--> ABSTRACT: Miocene Reef Platforms from Northwestern Tuamotu Islands, Central Pacific, by Lucien F. Montaggioni; #91030 (2010)

Datapages, Inc.Print this page

Miocene Reef Platforms from Northwestern Tuamotu Islands, Central Pacific

Lucien F. Montaggioni

Reef deposits of Miocene age occur on several northwestern Tuamotu atolls as either pointed residual and scattered reliefs through the Holocene reef sequence (Mataiva, Rangiroa, Tikehau, Kaukura) or elevated atoll-shaped platforms (Makatea). Throughout the region considered, the depositional/diagenetic history of Miocene reefs can be reconstructed as follows. During early Miocene times (e-f range-biozones), reef platforms developed on top of older carbonate banks, capping a midplate volcanic ridge of early Tertiary age. More than 100 m thick, these platforms displayed concentrically zoned environments of deposition: a peripheral subemergent rim composed of coralgal-foraminiferal boundstones, and a very shallow central area in which foraminiferal and molluscan fine sands a d muds were subhorizontally deposited. Local evidence of internal unconformity surfaces and subaerially produced features indicates that periods of relative emergence occurred as the reef piles grew upward. The ultimate stage of platform development is believed to have been a complete upfilling of the backreef areas and subsequent emergence. Correlatively, a freshwater lens would have been formed close to the surface level of each of the so-formed islands. Dolomitization may have been initiated in the marine water/freshwater phreatic mixing zone. During lowstands, severe meteoric alteration affected emergent carbonate deposits, forming incipient cavity systems; the usual atoll morphology is considered to have been initiated at this time (presumably middle Miocene).

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.