Liassic Limestones Research Articles

Fracture surface markings in Liassic limestone at Lavernock Point, South Wales

Fracture surface markings in Liassic limestone at Lavernock Point, South Wales

Mineralogy and petrology of the Polino Monticellite Calciocarbonatite (Central Italy)

Two small diatremes, about 0.25 my old, cut through Liassic limestones about 1 km NNE of the village of Polino (Long. 12°50'54″E-Lat. 42°35'34″N; Central Italy). The material filling the larger diatreme is mainly composed of a tuffisite with abundant lapilli showing concentric structure. Both unaltered country-rocks and massive hypabyssal carbonatite occur in the tuffisite as angular clasts and blocks, from a few mm up to more than 1 m in diameter. The Polino rock occurs in a strongly-potassic igneous district (Umbria Latium Ultra-alkaline District) which comprises phonolitic pyroclastic rocks and very rare kamafugitic lavas. Massive carbonatite blocks have an average mode of 53% Sr-Ba-rich calcite, 23% Fe-monticellite, 9% Th-perovskite plus Ti-magnetite, 6% Cr-phlogopite, 6% forsteritic olivine, about 2% Zr-schorlomite and ca. 1% Si-CO-OH apatite. Perovskite, schorlom ite, and apatite form cognate phases, whereas olivine and phlogopite, often replaced by monticellite, occur as nodules and as discrete grains with compositions and deformation features typical of mantle xenocrysts found in alkali basalts and ultramafic rocks. High modal content of Ca-carbonate, high Sr, Ba and LREE contents of calcite, the presence of rare minerals peculiar to carbonatitic rocks and an essential amount of monticellite indicate classification of the Polino rock as a monticellite calciocarbonatite. The Polino rock represents a carbonatitic melt strongly contaminated by mantle-crystal debris. It displays unusual geochemical features having trace elements closer to those of the regional-associated kamafugitic rocks rather than to those of common carbonatites.

Importance d'une tectonique de distension pliocène dans le rif central (Maroc) : la nappe de kétama existe-t-elle?

Liassic limestone outcrops of the Tifelouest and the Tafraout massives was explained according to two different ways: 1. cores of recumbent folds settled at the front of the Ketama nappe; 2. mega-olistoliths reworked into a Tortonian matrix. In the studied area we show that: 1. a major Messinian fault network consisting of conjugate dextral and senestral strike slip faults, intersected by Pliocene normal faults with 1 to 3.5 km throw, explains in itself the uplift of the Liassic limestone massives; 2. the alleged “metamorphic Miocene”, also called “Miocène des fenêtres”, is Upper Oligocene in age and is not metamorphic. Since it unconformably overlies the older sequences, the “Miocène des fenêtres” is not cropping out in a tectonic window; 3. the Liassic limestone of the Tifelouest and the Tafraout massives represents the oldest sequence (anticline core) of the Ketama domaine. We think that there is no major thrust in the rifian domain, between the Prerif to the South and the flysch domain to the North.

Stratigraphy of the Triassic, Lower Jurassic and Middle Jurassic (Aalenian) from the Fastnet Basin, Offshore South-west Ireland

The stratigraphy of the Triassic, Lower Jurassic and Middle Jurassic (Aalenian) of the Fastnet Basin is described. The sequence has been divided using wireline log criteria. Six rock units are recognized in the Triassic and 12 in the Lower Jurassic and Middle Jurassic (Aalenian). None of these major rock units shows any significant diachroneity. Apparent breaks in the sequence due to unconformities or condensed sections have been identified within or bounding three of the rock units: the Liassic Limestone, Liassic Marl and Liassic Sandstone. Dating is provided by both microfaunas and microfloras extracted from ditch cuttings and sidewall cores. The ages of the Triassic rock units are mainly determined by correlation with dateable sequences in the North Celtic Sea Basin, whereas the Jurassic rock units yielded abundant short-ranging microfossils.

Slope stability problems in the carboniferous and liassic limestones : Williams, G D In: Cliff and slope stability — South Wales, P135–155. Publ Cardiff: University College Extra-mural Studies Dept, June 1980

Slope stability problems in the carboniferous and liassic limestones : Williams, G D In: Cliff and slope stability — South Wales, P135–155. Publ Cardiff: University College Extra-mural Studies Dept, June 1980

Mesozoic and Cenozoic Rocks from Malta Escarpment (Central Mediterranean)

Sedimentary rocks of Triassic-Neogene age are present on the Malta Escarpment of the eastern Mediterranean. Upper Triassic dolomitic limestones of shallow-water origin, at depths between 2.5 and 3.5 km, are similar in lithofacies to coeval platform carbonates of the Siracusa (Syracuse) belt of southern Sicily. Jurassic rocks include lower-middle Liassic shallow-water limestones followed by condensed hemipelagic lime deposits indicative of sinking and starving of the former platform. Cretaceous materials are represented by both red marls rich in planktonic faunas and reworked volcaniclastic breccias including shallow-water skeletal material. Paleogene rocks are both shallow-water limestones with corals, algae, and bivalves, and redeposited calcarenites of lithofacies similar to those from surface and subsurface of the Ragusa zone. Oligocene-?lower Miocene rocks from the escarpment are also similar in lithology to the coeval Ragusa deposits. Tortonian is represented by hemipelagic marls indicating open-marine environment. Pervasive dolomitization on lime crusts and on initial-stage fissure fillings with strongly positive isotopic oxygen ratio is thought to be a product of Messinian evaporitic drawdown. Pliocene sediments belong to the Trubi facies and consist of pelagic foraminiferal chalk. An impressive vertical relief existed by Miocene times, as attested by Messinian crusts and veins on or in rocks as old as Late Triassic. Our data do not provide evidence that this morphologic feature necessarily coincides with a continent-ocean transition. The present escarpment was produced by faulting, erosion, and defacement.

Diagenesis of English Lower Jurassic limestones as inferred from oxygen and carbon isotope analysis

Fifty-seven samples of mostly Liassic limestones and calcite spar were subjected to mass spectrometer analysis to determine δ 13C and δ 18O. The results are used to compare and interpret the changing isotopic composition through time of calcite-precipitating pore fluids and to assess the influence of rate and type of sedimentation, diagenetic reactions and meteoric water influx. In general microsparite beds and concretions formed sooner after deposition in Dorset than in Yorkshire, where sedimentation rates were usually higher. Calcite horizons in the Bridport Sands Formation of Dorset are entirely diagenetic in origin. Carbon isotope data from concretions in the Jet Rock Formation of Yorkshire support a model of changing organic reactions with increasing depth of burial. The influence of meteoric waters is substantially restricted to the formation of post-Liassic veins.

The Geometry of Shore Platforms in England and Wales

Platform gradient was investigated in three areas of England and Wales, providing a wide range of morphogenic and geological conditions. A correlation coefficient of 0-92 (n = 36) was obtained for platform gradient against tidal range and one of - o-6o (n = 36) for fetch perpendicular to coastal orientation; analysis of covariance demonstrated that there was little difference in the regression for Liassic limestones and shales and chalk. A further correlation coefficient of 0-79 (n = 23) was noted between platform gradient and cliff height for the chalk exposures. It is proposed that platform gradient in these areas is being maintained in dynamic equilibrium, at least in the early period of development. WIDE, gently sloping shore platforms are prominent features around much of the British coast- line. Several recent investigations have involved the precise measurement of platform geometry (C. E. Everard et al., 1964; C. L. So, 1965; L. W. Wright, 1967, 1970; A. Wood, 1968; A. S. Trenhaile, I969, I97I, I972), but the nature of the relationships between shore platforms and elements of the morphogenic environment have not been established. Although Trenhaile (1972) has attempted to investigate the effect of tidal range on platform width and slope in the Vale of Glamorgan, local studies lack the variety of morphogenic conditions necessary for the establish- ment of more meaningful relationships. Wright (I967, I970), and Trenhaile (I972), have examined the relationship between the height of the cliff-platform junction and the height of the Mean High Water Spring (MHWS) and Mean High Water Neap (MHWN) tides. The relation- ships, however, are affected by local lithological and to a lesser extent morphological factors which may induce some divergence from the expected level. There appears little reason to suppose that the relationship between the cliff-platform junction and the levels of high tidel would change through time, such that changes of platform geometry must largely, assuming linearity of profiles, involve changes in slope and width. Although A. B. Edwards (I94I) and

Contribution a l'etude stratigraphique du Lias des Dolomites italiennes (Italie du nord)

Abstract The gray limestone facies of the Italian Dolomites is confined to the lower Liassic and rests unconformably on the last Triasina-bearing beds of pre-Liassic age. Middle Liassic crinoidal limestones overlie the gray limestone and are overlain by upper Liassic chemical sediments. The only evidence for upper Liassic age strata is the presence of the ammonites Harpoceras discodes and Hammatoceras insigne. For the most part, the upper Liassic was a period of nondeposition.

Etude geologique de la region de Castello-Tesino (Alpes meridionales, province de Trente, Italie)

Abstract The sedimentary series of the Castello-Tesino region in the eastern Venetian Prealps comprise a sequence of marine rocks ranging in age from the Liassic to Miocene. The Liassic gray limestones and the Dogger ooelitic limestones are neritic or subreefal deposits. The Malm and the Cretaceous deposits indicate a deepening of the sea. The Eocene and Oligocene facies are more terrigenous, but in the Lutetian, Priabonian, and Oligocene become littoral. The Miocene marks the transgression of a neritic sea indicated by the accumulation of a slightly discordant molasse sequence. The folds trend in a WSW-ENE direction. The stratigraphy and paleogeography indicate that the region belongs to the Belluno zone between the zone of Friuli to the east and the zone of Trento to the west.

Etude geologique de la region situee a l'ouest de Rovereto (Alpes meridionales, province de Trente, Italie)

Abstract The NE-SW trending Stivo-Cornetto anticline (Trento province) forms a line of crests separating the Sarca valley from the Adige river valley. The entirely marine sequence includes Liassic and Dogger subreefal limestones succeeded by Malm, Cretaceous and lower Eocene deep water deposits. Emergence or regression resulted in the deposition of neritic facies during the middle and upper Eocene and the Oligocene and Miocene. The deposits are representative of the Tridentine zone.

The supposed Cambrian foraminifera from the Malverns

Summary The only foraminifera of Cambrian age with wall-structure preserved were described by Chapman in 1900. Originally considered to be derived from a calcareous band in the White Leaved Oak Shales (Upper Cambrian), these specimens are here shown to be derived from a loose fragment of Rhaetic of Lower Liassic limestone. As the earliest-known well preserved foraminifera , these have had a great influence on the classification of the group, and the views of certain authors as to the evolutionary sequence of foraminiferal types will have to be completely revised. The genera Lagena, Nodosaria, Dentalina, Cristellaria, Spirillina and Marginulina, previously considered to range unchanged from Cambrian to Recent, probably range from Mesozoic only. The isolation of Palaeozoic foraminifera becomes now much more marked and the incoming of Mesozoic types must have relatively rapid.

Y a-t-il coupure ou continuite entre le dynamometamorphisme et le metamorphisme regional?; a propos d'observations pres du glacier de Tre-la-Tete [with discussion

Abstract Presents arguments in support of the concept that dynamometamorphic processes (recrystallization by mechanical deformation during which no material is added from sources outside the rock mass being deformed) and regional metamorphism (rock alteration accompanied by the additionof material from adjacent terrain or from depth) are parts of a same process and not distinct independent processes. The concordance exhibited by a differentially metamorphosed mass of Liassic limestones wedged in crystalline rocks of the Mont Blanc massif, exposed in a gorge near the tongue of the Tre-la-Tete glacier, France, is cited as an example of recrystallization which took place during the regional metamorphism associated with Alpine crustal movements.

The Formation of the Hydraulic Limestones of the Lower Lias

AS a result of a study of the Liassic limestones of the Dorset coast, Dr. W. A. Richardson (1923) concluded that both the limestone bands and the nodules were of secondary origin, and largely displaced the associated marls and shales. Observations made during a study of the Hydraulic Limestone Series (pre-planorbis-johnstoni subzones) in south Nottinghamshire lend support to the hypothesis of concretionary origin, but do not accord with certain other of Dr. Richardson's suggestions.

III.—On some Chalk-pebbles from the Floor of the English Channel

In 1908 Mr. R. H. Worth described a number of stones which had been dredged by Mr. T. R. Crawshay, of the Marine Biological Association, from the floor of the English Channel to the east and south-east of the Lizard. These stones included a great variety of rocks such as granites, felsites, diorites, and other igneous rocks, gneisses, schists, slates, and quartzites, Devonian grits, Permian conglomerate, Triassic marl, sandstones of different kinds, Liassic limestones, hard chalks, and flints.