Ramp Sequences Research Articles

The Ramp Atlas: facilitating tissue and cell-specific ramp sequence analyses through an intuitive web interface.

Ramp sequences occur when the average translational efficiency of codons near the 5′ end of highly expressed genes is significantly lower than the rest of the gene sequence, which counterintuitively increases translational efficiency by decreasing downstream ribosomal collisions. Here, we show that the relative codon adaptiveness within different tissues changes the existence of a ramp sequence without altering the underlying genetic code. We present the first comprehensive analysis of tissue and cell type-specific ramp sequences and report 3108 genes with ramp sequences that change between tissues and cell types, which corresponds with increased gene expression within those tissues and cells. The Ramp Atlas (https://ramps.byu.edu/) allows researchers to query precomputed ramp sequences in 18 388 genes across 62 tissues and 66 cell types and calculate tissue-specific ramp sequences from user-uploaded FASTA files through an intuitive web interface. We used The Ramp Atlas to identify seven SARS-CoV-2 genes and seven human SARS-CoV-2 entry factor genes with tissue-specific ramp sequences that may help explain viral proliferation within those tissues. We anticipate that The Ramp Atlas will facilitate personalized and creative tissue-specific ramp sequence analyses for both human and viral genes that will increase our ability to utilize this often-overlooked regulatory region.

A comprehensive analysis of the phylogenetic signal in ramp sequences in 211 vertebrates

Ramp sequences increase translational speed and accuracy when rare, slowly-translated codons are found at the beginnings of genes. Here, the results of the first analysis of ramp sequences in a phylogenetic construct are presented. Ramp sequences were compared from 247 vertebrates (114 Mammalian and 133 non-mammalian), where the presence and absence of ramp sequences was analyzed as a binary character in a parsimony and maximum likelihood framework. Additionally, ramp sequences were mapped to the Open Tree of Life synthetic tree to determine the number of parallelisms and reversals that occurred, and those results were compared to random permutations. Parsimony and maximum likelihood analyses of the presence and absence of ramp sequences recovered phylogenies that are highly congruent with established phylogenies. Additionally, 81% of vertebrate mammalian ramps and 81.2% of other vertebrate ramps had less parallelisms and reversals than the mean from 1000 randomly permuted trees. A chi-square analysis of completely orthologous ramp sequences resulted in a p-value < 0.001 as compared to random chance. Ramp sequences recover comparable phylogenies as other phylogenomic methods. Although not all ramp sequences appear to have a phylogenetic signal, more ramp sequences track speciation than expected by random chance. Therefore, ramp sequences may be used in conjunction with other phylogenomic approaches if many orthologs are taken into account. However, phylogenomic methods utilizing few orthologs should be cautious in incorporating ramp sequences because individual ramp sequences may provide conflicting signals.

Synonymous variant rs2405442 in PILRA is associated with Alzheimer's disease and affects RNA expression by destroying a ramp sequence

AbstractBackgroundPaired Immunoglobulin‐like Type 2 Receptor Alpha (PILRA) recognizes specific O‐glycosylated proteins on various cell types, including microglia. A common missense mutation in PILRA, rs1859788, that likely causes the confirmed Alzheimer's disease risk locus at 7q21 is in linkage disequilibrium with synonymous variant rs2405442:T&gt;C. This synonymous variant affects a ramp of rare codons at the beginning of PILRA, which may decrease overall transcriptional efficiency. Since reduced inhibitory signaling in microglia has a protective effect on Alzheimer's disease, we propose that destroying a ramp sequence in PILRA will likewise protect against Alzheimer's disease by reducing the amount of PILRA inhibitory receptor.MethodsWe recently developed an algorithm, ExtRamp, to identify ramp sequences within specific gene sequences. Using ExtRamp, we calculated the relative codon adaptiveness of PILRA using all isoforms in GRCh38. We then calculated the relative codon adaptiveness of PILRA with synonymous variant rs2405442:T&gt;C and found that a ramp sequence is present in the reference isoforms but not the mutant isoforms. We predicted that although the mutant has a more common codon, it would have less overall mRNA expression because it lacks a ramp sequence. We performed biological validation using four sets of three qPCR replicates on the longest isoform to determine the transcriptional efficiency of the mutant versus the reference. We normalized the qPCR output by the number of cells.ResultsFigure 1 shows the relative adaptiveness of the longest PILRA reference isoform and the mutant gene averaged over a nine codon window. The mutant gene has a higher codon adaptiveness at the beginning of the gene sequence, which destroys the predicted ramp sequence. Figure 2 shows that our biological validation using qPCR confirms our prediction that the mutant gene has lower mRNA expression (p‐value = 4.45 × 10−9).ConclusionsAlthough higher GC content and more common codons generally increase mRNA levels, the ramp sequence appears to play an integral role in transcriptional efficiency in PILRA. Our results show that synonymous variant rs2405442:T&gt;C directly impacts transcriptional efficiency in PILRA and indicates that synonymous variants should be considered in future association analyses for their causal effects on transcriptional efficiency by modifying ramp sequences.

ExtRamp: a novel algorithm for extracting the ramp sequence based on the tRNA adaptation index or relative codon adaptiveness.

Different species, genes, and locations within genes use different codons to fine-tune gene expression. Within genes, the ramp sequence assists in ribosome spacing and decreases downstream collisions by incorporating slowly-translated codons at the beginning of a gene. Although previously reported as occurring in some species, no previous attempt at extracting the ramp sequence from specific genes has been published. We present ExtRamp, a software package that quickly extracts ramp sequences from any species using the tRNA adaptation index or relative codon adaptiveness. Different filters facilitate the analysis of codon efficiency and enable identification of genes with a ramp sequence. We validate the existence of a ramp sequence in most species by running ExtRamp on 229 742 339 genes across 23 428 species. We evaluate differences in reported ramp sequences when we use different parameters. Using the strictest ramp sequence cut-off, we show that across most taxonomic groups, ramp sequences are approximately 20–40 codons long and occur in about 10% of gene sequences. We also show that in Drosophila melanogaster as gene expression increases, a higher proportion of genes have ramp sequences. We provide a framework for performing this analysis on other species. ExtRamp is freely available at https://github.com/ridgelab/ExtRamp.

Sedimentology and chemostratigraphy of the late Neoproterozoic carbonate ramp sequences of the Hüttenberg Formation (northwestern Namibia) and the C5 Formation (western central Democratic Republic of Congo): Record of the late post-Marinoan marine transgression on the margin of the Congo Craton

Sedimentology and chemostratigraphy of the late Neoproterozoic carbonate ramp sequences of the Hüttenberg Formation (northwestern Namibia) and the C5 Formation (western central Democratic Republic of Congo): Record of the late post-Marinoan marine transgression on the margin of the Congo Craton

Architecture of a Neoproterozoic intracratonic carbonate ramp succession: Wynniatt Formation, Amundsen Basin, Arctic Canada

The Neoproterozoic Wynniatt Formation, part of the upper Shaler Supergroup, is exposed in the Minto Inlier of Victoria Island, Canada, and was deposited in the intracratonic Amundsen Basin. The unit consists of a southwest-thickening (480 to 1000m over ~300km) shallowing-upward succession of three carbonate ramp sequences separated by regional unconformities. In ascending order: 1) inner to outer ramp carbonate facies, gradationally overlain by siliciclastic rocks of a pro-delta slope setting; 2) inner to mid-ramp subtidal carbonate facies, including a regional stromatolitic barrier system; and 3) outer ramp carbonate (gravity flow) facies overlain by shallowing-upward subtidal to intertidal, mixed siliciclastic-carbonate inner ramp facies. Spatial arrangements of nineteen lithofacies illustrates that each carbonate ramp sequence represents part of a distally steepened, storm-dominated carbonate ramp, with an interval of deep-water carbonate rocks coincident with oceanic restriction that elevated salinity. Migration of depocentre loci for successive ramp stages reflects changing patterns of subsidence. This may identify far-field extensional effects in this intracratonic basin because ages of the lower (~850Ma) and middle (~761Ma) formation bracket initiation of supercontinent (Rodinia) break-up. Our work offers an improved sedimentary framework for interbasinal correlation with coeval Neoproterozoic basins. It highlights temporal changes in carbonate facies compared to older carbonate successions in the Shaler Supergroup, and it defines depositional context for the Tawuia-Chuaria assemblage zone, providing important interbasinal biostratigraphic correlation.

Upper Ordovician sequences of western Estonia

The Upper Ordovician (uppermost Caradoc-Ashgill) section of western Estonia consists of a series of seven open-shelf carbonate sequences. Depositional facies grade laterally through a series of shelf-to-basin facies belts: grain-supported facies (shallow shelf), mixed facies (middle shelf), mud-supported facies (deep shelf and slope) and black shale facies (basin). Locally, a stromatactis mud mound occurs in a middle-to-deep shelf position. Shallow-to-deep shelf facies occur widely across the Estonian Shelf and grade laterally through a transitional (slope) belt into the basinal deposits of the Livonian Basin. Each sequence consists of a shallowing-upward, prograding facies succession. Sequences 1 (Upper Nabala Stage) and 2 (Vormsi Stage) record step-wise drowning of underlying shelf units (lower Nabala) that culminated in the deposition of the most basinal facies (Fjäcka Shale) in the Livonian Basin. Sequences 3–6 comprise the overlying Pirgu Stage and record the gradual expansion of shallow and middle-shelf facies across the Estonian Shelf. The Porkuni Stage (sequence 7) is bracketed by erosional surfaces and contains the shallowest-water facies of the preserved strata. The uppermost part of the section ( Normalograptus persculptus biozone) is restricted to the Livonian Basin, and includes redeposited carbonate and siliciclastic grains; it is the lowstand systems tract of the lowest Silurian sequence 8. Sequence 7 and the overlying basinal redeposited material (i.e., the lowstand of sequence 8) correspond to the latest Ordovician (Hirnantian) glacial interval, and the bracketing unconformities are interpreted as the widely recognized early and late Hirnantian glacial maximums. The sequences appear correlative to Upper Ordovician sequences in Laurentia. Graptolite biozones indicated that the Estonian sequences are equivalent to carbonate ramp sequences in the western United States (Great Basin) and mixed carbonate-siliciclastic sequences in the eastern United States (Appalachian Basin–Cincinnati Arch region). These correlations indicate a strong eustatic control over sequence development despite the contrasting tectonic settings of these basins.

Comparison of the ‘strike‐slip’ versus the ‘episodic rift‐sag’ models for the origin of the Isa Superbasin

In this paper we assess two competing tectonic models for the development of the Isa Superbasin (ca 1725–1590 Ma) in the Western Fold Belt of the Mt Isa terrane. In the ‘episodic rift‐sag’ tectonic model the basin architecture is envisaged as similar to that of a Basin and Range province characterised by widespread half‐graben development. According to this model, the Isa Superbasin evolved during three stages of the Mt Isa Rift Event. Stage I involved intracontinental extension, half‐graben development, the emergence of fault scarps and tilt‐blocks, and bimodal volcanism. Stage II involved episodic rifting and sag during intervening periods of tectonic quiescence. Stage III was dominated by thermal relaxation of the lithosphere with transient episodes of extension. Sedimentation was controlled by the development of arrays of half‐grabens bounded by intrabasinal transverse or transfer faults. The competing ‘strike‐slip’ model was developed for the Gun Supersequence stratigraphic interval of the Isa Superbasin (during stage II and the beginning of stage III). According to this model, sinistral movements along north‐northeast‐orientated strike‐slip faults took place, with oblique movements along northwest‐orientated faults. This resulted in the deposition of southeast‐thickening ramp sequences with local sub‐basin depocentres forming to the west and north of north‐northeast‐ and northwest‐trending faults, respectively. It is proposed that dilation zones focused magmatism (e.g. Sybella Granite) and transfer of strike‐slip movement resulted in transient uplift along the western margin of the Mt Gordon Arch. Our analysis supports the ‘episodic rift‐sag’ model. We find that the inferred architecture for the strike‐slip model correlates poorly with the observed structural elements. Interpretation is made difficult because there has been significant modification and reorientation of fault geometry during the Isan Orogeny and these effects need to be removed before any assertion as to the basin structure is made. Strike‐slip faulting does not explain the regional‐scale pattern of basin subsidence. The ‘episodic rift‐sag’ model explains the macroscopic geometry of the Isa Superbasin and is consistent with the detailed sedimentological analysis of basin facies architecture, and the structural history and geometry.

Rapid onset of late Paleozoic glaciation on Gondwana: Evidence from Upper Mississippian strata of the Midcontinent, United States

Direct evidence of the late Paleozoic glaciation of Gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the Namurian (Late Mississippian). However, the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances. Indirect evidence of glaciation preserved in unconformity-bounded, low-latitude ramp sequences in the Illinois basin, United States, suggests that geographically extensive continental glaciation of Gondwana actually began in the late Visean. An abrupt change from carbonate-dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate-siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three-fold increase in the magnitude of eustatic sea-level fluctuations. The increase in the magnitude of sea-level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late Paleozoic glaciation of Gondwana. A possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between Laurussia and Gondwana. Closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the Southern Hemisphere.

Stratigraphic Control on Facies and Diagenesis of Dolomitized Oolitic Siliciclastic Ramp Sequences (Pinda Group, Albian, Offshore Angola)

Pervasively dolomitized, oolitic to siliciclastic ramp sequences are prolific oil reservoirs in the Albian Pinda Group of northern Angola. During the Late Cretaceous, this reservoir series was segmented by salt tectonic gravitational gliding into halokinetic turtle-back and raft structures that provide hydrocarbon traps today. The Albian ramp sequences contain a large variety of reservoir facies, reaching from littoral sandstones with interparticle porosity to various types of dolomitized marine shelf to shoreline carbonates with moldic, vuggy, and intercrystalline porosity. Reservoir prediction is substantially improved by an integrated approach combining high-resolution sequence stratigraphy with carbonate geochemistry. As high-resolution stratigraphy documents, most of the important sandstone reservoirs formed at the base of stratigraphic sequences during shoreface transgression. Pisolitic dolostones with moldic porosity are the best carbonate reservoirs. They developed as transgressive shoreface sand sheets above the basal sandstone reservoirs. Regressive facies tracts contain oolitic and pisolitic dolomites with intercrystalline and moldic porosity that originated in progradational barrier and sand-belt settings. The combined stratigraphic and geochemical approach allowed us to determine the Pinda Group dolomites as early diagenetic in origin, whereas fluid inclusion and oxygen isotope analysis alone suggested a late burial dolomite formation. Dolomite neomorphism at higher burial temperatures modified most of the original geochemical signatures of early, near-surface dolomitization. Cathodoluminescence data and trace element analysis suggest that dolomitization was associated with gradually decreasing pore water salinity. Accordingly, barrier oolites were completely dolomitized and developed intercrystalline porosity during the earliest stages of diagenesis. At a later phase of early diagenesis, as waters became less saline and undersaturated with respect to calcium carbonate, fabric-selective dissolution of the remaining calcareous components occurred. The decrease in pore water salinity and associated porosity generation are genetically linked with high-frequency events of relative sea level lowering. This possible relationship implies that high-resolution sequence stratigraphy can be a valid reservoir prediction tool even in pervasively dolomitized series.

Contrasting flooding histories of Mississippian carbonate platforms revealed by marine alteration effects in palaeosols

ABSTRACTPalaeosols associated with exposure surfaces in Mississippian platform carbonate sequences in Britain invariably show evidence for later alteration by sea water. These alteration effects can be attributed to flooding of the emergent platforms during transgressions that terminated exposure surface development. A study of 230 palaeosol profiles representing 60 stratigraphic levels has revealed a two fold division of these marine hydromorphic effects. Palaeosols in ramp sequences (Chadian‐Arundian stages) are capped by ferroan dolomite horizons with carbonized rootlets, pyrite and thin coals. The ferroan dolomites exhibit δ13C and δ18O values indicative of formation in brackish waters. These are interpreted as coastal marshes that developed landward of a transgressive shoreline. Younger Asbian‐Brigantian palaeosols lack these dolomites but have been extensively pyritised. The pyrite also developed through marine hydromorphic alteration but flooding was relatively instantaneous over the flat topped platforms. These differences in flooding history reflect both different platform configuration and more rapid transgressions during the Asbian‐Brigantian, likely a result of glacio‐eustatic effects. Flooding characteristics of the Asbian‐Brigantian platforms differ from those associated with late Cainozoic examples, apparently because complete platform rims were not developed. Similar mineralogical alteration effects are likely to be common in other platform sequences in the geological record, but have not been documented.

Round-Up

Oxford Instruments has developed the IT6Ol, a cryostat temperature controller. The controller has a temperature resolution of 0.1 K with an update rate of 4 Hz. A simplified user interface allows one-button operation. For example, control of the temperature environment is achieved by depressing the Set Point button and dialling in the desired temperature. A microprocessor manages the advanced functions, such as temperature ramp and hold sequences. Stable temperatures are achieved by minimizing the difference between the measured and desired temperature using effective PID control. The accuracy with which the system temperature follows a requested profile is determined by the thermodynamic characteristics of the system being controlled.

Facies Distribution within Upper Albian Carbonate Ramp Sequences defined by a time-significant correlative horizon, West Texas: ABSTRACT

Facies Distribution within Upper Albian Carbonate Ramp Sequences defined by a time-significant correlative horizon, West Texas: ABSTRACT

Carbonate ramp depositional systems from a late Jurassic epeiric platform (Iberian Basin, Spain): a combined computer modelling and outcrop analysis

ABSTRACTNo counterparts to epeiric‐sea carbonate ramps are known in present‐day environments. This hinders the interpretation of the factors controlling the growth and evolution of these depositional settings. In this study we analyse the facies and geometries of two Jurassic examples both from outcrop study and through computer modelling. This analysis is constrained by two important features of these Oxfordian and Kimmeridgian ramps: firstly, they are very well exposed, allowing accurate reconstruction of a 200‐km section from proximal to distal ramp environments, and, secondly, a time framework for correlation, section reconstruction and modelling is provided by a well‐defined ammonite biostratigraphy. The modelling results in a synthetic stratigraphy which closely matches the reconstructed cross‐sections and, when integrated with the field study, constrains and provides additional quantitative data on the following aspects of carbonate ramp systems.Resedimentation by storms is an important process in maintaining the ramp profile through time. Down‐ramp transport distances of between 25 and 40 km are indicated from the distribution of storm beds and shallow‐water allochems and from model‐matching known stratigraphic thicknesses and geometries.Modelling sediment production within the time constraints from the ammonite biozones indicates that shallow‐water carbonate production was 1–2 orders of magnitude less than that predicted for present‐day open‐marine carbonate platforms. Deeper‐water production rates were reduced by lesser amounts. These proportionally higher, outer‐ramp production rates also help to maintain ramp geometries through time.The enigmatic slope crest of ramps is shown to result from a combination of higher, shallow‐water production and erosion rates, together with loss of accommodation during highstands and high‐stillstands in the modelled sea‐level curves.The most parsimonious modelling of the two ramp sequences comes from a relative sea‐level curve composed of a linear subsidence component superposed by 20‐ and 100‐kyr cycles on a third‐order cycle. The third‐order cycles and their timing do not correspond to those of the Exxon curve.

Human muscle spindle afferent activity in relation to visual control in precision finger movements.

1. Impulse activities of muscle spindle afferents from the finger extensor muscles were recorded in the radial nerve of human subjects. In addition to single unit activity, surface EMG was recorded as well as finger joint position and angular velocity. 2. All units were studied under two conditions of voluntary finger movements. In the visual condition, the subject tracked ramp and hold sequences at a single metacarpophalangeal joint. In the non-visual condition the subject was asked to produce the same movement while visual control was denied altogether. 3. With sixteen units, detailed statistical analyses failed to reveal significant differences in muscle spindle afferent activity between the visual and the non-visual task. However, with two group Ia units, impulse rate was marginally but significantly higher in the visual task even when differences in average movement velocity, velocity variability and EMG level had been factored out. 4. The findings suggested that access to visual information for movement control did not produce any large-scale differences in spindle afference, although a small effect of an increased and independent gamma-activation emerged in the statistical analysis in 11% of the units.

Carbonate ramp depositional systems

The classification, tectonic settings, stratigraphy and early diagenesis of carbonate ramp systems are reviewed. Carbonate ramps are common in all geological periods, but were dominant at times when reef-constructing organisms were absent or inhibited. Ramps can be subdivided into inner-, mid-, and outer-ramp environments. The mid-ramp zone extends from fair-weather wave base to normal storm wave base, although the water depths which these boundaries represent vary. An additional outer-slope environment occurs on distally steepened ramps. As with siliciclastic shelves, a range of wave-, storm-, and tide-dominated ramps can be recognised and this forms the most convenient basis for ramp classification. The carbonate productivity profile of ramps differs from that of rimmed shelves, with the inner ramp showing lower production rates than comparable shallow-water facies on rimmed shelves. The zone of greatest organic carbonate sediment production appears to have shifted from the mid-ramp to the inner ramp since the Late Jurassic. Carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas, as in foreland and cratonic-interior basins and along passive margins. The featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines. Some show low-angle sigmoidal or shingled clinoforms, suggesting that ramps may seldom be “homoclinal”, but possess subtle slope geometries which reflect depositional environments. Because of their low-angle slopes, ramps respond differently to rimmed shelves during relative sea-level changes although results seem to be strongly dependent on the rate of relative sea-level change. During a minor fall, shallow-ramp facies belts will simply shift basinwards in a “forced regression”. In contrast, the whole surface of a steep-sloped, flat-topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced. During a major fall, shallow ramp-bounded basins may empty completely. Conversely, ramps also flood gradually, whereas rimmed shelves do so more rapidly. Homoclinal ramps develop no resedimented lowstand deposits; rimmed shelves and distally steepened ramps, in contrast, may develop lowstand talus or turbiditic wedges. Distally steepened ramps may behave more like homoclinal ramps during minor base-level falls and like rimmed shelves during major base-level falls. Many ramps consist of layered successions of several ramp sequences stacked one upon the other. Ramp “stacks” of this sort may show gross vertical accretion, but individual ramp sequences seldom appear to develop in a “keep-up” style, apart from minor organic buildups, as with many rimmed shelves. Steepening of the outer-ramp margin due to tectonism, slope inheritance, or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf. A wide variety of organisms have constructed buildups in mid- and outer-ramp environments. Isolated buildups may seed early in ramp development, accrete to wave base or sea level, and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp. The location of isolated buildups on ramps is governed by tectonism, halokinesis, antecedent topography, or by the subtle slope geometry of the previous ramp sequence. Diagenesis on ramps shows some major variations compared with diagenesis on steep-sloped, flat-topped carbonate platforms. Ramp-bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution. Isolated buildups in the mid- and outer-ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts. Grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs. Grainstone sandbodies, occur in both highstand systems tracts and in prograding lowstand wedges.

SEQUENCE STRATIGRAPHY, BASIN-FLOOR FANS AND PETROLEUM PLAYS IN THE DEVONIAN – CARBONIFEROUS OF THE NORTHERN CANNING BASIN

A sequence stratigraphic study of 4 000 kilometres of seismic data and fifty wells from the northern part of the Canning Basin has improved vasdy our knowledge of the evolution of the basin succession and has identified new petroleum play concepts. The Devonian to Lower Carboniferous succession can be subdivided into at least sixteen 'Vail type' sequences. This shows two contrasting phases of development; a reef complex in the Frasnian—Early Famennian, and a ramp in the Late Famennian-Tournaisian. The reef complex was characterised by reciprocal sedimentation with thick clastic lowstand wedges deposited in the Fitzroy Trough and thinner transgressive and highstand carbonate sediments deposited on the Lennard Shelf. The reef complex shows an early phase of backstepping, related to rapid drowning of the platform, and a later phase of marked progradadon when relative subsidence was lower. The ramp, in contrast, has only poorly developed lowstand wedges. Early ramp sequences are lenticular and successively offlap basinward; later sequences are more tabular and progressively onlap landward.Sequence stratigraphy has provided a new perspective on the setting and evolution of the traditional Devonian reef play. It emphasises the attractiveness of the Frasnian cycle of reef growth where source, seal and reservoir potential appear to be better than in the younger, much more extensively drilled Famennian cycle.New and untested stratigraphic targets have been identified in Famennian-Tournaisian highstand ramps and in lowstand fans. These new stradgraphic targets are generally basinward of the more traditional target areas and need to be assessed by either wildcat or stratigraphic drilling. The lowstand fans, especially, are large and extensive and favourably located to trap migrating hydrocarbons. Several prospects, each with the potential to contain in excess of 100 million barrels of recoverable oil, have already been identified on seismic data recorded basinward of the Lennard Shelf.

Short Paper: A standardized model for Tethyan Tertiary carbonate ramps

Low latitude carbonates in massive and clinoform bedded sheets, termed ramps, occur throughout the Tertiary Tethyan realm, and are characterized by recurring biofacies usually including large foraminifera, rhodolithic algae, coralgal patch-reef and gastropod dominated sequences. All can be interpreted broadly within a standardized Tertiary carbonate ramp model. Biota can be used to define precise palaeobathymetric zones which have a predictive utility in palaeoenvironmental modelling, especially where data are limited. The carbonate ramp model of earlier authors, has been elaborated by Read (1982) and ramp formation occurs mostly in passive margin and extensional tectonic settings. Ramps are characterized by slope gradients of less than 1 degree and, once established, are conservative to change. Much use has been made of the ramp model for Palaeozoic and Mesozoic lithofacies modelling. In contrast, published work on Cenozoic ramps is limited, however, Tethyan ramps are particularly widespread and extend tens to hundreds of kilometres along strike and occupy tens of kilometres of slope. Many studies have dealt with Cenozoic ramp associations and sequences (e.g. Pedley 1983 ; Reiss &amp; Hottinger 1984; Purser 1973 ) and have demonstrated the diversity of biotal and sediment detail, but without ascribing them to a ramp model. Biota were quick to adapt to the Tertiary environments left vacant after the K–T boundary extinction events. New genera of Foraminifera, Mollusca, Bryozoa and Echinoder-mata rapidly replaced the extinct forms in bursts of innovative opportunism. Codiacean algae, Rhodophyta and marine angiosperms were equally adaptive colonizers of the carbonate platforms. Novel biofacies associations were derived from