Siltstone Formation Research Articles

The fluvial architecture of the upper Buntsandstein in the Iberian Basin, central Spain

ABSTRACTThe Cercadillo Sandstone and Siltstone (CSS) Formation forms the upper part of the Buntsandstein fluvial facies in the western margin of the Iberian Basin. Sedimentation was controlled by two major pre‐Triassic tectonic systems: the Iberian Ranges System (NW‐SE) and the Central System (NE‐SW). Fluvial sedimentation during this period took place in coexisting braided and meandering channels, together with associated ephemeral episodes. This unusual association was due to a combination of structural control by the main normal faults coupled with large discharge fluctuations.The CSS Formation consists of two major fluvial sequences with very similar vertical patterns comprising low sinuosity stream deposits that pass upwards into high sinuosity deposits associated with extensive floodplain sediments. A widespread calcrete horizon is developed at the top of the lower sequence and a surface with pedogenic features is present at the top of the upper sequence. These horizons are interpreted to be the result of subaerial exposure during a period of no subsidence and equilibrium in the erosion‐sedimentation processes in the area, probably due to quiescent periods on the master faults that delineate the basin.Minor changes within the sequences are probably due to discharge fluctuations of a climatic origin whereas the general vertical trend of the sequences is suggested to be tectonically controlled. Palaeocurrent data show a general flux of sediments to the south‐east, parallel to the axis of the Iberian Basin, but the final part of the upper sequence palaeocurrents to the north‐east are interpreted to indicate a local reactivation of secondary, transverse faults in the south‐east part of the study area.

Early proterozoic AuCoU mineralization in the Kuusamo district, northeastern Finland

Abstract The Kuusamo volcano-sedimentary belt is part of an Early Proterozoic rift system in the Fennoscandian Shield extending from the Norwegian Sea to Lake Onega. The rocks range in age from 2.5 to 2.0 Ga. Sulphide deposits are confined to the two lowermost sedimentary units, the Sericite Quartzite and Siltstone Formations. These are intruded by albite diabase and syenite dikes and sills. The mineralization is associated with pervasive hydrothermal alteration. Spilitization and albitization predate mineralization and appear to be premetamorphic. The later FeMg-silicate and K-silicate alteration is associated with mineralization in ductile shear zones, whereas carbonatization and silicification dominate in brittle zones. Ore deposits and occurrences can be divided into three groups: uranium deposits, CoAuU-bearing sulphide deposits, and Fesulphide deposits. Uranium deposits are of the sulphide-poor, stratiform sandstone type often associated with an albitization front. The U deposits are also related to albite diabase dikes and alkaline granitic intrusions. The CoAuU deposits can be subdivided into two end members: replacement ores in a ductile deformation zone and breccia ores in a brittle deformation zone. At Juomasuo the sulphide mineralization is located in a FeMg-silicate and K-silicate alteration zone within a ductile shear zone surrounded by a wide albitized zone. The ore reserves are 1 Mt grading 5–6 g/t Au and 0.2% Co. Other enriched elements are Cu, U, W, Mo, Se, Te and Bi. The Konttiaho deposit represents a breccia ore in a brittle deformation zone where the CoAuU mineralization is associated with carbonate and quartz within albitized country rocks. Typical ore minerals in both types are pyrite, pyrrhotite, cobaltite, Co-pentlandite, chalcopyrite, uraninite, molybdenite, scheelite, gold and tellurides. The Fe-sulphide deposits are similar to the CoAuU deposits but lack precious metals. Sulphide mineralization is epigenetic, post peak-metamorphic and related to the Svecokarelian orogeny at 1.8–1.9 Ga. The mineralization is controlled by stratigraphy, antiform structures and shear zones in the central part of the volcano-sedimentary belt. The broad elemental spectrum suggests a complex origin and probably a deep-seated source for the metals.

The effect of worn and chipped points on point load indices

The point load index is a simple, fast and inexpensive method for obtaining rock strength values. Extensive work by many researchers has been reported on the test procedure, the effect of different loading configurations, sample size and the need for size correction factors. However, no published information appears to exist regarding the effect of point wear on the resultant index values. After reviewing a study undertaken to investigate the effect of worn and chipped points on point load indices, the paper compares point load derived and laboratory rock strength values obtained from a siltstone formation in the Sydney Coalfield, Nova Scotia.

Plesiosaurs from Albian aged Bathurst Island formation siltstones near Darwin, Northern Territory, Australia

Eroded, fragmentary remains of a large elasmosaurid plesiosaur extends the range of Australian sauropterygians to the shallow Upper Albian seas of the central north of the continent. The plesiosaur is associated with abundant ichthyosaur (Platyptergius Von Heune) material which is also briefly described. The elasmosaurid affinity of the specimens is based on the morphology of a cervical vertebra and the large dimensions of the propodials. It resembles but cannot be positively identified as Woolungasuras Persson.

Petroleum prospects in North Canterbury, South Island, New Zealand

Abstract Late Cretaceous to Plio-Pleistocene sediments, unconformably overlying Jurassic greywacke basement, are folded and faulted in what is tectonically the southernmost part of the East Coast Fold Belt. Good porous sandstones occur in the lower part of the sequence, while impermeable cap rocks are found in clay, muddy siltstone, and dense marl formations, particularly in the Eocene-Oligocene and younger intervals. Geochemical analyses indicate a good potential oil and associated gas source in rocks of Eocene to Late Cretaceous age in the Kowai-1 well; these rocks, however, are moderately immature. With somewhat greater depth of burial basinwards, thermal maturity could increase sufficiently to generate hydrocarbons in commercial quantities. These may have migrated into the Kowai structure, while the flushing encountered in Kowai-l (which was drilled offstructure and was not a valid test) could create hydrodynamic trap conditions and enhance reservoir capacity. Other targets may be found underneath the...

The occurrence of Mangakotuku Siltstone in Northwest Port Waikato Region

Abstract Mangakotuku Siltstone is generally absent at the base of the Te Kuiti Group on the Port Waikato horst, but at two new and one already described localities, fossiliferous siltstones of lower Landon age occur along the planes of major faults within the horst. Both in their lithologic character and fossil content, the scltstones resemble the Mangakotuku Siltstone Formation and they are regarded as having been deDosited in small depressions picked out along the trace of pre-existing faults during initial transgression over the horst. Subsequent reactivation of the faults has resulted in incorporation of slivers of siltstones along fault planes as a gouge.

The caradocian rocks of the north and west berwyn hills, north wales

AbstractThe Caradoc of the Berwyn Hills is a thick sequence of marine mudstones and siltstones with interstratified sub‐aerial tuff formations. Near the top of the succession there is a sharp facies change to graptolitic shales. The sequence has been re‐mapped and two new formations (the Pen‐plaenau Siltstone Formation and Cwm Rhiwarth Siltstone Formation) and one new member are proposed. Assemblage zones can be traced round the outcrop in the lower part of the sequence (Soudleyan) but higher in the succession (Longvillian) there are differences between the faunal assemblages of the north and west. The northern faunas are referred to Dalmanella community which is believed to have occupied a shallower environment than the Nicolella community to the west. In spite of the presumed environmental control of the faunas, the sequence can be fairly precisely correlated with the classic sections in Shropshire and Bala.The Caradoc sedimentary sequence represents a mainly shallow sub‐tidal environment with periodic episodes of local emergence. The area deepened during the Longvillian, particularly in the west. There followed a period of non‐deposition with probably some erosion at the base of the Nod Glas which itself represents a period of reduced sediment.There is a well‐known stratigraphic break at the base of the Ashgill which rests on rocks of Onnian age and on different horizons of the Longvillian.

The diachronism of the Wenlock Limestone

A quick transgressive event occurs near the top of the Wenlock Limestone. The initiation of this is thought to be synchronous, proving the top of the Wenlock Limestone to be diachronous and younging southwards. As a result the top of this rock unit cannot be used satisfactorily as a time line. It is suggested that the initiation of the transgression be taken as the practical means for the correlation of the Wenlock-Ludlow Series boundary. The Birmingham Siltstone Formation is erected for the strata between Dudley and Ludlow which are younger than Wenlock Limestone and older than the transgression. The Wenlock Limestone of Usk was deposited after the transgression and is unrelated to the main Wenlock Limestone. Thus it is treated as a separate entity and named here the Usk Limestone Formation.

Tourmalinised rocks on Cuvier Island

Abstract Petrological examination of rocks from Cuvier Island (N.Z.M.S. 1, Sheet N36) collected by Messrs J. Healy and B. N. Thompson of the Geological Survey has indicated that certain contact rocks are highly tourmalinised (P 12992, 12993, 23185* A brief account of this discovery is incorporated in the Geological Map of New Zealand 1 : 250,000, Sheet 2B, Barrier, where it is stated, “The western end of Cuvier Island is composed partly of Moehau Formation siltstone metamorphosed to hornfels by quartz porphyry and plutonic intrusives. Both the hornfels and a large part of the intrusive rocks have been tourmalinised, silicified, and carbonated.” (Thompson, 1960.) The intrusive rocks are noritic quartz gabbros, biotite-augitequartz gabbros and quartz diorites, and can be correlated with similar rocks on Coromandel Peninsula (“Paritu Tonalite”).

Solum-Parent Material Relationships for Three Soil Profiles Developed from Sedimentary Deposits of Ordovician Age

The chemical and mineralogical relationships between three closely associated parent materials and the solum overlying each of them were studied. Methods common in soils research were employed. Curdsville limestone, Fairmount limestone, and Garrard siltstone formations were located in Garrard County, Kentucky. Profiles of Maury, Kenton, and Lowell soil series, locally associated with these formations, respectively, were sampled down to bedrock. The top 12 inches of bedrock was also sampled. Petrographic study indicated weathering of glauconite in the sand and silt fractions as the solum surface was approached. Likewise, a 10Å. component of the clay fraction, presumably glauconitic, decreased in abundance in the more weathered upper solum while vermiculite and other 2:1 expansible layer silicates became more abundant. Kaolinite also was more abundant in the upper solum.