GEOL 340 Sedimentology and Stratigraphy
Lecture 24
1. Lithocorrelations
2. Well Logs
3. Seismic Reflections
4. Sequence Stratigraphy
Lithocorrelations
Correlating rocks based on lithology type and stratigraphic
positioning
Hang correlation on marker beds
(Fig. 13.16, p. 476)
Colorado Plateau example (Fig. 13.19, p. 479)
Well Logs
Measure physical and chemical properties of lithologies by lowering instrumentation into well (Fig. 13.20, p. 480)
Measure electric, gamma, sonic, and many other parameters (Fig. 13.22, p. 483)
Example of St. Genevieve in southern Illinois and use of Landmark software (show figure)
Seismic Reflections
Mechanism
a. artificial propagation of seismic (elastic) waves (Fig.
14.1, p. 488)
b. reflected back to surface at discontinuities
c. velocities = 2 km/sec (some sediments) to 8 km/sec (ultramafics)
d. knowing the velocity allows calculation of the depth of the
reflector
e. first studied in 1848 by Robert Malletin England
f. variable-density mode display
Reflection Geometries
a. Rich (1951) (Fig. 14.7, p. 495)
undaform platform top
clinoform platform margin
fondaform - basin
b. reflection categories (Fig. 14.4 14.6, p. 492-494)
Sequence Stratigraphy
Depositional Sequence of Sloss (1963)
a. Definition: rock stratigraphic units of higher rank than
group, megagroup or supergroup, traceable over major areas of
continent and bounded by unconformities of interregional scope
b. Sloss (1963) figure
c. types of stratigraphic charts
- lateral distance versus rock thickness
- lateral distance versus time (Wheeler, 1958)
Depositional Sequence of Vail and Exxon
a. Definition: a stratigraphic unit composed of a relatively conformable
succession of genetically related strata that is bounded at it's
top and base by unconformities or their correlative conformities
(smaller rock units than Sloss' definition)
b. Mitchum et al. (1977)
c. Vail was a graduate student of Sloss', and studied seismic
reflection data
d. Exxon global cycle chart
Seismic Sequence Stratigraphy
a. based on concept that seismic reflections parallel bedding
planes, which are of chronostratigraphic significance
b. assumes that all strata within a depositional sequence were
deposited within the same given interval of time
c. diachronous = time lines cross bedding planes, equivalent lithologies
not age equivalent
d. development permitted
- ability to define of complex basin stratal architecture
- ability to identify, map, and correlate unconformities over
great distances