Skip to Main Content
Skip Nav Destination

A review of molar-tooth structures with some speculations on their origin

A. G. Smith
A review of molar-tooth structures with some speculations on their origin (in Belt Basin; window to Mesoproterozoic Earth, John S. MacLean (editor) and James W. Sears (editor))
Special Paper - Geological Society of America (August 2016) 522: 71-99


Molar-tooth structures generally form a network of interconnected vertical and horizontal calcite ribbons and occasional spheroidal objects or "blobs" found in fine-grained, probably marine sediments spanning the late Archean to late Neoproterozoic interval, a duration of approximately 1900 m.y., or nearly half Earth's stratigraphic record. Vertical ribbons, averaging 5 mm in thickness, are generally intricately folded or fragmented by compaction. Decompaction shows that some ribbons may have been up to a meter in length perpendicular to bedding, forming in sediments that originally contained approximately 70% water, implying formation in sediment depths of approximately 1.7 m or less. Though at least 10 processes have been suggested for the blobs and ribbons, they were most likely voids created by the rise of gas bubbles from the decay of microbial mats that were rapidly filled with calcite. Horizontal ribbons probably formed under conditions of high pore-fluid pressure due to an overlying seal attributed to extracellular polymeric substances (EPSs) associated with the microbial mats. Cathodoluminescence imaging reveals that several molar-tooth fills show two distinct components: (1) earlier granular cores (now calcite) that are overgrown by (2) polygonal calcite. The earlier cores may have begun as an amorphous calcium carbonate (ACC) phase that recrystallized as calcite. Molar-tooth structures appear to simply reflect the formation of compacted calcite-filled voids under a seal of microbial mats and EPSs. Molar-tooth structures were present on Earth and may have played a significant role in the earlier history of other rocky extraterrestrial bodies with aqueous environments.

ISSN: 0072-1077
EISSN: 2331-219X
Serial Title: Special Paper - Geological Society of America
Serial Volume: 522
Title: A review of molar-tooth structures with some speculations on their origin
Title: Belt Basin; window to Mesoproterozoic Earth
Author(s): Smith, A. G.
Author(s): MacLean, John S.editor
Author(s): Sears, James W.editor
Affiliation: Sedgwick Museum, Department of Earth Sciences, Cambridge, United Kingdom
Pages: 71-99
Published: 20160818
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 140
Accession Number: 2016-087182
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Source Note: Online First
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201643
Close Modal

or Create an Account

Close Modal
Close Modal