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Facies characterisation of a shallow-water deltaic succession: the Upper Jurassic Wagad Sandstone Formation of Kachchh, western India

Joseph J. K., Patel S. J.

Geologos

2018

Vol. 24, No. 2

137--150

Ancient deltaic facies are difficult to differentiate from tidally influenced shallow-marine facies. The Wagad Sandstone Formation of the Wagad Highland (eastern Kachchh Basin) is typified by offshore and deltaic facies with sedimentary characteristics that represent different conditions of hydrodynamics and related depositional processes. The study area, the Adhoi Anticline, constitutes a ~154-m-thick, shale-dominated sequence with progressive upward intercalations of bioturbated micritic sandstone and quartz arenite. Two thick Astarte beds (sandy allochemic limestone), with an erosional base and gravel blanketing, illustrate tidal amplification and high-energy stochastic events such as storms. Sedimentological characteristics document three depositional facies: an offshore, shale-dominated sequence prograding to proximal prodeltaic micritic sandstone and quartz arenite with sandy allochemic limestones, further prograding to mouth bars and abandoned channel deposits. The Wagad Sandstone Formation displays depositional environmental conditions that are dissimilar from those of coeval deposits in Kachchh sub-basins as well as on regional and global scales. This is attributed to a reactivation of the Kachchh Mainland and South Wagad faults which resulted in detachment and uplift of the Wagad block which then experienced prograding deltaic conditions.

The Wootton Bassett Mud Springs (Wiltshire, UK): an unusual Lagerstatten for Jurassic Foraminifera

Hart M., Henderson A., Frayling T.

Volumina Jurassica

2006

Vol. 4, no. 1

236-236

On the 6th January 1997 the mud springs at Templars Firs, Wootton Bassett (Wiltshire) were designated a Site of Special Scientific Interest (SSSI) under Section 28 of the Wildlife and Countryside Act 1981 (as amended). The springs are notified as an SSSI on the basis of their hydrogeological interest. Water seeping through the Lower Calcareous Grit and Coral Rag (of Oxfordian age) liquefies the Ampthill Clay Formation (uppermost Oxfordian) which then migrates to the surface in a series of mud springs. Many of the fossils brought to the surface still display their aragonitic shells and are quite beautifully preserved. An Autumn 2003 and again in Spring 2005 we have collected a series of samples with the permission of English Nature (Wiltshire Team) and these have been washed for foraminifera and ostracods. The microfauna have been described in a previous BGS report, although it is much more extensive and yields all the taxa associated with this stratigraphical interval. Many aragonitic taxa (epistominids) are present and beautifully preserved, including some of the stratigraphically significant taxa. Large agglutinated foraminifera appear to dominate one of the five active vents and are in an exceptional state of preservation. In the literature, many of these Jurassic taxa have been referred to modern, extant taxa, although this is almost certainly incorrect. The material from Wootton Bassett should allow for a more appropriate determination of these taxa. Also recorded are small planktic Foraminifera which extend our knowledge of the early evolution of the poorly-known Jurassic plankton.