Sediment geochemistry of the Lower Jurassic Gordondale Member, northeastern British Columbia

Abstract

Paleoenvironments during the Jurassic Gordondale Member sedimentation have been investigated using detailed geochemistry. Four offshore marine litho-stratigraphic units occur within the Gordondale in the Peace River Embayment area of northeastern British Columbia (NE B.C.). The basal mudstone conglomerate/breccia unit (unit A) represents the initiation of a transgression across the basin. The overlying phosphatic marlstone (unit B) was deposited during a time of high organic productivity, characterized by enrichments in the productivity proxying element P 2 O 5 and total organic carbon (TOC) contents averaging 5.5 weight percent. Under these conditions, bio-productivity elements (V, Cr, Cu, Ni, Zn) were effectively incorporated with the organic fraction (matrix bituminite). The co-occurrence of the marine phosphate francolite and pyrite suggests the dysoxic-anoxic redox boundary oscillated vertically in the sediment with time.A shift in geochemistry occurs at the onset of the overlying unit C deposition. Unit C sediments are highly siliceous, low in detrital proxying elements (e.g. Al 2 O 3 , K 2 O, Fe 2 O 3 , TiO 2 , Rb, Co, Zr, Nb) and characterized by high TOC (6-21 weight percent). Excess SiO 2 (i.e. silica which cannot be accounted for by the aluminosilicate phase) accounts for up to 94% of the SiO 2 in the organic-rich sections, suggesting a biosiliceous source. A productive water column is also inferred by relatively high Ba concentrations. The low concentrations of all other major oxides and trace metals in unit C reflect silica dilution in the depositional basin. Carbon-S-Fe plots show a sulfidic bottom-water environment persisted for much of unit C deposition where S was concentrated into the organic fraction (alginite and matrix bituminite) due to the lack of Fe available for pyrite formation.Unit D represents two different stages of sedimentation. The contact between units C and D is marked by a phosphatic rich-marlstone, depleted in all major and trace elements except CaO, P 2 O 5 and Mn. The enrichment of Mn in the carbonate suggests dissolved oxygen was present in bottom waters. Thereafter, unit D is dominated compositionally by detrital proxying elements (clays and associated elements such as Ti, K and Fe) reflecting an increase of terrigenous input. However, despite the sediment-dilution by aluminosilicate phases, TOC contents are comparable to unit B, averaging 5.6 weight percent. RÉSUMÉLes paléoenvironnements durant la sédimentation du Membre Gordondale du Jurassique ont été étudiés en utilisant une géochimie détaillée. Quatre unités lithostratigraphiques marines hauturières apparaissent à l'intérieur du Gorgondale dans la région de la baie de Peace River au nord-est de la Colombie Britannique (NE CB). L'unité de base de conglomérat /brèche de mudstone (unité A) représente le déclenchement d'une transgression à travers le bassin. La marlstone phosphatée superposée (unité B) s'est déposée durant une production organique élevée, caractérisée par des enrichissements dans la productivité d'éléments...

Analysis of geological effects on methane adsorption capacity of continental shale: a case study of the Jurassic shale in the Tarim Basin, northwestern China

“…The Jurassic shale in the Tarim Basin is lower in the TOC content compared to the marine shales in North America and South China. Therefore, they are lacking organic‐lean samples and indicate no piecewise characteristic (Ross and Bustin, , ; Hickey and Henk, ; Chalmers and Bustin, ).…”

“…However, researches on marine shale adsorption capacity manifest that organic matter and mineral matter are the two dominant effects, which can provide an insight into the possible influences for continental shale. An apparent positive linear relationship between methane adsorption capacity and TOC content has been proved (Lu et al ., ; Ross and Bustin, , ; Hickey and Henk, ; Chalmers and Bustin, , ). The clay minerals have certain adsorption capacity in spite of their lower surface area than organic matter (Faiz et al ., ; Yee et al ., ; Crosdale et al ., ; Laxminarayana and Crosdale, ).…”

Sedimentary and residual gas geochemical characteristics of the Lower Cambrian organic-rich shales in Southeastern Chongqing, China

“…Hence, in marine sediments, the use of quartz as a proxy for detrital input must be performed with caution. Biogenic quartz has been reported in an extensive study of North American black shales (Turgeon and Brumsack, 2006;Ross and Bustin, 2006;Chalmers et al, 2012).…”

Chemo‐ and Biostratigraphy of the Jurassic Oil Shales from the Qiangtang Basin, Northern Tibet, China: A Case Study of the Toarcian Oceanic Anoxic Event

“…The higher Ni/ Co and V/Cr ratios relate to increasingly deficient oxygen levels during deposition (Jones and Manning, 1994), due to the relative easiness at which Ni and V is sequestered by organic matter in reducing sediments. In addition, Cr and Co concentrations are thought to be a function of detrital content and not influenced by redox conditions (Ross and Bustin, 2009).…”