Shelby Anderson
GEO 1131.002
Dr. Suarez
December 18, 2014
Deposition History of North Eastern Canada
Chuar Group
The Chuar Group was first deposited in the Proterozoic Eon. Index fossils of early
shallow marine organisms, such as
stromatolites (Figure 1), provide the link to the
beginning of life organisms on Earth during an
expanding glaciation period. The Chuar Group
was predominately mudstone combined with
the early stromatolite organisms in the upper
Figure 1
portion of the group.
Tremadoc Formation and Labrador Formation
As sea level rose during the Sauk Sequence, the deposition of the Tremadoc and
Labrador Formations, were next deposited over the Chuar Group. The rise of sea
level lasted through the Cambrian Period effecting the early Tremadoc and Labrador
Formations. First the Tremadoc Formation, consisting of mostly shale and limestone
was deposited with indications of reef builders such as Archeocyatha (Figure 2),
from the Camberia Period and the mullosca Endoceras (Figure 3). Following, the
Labrador Formation, consisting of shale and limestone as well was deposited with
fauna such as Olenellus in the Cambrian and Tetragraptus in the Ordovician top. The
Tippecanoe Sequence then resulted in a transgression of seawater causing a trust
fault of these two Formations. The older, Ordovician, strata was thrust up over the
younger, Cambria, strata. This resulted in folding and erosion of these two
formations.
Figure 3
Figure 2
Percha Shale
Following the Cambria-Ordovician Formations the Percha Shale was deposited
creating an angular unconformity. This including rich shale with the presence of
sand. The Percha Shale was deposited during the Silurian Period. Many types of
sponges (Table 1) were found near the base of the shale suggesting rapid burial
from the regresstion of the Kaskaskia Sequence.
Table 1
Formation
Index Fossil
Age
Deposition
Percha Shale
Astraeospongia
Silurian
Marine Reef
Percha Shale
Astylospongia
Silurian
Marine Reef
Salem Limestone
The Salem Limestone is dominated by limestone, which
suggests a marine environment, and with the help of
index fossils this can be proven. The limestone is full of
diverse marine organisms, such as the Phacops (Figure
4). When the Salem Limestone was deposited,
conformable contact on top of the Percha Shale was
present meaning there was not a time gap present.
Younger Devonian fauna from the Salem Limestone was
Figure 4
deposited directly on top of the Silurian fauna present in the Percha Shale.
Paradox Formation
Next, the Paradox Formation was deposited during the Abroska Sequence
suggesting the rise of sea level. This
suggestion is indicated by fauna, such as
Archimedes (Figure 5) and Conularia. These
index fossils date back to the Pennsylvanian
Period signifying the absence of
Figure 5
Mississippian rocks or fauna after the Salem Limestone. This absence is called a
Paraconformity.
Pierre Shale
Finally, the Pierre Shale was deposited as an angular unconformity on top of the
eroded Percha Shale, Salem Limestone and Paradox Formation. This Shale has a
range of index fossil from small mullosca Tigonia (Figure 6) to larger Belemnite
(Figure 7). This indicates that sea level was high during the Zuni Sequence of the
Cretaceous period in which these index fossils date from.
Figure 6
Figure 7