Standardised Sequential Loss-on-Ignition (LOI) Analysis for Geoarchaeological Applications v1

Loss-on-ignition (LOI) is one of the most widely used techniques for estimating sediment moisture, organic matter and carbonate contents owing to its simplicity, low cost and analytical reproducibility. Despite its widespread application, published LOI protocols differ considerably in the temperatures adopted for sequential drying and ignition, limiting methodological standardisation and reducing comparability among studies. This study presents a standardised sequential LOI protocol for sediment characterisation based on three thermal steps: drying at 70°C to determine moisture content, ignition at 500°C to quantify organic matter, and ignition at 950°C to estimate carbonate content. These temperatures were selected to maximise the analytical selectivity of each stage while minimising overlap between successive thermal reactions and limiting unnecessary mineralogical alteration. Drying at 70°C provides effective removal of free and adsorbed water while preserving sediment integrity; ignition at 500°C promotes efficient oxidation of organic matter with minimal interference from inorganic mineral phases; and heating at 950°C is generally sufficient to achieve complete decarbonation of the dominant carbonate minerals commonly present in sediments. The proposed protocol provides a simple, robust and reproducible workflow for the sequential determination of sediment moisture, organic matter and carbonate contents across a wide range of sediment types. Its application to sedimentological and geoarchaeological investigations facilitates methodological consistency, improves comparability among datasets and offers an analytically efficient approach for routine sediment characterisation. Introduction Loss-on-ignition (LOI) is a widely applied stepwise thermogravimetric method for the routine determination of moisture, organic matter and carbonate contents in sediments, through successive measurements of mass loss following controlled heating. Owing to its simplicity, cost-effectiveness, limited instrumentation requirements and high analytical reproducibility, LOI remains one of the reference methods for routine sediment characterisation in sedimentology, geoarchaeology, palaeolimnology, soil science and environmental research (Ball, 1964; Dean, 1974; Bengtsson & Enell, 1986; Boyle, 2001; Last & Smol, 2001; Heiri et al., 2001; Santisteban et al., 2004; Plater et al., 2015; Hoogsteen et al., 2015; Bensharada et al., 2022). This protocol was developed within the framework of the ERC Consolidator Grant project CAMP – (Re)Constructing the Archaeology of Mobile Pastoralism (ERC CoG 2022, Grant No. 101088842), which investigates the formation, preservation and archaeological visibility of anthropogenic deposits associated with mobile pastoral occupations in arid and semi-arid environments through an integrated geoethnoarchaeological approach (Biagetti, 2025; Biagetti et al., 2026). The protocol is intended for the routine characterisation of unconsolidated terrestrial sediments collected from archaeological and ethnoarchaeological contexts in arid areas, including occupation surfaces, activity areas, buried soils and natural sedimentary deposits associated with anthropogenic sites. Within CAMP, LOI analysis provides complementary geochemical information that supports the interpretation of anthropogenic chemical signatures, site formation processes and the preservation of occupation deposits across both modern and archaeological pastoral landscapes. LOI is based on the progressive determination of mass loss during successive thermal steps, each targeting specific sediment fractions according to their thermal stability (Mackenzie, 1970; Brown, 1988). Initial drying removes free and adsorbed water, intermediate temperatures promote oxidation of sedimentary organic matter, whereas higher temperatures induce the thermal decomposition of carbonate minerals through decarbonation reactions accompanied by the release of carbon dioxide (Dean, 1974; Heiri et al., 2001; Santisteban et al., 2004). The cumulative mass loss recorded after each thermal step provides indirect estimates of sediment moisture, organic matter and carbonate contents and forms the basis of routine LOI determinations. Although LOI provides indirect rather than direct measurements of sediment fractions, the technique has been widely validated by previous research (e.g. Dean, 1974; Boyle, 2004; Heiri et al., 2001; Santisteban et al., 2004; Plater et al., 2015; Bensharada et al., 2022). Despite its widespread use, no universally accepted analytical protocol has been established. Published methodologies differ considerably in drying temperatures, ignition temperatures, heating duration, sample weight and furnace characteristics, reflecting differences in sediment composition, analytical objectives and laboratory practice (e.g. Boyle, 2001; Plater et al., 2015; Bensharada et al., 2022). Consequently, drying temperatures reported in the literature generally range between 40 and 105 °C, organic matter is commonly determined following ignition between 450 and 550 °C, whereas carbonate content is estimated after ignition between 900 and 1100 °C. Variations in these analytical conditions influence the extent to which individual sediment constituents contribute to mass loss during each thermal step because dehydration, organic matter oxidation, clay dehydroxylation and carbonate decomposition may partially overlap. Careful selection of drying and ignition conditions is therefore essential to maximise thermal discrimination between successive reactions while minimising physicochemical alterations that could bias mass-loss measurements. The analytical conditions adopted in this protocol were selected through critical evaluation of the published LOI literature and optimised for the routine characterisation of unconsolidated sediments from dry archaeological and ethnoarchaeological contexts investigated within the CAMP project. Rather than proposing a novel LOI methodology, the protocol provides a standardised and reproducible analytical workflow that integrates established experimental evidence with the specific sedimentological characteristics and research objectives of CAMP. The selected temperatures (70 °C for moisture determination, 500 °C for organic matter oxidation and 950 °C for carbonate decomposition) were established primarily through comparison with published LOI protocols and previous literature, supported by preliminary experimental observations. They were chosen to maximise thermal discrimination between successive analytical steps while minimising physicochemical alterations and overlapping reactions that could compromise the accuracy and reproducibility of mass-loss determinations.