Slope and glacis sedimentation on the margin of a promontory : the Ile d'Orleans Group, Quebec Appalachians

Hugues Longuépée, Ph.D. thesis.

Ph.D. thesis in mineral ressources under the supervision of Dr. Pierre A. Cousineau.

Project description

Cambrian and Lower Ordovician rocks from the Quebec Appalachians are the remains of the Iapetus ocean passive margin. In eastern Quebec those rocks are deep-water turbidites, while in western Quebec they are wide platform deposits. It is thus difficult hard to correlate rocks from each sides of Quebec City. It is permitted to think that there is a brutal change in sedimentation style (and palaeogeography) in the area. One reason for that change might be the presence of the Montmorency promontory. Such of feature would be result in a particular sedimentary sequence. The Ile d'Orléans Group might represent that sequence.

The Ile d'Orléans Group is mainly found in the Bacchus Nappe, which is the external-most of the allochthonous thrust sheet. The Group is composed of the Anse Maranda, Lauzon and Pointe-de-La Martinière Formations. All these Formations have been previously interpreted as deep-water turbidites because they have a similar look as the rocks from eastern Appalachians. However, a closer look at the Formations suggests otherwise. The purpose of the project is to define the sedimentary environment of the Ile d'Orléans Group and to establish its relation with the Montmorency promontory.

The thesis is part of the NATMAP/CARTNAT project of the Geological Survey of Canada.

Phase 1: The Anse Maranda glauconite (paper submitted)

The Anse Maranda Formation is unique in the Quebec Appalachians because it is the only one containing a significant amount of glauconite. This mineral is of interest because 1) it gives to the rock its green color (on which previous correlations have been made) and 2) it suggests low sedimentation rates. Petrographic, textural and geochemical studies showed that the Anse Maranda green pellets are formed of glauconite and that they are autochthonous, thus the Anse Maranda was deposited in a low sediment input environment. The rocks green color is however caused by the presence of diagenetic chloritization of feldspar.

An interesting result from the glauconite study is its high aluminium nature. It is the result of early diagenetic aluminium - iron substitution. There is a potassium loss associated with the substitution. This loss has an effect on the glauconite maturity evaluation. The factor controlling this substitution is thought to be an enhance mobility of ferrous iron in presence of organic matter, but this hypothesis will not be tested in the current project.

Phase 2: Sedimentology of the Anse Maranda Formation (in redaction)

The Anse Maranda is a Cambrian coarsening-upward sequence. It is unique in the Quebec Appalachians because it is glauconite-rich. It is also particular because there are almost no primary sedimentary structures left. What have been previously interpreted as T_a and T_e turbidites are in fact alternating bioturbated sandstones and mudstones. Identified burrows are Planolites, Chondrites, Palaeophycus and Helminthopsis. There are some indications as for the occurrence of other traces such as Skolithos, thalassinoids, ophiomorpha and Bergaueria. All these traces are part of the Cruziana, Skolithos and Zoophycos ichnofacies which suggest an outer shelf environment.

The Anse Maranda Formation would represent an outer shelf environment (ichnology) with low sediment influx (glauconite) deposited during a sea-level fall (coarsening-upward sequence). Achritarch biostratigraphy indicates that the Anse Maranda Formation what deposited was deposited during the Sauk II para-sequence. The eustatic variations interpreted for the Anse Maranda Formation are similar to those on the inner shelf in the Montreal and Ottawa areas.

The study of the Anse Maranda Formation will also lead to a modification in the Appalachians stratigraphy. The Saint-Bernard-sur-Mer Formation, located exclusively on the Ile-aux-Coudres, will be abandoned because it is a lateral extension of the Anse Maranda Formation.

Phase 3: Sedimentology of Lauzon and Pointe-de-La Martinière Formations (thinking about it)

There is still some data to be collected (XRD) but otherwise all field and lab work is done. At the first sight, there are two points worthy of attention.

1) What have been mapped as ABCDE turbidites in the Lauzon Formation are in fact reworked turbidites. Reworking by either storm wave or contour current indicates a shallower depth than the deep-water setting previously interpreted.

2) Occurrence of conglomerate in the Pointe-de-La Martinière makes it a proximal equivalent of the well-known Rivière Ouelle Formation. Two points have to be checked for the Pointe-de-La Martinière Formation: a possible source duality (passive margin and taconnian orogen) and an influence from the peripheral bulge.

Papers, talks and other

Longuépée, H. and Cousineau, P.A. (accepted). Reappraisal of the Cambrian glauconite-bearing Anse Maranda Formation, Québec Appalachians: from deep-sea turbidites to clastic shelf deposits. Canadian Journal of Earth Sciences.

Longuépée, H. and Cousineau, P.A., 2003. Palaeogeography of the Cambrian Laurentian Margin within the Quebec Reentrant. GSA Northeastern - AGS joint meeting 2003. Halifax, N.S.

Hill, P.R., Meulé, S. and Longuépée, H., 2003. Combined-flow processes and sedimentary structures on the shoreface of the wave-dominated Grande-rivière-de-la-Baleine delta. J. of Sedimentary Research, vol. 73 (2)

Cousineau, P.A. and Longuépée, H., 2003. Lower Paleozoic configuration of the Quebec reentrant based on improved along-strike paleogeography. Canadian J. of Earth Sciences, vol. 40, p. 207-219.

Longuépée, H. and Cousineau, P.A., 2002. Chemical modification of autochtonous glauconite during diagenesis. The clay mineral Society Annual Meeting, Boulder, Colorado. June 8-13, 2002, p. 119.

Longuépée, H., and Cousineau, P.A., 2001, New depositional environment for the Île d'Orléans Group, Quebec Appalachians., Geological Survey of Canada, Current Research 2001-D14, p. 7.

Longuépée, H., 2000. Distribution des figures et faciès sédimentaires d'un delta en régression forcée, Grande-Rivière-de-la-Baleine, Nouveau Québec. Mémoire de maîtrise en océanographie. UQAR, 181 pages.

Question or commentary contact me: hugues_longuepee@uqac.ca.