Mixed Clastic–Carbonate Cycles and Sequences: Quaternary of Egypt and Carboniferous of England

Abstract

There are various types of mixed clastic–carbonate sequences andparasequences in the geological record and sea-level change is oneof the major controls on their development, as well as the obviousavailability of terrigenous material. Mixed-lithology sequences areespecially well-developed in icehouse times, as in the Permo–Carboniferous and Quaternary. The two major types, lower carbonate – upper clastic and lower clastic – upper carbonate sequences, reflect the rates of sea-level change and the source of clastic sediment – whether itis brought across the carbonate platform from the adjacent landmassor supplied axially to the basin. Two examples of carbonate–clastichigh-frequency sequences are discussed: 1) from the Red Sea coastof Egypt, Quaternary transgressive/highstand shallow-water carbonatesand late highstand/falling-stage/lowstand clastics deposited inincised-valley fills and fan deltas, and 2) from northern England,mid-Carboniferous ‘Yoredale’ cycles of transgressive shelf carbonatespassing up into highstand coarsening-up deltaic and shoreline clastics,capped by palaeosoils and coal. Locally, falling-stage incised-valleyssupplied sediments to the adjoining basin. One significant differencebetween these two examples is the palaeoclimate: arid in the Red Sealeading to the episodic supply of sand and gravel, and humid in theCarboniferous resulting in the more continuous supply of mud andsand, each having a different effect on carbonate deposition.