Chronology, time averaging, and oxygen isotope composition of harvested marine mollusk assemblages from Ifri Oudadane, northeast Morocco

Abstract

The archaeological site of Ifri Oudadane, NE Morocco, contains well-preserved marine mollusk concentrations throughout the Epipaleolithic (hunting-gathering) and Neolithic (food production) cultural phases, useful to test hypotheses driving such transition. However, the chronology and stratigraphy of harvested shells is complex due to the confluence of human activity and natural deposition processes. This work first quantifies the age and degree of time averaging of archaeological shells and then estimates sea-surface temperatures (SSTs) from the oxygen isotopes of selected specimens. Thirty-four radiocarbon-dated shells exhibited significant time averaging between 310 to 1170 yr that could not be explained by analytical error alone. This finding illustrates the need for individually dating shells in future paleoclimate investigations aiming for high temporal resolution. Nine isotopically analyzed shells dated to the Neolithic phase, between 5700 and 7600 cal yr BP, indicate that assuming constant oxygen isotopes of seawater, SSTs remained consistently warm, between 20°C and 22°C, that is, 2°C–4°C warmer than today. Results point to warmer conditions during the Neolithic, supporting the hypothesis that the rise of a food production mode of life in NE Morocco could have in part been triggered by warming conditions following the colder 8.2 event.

Comparing MICADAS Gas Source, Direct Carbonate, and Standard Graphite 14C Determinations of Biogenic Carbonate

“…The ability to rapidly measure the 14 C content of sub-milligram quantities of biogenic carbonate without conversion to graphite has risen in popularity over the past decade (e.g., Lougheed et al 2012Lougheed et al , 2018Bush et al 2013;Longworth et al 2013;Wacker et al 2013aWacker et al , 2013bDominguez et al 2016;Kosnik et al 2017;Ritter et al 2017Ritter et al , 2023Gottschalk et al 2018;Kowalewski et al 2018;Tuna et al 2018;Fagault et al 2019;Lindauer et al 2019;New et al 2019;Parker et al 2019;Albano et al 2020Albano et al , 2023aAlbano et al , 2023bMissiaen et al 2020;Dolman et al 2021;Mollenhauer et al 2021;Nawrot et al 2022;Sanchez et al 2022;Steger et al 2022). Dating small carbonate samples has become increasingly popular in time averaging or population structure studies (e.g., Kowalewski et al 2018;Nawrot et al 2022;Ritter et al 2023) and in the field of marine geochronology where a few dozen or even single large foraminifera can be dated (e.g., Lougheed et al 2018;Mollenhauer et al 2021).…”