Boomplaas Cave

Boomplaas Cave is located in the Cango Valley in the foothills of the Swartberg mountain range, north of Oudtshoorn, Eden District Municipality in the Western Cape Province, South Africa. It has a deep stratified archaeological sequence that spans the past 60,000 to 80,000 years, representing discontinuous occupations and hunter-gatherer/herder acculturation. The cave has served multiple functions during its occupation, such as a kraal for animals, a place for the storage of oil rich fruits, and as a home-base for hunter-gatherers. The site's documentation contributed to the reconstruction of palaeo-environments in the context of changes in climate within periods of the Late Pleistocene and the Holocene. Faunal remains and plant material have also been used to reconstruct the diets of the sites occupants. Stone Age adzes have been found at the site, along with lithics from the Wilton, Albany, Robberg, Howiesons Poort industries. Other notable finds include painted marker stones and pottery.

Excavation

The excavation of Boomplaas Cave A was conducted by H.J. Deacon from 1974 to 1979 as part of an archaeological and palaeo-ecological study to provide information on changes in vegetation and fauna, the cultural sequence, and the function of the cave in the area. This project was associated with excavations at the Klasies River and sites between the Cape Fold Mountains and the coast. Boomplaas was selected as the site for investigation due to its extensive stratigraphic sequence of human occupation during the Holocene and Upper Pleistocene and it being a limestone cave with conditions favorable for preserving bone.
The early research executed by H.J. Deacon and his collaborators and the ongoing excavation efforts produce a chronology of the cave's nonoccupational and occupational layers, complete with evaluations of the botanical remains, faunal remains, and the Middle Stone Age and Late Stone Age lithic assemblages found at the site.

Dating Methods

Until recently, the older layers at Boomplaas could not be dated due to the time cap for radiocarbon dating, prompting a need for alternative dating methods at the site.
The members associated with the Howieson's Poort technocomplex were dated using amino acid racemization on ostrich eggshell beads. Ostrich egg shells were selected as the cultural material to date with AAR as they were thought to represent a closed amino acid system. This dating method at the site was an effort to provide context for the Howiesons Poort Industry and its date ranges beyond the limited capacity of radiocarbon dating. For the OLP member, a date range of 40 ka to 48 ka with a range of 50 ka to 62 ka for the Howiesons Poort assemblages. However, these results were controversial as there was a low sample size of ostrich eggshell at Boomplaas. A linear fit calibration was completed in the same publication to account for the potential error in the results, placing the date range at 59 ka to 71 ka.
Uranium series analysis was conducted on dripstone at the site in an attempt to date the Howiesons Poort OCH member of Boomplaas. Using this dating method, uranium and thorium isotopes were evaluated in a small stalagmite uncovered in the OCH member. This dating method produced an age range for the Howiesons Poort technocomplex of 60 ka to 70 ka.
The most recent dating efforts using accelerator mass spectrometry C14 provide new dates for all members excluding BOL through LOH, contextualizing occupation intensity and technological adaptation at the site. The AMS dates and previous C14 dates were modeled using Bayesian statistical methods and Deacon's established stratigraphic sequences. Occupation intensity was gauged by comparing the stone tool frequency, associated material, and the age of each depositional layer.

Deposits

The formation process for Boomplaas Cave is slow, resulting from a combination of washed in silts and sand and the natural weathering of limestone. The age of the members range from the Late Pleistocene to the 19th century, with the deposition of sediments occurring at a rate of 50 mm per one thousand years.
Boomplaas has a current cave floor size of 225 m², which has decreased in the far past because of roof collapse. The stratigraphy of the Boomplaas deposits is documented in sets of broadly contemporary layers, individual layers and parts of layers. The members recognized in the Boomplaas sequence are described as follows, from the top to bottom:

Member	Dating	Important Information
CBM	19th century	Member CBM corresponds to nineteenth-century historical documentation indicating that colonial Europeans used the cave as a kraal for sheep. The sediment consists of thick, burnt sheep dung.
DGL	1,800–1,000 cal BP	Member DGL consists of white, calcified dung layers and gray soil. During this period, Boomplaas cave was intermittently occupied and used as a stock post by the ancestral Khoikhoi. Notable finds within this Member include pottery fragments, hearth features, stone artifacts, and wild and domesticated animal remains.
BLD	4,100–1,400 cal BP	In member BLD, the cave was used to store jacket plum fruit in storage pits lined with gifbol leaves. Sixty pits were found in total, with the complete remains of three pits still intact. Ethnobotanical research suggests that the fruit was most likely stored for cosmetic purposes instead of sustenance due to the oil it produces. The harvesting and storage of these fruits would have occurred on a seasonal basis. Edible staple foods, such as Hypoxia villosa and bulge lily corms, were also found in the member. Other finds include painted marker stones.
BLA	9,200–4,400 cal BP	Dating to the mid-Holocene, the BLA member includes elongated charcoal-filled beds of an unknown function. The features are located in the same portion of the cave as the storage pits in Member BLD. Other notable finds from member BLA include lithics from the Wilton technocomplex and a painted marker stone.
BRL	14,100 and 9,700 cal BP	The BRL Member in Boomplaas coincides with the early Holocene and terminal Pleistocene and consists of sandy sediment with partial rubification. The layer is characterized by circular hearths, stone tools of the Albany technocomplex, and animal remains discarded by humans. Artifact concentration in Member BRL suggests brief occupation sequences.
CL	17,400–14,000 cal BP	Member CL consists of carbonized sandy loam and connects to the terminal Pleistocene. The high density of the artifacts and faunal remains in Member CL characterizes Boomplaas Cave as a potential home-base site with long occupation sequences. Archaeological finds in Member CL include stone tools from the Robberg Industry, tortoiseshell bowls, bone tools, charred plant remains, faunal remains, and beads and water containers made from ostrich eggshells.
GWA/HCA	21,600–17,600 cal BP	GWA/HCA consists of leached, ashy deposits. The lithic assemblage of GWA/HCA diverges from member LP in raw material preference, tool reduction strategy, and retouched tool frequency.
LP	25,400–21,700 cal BP	Member LP was occupied during the Last Glacial Maximum. The sediment is composed of dark brown loam with clasts from the cave ceiling. The stone tools of member LP have been attributed to the early LSA with the presence of bipolar cores, single platform irregular cores, and thin unretouched flakes. Other artifact finds include ostrich eggshell fragments.
LPC	27,300–25,800 cal BP	LPC is characterized by multiple occupational sequences with sediment consisting of brown organic loam and charred plant material. Archaeological materials obtained from LPC include quartz miniaturized bladelets, and bone points.
YOL	30,100–27,600 cal BP	Named after its sediment composition of yellow oxidized loam, member YOL is a non-occupational deposit. YOL contains both MSA and LSA stone tools with a raw material preference for vein quartz.
BP	49,000–29,800 cal BP	The sediment for member BP exhibits unoccupied sequences with a prevalence of micromammals and occupied units characterized by charred plant material and hearths. The lithic assemblage, associated with the ash features, includes long late MSA flake blades.
OLP	45,400–40,300 cal BP	OLP consists of brown and dark yellow loam with clast rock fragments. OLP 2 exhibits a high frequency of micromammal bone that has been used to reconstruct humidity levels in the paleoenvironment. These micromammal bones have also been used to indicate longer periods without human occupation. Archaeological evidence within OLP includes a MSA lithic assemblage and two ostrich eggshell beads.
BOL	59,800–45,600 cal BP	BOL is sediment comprising brown sandy loams and carbonized material. The stone tools found in BOL are classified as MSA and include triangular flakes on facetted platforms and blades.
OCH	65,300–56,800 cal BP	OCH consists of unweathered limestone that fell to the cave floor from the walls and ceiling. Previous uranium-series AAR dating placed the age estimate of member OCH at ~60–65 ka. Occupation during this period was fleeting as carnivores and raptors are believed to be responsible for the accumulation of faunal remains in the member. The limited archaeological assemblage of OCH includes stone tools identified as belonging to the Howiesons Poort Industry with an array of unifacial points and a singular biface point recovered from the member.
LOH	> 65,000 cal BP	LOH is the basal layer directly above bedrock, consisting of sandy loam. A small assemblage of lithic implements was recovered here, including laterally retouched scrapers and adzes. These tools were generally classified as belonging to the MSA with no industry specified.