INTRODUCTION

Descriptions of the Lea Park and Belly River formations of east-central Alberta have been included in a number of previous papers. The last of these by Nauss (1945) is based on data available to the end of 1942. Since 1942, many core-test holes and deep tests have been drilled in the area; hence, it is now possible to eliminate a number of previous problems and to establish a more regional correlation. The purpose of the present paper is to supplement previous reports rather than to deal comprehensively, with the subject. The paleontology of the formations was included in Nauss' studies and has been published (1947); it is therefore excluded from this paper.

PREVIOUS WORK

The principal contributions to nomenclature, as correlated and compared with the classification proposed by the present writers, are shown in Table I.

DESCRIPTION OF FORMATIONS

The proposed classification of lithologic units is shown in Table II.

LEA PARK FORMATION

The Lea Park formation was named by Allan (1918) for a marine shale

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Table I. STRATIGRAPHIC SECTIONS OF VARIOUS WRITERS

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Table II. TABLE OF FORMATIONS

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formation cropping out in the vicinity of Lea Park on the North Saskatchewan River.

The formation is a uniform series of gray, silty shales with local intercalations of sandy shale, ironstone concretionary bands, and bentonite. The formation underlies the entire area, ranging in thickness from 450 to 810 feet. The thickness increases northeast as a result of successive lensing-out of several deltaic sand members of the Belly River formation in this direction and the inclusion of the silty marine shale off-shore facies of these sand members in the Lea Park formation. This relationship is illustrated in Figures 1, 2, 3, and 4. Within itself the Lea Park formation thickens slightly in the opposite direction as illustrated by the electric-log correlation lines a to j in Figures 2, 3, and 4. The formation was deposited in an epi-continental sea and the main source was fro a distant borderland on the southwest.

The lower boundary of the formation is marked by the top of the "First White Speckled shale" zone of the Colorado marine shales. This is a consistent and reliable marker throughout the western plains of Canada and can be determined readily by either lithologic examination or electric-log correlation; it is used, therefore, as the datum in Figures 2, 3, and 4. The upper boundary of the Lea Park formation is gradational into the sands of the Belly River formation. The marine shale tongues which interfinger with the deltaic sands of the Belly River are being arbitrarily placed as members of that formation. Accordingly, the contact has a "stair-step" character as illustrated by Figures 2, 3, and 4.

Figure 2 shows the correlation of the Lea Park formation with the Milk River and Pakowki formations of the southern plains of Alberta.

BELLY RIVER FORMATION

The term "Belly River" was originated by Dawson (1875) for a series of predominantly continental deposits in the southern plains of Alberta, and Tyrrell (1887) in 1886 applied the name to similar deposits in east-central Alberta. Later information and correlation have confirmed Tyrrell's application of the name in east-central Alberta. In the intervening years, however, the term "Belly River" has been raised to a group name in the type area where it consists of Russell's (1940) Foremost and Oldman formations. In east-central Alberta, this subdivision can not be maintained and the term "Belly River" has to be used as a formation name. On the northeast in east-central Alberta, the formation becomes an interfingering succession of marine shales and deltaic sands; hence, it can be subdivi ed into a number of members as listed in Table II and illustrated by Figures 1, 2, 3, and 4. The formation underlies the greater part of the area; it thickens on the southwest as illustrated by Figures 3 and 4, indicating a source from highlands on the southwest.

The undivided formation consists of a series of gray to brownish-gray to greenish-gray, argillaceous, bentonitic sand closely interbedded with brownish-gray to gray, carbonaceous shales and silts. Thin carbonaceous layers are characteristic

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Fig. 1. Index map of east-central Alberta.

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Fig. 2. Correlation from Jenner to Lloydminster, along line AB of Fig. 1.

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of the normal facies. Thin coal seams characterize the continental to marine transition facies.

The environment of the typical Belly River beds appears to have been a peneplain between the highlands on the southwest and the epi-continental seas on the northeast. This peneplain was locally swampy and provided a suitable habitat for dinosaurs and other reptiles, the remains of which have been found in abundance, particularly on the Red Deer River south of east-central Alberta.

The lower boundary of the Belly River formation has been described in the description of the Lea Park formation. The Belly River is overlain by the marine Bearpaw formation or the continental Edmonton formation. Southeast of the area, the Bearpaw formation is typically a marine shale, but in the area itself it becomes progressively transitional northwestward into the overlying continental beds of the Edmonton formation. This transition becomes complete in the vicinity of the city of Edmonton where the main coal measures of the Edmonton formation were deposited in a coastal-swamp environment contemporaneously with the basal beds of the marine Bearpaw formation and thus directly overlie the Belly River formation. Two hundred miles northwest, a series of continental beds essentially cont mporaneous with the Belly River, Bearpaw, and Edmonton formations has been designated the Wapiti formation by Dawson (1881).

Brosseau member:
The name "Brosseau" was introduced by Allan for sands exposed along the North Saskatchewan River Valley between Shandro Ferry and Fort Island. Allan (1918) described the beds as follows: "The upper part of the formation consists of flaky sandstones and clayey sandstones... The lower part of the formation consists of brown sandy shales, thin-bedded sandstone, and thin seams of coal." Elsewhere, from subsurface information, the member consists of fine, gray, calcareous sandstone and sandy, brownish-gray shale. The depositional environment of the member was continental and marine deltaic.

Allan (1918) and Slipper (1918) considered the Brosseau formation as the equivalent of the Ribstone Creek formation cropping out near the mouth of Ribstone Creek and along the Battle River. Core-test and deep-test information show that the Brosseau beds are correlative with a deltaic sand which lies considerably below the Ribstone Creek formation. The sand is developed particularly well in the vicinity of the town of Provost. In keeping with the plan to designate as members each of the Belly River subdivisions in the northeast half of the area, it is proposed to reduce the Brosseau to member status.

On the basis of a great many subsurface data, the Brosseau member ranges in thickness from almost nothing to 100 feet.

The present northeasterly extent of the member, insofar as it can be mapped by subsurface information, is shown in Figure 1.

Shandro member:
The name "Shandro" was applied by Allan (1918) to exposures of "... dark gray marine shales containing calcareous and arenaceous concretions" exposed along the North Saskatchewan River below the mouth of White-Earth River. Supplementary subsurface data indicate that the member

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Fig. 3. Correlation from Leduc to Lloydminster, along line CB of Fig. 1.

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Fig. 4. Correlation from Castor to Lloydminster, along line DE of Fig. 1.

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also contains carbonaceous shales and brownish gray, silty shale with carbonaceous specks. The thickness ranges from less than 1 to 85 feet. The environment of deposition was marine neritic.

In areal extent the member is indicated in Figure 1 as lying between the southwesterly limits of the Shandro member and the northeasterly limits of the Brosseau member.

Victoria member:
The name "Victoria" was introduced by Allan (1918) for "massive beds of yellow sandstone" cropping out in the North Saskatchewan River Valley 3 miles below Pakan. The exposure forms the Victoria rapids. Allan (1918) and Slipper (1918) considered the Victoria sandstone the equivalent of the Birch Lake sandstone on the southeast. Subsurface data now available indicate, however, that the Victoria lies considerably below the Birch Lake and is equivalent to the lower Ribstone Creek sandstone as described by Nauss (1945). The name "Victoria" supersedes Nauss' name; therefore, it is proposed that the name lower Ribstone Creek be discarded.

An abundance of presently available subsurface information indicates that the lithologic character of this member varies from Allan's description to include fine- to medium-grained gray sandstone and brownish-gray, carbonaceous, silty shale with local, thin coal seams. The thickness ranges from almost nothing to 95 feet. The depositional environment was continental and marine deltaic. The present areal extent of the member is shown in Figure 1.

Vanesti member:
The "Vanesti" member was named by Nauss (1945) for exposures along the Battle River Valley near the mouth of Grizzly Bear Coulee. The member consist of gray shale, silty shale, clayey shale, and fine sand. Its thickness ranges from less than 1 to 140 feet. The depositional environment was marine neritic. The present areal extent of the member is shown in Figure 1.

Ribstone Creek member:
The name "Ribstone Creek" was applied by Slipper (1918) to "greenish yellow, massive, soft sandstone at top; green and carbonaceous shale and coal, light grey sandstone at base," exposed principally near the mouth of Ribstone Creek. The colors described by Slipper are due to weathering. Fresh samples are, for the most part, gray in color. The thickness of the member ranges from almost nothing to 120 feet. The depositional environment was continental and marine deltaic. Locally, both marine fossils and coal seams occur in the member. The member extends eastward far into the Province of Saskatchewan; it appears to be the most extensive of the Belly River deltaic deposits.

Grizzly Bear member:
The name "Grizzly Bear" was applied by Slipper (1918) to the dark blue-gray, marine shale, containing ironstone and sandstone nodules with some beds of yellow incoherent sandstone, exposed principally on the lower part of Grizzly Bear Coulee. The member ranges in thickness from less than 1 to 140 feet. The depositional environment was marine neritic. The present areal extent is shown in Figure 1.

Lower Birch Lake member:
The name "Birch Lake" was applied by Slipper (1918) to "massive, cross-bedded sandstone, buff-coloured, containing lenses of

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harder sandstone" exposed on Birch Lake and in other near-by localities. Nauss (1945) determined that a marine shale wedge entering from the northeast divided the beds into upper and lower members. The lower member consists predominantly of greenish-gray to gray sands. The thickness ranges from almost nothing to 115 feet. The depositional environment was continental and marine deltaic. The present areal extent of the member is fairly limited and can be deduced to some extent by reference to Figures 3 and 4.

Mulga member:
The name "Mulga" was applied by Nauss (1945) to the gray shale with silt lenses and some carbonaceous material penetrated between the upper and lower Birch Lake members in four core-test holes south of Mannville. The type section is in Imperial Core Test No. 44 in ls. 13, sec. 14, tp. 49, rge. 9 w. 4th mer. The present study has resulted in recognizing the member over a greater area. The thickness ranges from less than 1 to 45 feet. The depositional environment was marine neritic. The present southwesterly extent of the member is shown in Figure 1.

Upper Birch Lake member:
The name "Upper Birch Lake" was applied by Nauss (1945) to the upper part of Slipper's (1918) Birch Lake sandstone. The member consists of gray to slightly yellow, medium-grained sand which weathers to a light rusty color. Thickness is from almost nothing to 50 feet. Depositional environment was continental and marine deltaic.

Oldman member:
The term "Oldman" was introduced by Russell (1940) as a substitute for the term "Pale Beds" as applied to the upper division of Dawson's (1875) Belly River series in southern Alberta. Slipper (1918) carried the term "Pale Beds" to the central Alberta plains; subsequently, Nauss (1945) following Russell, substituted the term "Oldman" for the term "Pale Beds" in east-central Alberta. The term "Oldman" has formational status in southern Alberta and Nauss gave it formational status in east-central Alberta. In keeping with their general plan, the present writers propose reducing it to member status in east-central Alberta. Moreover, the present writers propose that the Oldman member also include the Pakan beds of Allan (1918) and Nauss (1945) and the equivalent "Variegated beds" of Slipper (1 18). Subsurface geologists have been unable to differentiate between the "Pale" and "Variegated" beds in well samples. Accordingly, this subdivision is considered impractical even though perhaps technically justified. The Pakan beds (Variegated) undoubtedly represent a narrow transitional facies between the continental beds on the southwest and the marine and deltaic tongues which are developed on the northeast. Accordingly, the facies has a strong oblique attitude with respect to time levels. The Oldman member in reality represents the northeastward pinch-out of the typical continental Belly River facies; hence, the lithologic character and environment are similar to those described for the undivided Belly River formation.

CORRELATION METHODS

A fair understanding of Lea Park and Belly River relationships in the area was developed through the interpretation of the data obtained from an extensive

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core-drill program. This interpretation was greatly aided by the previous work of Nauss (1945) in the Vermilion part of the area. To arrive at the more regional correlations shown in Figures 1, 2, 3, and 4, it was necessary to apply more local knowledge to the deep-test records throughout the larger area. It was found possible to interpret and correlate the deep-test sections almost completely by electric logs. Many deep-test electric logs were used to confirm correlations and to map, to as great an extent as possible, in three dimensions. The top of the Colorado group provides the best electric-log marker throughout the area; hence, this marker was used as the datum. For each electric log, the datum was established first and correlation proceeded upward through the Lea Park formation without reference to higher features represented by the more variable Belly River beds. It was found that very slight electric-log features in the marine Lea Park could be traced for long distances; examples of such correlations are shown in Figures 2, 3, and 4. Confirmation of the main electric-log correlation characteristics was obtained by microfaunal zoning. In this connection it will be appreciated that the electric logs in the figures have lost much distinctive detail in reproduction. Once good correlation is effected through the Lea Park formation, the correlation of the various members of the Belly River formation becomes fairly obvious.

A few of the deep-test sections correlated in this manner have been included in the figures for illustration purposes. For the most part, a well within the area can be correlated by the electric log if located with its proper reference to the section lines AB, CB, or DE, and Figure 1.