Atypical diagenetic effects on strontium-isotope composition of Early Jurassic belemnites, Queen Charlotte Islands, British Columbia, Canada

2007 ◽  
Vol 44 (2) ◽  
pp. 181-197 ◽  
Author(s):  
Darren R Gröcke ◽  
Stephen P Hesselbo ◽  
Duncan J Findlay
Keyword(s):  
British Columbia ◽  
Isotope Composition ◽  
Early Jurassic ◽  
Striking Similarity ◽  
Geochemical Data ◽  
Screening Methods ◽  
Element Abundances ◽  
Queen Charlotte Islands ◽  
Diagenetic Alteration ◽  
Carbon And Oxygen Isotope

In this study, strontium-, carbon- and oxygen-isotope data are reported from Early Jurassic belemnites from Yakoun River, Queen Charlotte Islands (QCI), British Columbia. Assuming that the established ammonite correlations between Canada and Europe are accurate, the seawater 87Sr/86Sr curve between Europe and QCI should be similar. However, the Rarenodia planulata and Phymatoceras crassicosta ammonite biozones from Yakoun River record 87Sr/86Sr values that are lower than expected. This shift is interpreted to be a result of diagenetic alteration by later hydrothermal fluid (87Sr-depleted). In general, the diagenetic samples have more negative δ13Cbel and δ18Obel values, and higher Mn concentrations, but show no difference in Fe concentration. A δ13Cbel curve from diagenetically screened samples exhibits only slightly depleted values with respect to a similar curve generated from Europe. A similar curve for δ18Obel shows a striking similarity with that generated from Europe. This study illustrates that diagenetic effects on Sr-isotope composition can lower values from the expected seawater 87Sr/86Sr curve, thus potentially producing erroneous correlations between ammonite biostratigraphic schemes. Traditional screening methods for diagenesis, such as cathodoluminescence and trace-element abundances, were inadequate for evaluating diagenesis in the Yakoun River sections. Other such studies must also consider alternative and (or) a combination of methods in evaluating geochemical data from belemnites.

Late Precambrian marbles of unusual carbon-isotope composition, southeastern British Columbia

1985 ◽  
Vol 22 (3) ◽  
pp. 324-329 ◽  
Author(s):  
Edward D. Ghent ◽  
James R. O'Neil
Keyword(s):  
British Columbia ◽  
Carbon Isotope ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Large Reservoir ◽  
Kinetic Isotope ◽  
Carbon And Oxygen Isotope ◽  
Isotope Equilibrium ◽  
Mineralogical Phase ◽  
Isotope Analyses

Carbon- and oxygen-isotope analyses were made of both carbonates and graphites from several Precambrian metamorphic samples from British Columbia. The carbon-isotope data are unusual in that the δ13C values of many marbles are very high, up to 9.9, and the most positive values occur in the sillimanite-zone rocks. The δ13C values of graphite are also relatively high, and the 13C fractionations between calcite and graphite suggest that (1) the rocks attained and retained carbon-isotope equilibrium during metamorphism, and (2) the temperature of graphite equilibration in marbles from the sillimanite zone is 650–690 °C, in agreement with temperatures estimated from mineralogical phase equilibria.Possible precursor carbonates for the 13C-rich marbles in British Columbia include (1) Precambrian carbonate-secreting organisms such as algae that participate in reactions with large kinetic isotope effects, (2) carbonates that exchanged carbon isotopes with a large reservoir of organic material prior to metamorphism, and (3) travertines.

An Early Jurassic ichthyosaur from the Sandilands Formation, Queen Charlotte Islands, British Columbia

1990 ◽  
Vol 64 (5) ◽  
pp. 850-853 ◽  
Author(s):  
Shane S. Dennison ◽  
Paul L. Smith ◽  
Howard W. Tipper
Keyword(s):  
British Columbia ◽  
North America ◽  
Axial Skeleton ◽  
Early Jurassic ◽  
Vertebral Centra ◽  
Queen Charlotte Islands ◽  
Partial Skeleton

A partial skeleton, including a skull with part of the axial skeleton, part of a second skull, and fragments of ribs have been recovered from the Sinemurian of the Sandilands Formation exposed at Kennecott Point in the northwestern Queen Charlotte Islands. This material is the most complete Early Jurassic collection from North America reported to date; other occurrences include a forefin from the Nordegg Formation (Sinemurian) of Alberta positively identified as Ichthyosaurus (McGowan, 1978) and vertebral centra from the Nicely Formation (Pliensbachian), Oregon, not assigned conclusively to a genus (McGowan, 1978). The discovery of ichthyosaurs in the allochthonous insular belt of British Columbia adds weight to the contention that ichthyosaurs were cosmopolitan in their distribution (McGowan, 1978; Orr, 1986).

Dissolution and recrystallization in modern shelf carbonates: evidence from pore water and solid phase chemistry

1993 ◽  
Vol 344 (1670) ◽  
pp. 27-36 ◽  
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
Solid Phase ◽  
Chemical Exchange ◽  
Isotope Composition ◽  
Geochemical Data ◽  
Carbonate Sediments ◽  
Pore Waters ◽  
Carbonate Minerals ◽  
Carbonate Production

We present an overview of geochemical data from pore waters and solid phases that clarify earliest diagenetic processes affecting modern, shallow marine carbonate sediments. Acids produced by organic matter decomposition react rapidly with metastable carbonate minerals in pore waters to produce extensive syndepositional dissolution and recrystallization. Stoichiometric relations among pore water solutes suggest that dissolution is related to oxidation of H 2 S which can accumulate in these low-Fe sediments. Sulphide oxidation likely occurs by enhanced diffusion of O 2 mediated by sulphide-oxidizing bacteria which colonize oxic/anoxic interfaces invaginating these intensely bioturbated sediments. Buffering of pore water stable isotopic compositions towards values of bulk sediment and rapid 45 Ca exchange rates during sediment incubations demonstrate that carbonate recrystallization is a significant process. Comparison of average biogenic carbonate production rates with estimated rates of dissolution and recrystallization suggests that over half the gross production is dissolved and/or recrystallized. Thus isotopic and elemental composition of carbonate minerals can experience significant alteration during earliest burial driven by chemical exchange among carbonate minerals and decomposing organic matter. Temporal shifts in palaeo-ocean carbon isotope composition inferred from bulk-rocks may be seriously compromised by facies-dependent differences in dissolution and recrystallization rates.

III.—Recent Observations on the Glaciation of British Columbia and Adjacent Regions

1888 ◽  
Vol 5 (8) ◽  
pp. 347-350 ◽  
Author(s):  
Geo. M. Dawson
Keyword(s):  
British Columbia ◽  
Glacial Period ◽  
Coast Range ◽  
Coast Mountains ◽  
One Stage ◽  
Queen Charlotte Islands ◽  
Glacier Ice ◽  
Inland Ice ◽  
Great Valley ◽  
The U.S

Previous observations in British Columbia have shown that at one stage in the Glacial period—that of maximum glaciation—a great confluent ice-mass has occupied the region which may be named the Interior Plateau, between the Coast Mountains and Gold and Eocky Mountain Kanges. From the 55th to the 49th parallel this great glacier has left traces of its general southward or southeastward movement, which are distinct from those of subsequent local glaciers. The southern extensions or terminations of this confluent glacier, in Washington and Idaho Territories, have quite recently been examined by Mr. Bailley Willis and Prof. T. C. Chamberlin, of the U.S. Geological Survey. There is, further, evidence to show that this inland-ice flowed also, by transverse valleys and gaps, across the Coast Range, and that the fiords of the coast were thus deeply filled with glacier-ice which, supplemented by that originating on the Coast Range itself, buried the entire great valley which separates Vancouver Island from the mainland and discharged seaward round both ends of the island. Further north, the glacier extending from the mainland coast touched the northern shores of the Queen Charlotte Islands.

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