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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Nature, Origin, and Classification of
Peritidal Tepee Structures and Related
Breccias
By
Distinctive peritidal tepee antiform structures, buckled margins of saucerlike megapolygons, are common in marine vadose fenestral and pilolitic
limestones and/or dolomites of carbonate platform sequences. They occur in
intertidal and supratidal carbonates ranging in age from Silurian to Holocene.
These megapolygons commonly form, and are sometimes truncated, before the
deposition of the next sedimentary layer. The megapolygons result from the
expansion of surface sediments by as much as 15%. The expansion is caused by the
following continuously repeated sequence of processes: (1) desiccation and
thermal contraction causing small fractures: (2) phases of wetting causing
enlargement of fractures: (3) phases of crystallization of calcium carbonate and
other minerals causing the enlargement, fill, and cementation of the fractures
(precipitation is from brines and meteoric waters); (4) hydration of minerals,
thermal expansion, breaking waves, and faulting may add to this disruption. The development of the tepee fabric can be traced from an initially cemented,
subaerial fenestral crust exhibiting expansion and compressional structures to a
completely disrupted and brecciated sediment riddled by a labyrinth of fractures
and solution cavities. These spaces are filled by numerous phases of internal
marine and freshwater cement and sediment, the latter containing
penecontemporaneous or younger marine faunas. Peritidal tepees are useful tools for geologic
reconstruction and provide evidence of subaerial exposure, a tropical to
subtropical climate, and back-beach or back-barrier deposition. Proper
identification of tepees is of economic importance, because they proved good
early porosity and permeability for petroleum entrapment and a site for
mineralization. Aesthetically, tepee rocks are a fine kaleidoscopic decorative
stone. End_of_Record - Last_Page 5---------------