Landforms and Sediments Flashcards
What are the two principles concerning sedimentary and landform evidence?
- Inactive forms vs active forms (relict/fossil vs modern analogues and relict proxies).
- Sequences indicating system behaviour changes.
What key questions do we ask when using landform proxies?
- What controls landform ‘activity’/development?: Climate parameters, tectonic adjustment, human, precip-temp interaction.
- Can we be sure a landform is ‘fossil’?: issues of episodic activity, changes in activity state.
- Is the sequence fully preserved?
What makes fossil/relict landform systems a good data source?
- Correct identification of activity/inactivity.
- Dating to ascertain timing of development.
- Understanding of process controls on development.
Example of an obvious relict landform:
Shoreline not at the waters edge.
Glacial moraine with no adjacent ice, or valley/corrie with no ice.
Example of a hard to identify relict landform
Sand dunes: an active dune may have defined ridges, lack of vegetation and a 32 degree slope.
What change to lake shorelines indicate?
These are widely used as indicators of hydrological change. The lakes need to be closed basins so they are sensitive to input changes.
How do we build up a regional picture from lake status studies?
Use lake shorelines to assess how full lakes have been for the last 30,000 years. (Low, intermediate or high depth). Track these changes for many lakes in a region for a period of time to see how the overall picture changes.
Street-Perrott (1983)
Did a regional lake status study of SW USA. Found in recent times (last 6-7,000 years) has been very dry, yet 21,000 ya (LGM) the majority of lakes were completely full or intermediately full.
What might cause changes in lake levels?
- Precipitation change
- Temperature changes via precipitaiton/evaporation change.
- Non climate factors?
What might cause changes in river cross-section through time?
- Could be changes in precipitation?
- Could be changing base level via tectonic uplift
- Could be base level change via sea level change?
These different processes may result in the same change in the river… so we can only know the right cause if we look at other information sources, and dating river change events.
How can systems form landform sequences?
Some systems, e.g. glaciers, at any given time produce spatially variable landforms.
For glaciers we cannot expect to find abundant landforms everywhere as some zones will always be eroding and some always depositing.
Sequences are far more powerful than individual landforms for understanding landform producing processes.
What is an abiotic sediment?
A mineral sediment without any organic component.
E.g. Geikie, 1860, identified stratigraphic relations of till in Scotland, deducing it must have been glacial in the past.
What is a biotic sediment?
An organis sediment, containing plant, animal or pollen remains.
E.g. Emiliani revolutionized Quaternary science by understanding biotic ocean cores link to glacial cycles and could date them.
What can we learn from stratigraphic change within sediments?
Stratigraphic change can indicate changes in processes over time at a location. It could also be a natural sequence of change associated with one event or climate change.
What differences in characteristics are found between different fluid transport processes?
- Different particle sizes
- Different particle shapes
- Different grain surface textures
- Different depositional sedimentary structures.
- The potential to fingerprint sediments to their mode of deposition.
