Lake Mungo

Lake Mungo is a dry lake located in New South Wales, Australia. It is about 760 km (472 miles) due west of Sydney and 90 km (56 miles) north-east of Mildura. The lake is the central feature of Mungo National Park, and is one of seventeen lakes in the World Heritage listed Willandra Lakes Region. Many important archaeological findings have been made at the lake, most significantly the discovery of the remains of Mungo Man, the oldest human remains found in Australia, Mungo Woman, the oldest human remains in the world to be ritually cremated and as the location of the Lake Mungo geomagnetic excursion, the first convincing evidence that Geomagnetic excursions are a geomagnetic phenomenon rather than sedimentological.

Geology
Sediments at Lake Mungo have been deposited over more than 120,000 years. On the eastern side of the Mungo lake bed are the "Walls of China," a series of crescent-shaped sand dunes or lunettes, up to 40m in height, that stretch for more than 33 km, where most archaeological material has been found. There are three distinct layers of sands and soil forming the Walls. The oldest is the reddish Gol Gol layer, formed between 100,000 and 120,000 years ago. The middle greyish layer is the Mungo layer, deposited between 50,000 and 25,000 years ago. The most recent is the Zanci layer, which is pale brown, and was laid down mostly between 25,000 and 15,000 years ago.

The Mungo layer, which was deposited before the last ice age period, is the most archaeologically rich. Although the layer corresponded with a time of low rainfall and cooler weather, more rainwater ran off the western side of the Great Dividing Range during that period, keeping the lake full. It supported a significant human population, as well as many varieties of Australian megafauna. During the last ice age period, the water level in the lake dropped, and it became a salt lake. This made the soil alkaline, which helped to preserve the remains left behind in the Walls. Although the lake completely dried up several thousand years ago, ground vegetation remained on the Walls, which helped to stabilise them and protect them from erosion. With the arrival of European settlers in the area since the 1880s, introduced species, notably rabbits and sheep, have destroyed the vegetation cover. Herds of feral goats are also present in the region. This has led to increased erosion of the dunes. However, this erosion has led to the uncovering of many human and animal remains. Wind has moved sand and soil eastwards from the Walls, forming a mobile sand dune which moves farther east every year.

Lake Mungo Remains
The most publicized findings at Lake Mungo have been Mungo Man and Mungo Woman. Mungo Woman, a partially cremated body, was discovered in 1969 by Jim Bowler from the Australian National University (ANU). Mungo Woman was only partially cremated before the remainder of her bones were crushed. The time that was taken into her burial is demonstration of an advanced ritualistic process. Mungo Man was also discovered by Bowler, on 26 February 1974. The remains were covered with red ochre, in what is the earliest known incidence of such a burial practice. Red ochre is commonly used in burials for ritualistic purposes.

Mungo Woman was initially dated to 26,000 years ago through radiocarbon methods, meanwhile Mungo Man was dated to 42-45,000 years ago from thermoluminescence. Another study proposed that Mungo Man could be almost 80,000 years old using electron-spin resonance however the study was widely criticised for its contradictions with other research and uncertainty of using electron-spin resonance as a dating method for the site. Further work using OSL dating by Bowler in 2003 has modified the dating of both remains to 40,000 years ago, revealing both burials to be near in timing and confirming Mungo Woman to be the earliest known human to have been cremated. The drastic difference in age for dating the Mungo Woman with radiocarbon was explained by contamination of newer carbon in the samples analyzed.

Occupation chronology
11 silcrete flakes dating to 50,000 years ago represents the first evidence of human occupation in the lake. In 2014 a full study of the lunette sequence at the lake using single grain OSL was conducted revealing the different phases of the lake. 10,000 years after humans first arrived, the lake began fluctuating from full to drier conditions, this pattern would remain until the final drying of the lake around 15,000 years ago. The people in the area were able to adapt to the changing conditions of the lake. Although there was a decline of activity, people remained in the area after the lake dried.

In 2015 evidence of a "mega-lake" event was found after using dGPS to clarify the main shoreline of the lake and comparing the results with a line of beach gravel that was found to be more elevated than the main shoreline. The mega-lake was dated to a brief period at 24,000 years ago. As the lake volume increased, it connected with Lake Leaghur, which resulted in the north part of the lunette forming an island temporarily. There have been traces of human adaptivity found during this time on the island, including hearths indicating food being eaten on the island and stone artefacts sourced from off the island. Strangely there is no evidence for this mega-lake event in the southern part of the lunette.

Lifestyle
Fish otoliths have been recovered from hearths in the lake, using radiocarbon they were dated to 19,000 years ago. Analysis of the geochemistry of the otoliths confirmed that the fish came into the lake a few years before death, they came into the lake during flooding periods and became trapped when the lake was evaporating. The fish would've became sluggish from oxygen deprivation in the lake leading to the theory of humans coming to the lake during these evaporating periods to hunt easy fish.

17 sandstone tools have been found at Lake Mungo, 10 of these date to 25-14,000 years ago in the Pleistocene, 4 were deposited around 8,000 years ago in the Holocene, and 3 couldn't be dated with certainty. Comparing the usewear on these tools with ethnographic and experimental sandstones confirmed at least 14 tools were used for seed grinding (9 from the Pleistocene, all 4 Holocene tools, and 1 of the undated tools). Evidence for seed grinding in Australia during the Pleistocene is rare, only having been confirmed in 1 other site at Cuddie Springs. In addition there have been 3 shell tools found dating to 40-30,000 years ago, a possible 4th tool dating to older than 40,000 years ago was also found. Comparing the taphonomy and usewear of experimental shell tools established the addition of shells to the tool kit of the Pleistocene Australians.

Lake Mungo geomagnetic excursion
In 1972, Archaeomagnetic studies were conducted on the prehistoric aboriginal fireplaces occurring along the ancient shoreline of Lake Mungo. Magnetization preserved in oven-stones and baked hearths show that the axial dipole field moved up to 120 degrees from its normal position around 30,000 years ago. Called a geomagnetic excursion, the event occurred between 30,780 and 28,140 years BP with a very high field strength of 1 to 2×10−4 T (around 3.5 times higher than Earths current 5.8×10−5 T) which subsequently decreased to .2 to .3×10−4 T. There is also evidence of a second excursion around 26,000 BP with a field strength of .1 to .2×10−4 T. Because most of the excursions found before Lake Mungo were contained in sedimentary material, it had been suggested that the magnetic field directional anomalies were detrital or diagenetic in origin. The Lake Mungo results were due to thermoremanent magnetization, ruling out a sedimentological phenomenon.

Two excursions have been recorded in sediments from Skjonghelleren on Valderøy, Norway, with the Virtual Geomagnetic Pole (VGP) of one being synchronous with Lake Mungo. This suggests that the Lake Mungo event was global, rather than a local event. Data from lake sediments of a similar age in France having near identical magnetic field lines also support Lake Mungo being a global event. However, it has been suggested that Lake Mungo's anomalous field is the result of lightning strikes.

Lake Mungo today
The rich archaeological heritage of the site is very significant to the Aboriginal Australian people from the area. The Willandra region is inhabited by the Barkindji, Ngiyampaa and Mutthi Mutthi peoples, who have entered Joint Management Agreements with the Government of New South Wales to manage the lake and the Mungo National Park since 2001.