Radiocarbon Determinations and the Beas Drainage

Radiocarbon Determinations and the Beas Drainage

As discussed in the above, central to the research was a robust program of the collection of organic sediments and carbon. The latter have been discussed in the context of cultural deposits at Vainiwal and Lohoma Lal Tibba with respect to the onset and duration of settlement.

This discussion of the radiocarbon dates follows the order of the location of Beas related archaeological sites along a downstream axis that follows the course of the drainage to its confluence with the Indus trunk channel. For purposes of analysis it is convenient to subdivide the segments of the Beas into upstream, middle and downstream segments. The segmentation reflects general principles of drainage basin geomorphology that, to some degree, explains the sequence of geological events; typically downstream (alluvial) sedimentation is thicker and more recent than upstream. Cultural deposits from the mounds referenced in this study are typically housed in sediment complexes built up atop the uppermost alluvium. Radiocarbon determinations were performed on both organic sediment and carbon, with the latter dated almost exclusively in cultural deposits, which typically furnish features that attest to in situ activity areas and the most reliable radiometric determinations. Organic sediment was most widely sampled in natural sedimentary contexts, most specifically in alluvial sediments. Dated sediment consists of various contributions of degraded carbon-rich material in humic soils and other debris within a soil or alluvial sediment package; ages here are composite determinations of the humic fractions. Dates are best considered “mean ages” for the horizon or depositional layers from which they are taken. Both radiometric and Accelerator Mass Spectroscopy (AMS) assays were performed. 2 Sigma calibrated results (to 95% probability) are reported.

As a rule the organic sediment from alluvial deposits was dated to inform on the age of the floodplains, which pre-dated and supported the Harappan occupations. The dates were utilized to reconstruct floodplain histories and chronologies. The age spread was from terminal Pleistocene through Middle Holocene (ca. 15.7-6.0 ka). This confined range indicated that stream dynamism was high through the Middle Holocene and that when later Holocene human activity (Harappan or terminal pre-Harappan) was initiated the Beas and its adjacent Ravi River water courses flowed in relatively stable channels. Cultural deposits from the mounds corresponded exclusively to Harappan-era occupation, spanning the critical third millennium B.C. period of Indus civilization florescence. The implication is that stabilized stream flow and low level geomorphic activity was contemporaneous with a successful Harappan age adaptation within the flood basins of the Beas and Ravi floodplain and terrace environments.

For the Upper segment sampling was confined to archaeological site complexes and specifically to the larger sites of Lohoma Lal Tibba and Chak Purbane Syal (listed as Chak 126-9L and Chak 114-9L based on their designation by the PAS). The Beas team also performed radiometric assays on the only two known pre-occupation (Pleistocene) contexts at Harappa. The latter confirmed the existence of a deep soil at the Pleistocene-Holocene transition at the parent site.

Minimal radiocarbon dating was undertaken for the Middle segment, since there was only a single archaeological occupation, at Chak 90-12L, present along this reach. Nevertheless, as discussed earlier, the antiquity and range of the alluvial sediments and cultural deposits conformed to the age of the upstream segments in the elevated drainage basin terrain to the north-northeast.

Finally, upper segment reaches were sampled across an area that included both significant archaeological sites (most prominently Vainiwal) and the furthest downstream locations (Chak 27M, Chak 18/19M, and Chak 21M). The latter were largely leveled by destruction and/or development activities so that cultural distributions were chiefly surface manifestations. Accordingly, only sub-surface alluvial contexts were dated, and these conformed to the records of Pleistocene and Early and Middle Holocene antiquity that were represented elsewhere along the drainage. More detailed references to the radiocarbon record are documented in relevant sections of the text.