“A complete understanding of the extent and chronology of Quaternary glaciation requires evidence from both terrestrial and marine evidence – discuss. ” “Just as you cannot see your own footprint in the sand while your foot is covering it, you cannot see the effects of an active glacier at its base or sides. Only when the ice melts is its geological work of erosion and sedimentation revealed. ” -Press and Siever 2000- Introduction The effects of glaciations in the last quaternary were global, thus information about them is hidden both terrestrially and in marine sediments.
They type of information revealed in each of these areas varies both in detail and in what information they actually give. Depending on what information you require, it may be worth focusing on one particular information source. However, it may not be regarded as wise to do this, as you may inhibit your ability to obtain a complete understanding. It is marine sediment analysis that was first used to study Quaternary environments, with the first piston corers being developed in the USA in 1945 (kingdom drilling 2004).
With the aid of improved technologies for coring materials and data analysis, it could be said that scientists from then were encouraged to look at other sources of information (i. e. cores from ice sheets) for an even broader source range. Marine Evidence Ocean sediments provide a very much more complete geological record (Press and Siever 2000), partly due to the highly efficient preservation of sediment (Lowe and Walker 1997).
Striae for example are best protected from weathering in sub marine conditions (or, when exposed to the surface, covered in 0.4-0. 5m of till) (Kleman 1990). However, the top 50cm of sediment can be subject to bioturbation from marine organisms effectively ‘blurring’ the information. The sediment that does form from process such as ice rafting occur very slowly, but are very detailed with both organisms, elements such as Al, Ba, Ca, Cd and isotopes of C, O and U available for study for determining climatic conditions and dating (Kleman, J. 1990). The remains of organisms in marine sediment are particularly useful in estimating climatic conditions of the time.
CaCO3 stored in the shells of creatures such as foraminifera contain oxygen isotopes where during glaciations they become enriched in 18O due to 16O evaporation and entrainment in ice (Press and Siever 2000). Those that ‘survive’ the journey to the ocean floor are subsequently buried in more layers of sediment. Another example can be seen in Cytheropteron testudo, a cold-water marine creature, used as a marker for the beginning of the quaternary in Italy (Lowe and Walker 1997). Terrestrial Evidence Terrestrial evidence, here including ice sheets are particularly useful as they give a more diverse range of data also on a larger time scale.
However, detail may not be as good as with marine evidence, with gaps in the terrestrial record partly due to the effects of climate. Landforms such as moraines reveal periods of advance, retreat and stand stills (Nesje and Dahl 2000), or where ice has remained stationary for some time. These and glacial deposits such as till can be exposed to the surface for some time, and therefore be subject to weathering and other effects such as uplift, vegetation colonization, soil formation and climate changes (Menzies, J 2002) .
This could change the properties of a deposit and or lead to an inaccurate interpretation. Lowe and Walker (1997) also mention the damaging effects of destruction by melt water, postglacial erosion, weathering or subsequent fluvial activity. It may also be difficult to distinguish landforms which have undergone several periods of glaciation, where the most recent has not destroyed all the evidence of the previous one (Bennett and Glasser 1996).
The landforms of the Lake District can be hard to interpret for this reason. It is thus the job of a glacial stratigraphist to establish the relative order of sediments and landforms, and working out what climate conditions were like when they were formed (Bennett and Glasser 1996). The advantageous thing about landforms is the ability to use mapping techniques to observe the type and distribution of landforms, and any important details about them.
Advances in remote sensing techniques have allowed large areas to be mapped quickly (Lowe and Walker 1997), and in a form that reveals most information – infrared and radar monitoring will reveal different details for example. Lacustrine environments have been ranked as one of the best palaeoclimatic archives (Nesje and Dahl 2000) as lake deposits are directly affected by climatic change. In glacial periods, minerogenic salts and clays dominate, although over all there is a reduced presence of clastic and organic material (Nesje and Dahl 2000).
Recorded organism types will vary also, according to climatic conditions. In lakes, it is the usage of varves (annual deposits that occur annually and in two stages, over two seasons) to date an area. If a full set of varves is retrieved, the date at which the ice retreated exposing bare ground can be calculated (Pacific Institute 2004). This data can be compared with information given in pollen, plankton and diatom records as well as palaeomagnetic variations and geochemical changes taken from the sediments (Nesje and Dahl 2000) to obtain a better view.