School of Engineering and Science - Jacobs University

Chapter 7. Concluding remarks
The data presented in this thesis presumably constrain certain geochemical
features of seawater for the rather narrow period of time between 2.9-3.0 Ga. Studies of
seawater chemistry that focus on younger rocks benefit from both the increased
preservation of potential seawater archives as well as the greater occurrences of marine
carbonates. However, in many regards, the geochemistry of Archean seawater is poorly
constrained, particularly for the period of time prior to ~3.0 Ga. Though rocks older
than 3.0 Ga are not particularly rare, seawater archives from this time period are limited.
Further work is necessary to identify seawater archives older than 3.0 Ga, and data not
included in this thesis suggest that suitable material from southern Africa is available
for the time period between 3.2-3.6 Ga. Neodymium isotopic studies of these samples
would help refute or support the conclusion that bulk seawater Є Nd values were generally
positive with values between 0 and +2 from 3.0-3.8 Ga.
For younger rocks, unpublished Nd isotopic data indicates that shallow water
marine carbonates from the Transvaal Supergroup in South Africa possess Є Nd (2.5 Ga)
between -0.3 and -2.2, consistent with the conclusions of the Pongola IF study that
weathering of continental crust significantly influenced seawater chemistry near the
Kaapvaal craton after 2.9 Ga. Furthermore, Mn sediments from the ~2.25 Ga Hotazel
Formation in South Africa display seawater-like REY patterns, and possess Є Nd values
between -2.2 and -4.2. These data are consistent with an increasingly important flux of
solutes derived from weathering of continental crust in younger marine chemical
precipitates. A possible test of this hypothesis would be Nd isotopic studies on late
Archean (2.5-2.9 Ga) seawater archives of well defined age and representing a variety
of depositional environments. Such studies may resolve the question of whether or not
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