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What do geologists mean when they say - Cambrian/Precambrian Boundary problems or Cretaceous/Tertiary boundary problems?

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  • $\begingroup$ Can you please refer with a phrase or something more specific. ? Maybe this kind of problems are focused to find the geo-chronological - boundary. Or focused to study the type of gelogical-discontinuity $\endgroup$ – Paul Goyes Jul 6 '17 at 20:25
  • $\begingroup$ I was reading somewhere that there there is evidence of abundant fossil records in Palaeozoic rocks but the same is absent in Precambrian rocks. This has puzzled geologists and has also created difficulty in demarcating boundary precambrian/cambrian rock formations. $\endgroup$ – Pranav Shekhar Jul 6 '17 at 20:43
  • $\begingroup$ Yes. But according to International commission on stratigraphy www.stratigraphy.org there is a consensus about this boundary. $\endgroup$ – Paul Goyes Jul 6 '17 at 20:52
  • $\begingroup$ Thanks for the link Paul. Are there similar articles for - Permian/Triassic, Cretaceous/Tertiary and Pliocene/Pleistocene? Let me know the link from where I can search them. $\endgroup$ – Pranav Shekhar Jul 6 '17 at 21:08
  • $\begingroup$ @Tbb in this comments is my answer. The person who asked.. already has the answer ! But, should be better if I delete my answer ? But will be deleted all comments ** $\endgroup$ – Paul Goyes Jul 7 '17 at 0:00
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I believe what is being referred to here is the problem of determining where, in a continuous deposition sequence, a particular geologic time transition occurs. If you have uniform depositional conditions you look for a transition in fossil communities that have been agreed on as marking the transition. Life is not so simple and you could have a delta sequence overlaying a deep water deposit. Obviously the geologic aeon does not change everywhere at the contact between clay and sandstone and one must determine where in the clay the line is to be drawn and where in the sandstone. On a larger scale a time boundary that, in the type section, starts or ends at an unconformity needs to be more precisely defined so that correlations across geologic provinces can be made.

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