The Sedimentology and Depositional History of the St. Roch Formation near St. Jean-Port-Joli, Quebec

Abstract

<p>The St. Roch Formation (Cambrian), near St. Jean-Port-Joli, Quebec is composed of northeast striking, steep, southerly dipping strata. The stratigraphic sequence (minimum thickness 534 m) is disrupted by several northeast trending, high angle reverse faults which divide the area into a series of imbricated fault blocks.</p> <p>Eight sedimentary facies were recognized in the stratigraphic section: (1) Red mudstone (2) Massive sandstone (3) Pebbly sandstone (4) Classical turbidite - siliceous or calcareous (5) Slurry (6) Pebbly mudstone (7) Pillar greywacke (8) Slump - there are two types: calcisiltite and red mudstone - fine grained turbidite.</p> <p>These facies occur in associations which make up four types of lithologic units:</p> <p>1. The Red Mudstone Units - They are 10-90 m thick and are mainly composed of the red mudstone facies. The red mudstone-fine grained turbidite slump is found in one of these units.</p> <p>2. The Massive Sandstone Units - They are 30-95 m thick and are composed of two facies divisions: a slurry division composed of interbedded slurry beds and classical turbidites forms the lower part of these units and a massive sandstone division composed of the massive sandstone, the classical turbidite plus/minus the pillar greywacke facies forms the upper part.</p> <p>3. The Siliceous Classical Turbidite Units - They are 10-20 m thick and are composed of siliceous classical turbidites and slurry beds.</p> <p>4. The Calcareous Classical Turbidite Units - They are 30-100 m thick and are dominated by the classical turbidite facies. The only occurrences of the calcisiltite slump and the pebbly mudstone facies are found in these units.</p> <p>The stratigraphic section is characterized by the alternation of sandstone and mudstone units. The sandstone units in the lower part of the sequence show a coarsening and thickening upward sequence. No vertical trend in bed thickness or grain size is evident in individual units.</p> <p>The red mudstone, massive sandstone and siliceous classical turbidite units contain paleoflow indicators which have a vector mean of 140°. The calcareous classical turbidites interbedded with the red mudstones and forming the classical turbidite unit at the top of the section have a paleoflow vector mean of 90°. The petrology of the calcareous and noncalcareous sandstones indicates that they were derived from two different sources.</p> <p>The red mudstone, massive sandstone and siliceous classical turbidite units are interpreted as being formed as part of a submarine fan complex. The red mudstone units represent interlobe mud blankets that envelop upper and lower suprafan deposits. The calcareous classical turbidites represent encroachment on the fan system of sediments transported longitudinally along the basin from another source.</p>