Ejecta weathering

Figure 12 shows surface temperature and pCOz histories. These focus on Archaean and Hadean time. Results are shown for the different heat-flow histories. The models with ejecta weathering use equation (19). By construction these are... 

The materials that accumulate to form sedimentary rocks are (i) products of disintegration (weathering) of rocks, (ii) volcanic ejecta, (iii) insoluble decomposition products, (iv) precipitated substances from aqueous solutions, and (iv) bio-organically derived substances. 

Geochemical constraints on acid deposition come from the foram record of a spike in Sr/ Sr across the K/T boundaiy and from base cation leaching at terrestrial K/T sites in eastern Montana. A statistical analysis of the foram data of Martin and Macdougall [1] yields an enhancement in Sr/ Sr of 25 x 10 9x10 We considered two sources of this enhancement Sr leaching from impact ejecta and increased continental weathering due to acid deposition. Impact ejecta with the Sr concentration and ratio of Chiexulub melt rock, 300... 

Extrapolation to the K/T boundary requires consideration of the time scales of acid deposition. Nitric acid formation occurs rapidly by aqueous phase reaction of NO and NO2 with liquid water produced by tlie incident K/T bolide on both impact and infall of ejecta. For tlie quantities of NO produced by the K/T impact ( 10 5 moles), conversion to HNO3 occurred wiUiin days, assuming sufficient liquid water was available in the posl-K/T atmosphere. The nitric acid will form an acid rain of pH 0 for a liquid water content of 1 g/m (typical of tropospheric clouds) but will contain enough protons to weather only 3 x 10 moles of Sr, for Sr/(Ta -0.003 in soil and bedrock minerals. Sulfuric acid formation occurred on a time scale of years [7] due to the slow rate of gas phase SO2 oxidation. Spread evenly over 10 years, 10 moles of SO2 produced a global acid rain of pH —4, and released —3 x 10 moles of Sr. 

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