Transcript Sedimentary Rocks

Sedimentary Rocks
What is a Sedimentary Rock?
• Sedimentary rock is
formed by
– deposition and
consolidation of
sediment and organic
material
– precipitation of minerals
from solution
Where does sediment come from?
• Weathering is the
process that reduces
solid rock to rubble
• Two types
– Physical: solid rock to
rubble without changing
chemical composition
– Chemical: altering or
dissolving minerals in a
rock
Moving Rocks “Au Naturel”
Direction of transport
• Erosion: transportation
of sediment/ions
– streams, wind, glaciers
– super-strong hikers…
• Water is the most
efficient natural
transporter
– ~27 billion tons
annually)
Grain Size and Distance
• It’s the size that counts…
• Sediment far removed from its place of origin
– Small and round
• Sediment close to source
– Larger and angular
Lithification
• Sediment is deposited
in low spots
• Transportation
continues—new
sediment buries older
sediment
– Buried sediment is
compacted (loss of
empty space)
– Cementation—filling in
spaces
Compaction VS. Cementation
Types of Sed. Rocks
• Clastic
– formed from compacted sediment
• Organic
– formed from lithified plant/animal remains
• Chemical
– formed from direct precipitation of ions from
solution
• Bioclastic
– formed from broken shell fragments
Clastic Sed. Rocks
→Increasing Grain Size →
Shale
sandstone
siltstone
conglomerate
Organic Sed. Rocks
• Coal
– Buried and compressed
dead things
From this
To this
…in a matter of eons
Chemical Sed. Rocks
• Water evaporates
leaving behind mineral
deposits (evaporite
deposits)
Great Salt Lake, UT
Death Valley, CA
Bioclastic Sed. Rocks
• Seawater contains
dissolved ions
• Critters use these ions
to make their shells
• When they die, their
shells fall to the ocean
floor where lithification
can take place
coquina
Sedimentary Structures
• Features that develop in sediment during or
shortly after deposition
• Most common types
– Bedding
– Cross-bedding
– Ripple marks
– Mud cracks
Bedding
• Layering in sedimentary
rocks
• Sediment accumulates
layer by layer
Cross-Bedding
• Basically, lithified sand
dunes
Ripple Marks
• Small, parallel ridges
and troughs
• Created by wave and
wind action
Ancient ripples preserved in sandstone→
Modern ripples on a sand dune
Mud Cracks
• Polygonal cracks formed
as mud dries and
shrinks
Modern mud cracks→
Ancient mud cracks in mudstone→