LAB#4

To Determine the Relative Dating Of Given Geologic Sequence

OBJECTIVE:

To study lithological changes of a given area

RELATED THEORY:

Geological Time:

The geological time scale (GTS) is a system of chronological measurement that relates stratigraphy to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships between events that have occurred throughout Earth’s history. The table of geologic time spans presented here agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy

Absolute Dating:

Absolute dating is the process of determining an age on a specified time scale in geology. In geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young (radiocarbon dating with 14 C) to systems such as uranium-lead dating that allow acquisition of absolute ages for some of the oldest rocks on earth.

Relative Dating:

Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age, (i.e. estimated age). In geology rock or superficial deposits, fossils and lithology’s can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating which provided a means of absolute dating in the early 20th century, geologists were largely limited to the use of relative dating techniques to determine the age of geological events.

Though relative dating can only determine the sequential order in which a series of events occurred, not when they occur, it remains a useful technique especially in materials lacking radioactive isotopes

Principles of Relative Dating:

Original horizontalityThe principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal)

SuperpositionThe law of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. This is because it is not possible for a younger layer to slip beneath a layer previously deposited.

Faunal successionThe principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found.

Lateral continuityThe principle of lateral continuity states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.

Inclusions and componentsThe principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them.

Cross-cutting relationshipsThe principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault

Intrusive relationshipsThe principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock

Relative Dating Of Different Structures

Sequence of events:

Figure 1

Deposition of E,H,C,F,B Intrusion A Fault D Erosion G

Figure 1

Figure 2

Deposition of E,A, G Folding Intrusion F, Erosion of G Deposition of I Deposition D,H,B Intrusion C Erosion B

Figure 2

Figure 3

Deposition of F,P, Joint G Erosion of f,p Deposition of B,R Intrusion m Deposition of H,A Erosion Deposition of E,X Deposition of D, Fault K Erosion D,X Deposition of S,j Erosion of S,j

Figure 3

Figure 4

Deposition of V Joint C Erosion of C Deposition of O,M Folding of O,M Deposition of X Fault K Intrusion E Erosion of X Deposition of B Intrusion S Erosion of B, Deposition of z,J,G Figure 4 Erosion of J,G,B Deposition of L,F Fracture T Intrusion A Erosion of F, Deposition of H,D Fault P

REFERENCES:

http://en.wikipedia.org/wiki/Relative_dating http://en.wikipedia.org/wiki/absolute_dating

Figure 4