Calcite cements in carbonates of the Sverdrup Basin, Canadian Arctic Archipelago.
Creators: name: Savard, Martine.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1991
Subjects: subject: Geology.

description: Calcite cements from the Upper Paleozoic sequences 2, 3 and 4 of the Sverdrup Basin (Canadian Arctic Archipelago) are the subject of this study. On a micro-scale, petrography with light microscopy, cathodoluminescence (CL), scanning electron microscopy (SEM) and staining helped to identify two main textural groups of cements, neomorphic and primary. Both are, in turn, subdivided into two categories: calcitized aragonite and recrystallized high-magnesium calcite for the former, and meteoric calcite and burial (late) calcite, for the latter. In neomorphic cements, eleven micro-scale CL eleven patterns can be recognized. The combination of relationships of these patterns suggests that stabilization operated via numerous diagenetic systems and involved more than one dissolution-reprecipitation step. In an associated trace element study, application of Secondary Ion Mass Spectrometry (SIMS) enabled direct measurements of chemical composition in thin sections, constituting a precedent. The precisions obtained were 12, 6, 6 and 6% for Mg, Fe, Mn and Sr, respectively. Petrographic observations guided the micro-sampling for geochemical studies, including $\delta\sp $C, $\delta\sp $O, $\sp‡$Sr/$\sp†$Sr, Sr, Mg, Fe and Mn. For marine neomorphic cements, the CL patterns--or stages of textural preservation--do not correlate with preservation of the isotopic signal. Many texturally well preserved cements show clearly altered isotopic signatures and vice versa. Moreover, a detailed trace element study of uniform cathodoluminescence zones revealed that cements with less than about 1000 ppm of Fe and 225 ppm of Mn may be luminescent, nonluminescent or dull. The existence of this "undifferentiated" domain implies that the redox sensitive Fe-Mn pair is not the sole control of cathodoluminescence zoning. On a regional scale, analysis of the stratigraphic distribution of cements, and of their geochemical attributes, suggests the following main diagenetic trends in the three carbonate sequences. The general succession consists of (1) early marine cementation, (2) recrystallization of marine cements concurrent with late cementation during shallow burial, mostly in a marine environment, and (3) continuing burial cementation at greater depths. In sequence 2, the western region of the Moscovian Sverdrup Basin was affected by upward migration of oxygenated hot waters. This hydrothermal activity apparently ceased prior to burial. In contrast, the eastern early cements were possibly recrystallized first by cold marine waters following drowning, and subsequently by saline waters during shallow burial. In sequence 3, precipitation of early marine cements has been followed by partial exposure of the sequence to meteoric diagenetic realm that resulted, at least partly, in their dissolution and recrystallization. Through the studied time span, the best $\delta\sp $O and $\delta\sp $C estimates indicate that the Sverdrup Sea composition remained relatively constant. (Abstract shortened by UMI.)