Petrographic and seismic evidence for the depositional setting of giant turbidite reservoirs and the paleogeographic evolution of Campos Basin,offshore Brazil     

Marcos Fetter  Luiz F. De Ros  Carlos H.L. Bruhn 《Marine and Petroleum Geology》2009

The paleogeographic evolution of Campos Basin, a major oil province of Brazil, during the deposition of its giant turbidite reservoirs, was reinterpreted based on the integration of quantitative sandstone petrography and structural analysis of regional 3D seismic data. The major detrital compositional trends indicate that the geodynamic evolution of the continental margin, rather than global eustatic sea-level fluctuations, has exerted the main control on sand supply to the deepwater systems. This control was imposed by the interaction of three geodynamic processes: (i) escarpment retreat of the coastal mountain ridges, (ii) mantle plume-related dynamic uplift and magmatic activity, and (iii) tectonic reactivation of major basement fault-zones. The pattern of distribution of compositional and textural parameters within the turbidite sequences indicated that the sand supply to deepwater was also constrained by high-frequency stratigraphic processes of the climate Milankovitch band. This new approach to the controls on the formation of the sand-rich, deepwater systems in Campos Basin has a key importance for the generation of realistic models for the exploration of new turbidite reservoirs and for the optimized development of producing turbidite oilfields in such a world-class hydrocarbon province. The proposed integrated methodology can help to unravel the controls on the deposition of deepwater sand-rich, deepwater reservoirs in other divergent margin settings.  相似文献   

What is the topset of a shelf-margin prism?     

Ronald J. Steel  Cornel Olariu  Jinyu Zhang  Si Chen 《Basin Research》2020,32(2):263-278

The siliciclastic topset of a continental margin, or a shelf-margin prism in subsiding nonplate-margin deepwater basins, is the flat-lying upper part of the margin succession; it is coeval basinwards with deepwater slope clinoforms. Topsets develop by the aggradation of repeated, cross-shelf, shoreline regressions and transgressions, thereby hosting the shelf portion of stacked, fourth-order stratigraphic sequences. Sediment spreading downdip and along strike during the cross-shelf transit of the sediment delivery system, as well as process regime changes of deltas and shorefaces (regressive) and of estuaries, barrier–lagoon systems and shelf ridges (transgressive) are highly variable over short distances, so that correlation within a single stratigraphic sequence is far more difficult than correlation of the cross-shelf maximum flooding surface boundaries. Thickness of individual regressive–transgressive, fourth-order sequences is given by shelf accommodation, typically <10 m in embayment or on the inner shelf and up to 200 m on outer shelf. Tectonic subsidence and compaction will enhance this thickness only if rates are very high compared to shelf-transit time. In very high subsidence rate settings, the transgressive tracts are well preserved and often thickly developed. Topset sequences in an Icehouse climate setting tend to have a high proportion and greater landward development of marine vs nonmarine deposits, compared to Greenhouse sequences, because of the importance of eustatic rise of sea level in the former. Previous numerical experiments show that even for very wide shelves and irrespective of Icehouse or Greenhouse conditions, deltas rarely take more than 10 s of ky to reach their shelf edge, suggesting that it is fourth-order (or higher) sequences that are the fundamental ones in sequence stratigraphy.  相似文献   

Criteria for recognizing shelf-slope clinoforms in outcrop; Jurassic Lajas and Los Molles formations,S. Neuquén Basin,Argentina     

Cornel Olariu  Ronald J. Steel  Nataleigh K. Vann  Eugen P. Tudor  Moonsoo Shin  René R. Winter  Yuqian Gan  Eunsil Jung  Flavio N. De Almeida Jr.  Gabriel Giacomone  Daniel Minisini  Walter Brinkworth  Maria L. Loss  Juan Iñigo  Raul Gutierrez 《Basin Research》2020,32(2):279-292

Seismic-reflection data show that most deepwater (>200 m water depth) basins are filled by sand and mud dispersed across clinoformal geometries characterized by gently dipping topsets, steeper foresets and gently dipping bottomsets. However, the entire geometry of these ubiquitous clinoforms is not always recognized in outcrops. Sometimes the infill is erroneously interpreted as “layer cake” or “ramp” stratigraphy because the topset-foreset-bottomset clinoforms are not well exposed. Regional 2-D seismic lines show clinoforms in the Lower to Middle Jurassic Challaco, Lajas, and Los Molles formations in S. Neuquén Basin in Argentina. Time equivalent shelf, slope and basin-floor segments of clinoforms are exposed, and can be walked out in hundreds of metres thick and kilometres-wide outcrops. The studied margin-scale clinoforms are not representing a continental-margin but a deepwater shelf margin that built out in a back-arc basin. Lajas-Los Molles clinoforms have been outcrop-mapped by tracing mudstones interpreted as flooding surfaces on the shelf and abandonment surfaces (low sedimentation rate) in the deepwater basin. The downslope and lateral facies variability in the outcrops is also consistent with a clinoform interpretation. The Lajas topset (shelf) is dominated by fluvial and tidal deposits. The shelf-edge rollover zone is occasionally occupied by a 40–50-m-thick coarse-grained shelf-edge delta, sometimes incising into the underlying slope mudstones, producing oblique clinoforms expressing toplap erosion on seismic. A muddy transgressive phase capping the shelf-edge deltas contains tidal sandbodies. Shelf-edge deltas transition downslope into turbidite- and debris flow-filled channels that penetrate down the mud-prone Los Molles slope. At the base-of-slope, some 300m below the shelf edge, there are basin-floor fan deposits (>200 m thick) composed of sandy submarine-fan lobes separated by muddy abandonment intervals. The large-scale outcrop correlation between topset–foreset–bottomset allows facies and depositional interpretation and sets outcrop criteria recognition for each clinoform segment.  相似文献   

Base-salt relief controls salt-related deformation in the Outer Kwanza Basin,offshore Angola     

Sian L. Evans  Christopher A.-L. Jackson 《Basin Research》2020,32(4):668-687

Salt-influenced passive margins are widespread and commonly hydrocarbon-rich. However, they can be structurally complex, with their kinematic development being poorly understood. Classic models of salt tectonics divide such margins into updip extensional, mid-slope translational and downdip contractional kinematic domains. Furthermore the faults, folds, and salt walls associated with each kinematic domain are typically assumed to form perpendicular to the maximum principal stress, which in gravitationally driven systems means broadly perpendicular to base-salt dip. We use high-resolution 3D seismic reflection data from the Outer Kwanza Basin, offshore Angola to show that these models cannot explain the diversity of salt structures developing on passive margins, especially those defined by considerable relief on the base-of-salt surface. Overburden seismic-stratigraphic patterns record the basinward translation and rotation, allowing us to reconstruct the origin and evolution of the salt structures. We show structures in the transitional domain of the Outer Kwanza Basin display three dominant trends, each characterised by different structural styles: (a) salt walls perpendicular to the overall base-salt dip, (b) salt walls parallel to the base-salt dip and (c) salt walls oblique to the base-salt dip. We show that each set of walls has a unique history, with synchronous phases of extension and compression occurring in adjacent structures despite their close spatial relationship. Our analysis suggests that, in the Outer Kwanza Basin, the structural evolution of the salt and overburden is predominantly controlled by translation over relief on the base-salt surface formed above fault scarps associated with a preceding phase of rifting. Changes in the downdip volumetric flux and velocity of the salt over topographic features can cause local extension or contraction of the salt and its overburden, associated with local acceleration or deceleration of the salt, respectively. This interaction with base-salt relief creates locally variable stress fields that deform the salt and its overburden, overprinting the broader, margin-scale salt tectonics typically associated with gravity gliding and spreading.  相似文献   

Upslope-climbing shelf-edge clinoforms and the stepwise evolution of the northern European glaciation (lower Pleistocene Eridanos Delta system,U.K. North Sea): When sediment supply overwhelms accommodation     

Stefano Patruno  Vittorio Scisciani  William Helland-Hansen  Nico D'Intino  William Reid  Claudio Pellegrini 《Basin Research》2020,32(2):224-239

Clinoforms are basinward-dipping and accreting palaeo-bathymetric profiles that record palaeo-environmental conditions and processes; thus, clinothems represent natural palaeo-archives. Here, we document shelf-edge scale clinoform sets which prograded through the entire width of an epicontinental marine basin (ca. 400 km), eventually encroaching onto the opposite basin flank, where they started to prograde upslope and landward, in defiance of gravity (“upslope-climbing clinoforms”). The giant westward-prograding Eridanos muddy shelf-edge clinothem originated from the Baltic hinterland in the Oligocene and achieved maximum regression in the Early Pleistocene, on the UK Central Graben (CG) and Mid North Sea High (MNSH), after crossing the whole North Sea mesopelagic depocentre and causing near complete basin infill. Here we integrate well and seismic data through the MNSH and CG and examine the Eridanos final heyday and demise, identifying five clinothem complexes (A1, A2, A3, B and C) and six depositional sequence boundaries (SB1 to SB6) in the Miocene-Recent section. Tectonic and climatic events drove the recent evolution of this system. Early Pleistocene climate cooling, in particular, resulted in a stepwise increase in sediment supply. This climaxed in the earliest Calabrian, following a likely Eburonian eustatic fall (=SB3) when the Eridanos clastic wedge was restructured from a 100–300 m thick compound shelf-edge and delta system to a “hybrid” shelf-edge delta at sequence boundary SB3 (ca. 1.75 Ma). In the ca. 40 kyr that followed SB3, a progradation rate peak (>1,000 m/kyr) is associated with clinoforms starting to accrete upslope, onto the east-dipping slope between CG and MNSH. This “upslope-climbing clinoform” phase was quickly followed by the maximum regression and final retreat of the Eridanos system in the Early Calabrian (=SB4), likely as the result of climate-driven changes in the Baltic hinterland and/or delta auto-retreat. To our knowledge, this contributions represents the first documentation of “upslope-climbing clinoforms” recorded in the stratigraphic record.  相似文献   

Coseismic slip model of the 2007 August Pisco earthquake (Peru) as constrained by Wide Swath radar observations   总被引：1，自引：0，他引：1  

Mahdi Motagh  Rongjiang Wang  Thomas R. Walter  Roland Bürgmann  Eric Fielding  Jan Anderssohn  Jochen Zschau 《Geophysical Journal International》2008,174(3):842-848

The Pisco earthquake ( M _w 8.0; 2007 August 15) occurred offshore of Peru's southern coast at the subduction interface between the Nazca and South American plates. It ruptured a previously identified seismic gap along the Peruvian margin. We use Wide Swath InSAR observations acquired by the Envisat satellite in descending and ascending orbits to constrain coseismic slip distribution of this subduction earthquake. The data show movement of the coastal regions by as much as 85 cm in the line-of-sight of the satellite. Distributed-slip model indicates that the coseismic slip reaches values of about 5.5 m at a depth of ∼18–20 km. The slip is confined to less than 40 km depth, with most of the moment release located on the shallow parts of the interface above 30 km depth. The region with maximum coseismic slip in the InSAR model is located offshore, close to the seismic moment centroid location. The geodetic estimate of seismic moment is 1.23 × 10²¹ Nm ( M _w 8.06), consistent with seismic estimates. The slip model inferred from the InSAR observations suggests that the Pisco earthquake ruptured only a portion of the seismic gap zone in Peru between 13.5° S and 14.5° S, hence there is still a significant seismic gap to the south of the 2007 event that has not experienced a large earthquake since at least 1687.  相似文献   

Sediment supply: The main driver of shelf-margin growth   总被引：1，自引：0，他引：1  

Cristian Carvajal  Ron Steel  Andrew Petter 《Earth》2009,96(4):221-248

Despite the obvious importance of sediment supply to shelf-margin architecture and to the potential of margins to contain and bypass deep-water sands, the role of supply in shelf-margin growth has received limited attention. High cross-shelf sediment flux is critically important for the occurrence of deep-water sands, not least on Greenhouse or rapidly subsiding margins where the impact of eustatic sea-level fall may be insufficient to drive sediment delivery out across the shelf into deep-water areas. To draw greater attention to the supply parameter we review a number of shelf margins that have grown chiefly through supply by shelf-edge deltas and associated sediment-gravity flows. Based on structural style and water depth, we recognize two broad types of shelf-margin. Moderately deep-water margins produce clinoforms < 1000 m high and show rates of shelf-edge progradation < 60 km/My and aggradation < 270 m/My, and consequently, infill their basins relatively rapidly, and develop more progradational architectures with morphologically smooth and relatively undeformed slopes. Very deep-water margins produce clinoforms > 1000 m high and generally show rates of shelf-edge progradation < 40 km/My and aggradation < 2500 m/My, and therefore infill their basins more slowly and develop more aggradational architectures with much gravity-driven slope deformation, proneness to failure and ponded architectures (salt or shale driven). On both margin types, long-term (> 1 My) rates of shelf-edge progradation of several tens of km/My tend to be linked to the delivery of relatively large volumes of sand into the deep-water basin. Delivery of this sand beyond the shelf-edge happens despite Greenhouse conditions and is likely recurrent and periodic (delivery cycles in the order of 100′s ky). Such prominent margin growth is a strong indication that sediment influx was relatively high and we refer to these margins as “supply-dominated” shelf margins. The Gulf of Mexico margin is a well-known and data-rich example of a “supply-dominated” shelf-margin during certain times (e.g., Paleocene). In contrast, on both margin types, low rates of shelf-edge progradation are linked to diminished (or even non-existent) and less frequently recurrent deep-water sediment delivery suggestive of relatively low sediment influx. Occurrence of deep-water sand delivery under low sediment influx probably requires fall of relative sea level. The differences between rapidly and slowly prograding margins indicate that sediment supply (and not sea level) is likely to be the key limiting factor on the growth of shelf margins and that sediment supply, as interpreted through progradation rate, can therefore be used to make a first-order prediction of relative amounts of sand passed to deep-water areas.  相似文献   

The extension of the Late Weichselian/Late Devensian ice sheets in the North Sea Basin     

Jürgen Ehlers  Robin Wingfield 《第四纪科学杂志》1991,6(4):313-326

The distribution of large channel-like features, comprising Weichselian/Devensian incisions, in the western North Sea provides evidence for a much larger extension of the last ice sheet than currently assumed. Morphological comparison of the incisions with those in North Germany and Poland reveals a striking similarity in shape and distribution. The features on the North Sea floor are interpreted as being formed by meltwater erosion within the margin of the ice sheet. The widespread absence of Weichselian/Devensian till in the area under consideration may be attributed to later erosion. Large-scale reworking and redistribution of sediments is indicated by the complete sediment infill of the majority of the incisions.  相似文献   

Volcanic passive margins     

Laurent Geoffroy 《Comptes Rendus Geoscience》2005,337(16):575

Compared to non-volcanic ones, volcanic passive margins mark continental break-up over a hotter mantle, probably subject to small-scale convection. They present distinctive genetic and structural features. High-rate extension of the lithosphere is associated with catastrophic mantle melting responsible for the accretion of a thick igneous crust. Distinctive structural features of volcanic margins are syn-magmatic and continentward-dipping crustal faults accommodating the seaward flexure of the igneous crust. Volcanic margins present along-axis a magmatic and tectonic segmentation with wavelength similar to adjacent slow-spreading ridges. Their 3D organisation suggests a connection between loci of mantle melting at depths and zones of strain concentration within the lithosphere. Break-up would start and propagate from localized thermally-softened lithospheric zones. These ‘soft points’ could be localized over small-scale convection cells found at the bottom of the lithosphere, where adiabatic mantle melting would specifically occur. The particular structure of the brittle crust at volcanic passive margins could be interpreted by active and sudden oceanward flow of both the unstable hot mantle and the ductile part of the lithosphere during the break-up stage. To cite this article: L. Geoffroy, C. R. Geoscience 337 (2005).  相似文献   

Some effects of lateral heterogeneities in the upper mantle on postglacial land uplift close to continental margins   总被引：2，自引：0，他引：2  

G. Kaufmann  P. Wu  D. Wolf 《Geophysical Journal International》1997,128(1):175-187

We investigate the effects of lateral heterogeneities in the upper mantle on the calculation of postglacial land uplift. For the model calculations we use a commercial finite-element code, which enables us to solve the equations governing a layered, isotropic. incompressible, Maxwell-viscoelastic half-space with laterally varying layer thicknesses and physical properties. Following previous investigations performed by Sabadini. Yuen & Portney (1986) and Gasperini & Sabadini (1989), we extend their results using a more realistic loading history and different earth models. We then focus our attention on the question whether lateral heterogeneities in the upper mantle can be modelled correctly using a set of homogeneous earth models. To this end, a comparison of model calculations using both laterally homogeneous and heterogeneous earth models is performed.
We find that lateral heterogeneities in the upper mantle significantly influence the calculated postglacial land uplift. The resolving power of relative sea-level observations for the prescribed lateral heterogeneities used in this study is mainly focused on observations around the load margin and outside the glaciated areas, where differences in predicted land uplift between individual models are large enough to be resolved by observations.
We can qualitatively determine lateral heterogeneities in the upper mantle using a set of laterally homogeneous earth models, if the geological structure, for example a continental margin, is known. However, in order to infer the correct values of lithospheric thickness and asthenospheric viscosity, we need to use laterally heterogeneous models.  相似文献