Magnitudes of Error in Tectonic Subsidence Curves for Ancient Passive Margins with Examples from Early Paleozoic of Appalachian-Caledonide Orogene, North America and Greenland

Gerard C. Bond, Michelle A. Kominz, Peter A. Nickeson

Tectonic subsidence curves provide useful information on subsidence mechanisms in ancient passive margins that is difficult to obtain with other methods. However, these curves contain errors owing to uncertainties in analytical models and in input variables such as compaction factors and numerical ages. We analyzed errors with one- and two-dimensional subsidence models. If stratigraphic data were selected from post-rift strata more than 1.5 km thick, the curves accurately record the exponential form of thermal-controlled subsidence, and they constrain the age (T_o) for initiation of cooling and onset of drift in the adjacent ocean to between ±10 and 20 m.y. Conventional, one-dimensional stratigraphic sections can be used without knowledge of the rifting mec anism or restored dimensions of the margin. The effects of flexure and lateral heat flow can be ignored so that two-dimensional thermomechanical subsidence modeling, which is expensive, time consuming and subject to large errors, is unnecessary.

Simple analytical procedures rapidly generate valuable information from the large volume of stratigraphic data available from the continents. For example, tectonic subsidence curves for the early Paleozoic passive margin in Virginia have a smooth, exponential form and a T_o of 570 ± 20 m.y. There, marked deflections from the exponential occur at about 480 Ma, and clearly signal the initial (Taconian) destruction of the Iapetus passive margin. From Newfoundland to Greenland, however, similar deflections from an exponential occur at about 505 Ma, significantly predating any currently recognized compressional structures on this segment of the margin.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.