w Sediment Ology
description
Transcript of w Sediment Ology
What is sedimentology?
Sedimentology is the study of the sequence of deposits and the processes thatcause the formation of those deposits. These deposits comprise the uppermostpart of the Earth’s crust.
One of the basic tenets of sedimentology is that newer deposits overlie olderdeposits. Geologists call this superposition.
You can always remove older deposits, but the deposits that remain alwaysremain in the order that were produced.
The pattern of deposits and its order is sometimes called stratigraphy.
New
OldOlderOldest
Ground surface
How do you tell the difference between deposits?
- Grain-size distribution
- Stratification
- Lithology
- Radioisotopes
- Magnetism
Common stratigraphy found in theuppermost sediments of the Puget Sound
Soil
Till
Clean sand
Clay
“Bedrock”
20,000-25,000 yearsago
Formation of the Lawton Clay
Glacier
Shallowglacial
lake
Glacier
Shallowglacial
lake
Drainage to Grays Harbor
20,000-18,000 yearsbefore presentFormation of theEsperance Sand
Outwash at an advancing glacial front
~18,000 years ago
Formation of the Vashon Till
Glacier
Glacier
Freshwaterlake
18000-16000 yearsbefore present
Glacial retreat - no deposits
The last ~6000 years
Modern conditions
15000-6000 years agoGlacial rebound and sea-level rise
Beaches or “the nearshore” can be divided into two broad categories
Constructionalsand/material comes from elsewhere
Degradationalmaterial is removed
What does this mean for the shoreline?
beach beach
old surface
waterlevel
waterlevel
The most common result...
Foreshore, or “beach face”, covered mostlywith loose gravel
Some sand andremnant cobbles on
low-tide terrace
Receding bluff
In deep water drape of sandand mud OR exposed
till/bedrock
low-tide line(MLLW)
Material removedby wave action
Post-glacial surface
Bluff face comprised of till