Previous to this, on the great plains, were millions and millions and of years of deposition of marine sediment still visible in parts of river valley's in Southern Alberta. The rise of the Rocky Mountains, caused the marine sediments to be somewhat evenly blanketed over Southern Alberta. Over millions of years, approximately 30-35 million years (30 million to 35 million years ago), is a period of great accumulation of terrestrial sediment of from the newly formed rivers of the Rocky Mountains. These rivers deposited vast amounts of their erosionary products over the great plains.Information about what landscape looked like in the Tertiary area can be deduced from gas and logs, even though most of the bedrock is buried deep under glacial sediments. The tertiary landscape is believed to have been a rolling one, which would later be flattened by the Laurentide ice sheets some 1 million to 10,000 years ago; where numerous glacial advances advances and retreats laid down up to 100 meters of various till and lacustrine deposits, and flatened the prarrie landscape. Meltwater at the end of this glaciation, known as the Wisconsin Glaciation, would forge out the coulee landscape which have become the typical Southern Alberta landscape in so many minds.If you ever travel along the Oldman River, and especially in places where banks have been exposed by various types of erosion, you can see the past 1.2 million years of history of deposition along the Oldman River. Strata, or layers, have been forming here in great abundance since the Quaternary period of the earths history. However, to generalize the stratigraphy over the entire region of the Oldman River would be difficult. Geologists have combed through the strata to make some generalizations about the formation, and types of strata in this region.One of these types is called mega blocks.
Mega Blocks
A mega block near west Lethbridge Alberta. When looking closely at it. There is what appears to be a white band in the rocks.
The Oldman Valley, at Lethbridge, contains a number of quite visible glacial landforms. None, are perhaps more visible then those of mega blocks. Looking at it you see the light grey slab of sandstone bedrock, sandwiched between the tills. This particular landform is called the Laundry Hill mega block. Mega blocks, are an unusual feature. The Laundry Hill mega block, was sandstone, from the exposed Oldman Formation northwest of the city and transported south to this location by glaciers. It was then dislodged as the glacier approached the valley. Geomorpholigists, such as Renee Barendregt, suggest that the mega block on Laundry Hill, may have been 1 square kilometer in size. Mega blocks are essentially formed when glaciers are able to dig large slabs of bedrock, and transport them to new locations.
To claim your find, you must E-mail (not post) the cache owner the answers to the following questions. You should submit your answers at the same time as your log, if not before. Failure to do so will cause your log to be deleted.
1. Estimate the length and height at the widest point of the bedrock layer formed.
2. There are also the same formation to the north along the coulee hill, how many other mega block forms do you do you see and what is your best estimated guess of the length and height of those?
3. Post of picture of yourself or you GPSr in front of the mega block at the posted coordinates. This is not necessary for the log.