Origin of Silurian reefs in the Alexander Terrane of southeastern Alaska
- Mary Ingraham Bunting Inst., Cambridge, MA (United States)
Lower to Upper Silurian (upper Llandovery-Ludlow) limestones belonging to the Heceta Formation record several episodes of reef growth in the Alexander terrane of southeastern Alaska. As the oldest carbonates of wide-spread distribution in the region, the Heceta limestones represent the earliest development of a shallow-marine platform within the Alexander arc and the oldest foundation for reef evolution. These deposits provide important insights into the dynamic processes, styles, and bathymetry associated with reef growth in tectonically active oceanic islands. Massive stromatoporoids, corals, and red algae are preserved in fragmental rudstones and represent a fringing reef that formed at the seaward edge of the incipient marine shelf. Accessory constituents in this reef include crinoids and the cyanobacterium Girvanella. Small biostromes were constructed by ramose corals and stromatoporoids on oncolitic substrates in backreef or lagoonal environments. These buildups were associated with low-diversity assemblages of brachiopods and with gastropods, amphiporids, calcareous algae and cyanobacteria. Microbial boundstones reflect the widespread encrustation of cyanobacteria and calcified microproblematica on shelly debris as stromatolitic mats that resulted in the development of a stromatactoid-bearing mud mound and a barrier reef complex. Epiphytaceans, other microbes, and aphrosalpingid sponges were the primary frame-builders of the barrier reefs. These buildups attained significant relief at the shelf margin and shed detritus as slumped blocks and debris flows into deep-water sites along the slope. The similarity of these stromatolitic-aphrosalpingid reefs to those from Siluro-Devonian strata of autochthonous southwestern Alaska suggests paleobiogeographic ties of the Alexander terrane to cratonal North America during the Silurian.
- OSTI ID:
- 5891292
- Journal Information:
- Palaois; (United States), Journal Name: Palaois; (United States) Vol. 6:2; ISSN PALAE
- Country of Publication:
- United States
- Language:
- English
Similar Records
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Cyclicity in Silurian island-arc carbonates, Alexander terrane, Alaska
Related Subjects
580000* -- Geosciences
ALASKA
ALGAE
ANIMALS
CARBONATE ROCKS
CNIDARIA
COELENTERATA
COMPARATIVE EVALUATIONS
CONTINENTAL MARGIN
CORALS
DEVELOPED COUNTRIES
EVALUATION
FOSSILS
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
INVERTEBRATES
LIMESTONE
NORTH AMERICA
ORIGIN
PALEOZOIC ERA
PLANTS
REEFS
ROCKS
SEDIMENTARY ROCKS
SILURIAN PERIOD
TECTONICS
USA