麻豆传媒

B. Sc. Honours Thesis

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It is the purpose of this study to interpret the sedimentary environment which produced the St. Mary River Formation (SMRF) . This study attempts to expand on the preliminary sedimentological work of previous authors py integrating outcrop and subsurface data.

The data base used includes the formation outcrop where a 95m vertical section was measured, well logs, seismic profiles and published reports. The interpretation is based on the geological setting as established from the literature, the stratigraphic relationships as determined from well logs, and a facies analysis from sedimentary facies identified in the measured section.

A review of the structural setting from the literature is undertaken as a prerequisite to interpreting the sedimentary environment. A new structural cross-section is presented based on seismic profiles and exploratory oil wells.

The SMRF is identified en well logs by characteristic resistivity and sonic log character. From logs the formation is subdivided into two members, a thick upper member ( 405m-4 ?Om) and a rruch thinner l:::a.sal member (about 30m).

The SMRF is well established in the literature as a terrestrial deposit and is interpreted as a fluvial sequence. Four sedimentary facies are recognized; 1) a mudstone facies, representing overbank deposition fran suspension; 2} a trough cross-bedded sandstone facies, representing channel deposits; 3) a rippled sandstone facies, representing overbank deposition of coarse grained sediments onto the flood. plain; and 4) a coarsening upward facies, representing the overbank deposits of crevasse splays.

In attempting to interpret a specific fluvial system for the SMRF, several established models were used for comparison. The &4RF shares many attributes of both meandering and low-sinuosity river systems, making a specific system difficult to determine. However, a low-sinuosity river system is preferred.

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Pages: 75
Supervisor:听 Martin Gibling / G. C. Milligan