Basin-bounding Fault System Research Articles

Fault-controlled fluid circulation and diagenesis along basin-bounding fault systems in rifts – insights from the East Greenland rift system

Abstract. In marine rift basins, deep-water clastics (>200 m) in the hanging wall of rift- or basin-bounding fault systems are commonly juxtaposed against crystalline “basement” rocks in the footwall. A distinct feature of such fault systems is therefore the juxtaposition of relatively highly permeable, unconsolidated sediments against relatively low-permeable basement rocks. Due to limited surface exposure of such fault zones, studies elucidating their structure and evolution are rare. Consequently, their impact on fluid circulation and diagenesis within and proximal to the fault zone as well as into the hanging wall strata are also poorly understood. Motivated by this, we here investigate a well-exposed strand of a major basin-bounding fault system in the East Greenland rift system, namely the Dombjerg Fault which bounds the Wollaston Forland Basin, northeast (NE) Greenland. Here, syn-rift deep-water clastics of Late Jurassic to Early Cretaceous age are juxtaposed against Caledonian metamorphic basement. Previously, a ∼ 1 km wide zone of pervasive pore-filling calcite cementation of the hanging wall sediments along the Dombjerg Fault core was identified (Kristensen et al., 2016). In this study, based on U–Pb calcite dating, we show that cementation and formation of this cementation zone started during the rift climax in Berrisian–Valanginian times. Using clumped isotope analysis, we determined cement formation temperatures of ∼ 30–70 ∘C. The spread in the formation temperatures at similar formation age indicates variable heat flow of upward fluid circulation along the fault in the hanging wall sediments, which may root in permeability variations in the sediments. Calcite vein formation, postdating and affecting the cementation zone, clusters between ∼ 125 and 100 Ma in the post-rift stage, indicating that fracturing in the hanging wall is not directly related to the main phase of activity of the adjacent Dombjerg Fault. Vein formation temperatures at ∼ 30–80 ∘C are in a similar range as cement formation temperatures. Further, similar minor element concentrations of veins and adjacent cements indicate diffusional mass transfer into fractures, which in turn infers a subdued fluid circulation and low permeability of the fracture network. These results imply that the cementation zone formed a near-impermeable barrier soon after sediment deposition, and that low effective permeabilities were maintained in the cementation zone even after fracture formation, due to poor fracture connectivity. We argue that the existence of such a cementation zone should be considered in any assessments that target basin-bounding fault systems for, e.g., hydrocarbon, groundwater, geothermal energy, and carbon storage exploration. Our study highlights that the understanding of fluid flow properties as well as fault-controlled diagenesis affecting the fault itself and/or adjacent basinal clastics is of great fundamental and economic importance.

Growth and linkage of a basin-bounding fault system: Insights from the Early Cretaceous evolution of the northern Polhem Subplatform, SW Barents Sea

Normal faults grow by either simultaneous increase in displacement and length (isolated model), or by rapid establishment of their final length before accumulating significant displacement (constant-length model), or a combination of these tow end-members. In this study, we integrate stratigraphic and structural observations with throw backstripping and time thickness maps to define the growth processes of a basin-bounding normal fault in the northern Polhem Subplatform, SW Barents Sea. During the initial 15 My of Early Cretaceous rifting, the fault system consisted of at least five en-echelon segments, which were ca. 5–10 km long. Throw backstripping indicates that fault segments were hard-linked after this initial stage to form a single 40 km long fault zone. Fault linkage resulted in displacement redistribution, with the locus of faulting being shifted from the center of each paleo-segment, to the center of the through going fault. Across fault incised valleys provide additional information on the topographic response to fault growth. Major valley incisions at the fault linkage zones outline the extent of the individual fault segments and support early isolated fault growth. Fault backstripping results suggest that valley incision and sedimentation rates kept up with fault slip rate, such that the incised valleys remained unaffected by the uplift of the latter fault linked stage. This study illustrates the importance of integrating stratigraphic and structural observations when reconstructing the evolution of basin-bounding normal faults. In particular, syn-rift erosional features, sediment thickness variations, sediment distribution, stratal geometries and onlap/truncation relationships are critical for estimating the growth of these structures.

The Mesozoic structural evolution of the Gorgon Platform, North Carnarvon Basin, Australia

ABSTRACTThe Gorgon Platform is located on the southeastern edge of the Exmouth Plateau in the North Carnarvon Basin, North West Shelf, Australia. A structural analysis using three-dimensional (3D) seismic data has revealed four major sets of extensional faults, namely, (1) the Exmouth Plateau extensional fault system, (2) the basin bounding fault system (Exmouth Plateau–Gorgon Platform Boundary Fault), (3) an intra-rift fault system in the graben between the Exmouth Plateau and the Gorgon Platform and (4) an intra-rift fault system within the graben between the Exmouth Plateau and the Exmouth Sub-basin. Fault throw-length analyses imply that the initial fault segments, which formed the Exmouth Plateau–Gorgon Platform Boundary Fault (EG Boundary Fault), were subsequently connected vertically and laterally by both soft- and hard-linked structures. These major extensional fault systems were controlled by three different extensional events during the Early and Middle Jurassic, Late Jurassic and Early Cretaceous, and illustrate the strong role of structural inheritance in determining fault orientation and linkage. The Lower and Middle Jurassic and Upper Jurassic to Lower Cretaceous syn-kinematic sequences are separated by unconformities.

Physiography of the NE margin of the Permian Salt Basin: new insights from 3D seismic reflection data

Three-dimensional seismic reflection data from the Egersund Basin, offshore Norway image geomorphological features that record mid-Permian footwall degradation of basin-bounding fault systems. This ancient landscape was subsequently flooded during the pan-European, Late Permian transgression of the North Permian Salt Basin and was fossilized beneath Zechstein Supergroup evaporites. We provide the first conclusive evidence for pre-Zechstein normal faulting in the Egersund Basin, indicating that extensional strain was shared between Permian and Late Jurassic–Early Cretaceous rift events. Supplementary materials: Uninterpreted versions of the seismic sections shown in Figure 2 are available are available at www.geolsoc.org.uk/SUP18678 .

Rift-basin development: lessons from the Triassic–Jurassic Newark Basin of eastern North America

Abstract We use seismic, field, core, borehole and vitrinite-reflectance data to constrain the development of the Newark Rift Basin, one of the largest and most thoroughly studied basins of the eastern North American rift system that formed during the break-up of Pangaea. These data provide critical information about the geometry of the preserved synrift section and the magnitude of post-rift erosion. We incorporate this information into a new structural restoration of the basin. Our work shows that the Newark Basin was initially narrow (<25 km) and markedly asymmetric; synrift strata show significant thickening towards the basin-bounding faults. Subsequently, the basin became wider (perhaps >100 km wide), deeper (up to 10 km) and less asymmetric; synrift strata exhibit subtle thickening towards the basin-bounding fault system. Several intrabasin faults dissected the Newark Basin after synrift deposition, and the basin fill was tilted ( c. 10°NW) and folded. Erosion (up to 6 km) accompanied the intrabasin faulting, NW tilting and folding, significantly reducing the basin size. Our work suggests that the eastern North American rift system is characterized by a very broad zone of upper-crustal extension in which a few, wide, deep, long-lived, fault-bounded basins (like the Newark Basin) accommodated much of the extension.

The Cilicia–Adana basin complex, Eastern Mediterranean: Neogene evolution of an active fore-arc basin in an obliquely convergent margin

Detailed interpretation of multi-channel seismic reflection profiles showed that the deposition of the Miocene successions in the Cilicia–Adana basin complex occurred within a foredeep, south of the arcuate Tauride fold–thrust belt. The Misis–Kyrenia fault zone defined the northernmost of a number of smaller thrust culminations developed within this foredeep. Fluvio-deltaic successions suggest that the Adana and Inner Cilicia basins became emergent during the Tortonian, when the western portion of the piggy-back basin retained a marine connection. The entire region became emergent during the Messinian salinity crisis, and up to 1000 m of evaporites were deposited in the Cilicia and southern Adana basins. Stratigraphic and structural relationships demonstrated that the late Plio-Quaternary Cilicia–Adana basin complex evolved as an asymmetric piggy-back basin on the hanging wall of the large south-verging Misis–Kyrenia thrust culmination. On the Misis–Kyrenia segment of the culmination, thrust activity ceased in early Messinian, whereas on the Kyrenia segment, it continued to the present. The shift in the kinematics is expressed by the development of the NE–SW trending steep faults with extensional separations bounding the Plio-Quaternary depocentre in the Adana and Inner Cilicia basins. These basement-rooted faults are incompatible with the contractional regime that existed in this part of the basin complex during the Miocene. In the Outer Cilicia Basin, the incompatibility between a domain of continued south-directed fold–thrust activity and uplift on the Kyrenia Range and a domain of extension associated with the development of Plio-Quaternary depocentre indicates that strain is strongly partitioned across the E–W trending southern basin-bounding fault system along the southern margin of the Outer Cilicia Basin. Progressive westward displacement of the Tauride block within the Aegean–Anatolian microplate created a localised transtensional regime within the Inner Cilicia and Adana basins, suggesting the presence of hard intra-plate fault boundaries centred along the Misis–Kyrenia horst block and the southern basin-bounding fault system. The northern basin-bounding fault system, including the Kozan fault in the Cilicia Basin, is a set of large antithetic structures linked to the master faults. The westward pull-out of the Tauride block is related to the overall westward escape of the Aegean–Anatolian microplate during the latest Miocene to early Pliocene, whereas the continued contraction south of the basin complex across Cyprus is related to the evolving collision and under-plating of the continental micro-fragment, the Eratosthenes. We propose that the southern master fault of the Outer Cilicia Basin primarily functions as a boundary separating a contractional microplate domain to the south from a transtensional microplate domain to the north.

East-west extension and Miocene environmental change in the southern Tibetan plateau: Thakkhola graben, central Nepal

East-west extensional basins are distributed across the southern half of the Tibetan plateau at an elevation of ∼4 km. These basins have generated much interest because of their potential implications for the regional tectonics and force distribution in the plateau. This study documents the sedimentology of the Miocene–Pliocene Thakkhola graben fill in order to reconstruct basin evolution and paleoenvironment. Analysis of depositional systems, paleodrainage patterns, and conglomerate clast provenance of the >1-km-thick graben fill sets limits on the timing of activity of the basin-bounding faults and the development of southward axial drainage in the basin. During the deposition of the oldest basin fill (Tetang Formation, ca. 11–9.6 Ma), probably in a restricted basin, minor motion occurred on the basin-bounding fault systems. An angular unconformity separates the Tetang and overlying Thakkhola Formations, where this contact can be observed in the southern part of the basin. Southward axial drainage was established by ca. 7 Ma with the onset of deposition of the Thakkhola Formation. Several episodes of damming of this drainage system are recorded by widespread lacustrine deposits in the southern part of the basin. Facies distribution and the progressive rotation of strata in the Thakkhola Formation indicate that the Dangardzong fault on the western edge of the basin was active at this time, and drainage ponding may have been related to displacement on normal faults associated with the South Tibetan detachment system to the south of Thakkhola graben. Contrasts between deposits of the Tetang and Thakkhola Formations provide evidence for environmental change in the basin. In the Tetang Formation, the abundance of lacustrine facies, the pollen record, and the absence of paleosol carbonate suggest that conditions were more humid than during subsequent deposition of the Thakkhola Formation. Environmental change in the Thakkhola graben coincided with environmental change observed in the Siwalik foreland basin sequence, Arabian Sea, and Bay of Bengal at ca. 8–7 Ma. Although this climate change event has been previously attributed to intensification of the Asian monsoon in response to uplift of the Tibetan plateau, paleoaltimetry data indicate that this region had already attained a high elevation by ca. 11 Ma. Thus, the Thakkhola graben stratigraphic record suggests that uplift of the southern Tibetan plateau and the onset of the Asian monsoon as inferred from paleoclimatic indicators were not directly related in a simple way.

Distinction between fault and salt control of Mesozoic sedimentation on the southern margin of the Mid-North Sea High

Abstract The North Dogger Fault Zone (NDFZ) is situated at the northern margin of the UK Southern North Sea Basin at the northern limit of the mobile Zechstein Supergroup. This fault zone underwent movement during late Triassic and probably early Jurassic times. The NDFZ is comparable with the southern part of the Dowsing Fault Zone (SDFZ), which was initiated during late Scythian times and continued to move until at least mid-Carnian times. The SDFZ is located at the southwestern edge of mobile salt. Both fault zones form part of the basin-bounding fault system, which is proposed to have been initiated as a response to the growth of salt swells in the centre of the Southern North Sea Basin. The fault formation is due to folding of the Triassic strata over the swells and overall shortening of the Triassic cover. The shortening was taken up as extension at the basin margins, corresponding to the edge of the mobile Zechstein salt.

Halokinetic initiation of Mesozoic tectonics in the southern North Sea: a regional model

AbstractThe North Dogger Fault Zone is located at the northern margin of the UK Southern North Sea Basin, at the edge of the mobile Zechstein Supergroup, and was particularly active during late Triassic and early Jurassic times. It resembles geometrically, and is related tectonically to, the Dowsing Fault Zone which was initiated in late Scythian time along the southwestern edge of the mobile salt. It is proposed that both of these basin-bounding fault systems were initiated in response to the buoyant growth of salt swells in the centre of the Southern North Sea Basin. Passive folding of the Triassic strata over the swells, which accommodated the shape changes caused by halokinesis, led to extension on the fault zones at the edge of the mobile Zechstein salt.