"New development in the history of the Maritimes Basin: More that a pinch of salt" by Professor John Waldron

John Waldron grew up in the UK, where he developed a teenage enthusiasm for collecting fossils. He attended Cambridge and Edinburgh Universities and carried out graduate research in the Taurus Mountains of western Turkey. In 1981, he came to Canada as a post-doctoral fellow at Memorial University of Newfoundland. From 1981 until 2000 he worked at Saint Mary's University, Halifax Nova Scotia, before moving as a professor to the University of Alberta in 2000. He teaches introductory Earth science, tectonics, structural and field geology, and developed an outdoor classroom, the Geoscience Garden, at the University of Alberta. His research deals with the deformed sedimentary rocks of mountain belts from both sedimentary and structural geological perspectives, and with a particular focus on the Appalachian orogen of Atlantic Canada and its continuation as the Caledonides of the British Isles. He has also worked on deformed sedimentary basins ranging from the Archean of the Slave Craton in the Canadian Shield, to the Cenozoic foothills and thrust front of the Nepal Himalaya. John Waldron received the Gesner medal of the Atlantic Geoscience Society in 2009, and is adjunct at Acadia, Dalhousie, and St. Mary's Universities.

'New development in the history of the Maritimes Basin: More that a pinch of salt'

Abstract: The Maritimes Basin of Atlantic Canada is a broad and deep sedimentary basin underlying large parts of Atlantic Canada. The basin fill is predominantly Devonian to Permian non-marine clastic sedimentary rocks, but the Mississippian Windsor Group, and the correlative Codroy Group of Newfoundland, contain substantial evaporites, including gypsum and anhydrite, halite, and potash. Laterally correlative limestone-evaporite-shale cycles have been traced throughout the middle and upper parts of the Windsor Group.

Windsor evaporites have played a major role in the tectonics of the Maritimes Basin. In addition to diapiric features generated by primarily vertical tectonics, there are extensive low-angle deformation surfaces characterized by anomalous breaks in the basin-wide stratigraphic succession. These breaks were originally interpreted as thrust faults, but later investigations, noting substantial omission of stratigraphy, led to their re-interpretation as a single low-angle detachment - the Ainslie Detachment. The availability of industry seismic reflection data allows these structures to be again reinterpreted, in the light of recent advances in evaporite tectonics on passive continental margins as salt welds.

For example, the famous Joggins Pennsylvanian succession was rapidly deposited in accommodation space created by salt expulsion, showing that Windsor Group salt remained in place until the Pennsylvanian before rapidly moving into diapiric salt walls.

Elsewhere, for example in the eastern Cumberland sub-basin and in the Bay St. George sub- basin of SW Newfoundland, evaporite expulsion was already controlling sedimentation during Mississippian deposition of the middle and upper Windsor and the overlying Mabou group.

These observations suggest an interpretation in which movement of the thick lower Windsor evaporites began within a few million years of their deposition. Feedback between halokinesis and sedimentation occurred from mid-Viséan onward. Multiple minibasins were simultaneously flooded by eustatic sea-level rises, related to glacial cycles on Gondwana, accounting for the laterally correlative limestones.

The tops of evaporite diapirs have probably remained near the surface, producing areas of subsidence and karst development, throughout much of Nova Scotia's subsequent history. The distribution of near-surface evaporites continues to be marked by widespread development of sinkholes at the present day.

John W.F. Waldron, Morgan E. Snyder

Department of Earth and Atmospheric Sciences, Edmonton, Alberta T6G 2E3 Canada and Department of Earth and Environmental Science, Acadia University, Wolfville NS B4P 2R6 Canada