Caracteres structuraux et dynamiques d'un bassin en transtension; la plate-forme tunisienne a l'Ypresien terminal

In Tunisia, Ypresian carbonate deposits occur on a platform preserving vestige of an inherited fault network. The fault network delineates blocks of different sizes accounting for the platform morphology and in turn for variation in thickness of the Ypresian sequence. The nummulitic limestone carapace of the Ypresian sequence is fractured by faults and joints of various orientations which are systematically sealed by marly beds of early Lutetian age. This indicates that the fault network was reactivated during late Ypresian. Geometric and kinematic study indicates that this strike slip late reactivation is accomodated by normal fault. These structures originated in soft sediment undergoing diagenesis. Depending on bed competency, both ductile and brittle deformation features were recognized in the fault. This superficial tectonic event represents, a recent reactivation of ancient fractures cartographically located on the boundaries of late Ypresian megablocks. Kinematic study of the deformation within and along the boundaries of one of these blocks, (Ousseltia block), indicates a late Ypresian, early Lutetian strike-slip distensive faulting dynamic. Stress-field orientation indicates a rapid re-orientation in time from a predominantly NW-SE extensional tectonic to a NE-SW extensional event. Stratigraphic dating of that tectonical crisis coincides with a turbulent period of relative motions between Europe and Africa.

On the Geological Features of the Oil Region in the Northern Punjab (British India)

Occurrence of the Oil.—The oilfield of Jaba and those of Rawalpindi and Fatehjang are identical from the stratigraphical point of view. At Jaba, too, the oil is to be found in the contact zone between the Nummulitic limestone and the younger gypsiferous clays of the Upper Nummulitic. These gypsiferous clays represent a bed well adapted to favour the accumulation of oil, wherever they cover the limestone at a moderate inclination. The oil issues only from the limestone, but the cellular limestone, too, may be oil-bearing in depth. It may be pointed out that cellular limestones of the same character accompany the oil-shows at Gunda, the main oil-spring in the neighbourhood of Fatehjang.

IV.—Note on the occurrence of Nummulitic Limestone in South-Eastern Africa

The object of this communication is to place upon record the existence of Nummulitic rocks in South-Eastern Africa; the result of an examination of specimens brought me by their discoverer, Mr. David Draper, F.G.S., of Johannesburg, the enterprising Secretary of the Geological Society of South Africa.