Carbonate Diagenesis of the Cenozoic Sedimentary Succession from the CRP-3 Core, Ross Sea, Antarctica
F.S. Aghib 1, C.R. Fielding2 & T.D. Frank2
1CNR - Istituto per la
Dinamica dei Processi Ambientali, Via Mangiagalli, 34, 20133 Milano - Italy
2Department of of Geosciences,
University of Nebraska–Lincoln, Lincoln, NE 68588-0340 – U.S.A
Received 23 January 2001;
accepted in revised form 26 May 2003
Abstract
- The diagenetic features of the Cenozoic glacigenic sedimentary succession
recovered at the CRP-3 drillhole were first described and logged in the
stratigraphic description of the CRP-3 Initial Report. Further investigations
are reported herein. Sixty-seven samples from the 790 m of penetrated section
were selected to study the main fabric, texture, ultratexture, mineralogy
and stable isotope composition.
Authigenic calcite is the most abundant precipitate throughout the
CRP-3 core. Fossiliferous concretions/nodules occurring in the upper 350
m of the sedimentary succession exhibit an early marine, shallow burial
cementation by fringing/sparry low-Mg calcite, related to dissolution of
calcareous skeletal material. The isotopic composition of this cement (∂18O
= -7.3 to -10.1 ‰ PDB; ∂13C = -6.2 to -14.3 ‰ PDB) suggests
that glacial meltwaters comprised 25–40% of the precipitating fluid.
Carbonate cementation is prevalent below 350 mbsf in sandstone lithologies
and is represented by an early stage of fringing Fe-rich calcite or siderite
that is overlain by blocky crystals of calcite containing no Mg.
Pressure solution patterns along the framework grains suggest that cement
formation is related to compaction. 18O depletion (∂18O = -12.6 to -18.2
‰ PDB) in these cements suggest that meteoric waters make up >60% of
the diagenetic fluid, which is consistent with environmental changes inferred
from the interpretations of the sedimentary facies.
Associated with carbonate cements are authigenic zeolite and smectite
minerals, representing early precipitates. Pyrite commonly occurs either
as a discrete cement phase fringing coal particles or as framboids dispersed
within the organic-rich matrix, and within biogenic tests.
*Corresponding author (fulvia.aghib@unimi.it)