A STRATIGRAPHIC PERSPECTIVE ON THE HEART MOUNTAIN PROBLEM
A stratigraphic context is more appropriate for the distal areas of the HMD. Here, the allochthonous rocks can be viewed as a teramictite (Sundell and Fisher, 1985), and a lithostratigraphic unit within the Eocene Absaroka Volcanic Supergroup. The allochthonous rocks are similar in texture, thickness, structure, composition, and areal extent, as debris-avalanche deposits which are reported in many Quaternary volcanic terranes. The geometric features within allochthonous rocks can alternatively be regarded as textures and primary structures within a stratigraphic unit. Blocks, individually as large as several km in maximum dimension, are separated by matrix. Some blocks are volcanic and Eocene in age; others are limestone and Paleozoic in age. The basal contact is irregular and has more than 1 km of relief, and underlying rocks range in age from Mississipian to Eocene. The allochthonous rocks are sometimes older, where they are Paleozoic carbonates, and sometimes younger, where they are Eocene volcanic, than the underlying strata. The footwall and side-wall ramps can be viewed as erosional paleotopography.