High-Latitude Versus Low-Latitude Lacustrine Rift Basins: Controls on Stratal Architecture in the Baikal and East African Rifts

Christopher A. Scholz

Lake Baikal, Siberia, and Lake Malawi, East Africa are among the archetypical examples of lacustrine rift basins. Seismic data acquired on these lakes over the past several years have provided new insights to the character of the stratal architecture of lacustrine rift systems.

These two lakes are among the world's largest and oldest modern lakes. Lake Baikal contains more than 8 km of syn-rift sedimentary fill, and is situated in a high-latitude temperate climate, between about 51° and 56° N. Lake Malawi is a tropical lake located between about 9° and 14° S.

The hydrologies of the two systems are very different. In the Lake Baikal basin, about 90% of the annual water loss is through the outflow of the Angara River; only about 10% is lost through evaporation. Water levels are relatively insensitive to minor changes in the evaporation:precipitation ratio, and are effectively controlled by the elevation of the shallow sill at the lake outlet. In Lake Malawi however, on the order of 90% of the annual water loss is via evaporation. This results in seasonal fluctuations in water level of 1-2 meters, and fluctuations of more than 100 m over a time scale of centuries. Lake level fluctuations of more than 300 m are thought to have occurred on time scales of 1-25 kYr.

The net effect on stratal architecture is that abundant shallow erosional unconformities are observed in Lake Malawi, particularly on the flexural margins of half-graben basins. Such boundaries are not prevalent in Lake Baikal. Whereas climate and tectonics are both dominant controls on the stratal architecture of tropical lacustrine rift basins, tectonic processes probably dominate the development of the stratigraphy of high-latitude lacustrine rift basins.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995