Tectono-stratigraphic units division for the Upper Cambrian through Upper Cretaceous successions of the Wadi Sirhan Basin, SE Jordan: a case study of stratigraphic features and implication for hydrocarbon prospectivity

The Olkaria geothermal field is located in the Kenya Rift valley, about 120 km from Nairobi. Geothermal activity is widespread in this rift with 14 major geothermal prospects being identified. Structures in the Greater Olkaria volcanic complex include: the ring structure, the Ol’Njorowa gorge, the ENE-WSW Olkaria fault and N-S, NNE-SSW, NW-SE and WNW-ESE trending faults. The faults are more prominent in the East, Northeast and West Olkaria fields but are scarce in the Olkaria Domes area, possibly due to the thick pyroclastics cover. The NW-SE and WNW- ESE faults are thought to be the oldest and are associated with the development of the rift. The most prominent of these faults is the Gorge Farm fault, which bounds the geothermal fields in the northeastern part and extends to the Olkaria Domes area. The most recent structures are the N-S and the NNE-SSW faults. The geochemistry and output of the wells cut by these faults have a distinct characteristic that is the N-S, NW-SE and WNW-ESE faults are characterized by wells that have high Cl contents, temperatures and are good producers whereas the NE-SW faults, the Ring Structure and the Ol’Njorowa gorge appear to carry cool dilute waters with less chloride concentration and thus low performing wells. Though the impacts of these faults are apparent, there exists a gap in knowledge on how wide is the impact of these faults on the chemistry and performance of the wells. This paper therefore seeks to bridge this gap by analysis of the chemical trends of both old wells and newly drilled ones to evaluate the impacts of individual faults and then using buffering technique of ArcGis estimate how far and wide the influence of the faults is. The data was obtained after the sampling and analysis of discharge fluids of wells located on six profiles along the structures cutting through the field. Steam samples were collected with a stainless steel Webre separator connected between the wellhead and an atmospheric silencer on the discharging wells whereas the analysis was done in house in the KenGen geochemistry laboratory. The results indicates that Olkaria field has three categories of faults that control fluid flow that is the NW-SE trending faults that bring in high temperature and Cl rich waters, and the NE-SW trending Olkaria fracture tend to carry cool temperature waters that have led to decline in enthalpies of the wells it cuts through. The faults within the Ol Njorowa gorge act to carry cool, less mineralized water. Though initially, these effects were thought to be in shallow depths, an indication in OW-901 which is a deeper at 2200 m compared to 1600 m of OW-23 well that proves otherwise. This is, however, to be proved later as much deeper wells have been sited.

The variability and complexity of active plate margins require that the identification of units of previously active margins in orogenic belts be done with care and sophistication. Tectonostratigraphic units from active margins vary not only as sedimentation and plate kinematic parameters change spatially, but also temporally, as these parameters evolve. Deposits from the trench, lower slope basins and upper slope or forearc basins may be distinguished using the distinctive structural styles, sedimentation pat terms, and lithologic content observed within each unit. The relative positions and characteristics among the units are equally important criteria. INTRODUCTION Recent geological and geophysical investigations, interpreted in the framework of plate tectonics, have produced a general geological model of convergent plate margins. Nevertheless, one of the most important objectives, that of identifying various elements of a previously active margin within an orogenic belt, remains elusive. The field geologist, if he is to interpret the evolution of the complexly deformed mountain belts formed by plate convergence, must be able to deduce the original tectonic settings of the various tectonostratigraphic units which are now deranged by younger overprinting and by large-displacement faulting. The purpose of this paper is to review diagonistic characteristics of the various packages of rocks produced within a convergent plate margin with which these units might be identified after their morphology is destroyed. An admonition is immediately required. There is no typical arc system, but rather a broad spectrum of responses arising from a single basic process. As a result, in this setting, perhaps more than in any other, identification using simple criteria can lead to serious error. Only a comprehensive integration of data and an adequate knowledge of arc behavior is likely to produce the correct interpretation. Convergent plate margins range from oceanic island arcs involving very little sediment to continental margin arcs which often have several kilometers of sediment on the descending plate. These differences are reflected in wide variations in size, shape, and lithologic content of units [Fig. 1]. Not only do convergent margins vary spatially, but also temporally as sedimentation and kinematic parameters change. To compound the difficulty, morpho tectonic units are the basis for subdivision in active arc systems whereas in orogenic belts, only lithologic structural entities (tectonostratigraphic units) remain. These may differ because a given tectonostratigraphic unit may be involved in several different morphotectonic units the arc evolves. For example, a block of trench turbidite rapidly becomes part of the lower trench slope. Later this same block of rock may become part of the basement beneath a forearc basin or even later may become part of the frontal arc, but when mapped in the field as a melange, it cannot be used to locate that frontal arc until temporally correlative information on other arc units is available.

For the identification of the North European platform below the Western Carpathian Flysch belt and for the definition of the lithospheric and crustal relationships in the collisional zone between the Western Carpathian block and the North European platform, two migrated reflection seismic profiles with deep registration were chosen in the eastern sector of the Western Carpathians. Both of them were newly reprocessed (1999–2000), deep and composite seismic profiles, which define some new features in the geological structure in the eastern part of the Western Carpathians. From a general point of view, both seismic profiles are dominated by a fanwise (flowerlike) structure. However, we define this structure as fanwise, because in many features, it looks like a classic flower structure. The described fanwise structure has a great impact on the final form of the collisional zone. The impact of the fanwise structure is also clearly visible on both seismic sections in the area of the Inner Carpathian Paleogene basin. The Inner Carpathian Paleogene basin base dips moderately toward the Pieniny Klippen Belt in the northeast, and according to our interpretation of seismic lines, the Inner Carpathian Paleogene basin sedimentary package is divided into three or four structural levels (the oldest level is built up by basal Paleogene sediments, and the overlying folded Sambron Member beds consist of two structural levels and three structural levels [our opinion] of sediments; see mainly seismic section AB below). What is very interesting is that the uppermost level of the Sambron Member beds displays clear extensional features. The Pieniny Klippen Belt is a major tectonic unit at the surface, where it separates the Outer and Inner Western Carpathians. However, both seismic lines reveal that the Pieniny Klippen Belt has no continuous depth prolongation as a tectonostratigraphic unit. The seismic image allows an interpretation of an older subhorizontal structure of laterally wedging-out and interfingering rock units that originated by collisional processes in a wider zone associated with the Pieniny Klippen Belt. Younger and steep brittle structures that accompany the Pieniny Klippen Belt and its surroundings may be traced to great depths where they merge into a subvertical fault zone. This fanwise fault zone closely resembles a transpressional flower structure. From the point of view of hydrocarbon prospection, the most important feature of both seismic lines is the anticline structure of the North European platform below the thrust stack of the Flysch belt. This strong reflection package probably indicates the presence of carbonates in the North European platform cover (see seismic profile AB below). In our opinion, this structure is the most attractive for hydrocarbon exploration in the eastern part of the Slovakian Flysch Belt.

In the supercontinent of Rodinia, Baltica occurred next to Amazonia, then the two drifted away when Rodinia broke up. By the end of the Neoproterozoic, Baltica became an independent continent. At that time, Timanide orogen developed at its modern northeastern margin. In most paleogeographical reconstructions, the opposite (SW, Tornquist) edge faced the Tornquist Ocean and remained just a passive margin till the arrival of the Gondwana-born East Avalonia in the late Ordovician. However, preliminary isotopic studies of detrital zircons from the Tornquist passive margin succession hinted that rock components of Gondwana derivation reached Baltica already in the early Cambrian. In this paper, we examine 18 drill-cores of Ediacaran-Cambrian and Ordovician siliciclastic rocks from the tectonostratigraphic units along the SW–NE transect from Upper Silesia (USB) via Małopolska (MB) and the Holy Cross Mts (HCM) to the East European Platform (EEP), SE Poland, in terms of the provenance data gained from the LA-ICP-MS and SHRIMP analyses of 32 zircon samples. Rocks from all the units revealed abundant Cadomian 0.7–0.55 Ga detrital zircons (15–50% of the total analyzed grains) and other grains that yielded peaks at 0.9–1.2, 1.4–1.6, 1.8–2.2, 2.7–3.0 Ga assignable to Baltica rather than Amazonia. Such age spectra in the USB, HCM and EEP prove the proximity of peripheral (peri-Gondwanan) fragments of the Cadomian orogen to Baltica. These fragments formed the Teissyere-Tornquist Terrane Assemblage (TTA) that obliquely docked and overrode the thinned southwestern edge of Baltica which earlier accumulated Neoproterozoic rift and passive margin deposits. Our data show that in the late Ediacaran-early Cambrian, parts of the Cadomian orogenic belt became accreted to Baltica.

The Vienna Basin is located in the transition zone between the Alps and the Carpathians. Its tectonostratigraphic structure is complex, and includes from base to top crystalline basement, autochthonous Mesozoic sediments, Cenozoic foreland basin deposits, the Alpine nappe system and a thick Neogene basin fill. The Vienna Basin area hosts one of the major hydrocarbon provinces of Central Europe, but also a significant geothermal potential. The petroleum system is mainly based on the Upper Jurassic Mikulov source rock in the authochthonous succession, which became mature during nappe stacking and Neogene basin subsidence. Migration along faults and via basement highs filled oil and gas reservoirs in all tectonostratigraphic units. Despite a 100-year-long exploration history, new discoveries are still being made. Two geothermal systems are known in the Vienna Basin. One system is based on hot fluids ascending along the major faults in the southern part of the basin and has been used for balenological purposes since Roman times. The other is based on deeply buried, highly permeable carbonate rocks in the Alpine wedge (e.g. Hauptdolomite Formation) and clastic reservoirs in the Neogene basin fill. Current projects aim to supply the city of Vienna with geothermal heat from Lower Miocene fluvial conglomerates.

Subduction accretionary complexes are composed of major and minor structural, stratigraphic, and tectonostratigraphic units. The major architectural units, Accretionary Units (AUs), are bounded by major faults, but differ from terranes in that they may contain units stratigraphically correlative with units in other AUs and they are smaller than the largest terranes. AUs occur in three basic formats – (1) singular sheets or blocks of stratigraphic layers, dismembered formation, or mélange, (2) folded units composed of one or more stratigraphic or block-in-matrix units, and (3) faulted stratigraphic masses (i.e., broken formations). Composite AUs with multiple units and multiple attributes are common. Multiple suites of structures may arise in AUs from progressive early deformation or later superimposed deformational events. AUs may be subdivided through detailed mapping into sub-units such as fault blocks, mélanges, dismembered formations, broken formations, intact formations, and members. Each AU should be defined on the basis of unique characters that derive from a thorough description of the AU, including its distinct rock types and character; and where possible, lithofacies, metamorphic facies, structures, and unit history. Descriptions of partially described AUs from the Franciscan Complex of California and the Miura-Boso area of Japan provide examples of the character of AUs. Ideally, the architecture and history of a subduction complex can be reconstructed by assembling detailed map and text descriptions of the constituent AUs, their 3D-positions, their relationships, and their histories.

Seismic stratigraphic interpretation of megasequence and sequence framework in the Upper Cambrian through Devonian formations in the central part of the Darling Basin, western New South Wales, Australia

Structure and geodynamic evolution of the Central Bransfield Basin (NW Antarctica) from seismic reflection data

The Franciscan subduction complex of northern California includes several tectonostratigraphic units. We have used the technique of vitrinite reflectance to document levels of thermal maturity for the Central Belt and the Yager, Coastal, and King Range terranes. Spatial variations in thermal maturity help define the thermal structure of each Franciscan terrane, and each terrane displays a different geometry of thermal structure. These differences are controlled by the style of structural deformation, the overprinting effects of deformation following metamorphism, and thermal overprinting caused by hydrothermal circulation. Anomalies along and contrasts across terrane boundaries help establish the relative timing and the structural mechanisms of terrane amalgamation. For example, localized anomalies are evident along the Eel River fault (Central-Yager boundary), and these increases in thermal maturity may be due to shear heating, hydrothermal discharge, or conductive heat transfer across the fault. Cross-c...

Underground storage of green hydrogen in depleted gas fields could provide Aotearoa New Zealand (ANZ) with a storage option critical for meeting peak energy demands and realising green hydrogen ambitions. During early de-risking of specific sites, it is important to develop an accurate geological model to test whether the reservoir has the desired containment, volume and hydrogen deliverability. However, where seismic reflection lines and well data are limited and/or the storage system is structurally complex, the resulting geological models may be non-unique. Therefore, injection and withdrawal simulations using different structural end members is critical to constrain how a hydrogen plume may flow within (and out of) the container and interact with existing reservoir fluids.Here we present workflows for modelling a multi-year injection and withdrawal cycle of hydrogen into a depleted gas field. We use data from the Tariki Sandstone Member of the Ahuroa field in the Taranaki Basin, currently used to store natural gas in ANZ. This reservoir is located 2 km deep at the crest of an anticline above a major thrust fault, with marine mudstones forming the top seal and low-permeability fault rock the lateral seal. With only mixed quality 2D seismic reflection lines and a tight well cluster, the precise geometry of the thrust fault and its relations to smaller secondary faults is poorly constrained.To capture this uncertainty in our simulations, we have developed two 3D geological models of the Ahuroa field in Leapfrog Energy software. We use these geological models to conduct dynamic simulation of hydrogen injection and withdrawal using the massively-parallel simulator PFLOTRAN-OGS. We develop simulations that allow us to, over a 10-year cycle, test for closure or spill into adjacent fields, and predict the amount of mixing with remnant natural gas and formation water. During the simulations, we see major differences between the two geological models related to cushion injection and working H2 volumes, rates of water production and impurities due to natural gas. Additionally, one model has high risks of unrecoverable H2 gas loss when over-pressurised. Finally, we reimport the results back into Leapfrog for visualisation of the behaviour of the two hydrogen plumes over time.

The Pacheco Pass area, well known for the relatively high-pressure, low-temperature mineral assemblages developed in a well-ordered section of chiefly metaclastic strata, was restudied in order to elucidate the geologic, paragenetic, and textural relationships among the various lithologic units. The mapped 7½ minute quadrangle extends from 4 km west of the range crest eastward to the Ortigalita fault, tectonic contact of the Franciscan assemblage with coeval Great Valley strata. Semicontinuous metachert beds, underlain by scraps of Na-cpx- and/or Na-amphibole-bearing metabasaltic rock, mark the base of terrigenous tectonostratigraphic units, evidently decoupled from the downgoing, oceanic-crust-capped plate. Underplating along newly recognized bedding-plane faults has juxtaposed members of an apparently conformable Franciscan sedimentary sequence. Four depositional units, each consisting of monotonous metagraywacke and interlayered metashale, are stacked within the accretionary section: from top down, these are tectonostratigraphic members A, B, C, and D. Unit D differs from overlying members in possessing a greater abundance of bluestone/greenstone pods, minor serpentinite bodies, and rare metaconglomerate lenses; varying degrees of stratal disruption indicate that it has been arrested in the transformation to broken formation. The Ortigalita fault is nearly vertical, strikes north-northwest, and exhibits apparent dextral offset; it truncates the east-west-striking Gonzaga fault and other Franciscan structures. The topographic low occupied by San Luis Reservoir is a Cenozoic tectonic depression sited at a releasing bend on the Ortigalita fault. Newly acquired textural, chemical, mineralogic, and areal relations of albitic and jadeitic pyroxene-bearing Franciscan metagraywacke near Pacheco Pass demonstrate that (1) Na-cpx and Na-amphibole are metamorphic minerals, not clastic materials; (2) pumpellyite is a minor neoblastic phase in albite-bearing metagraywacke west of Pacheco Pass, and in the north-western corner of the quadrangle, but it does not occur in jadeitic pyroxene-bearing metaclastic rocks; (3) higher textural grade metagraywacke specimens generally contain higher modal proportions of jd; (4) abundance, textural grade, and chemistry of Na-cpx are not related to tectonostratigraphic units; and (5) because of sluggish reaction rates, albite persisted metastably into the higher pressure, jadeitic pyroxene + quartz P-T field. Production of Na-cpx resulted from a reaction of the sort ab + chl = jd + Iws + qtz ± gln ± H 2 O. Irregular, oscillatory zoning within single jadeitic pyroxene prisms and variable jd/ab modes for rocks of the same bulk composition reflect growth governed by diffusion rather than recrystallization within a P-T transition zone; high-pressure overstepping of the phase boundary explains variable modal proportions of ab and jd, as well as chemical heterogeneity of the jd. Elevated P attended metamorphism of Na-cpx-bearing rocks exposed in the Pacheco Pass area, as indicated by the wide-spread coexistence of quartz and NaAlSi 2 O 6 - rich pyroxene. Inferred physical conditions of prograde metamorphism were 150 ± 50 °C at 7-8 kbar or more. Franciscan rocks in the east-central Diablo Range underwent subduction-zone metamorphism accompanying paleo-Pacific lithospheric plate descent during mid-Cretaceous convergence. Underplating, contraction, and sequestering of the tectonostratigraphic assembly at depths of 25-30 km during underflow, followed by gradual rise, took place under conditions of refrigeration due to protracted descent of the oceanic slab. Paleogene diapiric uplift and extension followed, indicating more complete decoupling of the buoyant trench complex from the downgoing plate. Finally, passage of the East Pacific Rise triple junction in Neogene time initiated the present dextral-slip regime in the California Coast Ranges.

The emplacement of igneous material into upper crustal rocks of sedimentary basins is likely to be strongly controlled by the geometry of the pre-existing basin structures. These controls are investigated using examples from the Tertiary igneous complexes of Skye, part of the Sea of Hebrides basin of NW Scotland. The basin consists of an array of half-graben related to SE-dipping normal faults. These pre-volcanic, Mesozoic structures are traced near the igneous complexes using geological relationships preserved unconformably beneath the widespread basaltic lava fields. The unconformity represents a period of Cretaceous uplift and denudation of the basin and its flanks, entirely pre-dating the Tertiary volcanism of NW Scotland. This unconformity seals stratigraphically the major basin faults, preserving field relationships that permit the tracing of these faults in the country rocks to the Tertiary intrusions. The major Camasunary fault is separated from the Raasay fault via a series of minor graben, linked by a series of steep, NW–SE-trending faults that transfered Mesozoic displacements between the principal fault strands. A broad range of igneous material of various compositions was intruded into part of the Mesozoic Sea of Hebrides basins and their flanks during Palaeocene times. Different emplacement styles and different structural controls are found. The major gabbroic centres do not appear to be controlled by upper crustal structures, having been emplaced into the footwalls of major faults. However, minor synmagmatic displacements on the basin faults may have been sufficient to generate dilatational sites in these footwall positions, thereby facilitating emplacement. In contrast, the granitic melts have been emplaced as sheets and domed into the sediments and overlying lava pile, reactivating segments of the basin fault network. Doming occurred from an array of sills, the stratigraphic levels of which can be reconstructed using structural relationships preserved in the roofs and walls of the intrusions. The sill levels and their transgressive forms are strongly related to inferred Mesozoic basin structures. The major fold structures of Tertiary age in southern Skye are interpreted as accommodating granitic emplacement rather than crustal shortening. The NW-SE Mesozoic transfer fault trend appears to have strongly influenced the segmentation of the granite domes. These interpretations are illustrated using field relationships mapped in the vicinity of the Coire Uaigneich granophyre. It is concluded that although the higher parts of the basin faults were reactivated to facilitate the doming of granitic intrusions, the deeper levels of the Mesozoic faults show no evidence of substantial reactivation.

The granite‐greenstone terranes of the Eastern Goldfields Province, Yilgarn Craton, Western Australia, are a major Australian and world gold and nickel source. The Kalgoorlie region, in particular, hosts several world‐class gold deposits. To attempt to understand why these deposits occur where they do, it is important to understand the crustal architecture in the region and how the major mineral systems operate in this architecture. One way to understand these relationships is to develop a detailed 3–D geological model for the region. The best method to map the 3–D geometry of major geological structures is by acquisition and interpretation of seismic‐reflection profiles. To contribute to this aim, a grid of deep seismic‐reflection traverses was acquired in 1999 to examine the 3–D geometry of the region in an area including the Kalgoorlie mineral region and mineral fields to the north and west. This grid was tied to the 1991 regional deep seismic traverse and 1997 high‐resolution seismic profiles in the same region. The grid covers an area measuring approximately 50 km wide by 50 km long and extended to a depth of approximately 50 km (below the base of the crust in this region). The resulting 3–D geological model was further constrained by both surface geological data and geophysical interpretations, with the seismic interpretations themselves also constrained by gravity and magnetic modelling. The 3–D model was used to investigate the geometric relationships between the major faults and shear zones in the area, the relationship between the granite‐greenstone succession and the basement, and the spatial relationships between the greenstones and the granites. Interpretation of the grid of seismic lines and construction of the 3–D geological model confirmed the existence of the detachment surface and led to the recognition that the granite‐greenstone contact usually occurs at a much shallower level than the detachment. Also, west‐dipping faults in the vicinity of the Golden Mile, including the Abattoir Shear through to Boulder‐Lefroy Fault, appear to be more important than previously thought in controlling the structure of that area. An antiformal thrust stack occurs beneath a triangle zone centred on the Golden Mile. The Black Flag Group was deposited in a probable extensional setting, and late extension was also probably more important than previously thought. The granite‐gneiss domes were uplifted by the formation of antiformal thrust stacks at depth beneath them.

The late Cambrian–Early Ordovician siliciclastic sequence in central northern Tasmania represents an excellent case study to document the transition from an active rifting succession to a post-rift system. Initial rifting created a complex system of half-graben, providing accommodation space for large volumes of basement-derived material. These half-graben were initially filled with coarse-grained alluvial fan sediments and a thick, syn-rift, low-sinuosity, multiple-channel braided fluvial succession. The uppermost sequence comprises a post-rift, regional, shallow marine, transgressive sandstone and mudstone package. Six broad lithofacies have been recognised in the late Cambrian–Early Ordovician siliciclastic sequence: Four lithofacies are interpreted to represent terrestrial alluvial fan (displaying debris flow, sheet-flow and channel-flow geometries) and braided fluvial deposits (transitioning between proximal and distal sedimentological characteristics upsection), while two represent marginal-marine (tidal) to shallow marine environments (dominated by heterolithic bedding, and varying degrees and styles of bioturbation). Adjacent lithofacies often display marked lateral variations in both thickness and grain-size, suggesting accelerated changes in the volume of sediment flux and/or the rate of tectonic subsidence, particularly of the basal, coarse-grained, conglomerate-rich sequences where the varying composition and texture suggests considerable relief on hinterland palaeotopography. A revised stratigraphic framework for the late Cambrian–Early Ordovician siliciclastics of central northern Tasmania is presented based on lithofacies and lithofacies associations. The Roland Formation forms the lower stratigraphic unit and comprises generally fining-up, conglomerate-dominated alluvial fan and proximal, low-sinuosity, multiple-channel braided river successions associated with syn-rift sedimentation. A hiatus in the extensional tectonics is recorded by a regionally extensive unconformity between the Roland Formation and the overlying Moina Formation, named the intra-Owen Group Unconformity. The Moina Formation marks a transition from high energy, terrestrial, conglomerate-rich sequences of the Roland Formation, to more moderate energy sandstone-dominated sequences that typically display an increasing marine signature towards the top of the unit. Three distinct sedimentary successions are recognised within the Moina Formation, and member status has been given to each of these since the distribution and relationships between these stratal packages is fundamental in understanding the mature phase of the late Cambrian–Early Ordovician extensional event, and the post-rift transgressive system. The terrestrial braided fluvial, channelised sandstone and minor conglomerate of the Badgers Range Member are superseded by interbedded, fine- to medium-grained sandstone deposited in a tidal regime (Deloraine Member) that is in turn overlain by thinly bedded, heavily bioturbated, shallow marine mudstone and fine-grained sandstone (Caroline Creek Member). Sedimentological principles, including provenance studies and palaeocurrent analysis, are used to document the basin configuration and structural framework of the rift system. The spatial and temporal migration of depocentres can be documented such as in the Badgers Range where two fining-up successions are separated by the intra-Owen Group Unconformity with the lower quartzite-dominated Roland Formation being succeeded by the chert lithic-rich Moina Formation. It is apparent that depocentres were compartmentalised by topographic highs, and the sedimentary fill of these depocentres reflects the lithological composition of these highs. In addition, the observed general decrease in grain-size is not uniform, and there are numerous changes in sedimentation as a consequence of fluxes in uplift and subsidence in the source and basinal areas. The distribution of thickly-bedded, coarse-grained conglomerate sequences, the juxtaposition of differing lithological successions, and the construction of geological cross-sections give insights to the location and position of several major bounding faults. These faults were subsequently reactivated during the Early–Middle Devonian Tabberabberan Orogeny, and a significant amount of reverse movement is recorded on the basis of structural restorations. Regional palaeogeographic reconstructions of the Early Ordovician (Tremadocian; 480 Ma) (Cocks, 2001) demonstrate that Tasmania was located outboard of the eastern margin of Gondwana, situated north of the palaeoequator between latitudes 10° and 20°. The late Cambrian through Ordovician tropical climate was dominated by the influence of a strong, extended greenhouse effect. The lack of sediment stabilisation by plants and rootlets in this Early Palaeozoic, vegetation-free, terrestrial landscape resulted in alluvial and fluvial depositional processes being markedly different from their present day counterparts, since vegetation exerts significant influence on a variety of environmental factors. In particular, energy levels and run-off rates would have been greater, fluctuations in energy levels more extreme, and high energy events more frequent. These conditions would likely have been amplified by the relatively high precipitation rates associated with the tropical palaeogeographic position of Tasmania. Likewise, wind processes would have played a far greater role than present with regards to the removal of clay- and silt-sized particles from the depositional setting, and this may explain the paucity of claystone and siltstone in these terrestrial environments.

The deposition of the Paleogene sediments in Central Sarawak occurred in four successive stages, its axis of depocentre generally advancing and younging to the northeast in response to progressive southwest subduction-accretion of a Mesozoic oceanic lithosphere and its sedimentary cover under West Sarawak. The younger sediments were deposited on top or in front of an older accreted sediments. The timing of deposition and accretion is uncertain due to lack of precise age indicators. However, based on regional considerations, the accretion is interpreted to have occurred sometimes during the Early Paleocene, Middle Eocene, Upper Eocene and Upper Oligocene, respectively, along major fault zones, producing four tectono-stratigraphic units. The older sediments were subjected to polyphase deformation as younger units were accreted.