麻豆传媒

B. Sc. Honours Thesis

(PDF - 7.1 Mb)

Previous studies have documented the presence of magnetic polarity reversals, which could represent the earliest M0 or M1 reversal of the M-Sequence, in the Early Cretaceous (Aptian-Barremian) sedimentary/volcanic stratigraphic sequence of Axel Heiberg Island. These reversals occur within uncorrelated tholeiitic basalts of the Walker Island Member of the Isachsen formation which have within-plate to N-type MORB characteristics. The two main goals of this study are to accurately correlate the basalt units and to then date the determined reversal(s) by the whole-rock ⁴⁰Ar/³⁹Ar procedure. A combination of standard trace element analysis and multivariate statistics (Chernoff's icons) was used successfully to correlate chemically similar flows. Both types of analysis confirm the existence of only one reversal (M0) in the study area. This is the first time icons have been used to represent the chemical relationships in basaltic sequences and the success with this study may encourage future applications.

The results of the whole-rock ⁴⁰Ar/³⁹Ar age analysis provide an age (89-93 Ma), too young for the Walker Island Member that has an Aptian to Barremian (115-125 Ma) paleontological age constraint. One dated sample exhibits an excellent age plateau which is attributed to the argon degassing of a potassium feldspar-bearing crystallization product formed from the original glasses in the sample. As a result, the anomalously young age is interpreted as dating a thermal event which may have coincided with the eruption of the younger (Late Albian to Early Cenomanian) Strand Fiord Formation.

Keywords: Chernoff's icons, basalt, Walker Island Member, Isachsen Formation, Strand Fjord Formation, whole-rock ⁴⁰Ar/³⁹Ar, magnetic polarity, M-Sequence, MO.
Pages: 102
Supervisor: Gunter Muecke