First of all, let's remind ourselves of the current glacial transport hypothesis: The non-sarsen boulders, slabs, pillars, stumps, stones and "debitage" found in the Stonehenge area come from an assemblage of glacial erratics transported from West and South Wales towards Salisbury Plain by a powerful ice stream, and were later discovered and exploited by the builders of the stone monument.
Now, to the latest paper by Ixer, Bevins, Pirie, Turner and Power, and published in the Wiltshire Archaeological and Natural History Magazine with a 2020 date. Here are the details:
‘No provenance is better than wrong provenance’: Milford Haven and the Stonehenge sandstonesby Rob A. Ixer, Richard E. Bevins, Duncan Pirrie, Peter Turner and Matthew Power.
Wiltshire Archaeological and Natural History Magazine 113, 20220, pp 1-15.
For over 70 years there has been confusion within the archaeological literature between the Stonehenge ‘Old Red Sandstone’ Altar Stone, the Stonehenge Ordovician-Silurian Lower Palaeozoic Sandstone debitage, and the previously postulated source rocks, the Old Red Sandstone (Devonian) Cosheston Group sandstones. However, petrographic data show that all three are very different lithologies with separate geographical origins. The Altar Stone is most likely to be from eastern Wales and the Lower Palaeozoic Sandstone from west or central Wales, north and east of the Mynydd Preseli; neither of these two Stonehenge-related sandstones is from Mill Bay, Milford Haven as has been suggested. The revised provenance determinations do not support the theory that the Stonehenge bluestones were shipped over sea from the Milford Haven area along the Bristol Channel.
re the 3 sandstone groups: Each sandstone is distinctive in term of its minor accessory/heavy minerals (reflecting its source area), diagenetic history as determined by its authigenic cements and clay minerals, and its tectonic and metamorphic history as seen by its clay mineralogy and presence/absence of any tectonic fabric. (p 12)
This is interesting, and it will be good to see where this leads -- but a word of caution. In due course, geologists may well show that some of the Stonehenge fragments analysed may have come from the Senni Beds in eastern Wales. But that does not mean that that is where the Altar Stone came from. We still do not have absolute certainty that any of the samples examined really did come from the Altar Stone (see also "The Stonehenge Bluestones", pp 172-176 for a more detailed discussion).
IXER, R. A., BEVINS, R. E., TURNER, P., POWER, M. and PIRRIE, D., 2019. Alternative Altar Stones? Carbonate-cemented micaceous sandstones from the Stonehenge Landscape. WANHM 112, 1–13.
Entrainment and Transport
Indeed, why would Neolithic tribesmen have bothered to quarry for monoliths at all, since there is no evidence of any preferential use of specific rock types (eg spotted dolerite, foliated rhyolite, Devonian sandstone, or Lower Palaeozoic sandstone) anywhere in the British Neolithic. In Wales, cromlechs and standing stone settings were always made of whatever handy lumps of stone happened to be lying around in the vicinity. It is entirely logical to assume that the same principle of monolith collection and use applied at Stonehenge.
As indicated in my book "The Stonehenge Bluestones", entrainment in the compression zone of ice flowing up and over Preseli sits easily with glaciological theory.
PS. Thanks to Rob Ixer for correcting a slip of the pen. Duly corrected.