TECTONIC IMPLICATIONS OF DEEP SEA LIMESTONE AND PLANKTONIC FORAMINIFERA OF THE NEW CALEDONIA BASIN FROM DSDP SITE 206

There is debate as to the location and orientation of subducted zone and the configuration of both the continental margin and the Eocene arc. The complexity of the region predates the breakup of Gondwanaland; its timing and location of subduction zones and rift zones do not fit well into current tectonic models. By studying the planktonic foraminifera within the Paleocene and Eocene epochs found at DSDP site 206 and constructing a paleoceanographic model, a better idea of the regions tectonic history and eustatic sea level relationship can be deduced. Foraminifera have distinct time frames based on the specific conditions they lived, foraminifera are sensitive to ocean temperatures, depth and salinity, and the taxa vary depending on the conditions. Hence, specific insight can be gained about the relationship between the New Caledonia basin and the island of New Caledonia, and the basin’s relationship to the Lord Howe Rise.

Thin sections were analyzed from DSDP site 206 under a petrographic microscope for any Paleocene-Eocene planktonic foraminifera. The identified taxa were then compared to paleoceanographic models of the South Pacific in order to better constrain the tectonic deformation of the region.

The initial hypothesis is the Eocene planktonic foraminiferal assemblages studied in this core will correlate with the assemblages seen on land in New Caledonia at locations such as Rocher et Voiles, Illot Brun Section, Noumea, Sommet Khian and Koumac. This indicates a forced tectonic uplift on the island of New Caledonia. In support of this hypothesis is the significant counts of  Acarinina bullbrooki, Globigerinitheka mexicana, Globigerina kulgeri, Guembelitroides nuttali, Morozovelloides crassatus, Turborotalia cerroazulensis and Astrotalia palmerae, all a part of the Globigerina Limestone assemblage noted on land. Additionally, Orbulinoides beckmanni was observed in this study, which has its own narrow time index (E12) as well as Morozovella allisonesis which has a narrow time index (E1) and serve as an excellent time indices. Additionally, large concentrations of alveolinids and nummulites were observed. Specifically, providing evidence for tectonic subsidence of the shelf and providing the needed accommodation space for the taxa to reach the basin through carbonate platform flooding and shedding.