Age et position des calcaires de Saint-Jean-de-la-Riviere dans le Cambrien des Moitiers d'Allonne (Manche)

1963 ◽  
Vol S7-V (5) ◽  
pp. 722-729
Author(s):  
Francis Dore
Keyword(s):  
Lower Cambrian ◽  
Early Precambrian ◽  
Red Sandstone ◽  
Type Section ◽  
Lower Ordovician ◽  
Sandy Shale ◽  
Sandstone Facies

Abstract The type section for the Saint-Jean-de-la-Riviere limestone outcrops on the Moitiers d'Allonne anticline in the Douits valley north of Carteret and east of Moitiers (France). The limestones are younger than the sandy shale of the Cap Carteret series and between Moitiers and Bosquet the sequence is overlain by shales and red sandstones separating it from the Armorican sandstones. The lower Cambrian of the area presents a complete sedimentary section ending with a red sandstone facies of a regressing sea. A significant hiatus is evident before lower Ordovician transgression and continued deposition. Hyolothides and sponges, believed to be Azoic (early Precambrian) and older than Archaeocyathidae and Bigotina, are found in calcareous sandstone nodules on the beach at Carteret.

Notes of a Geologist in Ireland During August and September, 1857

The Geologist ◽  
1858 ◽  
Vol 1 (8) ◽  
pp. 330-335
Author(s):  
W. S. Symonds
Keyword(s):  
Lower Cambrian ◽  
Red Sandstone ◽  
Upper Silurian ◽  
Cover Up

On leaving Dublin, we travelled northwards, for the purpose of examining the carboniferous rocks, and visiting the magnificent collection of fossil-fishes in the museum of the Earl of Enniskillen; we then journeyed south for Killarney and the Dingle district, but as it may be more convenient to the reader to travel geologically, we will reverse the order of our journey, and visit the Upper Silurian and Old Red Sandstone districts before we examine the carboniferous deposits.The lower Cambrian rocks of Wales, of which the Oldhamia-schists of Ireland are believed to be the equivalents, pass upwards by insensible gradations into the Lingula-flags, to which they are altogether conformable. The Lingula-flags are reckoned to be four or five thousand feet thick, and the Llandeilo or Builth-beds, which cover up these, are probably as thick; but geologists are, as yet, uncertain whether they possess in Ireland any true equivalents either of the Lingula-flags or of the Llandeilo and Builth deposits. There are, however, fossiliferous rocks of the Bala and Caradoc age in Ireland similar to those which, in Wales, succeed conformably to the Llandeilo and Builth beds, and they may be examined at Courtown, in the county of Wicklow, and again at Tramore, south of Waterford. They are unconformable to the rocks below, which are undoubtedly Cambrian, and thence, we imagine, has arisen the suspicion that the Lingula-beds and Llandeilo-flags have never been deposited in Ireland, or that if they were, they have been denuded and swept away before the deposition of the Bala or Caradoc strata.

The Developmental Biology of Brachiopods

2001 ◽  
Vol 7 ◽  
pp. 69-88
Author(s):  
Gary Freeman
Keyword(s):  
Developmental Biology ◽  
Life History ◽  
Fossil Record ◽  
Lower Cambrian ◽  
Comprehensive Treatment ◽  
Next Generation ◽  
Lower Paleozoic ◽  
Short Course ◽  
Invertebrate Paleontology ◽  
Lower Ordovician

The chapter on anatomy in the Treatise on Invertebrate Paleontology (Part H, Brachiopoda, revised) (Williams et al., 1997) is the most current and comprehensive treatment that we have of reproduction and development in these animals. My contribution to this short course is a commentary on and addendum to this review. The study of the developmental biology of extant brachiopods describes a large part of their life history and defines several of the parameters that have to be taken into account when thinking about how a given set of genes will make it to the next generation (Havenhand, 1995). Some extant brachiopod genera like Discinisca and Crania (Neocrania) belong to families that first appeared in the fossil record during the Lower Ordovician or, as in the case of Glottidia, to a superfamily that first appeared during the Lower Cambrian. Studies on the development of these extant animals provide a picture of what the development of their Lower Paleozoic ancestors might have been like.

Non-trilobite arthropods from the Silver Peak Range, Nevada

2003 ◽  
Vol 77 (4) ◽  
pp. 706-720 ◽  
Author(s):  
Ben Waggoner
Keyword(s):  
Great Basin ◽  
Lower Cambrian ◽  
Upper Cambrian ◽  
Extant Taxon ◽  
Lower Ordovician

Two non-trilobite arthropods are described from the Emigrant Formation (Lower Cambrian-Lower Ordovician) in the Silver Peak Range, Esmeralda County, Nevada. A Middle or Upper Cambrian “arachnomorph” arthropod with a phosphatic exoskeleton has been noted in previous faunal lists, but has not been previously described. This fossil is here named Quasimodaspis brentsae gen. et sp. nov. Q. brentsae belongs in the Aglaspidida, a close outgroup to the true chelicerates; this is the second report of an aglaspidid from the Great Basin. Esmeraldacaris richardsonae gen. et sp. nov. is a newly discovered arthropod from the lower Ordovician, from beds transitional between the Emigrant Formation and the overlying Palmetto Formation. It is a survivor of an early arthropod lineage that does not belong in any extant taxon, but which may also include the Ordovician Corcorania and the Cambrian Mollisonia.

A probable late Neoproterozoic age for the Kennedy Channel and Ella Bay formations, northeastern Ellesmere Island and its implications for passive margin history of the Canadian Arctic

2004 ◽  
Vol 41 (9) ◽  
pp. 1013-1025 ◽  
Author(s):  
Keith Dewing ◽  
J C Harrison ◽  
Brian R Pratt ◽  
Ulrich Mayr
Keyword(s):  
Lower Cambrian ◽  
Canadian Arctic ◽  
Passive Margin ◽  
Early Cambrian ◽  
Channel Formation ◽  
Type Section ◽  
Small Shelly Fossils ◽  
History Of ◽  
Basin Formation ◽  
Late Neoproterozoic

The Kennedy Channel and Ella Bay formations are the two oldest stratigraphic units exposed in the Franklinian margin sedimentary sequence in the Canadian Arctic Islands. An Early Cambrian age had previously been accepted by the occurrence of trilobites and small shelly fossils in the type section of the Kennedy Channel Formation. Reinvestigation of the area around the type section shows that several large strike-slip faults cut the succession and that the olenelloid trilobites are from an infaulted slice of a younger unit, the Lower Cambrian Kane Basin Formation. Thus, there is no unambiguous paleontological evidence for the age of either the Kennedy Channel or Ella Bay formations. However, the abundance of stromatolites, absence of trace fossils, and separation from overlying Lower Cambrian clastics by a regional angular unconformity indicate a probable late Neoproterozoic age for these two formations. The Ella Bay Formation likely correlates with the Portfjeld Formation in North Greenland, the Spiral Creek Formation in East Greenland, and the Risky Formation of the Mackenzie Mountains in northwestern Canada. The passive margin that existed in northern Laurentia during the early Paleozoic was, therefore, established in the late Neoproterozoic, and the onset of rifting must have preceded this, rather than occurring in the Early Cambrian as some authors have suggested.

scholarly journals Slope apron and deep shelf sediments of the Brønlund Fjord and Tavsens Iskappe Groups (Lower Cambrian – Lower Ordovician), North Greenland: stratigraphy, facies and depositional setting

1994 ◽  
Vol 169 ◽  
pp. 7-24
Author(s):  
J.R Ineson ◽  
F Surlyk ◽  
A.K Higgins ◽  
J.S Peel
Keyword(s):  
Lower Cambrian ◽  
Lower Ordovician ◽  
Shelf Sediments ◽  
Depositional Setting ◽  
The Relationship ◽  
New Formation ◽  
North Greenland

The aim of this paper is to present a review of the stratigraphy and regional depositional setting of the Brønlund Fjord and Tavsens Iskappe Groups in their northern outcrop. In addition, the Kap Stanton Formation, a new formation of the Tavsens Iskappe Group, is formally defined. In particular, the aim is to clarify the relationship between these northern sections and the better known, more proximal shelf sediments of the southern outcrop belt.

scholarly journals Vision in fossilised eyes

2015 ◽  
Vol 106 (4) ◽  
pp. 209-220 ◽  
Author(s):  
Brigitte Schoenemann ◽  
Euan N. K. Clarkson
Keyword(s):  
Lower Cambrian ◽  
Recent Literature ◽  
Upper Permian ◽  
Compound Eyes ◽  
Animal Kingdom ◽  
Evolutionary Transitions ◽  
Lower Ordovician ◽  
Recent Developments ◽  
Sensory Structures ◽  
Physical Tools

ABSTRACTThis paper presents a review of recent developments in the study of vision in fossil arthropods, beginning with a discussion of the origin of visual systems. A report of the eyes of Cambrian arthropods from different Lagerstätten, especially the compound and median arthropod eyes from the Chengjiang fauna of China, is given. Reference is made also to compound eyes from the lower Cambrian Emu Bay Shale fauna of Australia and the Sirius Passet fauna of Greenland; also to the three-dimensionally preserved ‘Orsten’ fauna of Sweden. An understanding of how these eyes functioned is possible by reference to living arthropods and by using physical tools developed by physiologists. The eyes of trilobites (lower Cambrian to Upper Permian) are often very well preserved, and the structure and physiology of their calcite lenses, and the eye as a whole, are summarised here, based upon recent literature. Two main kinds of trilobite eyes have been long known. Firstly, there is the holochroal type, in which the lenses are usually numerous, small and closely packed together; this represents the ancestral kind, first found in lowermost Cambrian trilobites. The second type is the schizochroal eye, in which the lenses are relatively much larger and each is separated from its neighbours. Such eyes are confined to the single suborder Phacopina (Lower Ordovician to Upper Devonian). This visual system has no real equivalents in the animal kingdom. In this present paper, the origin of schizochroal eyes, by paedomorphosis from holochroal precursors, is reviewed, together with subsequent evolutionary transitions in the Early Ordovician. A summary of new work on the structure and mineralogy of phacopid lenses is presented, as is a discussion of the recent discovery of sublensar sensory structures in Devonian phacopids, which has opened up new dimensions in the study of trilobite vision.

Contribution a la stratigraphie du Cambro-Ordovicien dans le bassin saharien occidental

1962 ◽  
Vol S7-IV (1) ◽  
pp. 123-131 ◽  
Author(s):  
Philippe Legrand ◽  
Genevieve Nabos
Keyword(s):  
Lower Cambrian ◽  
Western Sahara ◽  
Type Section ◽  
Sandstone Formation

Abstract Lithostratigraphic study of cores in the vicinity of Hassi Messaoud and Oued Mya, Erg el Anngueur, and Fort Miribel (Algeria) has resulted in the description of a type section for the Cambro-Ordovician series in the western Sahara which includes five stratigraphic units. The lower Cambrian is represented by the Hassi Messaoud sandstone group, overlain by the Cambrian-Ordovician Isometric sandstone formation. The Ordovician is represented by the Tremadocian lower argillite formation and the lower Arenig intermediate quartzites. In the Erg el Anngueur area a shale-sandstone complex overlies the lower argillites The Ol.1 sandstone is transgressive on the stage below and is overlain by the upper argillite formation and the terminal sandstone-shale complex which represent undifferentiated Arenigian-Llanvirnian. A brief outline of the paleogeographic aspects of the region is discussed in relation to each unit.

The Torridon Group

2002 ◽  
Vol 24 (1) ◽  
pp. 29-46 ◽  
Keyword(s):  
Lake Sediments ◽  
Lower Cambrian ◽  
Red Sandstone ◽  
Maximum Thickness ◽  
Lithostratigraphic Unit ◽  
Gneiss Complex ◽  
Head Formation ◽  
Group Form ◽  
Lake Deposits ◽  
Unconformity Surface

The group unconformably overlies both the Lewisian gneiss complex and the Stoer Group, and is in turn unconformably overlain by the Lower Cambrian (Figs 2 & 22). The unconformity surface at the base is generally rugged, with relief reaching 600 m. The maximum thickness of the Torridon Group is about 7 km onshore and 6 km offshore in the Sea of the Hebrides basin (Stein 1988, fig. 11; 1992, fig. 2B), but albitization of the highest beds indicates that the original thickness was 3-4 km greater. Lake deposits at the bottom of the group occupying palaeovalleys in the gneiss are followed by kilometres of red sandstones, all deposited in a subsiding rift. Alluvial sands interfinger with lake sediments to form cyclothems at the top of the group. As mentioned in the Introduction the Torridon Group is by far the most extensive and voluminous part of the Torridonian (see Plate 1), but nevertheless poses fewer problems of interpretation than the Stoer and Sleat Groups.The formal stratigraphy established by the Geological Survey (Geikie 1894) has been retained even though it is in some respects unsatisfactory. The sediments filling the palaeovalleys at the base of the group form a well-defined lithostratigraphic unit, the Diabaig Formation, characterized by breccias and sandstones derived from the immediately adjacent basement (Fig. 23). The Cailleach Head Formation at the top of the Group is also a valid lithostratigraphic unit, formed of coarsening-upward cyclothems of grey shale and red sandstone. The bulk of the Torridon Group, however, is

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