GEOL 340 Sedimentology and Stratigraphy
Lecture 23
1. Lithostratigraphy Definitions
2. Contacts
3. Vertical and Lateral Successions
Lithostratigraphy Definitions
North American Stratigraphic Code (p. 649-675)
Lithology = all physical and chemical characteristics of a rock
Lithostratigraphy = defining and correlating units of rock based solely on lithology without interpretations of age equivalency and lateral facies changes
Law of Superposition = in an "undisturbed" lithostratigraphic succession, older rocks are at the bottom and are overlain by younger rocks
Stratotype (Type Section) = outcrop exhibiting all the most
common or classic characteristics of a particular lithostratigraphic
sequence
(example = Maastricht, Netherlands, for the Maastrichtian)
Lithosome = masses of rock essentially uniform in character
Lithostratigraphic Units Hierarchy
supergroup
group
formation
member
beds
Names given according to some aspect of the region in which they
are found
Contacts
Contacts = planar or irregular surfaces between lithostratigraphic units
Vertical Contacts (Fig. 13.1, p. 453)
a. conformable contacts
abrupt - most bedding planes represent some small interuption
in deposition
diastems = small breaks in deposition with little or no erosion
gradational - gradual change in lithology
progressive
intercalated
b. hiatus (Fig. 13.5, p. 456)
unconformable = unconformity = surface of erosion or nondeposition
angular unconformity = change in bedding orientation
disconformity = erosional surface parallel to bedding
paraconformity = no discernable contact
nonconformity = sed contact with eroded igneous or metamorphics
Lateral Contacts (Fig. 13.1, p. 453)
a. pinch-out
b. intertonging
c. lateral gradation
Vertical and Lateral Successions
Characterization of Vertical Successions
a. lithologic uniformity
b. lithologic heterogeneity
c. cyclic successions - repetitive orderly arrangement of strata
Cyclic Successions - scales of laminae to whole formations
a. autocyclic (Fig. 13.7, p. 459)
internal driving mechanisms
local effects not widely geographically distributed
examples:
a. delta channel and lobe switching
b. wind and current movement of sediments
c. storm deposits
d. turbidites and slumping
b. allocyclic (Fig. 13.7, p. 459)
external driving mechanisms
wide geographic distributions, regional to global effects
examples:
a. sea level changes
b. climate changes affecting erosion
c. changes in seawater chemistry (i.e. OAE's)
d. orbital forcing and Milankovitch cycles
Relationship of Vertical and Lateral Facies
a. if facies shift laterally, they will lie above adjacent facies
(Fig. 13.12, p. 466)
b. Walther's Law
facies in conformable vertical successions also occurred in laterally
adjacent environments
facies occurring side-by-side can be superimposed atop each other
vertically