CONTROLS ON FACIES DISTRIBUTION AND RESERVOIR DEVELOPMENT OF UPPER TRIASSIC RIFT CONTINENTAL SYSTEMS IN INTERMONTANE RIFT SETTINGS: A COMPARATIVE STUDY OF EXTENSIVE OUTCROPS IN SW MOROCCO
Redfern, Jonathan1; Mader, Nadine2; Fabuel Perez, Ivan3; Hodgetts, David3; El Ouataoui , Abedelmajid4
1University of Manchester Williamson building, Oxford Road, Manchester, Gt Manchester, M139Pl, United Kingdom; 2Hess Ltd, London, Greater London, WC2N 6AG, United Kingdom; 3Williamson building, Oxford Road, Manchester, Gt Manchester, M139Pl, United Kingdom; 4ONHYM, Rabat, xx, 10050, Morocco
Upper Triassic (Carnian) sediments in SW Morocco comprise a continental red bed sequence deposited in discrete rifted basins following the break up of Pangea and opening of the Atlantic. This comparative study examines extensive outcrops of the Oukaimeden Sandstones Formation (F5) in the High Atlas and Unit T6 in the Argana Basin, SW Morocco, deposited within a series of narrow fault bounded intermontane basins. Both contain a variety of braided fluvial, overbank, shallow ephemeral lacustrine, alluvial fan and aeolian facies.
Traditional sedimentological data (sedimentary facies logs, palaeocurrent information, gamma ray logs etc) has been combined with high resolution 3D laser (LIDAR) and Differential Global Positioning System (DGPS) to map these outcrops and provide a detailed dataset.
On a basin scale, the often complex facies distribution evident in the Argana Basin suggests a highly variable fill within these basin types. Correlation of individual facies elements is often difficult and relies on identification of key stratal surfaces. Local tectonics control accommodation and influence facies patterns, such as development of alluvial fans and entry points of major drainage systems. Significant changes in fluvial style, from ephemeral to perennial, are recognized in both basins within this interval, which suggests rejuvenation of the source areas and a potential interplay of climatic and tectonic control. An overall drying upward pattern is observed, with increasing influence of aeolian processes towards the top of both the Oukaimeden sandstone (F5) and T6 of Argana. This supports previous work that has demonstrated a change from humid to increasingly arid conditions during the Upper Triassic, recognized both throughout SW Morocco and in the Fundy Basin, Canada, and highlights the climatic control on the depositional system.
These studied sections offer potential analogues for subsurface Triassic hydrocarbon systems in similar settings, and provide valuable information on the tectonic and climatic control on depositional facies and architecture. Analysis of basin-wide facies variation, provenance and sediment pathways provide regional scale analogue data. More detailed field scale reservoir models have also been developed for the high net:gross intervals in the Oukaimeden sandstone.
RESERVOIR CONNECTIVITY ANALYSIS, HYDROCARBON DISTRIBUTION, RESOURCE POTENTIAL & PRODUCTION PERFORMANCE IN THE CLASTIC PLAYS OF THE SABLE SUBBASIN, SCOTIAN SHELF
Richards, Bill 1; Fairchild, Lee H. 2; Vrolijk, Peter J. 3; Hippler, Susan J. 4
1 ExxonMobil Canada 1701 Hollis Street, P.O.Box 517, Halifax, Nova Scotia, B3J 3MB, Canada; 2Gorge Geotechnical, Parkdale, Hood River, Oregon, 97041, United States; 3ExxonMobil Upstream Research Company, P.O.Box 2189, Houston, Texas, 77098 , United States; 4ExxonMobil Exploration Company, 233 Benmar, Houston, Texas, 77060, United States
Reservoir Connectivity Analysis is a systematic approach to understanding reservoir "plumbing". It is based on well-known physical principles and is documented in a 2005 SPE paper (Vrolijk et al, SPE-93577-PP).
RCA is central to understanding fluids, pressures and field/pool size distribution in the clastic reservoirs of the Sable Subbasin. We will illustrate this approach with examples from the five producing Sable gas fields, other significant discoveries, and, the recent, third tranche of exploration and delineation drilling.
Hydrocarbon traps in the clastic system at Sable vary progressively from linear, low relief, extensional fault bend folds (which have small scale internal faulting), to high relief, heavily faulted domes where salt movement is involved in addition to listric faulting. It was recognized pre-production that despite complex overpressure distribution (attributed to recent charge) hydrocarbon accumulations are dominantly controlled geometrically, by "fill & spill" mechanisms: spill and breakovers at structural saddles, and critically, juxtapositional connections at internal and bounding faults. Because the Sable Subbasin is predominantly a high net-to-gross, marginal marine system with limited thick topseals there is - with a few very important exceptions - a propensity for "leaky traps", short hydrocarbon columns, and numerous small hydrocarbon pools.
In the absence of direct seismic indications of hydrocarbons, RCA has been the most effective technique for fluid prediction ahead of the drill. Previous speculation that fault processes and ensuing “fault rocks” would provide lateral seals, with longer gas columns and a larger resource is inconsistent with drilling results and production history.
SLOPES, BASIN FLOORS, DIAPIRS, AND CANOPIES: REGIONAL-SCALE SALT-SEDIMENT INTERACTION IN THE NORTHERN GULF OF MEXICO AND THE SCOTIAN OFFSHORE
Rowan, Mark G.1
1Rowan Consulting, Inc. 850 8th St., Boulder, CO, 80302, United States
Salt diapirs and allochthonous canopies are well known from the northern Gulf of Mexico and the Nova Scotian offshore. Canopies can be divided into two end-member styles: salt-stock canopies, in which the canopy is linked to the autochthonous salt layer by vertical feeder diapirs and intervening minibasins are characterized by turtle structures; and salt-tongue systems, where the canopies are connected to the deep layer by counterregional welds that have basinward-dipping expulsion-rollover structures in their hanging walls.
The fundamental difference between the two styles is the degree of asymmetry. In salt-stock canopies, diapirs grow vertically and spread radially before amalgamating, and sub-canopy withdrawal geometries tend to be symmetrical. In salt-tongue canopies, diapirs grow up and basinward and extrude basinward, and the withdrawal basins are correspondingly asymmetric. Because both diapirs and allochthonous bodies grow passively at the sea floor, the simplest explanation for the difference is the slope of the sea floor. If it is horizontal, there will be no preferred direction of growth and extrusion, resulting in vertical diapirs and salt-stock canopies. If the sea floor slopes, diapirs will lean basinward and extrude salt tongues basinward. Thus, the structural style is largely determined by the evolving bathymetric profile of the passive margin, which in turn is controlled by the history of sediment progradation.
In the northern Gulf of Mexico, a regional boundary between more proximal salt-tongue canopies and more distal salt-stock canopies roughly parallels the margin and probably represents a long-lived base of slope initially established during Paleogene Wilcox deposition. In the Scotian deepwater, a similar boundary is oriented highly oblique to the margin, with vertical diapirs to the southwest (Shelburne Subbasin) and salt-tongue canopies to the northeast (Sable Subbasin). The structural boundary is located along the southwestern edge of the Upper Jurassic to Lower Cretaceous Mic Mac and Missisauga progradational system, and thus represents a lateral boundary to a broad slope to the northeast, with a basin floor along strike to the southwest. One of the key applications of this model is that it can be used to estimate the paleo-toe of slope and thus regional turbidite facies distribution, with channelized slope facies dominant in areas of salt-tongue canopies and ponded basinal facies more likely in areas with vertical diapirs and salt-stock canopies.
UNUSUAL JURASSIC CONDENSATE OF THE HUDSON CANYON AREA, U.S. ATLANTIC
Sassen, Roger 1; Post, Paul J.2
1Geochemical and Environmental Research Group (GERG) 833 Graham Road, College Station, TX, 77845, United States; 2U.S. Department of the Interior, Minerals Management Service, Office of Resource Evaluation / 1201 Elmwood Park Blvd., New Orleans, LA, 70123, United States
Gas and minor condensate was discovered in Late Jurassic and Early Cretaceous reservoirs in the Hudson Canyon (HC) 598 area of the Baltimore Canyon Trough (BCT).
The oldest sedimentary rocks in the BCT are interpreted to be Triassic syn-rift deposits. Predominantly carbonate Early to Middle Jurassic units overlie the Triassic and underlie the Late Jurassic–Early Cretaceous siliciclastic reservoirs.
Condensates from the Kimmeridgian (HC 598-1) and Albian (HC 642-2) reservoirs originate from the same source rock. While biomarkers are absent or in low relative abundance in the condensate, diamondoids, consisting primarily of adamantane and diamantane, along with their methyl and ethyl derivatives, are relatively abundant. The diamondoids have been concentrated during intense thermal cracking of an original oil. The carbon isotopic properties of the condensate are extremely enriched in 13C (-23.7‰ to -24.6‰ PDB), consistent with a Jurassic marine kerogen source. Triassic source rocks appear unlikely to have sourced these condensates because Triassic-sourced oils in the Newark and Culpepper basins are strongly depleted in 13C. The unusual geochemistry of the condensate is interpreted to be the result of extreme thermal cracking of oil sourced from the underlying Early to Middle Jurassic carbonate-rich source rocks. Diamondoid maturity indices suggest that the maturity of the condensate ranges from ~1.3% to ~1.6% vitrinite reflectance (Ro), significantly higher than the estimated ~0.9% Ro of the deepest Kimmeridgian reservoir. Vertical migration of deeper, more mature hydrocarbons into shallower reservoirs was facilitated by faults connecting the source and the reservoir.
The enrichment of diamondoids and 13C are similar to condensates sourced by the Late Jurassic Smackover Formation of the U.S. Gulf Coast. The role of Jurassic oil-prone source rocks in the Central Atlantic is underappreciated.
UNUSUAL JURASSIC CONDENSATE OF THE HUDSON CANYON AREA U.S. ATLANTIC
Sassen, Roger1; Post, Paul1
1 TexasA&M University 16017Woodlake Dr., College Station, TX, 77845, United States
The abstract for the meeting has already been submitted (several months ago) to Ms. Trudy Lewis and it was accepted. Please see the accepted text of the abstract.
CHARACTERIZATION OF PARALIC PALEOENVIRONMENTS USING BENTHIC FORAMINIFERA AND THECAMOEBIANS FROM EARLY CRETACEOUS SEDIMENTS (SCOTIAN SHELF)
Fiorini, Flavia 11; Wach, Grant D2; Scott, David B2
11Smithsonian Tropical Research Institute, Ancon, Panama, none, Panama; 25 Edsel dr, Halifax, Nova Scotia, B3H3J5, Canada
The benthic foraminifera and thecamoebians from an early Cretaceous cored interval of Cohasset A-52 well (located on the Scotian Shelf- North Atlantic), were used to interpret the depositional environments of these sediments. Paleoenvironmental interpretation was based on the analysis of samples from four cored intervals of A-52 corresponding to 25 m of interbedded, gray-black shale, mudstone and sandstone belonging to the Cree Member of the Logan Canyon Formation (Aptian –Albian). The foraminiferal association recovered from the samples is comprised mainly of agglutinated species of Trochammina, Haplophragmoides, Ammobaculites and Verneulinoides which are comparable at the generic level with the microfauna that live in modern marshes. A scattered occurrence of calcareous benthic foraminifera (typical of marginal marine environment) and thecamoebians (freshwater to brackish environment) is also recorded. The comparison of this microfauna with modern and fossil foraminiferal associations from paralic environment suggests that the sediments in the Cretaceous of A-52 were deposited in a marsh-estuarine environment. Additionally the species from A-52 were identical to those found in the Cretaceous of Alberta’s Bearpaw Fm.
PERMO-TRIASSIC BASINS FROM IRELAND TO NORWAY: BASIN ARCHITECTURE AND CONTROLS
Shannon, Patrick M.1; Stolfova, Katerina2
1University College Dublin UCD School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland; 2UCD School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland
Permo-Triassic strata are locally preserved in a swath of elongate basins of various shapes and sizes along the European margin of the North Atlantic. The burial of these basins beneath Jurassic, Cretaceous and Cenozoic strata, combined with tectonic effects of later rifting and continental breakup, means that the original extent and the large-scale depositional geometries of these basins are poorly constrained. This study uses seismic data, supplemented by core, wireline and outcrop information, to document the extensive development of proven (but poorly dated), largely non-marine, Permo-Triassic strata along the Irish, UK and Norwegian Atlantic margins. Data are examined from basins of different sizes, thicknesses and structural settings in the European North Atlantic region. A wide range of regional depositional geometries is identified within the Permo-Triassic to lowermost Jurassic succession. In some areas basins show pronounced asymmetry, controlled by long-standing reactivated faults. In other areas subtle broad fault-controlled geometries with switching fault polarities are documented. In yet other areas the Permo-Triassic to Lower Jurassic succession is characterized by simple uniform thicknesses across large regions. The basin architecture is controlled by a complex interplay of crustal thickness and thermal structure, inherited Variscan, Caledonian and older basement fabrics, inherited palaeotopography and the spatial and temporal rift history.
MID TO LATE CRETACEOUS STRUCTURAL AND SEDIMENTARY ARCHITECTURE AT THE TERRA NOVA OILFIELD, OFFSHORE NEWFOUNDLAND – IMPLICATIONS FOR TECTONIC HISTORY OF THE NORTH ATLANTIC
Sinclair, Iain1; Withjack, Martha O.2
1Husky Energy Suite 901, Scotia Centre, 235 Water St., St. John's, NL, A1C 1B6, Canada; 2Rutgers University, Geological Sciences, 610 Taylor Road , Piscataway, NJ, 08854-8066, United States
Multiple exploration, delineation, and development wells, in association with a high-quality 3D seismic survey over the Terra Nova oilfield, provide a detailed data set for the analysis of the mid to Late Cretaceous structural and stratigraphic development of the Jeanne d’Arc basin on the Grand Banks of Newfoundland.Closely spaced wells allow for recognition of multiple parasequences of shoreface to shelf silciclastic sediments deposited during falling relative sea level in Hauterivian through Barremian time.The northward translation of the coastline with progressive truncation of the parasequences to the south demonstrates that regional uplift of the southern margin of the Jeanne d’Arc basin occurred during and immediately following deposition of these progradational parasequences.The upper bounding surface, defined by an angular unconformity with widespread evidence of valley incision, is dated as mid-Aptian.Highly variable thicknesses of back-stepping coastal plain, shoreface and marine shelf strata document a long-term increase in relative sea level accompanied by abrupt changes in subsidence rates occurring across W- to NW-striking, syn-depositional normal faults active during the mid-Aptian through Middle or Late Albian. What do these patterns of uplift, subsidence, and faulting reveal about the tectonics of the Jeanne d’Arc basin during the mid-Cretaceous? Specifically, are the W- to NW-striking normal faults related to gravity-driven processes or plate-tectonic processes?Although the basin tilting and the presence of Triassic/Jurassic salt would support gravity-driven processes, erosion in the south and deposition in the north would inhibit the northward flow of salt.Additionally, evidence of synchronous detached shortening is lacking.Basement-involved extension would produce W- to NW-striking subsalt and suprasalt normal faults.These decoupled faults occur exclusively to the east of the border fault of the Jeanne d’Arc basin (i.e., the Murre fault).Thus, the Murre fault would have had both normal and strike-slip components of displacement during the mid-Cretaceous extension.
BIOSTRATIGRAPHIC STUDY OF CENOZOIC STRATA OF THE GRAND BANKS, NEWFOUNDLAND
Skilliter, Deborah1; Williams, G.L.2; Fensome, R.A.2; Guerstein, G.R.3; MacRae, R.A. 4; Wach, G.5
1Nova Scotia Museum 1747 Summer Street, Halifax, N.S., B3H 3A6 and Dalhousie University, Department of Earth Sciences, Halifax, NS, B3H 4R2 , Canada; 2Natural Resources Canada, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, 1 Challenger Drive, P.O. Box 1006, Dartmouth, Nova Scotia , B2Y 4A2, Canada; 3Lab de Palinologia, Depart. de Geologia, Universidad Nacional del Sur, San Juan 670, 8000 Bahia Blanca, República Argentina, Argentina; 4Saint Mary’s University, Geology Department, 923 Robie Street, Halifax, Nova Scotia, B3H 3C3, Canada; 5Dalhousie University, Department of Earth Sciences, Halifax, N.S., B3H 4R2, Canada
The only extensively cored Cenozoic sections from offshore eastern Canada were recovered from a series of coreholes drilled in 1965 by Pan American Petroleum Corporation (now part of BP P.L.C.) and Imperial Oil Canada. The coreholes are from several basins, including the Scotian, Horseshoe, South Whale and Jeanne d’Arc. Previously, only preliminary palynological studies have been made on materials from the coreholes. The current study focuses on Corehole 16 from the southern Jeanne d’Arc Basin and Corehole 2 from Bear Ridge. Corehole 16 penetrates a broadly fining-upwards section through the Banquereau Formation, with excellent dinocyst recovery, spanning the middle Eocene through the middle Miocene. Preliminary results indicate that Corehole 2 represents a similar sequence through broadly fining-upwards strata in the Banquereau Formation, spanning the Late Eocene to Pleistocene. By incorporating pollen and spores with dinocysts, we plan to consolidate the taxonomy, develop detailed event biostratigraphy, interpret local paleoenvironments, and determine the prevalence and age of offshore currents, particularly the Proto-Gulf Stream. The results will provide new insights into the Cenozoic history of offshore eastern Canada, including an awareness of climate change during this time.
LOWER TERTIARY MASS TRANSPORT SYSTEMS EXHIBITED IN UPPER CRETACEOUS WYANDOT CHALK
Smith, Brenton1
1CNSOPB 1791 Barrington St, Halifax, NS, B3J3K9, Canada
The Upper Cretaceous Wyandot formation is a thick, continuous package of limestones, marls and chalks representing deposition on a stable, shallow, open-marine continental shelf.
Extremely detailed mapping of this surface is made possible by the strong seismic signature at the top of the Wyandot limestone. Interpretation of 16 3-D surveys covering 12,000 km2 has described a complicated surface with varying degrees of erosion and has detailed several erosional features. The mapping results are displayed as a 3-D surface from which the following can be observed.
- A polygonal pattern covering much of the original chalk surface, possibly caused by brittle deformation of the Wyandot, has widths of up to 150 m.
- Early tertiary deltas prograding onto the Wyandot surface formed a series of troughs and ridges along the toe of these deltas. Most of these patterns were eroded by subsequent mass transport systems.
- Slope failure of the prograding Paleocene and Eocene deltas resulted in erosion of the upper Wyandot formation. A failure plane in the upper Wyandot detached creating a clearly defined head scarp of ~80m in height. This scarp is over 100 km in length. A 5 km wide mass transport corridor leading out to the shelf break is also clearly imaged.
- Large slide blocks over 1 km long within the mass transport systems can be observed. Numerous failure events have overprinted, resulting in a complicated pattern of mass transport systems and varying degrees of Wyandot erosion.
These observations indicate that large quantities of transported Wyandot chalkswere redeposited out to at least the upper slope. These chalks would be mixed with Tertiary delta sediments. Redeposited chalks are a major reservoir in the North Sea. Demonstrating that tertiary deltas transported sediments to the slope provides additional evidence that similarly situated, early and middle Cretaceous deltas may have also transported sediments to the slope.
A QUANTITATIVE 3D OUTCROP MODEL OF A GRAVEL DOMINATED FLUVIAL SYSTEM (LATE TRIASSIC, MINAS BASIN, NOVA SCOTIA, CANADA)
van Lanen, Xavier1; Hodgetts, David2; Redfern, Jonathan2; Williams, Brian3; Leleu, Sophie3
1PhD student Williamson Bld, Oxford Road, Manchester , Lancashire, M13 9PL, United Kingdom; 2Williamson Bld, Oxford Road, Manchester , Lancashire, M13 9PL, United Kingdom; 3Department of Geology & Petroleum Geology, King's College, Aberdeen, Aberdeenshire, AB24 3UE, United Kingdom
The Wolfville Formation was deposited in a rift basin setting during Anisian to Norian age. It is superbly exposed in both cliff sections and on extensive wave-cut platforms along the Minas Basin shore, Nova Scotia (Canada). This nature of the exposure provides unique three-dimensional sections, offering a valuable insight in the sedimentology and the facies geometries and distribution of a red bed braided fluvial-aeolian facies suite.
The selected study area is located on the southern Minas Basin shore and represents the lower unit of the Wolfville Formation. The area measures 400 m by 350 m and comprises Carnian to Norian age sediments that show a cyclicity of conglomerate / pebbly rich sandstone to a coarse lithic sandstone with sparse pebble sized clasts. The limited amount of preserved finer grained material throughout this gravel dominated system contains the faunal remains and palaeosol horizons. The base is characterised by the discordant contact with the Carboniferous and a thin alluvial breccia unit.
To obtain quantitative outcrop data, both LiDAR and DGPS data were collected and integrated with traditional geological field and laboratory data into a digital outcrop model (DOM). In the DOM the observed geological object are mapped and their geometries and distribution evaluated. The results offer a better understanding of the depositional system, and provide a geological framework for reservoir models. Such information aids improved reservoir characterisation and geostatistical modelling, as well as help explain seismic reflection data and improve flow model simulations for subsurface reservoirs.
LITHOSPHERIC DENSITY VARIATIONS AND MOHO STRUCTURE OF THE IRISH RIFTED CONTINENTAL MARGIN FROM CONSTRAINED 3-D GRAVITY INVERSION
Welford, J. Kim1; Hall, Jeremy2; O’Reilly, Brian3
1Memorial University of Newfoundland 300 Prince Philip Drive, St. John’s, NL, A1B 3X5, Canada; 2300 Prince Philip Drive, St. John’s, NL, A1B 3X5, Canada; 3Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin, 2, Ireland
The structurally complex Irish margin was separated from its conjugate pair, the northern Flemish Cap/Orphan Basin region, during Late Cretaceous rifting of the North Atlantic. While crustal-scale 2-D seismic surveys have been collected across many parts of the margin, the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling. We have undertaken a 3-D gravity inversion of the free air data over the Irish margin in order to generate a 3-D density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage. We use the GRAV3D inversion algorithm and constrain our inverted model with bathymetric and sediment thickness information. We are able to closely reproduce the observed gravity anomalies over the margin and use the resultant density anomaly model to interpret the regional Moho structure by identifying a density isosurface appropriate for the crust-mantle transition. Our interpreted Moho shows good correspondence with Moho depths from seismic results while providing a more detailed Moho depth map over the region. This map allows the lateral extent of crustal thinning beneath the Rockall Trough, the Porcupine Seabight Basin and south of Goban Spur to be investigated. We present regional cross-sections through the 3-D model to highlight lateral variations in Moho structure and lithospheric densities. We also compare sediment and crustal thickness across the margin to show deviations from local isostatic compensation. These deviations correlate with faults and rifting trends along the boundaries of most of the main structural features. Ultimately, the insights provided by our results must act as constraints for future paleoreconstructions of North Atlantic rifting.
STRUCTURE AND RIFTING EVOLUTION OF THE NORTHERN NEWFOUNDLAND BASIN FROM ERABLE MULTICHANNEL SEISMIC REFLECTION PROFILES ACROSS THE SOUTHERN MARGIN OF FLEMISH CAP
Welford, J. Kim1; Smith, Julie 2; Hall, Jeremy2; Deemer, Sharon2; Srivastava, Shiri 3; Sibuet, Jean-Claude 4
1Memorial University of Newfoundland 300 Prince Philip Drive, St. John’s, NL, A1B 3X5, Canada; 2300 Prince Philip Drive, St. John’s, NL, A1B 3X5, Canada; 3Geological Survey of Canada, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, NS, B2Y 4A2, Canada; 4Ifremer, Centre de Brest, Département des Géosciences Marines, B.P. 70, 29280 Plouzané, France
We present four multichannel seismic reflection profiles from the 1992 ERABLE experiment collected over the southern margin of Flemish Cap and extending into the Newfoundland Basin. These profiles are between and sub-parallel to lines 1 and 2 from the 2000 SCREECH seismic experiment and provide more comprehensive data coverage over the region. Combining these data with the SCREECH seismic profiles, two ODP drill sites, and other geophysical data has allowed the mapping of distinct zones of continental, transitional, and oceanic crust in this region. Comparisons with mapped crustal boundaries on the Iberian margin from detailed seismic surveys and drilling show asymmetry in the conjugate pair, with the zone of extended continental crust and transitional crust being much wider on the Iberian margin compared to the Newfoundland margin. Furthermore, while detachment faulting is evidenced on both margins, it is less widespread on the Newfoundland margin. We propose either a simple shear or a simple shear/pure shear combination model involving a westward dipping detachment fault, with the Newfoundland margin acting as the upper plate. Along- margin variations in the present- day structure, which deviate from the simple 2-D rifting model, are explained within the context of Late Jurassic to Early Cretaceous rifting and break-up.
THERMOCHRONOLOGY EVIDENCE FOR MESOZOIC AND CENOZOIC INVERSIONS OF THE CONTINENTAL MARGIN OF NOVA SCOTIA, CANADA
Zentilli, M.1; Grist, A. M.2; Ryan, R.3; Ravenhurst, C. E.1; Li, G.1
1Department of Earth Sciences Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; 2Department of Earth Sciences, University of Queensland, Brisbane, Queensland, 4072, Australia; 3Nova Scotia Department of Natural Resources, PO Box 698, Halifax, Nova Scotia, B3J 2T9, Canada
Considerable erosion followed the folding, metamorphism and grainotoid intrusion (ca. 380 Ma) of the Devonian Acadian Orogeny. By the Early Carboniferous (ca. 350 Ma) coarse clastics - followed by extensive marine carbonates and evaporites - were deposited non-conformably on exhumed granitoids and metamorphic rocks. The Carboniferous-to-Permian Maritimes Basin developed, accumulating clastic sediments in excess of 12 km in its depocentre further north. Maximum burial of the basin was attained in the Late Carboniferous (ca. 300 Ma), and the youngest sediments preserved in this basin are Lower Permian in age. Apatite fission track thermochronology studies have shown that basin inversion led to erosion of ca. 5 km of strata in the Late Triassic, coinciding with the Atlantic break-up unconformity, and preceding extensive but short-lived basaltic magmatism (ca. 200 Ma). The traditional view of gradual exhumation and peneplanation of the Nova Scotia margin since the Triassic-Jurassic is untenable. During the Aptian-Albian, continental sediments were deposited throughout Atlantic Canada over a weathered surface that included karst and has wide expression along the margin. The exhumation of the land went hand in hand with deposition in the adjacent Scotian Basin, part of the present Atlantic passive margin, an active depositional basin from the Late Triassic-Early Jurassic to the present. In such a passive margin it was expected that rocks deep in offshore wells would be at their maximum temperature today. However, our apatite fission track thermochronology data indicates that rocks in offshore wells were once tens of degrees hotter (e.g. within the oil window) than at present, and that substantial post-Paleocene cooling has occurred. Although higher paleo-mean annual surface temperatures in the Late Cretaceous may account for some of the thermal anomaly detected, the most probable cause for this cooling is inversion of the margin and erosion of ca. 1 km of post-Albian cover from onland and offshore, probably in the Eocene - Oligocene. This Tertiary inversion may have important implications for hydrocarbon maturation, the distribution of deep-water sand bodies, overpressures, and post-Paleocene canyons and unconformities.
THERMAL EFFECTS OF SALT ON THE PETROLEUM SYSTEM: EVIDENCE FROM FISSION TRACK THERMOCHRONOLOGY, FLUID INCLUSIONS AND BASIN MODELLING
Zentilli, M.1; Wielens, H. 2; Grist, A. M. 3; Kettanah, Y. 4; Negulic, E. 4; Brown, E. 5
1Department of Earth Sciences Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; 2Geological Survey of Canada – Atlantic, NRCAN, Dartmouth, Nova Scotia, B2Y 4A2, Canada; 3Department of Earth Sciences, University of Queensland, Brisbane, Queensland , 4072, Australia; 4Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; 5Dept. of Geology, St. Mary's University, Halifax, Nova Scotia, B3H 3C3, Canada
The thermal conductivity of salt is up to four times greater than other sedimentary rocks, thus salt diapirs focus geothermal heat resulting in a high-temperature anomaly in overlying basinal sediments. Depending on the shape of the salt body and its depth, the heat flow over the salt can be 2 to 3 times greater than away from the salt, with consequent drastic effects on diagenesis and hydrocarbon maturation; i.e., over mature above, and under mature below salt. In addition to heat conduction, advection of warm fluids (brines, oil and gas) produces highly localized heat anomalies on top of diapirs, as previously proposed by others for offshore Atlantic Canada.
In the Maritimes basin, Early Carboniferous salt of the Windsor Group has risen to the surface locally from a depth of ca. 8 km. Apatite fission track data indicate that the basin was inverted and rocks now at surface cooled below ca. 100oC during the Triassic-Jurassic Atlantic margin breakup, whereas apatite within siltstone in the salt diapir yields apparent Cretaceous ages; the temperature-sensitive fission-track lengths having been significantly shortened (equivalent to what happens >3 km depth in a well). Time-temperature modelling of the data requires re-burial of the salt structure post-Early Cretaceous, and heating the diapir to higher temperatures than the regional background, confirming the focused thermal effects of the diapir. We have demonstrated similar thermal effects from evaporite diapirs in the Sverdrup Basin in the Canadian Arctic.
We have studied fluid inclusions in autochthonous and allochthonous salt in Atlantic Canada. Supposedly impermeable salt contains a variety of generations of fluid inclusions, some with brines, some with oil and gas. It is evident that salt has been permeable to various fluids. Entrapment temperatures of the fluids vary from 25oC to more than 100oC. For autochthonous Jurassic salt this implies a sub-salt source rock or an algal source within the salt.
Modelling of Scotian Basin wells; e.g., Wyandot, using Petromod® shows that the presence of salt in the stratigraphic column results in drastic changes in the thermal evolution of the petroleum system.
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