--> Abstract: Cathodoluminescence and Trace-Element Geochemistry of Carbonate Cements Formed with Burial in Seawater, by D. A. Budd; #91004 (1991)

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Cathodoluminescence and Trace-Element Geochemistry of Carbonate Cements Formed with Burial in Seawater

BUDD, D. A., University of Colorado, Boulder, CO

The diagenetic fate of metastable carbonates that are buried solely in seawater is not well known. To this end, the cementation of Miocene and Early Cretaceous carbonate turbidite and debris-flow deposits from DSDP sites 534 and 416 have been examined. All samples consist of resedimented shallow-water allochems. All interparticle and most intraparticle cements in these samples formed with burial in seawater.

Petrographic, trace-element, and cathodoluminescent relationships document three phases of calcite cementation at both sites: (1) nonluminescent, Fe- and Mn-poor, medium- to coarse-crystalline syntaxial overgrowths, (2) a thin zone of brightly luminescent, Mn-rich syntaxial overgrowths, and (3) weakly luminescent, Fe-rich, very fine- to medium-crystalline syntaxial overgrowths and pore-filling mosaics. Phase 1 probably corresponds to initial mineralogical stabilization with very shallow burial; it also preceded mobilization of Fe(2+) and Mn(2+) from surrounding siliciclastics or concomitant oxyhydroxides. Phase 2 may reflect a narrow period of time in which Eh-pH conditions favored Mn(2+) but not Fe(2+) (Barnaby and Rimstidt, 1989). Phase 3 corresponds to continued burial and mineralo ical stabilization under reducing conditions with Fe(2+) and Mn(2+) derived mainly from associated siliciclastics.

Samples from site 416 also contain a fourth cement that consists of nonluminescent, medium-crystalline, ferroan dolomite. Samples containing this dolomite exhibit little mechanical compaction and no grain-to-grain pressure solution, suggesting an early formation of the dolomite.

It is concluded that the characteristics of site 416 and 534 cements, which formed during burial in seawater, are similar in many respects to the characteristics of cathodoluminescent-zoned cements interpreted to be of freshwater or basinal brine origins in many ancient limestones.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)