Confirmation of a late, deep-burial origin for Haynesville secondary microporosity is based on physical relationships observed in numerous cores, regional petrography and geochemical data. Nearly all primary porosity in the Haynesville is now occluded by carbonate cement. Resultant micropores are a few microns across or less complete dissolution of ooids to form oomoldic macroporosity is not observed in Haynesville limestones. Haynesville micromoldic porosity development is confined principally to ooids but also occurs in normally "stable" calcitic skeletal grains like oysters. Haynesville diagenetic and porosity relationships are consistent along the entire length of the east flank of the East Texas Basin, a distance greater than 100 km identical relationships have also been observed along the west flank of this basin. Microporosity development is strictly controlled by depositional texture and is restricted to either active shoal complex grainstones or thicker grainstones shed downramp by storm processes. Petrographic and geochemical relationships establish that development of this microporosity postdates emplacement of bitumen and most pressure solution fabrics in the reservoir grainstones. Secondary micromoldic porosity generated during deep-burial diagenesis occurs pervasively in Upper Jurassic Haynesville oolitic grainstones in East Texas and constitutes the major pore type in these gas reservoirs. Using a previously published dataset from the Bahamas, we demonstrate that the model captures the main trends of the data as a function of burial depth and thus appears applicable to a range of depositional settings.ĭeep-burial microporosity in upper Jurassic Haynesville oolitic grainstones, East Texas We then explore whether the model is applicable to shallow-water settings commonly preserved in the rock record. Specifically, the combination of the diagenetic model and data support previous work that indicates equatorial sea-surface temperatures were warmer in the Paleogene as compared to today. We demonstrate that the use of the model with accompanying carbonate clumped-isotope and carbonate Î♁8O values provides new constraints on both the diagenetic history of deep-sea settings as well as past equatorial sea-surface temperatures. This dataset is used to ground truth the model. We apply the model to a new dataset from deep-sea sediments taken from Ocean Drilling Project site 807 in the equatorial Pacific. Here we derive a quantitative model of diagenesis to explore how diagenesis alters carbonate clumped-isotope values. However, dissolution-reprecipitation (i.e., recrystallization) reactions, which commonly occur during sedimentary burial, can alter a sample's clumped-isotope composition such that it partially or wholly reflects deeper burial temperatures. The measurement of multiply isotopically substituted ('clumped isotope') carbonate groups provides a way to reconstruct past mineral formation temperatures. Modeling the effects of diagenesis on carbonate clumped-isotope values in deep- and shallow-water settings Limestone from the water zone of the North sea Chalk Group follows the same stress trend as deep sea limestone. on particles apparently is low and not correlated with porosity, probably because the pore-filling cementation in this interval causes Biot's coefficient to decline as burial increases. In the chalk section, contact cement is probably the reason why particles become less strained as porosity declines. In the ooze, we find that the natural compaction causes an increasing stress on grain contact area, indicating that the ooze particles become strongly strained. When the effective burial stress is normalized to total horizontal. The porosity decrease is accompanied by an increasing velocity to elastic waves, and consequently a decreasing Biot's coefficient, as estimated from velocity and density of core samples. To limestone as burial increases and porosity decreases. Burial diagenesis of deep sea chalk as reflected in Biot's coefficientįabricius, Ida Lykke Alam, Mohammad Monzurul
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