DIAGENESIS OF GLACIOMARINE SANDSTONES RELATED TO CLIMATE AND GLACIAL PROCESSES IN MCMURDO SOUND, ANTARCTICA

Controls on the diagenesis of polar sedimentary successions are not yet well-constrained. This work investigates the diagenesis of sandstones from the Cape Roberts Project (CRP) 2A drilled in McMurdo Sound, Antarctica in 1998. Thirty-eight thin sections were sampled from the Oligo-Miocene section spanning 27-624 m below sea floor (mbsf) for systematic petrographic documentation of diagenetic phases within the context of a well-established sequence stratigraphic framework using standard petrography, point counting microscopy methods, and cathodoluminescence microscopy. Thin section analysis reveals a complex diagenetic history in the sandstones, ranging from early (pre-compaction) to coarse late (burial) intergranular cements. Secondary carbonate occurs as replacement and cement phases in microcrystalline, blocky and poikilotopic forms. Texturally submature and mature sandstones dominate the Oligocene section (below c. 302 mbsf), while the Miocene section consists of predominantly textually immature and heavily carbonate-cemented sandstones indicating little chemical weathering. Secondary porosity is enhanced due to the dissolution of matrix, intergranular cements, feldspars and sedimentary lithic fragments, particularly in the Oligocene section. The depth coincides with the onset of Mi-1 Glaciation at the Oligo-Miocene boundary (c. 34 Ma), which terminated the temperate climate conditions through the Oligocene and established the Antarctic cryosphere. In addition, texturally immature sandstones with limited chemical weathering appearing within multiple Oligocene sequences suggest frigid climate periods during the Oligocene.

Paragenesis patterns in the CRP-2A core highlight the influences of climate and glacial processes on sandstone diagenesis. Furthermore, significant sandstone porosity (~30%) preserved in multiple glacial advance and retreat cycles indicates high reservoir potential in glaciogenic deposits, which could serve as an analog for ancient glaciogenic hydrocarbon reservoirs worldwide. Future work will integrate geochemical methods to fingerprint the origin and distribution of diagenetic fluids and examine relationships between climate change and glacial processes in the CRP-2A core as well as other cores recovered in McMurdo Sound.