A REVIEW AND REINTERPRETATION OF EVIDENCE CONCERNING THE ORIGIN OF VICTORIAN BROWN COAL

The nature of the depositional environments which led to the formation of the very extensive Victorian Brown Coal deposits located in Southeastern Australia, has been the subject of numerous publications. Previous publications on this subject have suggested that these coals were laid down in an extensive series of peat swamps similar to the Florida Everglades (U.S.A.). One of the central premises of this depositional model has been that lithotype formation is dependent on the degree of inundation of the original peat-forming environment. Specifically, it proposes an inverse relationship between the degree of inundation and the "lightness" (of colour) of the resulting lithotype, with the light and pale lithotypes being deposited in fully inundated environments. In this manuscript, the evidence on which this depositional model is based, and other data, from a variety of disciplines, relevant to the question of the nature of the depositional environments of these coals, is reviewed. The resulting synthesis of data has led the present authors to conclude that previous depositional models cannot fully account for the observed chemical, physical and geological characteristics of these coals. Therefore, a new depositional model is proposed which seeks to account for these observed characteristics. It is concluded by the present authors that deposition of these coals probably took place in an extensive and long-lived series of ombrogenous (raised or domed) forested peat swamps, structurally analogous to modern peat accumulations in SE Asia. Further it is suggested that lithotype formation is governed not by the degree of inundation of the original peat-forming environments, but rather by the degree of aerobic degradation experienced by the initial peat accumulations, with pale and light coals representing the products of the most severely degraded peats.