DETERMINATION OF THE PROCESSES GOVERNING THE TERMINATION OF FAULT-CONTROLLED DOLOSTONE BODIES

Abstract

The origin and evolution of fault-controlled, high temperature dolomitization (HTD) have been widely studied and documented throughout the geological records. Their formation is relatively well understood; however, little is known about what controls their transition and termination into the host limestone (i.e. genesis of dolomitization fronts). This is compounded by the lack of agreement on how the HTD can form extensive dolostone bodies and what is the actual source of magnesium. This study attempts to resolve some of these issues and the main findings of this research are summarized in four different chapters in this thesis. Chapter three highlights the occurrence of shallow burial, high-temperature fault-controlled dolomitization in the Middle Cambrian Western Canada Basin (WCSB) as the mechanism responsible for creating large-scale HTD dolostone bodies in the Mount Whyte Formation. Chapter four proposes a dynamic self-limiting dolomitization in the form of sudden depletion of Mg/Ca ratio at the head of dolomitizing fluids and decreased in permeability close to fluid source as the main governing processes in controlling the extent of dolomitization. Chapter five hypothesizes that the Jurassic dolomitization fronts were developed before fracturing due to changes in fluid chemistry and the fracture preferentially developed along the dolomitization fronts because it provides a zone of mechanical contrast between dolostone and limestone. Chapter six documents the different styles of dolomitization fronts from the four study locations and proposes, for the first time, a genetic classification of dolomitization fronts that should be applicable to different scales and across geological records. The new insights provided in this study may help to unravel different long-standing problems in dolomite research, including: (i) how to determine multiphase HTD dolomitization; (ii) how the porosity is formed and where to find it within the dolostone bodies Ultimately, this research contributes to our overall understanding and clarifies some misconceptions of HTD dolomitization.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Catherine Hollis (Supervisor)