Abstract
Palaeomagnetic analysis indicates that Haasgat, a fossil-bearing palaeocave in the Gauteng Province of
 South Africa, is dominated by reversed magnetic polarity in its oldest, deepest layers and normal polarity in
 the younger layers. The presence of in-situ
 Equus
 specimens suggests an age of less than ~2.3 Ma, while
 morphological analysis of faunal specimens from the ex-situ assemblage suggests an age greater than
 1.8 Ma. Given this faunal age constraint, the older reversed polarity sections most likely date to the beginning
 of the Matuyama Chron (2.58–1.95 Ma), while the younger normal polarity deposits likely date to the very
 beginning of the Olduvai Sub-Chron (1.95–1.78 Ma). The occurrence of a magnetic reversal from reversed
 to normal polarity recorded in the sequence indicates the deposits of the Bridge Section date to ~1.95 Ma.
 All the in-situ fossil deposits that have been noted are older than the 1.95 Ma reversal, but younger than
 2.3 Ma. Haasgat therefore dates to an interesting time period in South African human evolution that saw
 the last occurrence of two australopith species at ~2.05–2.02 Ma (Sts5
 Australopithecus africanus
 from
 Sterkfontein Member 4) to ~1.98 Ma (
 Australopithecus sediba
 from Malapa) and the first occurrence of
 early
 Homo
 (Sk847),
 Paranthropus
 and the Oldowan within Swartkrans Member 1 between ~2.0 Ma and
 ~1.8 Ma.
Highlights
The exposed Malmani dolomite to the west of Johannesburg and Pretoria in South Africa is the host rock for thousands of cave systems that have been forming throughout most of the Quaternary and perhaps as early as the beginning of the Pliocene (5.3 Ma)
With two species of Equus recovered within the ex-situ HGD faunal sample[22], and a nearly complete Equus metacarpal exposed in the in-situ calcified sediment sequence at a level equivalent to reversed polarity layers in Tetley’s Hall Southern Section (THSS), the majority of the fossiliferous deposits are likely not older than ~2.3 Ma and the majority of other fauna suggest the site is older than Gondolin GD2 at 1.95–1.78 Ma1,22,35
An age assessment for the deposits based on magnetobiostratigraphy requires the identification of a longer period of reversed polarity as seen in the Western Deposits and the base of the Bridge Deposits followed by a reversal to a period of normal polarity as seen in the top of the Bridge Deposits (Figures 4 and 9)
Summary
The exposed Malmani dolomite to the west of Johannesburg and Pretoria in South Africa is the host rock for thousands of cave systems that have been forming throughout most of the Quaternary (last 2.6 Ma) and perhaps as early as the beginning of the Pliocene (5.3 Ma) These cave systems are well known for their wealth of archaeological and fossil-bearing infills, including abundant hominin remains.[1,2,3] While a large body of research exists on the hominin-bearing palaeocave deposits such as Sterkfontein[4,5,6] and Swartkrans[7], recent results from less intensively worked or new fossil localities, such as Malapa[8,9,10,11], the Bolt’s Farm complex[12,13], Gondolin[1,14,15,16] and Hoogland[17], have highlighted the importance of wider regional sampling for understanding geographical and temporal variability in Plio-Pleistocene karst development, faunal evolution, taphonomy and palaeoecology that underlie interpretations of the South African hominin and primate fossil record. Recent improvements in palaeomagnetic correlation methods for South African karstic systems[6,9,10,15,17,20,21] and integration of uranium-lead dating[5,9,10] with electron spin resonance[1,6] have begun to unravel the complex history of these sites; for some deposits, the application of multiple methods has provided the first reliable age estimates[1,2,3]
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