Burchette, T. P., and V. P. Wright, 1992, Carbonate ramp depositional systems: Sedimentary Geology, v. 79, p. 3-57.
This paper is a thorough compilation and discussion of carbonate ramp systems, a type of carbonate depositional profile first identified by Ahr (1973) as an alternative to the rimmed-shelf model. Burchette and Wright present a table of ramps and their characteristics, from Precambrian through Tertiary, which forms the basis for exploring multiple aspects of carbonate ramps, including their profiles and facies, systems tracts, diagenesis, tectonic settings, stratigraphic evolution, and distribution through time. They plot the organisms important to ramp facies through time and observe that the zone of greatest organic carbonate sediment production appears to have shifted from the mid-ramp to the inner ramp since the Late Jurassic, in concert with the rise of calcareous, pelagic foraminifera. They also compare the response of ramps and rimmed shelves to sea-level changes, noting that during sea-level falls ramps may gradually down-step and form forced-regressive wedges, in contrast to flat-topped, rimmed shelves on which carbonate production may cease because of subaerial exposure. A further important aspect of this paper from a petroleum geology perspective is the authors' discussion of the economic importance of carbonate ramps, including reservoir types (buildups and grainstones), source potential, and play types.
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.
Fischer, A.L. 1964. The Lofer cyclothems of the Alpine Triassic. Kansas Geological Survey Bulletin, v. 169, p. 107-149.
Fischer's introduction to 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 outlined by Vail and others, the work of Goldhammer and Read 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.
Ginsburg, R. N., 1964, South Florida carbonate sediments: Guidebook #1, GSA Annual Convention, 72 p.
This 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 University of Miami Rosensteil School of Marine and Atmospheric Science. Results outlined the salient features of the modern carbonate settings 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, as their ideas continue to have a major influence on carbonate sedimentologic research today.
Hallock, P., and W. Schlager, 1986, Nutrient excess and the demise of coral reefs and carbonate platforms: Palaios, v. 1, p. 389-398.
The potential for drowning of carbonate platforms caused by effects of excess nutrients supply is the subject of this paper. Growth rates of corals on Holocene reefs indicate that carbonate platforms should be able to keep up with rates of long-term subsidence and sea-level changes. However, examples of "drowned" reefs and platforms are found throughout the Phanerozoic. Because coral reefs thrive in nutrient-deficient environments, the authors suggest that an excess supply of nutrients is a probable explanation for decreased coral growth rates, allowing relative rises in sea level to outpace reef and carbonate platform ability to maintain their positions in the photic zone. This occurs for several reasons according to the authors, including stimulation of plankton growth, resulting in decreased water transparency. That limits the depth that calcareous algae and zooxanthellae in corals can thrive and thereby negatively impacts carbonate production while positively impacting the growth of fleshy algae and ahermatypic suspension-feeding animals — both of which are coral competitors and some of which are bioeroders that destroy reefs. The authors state that carbonate rates of production and bioerosion are similar so that a modest increase in nutrients to the carbonate system can result in a change from net carbonate production to net erosion. With regard to possible nutrient-induced effects on ancient reefs, Hallock and Schlager note that zooxanthellae have been symbionts in Scleractinian corals since the Late Triassic and were likely present in Rudistids, important platform builders of the Late Jurassic and Cretaceous. Algal symbionts may also have occurred in some Permian bivalve and brachiopods and larger forams of the Permian, Pennsylvanian, Cretaceous, Eocene, late Oligocene, and early Miocene. Although "drowning" of carbonate platforms has been linked to anoxic events, the authors suggest that, in several cases, recycling of nutrients via overturn of stratified, mid-ocean waters may be the real culprit. This paper casts further light on the complex nature of carbonate systems and the many variables that control the growth and death of carbonate platforms and reefs.
This classic paper gives the theoretical basis for assessing epeiric carbonate sedimentation that lacks a modern analogue. 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, sedimentologists and explorationists to re-assess their ideas concerning facies relationships through time in shallow marine conditions in an epeiric setting. Irwin 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.
James, N. P., 1997, The cool-water carbonate depositional realm, in N. P. James and J. A. D. Clarke, eds., Cool-water carbonates: SEPM Special Publication No. 56, p. 1-20.
In this succinct description of cool-water carbonates, James first describes the history of research on this system, noting that they have typically played second fiddle to their warm-water cousins. The common biota of cool-water carbonates includes molluscs, foraminifers, echinoderms, bryozoans, barnacles, ostracods, sponges, worms, ahermatypic corals, and coralline algae; conspicuously absent are hermatypic corals and or calcareous green algae, both common constituents of warm-water carbonates. James describes the conditions under which modern, temperate (generally colder than 20oC) carbonates form (temperature, salinity, nutrients) and controls on their deposition and patterns of sedimentation, including terrigenous input, light and hydrodynamic conditions, oceanography, and sea-level history. He goes on to describe facies patterns on cool-water ramps and open shelves and derives facies models for temperate and polar realms, noting that in addition to their modern-day importance as marine sediments, they are quite similar to many Paleozoic and Mesozoic skeletal limestones (especially Ordovician through Permian), making them excellent analogues. Another interesting aspect of Cenozoic cool-water skeletal limestones is that they remain largely uncemented in the meteoric zone because they are dominated by calcite and not aragonite, resulting in greater susceptibility to physical compaction and stylolitization – another common characteristic of some Paleozoic limestones of similar composition.
James' paper is an excellent summary of a type of carbonate system that is less well represented than warm-water carbonates in today's oceans but, in terms of sediment composition, may have been much more prevalent in the past.
Pomar, L., 2001, Types of carbonate platforms: a genetic approach: Basin Research, v. 13, p. 313-334.
Pomar takes a different approach to classifying carbonate platforms from the more traditional descriptive classifications based mostly on depositional profile, size, and whether a platform is attached or detached from a landmass. Instead, he uses a genetic approach that describes carbonate depositional profiles as a function of sediment type (basically grain size), the loci of sediment production (relative to the photic zone), and the hydraulic energy of the system. He identifies three groups of carbonate-producing biota based on their dependence upon light: euphotic (well-lit in shallow, wave-agitated areas); oligophotic (low light in deeper, commonly non-wave-agitated areas); and photo-independent biota in all water-depth ranges. These considerations lead to interpretations that may not have occurred using the more common approach to classifying carbonate platforms. For example, Pomar states that the well-known concept of rimmed platforms, is mostly based on present-day coral reefs, which typically build to sea level and are dominated by Scleractinian corals. However, Scleractinian corals did not become prominent until the late Paleocene and older rimmed platforms developed as a result of differences in both types of frame-producing processes (biotic and/or chemical) and the location of the frame-producing processes. The reef rim of the well-studied Upper Permian Capitan reef of New Mexico and Texas is formed of marine-cemented, microbial, calcareous sponge, algal, bryozoan, Archaeolithoporella, Tubiphites framestone and bindstone that was deposited below storm wave base at the shelf-slope break in water depths ranging from 30 to 80 m. The Capitan reef had a rigid rim, but it formed in the meso- to oligophotic zone and did not restrict circulation and wave energy on the shelf behind it as would be characteristic of euphotic, reef-rimmed platforms today. Pomar's paper offers a cautionary tale for interpreting facies distributions based on carbonate-profile type, especially for those interpretations based on seismic data where little or no lithofacies information is available.
In this paper, Read expands on his 1982 classification of carbonate platform profiles into ramps, rimmed shelves, isolated platforms, and drowned platforms, and subdivides them based on facies distribution and profile, resulting in seven ramp and five shelf models. Ramp models are fringing bank, barrier bank, isolated shallow ramp and downslope buildups, ooid-pellet fringing complex, ooid-pellet barrier, distally steepened, and swell-dominated distally steepened. Rimmed-shelf models are accretionary, bypassed margin gullied slope, bypass margin escarpment, erosional margin, and deep rim. Examples (both outcrop and subsurface) are described to illustrate each model and its likely tectonic setting. Read also discusses how one profile type may evolve into another based on subsidence, eustatic controls, and platform drowning. For example, drowning of a rimmed shelf would result in a distally steepened ramp if the carbonate factory is able to back-step. Examples of hydrocarbon reservoirs are presented for each platform type. This, together with the descriptions of the models and their potential evolution, which can provide guidance when interpreting carbonate-platform seismic profiles and geometries, make this a highly useful paper for petroleum geologists.
Sarg, J. F., 1988, Carbonate sequence stratigraphy, in C. K. Wilgus, B. S. Hastings, H. W. Posamentier, J. Van Wagoner, C. A. Ross, and C. G. St. C. Kendall, eds., Sea level changes: an integrated approach: SEPM Special Publication No. 42, p. 140-155.
Sarg's paper forms the fundamental basis for interpreting carbonate systems within the Exxonian concepts of sequence (including seismic) stratigraphy. His paper significantly builds on Wilson's (1967) paper on cyclic and reciprocal sedimentation by incorporating sequence-stratigraphic concepts to the interpretation of seismic and well-log stacking patterns and stratal geometries, using examples from the, Silurian of the Michigan basin; Pennsylvanian of the Midland basin; the Jurassic, Smackover-Haynesville succession in Louisiana; Miocene, Natuna platform, offshore Borneo — of particular interest is the seismic line shot near the well-exposed and well-studied Permian succession in the Guadalupe Mountains, which allows direct comparison of outcrop and seismic stratal geometries. The author describes highstand carbonate systems as being characterized by either catch-up or keep-up geometries, reflecting their growth rates relative to relative sea-level rise, with implications for the composition and porosity of the shelf-margins. Sarg describes criteria for recognizing type 1 and type 2 sequence boundaries in carbonate successions where the rate of eustatic fall is interpreted to be greater and lesser, respectively, than the rate of subsidence at the platform/bank margin, and the implications for diagenetic alterations during subaerial exposure associated with those boundaries. He recognizes three types of carbonate deposits during sea-level lowstands: allochthonous material derived from erosion of the slope; autochthonous wedges deposited on the upper slope during type 1 sea-level lowstands; and platform-margin wedges associated with type 2 sequence boundaries. He also applies sequence-stratigraphic concepts to the interpretation of evaporites. This paper was instrumental in promoting the concepts of sequence stratigraphy as applied to carbonate successions.
Schlager, W., 1981, The paradox of drowned reefs and carbonate platforms: GSA Bulletin, v. 92, p. 197-211.
Schlager investigates the potential causes of reef and carbonate platform "drowning", i.e., when a relative rise of sea level (tectonic plus eustatic movements) outpaces carbonate accumulation so that the platform or reef becomes submerged below the euphotic zone of prolific carbonate production. As Schlager shows through a table of drowned carbonate platforms, this phenomenon has occurred throughout the Phanerozoic. The paradox is why this has happened given the relatively rapid growth rates carbonate reefs and platforms are capable of attaining (a conservative estimate of 1,000 μm/yr).
Schlager shows that the rates of long-term processes, including subsidence of newly formed ocean crust, basin subsidence, and sea level rises resulting from increased sea-floor spreading are at least an order of magnitude too slow to drown carbonates. Schlager examines alternative potential causes and offers examples of drowning including: reduction of growth caused by environmental stress (Late Devonian), such as drastic decreases or increases in salinity or drift to higher latitudes associated with seafloor spreading (Mesozoic platforms of western North Atlantic); or rapid increases in relative sea level driven by eustasy, tectonics (Mesozoic margins of the Tethys Sea) or a combination of both. This paper shows the complexity involved in understanding the controls on carbonate reef and platform growth and demise, and how those controls may have varied throughout the Phanerozoic.