Australia: The Land Where Time Began

A biography of the Australian continent 

Emu Tracks 2, Kangaroo and Echidna, and 2 Moths, Further Radiocarbon Ages

A number of Aboriginal sites were excavated in the Upper Mangrove Creek catchment, central coast of New South Wales as part of the Mangrove Creek Dam Salvage Project (MCDSP) between 1979 and 1987(Attenbrow, 1981, 1982a; Vinnicombe, 1984) and PhD research (Attenbrow, 1982b, 2004).

For this study 20 radiocarbon ages were obtained for 15of the 28 sites that had been excavated (Attenbrow, 2004). The ages of initial habitation sites and the ages of selected levels in some sites were estimated on the basis of diagnostic criteria:

1)    Bondi points -  presence/absence/abundance;

2)    Bipolar artefacts – varying abundance; 

3)    Quartz and unidentified fine-grained siliceous (FGS) materials, excluding silcrete and tuff – varying abundance; and

4)    Depth of deposit – in some cases (Attenbrow, 1981, 2004:75).

Excavated sites in the central and south coasts of New South Wales, as well as those that had been excavated during the MCDSP, particularly Loggers, Mussel and Deep Creek, were the basis for timing of changes in the diagnostic criteria (Attenbrow, 1981, 1982a, 1982b; Hiscock & Attenbrow, 1998, 2005: 72-76).

In order to confirm the original age estimates for 2 sites that had previously not been dated: Emu Tracks 2 and Two Moths, Radiocarbon ages had been obtained. Also, further dates were obtained for Kangaroo and Echidna where there had been uncertainty about the initial habitation age. The radiocarbon ages that had been obtained were discussed prior to including these results and using calibrated radiocarbon ages in place of the conventional ages that had previously been used to produce a model of habitation, subsistence and land use for the catchment (Attenbrow, 2004: Table 10.4).

Emu tracks 2

This is a small rockshelter, 8.3 m x 2.2 m x 2m, that faces east on the eastern watershed of Upper Mangrove Creek. Excavations were carried out in order to determine the age of initial habitation, the cultural materials that were present, stone artefact assemblage changes, and the age of 15 engraved emu tracks that are on the lower part of the back wall. Similar engravings are present in other rockshelters in the Sydney Basin: to the north of the Hawkesbury River (Wattagan State Forest), the Blue Mountains (Caves Hotel on the Bells Line of Road), and the Illawarra region (Kiama and Woronora Plateau) (Clegg, 1984: 16; Koettig, 2002; Maynard, 1976: Table 6.3, Fig. 6.23; Sefton, 2005: 18; Stockton, 1993: 65-66, Fig. 4.6). These engravings have often been described as Panaramitee, a style in which motifs are mostly tracks, that are considered to be more than 6,000 years old (Maynard, 1976: 193; also see Layton, 1992: 212-228). The engraved tracks were shown not to extend below the current floor level Test pit T1 that was excavated against the back wall immediately below the engraved tracks. Therefore the excavation of the engraved tracks in eastern New South Wales did not give an indication of when they were made.

T2a and T2b, 2 adjoining squares that were each of 50 cm2, were excavated to a maximum depth of 80 cm (Attenbrow, 2004: Tables 3.4, A1/25, A1/36). About 7,000 stone artefacts were retrieved; among which were 63 backed artefacts.

The original age estimate of habitation at Emu Tracks 2 was 3,500-3,300 BP (Attenbrow, 2004: Table A2/9), and the bondi points that were retrieved from pits T2/5 to T2/13were estimated to have accumulated between 3,100 and 1,600 BP. The most abundant raw material in pits T2/1-11 was quartz, and in the pits below the predominant raw material was FGS, silcrete and chert (tuff). A change in abundance from FGS material to quartz occurred about 2,700-2,800 BP in other sites in the catchment (Attenbrow, 1981, Attenbrow, 2004).

Radiocarbon ages were obtained for charcoal from Square T2a, 4 conventional and 1 AMS (NZA 19201). Originally samples were submitted from spit 2 (Wk-14104), which is the highest level that was unlikely to have been contaminated by recent charcoal; spit 5 (Wk-14106), in which quartz began to predominate; and spit 15 (NZA-19201), the lowest level containing stone artefacts. After the receipt of the inverted radiocarbon ages for splits 11 and 15, a further determination was obtained for spit 13 (Wk-16547); the lowest backed artefact was present in this level.

Prior to receiving the radiocarbon ages, the change sequence in the assemblages, such as the lack of bondi points in spits 1-4 and change to quartz abundance in spit 11, did not provide an indication that the deposits in Square T2a-b had been disturbed. And the stratigraphy did not indicate any disturbance; the colour of the deposits that resulted from the loss of organic matter with depth was the only changes to the deposits, with a uniform damp brown sand comprising the bottom 55-60 cm of the deposit. The inverted lower radiocarbon ages suggested, however, that either the deposits had been disturbed, or some of the charcoal in the sample that had been submitted for dating was intrusive to T2a/15 – possibly small pieces had moved down through the deposit over time, or had been knocked down from a higher level during excavation. In order to investigate these possibilities, 745 flaked artefacts as well as non-artefactual pieces of chert (aka tuff, indurated mudstone had been excluded) from Squares T2a-b were examined to document surface weathering pattern changes throughout the deposit. At other sites in the Sydney Basin, such as Capertee 3 and 95-101 George St., Parramatta,  the colour of chert artefacts had been observed to change with age/depth as a result of the extent of weathering over time (Austral Archaeology Pty Ltd 2007; Hiscock & Attenbrow, 2005). It was assumed by Attenbrow that if the shelter deposits had been undisturbed the pieces of chert would display a gradual change throughout the depth of the deposit in the degree of weathering that was expressed as colour changes. A lack of any clear trends in the pattern of weathering would indicate disturbance.

The chert pieces that had been recovered from Emu Tracks 2 were assigned to 5 categories of weathering, which was based on their colour according to Munsell Soil Colour Charts (Kollmorgan Corporation, 1975). The surface of the chert changes with age and weathering from dark grey to light grey then to very pale grey or cream.

It is indicated by the percentage frequencies of all chert pieces in each weathering category in each split that the chert pieces were subjected to a gradual change in the degree of weathering over time. In Spit 15 the presence of LW2 specimens (the only chert pieces that were found in this spit), as well as to the downwards increase in the percentage of LW1 chert in spits 10, 11 and 13, indicates that at some time ln the past disturbance did occur. The disturbance that is reflected by the displacement of these artefacts could account for the inverted radiocarbon ages. The presence of stratigraphic layering in the upper deposit to a depth of 15-25 cm (though it is caused by loss of organic matter), however, and the correct ordering of radiocarbon determinations for spits 2 and 5 to a depth of 26.5 cm, indicates that the lower part of the deposit was the only part to be disturbed. Also, it was found that each artefact was within the range of weathering categories of other chert pieces in the spits in which they occur, when the backed artefacts, retouched flakes and cores were examined individually. It is suggested by this that little vertical movement had occurred for items in these categories of artefact.

Some mixing of the fragments of charcoal in spits 10-15 is assumed based on the foregoing analysis. It is likely that some of the charcoal from spits 11 and 13 which were analysed for radiocarbon ages and were dated to 3423 ± 35 BP (14106) and 3,241 ± 45 BP (Wk-16547) respectively, is likely to have originally been incorporated into the deposits in the shelter at a lower level after which they moved upwards during disturbance. Consequently, it is more likely that Wk-14106 is more likely to provide  to provide a truer indication of the time of the earliest habitation than NZA-19201 (2,464 ± 40 BP), as some charcoal that came from spit T2/15 may have been incorporated in the deposits at a higher level and then moved downwards during disturbance.

Based on a depth/age curve that used calibrated radiocarbon ages, it was considered by Attenbrow that initial occupation of this shelter occurred between 3,780 and 3,540 cal. BP, and bondi points were deposited from 3,250-3,120 cal. BP until sometime between 1420 and 1100 cal. BP.

Kangaroo and Echidna

This is a large shelter (46 x 9.8 x 13.5 at maximum height), that faces to the west. Along the back wall of this shelter there are charcoal drawings of animals including a kangaroo and echidna. There are seepage points along the back wall which keep much of the floor damp, apart from a higher dry area about 50 m² at the southern end. There were 2 test pits that were excavated, in the lower damp area, T1, and T2 in the higher dry area. Square T1 was abandoned at a depth of 43 cm, with only 2 artefacts being recovered. Square T2 was excavated as 4 adjoing squares of 50 m² (T2a-d). T2b, one of these squares, reached that maximum depth of 71 cm (Attenbrow, 2004). There were 61 artefacts that were recovered from T2, spits 1-5. The results suggest that the preferred space to use was the upper dry area.

Based on the original radiocarbon age of 6,700 ± 150 BP (SUA-2172) a depth/age curve suggested that about 9,800 BP was the time when the rockshelter was first occupied (Attenbrow, 2004). This extrapolated age was very much earlier, however, than the radiocarbon age, i.e. 3,000 years earlier, though the depth between the level that had been radiocarbon dated (T2ab/4, 22-28 cm below the surface) and the base of the archaeological/cultural deposit is not very large (T2b/5, 28-41.5 cm). At about 9,800 BP the initial habitation therefore seemed improbable and an estimate that was more conservative, 7,000-6,000 BP was used in the habitation and artefact indices and model building (Attenbrow, 2004). Another 2 radiocarbon ages have now been obtained for samples of charcoal that were recovered from Square T2, and it was confirmed that the initial cautious approach was warranted.

According to Attenbrow the assemblage from Square T2 was unusual, for the small size of both the areas that were excavated and assemblage, it contained a number of diagnostic artefacts: a single bondi point, 3 complete ground-edge implements and 5 bipolar cores/flakes. With the exception of 3 of the bipolar artefacts all of these artefacts were recovered from spit 3, (Attenbrow, 2004).  It is indicated by the distribution of these artefacts there was a lack of bondi points in the upper spits, bipolar artefacts increased as did the quartz over the FGS/chert/silcrete, replicates the sequence in other catchment sites. It is suggested by the presence of 3 ground-edge implements clustered in 2 squares that were adjoining, T2a and T2b in a single spit (3), that they were cached.

It was originally estimated that spit 3 accumulated between 5,000 and 2,800 BP, based on the presence of the bondi point and the high proportion of FGS material. The radiocarbon age for spit 3-lower (2942 ± 35 BP, Wk-14102) that were obtained recently suggests the upper limit of the original estimate was too early and it range of ages was more restricted. The time range indicated on a depth/age curve that used the 3 radiocarbon ages, i.e. 5000 Cal. BP, does not support this. The depth/age curve was, however, once again considered to be misleading because of the date, that were very much earlier, obtained for spits 4 and 5, both of which dated to about 6700 BP (7500 Cal. BP).

There were no sterile stratigraphic breaks in the deposit between spits 3 and 4, though the deposit in spit 4 had merged from a brown sand in spit 3 to a darker orange-brown. The dates that were obtained and the distribution of stone artefacts, i.e. only a single artefact in spit 4, suggests that there had been a gap in the use of this shelter. If that is the case there is a plausible interpretation is that when it was first used in the Early Holocene, about 7500 BP, then not used again until much later, between 4000-3000 cal. BP, when use began again.

2 moths

This is a shelter that faces to the north, which has dimensions of 10 m x 7.9 m x 1.7 m max. height. No stone artefacts were visible on the surface of the deposit at the time it was first recorded, and there were not any painted, engraved or drawn images seen on the walls of the shelter to give an indication it had been used. Initially it was listed as a shelter that had archaeological potential. A 50 cm² test pit was excavated to a maximum depth of 52.5 cm but no stone artefacts were uncovered. A large fragment and a small fragment of a freshwater mussel shell were recovered from pit 5, as well as many small animal bones throughout the deposit. Also noted during excavation from spit 5 to spit 8 were very tiny fragments of shell that passed through the 3 mm sieve that were not retained. The largest fragment of mussel shell was of a size that Ken Aplin considered to have been derived from human activity, though the bones were not of human origin. Some species of bird, water rats and dingoes eat freshwater mussels and they could have been taken back to a rockshelter by these animals, it was considered to be unlikely in the case of the large 2 moths specimen (Attenbrow, 2004). Attenbrow was advised by Su Solomon in a pers. Comm. 1986 that the largest fragment of shell she had observed in dingo scats was 4 cm; the largest 2 moths fragment was 6 cm long. The shell was classified as cultural material, and therefore evidence the shelter was used by humans, and it was recorded as having an archaeological deposit.

The spit from which the large shell fragment had been recovered, spit 5, was 18.5-24.5 cm deep, and its time of accumulation was estimated to have been sometime between 2000 and 1000 BP (Attenbrow, 2004). Analysis of the accumulation rates of sediment in shelters that had been dated by radiocarbon in the catchment that had similar morphology and topographic location was the basis for this estimate (Attenbrow, 2004). The radiocarbon age of 2026 ± 46 BP (Wk-14266) confirmed for spit7 at a depth of 30.5-35.5 cm, which was the lowest spit that contained enough charcoal for a conventional radiocarbon age determination. In a level below the large shell fragment charcoal was submitted and a date was obtained for the earliest occurrence of shell, though the origin of the tiny fragments was indeterminate, and the large 6 cm fragment was accepted as evidence that humans had used the shelter.

Conclusions

It is indicated by radiocarbon ages that Emu Tracks 2, Kangaroo and Echidna, and 2 Moths shelters were first used in the 4^th, 7^th and 2^nd millennia BP respectively; the same millennia as originally estimated (Attenbrow, 2004).

The general trends in the indices that are used to produce the models of changes in the Holocene of land use patterns in the catchment of Upper Mangrove Creek, i.e. the rate of establishment of habitation, number of habitations used per millennium and the rates of artefact accumulation, are not affected by variations between the original estimates of ages for the establishment of habitation and those that were based on the radiocarbon ages, and the gap in use that has been hypothesised at Kangaroo and Echidna.

A longer timeframe for use by Aboriginal people of the catchment is indicated by the use of calibrated ages, which previously was not adopted, extending the earliest period for use of Loggers and for the catchment as a whole from the 12^th millennium BP on conventional radiocarbon dating during the 14th mi^llennium cal. BP.  The initial use of Kangaroo and Echidna, as well as 2 other shelters, White Figure and Uprooted Tree, is placed in an earlier millennium that was indicated previously. This extended time frame, nevertheless, does not alter the general trend of a few, though slowly increasing habitations, in the catchment in the Early Holocene. The trend post-5000 BP when there was a dramatic rise in the habitation indices in the 2^nd millennium BP does not change at all, but the artefact rates of accumulation that were estimated in the catchment rates in the 1^st to 3^rd millennium BP vary considerably. This occurs as a result of converting conventional radiocarbon ages to calibrated ages changes the duration of some spits at individual sites, and as a consequence of the estimated numbers of artefacts, in particular at Emu Tracks 2 when combined with the effect of the younger than the radiocarbon age that was estimated for T2a/2. The dramatic increase that occurred in the 3^rd millennium BP and the major decrease in the rates of accumulation in the 1^st millennium BP remain.

Sources & Further reading

1. Attenbrow, V. (2007). Emu Tracks 2, Kangaroo and Echidna, and Two Moths: Further Radiocarbon Ages for Aboriginal Sites in the Upper Mangrove Creek Catchment, New South Wales.