## 1 Introduction  
Bones are complex biological systems containing information at many different levels (i.e., isotopic, molecular, biochemical, and structural). They are mainly composed of bioapatite crystals consisting of inorganic nanosized crystallites of hydroxyapatite, Ca\({}_{5}\)(PO\({}_{4}\))\({}_{3}\)(OH), that are closely intertwined with an organic matrix composed by type I collagen and proteins [1]. After death, bones are subjected to modifications in terms of structure, morphology, and chemical composition; in general, the organic matrix is degraded, while the biomineral component undergoes a transformation to a more crystalline status, with the substitution of hydroxyl (OH-) or phosphate (PO\({}_{4}\)\({}^{3-}\)) groups with (CO\({}_{3}\))\({}^{2-}\) ions (type A and B carbonated hydroxyapatite, respectively) and the replacement of Ca\({}^{2+}\) with other cations [1; 2; 3]. These alterations, which are also triggered by the environmental conditions and addressed as diagenesis, depend on several factors, including the uptake of cations, ions' exchange, degradation and leaching of collagen, microbiological attack, alteration, and, in some cases, leaching of the mineral matrix, infilling with mineral deposits, etc. [4; 5; 6]. The precise evaluations of the extent of diagenesis in archaeological bones is crucial for the reliable use of specific parameters, such as the chemical and isotopic composition, for studies regarding the diet and provenance of ancient populations [7]. In fact, diagenesis is not only concerned with the changes taking place in bones during burial, but it is also related to how the environment affects these changes to alter specific information [8]. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy is a quick, cost-effective, and non-destructive technique that is useful for studying the chemical and structural features of solid samples, including bones and teeth, which cannot be analyzed in transmission mode, since the radiation cannot pass through [9; 10; 11; 12]. This technique obtains qualitative and quantitative information at a molecular level, not only regarding the mineral component, but also the organic matrix [10]. ATR-FTIR spectroscopy relies on the use of high refractive index crystals, such as diamonds and germaniums, within which the IR radiation can propagate as an internal reflection [13]. Even if the radiation is quite completely refracted by the surface of the sample, an evanescent wave is generated, which penetrates the sample and generates the corresponding IR spectrum. ATR-FTIR presents several advantages with respect to other conventional methods; in fact, it works independent of the sample type or thickness, and, therefore, a broad variety of materials can be measured [14]. The average spatial resolution of this technique is in the range of 100 \(\upmu\)m, which is not high compared to other molecular spectroscopic techniques [15]. As an example, it has been used to assess postmortem changes in the bioapatite crystals (by analyzing specific spectral parameters, such as IRSF, FWHM\({}_{603}\), C/P, and MM) and in the organic matrix, by evaluating the amount of proteins with respect to inorganic phosphates [5; 10; 16; 17]. The basis of Fewet is located along the upper course of Wadi Tanezzuft, about 1200 km south of Tripoli and SE to Hammada El-Hamra in the Fezzan, which is next to the border between Libya and Algeria. The geomorphological description of the area has already been reported [18; 19]. Excavations in the Fewet oasis revealed a rural village with a necroolis dated to the Garamatian time (3 rd century B.C.-2 nd century A.D.) [20], which represents one of the oldest settlements in SW Fezzan. This necroolis covers an area of approximately 150 hectares [21] and is set on the plateau located E to S of the Fewet village (Figure 1) hosting the Hasawnah Formation.