Abstract: Analysis of Effect on Graded Beds of Changing Gravitational Acceleration with Time--a Prototype Paleogravimeter

Steven Solomon Barrell

Over the past century physicists have postulated that the universal constant of gravitation, G, is decreasing with time. If an annual rate of decrease of 10^-10 parts per year is assumed, the gravitational acceleration of the earth, g, would have been 22% greater 2 b.y. ago. Distal turbidites are present in geologic deposits as old as 2.5 b.y. Using the relations developed by Scheidegger and Potter, a functional relation between g and measurable characteristics of a graded bed may be constructed. This relation, a "paleogravimeter," was tested in terms of sensitivity to changes in g, as well as possible confounding effects such as sediment concentration, density, and grain packing. Only the sediment concentration in the turbidity current had a measurable effect. By using Middleton's result that the transition between "distribution" grading and "coarse-tail" grading occurs at particle concentrations of 30%, a selection criteria can be established. In this manner, it is possible to measure only those beds deposited from currents of the same particle concentration. When this is done the paleogravimetric change can be measured. The paleogravimeter can be improved by substituting more realistic relations for Stokes' law and allowing viscosity to vary as suggested by Roscoe. Preferably, however, a purely physical model for sedimentation from a turbidite should be developed in place of the Scheidegger-Potter relation.

AAPG Search and Discovery Article #90964©1978 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah