--> Abstract: Post-Meteoric Marine Diagenesis In Submerged Pleistocene Carbonates, Oahu, Hawaii, by C. E. Sherman, C. R. Glenn, and C. H. Fletcher; #90928 (1999).

Datapages, Inc.Print this page

SHERMAN, C. E., C. R. GLENN, and C. H. FLETCHER
Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822

Abstract: Post-Meteoric Marine Diagenesis in Submerged Pleistocene Carbonates, Oahu, Hawaii

A fossil reef complex, formed during marine oxygen isotope stage 7, comprises the bulk of a nearshore terrace that occurs around the island of Oahu at ~-20 m. As a result of late Quaternary sea-level fluctuations the terrace has undergone alternating periods of emergence and submergence and exposure to both meteoric and shallow-marine diagenetic environments. Following submergence of the terrace during the last deglaciation, dynamic flow of seawater through the reef has led to precipitation of cements which overprint pre-existing diagenetic fabrics.

Within framestones and rudstones deposited in high-energy reef-crest and reef-front environments, early-marine diagenetic processes include pervasive cementation by aragonite and Mg calcite. In contrast, within low-energy back-reef floatstones and bafflestones, early-marine cements are largely absent and micritization is the dominant early-marine diagenetic process. During following periods of emergence, limestones were lithified by and stabilized to calcite in a meteoric vadose environment and underwent partial dissolution and creation of new vug and channel porosity. Upon subsequent resubmergence, the now stablized substrate along with conduit or channel-type porosity led to high flow rates induced by channelized sea water, evidenced by visible flow of water in and out of open core holes. This, in turn, has led to modern precipitation of thick isopachous rims of bladed Mg calcite spar lining the walls of large voids. These post-meteoric marine cements occur in all facies including the back-reef facies which otherwise contain little or no evidence of early-marine cementation. These data highlight the complexity of diagenetic fabrics in shallow-marine carbonates due to high-frequency sea-level changes and the need for caution when interpreting the timing of marine cementation in ancient shallow-marine carbonates.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas