By Joe Shimmin
The Quaternary contains the Pleistocene and the Holocene and is the youngest of the geological intervals. It dates from roughly 1.8 million years in the past proper as much as the current, with the big majority of this time being crammed by the Pleistocene. The Holocene spans a geological ‘blink of an eye fixed’, starting solely 10,000 years in the past at first of the current interglacial and continues right now.
What units the Quaternary other than different geological intervals is a set of excessive frequency local weather fluctuations, with very chilly levels being interspersed by hotter levels. Any such local weather fluctuation is believed to have occurred at varied different occasions within the Earth’s historical past, however many of the proof for these has been worn out over hundreds of thousands of years. Nevertheless, the glacial/interglacial or heat/chilly levels of the Quaternary have, in lots of instances, left us sufficient proof of their existence for the Quaternary scientist to have the ability to try and reconstruct these previous environments with a point of success.
Serbian mathematician, Milutin Milanković, formulated the accepted idea for why local weather oscillations have occurred on this interval, within the first half the 20th century. In keeping with ‘Milanković, Quaternary local weather was, and is, influenced by three elements:
- Issue 1: the form or ‘eccentricity’ of the Earth’s orbit across the solar, which varies over a cycle of roughly 100,000 years.
- Issue 2: The lean or ‘obliquity, of the Earth’s axis, which varies over a cycle of roughly 41,000 years.
- Issue 3: The wobble of the Earth’s axis of rotation, in any other case referred to as ‘the procession of the equinoxes’, which varies over a cycle of roughly 21,000 years.
It’s past the scope of this small article to enter the ins and outs of the above, however suffice to say that these astronomical elements have an effect on the quantity of photo voltaic radiation that the Earth receives and therefore its local weather.
Nobody is bound precisely what number of chilly and heat intervals there have been within the Quaternary. Proof is scattered and fragmented on land and, in areas affected by glaciation, has usually been obliterated by subsequent glaciations. A extra full file is held within the sediments of the deep oceans. Right here will be discovered sequences of sediments which have amassed, uninterrupted, over lengthy intervals – in some instances the entire of the Quaternary. Inside these sediments are discovered the shells of micro-organisms and, by analysing these shells, inferred climatic knowledge will be collected.
This deep ocean file is a wonderful useful resource with which Quaternary scientists, researching deposits on land, do their greatest to correlate the sediments that they’re investigating. The fragmentary nature of the deposits left on land imply {that a} useful resource corresponding to this is a vital device, because it supplies a framework inside which to suit the varied items of information obtained from finding out terrestrial websites.
The Quaternary Interval in Kent
I reside in an space of England that was not lined by glaciers at any level through the chilly levels of the Quaternary. Right here, in Kent, as a substitute of ‘U’-shaped valleys, corries, striations, moraines and all the rest of the glacial features that can be found (for instance, in the Lake District), we have landforms brought about by successive cycles of periglacial and temperate climates.
These landforms may be less dramatic than those that make up the scenery one admires in the Lake District, but they can contain a great deal more information. Of most interest are river terrace deposits. These are found as patches of sediments or gravels on valley sides and were formed in response to the Quaternary climate fluctuations, coupled with regional crustal uplift.
During the cold stages, there was less vegetation, bedrock was exposed and the cold weather caused a great deal of erosion. Water seeped into cracks in the rock and, when it froze, it expanded and enlarged the cracks. Over time, rocks were broken down and large volumes of gravel accumulated on a river’s flood plain. Most water was locked up, as ice and the relatively small quantity of liquid water that did flow in rivers did not have enough energy to erode through this accumulating sediment in response to the regional uplift. However, when the cold stage began to subside and the ice melted, the rivers became swollen and had enough energy to cut down into the accumulated gravels and sediments.
Successive cycles of aggradation during the cold stages and down-cutting during the warm stages leave us with a staircase pattern of deposits, with the oldest found at the top and the youngest at the bottom.
Investigating Terrace Deposits
Within terrace deposits can be found a wealth of relics such as animal fossils (including beetles, molluscs, fish bones and mammal bones and teeth), plant fossils (such as wood, seeds, leaves and pollen) and artefacts produced by our human ancestors. In addition, there are numerous diagnostic sedimentological features as well as an array of other things that give us clues as to the age of the deposit, the climate at the time it was formed and the habitat type which prevailed in the area at that time. Information relating to how our ancient human ancestors lived can also be found.
It is important, when investigating any Quaternary deposits, to study the overall assemblage of evidence that is present. The various sediments in a section should be investigated, animal and plant material should be collected for identification, counting and statistical analysis, and human artefacts should be drawn, catalogued and studied. Using all available lines of evidence together, a reliable and comprehensive environmental reconstruction can be often be achieved.
Fig. 4. Back of a Mesolithic/Neolithic blade.
The digging involved when studying Quaternary sediments is often extremely hard work, but the results are well worth it. Within the gravels and sediments that I have already extracted, I have found foraminifera, ostracods, molluscs, small mammal bones and teeth, an elephant tooth and a large number of flint flakes produced during the production of stone tools. I find this work extremely rewarding and feel lucky to have such a topic to sink my teeth into.
Over the next few years I hope to investigate many more sites in Kent with the aim of revising and broadening the information provided by previous work in this area. I hope to be able to build up a picture of north-east Kent’s previous environments over a timescale of hundreds of thousands of years and I know that, during this work, I will hold in my hands some fascinating pieces of natural history. The task will be a big one, but I can’t wait.
References
J. J. Lowe and M. J. C. Walker (1997). Reconstructing Quaternary Environments. Longman
Bridgland, D., Maddy, D. and Bates, M (2004). River terrace sequences: templates for Quaternary geochronology and marine-terrestrial correlation. Journal of Quaternary Science, Vol. 19, 203-218.
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