The tufa deposits are terrestrial carbonate rocks that are
products of calcium carbonate precipitation from springs,
fluvial streams, stagnant pools, water cascades, and shallow
lakes (Pedley 1990, 2009; Ford and Pedley 2006). The tufas
precipitate primarily from CaCO3-
rich waters at ambient
temperatures due to CO2
degassing and/or microbial and
physiochemical activities (Pentecost 1985; Pedley 1990,
2009). The tufa deposits form a thin, surficial, soft, spongy,
cellular or porous texture, semi-friable incrustation around
the mouth of calcareous springs or seeps, or along fluvial
streams carrying calcium carbonates (Chafetz and Folk
1984; Ford and Pedley 2006). The tufa deposits have been
studied worldwide as their depositional, geochemical, and
isotopic signatures can provide critical records of paleoenvironment
and paleoclimatic conditions (Chafetz and Folk
1984; Ford and Pedley 2006; Andrews 2006; Pedley 2009).
The Kurkur Oasis area in southern Egypt consists mainly
of a thick sedimentary succession of Late Cretaceous–Quaternary
age (Issawi 1968; Issawi and Sallam 2018). This
succession is made up of the Nubia Formation (Coniacian-
Santonian) at the base, followed upward by the Dakhla
Shale (Maastrichtian), Kurkur and Garra (Paleocene–Early
Eocene), and Dungul (Early Eocene) formations, respectively.
In the Kurkur Oasis area, the Quaternary tufa deposits
are characterized by highly macrobiological components
such as phytoherms such as plant stems, reeds, grasses and
mosses (Fig. 1). Previous studies provide significant clues
to the formation conditions of the Kurkur’s tufa deposits
(Ahmed 1996; Crombie et al. 1997; Nicoll and Sallam
2017; Gaber et al. 2018; Sallam and Ruban 2019; Kele et al.
2018, 2020). For example, Issawi (1968) and Ahmed (1996)
concluded that the tufa deposits in the Kurkur Oasis area
were fossilized over different topographic levels. Some of
these tufas were accumulated over 400 m a.s.l. erosional
surface, whereas others were formed over 300 and 200 m
a.s.l.. Structural controls affecting the development of
Kurkur’s oasis tufas include fissure, cracks, and faults that
would have enhanced groundwater recharge and emergence
of carbonate-saturated springs (Nicoll and Sallam 2017).
Jimenez (2014) assigned 76–246 ky to the lower tufa levels,
while 514 ky to the higher tufa levels. Gaber et al. (2018)
concluded that the older tufas in the Kurkur Oasis area were
developed during warm pluvial periods, while the younger
tufas were formed in drier conditions. Gaber et al. (2018)
also suggested that the densely vegetated tufas were deposited
along the shoreline of a lagoon.
The sedimentary and geomorphological rarity of the paleospring
tufa carbonates in the Kurkur Oasis area allowed
Sallam et al. (2018) to recommend the creation of "Tufa
World Geopark" which, in turn, will facilitate geotourism
activities, geological heritage conservation, and sustainable
socio-economic development in this area. |
