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CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 35 (1987), No. 3. (September), Pages 239-250

Diagenesis in the Lacustrine Facies of the Albert Formation, New Brunswick, Canada: A Geochemical Evaluation

D.J. Mossman, J.F. Macey,, P.D. Lemmon,

ABSTRACT

The Upper Devonian to Lower Carboniferous terrestrial strata of the fault-bounded Moncton Sub-basin of the Maritimes Basin include the Albert Formation, a predominantly lacustrine facies. Major lithotypes of this facies are calcareous/dolomitic shales, siltstone and fine-grained sandstone. The maturation level of kerogen in oil shale and related units is typical of an early diagenetic stage equivalent to the clay carbonate facies of burial metamorphism. Diagenesis involved the growth of new minerals, recrystallization, and movement of fluids. Maturation resulted in the release of bitumen from kerogen. Although some redistribution of inorganic elements also took place, the element associations preserved in these rocks were determined primarily by syngenetic conditions.

Geochemical data indicate that the shales of the Albert Formation contain as much or more mental than any other lithotype, except for Ti and Sr in some sandstone samples. Enrichment of the lacustrine facies in certain elements, notably Ti, Y and Zr, is explicable in terms of known bedrock provenances. New geochemical data for 16 elements in each of 68 samples from various sections through the lacustrine facies have been analyzed using R-mode Previous HitfactorNext Hit vector analyses. Three distinct associations of metals are recognized, namely: Sr-Ga-Cr-Rb-Zn-Nb-Ti, V-Ni-Th-Y-P, and Zr-Pb-Ba-Cu. Statistical analysis supports the contention, defensible on strictly geological grounds, that the three principal processes that account for geochemical variation among samples are, in order of decreasing importance: 1. syngenesis, 2. lateral secretion (i.e., early diagenetic processes), 3. post-depositional circulation of ground waters.

DIAGENESE DANS LES FACIES LACUSTRES DE LA FORMATION ALBERT, NOUVEAU-BRUNSWICK, CANADA -- UNE EVALUATION GEOCHIMIQUE

RESUME

La formation Albert, un facies a predominance lacustre, est comprise dans les strates continentales du Devonien superieur au Carbonifere inferieur du sub-bassin Moncton, qui est borne par des failles et qui fait partie du Bassin Maritime. Les lithotypes principaux de ce facies sont des argiles calcaires/dolomitiques, des microgres et des gres a grain fin. Le niveau de maturation du kerogene dans les schistes bitumineux et les strates connexes est typique d'une etape du debut de la diagenese qui equivaut au facies des roches carbonatees argileuses du metamorphisme d'enfouissement. La diagenese impliqua la croissance de nouveaux mineraux, la recrystallisation, et le deplacement de fluides. La maturation aboutit a la liberation de bitume du kerogene. Quoiqu'une redistribution partielle des elements inorganiques eut aussi lieu, les groupements d'elements conserves dans ces roches ont ete determines principalement par les conditions syngenetiques.

Les donnees geochimiques montrent que les argiles de la formation Albert contiennent autant ou plus de Previous HitmetalNext Hit que n'importe quel autre lithotype, excepte la teneur en Ti et en Sr de certains echantillons de gres. L'enrichissement des facies lacustres en certains elements, notamment le Ti, l'Y et le Zr, est explicable en termes de connaissance de provenance d'un substratum rocheux. Des donnees nouvelles, pour 16 elements dans chacun des 68 echantillons tires de diverses coupes a travers les facies lacustres, ont ete analysees en utilisant l'analyse vectorielle du facteur R-mode ("R-mode Previous HitfactorTop vector analysis"). Trois associations distinctes sont reconnues, c'est-a-dire: Sr-Ga-Cr-Rb-Zn-Nb-Ti, V-Ni-Th-Y-P, et Zr-Pb-Ba-Cu. L'analyse statistique appuie l'affirmation, soutenable par des donnees strictement geologiques, que les trois principales operations expliquant les variations geochimiques parmi les echantillons sont, par ordre d'importance descendante; 1. syngenese, 2. secretion laterale (c.-a-d. operations diagenetiques precoces), 3. circulation post-sedimentaire des eaux souterraines.


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