Steineke et al. (1958) formally
named three formations for the Miocene of the Kingdom of Saudi Arabia.
At base, the early Miocene Hadrukh Formation, disconformably overlying
Eocene rocks of Ypresian or Lutetian age, has produced rodents, a bovid
and plants (Whybrow et al., 1982,
Collinson, 1982). The Hadrukh is
overlain by the middle Miocene (Burdigalian), mostly marine, Dam Formation.
From continental equivalents of the Dam Formation in the eastern region
of the Kingdom of Saudi Arabia, a diverse mammalian fauna has been discovered
(Anon. 1975; Hamilton
et al., 1978; Thomas et al., 1982; Thomas
et al., 1978; Whybrow, 1987) that includes the first primate discovered
in Arabia, Heliopithecus leakeyi (Andrews
and Martin, 1987).
The Dam is disconformably succeeded
by clastics of the Hofuf Formation. Powers et al. (1966) state: "The
Hofuf Formation is chiefly unfossiliferous although occasional nondiagnostic
fresh-water fossils including Lymnaea and Chara occur. Since
the Hofuf represents the closing unit of the Arabian Tertiary deposits,
it may be either late Miocene or Pliocene". Thomas
et al. 1978 (see also Thomas 1983), provided the first date to a section
of the Hofuf Formation exposed in eastern Saudi Arabia. The carnivores,
proboscideans, rhinoceros, suids, giraffids and especially the bovids
that were found at Al Jadidah could be linked to the faunas found at Fort
Ternan, East Africa, and thus the age of the Hofuf fossil locality was
estimated at about 14 Ma. Thomas et al. (1978:70) note that about 70 metres
of Hofuf sandstones overlie the vertebrate bearing unit, and that sediments
found at Barj er Rukban (type locality of the Hofuf Formation), about
20 km to the east of the Al Jadidah locality had important lateral facies
variations. Powers et al. (1966:D93)
state that thickening of the continental beds "... in the south is
more drastic, reaching as much as 300 metres before passing under the
sands of the Rub 'al Khali."
In general, Hofuf continental deposition in eastern Arabia is known from outcrop observation, in the absence of subsurface information. It commences with extraformational conglomerate overlying the marine Dam Formation, is succeeded by about 30 metres of sandy limestones and clays with minor conglomerates, and underlies 40 metres of unfossiliferous, homogeneous sandstones, whose origin may be either fluvial or aeolian. The top of the Hofuf is the upper limit of the exposures in the Hofuf (Saudi Arabia) area, "... commonly an old surface showing strong calcium carbonate enrichment of duricrust-caliche type" (Steineke et al., 1958).