--> ABSTRACT: Hydrological Controls on Diagenesis in the Bow Island Formation, Alberta, Canada, by Scott McLellan, Ian Hutcheon, H. R. Krouse; #91020 (1995).
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Hydrological Controls on Previous HitDiagenesisNext Hit in the Bow Island Formation, Alberta, Canada

Scott McLellan, Ian Hutcheon, H. R. Krouse

Regional maps of water chemistry in the Bow Island Formation of southern Alberta, Canada reveal two hydrochemical systems which meet along a well-defined mixing zone. The first consists of meteorically-derived recharge waters and the second consists of more evolved, deep-basinal waters. Coincident with the zone of mixing between these waters are abrupt changes in gas chemistry and in the sequence of diagenetic events observed in Bow Island sandstones.

Isotopic measurements on gases across the mixing zone show that the displacement of evolved formation waters by meteorically-derived waters has led to the bacterial consumption of organic acids and to the production of bacterial methane. This has increased the dry gas index (C1/^Sgr(C1-Cn)) and has left a distinct bacterial isotopic signature in the resultant gas (^dgr13C = -50 to -75 ^pmil PDB). Both change abruptly across the mixing zone and systematically towards the recharge area.

The advance of the mixing zone has also resulted in intense secondary porosity development through the dissolution of quartz and feldspar grains and of authigenic overgrowths on these grains. This porosity-enhancing episode did not effect the Bow Island Formation beyond the limit of recharge. This intense dissolution was followed by widespread, facies-specific calcite and kaolinite precipitation. Both of these authigenic phases bear meteoric oxygen isotope signatures and calcite ^dgr13C values are highly depleted, reflecting a hydrocarbon-derived carbon component.

Clearly, understanding regional Previous HithydrologyNext Hit and associated Previous HitdiagenesisTop in the Bow Island Formation is essential to maximizing production from this zone.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995