LAKE TAHOE, USA: WORLD’S THIRD OLDEST FRESH-WATER PERMANENT LAKE?

Lake Tahoe, located along the border of California and Nevada, USA, is at least 2.3 Ma based on ⁴⁰Ar-³⁹Ar dating of basalts and trachyandesites that flowed into and over lacustrine sediments deposited in the NW part of the early, shallower lake, referred to as proto-Tahoe. Basalts and trachyandesites interacted with the contemporaneous lacustrine sediments during three different time intervals, at 2.3 Ma, 2.0 Ma, and 0.92 Ma forming pillow lava with glassy, palagonitic rinds, peperites, and baked margins in the sediments, among other hydrovolcanic features. Several of the sediment samples contain Pliocaenicus diatoms, corroborating the ancient age of the lake as well as the warmer, shallower lake conditions that existed in this part of the lake during the basaltic volcanism as compared to the deep (1645 ft (498 m)), cold-water conditions that currently prevail. Lake Tahoe resides in a tectonically active, extensional fault-block basin that has enabled the lake to endure, consistently, through the millions of years rather than succumb to sediment infilling as is typical of most lakes. Two of the oldest fresh-water permanent lakes in the world, Lake Baikal, Siberia (5-10.3 Ma, based on dating of continuous sedimentary sequences recovered through core drilling) and Lake Tanganyika, East Africa (8-10 Ma, similarly determined by dating of a continuous sedimentary sequence from drill core) are also located in extensional fault-block basins, with Lake Tanganyika occupying one of the deepest basins of the East African Rift. Other lakes considered to be among the world’s oldest fresh-water permanent lakes are Lake Biwa, Japan (1.5 Ma in current basin), Lake Pingualuk, Nunavik, Canada (1.4 Ma based on date of meteor impact), Lake Ohrid, Balkins (1.36 Ma based on tephrochronologic and paleomagnetic studies of the lacustrine sediments), Lake Malawi, southeast Africa (1.2 Ma based on tephrochronology and luminescence dating of drill core), and Lake Titicaca, Bolivia/Peru (0.37 Ma from drill core analysis). Much older ages for many of these lakes and others appear to have been derived from dating the inception of basin development as a proxy for lake ages or on undocumented general statements. Evaluating known ages of the world’s oldest lakes leads to the conclusion that Lake Tahoe may be the third oldest fresh-water permanent lake in the world.