Northern Basin Margin Research Articles

The stratigraphic architecture and evolution of the Burdigalian carbonate—siliciclastic sedimentary systems of the Mut Basin, Turkey

This study describes the coeval development of the depositional environments in three areas across the Mut Basin (Southern Turkey) throughout the Late Burdigalian (early Miocene). Antecedent topography and rapid high-amplitude sea-level change are the main controlling factors on stratigraphic architecture and sediment type. Stratigraphic evidence is observed for two high-amplitude (100–150 m) sea-level cycles in the Late Burdigalian to Langhian. These cycles are interpreted to be eustatic in nature and driven by the long-term 400-Ka orbital eccentricity-cycle-changing ice volumes in the nascent Antarctic icecap. We propose that the Mut Basin is an exemplary case study area for guiding lithostratigraphic predictions in early Miocene shallow-marine carbonate and mixed environments elsewhere in the world. The Late Burdigalian in the Mut Basin was a time of relative tectonic quiescence, during which a complex relict basin topography was flooded by a rapid marine transgression. This area was chosen for study because it presents extraordinary large-scale 3D outcrops and a large diversity of depositional environments throughout the basin. Three study transects were constructed by combining stratal geometries and facies observations into a high-resolution sequence stratigraphic framework. 3346 m of section were logged, 400 thin sections were studied, and 145 biostratigraphic samples were analysed for nannoplankton dates (Bassant, P., 1999. The high-resolution stratigraphic architecture and evolution of the Burdigalian carbonate-siliciclastic sedimentary systems of the Mut Basin, Turkey. PhD Thesis. GeoFocus 3. University of Fribourg, 277 p.). The first transect (Alahan) is on the northwestern basin margin. Here, the siliciclastic input is high due to the presence of a river system. The siliciclastic depocentre migrates landwards during transgressions, creating an ecological window allowing carbonates to develop in the distal part of the delta. Carbonate production shuts down during the regression when siliciclastics return. The second transect (Pirinç) is also situated on the northern basin margin 12 km to the east of the Alahan section. It shows a complete platform-to-basin transition. An isolated carbonate platform complex develops during the initial flooding, which is drowned during a time of rapid sea-level rise and environmental stress, associated with prograding siliciclastics. The shelf margin then retrogrades forming large-scale clinoform geometries and progrades before a major sea-level fall provokes slumping collapse, followed by rebuilding of the shelf margin as sea level rises again. The third transect (Silifke) has a steep asymmetric Pre-Miocene valley-topography, forming a narrow strait, linking the Mut Basin to the Mediterranean. Strong tidal currents are generated in this strait area. Siliciclastic input is low and localised. Eighty metres of cross-bedded bioclastic sands are deposited in a tidal regime at the base. Subsequently, carbonate platforms backstep against the shallow-dipping northern flank, while platforms only develop on the steep southern flank when a firm wide shallow-marine substrate is provided by a bench on the footwall block. The energy of the environment decreases with increased flooding of the strait area. Third-order sequences and higher-order parasequences have been identified in each transect and correlated between transects. Correlations were made using biostratigraphic data and high-resolution sequence stratigraphy in combination with the construction of the relative sea-level curve for each site. The third-order highstands are stacked in a proximal position and separated by exposure surfaces, while the lowstands, deposited in a distal setting, are separated by deep-marine (offshore or subphotic) deposits. The parasequences produce dominantly aggradational and progradational geometries with transgressive ravinement surfaces and exposure surfaces developing at times. Reconstruction of the depositional profile shows that the third-order sequences are driven by relative sea-level oscillations of 100–150 m, and that these may be attributed to 400-Ka orbital eccentricity cycles. The parasequences are driven by eustatic 20–30 m sea-level oscillations, which may be attributed to the 100-Ka orbital eccentricity cycles. The isolated carbonate build-ups in the Pirinç and Alahan transects develop at the same time as bioclastic tidal deposits in the Silifke area during the transgression of sequence 1. This is caused by a difference in hydrodynamic regime: a direct result of basin morphology funneling tidal currents in the Silifke area. We also demonstrate how during the highstands a siliciclastic delta system progrades in the Alahan area, while only 12 km to the east, a fringing carbonate platform develops, showing how siliciclastic input can have a very localised effect on carbonate environments. The exceptional quality of the outcrops with its variety of environments and its location at the Tethyan margin make this site a good candidate for a reference model for Burdigalian reef and platform architectures.

Numerical modelling of the thermal evolution of the northwestern Dniepr–Donets Basin (Ukraine)

The Dniepr–Donets Basin (DDB) is a Late Devonian rift structure located within the East-European Craton. Numerical heat flow models for 13 wells calibrated with new maturity data were used to evaluate temporal and lateral heat flow variations in the northwestern part of the basin. The numerical models suggest that heat flow was relatively high during Late Carboniferous and/or Permian times. The relatively high heat flow is probably related to an Early Permian re-activation of tectonic activity. Reconstructed Early Permian heat flow values along the axial zone of the rift are about 60 mW/m 2 and increase to 90 mW/m 2 along the northern basin margin. These values are higher than those expected from tectonic models considering a single Late Devonian rifting phase. The calibration data are not sensitive to variations in the Devonian/Carboniferous heat flow. Therefore, the models do not allow deciding whether heat flows remained high after the Devonian rifting, or whether the reconstructed Permian heat flows represent a separate heating event. Analysis of the vitrinite reflectance data suggest that the northeastern Dniepr–Donets Basin is characterised by a low Mesozoic heat flow (30–35 mW/m 2), whereas the present-day heat flow is about 45 mW/m 2.

Reservoir modelling of the Hamitabat Field, Thrace Basin, Turkey: an example of a sand-rich turbidite system

Abstract The inter-montane, fault bounded Thrace Basin of northwestern Turkey is one of the largest Tertiary sedimentary basins in Turkey. Tertiary sedimentation within the basin comprises interbedded fine- to coarse-grained clastics from a variety of depositional environments, muddy carbonates with local reef developments, and tuff horizons. A thick pile of Quaternary alluvial deposits overlies this marine-dominated succession. Accommodation space, and hence sedimentation, has been influenced by the structural history of the basin, reflecting the active compressional setting adjacent to the North Anatolian Fault System. The Hamitabat Field, located towards the northern basin margin, is the largest developed gas field in the Thrace Basin. The trapping mechanism is by an anticlinal structure bounded to the north by a northwest-southeast striking reverse fault and to the south by a set of antithetic normal faults with a general east-west strike orientation. The main reservoir is the middle to upper Eocene Hamitabat Formation, comprising sandstones deposited by episodic gravity flow events in a shallow marine shelf to slope environment, with sediment sourced from fluvial/deltaic systems to the north and northeast. Correlation, based mainly on upward-fining cyclical successions, indicates lobate depositional geometries and topographic control on sediment dispersal (compensation). Progradational shallow marine sandstones, which infill earlier topography, overlie the turbidite succession. A three-dimensional geocellular reservoir model of the field, based on well and seismic data, has been constructed. The model has been subdivided on the basis of the stratigraphical correlation and populated with facies objects with dimensions based on analogue data. These facies have then been populated with petrophysical parameters. The model has been upscaled and simulated fluid flow through the modelled volume has been compared with the production history. This history matching provides an opportunity to assess and refine the model and to determine a strategy for future field development.

Upper Jurassic (Oxfordian) Smackover carbonate petroleum system characterization and modeling, Mississippi Interior Salt Basin area, northeastern Gulf of Mexico, USA

The Upper Jurassic (Oxfordian) Smackover Formation is a prolific oil and gas reservoir in the northern Gulf of Mexico, including the Mississippi Interior Salt Basin area. The Smackover petroleum system is categorized as a giant petroleum system and ranks fourth among recognized Upper Jurassic petroleum systems. In the Mississippi Interior Salt Basin area, the components of the Smackover petroleum system include pre rift, syn rift and post rift siliciclastic, evaporite, and carbonate underburden and overburden rocks, Smackover subtidal lime mudstone source rocks, uppermost Smackover anhydrite and Buckner Anhydrite Member subaqueous saltern and sabkha seal rocks, and upper Smackover shoal complex and tidal flat complex packstone, grainstone, boundstone and dolostone reservoir rocks. The critical events include the initiation of the generation of crude oil, the commencement of hydrocarbon expulsion, the initiation of hydrocarbon migration, and the entrapment of hydrocarbons during the Early to Late Cretaceous. The critical moment for the Smackover petroleum system is the time of peak hydrocarbon expulsion in the mid to late Early Cretaceous in basin center areas and mid to latest late Cretaceous in areas along the northern basin margin. *** DIRECT SUPPORT *** A00QA034 00003

Depositional environments, architecture, and controls of Early Cretaceous non-marine successions in the northwestern part of Kyongsang Basin, Korea

In the northwestern part of Kyongsang Basin, southeast Korea, non-marine successions of interbedded sandstone and mudstone are divided into successive stratigraphic units on the basis of facies assemblages and sandstone architecture. Parts of the successions (Sinpyong–Anpyong and Jotap units), formed in southward- or southeastward-draining fluvial systems, are documented in detail in terms of macroform-scale to stratigraphic-level architecture for the assessment of fluvial styles and evolution of non-marine depositional environments. The Sinpyong–Anpyong unit consists of thick sandstone bodies (2–47 m thick), thin sandstone bodies (generally <2 m thick), and mudstone-dominated bodies. The thick sandstone bodies are characterized by superposition of numerous bars and channels, indicative of braided-channel systems. The channels are estimated at a few to 10 m deep and 9 m to tens of meters wide. The thin sandstone bodies comprise planar beds of massive, horizontally stratified, and trough cross-stratified sandstones, interpreted as sand sheets and splays. The mudstone-dominated bodies largely consist of purple siltstone in the northern (proximal) part and gray mudstone in the southern (distal) part, representing well-drained floodplains and poorly drained floodplains with local shallow lakes, respectively. In the basal and uppermost parts of Sinpyong–Anpyong unit, the distal poorly drained facies (gray mudstone) expands to the northern basin margin. The Jotap unit, overlying the Sinpyong–Anpyong unit, comprises thick sandstone bodies (2–10 m thick), interbedded sandstone/siltstone bodies, and siltstone-dominated bodies. The thick sandstone bodies are dominated by the deposits of small bars and dunes with common lenticular beds of purple siltstone and internal scour surfaces, suggestive of bedform-dominated channels with ephemeral discharges. The channels are estimated at generally a few meters in depth and a few tens to hundreds of meters in width. The interbedded sandstone/siltstone bodies comprise thin, sheet-like and lenticular sandstone beds (<2 m thick) interbedded with purple siltstone, interpreted as channel-proximal floodplains where sand was frequently deposited as sand sheets and splays, levees, and crevasse-channel fills. The siltstone-dominated bodies consist mostly of purple siltstone with subordinate thin sandstone beds, representing channel-distal, well-drained floodplains. Along with the marked change in fluvial styles, the successions show systematic variations in the proportion and connectedness of channel sandstone bodies and the distribution of floodplain/lake facies. The basal and uppermost parts of the Sinpyong–Anpyong unit are characterized by the sourceward expansion of distal, poorly drained floodplain/shallow lake facies and the low proportion and connectedness of channel bodies. Following these gray mudstone-dominated sequences, the middle part of Sinpyong–Anpyong unit and Jotap unit show increases in the proportion, connectedness, and grain size of channel bodies and basinward expansion of proximal, well-drained floodplain facies. Such a stratigraphic architecture can be attributed to the fluctuations in the ratio of accommodation space/sediment supply, regulated by repeated basin subsidence.

Sequence stratigraphy with emphasis on platform-related parasequences of the Zechstein 2 carbonate (Ca2) – the northern platform margin of the Southern Permian Basin (NE Germany)

Facies analysis combined with sequence stratigraphic interpretation of the Upper Permian carbonate (Ca2) of NE Germany (i.e. northern basin margin of the Southern Permian Basin) confirm the existence of a rimmed platform with a steep and tectonically structured slope. The karstified A1 platform is overlain by deposits of a thin transgressive systems tract (TST) and a thick highstand systems tract (HST) which shows two larger-scale regressive shallowing-upwards cycles (4th order) with typical stacking patterns of small-scale cycles (5th order). The TST consists of bitumen-rich mudstones with reworked clasts of anhydrite and early cemented wacke- to grainstones, and it shows two, probably 5th-order, deepening-upwards cycles. The first larger-scale shallowing-up cycle on the Ca2 platform (4th-order) is dominated by aggradation of the bar and shoal deposits, whereas the second one is dominated by progradation. The tops of both cycles are characterised by erosional and exposure surfaces. Various types of small-scale shallowing-upwards cycles (5th-order) are observed in the bar, in the intertidal and in the algal-dominated supratidal environment, showing pronounced transgressive boundaries. On the slope and in the basin, equally thick TST and HST are observed. These incorporate carbonate turbidites which indicate "highstand shedding" from the platform. Various orders of relative sea-level variations are discussed. Controlling factors include tectonics, climate, and eustatic processes. A combined carbonate and evaporite sequence was found on the upper Ca2 slope, which may indicate a Ca2-lowstand systems wedge.

Inversion tectonics of the northern margin of the Basque Cantabrian Basin

Abstract The northern margin of the Basque-Cantabrian Basin was analysed combining stratigraphic and structural data from both surface and subsurface together with reflectance of vitrinite data from oil wells. The use of cross-section balancing techniques in addition to thermal modelling enabled us to reconstruct the tectonic, burial and thermal evolutions of the basin margin as well as those of the Landes High to the N in two different periods. The section restoration at the end of the Cretaceous shows a northern basin margin structure influenced by evaporites related to south-dipping normal faults. The reconstruction in middle Eocene times yielded up to 1 800 m of Paleocene-middle Eocene deposits on top of the basin margin. Subsequent tectonic inversion related to the Pyrenean compression led to the north-directed thrusting of basement units and to the formation of thrust slices or inverted folds in the cover along the northern margin of the basin. Tectonic subsidence analysis together with maturity data provided evidence that oil was generated in the basin during the late syn-rift and post-rift stages in the Late Cretaceous and became overmature during the period of incipient inversion after 55 Ma. In the autochthonous Landes High, the oil was generated after the tectonic inversion period 37 Ma.

Physiography of an active transpressive margin basin: high-resolution bathymetry of the Santa Barbara basin, Southern California continental borderland

High-resolution swath bathymetry and backscatter data from the Santa Barbara basin reveal a distinct assemblage of morphologic and sedimentologic features characteristic of the tectonically active setting of the basin. Such characteristics include the north–south asymmetry of the basin, the presence of an intra-basinal structural and morphologic high, extensive mass wasting, and fields of mounds and pockmarks. The north–south asymmetry of the basin and the increased abundance of slope failure along the northern basin slope likely reflect higher rates of tectonic shortening and sediment accumulation along the northern basin margin. High sedimentation rates lead to high pore water content of the sediment which, in combination with seismic shaking, may explain the abundance of mass wasting features even on shallowly inclined lower basin slopes. Mounds and pockmarks are the surface expression of locally extensive fluid seepage which we interpret to be driven by a combination of high sedimentation rates, a high organic content of sediment, and anoxic bottom water conditions during extended periods in Neogene and Quaternary times. During ROV dives we observed active fluid seepage to have occurred preferentially on the shelf and on a structural and topographic high, presumably due to structural focusing of migrating formation fluids. The preferred alignment of some pockmarks along faults is consistent with structurally controlled expulsion of formation fluids from underlying Neogene units. Despite the high tectonic activity of the basin, fault scarps are rare and only observed in areas of low sediment accumulation on the shelf and on topographic highs. Mass balance considerations suggest that sedimentation rates averaged over interseismic time scales are too high and scarp growth rates too low for scarps to be characteristic features of the basin floor. Long-term sediment accumulation rates that account for the effect of sediment compaction are low enough, however, to lead to long-wavelength surface expressions of the most active faults.

The Donets Basin (Ukraine/Russia): coalification and thermal history

The Donets Basin (Donbas) is one of the major late Paleozoic coal basins in the world. The Donbas Foldbelt is an inverted part of the Donets Basin characterized by WNW–ESE-trending folds and faults. The age of basin inversion is under discussion. Large parts of the Donets Basin host anthracite and meta-anthracite. Low-rank coals are restricted to the western and northern basin margins. Vitrinite reflectance patterns along the Gorlovka Anticline indicate syn-deformational coalification. Vitrinite reflectance isolines are displaced along thrusts, clear evidence that main coalification predates late faulting. 1-D and 2-D numerical models were applied to elucidate the factors that control coalification in the western Donets Basin (Krasnoarmeisk Monocline, Kalmius–Torets Depression, South Syncline). The models indicate that the depth of the seams and the heat flow during maximum (Permian) burial are the most important parameters. The thickness of late Carboniferous and Permian rocks increased from the southwestern basin margin towards the basin center. Permian erosion along the Krasnoarmeisk Monocline and in the Kalmius–Torets Depression was on the order of 2–3 km. More rocks were eroded southeast of the Donetsk–Kadievka Fault Zone (4–5 km). Heat flow during maximum burial was in the range of 40–75 mW/m 2. Heat flow in the Krasnoarmeisk Monocline and the Kalmius–Torets Depression increased in a northeastward direction from 40 to 55 mW/m 2. Heat flow at the eastern edge of the Kalmius–Torets Depression and in the South Syncline was in the range of 60–75 mW/m 2 and increased towards the southeast. The resulting coalification pattern in this area was overprinted by thermal events in the northern Krasnoarmeisk Monocline and the South Syncline. These are probably related to (Permian?) magmatic intrusions. Coked coal occurs at the contact to presumed Permian sills and dikes southwest of Donetsk.

Large-Scale Cycle Architecture in Continental Strata, Hornelen Basin (Devonian), Norway

ABSTRACT Nine large-scale stratigraphic cycles, each about 100 m thick, along the northern margin of the Hornelen basin, western Norway, record systematic expansions and contractions of alluvial-fan, braidplain, and lake facies tracts. The braidplain facies tract occupies the basin center, from time to time expanding toward the margins, and constitutes the deposits of axial or longitudinal drainage from an eastern source. The alluvial-fan facies tract, which comprises the deposits of high-gradient transverse drainages, occupies a narrow belt close to the fault-bounded basin margin. The lake facies tract is between the alluvial-fan and braidplain facies tracts. Physical correlation of strata shows that the large-scale cycles are symmetric in all facies tracts. The symmetry of the large-scale cycles, in which the base-level rise and fall hemicycles of each cycle are of approximately the same thickness, indicates that sediment accumulated in all environments during the entire base-level cycle. Absence of regional unconformities (sequence boundaries) also indicates approximately continuous sediment accumulation in the basin during base-level cycles. The base-level fall-to-rise turnaround is represented by an interval of strata, rather than by a sequence boundary, at the maximum expansion of the alluvial-fan facies tract. Condensed sections are also absent. They are represented mainly by intervals of lake strata at base-level rise-to-fall turnarounds. Strata in the base-level fall hemicycle (decreasing accommodation) accumulated as the braidplain and alluvial-fan facies tracts expanded from the basin center and the northern basin margin, respectively. Expansions of these two facies tracts filled the basin, while the lake facies tract contracted. Strata in the base-level rise hemicycle accumulated as the alluvial-fan and braidplain facies tracts contracted sourceward, respectively toward the northern and eastern basin margins, during times of increasing accommodation. This sourceward retreat of the alluvial-fan and braidplain facies tracts was coincident with expansion of the lake facies tract. At the rise-to-fall turnarounds, alluvial-fan and braidplain sediments are stored near their respective sources toward the basin margins, and the centers of mass of these facies tracts are at basin-margin positions. During base-level fall time, the centers of mass of the alluvial-fan and braidplain facies tracts migrate basinward. The alluvial-fan and braidplain facies tracts usually expand toward each other simultaneously, and then move away from each other simultaneously. This in-phase relationship is replaced by a reciprocal stacking pattern when the two facies tracts abut each other near base-level fall-to-rise turnarounds. When the two facies tracts are in contact, the higher-gradient alluvial-fan facies tract initially blocks expansion of the braidplain. As the alluvial-fan facies tract retreats toward the basin margin and fan-margin gradients are reduced, however, the braidplain expands across former fan margins. In the reciprocal configuration, the two facies tracts move in tandem in the same direction. This reciprocal pattern plus changes in aggradation-to-progradation ratio of the alluvial-fan facies tract suggest that alluvial-fan morphology changes during base-level cycles. Large-scale cycle stacking patterns show significant changes in basin-fill architecture through time, including syndepositional structural changes accompanied by changes in stratal geometries, a change from ephemeral to permanent lakes, permanent increase in alluvial-fan gradients, and permanent reduction of alluvial-fan radii and volume at the northern basin margin. Consideration of these changes and the largely in-phase relationships between facies tracts sourced by two separate sediment supplies suggest that an interplay of climate, self-regulatory, and tectonic factors controlled sedimentary accumulation within the Hornelen basin.

Formation, evolution, and inversion of the middle Tertiary Diligencia basin, Orocopia Mountains, southern California

The Diligencia basin, located in the eastern Orocopia Mountains of southern California, contains 1500–2000 m of Oligocene−Miocene continental, siliciclastic sedimentary rocks and subordinate limestone and evaporite deposits, intercalated with basaltic lavas. These rocks are locally intensely folded and faulted, defining in present-day coordinates an elongate east-west−trending basin, and are unconformably overlain by flat-lying late Pliocene(?) and Pleistocene alluvial deposits. The sedimentological, stratigraphic, and structural history of the basin is compatible with late Oligocene−early Miocene formation as a half-graben basin produced by orthogonal, Basin and Range−type extension, and latest Miocene to Pliocene basin inversion in either a localized transpressional Transverse Range regime, or a more diffuse compressional regime associated with north-south shortening of the entire Mojave block. Facies associations in the lower part of the Diligencia basin display a distinctly asymmetric distribution across the basin, indicating deposition in a half-graben with a steep, possibly fault controlled, south-facing northern escarpment and a more gentle north-facing southern slope. Paleocurrent data, particularly from high-energy deposits on the northern basin margin, indicate stream flow toward the southeast to south-southeast, oblique to the deformed basin margins, and suggest an approximate northeast to east-northeast strike for the basin before deformation. Previously published paleomagnetic data, however, indicate that the elongate, currently east-west−trending, fault block containing the Diligencia basin has rotated clockwise by as much as 110° about a vertical axis (angle depends on data and model used) since deposition ceased. If correct, this would suggest that the basin may have originally opened to between the northeast and east-northeast, subparallel to well-documented extension directions in Miocene age basins in the Mojave Desert to the east. Clockwise rotation on east-west fault blocks exposed in this region has previously been bracketed as between ca. 10 and 4.5 Ma. Structural and paleomagnetic data indicate that inversion of the Diligencia basin occurred after block rotation, implying a latest Miocene to Pliocene age for inversion. We speculate that basin inversion within a north-south (and still active) compressive stress field resulted from the locking, and subsequent internal deformation, of this previously passively rotating elongate crustal block.

The Neogene Fohnsdorf Basin: basin formation and basin inversion during lateral extrusion in the Eastern Alps (Austria)

The evolution of the early/middle Miocene Fohnsdorf Basin has been studied using borehole data, reflection seismic lines, and vitrinite reflectance. The basin is located along the sinistral Mur-Murz fault system and probably formed as an asymmetric pull-apart basin, which was subsequently modified by halfgraben tectonics, as a consequence of eastward lateral extrusion. Sedimentation started with the deposition of fluvio-deltaic sediments. Thick coal accumulated in the northwestern basin. Thereafter subsidence rates increased dramatically with the formation of a lake several hundred meters deep. The lake was filled mainly from the north with more than 1500 m of sediments showing a coarsening-upward trend due to southward prograding deltaic lobes. A sequence of more than 1000 m of boulder gravels (Blockschotter) in the southeastern part of the basin are interpreted as the upper part of a coarse-grained fan delta succession, which accumulated along a normal fault along the southern basin margin. Fan deltas reached the central basin only during the early stages of sedimentation and during the late stages of basin formation. Miocene heat flow was approximately 65–70 mW/m2, which is significantly lower than in other basins along the Mur-Murz fault system. The present-day southwestern basin margin is a recent feature, which is related to transpression along the dextral Pols-Lavanttal fault system. It is formed by reverse faults constituting the northeastern part of a flower structure. Miocene sediments in the Feeberg valley are preserved along its southwestern part. Uplift of the central part of the flower structure was at least 2.4 km. North–south compression resulted in the deformation of the basin fill, uplift of the E/W-trending basement ridge separating the Fohnsdorf and Seckau basins, and in the erosion of 1750 m of sediments along the northern basin margin.

Wide-angle seismic control on the development of the Munster Basin, SW Ireland

Abstract Three wide-angle seismic profiles were acquired from onshore southern Ireland during VARNET-96. These data provide the only subsurface seismic images of a series of predominantly Late Palaeozoic sedimentary basins. The Dingle Basin is a broadly symmetrical rift on the Dingle peninsula, but assumes a half-graben geometry to the east. The southern syn-rift basin margin is defined by the north-dipping Dingle Bay-Galtee Mountains Line. A south-dipping normal fault at Kerry Head marks the northern basin margin in the west, with displacement on this structure decreasing towards the east. The Dingle Basin is separated from the Munster Basin to the south by a basement horst. Seismic data strongly suggest that the Killarney-Mallow Fault Zone, located on the southern margin of this positive feature, is the Munster Basin northern syn-rift marginal fault. The preserved extensional displacement on this detachment decreases from c. 2.5 km in northern Iveragh, to c. 1 km at Mallow, suggesting that the fault tips out to the east of Mallow. A tilted fault block, possibly cored by shallow granite, is imaged in the northern Munster Basin. This fault terrace is bounded to the south by the Cork-Kenmare Line. The combined Munster Basin and South Munster Basin succession thickens across the Cork-Kenmare Line to a maximum thickness of 8 km on the Beara peninsula. A tectonic thickness of 6 km of sediment is modelled at the Old Head of Kinsale, increasing to 7 km in the southwest.

The tectonosedimentary evolution of the northern margin of the Carboniferous foreland basin of NE Germany

The geometry and evolution of the northern margin of the Carboniferous foreland basin in NE Germany was examined in terms of depositional environments, petrographic and geochemical data. Lower Carboniferous units are carbonate-rich and predominantly marine. By Namurian times continental environments are established along the northern basin margin with turbiditic sedimentation persisting in the south. The Upper Carboniferous succession is continental and clastic. The sandstones were derived from a quartz-rich source, located to the north, with subordinate sedimentary input. Basin evolution and the development of a characteristic marine-to-continental sedimentary succession, while being predominantly controlled by flexure induced by the Variscan Orogen to the south, was also influenced by eustatic sea-level variations and more localised tectonic movements.

Tertiary facies architecture in the Kutai Basin, Kalimantan, Indonesia

The Kutai Basin occupies an area of extensive accommodation generated by Tertiary extension of an economic basement of mixed continental/oceanic affinity. The underlying crust to the basin is proposed here to be Jurassic and Cretaceous in age and is composed of ophiolitic units overlain by a younger Cretaceous turbidite fan, sourced from Indochina. A near complete Tertiary sedimentary section from Eocene to Recent is present within the Kutai Basin; much of it is exposed at the surface as a result of the Miocene and younger tectonic processes. Integration of geological and geophysical surface and subsurface data-sets has resulted in re-interpretation of the original facies distributions, relationships and arrangement of Tertiary sediments in the Kutai Basin. Although much lithostratigraphic terminology exists for the area, existing formation names can be reconciled with a simple model explaining the progressive tectonic evolution of the basin and illustrating the resulting depositional environments and their arrangements within the basin. The basin was initiated in the Middle Eocene in conjunction with rifting and likely sea floor spreading in the Makassar Straits. This produced a series of discrete fault-bounded depocentres in some parts of the basin, followed by sag phase sedimentation in response to thermal relaxation. Discrete Eocene depocentres have highly variable sedimentary fills depending upon position with respect to sediment source and palaeo water depths and geometries of the half-graben. This contrasts strongly with the more regionally uniform sedimentary styles that followed in the latter part of the Eocene and the Oligocene. Tectonic uplift documented along the southern and northern basin margins and related subsidence of the Lower Kutai Basin occurred during the Late Oligocene. This subsidence is associated with significant volumes of high-level andesitic–dacitic intrusive and associated volcanic rocks. Volcanism and uplift of the basin margins resulted in the supply of considerable volumes of material eastwards. During the Miocene, basin fill continued, with an overall regressive style of sedimentation, interrupted by periods of tectonic inversion throughout the Miocene to Pliocene.

Tectonics and sedimentation in the hangingwall of a major extensional detachment: the Devonian Kvamshesten Basin, western Norway

The Middle Devonian Kvamshesten Basin in western Norway is a late‐orogenic basin situated in the hangingwall of the regional extensional Nordfjord–Sogn Detachment Zone. The basin is folded into a syncline with the axis subparallel to the ductile lineations in the detachment zone. The structural and stratigraphic development of the Kvamshesten Basin indicates that the basin history is more complex than hitherto recognized. The parallelism stated by previous workers between mylonitic lineation below the basin and intrabasinal fold axes is only partly reflected in the configuration of sedimentary units and in the time‐relations between deposits on opposing basin margins. The basin shows a pronounced asymmetry in the organization and timing of sedimentary facies units. The present northern basin margin was characterized by bypass or erosion at the earliest stage of basin formation, but was subsequently onlapped and eventually overlain by fanglomerates and sandstones organized in well‐defined coarsening‐upwards successions. The oldest and thickest depositional units are situated along the present southern basin margin. This as well as onlap relations towards basement at low stratigraphic level indicates a significant component of southwards tilt of the basin floor during the earliest stages of deposition. The inferred south‐eastwards tilt was most likely produced by north‐westwards extension during early stages of basin formation. Synsedimentary intrabasinal faults show that at high stratigraphic levels, the basin was extending in an E–W as well as a N–S direction. Thus, the basin records an anticlockwise rotation of the syndepositional strain field. In addition, our observations indicate that shortening normal to the extension direction cannot have been both syndepositional and continuous, as suggested by previous authors. Through most of its history, the basin was controlled by a listric, ramp‐flat low‐angle fault that developed into a scoop shape or was flanked by transfer faults. The basin‐controlling fault was rooted in the extensional mylonite zone. Sedimentation was accompanied by formation of a NE‐ to N‐trending extensional rollover fold pair, evidenced by thickness variations in the marginal fan complexes, onlap relations towards basement and the fanning wedge geometry displayed by the Devonian strata. Further E–W extension was accompanied by N–S shortening, resulting in extension‐parallel folds and thrusts that mainly post‐date the preserved basin stratigraphy. During shortening, conjugate extensional faults were rotated to steeper dips on the flanks of a basin‐wide syncline and re‐activated as strike‐slip faults. The present scoop‐shaped, low‐angle Dalsfjord fault cross‐cut the folded basin and juxtaposed it against the extensional mylonites in the footwall of the Nordfjord–Sogn detachment. Much of this juxtaposition may post‐date sedimentation in the preserved parts of the basin.Basinal asymmetry as well as variations in this asymmetry on a regional scale may be explained by the Kvamshesten and other Devonian basins in western Norway developing in a strain regime affected by large‐scale sinistral strike‐slip subparallel to the Caledonian orogen.

Late highstand patterns of shifting and stepping coastal barriers and washover-fans (late Messinian, Sorbas Basin, SE Spain)

The late Messinian Sorbas Member, up to 75 m thick, consists in its type area of a parasequence set of three prograding coastal barriers (sequences I–III), associated with lagoon and washover sediments. Around the town of Sorbas these strata can be studied exceptionally well due to absence of burrowing by raised Messinian salinities and exposure along a network of up to 30 m deep canyons. Fifteen vertical sections were logged and carefully correlated. This permits to reconstruct and discuss patterns of relative sea-level movements between decimetres, up to 15 m within a parasequence. Excellent examples of non-tidal transgressive facies are characterized by lagoon and washover sediments instead of the usual combination of washover and tidal deposits (channel and flood-tidal delta). Implications for the sandstone connectivity are given. The lower two sequences are deposited in a relatively large, tectonically enhanced wedge-shaped accommodation space. They show both fining-up, deepening sequences, followed by prograding coarsening-up shoaling sequences and can be compared to the classical parasequences of the Western Interior Basin (USA). Progradation of sequence II was interrupted by a major slide event (most likely triggered by an earthquake), which caused more than 400 m seaward slumping of a stretch of 1 km of coastal sands. The architecture of sequence III is more complex due to limited accommodation space characteristic for the late highstand, so that this setting was very sensitive to sea-level fluctuations. This resulted in an intricate pattern of juxtaposed and superposed lagoonal muds, washover fans and swash zones. So-called ‘stranded’ coastal barriers occur, which were left behind after seaward jump of the coastline over more than 1.5 km during forced regression. The pattern of reconstructed sea-level positions is well comparable to the sequential pattern shown by the correlated equivalents along the northern basin margin, which belong to the so-called Terminal Carbonate Complex. The problem of ranking the complex sequence III as one or more parasequences and its consequences for cyclostratigraphy are shortly discussed. Two models of washover formation are given, respectively during more rapid and more slow sea-level rise. The influence of synsedimentary folding on the location of barriers is discussed and also the source area of extra- and intraclasts supplied to barriers and washovers. After deposition of the Sorbas Member the sea withdrew from the Sorbas Basin, probably as a result of the major downdrop in the Mediterranean at the maximum isolation during the Salinity Crisis. It is suggested that the semi-enclosed setting of the basin resulted only in limited, localized erosion, in contrast to the deeper adjacent Vera Basin, which was more open to the Mediterranean.

Recognition of a Santonian Submarine Canyon, Great Valley Group, Sacramento Basin, California: Implications for Petroleum Exploration and Sequence Stratigraphy of Deep-Marine Strata

Seismic stratigraphic and outcrop interpretation of Santonian-Campanian portions of the Great Valley group in the north-central Sacramento basin, California, reveal the presence of a large, north-south-oriented submarine canyon. Named after an overlying town, Williams canyon appears to have been cut during the middle Santonian and filled during the late Santonian and early Campanian (approximately 85-80 Ma). This fossil canyon is more than 100 km in length, ranges from 12 to 22 km in width, and contains compacted sedimentary fill with a maximum thickness of 1.5 km over its mapped extent. Williams canyon is comparable in scale to the Paleogene gorges of the Sacramento basin. Stratigraphic relations indicate active folding locally during the Turonian-Santonian and probable structural control on the location of the canyon. Regional correlations showing uplift and regression along the northern basin margin synchronous with transgression of the eastern basin margin during canyon incision suggest that tectonic tilting of the basin initiated cutting of Williams canyon, whereas the role of eustatic sea level change appears to have been negligible. Delineation of Williams canyon clarifies geometries of outcropping and subsurface strata because some of the canyon fill previously has been correlated to older strata, and canyon boundaries locally have been misinterpreted as faults. Over most of its areal extent, the sequence boundary associated with canyon incision is characterized by facies associations that do not conform to widely cited sequence stratigraphic models of deep-marine deposits, suggesting that such models are oversimplified. Combination trapping geometries created by Williams canyon cut-and-fill represent an untested gas exploration play.

Distinctive characteristics of a streamflow-dominated alluvial fan deposit: Sanghori area, Kyongsang Basin (Early Cretaceous), southeastern Korea

In the northwestern part of the non-marine Kyongsang Basin (Early Cretaceous), conglomeratic deposits occur at intervals along the northern basin margin and grade basinward into interbedded sandstone and mudstone. One of these conglomeratic deposits, referred to as the Sanghori deposit, is 150 m thick and characterized by amalgamated sheets of conglomerate and sandstone (facies assemblages 1 and 2) alternating with interbedded sandstone and purple siltstone (facies assemblage 3). Facies assemblage 1 comprises clast-supported, disorganized and organized sheet conglomerates interbedded with massive to stratified sandstones. This assemblage is interpreted as the product of proximal gravel-bed stream deposition. Facies assemblage 2 consists of trough and planar cross-stratified and horizontally stratified sandstones. It represents sandy braided-stream deposits in which sand bars and dunes were common. Sedimentary facies and architecture of the coarse-grained facies assemblages suggest that the gravel-bed and sandy braided streams were wide and shallow, and rapidly aggraded during flash floods. Facies assemblage 3 consists of interbedded purple siltstone and tabular sandstone which show evidence of weak pedogenic modification and bioturbation. These characteristics are interpreted as the result of floodplain processes. Sediments were supplied from the north and dispersed radially, forming a streamflow-dominated alluvial-fan system. The Sanghori alluvial system was most probably fed from a large drainage basin, resulting in the predominance of streamflow deposits and rounded clasts. The alternation of the gravel-bed stream and floodplain deposits was due to autocyclic switching of active fan sectors under the conditions of relatively slow and steady basin subsidence.

The Maastrichtian Breakup of the Otway Basin Margin – a Model Developed by Integrating Seismic Interpretation, Sequence Statigraphy and Thermochronological Studies

The generally accepted model of a 95 Ma breakup event in the Otway Basin has several unresolved inconsistencies, including evidence of significant post-95 Ma aged crustal extension. An alternative model is proposed: oceanic breakup took place at the end of the Late Cretaceous. A phase of extension during the pre-Aptian was followed by thermal subsidence before renewal of rifting (Cenomanian). Rifting of the already attenuated crust allowed the region to subside below sea level, resulting in marginal to nearshore marine conditions throughout most of the Late Cretaceous.Continental breakup in the Late Maastrichtian (approximately 67 Ma) was marked by regional uplift along the northern basin margin, and towards the incipient continent-ocean boundary. This uplift is parallel to the present-day shelf. The age of this event is derived from palynological and seismic interpretations, and is consistent with previous thermochronological work. Broad anticlinal features on the basin margin may be associated with ridge-push associated with early oceanic crust development.The first post-rift depositional cycle was during the latest Maastrichtian. A significant transgression flooded a peneplain (67 Ma unconformity surface). A maximum flooding surface was developed near the Cretaceous/Tertiary boundary, with subsequent highstand deposition developed through most of the basin. A second unconformity marks a depositional hiatus at the end of the deposition of this sequence.Later cycles of post-rift sedimentation began in the Late Paleocene (55 Ma) with deposition of the ‘Wangerrip Megasequence’. Several eustatic sequences were deposited in a deltaic environment during the subsequent 8 million years.