Dolomitization and recrystallization of middle Silurian reefs and platformal carbonates of the Guelph Formation, Michigan Basin, southwestern Ontario
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Research Article| June 01, 2003 Dolomitization and recrystallization of middle Silurian reefs and platformal carbonates of the Guelph Formation, Michigan Basin, southwestern Ontario Mario Coniglio; Mario Coniglio Department of Earth Sciences, University of Waterloo, Waterloo, ON N2L 3G1, coniglio@uwaterloo.ca Search for other works by this author on: GSW Google Scholar Qing Zheng; Qing Zheng Leling Phoenix Brake Canada Inc., 100 Pinebush Road, Cambridge, ON N1R 8J8, cnczheng@aol.com Search for other works by this author on: GSW Google Scholar Terry R. Carter Terry R. Carter Petroleum Resources Centre, Ministry of Natural Resources, 659 Exeter Road, London, ON N6E 1L3, terry.carter@mnr.gov.on.ca Search for other works by this author on: GSW Google Scholar Author and Article Information Mario Coniglio Department of Earth Sciences, University of Waterloo, Waterloo, ON N2L 3G1, coniglio@uwaterloo.ca Qing Zheng Leling Phoenix Brake Canada Inc., 100 Pinebush Road, Cambridge, ON N1R 8J8, cnczheng@aol.com Terry R. Carter Petroleum Resources Centre, Ministry of Natural Resources, 659 Exeter Road, London, ON N6E 1L3, terry.carter@mnr.gov.on.ca Publisher: Canadian Energy Geoscience Association Received: 17 Sep 2002 Accepted: 18 Feb 2003 First Online: 02 Mar 2017 Online ISSN: 2368-0261 Print ISSN: 0007-4802 © The Society of Canadian Petroleum Geologists Bulletin of Canadian Petroleum Geology (2003) 51 (2): 177–199. https://doi.org/10.2113/51.2.177 Article history Received: 17 Sep 2002 Accepted: 18 Feb 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Mario Coniglio, Qing Zheng, Terry R. Carter; Dolomitization and recrystallization of middle Silurian reefs and platformal carbonates of the Guelph Formation, Michigan Basin, southwestern Ontario. Bulletin of Canadian Petroleum Geology 2003;; 51 (2): 177–199. doi: https://doi.org/10.2113/51.2.177 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Regional study of the Guelph Formation (middle Silurian) in the subsurface of southwestern Ontario highlights the role of recrystallization during burial diagenesis in producing massive dolomites with relatively uniform petrographic features but complicated geochemistry. The dolomite is composed mainly of replacive, unimodal to polymodal mosaics characterized by uniform, dull to weak red cathodoluminescence. Whereas patch reefs on the platform and most pinnacle reefs on the upper basin slope are pervasively dolomitized, reefs on more basinward parts of the slope may be partially dolomitized, usually in their lower portions, or they remain limestone. The lithology of overlying carbonates in the lower Salina Group mimics closely that of the underlying Guelph Formation. Initial shallow burial dolomitization occurred in the Late Silurian in response to isolation and hydrological drawdown of the Michigan Basin. The basinward-decreasing dolomite trend resulted from continuous seawater flux from the middle (back reef) platform downward through Guelph limestones to the discharge areas on the slope and beyond. Reefs at the distal end of the regional paleoflow system, or those that were poorly connected to the system remained limestone. Both dolomite δ13C values, which range from +1.1 to +5.0 ‰ (PDB), and 87Sr/86Sr ratios, which range from 0.70845 to 0.70910, reflect a Silurian seawater source.Values for δ18O range from −5.2 to −9.7‰ (PDB) but cannot be explained by the above mechanism alone. Recrystallization likely occurred during the progressive burial of these rocks to depths of up to 2 km, and may at least in part explain the lack of correlation among dolomite crystal size, cathodoluminescence characteristics and the various geochemical parameters measured in this study. The reason for the wide spread in δ18O values both geographically and stratigraphically reflects varying degrees of recrystallization as a function of macro- to micro-scale permeability and porosity differences in the precursor lithology and their control on fluid-rock interactions during recrystallization. The cause of the apparent decrease in dolomite δ18O values from patch reefs on the platform (average δ18O = ~ −6‰) to the lower slope (average δ18O = ~ −8.5‰) is unknown, but may have resulted from a combination of a basinward increase in burial depth and a basinward increase in heat-flow, which are now only subtly preserved through the “noise” of multiple recrystallizations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.Keywords:
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Oligocene to middle Miocene, deep-shelf, bryozoan-rich limestones across southern Australia are variably replaced by green to orange, Ca-rich, zoned, medium-crystalline, sucrosic dolomite. The degree of replacement varies from scattered rhombs in limestone to complete dolostones a few tens of meters in thickness and a few kilometers in lateral extent. Dolostone texture ranges from dense and well lithified to completely unlithified, resembling a loose sand of dolomite rhombs. Dolomitization is fabric specific; calcite and Mg-calcite bryozoans are either the last components to be replaced or are molds. The timing and locale of dolomitization are tightly constrained; Sr isotopes indicate a middle to late Miocene age while clasts of dolostone in overlying Pliocene limestones above a regional unconformity confirm a shallow-burial, pre-Pliocene origin. {delta}{sup 13}C and {delta}{sup 18}O values support a marine source for the carbonate; the influence of meteoric fluids appears to have been negligible. Quaternary exposure has resulted in local dedolomitization and/or subaerial erosion, especially in the Murray basin. These rocks are excellent analogues for localized, lenticular dolostone bodies in calcite-rich Paleozoic platform carbonates.
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Narrow (tens of meters) vertical bodies of dolomite replace a nonporous Upper Ordovician (lower Chatfieldian) limestone along the leading limb of an asymmetric faulted anticline well inboard (∼300 km) of the northern Appalachian orogen, central-east Canada. Patterns of geometry, texture, and geochemistry suggest that dolomitizing fluids were focused (possibly along microfractures) within a paleosinistral transpressive stress field generated with reactivation of an underlying Neoproterozoic fault system. Strike-slip failure of the developing anticline resulted in fracture- and fault-controlled fluid flow from which precipitated saddle dolomite. A paragenetic succession of Fe-poor planar-e to ferroan planar-s dolostone marks the peak phase of replacement dolomitization. A subsequent increase (20%–30%) in porosity created through local dissolution of relict limestone was partially occluded by ferroan planar dolomite that, geochemically, is similar to later fracture-fill saddle dolomite. Replacement dolomitization is associated with a slight rise in Sr-isotope ratios (to 0.71085) from Late Ordovician–early Silurian marine signatures. Isotope (C, O, Sr) signatures support influx and mixing of burial fluids that had interacted with local Mg-rich (gabbro, anorthosite, syenite) crystalline basement with a background fluid similar to Late Ordovician seawater or dissolved marine limestone. Dolomitization predated maximum burial in the Late Paleozoic. Fluid inclusion and isotope paleothermometry suggest that dolomitizing temperatures (100°–120°C) were 20°–30°C warmer than associated with prior limestone diagenesis. The dolomitized limestone is an archival record of structure, hydrology, and heat flux that best fits with Taconic tectonism in the latest Ordovician through earliest Silurian.
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ABSTRACT Cores from Rosevear Field and surrounding areas were studied to determine controls on reservoir porosity and hydrocarbon distribution in the Swan Hills Formation (Middle to Late Devonian; Givetian to Frasnian) in west-central Alberta. Most reservoir porosity (3-15%) in the Rosevear area is in dolomites of the middle Swan Hills Formation. Dolomitization was facies-controlled, occurring mainly in peloid-bioclast and Amphipora-peloid grainstones. Porous dolomitized grainstones at Rosevear accumulated along the rims of a trough initiated by structural downwarp during Swan Hills time. The depositional trough is recognized by the distribution of facies as well as a 20 m thickening of the Swan Hills Formation within and on the flanks of the trough. Porous dolomitized grainstones also occur along the middle Swan Hills shelf margin. Lime mud-rich shelf-interior limestones and lime mud-rich slope to basinal limestones are generally not porous. Previously published geochemical and petrographic data suggest that most dolomite precipitated at relatively high temperatures during moderate to deep burial. The geochemical signature and stratigraphic distribution of dolomite may have been produced by (1) pervasive recrystallization of an early facies-controlled dolomite, or (2) dolomitizing fluids moving laterally and preferentially through porous shelf-margin and trough-margin grainstones after substantial burial. The geometry of the Swan Hills dolomite is critical for the stratigraphic trapping of gas. In Rosevear's southwestern pool, porous dolomitized grainstones pinch out updip (to the northeast) into nonporous slope to basinal limestones of the trough. In the northeastern pool, porous dolomitized grainstones pinch out updip (to the northeast) into nonporous shelf interior limestones. The gas-water contacts at Rosevear are at elevations that approximate the spill-point of Rosevear dolomites into a porous shelf margin dolomite trend. Many wells south and west of Rosevear have porous dolomite filled with water. The Rosevear dolomite bodies have enough of a north-south orientation to trap gas migrating from the south along the shelf margin. RESUME Des carottes provenant du champ de Rosevear et des regions environnantes ont ete etudiees pour determiner les controles regissant la porosite de reservoir et la distribution des hydrocarbures dans la Formation de Swan Hills (Devonien moyen a superieur, Givetien a Frasnien) dans le centre-ouest de l'Alberta. La plupart de la porosite de reservoir (3-15%) dans la region de Rosevear est dans des dolomies de la Formation de Swan Hills moyen. La dolomitisation a ete controlee par les facies, se presentant surtout dans les grainstones a bioclastes-peloides et a Amphipora-peloides. Les grainstones poreux dolomitises de Rosevear se sont accumules le long des marges diune fosse initiee par l'affaissement structural durant la periode Swan Hills. La fosse de sedimentation est reconnaissable par la distribution des facies et un epaississement de 20 m de la Formation de Swan Hills a l'interieur et sur les flancs de la fosse. Les grainstones dolomitiques poreux se presentent aussi le long de la marge de la plate-forme de Swan Hills moyen. Les calcaires riches en boue calcareuse de l'interieur de la plate-forme et les calcaires riches en boue calcareuse de la pente et de bassin sont generalement non-poreux. Les donnees geochimiques et petrographiques publiees precedemment suggerent que la plupart de la dolomite se soit precipitee a des temperatures relativement elevees durant un enfouissement modere a profond. La signature geochimique et la distribution stratigraphique de la dolomite ont possiblement ete produites par: (1) une recristallisation intense d'une dolomite precoce controlee par les facies, ou (2) les fluides dolomitisants se sont deplaces lateralement et preferentiellement a travers les grainstones de marge de plate-forme poreuse et de marge de fosse apres un enfouissement substantiel. La geometrie de la dolomie de Swan Hills est critique pour le piegeage du gaz. Dans le reservoir du sud-ouest de Rosevear, les grainstones dolomitises poreux se biseautent en amont-pendage (vers le nord-est) pour passer a des calcaires non-poreux de pente a bassin de fosse. Dans le reservoir du nord-est, les grainstones dolomitises poreux se End_Page 458------------------------ biseautent en amont-pendage (vers le nord-est) en calcaires non-poreux d'interieur de plate-forme. Les contacts gaz-eau a Rosevear sont a des elevations qui sont approximativement a la hauteur du point de debordement des dolomies de Rosevear dans un axe de dolomies poreuses de marge de plate-forme. Plusieurs puits au sud et a l'ouest de Rosevear ont des dolomies poreuses remplies d'eau. Les corps de dolomie de Rosevear ont une orientation suffisamment nord-sud pour pieger du gaz qui migre a partir du sud le long de la marge de la plate-forme. Traduit par Lynn Gagnon
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Late diagenetic dolomitization of the Lower Ordovician, Upper Knox Group in the southern Appalachian basin was closely associated with widespread secondary porosity development, hydrocarbon migration, and local Mississippi Valley-type mineralization. Regionally extensive (^sim70,000 km2), late diagenetic dolomites consist of replacement dolomites and zoned dolomite cements. Late diagenetic replacement dolomites comprise 15 to 50% of all Knox matrix dolomites. The ^dgr18O (-11.9 to -5.3^pmil), ^dgr13C (-3.8 to +0.9^pmil), and 87Sr/86Sr (0.70895 to 0.70918) values of late diagenetic replacement dolomites overlap with those of the first zone of dolomite cements (zone 2), early replacement dolomites, and Lower Ordovician arine calcites, reflecting rock buffering of initial dolomitizing fluids and extensive neomorphism of replacement dolomites by subsequent late diagenetic fluids. Nonporous to sucrosic, late diagenetic dolomites have porosities (1 to 16%) and permeabilities (0 to 1030 md) significantly greater than those of early diagenetic replacement dolomites and host limestones ( 165°C), saline (13 to 22 wt.% NaCl equivalent) basinal brines that underwent extensive fluid-rock interaction with clastics. Precipitation temperatures of late diagenetic dolomites estimated from fluid inclusion homogenization temperatures and systematic trends in ^dgr18O va ues record a regionally developed, prograde-to-retrograde thermal history. Knox late diagenetic dolomites are interpreted to record the spatial and temporal evolution of large-scale fluid flow systems that developed in response to different burial and tectonic stages of the southern Appalachian basin. The occurrence of zoned dolomite cements in tectonic fractures and breccias, and their close association with noncarbonate diagenetic minerals of Pennsylvanian to Early Permian ages, suggest that most Knox late diagenetic dolomites record deep subsurface (2 to >5 km) fluid migration in response to late Paleozoic Alleghenian tectonism (330 to 265 Ma). Late diagenetic matrix dolomites served as long-lived conduits that focused and channeled diagenetic fluids in the deep subsurface. The occurrence of bitumen in secondary porosity within late diagenetic dolomite indicates that they likely were the most viable reservoirs during hydrocarbon migration in the late Paleozoic.
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Zinc-lead mineralization in the Sheffield channel is hosted in Early Permian shelf-marginal dolomites adjoining basinal facies, and inner shelf dolomites and evaporites. Sulfur isotopes, fluid inclusions, and burial-geothermal reconstructions suggest emplacement at approximately 96/sup 0/C during maximum burial in the late Mesozoic to early Tertiary. Sulfide mineralization can be placed into a paragenetic framework that is found in other areas of the Delaware basin. Early syndepositional and postdepositional dolomitization of shelf strata probably resulted from basinward reflex and, perhaps later, from Kohout convection. With progressive burial into the shallow mesogenetic realm, regional fluid-flow patterns reversed as a result of compactional dewatering of basinal shales. These fluids affected minor silicification, dolomitization, and dissolution of basinal and shelf-marginal strata. Maximum burial was coincident with (eastward) Laramide tilting of the Delaware basin, which created a gravity-driven flow system that discharged heated fluids to the Sheffield channel area. Sulfide emplacement at this time was accompanied by dissolution of the host dolomites, and late cementation by calcite and dolomite. Similar paragenetic trends recognized elsewhere may suggest regional controls on carbonate diagenesis, porosity history, and hydrocarbon migration related to the hydrodynamic evolution of the Delaware basin.
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The spectacularly exposed Triassic carbonate platforms of the Dolomites, northern Italy, have been studied for almost two centuries, but the origin of the dolomite remains unresolved. In the partly dolomitized Ladinian-age Latemar platform, 5 km across and 1 km high, dolomitization patterns as well as primary sedimentary and early diagenetic features are preserved. Mapping has allowed three-dimensional reconstruction of the dolomite front geometry which records the frozen pathways of dolomitizing fluids. Massive alteration of limestone to coarse-grained, vuggy, sucrosic dolomite (at least 10% of the buildup) occurs along an upward and outward branching fracture system associated with nearby late-ladinian intrusions. A central pipe of dolomite (300 m wide) cuts vertically upward through 400 m of early-cemented subtidal grainstones of the lower platform. The dolomitized zone then expands to a mushroom-like shape which encompasses 1.5 km/sup 2/ of the overlying cyclical facies (120 m thick) where dolomitizing fluids utilized bedding-planes and uncemented grainstones in addition to fractures. Dolomitization enlarges intergranular pores and alters limestone fabrics to a network of interlocking rhombs (.25-2 mm in size) of zoned, ferroan dolomite. It also obliterates early, fine-grained, selective dolomite in shallowing-upward cycle caps. The alteration patterns clearly indicate upward moving fluids in the coremore » of the buildup. This suggests circulation of the fluid (the surrounding seawater.) through the fracture and pore network driven by either heat from the late-Ladinian intrusions or Kohout convection. In this regard, later cements of saddle dolomite provide evidence that hydrothermal circulation was active in the Latemar buildup during Ladinian time.« less
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