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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 63 (1979)

Issue: 3. (March)

First Page: 534

Last Page: 534

Title: Clay-Carbonate Diagenesis of Deltaic Sandstones--Basal Belly River Formation (Upper Cretaceous), Central Alberta, Canada: ABSTRACT

Author(s): Sidney R. Storey

Article Type: Meeting abstract

Abstract:

The Upper Cretaceous (Campanian) basal Belly River Formation from the subsurface of central Alberta averages 20 m in thickness and consists of a small, lobate, high, constructive delta prograding into a shallow basin. The major sandy facies are: distributary channel, distributary-mouth bar (formed during constructional phases), interdistributary beach (and other poorly defined facies formed by destructional processes), and fluvial channels of the delta plain.

The sediment is predominantly a mineralogically immature fine sand consisting of quartz, chert, feldspar, polycrystalline quartz, and volcanic lithic grains. Detrital mineralogy varies with lithofacies, reflecting a depositional process of controlled sorting, winnowing, and selective destruction of the sediment, which results in an increase in the quartz content of interdistributary beach facies and more abundant mica in mouth-bar facies.

These sandstones have had extensive diagenetic modification in the form of widespread calcite and/or clay cementation.

Calcite cementation is more extensive at the margins of the delta sand bodies and extends inward as discrete subhorizontal layers. Texturally these cements range from large poikilotopic crystals to spherulitic and isopach rims. Open packing of siliciclastic grains, lack of other diagenetic minerals, and the preservation of unstable detrital minerals within these tightly cemented zones suggest an early diagenetic origin.

"Authigenic" clays are abundant in these sandstones and include kaolinite, chlorite, illite, and minor amounts of montmorillonite and expandable interlayers. Kaolinite is present as pore-filling booklets. Other clays form as sequential coatings on grains and earlier cements. The distribution of clay minerals within these sand bodies appears to be at least in part facies related. Chlorite and kaolinite occur predominantly in fluvial facies, in illite/montmorillonite with less kaolinite occurs in destructional facies. This variation is in response to facies-controlled variation in detrital mineralogy, texture, and primary pore fluids.

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