New Zealand Journal of Geology and Geophysics abstracts
A fluid flow perspective on the diagenesis of Te Aute limestones
Brian D. Ricketts*
Vincent Caron
Campbell S. Nelson
Department of Earth Sciences
University of Waikato
Private Bag 3105
Hamilton, New Zealand
*Present address: Department of Geology, University of
Auckland, Private Bag 92 019, Auckland, New Zealand.
Email: b.ricketts@auckland.ac.nz
Abstract Pliocene cool-water, bioclastic Te Aute
limestones in East Coast Basin, New Zealand, accumulated either in
shelfal shoal areas or about structurally shallow growth fold
structures in the tectonically active accretionary forearc prism. Up to
five stages of carbonate cementation are recognised, based on cement
sequence-stratigraphic concepts, that formed on the seafloor during
exposure of the limestones before burial, during burial, uplift, and
deformation. Two principal fluid types are identified—topography-driven
meteoric fluids and compaction-driven fluids. We have developed
conceptual and quantitative models that attempt to relate the physical
characteristics of fluid flow to the cement paragenesis. In particular,
we have simulated the effects of uplift of the axial ranges bordering
East Coast Basin in terms of the degree of penetration of a meteoric
wedge into the basin. The dynamics of meteoric flow changed
dramatically during uplift over the last 2 m.y. such that the modelled
extent of the meteoric wedge is at least 40 km across the basin,
and the penetration depth 1500 m or more corresponding with
measured freshwater intersections in some oil wells. Cement-fluid
relationships include: (1) true marine cements that precipitated in
areas remote from shallow freshwater lenses; (2) pre-compaction cements
that formed in shallow freshwater lenses beneath limestone “islands”;
(3) post-compaction cements derived from compaction-driven flow during
burial; (4) early uplift-related fracture-fill cements formed during
deformation of the accretionary prism and uplift of the axial ranges;
and (5) late uplift-related cements associated with uplift into a
shallow meteoric regime.
Keywords diagenesis; cement sequence; meteoric
wedge; topography-driven flow; freshwater lens; compaction; modelling;
Te Aute limestones; Pliocene–Pleistocene; New Zealand
G03056; Received 29 May 2003; accepted 28 October 2003; Online
publication date 1 December 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47:
823–838
0028–8306/04/4704–0823© The Royal Society of New Zealand 2004
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