Stratigraphy of the Ordovician of the Lac Saint-Jean and Chicoutimi outliers, Quebec

Abstract

Four previously defined formations within the Chicoutimi outlier are extended to the Lac Saint-Jean outlier; these formations are gradational into one another. The lowest of these formations, the Tremblay, is restricted to siliciclastic strata (predominantly coarse-grained sandstones); the overlying Simard, to micritic limestones. This last-named formation is succeeded by the highly fossiliferous Shipshaw Formation, composed of alternating limestones and shales, whereas the youngest of the previously named carbonates, the Galets Formation, is made up of echinodermal calcarenites. Graptolitic shales, herein assigned to the new Pointe-Bleue Shales, overlie in sharp contact the Galets; the youngest limestones of the area, previously assigned to the Richmondian, are different from the other Ordovician limestones. Trilobite faunas from the Shipshaw (and Galets) are correlated with the Edenian; the same correlation is probable for the uppermost of the four informal units recognized within the Simard Formation. The lowest three informal units of the Simard Formation are assigned to the Kirkfieldian; Shermanian strata have not been identified but are probably present. The Pointe-Bleue Shales were previously assigned to the Maysvillian. The Simard Formation contains an "Arctic" fauna, also present in the Manicouagan outlier but yielding in this last case a Shipshaw–Galets trilobite fauna. The Simard fauna, previously correlated with the "Black River," is thus interpreted as significantly time transgressive and of limited stratigraphic use. Depositional environments present in the Lac Saint-Jean and Chicoutimi outliers, but absent in southern Ontario during the Shermanian and Edenian, account for the necessity of significantly increasing the biozones of numerous taxa.

Forced regressive deposits of a deglaciation sequence: Example from the Late Quaternary succession in the Lake Saint‐Jean basin (Québec, Canada)

“…It is located at the north‐western end of the Saguenay graben. Overlaying the Proterozoic igneous basement (Dimroth et al ., ; Rivers, ; Hebert & Van Breemen, ), sedimentary rocks consist of Ordovician limestones (Desbiens & Lespérance, ; Lavoie & Asselin, ). Above, no sediment older than the Late Pleistocene (Late Wisconsinan) has yet been identified (Tremblay, ).…”

Lower Paleozoic configuration of the Quebec reentrant based on improved along-strike paleogeography

“…It is not known if the sandy flysch and the molasse deposits were removed by later erosion or were never present in the area. The Pointe-Bleue Shales (Desbiens and Lespérance 1989) are a calcareous mudstone located at the head of the Saguenay River (Fig. 2) that is a correlative to the lower flysch of the FRA (Harland et al 1985).…”

Upper Ordovician facies in the Lac Saint‐Jean outlier, Québec (eastern Canada): palaeoenvironmental significance for Late Ordovician oceanography

“…Outliers of Upper Ordovician strata have been known there since the turn of the century ( Dresser, 1916). Subsequent studies have been directed at mapping these outliers, and on details of their palaeontology, stratigraphy and sedimentology ( Sinclair, 1953; Benoit & Valiquette, 1971; Harland et al ., 1985 , Harland et al , 1987 ; Harland & Pickerill, 1989; Desbiens & Lespérance, 1989; Fillion et al ., 1990 ).…”

“…In this paper, we follow the designation of units introduced by Sinclair (1953) and expanded by Desbiens & Lespérance (1989) which consists of a lower siliciclastic unit (Tremblay Formation) overlain by various limestone units (Simard, Shipshaw and Galets formations) and capped by shales (Pointe‐Bleue Shales). From macrofaunas, Desbiens & Lespérance (1989) considered that the carbonate succession spanned the Kirkfieldian (Trentonian) to Edenian (Cincinnatian) substages (middle to upper part of the Caradocian). New chitinozoan biostratigraphic data confirm that age assignment ( Asselin et al ., 1996 ).…”

“…1). Relying on published information ( Harland et al ., 1985 , 1987; Harland & Pickerill, 1989, Desbiens & Lespérance, 1989), Lavoie (1995) proposed that the transition to cool‐water‐like sedimentation did not reach the Lac Saint‐Jean area in central Québec ( Fig. 1), thus defining a c. 15°S palaeolatitudinal northernmost limit for that event.…”