Stable isotope compositions between fresh and saline environments also vary widely, which is reflected in the compositions of tui chub bone. Isotope provenance indicates all analyzed fish remains were derived within the Chewaucan basin. Tui chub were derived from an expansive Lake Chewaucan throughout the Bølling/Allerød, but mainly from freshwater-influenced sources by the late Younger Dryas to the present. Fish abundance dropped sharply through the Younger Dryas and early Holocene, when isotope compositions indicate a mix of habitats. Isotope compositions indicate the driest conditions during the middle Holocene, followed by slightly wetter conditions up to the present. This record agrees well with recent shoreline-based lake level constraints, and demonstrates the potential for use of similar methods in other sites in the Great Basin and beyond.