Jurassic Middle

The Jurassic, Middle Cretaceous, and Late Cretaceous ages of dykes spatially associated with the mineralization suggests that the mineralization age may be extended beyond the unique Late Cretaceous age assigned to mineralization (Smukefa/. 1999). 

Petersen, H.I., Depositional environments of coals and associated siliclastic sediments in the Lower and Middle Jurassic of Denmark, Geological Survey of Denmark, series 33, Copenhagen, 1994. 

The Middle Jurassic consists mainly of marls. The Upper Jurassic formations are massive (over 100 m thick) and are made up exclusively of limestones. During Upper Jurassic and Lower Cretaceous the limestone deposits have been uplifted and resulted in a paleo-karst surface that hosts discontinuous bauxite deposits. Lower... 

The Late Cretaceous Pebble deposit is located within the southern part of the Late Jurassic to Early Cretaceous Kahiltna terrane, which is bounded to the southeast by the Peninsular terrane (Late Triassic to Late Jurassic) and to the northwest by flysch of the Kuskokwim Group (middle to Late Cretaceous) (Fig. 1). The southern Kahiltna terrane consists predominately of Jurassic to Cretaceous turbidite deposits and can be divided into two major lithologic units the Koksetna River sequence and the Chilikadrotna Greenstone (Wallace etal. 1989). The... 

The Ligurian complex tectonically superimposed on the Tuscan units, consisting of middle to late Jurassic ophiolites and radiolarites plus Cretaceous to Eocene pelagic limestones and flysch sequences. 

Jurassic Period Middle period of the Mesozoic Era, between 185-135 million years ago. Characterized by the (possible) origin of angiosperms and the continued split of the worldwide supercontinent of Pangaea. 

Mahoney J. B., Friedman R. M., and McKinley S. D. (1995) Evolution of a Middle Jurassic volcanic arc stratigraphic, isotopic and geochemical characteristics of the Harrison Lake Formation, southwestern British Columbia. Can. J. Earth Sci. 32, 1759-1776. 

Girard J.-P. (1998) Carbonate cementation in the Middle Jurassic Oseberg reservoir sandstone, Oseberg field, Norway a case of deep burial-high temperature poikilotopic calcite. In Carbonate Cementation in Sandstones. Distribution Patterns and Geochemical Evolution (ed. S. Morad). International Association of Sedimentologists, Oxford, vol. 26, pp. 285-308. 

Harris N. B. (1990) Diagenetic quartz arenite and destruction of secondary porosity an example from the Middle Jurassic... 

Walderhaug O. (2000) Modeling quartz cementation and porosity in Middle Jurassic Brent Group sandstones of the Kvitebjorn Field, northern North Sea. Am. Assoc. Petrol. Geologists Bull. 84, 1325-1339. 

Several more island arcs struck western North America since the middle Jurassic period. The granite mountains of the Sierra Nevada are the roots of one of these island arcs. Landmasses created on the Pacific Plate have been scraped off it like the roof of the sports coupe mentioned earlier would be scraped off as it crammed itself under the rear bumper of a tractor-trailer. This mechanism is the origin of the west coast s ranges, the Cascades, and much of British Columbia and Alaska s southern coast. 

UJ = Upper Jurassic sands MJ = Middle Jurassic sands LJ = Lower Jurassic sands TR = Triassic sands NW = Norwegian well UK = British well... 

Dake, L.P. 1982. Application of the repeat formation tester in vertical and horizontal pulse testing in the Middle Jurassic Brent Sands. Paper EUR 270, Proc. Eur. Offshore Pet. Conf. 1982. 

Data for this study include cores from Middle Jurassic sediments in the North Sea and Haltenbanken offshore Norway, and onshore faulted sediments from the Gulf of Corinth (Greece), Brora (Scotland) and Kvalvigen (Spitsbergen). 

An interpreted regional seismic profile which includes parts of the Horda Platform (Fig. 3) show that the Triassic and lower-middle Jurassic sediments are offset up to 500 m along upper Jurassic block bounding and intra-block faults in a NW-SE profile. At the level of the Base Cretaceous Unconformity, however, only minor offsets are observed. Nearly all faults which cut the Base Cretaceous die out rapidly upsection. Only few faults can be observed on seismic lines in this area to extend upwards beyond the Cretaceous, which is similar to what has been described by for instance Glennie (1990). In this study... 

Pore pressure gradients are very difficult to estimate with the same accuracy in shales outside the reservoir zones, where RFT or DST measurements are impossible. We have, however, estimated pressure gradients in three wells on the border between the Melke and Gam Formations, based on the drilling data in Fig. 5. We have attempted to calculate the flow of water from the overpressured Upper Jurassic and Lower Cretaceous shales, into the underlying Middle Jurassic sandstones. The main uncertainty in... 

The field is covered by high quality 3-D seismic and has been delineated by seven wells. Four wells proved to have producible hydrocarbons in marginal marine, heterogenous sandstone reservoirs of Early-Middle Jurassic age (Tilje and lie Formations). 

Hudson, J.D. Andrews, J.E. (1987) The diagenesis of the Great Stuarine Group, Middle Jurassic, Inner Hebrides, Scotland. In Diagenesis of Sedimentary Sequences (Ed. Marshall, J.D.), Spec. Publ. geol. Soc. London, 36, 259-276. 

Kantorowicz, J.D. (1990) Lateral and vertical variations in pedogenesis and other early diagenetic phenomena. Middle Jurassic Ravenscar Group, Yorkshire. Proc. Yorks. Geol. Soc. 48, 61-74. 

Lundegard, P.d. (1994) Mixing zone origin of C-depleted calcite cement Osberg Formation sandstones (Middle Jurassic), Veslefrikk Field, Norway. Geochim. Cosmochim. Acta, 58, 2661-2675. 

Fig. 5. Subsidence curve for strata in well 34/4-1. The latest Jurassic-earliest Cretaceous uplift caused the erosion of about 1300 m of sediments above the Middle Lunde Member.

Snorre fault block is complex (Fig. 5). It includes an initial period of subsidence down to a depth of about 1500-1600 m until the Middle Jurassic (Bathonian-Callovian), followed by a period of uplift and erosion during the Late Jurassic and Early Cretaceous. The uplift culminated with a removal of 1200-1500 m of sediments, followed by a second period of subsidence with an onset in Valanginian-Hauterivian. A phase of very rapid subsidence took place during Late Cretaceous (Campanian-Maastrichtian), and another phase of high subsidence rate started in Pliocene-Pleistocene and is still going on. 

The Late Jurassic to Early Cretaceous Kimme-rian uplift and tilting of the Snorre fault block caused the formation of an erosional surface that cuts into the underlying succession of strata to various stratigraphical depths. Thus, the top of the cored middle Lunde section in well 34/4-1 is located 24 m beneath this subaerial unconformity, whereas the top of the cored middle Lunde interval... 

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