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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 273

Last Page: 273

Title: Regional Cement Stratigraphy and Diagenetic History of Waulsortian Limestones, Eastern Midlands, Republic of Ireland: ABSTRACT

Author(s): David E. King, William J. Meyers

Article Type: Meeting abstract


The Lower Carboniferous Waulsortian Limestones, eastern Midlands, Republic of Ireland, contain 7 distinct luminescent zones in clear calcite cements that overlie inclusion-rich, marine cements in cavities and also fill fractures and aragonite-skeleton molds. The luminescent sequence, which records precipitation from increasingly reducing pore waters, is regionally and stratigraphically consistent over an interval more than 1,200 ft thick. Zone 1 cements are nonluminescent; zone 2 cements are brightly luminescent; and zones 3-7 cements are ferroan with a moderate to dull luminescence. Zone 1 cements (mean -2.6% ^dgr18O/+3.3% ^dgr13C PDB) are slightly depleted in oxygen relative to radiaxial-fibrous cements (mean -1.8%^dgr18O/+3.5%^dgr1 C PDB) which have a composition that reflects Lower Carboniferous seawater. Zone 4 cements (mean -4.1%^dgr18O/+3.1%^dgr13C PDB) are depleted in oxygen relative to zone 1, whereas zone 5 cements (mean -11.8%^dgr18O/+1.1^dgr13C PDB) are extremely depleted in oxygen and somewhat in carbon.

Locally intense dolomitization includes 2 regionally extensive generations of ferroan saddle dolomite. Petrographic relationships demonstrate these dolomite generations were replaced by zone 5 cement. Sulfide mineralization, principally pyrite and sphalerite, occurred after the precipitation of zone 5 cement.

Much of diagenesis occurred during a brief period in the Lower Carboniferous. Zones 1-6 and saddle dolomites are contained in Chadian (upper Osagean), shallow-marine facies overlying the Waulsortian. Fractures filled by zone 5 cements are truncated at the margins of Waulsortian clasts contained in a conglomerate overlying an early Arundian (early Meramecian) unconformity.

In the proposed model, marine pore waters were displaced by oxidizing meteoric waters, which became reducing with shallow burial. Warm brines were introduced during later stages of diagenesis and were involved in late calcite cementation (zone 4?-7), saddle dolomitization and sulfide mineralization.

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