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TitleDiagenetic barite and sphalerite in middle Mesozoic sandstones, Scotian Basin, as tracers for basin hydrology
AuthorPe-Piper, G; Piper, D J W; Zhang, Y; Chavez, I
SourceAmerican Association of Petroleum Geologists Bulletin vol. 99, no. 7, 2015 p. 1281-1313,
Alt SeriesEarth Sciences Sector, Contribution Series 20130367
PublisherAmerican Association of Petroleum Geologists
Mediapaper; on-line; digital
File formatpdf
ProvinceEastern offshore region
AreaScotian Shelf; Scotian Basin; Sable Sub-basin; La Have platform; Abenaki Sub-basin; Orpheus Graben; Laurentian Sub-basin
Lat/Long WENS -64.0000 -53.0000 45.0000 43.0000
Subjectsigneous and metamorphic petrology; marine geology; sedimentology; geochemistry; structural geology; sandstones; lithology; petrography; sedimentary petrology; detrital minerals; barite; sphalerite; cementation; detritus; diagenesis; paragenesis; trace element geochemistry; major element geochemistry; structural analyses; structural interpretations; Lower Cretaceous; scanning electron microscopy; electron microscope analyses; Lower Missisauga Formation; Wenonah J-75 well; South Desbarres O-76 well; Onondaga O-95 well; Sable Island C-67 well; Mesozoic; Cretaceous
Illustrationslocation maps; stratigraphic sections; tables; photomicrographs; cross-sections
ProgramFrontier basin analysis, Geoscience for New Energy Supply (GNES)
AbstractCementation of sandstone by minor late barite and sphalerite is widespread in the Scotian Basin at burial depths > 2 km, providing information on fluid flow in the basin. The texture and geochemistry of these minerals was analysed by scanning electron microscopy and electron microprobe on samples from conventional core. Barite and sphalerite post-date silica and carbonate cementation, occurring in veins or occupying secondary porosity. They occur with diagenetic chlorite, kaolinite, pyrite, titania minerals, kutnohorite and Mn-siderite. This study relates barite and sphalerite to the salt-tectonic evolution of the basin, based on seismic interpretation, and the thermal history of the basin, based on fluid inclusion studies. Barite is readily transported in basinal fluids >100 °C, yet is consistently a very late diagenetic mineral, implying that the source of Ba is due to late diagenetic breakdown of K-feldspars at 2¿3 km depth, confirmed by co-variation of Ba and Rb in sandstones. Sulfur isotope data suggest that the SO42+ was derived from Argo Formation evaporites which include 1¿7% anhydrite. Sphalerite is mobile only in saline formation water >140 °C and requires long-distance transport through sandstones with Zn-rich Fe-Ti oxides. Active detachment faults on salt welds provide pathways and a source of salt for migrating formation water. The particularities of source and transport of both barite and sphalerite allow the pathways of basinal fluids and their relationship to active salt tectonics to be inferred, providing indirect dating of the later stages of diagenetic paragenesis corresponding to times of hydrocarbon charge.
Summary(Plain Language Summary, not published)
The movement of water and hydrocarbons in the Scotian basin, from source shales to petroleum reservoirs, can be tracked using two unusual minor minerals, barite and sphalerite. They show how the movement of fluids in the basin is strongly controlled by the evolving salt tectonics.