Lower Palaeozoic Stratigraphy Research Articles

Lower Palaeozoic Stratigraphy

Les Temps Fossiliferes Par Prof. Henri Termier et Genevieve Termier. 1: Palaeozoique Inferieur. Pp. v + 690. (Paris: Masson et Cie., 1964.) 270 francs.

The Lower Palaeozoic stratigraphy of central Murrisk, County Mayo, Ireland, and the evolution of the south Mayo trough

The Ordovician and Silurian rocks of central Murrisk, County Mayo, Ireland, are described with reference to their stratigraphy, provenance, and conditions of deposition; 36 000 ft of Ordovician rocks are overlain, unconformably, by 5600 ft of Silurian strata. The Arenig rocks are divided into two series: the Owenmore Series (2000 ft) below and the Murrisk Series (15 000 ft) above. The Owenmore Series (boulder-slides, turbidites, and black slates) was derived entirely from the north; the Murrisk Series (tuffs and turbidites) was derived from the east and south. The Glenummera Series (4000 ft of green slates with thin psammitic turbidites) follows and is overlain by the Partry Series (15 000 ft). The Partry Series is divided into two groups; the Mweelrea Group below, and the Maumtrasna Group above. The Mweelrea Group (7000 ft of current-bedded deltaic grits) contains six beds of ignimbrite, deposited by nuées ardentes with a south-easterly provenance. Periodic westward tilting caused the eastward recession of the delta-front with the concurrent development of boulder-slides and turbidites. The Maumtrasna Group is similar to the Mweelrea Group but contains no ignimbrites, and the grits are coarser, with many interbedded conglomerates. The Silurian rocks are divided into the Lower Owenduff Group (Upper Llandovery, 0 to 20 ft) below, and the Croagh Patrick Series (Wenlock, 5600 ft) above. The Lower Owenduff Group was deposited in a complex littoral environment and contains a large amount of pyroclastic material. The Croagh Patrick Series is divided into six groups (Cregganbaun Group, 500 ft; Pollanoughty Group, 450 ft; Oughty Group, 360 ft; Fiddaunarinnia Group, 600 ft; Lough Nacorra Group, 1500 ft; Owenwee Group, 2000 ft), the Oughty Group containing five tuff bands. The Croagh Patrick Series was deposited in a northwardly transgressive littoral and sub-littoral belt and was derived exclusively from the north and east. The Silurian rocks rest unconformably upon the Owenmore Series as the result of strong pre-Upper Llandovery thrusting, concentric folding, and uplift. During most of Ordovician times, the northern margin of an e-w trough (the South Mayo trough) was denned by a normal fault. The southern margin was defined throughout most of Ordovician times and the whole of the Silurian by a rising Cordillera in Conne-mara. Dal radian rocks provided the source for nearly all the clastic material.

A Note Concerning the Age of the Metamorphism of the Dalradian Rocks of Western Ireland

AbstractEvidence is adduced to relate the published minimum absolute date of — 475 m.y., for the metamorphism of the Connemara Schists, to its correct position in the Lower Palaeozoic stratigraphy of Western Ireland. The metamorphism pre-dates the Didymograptus extensus zone of the Arenig in Connemara and South Mayo and an Upper Cambrian or Tremadocian age is considered likely.