In late 2011, I was invited to write a chapter for an upcoming book on the Quaternary geology of Queensland. Not being a geologist, I was initially hesitant to take on the job. I thought about it for a bit though- I work in the Quaternary (i.e, the last 2.6 million years of Earth’s history) and in Queensland, so I eventually thought to myself, “why not?!” It turns out that it was one of the most challenging things that I have ever done, but also one of the best moves that I could have made.
Quaternary chapter for ‘Geology of Queensland’ (2013; ed. Dr Peter Jell)
Over the course of a month or so, I read a huge number of papers. I already knew the palaeontology side of Queensland’s Quaternary pretty well so that was not a big problem, but I also had to had to get stuck into loads of papers on palaeoclimates, fluvial and aeolian deposits, speleogenesis, soil formation and weathering, and volcanism- the sorts of things that aren’t normally on my reading list. But I learnt so much.
What really struck me was that although Queensland doesn’t have too much going in the way of Quaternary economic geology, most research had a strong palaeoclimate / palaeoenvironmental theme. And what really stood out was the role of geochronology (dating) in tying all of these seemingly disparate records of Queensland’s Quaternary together. Back in the early 1960’s, the time of the first modern review of Queensland geology, there were very few methods with which to date the important deposits. However, since then numerous geochronological approaches have been developed that allow for the development of a reliable temporal framework critical for understanding how climate change has impacted upon and shaped Queensland over the past 2.6 million years.
The modern Channel Country of western Queensland in flood (photo: G. Nanson)
By combining all of the results of the different studies, it immediately became clear that there have been some massive climate-driven environmental changes in Queensland, and more broadly through Australia, over the course of the Quaternary. The first part of the Quaternary was relatively warm and humid, and less seasonal than it is today. Up until around 300 thousand years ago, conditions were so good that extensive rainforests grew much of the way along the eastern coast. The arid interior was not even that arid at that time. In fact, it was fairly well-watered, possibly with semi-permanent La Niña conditions in place for several thousands of years (incidentally, the La Niña climate systen is what caused the terrible flooding of 2011-13 in eastern Australia; but it was even wetter 300 thousand years ago!).
After around 300 thousand years ago, long before the first humans traipsed onto Australia’s shores, the climate started to shift, so much so that the rainforests of the east started to contract northwards; the arid inland rivers began to dry up; and numerous species started disappearing from their formally well-watered environments.
Late Quaternary stalagmite that grew from 20-7.8 thousand years ago
The results showed that long-term shifts in climate oscillation, in line with orbital forcing, saw Queensland descend into an intense last glacial cycle or ‘Ice Age’. The late Pleistocene (beginning around 130 thousand years ago) started with a massive marine transgression of the Gulf of Carpentaria, which coincided with incredible fluvial activity both in north Queensland and the western Channel Country (flowing into Lake Eyre in central Australia). The warm, wet conditions persisted through 120-90 thousand years ago. Temperatures then plummeted, causing sea levels to fall so low that the Gulf of Carpentaria became a lake! The change is also associated with a major vegetational reorganisation in the tropics, with other records suggesting reduced monsoonal activity at that time. Through this period, you can see a progressive decline in megafaunal diversity in southeastern Queensland.
After around 47 thousand years ago, fluvial activity basically ceased in the Channel Country, and dune building became the dominant sedimentological process. This coincided with the time that saw the final ever filling of the Lake Eyre megalakes (the connection of Lake Eyre to other central Australian lakes). There is also the last direct, dated evidence for megafauna at that time (the youngest assemblage that we know about – Neds Gully – had only two or three large-bodied megaherbivores, rather than the 65+ species that are commonly regarded as having being extant at that time). The earliest record of humans in the State is around 40 ka. The intense climatic / biological events were clearly in-train before that.
One of the youngest Diprotodon skulls known (this specimen is from Neds Gully, Darling Downs)
The vegetation shifts after 45 ka and up to the Last Glacial Maximum (around 20 ka) were similar to previous changes from earlier glacial maxima in some ways, but was markedly more intense in terms of its aridity. The sedimentological record of Lake Carpentaria from the early penultimate last glacial maximum (just before 130 ka) saw vast rivers flowing across the lake, whereas as the period leading into the Last Glacial Maximum saw the lake transition through phases where there was almost total desiccation. The period around the Last Glacial Maximum also saw significant landscape instability (in part, a function of a change in vegetation cover from forest to open habitat). Post-Ice Age warming meant a return of the monsoon, leading to Lake Carpentaria expand to capacity size and all-time lows in salinity, then full marine transgression by around 10 thousand years ago. Speleothem (e.g., stalagmites) records suggest an enhanced monsoon after that time as well. This is of course all associated with another vegetation shift where forests returned and swallowed up the open areas.
The implications of this synopsis are massive when it comes to trying to understand the causes of megafaunal extinctions. Although it is regularly argued that climate change was not significant in the last glacial cycle and that there was no climate change when the megafauna supposedly went extinct between 40-50 thousand years ago, the data just do not support such an inference. There were incredible changes at that time and were part of a long-term shift towards increasingly arid climates. This doesn’t mean that climate alone caused the final megafaunal extinctions (the earliest humans, arriving around 50 thousand years ago could also have made a contribution), but we can no longer ignore it.
My chapter was published in the book ‘Geology of Queensland’ (edited by Dr Peter Jell) earlier this year. The rest of the book documents all other aspects of what we know about Queensland’s geology, not just the Quaternary. It’s an incredible book- I highly recommend it to one and all. It’s a huge read- over 900 pages, full colour, hardback, and retails at only around $75! Such good value and one of the most important books ever written on any aspect of Australian science. You can order it here.
Summary of major climatic and biological events for the last 350 thousand years in Queensland relative to the oxygen isotope curve
