Altered cropping pattern and cultural continuation with declined prosperity following abrupt and extreme arid event at ~4,200 yrs BP: Evidence from an Indus archaeological site Khirsara, Gujarat, western India

Abstract

Archaeological sites hold important clues to complex climate-human relationships of the past. Human settlements in the peripheral zone of Indus culture (Gujarat, western India) are of considerable importance in the assessment of past monsoon-human-subsistence-culture relationships and their survival thresholds against climatic stress exerted by abrupt changes. During the mature phase of Harappan culture between ~4,600-3,900yrsBP, the ~4,100±100yrsBP time slice is widely recognized as one of the major, abrupt arid-events imprinted innumerous well-dated palaeo records. However, the veracity of this dry event has not been established from any archaeological site representing the Indus (Harappan) culture, and issues concerning timing, changes in subsistence pattern, and the likely causes of eventual abandonment (collapse) continue to be debated. Here we show a significant change in crop-pattern (from barley-wheat based agriculture to 'drought-resistant' millet-based crops) at ~4,200 yrs BP, based on abundant macrobotanical remains and C isotopes of soil organic matter (δ13CSOM) in an archaeological site at Khirsara, in the Gujarat state of western India. The crop-change appears to be intentional and was likely used as an adaptation measure in response to deteriorated monsoonal conditions. The ceramic and architectural remains of the site indicate that habitation survived and continued after the ~4,200yrsBP dry climatic phase, but with declined economic prosperity. Switching to millet-based crops initially helped inhabitants to avoid immediate collapse due to climatic stresses, but continued aridity and altered cropping pattern led to a decline in prosperity levels of inhabitants and eventual abandonment of the site at the end of the mature Harappan phase.

Fig 1

Panel (A) Map of Gujarat showing Khirsara and other Harappan sites discussed in the text. Panel (B, C) General layout of trenches for excavation and excavated trench showing exposed structures and floor level. Panel (D) shows kitchen area with hearth and earthen girdle. Panel (E) shows water well exposed at the site.

Fig 2

Archaeological artifacts recovered from Khirsara (A) Mature Harappan ceramics (painted and plain) (B) Red Ware Harappan pot (C) Gold beads (D) Fish hook made of copper (E) Copper objects (F) Beads of semiprecious stones (G) Seal with bison (H) Seal bearing Harappan characters. These antiquities have been stored at the office of Excavation Branch-V, ASI, Vadodara, Gujarat, India.

Fig 3

Macroscopic plants remains of cultivars, weeds and wild taxa (1) Hordeum vulgare (2) Triticum aestivum/durum (3) T. cf. dicoccum (4) T. cf. sphaerococcum (5) Pennisetum glaucum (6) Sorghum cf. bicolor (7) cf. Eleusine coracana (8) Panicum cf. miliaceum (9) Setaria cf. italica (10) Pisum cf. arvense (11) Lathyrus sativus (12) Cicer cf. arietinum (13) Vigna cf. radiata (14) Macrotyloma uniflorum (15) cf. Luffa sp. (16) Linum cf. usitatissimum (17) Sesamum indicum (18) Gossypium arboreum/herbaceum (19) Setaria sp.(20) Celosia sp. (21) Sida sp. (22) Trianthema cf. triquetra (23) Indigofera sp. (24) Indigofera cf. hirsuta (25) Trigonella cf. occulta (26) Cyperus sp. (27) Scirpus sp. (28) Rumex sp. (29) Polygonum sp. (30)Asphodelus sp. (31) Abutilon sp. (32) Ipomoea sp. (33) Scleria sp. (34) Solanum sp. (35) Ziziphus cf. nummularia. All the macrobotanical remains are stored in the Museum of Birbal Sahni Institute of Palaeosciences, Lucknow, U.P., India (BSIP St. no. 1439).

Fig 4. Left panels show pie-charts displaying relative abundance of crop plants and right panels show corresponding histograms for three distinct phases of overall subsistence changes in the archaeological site Khirsara.

Fig 5. Photograph of trench AF-35 from where samples were taken for C isotope analysis.

Right panel shows stratigraphic appearances with finds of archaeological artefacts. Depth-profiles of TOC (wt.%) and δ¹³C_TOC of the trench AF-35 is shown in lower panels. Calibrated ¹⁴C age based chronological constraints are shown as + symbols.