Studies of assemblages from the Lower Triassic of the Salt Range of West Pakistan are presented, following earlier work by the author on assemblages from the uppermost Permian of that region. The assemblages are of very small average size, and characteristically simple morphology; the most abundant genera by far are Micrhystridium and Veryhachium. In consequence, care and patience are needed in their study. The Permian assemblages already described by the author show stronger affinity with the Triassic than with the Paleozoic; nevertheless, the entry of many new types in the lowest Triassic assemblages makes it readily possible to differentiate between Permian and Triassic. The acritarchs therefore seem to offer potential value as stratigraphic indices for determining the position of the Permian-Triassic boundary; however, it will clearly be necessary to make comparative studies in other regions before this can be confirmed, since paleoecological controls cannot, at present, be entirely ruled out.

If the acritarchs prove as useful as this study suggests, they will be especially valuable, in view of their great abundance in small samples, in establishing this boundary in borehole studies. The absence of dinoflagellate cysts in all Triassic asemblages described to date is puzzling; it may reflect extreme climatic stability, rendering encystment during adverse conditions unnecessary. The aritarchs are certainly a polyphyletic assemblage of morphologically similar but unrelated forms. Although it seems virtually certain that these also are cysts, it cannot be conclusively affirmed that they are produced in response to adverse environmental conditions; encystment may be a necessary prerequisite to cell division, and unrelated to environmental seasonality.

End_of_Record - Last_Page 352-------