Transgression by the Western Interior Sea during the Late Cretaceous in southwestern Minnesota caused swampy conditions to be imposed upon a laterite consisting of gibbsite, goethite and kaolinite. Reducing conditions overprinted upon the laterite reduced ferric Fe in goethite for incorporation of ferrous Fe into Fe-berthierine. Attendant oxidation of organic matter provided CO2 for siderite's formation. Thermodynamic calculations indicate that berthierine, gibbsite, goethite, kaolinite and siderite were in equilibrium with a solution whose pH was 5.2 and whose pCO2 was on the order of 0.3 atm. Formation of Fe-berthierine is favored by solutions having: 1) low silica concentration; 2) low [Mg2+]/[Fe2+] ratio; 3) high pCO2; 4) extremely low sulfate content before reduction takes place; and 5) moderate reducing conditions (Eh around −0.05 V).

In vaginally delivered births (including a few cases where the mothers were under epidural anesthesia), differences between first and second born twins were compared according to presentation at delivery. Of twins with vertex/vertex presentation in 15 primipara cases and in 14 multipara cases, pO2 levels for the second born were significantly lower (both being p < 0.05) than for the first born. Of twins vertex/non-vertex presentation, the second born in 9 primipara cases showed significantly lower pH, pO2 and HCO3 levels (p<0.05). Also for multipara twins, the second born had significantly lower pH (p<0.05) and significantly higher pCO2 (p<0.05) values. Umbilical cord blood gas value findings indicate unfavourable conditions for second born twins.