Philip Bruce Heywood
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- Jul 8, 2020
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I've never heard this, have you got a source?
Greetings, Kylie, The Cambrian system is standout remarkable and unique in many ways. As in some ways are the strata immediately underlaying it.
I quickly grabbed something off the 'net which although decades old as far as I know has not been altogether superseded by new information. To obtain believable radiometric dates from that far back requires volcanics and the volcanic deposit to be useful must be in a stratigraphic configuration which results in the date having meaning for other strata of the system. Below, we learn that in 2005 the only likely certainty age-wise was the absolute top and bottom of the system. I have not heard of that changing but it may have done so.
The remarkable shales in which are preserved even brains and eyes, are rare geologic features -- excepting in the Cambrian. Which to my knowledge can not at this stage be radiometrically dated. Cambrian 'explosion'? Time scale? Close the eyes and make a stab?
Hughes and Heim, 2005, Encycloepedia of Geology. Quote:
"The Namibian sequence, which has the best paleontological constraints, suggests an age close to 540 Ma for base of the Cambrian, whereas the Oman sequence, which probably has better radiometric control, suggests 541 Ma. The two ages overlap in their uncertainty brackets, indicating good control on the age of this important stratigraphic boundary. Bowring and Schmitz (2003) regarded the Oman data as providing the best constraints on the age of the boundary. Pending further information, we regard 541.0 ± 0.63 Ma to be the maximum age for the Ediacaran/Cambrian boundary and for the base of the Paleozoic and Phanerozoic. The difference between the age of the top of the Cambrian Period (i.e. of the beginning of the Ordovician) at 485.4 Ma, and the bottom, 541.0 Ma, gives 55.6 myr for the duration of the period."
Greetings, Kylie, The Cambrian system is standout remarkable and unique in many ways. As in some ways are the strata immediately underlaying it.
I quickly grabbed something off the 'net which although decades old as far as I know has not been altogether superseded by new information. To obtain believable radiometric dates from that far back requires volcanics and the volcanic deposit to be useful must be in a stratigraphic configuration which results in the date having meaning for other strata of the system. Below, we learn that in 2005 the only likely certainty age-wise was the absolute top and bottom of the system. I have not heard of that changing but it may have done so.
The remarkable shales in which are preserved even brains and eyes, are rare geologic features -- excepting in the Cambrian. Which to my knowledge can not at this stage be radiometrically dated. Cambrian 'explosion'? Time scale? Close the eyes and make a stab?
Hughes and Heim, 2005, Encycloepedia of Geology. Quote:
"The Namibian sequence, which has the best paleontological constraints, suggests an age close to 540 Ma for base of the Cambrian, whereas the Oman sequence, which probably has better radiometric control, suggests 541 Ma. The two ages overlap in their uncertainty brackets, indicating good control on the age of this important stratigraphic boundary. Bowring and Schmitz (2003) regarded the Oman data as providing the best constraints on the age of the boundary. Pending further information, we regard 541.0 ± 0.63 Ma to be the maximum age for the Ediacaran/Cambrian boundary and for the base of the Paleozoic and Phanerozoic. The difference between the age of the top of the Cambrian Period (i.e. of the beginning of the Ordovician) at 485.4 Ma, and the bottom, 541.0 Ma, gives 55.6 myr for the duration of the period."
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