Sabkha Cycles in the Arab/Darb Formation Off the Trucial Coast of Arabia

Abstract

Study of 176 ft. (53.7 m) of core from the Arab/Darb Formation of the Umm Shaif Field, Abu Dhabi Marine Areas, has revealed a sequence of sediments which can be related to nine distinct cycles of sabkha formation. The sabkha cycle consists of a basal algal grainstone/boundstone (which is interpreted as a shoal) passing upwards through lagoonal dolomite, intertidal algal mat and into a final supratidal development of nodular anhydrite and associated dolomite. Dolomitisation and the formation of nodular anhydrite were early-stage products of diagenesis. Poikilotopic anhydrite is common in the lagoonal dolomites but it is thought that this was not formed until the sediment was completely lithified.Stylolites, although of small amplitude, are more common in dolomite than in limestone; a generalisation which is at variance with earlier observations. ~~ "Sabkha" is the Arabic word for flat salt-crusted desert.Sedimentology, 12 (1969) 165-191 G . V. WOOD A N D M. J. WOLFE Sedimenfology, 12 (1969) 165-191 KEY TO SYMBOLS USED IN FIGURE 2 PELLET GRAINSTONE CURRENT BEDMNG GRADATION AL,CONTACT A. 67ft. 8 inches (20.6 m ) . Dolomite. Horizontal algal (?) laminations are broken, probably the result of gas extrusions before sediment consolidation. B. 54 ft. 3 inches (16.55 m ) . Bird's eye dolomite. 69ft. 3 inches (21.1 m ) . Stylolite with vertical columns truncating an inclined set of algal laminations. Host rock is dolomite. C .Sedimentology, 12 (1969) 165-191

Diagenesis and stratigraphy of the Lisburne Group limestones of the Sadlerochit Mountains and adjacent areas, northeastern Alaska

“…Poikilotopic anhydrite (as much as 1 mm in diameter) enclosing abundant microdolomite. Interpretation.-The crystal habits of the anhydrite are closely comparable with those described and illustrated by Wood and Wolfe (1969) from the Arab-Darb Formation of the Arabian Gulf. An arid supratidal (sabkha) origin has been suggested for the Arab-Darb Formation.…”

“…The preferential development of dolomite in fine-grained carbonate rock suggests that the original rock in this interval contained a high proportion of carbonate mud. Algal-mat sediments were recorded at 760 feet in this section by Armstrong and this fact suggests that the dominant environment was intertidal to supratidal (Wood and Wolfe, 1969).…”

“…In spite of their comment that they were dealing with ~~true dolomite," their data showing the existence of dolomites with a Ca:Mg ratio up to 55:45 are comparable to the protodolomites of the Coorong Lagoon (Alderman and Skinner, 1957). Wood and Wolfe (1969) have described Jurassic-Cretaceous rocks from Abu Dhabi that were deposited in an environment similar to those from Qatar, but the dolomite rhombs average 50 micrometres in size, suggesting that extensive grain growth has taken place during diagenesis-a process that could be associated with the loss of Ca2+ from the original protodolomite. In general, protodolomites probably lose their excess Ca 2 + and gradually revert to the stoichiometric composition.…”

The role of bacterial sulphate reduction in carbonate replacement of vanished evaporites: examples from the Holocene, Jurassic and Neoarchaean

“…This facies is generally buff-coloured, partly due to oil staining, and is finely crystalline, with pyrite-rich patches and mottles ( Fig. 4) that have been interpreted as "birds eyes" (Wood & Wolfe, 1969), but show no signs of visible porosity.…”

The Triassic Chitistone Limestone, Wrangell Mountains, Alaska: stressing detailed descriptions of sabkha facies and other rocks in lower parts of the Chitistone and their relations to Kennecott-type copper deposits

“…Wood and Wolfe (1969) could be classified as microspars (Folk, 1965). which may represent recrystallized fibrous aragonite cement (Kendall and Tucker, 1973); (6) final void filling by coarse sparry calcite, which probably occurred in a fresh-water diagenetic environment.…”