Transcript Lecture 11 / Sedimentary Rocks

Sedimentary Rocks
& Processes
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Sedimentary
Rocks
Sedimentary
Rocks
Sedimentary Structures
 Features that form when sediment
is deposited
 Can provide important clues in
sedimentary rocks
Sedimentary
Rocks
Sedimentary Structures
Bedding
 Water-laid sediments are originally deposited in horizontal
layers (beds)
 Bedding = layering in sedimentary rocks
bedding forming today
bedding in rocks
Sedimentary
Rocks
Sedimentary Structures
Graded Bedding
 A bed with particles that decrease in size upwards
> Represents waning flow after a flood event
Sedimentary
Rocks
Sedimentary Structures
Graded Bedding
How do graded beds form?
Sedimentary
Rocks
Sedimentary Structures
Ripple Marks
 Small ridges in sand/mud formed by currents (wind or water)
 Asymmetrical ripples are useful in
telling current direction
currents forming ripple marks
in sand today
ripple marks in sandstone
(ancient currents)
Sedimentary
Rocks
Sedimentary Structures
Cross Bedding
 Tilted layers within a single bed
 Represent the cross section of ancient
sand dunes
 Useful in telling current direction &
“up” direction
bed
Sedimentary
Rocks
Sedimentary Structures
Cross Bedding
How do cross beds form?
Sedimentary
Rocks
Sedimentary Structures
Cross Bedding
cross bedding forming in a sand dune today
cross bedding in sandstone
(ancient sand dunes)
Sedimentary
Rocks
Sedimentary Structures
Desiccation Cracks (Mud Cracks)
 Wet, fine-grained sediment is exposed to air, dries, & shrinks
desiccation cracks forming in mud today
desiccation cracks in mudstone
(ancient mud cracks)
Sedimentary
Rocks
Sedimentary Structures
Trace Fossils
 Tracks, trails, burrows - Reworking of soft sediment by
organisms
 Can describe critters & their movement and behavior
Sedimentary
Rocks
Depositional Environments
continental
transitional
marine
Sedimentary
Rocks
Depositional Environments
Sedimentary
Rocks
Turning Sediment Into Rock
 Lithification – Compaction & cementation after deposition
sediment
sedimentary
rock
Turning Sediment Into Rock
sediment
gravel
carbonate
mud
conglomerate
limestone
Clastic texture (made of pieces)
Chemical texture (crystalline)
sedimentary rock
Sedimentary
Rocks
Sedimentary
Rocks
Sedimentary Rocks
Sedimentary
Rocks
Sedimentary Rocks
Clastic Rocks
Gravel-sized pieces
Sedimentary breccia
Conglomerate
Sedimentary
Rocks
Sedimentary Rocks
Clastic Rocks
Sand-sized pieces
Sandstone
Quartz Sandstone
(“clean”)
Arkose
(“dirty”)
Graywacke
Sedimentary
Rocks
Sedimentary Rocks
Clastic Rocks
Mud-sized pieces
Mudstone (Siltstone, Shale)
Sedimentary
Rocks
Sedimentary Rocks
Chemical Rocks
Carbonate rocks (CaCO3)
Limestone, Dolomite
Sedimentary
Rocks
Sedimentary Rocks
Chemical Rocks
Chert (SiO2)
Sedimentary
Rocks
Sedimentary Rocks
Chemical Rocks
Evaporites
Rock gypsum, Rock salt
Sedimentary
Rocks
Sedimentary Rocks
Biochemical Rocks
Coal
 Unoxidized, organic-rich (carbon) remains of plant material
Sedimentary
Rocks
Interpreting Sedimentary Rocks
River Flood Plain
 Common “flood plain” rocks = mudstone, sandstone
>
Ripple marks, graded beds, mud cracks, abundant land plant
& critter fossils
>
Interpretation: low-energy deposition in shallow water, floods,
exposed to the atmosphere
Sedimentary
Rocks
Interpreting Sedimentary Rocks
River Flood Plain
 Example of a “flood plain” rock formation:
Permian Hermit Formation
(Grand Canyon)
Sedimentary
Rocks
Interpreting Sedimentary Rocks
Sand Dunes
 Common “sand dune” rocks = quartz sandstone
>
X-beds, ripple marks, sparse critter trace fossils
>
Interpretation: wind deposited dunes (desert or beach)
Sedimentary
Rocks
Interpreting Sedimentary Rocks
Sand Dune
 Example of a “sand dune” rock formation:
Permian Coconino Sandstone
(Grand Canyon)
Sedimentary
Rocks
Interpreting Sedimentary Rocks
Shallow Marine
 Common “shallow marine” rocks = limestone, sandstone, mudstone
>
X-beds, ripple marks, graded beds, marine fossils
>
Interpretation: mostly low-energy deposition in a shallow
(0-135 m) ocean
Sedimentary
Rocks
Interpreting Sedimentary Rocks
Shallow Marine
 Example of “shallow marine” rock formations:
Cambrian
Muav Limestone
Mississippian
Redwall Limestone
Permian
Kaibab Limestone
Sedimentary
Rocks
WWW Links in this Lecture
> Bedding - http://en.wikipedia.org/wiki/Bed_%28geology%29
> Graded bedding - http://en.wikipedia.org/wiki/Graded_bedding
> Ripple marks - http://en.wikipedia.org/wiki/Ripple_marks
> Cross-bedding - http://en.wikipedia.org/wiki/Cross-bedding
> Trace fossil - http://en.wikipedia.org/wiki/Trace_fossil
> Depositional environment - http://en.wikipedia.org/wiki/Sedimentary_depositional_environment
> Lithification - http://en.wikipedia.org/wiki/Lithification
> Sedimentary breccia - http://en.wikipedia.org/wiki/Clastic_rock#Sedimentary_breccias
> Conglomerate - http://en.wikipedia.org/wiki/Conglomerate_%28geology%29
> Sandstone - http://en.wikipedia.org/wiki/Sandstone
> Arkose - http://en.wikipedia.org/wiki/Arkose
> Graywacke - http://en.wikipedia.org/wiki/Greywacke
> Mudstone - http://en.wikipedia.org/wiki/Mudstone
> Carbonate rock - http://en.wikipedia.org/wiki/Carbonate_rock
> Limestone - http://en.wikipedia.org/wiki/Limestone
> Dolostone - http://en.wikipedia.org/wiki/Dolomite
> Chert - http://en.wikipedia.org/wiki/Chert
> Evaporite - http://en.wikipedia.org/wiki/Evaporite
> Coal - http://en.wikipedia.org/wiki/Coal