Stromatolite modeling

Stromatolites are layered structures formed primarily in shallow marine environments by the combined effects of sedimentation, precipitation, and growth of benthic microbial communities dominated by photosynthetic microbes. In addition to their paleontological value, they represent a potentially rich reservoir of information regarding length of day, obliquity (earth’s tilt), paleogeography, lunar orbit evolution and other valuable data spanning approximately 3 billion years of Earth history. On the right, stromatolites grow near the shoreline of an ocean on the ancient earth, before all other life existed, and the moon was much closer to the earth than it is now. With the help of his father, Dr. Richard Ojakangas (professor emeritus of geology, University of Minnesota Duluth), and Dr. James Vanyo (UC Santa Barbara)  Dr. Gregory Ojakangas was able to procure several samples of stromatolites from the Mesabi Iron Range, northern Minnesota.  Their original orientation was carefully measured before removal from outcrop.  The specimens were slabbed thinly at the Natural Resources Research Institute in Duluth, MN, by John Heine. The layers were coated with mineral oil and scanned at 1800DPI at Drury University by Ojakangas. A thee-dimensional virtual environment was created in Matlab, so that all surfaces of the specimens could be examined relative to each other in an interactive manner. Below are some images resulting from this procedure. Ojakangas has spent years trying to extract secrets from these beautiful specimens.  Current work continues with Dr. Stanley Awramik of UC Santa Barbara.

I have spent enormous effort trying to understand the Biwabik stromatolite specimens, through mathematical modeling of various forms. At the left is an example of one of my three-dimensional computer simulations of stromatolite growth. The model stromatolite is growing at latitude 46 degrees on an earth with an obliquity of 67 degrees. Strong dependence of growth rate on solar irradiance leads to flattened tops during summer. This growth site is within the Tropic of Cancer because obliquity exceeds latitude. This outrageously large obliquity is necessary in order to match features I measure in Biwabik stromatolites with flat tops of similar orientation.  On the right is a comparison between one of my models (blue) and part of a Biwabik stromatolite specimen, suggesting that the earth’s tilt (obliquity) may have been very large 1.85 billion years ago.  This work is not yet published.