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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Research
Vol. 77 (2007), No. 10. (October), Pages 797-808
Perspectives

A Proposed Integrated Multi-Signature Model for Peritidal Cycles in Carbonates

Guy H. Spence, Maurice E. Tucker

Abstract

A new integrated multi-signature model for meter-scale peritidal carbonate cycles presented here is relevant to the interpretation of these cycles in the stratigraphic record. Meter-scale shallowing-upward (micro)facies cycles are the most common type of peritidal parasequence. Peritidal parasequences are a fundamental component of carbonate sequence stratigraphic models. However, the existence of meter-scale cycles in the geological record has been questioned owing to the failure to prove statistically the existence of these cycles using data on (micro)facies and stacking pattern taken from previous studies. Nevertheless, the shallowing-upwards (micro)facies interpretive template remains widely used to identify these cycles and parasequences.

We propose that the sedimentary signatures of meter-scale peritidal cycles vary systematically during the various phases of an underlying 3rd-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit Previous HitcycleNext Hit. Although during specific phases of a 3rd-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit Previous HitcycleNext Hit meter-scale peritidal cycles may be characterized by shallowing-upward units (e.g., early transgressive Previous HitsystemsNext Hit tract), during other periods the stratigraphic signal of cyclicity may be more cryptic and complex, causing them to be overlooked (e.g., late transgressive Previous HitsystemsNext Hit tract and highstand Previous HitsystemsNext Hit tract). We also propose that there is a half-Previous HitcycleNext Hit Previous HitphaseNext Hit shift in periods of deposition and the formation of drowning surfaces, relative to 4th- to 5th-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit cycles, over the course of a 3rd-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit Previous HitcycleNext Hit.

These points have ramifications for defining parasequences and using stacking patterns to determine peritidal Previous HitcycleNext Hit periodicity. Specifically, parasequences defined using flooding surfaces identify sedimentary units that inconsistently partition 4th- to 5th-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit cycles at different stages of a 3rd-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit Previous HitcycleNext Hit. We propose testable, new physical stratigraphic signatures for identifying meter-scale cycles that have consistent genetic significance, each Previous HitcycleNext Hit recording a relative Previous HitseaNext Hit-Previous HitlevelNext Hit Previous HitcycleNext Hit characterized by a 4th- to 5th-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit rise and fall. Meter-scale peritidal cycles are recorded by an ordered pattern of systematically varying (micro)facies signatures related to their position within a 3rd-order relative Previous HitseaNext Hit-Previous HitlevelNext Hit Previous HitcycleNext Hit. The integrated multi-signature model of meter-scale peritidal carbonate cycles we propose here may assist in explaining the apparently contradictory evidence both for and against their existence in the geological record. As a result of the detailed consideration in this paper of the nature of parasequences and their variations with 3rd-order relative Previous HitseaNext Hit-Previous HitlevelTop changes, a redefinition of parasequence is required and one is presented here.


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