Gk. Pedersen et al., THE SYN-VOLCANIC NAAJAAT LAKE, PALEOCENE OF WEST GREENLAND, Palaeogeography, palaeoclimatology, palaeoecology, 140(1-4), 1998, pp. 271-287
The Naajaat lake in the Nuussuaq Basin on Disko and Nuussuaq formed in
a geological setting between cratonic crystalline Precambrian rocks o
verlain by Cretaceous sediments and an actively forming Paleocene volc
anic province. The lacustrine deposits, shales as well as hyaloclastit
e breccias, accumulated in low-lying areas inundated by fresh water an
d sealed off from marine transgressions by a broad subaerial volcanic
terrain. Foreset-bedded hyaloclastite breccias demonstrate water depth
s of up to 450 m, and the area of the lake was 2500 km(2) at its maxim
um extent. The lake probably existed for less than 0.5 million years.
The lake received clay and silt from two provenance areas. Quartz cont
ents of more than 25% in the majority of the sediment samples indicate
that large amounts of material were continuously supplied to the lake
from the crystalline terrain, whereas the volcanic terrain supplied s
mectite and mixed-layer minerals to the lake, High kaolinite contents
stem from the crystalline or both provenance areas, The shales are cha
racterized by high TOC (up to 11%), lack of pyrite, presence of terres
trial spores and pollen and lack of marine dinoflagellates. The lacust
rine sediments rest on an erosional unconformity and its correlative c
onformity. The unconformity developed during the latest Cretaceous and
Early Paleocene. Five stages are recognized in the geological develop
ment of the lake. Stages 1-4 are characterized by accumulation of hyal
oclastite breccias, rise in lake level, and eventual transgression of
subaerial terrains. The rises in lake level were caused by stemming of
fluvial run-off behind the aggrading volcanic pile. Stage 5 correspon
ds to cessation of volcanic activity, a stable lake level, and prograd
ation of elastic sediments, resulting in infilling of the lake. During
the lacustrine transgression only sediment in suspension was transpor
ted into the central parts of the lake. (C) 1998 Elsevier Science B.V,
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