Print this pageStructural and Stratigraphic Control of Diagenetic Alteration in Mixed Temperate Carbonate-Siliciclastic Strata, Plio-Pleistocene, North Island, New Zealand
HAYWICK, DOUGLAS W.
Plio-Pleistocene cyclothemic sedimentary rocks of central Hawke's Bay, New Zealand are products of inner- to mid-shelf sedimentation and were deposited during multiple glacio-eustatic sea level fluctuations. The strata are wholly contained within a single uplifted block some 450 km{2} in size that is tilted 2 to 100 eastward. This structural inclination produced a series of 5 aquifer-aquiclude couplets which ultimately controlled the flow of pore fluids and the diagenetic alteration of the strata. Temperate shelf carbonate sediments dominated by aragonitic faunas comprise the upper three aquifers of the strata. All three limestones are characterized by the same diagenetic history of shell alteration and calcite cementation. Five phases of cement are recognized: 1) pore-lining, bladed spar (rare; possibly marine phreatic), 2) isopachous, ferroan, equant spar (meteoric phreatic), 3) moderately ferroan, equant spar (meteoric phreatic), 4) non-ferroan, equant spar (meteoric phreatic) and 5) sinter-related cements (meteoric vadose).
That all three carbonate aquifers display consistent cement stratigraphies and alteration pathways suggests that pervasive diagenesis did not occur until regional deformation had uplifted the area into the meteoric regime. No evidence exists to support eustasy-induced diagenesis anywhere in the study area.