Origin of massive dolomite, Leg 143, Hole 866A. Resolution Guyot, Mid-Pacific Mountains

Abstract

Dolomite is ubiquitous in Barremian age sediments at depths below 1200 mbsf in core from Hole 866A. Two distinct dolostones occur; one brown, the other white. Dolostone rock textures include unimodal planar-s type, with nonmimically replaced to partially replaced allochems. Strontium, oxygen, and carbon stable isotopic compositions reveal two distinct pulses of dolomitization, both of which post-date the depositional age of the shallow-water carbonate sediments. Pulse I dolomitization could have occurred during the early Aptian or late Albian, after the shallow-water carbonate platform had subsided some 600 to 1200 m. Pulse II is restricted to a narrow stratigraphic interval. Its age, at 24 Ma, is 100 m.y. younger than the depositional age and may correlate with events occurring about the time of the end of the Paleogene. Marine waters percolating through the guyot may be responsible for both pulse I and II dolomitization events. Geothermal endo-upwelling is one possible mechanism for driving the convective fluids through the subsiding carbonate platform, thereby promoting dolomitization. -from Authors