sediment movement Flashcards
How do sediments change into sedimentary rocks?
- sediments become lifified due to:
- compaction: decrease in rock volume due to weight of overlaing sediment
- cementation: binds grains together with cement (carbonate CaCO3 or silica SiO2)
How are sediments classified?
composition and grain size
composition
- clastic sedimetns made of loose particles (clasts)
- clasts (grains)
- matrix betweenlarge grains
- cement
non-clastic sediments
- made of chemical preciptiaties such as phosphates, evaporties, some carbonates (cant see with the naked eye)
grain size
- use standardized scales
- wentworth scale SEE IN NOTES
- grain size affects the compoation
- clay (very fine grained)
- boulders (coarse grained)
How do sediments move?
- 3 main ways
- transported by water, wind or ice
- 4th way humans (think climate change)
What paleoenvironmental (old/ancient) information can be gained from analysis of sediments/sedimentary rocks?
- energy levels in depostional environment: coarse-grained sedimetns need high energy flow
- distance of transport: coarse grained depostis form close to source area; finer grained sedimetns travelled farther
- grainsize and structures can also indicate: terrestrial, marine, or lacustrine settings
- mudstones, shales often in deep marine
- terrestrial depostis often coarse grained (fluvial sands and gravels)
- may ve associated with features that indicate subaerial exposure (mudcracks, fossil footprints)
- climate: glacial depsoits, eolian deposits (deserst)
what are sediments
- loose solid partiles formed by weathering or erosion of pre existing rock or by chemical precipitation from solution
- eroded to different sizes
- can be larger (pebbles) and small (salt)
what are sedimentary rocks
- 2 main categories
- clastic and non-clastic (chemical)
clastic sedimentary rocks
- made of fragments of pre existing rocks or fossils
- ex. sandstone
non-clastic (chemical) sedimentary rocks
- rocks are made of minerals precipitated from solution
- ex. rock salt (halite)
lithification
- the process (compaction and cementation) that converts loose sediment into sedimentary rock
- takes a long time
why do we need to understand sediments and sediment movement?
- reconstruction of past environmental conditions, past climates, paleogeographies, changes through time
- paleoenvironmental reconstructions
- analyzing the layers can tell us about the climate in the past
- analyze and know about past environment
- ex. reconstruction of west anartic turonian-santonian temperate rainforest
- resource exploration (oil and gas, gypsum, salt, construction materials)
- environmental issues (cosatl erosion, sediment movement, aquifer characteristis)
- need to know about sedients so you know if you have aquifers which are important for storing groundwater
categorizes of wentworth scale
from most to least coarse:
- gravel (conglomerate/breccia)
- sand (sandstone)
- silt (siltstone)
- mud (claystone)
bedload
- grains move in continuous or intermittent contact with the bed
- rolling or jumping (saltation)
- coarse grained sediment
- mostly in streams
- relatively large sediments
- move by alwaystouching bed or jumping
suspended load
- sediment carried in fluid without coming into contact with the bed
- fine grained sediment (silt and clay0
- deposition under low energy conditions
- deep marine environments or very slow streams
bedforms
- totogrpahic features on the bed
- different bedforms develop as current velocities change
Flow velocity: bedform
very low: plane bed (flat)
low: ripples (bumps)
moderate: dunes (bigger, less frequent bumps)
high: plane bed
- can know if high or low by looking at what is above and below it
sedimentary structures
- bedforms are preserved as sedimentary structures
- flat bed= horixontal lamination
- ripple= ripple x-lamination
- dunes = cross bedding
