Table11_Thermo-microstratigraphy of shells reveals invisible fire use and possible cooking in the archaeological record.XLSX

The archaeological visibility of hearths related to shellfish cooking methods is limited, particularly in pre-ceramic shell midden contexts. Important evidence for use of fire is the thermal alteration of components, namely the identification of burnt shells. Mollusk shells that mineralize as aragonite are particularly indicative of burning due to the conversion of aragonite to calcite through recrystallization at known temperature thresholds. However, roasting temperatures needed to open bivalves, do not necessarily cause thermal alterations in the cooked shell. This complicates the significance of shell mineralogy by itself to recognize cooking, and discerning pre-depositional from in situ heating. To distinguish between cooking and burning, we combine micromorphological analyses with microscopic Fourier transformed infrared spectroscopy to investigate mineralogical thermo-alterations alongside microstratigraphic formation studies. Experimentally heated specimens of Cerastoderma edule and Scrobicularia plana are used to identify the temperature thresholds of biogenic calcium carbonate phase alteration at the micro-scale. These results are then used to interpret mineral alterations in deposits from two Mesolithic shell midden contexts from Portugal. Micro-stratigraphically controlled mineralogy proved to be particularly useful to distinguish between pre-depositional heating from in situ heating, configuring a novel methodology for recognition of traces of cooking shellfish versus traces of fire used for other purposes. Mapping the mineral phase conversion at a micro stratigraphic scale also allows us to identify instances of in situ fire events that were invisible macroscopically. This combined microstratigraphic and mineralogical methodology considerably increases our capacity of deciphering intricate shell midden stratigraphy and occupational events.与贝类烹饪相关的火塘（hearths）的考古可识别性有限，在前陶时期贝丘（shell midden）遗址背景中尤为显著。判断用火行为的关键证据在于遗存的热变质作用（thermal alteration），即烧过的贝壳（burnt shells）的识别。以文石（aragonite）作为稳定矿物相的软体动物贝壳，其受热特征尤为显著，因为在已知温度阈值（temperature thresholds）下，文石会通过重结晶（recrystallization）作用转变为方解石（calcite）。然而，打开双壳类（bivalves）所需的焙烧温度，未必会使被烹饪的贝壳发生热变质。这使得仅凭贝壳矿物学来识别烹饪行为，以及区分沉积前热事件（pre-depositional heating）与原位加热（in situ heating），都变得更为复杂。为区分烹饪用火与其他用途的用火，我们结合微形态分析（micromorphological analyses）与显微傅里叶变换红外光谱（microscopic Fourier transformed infrared spectroscopy），在微地层形成研究的基础上，同步探究矿物学热变质特征。我们以食用鸟蛤（Cerastoderma edule）和平滑斜纹蛤（Scrobicularia plana）的实验加热标本为研究对象，在微观尺度上确定生物成因碳酸钙（biogenic calcium carbonate）物相转变的温度阈值。随后利用这些结果，解读葡萄牙两处中石器时代（Mesolithic）贝丘遗址沉积物中的矿物变质特征。经证实，受微地层控制的矿物学分析方法，在区分沉积前热事件与原位加热方面尤为实用，由此构建了一套识别贝类烹饪痕迹与其他用途用火痕迹的全新研究范式。在微地层尺度上绘制矿物相转变图谱，还能帮助我们识别那些宏观上不可见的原位用火事件。这套结合微地层与矿物学的研究方法，极大提升了我们解读复杂贝丘地层与人类活动遗存的能力。