Records of Ancient Human-Environmental Interaction from Mayan Southern Petén, Guatemala
Part 1:  A 1300-year record of human activity and climate change from Cancuén

Appendix 1.  Sediment descriptions

Unit I:  Below c. 2.25 m

Light grey brown (10YR 3/2) consolidated clayey silt with very rare fine sand particles. Some soil development, no micro-stratigraphy, occasional decayed plant matter + roots on growth position, very rare fragments of CaCO₃. No cultural debris; ceramics, bones, jade or quartz. There is a gradual transition to the overlying stratum, which is not reflected in the sediment chemistry, which changes markedly. This unit of pre-Maya soil extends to c. 2.70 m depth in this part of the gully, perhaps even deeper further eastwards.

Unit II:  2.25 to 2.10 m depth

Greyish brown (10YR 5/2) predominantly silt, poorly consolidate colluvium. High density of ceramic fragments in moderate to poor states of preservation often decayed into the soil. No skeletal remains observed. Frequent CaCO₃ fragments of up to 20 mm recorded. Sharp, wavy boundary with overlying stratum.

Unit III:  Burnt layer, 2.10 to 1.90 m

This stratum consists nearly entirely of burnt material, very dark brown to black in colour. High concentration of poorly preserved ceramic fragments and very small concretions of CaCO₃ material were observed. Sediments are predominantly poorly consolidated silt, with no evidence of pedogenesis. On average, charred material is 100 mm in depth, but was found to be up to 200 mm at its greatest depth. The stratum consists mostly of burnt in situ soil and cultural material, and extensive quantities of charcoal, up to 100 mm in length. There is a sharp, wavy contact with the overlying stratum. Some human remains found imbedded in the upper 20 mm of burnt layer, however these are not burnt, and are not contemporaneous with the fire that burnt these sediment. These bones are considered to have subsided into the less dense burnt layer through time from the overlying stratum.

Unit IV:  1.90 to 1.50 m depth

Greyish brown (10YR 5/2) silt, some coarse silt material. Much lower plant organic matter content, frequent fragments of CaCO₃ material 1-3 mm diameter (up to 50% of sediments). A moderate amount of ceramic fragments, decreasing in frequency upwards, were noted. Extensive human skeletal remains, some partially disarticulated. Frequency of human remains decreasing upwards as well. Bones towards 1.50 m depth are typically disarticulated, single bones, rather than near-complete skeletons found towards 1.90 m depth. Gradual, wavy boundary with overlying stratum.

Unit V:  1.50 to 0.90 m depth

Very dark grey (10YR 3/1) clayey silt, increasingly consolidated with depth. Moderate plant organic matter, mainly fine rootlets. Some human bones, of poor preservation, typically near base of this stratum. Decreasing amounts of ceramic material upwards, often very small in size. Rarer, larger fragments have rounded corners, denoting their erosion from upslope formerly occupied structures. Very fine fragments of CaCO₃ throughout. Rare, very fine flecks of charcoal were observed.

Unit VI:  Flood deposits

10YR 6/3 pale brown silty clay flood deposit, finely laminate with occasional flecks of charcoal. Rare laminated plant matter, otherwise very low organic matter content. Very sharp boundaries with adjoining strata.

Unit VII:  Upper slope-derived sediments

Relatively high plant matter (roots in growth position, rootlets, leaf remains), some gritty texture from decaying organic matter, however, mainly dark grey (10YR 4/1) clayey silt texture. Rare CaCO₃ fragments, possible thin laminae of flood-born clays towards top of sequence, though difficult to distinguish. Very rare, small (1-2 mm) and decayed ceramic fragments. From 0.40 to 0.20 m, large dark grey rock fragments observed, thought to represent increasing erosion intensity and human disturbance.

Unit VIII:  Forest floor

Partially decomposed leaf and plant litter, little or no soil material. Not sampled.

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