Quaternary glacial and periglacial geology (Component 3 option): glacial and periglacial processes and their deposits and landforms (till, moraines, drumlins, eskers, outwash, periglacial features); the evidence for Quaternary climate change (glacial-interglacial cycles, oxygen isotopes, ice cores); sea-level change; and the methods used to date and reconstruct Quaternary environments.

What this dot point is asking

This is one of the Component 3 option themes. Eduqas wants you to describe glacial and periglacial processes and their deposits and landforms (till, moraines, drumlins, eskers, outwash, periglacial features), to set out the evidence for Quaternary climate change (glacial-interglacial cycles, oxygen isotopes, ice cores), to explain sea-level change, and to describe the methods used to date and reconstruct Quaternary environments. It applies the palaeoenvironment and dating skills to the most recent slice of geological time.

The answer

Glacial processes and deposits

Glaciers erode, transport and deposit material. The processes are abrasion (debris in the ice scratches the bedrock, producing striations and smoothed surfaces) and plucking (ice freezes onto and pulls away blocks of rock).

The deposits and landforms include:

• Till (boulder clay): material deposited directly by ice, so it is poorly sorted (clay to boulders mixed), unstratified, with angular, striated clasts and erratics (far-travelled rock types). Lithified till is a tillite.
• Moraines: ridges of till marking the position of the ice (terminal, lateral, medial and ground moraine).
• Drumlins: streamlined hills of till, elongated in the direction of ice flow (steep, blunt up-ice end; gentle, tapering down-ice end).
• Erratics: large clasts carried far from their source, used to trace ice movement.

Periglacial processes and features

Periglacial conditions occur near, but beyond, the ice, in cold ground with permafrost:

• Frost shattering (freeze-thaw) produces angular scree and blockfields.
• Patterned ground and ice wedges form by repeated freezing; relict ice-wedge casts in older rocks are evidence of past permafrost.
• Solifluction (the slow downslope flow of waterlogged, thawed surface soil over frozen ground) produces sheets of poorly sorted material.

Fluvioglacial (meltwater) deposits

Meltwater reworks glacial debris, giving sorted, stratified, rounded deposits, the opposite of till:

• Outwash (sandur): sorted, bedded sand and gravel deposited by braided meltwater streams beyond the ice.
• Eskers: sinuous ridges of sorted sand and gravel deposited in tunnels beneath the ice.
• Kames and kettle holes: mounds of sorted debris and hollows left by buried melting ice.

The sorting, stratification and clast roundness distinguish all of these from till.

Evidence for Quaternary climate change

The Quaternary (the last roughly 2.6 million years) was dominated by repeated glacial-interglacial cycles. The key evidence:

• Oxygen isotopes. The light isotope $^{16}\mathrm{O}$ evaporates preferentially and is locked into ice during glacials, enriching the oceans in $^{18}\mathrm{O}$. The $^{18}\mathrm{O}/^{16}\mathrm{O}$ ratio in foraminifera shells in deep-sea cores and in ice cores therefore tracks global ice volume and temperature, showing the cyclic pattern.
• Ice cores also trap air bubbles, giving a direct record of past atmospheric carbon dioxide.
• Glacial and periglacial deposits (tills, ice-wedge casts) in the rock record mark past cold stages.

Sea-level change and dating

During glacials, water is locked up in ice, so global (eustatic) sea level falls; during interglacials it rises. Locally, the crust depressed by ice rebounds after melting (isostatic recovery), producing raised beaches. Quaternary environments are dated and reconstructed by radiocarbon dating (organic material within range), oxygen-isotope stratigraphy (matching cores to the global record), varve counting (annual lake layers), and the relative stratigraphy of tills and interglacial deposits.

Examples in context

Example 1. The drumlin fields of northern Britain. Swarms of streamlined till hills record the direction of ice flow during the last glaciation, their steep ends facing up-ice and tapering ends pointing the way the ice moved.

Example 2. Raised beaches of western Scotland. Former shorelines now stranded above sea level record isostatic rebound of the crust after the heavy ice sheet melted, a direct record of post-glacial uplift.

Try this

Q1. State three characteristics of glacial till. [3 marks]

• Cue. Any three of: poorly sorted; unstratified (no bedding); angular clasts; striated clasts; contains erratics.

Q2. Explain how a drumlin indicates the direction of ice flow. [2 marks]

• Cue. A drumlin is streamlined, with a steep blunt end facing up-ice and a gently tapering end pointing down-ice, so its long axis and shape record the flow direction.

Q3. State what a high $^{18}\mathrm{O}/^{16}\mathrm{O}$ ratio in foraminifera shells indicates about climate. [2 marks]

• Cue. A glacial (colder) stage with large ice volume, because the light oxygen-16 is locked into the ice, enriching the ocean in oxygen-18.