Although the biota, facies, stacking patterns, sequence stratigraphy, and diagenesis of numerous isolated carbonate platforms have been described and interpreted, trends in the genesis, evolution, and sizes among Phanerozoic examples remain poorly quantified. To provide broad perspectives on Miocene isolated platforms of Central Luconia and Southeast Asia (the focus of this volume), this study summarizes the results of qualitative review of the literature and a quantitative analysis of a relational database of attributes in initiation, growth, character, and demise of more than 850 Phanerozoic isolated platforms. The data and comparisons among parameters reveal numerous trends, including observations that (1) syndepositional tectonics has been interpreted to play an important role in initiation, growth, or demise of more than 44% of isolated platforms; (2) tectonically active platforms are more likely to have higher aspect ratios (more elongate in plan-view and more squat in cross section); (3) stratal geometries are not distributed randomly in time (by era, p = 0.00, and by system, p = 0.04), although aggradational isolated platforms are most common within and among all eras (63% of all platforms); (4) sizes (area, long axis length), thicknesses, and aspect ratios (long axis:short axis; long axis:thickness) of isolated platforms are distinct among Phanerozoic platforms of different eras and systems; (5) although individual platforms steepen as they grow taller, syndepositional relief is not correlated (R2 = 0.04) with depositional gradient among isolated platforms across the Phanerozoic; (6) causes of isolated platform termination vary nonrandomly through the Phanerozoic (by era, p = 0.00, and by system, p = 0.00). Of all eras, Cenozoic platforms are most likely to drown (68%), in some instances through an association with clastic influx (19%). Subaerial exposure more commonly contributed to the demise of Mesozoic (45%) and Paleozoic (37%) platforms than to that of Cenozoic (13%) platforms. These results, supplemented by more granular comparison of numerous individual platforms, compliment earlier syntheses that focus on the nature of secular changes. The insights suggest that although each platform is unique in many ways, Phanerozoic isolated carbonate platforms include numerous themes that are persistent across ages, sizes, settings, and component biota.

Shallow marine mixed siliciclastic–carbonate shoals, a carbonate platform, and the subsequent development of a reefal buildup occur in sequence from the late Chattian to the Aquitanian in the Niah area of Sarawak. They document the transition from larger foraminifera-dominated, calcitic environments to scleractinian coral-dominated, aragonitic environments in SE Asia, which correspond to a significant increase in biodiversity. A late Chattian to early Aquitanian phase of carbonate sedimentation was initiated by larger foraminifera on shallow marine argillaceous shoals raising from the seabed at about 60 m in water depth occasionally up to near sea level. Carbonate production is almost entirely the result of the accumulation of larger foraminiferal shells dominated by Eulepidina dilatata, a species that could thrive thanks to its photosymbiosis with microalgae. Such mixed carbonate–clastic shoals formed repeatedly on a muddy shelf during a period stretching from about 23.5 Ma to 22.3 Ma. Following a period of siliciclastic deposition, a roughly circular carbonate platform with an area of some 25 km2 was formed at around 21.2 Ma in stratigraphic continuity with the underlying shallow marine sandstones of the Nyalau Formation. Known as the Subis Limestone, it consists at first of bedded carbonates characterized by the presence of red algae, a high diversity of free benthic and sessile endosymbiotic sessile foraminifera, and a variety of organisms typical for reefal environments, including colonial corals. A reefal buildup started forming on the carbonate platform as early as 21.1 Ma. This phase of growth was likely initiated by low-relief patch reefs, 150 to 200 m in diameter and 60 to 80 m in height, such as those exposed in a southern quarry. Analogous with same-age reefal development models from the Java Sea, it is proposed that the patch reefs coalesced through time to form a larger isolated carbonate buildup that grew up at least until the end of the Aquitanian at 20.4 Ma. This Subis buildup reached an area of 16 km2; it has a preserved thickness of 260 to 280 m and had a paleo-relief of about 100 m above the surrounding sea floor. It is asymmetrical, with a reef wall forming high, west-facing cliffs and another reef wall likely extending on the NE edge of the buildup, beyond the Niah Great Cave. A further increase in faunal and floral diversity occurred during this phase, concomitant with the diversification of ecological niches within the buildup. Reefal and peri-reefal environments are dominated by red algae; solitary and colonial corals (domal, branching, and platy), with subordinate foraminifera (large and small benthic); and associations of foraminifera and algae forming laminar foralgal binding tissues, sponges, hydrozoans, bryozoan, bivalves, echinoderms, and serpulids. The reef rim consists of coral framestone and algal-foraminiferal bindstone. The backreef facies is characterized by rudstones and floatstone with coral debris, and the lagoon facies includes microbial crusts, green algae, articulated and nonarticulated red algae, benthic foraminifera (Miliolids), ostracods, gastropods, and up to 4-m-high platy corals pillars. Forereef deposits include grain- and mud-supported reef debris; a debris apron present some 2.5 km away from the western edge of the buildup consists of debris flows and calciturbidites embedded in outer neritic shales. The upper part of the buildup is missing as a result of recent subaerial erosion. Three successive steps in the development of carbonate ecosystems are identified, which are linked to a series of innovative symbiotic relationships established during the late Chattian and the Aquitanian. During an early phase (23.5–22.3 Ma), monospecific populations of endosymbiotic larger benthic foraminifera thrived on shallow marine muddy shoals. At around 21.2 to 21.1 Ma, new species of endosymbiotic larger benthic foraminifera, sessile-encrusting foraminifera, and coralline algae colonized shallow marine grounds and created a carbonate platform. From about 21.1 to at least 20.4 Ma endosymbiotic scleractinian corals, red algae, and a diverse association of organisms created patch reefs and a buildup.

This paper presents a brief synopsis of the Miocene Epoch, an important transitory chapter in the history of the Earth. It was during the Miocene that the major continents and oceans attained a “modern” configuration in terms of paleogeography and tectonics, oceanic ventilation and circulation, ocean chemistry, and faunal and floral assemblages. It also was during the Miocene that global climate fully transitioned into its current icehouse state, including marked growth of the Antarctic ice sheet and initiation of the Arctic ice cap. Long-term global cooling was controlled by a number of factors including tectonics, the large-scale changes in the distribution of flora, particularly the expansion of grasslands, and by fluctuating orbital parameters of the Earth. This global cooling trend was briefly interrupted by a short period of warming in the middle Miocene. Miocene sea-level changes consisted of a number of glacio-eustatic third-order (1–5 million year [m.y.] duration) cycles superposed upon three longer-term, second-order (5–20 m.y. duration) supercycles. Development of large-scale tropical carbonate systems in the Miocene was relegated to three main geographic regions: the circum-Caribbean, Mediterranean, and Indo-Pacific. In addition, a pronounced cool-water platform system developed along the southern margin of Australia. Miocene reefal buildups were dominated by tropical to subtropical framework assemblages consisting primarily of large scleractinian corals, encrusting red algae, and rhodoliths (free-living coralline red algae) that grew on platform margins and interiors or on isolated atolls. Miocene carbonates were deposited in a variety of oceanic and structural settings and constitute important petroleum reservoirs, particularly in Southeast Asia. Deep-water terrigenous clastic sediments of Miocene age are also important petroleum reservoirs in some regions. In addition, the Miocene interval contains numerous prolific petroleum source rocks, most composed of Type III (gas-prone) kerogen.

A generic strategy for modelling gas fields in Miocene isolated carbonate platforms leverages insights from over 20 analogue fields in the Central Luconia Province in Malaysia, some with 30+ years of development and production history. The strategy advocates customizing modelling efforts to answer the questions required to make business decisions at hand (decision-based modelling) while keeping the models as simple as possible (fit-for-decision models). Four presented examples vary from (1) a conceptual, scaled simulation model that is used to investigate various host tie-back options (screening development options—two examples), through (2) a static reservoir model with seismically constrained reservoir properties combined with a simulation that uses local multipliers to test the impact of key heterogeneities on well-placement options (development optimization), to (3) a full-field static and dynamic reservoir model that is matched to a long and detailed production history to accurately forecast late-field-life gas and water production (wells, reservoir, and facilities management). In combination with standardized work flows for reservoir property modelling, the strategy shifts the modelling focus from elaborate base-case models with uncertainty ranges to testing multiple scenarios that span the range of possible outcomes. The use of this generic modelling strategy has led to faster turnaround of subsurface work, enabling faster development and asset management decisions. Although the examples presented in this paper are specific to Miocene carbonates in Central Luconia, a similar strategy could be suitable for other geological settings.

In Southeast Asia, Cenozoic carbonates commonly were initiated or terminated at times of tectonic change, and they are bound by unconformities. A review of the timing of several of the largest unconformities shows they correlate over wide areas. These unconformities divide the stratigraphic record of Sundaland into episodes, with times of rapid basinal re-adjustment separated by periods of relative stasis. These generalizations are true not only in the successions deposited during the dominantly extensional later Eocene to early Miocene, but also in the often-compressional middle Miocene and younger deposits, in which at least three phases of rapid tectonic and stratigraphic change can be correlated over multiple depocenters. A detailed review of many areas of Southeast Asia using quantitative biostratigraphic methods indicates that tectonism resulted in relative changes in sea level, with no indication that eustasy was an important driving force. The boundaries between these sedimentary episodes vary in their effect and distribution, depending upon the tectonic cause. As a consequence, there is no uniform subdivision of the stratigraphic record across the region, which precludes a simple Sundaland-wide classification of primary sedimentary sequences. This review concentrates on both event timing and rates of change within and between basins, especially those changes that initiated or terminated carbonate deposition. In addition, some short-lived carbonate buildups that developed during transitional periods are described. This review provides the beginnings of a new stratigraphic framework for the Cenozoic carbonates and related deposits of Southeast Asia. It requires an inductive analytical methodology, in contrast to the model-driven and deductive approaches that have been applied in recent years. This episodic stratigraphy approach includes integration of large amounts of analytical data, for which the Cenozoic tropical sediments of Southeast Asian basins are particularly well suited.