Palynological biozonation of the Permian of Oman and Saudi Arabia: progress and challenges

Abstract

ABSTRACT Extensive palynological work in sequences in Oman and Saudi Arabia, has allowed a framework of eight biozones for the uppermost Carboniferous to Permian rocks in that region. Five of these are established in the palyniferous uppermost Carboniferous to Lower Permian sequence in Oman, and to some extent these are recognisable in sequences of central and southern Saudi Arabia. OSPZ1 (Oman and Saudi Arabia Palynological Zone 1), associated with the lower parts of the Al Khlata Formation and the Unayzah C member, is probably Stephanian in age. OSPZ2 is Asselian-Sakmarian in age, and is associated with the upper part of the Al Khlata Formation and the Unayzah B member. OSPZ3, which is subdivided into three sub-biozones, is associated with the Lower Gharif member; its age may lie in the range late Sakmarian to Artinskian, based on palynology and brachiopod-based ages for the Haushi Limestone, locally present toward the top of the Lower Gharif member. The composition of assemblages from OSPZ1 to OSPZ3 is similar to that of coeval sequences in other former Gondwana countries and the chronostratigraphical ages assigned to them are partly gained from correlation with faunally-calibrated Western Australian palynological biozones. At the level of OSPZ4, such correlation becomes difficult because significant differences are evident between Western Australian and Arabian assemblages, and because other Gondwana palynological biozonations, with which Arabia has greater affinity, are poorly constrained chronostratigraphically. OSPZ4 and the succeeding two biozones are established in the sporadically palyniferous Middle and Upper Permian sequences of Oman and Saudi Arabia. OSPZ4, though poorly characterised due to low palynological recovery, is probably ‘mid-Artinskian’ to Kungurian in age, and is associated with the Middle Gharif member. OSPZ5, present in southeast Saudi Arabia and Oman appears to be associated with the lower to middle parts of the Upper Gharif member, and is constrained in age, partly by the faunally-dated overlying Oman Khuff carbonates, as being Roadian or earliest Wordian in age. So far the assemblages of the highest biozone, OSPZ6, have been recovered only from the ‘basal Khuff clastics’ of central Saudi Arabia, and are believed to be younger than those of OSPZ5; dating by palynological means is difficult but recent microfaunal studies of the ‘basal Khuff clastics’ suggest a Capitanian age. Further study in appropriate palyniferous sections in other Middle Eastern countries may allow a more complete palynological succession to be established.