(1) Vrije Universiteit/Earth & Life Sciences, 1081 HV Amsterdam, Netherlands
ABSTRACT: M-Factory -- the Principal Carbonate Production System of Mud Mounds
There are three principal modes of marine carbonate precipitation: abiotic, biotically induced, and biotically controlled ("skeletal carbonate"). In the Phanerozoic, these precipitation modes combined in characteristic ways to create three common benthic production systems or factories. The tropical T-factory is dominated by biotically controlled precipitation, typically by photo-autotrophic organisms such as corals and green algae; the C-factory of cool waters produces largely biotically controlled precipitates by heterotrophic organisms; finally, the M-factory, is characterized by biotically induced precipitates, mainly micrite formed in the depositional environment by the activity of microbes.
Mud-mounds with their characteristic framework of in-situ micrite ("automicrite") and abiotic, vug-filling cement are typical products of the M-factory. The mounds form by locally rapid growth, much like patch reefs of the T-factory. Unlike shallow patch reefs, most mud mounds grew below the zone of intensive wave action and thus developed convex tops. The production window of the M-factory extends from sea level to over 1000 m, with optimal production normally below the photic zone where the T-factory dominates. The M-factory dominated the photic zone only when the biota of the T-factory was decimated by extinctions or by locally adverse conditions.
The M-factory may be subdivided into: (a) accumulations of low-oxygen, nutrient-rich waters such as in the oceanic thermocline; (b) carbonate precipitates around methane seeps; (c) precipitates at hydrothermal vents. However, recognition of these subclasses is often difficult.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.