Table 1.
Earliest known instances of shell beads.
Fig 1.
Location of the site and of lacustrine fossil deposits where Corbicula shells were found.
Stars: Shuidonggou site complex (38°17´N, 106°30´E); 2. BaijianHu Beach (39°09´N, 104°10´E); 3. Tudongcao (39°33´N, 103°49´E); 4. Duantouliang (39°34´N, 103°57´E); 5. Zhangjiakeng (38°56´N, 102°15´E); 6. Jinantai (39°50´N, 105°35´E); 7. Ejina Basin (42°21´N, 101°15´E); 8. the Jingerwa section (40°06´N, 114°20´E); 9. Chagan Nur (43°25´N, 114°55´E); 10. The Shell Bar (36°30´N, 96°12´E).
Fig 2.
Vertical distribution of selected finds categories at Shuidonggou Locality 2.
Cultural layers (CL) and the location of the shell analysed in this study are indicated. Vertical and horizontal scales in metres. Reprinted from Chen et al. [93] under a CC BY license, with permission from Acta Anthropologia Sinica, original copyright 2012.
Table 2.
Radiometric dating of Shuidonggou Locality 2 (data after Gao et al. 2013, Li et al. 2013).
Fig 3.
Stages of degradation recorded on the Corbicula fluminea reference collection created for this study.
Fig 4.
Photo of both sides of flint tools used to experimentally engrave Corbicula fluminea and Spisula solida valves.
Fig 5.
Broken shell bead from Shuidonggou Locality 2, Cultural layer 3.
Horizontal yellow lines indicate the location of the ground facet. The blue vertical line identifies the area where the incised line is observed.
Table 3.
Occurrence of modern Corbicula fluminea at different stages of degradation.
Fig 6.
Umbos of Corbicula fluminea shells at different stages of degradation.
a. Stage I, living shell; b. Stage IV; c. Stage VI.
Fig 7.
Freshwater shells visible in the Shell Bar Section, Salt Lake Qarhan, Qaidam Basin (photo H. Zhang).
Reproduced with the permission of the author.
Fig 8.
a. facet produced by grinding, present on the umbo of the Shuidonggou shell; b. close-up view of the ground area; c. SEM photo of the striations. (a, c: scale = 1 mm; b: scale = 100 μm).
Fig 9.
Microscopic images and 3D reconstructions obtained with a confocal microscope of facets produced by experimentally grinding Corbicula fluminea umbos on different grindstones. a-c. granite; d-f. basalt; g-i. coarse-grained sandstone; j-l. fine-grained sandstone.
Fig 10.
a. incision on the exterior surface of the Shuidonggou shell; b. close-up view of the center of the incision (a: scale = 1 mm; b: scale = 100 μm).
Fig 11.
Tracings of the shell bead with incised line (in black) and possible traces of utilisation (in gray).
Fig 12.
a. straight lines produced by experimentally engraving a Corbicula shell with pronounced growth ridges; b-d. momentary interruptions (b-c) and change of direction (d) of grooves produced by engraving lines on shells with less pronounced growth ridges (a, b: scale = 1mm).
Fig 13.
a. Shell drawing with location of photos b-d; b. microstriations located between the ground facet and the engraved line; c. microstriations close to the engraved line with arrows indicating possible pigment residues; d. microstriations close to the valve distal fracture (b-d: scale = 100 μm).