Lithostratigraphy

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Lithology. The study and description of the physical character of rocks, particularly hand samples and outcropsRefers to the physical characteristics: rock type, color, mineral composition, grain size, lithological characteristics. Historical Principles. Nicolaus StenoDanish Physician1638

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Lithostratigraphy

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1. Lithostratigraphy

2. Lithology The study and description of the physical character of rocks, particularly hand samples and outcrops Refers to the physical characteristics: rock type, color, mineral composition, grain size, lithological characteristics

3. Historical Principles Nicolaus Steno Danish Physician 1638 – 1687 Superposition

4. Steno’s Second Principle Principle of Original Horizontality

5. Steno’s Third Principle Principle of Original Lateral Continuity

6. Steno’s Laws (Principles) Foundation for Stratigraphy

7. Lithostratigraphic units Stratotype – a designated type unit or type section Type section Type locality Lithosome – mass of rock of essentially uniform character and having intertonguing relationships with adjacent masses of different lithology. (lithology)

8. Rock Units Lithostratigraphic units Formation Group Supergroups Member Beds

9. Stratrigraphic relationships Contacts Conformity Unconformity

10. Contacts

11. Conformable contacts Abrupt contacts Gradational contacts Progressive gradual contacts Intercalated contacts – increased number of thin interbeds.

12. Contacts

13. Contacts between laterally adjacent lithosomes Pinch-outs Intertonguing Progressive lateral gradation See Figure 12.1

14. Contacts

15. Unconformity Diastem – little hiatus, little or no erosion, minor depositional break Hiatus – that part of a lacuna that is represented by nondeposition Lacuna Cavity, hole or gap Unrecorded stratigraphic record at an erosion surface, consisting of (a) the record destroyed by erosion = erosional vacuity (b) the record never represented by strata = hiatus

16. Types of Unconformities Angular unconformity Nonconformity Disconformity Paraconformity

17. Nonconformity

18. Angular unconformity

19. Disconformity plus

20. Vertical successions of Strata Cyclic successions Cyclic sedimentation Rhythmic sedimentation – Rhythmites Varves Cyclothems Autocyclic sucessions – controlled by processes within the basin Storm beds, turbidites Allocyclic sucessions – caused by variations external to the depositional basin Changes in climate – eustatic sea level changes Tectonic movement Larger area of influence

21. Allocyclic Succession scales First-order cycles – Eustatic cycles, 200-500 million years Too large to see in normal outcrop, large sets of data and outcrops or subsurface data Major tectonic episodes, construction of Pangea, major continental rifting.

22. Second – order cycles Icehouse states – cool periods Greenhouse states – warm periods, greenhouse gases, CO2 were abundant. Supercycles Transgressive sequences – cratonic sequences. 10 to 100 of millions of years

24. Third-order cycles Episodicities on the order of 1 to 10 million years Regional scales

25. Bed-scale cycles Meter-scale cycles Less than 1 million years, 0.2 to 0.5 million years, 200,000 to 500,000 years Fourth-order scales

26. Fifth-order scales 0.01 to .2 million years 10,000 years to 200,000 years Orbital parameters

27. Milankovitch cycles

28. Orbital Forcing Link between orbital cycles, climate, and sea level Quaternary deposits, back to Miocene

29. Cyclostratigraphy Relationship of strata to the various cyclic sedimentation causes

30. Facies A stratigraphic body as different appearance or composition, general appearance or nature of one part of a rock body as contrasted with other parts. Lithofacies – ss, ls, cong, silt, sh Biofacies – fossil content – no lithology Subfacies – subdivisions of facies Microfacies – thin section facies

31. Law of the correlation (or succession) of facies Walther’s Law

32. Walther’s Principle A conformable vertical sequence of facies was generated by a lateral sequence of environments.

33. Lateral Succession

34. Lithofacies changes Onlap = Transgression Fining upward sequence Offlap = Regression Coarsening upward sequence

35. Sea level changes Eustatic Sea-level changes – world wide sea level changes Relative sea-level – eustatic to regional

36. Mechanisms of sea-level change Ocean steric (thermohaline) volume changes – on the order of 1 m. Glacial accretion and wastage – 1 to 10 m. Liquid water on land – generally less than 1 m. Crustal deformation – 1 to 100 m. Glacial rebound sedimentation

37. Major types of stratigraphic units Lithostratigraphic units Biostratigraphic units Magnetopolarity units Geochronologic units Table 12.3 you can read and know these.

38. Correlation Demonstration of equivalency of stratigraphic units Physical correlation Physical characteristics to match equivalent beds or units Lateral continuity – trace bed or laminae from area to area Lithologic similarity – unique kinds of rocks Sequence of beds – multiple units used by their sequence. Geophysical characteristics – seismic, electrical logs, sonic, radioactive, magnetic properties

39. Correlation Lithocorrelation – similar lithology, stratigraphic position Marker beds, key beds Biocorrelation – fossil content Chronocorrelation - age

40. Correlation

41. Electric logs

42. Electric log

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