Marine Turbidites Research Articles

Silurian to mid-Devonian basin development of the Melbourne Zone, Lachlan Fold Belt, southeastern Australia

The Melbourne Zone comprises Early Ordovician to Early Devonian marine turbidites, which pass conformably upward into a mid-Devonian fluviatile succession. There are four pulses of Silurian to mid-Devonian deep-marine sandstone-dominated sedimentation: Early Silurian (late Llandovery), Late Silurian (Ludlow), earliest Devonian (Lochkovian) and late Early Devonian (Emsian). Two dispersal patterns have been defined using more than 1100 palaeocurrent measurements, mainly from sole marks and cross-laminations in graded beds, together with sandstone compositions. The older pattern, of Silurian to earliest Devonian age, contains the lowest three sandstone pulses. Palaeocurrents and provenance define a wedge of southwesterly derived sediment, of largely cratonic provenance, thinning eastward. This older dispersal pattern is part of an Early Ordovician to earliest Devonian east-facing passive continental margin succession. Palaeocurrents and provenance in the Emsian sandstone pulse comprise three patterns: (1) west- to southwesterly directed palaeocurrents associated with fine- to coarse-grained, locally conglomeratic, lithic sandstones containing a high proportion of volcanic detritus; (2) east- to northeasterly directed palaeocurrents associated with fine- to medium-grained quartz-lithic sandstones; (3) north- to northwesterly and south- to southeasterly directed palaeocurrents associated with fine- to medium-grained sandstones of variable lithic composition. The palaeocurrent and provenance pattern defines a NNW-elongate basin with a tectonically active eastern margin, and is similar to the coeval Mathinna basin of northeastern Tasmania. Both basins are part of the same system of wrench basins, which developed along the western side of the Wagga–Omeo Metamorphic Belt during the earliest Devonian to Middle Devonian. The change in tectonic setting in the earliest Devonian appears to have occurred during an interval of significant dextral translation of the eastern Lachlan Fold Belt towards the SSE along the Governor and associated fault zones.

MID TO LATE JURASSIC SHALLOW MARINE SEQUENCES OF THE EASTERN BARROW SUB-BASIN: THE ROLE OF LOW-STAND DEPOSITION IN NEW EXPLORATION CONCEPTS

Several wells drilled along the fault-terraced eastern margin of the Barrow Sub-basin of the Australian North West Shelf have shed light on the pattern of Callovian to Tithonian sedimentation in the area. Much of this section has historically been interpreted as a product of deep marine depositional environments.Sandstone reservoirs cored in Linda–1/ST1, Linda–2 (both Wanaea spectabilis b age) and Denver–1/ST1 (Rigaudella aemula age) exhibit coarsening-upward cycles typical of marine parasequences, and possess sharp, erosive lower contacts with underlying claystone. In the case of Denver–1/ST1, the sandstones are heavily bioturbated with a distinct shallow marine trace fossil assemblage. Burrows are less evident in the sandstones from the Linda wells, although several thin bioturbated horizons—also with shallow marine trace fossils—are encountered. Similar patterns of shallow marine deposition are observed in previously drilled wells within the study area, and evidence of pedogenesis is found in core from Georgette–1 (R. aemula age), suggesting that exposure occurred on some of the higher fault terraces during low-stand conditions in the Middle to Late Jurassic.Further to the west, deepwater submarine fan sediments, deposited during low-stands, have been recognised. A range of time equivalent low-stand deposits—which are spatially and genetically exclusive— therefore exists within the sub-basin. Indeed such a spectrum should be expected in complex and tectonically active areas such as the Jurassic Barrow Sub-basin.The recognition of shallow marine deposits in the area has major implications with respect to the location and geometry of reservoir sandstones. The low-stand shoreface model, as opposed to the deep marine turbidite model, leads to the prediction of sandstone deposition aligned roughly parallel—rather than perpendicular— to the palaeo-shoreline and the potential for deeperwater sandstones further downdip.

Geochronology of clasts in allochthonous Miocene sedimentary sequences on Mykonos and Paros Islands: implications for back-arc extension in the Aegean Sea

In the Cyclades, low-angle normal faults juxtaposed Miocene sedimentary rock units lying over Alpine blueschist- and greenschist-facies metamorphic rocks and Miocene granites. The sedimentary units in the hanging wall were deposited in fault-bounded basins while their footwalls progressively emerged through the ductile and brittle crust. The sedimentation in the basins evolved from marine turbidites in the Early Miocene to shallow/continental conglomerates during the Late Miocene. The transition from marine to fan delta sedimentation was coeval with widespread magmatism and possibly reflects true crustal uplift. It is inferred that the sequence is no younger than 8 Ma. K–Ar and 40 Ar/ 39 Ar geochronology, petrology and petrography of the clasts deposited on the hanging wall provide proof of progressive exhumation of the footwall and reveal the nature of the overburden that covered the Cycladic blueschist belt during Alpine orogeny in the Tertiary. Abundant metamorphic clasts yielding mica cooling ages between 80 and 100 Ma occur throughout the sedimentary section and probably pertain to a vast Pelagonian-type rock mass that covered the internal Hellenides from the Olympos to the central Cyclades. In addition, volcanic clasts dated at 10 Ma reveal the existence of a hitherto unknown volcanic province of that age in the central Aegean. Miocene crustal extension and exhumation of granitic plutons is recorded in the detrital sequence in a concentration of 10 Ma granitic clasts restricted to the top of the conglomerate sequence. A group of metamorphic clasts that yielded ages of 13–16 Ma possibly represents exhumation of mid crustal levels. Clasts similar to the currently-exposed Cycladic Blueschist Unit, such as 40 Ma old blueschists, eclogites and marble, were not found, thus indicating the very late exposure of these footwall rocks.

Sedimentation and basin evolution of the Oligocene-Miocene Mesohellenic basin, Greece

The Oligocene-Miocene Mesohellenic basin of northern Greece and southern Albania is filled with up to 4 km of marine turbidites and basin margin strata. Surface outcrops include fan deltas, prodeltaic facies, and sandy and shaly submarine fan facies. All these facies in outcrop can be directly correlated with seismic facies in the subsurface, which in turn are compared with seismic facies in modern sandy submarine fans. Twelve seismic markers provide a stratigraphic framework that has been dated by new nannofossil biostratigraphy. Lowstand facies include erosional channels on the basin slope that aggrade basinward with sandy overbank levees to give composite sand bodies with an overall lobelike character. Distally, these pass into sandy channel-termination depositional lobes. Highstand facies are characterized by shaly basin slopes and shaly turbidites in the basin, with irregular reflections interpreted to represent shallow channels and slumps. The stratigraphic occurrence of lowstand facies compares closely with published eustatic sea level curves. The basin has the potential for significant gas, principally in stratigraphic traps. The Mesohellenic basin developed as a strike-slip half graben, synchronous with the Ionian foreland basin to the west of a mountain belt formed by the Pindos nappes.

Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador

New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin.

Siliciclastic shoreline to growth‐faulted, turbiditic sub‐basins: The Proterozoic River Supersequence of the upper McNamara Group on the Lawn Hill Platform, northern Australia

The River Supersequence represents a 2nd‐order accommodation cycle of approximately 15 million years duration in the Isa Superbasin. The River Supersequence comprises eight 3rd‐order sequences that are well exposed on the central Lawn Hill Platform. They are intersected in drillholes and imaged by reflection seismic on the northern Lawn Hill Platform and crop out in the McArthur Basin of the Northern Territory. South of the Murphy Inlier the supersequence forms two south‐thickening depositional wedges on the Lawn Hill Platform. The northern wedge extends from the Murphy Inlier to the Elizabeth Creek Fault Zone and the southern wedge extends from Mt Caroline to the area south of Riversleigh Station. On the central Lawn Hill Platform the River Supersequence attains a maximum thickness of 3300 m. Facies are dominantly fine‐grained siliciclastics, but the lower part comprises a mixed carbonate‐siliciclastic succession. Interspersed within fine‐grained facies are sharp‐based sandstone and conglomeratic intervals interpreted as lowstand deposits. Such lowstand deposits represent a wide range of depositional systems and palaeoenvironments including fluvial channels, shallow‐marine shoreface settings, and deeper marine turbidites and sand‐rich submarine fans. Associated transgressive and highstand deposits comprise siltstone and shale deposited below storm wave‐base in relatively quiet, deep‐water settings similar to those found in a mid‐ to outer‐shelf setting. Seismic analysis shows significant fault offsets and thickness changes within the overall wedge geometry. Abrupt thickness changes across faults over small horizontal distances are documented at both the seismic‐ and outcrop‐scales. Synsedimentary fault movement, particularly along steeply north‐dipping, largely northeast‐trending normal faults, partitioned the depositional system into local sub‐basins. On the central Lawn Hill Platform, the nature of facies and their thickness change markedly within small fault blocks. Tilting and uplift of fault blocks affected accommodation cycles in these areas. Erosion and growth of fine‐grained parts of the section is localised within fault‐bounded depocentres. There are at least three stratigraphic levels within the River Supersequence associated with base‐metal mineralisation. Of the seven supersequences in the Isa Superbasin, the River Supersequence encompasses arguably the most dynamic period of basin partitioning, syndepositional faulting, facies change and associated Zn–Pb–Ag mineralisation.

The Rı́o Lácteo Formation of Southern Chile. Late Paleozoic orogeny in the Andes of southernmost South America

The late Paleozoic Rı́o Lácteo Formation forms the metamorphic basement of the Mesozoic and Cenozoic Andean orogenic belt in the Lago General Carrera area (about 45°S) of southern Chile. The rocks were emplaced during a late Paleozoic orogeny on the active continental margin of southernmost South America. They form part of a SW to NE striking fold belt with dominant overthrusting towards the SE. The metamorphic grade and structural style are indicative of deformation in the crystalline core of an orogenic belt, probably resulting from microplate interactions, rather than fore-arc accretion. The Rı́o Lácteo Formation represents metamorphorphosed marine turbidites, limestones and pyroclastic rocks which accumulated in an intraplate setting. The strata were intensely deformed and subjected to medium grade, greenschist to epidote-amphibolite facies metamorphism in pre-late Carboniferous times. Four phases of deformation have been identified. The first phase produced a strong planar fabric. This was followed by subhorizontal SW to NE stretching and NW to SE compressive shortening. The third phase formed a spaced cleavage related to E-W extension. The fourth episode produced broad shear zones, characterised by chevron folding and intrusive dykes of crush breccia, related to thrusting towards the southeast.

Towards a more complete record of magmatism and exhumation in continental arcs, using detrital fission-track thermochrometry

The NE Asian margin was the locus of an Andean-style subduction zone during most of the Mesozoic and Cenozoic. The Ukelayat flysch is a 10 to 15 km thick section of marine turbidites that were deposited in a 500 km long forearc basin along the outboard edge of this convergent margin. It was structurally overridden during the early Tertiary by an obducted island arc, the Olytorsky terrane. We present new fission-track (FT) grain ages from unreset detrital zircons. These data provide precise information about depositional age of the Ukelayat and the temporal evolution of the Asian margin continental arc, which provided much of the sediment for the Ukalayat. Because all sandstones contain a large fraction of first-cycle volcanic zircons (euhedral, colorless), we infer that the youngest component of the FT grain age distribution, designated P1, closely approximates the time of deposition. Twenty-seven samples have yielded P1 ages ranging from ~44 to 88 Ma, which indicates continuous magmatic activity in the arc from the Late Cretaceous to Middle Eocene. A second component (P2) records progressive exhumation of the basement to the Okhotsk-Chukotka arc. The difference between P1 and P2 ages indicates steady exhumation at ~200–400 m/Myr from ~90 to 44 Ma. This finding implies the removal of 9 to 18 km of rock in the most deeply exhumed parts of the source region. A change in exhumation rates at ~70 Ma may coincide with an eastward shift in the locus of volcanism from the Okhotsk-Chukotka arc to the younger Western Kamchatka-Koryak arc.

Structure and stratigraphy of the south flank of the Kisseynew Domain in the Trans-Hudson Orogen, Manitoba: implications for 1.845-1.77 Ga collision tectonics

On the south flank of the Kisseynew Domain, orthogneisses derived from 1.92-1.85 Ga volcano-plutonic rocks are overlain by paragneisses (Burntwood and Missi groups) derived from 1.855-1.84 Ga marine turbidite and 1.845-1.83 Ga terrestrial clastic and volcanic rocks. The sediments in these groups are interpreted as having been shed into the Kisseynew paleobasin from an active margin bordering the Flin Flon Belt. The sedimentation apparently followed early microcontinental collision and accompanied the last arc magmatism in the Trans-Hudson Orogen. The sedimentary rocks and their basement were deformed into a complexly refolded stack of large recumbent folds. Premetamorphic F1 structures represent a fold and thrust system initiated during the sedimentation. These structures are interpreted as transported toward the Kisseynew Domain in the northeast and the hinterland in the southwest. F2 structures (~1.82 Ga) comprise westerly transported nappes. During 1.82-1.80 Ga high-grade metamorphism, the early structures were overturned, amplified, and refolded. Basement-cored culminations and sheet-like synforms of paragneiss were horizontally attenuated and transported south and southwest. North- and northeast-trending F4 folds and F5 faults formed after 1.79 Ga. The whole cycle of deformation is related to stages of continental collision between the internal (juvenile) zone of the Trans-Hudson Orogen and the three surrounding Archean cratons (Sask, Superior, and Hearne). The F4 upright folds and steep F5 faults are interpreted as the record of intracontinental transpression, strongly controlled by the Superior Craton boundary.

Petroleum systems analysis of the Paleocene play in the West of Shetland area

The Lower Tertiary petroleum system in the West of Shetland area has been reconstructed by integrating sequence stratigraphical interpretation, pressure data analysis and basin modelling with hydrocarbon migration pathways prediction. Twelve sequences in the Paleocene–Early Eocene section can be grouped into three sequence sets. The lower two sequence sets are dominated by deep marine turbidite fan reservoir sandstones encased within hemipelagic shales. The youngest sequence set is dominated by a series of prograding delta facies rocks. A regionally extensive shale, deposited during a marine flooding event sits at the top of the oldest sequence set. This shale is an effective regional seal and pressure barrier. A study of well pressure data and sedimentary facies variations within the oldest sequence set has led to the identification of three pressure cells. Structural modelling, heat flow mapping, vitrinite reflectance and apatite fission track analysis were used to reconstruct the thermal history West of Shetland. From this dataset, the Kimmeridge Clay Formation source-rock maturity and hydrocarbon generation history were modelled for several time periods. These results were used to generate migration pathways at the Base Tertiary unconformity which sits stratigraphically below the reservoirs in the oldest Paleocene to Eocene sequence set. The resulting model predicts an oil-prone southern province and gas-prone central province which accords with the Foinaven and Schiehallion oil fields in Quadrant 204 and the gas discoveries in Quadrants 206 and 214. The model also suggests the possibility of further oil potential in Quadrant 208.

Magnetic stratigraphy and tectonic rotation of the Middle Eocene Matilija Sandstone and Cozy Dell Shale, Ventura County, California: implications for sequence stratigraphic correlations

The Matilija Sandstone and Cozy Dell Shale in the western Transverse Ranges of California record a long history of Eocene regression from deep marine turbidites to non-marine red shales and then transgression to deep marine shales in a rapidly subsiding tectonic basin. In its type area along the Ventura River north of Ojai, the Matilija Sandstone consists of over 800 m of deep marine to non-marine sandstones, and the Cozy Dell Shale contains over 760 m of deep marine shales and turbidite sandstones. Paleomagnetic sampling of these rocks yielded a stable magnetic remanence which passed both a fold test and a reversal test; some samples were reversed at NRM after dip correction. Based on calibration from planktonic microfossils, the Matilija Sandstone spans the interval from Chron C21r to early Chron C20r (46.0–48.5 Ma), and the Cozy Dell from late Chron C20r to C19r (46.0–42.0 Ma). The samples show a tectonic rotation of approximately 85±18° clockwise, consistent with previous results reported for this tectonic block. Previous sequence stratigraphic correlations of these rocks are inconsistent with this chronostratigraphy. None of the sequence boundaries predicted from these sections matches the global sequence chart.

Accelerating late Quaternary uplift of the New Georgia Island Group (Solomon island arc) in response to subduction of the recently active Woodlark spreading center and Coleman seamount

The New Georgia Island Group of the Solomon Islands is one of four places where an active or recently active spreading ridge has subducted beneath an island arc. We have used coral reef terraces, paleobathymetry of Neogene sedimentary rocks, and existing marine geophysical data to constrain patterns of regional Quaternary deformation related to subduction of the recently active Woodlark spreading center and its overlying Coleman seamount. These combined data indicate the following vertical tectonic history for the central part of the New Georgia Island Group: (1) subsidence of the forearc region (Tetepare and Rendova Islands) to water depths of ∼1500 m and deposition of marine turbidites until after 270 ka; (2) late Quaternary uplift of the forearc to sea level and erosion of an unconformity; (3) subsidence of the forearc to ∼500 m BSL and deposition of bathyal sediments; and (4) uplift of the forearc above sea level with Holocene uplift rates up to at least 7.5 mm/yr on Tetepare and 5 mm/yr on Rendova. In the northeastern part of the New Georgia Island Group, our combined data indicate a slightly different tectonic history characterized by lower-amplitude vertical motions and a more recent change from subsidence to uplift. Barrier reefs formed around New Georgia and Vangunu Islands as they subsided >300 m. By 50–100 ka, subsidence was replaced by uplift that accelerated to Holocene rates of ∼1 mm/yr on the volcanic arc compared with rates up to ∼7.5 mm/yr in the forearc area of Tetepare and Rendova. Uplift mechanisms, such as thermal effects due to subduction of spreading ridges, tectonic erosion, or underplating of deeply subducted bathymetric features, are not likely to function on the 270-ka period that these uplift events have occurred in the New Georgia Island Group. A more likely uplift mechanism for the post-270-ka accelerating uplift of the forearc and volcanic arc of the New Georgia Island Group is progressive impingement of the Coleman seamount or other topographically prominent features on the subducting plate. Regional effects we relate to this ongoing subduction-related process include: (1) late Quaternary (post-270 ka), accelerating uplift of the Rendova–Tetepare forearc area in response to initial impingement of the Coleman seamount followed by exponentially increasing collisional contact between the forearc and seamount; (2) later Quaternary propagation of uplift arcward to include the volcanic arc as the area of collisional contact between the forearc and seamount increased; and (3) large-wavelength folding that has produced regional variations in late Holocene uplift rates observed in both forearc (southern Rendova, Tetepare) and volcanic arc (New Georgia Island) areas. We propose that the dominant tectonic effect of Coleman seamount impingement is horizontal shortening of the forearc and arc crust that is produced by strong coupling between the subducting seamount and the unsedimented crystalline forearc of the New Georgia Island Group. The horizontal forces due to mechanical resistance to subducting rugged ridge and seamount topography may have terminated spreading of the Woodlark spreading center entering the trench (Ghizo ridge) and converted it to a presently active strike-slip fault zone.

Análise estratigráfica de fácies, proveniência e paleocorrentes do grupo Camaquã (transição Proterozóico-Fanerozóico) na Mina Uruguai e suas implicações na evolução tectono-sedimentar da Bacia do Camaquã, RS

The open pit of the Uruguai Mine, in the Minas do Camaquã region, presents the best exposures of the Camaquã Group. Stratigraphic analysis of facies, paleocurrents and provenance show that the Camaquã Group deposits are organized in two lithostratigraphic units: Rhythmites and Sandstones at the base of the exposure and Conglomerates and Sandstones at the top. The top unit was divided by the CBC (Companhia Brasileira do Cobre) team into three sub-units: Lower Conglomerate, Intermediate Sandstone and Upper Conglomerate. The Rhythmites and Sandstones unit is represented by marine turbidites and sandstones of shallow water and transitional environments. The Lower Conglomerate unit is composed mainly by pebbly conglomerates and sandstones formed in subaqueous fans. Provenance and paleocurrents analysis of these two units indicate source áreas composed of volcanic acid rocks, granites and metamorphic rocks located S and SW. The Upper Conglomerate is composed by cobble and boulder conglomerates of alluvial fan environment, derived from mylonites and granites located SE and reworked sedimentary rocks of the lower units of the Camaquâ Group.

The Triassic and associated rocks of the Nakhlak and Aghdarband areas in central and northeastern Iran as remnants of the southern Turanian active continental margin

ABSTRACT The Triassic succession of the Nakhlak area in central Iran consists of (1) the LithologicallAlam Formation, which is a sequence of shallowing- and coarsening-upward marine turbidites deposited equon the forearc side of an accretionary prism; (2) the Baqoroq Formation, a resentatsequence of coarse to fine, polymictic, fluvial conglomerates; and (3) the Ashin For- mation, which comprises alternating, distal marine shales and sand- stones that have turbiditic characteristics. These rocks are wnot litholog- ically similar to time-equivalent lithostratigraphic units of Late Permian – Triassic age of the Aghdarband area of northeastern Iran (which are interpreted to be forearc deposits), but they may have formed in close association with them in a single tectonic and sedimen- tary framework. Accepting the 135° counterclockwise rotation of the central-east Iranian microcontinent authorwith respect to the Turan plate since Triassic time, and assuming that the Triassic rocks of the Nakhlak and the Late Permian to Triassic rocks of the Aghdarband formed in a single tectonosedimentary framework on the no rthern side of the paleo-Tethyan oceanic realm, we present here a sequential develop- ment. In this scheme, rocks of the bNakhlak and Aghdarband areas are considered deposits of a forearc, basin-ridge-slope centralenvironment. The separation of the Nakhlak succession from the rest of the Turan plate and its transportation to central Iran might have occurred as (1) a lithospheric segmen t of the Turan plate, first detached from Turan and then attached to the Iranian plate, and finally rotated with it in a coun- terclockwise direction to successionits present site; or (2) as a thin thrust slice first obducted over th e Iranian continental shelf and then displaced to cen- tral Iran by its counterclockwise rotation. INTRODUCTION

Tectonic controls on facies transitions in an oblique collision: The western Solomon Sea, Papua New Guinea

The western Solomon Sea is the site of a closing ocean basin and an incipient arc-continent collision between the Bismarck arc and the Australian continental margin in Papua New Guinea. Migrated seismic reflection profiles and HAWAII MR1 sidescan sonar data indicate that sedimentation within the Solomon Sea basin is controlled by topographic gradients generated by flexure of the Solomon Sea plate. Turbidites delivered to the basin by the submarine Markham Canyon extend farther eastward down the axis of the deeper New Britain Trench (north side of the Solomon Sea) than they do in the shallower Trobriand Trough (south side of the Solomon Sea). The stratigraphic record of the foredeep, in the zone of arc continent collision, is controlled by the steep topography of the Australian continental margin. A long (1.5–3 m.y.) period of deep marine turbidite deposition is followed by a short (50–100 k.y.) period of shallow-marine deposition and a long (0.5–1 m.y.) period of fluvial deposition. Comparisons between the foredeep record of Taiwan and the Papua New Guinea collision indicate that the steep topography of the Australian continental margin exerts significant control over the evolution of the foredeep, and the Taiwan foredeep is more controlled by the dynamic link between the flexural properties of the lithosphere and the orogenic load.

Late Eocene to Early Miocene depositional environments of the Mesohellenic Basin, North-Central Greece: Implications for hydrocarbon potential

Late Eocene to Early Miocene Mesohellenic Basin deposits accumulated in a tectonically controlled basin with irregular and narrow shelves. The boundaries between the Eocene-Oligocene Krania-Eptachori Formations and the Oligocene-Miocene Eptachori-Pentalophos Formations record the global sea-level falling during the corresponding time intervals. The sediments of the Mesohellenic Basin have characteristics of lowstand fan deposits without coastal onlap. It is suggested that the concept of the hydrocarbon habitat is applicable to the Mesohellenic Basin due to the following characteristics of the studied deposits: (a) The outer fan sandstones lobes, classified in this work as suprafan lobes, are characterized by stacked channel sand bodies with good lateral and vertical communications. These features constitute excellent reservoir facies. (b) The fme-grained, lobe-fringe and basin-plain deposits of the studied marine turbidites may have operated as either fertile source rocks or topseals. (c) The geometry ofthe lobes (stacked channel sand bodies) and the internal unconformities (between the four formations) present excellent stratigraphic traps. (d) The synchronous evolution of these deposits assures the timely relationship among all factors listed above. Since the studied sediments correspond mostly to the western margin deposits it is very possible that basinwards, in the direction of the progradation, the interchannel deposits must laterally pass into, the outer fan sandstone lobe, lobe fringe and basin plain deposits. Therefore, sediments of the basin interior not presently exposed are very likely to support favourable conditions for petroleum play.

Play concepts-northwest Palawan, Philippines

The offshore area of northwest Palawan, Philippines, contains a number of provenexploration plays. These include u • pinnacle reefs developed on Nido carbonate platforms (e.g. Nido, Matinloc, Cadlao); • a seaward horst block reef fairway with large pinnacle reefs (e.g. Malampaya—Camago trend); • early Miocene Galoc Clastic Unit turbidites (e.g. Octon, Galoc); and • four-way dip closures (e.g. West Linapacan, Octon). The recent discovery by Fletcher Challenge Petroleum at Calauit Field has shown a potentialexploration play in deep-water Nido Limestone turbidites. The traditional and, to date, only economically productive play in northwest Palawan has been the Nido Limestone reefs. This paper presents a review of the old play types and presents new untested play types. These new play types include u • pre-Nido syn-rift plays; • pre-Nido marine turbidite play: and • mid-Miocene reefs. It also presents new insights into factors controlling reef development on the carbonate platforms where four reef types are now recognized. The Galoc Clastic Unit turbidite play is discussed and new play fairways presented.

Play concepts-northwest Palawan, Philippines

The offshore area of northwest Palawan, Philippines, contains a number of provenexploration plays. These include u • pinnacle reefs developed on Nido carbonate platforms (e.g. Nido, Matinloc, Cadlao); • a seaward horst block reef fairway with large pinnacle reefs (e.g. Malampaya—Camago trend); • early Miocene Galoc Clastic Unit turbidites (e.g. Octon, Galoc); and • four-way dip closures (e.g. West Linapacan, Octon). The recent discovery by Fletcher Challenge Petroleum at Calauit Field has shown a potentialexploration play in deep-water Nido Limestone turbidites. The traditional and, to date, only economically productive play in northwest Palawan has been the Nido Limestone reefs. This paper presents a review of the old play types and presents new untested play types. These new play types include u • pre-Nido syn-rift plays; • pre-Nido marine turbidite play: and • mid-Miocene reefs. It also presents new insights into factors controlling reef development on the carbonate platforms where four reef types are now recognized. The Galoc Clastic Unit turbidite play is discussed and new play fairways presented.

Reservoir architecture of syn-rift lacustrine turbidite systems, early Cretaceous, offshore South Gabon

Abstract The Lucina Formation of offshore South Gabon comprises deep lacustrine facies deposited in an early Cretaceous rift lake. Both channellized and non-channellized turbidite sandbodies occur enclosed in deep-lacustrine mudstones. These sandbodies provide reservoirs in the Lucina and Lucina West Marine fields. Dramatic changes in sandstone body thickness occur from SW to NE across the strike of the rift lake. This was a consequence of the confinement of high-density sandy turbidity currents in fault-related lake-floor depressions. Limited palaeoccurrent data from orientated core indicate sediment transport from the SW towards the NE. This represents supply from the ramp margin of the lake towards the fault system bounding the lake along its northeastern margin. The modern Lake Malawi provides an analogue in terms of genetic elements and sediment distribution patterns. In addition, ancient marine turbidite systems such as those of the Oligo-Miocene fill of the Tertiary Piedmont Basin, Northwest Italy, provide insights into the relationships between topography in the receiving basin and sandbody geometries.

Appraisal geology of the Saltire Field, Witch Ground Graben, North Sea

Saltire is a structurally and stratigraphically complex field that lies within the Witch Ground Graben. It is located 200 km northeast of Aberdeen, Scotland in UK North Sea Block 15/17. Three sandstone reservoirs contain an estimated 224 × 10 6 BBL of oil-in-place within a 2500 acre closure. The field was discovered in 1988. Subsequent appraisal drilling incorporated 3D seismic and detailed stratigraphic studies to produce the coherent geological reservoir models needed for development planning. Field production will begin in 1993. The Upper Jurassic section contains the Piper and Galley sandstone reservoirs which occur within a broad, E-W-orientated fault terrace. Northerly closure results from a down-to-the-south normal fault. Southern and westerly closures result from Piper sandstone erosional truncation and Galley sandstone pinch-out. Both reservoirs have easterly dip closure. The Piper Formation is a fluvial to wave-influenced deltaic marine sequence of latest Oxfordian to mid-Kimmeridgian age. It is up to 280 ft thick. The reservoir is fault separated into Main and Western areas with API oil gravities of 42.5° and 38°, respectively. The Galley sandstone reservoir contains 42.5° API gravity oil and occurs within the northeast area. It is a deep marine turbidite sequence of late Kimmeridgian age and has a maximum reservoir thickness of 205 ft. An Early Cretaceous sandstone reservoir occurs within the upper Valhall Formation. It comprises two marine turbidite sandstones of late Barremian to early Aptian age, with up to 95 ft of composite thickness. The reservoir has three-way dip closure, pinches out by onlap to the north and contains 33° API gravity oil.