Incised Valley System Research Articles

DIAGENETIC EVOLUTION OF INCISED CHANNEL SANDSTONES: IMPLICATIONS FOR RESERVOIR CHARACTERISATION OF THE LOWER CARBONIFEROUS MARAR FORMATION, GHADAMES BASIN, WESTERN LIBYA

This paper assesses the diagenetic history of potential fluvial hydrocarbon reservoir rocks deposited within incised valley systems of the Lower Carboniferous Marar Formation in western Libya. Outcrop data were collected in the Tinedhan Anticline, located at the southern margin of the Ghadames Basin. Four discrete intervals with channelized sandstones were identified in a section dominated by alternating offshore mudstones and shallow‐marine clastics. The incised channels were cut during major sea‐level lowstands, and filled by fluvial sandstone packages up to 50 m thick. Fifty‐eight samples from four different localities, representing three lowstand systems tracts, were analysed to obtain a statistically meaningful mineralogical and compositional dataset.In addition to burial compaction, three main diagenetic events influenced the reservoir quality of the sandstones. Firstly, early eodiagenesis involved kaolinitization of plagioclase grains. This began before subsequent calcite cementation, probably as a result of flushing by meteoric pore‐waters. The deformation of kaolinite during later compaction resulted in the formation of pseudomatrix which further reduced porosity and permeability. Kaolinite is commonly transformed to illite at temperatures above 140°C in the presence of K‐feldspar. Although K‐feldspar was recorded in the samples, no illite was observed, suggesting that the Lower Carboniferous strata in the study area were not buried in excess of approximately 3.5 km.The second diagenetic phase was the precipitation of calcite cement, present either dispersed throughout the sandbodies or as concretions up to 2 m across, in both cases reducing reservoir quality. The high intergranular volumes (IGV) of calcite‐cemented sandstones (ranging between 35% and 40%) suggest that cementation occurred at burial depths of <500 m. Sandstones without calcite cement have lower IGV of between 17% and 25% as a result of mechanical and chemical compaction. Stable C and O isotope analysis of the calcite cement also supports precipitation at shallow burial depths, indicating a meteoric pore‐water source for the calcite. The third and final diagenetic stage was partial chloritisation of kaolinite during meso‐diagenesis. The elevated temperatures required for this transformation indicate burial to a minimum depth of approximately 2.5 km, which is consistent with the compaction data.Despite these diagenetic effects, the fluvial sandstones have an average porosity of 12%, with a range from 0.5% up to 25%. Permeability measurements on four sandstone samples indicate that the development of pseudomatrix did not reduce permeability significantly.

The Holocene infill of Lake Conjola, a narrow incised valley system on the southeast coast of Australia

A detailed Holocene sedimentological and geomorphological history of the sedimentary infill of Lake Conjola, a barrier estuary on the southeast coast of Australia, is presented. Results show that a remnant Last Interglacial barrier system is preserved in the mouth of a narrow incised valley. During the early stage of Holocene sedimentary infill, a laterally extensive transgressive sand facies was deposited as rising post-glacial sea-level breached remnants of the Last Interglacial barrier ca. 7500 cal BP. From 7500 to 4000 cal BP sediment continued to accumulate within the mouth of the incised valley, forming an extensive flood-tide delta within the drowned river estuary. Marine influences were restricted by further sediment accumulation at the mouth of the estuary, leading to the development of mid-Holocene barrier and back-barrier depositional environments. This research adds detail to stratigraphic models of the sedimentary infill and geomorphological evolution of barrier estuaries formed in narrow incised valley systems on the southeast coast of Australia, and provides a global model for estuarine deposition in regions that have been tectonically stable over the late Quaternary.

Geomorphology of a dryland fluvial system: the Lower Balonne River, southern Queensland

The floodplain of the Lower Balonne River is in the upper reaches of the Murray–Darling Basin. The region has been extensively developed for agriculture, in particular irrigated cotton, and is highly productive. Multidisciplinary investigations to inform land management generated extensive sets of remotely sensed data including Landsat TM, airborne gamma-ray radiometrics, aerial photography, ASTER imagery and digital elevation models. These datasets provided the basis for regolith and geomorphic mapping. The wealth of data has allowed characterisation of the Lower Balonne River system, which is typical of many of the dryland rivers of southern Queensland. The geomorphic map of the Lower Balonne floodplain has eight major units based on landform and geomorphic processes. Bedrock consists of the slightly deformed and extensively weathered marine Cretaceous Griman Creek Formation. Coincident with erosion and weathering, Paleogene quartz gravels were deposited and are now extensively cemented and preserved as remnants forming zones of inverted relief. Much of the present landscape consists of a series of juxtaposed depositional units that have infilled an incised valley system. The different depositional units show the paleo-Balonne River migrating to the west. This is interpreted to be a result of tectonic depression and tilting to the west, causing avulsion and anastomosing of the paleochannels. The modern Balonne River system consists of a number of easily recognised segments. In the north, the modern channel is incised as a single channel. To the south the channel opens out onto an anastomosing plain with branching and reconnecting small-scale channels. Source-bordering dunes, currently inactive, have also formed along the western and eastern sides of the modern river and are prominent in large dunes in the south along the present Moonie River. Their absence in older landscape elements points to increasing aridity over time in the river system.

A Holocene incised valley infill sequence developed on a tectonically active coast: Pakarae River, New Zealand

A sequence of fluvio-estuarine sediments exposed beneath the highest Holocene marine terrace at Pakarae, North Island, New Zealand, records the early-mid Holocene infilling of the Pakarae valley. This sequence was developed on an active, coseismically uplifting coastline and provides a valuable comparison to widely used facies models for estuaries, which were developed exclusively from stable coastal settings. We describe eight sedimentary sections, distributed along a 220 m stretch of riverbank and present twelve new radiocarbon ages. Sedimentology and benthic foraminifera are used to divide the sequence into eight bio-lithofacies. These units are grouped into four paleoenvironmental facies associations: barrier, estuarine, estuary-head delta and floodplain. We compare the distribution of the Pakarae paleoenvironmental facies associations to those in models of incised valley infill sequence models and case studies of infilled valleys. These data allow us to present new contributions to the development of a facies model for the sedimentary infilling of an incised valley system that was experiencing coseismic uplift synchronous with deposition. We suggest the distinctive characteristics of such a model would include (1) part, or all, of the transgressive and lowstand sequences may now lie above modern sea level, (2) the transgressive sedimentary sequence is typically condensed relative to the coeval amount of eustatic sea level (SL) rise that occurred during that period, and (3) evidence of relative SL falls, such as transitions from estuarine to fluvial environments, despite conditions of rapid and continuous eustatic SL rise.

Pleistocene macrotidal tide-dominated estuary–delta succession, along the Dong Nai River, southern Vietnam

This paper focuses on the facies and sequence stratigraphic interpretation of a tide-dominated incised-valley system that is rare among geological records of the world for its completeness. The subject is the Middle–Upper Pleistocene Ba Mieu and Thu Duc formations exposed along the Dong Nai River, southern Vietnam. Both the Ba Mieu and the Thu Duc formations are interpreted as a transgressive tide-dominated estuary succession overlain by a highstand tide-dominated delta succession. The tide-dominated estuary succession is generalized as follows, in ascending order: fluvial facies in landward portions, tidal flat, upward-coarsening and -thickening succession of marine sands with a tidal ravinement surface (TRS; created by tidal scouring during transgression) at the base, and subtidal lag in seaward portions. This tide-dominated estuary is distinguished from wave-dominated and wave- and tide-dominated estuaries by (1) the lack of a central basin (lagoon), tidal delta, or bayhead delta facies; (2) the widespread presence of marine sands; (3) the presence of a subtidal lag; and (4) the presence of an upper-flow-regime sand flat facies. The tide-dominated delta succession is generalized as follows, in ascending order: upward-convex unit of marine sand and onlapping tidal flat deposits, a thick upward-fining succession of tidal flat–salt marsh deposits, and coarse fluvial deposits. This delta is distinguished from an estuary as follows. (1) It shows thick, regional, upward-fining successions indicating shallowing, whereas upward-coarsening successions indicating deepening are recognized in an estuary. A maximum flooding surface (MxFS) is recognized in the coarsest part of the succession, in marine sand and tidal flat deposits. (2) Fluvial processes dominate the sediment supply, in contrast to an estuary, in which a thick marine sand body fed from marine sources is dominant. (3) Ebb tidal currents are dominant, whereas flood tidal currents are dominant in an estuary. Key features of the incised-valley system are (1) amplification of the incised-valley geometry by tidal ravinement erosion; (2) development of tidal channels filled with mud clasts in the estuary; (3) a thick marine sand body in the estuary; and (4) upward-convex unit of marine sand and a thick tidal flat–fluvial succession in the delta. The Ba Mieu Formation is recognized as depositional sequence (SQ) 1 between sequence boundary (SB) 1 below and SB2 above. SQ1 consists of transgressive systems tract (TST) 1 and highstand systems tract (HST) 1. SQ1 was formed by a transgression–regression cycle during marine isotope stage (MIS) 7. SB2 was formed by fluvial incision during the MIS 6 lowstand and is amalgamated with the TRS of MIS 5. The Thu Duc Formation is recognized as SQ2 between SB2 below and SB3 above, and it consists of TST2 and HST2. SQ2 was formed by a major transgression–regression cycle on which a lower-rank cyclicity was superposed during MIS 5. TST2 thins seaward as a result of tidal ravinement erosion. The landward extent of marine environment in MIS 5 is inferred to have been of greater scale than that in MIS 7 from the distribution of the facies and the TRS.

Sedimentologic and tectonic origin of an incised-valley-fill sequence along an extensional marginal-lacustrine system in the Basin and Range province, United States: Implications for predictive models of the location of incised valleys

Incised valleys in extensional lacustrine systems should be common and significant petroleum targets, yet documentation and analysis of these systems are limited and, hence, so are predictive models for their location. Geologic mapping of the Miocene–Pliocene Humboldt Formation in Knoll basin, northeastern Nevada, has revealed a significant incised-valley system formed along the lacustrine margins of an extensional basin. The valley formed during a relative lake-level fall and incised into lacustrine shoreface and offshore sandstone and subsequently was filled with fluvial and eolian sediment as lake level rose. The valley's location was tectonically influenced; it is situated in the hinge zone of a syncline near the tip of the range-bounding fault system. Folding of the syncline was broadly synchronous with incision and filling, and it appears to have localized the valley along the topographically low hinge zone. Furthermore, the large relative lake-level change that produced the valley is only recorded in strata in the syncline area, suggesting that the location and cause of incision was greatly influenced by tectonics. Thus, the location of similar incised valleys in other extensional basins may be predictable if comparable tectonic features and processes are recognized. Our study suggests that the best locations to develop and preserve incised valleys are near the tips of normal faults during periods of overall high tectonic subsidence. Specific areas along basin-bounding faults where tectonically influenced incised valleys are more likely to form include fault-propagation folds, synthetic relay ramps near transfer faults, and areas that have large changes in fault slip. Although lake volume changes caused predominantly by climate change can be an important factor in producing incised valleys, tectonically influenced incised valleys are likely to be larger, better preserved, and more petroleum prone compared to climate-controlled incised valleys.

An intense terminal epoch of widespread fluvial activity on early Mars: 1. Valley network incision and associated deposits

We present evidence that a final epoch of widespread fluvial erosion and deposition in the cratered highlands during the latest Noachian or early to mid‐Hesperian was characterized by integration of flow within drainage networks as long as 4000 km and trunk valley incision of 50 to 350 m into earlier Noachian depositional basins. Locally deltaic sediments were deposited where incised valley systems debouched into basins. Large alluvial fans of sediment deposited from erosion of alcoves in steep crater walls probably formed contemporaneously. The depth of incision below Noachian surfaces correlates strongly with the gradient and the total valley length, suggesting consistent regional hydrology. Estimated discharges from channel dimensions indicate flow rates equivalent to mean annual floods in terrestrial drainage basins of equivalent size. Such high flow rates imply either runoff directly from precipitation or rapid melting of accumulated snow. Development of duricrusts on the Noachian landscape may have contributed to focusing of late‐stage erosion within major trunk drainages. This late‐stage epoch of intense fluvial activity appears to be fundamentally different than the fluvial environment prevailing during most of the Noachian Period, which was characterized by widespread fluvial erosion of highlands and crater rims, deeply infilling crater floors, and intercrater basins through ephemeral fluvial activity, and development of local rather than regionally integrated drainage networks.

Multi-attribute seismic analysis - tackling non-linearity

Later, instead of neural networks, a different mathematical approach using cubic b-splines was utilized for the same purpose. The results were found to be similar, suggesting that apart from neural networks, the cubic b-splines could be used as a tool for tackling non-linearity in multi-attribute seismic analysis. AVO inversion for Lame parameters The target area is a Lower Cretaceous glauconite filled fluvial channel, deposited within an incised valley system. A 3D seismic survey was acquired in order to create a stratigraphic model, consistent with all available well control and matching the production history. The ultimate goal was to locate undeveloped potential within the gas sands. The field has been producing since the early 1980s and two of the earliest, most prolific producers have begun to water out. As the objective was stratigraphic in nature, the seismic data were processed with the objective of preserving relative amplitude relationships in the offset domain to allow for the use of AVO attribute analysis. AVO inversion for Lame parameters (λρ and µρ) has become a common practice as it serves to enhance identification of reservoir zones. Also, integration of AVO-derived attribute volumes with other non-AVO derived seismic attribute volumes can provide meaningful geologic information when tied back to well data and verified as correlating with rock properties. Computation of reservoir properties for determination of mathematical relationships between variables derived from well logs, for example, is usually done with non-linear multivariate determinant analysis using neural networks. This paper provides a case study of a 3D seismic survey in southern Alberta, Canada, where a probabilistic neural network solution was first employed on AVO attributes (Pruden, 2002, Chopra & Pruden, 2003). Using the gamma-ray, acoustic and bulk density log curves over the zone of interest, gamma-ray and bulk density inversions were derived from the 3D attribute volumes. This methodology was successful, in that two new drilling locations derived from this work encountered a new gas charged reservoir, that not only extended the life of the gas pool but added new reserves as well.

Facies architecture in a tectonically influenced estuarine incised valley fill of Miocene age, northern Brazil

The Miocene Barreiras Formation in the Middle Rio Capim area records an incised valley system for which facies analysis and ichnology ( Skolithos, Ophiomorpha, Planolites, Gyrolithes, Taenidium) suggest an estuarine character. Three stratigraphic units are recognized (from bottom to top): Unit 1 includes an inner estuarine tidal channel complex and tidal flat/salt marsh deposits; Unit 2 consists of estuarine bay/lagoon and flood tidal delta deposits related to the estuary mouth; and Unit 3 includes a tidal channel with a tidal point bar, as well as tidal flat/salt marsh deposits similar to those from Unit 1. These units and their bounding surfaces record the history of relative sea level changes in the estuary. After a sea level drop, the valley was inundated and formed an amalgamated sequence boundary and transgressive surface. Transgression (Unit 1) promoted the landward shift of flood tidal deltas and lagoon settings (Unit 2). The system then moved seaward, with the superposition of inner estuarine deposits (Unit 3) over Unit 2. Facies architecture seems to have been controlled by tectonics, as shown by: the paleovalley orientation according to the main tectonic structures of the basin; the presence of faults and fractures that displace the basal unconformity; and the abundance of soft sediment deformation.

Architecture and morphology of the outer segment of a mixed tide and wave-dominated-incised valley, revealed by HR seismic reflection profiling: the paleo-Charente River, France

We present new single-channel high-resolution seismic reflection profiles, ground-truthed by vibrocore data, dedicated to the outer segment of an incised valley connected to the Charente River (French Atlantic coast). The present-day Charente is located about 50 km northward of the well-known Gironde estuary. Those river mouths are comparable in terms of marine hydrodynamic parameters, but strongly differ by their water discharge and catchment area. Seismic data are processed and interpreted to develop a three-dimensional seismic stratigraphic framework for the Charente-incised valley fill. The channel network of the drowned Charente valley is evidenced for the first time, and shows a seaward distributary pattern which is likely influenced by neotectonic control. Incision depth and width of the Charente and Gironde-incised valleys are similar, supporting the idea that correlation between valley width and modern hydrology is poor.The internal geometry of the Charente valley fill shows in seismic lines high to middle angle dipping reflectors at the base and a top of sequence with an intervening low angle seismic unit. This pattern is associated with a landward migration of the seismic unit depocentres. Sedimentary facies of the main seismic units suggests an upward and landward shift from estuarine mixed sands and muds, to estuary mouth massive sands, topped by fine marine sands. The described sedimentary and seismic characters, and the Holocene age of the valley fill near the present-day Charente river mouth, suggest that the drowned Charente valley infill mainly corresponds to a single transgressive sequence emplaced during the last sea level rise. Beyond the local interest, the dense seismic grid recorded across the Charente drowned valley gives a seismic validation for the model of large valley fill proposed by Ashley and Sheridan [Ashley, G.M., Sheridan, R.E., 1994. Depositional model for valley fills on a passive continental margin. In: R.W. Dalrymple, R.J. Boyd, B.A. Zaitlin (Eds.), Incised Valley Systems: Origin and Sedimentary Sequences. SEPM (Soc. Sediment. Geol.) Spec. Publ., Tulsa, Vol. 51, pp. 285–301.]. We propose that high–low–high internal reflection pattern succession represents the “Seismic Sandwich” in reference to the Ashley and Sheridan [Ashley, G.M., Sheridan, R.E., 1994. Depositional model for valley fills on a passive continental margin. In: R.W. Dalrymple, R.J. Boyd, B.A. Zaitlin (Eds.), Incised Valley Systems: Origin and Sedimentary Sequences. SEPM (Soc. Sediment. Geol.) Spec. Publ., Tulsa, Vol. 51, pp. 285–301.] “Sedimentary Sandwich”. Such seismic pattern is also recognized in the Gironde valley [Mar. Geol. 175 (2001) 183.].

Deltaic Infill of a Deglaciated Arctic Fjord, East Greenland: Sedimentary Facies and Sequence Stratigraphy

ABSTRACT The deltaic fill of a deglaciated side-entry fjord in western Jameson Land, East Greenland, shows the record of an interplay between regional and local controls, including climate and relative sea-level change, onshore and offshore topography, and sediment yield. A four-phase model is suggested for the delta development and fjord filling. At the deglaciation stage (phase 1), the newly flooded fjord floor primarily accumulated sediment from reworked glacial material. These deposits were relatively thin, and draped the uneven sea-floor topography. The subsequent onset of paraglacial delta sedimentation (phase 2) was characterized by a high meltwater runoff and extreme sediment yield, and corresponded to the highstand and gradual fall of relative sea level. A Gilbert-type delta with a short distributary plain formed at the head of the tributary fjord, which received a very high amount of fine-grained sediment. The stage of enhanced delta progradation (phase 3) was characterized by decreased sediment yield and runoff, and a rapid fall of relative sea level. Delta progradation was fast because of rapidly decreasing accommodation space, and a solitary river channel deeply incised the delta. The equilibrium stage (phase 4) spanned most of Holocene time and involved a lowered rate of relative sea-level fall. Seasonal runoff supplied limited amounts of sediment to the river mouth, and the delta front became increasingly reworked by wave action and longshore drift. The side-entry fjord, a small deglaciated valley invaded by the sea, was filled chiefly by highstand and regressive systems tracts, whereas relatively little sea-floor aggradation was associated with the transgressive systems tract. The stratigraphic pattern documented in this paper contrasts with the pattern usually reported from nonglaciated incised-valley systems, which are filled mainly by the transgressive systems tract, typically involving a retreating estuarine system. The pattern also differs from some large, gradually deglaciated fjord valleys containing thick, transgressive, glaciomarine deposits accumulated during glacier retreat. The study demonstrates the large variability of valley fills and illustrates the importance of topography, sediment supply, and climate as well as the style of deglaciation on the sediment filling of a fjord valley.

Three-Dimensional Numerical Modeling of Deltaic Depositional Sequences 1: Influence of the Rate and Magnitude of Sea-Level Change

ABSTRACT A three-dimensional numerical model of deltaic deposition is used to investigate the influence of sea-level changes on delta development and sequence variability. Results illustrate the three-dimensional morphology of key stratal surfaces and architecture of stratal units (systems tracts) and highlight the importance of the rate and magnitude of sea-level change in controlling the evolution of deltaic depositional sequences. High rates of sea-level fall lead to the development of a limited number of major incised channels that focus sediment supply to a few elongate, finger-like forced regressive lobes separated by large areas of nondeposition. In contrast, low rates of sea-level fall cause only minor channel incision, which occurs late during sea-level fall. As a result, sediment is supplied more uniformly to the delta front, leading to an attached, laterally continuous forced regressive apron. During lowstand and subsequent sea-level rise, the delta morphology and internal geometry are strongly controlled by the rate of rise. High rates lead to: i) poorly developed lowstand wedges that are drowned early, ii) high-magnitude transgressions, and iii) the late development of maximum flooding surfaces. The stratigraphy developed during sea-level rise is also strongly influenced by the incised-valley system created during the preceding sea-level fall. If deep, major valleys developed that captured most of the sediment supply, the resultant stratigraphy has well developed lowstand wedges that are flooded relatively late during sea-level rise. Even within a single delta, systems tracts and key stratal surfaces show three-dimensional variability and two-dimensional sections often lack significant elements of the stratigraphy. As a result, analysis of two-dimensional sections can often lead to miscorrelation and erroneous interpretations of the controlling processes.

Submersible-based observations of in-situ fossil tree trunks in Late Cretaceous seafloor outcrops, Orange Basin, western offshore, South Africa

Research Article| December 01, 2003 Submersible-based observations of in-situ fossil tree trunks in Late Cretaceous seafloor outcrops, Orange Basin, western offshore, South Africa Ian R. Stevenson; Ian R. Stevenson De Beers Marine, P.O. Box 87, Cape Town 8000, South Africa, email: ian.stevenson@debeersgroup.com Search for other works by this author on: GSW Google Scholar Marion K. Bamford Marion K. Bamford Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa, e-mail: bamfordm@geosciences.wits.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information Ian R. Stevenson De Beers Marine, P.O. Box 87, Cape Town 8000, South Africa, email: ian.stevenson@debeersgroup.com Marion K. Bamford Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa, e-mail: bamfordm@geosciences.wits.ac.za Publisher: Geological Society of South Africa First Online: 07 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2003 Geological Society of South Africa South African Journal of Geology (2003) 106 (4): 315–326. https://doi.org/10.2113/106.4.315 Article history First Online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ian R. Stevenson, Marion K. Bamford; Submersible-based observations of in-situ fossil tree trunks in Late Cretaceous seafloor outcrops, Orange Basin, western offshore, South Africa. South African Journal of Geology 2003;; 106 (4): 315–326. doi: https://doi.org/10.2113/106.4.315 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract A submersible dive undertaken over seabed outcrop situated on the middle shelf off the Namaqualand coast, at a depth of 136 to 140 mbsl, about 32km offshore, revealed an abundance of in-situ fossil tree trunks in exposed Late Cretaceous (Late Coniacian) seafloor outcrop. Based on regional Side Scan Sonar interpretations, it would appear that this outcrop is unique to the dive location, covering an approximate 2km2 area of seabed. Integration of these observations with a regional seismic stratigraphic and biostratigraphic framework has enabled more accurate constraints to be placed on the ages of the wood than was previously possible. Two species of fossil wood belonging to the Podocarpaceae were identified from samples collected by the submersible: Podocarpoxylon jago Bamford and Stevenson and P. umzambense Schultze-Motel. Palaeoenvironmental analysis shows that the proximal Coniacian succession for the Orange Basin was typified by a well-vegetated coastal plain, which was periodically waterlogged. The coastal plain experienced repeated periods of progressive drowning of the incised valley systems cutting through the coastal plain and the subsequent development of wave-dominated estuarine incised valley fill systems. The fossil wood recovered from the dive-site is typified by a lack of distinct growth ring development. This implies either a lack of seasonality or sufficient available water all year round, with no low temperatures to stop plant growth. This observation, together with complementary sedimentological and micropalaeontological analysis suggests a temperate palaeo-climate for the area. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Effect of Sea Level, Climate, and Shelf Physiography on the Development of Incised-Valley Complexes: A Modern Example From the East China Sea

ABSTRACT Analysis of high-resolution seismic reflection and sonar data from the East China Sea (ECS) continental shelf reveals the presence of an extremely broad (> 330 km) and deep (maximum incision of 72 m) incised-valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle ( 20,000 yr BP to present). Results from this study indicate that sea-level change, climate-controlled discharge and sediment supply, and shelf physiography were important factors in the development and subsequent fill of the ECS incised- valley complex. For example, wet climatic conditions during the initial Marine Oxygen Isotope Stage (MIS) 2 fall of sea level promoted fluvial erosion of the exposed shelf. However, the trend toward drier conditions during the MIS 2 fall of sea level slowed the overall development of the incised-valley complex to the point where only minor incision occurred during the maximum lowstand. Furthermore, the low-gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise. Instead, fluvial systems migrated laterally, creating a shallow ( 300 km) incised-valley system on the outer shelf. During the late MIS 2 rise of sea level, accommodation was generated within the flooded reaches of the valley complex. However, arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised-valley complex. Thus, the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley-wide tidal-bar and tidal sheet complex. Wetter climatic conditions during middle to late MIS 1 resulted in abundant sediment delivery to the drowned parts of the valley complex (estuary) and buried lowstand fluvial deposits below the depth of tidal ravinement, where they remained undisturbed. Current sequence stratigraphic models can be applied to the late Quaternary stratigraphic secession of the ECS. However, these models are too simplistic because they rely largely on rates and directions of sea-level change to explain stratal architectures. Although the extent and rate of sea-level change is extremely important, this study shows that high-frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures. These factors are particularly important for the development of incised valleys, where they directly influence incised-valley morphology and facies distributions.

The Jurassic of Kuhn Ø, North-East Greenland

The Middle–Upper Jurassic succession of Kuhn Ø, North-East Greenland accumulated in a major half-graben and is an excellent analogue for the subsurface of the mid-Norwegian shelf. On Kuhn Ø, peneplaned crystalline basement was incised by a drainage system during a major base-level lowstand, probably in late Early or early Middle Jurassic times. It was filled with fluvial conglomerates of the newly defined Middle Jurassic Bastians Dal Formation during subsequent base-level rise. As sea level continued to rise, precursor-peat of the coals of the Muslingebjerg Formation formed in swamps which covered the conglomerates and filled the remaining space of the incised valley system. The valley and interfluve areas were flooded in Late Bathonian – Callovian times and tidally-dominated, shallow marine sandstones of the Pelion Formation were deposited on top of the valley fill and over the adjacent basement peneplain. These sandstones are overlain by the newly defined shallow marine Oxfordian Payer Dal Formation which is subdivided into a lower unit and an upper unit, separated by a major drowning surface. The Payer Dal Formation sands were flooded in the Late Jurassic and organic-rich, offshore mudstones of the Bernbjerg Formation were deposited. The Jurassic succession of Kuhn Ø can thus be subdivided into large-scale sedimentary units separated by major drowning surfaces. They are of regional extent, and in combination with biostratigraphic and 87Sr/86Sr isotope data they allow the correlation of the sedimentary units on Kuhn Ø with more offshore deposits to the south in Wollaston Forland and more landwards successions to the north in Hochstetter Forland. Petrographically, the trough cross-bedded sandstones of the Pelion Formation and the lower unit of the Payer Dal Formation include both calcite-cemented and poorly cemented quartz sandstones. The calcite cement was derived from dissolution of abundant calcareous fossils and forms concretionary horizons. The upper unit of the Payer Dal Formation mainly consists of weaklycemented quartz sandstones with porosities around 30%. The sandstones of the Pelion and Payer Dal Formations on Kuhn Ø are petrographically very similar to Jurassic sandstones from the mid- Norwegian shelf and the Barents Sea with regard to original mineralogical composition, sorting and grain size. The Bernbjerg Formation mudstones are comparable to the Upper Jurassic source rock of the mid-Norwegian shelf and the Barents Sea, but have lower hydrogen index (HI) values due to terrigenous input in a relatively proximal setting. Coals of the Muslingebjerg Formation have significant source rock potential with measured HI values up to 700, kerogen types II–III and total organic carbon (TOC) values above 50%.

Controls on the Geometry of Incised Valleys in the Basal Quartz Unit (Lower Cretaceous), Western Canada Sedimentary Basin

In southern Alberta, multiple episodes of fluvial erosion occurred during Lower Mannville, Basal Quartz time (Early Cretaceous), creating a series of incised-valley systems. This study examines two of these valley networks, in order to illustrate the geomorphic and genetic complexity of incised-valley systems. Both valley networks are filled by a transgressive succession of fluvial to estuarine deposits. Isopach mapping of these deposits over an area of approximately 10,000 km 2 in southern Alberta shows that both systems are dendritic to rectilinear in character, with the trunk valley flowing from south to north along the length of the Western Canada Sedimentary Basin. These systems were fed from the west, south, and east by a network of tributaries. Eustatic sea-level changes may have played a role in initiating river incision, but regional tectonic movements had an important influence on the history of accommodation change. The periods of erosion appear to have been relatively brief because the valleys are narrow, although confinement within cohesive, mudstone-rich paleosols of the underlying incised-valley deposits may have slowed valley widening. A relatively wet paleoclimate may also have contributed to the formation of narrow valleys by favoring the existence of single-channel rivers. The general morphology of the Alberta foreland basin, together with the distribution of unfilled relief associated with a preceding valley system and/or of less resistant, slightly older deposits, determined the location of the trunk valleys. Uplift of the Bow Island Arch (Sweetgrass Arch) to the east may have been responsible for a shift in the valley headwaters between the formation of the two valley systems. Synerosional block faulting in response to flexural loading had a significant influence on the geometry of the valley network through its control on the location and geometry of major tributary valleys. The trunk valley is also significantly narrower and more deeply incised where it crosses the most pronounced uplifted block. Enhanced erosion at tributary junctions and valley bends produced localized areas (ca. 2-3 km in diameter) where the valley fill is up to five times thicker and considerably coarser grained than the adjacent valley deposits. Such localized scour fills represent prime petroleum-exploration targets.

Late Yeadonian (Upper Sandstone Group) incised valley supply and depositional systems in the South Wales peripheral foreland basin: implications for the evolution of the Culm Basin and for the Silesian hydrocarbon plays of onshore and offshore UK

Abstract The Upper Sandstone Group of South Wales has previously been interpreted as a simple NNW–SSE trending incised valley that was filled during the late Yeadonian (Namurian G1b). Data presented in this study indicate a far more complex scenario. The group is well developed in the Pembrokeshire sub-basin but it is absent from the main part of the South Wales Basin located to the east of the Penlan Axis. The principal source area for sediment flux was the forebulge of the basin located to the north in Lower Palaeozoic (foreland) strata. Variscan flexural uplift of this source area and an accompanying rapid, high magnitude fall in sea level produced a very high sediment budget. Thus, during the late Yeadonian lowstand of sea level, massive amounts of sediment were being generated and transported via an incised valley system across the western part of the South Wales peripheral foreland basin. The location and orientation of the incised supply system and its related interfluves were controlled by intrabasinal, synsedimentary Variscan structures, many of which were reactivated Caledonian extensional faults. During the succeeding sea-level rise the incised valley was filled, initially by fluvio-deltaic sands and later by estuarine argillaceous sediments. The implications of this combined tectonic–sedimentological–high resolution sequence stratigraphic model for the evolution of the late Namurian (Crackington Formation) turbidites of the Culm Basin are discussed. Examples of Silesian incised valley fill sandstone reservoirs developed in the East Midlands Oilfield and the Southern Gas Basin are briefly summarised and their spatial and temporal distributions are appraised. Data, generated from these case studies, are assessed in terms of their use for the modelling of incised valley fill sequences in foreland basins and other tectonic settings.

Sedimentology of magmatically and structurally controlled outburst valleys along rifted volcanic margins: examples from the Nuussuaq Basin, West Greenland

ABSTRACT After a period of early Palaeocene faulting and uplift of the Nuussuaq Basin, West Greenland, two valley systems were incised into the underlying sediments. Incision of the older Tupaasat valley took place during a single drainage event of large water masses, which resulted in catastrophic deposition. The valley was cut along early Palaeocene NW‐ to SE‐trending normal faults, clearly showing that the trend and the relief of the valley were structurally controlled. The valley fill is up to 120 m thick and consists of a lower part of sandstones and conglomerates deposited from catastrophic flows characterized by very high concentrations of suspended coarse‐grained sediment load. Catastrophic deposition was followed by rapid decrease in flow discharge and the establishment of a lacustrine environment within the valley characterized by the deposition of heterolithic sediments. The younger Paatuutkløften valley system was mainly cut into the Tupaasat valley fill, which was completely or nearly completely eroded away in many places. The younger valley is 1–2 km wide and up to 190 m deep. Incision of the Paatuutkløften valley probably reflected renewed tectonic activity and uplift of the basin. This phase was shortly followed by rapid major subsidence. The valley‐fill deposits comprise a uniform succession of fluvial and estuarine sandstones. The valley fill is topped by shoreface sandstones, which are succeeded abruptly by offshore mudstones deposited shortly before and during the initial extrusion of a thick hyaloclastite succession. The Paatuutkløften valley fill is attributed to a very rapid rise in relative sea level contemporary with extensive volcanism. It is suggested that this sequence of events coincided with the arrival of the North Atlantic mantle plume. In several respects, the early Palaeocene valley‐fill deposits of the Nuussuaq Basin are different from idealized facies models for incised valley systems and represent very special cases of incised valleys. Major differences from published examples include the dominance of catastrophic deposits and indications of large changes in relative sea level of several hundreds of metres taking place rapidly in less than 1 Myr. These changes were governed by the rise of the North Atlantic mantle plume.

ABSTRACT: Paleogeomorphology and Facies Architecture of Pennsylvanian Trunk-Tributary Incised Valley Systems: New River Formation, Southern West Virginia

ABSTRACT: Paleogeomorphology and Facies Architecture of Pennsylvanian Trunk-Tributary Incised Valley Systems: New River Formation, Southern West Virginia

Architecture and sequence stratigraphy of Pleistocene fluvial systems in the Malay Basin, based on seismic time-slice analysis

The Malay Basin is underlain by a productive, gas-prone, nonmarine Cenozoic section. Exploitation of the gas reserves is largely based on three-dimensional (3-D) seismic surveys, which have also gen erated much data from the nonproductive, near-subsea Pleistocene section. Seven seismic time-slice images at 12 ms two-way travel time (TWTT) spacings that document the 29-86 m sub-sea-floor section of this Pleistocene succession in the northern Malay Basin are analyzed here. These images reveal at least five types of fluvial systems of widely varying style and cross section dimensions, rang ing from braided systems with channel-belt widths of more than 4 km to small-scale meandering systems with meander-belt widths of a few hundred meters. An incised-valley system estimated to be 40 m deep is intersected by five of the images and forms the basis for an interpretation of one of two sequence boundaries revealed by this data set. The wide variation in channel style and scale in the project area contrasts with the rather uniform fluvial styles that are assumed in many production models for nonmarine oil and gas fields and should serve as a warning against making simplistic as sumptions about the consistency of these parameters during archi tectural and reservoir modeling and paleohydraulic reconstruction.