School

3. Remember – sands and gravels on outwash plains are sorted and graded! Source: http://uregina.ca/~sauchyn/geog323/342.jpg

6. 3. VARVES These are the vertical stratification of sediments and are found in the bottom of pro-glacial lakes. Sediment carried by meltwater streams is deposited when water enters a pro-glacial lake as the energy of the stream is lost. Meltwater streams vary in discharge seasonally and Varves have alternative sequences of coarser (sand and gravel) and finer (clay and silt) bands. 1. Coarse sediment – deposited in summer (greatest because of fast melting – higher energy – larger material transported) 2. Finer sediment – deposited in winter – little or no coarse sediment washed into lake Each pair of varves represent’s a year’s accumulation (can therefore count varves to calculate age of sediment) Thickness varies (according to weather – can indicate climate change fluctuations) – thicker bands – indicate warmer conditions – more meltwater and more load – if darker – may indicate more organic matter and again therefore warmer conditions.