> I'll be interested in more on Lake McLeod if you find the book.
>
It has been returned! The book is "The MacLeod evaporite basin, by B. W. Logan
and published in 1987 as AAPG Memoir 44. The book consist of four sections. They
are on evaporite chemical and hydrological models, geological framework of the
basin, the modern environmental system, and the evolution of the basin.
Lake MacLeod formed in a Late Miocene graben filled by 70 m of redbeds. A horst
forms the sill between it and the Indian Ocean. Closure of the sill has been aided
by development of coastal aeolianites in the Pleistocene. The bed of the lake lies
between 0 and more than 4 m below sea level. Sea water percolates through the
barrier and under the impermeable lake sediments. Discharge occurs mainly round
the margins, especially on the western side nearest the barrier. The modern lake is
about 130 km long and 45 km across.
The evaporitic fill of the basin is up to 8m thick. Most of this is halite,
underlain and capped by gypsum ands carbonate. The halite is coarsely crystalline
with thin gypsum layers. The gypsum is bedded to laminated with some coarsely
crystalline units. The evaporite basin is driven by a complex interaction between
influx of water though the barrier and evolution of the brine. Currently it is
near equilibrium with sea level. Carbonate and possibly minor gypsum deposition is
still taking place.
Logan regards the basin fill as entirely Holocene and occurring in 6 stages.
Sedimentation began at 9400 BP when rising sea level at the end of the last
glacial allowed seepage across the barrier to enter the basin. The sea flooded
the basin at 7900 BP resulting in a lagoon about 13 m deep. The basin was
isolated from 5100 BP and reached equilibrium about 1500 BP. The bulk of evaporite
deposition occurred between 5100 and 1500 BP.
Lake MacLeod is significant because it represents one of the best examples of a
Holocene barred basin that became isolated from the sea and deposited a relatively
thick evaporite sequence. It is a processes analogue for many larger evaporite
systems and illustrates the complex interplay of climate, geomorphology, and
hydrology that forms such system. It nicely complements other Holocene halite
depositing systems like the Gulf of Karbogaz , the Dead Sea, and the Andean Salars.
God bless
Jonathan