DOI: 10.5061/dryad.6m905qg1b
title: Geochemical and physical characterization of lithic raw materials in the Olduvai Basin, Tanzania

description: The invention and proliferation of stone tool technology in the Early
 Stone Age (ESA) marks a watershed in human evolution. Patterns of lithic
 procurement, manufacture, use, and discard have much to tell us about ESA
 hominin cognition and land use. However, these issues cannot be fully
 explored outside the context of the physical attributes and
 spatio-temporal availability of the lithic raw materials themselves. The
 Olduvai Basin of northern Tanzania, which is home to both a wide variety
 of potential toolstones and a rich collection of ESA archaeological sites,
 provides an excellent opportunity to investigate the relationship between
 lithic technology and raw material characteristics. Here, we examine two
 attributes of the basin's igneous and metamorphic rocks: spatial
 location and fracture predictability. A total of 244 geological specimens
 were analyzed with non-destructive portable XRF (pXRF) to determine the
 geochemical distinctiveness of five primary and secondary sources, while
 110 geological specimens were subjected to Schmidt rebound hardness tests
 to measure fracture predictability. Element concentrations derived via
 pXRF show significant differences between sources, and multivariate
 predictive models classify geological specimens with 75–80% accuracy. The
 predictive models identify Naibor Soit as the most likely source for a
 small sample of three lithic artifacts from Bed II, which supports the
 idea that this inselberg served as a source of toolstone during the early
 Pleistocene. Clear patterns in fracture predictability exist within and
 between both sources and rock types. Fine-grained volcanics show high
 rebound values (associated with high fracture predictability), while
 finer-grained metamorphics and coarsegrained gneisses show intermediate
 and low rebound values, respectively. Artifact data from Bed I and II
 suggest that fracture predictability played a role in raw material
 selection at some sites, but other attributes like durability, expediency,
 and nodule size and shape were more significant.
description: A total of 244 rock specimens (aka "geological
 specimens") were collected from eight primary (six granulite
 outcrops, one gneiss outcrop, one phonolite outcrop) and one secondary (a
 seasonal drainage containing basalt blocks) lithic raw material sources in
 the Olduvai Basin. Rock specimens were flaked directly from the
 sources with a rockhammer. Only granulite specimens with visually
 quartz-rich compositions were selected. Five quartz-rich metamorphic
 artifacts (aka "archaeological specimens") from BK East, a ca.
 1.5 million-year-old site on the south wall of the side gorge in Olduvai
 Gorge, were also included. Portable XRF (pXRF) analyses were conducted
 with an Innov-X Delta Classic Environmental Analyzer equipped with a 4W Au
 anode X-ray tube and a Si-PIN diode detector. All analyses were performed
 while the instrument was docked into a stable, hands-free test stand. An
 unweathered, non-cortical surface free of sediment matrix was placed over,
 and completely covered, the detector window. Each specimen was measured
 for 360 seconds using all three of the instrument's beams (120
 seconds/beam). After an initial energy scale calibration test with a
 factory issued metal coin of known composition, the following protocol was
 observed: (1) a powdered sample of Standard Reference Material (SRM) 2702
 with elemental concentrations certified by NIST was measured; (2) four
 geological/archaeological specimens were then measured; (3) the fifth
 geological/archaeological specimen in a series was measured five times
 (that is, five consecutive 360-second cycles) without being moved or
 reoriented; (4) after the fifth geological/archaeological specimen was
 measured, the SRM 2702 sample was measured once again, which initiated the
 next series of measurements. Element concentrations were derived with the
 Compton Normalization correction model and the factory-set “Soil
 Environmental” calibration.
description: Variable Description 
 Type 
 Type of sample (calibration = calibration coin for Delta Innov-X
 Analyzer; standard = NIST geological standard; geological = geological
 sample from lithic raw material source; artifact = archaeological
 specimen) 
 Replicate Replicate measurement
 (Yes or No) 
 Source Geological source (delta =
 Delta Innov-x Analyzer calibration coin; nist = National Institute of
 Standards and Technology (NIST) geological standard; NS = Naibor Soit; NH
 = Naisuisui Hill; OL = Oldonye Okule; LD = Lemagarut drainage; SS =
 Shifting Sand; KG = Kelogi Hills; EN = Engelosin) 
 Outcrop 
 Individual outcrop within geological source (NSM = Naibor Soit
 Main Hill; NSMH = Naibor Soit Manyata Hill; NSSO = Naibor Soit Southern
 Outlier; NH = Naisuisui Hill; LD1 = Lemagarut Drainage 1; LD2 = Lemagarut
 Drainage 2; BKE = BK East; SS = Shifting Sand; KG = Kelogi Hills; EN =
 Engelosin; NA = Not applicable) 
 Specimen Individual
 find or sample number 
 Material Raw material type (QTZ =
 "Quartz-rich"; GN = Gneiss; FGV = Fine-grained
 volcanic) Element
 concentration estimate Reported for each element
 (e.g., P, Cl, Ca; empty cells are "non-detect")
 Analytical error
 Reported for each element (e.g., P +/-, Cl +/-, Ca +/-; no error
 reported for "non-detect" elements) 
 The published analysis focused only
 on granulite specimens (n = 186) and, more specifically, on six elements
 (Fe, Ti, Zr, K, Sr, and Y) that had detection rates &gt;75% in the
 granulite specimens (that is, these elements were detected in more than
 75% of the granulite specimens). These elements were used in the
 predictive models from the published analysis. Two of the 186 granulite
 specimens were missing values for five out of the six elements and
 were therefore not included in the statistical analyses. Of the remaining
 184 specimens, 55 had missing data for one element, and two of those 55
 had missing data for two elements. These missing values were treated as
 censored data (that is, the element is present but could not be measured
 precisely enough for the instrument to report a value). These missing
 values were interpolated in one of two ways. For those specimens subjected
 to replicate pXRF runs (n = 7), the missing value was replaced with the
 mean value of the replicates. The missing values for the remaining
 specimens (n = 48) were replaced with the mean of the four closest (as
 determined in two-dimensional space) specimens with measured (rather than
 interpolated) values. The main data file does not include these
 interpolated values. Should analysts choose to use them, interpolated
 values can be found in the additional .csv file.