Field Trip 1 - Introduction to the last glaciation, Waterloo Region, Ontario (Canada)

Summary

This virtual field trip explores the Quaternary geology of the Waterloo region, focusing on the last glacial maximum and its impact on the area's stratigraphy. The ice sheet, about 1.5 kilometers thick, caused significant erosion, transporting and depositing a range of materials. The Catfish Creek till, a key marker bed, is introduced as a stiff, over-consolidated glacial deposit. The session further covers the characteristics of this till, including its calcareous matrix and its high content of Canadian Shield-derived clasts. Additionally, the Maryhill till is discussed, revealing how glacial lake sediments were re-entrained during ice re-advances, forming distinct layers.

Takeaways

• 😀 The Waterloo region was fully covered by the Laurentide Ice Sheet during the Last Glacial Maximum (LGM), with the ice being about 1.5 kilometers thick.
• 😀 Glacial erosion, transport, and deposition occurred due to the ice sheet's movement, which deformed under its own weight and eroded materials from the bedrock.
• 😀 The ice flow in the region was primarily southward due to the thickness of the ice, which was not strongly influenced by local topography.
• 😀 Erosional indicators such as striations and grooves on bedrock, as well as the orientation of clasts in sediments, help us determine the direction of ice flow.
• 😀 The Grand River's erosional banks expose various Quaternary units, including the Catfish Creek Till, a key glacial deposit.
• 😀 The Catfish Creek Till is a matrix-supported diamicton, characterized by angular, faceted clasts, and high carbonate content, specifically dolomite.
• 😀 This till is overconsolidated due to the pressure from the thick ice, making it very stiff and difficult to dig into.
• 😀 The Catfish Creek Till is a laterally extensive unit that is generally about 15 meters thick, though it can reach up to 60 meters in some areas.
• 😀 The Catfish Creek Till contains a high percentage of clasts derived from the Canadian Shield, indicating the southward flow of the ice.
• 😀 Younger deglacial sediments, such as glaciolacustrine deposits, are present above the Catfish Creek Till, and these materials tend to have higher clay content.

Q & A

What is the main focus of the virtual field trip described in the transcript?

The main focus of the virtual field trip is the Quaternary stratigraphy of the Waterloo region, specifically looking at the effects of the last glacial maximum and the characteristics of glacial deposits in the area.

What is the significance of the Laurentide Ice Sheet in the context of the field trip?

The Laurentide Ice Sheet was about 1.5 kilometers thick and fully covered the region during the last glacial maximum. Its movement and interaction with the environment, including erosion, transport, and deposition of materials, are key to understanding the geological history of the area.

What are some of the erosional indicators that help determine ice flow direction?

Erosional indicators such as striations on bedrock, grooves, and the orientation of clasts in sediments are used to infer the direction of ice flow during the last glacial maximum.

What is the 'catfish creek till,' and why is it important?

The catfish creek till is a glacial deposit found in the Waterloo region that is characterized by its stiff, over-consolidated nature, making it easily identifiable. It is a significant marker bed due to its distinctive characteristics and lateral continuity.

What causes the over-consolidation of the catfish creek till?

Over-consolidation occurs because the catfish creek till was subjected to the immense weight of the thick Laurentide Ice Sheet, which compressed the material, increasing its density and making it very stiff.

What is a 'matrix-supported diamicton' in the context of glacial deposits?

A matrix-supported diamicton is a type of glacial sediment where the clasts (large particles) are embedded in a matrix of finer material such as clay or silt. In the case of the catfish creek till, the clasts are not touching each other and are suspended in a calcareous matrix.

Why do some clasts in the catfish creek till show faceted and striated features?

Clasts in the catfish creek till show faceted and striated features due to the abrasive action of the moving ice, which grinds the clasts against each other and the bedrock, creating distinctive wear patterns such as faceting and striations.

What does the presence of striations on clasts indicate about their transport history?

The presence of striations on clasts indicates that they were transported by glacial ice, as the striations result from the clasts scraping against other materials or bedrock beneath the ice, a process unique to glacial environments.

How does the composition of the catfish creek till differ from other tills in the region?

The catfish creek till has a higher content of Canadian Shield-derived material, such as granite and gneiss, compared to other tills in the region. It also has a distinctive calcareous matrix with a higher concentration of dolomite.

What is the Maryhill till, and how does it differ from the catfish creek till?

The Maryhill till is a younger, deglacial deposit that is believed to be a mixture of glacial lake sediments and new till re-entrained by ice re-advances. Unlike the catfish creek till, it has a lower clast content and is more clay-rich, forming a massive, class-poor, silty to clayey material.