Paper No. 2
Presentation Time: 8:30 AM
LAYERCAKE STRATIGRAPHY IN THE AMERICAN WEST: PERSPECTIVES FROM THE POWELL, HAYDEN AND KING SURVEYS
Geologists of three great western post-Civil War surveys employed biostratigraphy and lithology to correlate sedimentary formations. All Paleozoic and some Mesozoic formations are marine, regionally extensive and their composition was thought to reflect eustasy. Although facies changes were recognized within some units, lateral lithologic homogeneity of formations was emphasized and formation contacts were viewed as being largely isochronous, within the limits of age-dating utilizing fossils. Of Colorado Plateau stratigraphy, Clarence Dutton [Powell Survey] states: The beds are remarkable for their homogeneity and constancy over vast areas, though the different formations vary greatly in lithological character; that is to say, homogeneity in horizontal range, with great heterogeneity in vertical range. Even the minuter structure of the beds is similarly maintained, and features which are almost abnormal are equally constant. Ferdinand Hayden, reviewing Colorado stratigraphy endorses ..the belief that the sedimentary strata formerly extended uninterruptedly across the area now occupied by the Metamorphic mass of the mountain ranges and confirms ..my belief in the continuity of all the great formations from the Silurian to the present time . Clarence King notes: There is always a ..nonconformity between the crystalline Archean topography and the superjacent sediments. ..the Paleozoic series constituted a conformable body, laid down over the rugged Archean mountain system. ..Throughout all Paleozoic time only 1,000 feet of strata accumulated over our part of the Rocky Mountains ..Passing westward, the series gradually thickens to 32,000 feet in the region of the Wahsatch and about 40,000 feet at the extreme western Paleozoic limit, ..where, from the evidences of shore-phenomena, ..we are warranted in assuming the Paleozoic coast. These layercake interpretations of the stratigraphic record perhaps are a legacy of Neptunian theory since these geologists envisioned initial flooding of a Precambrian land surface upon which strata accumulated as sea level lowered through time. King, however, noting evidence of Cenozoic effusive volcanism and glacially-induced flooding, felt that catastrophic events played a significant role in earth history.