Chrono,chemo and Dalradian stratigraphy Flashcards
What is required for chronostratigraphy and chemostratigraphy?
Chrono - age of formations
Chemo - reliable chemival data sets for calibration
What is required for chronostratigraphy and chemostratigraphy?
Chrono - age of formations
Chemo - reliable chemival data sets for calibration
What is required for chronostratigraphy and chemostratigraphy?
Chrono - age of formations
Chemo - reliable chemival data sets for calibration
What is the basic age equation?
D = Do + N (e^t - 1)
What are the four ideal conditions for chronostratigraphy?
No daughter in mineral initially
All daughter isotope retained in mineral
Back up of more than one age
Mineral present in a variety of different rock types
What are the advantages of zircon?
No initial Pb Low diffusion rates Host doesn't easily alter Presnt in many rocks Used in two age systems, 235U/207Pb an d238U/206Pb
What is Alvarez’s hypothesis?
Ir anomaly at K-T boundary associated with large meteorite impact
Why is calcite useful in calculating Sr rates?
Contans lots of Sr and no Rb
What do fluctuations in Sr ratio show?
The balance between high continental crust input and low oceanic mantle input. Increase with high river input and decreased mantle volcanism, decrease with low river input and high mantle volcanism.
What is the carbon isotope ratio dictated by?
Biological productivity and organic burial. Organisms take in 12C and 13C rises. When negative C13 then mass extinction
What are the advantages and disadvantages of using carbon isotopes?
Advantages,
Global data base of C13 well constrained for snowball earth
Limestones relatively abundant in Dalradian successions
C13 has a relatively robust geochemical signature
Disadvantages,
Matching peaks and troughs difficult with incomplete sequence
What are the problems and implications of Sr isotopes?
Problems,
Poorly constrained
Poor agreement with apparently reliable chronostratigraphy
Implications, All younger than 800 Ma
Suggest a break in stratigraphy within Argyll Group
What is the basic age equation?
D = Do + N (e^t - 1)
What are the four ideal conditions for chronostratigraphy?
No daughter in mineral initially
All daughter isotope retained in mineral
Back up of more than one age
Mineral present in a variety of different rock types
What are the advantages of zircon?
No initial Pb Low diffusion rates Host doesn't easily alter Presnt in many rocks Used in two age systems, 235U/207Pb an d238U/206Pb
