With the rise of carbonate research in the 1950's there was the recognition that communication of research findings would be aided by agreement on a standard way of describing carbonate rocks. While there were a number of classification systems proposed, Dunham's classification quickly became the dominant carbonate rock classification used by industry and academia.
The basis of this classification is its similariety to siliciclastics (mudstone, wackestone and grainstone), its basic tie to carbonate petrophysics (grain support vs mud support etc.) and its flexibility (it can be applied grossly with a hand lens for core or hand speciment description, or in great detail using modifiers in thin section for research applications).
The impact of this work cannot be overstated, particularly in the oil and gas industry. It has allowed the communication of critical carbonate rock data, generated by line geologists from core and outcrop, to explorationists, engineers and reservoir modelers regardless of language or location.
This classic paper gives the theoretical basis for assessing epiric carbonate sedimentation that lacks a modern analog. Irwin sets the scale and bathymetry of an environment that continues to be difficult to grasp.
This rather unassuming paper provoked a generation of stratigraphers, sedimentologiststo and explorationists to re-assess their ideas concerning facies relationships through time in shallow marine conditions in an epiric setting. He introduced the concept of the "kick back", or the point at which a transgressive shoreline switched to a regressive one, and its potential role as a time horizon.
These concepts led to or became part of the overall fabric of sequence stratigraphy (maximum flooding surface) the ramp model and the impetus of exploration during the 70's and 80's.
Fischer, A. G. (1964), The Lofer cyclothems of the Alpine Triassic, Princeton University press
Fischer's book on the Lofer cycles of the Alpine Triassic describes these classic, engimanic carbonate-shale doublets and paints a masterful case for the factors controlling their origin, chiefly eustasy. It goes without saying that this work and his subsequent efforts set the stage for our modern understanding of the important role of eustacy in the development of edpositional stacking patterns and the overall architecture of carbonate successions and the recognition of the importance of allocyclic processes.
The basic tenets of sequence stratigraphy as outline by Vail and others, the work of Goldhammer, and Van Waggnor on carbonate stacking patterns, Sarg on the application of sequence stratigraphy to carbonates and countless other modern researchers owe much to this seminal work of one of our most productive, innovative scientists.
This contribution to our understanding of carbonate petrology by one of the most important modern sedimentary petrologist (clastics or carbonates) came at a time when geologists of all stripes began to seriously consider and use the petrology of carbonate rocks as a tool to interpret ancient environments of deposition and their diagenetic history.
Folk gave the petrologist the framework needed to discern and describe those fabrices attributable to the complex changes carbonate sediments undergo as they come into contact with changing fluids and temperature/pressure regeimens during their journey from surface conditions into their ultimate burial in the subsurface.
It has been of inestimable value in our modern studies of carbonate rock history, porosity evolution which has become an integral part of any modern exploration/exploitation strategy.
Land, L. S. (1985), The origin of massive dolomite, Journal of Geological Education, 33, 112-125.
Lynton Land as geochemist, petrologist and sedimentologist has made many important contributions to our understanding of carbonate geology but none as important as his masterful evaluation of the "dolomite problem"ourlined in this paper.
He documented the modern understanding of why and where massive dolomite occurs. His hydrologic and mass transport arguments are generally responsible for the consensus that most massive dolomite is formed in near-surface, open hydrologic systems that have access to the only really viable source of magnesium for massive dolomite formation-sea water or modified sea water.
These observations and conclusions came at a time when the concept of mixed fresh/marine water dolomitization was one of the favored dolomitization models. This paper essentially made this concept untenable. His evaluation was so compelling that his concept of marine water dolomitization has become fundamental to any modern discussion of massive, regional dolomitization and is of prime importance to explorationists.
As in the case of carbonate rock classifications, the advent of intense research in carbonate reservoirs, porosity evolution and diagenesis necessisitated the development of a standardized nomenclature to describe pore types in carbonate rocks and reservoirs. Their porosity types were based on those pores that were fabric selective such as interparticle porosity and those pores that were not fabric selective such as fracture and vug porosity.
This classification is geologic based and stresses the evolutionary nature of porosity through time, from deposition through its burial history, making it particularly useful in diagenetic studies and exploration for hydrocarbon reservoirs.
Other classifications such as that developed by Jerry Lucia, are basicallly engineering based and are particularly useful for production geologists and reseervoir engineers during the reservoir characterization studies and reservoir modeling.
The Choquette and Pray porosity classification has had an imeasurable impact on hydrocarbon exploration as well as on carbonate diagenesis and porosity evolution research. As a testimony to its usefulness and importance it remains the most widely used porosity classification 44 years since its publication in the AAPG Bulletin.
Ginsburg, R.N. (1964), South Florida carbonate sediments, Guidebook #1, GSA convention, 72p.
This GSA guidebook exemplifies the huge body of critical science developed on modern tropical carbonate environments begun in the 50's by Bob Ginsburg and co-workers at the Shell research station in Coral Gables and continuing today at the Rosensteil School of Marine and Atmospheric Scinces.
This work outlined the salient features of the modern carbonate depositional environments and the important relationships between the sediments and the organisims living and dying in these south Florida carbonate environments.
This rather small guidebook pointed the way for a generation of carbonate sedimentologist. Our understanding of modern and ancient tropical carbonate platforms is closely tied to the work and influence of R.N.Ginsburg and his colleagues. Their ideas still have a major influence on carbonate sedimentologic research today.
This paper outlines the archicture of a carbonate setting rarely seen in modern depositional environments. It consists of a wide, low angle remp progressively deepning seaward, possessing no abrupt shelf margin and a high-energy shoreline seperated from continental environments by a narrow, shallow lagoon.
This model gave the carbonate sedimentologist a viable alternative to Wilson's shelf facies tract exhibiting an abrupt change of slope at the shelf margin, a very wide, often deep lagoon and a relatively low-energy transisition to continential environments. It was also an alternative to the Florida-Bahamas model of an isolated carbonate platform with no ties to continental land masses.
Ahr's paper stimulated critical discussions of the architecture of carbonate platforms throughout the 80's such as Fred Reed's 1985 AAPG paper on carbonate platform models. These discussions ultimately led to a better understanding of the archicture of ancient carbonate platforms that have had a significant impact on modern carbonate research and exploration.