I. Strike and dip
B. Dip
click here to see strike and dip
II. Folded structures
1. Anticline
·
is a series of up-arched strata with side portions (limbs)
dipping in opposite directions away from the central portion of fold split by a
plane called the axial plane and observed in the top (plan) view as the fold
axis--an eroded surface indicates the rocks become progressively younger away
from the fold axis
·
click here to see the parts of
an anticline ----
·
click here to see a photo of an anticline
·
is a series of down-arched strata with limbs dipping inwards
in opposite directions towards the fold axis--an eroded surface indicates the
rocks become progressively older away from the fold axis
·
click here to see a photo of a
syncline --- see pages 417-419
in the text for more examples of anticlines and synclines
B. Specific types of anticlines and synclines---see
page 418 in text
1. Symmetrical fold--is a fold with
the sides showing a mirror image with respect to the axial plane
2. Asymmetrical fold--a fold without
a mirror image in respect to the axial plane
3. Overturned fold--a fold in which
the axial plane is tilted and beds may dip in same direction on both sides of
the axial plane
click here to see symmetrical, asymmetrical, and overturned
folds
4. Recumbent fold--a fold with the
axial plane horizontal
·
click here to see a photo of
a recumbent fold
5. non-plunging and plunging folds
·
plunging is the tilting of the fold towards the front or
back end--all anticlines and synclines have some degree of plunge
·
in non-plunging folds contact lines separating formations
shown in the surface view are parallel and straight---the contact lines in one
of the two profile views are horizontal and parallel---the contacts in the
other profile view are arched up or down--in plunging folds contact lines in
the surface view are curved---contact lines in one of the profile views dip in
the direction of plunge---contact lines in the other profile view are arched up
or down--the surface contact lines between formations are convexed
(closed) in the direction of plunge for the anticline and concave (open) in the
direction of plunge for the syncline
6. formation and
location of petroleum and natural gas is associated with anticlines and
synclines— see page 529 in text to see
this
click here to see the formation contacts of plunging
anticlines and synclines
3. Dome
·
is an up-arched series of strata with beds on all sides
dipping away from the center throughout 360 degrees--an eroded surface
indicates the rocks become progressively younger away from the center of the
structure
4. Basin
·
is a down-arched series of strata with beds on all sides
dipping in towards the center throughout 360 degrees--an eroded surface
indicates the rocks become progressively older away from the center of the
structure
click here to see a dome and basin ---
see page 420 to see another example
of a dome and basin
5. Monocline
·
is a bend in the strata resulting in a local steepening in
dip of the strata which is almost flat lying on both sides away from the bend--
there is only one direction of dip in the monocline
·
click here to see the monocline
– see another example on page 421 in
text
III. Fault structures
A. Definition
B. Types of faults
1. Vertical or dip slip fault
·
is that type with movement along the dip of the fault--the
concepts of hanging wall and footwall are important in defining the different
types of vertical faults
·
if the angle of dip is not 90 degrees the side of the fault
with the portion of land which appears to be hanging over a lower portion
before movement is called the hanging wall and that on the bottom, the footwall
·
see
below
·
·
Normal fault--hanging wall moves down in respect to footwall
·
Reverse fault--hanging wall moves up in respect to
footwall--a low angled reverse fault is called a thrust fault
click
here to see hanging wall-footwall related to normal and reverse faults
or see page
422 at bottom in text
click
here to see a photo of a normal fault
·
Horst and graben--a wedge of land
which moves up (horst) or down (graben) between 2
normal faults--best example is the Rhine River Graben
in Europe
·
click here to see a horst and graben—
see middle of page 423 for another
example of a horst and graben
2.
Horizontal or strike slip fault
·
is that type with horizontal movement along the cracked
rock--movement can be left lateral or right lateral--best example of right
lateral strike slip fault is the San Andreas fault in California--looking down
the fault line in the front plan view, the right side of the fault appears to
have moved towards you if a right lateral fault or left side moves towards you
if a left lateral fault
·
click here to see a right
lateral strike slip fault --- see
page 422 at bottom in text for an example of a right lateral strike slip fault
and page 424
3. Oblique fault
·
is a fault which has a major dip slip and strike slip
component
IV. Joint structures
A. Definition of joints
B. Causes of joints
1. Unloading or sheeting effects
(see Weathering)
2. Stresses in a cooling magma
·
can cause columnar jointing in which there are 6-sided
fractures comprising the jointing pattern--best example is Devil's Tower,
Wyoming
·
click here to see a photo of
Devil's Tower --- see
another picture of columnar jointing on page 83 of text
V. Unconformity structures
A. Definition
·
a series of sedimentary rocks form, next a non-deposition or
massive erosion event occurs, then a series of more sedimentary rocks are
deposited
·
a series of sedimentary rocks form, next rocks are folded or
tilted, next a non-deposition or massive erosion occurs, then a series of more
sedimentary rocks form
·
igneous or metamorphic rock form, next a non-deposition or
massive erosion event occurs, then a series of sedimentary rocks form
·
click here to see a photo of
a nonconformity
VI. Importance of geologic structures
357 click to
return
page 359
click to return
page 363
click to return
page 362
click to return
page 360
click to return
anticline
click to return
syncline
click to return
recumbent fold
click to return
page 361
click to return
page 365
click to return
page 364
click to return
page 365
click to return
page 368
click to return
page 369
click to return
disconformity
click to return
angular unconformity
click to return
nonconformity
click to return
unconformities
click to return