Thrombolites of the lower devonian Manlius Formation of central New York
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The Manlius Formation of the Lower Devonian Helderberg Group in central New York State contains decimeter-scale thrombolites. Internally, thrombolites comprise centimeter-scale, digitate to irregularly-shaped clots surrounded by skeletal wackestone. The clots are composed of variable amounts of: 1) millimeter-scale hemispheroids with radial and concentric structure that resembleKeega; 2)Renalcis-like forms; 3) stromatolitic laminae of mudstone; 4) peloidal mudstone laminae with filament molds; and 5) rare fossils. The thrombolites themselves are interbedded with grainstones, mudstones, graded beds, and intraclastic conglomerates. A low diversity fauna is found in many of these associated rocks.
Manlius Formation thrombolites are interpreted to have been rigid structures built by calcified cyanobacterial communities and encrusting and framework-building skeletal algae. Thrombolites are interpreted to have formed in a subtidal, restricted lagoonal setting. The low diversity of associated skeletal remains suggests that the environment was unfavorable for most organisms which would compete for space or consume the mound-building organisms.
KeywordsMudstone Ordovician Stromatolite Grainstone Wackestone
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