Transcript Rock Classification

Sedimentary Rock Classification
Rock cycle
What are Sedimentary Rocks?
 What are sediments?
 How do sediments form sedimentary rocks?
 Where do sedimentary rocks form?
General Features
sedimentary rocks
usually come from
SEDIMENTS (mud,
sand, pebbles, etc.)
 sediments are pressed
into layers (strata)

Ernst Tinaja
Big Bend National Park
Ernst Tinaja
Thin-bedded orangish rock =
Del Rio Clay,
 Stratigraphically just below
the Buda Limestone
 The massive white rock
below the Del Rio is the
Santa Elena Limestone
 Time lapse between the
deposition of the Santa
Elena and the Del Rio =
unconformity

Formation
sediment comes from the
weathering and erosion
of other rocks
 wind and water move
sediment

Formation ctd.
 once sediments are settled, lithification (making
a rock) begins
 lithification can involve two main processes:
 compaction: sediments are pressed together by
weight, and water is forced out
 cementation: minerals deposit out of water and
“cement” together sediments
Rock Cycle
Types of Sedimentary Rocks:
1. Clastic
clastic rocks come from
broken pieces of other
rock (as was just
described)
 they are further classified
according to their pieces

Clastic Rocks ctd.
conglomerates have
large, round, pieces (see
last slide)
 breccias have large,
angular pieces
 clastic rocks from smaller
pieces can be
sandstones or mudrocks
 Shale

2. Organic Rocks
form directly or indirectly
from living material
(despite our definition of
minerals)
 example: limestone is
calcium carbonate from
the shells of dead clams
and oysters

3. Chemical Rocks
form by chemical processes
(not regular compaction)
 Limestone:
a. grainstone
b. boundstone
 “evaporites” form when water
evaporates, leaving just
minerals
 ex: gypsum, halite, and even
some limestone are from
evaporating water

FIELD GEOLOGY

Tools of a Geologist
Grain size scale
Roundness scale
Hand lens

Field notebook
Make good observations
and notes
Summary Questions

What might tip you off that you’re looking at a sedimentary rock?

What are two ways that limestone can form?

How are chemical rocks different from other sedimentary rocks?