Late Ordovician tunnel valleys in southern Jordan

TheUpperOrdovicianglacialrecordofsouthernJordan(AmmarFm.)essentiallycon- sists of palaeovalley infills and of a subordinate time-transgressive fluvial to shallow-marine suc- cession overstepping both the palaeovalleys and interfluvial areas. Valley size (depth, 60 – 160 m; width, 1–3 km), steep (20–508) margins, internal organization and depositional facies point to an origin as tunnel valleys. The tunnel valleys are infilled by either fluvioglacial sandstones or fluvio- deltaic coarsening-upward successions including fine-grained clayey sediments. Re-occupation of previous valleys is evident in places. At least three generations of tunnel valleys are inferred from cross-cutting relationships, although they most probably only reflect temporary standstills and minor re-advances related to the overall recession following the main glacial advance recorded in Saudi Arabia. Petrophysical measurements indicate that higher permeabilities are located in the glacially related strata (1.5 – 3 darcy in fluvioglacial infills), with a somewhat reduced porosity (22–28%) relative to the preglacial sandstones owing to a higher clay content, probably of diagenetic origin. Sandstone amalgamation, however, gives the fluvioglacial sandstones a high reservoir quality.