Tony Swiecicki

Abstract Despite broad similarities there exist significant differences in tectono-stratigraphic development of the Cuu Long Basin, Nam Con Son Basin and the West Natuna Basin. Both the West Natuna Basin and Cuu Long Basin show evidence of rift initiation in Late Eocene/Early Oligocene. All three basins show evidence of Mid Oligocene rifting coincident with sea-floor spreading in South China Sea/East Sea. The Cuu Long Basin shows evidence of compressional reactivation of strike-slip faults in Late Oligocene whilst inversion of early grabens occurred in West Natuna Basin in the Early, Middle and Late Miocene. The Nam Con Son Basin shows clear evidence for second period of rifting in the Middle Miocene coincident with end of sea-floor spreading. Keywords: Three Pagodas Fault • Mai Ping Fault • Shan Thai Block • Malaya Block • Bentong Raub Suture • Sra Kaeo Structure • Indochina Block • Tien Cau Syn Formation • Cau Formation • Dua Formation • Mang Cau Syn Formation • Nam Con Son Formation • Bien Dong Formation Presented at: 2009 South East Asia Petroleum Exploration Society (SEAPEX) Conference, Singapore, 2009

Abstract The Abadi field is Indonesia's first discovery in the Middle Jurassic Plover Formation. This potentially giant gas discovery is located some 350 km east of Timor Island and 350 km north of Darwin, Australia. It lies just north of the international boundary with Australia, in 400–800 m water depth. The Masela Production Sharing Contract (PSC) was awarded to Inpex as Operator with 100% interest in November 1998. The discovery well Abadi-1 was drilled and completed in late 2000. Following discovery, a 2,060 km2 3D seismic survey was acquired in 2001 and two successful appraisal wells were drilled in 2002. Geologically, the field comprises relatively undeformed Australian continental margin that extends into Indonesian waters. It lies on the eastern extremity of the Sahul Platform and occupies a large tilted fault block bounded to the east and south by the Calder-Malita Grabens. The accumulation contains a significant gas column, reservoired within shallow-marine, highly mature, quartzose sandstone of the Middle Jurassic Plover Formation. Close analogues are to be found in the giant Greater Sunrise and Bayu-Undan fields. Reservoir quality, at a depth of ~3,900 m, varies from surprisingly good to poor, reflecting a complex interaction of primary depositional controls and later diagenetic influences. A preliminary estimate of reserves size is about 5 TCF. Inpex has undertaken a variety of exploration projects and studies, including high-resolution sequence stratigraphy and seismic-driven paleofacies reconstructions to model the reservoir architecture. Utilizing this framework, a full-field 3D model is currently being developed to better characterize the likely range of reserves and to provide the basis for a more accurate understanding of the economic value of Abadi.

Abstract Very thick sequences, up to 25 000 ft, of Permo-Triassic sediment are preserved within the Papa and East Solan Basins, in the West Shetlands area. The active margin of this Permo-Triassic basin lay along the West Shetland Spine Fault. Due to severe erosional truncation, the position of the westerly passive margin cannot be delineated. The Triassic basin fill, referred to the Papa Group, has been proven by drilling to be at least 8000 ft thick. A combination of palynological, log and sedimentological analyses have allowed the succession to be informally subdivided into lithostratigraphic units. The oldest, of earliest Triassic age, is the Otter Bank Shale Formation deposited in a coastal/alluvial plain setting. This is gradationally succeeded by the coarse-grained Otter Bank Sandstone Formation comprising sediments derived from the interdigitation of sheetflood, braidplain and aeolian environments of deposition. These represent the initial erosional products derived from the uplifted, rifted basin margin. This major phase of Early Triassic rifting is believed to have taken place during the Scythian. The succeeding Foula Sandstone Formation marks the establishment of predominantly axial braidplain systems, deposited during a period of intermittent but waning tectonic influence during Middle to Late Triassic times. The Papa Group is referred to the New Red Sandstone Supergroup.

Abstract Very thick sequences, up to 25 000 ft, of Permo-Triassic sediment are preserved within the Papa and East Solan Basins, in the West Shetlands area. The active margin of this Permo-Triassic basin lay along the West Shetland Spine Fault. Due to severe erosional truncation, the position of the westerly passive margin cannot be delineated. The Triassic basin fill, referred to the Papa Group, has been proven by drilling to be at least 8000 ft thick. A combination of palynological, log and sedimentological analyses have allowed the succession to be informally subdivided into lithostratigraphic units. The oldest, of earliest Triassic age, is the Otter Bank Shale Formation deposited in a coastal/alluvial plain setting. This is gradationally succeeded by the coarse-grained Otter Bank Sandstone Formation comprising sediments derived from the interdigitation of sheetflood, braidplain and aeolian environments of deposition. These represent the initial erosional products derived from the uplifted, rifted basin margin. This major phase of Early Triassic rifting is believed to have taken place during the Scythian. The succeeding Foula Sandstone Formation marks the establishment of predominantly axial braidplain systems, deposited during a period of intermittent but waning tectonic influence during Middle to Late Triassic times. The Papa Group is referred to the New Red Sandstone Supergroup.

The Abadi field is Indonesia's first discovery in the Middle Jurassic Plover Formation. This potentially giant gas discovery is located some 350 km east of Timor Island and 350 km north of Darwin, Australia. It lies just north of the international boundary with Australia, in 400–800 m water depth. The Masela Production Sharing Contract (PSC) was awarded to Inpex as Operator with 100% interest in November 1998. The discovery well Abadi-1 was drilled and completed in late 2000. Following discovery, a 2,060 km2 3D seismic survey was acquired in 2001 and two successful appraisal wells were drilled in 2002. Geologically, the field comprises relatively undeformed Australian continental margin that extends into Indonesian waters. It lies on the eastern extremity of the Sahul Platform and occupies a large tilted fault block bounded to the east and south by the Calder-Malita Grabens. The accumulation contains a significant gas column, reservoired within shallow-marine, highly mature, qua...

The Cretaceous System, proposed by d'Omatius d'Halloy in 1822, takes its name from Creta-the Latin for chalk. Chalk is the most distinctive rock type of the System, not only in Britain (Fig. 7.1), but over a considerable area of the globe. Upper Cretaceous sediments at one time covered the whole of northwest Europe, save for a few isolated areas of ancient massifs like the Baltic Shield. Today, sediments of Cretaceous age are limited (onshore) to a narrow band down eastern England, together with a wide tract of country across southern England. Offshore, Cretaceous strata are more extensive, covering, or known from, large areas of the North Sea Basin, the English Channel, the Celtic Sea and the South West Approaches Basin.

The Solan Basin lies in a part of the West Shetland continental margin that has had a complex tectonic history, dominated by extension but punctuated by several episodes of inversion, transpression and extensive erosion. The oldest sedimentary sequence, identified on seismic but not yet penetrated by drilling, may comprise Devono–Carboniferous clastics. In the Permo-Triassic a large system of half-grabens was filled with a thick succession of coarse, continental clastics. These appear to have entered the basin system in two discrete pulses and it is speculated that a third pulse, representing a transition to marginal and fully marine environments, occurred in the Early Jurassic. The area was effectively peneplaned in the late Middle to early Late Jurassic, with the removal of up to 1.5 km of section. Overlying this unconformity is a thin sequence of marginal marine sandstones and organic-rich marine shales, deposited in the latest Jurassic to earliest Cretaceous. Although parts of t...

Onshore Maastrichtian strata in the United Kingdom are limited to a few small, isolated blocks of chalk floating within glacial sediments on the Norfolk coast. Isolated outcrops of Campanian and Maastrichtian chalks used to be available around Norwich but the majority of these exposures are now badly degraded. Offshore, in the North Sea Basin, there are complete chalk successions that range throughout the Upper Cretaceous and Lower Cenozoic. There is a limited succession of Maastrichtian chalks exposed on the north coast of Northern Ireland below the Cenozoic flood basalts. In the Western Approaches Basin, Maastrichtian and Danian chalks are known from exploration wells and core samples. West of the United Kingdom a number of DSDP/ODP boreholes have penetrated the Upper Cretaceous succession.Beginning in the Cenomanian, in southeast England, the whole of the Upper Cretaceous is within the chalk facies, possibly one of the longest intervals of relatively stable environment in the geo...

Despite broad similarities there exist significant differences in tectono-stratigraphic development of the Cuu Long Basin, Nam Con Son Basin and the West Natuna Basin. Both the West Natuna Basin and Cuu Long Basin show evidence of rift initiation in Late Eocene/Early Oligocene. All three basins show evidence of Mid Oligocene rifting coincident with sea-floor spreading in South China Sea/East Sea. The Cuu Long Basin shows evidence of compressional reactivation of strike-slip faults in Late Oligocene whilst inversion of early grabens occurred in West Natuna Basin in the Early, Middle and Late Miocene. The Nam Con Son Basin shows clear evidence for second period of rifting in the Middle Miocene coincident with end of sea-floor spreading. Keywords: Three Pagodas Fault • Mai Ping Fault • Shan Thai Block • Malaya Block • Bentong Raub Suture • Sra Kaeo Structure • Indochina Block • Tien Cau Syn Formation • Cau Formation • Dua Formation • Mang Cau Syn Formation • Nam Con Son Formation • Bie...

Introduction The palaeogeography of the Sunda region has been subject to dramatic change during the Cenozoic. These changes have been driven by tectonic events and by fluctuations in sea level and climate. After the Mesozoic assembly of the broad area from microplates derived from Gondwana, widespread rifting took place across the region following the initial collision of the Indian Plate with Asia. Further dramatic palaeogeographic changes relate to the opening of the South China Sea and the closure of the Proto-South China Sea, coupled closely with the Sabah Orogeny, which resulted in widespread uplift in Borneo. The collision of the Australian Plate with the region during the Neogene also resulted in major changes with further uplift, as well as modifying marine currents, and causing changes in regional climate.

The Solan Basin lies in a part of the West Shetland continental margin that has had a complex tectonic history, dominated by extension but punctuated by several episodes of inversion, transpression and extensive erosion. The oldest sedimentary sequence, identified on seismic but not yet penetrated by drilling, may comprise Devono-Carboniferous elastics. In the Permo-Triassic a large system of half-grabens was filled with a thick succession of coarse, continental elastics. These appear to have entered the basin system in two discrete pulses and it is speculated that a third pulse, representing a transition to marginal and fully marine environments, occurred in the Early Jurassic. The area was effectively peneplaned in the late Middle to early Late Jurassic, with the removal of up to 1.5 km of section. Overlying this unconformity is a thin sequence of marginal marine sandstones and organic-rich marine shales, deposited in the latest Jurassic to earliest Cretaceous. Although parts of the region received a major influx of sand derived from the West Shetland Platform in the Early Cretaceous, the equivalent strata throughout most of the Solan Basin are a thin succession of pelagic shales and carbonates. In the early Turonian the basin was inverted. During the Late Cretaceous, extension, related to rifting along the line of the Faeroe-Shetland Trough, resulted in the development of large normal fault systems, providing the space in which a thick sequence of deep marine shales was deposited. In the earliest Paleocene, transpressional reactivation of some faults produced intense, but localized, inversion structures. Generally, however, sedimentation continued uninterrupted through the Paleocene, with the accumulation of deep marine sandstones in the east of the basin. The culmination of Thulean volcanism in the earliest Eocene was marked by the deposition of tuffaceous mudstones, which are overlain by thin coal-bearing, paralic to continental sediments. Regional thermal subsidence began in the early Eocene and continued into the Oligocene with the deposition of a thick sequence of marine elastics. In the Miocene, erosion removed up to 1.2 km of sediment from parts of the Rona Ridge and produced a basin-wide unconformity. This is overlain by Pliocene to Recent glacio-murine sands and gravels.

The Cretaceous System, proposed by d'Omatius d'Halloy in 1822, takes its name from
Creta-the Latin for chalk. Chalk is the most distinctive rock type of the System, not only
in Britain (Fig. 7.1), but over a considerable area of the globe. Upper Cretaceous sediments at one time covered the whole of northwest Europe, save for a few isolated
areas of ancient massifs like the Baltic Shield. Today, sediments of Cretaceous age are limited (onshore) to a narrow band down eastern England, together with a wide tract
of country across southern England. Offshore, Cretaceous strata are more extensive,
covering, or known from, large areas of the North Sea Basin, the English Channel, the Celtic Sea and the South West Approaches Basin.

The genus Bolivinoides Cushman 1927 has been widely recorded from strata ranging in age from Upper Santonian to Paleocene. The genus has received considerable attention, not least for its proven value for biostratigraphic correlation. The sole published work concerning the distribution of the genus in the British Isles, however, is that of Barr (1966), who recorded nine species of Bolivinoides from a series of spot samples from southern England, Northern Ireland and Eire. During the course of a detailed investigation into the foraminiferal biostratigraphy of the Campanian and Maastrichtian stages within the United Kingdom (Swiecicki, 1980), the stratigraphically important species Bolivinoides paleocenicus was recorded for the first time in this country. Bolivinoides paleocenicus was first described by Brotzen (1948) from strata of
Paleocene age in Sweden. Since then, it has been widely reported from strata of Maastrichtian to Lower Paleocene age in both the Boreal and Tethyan realms . B. paleocenicus is morphologically distinctive; its compressed, rapidly expanding test and intersecting network of narrow ridges, suggest that it developed from the phylogenetic lineage B. laevigatus praelaevigatus Barr 1966-B. laevigatus laevigatus Marie 1941-B. peterssoni Brotzen 1945. Certainly it appears to continue the trends towards increased test compression and restriction of ornament displayed by this lineage. However, no forms intermediate between B. peterssoni and B. paleocenicus have been observed in the British material. B. paleocenicus was encountered in material from the classic mid-Lower Maastrichtian locality of Sidestrand, Norfolk. Samples from this locality were collected with the invaluable field assistance of Mr N. B. Peake, and with reference to the lithostratigraphic sequence described by Peake & Hancock (1961, 1970). B.
paleocenicus was found to occur consistently as a rare ( < 2%) member of the microfauna recovered from the 180/, sieve fraction in samples within and above the
Sidestrand "Sponge Beds". B. paleocenicus was also found rarely in material of
Maastrichtian age from the North Sea (U.K. sector). Such a stratigraphic distribution is in close agreement with ranges reported by Reiss (1954) from Israel, and Koch (1977) from N.W. Germany, where B. paleocenicus first appears some way above the base of the Lower Maastrichtian. The exact stratigraphic level of the Sidestrand "Sponge Beds" is a matter of some debate. Wood (1967) and Rawson et al. (1978) considered, on the basis of the distribution of belemnites, that these beds spanned the boundary between the lower and upper Lower Maastrichtian (zones of Belemnella lanceolata and B. occidentalis). The foraminiferal evidence is somewhat at variance with these conclusions, however, as the widely recognized (van Hinte, 1976; Koch, 1977) index species for the upper Lower Maastrichtian Bolivinoides draco (Marsson, 1878) has not been recorded from any onshore sections in the British Isles (Barr, 1966; Swiecicki, 1980), despite the fact that it is extremely abundant in material from the North Sea (Swiecicki, 1980). Thus the foraminiferal evidence suggests a lower Lower Maastrichtian age for the entire Sidestrand complex. Whether such conflicting age assignments are due to actual discrepancies, or to more complex factors, such as palaeoecological controls on the distribution of the index belemnites and/or foraminifera, is a matter for further study.

The stratigraphic successions in the Pattani, Malay, Penyu, West Natuna and Nam Com Son Basins show many features in common, with a generalised succession driven by regional tectonics. In each basin a Late Eocene and Early Oligocene synrift phase was followed by postrift deposition from the Late Oligocene onward. The Early and Middle Miocene was characterized by variable degrees of inversion and also by extension in Nam Con Son Basin, followed by regional subsidence during the Late Miocene and Plio-Pleistocene. Accurately dating and correlating these successions has proved problematic since marine index fossils are of limited occurrence. However, using an integrated multidisciplinary sequence biostratigraphic approach tied to lithologies and seismic, it is possible to divide the succession into discrete genetic packages, which can be considered as stratigraphic sequences and can be correlated across the entire region.

The stratigraphic successions in the Pattani, Malay, Penyu, West Natuna and Nam Com Son Basins show many features in common, with a generalised succession driven by regional tectonics. In each basin a Late Eocene and Early Oligocene synrift phase was followed by postrift deposition from the Late Oligocene onward. The Early and Middle Miocene was characterized by variable degrees of inversion and also by extension in Nam Con Son Basin, followed by regional subsidence during the Late Miocene and Plio-Pleistocene. Accurately dating and correlating these successions has proved problematic since marine index fossils are of limited occurrence. However, using an integrated multidisciplinary sequence biostratigraphic approach tied to lithologies and seismic, it is possible to divide the succession into discrete genetic packages, which can be considered as stratigraphic sequences and can be correlated across the entire region.

Onshore Maastrichtian strata in the United Kingdom are limited to a few small, isolated blocks of chalk floating within glacial sediments on the Norfolk coast. Isolated outcrops of Campanian and Maastrichtian chalks used to be available around Nor-wich but the majority of these exposures are now badly degraded. Offshore, in the North Sea Basin, there are complete chalk successions that range throughout the Upper Cretaceous and Lower Cenozoic. There is a limited succession of Maastrichtian chalks exposed on the north coast of Northern Ireland below the Cenozoic flood basalts. In the Western Approaches Basin, Maastrichtian and Danian chalks are known from exploration wells and core samples. West of the United Kingdom a number of DSDP/ODP boreholes have penetrated the Upper Cretaceous succession. Beginning in the Cenomanian, in southeast England, the whole of the Upper Cretaceous is within the chalk fades, possibly one of the longest intervals of relatively stable environment in the geological record. The Foraminiferida of the chalk have been studied for more than a hundred years and therefore the fauna is exceptionally well known and fully documented. Fifty years ago, the benthonic Foraminiferida were identified as having the potential to provide a viable zonation of the chalk facies and we now have precise, cross-basinal correlation using these taxa. The planktonic fauna is restricted by both palaeolatitude and water depth. The latter appears to be the most influential as the faunas from onshore are more limited than those recorded from the deeper waters of the North Sea Basin and the Atlantic Margin. Even with this restricted fauna, however, it is still possible to develop a general correlation with the standard Tethyan zonation based on planktonic taxa.

The foraminiferal fauna from twenty-seven sections of Campanian and Maastrichtian chalk from both the onshore and offshore United Kingdom have been studied. In total, 160 species and subspecies belonging to 54 genera have been recorded and a complete revision of their systematics, with full synonomies and descriptions, has been given. The detailed stratigraphic distribution of these species has been studied, and 65 species and subspecies of prime stratigraphic importance have been recognised and employed in the definition of a tripartite biozonal scheme based on planktonic foraminifera, Bolivinoides lineages and faunal assemblages respectively. This biozonal scheme has been accurately related to local rock units as well as to current macrofossil zonations. Correlation of all sections studied has been achieved by use of the proposed biozonal scheme.
            Broad similarities have been noted between the British foraminiferal faunas of the Upper Cretaceous and those of wide areas of northern Europe, clearly placing Britain within the Transitional biogeoprovince. Palaeoecological study has indicated that marine conditions with normal salinities prevailed throughout the Campanian and Maastrichtian. Palaeotemperatures appear to have gradually declined throughout this time, with a short-lived warm phase in the latest Maastrichtian. Depths of deposition of the chalk are interpreted as having been between 150 - 250m., though greater depths probably prevailed in the North Sea basins. A transgressive phase is indicated for the Upper Campanian and a regressive phase for the Maastrichtian.

The structure and stratigraphy for many of the rift basins in the Gulf of Thailand and southern Vietnam shelf are individually well understood. However, the understanding of the region as a whole, and the relationships from one basin to another, is less clear. Regional paleogeography maps help portray the structural and stratigraphic evolution of the basins, and when constructed with precise chronostratigraphic control, provide a constraint to the interpretations of the facies distributions in individual basins. Accurate basement maps are key to understanding the tectonic framework. A number of published and proprietary maps of the pre-Tertiary exist, and all are different, some substantially so. Well data, seismic data and published/proprietary maps were used to hand contour basement across the region. A contour interval of 200 m was used to further constrain the maps. There are 22 Tertiary rift basins in the region (Figure 1), although some of the basins are composite basins consisting of several coalesced rift basins. Well data, seismic data and published/proprietary maps were also used to hand contour the top of the synrift section across the region using a contour interval of 100 m (Figure 1). The age of the top synrift section varies across the map area from Middle Oligocene in the east to Early Miocene in the northwest. Palaegeographical maps for the Oligocene and Miocene extending from the Gulf of Thailand to the Vietnam Shelf were constructed based on the succession of sequences of Morley, Swiecicki and Dung (2011). The stratigraphic framework shown in Figure 2 is color coded by the basin's tectonic activity at the time, rifting, transitional from rift to post-rift, post-rift, and inversion.