Differential early diagenetic low-Mg calcite cementation and rhythmic hardground development in Campanian-Maastrichtian chalk

Molenaar, Nicolaas; Zijlstra, Jan J

doi:10.1016/s0037-0738(96)00064-4

Cited by 33 publications

(20 citation statements)

References 40 publications

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“…This shows that large basement re-arrangements took place during the Campanian inversion event, which could have reactivated some of the older faults. During times of low sedimentation rates, early cementation can occur at some distance below the seafloor under the influence of organic degradation and internal bioclastic carbonate redistribution (Molenaar & Zijlstra, 1997). the RPM), which is expressed as a hiatus at the Ryan Anticline (four subzones missing), while deposition continued at the more basinal Sine-1X location (Figure 3a).…”

Section: Erosion and Condensation Forming Early Intra-chalk Sealsmentioning

confidence: 99%

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

et al. 2018

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Kilometre-scale geobodies of diagenetic origin have been documented for the first time in a high-resolution 3D seismic survey of the Upper Cretaceous chalks of the Danish Central Graben, North Sea Basin. Based on detailed geochemical, petrographic and petrophysical analyses, it is demonstrated that the geobodies are of an open-system diagenetic origin caused by ascending basin fluids guided by faults and stratigraphic heterogeneities. Increased amounts of porosity-occluding cementation, contact cement and/or high-density/high-velocity minerals caused an impedance contrast that can be mapped in seismic data, and represent a hitherto unrecognized, third type of heterogeneity in the chalk deposits in addition to the well-known sedimentological and structural features. The distribution of the diagenetic geobodies is controlled by porosity/permeability contrasts of stratigraphic origin, such as hardgrounds associated with formation tops, and the feeder fault systems. One of these, the Top Campanian Unconformity at the top of the Gorm Formation, is particularly effective and created a basin-wide barrier separating low-porosity chalk below from high-porosity chalk above (a Regional Porosity Marker, RPM). It is in particular in this upper high-porosity unit (Tor and EkofiskFormations) that the diagenetic geobodies occur, delineated by "Stratigraphy Cross-cutting Reflectors" (SCRs) of which eight different types have been distinguished. The geobodies have been interpreted as the result of: (i) escaping pore fluids due to top seal failure, followed by local mechanical compaction of highporous chalks, paired with (ii) ascension of basinal diagenetic fluids along fault systems that locally triggered cementation of calcite and dolomite within the chalk, causing increased contact cements and/or reducing porosity. The migration pathway of the fluids is marked by the SCRs, which are the outlines of highdensity bodies of chalk nested in highly porous chalks. This study, thus, provides new insights into the 3D relationship between fault systems, fluid migration and diagenesis in chalks and has important applications for basin modelling and reservoir characterization.---

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Section: Erosion and Condensation Forming Early Intra-chalk Sealsmentioning

confidence: 99%

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

et al. 2018

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“…In this study, we used chalk from Liège, suggested as the best match for the reservoir successions in the North Sea (Hjuler and Fabricius, 2009). The sampled chalk at Liège belongs to the Campanian to late early Maastrichtian Gulpen Formation, which has been deposited from the Campanian until the late early Maastrichtian (Molenaar and Zijlstra, 1997). The samples here originate from the basal succession, the ZevenWegen Member (Robaszynski et al, 2001) with an age of 75.5-78.0 Ma (belemnite zone Belemnitella mucronata after Slimani, 2001).…”

Section: Geologic Backgroundmentioning

confidence: 99%

“…The chalk was studied earlier in detail regarding its petrology and mineralogical and rheological characteristics (Felder, 1975;Molenaar and Zijlstra, 1997;Slimani, 2001;Strand et al, 2007;Hjuler and Fabricius, 2009). The samples were broken out as large blocks of 0.5-1 m 3 and then sampled directly from cleaned fresh surfaces.…”

Section: Samplingmentioning

confidence: 99%

Evaluation of the compositional changes during flooding of reactive fluids using scanning electron microscopy, nano-secondary ion mass spectrometry, x-ray diffraction and whole rock geochemistry

Zimmermann¹,

Madland²,

Nermoen³

et al. 2015

Bulletin

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Outcrop chalk of late Campanian age (Gulpen Formation) from Liège (Belgium) was flooded with MgCl 2 in a triaxial cell for 516 days under reservoir conditions to understand how the nonequilibrium nature of the fluids altered the chalks. The study is motivated by enhanced oil recovery (EOR) processes because dissolution and precipitation change the way in which oils are trapped in chalk reservoirs. Relative to initial composition, the first centimeter of the flooded chalk sample shows an increase in MgO by approximately 100, from a weight percent of 0.33% to 33.03% and a corresponding depletion of CaO by more than 70% from 52.22 to 14.43 wt.%. Except for Sr, other major or trace elements do not show a significant change in concentration. Magnesite was identified as the major newly grown mineral phase. At the same time, porosity was reduced by approximately 20%. The amount of Cl − in the effluent brine remained unchanged, whereas Mg 2+ was depleted and Ca 2+ enriched. The loss of Ca 2+ and gain in Mg 2+ are attributed to precipitation of new minerals and leaching the tested core by approximately 20%, respectively. Dramatic mineralogical and geochemical changes are observed with scanning electron microscopy-energy-dispersive x-ray spectroscopy, nano secondary ion mass spectrometry, x-ray diffraction, and whole-rock geochemistry techniques. The understanding of how fluids interact with rocks is important to, for example, EOR, because textural changes in the pore space affect how water will imbibe and expel oil from the rock. The mechanisms of dissolution and mineralization of fine-grained chalk can be described and quantified and, when understood, offer numerous possibilities in the engineering of carbonate reservoirs.

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“…It is highly probable that the cementation occurred within the sediment at some distance below the seafloor as a result of bacterial organic matter degradation and internal redistribution of bioclastic carbonate. Bacterial organic matter degradation caused dissolution of relatively unstable high-Mg calcite (and/or aragonite) in the oxic zone followed by precipitation of calcite cement as a consequence of bacterial iron reduction (Molenaar and Zijlstra, 1997).…”

Section: Discussionmentioning

confidence: 99%

Pyritized mudstone and associated facies in the Permian–Triassic boundary of the Çürük Dağ section, Southern Turkey

Varol

Koşun

Pinar

et al. 2011

Journal of Asian Earth Sciences

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Differential early diagenetic low-Mg calcite cementation and rhythmic hardground development in Campanian-Maastrichtian chalk

Cited by 33 publications

References 40 publications

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

Evaluation of the compositional changes during flooding of reactive fluids using scanning electron microscopy, nano-secondary ion mass spectrometry, x-ray diffraction and whole rock geochemistry

Pyritized mudstone and associated facies in the Permian–Triassic boundary of the Çürük Dağ section, Southern Turkey

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