Bulletin 020

Bulletin 020

BUL 020

Cretaceous Foraminifera of the Rocky Mountain Foothills, Alberta

Author(s) Wall, J.H. Date 1967-01-01

A succession of ten microfaunas is recognized in the Alberta Group (Cretaceous) and equivalent strata in the Rocky Mountain Foothills. In ascending stratigraphic order these are: 1.Miliammina manitobensis; 2.Verneuilinoides kansasensis; 3.lower pelagic and 4.Pseudoclavulina sp. from the Blackstone Formation; 5.Trochammina sp. 1; 6.Brachycythere-Bullopora; 7.Anomalinoides henbesti; 8.upper pelagic; 9.Trochammina ribstonensis and 10.Lenticulina from the Wapiabi Formation.

An unnamed sparse microfauna is present in the Cardium Formation between the Blackstone and Wapiabi Formations. A knowledge of these assemblages may be applied toward the identification of strata in the Foothills; viz. microfaunas (4) and (5) indicate stratigraphic positions below and above the Cardium Formation, respectively. Most of the microfaunas have a distribution extending well beyond the Foothills and are of value in Foothills Plains correlation studies, viz. microfauna (1) between the fish scale sand' and the Viking Formation in the Colorado Group, and microfauna (9) in the basal beds of the Montana Group of the Plains.

Correlations based on microfaunas and megafaunas are in general accord within the Blackstone Formation and basal portion of the Wapiabi Formation but differ in other parts of the latter. The Thistle Member seems to be essentially isochronous with respect to its position in the megafaunal zonation but is shown to be markedly diachronous, becoming younger from south to north, when the upper pelagic microfauna (8) associated with the first white-speckled shale 'zone' is used as a datum plane. Based on their relationships with the zonal ammonites, the Brachycythere-Bullopora (A) and upper pelagic (8) microfaunas apparently become younger from north to south. Two complete cycles and one partial cycle of transgression, widespread flooding and regression are revealed by the succession of microfaunas in the Alberta Group. In the first cycle, within the Blackstone Formation, the transgressive phase is indicated by microfaunas (1) and (2), the widespread flooding by microfauna (3) and the regressive phase by microfauna (4). This regressive phase is continued through the Cardium Formation, as shown by its sparse agglutinated microfauna. In the second cycle, within the Wapiabi Formation, the early and advanced stages of the transgression are indicated by microfaunas ( 5 ) and ( 6 ), the widespread flooding by microfaunas (7) and (8) and the regression by microfauna (9). A condensed third cycle is represented in the Nomad Member of the Wapiabi Formation by microfauna (10). The advancing Blackstone sea reached the southern Foothills at progressively later stages, as shown by the successive southward disappearance of microfaunas (1) and (2). The Late Cretaceous sea persisted longer in the central and northern Foothills than in the southern Foothills, as shown by the presence of microfauna (10) in the former sectors and its absence in the latter.

A total of 84 species of foraminifera are described, comprising 49 agglutinated and 35 calcareous forms. All species are either referred to previously published taxa or treated as nomina aperta. The agglutinated species belong to 20 genera included in 9 families; the calcareous species belong to 21 genera included in 12 families. With some exceptions among the pelagic forms and Anomalinoides, numbers of individuals are considerably greater in the agglutinated species.

Wall, J.H. (1967): Cretaceous Foraminifera of the Rocky Mountain Foothills, Alberta; Research Council of Alberta, RCA/AGS Bulletin 20, 195 p.