Plate Reconstructions Using Stromatolite Heliotropism: Principles and Applications

Fossilized columnar stromatolites and other microbialites, when heliotropic, incline toward averaged incident solar radiation and preserve information useful for plate reconstructions. Some fast growing small diameter living heliotropic microbialites form sinusoidal columns by recording seasonal changes in solar inclination. Others simply incline toward the equator. Fossilized heliotropic stromatolites have the same potential for recording information about past positions of the sun relative to the strata they are preserved in, and can be used to infer lines of paleolongitude (plane of column inclination and/or sinusoidal oscillation) and paleolatitude (amount of net inclination). To reconstruct past configurations of continents using heliotropic stromatolites the apparent deviation from vertical growth in individual columns is measured, corrected for refraction and strain, and used as a minimum paleolatitude. The plane perpendicular to beds and containing the inclined stromatolite columns is equated with a great circle of paleolongitude. The paleogeographic poles are located along this great circle using paleolatitude information or independently using the intersection of the paleolongitude of two separate but contemporaneous specimens. Paleolatitudi-nal and paleolongitudinal data extracted in this way produce paleoheliotropic apparent polar wander paths. The method has the advantage of yielding true lines of paleolongitude and information about true paleolatitude, because heliotropism refers to the earth's rotational poles, and not an assumed stationary magnetic pole. Stromatolites are abundant in the geological record, and analysis for heliotropism may yield information about plate rotations and correlate paleomagnetic and geographic pole positions for most of earth history.