1. CORRELATION OF LITHOSTRATIGRAPHIC UNITS

2. I) Intro A. Correlation--shows units are equivalent, or match 1. thought to represent similar geologic age in past 2. equivalency by lithology, paleontology, chronology 3. must identify nature of correlation B. Correlation--important in strat reconstruction 1. to understand facies relationship C. Attributes for correlation: 1. lithologic homogeneity & constancy 2. heavy mineral, trace elements, seismic velocity 3. do not have to correlate with time 4. marker-defined--e.g. key beds in monotonous strata i. could be l.s., bentonite, ss in shale

3. Simplified Lithostratigraphic Correlation Blue Ridge Mtn Geology

4. More Lithostratigraphic Correlations

5. Correlation Across Texas

6. II) Methods A. Many methods 1. choice depends on nature of problem B. measure several sections in loop 1.called closed correlation traverse C. Tracing lateral continuity 1. map strat units from outcrop to outcrop 2. = walking out unit 3. contacts well-defined 4. best where have good exposure or use aerial photographs D. lithologic identity 1. identify key characteristics in rocks i. color, weathering pattern, bedding, thickness, mineralogy, sed structures 2. finer detail--use IC5 attributes 3. use anything observable to distinguish unit 4. fossils i. esp. rk units composed of fossil frag--independent of time ii. may be identified by assemblage zones

7. II Methods Continued E. Position in sequence 1, must establish strat succession 2. unit may not be litho distinct--strat succession may be only satisfactory method 3. Example-- 3 similar l.s i. L.s. 1--shale below/ss above ii. L.s. 2--dolomite below/red bed above 4. more difficult in cyclothems i. e.g. Perm cyclothem ii. cyclical sequence=similar lith successions F. Structural relationships 1. Sequential position relative to unconformity, folds, faults, etc 2. not observable over broad area

8. Lateral Tracing of Units

9. Several Sections in Loop

10. Tracing lateral continuity Kansas limestones

11. lithologic identity

12. Position in sequence

13. Position in Sequence

14. Problem—cyclical sequence Figure 3: The Milroy Member of the Middle Ordovician Loysburg Formation (Mark Patzkowsky for scale, lower right). Four of the six measured carbonate cycles are visible and their tops are delineated with dashed lines. The darker rock is the subtidal facies; the lighter rock is the intertidal facies. Cycle thicknesses are greater at the base and thinner in the middle. Located at intersection of Rt. 322 and Rt. 26, State College, Pa.. hydro.geosc.psu.eduhydro.geosc.psu.edu

15. Structural Relationships Rim of the Grand Canyon. Horizontal Tapeats Sandstone overlie tilted Grand Canyon Supergroup Lower portion of Canyon Sin Nombre, Carrizo Plains www.geoepicenter.comwww.geoepicenter.com

16. How do we establish correlation or equivalency of units?

17. Dealing With Removal of Section

18. Dealing With Changes in Thickness

19. Procedures for Extending Lithostratigraphic Units-Lithostratigraphic Correlation A lithostratigraphic unit and its boundaries are extended away from the type section or type locality only as far as the diagnostic lithologic properties on which the unit is based may be identified. 1. Use of indirect evidence for identification of units and their boundaries. Where lithologic identity is difficult to determine because of poor or no outcrops, a lithostratigraphic unit and its boundaries may be identified and correlated on the basis of indirect evidence: geomorphic expression, wire-line logs, seismic reflections, distinctive vegetation, etc. 2. Marker beds used as boundaries. The top or the base of a marker bed may be used as a boundary for a formal lithostratigraphic unit where the marker bed occurs at or near a recognizable vertical change in lithology.