Age and depositional environment of the Sainte-Anne Formation (Armorican Massif, France): the oldest (Emsian) evidence for mountain erosion in the Variscan belt

2009 ◽  
Vol 180 (6) ◽  
pp. 529-544 ◽  
Author(s):  
Céline Ducassou ◽  
Christine Strullu-Derrien ◽  
Michel Ballevre ◽  
Marie-Pierre Dabard ◽  
Philippe Gerrienne ◽  
...  
Keyword(s):  
Depositional Environment ◽  
Source Area ◽  
Variscan Orogeny ◽  
Variscan Belt ◽  
Delta Front ◽  
Volcanic Origin ◽  
Sedimentary Sequences ◽  
Erosion Level ◽  
Continental Area ◽  
Armorican Massif

Abstract The palaeogeography of the internal zones of the Variscan belt during the early stages of the convergence remains unclear. Sedimentary sequences that recorded the denudation of an early relief have generally been removed by erosion. In the Chalonnes area (southeast of the Armorican Massif), the reefal carbonates of the Chalonnes Formation (Fm) are overlain by the immature, poorly-sorted sandstones of the Sainte-Anne Fm. This formation is characterised by the occurrence of gravity flow deposits and contains immature and poorly sorted sandstones with a large amount of plant debris and lithic fragments, suggesting a depositional environment in a delta front dominated by floods. A revision of the palaeoflora content allows to assign an Emsian age to the Sainte-Anne Fm. Lithic fragments are mainly of sedimentary and volcanic origin, suggesting moderate erosion level of the source area. Palaeocurrent data indicate a southern origin for the sediments. These features collectively demonstrate that the Sainte-Anne Fm is the record of the erosion of a continental area located farther south, and experiencing incipient tectonic uplift during the Emsian. The Sainte-Anne Fm could represent therefore the earliest record in France of the very first stages of the Variscan orogeny.

scholarly journals Relations between basalts and adakitic–felsic intrusive bodies in a soft-substrate environment: the South Ouessant Visean basin in the Variscan belt, Armorican Massif, France

2016 ◽  
Vol 53 (4) ◽  
pp. 441-456 ◽  
Author(s):  
Martial Caroff ◽  
Bernard Le Gall ◽  
Christine Authemayou ◽  
Denise Bussien Grosjean ◽  
Cyrill Labry ◽  
...  
Keyword(s):  
High Pressure ◽  
Early Stage ◽  
Variscan Orogeny ◽  
Variscan Belt ◽  
Soft Substrate ◽  
Mafic Intrusions ◽  
Partial Remelting ◽  
Pressure Fractionation ◽  
Peraluminous Granites ◽  
Armorican Massif

The metasedimentary and magmatic terranes in the southern part of the Ouessant Island (Western Brittany, France) are the offshore prolongation of the Léon Variscan metamorphic domain. They mainly consist of micaschists and subordinate amphibolitic lenses (meta-pillow lavas and volcaniclastic successions) cut by a swarm of trondhjemite sills, together with a large porphyritic monzogranite body, newly dated at 336 Ma, and later syeno-leucogranitic intrusions. A large spectrum of fluidal peperites, including spectacular “fiamme”-bearing breccias, is observable at the contact between metasediments and most of the intrusives. The coexistence of amphibolitized basalts, adakitic trondhjemites, and peraluminous granites in the inferred South Ouessant basin is assigned to a variety of deep subcontemporaneous processes, including asthenospheric partial melting, high-pressure fractionation in lithospheric reservoirs (or partial remelting of deep crystallized mafic intrusions), and continental crust melting. Implications of these new results are discussed in the Visean basinal framework of the Armorican Massif, formed at an early stage of the Variscan orogeny.

Sur les rhyolites et les granites prevarisques en Normandie et en Vendee

1943 ◽  
Vol S5-XIII (4-6) ◽  
pp. 139-151
Author(s):  
Gilbert Mathieu
Keyword(s):  
Variscan Orogeny ◽  
The South ◽  
The North ◽  
Rigid Mass ◽  
Armorican Massif

Abstract An account of the pre-Carboniferous rhyolites and granites of Normandy and Vendee, France. Precambrian granite masses and Precambrian and Cambrian conglomerates containing ancient granite and rhyolite pebbles occur in both regions, and indicate that the Carboniferous granites of the Armorican massif were emplaced during the Variscan orogeny in a zone of subsidence between the rigid mass of Normandy to the north and Vendee to the south.

How does a monzogranite turn into a trachydacitic extrusion mantled by basinal volcaniclastics and peperites? The case of South-Ouessant, Armorican Variscides (France)

2020 ◽  
Vol 177 (6) ◽  
pp. 1161-1167
Author(s):  
Martial Caroff ◽  
Bernard Le Gall ◽  
Christine Authemayou
Keyword(s):  
Sedimentary Basin ◽  
Coarse Grained ◽  
Soft Substrate ◽  
Volcanic Origin ◽  
Pillow Lavas ◽  
Magmatic Body ◽  
Load Effects ◽  
New Perspective ◽  
Armorican Massif ◽  
Highly Strained

How many volcanic bodies are being confused with plutonic ones worldwide? The purpose of this study is not to provide an answer to this question, but rather to illustrate this issue through an example from the French Armorican Variscides. It concerns a magmatic body cross-cutting highly strained terranes in the Ouessant Island, regarded for decades as a granitoid (monzogranite) on the basis of both its coarse-grained texture and its mineralogy. However, the volcanic origin of the metamorphosed series flanking this foliated body is here recognized by pillow lavas, deposit layers, and fiamme-bearing volcaniclastics, all emplaced onto the soft-substrate floor of a fault-bounded basin. Among other things, similarities between feldspar megacrysts/porphyrocrysts in both the volcaniclastics and the adjoining (formerly) monzogranitic massive body lead us to reinterpret the latter as a trachydacitic extrusion. In our model, the corresponding viscous lava progressively flowed in the basin, recovering the earlier volcanic formations and inducing load effects on the underlying soft sediments, along with compaction of the previously deposited pumices, to produce fiamme. The interpretation of the South-Ouessant area as a Visean transtensional volcano-sedimentary basin provides a new perspective on the distribution of the Variscan pull-apart basins in the Armorican Massif.

Geochronology and geochemistry of Ordovician felsic volcanism in the Southern Armorican Massif (Variscan belt, France): Implications for the breakup of Gondwana

2012 ◽  
Vol 21 (4) ◽  
pp. 1019-1036 ◽  
Author(s):  
M. Ballèvre ◽  
S. Fourcade ◽  
R. Capdevila ◽  
J.-J. Peucat ◽  
A. Cocherie ◽  
...  
Keyword(s):  
Variscan Belt ◽  
Felsic Volcanism ◽  
Armorican Massif

Lithofacies and fluvial–lacustrine environments of the Palaeogene Sevkhuul and Ergil members (Ergiliin Zoo Formation, South Gobi, Mongolia)

2006 ◽  
Vol 143 (2) ◽  
pp. 165-179 ◽  
Author(s):  
H. G. DILL ◽  
S. KHISHIGSUREN ◽  
J. BULGAMAA ◽  
KH. BOLORMA ◽  
F. MELCHER
Keyword(s):  
Source Area ◽  
Field Work ◽  
Late Eocene ◽  
Climatic Conditions ◽  
Heavy Minerals ◽  
Gobi Desert ◽  
Carbonate Minerals ◽  
Delta Front ◽  
Delta Plain ◽  
Sheet Silicates

The clastic sequence of the Ergiliin Zoo Formation stretches along the Mongolian–Chinese border in the southern Gobi Desert, Mongolia. Its members (Sevkhuul, Ergil) exposed in the Erdene Sum region are well known for their vertebrate remains of Late Eocene and Oligocene age. Based upon field work, the continental red beds were subdivided into four units described as (I) prodelta/mud-sand flat, (II) delta front, (III) delta plain and (IV) calcretes. All sub-environments are in a fluvial–lacustrine setting. Electronmicroprobe analysis, in addition to conventional thin-section examination, was applied to shed some light on the complex mineral association made up of light minerals (quartz, plagioclase, ternary feldspar, orthoclase, smectite, illite, rare palygorskite), heavy minerals (almandine–pyrope solid solution series, zoisite–epidote s.s.s.) and abundant goethite and carbonate minerals (calcite, dolomite). Igneous rocks being exposed in the source area have contributed to the formation of carbonate minerals and Mg-bearing sheet silicates during diagenesis. Higher up on the delta plain transitional between distal alluvial and deltaic deposits, fluids emerged from the distal alluvial–fluvial deposits and formed calcareous duricrusts. Drawing conclusions from the rock colour, the mineral assemblage and the palaeoecological data, the climatic conditions may be described as alternating wet and dry seasons, closely resembling those conditions of a modern savannah.

scholarly journals The occurrence of marine fossils in the Upper Cretaceous deltaic sediments at Pautut, central West Greenland

1991 ◽  
Vol 39 ◽  
pp. 111-122
Author(s):  
Torben Olsen ◽  
Gunver Krarup Pedersen
Keyword(s):  
Depositional Environment ◽  
Upper Cretaceous ◽  
Sediment Accumulation ◽  
Accumulation Rates ◽  
Delta Front ◽  
Delta Plain ◽  
Facies Associations ◽  
Marine Fossils ◽  
Stratigraphic Position ◽  
Marine Influence

Finds of Upper Cretaceous marine macrofossils from Pautut have been reported since 1874. Subsequent investigations have led to contrasting views concerning the stratigraphic position of the fossils, the general depositional environment, and the amount of marine influence. During a brief visit to Pautut in the summer of 1989, a section of the exposed sediments was described. The sediments can be divided into 4 facies associations reflecting deposition on a prograding delta front, in distributary channels, on a subaerial to limnic delta plain and on an abandoned delta lobe during a marine transgression. The sedimentological model predicts that marine fossils, if present, should occur in the delta front association. The sediments were thoroughly searched for marine macrofossils, which were found in the lower part of the prominent coarsening-upward delta front sequences. The number of fossils is generally low. Bivalves and echinoids constitute the dominant groups of fossils and seem to have been well adapted to a life in muddy marine bays, subject to fluctuations in salinity and rate of deposition and with much suspended sediment. The fossils indicate that the beds at Pautut were deposited during latest Santonian to earliest Campa­nian times. Sediment accumulation rates were high. The stratigraphy within the Pautfit area is discussed and all the Cretaceous sediments are referred to the Atane Formation.

Lithostratigraphy of the Kookfontein Formation (Ecca Group, Karoo Supergroup), South Africa

2017 ◽  
Vol 120 (3) ◽  
pp. 447-458
Author(s):  
H. de V. Wickens ◽  
D.I. Cole
Keyword(s):  
South Africa ◽  
Depositional Environment ◽  
Delta Front ◽  
Southwestern Part ◽  
Fine Grained ◽  
Karoo Basin ◽  
Deformation Features ◽  
Stratigraphic Position ◽  
Shelf Margin ◽  
Upper Slope

Abstract The Permian Kookfontein Formation forms part of the upper Ecca Group in the southwestern part of the main Karoo Basin of South Africa. It occupies a stratigraphic position between the underlying Skoorsteenberg Formation and the overlying Waterford Formation, with its regional extent limited to the cut-off boundaries of the Skoorsteenberg Formation. The Kookfontein Formation has an average thickness of 200 m, coarsens upwards, and predominantly comprises dark grey shale, siltstone and thin- to thick-bedded, fine- to very fine-grained, feldspathic litharenite. Characteristic upward-coarsening and thickening successions and syn-sedimentary deformation features reflect rapid deposition and progradation of a predominantly fluvially-dominated prodelta and delta front slope environment. The upward increase in the abundance of wave–ripple marks further indicates a gradual shallowing of the depositional environment through time. The upper contact with the Waterford Formation is gradational, which indicates a transition from deposition in an unstable upper slope/shelf margin environment to a more stable shelf setting.

Sign in / Sign up

Export Citation Format

Share Document