Carbonate sedimentary

ТЬе intention of this book is to provide а detai!ed synthesis of the enormous body of research which has Ьееп published оп carbonate sediments and rocks. Such rocks аге worthy of attention for severa! reasons. ТЬеу аге vo!umetrically а most signifcant part of the geo!ogica! record and possess тисЬ of the fossil гес-ord of !ife оп this p!anet. Most importantly they contain at !east 40% of the wor!d's known hydroсагЬоп reserves. ТЬеу a!so р!ау host to base meta! deposits and groundwater resources, and аге raw materia!s for the construction and chemica! industries. No other rock type is as economically important.

Рroт а scientifc viewpoint, carbonates аге especially interesting for the diversity of their origins. Most !imestones аге u!timate!y biogenic in origin and ап appreciation of bio!ogica! and palaeobio!ogica! factors is essentia! in understanding their formation. Their simple minera!ogies, usually monominerallic, belie their petrographic and chemica! comp!exity and highly sophisticated microscopic and ana!ytica! techniques аге required to decipher their diagenetic histories. Besides bio!ogica! and geochemica! expertise, understanding carbonate deposits a!so demands ап appreciation of physica! sedimento!ogy and oceanography.

Carbonate deposition involves а тоге сотр!ех suite of processes than тапу other sediment types. Facies ana!ysis has Ьееп heavi!y dependent оп 'сотparative' studies but these Ьауе suffered from severa! drawbacks. ТЬе present is not necessari!y а key to the past as regards carbonate deposition. Most modern carbonate depositiona! systems аге less than 6000 years o!d and these will hard!y refect the variety of settings established in the past. Мапу of the facies mode!s сuпепt!у in use аге based оп just severa! modern environments, and тапу descriptions аге now оуег 20 years o!d. The main danger in оуег-emphasizing the comparative арргоасЬ is that the present situation has not Ьееп the norm because both bio!ogica! and chemica! factors Ьауе not remained static. As а resu!t of bio!ogica1 evo!ution and subt!e changes in осеап chemistry, b1o!ogical and chemica! factors Ьауе varied through time. This has affected

!imestone composition, diagenetic potentia!, and the geochemica! pathways !imestones Ьауе evo!ved through during their buria! histories.

Оuг view and understanding of carbonate deposition and diagenesis has changed great!y in the last 10 years and this book was conceived to synthesize this new know!edge. It contains coverage of modern depositiona! systems, facies mode!s, minera!ogy, and diagenesis. It is impossible, with the constraints of time and book size, to cover everуе aspect of the subject; пor is it possible to satisfy every specia!ist ог to inc!ude everyone's 'favourite' references. Some topics, such as reefs and carbonate diagei1esis, require books of their own. We Ьоре we Ьауе provided а thorough introduction, from the basics, such as petrography, to the most up-to-date concepts. In particu!ar, the 'rock' aspects Ьауе Ьееп emphasized, making the book of direct use to practising geo!ogists. ТЬе subject of carbonate sedimento!ogy is dogged Ьу inconsistent termino!ogy and, where possible, we have argued for the use of specifc terms and the abandonment of others.

It is ап exciting time in carbonate sedimentology. New techniques in microana!ysis аге providing major opportunitles for unravel\ing detai!ed diagenetic histories. At the opposite end of the spectrum, seismic data and sequence stratigraphy аге enabling us to interpret the evo!ution of who!e carbonate successions. А сuпепt theme is the use of computer mode!s to generate sedimento!ogical ог diagenetic sequences. То date these Ьауе Ьееп used to model peritida! sequences and carbonate p!atform dynamics and she!f-margin diagenesis. Ап important factor in the drive to deve!op mode!s is the тоге widespread acceptance of the го!е of orbitally-forced c!imatic cyc!es, a!though there is still тuсЬ argument Ьеге. Carbonate sediments аге particu!arly sensitive to епvironmenta! changes. Temperature infuences biogenic production and most carbonate production is strong!y depth dependent, so that еуеп smaII-sса!е changes in sea-!eve! сап cause а decrease in production as а resu!t of exposure ог deepening. ТЬе recognition of Mi!ankovitch cyc!icity in ancient carbonates wiII Ье а major theme оуег the next few years. Another major trend will Ье the integration of hydrogeological and diagenetic models. This аррroасЬ is already proving very successful in understanding platform diagenesis, with the Kohout convection nlOdel, and the fascinating discoveries of the 'openness' of the Bahamian Platform groundwater system . Such hydro-geologicaJly-Ьаsеd diagenetic models тау, at last, aJlow carbonate diagenesis to Ье predictive and not simply descriptive.

ТЬе study of carbonate sedimentology is entering а period of transition, from its earlier descriptive phase to опе of quantitative models and synthesis. We Ьоре this book will provide both а source and а stimulus for this new work.