Equatorial Carbonate Depositional Systems of Indonesia
Robert K. Park, Paul D. Crevello, Wahyoe Hantoro, 2010. "Equatorial Carbonate Depositional Systems of Indonesia", Cenozoic Carbonate Systems of Australasia, William A. Morgan, Annette D. George, Paul M. (Mitch) Harris, Julie A. Kupecz, J. F. (Rick) Sarg
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The fundamental processes and controls on carbonate deposition are well established. These include: water depth, temperature, salinity, clarity, and an abundance of sunlight, all of which control rates of growth among the biota while wave and current energy ensure a steady supply of nutrients. The aragonite-dominated systems of the tropical latitudes gave way to calcite dominance in higher latitudes. Mud-rich tidal-flat sequences characterize the Bahamian and Persian Gulf settings, while mud-free systems dominate the higher-energy settings of the Great Barrier Reef and cooler-water environments. With the inclusion of recently documented Lophelia “reef mounds” in deep arctic waters, together with studies of deep-water pelagic limestones, the globalization of carbonates was nearly complete - almost.
One part of the global distribution pattern remains understudied and underappreciated, namely the equatorial belt. In old mariner terminology this latitudinal belt is known as the doldrums, notorious for its unpredictable calms and seasonal monsoon shifts in the wind and surface currents. In recent years, the Indonesia - Philippines archipelago has received particular attention from oceanographers and climatologists in recognition and growing awareness of the role of El Nino Southern Oscillation (ENSO) and the Indonesian Throughflow (ITF) and its relation to upwelling and changes in sea-surface temperature (SST), resulting in widespread reef death throughout the region.
The archipelago straddles the equator and lies squarely within this equatorial belt. Average sea-water temperatures are ∼ 28–30°C, and salinities are much lower than normal, ∼< 32–34%. These values test the tolerance limits of many reef community members, hence their susceptibility to El Niño events. Collision tectonics has defined the structural style, geography, and hydrography of the archipelago since the earliest Tertiary and has profoundly influenced modern and Cenozoic depositional systems. Shifts in relative sea level are frequent and often dramatic, affecting not only depositional patterns but also diagenesis, with repeated subaerial and flooding events.
The symmetry of the seasonal shifts introduces a bimodal pattern while the energy of the system reduces mud accumulation on the shallow platforms. Nearshore fringing reefs are limited by the high clastic discharge associated with high rainfall and landform topography. Coastal plains are clastic dominated, with mangrove swamp peats replacing the microbial mats that typify large tracts of the Bahamian and Persian Gulf platform settings.
Thus, the region offers an excellent opportunity to study modern and ancient carbonate systems under this particular climatic and, perhaps just as importantly, tectonic setting. That almost half of Indonesia’s hydrocarbon reserves and production derive from these same Cenozoic carbonates provides additional reason for further study.
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Cenozoic Carbonate Systems of Australasia
The Cenozoic carbonate systems of Australasia are the product of a diverse assortment of depositional and post-depositional processes, reflecting the interplay of eustasy, tectonics (both plate and local scale), climate, and evolutionary trends that influenced their initiation and development. These systems, which comprise both land-attached and isolated platforms, were initiated in a wide variety of tectonic settings (including rift, pas-sive margin, and arc-related) and under warm and cool-water conditions where, locally, siliciclastic input af-fected their development. The lithofacies, biofacies, growth morphology, diagenesis, and hydrocarbon reser-voir potential of these systems are products of these varying influences. The studies reported in this volume range from syntheses of tectonic and depositional factors influencing carbonate deposition and controls on reservoir formation and petroleum system development, to local studies from the South China Sea, Indonesia, Kalimantan, Malaysia, the Marion Plateau, the Philippines, Western Australia, and New Caledonia that incor-porate outcrop and subsurface data, including 3-D seismic imaging of carbonate platforms and facies, to un-derstand the interplay of factors affecting the development of these systems under widely differing circum-stances. This volume will be of importance to geoscientists interested in the variability of Cenozoic carbonate systems and the factors that controlled their formation, and to those wanting to understand the range of po-tential hydrocarbon reservoirs discovered in these carbonates and the events that led to favorable reservoir and trap development.