Submarine lithification of carbonate sediments.

Area of Science:

• Geology
• Oceanography
• Isotope Geochemistry

Background:

• Guyots are submerged extinct volcanoes that can host unique geological formations.
• Marine carbonate diagenesis is influenced by water chemistry and burial rates.
• Oxygen isotopes in carbonates record environmental conditions at the time of formation.

Purpose of the Study:

• To investigate the diagenetic processes affecting planktonic limestones from North Atlantic guyots.
• To determine if the recrystallization of these limestones occurred under marine or meteoric conditions.
• To understand the role of seawater in the lithification of deep-water carbonates.

Main Methods:

• Oxygen-isotopic analysis of recrystallized planktonic limestones.
• Geochemical analysis of carbonate mineralogy (e.g., calcite composition).
• Comparison of isotopic and chemical data with ambient North Atlantic seawater conditions.

Main Results:

• Recrystallized limestones are in oxygen-isotopic equilibrium with present-day ambient North Atlantic waters.
• Evidence suggests early-stage lithification involves magnesium-rich calcite, which inverts to magnesium-poor calcite over time.
• The observed lithification likely requires extremely low rates of sediment accumulation.

Conclusions:

• Submarine lithification and recrystallization are the dominant diagenetic processes for these guyot limestones.
• The transformation from magnesium-rich to magnesium-poor calcite is a key indicator of prolonged sub-seafloor alteration.
• Low sediment accumulation rates are crucial for facilitating extensive submarine diagenesis in carbonate platforms.