Australia: The Land Where Time Began

A biography of the Australian continent 

Murray Springs Clovis Site – Pleistocene Extinction Question of Extraterrestrial Impact

According to Haynes Jr. et al. samples collected from Murray Springs, which is a Clovis archaeological site, southwestern Arizona, provided evidence for the recent hypothesis that an extraterrestrial impact led to the megafaunal extinctions of the Late Pleistocene (Firestone et al., 2007). In this paper Haynes et al describe the sampling and analyses of magnetic separates from within, above, and below the lower boundary of the Younger Dryas (LYDB) black mat at Murray Springs, as well as radiation measurements from the LYDB at Murray Springs and 2 other Clovis Sites that were well stratified. Maghemite is the main magnetic fraction from Murray Springs. Though magnetic microspherules have terrestrial origins, they also occur as cosmic dust particles. Haynes et al. did not find radiation anomalies or iridium. They addressed the evidence for massive burning of biomass at Murray Springs and no evidence of massive burning of biomass was found. The findings of Haynes et al. do not preclude a cosmic event at the terminal Pleistocene. They failed to substantiate some of the claims by Firestone and others, but their findings do not preclude a cosmic event at the terminal Pleistocene.

According to a recent proposal an extraterrestrial impact over North America was the cause of the Racholabrean megafaunal extinction, the onset of the cooling of the Younger Dryas (YD), and the end of the Clovis culture, and extensive burning of biomass across North America (Firestone et al., 2007; Firestone, West & Warwick-Smith, 2006; Kennett et al., 2008; Kennett et al., 2009). The Clovis site at Murray Springs, Curry Draw, Cochise County, southern Arizona, is one of the key sites that provides their evidence. At Murray Springs the occupation surface of the Clovis culture is a sharp stratigraphic contact that is covered by the black mat, black organic clay, which is believed to result from an algal bloom (Haynes Jr, 2007). The black mat at Murray Springs covers and preserves the landscape from the Clovis age. Beneath the black mat archaeological excavations uncovered hundreds at Clovis stone artefacts that are in direct association with the skeletons of 2 mammoths, 11 bison, and bones of dire wolf and horse (Haynes Jr & Huckell eds, 2007). Ash wood (Fraxinus sp.) charcoal, that probably originated in hearths, produced 8 ¹⁴C dates that average 10,900 BP (12,900 calendar years). Stratum F₂ of the black mat had a radiocarbon age of about 19,700 BP at the base to about 9,700 BP at the top, which indicates it was deposited during the cooling period of the Younger Dryas, a reversal from the reversing trend of the Bølling-Allerød (Haynes Jr, 2007; Jull et al., 1999).

The F₁ stratum of the black mat from the Younger Dryas is generally a layer of organic clay that is 2 to 10 cm thick. It covers a stream channel of Clovis age of sand and gravel, stratum F₁, as thin black stringers that are separated by several centimetres of white facies. Away from the channel the black mat rises gently over an older surface up to 10 cm thick at trench 22 (Haynes Jr, 2007). At the Murray Springs site sediment samples were collected at, above and below the lower Younger Dryas band at Profile B and Trench 22 North.

Following several analyses it was reported by Firestone et al. (Firestone et al., 2007) that at Murray Springs the Clovis surface contain:

a.      A spike of magnetic particles,

b.     Including magnetic microspherules,

c.      Carbon microspherules,

d.     Fullerenes,

e.      A helium-3 anomaly,

f.       An iridium anomaly,

g.     A radiation anomaly,

h.     Abundant charcoal, and more recently,

i.       Nanodiamonds (Kennett et al., 2009).

This paper reports on the attempts of Haynes et al. to reproduce some of their most readily tested finding. Haynes et al. collected at the same locations as Firestone et al., and according to Haynes et al. they therefore have virtually identical samples.

In this paper Haynes et al., report the concentration of magnetic separates from 6 samples that were collected from stratified alluvial sediments at the Murray Springs site, as well as comparative samples that include channel sands collected from the modern stream bed of Curry Draw (16MS07) and aeolian fine sands and silts that had been collected from a polymer-coated roof in Tucson, Arizona (1AZ07). Sample 95MA07 represents the lower Younger Dryas boundary, which includes about 0.5 cm on either side of the contact F_2a1/F_1a2 of the basal black mat, F_2a, and the top of the channel fill of Allerød age, F_1a at Profile B₁. Sample 3-5MS07 was confined to the top 1.0 cm of the Clovis (F₁) sands from the stream channel. Included in sample 26MS07 is about 0.5 cm of basal black mat (F_2a) as well as about 1.0 cm from the top stratum (F_1a) on either side of the contact F_2A/F_1A at profile B₃. Following Allen West (Kennett et al., 2009), a 4^th sample was collected from Trench 22 which included about 1.0 cm of sediment on either side of the contact F2/D. However, at this site the black mat overlies a surface that is much older and was omitted from the sample. Magnetic particles and microspherules were contained in samples 1AZ07, 16MS07, 26MS07, and 3-5MS07 that were examined by electron microprobe and inductively coupled plasma-mass spectrometry (ICPMS).

A radiation anomaly was also found at the lower Younger Dryas boundary at the Murray Springs site and at the type Clovis site in Blackwater Draw, New Mexico. 1-minute counts were taken with a radiation alert monitor 4 Geiger Counter by the leading author at the Clovis occupation surface at 2 locations at the Murray Springs site (Profile-B1 and trench 22), at Blackwater Draw and at the Sheaman Clovis site, eastern Wyoming. Also, 1-minute counts were made at 5- and/or 10-cm intervals above and below the Clovis surface.

Conclusions

Haynes et al. say they found no compelling evidence that a cosmic catastrophe took place at the Murray Springs site, based on the data presented in this paper. They believe the stratigraphic distribution of magnetic particles and microspherules that were included can be explained by these sediments being affected by fluvial dynamics, some of which originated from the normal flux of cosmic dust to the Earth as has been suggested (Pinter & Ishman, 2008). Haynes et al. did not observe an iridium anomaly at the LYDB relative to the local geological background. Also, the carful chemical pretreatment of dozens of basal Younger Dryas black mat samples collected from the upper San Pedro Valley did not find adequate charcoal to support the hypothesis of the extensive burning of biomass.

Haynes et al. are still of the opinion that an understanding of what happened approximately 12,900 calendar years BP that terminated the major elements of the megafauna from the Pleistocene (Haynes Jr, 2008) has yet to be achieved. The extraterrestrial impact hypothesis has sparked a number of investigations that are leading to new knowledge, and though the data collected by Haynes et al. from the Murray Springs site, as well as elsewhere, do not support it, they do not preclude it.

Sources & Further reading  

1. Haynes, C. V., et al. (2010). "The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact." Proceedings of the National Academy of Sciences 107(9): 4010-4015.