super(4) super(0) Ar/ super(3) super(9) Ar systematics and argon diffusion in amber: implications for ancient earth atmospheres

• Published in: Global and planetary change 1991-01, Vol.5 (1/2), p.63-67
• Main Authors: Landis, G P, Snee, L W
• Format: Article
• Language: English
• ISSN: 0921-8181

Argon isotope data indicate retained argon in bulk amber (matrix gas) is more radiogenic [ super(4) super(0) Ar/ super(3) super(6) Ar identical with 320] than the much more abundant surface adsorbed argon [ super(4) super(0) Ar/ super(3) super(6) Ar identical with 295.5]. Neutron-induced super(3) super(9) Ar is retained in amber during heating experiments to 150 degrees -250 degrees C, with no evidence of recoiled super(3) super(9) Ar found after irradiation. A maximum permissible volume diffusion coefficient of argon in amber (at ambient temperature) D less than or equal to 1.5 x 10 super(-) super(1) super(7) cm super(2) s super(-) super(1) is calculated from super(3) super(9) Ar retention. super(4) super(0) Ar/ super(3) super(9) Ar age calculations indicate Dominican Republic amber is identical with 45 Ma and North Dakota amber is identical with 89 Ma, both at least reasonable ages for the amber based upon stratigraphic and paleontological constraints and upon the small amount of radiogenic super(4) super(0) Ar. To date, over 300 gas analyses of ambers and resins of Cretaceous to Recent age that are geographically distributed among fifteen noted world locations identify mixtures of gases in different sites within amber (Berner and Landis, 1988). The presence of multiple mixing trends between compositionally distinct end-member gases within the same sample and evidence for retained radiogenic argon within the amber argue persuasively against rapid exchange by diffusion of amber-contained gases with modern air. Only gas in primary bubbles entrapped between successive flows of tree resin has been interpreted as original ``ancient air,'' which is an O sub(2) -rich end-member gas with air-like N sub(2) /Ar ratios. Gas analyses of these primary bubbles indicate atmospheric O sub(2) levels in the Late Cretaceous of identical with 35%, and that atmospheric O sub(2) dropped by early Tertiary time to near a present atmospheric level of 21% O sub(2) . A very low argon diffusion coefficient in amber persuasively argues for gas in primary bubbles trapped in amber being ancient air (possibly modified only by O sub(2) reaction with amber).