Developing concepts of high-resolution diagenetic stratigraphy for Pliocene cool-water limestones in New Zealand, and their sequence stratigraphy

• Autores: Vincent Caron, Campbell S. Nelson
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 18, Nº. 1, 2003, págs. 63-85
• Idioma: inglés
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• Resumen

  • The diagenetic evolution of calcitic cool-water limestones can be markedly different from that for aragonite-dominated tropical carbonates. This petrographic study develops a "sequence stratigraphic" approach to cool-water carbonate diagenesis based on the chronological occurrence of all diagenetic features (not only cement phases) within sedimentary successions, their vertical and lateral distribution, and their grouping into discontinuity-bounded (by dissolution surfaces, fractures, renucleation events) suites at a thin-section scale. The progression of diagenetic environments that moved through a succession is related to diagenetic discontinuities correlatable throughout the study area. In our limestones a critical discontinuity event to decipher is the first evidence of mechanically-induced skeletal fracturing, enabling the definition of precompaction and post-compaction diagenetic features. A comparison of just the pre-compaction diagenetic suites in samples from above and below significant outcrop disconformities enables isolation of the "specific diagenesis" of unconformity-bounded depositional units, which is that suite of diagenetic events associated with the evolution of the sedimentation realm of a unit, exclusive of diagenetic overprints shared with any overlying unit through an unconformity since these relate to some subsequent, different depositional stage. In turn, the specific diagenesis of a succession of depositional facies between consecutive unconformities may then be interpreted within a sequence stratigraphic framework.

    Sections of cool-water Pliocene skeletal limestones in eastern North Island, New Zealand, comprise deepening-and then sometimes shallowing-upwards, unconformity-bounded depositional packages, or sequences. We recognize ten different specific diagenetic signatures in these rocks that are correlatable to depositional lithofacies. The vertical distribution of specific diagenetic signatures within the sequences exhibits a trend from mainly constructive to mainly destructive diagenesis in the deepening-upwards member of the sequences, and constructive in their shallowing-upwards portion, that can be integrated in a sequence stratigraphic framework. Constructive diagenesis occurs in the lower part of the transgressive system tract (TST) and in the upper part of the regressive system tract (RST), whereas destructive diagenesis is dominant in the upper part of the TST, the highstand system tract (HST), and the lower part of the RST.