Mathematics – Logic
Scientific paper
Jun 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.2661l&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 12, pp.2661-2675
Mathematics
Logic
Scientific paper
Carbonate cement is one of the more volumetrically important diagenetic components of sandstones. The sandstones of the fan delta facies of the Oseberg Formation (Brent Group) in Veslefrikk field contain abundant carbonate cemented zones, commonly comprised of 30-40% carbonate by volume. The cement is predominantly poikilotopic, ferroan calcite, with minor amounts of ankerite and siderite. Petrographie evidence for high porosities at the time of calcite precipitation indicate that cementation occurred under shallow burial conditions, probably less than 500 m. Crosscutting textural relations demonstrate that calcite cementation was predated and postdated by tectonic stresses that produced both grain fractures and through-going fractures, respectively. In the non-calcite cemented parts of the formation major compaction, pressure solution, feldspar dissolution, and cementation by quartz and clays postdated calcite cementation. The oxygen isotopic composition of the calcite averages - 8.5% 0 (PDB), and shows large variations within individual calcite cemented zones (up to 10% 0 in 18 O). The depleted and variable oxygen isotopic composition, in conjunction with evidence for shallow precipitation, indicate calcite growth occurred in a mixing zone environment, variably influenced by meteoric water. Isotopic variation within many individual cemented zones is symmetric about the center of the zones, indicating that growth of the cemented zones was from the center outwards in a concretionary fashion. The high Fe and Mn content of the calcite (avg. 1.3 mol% Fe, avg. 0.4 mol% Mn) and its association with disseminated pyrite indicate that porewater was reducing during precipitation. Carbon isotopic data (avg. 13 C = - 15.7% 0 PDB, RANGE = - 3 to - 3 1% 0 ) show that major amounts of organic carbon, at least partly derived by sulfate reduction of biogenic methane, were incorporated in the calcite. Other documented occurrences of early, 13 C-depleted carbonate-cemented sandstones are similar to the carbonate cement in Veslefrikk Field in their association with methane oxidation and their low temperature formation. However, the cement at Veslefrikk differs in its mineralogical and morphological occurrence and in the fact that it formed from a porewater strongly influenced by mixing with meteoric water. Key geologic factors that determined the traits of calcite cement in Veslefrikk Field are the combination of nearshore marine deposition of permeable sands, close proximity of organic-rich marine muds, and variations in relative sea level, which provided opportunities for invasion by meteoric water. These geologic factors had a similar impact on other Brent Group deltaic sandstones and are believed to explain some of the differences between the geochemistry of carbonate cements in deltaic and shelf sandstones of the North Sea and elsewhere.
No associations
LandOfFree
Mixing zone origin of 13 C-depleted calcite cement: Oseberg Formation sandstones (Middle Jurassic), Veslefrikk Field, Norway does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Mixing zone origin of 13 C-depleted calcite cement: Oseberg Formation sandstones (Middle Jurassic), Veslefrikk Field, Norway, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mixing zone origin of 13 C-depleted calcite cement: Oseberg Formation sandstones (Middle Jurassic), Veslefrikk Field, Norway will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1865026