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From the Field: Benjamin Collins, Grassridge Rockshelter, South Africa

From the Field

Season two field crew (l-r): Cherene De Bruyn, Lisa Rogers, Dr. Christopher Ames, Dr. Benjamin Collins. Photo credit:  Dr. Benjamin Collins. Season two field crew (l-r): Cherene De Bruyn, Lisa Rogers, Dr. Christopher Ames, Dr. Benjamin Collins. Photo credit:  Dr. Benjamin Collins.

Dr. Benjamin Collins and Dr. Christopher Ames recently concluded a second season of Leakey Foundation-funded excavations at Grassridge rockshelter. The shelter is located at the base of the Stormberg Mountains in the Eastern Cape of South Africa, approximately 200 kilometers inland from the Indian Ocean. These excavations are part of the Grassridge Archaeological and Paleoenvironmental Project (GAPP), which explores the relationships between behavioral diversity, social network formation, and climatic variability during the enigmatic late Middle Stone Age period (MSA), which spans from ~50,000 to 25,000 years ago.

Current research suggests that the late MSA was subject to periods of severe aridity and rapid climatic change. These findings have led researchers to suggest that southern Africa was sparsely populated during the late MSA, with hunter-gatherer groups forming very small, localized social networks. The paucity of archaeological sites from this period has made it difficult to explicitly test this hypothesis. However, recent research focusing on late MSA occupations in parts of southern Africa, including the preliminary findings from Grassridge, is providing evidence, such as non-local ostrich eggshell and marine shell beads, and specific stone tool types that occur throughout southern Africa, to suggest that social networks were more extensive than previously thought.

Grassridge rockshelter was initially excavated in 1979 by Dr. Hermanus Opperman, who identified rich Later and Middle Stone Age occupations at the site. The original excavations focused on the Later Stone Age (LSA) occupation, dated to between 6,000 and 7,000 years ago. Dr. Opperman’s excavation also produced a single radiocarbon date of ~36,000 years before present near the base of the MSA layers. This date, however, is near the limit of conventional radiocarbon dating, and the lower age limit of the site remained uncertain.

GAPP’s main objectives for the first two field seasons were to re-evaluate the site stratigraphy, obtain a suite of dating samples from the original excavation, and begin a new excavation. Our Leakey Foundation-funded research has recently provided two new radiocarbon dates, one from near the top of the MSA sequence dating to ~35,000 radiocarbon years ago, and the other from the base of the sequence dating to >36,000 years ago. The latter date confirms that the base of the MSA sequence is older than the limit of radiocarbon dating, and luminescence methods are being pursued to determine how far back in time the Grassridge MSA sequence stretches.

We have opened a new 2 x 1 m excavation trench adjacent to the 1979 excavations. By the end of this most recent field season we had removed the overlying LSA deposit, and the first 5-10 cm of the MSA deposit. The excavations have been very fruitful, with the 3-dimensional provenience recorded for nearly 4000 artifacts – a density of ~3500 artifacts per cubic meter of sediment – and tens of thousands more pieces of bone and stone tools recovered from the excavated sediment. Other noteworthy finds include many ostrich eggshell beads, bone tools, and shell ornaments from the Later Stone Age deposits. The top 5-10 cm of MSA deposit so far excavated has produced many similar finds, and we expect this density of artifacts will continue as we proceed with our excavations of the MSA deposit in the coming field seasons.

Rock art panel documented during survey. Photo credit:  Dr. Christopher Ames. Rock art panel documented during survey. Photo credit:  Dr. Christopher Ames.

In addition to our excavations at Grassridge, GAPP documented three rock art sites during our survey of the surrounding area. These sites are located within 5 km of each other, and contain well-preserved, vivid, and detailed panels from two or more different periods.

We are spending the next six months analyzing geological and radiocarbon dating samples, stone tools, animal bones, ostrich eggshell, and other artifacts, to elucidate what life was like for the LSA and MSA hunter-gatherers at Grassridge. These important data, coupled with ongoing excavations and research at Grassridge, will provide valuable

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