Evaporite Deposition in Deep Water: ABSTRACT

Abstract

Reasoning by analogy with modern salinas, most geologists believe that ancient marine evaporite deposits were formed in shallow, slowly subsiding basins in regions of arid or semiarid climate. When this model is applied to several well-studied ancient salt deposits, however, inconsistencies arise which suggest the need for an alternative hypothesis. Sedimentation rates inferred for the Zechstein salts of Germany and the Salina of Michigan appear compatible with temperate rather than arid climates. More significantly, the thickness of evaporite salts in each of these localities requires either extremely rapid subsidence of the evaporite or salt deposition during a period of time substantially greater than that permitted by existing stratigraphic control. In addition, the petrography and bromine content of the halite in both basins may be reconciled with the model only with great difficulty. Most of the inconsistencies observed may be overcome by postulating salt deposition in a several hundred to several thousand feet deep. A basin model of evaporite deposition is developed in detail. The model is shown to be both geologically and oceanographically reasonable, and to be consistent with at least part of the depositional history of both Zechstein and Michigan evaporite basins. Direct stratigraphic evidence of deep-water evaporite deposition in the Midland is cited in further support of the model. The Elk Point evaporites of Alberta are examined in the light of the deep model, and certain implications of the model for the exploration geologist in this region are developed. End_of_Article - Last_Page 549------------