Radio Carbon Dates and phasing at the High Pasture Cave Site

Posted by steven on 15/11/2007 at 02:40 PM

Historic Scotland have now funded a total of 26 radiocarbon dates for the High Pasture Cave & Environs Project. These include determinations made on materials from Bone Passage (the cave), the stairwell, from the burnt mound spreads, from features relating to activities at the surface, and from the inhumation of the adult woman (closing deposit in stairwell). The dates given below are corrected to the 2 sigma level at 95% probability.

Although we have recovered flint artefacts relating to Late Mesolithic activity taking place somewhere around the site, and pottery of possible Late Neolithic date from Bone Passage and from a pit feature at the surface above the cave, our earliest secure date for activity at the site relates to the Bronze Age. Obtained from a piece of charcoal (corylus - hazel) recovered from pit feature F10.01, which had been cut into the natural karstic clay to NW of the cave entrance, the assay provided a date of:

SUERC-12296 (GU-14672) 3330+/-35BP 1730BC - 1510BC

Trench 10 - pit feature F10.01

However, it is around the transition from the Late Bronze Age to Early Iron Age that we start to see more continuous activity at the site, both in the cave (Bone Passage) and at the surface - especially in the formation of the burnt mound/spreads. The earliest deposits of the burnt mound sampled so far (Trench 9 - charcoal: Corylus) have provided a date of:

SUERC-12289 (GU-14668) 2495+/-35BP 790BC - 410BC

This ties in quite nicely with a date obtained on charcoal (Corylus) from the lowest floor horizon identified in Bone Passage (C1.09):

SUERC-14935 (GU-15522) 2550+/-40BP 810BC - 530BC

A date obtained on animal bone (domesticated pig) from the same floor horizon (C1.09) provided a date of:

SUERC-14938 (GU-15525) 2490+/-40BP 780BC - 410BC

Charcoal (Corylus) recovered from a post-hole (F7.01, C7.05) cut within the natural karstic clay to the NW of the cave entrance, also appears to be contemporary with this activity:

SUERC-12290 (GU-14669) 2450+/-35BP 760BC - 400BC

Post-hole F7.01

Charcoal (Corylus) recovered from below a set of large set paving slabs (feature F2.18), which may have been the earlier walkway accessing the cave before the stairwell was constructed, and which also formed the base of the multiple hearth settings located in the deep hollow outside the cave entrance. The resulting date also appears to be contempoary with the earlier activity in Bone Passage and formation of the burnt mound/spreads:

SUERC-12280 (GU-14662) 2425+/-35BP 750BC - 400BC

Feature F2.18 - the charcoal was recovered from immediately below the slabs for dating

Deposition of material then continues in the cave (Bone Passage) and a date obtained on charcoal (Corylus) from context C6.04 provided a date of:

SUERC-12276 (GU-14658) 2405+/-35BP 750BC - 390BC

It is most likely that shortly after the last date, the construction of the stairwell begins and probably took place in at least two phases. We hope to recover stratigraphic relationships and dateable material to confirm this in 2008. In the area immediately outside the stairwell entrance (covered by Trenches 2 and 15), within the deep natural hollow, the earlier revetment walls are most likely constructed (features F15.02, F15.08 and F15.11) to prevent the incursion of flood water into this area. The hearths and their associated deposits also continue to accumulate outside the stairwell - based on feature F2.18. During this build-up of deposits, a small slab-built hearth (F2.07) is constructed over the top of a thick layer of clay (C2.06/C15.34) and charcoal (Betula - Birch) recovered from this feature provided a date of: 

SUERC-12278 (GU-14660) 2265+/-35BP 400BC - 200BC

A large pit (F2.04) was excavated into the natural karstic clay just a few metres to the SE of the hearth at this time and a deposit of domesticated pig bone recovered provided a date of:

SUERC-14944 (GU-15528) 2275+/-40BP 410BC - 200BC

Pit feature F2.04 (left foreground)

The burnt mound/spreads also continue to accumulate at this time and a sample of charcoal (Betula) from Trench 9 provided a date of:

SUERC-12288 (GU-14667) 2235+/-35BP 390BC - 200BC

It also appears possible that burnt mound material and the associated bone deposits are being deposited in Bone Passage via the stairwell. A charcoal sample (Corylus) obtained from context C1.01 provided a date of:

SUERC-14934 (GU-15521) 2310+/-40BP 510BC - 200BC

It is also around this time that a major deposit of domesticated pig bone is taken into Bone Passage. Comprising the butchered remains of at least 27 animals and displaying unusual butchery techniques, it is possible that these animals were related to a major feasting event at the site.  A sample of pig bone from
C1.01 provided a date of:

SUERC-2435 (GU-11874) 2195+/-40BP 390BC - 160BC

Pig lower mandible from deposit in C1.01

A charcoal sample (Corylus) recovered from the base of the stairwell in Bone Passage (C6.08) also provided a similar date:

SUERC-12277 (GU-14659) 2195+/-35BP 380BC - 170BC

A charcoal sample (Betula) from burnt mound deposits in Trench 10 (C10.03), to the NW of the stairwell, provided a date of:

SUERC-12292 (GU-14671) 2210+/-30BP 380BC - 190BC

Burnt mound deposits C10.03, Trench 10

While a charcoal deposit (Betula) from the burnt mound deposits in Trench 9, to the SE of the stairwell entrance to Bone Passage, also provided a reasonably contemporary radiocarbon date:

SUERC-12287 (GU-14666) 2175+/-35BP 370BC - 110BC

A sample of charcoal (Pinus sylvestris - Scots Pine) recovered from a layer of deposits (C2.08) sealing the pit containing the pig bone (F2.04), a few metres to the SE of the stairwell entrance, provided a date of:

SUERC-12279 (GU-14661) 2165+/-35BP 370BC - 100BC

A small pit feature (F3.03) abutting the upper courses of stonework of the stairwell entrance also produced a similar date. The pit contained pottery sherds, animal bone and charcoal; a sample of the charcoal (Betula) providing a date of:

SUERC-12286 (GU-14665) 2165+/-35BP 370BC - 100BC

Activity within the burnt mound spreads now starts to decrease, along with the major depsosition of deposits in Bone Passage. However, it is around this time that the remains of two butchered cows are placed in the cave. Almost every element of a five years old cow is placed on a high ledge above the main stream passage and a date on one of the bones provided a date of:

SUERC-14940 (GU-15527) 2160+/-40BP 370BC - 90BC

The second animal bone sample came from a 15 months old cow, the butchered remains of which had been placed in a small boulder setting (F001) in Bone Passage and had subsequently been covered in a thick calcite deposit. The date was:

SUERC-14939 (GU-15526) 2110+/-40BP 350BC - 30BC

The last material to be deposited at the base of the stairwell in Bone Passage comprised a charcoal-rich sediment, which also contained glass beads, fragments of copper alloy plate and a degraded copper-alloy pin, worked antler mounts and handles, pottery sherds and a decorated stone palette (C2.52). A sample of charcoal from the deposit (Corylus) provided a date of:

SUERC-12281 (GU-14663) 2115+/-35BP 350BC - 40BC

Looking to the deposits at the base of the stairwell (C2.52)

Activities associated with this deposition event in the cave may be a lens of charcoal (C3.02) with abraded pottery sherds running down the slope from Trench 7 into the top of the stairwell. A sample of charcoal (Corylus) from this deposit provided a date of:

SUERC-12282 (GU-14664) 2155+/-35BP 360BC - 50BC

A small post-hole (F7.03) complete with packing stone, located a few metres to the W of the stairwell, appears to be contemporary with these events. A sample of charcoal (Corylus) provided a date of:

SUERC-12291 (GU-14670) 2105+/-35BP 350BC - 40BC

Post-hole F7.03

The other dates we have at this time relate to the closure of the stairwell, towards the end of use of the site. A sample of charcoal (Corylus) recovered from the backfill material at the top of the stairwell (F2.23/C2.44) provided a date contemporary with the deposit containing the glass beads and other small finds recovered from the base of the stairwell steps (C2.52):

SUERC-14937 (GU-14664) 2115+/-40BP 360BC - 30BC

Tthere must have been a time delay in the backfilling of the stairwell and the deposition of the human remains at the top of this feature. The two dates we have obtained from the human bone are:

SUERC-14945 (GU-15529) 1965+/-40BP 50BC - 130AD

SUERC-14946 (GU-15530) 1890+/-40BP 20AD - 230AD

The remains of the adult woman deposited at the top of the stairwell

The final date we have is from a charcoal sample (Betula) recovered from the material used to backfill around the top of the stairwell structure (F2.23), most likely during construction of the feature. A fragment of rotary quern recovered from this deposit (C2.03) refits with a fragment of the same quern recovered from the landing adjacent to the top of the stairwell (C2.03). The date is:

SUERC-14936 (GU-15523) 2280+/-40BP 410BC - 200BC

The sequence of radiocarbon dates form a nice chronological set and provides the opportunity to sample with more confidence the re-deposited samples at this site. It appears that deposition within the burnt mound/spreads, in Bone Passage, and in the deep organic midden outside the stairwell entrance, are well stratified and have formed in a reasonable chronological order. Along with additional dates from Trench 15, 14, 17 and other areas of the burnt mound, we should have the opportunity to build a sound chronological phasing for the site. This will also allow us to date with some confidence the wide range of small finds recovered so far, including the ceramics. 

Next entry: Cave of the Speckled Horses, Fiskavaig, Skye

Previous entry: Another fieldwork season comes to a close....Read on for details of the excavations in 2007


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