Rising from Below: Reframing the Cradle of Humankind Through a Hypogenic Speleogenetic Lens

Mike Buchanan (April 2025)

Abstract

The caves of the Cradle of Humankind have long been interpreted through an epigenic lens, where surface-derived waters slowly carved dolomitic voids over millions of years. This paradigm, however, neglects mounting evidence for hypogenic speleogenesis across the dolomite-rich Transvaal Supergroup. In this paper, I present a new model, all major dolomitic cave systems in Gauteng South Africa, including Sterkfontein, Swartkrans, and Rising Star, are fundamentally hypogenic in origin. This reinterpretation has profound implications for fossil preservation, paleoenvironmental reconstructions and the reliability of dating techniques. Through field-based observations, hydrogeological analysis, and geochemical insights, I argue that the hominin record must be recontextualised within a framework of rising, mineral-rich, thermally active waters.

Introduction

The Cradle of Humankind, a UNESCO World Heritage Site, holds some of the most significant paleoanthropological discoveries in human history. Yet, despite the attention paid to its fossils, the genesis of the cave systems housing these remains, remains insufficiently interrogated. The prevailing view assumes an epigenic origin for these dolomitic caves, where infiltration of meteoric water dissolves host rock and forms voids. This model has been foundational to interpretations of stratigraphy, taphonomy, and dating. However, emerging global karst research, detailed field evidence from the Transvaal Dolomites suggests that the epigenic model is fundamentally flawed in this context. I propose a hypogenic speleogenetic model instead, one in which deep-sourced, mineralised waters ascended to dissolve rock and form voids, later modified by surface processes. This approach challenges entrenched regional models such as those put forward by Breytenbach et al. (2014) reorients the way I understand fossil deposition and preservation in these systems (Klimchouk, 2007; Palmer, 2011).

Defining Hypogenic Speleogenesis

Hypogenic speleogenesis refers to cave formation driven by deep-sourced fluids typically thermal, anoxic and geochemically aggressive ascending through structural weaknesses independent of surface recharge. These systems are typically associated with:

  • Sulfuric acid speleogenesis
  • CO2-rich hydrothermal fluids
  • Deep fracture networks
  • Morphological indicators like cupolas, risers, blind pits, and bubble trails

Hypogenic caves are often isolated from surface weathering during their formation and exhibit pristine preservation of features formed under deep conditions (Klimchouk, 2014; Ford & Williams, 2007).

Evidence from Gauteng's Cave Systems

The dolomitic cave systems of Gauteng, including Sterkfontein, Swartkrans, Rising Star, Wonder Cave, all the +300 others, exhibit hallmark features of hypogenic speleogenesis:

  • Vertical conduits and risers unconnected to surface recharge zones
  • Massive calcite and dolomite crusts indicating repeated mineral saturation cycles.
  • Cupolas and blind shafts inconsistent with epigenic vadose formation
  • Anoxic depositional environments ideal for exceptional fossil preservation

Moreover, these systems display isotopic signatures consistent with deep-sourced thermal waters, including enriched δ18O and δ13C values in secondary carbonates (Verhagen et al., 1991).

Taphonomy and Diagenetic Implications

A hypogenic origin provides a coherent explanation for the exceptional preservation and spatial context of all key hominin fossils:

  • Little Foot's articulated skeleton and mineral-encased remains indicate rapid entombment in a saturated, low-oxygen environment (Clarke, 2002:)
  • Australopithecus sediba and Homo naledi appear in voids suggestive of hydrothermal chambering rather than gradual collapse (Dirks et al., 2015; Pickering et al., 2010)
  • Evidence of thermally altered bones and crystallisation patterns further supports high-temperature, mineral-rich depositional settings.

These conditions also facilitate rapid mineral replacement and recrystallisation of bone, which poses serious challenges for dating (Woodhead et al., 2006).

The Problem with Current Dating Techniques

All major dating techniques used at these sites U-Pb, ESR, cosmogenic nuclide and paleomagnetic stratigraphy, presume relatively closed-system behaviour. In hypogenic systems, however, repeated saturation with mineral-laden water can:

  • Reset isotopic clocks through recrystallisation.
  • Mobilise uranium, thorium, and other trace elements.
  • Introduce isotopic contamination from hydrothermal sources.
  • Growth of speleothem under the hypogene process are not reliable due to repetitive solution and dissolution corrupts the crystallisation process.

The net result is significant potential for misleading age estimates, especially when epigenic assumptions underlie the stratigraphic model (Palmer, 2011; Woodhead et al., 2006).

Expanding the Hypogenic Model Across the Transvaal Supergroup

The implications of a hypogenic model extend beyond Gauteng. Karst systems throughout the Transvaal Supergroup including the Penge and Malmani Subgroups show hypogenic features (Martini, 2006). Fossil localities as far afield as Makapansgat and Taung may need to be reinterpreted through this lens.

Even iconic fossils like "Lucy" from East Africa, preserved in contexts thought to be fluvial or lacustrine, warrant re-evaluation if deeper, hydrothermal influences played a role in their final deposition or diagenesis.

Cultural Inertia and Scientific Resistance

South African karst research has long operated within a compartmentalised dolomite framework, entrenched in the works of Vegter and later Breytenbach et al. (2014). Institutional pride and the sanctity of long-standing heritage designations have hindered acceptance of alternate models. But science must yield to evidence. A shift toward hypogenic understanding is not a threat, it is a liberation (Kuhn, 1962).

A Call for Change

I propose the formal recognition of a "Gauteng - Limpopo Hypogenic Karst Belt" (GHKB), defined by geochemical, morphological and hydrogeological markers. I urge:

  • Re-examination of dating protocols under hypogenic constraints
  • Interdisciplinary collaboration among hydrogeologists, geochemists, taphonomists, and paleoanthropologists
  • A regional reassessment of fossil site formation mechanisms

Conclusion

The story of human origins is one of emergence. Ironically, the ground from which our ancestors rose may itself have risen from below. Rewriting the origin of origins, demands I reframe the Cradle of Humankind not as a product of surface erosion, but of deep, ascending forces, hydrothermal, hypogenic, highly fractured and transformative.


References

  • Clarke, R. J. (2002). A deeper understanding of Sterkfontein fossil hominids and their place in the evolutionary tree. South African Journal of Science, 98(11–12), 515–519.
  • Dirks, P. H. G. M., et al. (2015). Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife, 4, e09561.
  • Ford, D. C., & Williams, P. W. (2007). Karst hydrogeology and geomorphology. John Wiley & Sons.
  • Klimchouk, A. B. (2007). Hypogene speleogenesis: Hydrogeological and morphogenetic perspective. National Cave and Karst Research Institute.
  • Klimchouk, A. B. (2014). Hypogene speleogenesis: A review and update. Cave and Karst Science, 41(3), 77–90.
  • Kuhn, T. S. (1962). The structure of scientific revolutions. University of Chicago Press.
  • Martini, J. E. J. (2006). The karst of South Africa. Acta Carsologica, 35(2), 83–96.
  • Palmer, A. N. (2011). Distinction between epigenic and hypogenic speleogenesis in carbonate rocks. Geomorphology, 134(1), 9–22.
  • Pickering, R., Dirks, P. H. G. M., et al. (2010). Australopithecus sediba at 1.977 Ma and implications for the origins of the genus Homo. Science, 328(5975), 205–208.
  • Verhagen, B. T., et al. (1991). Isotope study of karst hydrology and paleoclimate in Southern Africa. Chemical Geology: Isotope Geoscience section, 86(1-2), 191–202.
  • Woodhead, J., et al. (2006). U-series dating of calcite veins in South African hominid cave sites. Earth and Planetary Science Letters, 246(1-2), 152–167.
  • Breytenbach, T., Woodborne, S., & Pether, J. (2014). A conceptual model for karst evolution in the Cradle of Humankind, South Africa. South African Journal of Geology, 117(3), 241–258.

 

 

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