THE DESCRIPTIVE NOMENCLATURE AND CLASSIFICATION OF GROWTH FABRICS IN FOSSIL SCLERACTINIAN REEFS

Framework (sensu stricto) is a concept originally relating to modern r eefs and is defined by structural, ecological and sedimentological cri teria, However, in the geological literature the term 'framework' has come to be applied to almost any organically influenced in situ accumu lation, including non-calcareous, non-rigid facies associated with sea grasses. This drastic departure from the original meaning is misleadi ng and scientifically unhelpful. The concept of wave resistance is int egral to that of framework, but in the geological record it is not eas y to evaluate and the term may be of little comparative use between re ef environments. It is suggested that the term growth fabric be genera lly applied as a descriptive term for the presence of aggregated in si tu corals (or other organisms) in growth position within a facies. The term growth fabric should be used as an alternative to 'framework' as a purely descriptive term. The term framework should be restricted to its original definition and used only where the criteria for framewor k can be clearly demonstrated. Two end-member types of scleractinian g rowth fabric genesis are recognised, termed superstratal and constrata l (terms adapted from Gill, E., Masse, J.P., Skelton, P.W., 1995, Rudi sts as gregarious sediment-dwellers, not reef-builders, on Cretaceous carbonate platforms. Palaeogeogr., Palaeoclimatol., Palaeoecol. 118, 2 45-267). In a superstratal growth fabric, the constituent organisms co llectively projected decimetres to metres above the substratum creatin g positive topographic relief. In contrast, constratal growth is where vertical organic accretion occurred at a similar rate to sediment acc umulation; hence the majority of the skeletal material remained contin uously embedded in the sediments, and only a small proportion of the s keleton projected (centimetres) above the sediment surface. The archit ectural, palaeoecological, sedimentological and diagenetic implication s of different types of growth fabric genesis is discussed. A review o f the classification of reef fabrics suggests that there is currently no adequate system to describe fossil scleractinian growth fabrics. Th e most commonly used classification of reefal fabrics is that of Embry and Klovan (1971). [Embry, A,E, Klovan, J.E., 1971. A Late Devonian r eef tract on northeastern Banks Island, Northwest Territories. Bull. C an. Pet. Geol. 33, 730-781.] There are a number of shortcomings in thi s scheme which may be grouped into three categories: (1) the interpret ative nature of the classification; (2) problems in interpreting biolo gical effect from form; and (3) insufficient categories to adequately describe Mesozoic and Cenozoic growth fabrics. Moreover, there appears to be a lack of a standardised nomenclature for growth fabrics which has hindered meaningful comparisons of scleractinian growth fabrics th rough time and space. A descriptive system based on a modification and expansion of the Embry and Klovan system (1971) is proposed and a rev ised nomenclature for growth fabrics presented. The system is designed to be flexible in its application - it can be used simply to describe a growth fabric, or, through the use of genetic and non-genetic modif iers, to imply types of reef-building processes and growth fabric hete rogeneity. Although the concepts and terminology discussed in this pap er relate to scleractinian growth fabric, they are equally applicable to fabrics comprising other organisms. (C) 1998 Elsevier Science B.V. All rights reserved.