Sedimentary Dosimetry for the Saradj-Chuko Grotto: A Cave in a Lava Tube in the North-Central Caucasus, Russia.

Bonnie A B Blackwell,Clara L C Huang,Mehak F Kazi,Vladimir B Doronichev,Joel I B Blickstein,Liubov V Golovanova,Ekaterina V Doronicheva,Impreet K C Singh

doi:10.3390/mps3010020

Abstract

Karst caves host most European Paleolithic sites. Near the Eurasian-Arabian Plate convergence in the Caucasus’ Lower Chegem Formation, Saradj-Chuko Grotto (SCG), a lava tube, contains 16 geoarchaeologically distinct horizons yielding modern to laminar obsidian-rich Middle Paleolithic (MP) assemblages. Since electron spin resonance (ESR) can date MP teeth with 2–5% uncertainty, 40 sediment samples were analyzed by neutron activation analysis to measure volumetrically averaged sedimentary dose rates. SCG’s rhyolitic ignimbrite walls produce very acidic clay-rich conglomeratic silts that retain 16–24 wt% water today. In Layers 6A-6B, the most prolific MP layers, strongly decalcified bones hinder species identification, but large ungulates inhabited deciduous interglacial forests. Unlike in karst caves, most SCG’s layers had sedimentary U concentrations >4 ppm and Th, >12 ppm, but Layer 6B2 exceeded 20.8 ppm U, and Layer 7, >5 ppm Th. Such high concentrations emit dose rates averaging ~1.9–3.7 mGy/y, but locally up to 4.1–5.0 mGy/y. Within Layer 6, dose rate variations reflect bone occurrence, necessitating that several samples must be geochemically analyzed around each tooth to ensure age accuracy. Coupled with dentinal dose rates up to 3.7–4.5 mGy/y, SCG’s maximum datable ages likely averages ~500–800 ka.

Highlights

electron spin resonance (ESR) can establish absolute dates for fossils, like teeth and molluscs, which range from 4 Ma, depending on the radiation dose rates that the fossils experience in their depositional history
This study examines how the sedimentary radioactivity in a Paleolithic site found in a lava tube affects the ESR dating analyses by examining the dosimetry on Saradj-Chuko Grotto (SCG), a newly discovered Middle Paleolithic (MP) site occurring in a lava tube in the north-central Caucasus in Kabardino-Balkaria (Figure 1; Table 1)
Since clays adsorb Th, the SCG sediment contains 10–20 ppm more [Thsed] than those seen in most karst cave sediment

Summary

Introduction

ESR (electron spin resonance) can establish absolute (chronometric) dates for fossils, like teeth and molluscs, which range from 4 Ma, depending on the radiation dose rates that the fossils experience in their depositional history. Like the other trapped charge dating methods, like thermoluminescence (TL), optically stimulated luminescence (OSL), and radioluminescence (RL), ESR measures the intensity of a radiation-induced signal recorded in the datable mineral compared with the rate at which that radiation irradiates that mineral when deposited in sediment’s can date the hydroxyapatite in tooth enamel, carbonate minerals in molluscs and other invertebrates, and quartz in fault gouge and quartz-rich sediment. If a tooth experiences a low total radiation dose rate, DΣ(t), the minimum and maximum datable ESR age limits will be relative old, whereas a high DΣ(t) translates into much younger minimum and maximum age limits. By comparing the radiation doses accumulated in tooth enamel, AΣ, with DΣ(t) affecting the enamel, ESR dating can calculate an ESR age: t1

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Conclusion