The layers of rock that comprise the sedimentary fill of crustal depressions such as the Scotian Basin bear no obvious indication of age (other than in a very broad relative sense) in their rock (lithostratigraphic) make up or seismic profile. The rocks themselves and their seismic signatures do not tell us whether the age is Jurassic or Oligocene, Bajocian or Burdigalian. And we need this information in order to correlate the rocks from well to well, basin to basin and continent to continent. Only with accurate information identifying the age of sedimentary layers and their correlation can we interpret the physical properties of those layers meaningfully in terms of paleogeography, paleoenvironments and, ultimately, petroleum systems.

Section accross the scotian margin larger image [GIF, 104.7 kb, 600 X 450, notice]

Shown here is a section across part of the Scotian Margin through the wells indicated. Lines represent sequence boundaries, based on seismic markers that reflect physical changes in rock type. Note how the sequence boundaries are discontinuous across the section: correlation and age determination was by means of biostratigraphy (absolute ages of biostratigraphic events based on international calibrations with radiometrically dated rocks). (Figure from Wade et al. 1995, Canadian Journal of Earth Sciences, v.32, p.1462-1473).

Types of microfossils Right image: bisaccate conifer pollen grain (top left), fern spore (top right), angiosperm pollen grain (bottom left), dinoflagellate cysts (dinocysts) (2 larger images) larger image [GIF, 53.4 kb, 600 X 226, notice]

Because of the small size of most samples from offshore wells, microfossils must generally be relied upon for biostratigraphy. For Mesozoic and Cenozoic rocks, the microfossil groups generally employed can be subdivided into two groups: inorganic-walled microfossils, the subject matter of "micropaleontology" in the strictest sense, and organic-walled microfossils , the subject matter of (paleo)palynology. Examples of the fossil groups are shown above. Inorganic-walled microfossils (foraminifera) are shown in the figure to the left, and organic-walled microfossils (palynomorphs) are shown to the right. Of the palynomorphs, the top left illustration shows a bisaccate conifer pollen grain, the top right is a fern spore, the bottom left is an angiosperm pollen grain, and the two larger illustrations show dinoflagellate cysts (dinocysts).

Each fossil species has a first occurrence and a last occurrence, and a selection of such \"biostratigraphic events\" are used to establish ages. (The most famous biostratigraphic event is the extinction of the dinosaurs, 65 million years ago.)

For this project, palynomorphs, primarily dinoflagellate cysts, have been used, although some work on foraminifera and nannofossils has been done. Primarily the palynological work is reported on here (see New Research).