Stratigraphy and conodont biozonation of the lower Devonian limestones, Waratah Bay, Victoria
thesisposted on 2022-03-28, 20:38 authored by John C. Argent
The stratigraphical relationship of a number of limestone sequences belonging to two formations at Waratah Bay, Victoria, has been determined on lithographical and micro-faunal evidence. Two new members have been defined for the WARATAH LIMESTONE. The older, Lower Grinder Member, includes those sequences developed at Point Grinder (lower part). The Black Stack (new name), Robin Rocks and the uppermost part of the Bell Point section. The younger, Mushroom Rock Member, embraces Point Grinder (upper part), Kiln, Bird Rock, Gair Rock and Mushroom Rock sequences. The BELL POINT LIMESTONE, above the unconformity, has been re-defined, so that the uppermost part of the Bell Point section is now assigned to the Lower Grinder Member of the WARATAH FORMATION. The dark grey limestone sequences at the Bluff (Walkerville) and Point Grinder (uppermost part) are relegated to the BELL POINT FORMATION. Detailed description of the various carbonate sequences, together with field maps showing section traverses, are included under Appendix A; Section Profiles are in pocket. An early to middle Siegenian age is attributed to the Waratah Bay limestones on the presence of three diagnostic forms, Spathognothodus sulcatus (PHILIP), S. remscheidensis ZIEGLER and S. exiguous philipi KLAPPER. A conodont biozonation is proposed for part of the Lower Devonian with reference to KLAPPER's (1969) work on the conodont sequence at Royal Creek, Canada, in association with LENZ'S brachiopod stages. The Waratah Bay faunas permit the establishment of two zones and one sub-zone as follows: 1. Zone with Spagnognathodus victoriensis n.ps. and Ozarkodina grinderi n.sp., lying below the S. sulcatus zone; 2. Zone with S. sulcatus, associated with S. remscheidensis in the lower part (sub-zone). Of the 210 samples treated from Waratah Bay, 75 yielded conodonts, representing 13 genera and 40 species. Of these, 32 species are identifiable and 8 species are indeterminate. Six new species with short ranges within the Lower Devonian are described from Waratah Bay and figured on Plates 1 to 9. They are: Belodella australensis n.sp., Ligonodina waratahensis n.sp., Ozarkodina bischoffi n.sp., Ozarkodina grinderi n.sp., Spathognathodus victoriensis n.sp., and Trichonodella australis n.sp. A preliminary interpretation of the palaeo-environment, based on limited petrographic evidence together with conodont frequency, indicates that extremely variable conditions analogous to modern shore-line environments, were partly operative during deposition of the Waratah Bay limestones.