Biogenic Silica Microfossil Methodological and Results Detail

Home , Biogenic silica

Chronostratigraphy, Site Formation, and Palaeoenvironmental Context of Late Pleistocene and Holocene Occupations at Grassridge Rock Shelter (Eastern Cape, South Africa)

Christopher J.H. Ames1, 2, Luke Gliganic3, Carlos E. Cordova4, Kelsey Boyd1, Brian G. Jones1, Lisa Maher5, and B.R. Collins6, 7

1 – School of Earth, Atmospheric, and Life Sciences, University of Wollongong 2 – Department of Anthropology, University of Victoria 3 – Institute of Geology, University of Innsbruck 4 – Department of Geography, Oklahoma State University 5 – Department of Anthropology, University of California-Berkeley 6 – Department of Anthropology, University of Manitoba 7 – Department of Archaeology, University of Cape Town

Biogenic Silica Microfossil Methodological and Results Detail Biogenic silica particles The particles identified here as biogenic silica include phytoliths (Figure S3.1a-c), diatoms (Figure S3.1d), and sponge spicules (Figure S3.1e). Diatoms and sponge spicules appear in small amounts in some of the evaluated samples from Grassridge rock shelter, which suggests locally wet sediments and/or the existence of water nearby. Diatoms and sponge spicules may have entered the rock shelter by wind picking them up from dried streambed surfaces and redepositing them within the shelter or by saturation of the rock shelter sediments—a high concentration of both diatoms and sponge spicules may indicate the latter, either by seepage or possibly flood waters. Grass and woody plant phytoliths Identified silica phytoliths include short cells (Figure S3.2a-b), elongates (Figure S3.2c), acicular trichomes (Figure S3.2d), and bulliforms (Figure S3.2e-f). Of these varieties, those diagnostic for climate reconstruction are the grass short cells, referred to here and in the manuscript as grass silica short-cells (GSSC). Husk phytoliths (Figure S3.3) are typical of grass inflorescences usually from the glumes. They are generally rare in natural assemblages, but occur more commonly at archaeological sites suggesting a higher proportion of the parts of the grass containing seeds. The spheroids and semi-spheroids (Fig. S3.1b-c), are typically produced by trees. They are used here to indicate the presence of woody plants through the wood to grass ratio, whose high values represent high incidence of trees or tree-plant material at a given occupation layer. Diagnostic grass silica short-cells (GSSC) criteria The classification of GSSC used in this study (Fig. S3.4) follows closely the one previously published by Cordova (2013) and Cordova & Avery (2017), slightly modified and updated for the present study (Table 1). This classification has its basis on the nomenclature proposed by Madella et al. (2005) and uses terms from Piperno (2006) and a number of other studies (Fredlund & Tieszen 1994; Alexandre et al. 1997; Barboni & Bremond 2009; Neumann et al. 2009).

Figure S3.1. Examples of a) grass phytoliths, b–c) woody-plant/tree phytoliths, d) diatoms, e) sponge spicules.

Figure S3.2. Examples of identified phytolith morphotypes: a) short cell, panicoid bilobate; b)short cell, chloridoid bilobate; c) elongate; d) trichome; e) bulliform, keystone; f) bulliform; parallepipedal. Bars are 20 µm long.

Fig. S3.3. Example of an identified husk phytolith.

Fig. S3.4. Grass subfamilies and their corresponding diagnostic grass silica short cells (GSSC).

Data The biogenic silica microfossil data are presented mainly in the form of ratios, which are meant to represent the proportion of C3 in relation to C4 grasses and the proportion of Panicoideae to Chloridoideae rather than as percentages. The use of ratios reduces the influence of overproduction that occurs for certain morphotypes (Table S3.1). Similarly, the wood to grass ratio attempts to show the relationship of woody-plant/tree phytoliths to grass phytoliths—the former tend to be less numerous in grassland environment. Husk phytoliths are presented as percentages of the total number of grasses (Table S3.1). The percent of damaged phytoliths is indicative of adverse conditions that degrade silica, usually through silica dissolution, and signifies the reliability of interpretation. A very high percentage of damaged phytoliths reduces the value of an interpretation. In the present study, the percentage of damaged phytoliths increases with depth, but are still low enough to permit reliable interpretations of ratios and percentages. Diatoms and sponge spicules are presented as percent of the sum of all biogenic silica particles (Table S3.1).

Table S3.1 Biogenic silica data that is presented graphically in the manuscript (SU = stratigraphic unit).

Depth Graminoid Phytoliths per Below to non- Woody C3 to C4 Panicoidea to gram of Surface Graminoid Plant to Plants Chloridoidea % Husk % Damaged sediment % % Sponge SU (cm)* Ratio Grass Ratio Ratio Ratio Phytoliths Phytoliths (x1000) Diatoms spicules 1 6.9 2.6 74.0 0.4 1.8 0.4 16.7 75.2 0.5 1.3 2 11.4 2.6 79.0 0.7 2.4 0.0 14.0 71.0 0.2 0.2 5 19.4 1.7 85.0 1.0 1.1 0.0 18.4 105.0 0.3 0.3 8 26.6 4.4 41.0 0.8 1.2 0.0 15.8 64.3 1.5 0.0 10 33.6 1.2 71.0 0.3 1.1 2.0 21.2 41.3 0.3 2.0 12 40.0 1.4 5.0 0.4 2.0 1.8 20.7 150.0 2.0 1.3 14 43.0 1.7 5.0 1.1 2.3 0.0 36.4 2.6 2.3 2.3 15 45.7 3.1 83.0 0.7 0.5 0.0 14.1 143.9 1.8 2.0 16 50.6 4.0 13.0 1.5 3.0 0.6 12.1 5.3 0.0 3.2 17 54.0 3.7 1.0 1.0 NA 0.0 72.7 3.2 0.0 3.1 18 57.0 0.8 144.0 1.7 1.2 0.0 22.7 65.9 1.0 1.5 23 62.0 0.8 35.0 2.0 6.0 3.6 8.9 162.8 2.1 1.7 25 64.0 1.3 20.0 3.3 2.0 0.0 39.0 16.5 4.6 3.3 31 67.0 NA NA NA NA NA NA 0.0 NA NA 32 71.3 19.8 0.0 6.5 0.3 1.7 12.8 28.7 2.1 0.9 34 83.5 50.1 0.0 3.0 0.3 0.0 1.5 57.6 0.0 1.4 35 87.2 35.0 0.0 2.1 0.3 0.0 5.1 85.0 0.4 1.2 38 95.9 43.6 0.0 9.5 1.0 0.0 27.5 40.1 0.4 0.9 50 104.2 24.0 1.0 6.0 0.0 0.0 47.2 1.1 0.0 21.6 44 top 113.2 9.0 7.0 11.5 1.0 0.0 15.4 2.1 0.9 0.5 44 top 121.5 12.7 0.0 NA NA 0.0 84.2 0.4 0.0 0.0 45 131.9 20.8 0.0 6.0 0.8 0.0 11.9 35.8 1.8 11.0 47 141.6 5.7 19.0 2.6 0.0 0.0 46.7 0.6 0.7 14.5 *referenced to the uppermost surface elevation for the B-C 2/3 sequence and adjusted to preserve stratigraphic relationships

References: Alexandre, A., Meunier, J-D., Lézine, A-M., Vincens, A., and Schwartz, D. 1997. Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 136: 213–229. DOI: https://doi.org/10.1016/S0031- 0182(97)00089-8.

Barboni, D. and Bremond, L. 2009. Phytoliths of East African grasses: An assessment of their environmental and taxonomic significance based on floristic data. Review of Palaeobotany and Palynology, 158: 29–41. DOI: https://doi.org/10.1016/j.revpalbo.2009.07.002.

Cordova, C. and Avery, G. 2017. African savanna elephants and their vegetation associations in the Cape Region, South Africa: Opal phytoliths from dental calculus on prehistoric, historic and reserve elephants. Quaternary International, 443: 189–211. DOI: https://doi.org/10.1016/j.quaint.2016.12.042.

Cordova, CE. 2013. C3 Poaceae and Restionaceae phytoliths as potential proxies for reconstructing winter rainfall in South Africa. Quaternary International, 287: 121–140. DOI: https://doi.org/10.1016/j.quaint.2012.04.022.

Fredlund, GG. and Tieszen, LT. 1994. Modern Phytolith Assemblages from the North American Great Plains. Journal of Biogeography, 21: 321–335. DOI: https://doi.org/10.2307/2845533.

Madella, M., Alexandre, A., and Ball, T. 2005. International Code for Phytolith Nomenclature 1.0. Annals of Botany, 96: 253–260. DOI: https://doi.org/10.1093/aob/mci172.

Neumann, K., Fahmy, A., Lespez, L., Ballouche, A., and Huysecom, E. 2009. The Early Holocene palaeoenvironment of Ounjougou (Mali): Phytoliths in a multiproxy context. Palaeogeography, Palaeoclimatology, Palaeoecology, 276: 87–106. DOI: https://doi.org/10.1016/j.palaeo.2009.03.001.

Piperno, DR. 2006. Phytoliths: A Comprehensive Guide for Archaeologists and Paleoecologists. Oxford: Altamira Press.