Re: Geological periods

[Dinogeorge@aol.com]

In a message dated 96-01-22 15:27:48 EST, nking.ucs@smtp.usi.edu (King, Norm)
writes:

>The time scale published by 
>Harland et al. in 1982 pegs the beginning of the Triassic at 248 Ma, and 
>most current literature uses a figure between 250 and 245 Ma.  Do some 
>people who are knowledgable about radiometric age-dating disagree 
>significantly with the dates for Triassic and adjacnet strata in the 
>Harland et al. scale?  Earlier time scales (your reference was 1981) 
>often showed the Triassic beginning at 225 Ma.  But Harland's et al. 
>scale shows the LATE Triassic (Carnian Epoch) beginning 231 Ma, and the 
>oldest dinosaurs would be almost that old--I've seen 225 Mya most often.  
>The older time scales, showing 225 Ma for the beginning of the Triassic, 
>use about 205 Ma for the beginning of the Carnian. If I were you, I'd use 
>the Harland et al. dates.

There is a more recent editin of Harland et al.: 1989. These are the Mesozoic
dates (error brackets omitted) taken from that reference (use a uniform font
for printing):

                   MESOZOIC GEOLOGICAL STAGES
                  Datings and names as of 1989

Cretaceous     Late      Maastrichtian       65-74 Ma
                         Campanian           74-83 Ma
                         Santonian           83-86.6 Ma
                         Coniacian           86.6-88.5 Ma
                         Turonian            88.5-90.4 Ma
                         Cenomanian          90.4-97 Ma

               Early     Albian              97-112 Ma
                         Aptian              112-124.5 Ma
                         Barremian           124.5-131.8 Ma
                         Hauterivian         131.8-135 Ma
                         Valanginian         135-140.7 Ma
                         Berriasian          140.7-145.6 Ma

Jurassic       Late      Tithonian           145.6-152.1 Ma
                         Kimmeridgian        152.1-154.7 Ma
                         Oxfordian           154.7-157.1 Ma

               Middle    Callovian           157.1-161.3 Ma
                         Bathonian           161.3-166.1 Ma
                         Bajocian            166.1-173.5 Ma
                         Aalenian            173.5-178 Ma

               Early     Toarcian            178-187 Ma
                         Pliensbachian       187-194.5 Ma
                         Sinemurian          194.5-203.5 Ma
                         Hettangian          203.5-208 Ma

Triassic       Late      Rhaetian            208-209.5 Ma
                         Norian              209.5-223.4 Ma
                         Carnian             223.4-235 Ma

               Middle*   Ladinian*           235-239.5 Ma
                         Anisian*            239.5-241.1 Ma

               Early*    Spathian*           241.1-241.9 Ma
                         Nammalian*          241.9-243.4 Ma
                         Griesbachian*       243.4-245 Ma



* Dinosaurs not yet known from these intervals
Ma = Meganna (millions of years ago)