Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Where do Indiana’s rocks come from?
A short introduction to
sedimentary geology
P. David Polly
Department of Geological Sciences
Indiana University
Bloomington, Indiana 47405 USA
[email protected]
Tidal rhythmites in Mississippian aged carbonates, Monroe
County, Indiana
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Objectives
1. Sedimentary rocks - definitions and sources
2. Siliciclastic versus carbonate
3. Depositional environments
4. Types of siliciclastic rocks (clays, siltstones/shale, sandstones,
conglomerates)
5. Types of carbonate rocks (limestones, dolomites)
6. Rock types in Indiana
7. Denudation and erosion rates
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
The rock cycle
Formation
Weathering
Transport
Deposition
Subduction
Idaho, Joint School Districts 2
http://www.meridianschools.org/MHS/TeachersStaff/MP/
Nawrocki/Pages/Unit2RockCycle.aspx
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Sedimentary rocks
felsic rocks formed by weathering, transport, and
redeposition of existing rock or by biotic precipitation
Sedimentary rocks make up 75% of the surface
of Earth, but only 5% of the crust. They occur
only atop the outermost layers of the crust.
Globally, sediments blanket continents to
average depth of 3km and ocean basins to 300
m.
Include unconsolidated weathering products
(regolith or debris), soils (unconsolidated
material that has been stratified by organisms
and weathering) and lithified rock (cemented by
chemical precipitates into rock).
Sedimentary rocks have the greatest economic
importance of the three primary rock types.
Economically valuable sedimentary rocks
include marble, crushed rock, paving stones,
gravel, brick, lime, building stone.
Sanders Quarry, Salem Limestone, Bloomington Indiana (2006,
Wikimedia)
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Major classes of sedimentary rock
Siliciclastic rocks
•
Composed of silica-rich minerals, mostly formed by
weathering of igneous rocks, deposited by water and air
flow.
•
Typically deposited in rivers, lakes, deltas, or on
continental coasts
•
Siliciclastics weather into terrigenous debris that is
eventually transported to sea.
Devonian aged siliciclastica, Jefferson County, Kentucky
Carbonate Rocks
•
Composed dominantly of calcium carbonate precipitated
by the metabolic actions of organisms, deposited as
organic buildup.
•
Carbonates typically precipitated in shallow marine
waters.
•
Carbonates weather by dissolving, after which streams
carry the ions to the sea where they may reprecipitate.
Mississppian aged carbonates, Monroe County, Indiana
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Depositional environments
places where weathered sediment accumulates or
where carbonates precipitate
Continental – fluvial*, glacial*, desert
Transitional – deltas*, beaches, barrier islands
Marine – tidal flats*, carbonate banks*,
reefs*, continental shelf*, continental
slope, deep-ocean basin
* Important environment for Indiana rocks
Stanley, Earth System Processes
Department of Geological Sciences | Indiana University
Geol G-308
Paleontology and Geology of Indiana
(c) 2012, P. David Polly
Siliciclastics
Silici - with silica
clastic - formed of clasts (fragments)
Originate from material weathered from igneous rock, though
particles may be recycled through several iterations of erosion and
redeposition.
Common clasts include clay, silt, sand, and pebbles. Quartz and clay
minerals are common components.
Classified by dominant particle size
Stanley, Earth System Processes
Department of Geological Sciences | Indiana University
Geol G-308
Paleontology and Geology of Indiana
(c) 2012, P. David Polly
Clast size depends on water flow
The type of siliciclastic rock and its structures therefore provide
evidence for the velocity and energy of past water flows
Hjulström Diagram
Critical velocites required to move grains on plane bed with water depth of 1 meter
Boggs, Principles of Sedimentary Geology
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Take-home message from Hjulström
The larger the particle, the faster the water must be to move it.
The larger the particle, the sooner it drops out of moving water.
As water slows, it drops material in the following order:
1.
2.
3.
4.
5.
Gravel
Sand
Silt
Clay
Dissolved calcium carbonate (reprecipitation depends on factors other
than water flow)
Stanley, Earth System Processes
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Mississippi River Delta
Geol G-308
Paleontology and Geology of Indiana
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Deltaic depositional environments
Sediments include sands, silts, muds
(sometimes carbonates)
Stanley, Earth System Processes
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Sorting of sediments by energy flow
Coastal marine environments
Geol G-308
Paleontology and Geology of Indiana
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Modern deltaic environments
Mississippi River Delta, USA
(the future destination of almost all Indiana rocks)
Google Earth
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Carbonate rocks
Formed primarily of calcite or aragonite,
precipitated from seawater or formed through
the accumulation of skeletal remains of
organisms (shells, corals, etc.)
Carbonates are usually formed in marine,
shallow water, warm environments
Carbonate rocks include:
Limestone, Chalk, Dolomite, Travertine, Oolites
White cliffs of Dover, composed of chalk
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Modern carbonate platforms and banks
Bahama banks
Google Earth
Department of Geological Sciences | Indiana University
Geol G-308
Paleontology and Geology of Indiana
(c) 2012, P. David Polly
Evaporites
Sedimentary rocks that precipitate from evaporating water
Anhydrite and gypsum are the most
abundant. Halite is another example
(natural salt)
Evaporation pools in San Francisco Bay
Dolomite is a carbonate that may
form in evaporitic conditions
US Gypsum Mine, Shoals, Indiana
St. Louis Fm., Mississippian
Google Earth
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Rock types in Indiana
Sandstone - source was weathering of granite or other igneous rock, transport
was by high-energy water or wind, probably represents ancient dune, river
sand bar, or beach
Siltstone – source was weathering of igneous rock, transport was by mediumenergy water or wind, probably represents ancient river floodplain, swamp, or
delta
Shale – source was weathering of igneous rock, transport was by low-energy
water or wind, probably represents marine water below the wave base, farther
from river mouth
Limestone – source was precipitation by organisms, no transport, probably
represents shallow, tropical ocean floor
Dolomite – source was precipitation by organisms and alteration by very warm
temperatures, probably represents shallow ocean floor in very warm,
evaporating climate (or represents metamorphosis of ordinary limestone)
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Dominant lithologies of Indiana’s geological periods
Ordovician - marine silts, sands and carbonates
Silurian - carbonates and dolomites
Devonian - carbonates and marine shales
Mississippian - earlier: deltaic silts and sands, later: carbonates
Pennsylvanian - cycles of silts, sands, coals, carbonates, silts, sands coals
Department of Geological Sciences | Indiana University
Geol G-308
Paleontology and Geology of Indiana
(c) 2012, P. David Polly
Volume of sedimentary rock through the Phanerozoic
Can be used to estimate the rate of loss due to erosion and subduction
Wilkinson, B.H. 2005. Humans as geological agents: a deep
time perspective. Geology, 33: 161-164.
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Denudation rate (erosion) can be
estimated from rate of loss
Average = 24 m/my
Wilkinson, B.H. 2005. Humans as geological agents: a deep
time perspective. Geology, 33: 161-164.
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Geol G-308
Paleontology and Geology of Indiana
Rates of sediment loss in historical times
are two orders of magnitude higher
Soil loss from cleared agricultural land, construction, etc.
Average = 360 m/my
Average = 24 m/my
Wilkinson, B.H. 2005. Humans as geological agents: a deep
time perspective. Geology, 33: 161-164.
Department of Geological Sciences | Indiana University
(c) 2012, P. David Polly
Resources on soil loss in Indiana
Soil erosion in Indiana, Purdue Extension Service
http://www.extension.purdue.edu/extmedia/AY/AY-228.html
No-till and strip tillage
http://www.in.gov/isda/ccsi/notill.htm
Indiana Association of Soil and Water Conservation
Districts
http://www.iaswcd.org
Geol G-308
Paleontology and Geology of Indiana