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Carbonate cements: their regional distribution and interpretation in Mississippian limestones of southwestern New Mexico
Author(s) -
MEYERS W. J.
Publication year - 1978
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1978.tb00318.x
Subject(s) - geology , calcite , phreatic , micrite , mineralogy , meteoric water , carbonate , geochemistry , petrography , carbonate rock , sedimentary rock , paleontology , groundwater , materials science , geotechnical engineering , facies , structural basin , aquifer , metallurgy , hydrothermal circulation
Calcite cements in Mississippian skeletal packstones and grainstones of southwestern New Mexico are dominated by echinoderm‐syntaxial, inclusion‐free calcites that can be divided into four major compositional zones (from oldest to youngest: zone 1, 2, 3, 5) based mainly on varying Fe 11 and Mn II contents. These compositional zones are interpreted as‘time stratigraphic’ units as indicated by petrographic evidence for age gaps between zones, and by consistency of their ages on a regional scale. As such, these cement zones can be correlated over most or all of the approximately 30,000 km 2 of study area, based on similarity of age, number and sequence of major zones. The inclusion‐free calcite cements comprise approximately 95% of the total cements, of which the pre‐Pennsylvanian zones (zones 1, 2, 3) make up about 60%, and the post‐Mississippian zone 5 makes up about 40% of the total cements. These cements are interpreted as meteoric phreatic on the basis of Mn II and Fe II content, crystal clarity, cement morphology, substrate selectivity, low Mg content, and absence of marine and vadose characteristics. In the southern part of the study area zone 2 contains significant amounts of meteoric‐marine mixing‐zone phreatic cements. These mixing‐zone cements are identified by their similarity in morphology, luminescence and substrate selectivity to the inclusion‐free meteoric phreatic cements, but contain microdolomite inclusions indicative of former high‐Mg calcites. Their restriction to the south is interpreted to have resulted from relatively long residence time of the mixing zone in the south during zone 2 precipitation. Strictly marine subtidal and beachrock cements make up less than 1% of the total cements, and meteoric vadose cements are virtually absent. Regional distribution of the pre‐Pennsylvanian cement zones suggests a model of cementation during a world‐wide late Mississippian eustatic regression identified by Vail & Mitchum (1976). Specifically, pre‐zone 1 and zone 1 meteoric phreatic cements formed during regression within a shallow oxygenated (?) groundwater system; zone 2 formed during the later part of the regression and during stillstand in a deep‐seated, more extensive flow system; zone 3 formed during subsequent transgression in a shallow groundwater system. The post‐Chester, pre‐Pennsylvanian unconformity resulted mainly in microkarsting and weathering. The main difference, other. than scale, between this model and those derived from diagenetic studies of Quaternary limestones is that it implies that major cementation occurred during sea‐level changes in cpeiric settings, rather than only during stillstands.