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S.B.Misra, Department of Geology, Memorial University of Newfoundland, St. Johnís, Newfoundland, Canada

M.S.Thesis, Memorial University., Newfoundland. Canada, p.139., 1969.

Geology of Biscay Bay-Cape Race area, Avalon Peninsula,
South Eastern Newfoundland

MISRA, S.B., (1969a)

CONTENTS
1 CHAPTER I : INTRODUCTION
2 CHAPTER II : GENERAL GEOLOGY
3 CHAPTER III : PRIMARY SEDIMENTARY STRUCTURES
4 CHAPTER IV : SECONDARY STRUCTURES
5 CHAPTER V : PRECAMBRIAN LIFE
6 CHAPTER VI : DEPOSITIONAL HISTORY OF THE AREA
<<  Chapter IV Chapter VI >>

CHAPTER V

Precambrian Life



 
Mode of Occurrence
Description of fossils
  - Spindle -shaped Organisms
  - Leaf - shaped Organisms
  - Round lobate organisms
  - Radiating organisms
Discussion
Plates
Fossils in the Conception Group wee discovered by the author (Misra, 1968) in the map-area (Fig. 1-1)during the summer of 1967. A preliminary account of the fossil bearing rocks and a general discussion on the age of the rocks has already been given by Anderson and Misra (1968). Although only one type of impression was illustrated in the 1968 communication, three other new types have been found at the same locality and in addition two sub-types of the fossil already reported can be distinguished. The terms type and sub-type are used here in the non-technical sense and each type possibly includes one or more genera.

Prior to the discovery of Precambrian fossils in the Biscay Bay-Cape Race area, there was no record of life in the Precambrian rocks of eastern Newfoundland, except for the doubtful fossil Aspidella terranovica Billings from the St. John's Formation. Indeed, throughout the whole North American continent there are only a few Precambrian fossil occurrences (Bassler, 1941; Van Gundy, 1951; Alf, 1959; Frarey and McClaren, 1963). Most are doubtful except the apparent Jelly fish impression discovered by C.A. Van Gundy and reported by Bassler (1941), who classified the imprint as Brooksella canyonensis. This form resembles some of the round lobate types and other lobed fossil impressions of the map-area.

The most important Precambrian fossil locality thus far reported is in the Ediacara hills in South Australia. It was discovered by an Australian geologist, R.C.Sprigg, during field studies in 1947. The Ediacara hills fauna includes Jelly fish, soft corals related to Pennatulids, segmented worms, and other animals (Glaessner, 1961). Most of these organisms belong to the Phyla Coelentereta and Annelida (Glaessner and Wade, 1966). Precambrian fossils are known also from South Africa and England (Glaessner, 1959).

Mode of Occurrence

Fossils of the Precambrian Conception Group occur as hundreds of impressions on ripple marked surfaces of graded greywackes in the coastal exposures of the Cape Cove Formation near Mistaken Point. They have been observed at several horizons within a thickness of about 175 ft. and the fossil bearing planes are generally overlain by a 1-2cm. thick layer of volcanic tuff (see marginal areas of Fig. 5-6).

As the fossils probably represent floating organisms, they are interpreted as having come to rest on the flat muddy bottom and made either imprints on the mud or were entombed bodily. However, if they were not floating but sessile animals, they must have been living on the bottom of the sea during the intervening quiescent period between two successive turbidity currents and lived until they were covered by the sediments brought down by the currents. In either case, the surface of mud provided an ideal medium for preserving imprints and the forms, regardless of their size and shape, are clear and well defined.

The fossil bearing rocks are exposed only on the coast and the lateral extension of the beds inland is not known. Investigations at the projected same stratigraphic level at Cape Cove did not reveal fruitful results. It is probable that the population of organisms was most dense near Mistaken Point, and although lateral and vertical extension of the fossil bearing beds and change in the fossil characters with time are not known, the concentration of animal impressions in a limited area suggests that these soft bodied Metazoans constituted a flourishing fauna during the time of sedimentation of the Conception Group.

The number of main fossil types, as described below, is small compared with the Ediacara fauna of South Australia but the variations within each type are many. The detailed picture of these variations is as yet not clearly understood. Each fossil type is represented by numerous individuals ranging in size from less than one inch to as much as one foot, usually in random orientation.

The fossils are found on exposed surfaces and those within the reach of sea waves have become worn. However, the surfaces which are either protected or are attacked only occasionally by sea waves show well defined fossils with distinct details of their structure.

The argillites that contain the fossils are fractured and jointed, making it difficult to sample the actual specimens. However, four specimens were collected in the field and studied in thin section. These show no organic remains under the ordinary microscope. Studies under electron microscope or chemical studies may yield better results. In the absence of actual specimens of fossils, the work is confined to photographs and casts of the fossil impressions. Several casts were made in situ using Vinyl modeling clay and investigation on these is still in progress.

DESCRIPTION OF THE FOSSILS

In a very general manner the fossils can be grouped into the following types of impressions:
  1. Spindle-shaped forms
  2. Leaf-like forms
  3. Round lobate forms
  4. Radiating forms
These are the commonest types and each has variations as described below.

Spindle-shaped organisms

Spindle -shaped impressions are the most common of all the fossil types and have wide distribution throughout the locality. They are elongate in shape and are thinner at the ends. They have a bilateral symmetry with a median axis that runs along the entire length of the fossil (Fig. 5-3). The median in some cases is straight (Fig. 5-2) while in others it is zig zag (Fig. 5-2, left). It is not certain if these two shapes of the median axis represent dorsal and ventral views of the same form or if they are different forms.

The length of the Spindle-shaped forms is variable, ranging in most cases from 3cm to 30 cm. All are preserved in their entirety and some impressions exhibit a definite outline. Regardless of size, all contain lateral branches from the median axis, which are divided and sub-divided (Fig. 5-8). In most cases the number of branches on both sides of the median axis is the same but in other cases, one side of the median axis contains an additional branch compared to the other one.

The fossils that have a well defined outline lie in some cases in a position suggesting spiral movement (fig. 5-2D). Whether these forms were crawling is uncertain. However, these animals constitute only a small portion of the total number of Spindle-shaped organisms and the majority of them do not have an outline. Most of the Spindle-shaped organisms, on the basis of lateral branches, are regarded as new forms of a floating Hydrozoan, not previously reported, belonging to the Order Thecata (Glaessner, 1968, personal communication).

There are two other kinds of impressions which resemble Spindle-shaped animals in some respects and may be related to them. One of them (Fig. 5-6C) has branches only on one side of the median axis, is often curved, and is found stratigraphically below the Spindle-shaped impressions. The second kind, although it has body structure similar to that of the Spindle-shaped animals, differs from the common forms in having proportionately longer branches (Fig. 5-11). The form, however, is regarded as closely related to the Spindle-shaped animals, probably a different species.

Leaf-shaped Impressions

These are second in abundance to the Spindle-shaped animals. The fossils are oriented roughly in the direction of turbidity currents with the main part of their body always falling in the direction of flow, i. e. in a southward direction. The fossil impressions (Fig. 5-1) are thought to represent a colony of a Metazoan.

The fossil consists of three parts, a main body having a leaf-shaped structure with a terminal needle-shaped projection, a stalk, and a round base attached to the stalk (Fig. 5-15),. The main body is somewhat round (Fig. 5-`5), divided by branches, and imprints exhibit a definite outline. The form is considered as an imprint of a new floating colonial Hydrozoan and the disc shaped round base is probably a float or medusa. An alternative explanation is that the disc shaped base represents a hold-fast and the main body of the animal was supported on a stalk attached to the base with the long needle like projection upward (Fig. 5-1).

The animals in some cases were broken from the base and moved slightly in the current direction leaving the disc behind. In other cases the main body broke away and the base and stalk are found together (Fig. 5-1F). This is the only organism which is found separate in pieces as well as intact, the other forms are intact.

The sizes of different parts of the fossil were measured for ten specimens (Table 5-1) and these measurements suggest that the fossils represent all the stages of growth of these animals. In a few cases the main body is found compressed and its width reduced. These distorted forms were not used in making Table 5-1. Some forms seem to have lateral branches but others (Fig. 5-14) exhibit a somewhat lobate structure. The details of the fossil in casts are not very clear but the positions of base, stalk, and the main body are evident.

Round Lobate Forms

These fossils resemble Jelly fish (Fig. 5-2A) in shape and outline but do not seem to correspond to any of the recent forms. Two types are distinguishable; the first is a well defined round lobate fossil (Fig. 5-2A) while the second appears like a net in some forms (Fig. 5-2E) but has distinct lobate structure in the other forms (Fig. 5-9A)

An alternative explanation of these objects is that the round lobate forms are floats or Medusae as suggested by the base of the Leaf-shaped objects, yet the base of the Leaf-shaped objects do not show a lobate or any such structure.

Radiating Forms

The fossils are thought to represent as colony of animals rather than a single individual. In arrangement, their needles like bodies diverge from a point where they were joined to one another (Fig. 5-8A). The fossils are not abundant but are found on the entire fossil bearing horizons in the locality.

The fossils may be impressions of Spindle-shaped animals in a different preservation. However, it is also probable that the animals were attached to mud at the point of convergence from where their elongate bodies diverged upward. No actual specimen of the fossils could be collected but the details of structure are clearer in the casts (Fig. 5-13) than in the photographs of the actual specimens (Fig. 5-8A) taken in the field.

DISCUSSION

There are several difficulties in the investigation of these fossils. The first and the foremost difficulty is that the fossils cannot be easily collected so that the work has to be confined to photographs, casts, and a few poor samples. The fossils are found only as impressions, suggesting they were soft bodied Metazoans which constituted a flourishing fauna during late Precambrian times in the Conception Sea. It is not yet clear if, and to what extent, this Precambrian fauna of Newfoundland is related to the Ediacara fauna of South Australia. Some of the forms resemble Rangea, Charnia, Arborea, and Pteridinium which are believed to be related to living Pennatulid corals.

A tentative terminology of the fossils has been worked out and the outcome of the study suggests that the fossil impressions represent an entirely new fauna, heretofore unreported. They are interpreted as a new colonial floating Hydrozoan of the Order Thecata. This interpretation is based on the branching of Spindle-shaped impressions. The Round-lobate impressions may be floats as suggested by the base of the Leaf-shaped objects, or Medusae. The radiating forms may be essentially the same as the Spindles in a different preservation, and the Leaf-like structures may be related. The occurrence of possible Hydrozoa in the Precambrian is of special interest (Glaessner, 1968, personal communications). The taxonomy of the animals, therefore, can be written as follows:

 
Phylum Coelentereta
Class Hydrozoa
Order Thecata
Family Uncertain
Genera to be named

Plates

Fig. 5-2 Photograph showing the following fossils with Round Lobate form , Lobate form with a net like impression, Spindle-shaped organism with well defined outline and curved mid-line suggesting spiral movement, Stalk of a leaf shaped animal,Spindle-shaped organism with defined outline Photograph showing the following fossils with :
  • Round Lobate form
  • Lobate form with a net like impression
  • Spindle-shaped organism with well defined outline and curved mid-line suggesting spiral movement
  • Stalk of a leaf shaped animal
  • Spindle-shaped organism with defined outline F
Fig. 5-3   An enlarged picture of a Spindle-shaped colonial Hydrozoan having a well defined outline. Note also the bent animal above the main organism in the picture.
Fig. 5-4 Several individuals of Spindle-shaped animal and one specimen of leaf-shaped object are seen in the photograph. Several individuals of Spindle-shaped animal and one specimen of leaf-shaped object are seen in the photograph. The main body of the leaf-shaped object is compressed and reduced in width. The spindle-shaped animals are without a definite outline.
Fig. 5-5 Spindle-shaped animals without a definite outline, Radiating form, and a conjugate form of Spindle-shaped animal . Spindle-shaped animals without a definite outline, Radiating form, and a conjugate form of Spindle-shaped animal .
Fig. 5-6 Spindle-shaped animal showing clear structure but no outline, another Spindle-shaped animal with branches only on one side of the mid-line Spindle-shaped animal showing clear structure but no outline, another Spindle-shaped animal with branches only on one side of the mid-line (Fig. and a Leaf shaped impression with distinct structure of its main body .
Fig. 5-7 Spindle-shaped colonial animal with branches divided and subdivided , and several other fossils of the same type. Spindle-shaped colonial animal with branches divided and subdivided , and several other fossils of the same type.
Fig. 5-8 Photograph exhibiting the Radiating forms (centre) Spindle-shaped animals (right centre) & Round Lobate form (bottom centre)  Photograph exhibiting the following :
  • Radiating forms (centre)
  • Spindle-shaped animals (right centre)
  • Round Lobate form (bottom centre) 
  • Fig. 5-9 Round lobate form (Jelly fish) shows distinct lobate structure but is larger than usual and shows no outline. Round lobate form (Jelly fish) shows distinct lobate structure but is larger than usual and shows no outline. a Spindle-shaped animal is also seen lying next to the Round lobate fossil.
    Fig. 5-10 Cast of a Spindle-shaped organism. Note the divided and sub-divided branches from the mid-line. Cast of a Spindle-shaped organism. Note the divided and sub-divided branches from the mid-line.
    Fig. 5-11 Cast of the Spindle-shaped organism with its branches proportionately longer than usual. Cast of the Spindle-shaped organism with its branches proportionately longer than usual.
    Fig. 5-12 Cast of the Spindle-shaped animal with its branches divided and sub-divided Cast of the Spindle-shaped animal with its branches divided and sub-divided
    Fig. 5-13 Cast of the Radiating form Cast of the Radiating form
    Fig. 5-14 Cast of the Leaf-shaped object Cast of the Leaf-shaped object

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