Transcript 1. Clastic sedimentary rocks 2. Biogenic rocks a. limestones b. chert c. coal 3. Chemical and evaporite sedimentary rocks.

1. Clastic sedimentary rocks
2. Biogenic rocks
a. limestones
b. chert
c. coal
3. Chemical and evaporite
sedimentary rocks
a. LIMESTONES
Forams are part of the
PLANKTON in the
world's oceans, the
basis for the marine
food chain.
Away from the continental
margins (where the clastics
are dominant), the remains of
forams, called tests, are one
of the principal components
of marine sediments - called
calcareous ooze.
Most forams are in the sand size
category: 0.062 to 2.0 mm across.
CALCITE (CaCO3) is the dominant
mineral in limestones.
Forams from the local
marine "clays"
known as the
Presumpscot
Formation. Betsy
Littlefield '07 worked
on these for her
independent research
project in geology.
The ostracode below
was part of Jamie
Kline's '07 project.
Foram ooze covering basalts
of the Mid-Atlantic Ridge.
Coccoliths are also
calcareous - making
structures from
calcium carbonate.
They are SO SMALL that forams are
giant by comparison. Their remains
(as at right) are smaller than pollen
grains. Imagine, then, how MANY
of them it took to create THESE:
Chalk in the White Cliffs of Dover, United Kingdom
LITHOGRAPHIC
limestone is
particularly finegrained, and is
derived from algal
muds in quiet
lagoons.
Fossiliferous limestone is merely
any limestone with visible fossils,
like this. Much limestone is
made up of remains of shells of
brachiopods or other molluscs.
Coquina is entirely composed
of loosely cemented shell
fragments.
The calcium carbonate in these
fossils can also dissolve and be
recrystallized as calcite cement in
the clastic sedimentary rocks, like
sandstones and conglomerates.
SOME limestones show
some pretty awesome
structure when you
get to see a crosssection. But this also
is key to knowing
their source!
BUT, when you find
coralline limestone
in the Brooks
Range of northern
Alaska, it’s more
than informative!
A slab of Kaibab Limestone
from a quarry in northern
Arizona. The clear
stratification (layering)
makes it obvious that this
piece is standing on end.
The fossil organisms present
in this unit indicate it was
deposited in relatively
shallow water.
ALL of Bermuda, Puerto Rico, the Bahamas and the Yucatan
Peninsula consist of limestone.
Limestone is also widespread in surface rocks of the U.S.A.
The Bahama Bank is comprised almost
entirely of rounded grains of calcium
carbonate, called oolites.
These have
precipitated directly from the sea water
on a "seed grain" and been rounded by
constant wave action rolling them around.
What this yields when
the grains are
cemented together is
an oolitic limestone.
b. Chert
- Chert is made up of crypto-crystalline quartz (SiO2)
- This can form as a chemical precipitate directly from
sea water around volcanic vents on the ocean floor, OR,
more commonly, by recrystallization of remains of
diatoms and radiolaria.
Radiolaria and marine diatoms are throughout the oceans, BUT
commonly masked by the overwhelming dominance of the
forams. In waters below the carbonate compensation depth
(CCD), about 4 km deep, they become of major importance because the carbonates dissolve!
~ 4 km
Cherts & graywackes from the
Golden
Gate
north
into
Oregon provide evidence for a
Jurassic trench.
Distribution of modern marine sediments.
c. coal
Peat
The Everglades of Florida are another modern analog.
Lignite
Drag line mining
Bituminous
(soft) coal
Just to put a little perspective on the size
of that bucket ....
3. Evaporites & Chemical Sedimentary Rocks
- created by either chemical changes in water OR the
evaporation of waters that leave dissolved minerals behind
Tufa towers (freshwater limestone) at Mono Lake, California. The limestone
precipitates as cold, saturated groundwater from the Sierra Nevada enters
the warm water of the lake.
SALTS are left behind as water evaporates. In enclosed
basins, this can yield large quantities of salts (halite and
other water-soluble minerals).
Above, Owens Lake, eastern
California.
Above right, salt
pillars on the shore of the Dead
Sea, Israel. At right, the Devils
Golf Course in Death Valley,
California.
Salts of the Bonneville Salt
Flats in Utah are familiar for
the countless dozens of car
commercials filmed here.