Reef talus; a popular misconception

Online Access: Get full text
doi: 10.1016/j.earscirev.2013.11.002
Author(s): Braithwaite, Colin J. R.
Author Affiliation(s): Primary:
University of Glasgow, School of Geographical and Earth Sciences, Glasgow, United Kingdom
Volume Title: Earth-Science Reviews
Source: Earth-Science Reviews, Vol.128, p.169-180. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-8252 CODEN: ESREBW
Note: In English. 124 refs.; illus.
Summary: Reef fronts have traditionally been regarded as comprising debris derived by contemporaneous erosion of 'the reef'. However, evidence from wave transport indicates that on present-day reefs the bulk of the debris generated in this way accumulates in the back-reef area, with only finer-grained sediment carried off-reef by retreating flows or by overwash. Nevertheless, in contrast to this observation, 'fore-reef' debris slopes are commonly considered "characteristic" of Phanerozoic reefs. This apparent error reflects the conflation of processes defining contemporary growth and accretion of the reef, and the corresponding long-term accretion of the carbonate platform on which it rests. Present-day reefs are commonly (although not exclusively) additions to long-lived carbonate platforms. Growth of the latter is intermittent and has been moderated by changes in sea-level that, for recent reefs, have been on time scales of less than 100 ka. During low sea-level stands, growth ceases or is translated downslope and earlier deposits are subject to lithification and subaerial erosion. Similar changes are applied on a larger scale to the aggrading growth of carbonate platforms, but the bulk accretion of these includes quite different processes and reflects far longer timescales. During low sea-level stands, the margins of platforms commonly become unstable, with instability reflected in slope failure and in the shedding of blocks, ranging from metres to kilometres in diameter, associated with the generation of debris flows and turbidites. It is argued that these are the materials that are commonly described as 'reef talus' in ancient structures, although their formation is largely independent of any contemporary reef growth. Difficulties arise where 'the reef' and 'the platform' are treated as a single functional entity. It is important to recognize the conceptual distinction between them, 'reef talus' is a misleading description of the debris predominantly generated by platform erosion and slope failure. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 23 Surficial Geology, Geomorphology; Aggradation; Anthozoa; Atlantic Ocean; Beaches; Bottom features; Breccia; Carbonate platforms; Cnidaria; Coastal environment; Debris; Erosion; Erosion features; Failures; Great Bahama Bank; Invertebrata; Landforms; Leg 166; Littoral erosion; Megabreccia; North Atlantic; ODP Site 1003; ODP Site 1006; Ocean Drilling Program; Ocean floors; Reefs; Sea-level changes; Sediment transport; Slope stability; Straits of Florida; Talus slopes; Transport
Coordinates: N243245 N243245 W0791539 W0791539
Record ID: 2014073419
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands