Kenni Dinesen Petersen

An ∼60-Million-Year Periodicity Is Common to Marine 87Sr/86Sr, Fossil Biodiversity, and Large-Scale Sedimentation: What Does the Periodicity Reflect?

We find that the marine 87Sr/86Sr record shows a significant periodicity of m.yr. The 87Sr/86Sr record is out of phase with a 62 (±3)-m.yr. periodicity previously reported in the record of marine animal diversity. These periodicities are close to 58 (±4)-m.yr. cycles found for the number of gap-bounded sedimentary carbonate packages of North America. We propose that these periodicities reflect the operation of a periodic “pulse of the earth” in large-scale earth processes. These may be linked to mantle or plate-tectonic events, possibly uplift, which affects the earth’s climate and oceans and, thus, the geochemistry, sedimentation, and biodiversity of the marine realm.

A sub-crustal piercing point for North Atlantic reconstructions and tectonic implications

Plate tectonic reconstructions are usually constrained by the correlation of lineaments of surface geology and crustal structures. This procedure is, however, largely dependent on and complicated by assumptions on crustal structure and thinning and the identification of the continent-ocean transition. We identify two geophysically and geometrically similar upper mantle structures in the North Atlantic and suggest that these represent remnants of the same Caledonian collision event. The identification of this structural lineament provides a sub-crustal piercing point and hence a novel opportunity to tie plate tectonic reconstructions. Further, this structure coincides with the location of some major tectonic events of the North Atlantic post-orogenic evolution such as the occurrence of the Iceland Melt Anomaly and the separation of the Jan Mayen microcontinent. We suggest that this inherited orogenic structure played a major role in the control of North Atlantic tectonic processes.

The effect of gravitational compaction on estimation of vertical salt structure growth

Abstract The growth history of salt structures is reflected in the variation of the present thickness of the overlying and surrounding sediments in relation to the regional normal. A method for estimating the growth history of salt structures in the pillow and post-diapiric phase, including the effect of differential syn- and post-depositional compaction, is described. The assumption that stratigraphic thinning and established structural relief is a result of vertical salt movement alone is inadequate. A quantification of the true vertical movement of the salt crest necessitates a correction for compaction and differential basement subsidence. The on-structure thickness is compared to the regional normal for the time-stratigraphic interval under consideration. On the basis of the dominant porosity-reducing process, the minimum and maximum net growth can be calculated. The true net growth is assumed to be contained within these limits, probably closest to the minimum net growth. Two shallow salt diapirs in the Danish Basin exemplify the relationship between the observed stratigraphic thinning and structural relief and the differential compaction, differential basement subsidence, and vertical growth of the salt surface. The average minimum and maximum net growth of the salt surface at the Batum and Mors salt diapirs in the post-diapiric phase are calculated. The minimum and maximum net growth values for the Batum salt diapir are 731 m and 1303 m respectively, and for the Mors salt diapir 276 m and 996 m respectively, thus emphasizing the importance of including the effect of compaction in the calculations of salt structure net growth. The implications for storage of hydrocarbons, radioactive and chemical wastes, as well as for petroleum exploration, are emphasized.