TORONTO, April 5 (UPI) -- A Canadian modeling study has offered an explanation for an anomaly seen in the carbon and sulfuric isotope records of the Early Cretaceous period.
In modern-day sediment the rates of pyrite (iron sulfide) and carbon-based organic matter burial are positively related. But during the Early Cretaceous period, which began approximately 140 million years ago, those rates appear to be negatively related -- a relationship that has been difficult to explain.
In the new study, Ulrich Wortmann and Boris Chernyavsky of the University of Toronto show the puzzling relationship could be due to the deposition of evaporites -- mineral sediments that precipitate from water as it evaporates -- on the ocean floor as South Africa and South America moved apart and the South Atlantic Ocean basin formed.
The researchers note the evaporites contain sulfate, so their production removed sulfate from the surrounding waters in sufficient quantities as to reduce significantly the rate at which organisms in marine sediments formed pyrite and broke down organic matter.
That, said the scientists, might explain the negative relationship between the amount of pyrite and organic matter buried in marine sediments from that time.
The study is detailed in the journal Nature.
