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Luminescence Dating of Rock Surface. The Case of Monoliths from the Megalithic Sanctuary of Ossimo-Pat (Valle Camonica, Italy)

Luminescence Dating of Rock Surface. The Case of Monoliths from the Megalithic Sanctuary of... applied sciences Article Luminescence Dating of Rock Surface. The Case of Monoliths from the Megalithic Sanctuary of Ossimo-Pat (Valle Camonica, Italy) 1 , 2 , 2 , 3 4 Anna Galli * , Laura Panzeri * , Paolo Rondini , Ra aella Poggiani Keller and Marco Martini Istituto CNR-IBFM, via F.lli Cervi, 93, 20090 Segrate, Italy Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, via R. Cozzi 55, 20125 Milano, Italy; m.martini@unimib.it Dipartimento di Studi Umanistici, Università degli Studi di Pavia, Corso Strada Nuova 65, 27100 Pavia, Italy; paolo.rondini@unipv.it Già Soprintendente per i Beni Archeologici Della Lombardia- Ministero dei Beni e Delle Attività Culturali e del Turismo, 20100 Milano, Italy; rpoggianikeller@libero.it * Correspondence: anna.galli@unimib.it (A.G.); laura.panzeri@unimib.it (L.P.) Received: 30 September 2020; Accepted: 20 October 2020; Published: 22 October 2020 Featured Application: Dates obtained by optically stimulated luminescence (OSL) of rock artefacts and the underneath soils were shown to be in very good agreement with the archeological evidence. Highly satisfying results contribute to the understanding of a megalithic sanctuary. Abstract: Ossimo-Pat megalithic sanctuary (Valle Camonica, BS, Italy) is one of the most relevant archaeological findings of the southern alpine region, for the variety of its structures and the quality of its engraved monoliths. Its unique state of preservation gives the opportunity to apply the luminescence dating of the rock surface method. Here, we investigate the use of optically stimulated luminescence (OSL) for dating five cobbles from the site and compare cobble-surface derived ages to quartz OSL ages from sediments and to archaeological evidences. The obtained ages confirm the archaeological studies and open the way to a new hypothesis. Keywords: optically stimulated luminescence; surface dating; megalithic sanctuary 1. Introduction There are many examples of rock surfaces, rock art and stone structures of unknown age. In particular, in prehistoric archaeology, long-lasting building traditions can sometimes be dicult to date, if the context does not o er useful chronological tools, such as artifacts or organic remains associated to the structures. Moreover, this particular issue is not a marginal one, if we consider that the study of megaliths, drystone walls and other structures, such as cairns or mounds, is often crucial to our understanding of the society and traditions of very ancient cultures, devoid of other forms of communication. In this scenario, the Ossimo-Pat (Valle Camonica, BS, Italy, see Figure 1) megalithic sanctuary is an exemplary case. Appl. Sci. 2020, 10, 7403; doi:10.3390/app10217403 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 7403 2 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 9 Figure 1. Location of the Ossimo-Pat site in Middle Valle Camonica (GIS elaboration on LIDAR DTM base). Figure 1. Location of the Ossimo-Pat site in Middle Valle Camonica (GIS elaboration on LIDAR DTM base). Its construction started in the first half of the fourth millennium BCE and was structured and used during the Copper Age (late 4th–3rd millennium BCE), with ceremonial structures and engraved Its construction started in the first half of the fourth millennium BCE and was structured and monoliths articulated in a north-south alignment. The southernmost structure is a sequence of used during the Copper Age (late 4th–3rd millennium BCE), with ceremonial structures and ceremonial mounds, built upon a concentric series of stone circles enclosing an inner rectangular engraved monoliths articulated in a north-south alignment. The southernmost structure is a sequence space, which usually contained objects, such as flint weapons and tools or ornaments. The central of ceremonial mounds, built upon a concentric series of stone circles enclosing an inner rectangular part of the sanctuary was an alignment of monoliths of various lithologies, mainly sandstones of diverse granulometry, carved with figures and symbols and probably depicting mythical ancestors space, which usually contained objects, such as flint weapons and tools or ornaments. The central or gods. The alignment led to a monumental tomb and then to a series of at least five votive stone part of the sanctuary was an alignment of monoliths of various lithologies, mainly sandstones of circles, which contained, similarly to the southern mounds, a number of flint, stone, metal and ceramic diverse granulometry, carved with figures and symbols and probably depicting mythical ancestors artefacts, probably the result of unknown cult activity [1,2]. The site was frequented until its sudden, or gods. The alignment led to a monumental tomb and then to a series of at least five votive stone partial, dismantling and further abandonment, at the very beginning of Bronze Age, at the end of circles, which contained, similarly to the southern mounds, a number of flint, stone, metal and the 3rd millennium BCE. Later frequentation during the final Bronze Age and the whole Iron Age ceramic artefacts, probably the result of unknown cult activity [1,2]. The site was frequented until its is attested by a series of fireplaces that were lit in front and at the backside of the monoliths still sudden, partial, dismantling and further abandonment, at the very beginning of Bronze Age, at the vertically standing. Ossimo-Pat is one of the most relevant archaeological findings of the southern end of the 3rd millennium BCE. Later frequentation during the final Bronze Age and the whole Iron alpine region, for the variety of its structures and the quality of its engraved monoliths, as well as Age is attested by a series of fireplaces that were lit in front and at the backside of the monoliths still for its unique state of preservation, which gives the opportunity for a documentation of the exact vertically standing. Ossimo-Pat is one of the most relevant archaeological findings of the southern moment of its disuse. As part of the UNESCO World Heritage Site n.94 “Rock Drawings in Valle Camonica,” the sanctuary occupies an area of more than 4000 square meters, and it is located on the alpine region, for the variety of its structures and the quality of its engraved monoliths, as well as for right hydrographic flank of the medium Valle Camonica, at an altitude of 810 m asl. The site is arranged its unique state of preservation, which gives the opportunity for a documentation of the exact on the edge of a terrace overlooking a steep drop into the Valle dell’Inferno (the strikingly named moment of its disuse. As part of the UNESCO World Heritage Site n.94 “Rock Drawings in Valle “Valley of Hell”), placed on a wide elevated plateau comprised by two dominant peaks: the Pizzo Camonica,” the sanctuary occupies an area of more than 4000 square meters, and it is located on the Camino (2491 m asl) to the southwest and the Concarena (2549 m asl) to the north-east. The rocky right hydrographic flank of the medium Valle Camonica, at an altitude of 810 m asl. The site is substrate of the area is mostly made of Triassic (from the Scitic to the Carnic) limestones, while the arranged on the edge of a terrace overlooking a steep drop into the Valle dell’Inferno (the strikingly surfacing lithology is often covered by morainic deposits, left by the glaciers, which can be encountered named “Valley of Hell”), placed on a wide elevated plateau comprised by two dominant peaks: the up at an altitude of 1650 m asl. (source: F. Franzoni, Piano di Governo del Territorio, Comune di Pizzo Camino (2491 m asl) to the southwest and the Concarena (2549 m asl) to the north-east. The Ossimo, 2012 (http://www.comune.ossimo.bs.it/Allegati/all_50012_GEO_Relazione%20Geologica.pdf)). rocky substrate of the area is mostly made of Triassic (from the Scitic to the Carnic) limestones, while The monoliths chosen to be engraved are very likely coming come from these deposits, but the the surfacing lithology is often covered by morainic deposits, left by the glaciers, which can be geological survey and study is still ongoing. Excavations and analyses are being carried on since 1994 encount ande ar red e still upongoing, at an alunder titude o the f dir 165 ection 0 m as ofl. Ra (s ourc aellae: F Poggiani . FranKeller zoni, Pi (Figur ano d e 2i). Governo del Territorio, Comune di Ossimo, 2012 (http://www.comune.ossimo.bs.it/Allegati/all_50012_GEO_Relazione%20Geologica.pdf)). The monoliths chosen to be engraved are very likely coming come from these deposits, but the geological survey and study is still ongoing. Excavations and analyses are being carried on since 1994 and are still ongoing, under the direction of Raffaella Poggiani Keller (Figure 2). Appl. Sci. 2020, 10, 7403 3 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 9 Figure 2. Ortophotograph of the Ossimo-Pat site. Figure 2. Ortophotograph of the Ossimo-Pat site. There are two potential methods for dating the surfaces of such artefacts: the measure of There are two potential methods for dating the surfaces of such artefacts: the measure of cosmogenic radionuclides concentrations [3] and the application of luminescence dating (in particular cosmogenic radionuclides concentrations [3] and the application of luminescence dating (in Optically Stimulated Luminescence, OSL) [4,5]. The first approach depends on cosmogenic nuclides particular Optically Stimulated Luminescence, OSL) [4,5]. The first approach depends on cosmogenic 10 26 36 (e.g., Be, Al, Cl) build-up with time in minerals exposed to cosmic rays. Therefore, measuring 10 26 36 nuclides (e.g., Be, Al, Cl) build-up with time in minerals exposed to cosmic rays. Therefore, their concentrations allows determination of how long rocks have been exposed at or near the surface measuring their concentrations allows determination of how long rocks have been exposed at or near of the Earth. In this paper, we focus on the alternative approach based on OSL. This method was the surface of the Earth. In this paper, we focus on the alternative approach based on OSL. This originally developed to date the deposition of sediments [6] and it depends on the ability of some method was originally developed to date the deposition of sediments [6] and it depends on the ability minerals, such as feldspar and quartz, to absorb and store energy from environmental ionizing radiation. of some minerals, such as feldspar and quartz, to absorb and store energy from environmental When the light stimulates these minerals, they release the stored energy in the form of light, from which ionizing radiation. When the light stimulates these minerals, they release the stored energy in the the term luminescence is derived. Measuring the amount of energy released in conjunction with a form of light, from which the term luminescence is derived. Measuring the amount of energy released determination of the rate at which the energy was accumulated allows to calculate an age, indicating in conjunction with a determination of the rate at which the energy was accumulated allows to the time that has elapsed since the storage of energy began. calculate an age, indicating the time that has elapsed since the storage of energy began. Thus, if the OSL signal from mineral grains is normally used to date how long the sediment grains Thus, if the OSL signal from mineral grains is normally used to date how long the sediment were buried, recent works have shown that luminescence signals can also be used to determine the grains were buried, recent works have shown that luminescence signals can also be used to determine duration of daylight exposure for rock surfaces [4,7–9]. the duration of daylight exposure for rock surfaces [4,7–9]. The OSL surface dating technique exploits the depth-dependence of the resetting (bleaching) of The OSL surface dating technique exploits the depth-dependence of the resetting (bleaching) of the geological luminescence signal when exposed to daylight. Sohbati et al. [4,10] proposed a model the geological luminescence signal when exposed to daylight. Sohbati et al. [4,10] proposed a model that reproduces the dependence of the OSL signal on depth and exposure-time and predicts that the that reproduces the dependence of the OSL signal on depth and exposure-time and predicts that the longer the exposure duration, the deeper the resetting of the luminescence signal into the rock surface. longer the exposure duration, the deeper the resetting of the luminescence signal into the rock Analogously, this dependence has been evaluated for renaissance bricks [11]. surface. Analogously, this dependence has been evaluated for renaissance bricks [11]. Thus, there exists chronological information in the luminescence-depth profile, but despite Thus, there exists chronological information in the luminescence-depth profile, but despite some some applications of the OSL surface technique [8,9,12], the bleaching-depth model is yet to be applications of the OSL surface technique [8,9,12], the bleaching-depth model is yet to be validated validated experimentally; this is critical for further development of the technique. The emerging OSL experimentally; this is critical for further development of the technique. The emerging OSL surface surface dating technique has the potential to answer many new questions in the fields of geo- and dating technique has the potential to answer many new questions in the fields of geo- and archaeological sciences. archaeological sciences. Dating the sanctuary was mostly done through the combination of stratigraphy observations, Dating the sanctuary was mostly done through the combination of stratigraphy observations, typo-chronological study of the artefacts and with the use of a certain number of radiometric typo-chronological study of the artefacts and with the use of a certain number of radiometric measurements (14C) on charred coals from di erent parts of the site [1], mostly from the southern measurements (14C) on charred coals from different parts of the site [1], mostly from the southern mounds and the upper layers of the monoliths alignment. Therefore, to test the capability of the surface mounds and the upper layers of the monoliths alignment. Therefore, to test the capability of the dating technique, five pebbles were collected from three di erent areas. Three samples consisted of the surface dating technique, five pebbles were collected from three different areas. Three samples pebble itself and the sediment collected directly underneath the pebble. Dating was attempted on both consisted of the pebble itself and the sediment collected directly underneath the pebble. Dating was the underside of the pebble and on the sediment under the pebble, on the assumption that neither has attempted on both the underside of the pebble and on the sediment under the pebble, on the been exposed to light since the placement of the rock. In this way, we checked the predictability of the assumption that neither has been exposed to light since the placement of the rock. In this way, we reconstructed luminescence profiles into the buried rock surface. checked the predictability of the reconstructed luminescence profiles into the buried rock surface. The measured ages obtained from buried surfaces are in good agreement with those obtained from the sediments and with those obtained through archaeological methodology. Moreover, in some cases the ages obtained with luminescence dating are consistent with available 14C ages. Appl. Sci. 2020, 10, 7403 4 of 9 The measured ages obtained from buried surfaces are in good agreement with those obtained from the sediments and with those obtained through archaeological methodology. Moreover, in some cases the ages obtained with luminescence dating are consistent with available 14C ages. Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 9 2. Materials and Methods 2. Materials and Methods All experiments in this study were performed using rock samples and sediments collected from the All experiments in this study were performed using rock samples and sediments collected from Ossimo-Pat sanctuary (Figure 3). The Sample “3/2016” is a pebble taken from the stone accumulation the Ossimo-Pat sanctuary (Figure 3). The Sample “3/2016” is a pebble taken from the stone behind the big monolith known as “Pat 2,” presumably relative to the first stage of the abandonment of accumulation behind the big monolith known as “Pat 2,” presumably relative to the first stage of the the site. “1/2016” and “US 178” are samples from the northern votive stone circles, which are generally abandonment of the site. “1/2016” and “US 178” are samples from the northern votive stone circles, placed in the central phase of the site-life, around the first half of the 3rd millennium BCE, while the which are generally placed in the central phase of the site-life, around the first half of the 3rd samples “Pat12” and “Pat15”were collected from the housing pits of the fallen monoliths “Pat12” and millennium BCE, while the samples “Pat12” and “Pat15”were collected from the housing pits of the “Pat15.” All the cobbles have a diameter in the range of 100–150 mm. fallen monoliths “Pat12” and “Pat15.” All the cobbles have a diameter in the range of 100–150 mm. Figure 3. (a) Site map with sampling points; (b) detail of sample US178; (c) during the sampling Figure 3. (a) Site map with sampling points; (b) detail of sample US178; (c) during the sampling operation under the sunlight and under the dark (d). operation under the sunlight and under the dark (d). T To measure t o measure the he OSL d OSL depth epth profiles profiles and and t the h ae absorb bsorbed do ed ses, doses, the cobbles ha the cobbles have been ve been drilled under drilled under dim red light in laboratory. The reached depth was checked with a digital precision caliber. The polymineral dim red light in laboratory. The reached depth was checked with a digital precision caliber. The fine polymineral fine grain frac grain fraction with grain tion with grain sized between sized 4 and between 4 and 10 micrometers 10 m was icrometers w used. as used. For the sediments, the quartz grains have been extracted using the conventional procedure [13–16] For the sediments, the quartz grains have been extracted using the conventional procedure [13– under 16] under dim dim red light red light and an the d the lum luminescence inescence measur measurements ements were were conducted conducted on coa on coarse rse quartz quartz grai grains ns (180–250 (180–250 μm). m). All All samples, samples, both both cobbles cobbles an andd sediments, sediments, wer weree mo mounted unted on on stainle stainle ss ss stee steell discs. discs. The The O OSL SL measur measurement ementsswer wer ee performed performed w withith a Risø a RiTL sø /T OSL L/ODA20 SL DA20 reader. The sam reader. The samples p wer les were st e stimulated imulat byed by blue 2 2 2 2 LEDS blue LEDS (47 (470  30 0 ± nm, 30 nm 54 , 5 mW 4 m /cm W/c)m or ) o by r b IR y ILEDs R LED ( s (=λ = 830nm, 830nm360 , 360 m mW W /cm /cm) )and and the emi the emitted tted photons photons wer were det e detected ectedwith withan an EMI EMI 9 9235QB 235QB p photomultiplier hotomultipliecouple r coupl d ed w with ita h a UV UV filter filter (7.5 (7mm .5 mHoya m Hoy U-340) a U-34in 0) case in caof se o blue f blstimulation ue stimulation or with or wit a blue h a bl filter ue filt (Schott er (Schot BG39 t BG /Corning 39/Corni 7–59 ng 7– filter 59 fi combination) lter combinat in ion case ) in c ofa IR se stimulation. of IR stimula Blue tion.stimulation Blue stimulation was was used for used fo the samples r the samples in which the main dosimet in which the main dosimeter was the er was t quartz he and quart IR z and IR st stimulation imulat [13]ion [ for 13] for t the samples he sam rich ples rich in in feldspars. feldspars. To evaluate the absorbed dose the Single Aliquot Regenerative dose protocol (SAR) was applied for all samples. It is a well-known standard procedure for the optically stimulated luminescence dating in which the same aliquot is irradiated, heated and illuminated, during experimental cycles that are repeated (Table 1). The obtained signal is integrated, normalized and plotted in function of dose and the absorbed dose is calculated from interpolation of the natural signal on the constructed curve. Appl. Sci. 2020, 10, 7403 5 of 9 To evaluate the absorbed dose the Single Aliquot Regenerative dose protocol (SAR) was applied for all samples. It is a well-known standard procedure for the optically stimulated luminescence dating in which the same aliquot is irradiated, heated and illuminated, during experimental cycles that are repeated (Table 1). The obtained signal is integrated, normalized and plotted in function of dose and the absorbed dose is calculated from interpolation of the natural signal on the constructed curve. Table 1. Single Aliquot Regenerative dose protocol applied (L and T were calculated starting from the i i optically stimulated luminescence (OSL) curve, integrating the first 0.8 s minus a background estimated from the integral of the last 8 s). Step Rock Samples SAR Cycle Sediments SAR Cycle a a 1 Give dose, D Give dose, D i i 2 Preheat at T for 10 s Preheat at T for 10 s 0 0 3 Stimulated for 100 s at 125 C (OSL) or 50 C (IRSL), get L Stimulated for 40 s at 125 C (OSL) 4 Give test dose, D Give test dose, D t t 5 Cut heat to 220 C for 0 s Cut heat to 180 C for 0 s 6 Stimulated for 100 s at 125 C (OSL) or at 50 C (IRSL) Stimulated for 40 s at 125 C (OSL) 7 OSL or IRSL at 290 C for 40 s OSL at 290 C for 40 s 8 Return to 1 Return to 1 For the natural sample i = 0 and D = 0. Four regenerative doses plus a zero-dose measurement and a repeat dose were used; T depends on the sample. The pre-heat value was experimentally derived on the basis of the results of a dose recovery pre-heat plateau test [17] (see Table 2). Table 2. Pre-heat temperature for rock and sediment samples. Rock Samples Pre-Heat Sediment Samples Pre-Heat Sample Code Temperature ( C) Temperature ( C) 1/2016 260 US178 220 220 3/2016 200 Pat12 240 260 Pat15 200 220 90 90 Laboratory irradiations were given using a calibrated Sr/ Y beta source (5.50 GBq) mounted on the Risø TL/OSL reader (dose rate: 0.23 Gy/s for fine grain; 0.12 Gy/s for coarse grain). The absorbed dose is calculated from the weighted mean of values obtained from the analyzed aliquots (at least 10 for sample). The annual dose-rate absorbed by the samples is due to the contribution of the internal radioactivity of the material and the radioactivity of the surrounding environment. The radioactive families 238 U, 232 Th and 40 K are, in both cases, responsible for the natural imparted dose. There are also minor contributions from 87Rb and from cosmic rays. To take into account any non-homogeneity in the external contribution, the radioactivity of a sphere of the surrounding material (30 cm diameter centered at the sampling point) has to be measured [9]. The heterogeneity e ect was considered by measuring the radioactivity concentrations of the surroundings materials, i.e., sediments and cobbles. The contribution of each material to the annual dose-rate was evaluated applying the infinite matrix approximation, with updated conversion factors [18]. After radioactivity measurements, it is possible to assess the contribution of each layer calculating the relative volume of every material within the interaction sphere and normalizing the annual dose fractions in the age equation [19]. 40 K concentrations were measured through atomic absorption spectrometry; 238 U and 232 Th concentrations were obtained from total alpha counting technique. Although the water content of the cobbles is negligible, the surrounding sediment material does contain water, and thus, a water content correction is needed. This was based on the one calculated using the sediment material, specifically a mean water content equal to 75% of saturation value (20  10%) was used. Attenuation of the beta Appl. Sci. 2020, 10, 7403 6 of 9 dose was taken into account in case of sediments for which the coarse grains fraction was used to determine the absorbed doses [20], while alpha contribution was eliminated by an HF etching. Appl. Sci. 2020, 10, x FOR PEER REVIEW 6 of 9 3. Results 3. Results 3.1. Luminescence—Depth Profiles 3.1. Luminescence—Depth Profiles To test the application of luminescence rock surface dating to the surface of buried cobbles, To test the application of luminescence rock surface dating to the surface of buried cobbles, we first we first assessed the degree of bleaching of the surface itself. To investigate this, we measured the assessed the degree of bleaching of the surface itself. To investigate this, we measured the absorbed absorbed dose as a function of depth into all the five cobbles. As an example, the Figure 4 shows the dose as a function of depth into all the five cobbles. As an example, the Figure 4 shows the luminescence- luminescence-depth profiles from two di erent samples. Each point in the profile is obtained by the depth profiles from two different samples. Each point in the profile is obtained by the mean of the mean of the absorbed doses measured on 10 aliquots. absorbed doses measured on 10 aliquots. Figure 4. Figure 4. Luminescence depth Luminescence depth-pr -profiles ( ofiles (a a) 1/2 ) 1/2016 016 sample; ( sample; (b b) ) 3/2016 sample 3/2016 sample.. In the left panel, the absorbed dose increases with the depth and reaches a plateau (the so-called In the left panel, the absorbed dose increases with the depth and reaches a plateau (the so-called field saturation level) in the middle of the cobble. In the right panel, this plateau is reached in the first field saturation level) in the middle of the cobble. In the right panel, this plateau is reached in the first layers below the surface. It seems to have limited light exposure, insucient to fully reset the OSL layers below the surface. It seems to have limited light exposure, insufficient to fully reset the OSL signal in the layers below 1mm from the surface. Presumably, light exposure has not been suciently signal in the layers below 1mm from the surface. Presumably, light exposure has not been sufficiently long to totally bleach the luminescent signal throughout the cobble or this sample has a high attenuation long to totally bleach the luminescent signal throughout the cobble or this sample has a high coecient. For both samples, the absorbed dose at the surface is proportional to the time elapsed since attenuation coefficient. For both samples, the absorbed dose at the surface is proportional to the time the deposition. The calculated ages are reported in Table 3. elapsed since the deposition. The calculated ages are reported in Table 3. Table 3. Cobbles and sediments calculated ages. Table 3. Cobbles and sediments calculated ages. Absorbed Dose Rate Sample Code Sample Type Technique Absorbed Dose (Gy) Dose Rate (mGy/a) Date Sample Code Sample Type Technique Date Dose (Gy) (mGy/a) 1/2016 ROCK OSL 24.5 ± 3.5 5.15 ± 0.15 2760 BCE ± 500 US178 ROCK OSL 20.8 ± 3.5 2.95 ± 0.20 2675 BCE ± 500 1/2016 ROCK OSL 24.5  3.5 5.15  0.15 2760 BCE  500 US178 US178 SEDIMENT ROCK OSL OSL 15.4 ± 0.5 20.8  3.5 2.95 2.95 ± 0.0  0.20 7 2675 3220 B BCE C E ± 33 500 0 US178 SEDIMENT OSL 15.4  0.5 2.95  0.07 3220 BCE  330 3/2016 ROCK IRSL 42.3 ± 7.5 10.75 ± 0.30 1920 BCE ± 250 3/2016 ROCK IRSL 42.3  7.5 10.75  0.30 1920 BCE  250 Pat12 ROCK IRSL 30.5 ± 5.0 4.20 ± 0.12 5240 BCE ± 600 Pat12 ROCK IRSL 30.5  5.0 4.20  0.12 5240 BCE  600 Pat12 SEDIMENT OSL 17.2 ± 0.4 2.40 ± 0.08 5090 BCE ± 360 Pat12 SEDIMENT OSL 17.2  0.4 2.40  0.08 5090 BCE  360 Pat15 ROCK IRSL 22.9 ± 4.0 6.50 ± 0.25 2470 BCE ± 500 * Pat15 ROCK IRSL 22.9  4.0 6.50  0.25 2470 BCE  500 * Pat15 SEDIMENT OSL 12.8 ± 0.4 3.00 ± 0.05 2270 BCE ± 260 Pat15 SEDIMENT OSL 12.8  0.4 3.00  0.05 2270 BCE  260 * Fading-corrected date. * Fading-corrected date. 3.2. Fading Correction and Cobbles Ages 3.2. Fading By applyin Correction g the well-kno and Cobbles wn equation Ages age [6], the cobble burial ages were simply derived by dividing the cobbles surface absorbed dose values by the dose rate at the surface of the cobbles. By applying the well-known equation age [6], the cobble burial ages were simply derived by However, the luminescence signal from feldspars could be unstable: this phenomenon is known as dividing the cobbles surface absorbed dose values by the dose rate at the surface of the cobbles. ‘anomalous fading’ and can be taken into account by the conventional g value measurement [21]. For However, the luminescence signal from feldspars could be unstable: this phenomenon is known as the samples Pat12 and Pat15, we have quantified the fading rate as a percentage of IR signal loss with ‘anomalous fading’ and can be taken into account by the conventional g value measurement [21]. storage time after irradiation. Three aliquots from each sample were bleached in the reader using an For the samples Pat12 and Pat15, we have quantified the fading rate as a percentage of IR signal loss IR stimulation (for 500 s at 50 °C repeated after 60 s); a known dose has been imparted, and then the absorbed dose were measured, both immediately after irradiation and after a delay time of 6 h, 1 day, 19 days and 33 days. For the sample Pat12, the ratio between the imparted dose and the dose measured after the time delay are indistinguishable from unity, (Figure 5), thus, it possible to deduce that the phenomenon of anomalous fading is negligible. The cobble Pat15 is in a different condition: Appl. Sci. 2020, 10, 7403 7 of 9 with storage time after irradiation. Three aliquots from each sample were bleached in the reader using an IR stimulation (for 500 s at 50 C repeated after 60 s); a known dose has been imparted, and then the absorbed dose were measured, both immediately after irradiation and after a delay time of 6 h, 1 day, 19 days and 33 days. For the sample Pat12, the ratio between the imparted dose and the dose measured after the time delay are indistinguishable from unity, (Figure 5), thus, it possible to deduce that the Appl. Sci. 2020, 10, x FOR PEER REVIEW 7 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 7 of 9 phenomenon of anomalous fading is negligible. The cobble Pat15 is in a di erent condition: its signal fades by 10% in about a month. Therefore, we evaluate the fading rate with a g value of 2.4  0.5%, its signal fades by 10% in about a month. Therefore, we evaluate the fading rate with a g value of 2.4 its signal fades by 10% in about a month. Therefore, we evaluate the fading rate with a g value of 2.4 and in Table 3, the fading-corrected date is reported. ± 0.5%, and in Table 3, the fading-corrected date is reported. ± 0.5%, and in Table 3, the fading-corrected date is reported. 1.4 1.4 1.3 1.3 PA PA T12 T12 1.2 1.2 PA PA T15 T15 1.1 1.1 1 1 0.9 0.9 0.8 0.8 0 200 400 600 800 1000 0 200 400 600 800 1000 t (h) t (h) Figure 5. Normalized absorbed dose versus time. Figure 5. Normalized absorbed dose versus time. Figure 5. Normalized absorbed dose versus time. 3. 3.3. Se 3. Sedi dimen menttss’’ Age Agess 3.3. Sediments’ Ages The absorbed dose histogram, relative to more than 50 aliquots for each sample, as reported in The absorbed dose histogram, relative to more than 50 aliquots for each sample, as reported in The absorbed dose histogram, relative to more than 50 aliquots for each sample, as reported in Figure 6 for sample Pat15, shows a symmetric distribution with rather low dispersion of the data, Figure 6 for sample Pat15, shows a symmetric distribution with rather low dispersion of the data, Figure 6 for sample Pat15, shows a symmetric distribution with rather low dispersion of the data, evidencing a similar dose absorbed by all the aliquots. This is an indication that the surface sediments evidencing a similar dose absorbed by all the aliquots. This is an indication that the surface sediments evidencing a similar dose absorbed by all the aliquots. This is an indication that the surface sediments were fully blea were fully blea ched before ched before the cobbl the cobbles’ deposi es’ deposi ti ti on. This al on. This al ll o o ws to ws to use the wei use the wei g g hted mea hted mea n n to calcula to calcula tt e e were fully bleached before the cobbles’ deposition. This allows to use the weighted mean to calculate the absorbed doses by the samples that are reported in Table 3, together with the annual dose rates the absorbed doses by the samples that are reported in Table 3, together with the annual dose rates the absorbed doses by the samples that are reported in Table 3, together with the annual dose rates and and the OSL dates. and the OSL dates. the OSL dates. P P A A T 15 T 15 20 20 16 16 6 8 10 12 14 16 18 20 22 24 6 8 10 12 14 16 18 20 22 24 Dose (Gy) Dose (Gy) Figure 6. Sample “Pat15.” Distribution of absorbed doses. Figure 6. Sample “Pat15.” Distribution of absorbed doses. Figure 6. Sample “Pat15.” Distribution of absorbed doses. 4. Discussion and Conclusions 4. Discussion and Conclusions The doses ab The doses absorbed by th sorbed by the cobbles w e cobbles weere dir re direectly ctly deri derived by the ved by the aalliiqquots taken f uots taken frrom the om the ffiirst rst llaayer. Al yer. Although the uncert though the uncertaaiinty i nty inn the the dose dose iiss de deriv riveed from d from the the stand standaard rd erro error r of 10 aliquots, of 10 aliquots, the the Normalized absorbed dose Normalized absorbed dose Frequency Frequency Appl. Sci. 2020, 10, 7403 8 of 9 4. Discussion and Conclusions The doses absorbed by the cobbles were directly derived by the aliquots taken from the first layer. Although the uncertainty in the dose is derived from the standard error of 10 aliquots, the relative error spans between 15% and 30%, it is quite high, especially if compared with that obtained with sediments (5–6%). Due the scarcity of material for each considered layer, it has been impossible to extract quartz or feldspar grains from the samples. This may have led to luminescence signals with inadequate characteristics (slow decay rate, high background) that introduced a high error in the fitting to calculate the absorbed dose. For US178, Pat12 and Pat15, the age from cobble is in agreement with the sediment age at a level of 1 standard deviation, thus, they are consistent with each other. From a methodological point of view, these preliminary results show that it is possible to apply luminescence dating to the surfaces of the artefacts present in the Ossimo-Pat site. Despite the high error obtained on rock surfaces, the data obtained on sediments under the rock were more precise. This suggests that for future application of surface dating of megalithic structure, it is recommended to sample both rocks and the underlying sediments in order to reduce the age errors. Moreover, the results of the dating o er, from an archaeological point of view, an interesting feedback to the existing timeframe of the site. Even considering the range error of each date, we can compare the results with what was already established about the site, chronology-wise. The first sample (the rock “1/2016,” 2760 BCE  500) was taken from the northernmost of the votive stone circles. Its date is compatible with the other two samples from the nearby, similar, stone structures (samples “US 178,” rock, 2675 BCE  500, and sediments, 3200 BCE  330). There are no 14C dates available from these circles that have been dated to the first half of the 3rd millennium BCE based on the objects found inside the circles, namely a specific type of arrowheads, usually related this period. The three OSL dates from the area would seem to confirm the current chronological framework. The IRSL date from the rock sample “3/2016” (1920 BCE  250) seems equally aligned with the current chronology of the site. This rock was collected from the accumulation layer located behind the big monolith called “Pat 2,” one of the few still vertically standing. The small accumulation of soil and rocks is probably related to the first stage of abandonment of the site, right after its partial destruction and dismissal, and is usually dated around the 23rd–20th centuries BCE thanks to a charred coal 14C dating [1]. The samples taken from the monolith pits are the most intriguing ones, as we still do not have a full comprehension of the precise life cycles of these monuments. The samples taken from the housing pit of the monolith “Pat15” are related to its filling, which happened in time, after the dismissal of the site and the overthrowing of the monolith, which was pushed to the ground, out of its proper housing. The dating of rock and relative sediment (2470 BCE  500 and 2265 BCE  115, respectively) are perfectly coherent with the said action, which probably happened, as said, between the end of the 24th and the 21st centuries BCE. The dating of the samples from the housing pit “Pat12” (Rock: 5240 BCE  600; sediment: 5090 BCE 360), on the other hand, o er a very interesting result, related back to the end of the sixth millennium BC, before the foundation of the sanctuary. Nevertheless, these dates are perfectly coherent with another dating, obtained by 14C on a charcoal sample from the layer 181 [1], which was documented in this very sector of the site thanks to a deep stratigraphic trench. Layer 181, rich in charred coal and burnt wood, is believed to be the outcome of the very first action carried out in this place, namely a slash/burn activity, usually performed during the late Neolithic to open new pasture areas in medium and high-altitude locations. Evidently, the digging activity performed during the Copper Age to prepare the housing pit for the huge monolith “Pat12,” which is longer than 2 m and very heavy, led to reach the deeper and more ancient level of the site, to which our samples appear to belong. Author Contributions: Conceptualization, A.G. and L.P.; methodology, A.G., L.P. and P.R.; writing—original draft preparation, A.G. writing—review and editing, A.G., L.P., P.R., R.P.K. and M.M.; supervision, R.P.K. and M.M. All authors have read and agreed to the published version of the manuscript. Appl. Sci. 2020, 10, 7403 9 of 9 Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. References 1. Poggiani Keller, R. Copper Age Ancestral Sanctuaries and Landscapes in Valle Camonica; Archaeo Press Publishing: Oxford, UK, 2018; pp. 431–442. 2. Rondini, P. Digital Rocks. An integrated approach to rock art recording: The case study of Ossimo-Pat (Valle Camonica), monolith 23. Archeol. Calc. 2018, 29, 259–278. 3. Ivy-Ochs, S.; Kober, F. Surface exposure dating with cosmogenic nuclides. Quat. Sci. J. 2008, 57, 179–209. [CrossRef] 4. Sohbati, R.; Murray, A.S.; Chapot, M.S.; Jain, M.; Pederson, J. Optically stimulated luminescence (OSL) as a chronometer for surface exposure dating. J. Geophys. Res. 2012, 117, 117. [CrossRef] 5. Vafiadou, A.; Murray, A.S.; Liritzis, I. Optically stimulated luminescence (OSL) dating investigations of rock and underlying soil from three case studies. J. Archaeol. Sci. 2007, 34, 1659–1669. [CrossRef] 6. Aitken, M.J. An Introduction to Optical Dating. In The Dating of Quaternary Sediments by the Use of Photon-Stimulated Luminescence; Oxford University Press: New York, NY, USA, 1998. 7. Laskaris, N.; Liritzis, I. A new mathematical approximation of sunlight attenuation in rocks for surface luminescence dating. J. Lumin. 2011, 131, 1874–1884. [CrossRef] 8. Feathers, J.; More, G.M.; Quinterosc, P.S.; Burkholder, J.E. IRSL dating of rocks and sediments from desert geoglyphs in coastal Peru. Quat. Geochronol. 2019, 49, 177–183. [CrossRef] 9. Gliganic, L.A.; Meyer, M.C.; Sohbati, R.; Jain, M.; Barrett, S. OSL surface exposure dating of a lithic quarry in Tibet: Laboratory validation and application. Quat. Geochronol. 2019, 49, 199–204. [CrossRef] 10. Sohbati, R.; Murray, A.; Jain, M.; Buylaert, J.-P.; Thomsen, K. Investigating the resetting of OSL signals in rock surfaces. Geochronometria 2011, 38, 249–258. [CrossRef] 11. Galli, A.; Artesani, A.; Martini, M.; Sibilia, E.; Panzeri, L.; Maspero, F. An empirical model of the sunlight bleaching eciency of brick surfaces. Radiat. Meas. 2017, 107, 67–72. [CrossRef] 12. al Khasawneh, S.; Murray, A.; Thomsen, K.; AbuAzizeh, W.; Tarawneh, M. Dating a near eastern desert hunting trap (kite) using rock surface luminescence dating. Archaeol. Anthr. Sci. 2019, 11, 2109–2119. [CrossRef] 13. Mejdahl, V.; Christiansen, H. Procedures used for luminescence dating of sediments. Quat. Sci. Rev. 1994, 13, 403–406. [CrossRef] 14. Lang, A.; Lindauer, S.; Kuhn, R.; Wagner, G.A. Procedures used for Optically and Infrared Stimulated Luminescence Dating of Sediments in Heidelberg. Anc. TL 1996, 14, 7–11. 15. Mauz, B.; Bode, T.; Mainz, E.; Blanchard, H.; Higer, W.; Dikau, R.; Zöller, L. The luminescence dating laboratory at the University of Bonn: Equipment and procedures. Anc. TL 2002, 20, 53–61. 16. Stokes, S. Optical dating of young (modern) sediments using quartz: Results from a selection of depositional environments. Quat. Sci. Rev. 1992, 11, 153–159. [CrossRef] 17. Wintle, A.G.; Murray, A.S. A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols. Radiat. Meas. 2006, 41, 369–391. [CrossRef] 18. Guérin, G.; Mercier, N.; Adamiec, G. Dose-rate conversion factors: Update. Anc. TL 2011, 29, 4. 19. Galli, A.; Martini, M.; Maspero, F.; Panzeri, L.; Sibilia, E. Surface dating of bricks, an application of luminescence techniques. Eur. Phys. J. Plus 2014, 129, 1–9. [CrossRef] 20. Bell, W.T. Thermoluminescence dating: Radiation dose-rate data. Archaeometry 1979, 21, 243–245. [CrossRef] 21. Lamothe, D.J. Ubiquity of anomalous fading in K-feldspars and the measurement and correction for it in optical dating. Can. J. Earth Sci. 2001, 38, 1093–1106. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional aliations. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Sciences Multidisciplinary Digital Publishing Institute

Luminescence Dating of Rock Surface. The Case of Monoliths from the Megalithic Sanctuary of Ossimo-Pat (Valle Camonica, Italy)

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applied sciences Article Luminescence Dating of Rock Surface. The Case of Monoliths from the Megalithic Sanctuary of Ossimo-Pat (Valle Camonica, Italy) 1 , 2 , 2 , 3 4 Anna Galli * , Laura Panzeri * , Paolo Rondini , Ra aella Poggiani Keller and Marco Martini Istituto CNR-IBFM, via F.lli Cervi, 93, 20090 Segrate, Italy Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, via R. Cozzi 55, 20125 Milano, Italy; m.martini@unimib.it Dipartimento di Studi Umanistici, Università degli Studi di Pavia, Corso Strada Nuova 65, 27100 Pavia, Italy; paolo.rondini@unipv.it Già Soprintendente per i Beni Archeologici Della Lombardia- Ministero dei Beni e Delle Attività Culturali e del Turismo, 20100 Milano, Italy; rpoggianikeller@libero.it * Correspondence: anna.galli@unimib.it (A.G.); laura.panzeri@unimib.it (L.P.) Received: 30 September 2020; Accepted: 20 October 2020; Published: 22 October 2020 Featured Application: Dates obtained by optically stimulated luminescence (OSL) of rock artefacts and the underneath soils were shown to be in very good agreement with the archeological evidence. Highly satisfying results contribute to the understanding of a megalithic sanctuary. Abstract: Ossimo-Pat megalithic sanctuary (Valle Camonica, BS, Italy) is one of the most relevant archaeological findings of the southern alpine region, for the variety of its structures and the quality of its engraved monoliths. Its unique state of preservation gives the opportunity to apply the luminescence dating of the rock surface method. Here, we investigate the use of optically stimulated luminescence (OSL) for dating five cobbles from the site and compare cobble-surface derived ages to quartz OSL ages from sediments and to archaeological evidences. The obtained ages confirm the archaeological studies and open the way to a new hypothesis. Keywords: optically stimulated luminescence; surface dating; megalithic sanctuary 1. Introduction There are many examples of rock surfaces, rock art and stone structures of unknown age. In particular, in prehistoric archaeology, long-lasting building traditions can sometimes be dicult to date, if the context does not o er useful chronological tools, such as artifacts or organic remains associated to the structures. Moreover, this particular issue is not a marginal one, if we consider that the study of megaliths, drystone walls and other structures, such as cairns or mounds, is often crucial to our understanding of the society and traditions of very ancient cultures, devoid of other forms of communication. In this scenario, the Ossimo-Pat (Valle Camonica, BS, Italy, see Figure 1) megalithic sanctuary is an exemplary case. Appl. Sci. 2020, 10, 7403; doi:10.3390/app10217403 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 7403 2 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 9 Figure 1. Location of the Ossimo-Pat site in Middle Valle Camonica (GIS elaboration on LIDAR DTM base). Figure 1. Location of the Ossimo-Pat site in Middle Valle Camonica (GIS elaboration on LIDAR DTM base). Its construction started in the first half of the fourth millennium BCE and was structured and used during the Copper Age (late 4th–3rd millennium BCE), with ceremonial structures and engraved Its construction started in the first half of the fourth millennium BCE and was structured and monoliths articulated in a north-south alignment. The southernmost structure is a sequence of used during the Copper Age (late 4th–3rd millennium BCE), with ceremonial structures and ceremonial mounds, built upon a concentric series of stone circles enclosing an inner rectangular engraved monoliths articulated in a north-south alignment. The southernmost structure is a sequence space, which usually contained objects, such as flint weapons and tools or ornaments. The central of ceremonial mounds, built upon a concentric series of stone circles enclosing an inner rectangular part of the sanctuary was an alignment of monoliths of various lithologies, mainly sandstones of diverse granulometry, carved with figures and symbols and probably depicting mythical ancestors space, which usually contained objects, such as flint weapons and tools or ornaments. The central or gods. The alignment led to a monumental tomb and then to a series of at least five votive stone part of the sanctuary was an alignment of monoliths of various lithologies, mainly sandstones of circles, which contained, similarly to the southern mounds, a number of flint, stone, metal and ceramic diverse granulometry, carved with figures and symbols and probably depicting mythical ancestors artefacts, probably the result of unknown cult activity [1,2]. The site was frequented until its sudden, or gods. The alignment led to a monumental tomb and then to a series of at least five votive stone partial, dismantling and further abandonment, at the very beginning of Bronze Age, at the end of circles, which contained, similarly to the southern mounds, a number of flint, stone, metal and the 3rd millennium BCE. Later frequentation during the final Bronze Age and the whole Iron Age ceramic artefacts, probably the result of unknown cult activity [1,2]. The site was frequented until its is attested by a series of fireplaces that were lit in front and at the backside of the monoliths still sudden, partial, dismantling and further abandonment, at the very beginning of Bronze Age, at the vertically standing. Ossimo-Pat is one of the most relevant archaeological findings of the southern end of the 3rd millennium BCE. Later frequentation during the final Bronze Age and the whole Iron alpine region, for the variety of its structures and the quality of its engraved monoliths, as well as Age is attested by a series of fireplaces that were lit in front and at the backside of the monoliths still for its unique state of preservation, which gives the opportunity for a documentation of the exact vertically standing. Ossimo-Pat is one of the most relevant archaeological findings of the southern moment of its disuse. As part of the UNESCO World Heritage Site n.94 “Rock Drawings in Valle Camonica,” the sanctuary occupies an area of more than 4000 square meters, and it is located on the alpine region, for the variety of its structures and the quality of its engraved monoliths, as well as for right hydrographic flank of the medium Valle Camonica, at an altitude of 810 m asl. The site is arranged its unique state of preservation, which gives the opportunity for a documentation of the exact on the edge of a terrace overlooking a steep drop into the Valle dell’Inferno (the strikingly named moment of its disuse. As part of the UNESCO World Heritage Site n.94 “Rock Drawings in Valle “Valley of Hell”), placed on a wide elevated plateau comprised by two dominant peaks: the Pizzo Camonica,” the sanctuary occupies an area of more than 4000 square meters, and it is located on the Camino (2491 m asl) to the southwest and the Concarena (2549 m asl) to the north-east. The rocky right hydrographic flank of the medium Valle Camonica, at an altitude of 810 m asl. The site is substrate of the area is mostly made of Triassic (from the Scitic to the Carnic) limestones, while the arranged on the edge of a terrace overlooking a steep drop into the Valle dell’Inferno (the strikingly surfacing lithology is often covered by morainic deposits, left by the glaciers, which can be encountered named “Valley of Hell”), placed on a wide elevated plateau comprised by two dominant peaks: the up at an altitude of 1650 m asl. (source: F. Franzoni, Piano di Governo del Territorio, Comune di Pizzo Camino (2491 m asl) to the southwest and the Concarena (2549 m asl) to the north-east. The Ossimo, 2012 (http://www.comune.ossimo.bs.it/Allegati/all_50012_GEO_Relazione%20Geologica.pdf)). rocky substrate of the area is mostly made of Triassic (from the Scitic to the Carnic) limestones, while The monoliths chosen to be engraved are very likely coming come from these deposits, but the the surfacing lithology is often covered by morainic deposits, left by the glaciers, which can be geological survey and study is still ongoing. Excavations and analyses are being carried on since 1994 encount ande ar red e still upongoing, at an alunder titude o the f dir 165 ection 0 m as ofl. Ra (s ourc aellae: F Poggiani . FranKeller zoni, Pi (Figur ano d e 2i). Governo del Territorio, Comune di Ossimo, 2012 (http://www.comune.ossimo.bs.it/Allegati/all_50012_GEO_Relazione%20Geologica.pdf)). The monoliths chosen to be engraved are very likely coming come from these deposits, but the geological survey and study is still ongoing. Excavations and analyses are being carried on since 1994 and are still ongoing, under the direction of Raffaella Poggiani Keller (Figure 2). Appl. Sci. 2020, 10, 7403 3 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 9 Figure 2. Ortophotograph of the Ossimo-Pat site. Figure 2. Ortophotograph of the Ossimo-Pat site. There are two potential methods for dating the surfaces of such artefacts: the measure of There are two potential methods for dating the surfaces of such artefacts: the measure of cosmogenic radionuclides concentrations [3] and the application of luminescence dating (in particular cosmogenic radionuclides concentrations [3] and the application of luminescence dating (in Optically Stimulated Luminescence, OSL) [4,5]. The first approach depends on cosmogenic nuclides particular Optically Stimulated Luminescence, OSL) [4,5]. The first approach depends on cosmogenic 10 26 36 (e.g., Be, Al, Cl) build-up with time in minerals exposed to cosmic rays. Therefore, measuring 10 26 36 nuclides (e.g., Be, Al, Cl) build-up with time in minerals exposed to cosmic rays. Therefore, their concentrations allows determination of how long rocks have been exposed at or near the surface measuring their concentrations allows determination of how long rocks have been exposed at or near of the Earth. In this paper, we focus on the alternative approach based on OSL. This method was the surface of the Earth. In this paper, we focus on the alternative approach based on OSL. This originally developed to date the deposition of sediments [6] and it depends on the ability of some method was originally developed to date the deposition of sediments [6] and it depends on the ability minerals, such as feldspar and quartz, to absorb and store energy from environmental ionizing radiation. of some minerals, such as feldspar and quartz, to absorb and store energy from environmental When the light stimulates these minerals, they release the stored energy in the form of light, from which ionizing radiation. When the light stimulates these minerals, they release the stored energy in the the term luminescence is derived. Measuring the amount of energy released in conjunction with a form of light, from which the term luminescence is derived. Measuring the amount of energy released determination of the rate at which the energy was accumulated allows to calculate an age, indicating in conjunction with a determination of the rate at which the energy was accumulated allows to the time that has elapsed since the storage of energy began. calculate an age, indicating the time that has elapsed since the storage of energy began. Thus, if the OSL signal from mineral grains is normally used to date how long the sediment grains Thus, if the OSL signal from mineral grains is normally used to date how long the sediment were buried, recent works have shown that luminescence signals can also be used to determine the grains were buried, recent works have shown that luminescence signals can also be used to determine duration of daylight exposure for rock surfaces [4,7–9]. the duration of daylight exposure for rock surfaces [4,7–9]. The OSL surface dating technique exploits the depth-dependence of the resetting (bleaching) of The OSL surface dating technique exploits the depth-dependence of the resetting (bleaching) of the geological luminescence signal when exposed to daylight. Sohbati et al. [4,10] proposed a model the geological luminescence signal when exposed to daylight. Sohbati et al. [4,10] proposed a model that reproduces the dependence of the OSL signal on depth and exposure-time and predicts that the that reproduces the dependence of the OSL signal on depth and exposure-time and predicts that the longer the exposure duration, the deeper the resetting of the luminescence signal into the rock surface. longer the exposure duration, the deeper the resetting of the luminescence signal into the rock Analogously, this dependence has been evaluated for renaissance bricks [11]. surface. Analogously, this dependence has been evaluated for renaissance bricks [11]. Thus, there exists chronological information in the luminescence-depth profile, but despite Thus, there exists chronological information in the luminescence-depth profile, but despite some some applications of the OSL surface technique [8,9,12], the bleaching-depth model is yet to be applications of the OSL surface technique [8,9,12], the bleaching-depth model is yet to be validated validated experimentally; this is critical for further development of the technique. The emerging OSL experimentally; this is critical for further development of the technique. The emerging OSL surface surface dating technique has the potential to answer many new questions in the fields of geo- and dating technique has the potential to answer many new questions in the fields of geo- and archaeological sciences. archaeological sciences. Dating the sanctuary was mostly done through the combination of stratigraphy observations, Dating the sanctuary was mostly done through the combination of stratigraphy observations, typo-chronological study of the artefacts and with the use of a certain number of radiometric typo-chronological study of the artefacts and with the use of a certain number of radiometric measurements (14C) on charred coals from di erent parts of the site [1], mostly from the southern measurements (14C) on charred coals from different parts of the site [1], mostly from the southern mounds and the upper layers of the monoliths alignment. Therefore, to test the capability of the surface mounds and the upper layers of the monoliths alignment. Therefore, to test the capability of the dating technique, five pebbles were collected from three di erent areas. Three samples consisted of the surface dating technique, five pebbles were collected from three different areas. Three samples pebble itself and the sediment collected directly underneath the pebble. Dating was attempted on both consisted of the pebble itself and the sediment collected directly underneath the pebble. Dating was the underside of the pebble and on the sediment under the pebble, on the assumption that neither has attempted on both the underside of the pebble and on the sediment under the pebble, on the been exposed to light since the placement of the rock. In this way, we checked the predictability of the assumption that neither has been exposed to light since the placement of the rock. In this way, we reconstructed luminescence profiles into the buried rock surface. checked the predictability of the reconstructed luminescence profiles into the buried rock surface. The measured ages obtained from buried surfaces are in good agreement with those obtained from the sediments and with those obtained through archaeological methodology. Moreover, in some cases the ages obtained with luminescence dating are consistent with available 14C ages. Appl. Sci. 2020, 10, 7403 4 of 9 The measured ages obtained from buried surfaces are in good agreement with those obtained from the sediments and with those obtained through archaeological methodology. Moreover, in some cases the ages obtained with luminescence dating are consistent with available 14C ages. Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 9 2. Materials and Methods 2. Materials and Methods All experiments in this study were performed using rock samples and sediments collected from the All experiments in this study were performed using rock samples and sediments collected from Ossimo-Pat sanctuary (Figure 3). The Sample “3/2016” is a pebble taken from the stone accumulation the Ossimo-Pat sanctuary (Figure 3). The Sample “3/2016” is a pebble taken from the stone behind the big monolith known as “Pat 2,” presumably relative to the first stage of the abandonment of accumulation behind the big monolith known as “Pat 2,” presumably relative to the first stage of the the site. “1/2016” and “US 178” are samples from the northern votive stone circles, which are generally abandonment of the site. “1/2016” and “US 178” are samples from the northern votive stone circles, placed in the central phase of the site-life, around the first half of the 3rd millennium BCE, while the which are generally placed in the central phase of the site-life, around the first half of the 3rd samples “Pat12” and “Pat15”were collected from the housing pits of the fallen monoliths “Pat12” and millennium BCE, while the samples “Pat12” and “Pat15”were collected from the housing pits of the “Pat15.” All the cobbles have a diameter in the range of 100–150 mm. fallen monoliths “Pat12” and “Pat15.” All the cobbles have a diameter in the range of 100–150 mm. Figure 3. (a) Site map with sampling points; (b) detail of sample US178; (c) during the sampling Figure 3. (a) Site map with sampling points; (b) detail of sample US178; (c) during the sampling operation under the sunlight and under the dark (d). operation under the sunlight and under the dark (d). T To measure t o measure the he OSL d OSL depth epth profiles profiles and and t the h ae absorb bsorbed do ed ses, doses, the cobbles ha the cobbles have been ve been drilled under drilled under dim red light in laboratory. The reached depth was checked with a digital precision caliber. The polymineral dim red light in laboratory. The reached depth was checked with a digital precision caliber. The fine polymineral fine grain frac grain fraction with grain tion with grain sized between sized 4 and between 4 and 10 micrometers 10 m was icrometers w used. as used. For the sediments, the quartz grains have been extracted using the conventional procedure [13–16] For the sediments, the quartz grains have been extracted using the conventional procedure [13– under 16] under dim dim red light red light and an the d the lum luminescence inescence measur measurements ements were were conducted conducted on coa on coarse rse quartz quartz grai grains ns (180–250 (180–250 μm). m). All All samples, samples, both both cobbles cobbles an andd sediments, sediments, wer weree mo mounted unted on on stainle stainle ss ss stee steell discs. discs. The The O OSL SL measur measurement ementsswer wer ee performed performed w withith a Risø a RiTL sø /T OSL L/ODA20 SL DA20 reader. The sam reader. The samples p wer les were st e stimulated imulat byed by blue 2 2 2 2 LEDS blue LEDS (47 (470  30 0 ± nm, 30 nm 54 , 5 mW 4 m /cm W/c)m or ) o by r b IR y ILEDs R LED ( s (=λ = 830nm, 830nm360 , 360 m mW W /cm /cm) )and and the emi the emitted tted photons photons wer were det e detected ectedwith withan an EMI EMI 9 9235QB 235QB p photomultiplier hotomultipliecouple r coupl d ed w with ita h a UV UV filter filter (7.5 (7mm .5 mHoya m Hoy U-340) a U-34in 0) case in caof se o blue f blstimulation ue stimulation or with or wit a blue h a bl filter ue filt (Schott er (Schot BG39 t BG /Corning 39/Corni 7–59 ng 7– filter 59 fi combination) lter combinat in ion case ) in c ofa IR se stimulation. of IR stimula Blue tion.stimulation Blue stimulation was was used for used fo the samples r the samples in which the main dosimet in which the main dosimeter was the er was t quartz he and quart IR z and IR st stimulation imulat [13]ion [ for 13] for t the samples he sam rich ples rich in in feldspars. feldspars. To evaluate the absorbed dose the Single Aliquot Regenerative dose protocol (SAR) was applied for all samples. It is a well-known standard procedure for the optically stimulated luminescence dating in which the same aliquot is irradiated, heated and illuminated, during experimental cycles that are repeated (Table 1). The obtained signal is integrated, normalized and plotted in function of dose and the absorbed dose is calculated from interpolation of the natural signal on the constructed curve. Appl. Sci. 2020, 10, 7403 5 of 9 To evaluate the absorbed dose the Single Aliquot Regenerative dose protocol (SAR) was applied for all samples. It is a well-known standard procedure for the optically stimulated luminescence dating in which the same aliquot is irradiated, heated and illuminated, during experimental cycles that are repeated (Table 1). The obtained signal is integrated, normalized and plotted in function of dose and the absorbed dose is calculated from interpolation of the natural signal on the constructed curve. Table 1. Single Aliquot Regenerative dose protocol applied (L and T were calculated starting from the i i optically stimulated luminescence (OSL) curve, integrating the first 0.8 s minus a background estimated from the integral of the last 8 s). Step Rock Samples SAR Cycle Sediments SAR Cycle a a 1 Give dose, D Give dose, D i i 2 Preheat at T for 10 s Preheat at T for 10 s 0 0 3 Stimulated for 100 s at 125 C (OSL) or 50 C (IRSL), get L Stimulated for 40 s at 125 C (OSL) 4 Give test dose, D Give test dose, D t t 5 Cut heat to 220 C for 0 s Cut heat to 180 C for 0 s 6 Stimulated for 100 s at 125 C (OSL) or at 50 C (IRSL) Stimulated for 40 s at 125 C (OSL) 7 OSL or IRSL at 290 C for 40 s OSL at 290 C for 40 s 8 Return to 1 Return to 1 For the natural sample i = 0 and D = 0. Four regenerative doses plus a zero-dose measurement and a repeat dose were used; T depends on the sample. The pre-heat value was experimentally derived on the basis of the results of a dose recovery pre-heat plateau test [17] (see Table 2). Table 2. Pre-heat temperature for rock and sediment samples. Rock Samples Pre-Heat Sediment Samples Pre-Heat Sample Code Temperature ( C) Temperature ( C) 1/2016 260 US178 220 220 3/2016 200 Pat12 240 260 Pat15 200 220 90 90 Laboratory irradiations were given using a calibrated Sr/ Y beta source (5.50 GBq) mounted on the Risø TL/OSL reader (dose rate: 0.23 Gy/s for fine grain; 0.12 Gy/s for coarse grain). The absorbed dose is calculated from the weighted mean of values obtained from the analyzed aliquots (at least 10 for sample). The annual dose-rate absorbed by the samples is due to the contribution of the internal radioactivity of the material and the radioactivity of the surrounding environment. The radioactive families 238 U, 232 Th and 40 K are, in both cases, responsible for the natural imparted dose. There are also minor contributions from 87Rb and from cosmic rays. To take into account any non-homogeneity in the external contribution, the radioactivity of a sphere of the surrounding material (30 cm diameter centered at the sampling point) has to be measured [9]. The heterogeneity e ect was considered by measuring the radioactivity concentrations of the surroundings materials, i.e., sediments and cobbles. The contribution of each material to the annual dose-rate was evaluated applying the infinite matrix approximation, with updated conversion factors [18]. After radioactivity measurements, it is possible to assess the contribution of each layer calculating the relative volume of every material within the interaction sphere and normalizing the annual dose fractions in the age equation [19]. 40 K concentrations were measured through atomic absorption spectrometry; 238 U and 232 Th concentrations were obtained from total alpha counting technique. Although the water content of the cobbles is negligible, the surrounding sediment material does contain water, and thus, a water content correction is needed. This was based on the one calculated using the sediment material, specifically a mean water content equal to 75% of saturation value (20  10%) was used. Attenuation of the beta Appl. Sci. 2020, 10, 7403 6 of 9 dose was taken into account in case of sediments for which the coarse grains fraction was used to determine the absorbed doses [20], while alpha contribution was eliminated by an HF etching. Appl. Sci. 2020, 10, x FOR PEER REVIEW 6 of 9 3. Results 3. Results 3.1. Luminescence—Depth Profiles 3.1. Luminescence—Depth Profiles To test the application of luminescence rock surface dating to the surface of buried cobbles, To test the application of luminescence rock surface dating to the surface of buried cobbles, we first we first assessed the degree of bleaching of the surface itself. To investigate this, we measured the assessed the degree of bleaching of the surface itself. To investigate this, we measured the absorbed absorbed dose as a function of depth into all the five cobbles. As an example, the Figure 4 shows the dose as a function of depth into all the five cobbles. As an example, the Figure 4 shows the luminescence- luminescence-depth profiles from two di erent samples. Each point in the profile is obtained by the depth profiles from two different samples. Each point in the profile is obtained by the mean of the mean of the absorbed doses measured on 10 aliquots. absorbed doses measured on 10 aliquots. Figure 4. Figure 4. Luminescence depth Luminescence depth-pr -profiles ( ofiles (a a) 1/2 ) 1/2016 016 sample; ( sample; (b b) ) 3/2016 sample 3/2016 sample.. In the left panel, the absorbed dose increases with the depth and reaches a plateau (the so-called In the left panel, the absorbed dose increases with the depth and reaches a plateau (the so-called field saturation level) in the middle of the cobble. In the right panel, this plateau is reached in the first field saturation level) in the middle of the cobble. In the right panel, this plateau is reached in the first layers below the surface. It seems to have limited light exposure, insucient to fully reset the OSL layers below the surface. It seems to have limited light exposure, insufficient to fully reset the OSL signal in the layers below 1mm from the surface. Presumably, light exposure has not been suciently signal in the layers below 1mm from the surface. Presumably, light exposure has not been sufficiently long to totally bleach the luminescent signal throughout the cobble or this sample has a high attenuation long to totally bleach the luminescent signal throughout the cobble or this sample has a high coecient. For both samples, the absorbed dose at the surface is proportional to the time elapsed since attenuation coefficient. For both samples, the absorbed dose at the surface is proportional to the time the deposition. The calculated ages are reported in Table 3. elapsed since the deposition. The calculated ages are reported in Table 3. Table 3. Cobbles and sediments calculated ages. Table 3. Cobbles and sediments calculated ages. Absorbed Dose Rate Sample Code Sample Type Technique Absorbed Dose (Gy) Dose Rate (mGy/a) Date Sample Code Sample Type Technique Date Dose (Gy) (mGy/a) 1/2016 ROCK OSL 24.5 ± 3.5 5.15 ± 0.15 2760 BCE ± 500 US178 ROCK OSL 20.8 ± 3.5 2.95 ± 0.20 2675 BCE ± 500 1/2016 ROCK OSL 24.5  3.5 5.15  0.15 2760 BCE  500 US178 US178 SEDIMENT ROCK OSL OSL 15.4 ± 0.5 20.8  3.5 2.95 2.95 ± 0.0  0.20 7 2675 3220 B BCE C E ± 33 500 0 US178 SEDIMENT OSL 15.4  0.5 2.95  0.07 3220 BCE  330 3/2016 ROCK IRSL 42.3 ± 7.5 10.75 ± 0.30 1920 BCE ± 250 3/2016 ROCK IRSL 42.3  7.5 10.75  0.30 1920 BCE  250 Pat12 ROCK IRSL 30.5 ± 5.0 4.20 ± 0.12 5240 BCE ± 600 Pat12 ROCK IRSL 30.5  5.0 4.20  0.12 5240 BCE  600 Pat12 SEDIMENT OSL 17.2 ± 0.4 2.40 ± 0.08 5090 BCE ± 360 Pat12 SEDIMENT OSL 17.2  0.4 2.40  0.08 5090 BCE  360 Pat15 ROCK IRSL 22.9 ± 4.0 6.50 ± 0.25 2470 BCE ± 500 * Pat15 ROCK IRSL 22.9  4.0 6.50  0.25 2470 BCE  500 * Pat15 SEDIMENT OSL 12.8 ± 0.4 3.00 ± 0.05 2270 BCE ± 260 Pat15 SEDIMENT OSL 12.8  0.4 3.00  0.05 2270 BCE  260 * Fading-corrected date. * Fading-corrected date. 3.2. Fading Correction and Cobbles Ages 3.2. Fading By applyin Correction g the well-kno and Cobbles wn equation Ages age [6], the cobble burial ages were simply derived by dividing the cobbles surface absorbed dose values by the dose rate at the surface of the cobbles. By applying the well-known equation age [6], the cobble burial ages were simply derived by However, the luminescence signal from feldspars could be unstable: this phenomenon is known as dividing the cobbles surface absorbed dose values by the dose rate at the surface of the cobbles. ‘anomalous fading’ and can be taken into account by the conventional g value measurement [21]. For However, the luminescence signal from feldspars could be unstable: this phenomenon is known as the samples Pat12 and Pat15, we have quantified the fading rate as a percentage of IR signal loss with ‘anomalous fading’ and can be taken into account by the conventional g value measurement [21]. storage time after irradiation. Three aliquots from each sample were bleached in the reader using an For the samples Pat12 and Pat15, we have quantified the fading rate as a percentage of IR signal loss IR stimulation (for 500 s at 50 °C repeated after 60 s); a known dose has been imparted, and then the absorbed dose were measured, both immediately after irradiation and after a delay time of 6 h, 1 day, 19 days and 33 days. For the sample Pat12, the ratio between the imparted dose and the dose measured after the time delay are indistinguishable from unity, (Figure 5), thus, it possible to deduce that the phenomenon of anomalous fading is negligible. The cobble Pat15 is in a different condition: Appl. Sci. 2020, 10, 7403 7 of 9 with storage time after irradiation. Three aliquots from each sample were bleached in the reader using an IR stimulation (for 500 s at 50 C repeated after 60 s); a known dose has been imparted, and then the absorbed dose were measured, both immediately after irradiation and after a delay time of 6 h, 1 day, 19 days and 33 days. For the sample Pat12, the ratio between the imparted dose and the dose measured after the time delay are indistinguishable from unity, (Figure 5), thus, it possible to deduce that the Appl. Sci. 2020, 10, x FOR PEER REVIEW 7 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 7 of 9 phenomenon of anomalous fading is negligible. The cobble Pat15 is in a di erent condition: its signal fades by 10% in about a month. Therefore, we evaluate the fading rate with a g value of 2.4  0.5%, its signal fades by 10% in about a month. Therefore, we evaluate the fading rate with a g value of 2.4 its signal fades by 10% in about a month. Therefore, we evaluate the fading rate with a g value of 2.4 and in Table 3, the fading-corrected date is reported. ± 0.5%, and in Table 3, the fading-corrected date is reported. ± 0.5%, and in Table 3, the fading-corrected date is reported. 1.4 1.4 1.3 1.3 PA PA T12 T12 1.2 1.2 PA PA T15 T15 1.1 1.1 1 1 0.9 0.9 0.8 0.8 0 200 400 600 800 1000 0 200 400 600 800 1000 t (h) t (h) Figure 5. Normalized absorbed dose versus time. Figure 5. Normalized absorbed dose versus time. Figure 5. Normalized absorbed dose versus time. 3. 3.3. Se 3. Sedi dimen menttss’’ Age Agess 3.3. Sediments’ Ages The absorbed dose histogram, relative to more than 50 aliquots for each sample, as reported in The absorbed dose histogram, relative to more than 50 aliquots for each sample, as reported in The absorbed dose histogram, relative to more than 50 aliquots for each sample, as reported in Figure 6 for sample Pat15, shows a symmetric distribution with rather low dispersion of the data, Figure 6 for sample Pat15, shows a symmetric distribution with rather low dispersion of the data, Figure 6 for sample Pat15, shows a symmetric distribution with rather low dispersion of the data, evidencing a similar dose absorbed by all the aliquots. This is an indication that the surface sediments evidencing a similar dose absorbed by all the aliquots. This is an indication that the surface sediments evidencing a similar dose absorbed by all the aliquots. This is an indication that the surface sediments were fully blea were fully blea ched before ched before the cobbl the cobbles’ deposi es’ deposi ti ti on. This al on. This al ll o o ws to ws to use the wei use the wei g g hted mea hted mea n n to calcula to calcula tt e e were fully bleached before the cobbles’ deposition. This allows to use the weighted mean to calculate the absorbed doses by the samples that are reported in Table 3, together with the annual dose rates the absorbed doses by the samples that are reported in Table 3, together with the annual dose rates the absorbed doses by the samples that are reported in Table 3, together with the annual dose rates and and the OSL dates. and the OSL dates. the OSL dates. P P A A T 15 T 15 20 20 16 16 6 8 10 12 14 16 18 20 22 24 6 8 10 12 14 16 18 20 22 24 Dose (Gy) Dose (Gy) Figure 6. Sample “Pat15.” Distribution of absorbed doses. Figure 6. Sample “Pat15.” Distribution of absorbed doses. Figure 6. Sample “Pat15.” Distribution of absorbed doses. 4. Discussion and Conclusions 4. Discussion and Conclusions The doses ab The doses absorbed by th sorbed by the cobbles w e cobbles weere dir re direectly ctly deri derived by the ved by the aalliiqquots taken f uots taken frrom the om the ffiirst rst llaayer. Al yer. Although the uncert though the uncertaaiinty i nty inn the the dose dose iiss de deriv riveed from d from the the stand standaard rd erro error r of 10 aliquots, of 10 aliquots, the the Normalized absorbed dose Normalized absorbed dose Frequency Frequency Appl. Sci. 2020, 10, 7403 8 of 9 4. Discussion and Conclusions The doses absorbed by the cobbles were directly derived by the aliquots taken from the first layer. Although the uncertainty in the dose is derived from the standard error of 10 aliquots, the relative error spans between 15% and 30%, it is quite high, especially if compared with that obtained with sediments (5–6%). Due the scarcity of material for each considered layer, it has been impossible to extract quartz or feldspar grains from the samples. This may have led to luminescence signals with inadequate characteristics (slow decay rate, high background) that introduced a high error in the fitting to calculate the absorbed dose. For US178, Pat12 and Pat15, the age from cobble is in agreement with the sediment age at a level of 1 standard deviation, thus, they are consistent with each other. From a methodological point of view, these preliminary results show that it is possible to apply luminescence dating to the surfaces of the artefacts present in the Ossimo-Pat site. Despite the high error obtained on rock surfaces, the data obtained on sediments under the rock were more precise. This suggests that for future application of surface dating of megalithic structure, it is recommended to sample both rocks and the underlying sediments in order to reduce the age errors. Moreover, the results of the dating o er, from an archaeological point of view, an interesting feedback to the existing timeframe of the site. Even considering the range error of each date, we can compare the results with what was already established about the site, chronology-wise. The first sample (the rock “1/2016,” 2760 BCE  500) was taken from the northernmost of the votive stone circles. Its date is compatible with the other two samples from the nearby, similar, stone structures (samples “US 178,” rock, 2675 BCE  500, and sediments, 3200 BCE  330). There are no 14C dates available from these circles that have been dated to the first half of the 3rd millennium BCE based on the objects found inside the circles, namely a specific type of arrowheads, usually related this period. The three OSL dates from the area would seem to confirm the current chronological framework. The IRSL date from the rock sample “3/2016” (1920 BCE  250) seems equally aligned with the current chronology of the site. This rock was collected from the accumulation layer located behind the big monolith called “Pat 2,” one of the few still vertically standing. The small accumulation of soil and rocks is probably related to the first stage of abandonment of the site, right after its partial destruction and dismissal, and is usually dated around the 23rd–20th centuries BCE thanks to a charred coal 14C dating [1]. The samples taken from the monolith pits are the most intriguing ones, as we still do not have a full comprehension of the precise life cycles of these monuments. The samples taken from the housing pit of the monolith “Pat15” are related to its filling, which happened in time, after the dismissal of the site and the overthrowing of the monolith, which was pushed to the ground, out of its proper housing. The dating of rock and relative sediment (2470 BCE  500 and 2265 BCE  115, respectively) are perfectly coherent with the said action, which probably happened, as said, between the end of the 24th and the 21st centuries BCE. The dating of the samples from the housing pit “Pat12” (Rock: 5240 BCE  600; sediment: 5090 BCE 360), on the other hand, o er a very interesting result, related back to the end of the sixth millennium BC, before the foundation of the sanctuary. Nevertheless, these dates are perfectly coherent with another dating, obtained by 14C on a charcoal sample from the layer 181 [1], which was documented in this very sector of the site thanks to a deep stratigraphic trench. Layer 181, rich in charred coal and burnt wood, is believed to be the outcome of the very first action carried out in this place, namely a slash/burn activity, usually performed during the late Neolithic to open new pasture areas in medium and high-altitude locations. Evidently, the digging activity performed during the Copper Age to prepare the housing pit for the huge monolith “Pat12,” which is longer than 2 m and very heavy, led to reach the deeper and more ancient level of the site, to which our samples appear to belong. Author Contributions: Conceptualization, A.G. and L.P.; methodology, A.G., L.P. and P.R.; writing—original draft preparation, A.G. writing—review and editing, A.G., L.P., P.R., R.P.K. and M.M.; supervision, R.P.K. and M.M. All authors have read and agreed to the published version of the manuscript. Appl. Sci. 2020, 10, 7403 9 of 9 Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. References 1. Poggiani Keller, R. Copper Age Ancestral Sanctuaries and Landscapes in Valle Camonica; Archaeo Press Publishing: Oxford, UK, 2018; pp. 431–442. 2. Rondini, P. Digital Rocks. An integrated approach to rock art recording: The case study of Ossimo-Pat (Valle Camonica), monolith 23. Archeol. Calc. 2018, 29, 259–278. 3. Ivy-Ochs, S.; Kober, F. Surface exposure dating with cosmogenic nuclides. Quat. Sci. J. 2008, 57, 179–209. [CrossRef] 4. Sohbati, R.; Murray, A.S.; Chapot, M.S.; Jain, M.; Pederson, J. Optically stimulated luminescence (OSL) as a chronometer for surface exposure dating. J. Geophys. Res. 2012, 117, 117. [CrossRef] 5. Vafiadou, A.; Murray, A.S.; Liritzis, I. Optically stimulated luminescence (OSL) dating investigations of rock and underlying soil from three case studies. J. Archaeol. Sci. 2007, 34, 1659–1669. [CrossRef] 6. Aitken, M.J. An Introduction to Optical Dating. In The Dating of Quaternary Sediments by the Use of Photon-Stimulated Luminescence; Oxford University Press: New York, NY, USA, 1998. 7. Laskaris, N.; Liritzis, I. A new mathematical approximation of sunlight attenuation in rocks for surface luminescence dating. J. Lumin. 2011, 131, 1874–1884. [CrossRef] 8. Feathers, J.; More, G.M.; Quinterosc, P.S.; Burkholder, J.E. IRSL dating of rocks and sediments from desert geoglyphs in coastal Peru. Quat. Geochronol. 2019, 49, 177–183. [CrossRef] 9. Gliganic, L.A.; Meyer, M.C.; Sohbati, R.; Jain, M.; Barrett, S. OSL surface exposure dating of a lithic quarry in Tibet: Laboratory validation and application. Quat. Geochronol. 2019, 49, 199–204. [CrossRef] 10. Sohbati, R.; Murray, A.; Jain, M.; Buylaert, J.-P.; Thomsen, K. Investigating the resetting of OSL signals in rock surfaces. Geochronometria 2011, 38, 249–258. [CrossRef] 11. Galli, A.; Artesani, A.; Martini, M.; Sibilia, E.; Panzeri, L.; Maspero, F. An empirical model of the sunlight bleaching eciency of brick surfaces. Radiat. Meas. 2017, 107, 67–72. [CrossRef] 12. al Khasawneh, S.; Murray, A.; Thomsen, K.; AbuAzizeh, W.; Tarawneh, M. Dating a near eastern desert hunting trap (kite) using rock surface luminescence dating. Archaeol. Anthr. Sci. 2019, 11, 2109–2119. [CrossRef] 13. Mejdahl, V.; Christiansen, H. Procedures used for luminescence dating of sediments. Quat. Sci. Rev. 1994, 13, 403–406. [CrossRef] 14. Lang, A.; Lindauer, S.; Kuhn, R.; Wagner, G.A. Procedures used for Optically and Infrared Stimulated Luminescence Dating of Sediments in Heidelberg. Anc. TL 1996, 14, 7–11. 15. Mauz, B.; Bode, T.; Mainz, E.; Blanchard, H.; Higer, W.; Dikau, R.; Zöller, L. The luminescence dating laboratory at the University of Bonn: Equipment and procedures. Anc. TL 2002, 20, 53–61. 16. Stokes, S. Optical dating of young (modern) sediments using quartz: Results from a selection of depositional environments. Quat. Sci. Rev. 1992, 11, 153–159. [CrossRef] 17. Wintle, A.G.; Murray, A.S. A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols. Radiat. Meas. 2006, 41, 369–391. [CrossRef] 18. Guérin, G.; Mercier, N.; Adamiec, G. Dose-rate conversion factors: Update. Anc. TL 2011, 29, 4. 19. Galli, A.; Martini, M.; Maspero, F.; Panzeri, L.; Sibilia, E. Surface dating of bricks, an application of luminescence techniques. Eur. Phys. J. Plus 2014, 129, 1–9. [CrossRef] 20. Bell, W.T. Thermoluminescence dating: Radiation dose-rate data. Archaeometry 1979, 21, 243–245. [CrossRef] 21. Lamothe, D.J. Ubiquity of anomalous fading in K-feldspars and the measurement and correction for it in optical dating. Can. J. Earth Sci. 2001, 38, 1093–1106. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional aliations. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Published: Oct 22, 2020

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