Lecture 7 - Lecture notes for L8 Geosciences...

Lecture notes for L8 Geosciences 040-Arthur/Marone
(copyright Pennsylvania State University, 2005)
Sep 22nd
Reading: Chapt. 6 in Garrison
Add these notes in to continue from Lecture of Sep 20th
EVAPORATION and SALT PRECIPITATION
Evaporation of seawater produces predictable sequence of mineral salts
(minerals become saturated at certain point)
--after evaporation of a few % of water mass CaCO3 (Calcite)
precipitates;
--after evaporation of 81%, CaSO4 (Gypsum) fully precipitated;
--after evaporation of about 90.5%, NaCl (Halite) is fully
precipitated;
--at 96% evaporation, the K and Mg salts (w/ SO4 and Cl) drop out.
(Enough salt in ocean to cover land with layer 170 m thick)
Natural deposits from ancient oceans like this-- called "evaporites"
THE CHEMISTRY OF ANCIENT OCEANS
This is how we can tell something about the chemistry of ancient oceans
--types of salts and sequence in ancient evaporite deposits provide
indication
of ocean chemical change
--inclusions of "brines" in salt minerals also allow us to constrain
major
element ratios in ancient seawater
--new data suggests that ocean chemistry varied considerably in the
past,