Dear researcher,
Two rock sequences separated by thousands of kilometers contain no fossils in common. Does this necessarily mean that their ages are different? Why or why not?
Thanks
Abdulrasheed:
As we understand that the two rock sequences separated by thousands of kilometers are fossiliferous and yet contain no common mega- or microfossils, should obviously be of different ages. And yet by examining the order of superposition and index fossils in each sequence one could determine the difference in age.
Best
Syed
Thanks sir. The way I view it is this; since the fossil is used for relative dating, So I am thinking if radiometric dating method which determines absolute age of rock is applied, they may end up having the same age. and the absence of similar fossil may be due to loss in fossil record occasioned by a number of circumstances. In addition, I also think the difference in fossil record may be due to the distance between the sequences which may necessitate different environmental condition that allowed settlement of varying organism. Is my analogy ok sir?
Abdulrasheed:
Since you mentioned fossils, one would think of biostratigraphy. In absence of fossils one could apply a variety of other tools like Cyclostratigraphy, Chronostratigraphy, magnetostratigraphy etc. You may like to consult International Geologic Time Scale for nomenclature of STAGES tied to Absolute ages. Also you need to consult basic text book on principles of Stratigraphy and Correlation of all kinds of rock sequences. Kindly see this link:
http://www.eps.mcgill.ca/~courses/c186-425/stratconcepts.pdf
Best
Syed
If both the sequences separated by thousands of kilometers are fossiliferous but do not contain any common forms, they are likely to be of different ages. However, rock types are important in such cases because differences in fossil assemblages can be due to variations in rock patterns. Depositional environment and taphonomy also have to be considered before coming to any definite conclusions.
The sequences separated by thousands of kilometers are fossiliferous but are of not of same/ similar assemblage is only one of the criteria to assign the age.
The rocks can be also examined in terms of their lithological characters/ structural imprints/ depositional environments/ typical heavy mineral assemblage/ stratigraphic position with reference to associated litho-units. To obtain precise dates you can also go for geochronolgy.
Their depositional loci, i.e., lattitude-longitude specify the proliferation of particular species. This is applicable if they are comparitively of recent geological age, after stabilization of present position of tectonic plates.