- During the middle and late Carnian (Late Triassic), a lake system deposited black shale and siltstone as the Cow Branch Formation in the Dan River--Danville Basin. Developed by regional rifting, the Basin formed in crystalline rocks of the Piedmont. These rocks, and others long eroded, provided a major source of nutrients into possibly three lakes that collectively form "Fossil Lake Danville."., Based on mineralogy, chemistry, and biology, the late lake (upper member) was alkaline and saline. Mineral indicators include sodium-rich amphibole and feldspar; and albite that may be the remains of a precipitate such as analcite. The alternation of amorphous remains of presumed green and blue-green algae implies that the lake alternated between being open and closed, or fresher and more alkaline. The remains of only green algae in the deposits of the middle and early (lower member) lakes, and the lack of "riebeckite," suggests fresher water. However, all three lakes were alkaline based on structural degradation of palynomorphs., Aquatic food chains consisted of bacteria, presumed blue-green and green algae, worms, crustacean zooplankton (some of which were copraphagous), aquatic insects, herbivorous and carnivorous fish, aquatic lizards, and carnivorous phytosaurs. Growing in swamps and forests were spore- and pollen-producing bryophytes, lycopods, ferns, seed ferns, Voltziales, conifers, cycadeoids, and cycads., High nutrient availability, abundant organisms, and consequent anaerobic bottom conditions produced rocks that were once petroleum sources. Wurtzite, the high-temperature polymorph of sphalerite, suggests a hot spring bubbled into anaerobic bottom waters in the late lake. High heat flow associated with rifting apparently removed hydrogen, carbonized the liquid hydrocarbons, left condensed aromatic structures as residues, and raised the rank of associated coal to semi-anthracite and clays to 2M illite., and Processes in present-day rift valleys and lakes were studied to provide comparative data. Seismicity, subsidence, heat flow, geothermal gradients, thickness and banding of sediments, morphometrics and chemistry of lakes, mineralogy of lake muds, biology of peat-depositing wetlands, and aquatic food chains from genera of bacteria through top carnivores are presented for the Baikal, East African, Arabian, Rhine, and Rio Grande Rift Systems.
- Dissertation Note:
- Ph.D. The Pennsylvania State University 1982.
- Source: Dissertation Abstracts International, Volume: 43-01, Section: B, page: 7200.
View MARC record | catkey: 13611589