Base-level Rise Research Articles

Sedimentology and sequence stratigraphy of the late-Messinian - Early pliocene continental to marine deposits of the Boudinar basin (North Morocco)

During the Messinian Salinity Crisis (MSC), between 5.97 and 5.33 Ma, the marine connections between the Atlantic Ocean and the Mediterranean Sea were temporarily restricted. The post-MSC reflooding of the Mediterranean Sea by the Atlantic waters and its sedimentary record are debated. The Boudinar basin (North-Morocco) provides an exceptional record of this period between ca 5.32–5.27 and 4.37 Ma at youngest (Zanclean - Zone PL1). The sedimentary succession of this basin comprises seven facies associations corresponding to depositional settings ranging from continental to open marine environments.We provide a new sequence stratigraphic framework, based on twelve stratigraphic sections. Two orders of depositional sequences (4th, 3rd order), related to base-level changes during the Late-Messinian Early-Pliocene time interval, are correlated at the basin scale. According to our reconstruction, the post-MSC base level rise and the Zanclean reflooding lasted from a minimum of several tens up to hundreds thousands years, suggesting a gradual, not catastrophic event indicative of a progressive transgression.

Palaeoenvironmental changes recorded by speleothems of the southern Alps (Piani Eterni, Belluno, Italy) during four interglacial to glacial climate transitions

Three stalagmites, which grew in the high altitude (∼1800 m a.s.l.) Piani Eterni karst system (northern Italy), represent the longest speleothem palaeoclimate-environmental record from the southern Alps. U-Th dating shows their discontinuous formation during Marine Isotope Stage (MIS) 10, 8, 7d, 6 and 5d–b, with carbonate deposition prevented during both full interglacial and full glacial stages. Speleothem formation was inhibited during interglacial peaks because local base level rise, connected to global climate changes, caused the alluviation of the main epiphreatic levels of the cave system. Drainage of the hydrological pathways, caused by the progressive decrease of rainfall and the accumulation of a perennial snow pack, stopped carbonate deposition during glacials. Thus, Piani Eterni speleothems function as indicators of transitional interglacial to glacial (IG–G) climate periods over the last ∼400 thousand years (kyrs). Analysis of δ18O and δ13C suggest that: i) seasonal snow melt occurred in these high altitude terrains during IG–G times, allowing meteoric water to efficiently penetrate the karst network; ii) soils were restored during MIS 5c–b, but absent during MIS 10, 8, 7d and 6 due to denudation of the karst surfaces; and iii) rainfall perturbations modulated the IG–G shifts in the southern Alps. Rainfall variation is connected to solar radiation changes at orbital timescales during MIS 5c–b, and mimics Dansgaard-Oeschger (DO) cycle variability during DO 23 and 22. DO cycle-like variability is also suspected during MIS 10, 8 and 6. The most important result is that, from a geochemical perspective, this study demonstrates that drivers of δ18O in southern alpine speleothems are similar to Mediterranean, Middle Eastern and Asian speleothems in that they are prevalently controlled by the rainfall amount effect. This contrasts with speleothem records from the more continental northern alpine sector where the air temperature effect on δ18O of precipitation dominates.

Novel discrete element modelling of Gilbert‐type delta formation in an active tectonic setting—first results

AbstractGilbert deltas are now recognised as an important stratigraphic component of many extensional basins. They are remarkable due to their coarse‐grained nature, large size and steep foresets (up to 30–35°) and may exhibit a variety of slope instability features (faulting, slump scars, avalanching, etc.). They are also often closely related to major, basin‐margin normal faults. There has been considerable research interest in Gilbert deltas, partly due to their economic significance as stratigraphic traps for hydrocarbons but also due to their sensitivity to relative base level changes, giving them an important role in basin analysis. In addition to field studies, numerical modelling has also been used to simulate such deltas, with some success. However, until now, such studies have typically employed continuum numerical techniques where the basic data elements created by simulations are stratigraphic volumes or timelines and the sediments themselves have no internal properties per se and merely represent areas/volumes of introduced coarse‐grained, clastic and sedimentary material. Faulting or folding (if present) are imposed externally and do not develop (naturally) within the modelled delta body itself. Here, I present first results from a novel 2D numerical model which simulates coarse‐grained (Gilbert‐type) deltaic sedimentation in an active extensional tectonic setting undergoing a relative base level rise. Sediment is introduced as packages of discrete elements which are deposited beneath sea level, from the shoreline, upon a pre‐existing basin or delta. These elements are placed carefully and then allowed to settle onto the system. The elements representing the coarse‐grained, deltaic sediments can have an intrinsic coefficient of friction, cohesion or other material properties appropriate to the system being considered. The spatial resolution of the modelling is of the order of 15 m and topsets, foresets, bottomsets, faults, slumps and collapse structures all form naturally in the modelled system. Examples of deltas developing as a result of sediment supply from both the footwall and hanging‐wall of a normal fault, and subject to changes in fault slip rate are presented. Implications of the modelling approach, and its application and utility in basin research, are discussed.

A Conceptual Model For the Preservation of Thick, Transgressive Shoreline Successions: Examples from the Forearc Nanaimo Basin, British Columbia, Canada

Abstract Sequence stratigraphic models derived from passive margins and foreland basins characterize transgressive shorelines (excluding incised valleys) as recording periods of sediment starvation, and are commonly represented as thin ( 10 m) are more likely to be developed in active tectonic settings (e.g., forearc and rift basins), which generally experience high sedimentation rates and relatively rapid changes in base level. Settings with high sedimentation rates and moderate base-level rise lead to progradational trends despite overall transgression of the shoreline. In settings where changes in eustatic sea level mainly control the resulting stratigraphic architecture (e.g., passive margins), thin transgressive successions (1–10 m) are more likely to be produced. Finally, in settings defined by relatively slow base-level change (e.g., foreland basins), the resultant transgressive succession typically comprises a lag (< 1 m) overlain by offshore mudstones. This conceptual model highlights the importance of the interplay between sedimentation rates and base-level rise, and is intended as a guide for the predictive modeling of sedimentary basins.

Late Quaternary sedimentary evolution of the outer shelf of the East China Sea

This study investigated the late Quaternary sedimentary evolution of the outer shelf of the East China Sea (ECS) using borehole core data (DH02). Three unconformity-bounded sedimentary facies, namely, prodelta facies of marine isotopic stage (MIS) 3, intertidal to subtidal flat facies of the deglacial period, and offshore tidal sand ridge facies of the Holocene, were identified from the base upward according to combined evidence of lithology, microfossil assemblages, and geochronology. Through comparative analysis with other neighboring borehole cores, these three facies, along with the MIS 3 nearshore facies and the last glacial maximum (LGM) river facies, were found to constitute the late Quaternary sediment strata. Sedimentary processes of these five facies were interpreted based on a synthetic consideration of sea-level change, climate variation, paleotopographic setting, and paleoriver-sea interactions. In particular, the development of the delta was attributable to integration of the slow sea-level decline during the later stage of the MIS 3 and abundant sediment supply resulting from the warm-wet climate. The gentle shelf topography suggests the presence of shallow and wide rivers in the delta, and the lateral shift of river channels might have induced the local formation of nearshore facies at the abandoned river mouth. The LGM river facies, which was rarely observed (presumably due to marine erosion with deglacial transgression), was inferred to have been deposited during the latter half of the LGM in response to the rise in river base level. Occurrences of tidal flat facies imply the formation of a tide-dominated estuary with the deglacial transgression. Furthermore, tidal flat sediments were reworked by enhanced tidal currents in the estuary front environment, forming mud ridges during subsequent deglacial transgression. Formation of tidal sand ridges in offshore environments of the Holocene was attributable to the uneven base caused by the underlying estuarine erosion mud ridges, and this promoted the occurrence of tidal depositional processes. The sedimentary evolution in association with sea-level change was constructed using the above-mentioned results. Overall, this study systematically elucidates the late Quaternary sedimentary processes and evolution of the outer ECS shelf, and provides an insight into the sedimentary development of analogous shelves around the world.

Petrology and geochemistry of the Boolgeeda Iron Formation, Hamersley Basin, Western Australia

The Boolgeeda Iron Formation and overlying Turee Creek Group, Hamersley Basin, Western Australia, represent a conformable succession of sediment deposited between 2.45 and 2.22 Ga. This interval of geologic history is of significant interest because it spans the Great Oxidation Event (GOE), when oxygen first accumulated in Earth’s atmosphere. Here we present geochemical and petrographic data from the uppermost 45 m of the Boolgeeda Iron Formation and an additional 30 m of the overlying Kungarra Formation mudstones, as sampled from the Turee Creek Drilling Project 1 drill core (TCDP1). This core captures the termination of BIF deposition in the Hamersley Basin and coincides with a global decline in BIF deposition in the Paleoproterozoic. We provide a continuous, high resolution chemostratigraphic dataset of major and trace element concentrations, as well as Fe speciation data, to assess the relationship between the rise of atmospheric oxygen and the subsequent decline in BIF deposition. We also highlight the interplay between local and global controls on the preservation of redox signatures, including the rise and fall of local base-level, input of weathered continental material, influx of reduced sulfur species associated with the continental weathering, and global increases in atmospheric oxygen. We interpret Boolgeeda deposition to have taken place under shallow water, oxic conditions overlying anoxic ferruginous deep water. Intermittent periods of oxidative weathering led to influxes of redox sensitive trace elements from land as continental sulfide minerals were weathered. This also led to the temporary disappearance of MIF-S, but O2 remained below the threshold capable of completely eliminating S isotope signatures associated with the MIF-S recycling.

Drainage network reorganization affecting the Nene and Welland catchments of eastern England as a result of a late Middle Pleistocene glacial advance

AbstractBritain's latitude is critical for determining the southerly extent of western European ice sheet expansion. Palaeoclimate and palaeosea‐level reconstruction in Britain, however, is complicated by spatially discontinuous glacigenic deposits and genetic and stratigraphic interpretations have relied on their lithological characteristics. This study adopted a sedimentary facies approach combined with geomorphological analyses for investigating upper Middle Pleistocene deposits in two adjacent catchments: Nene and Welland. Detailed sedimentology determined not only genesis of ice‐contact (Welland) and glaciolacustrine (Nene) deposits but also provided insight on lake surface water levels. The ice‐contact deposits recorded a constant lake level at the same height as alluvial remnants upstream in the Welland valley. These alluvial remnants are located where present tributaries join the Welland, indicating they were formed where influent streams entered a former lake and therefore can be interpreted as fluvial terraces resulting from local baselevel rise. The glaciolacustrine deposits in the Nene valley recorded fluctuating lake levels, indicating that altitudinally separated sand and gravel bodies coincident with these fluctuations and located where influent streams entered the lake also can be interpreted as fluvial terraces, but resulting from fluctuating baselevel. Sand and gravel bodies at the southern end of a dry valley linking the two catchments are interpreted as alluvial fan remnants, and those occurring on interfluves downstream of the alluvial fan remnants as flood deposits emanating from lake overflow. This drainage reorganization probably occurred in marine oxygen isotope stage (MIS) 8, but the ice advance footprint is different to that in MI 6.

Electrical resistivity imaging of anastomosing river subsurface stratigraphy and possible controls of fluvial style change in a graben-like basin, Czech Republic

Subject to frequent channel avulsions due to the increased frequency of floods, rise of base level, and/or sediment overloading, anastomosing rivers are sensitive to external (climatic or tectonic) forcing in sedimentary basins. The Morava River, Czech Republic, shows a well-developed Holocene anastomosis, confined to the pull-apart type Upper Morava Basin (UMB). We studied the stratigraphy and aggradation rates of the UMB using electrical resistivity tomography (ERT), dipole electromagnetic profiling (DEMP), core data, and radiocarbon ages, with the aim of identifying factors triggering the anastomosis at the Pleistocene/Holocene transition. The ERT and DEMP proved to be excellent tools to visualize the shape and thickness of floodplain depositional units (abandoned meanders, scroll bars, etc.). The major geophysical surfaces identified are the base of the late Weichselian braided-stream deposits (OSL age = 34.53 ± 3.42 ka), interpreted as a palaeo-stream gradient of the Morava River, and their transition to Holocene floodplain deposits. In the late Weichselian, the river aggraded at an average rate of 0.2 mm/yr. The Holocene (oldest 14C age = 7.066 ± 0.072 ka) short-term aggradation rates reached up to 13.7 mm/yr, but the average long-term rates (~0.07 to ~0.4 mm/yr) are comparable to the late Weichselian. The stratigraphy and sediment ages indicate that the onset of anastomosis was not likely associated with accelerated basin subsidence. Possible controls of the anastomosis include upstream control by numerous tributaries, large wood debris in the floodplain forests, and changes in land use. The tectonic and geomorphic context of the UMB pull-apart basin probably favoured the development of the anastomosis.

Utilizing Integrated Prediction Error Filter Analysis (INPEFA) to divide base-level cycle of fan-deltas: A case study of the Triassic Baikouquan Formation in Mabei Slope Area, Mahu Depression, Junggar Basin, China

Abstract The Mahu Depression is an important hydrocarbon-bearing foreland sag located at the northwestern margin of the Junggar Basin, China. On the northern slope of the depression, large coarse-grained proximal fan-delta depositional systems developed in the Lower Triassic Baikouquan Formation (T1b). Some lithologic hydrocarbon reservoirs have been found in the conglomerates of the formation since recent years. However, the rapid vertical and horizontal lithology variations make it is difficult to divide the base-level cycle of the formation using the conventional methods. Spectral analysis technologies, such as Integrated Prediction Error Filter Analysis (INPEFA), provide another effective way to overcome this difficultly. In this paper, processed by INPEFA, conventional resistivity logs are utilized to study the base-level cycle of the fan-delta depositional systems. The negative trend of the INPEFA curve indicates the base-level fall semi-cycles, adversely, positive trend suggests the rise semi-cycles. Base-level cycles of Baikouquan Formation are divided in single and correlation wells. One long-term base-level rise semi-cycle, including three medium-term base-level cycles, is identified overall the Baikouquan Formation. The medium-term base-level cycles are characterized as rise semi-cycles mainly in the fan-delta plain, symmetric cycles in the fan-delta front and fall semi-cycles mainly in the pro-fan-delta. The short-term base-level rise semi-cycles most developed in the braided channels, sub-aqueous distributary channels and sheet sands. While, the interdistributary bays and pro-fan-delta mud indicate short-term base-level fall semi-cycles. Finally, based on the method of INPEFA, sequence filling model of Baikouquan formation is established.

A Sand‐Gravel Gilbert Delta Subject to Base Level Change

Laboratory experiments were conducted on a sand‐gravel Gilbert delta to gain insight on its dynamics under varying base level. Base level rise results in intensified aggradation over the topset, as well as a decrease in topset slope and topset surface coarsening, the signals of which migrate in an upstream direction. Preferential deposition of coarse sediment in the topset results in a finer load at the topset‐foreset break, which creates a fine signature in the foreset deposit. Base level fall has the opposite effects. Entrainment of the topset mobile armor causes a coarsening of the load at the topset‐foreset break and so a coarse signature in the foreset deposit. The entrainment of the topset substrate and fine top part of the foreset may follow, which causes a fining of the load and a fine signature in the foreset deposit. The fact that the upstream sediment supply requires a certain slope and bed surface texture to be transported downstream under quasi‐equilibrium conditions counteracts the effects of base level change. This information travels in the downstream direction. In nature base level change is likely so slow that the upstream sediment load maintains the topset slope and bed surface texture and so keeps the topset in a quasi‐equilibrium state. Base level change is therefore not expected to leave a clear signal in a mixed‐sediment Gilbert delta other than a change in elevation of the topset‐foreset interface.

Mapping a coastal transition in braided systems: an example from the Precipice Sandstone, Surat Basin

ABSTRACTThe Precipice Sandstone is traditionally interpreted as a braided fluvial deposit that transitions upwards into meandering channel deposits responding to a rise in base level that eventually deposits the overlying alluvial to lacustrine Evergreen Formation. This study found sedimentary evidence of tidal to marine influence within the Precipice Sandstone coincident with avulsion and diversion of the system from southward to northward-flowing channels as the system was transgressed. The north-flowing channels are interpreted to debouch into a shallow restricted marine embayment with tide and wave influence, which provides an alternative insight into this unit and suggests a Lower Jurassic north or northeasterly marine connection. The Precipice Sandstone is a regional aquifer, in places hosts hydrocarbons and has been considered as a storage unit for CO2 geosequestration. Outcrop analogues can provide geometries to accompany facies interpreted from sedimentary structures that are observable in core, to assist in characterising reservoir heterogeneity.

Permo-Triassic Qiseib Formation, Western Side of the Gulf of Suez, Egypt: A Link of Fluvial Facies with Sequence Stratigraphy

Facies analysis of the studied Permo-Triassic Qiseib Formation indicates the presence of five lithofacies. These lithofacies are: matrix-supported conglomerates facies (facies A), coarse-to medium-grained sandstone facies (facies B), heterolithic facies (interbedded sandstone and siltstone) (facies C), interbedded siltstone and claystone facies (facies D), and mixed clastic-carbonate facies (facies E). These facies were deposited in two fluvial environments: low sinuosity braided and high sinuosity meandering. The braided stream deposits dominate the southern portion of the studied area, whereas the meandering stream deposits prevailed in the northern portion. The fine-grained meandering stream deposits grade laterally to the northern part of the study area into tidally-influenced fine-grained meandering strata (estuarine mud). In terms of its sequence stratigraphy, the Qiseib Formation represents a fluvial depositional sequence bounded by two sequence boundaries. This fluvial sequence comprises lowstand-, transgressive- and highstand systems tracts. The Lowstand Systems Tract (LST) is predominantly characterized by braided coarse-grained sandstone deposits (Braided stream facies) with limited fine-grained clastics (floodplain facies). TST includes the coeval tidally-influenced fine-grained meandering strata that occur in the extreme north of the study area. The highstand systems tract (HST) is assigned to the sand bodies of the crevasse splay that encased within the floodplain mudstones, where base level rise slows down. Architectures of deposition of the studied Qisieb Formation were mainly controlled by tectonics and climate change. Influence of sea-level control could be developed during deposition in the northern part of the study area, where the tidally-influenced downstream deposits (estuarine mudsone and siltstone) dominated. Also, the relative proportion of fluvial channel sand bodies and fine over bank deposits of the Qisieb Formation were a result of changes in the balance between accommodation space (A) and sediment supply(S).

Depositional model for peat swamp and coal facies evolution using sedimentology, coal macerals, geochemistry and sequence stratigraphy

As one of the most important source rocks and reservoirs of unconventional natural gas, the sedimentary environment and mode of peat swamp (the predecessor of coal seam) is important to the coal seam’s spatial distribution, material composition, hydrocarbon generation potential, reservoir physical properties, etc. To reveal the depositional characteristics and history of environmental change in a terrestrial basin during a period of peat accumulation, the Middle Jurassic aged #7 coal from Gaoquan in the Qaidam Basin (NW China) was investigated using sedimentology, maceral composition, geochemistry and sequence stratigraphy. Based on identification of the sedimentary shoreline break belt, wave energy depletion point and position of wave base, the peat swamp system can be subdivided into (1) lakeside plain, (2) low energy lakeshore, (3) high energy lakeshore, and (4) shallow lake subfacies. A new method for determining coal facies is proposed based on the combination of environmental parameters including oxidation-reduction levels, energy conditions and the influence of terrigneous sediments. The evolution of the coal seam shows that peat was deposited mainly in the low energy lakeshore and lakeside plain subfacies. Five types of sequence stratigrpahic surface and two types of parasequence were identified. Forced lake regressions and normal lake regressions are attributed as the causes of sequence boundaries. The sequence stratigraphic framework comprises six sequences and corresponding system tracts, and the curve of base-level for each demonstrates a characteristic initial period of slow rising followed by fast rising and then returning to slow rising. A model indicating the relationship among base-level changes, coal facies evolution, and the environmental features in the swamp is proposed that shows the environmental features of the swamp were controlled by both base-level changes and coal facies. Accompanying depositional environment changes from a lakeside plain to lakeshore and shallow lake caused by increasing rate of base-level rise, water paleosalinity, acidity and the percentage of woody plants decrease, and the bog type alters from the low marsh to raised bog.

Late Quaternary Fluvial History of Santa Cruz Island, California, USA

The geologic history of fluvial systems on Santa Cruz Island (SCI) is complex, involving responses to both allogenic and autogenic forcings. During periods of low or lowering sea level, canyons on the island were eroded and sediment was transported off the island onto the exposed marine shelf. When sea level rose, streams aggraded, building a sedimentary wedge that progressed from the shelf upstream into the canyons. This cycle of erosion and aggradation in response to glacial–interglacial sea-level cycles was likely repeated numerous times during the Quaternary, although clear evidence of only the most recent cycle is present in the island’s alluvial sequences. Christy, Sauces, and Pozo Canyons contain thick packages of fine-grained sediments that were deposited as a result of the interaction between autogenic depositional processes and allogenic forcing of continuous base-level rise. Other canyons on the island either have little alluvial fill due to their steep gradients or are filled with coarse-grained, recent (likely late Holocene) alluvium that covers the older alluvial deposits. Differences in the nature and extent of the alluvial exposures on SCI relative to those on neighboring Santa Rosa Island reflect differences in the local topography, geology, and ranching histories of the 2 islands.

Evolution of fluvial system during the Pleistocene warm stage (Marine Isotope Stage 7) – A case study from the Błądzikowo Formation, N Poland

This paper discusses successive changes in the evolution of the fluvial system observed throughout the Błądzikowo Formation at the Mrzezino key site in northern Poland. The study focuses on the development of fluvial sedimentation during Marine Isotope Stage 7. The sedimentary record of the Pleistocene at the study site shows a well-developed sequence that is over 30 m thick. The Błądzikowo Formation shows a quick evolution of the fluvial system from a high-energy sandy braided river, to a meandering sandy river and, finally, to a low-energy meandering/anastomosing river with significant suspension settling. This transition is explained as a decrease in flow energy, increase in aggradation ratio and expansion of accommodation space during deposition time. A change in the fluvial system has not been manifested in the variations of the plant cover. Palynological analysis indicates that climate conditions were generally stable, cool and humid (boreal). Sediment transport occurred towards the N-NW, through a valley with a NW-SE axis. Infrared optically stimulated luminescence (IR-OSL) dating shows the sequence formed from 225.6 ± 17.2 to 210.5 ± 16.6 ka. Well preserved fluvial cycles and 35 m of thickness suggest the intensive accumulation of the Błądzikowo Formation with decreasing ratio of lateral erosion. It suggests an increasing influence of base level rise on evolution of fluvial system, mostly during MIS 7.

Understanding the geometry and distribution of fluvial channel sandstones and coal in the Walloon Coal Measures, Surat Basin, Australia

Understanding the controls on coal seam distribution and geometry is fundamental for planning coal seam gas production. In the Jurassic Surat Basin of South East Queensland, Australia, the spatial continuity of coal seams in the Walloon Coal Measures is highly variable and often difficult to map and predict, even with closely spaced (<1000 m) drillings. This paper investigates the frequency and location of thick sandstone in relation to thick coal seams or plies across three broad stratigraphic divisions, Upper Juandah (UJ), Combined Lower Juandah-Taroom (CLJT) and Condamine Coal Measures (CCM), within the Walloon Coal Measures. Basic depositional facies, e.g. channel, floodplain, marginal mire, and coal mire, were interpreted from geophysical logs. An in-house code was used to count the number of coal plies thicker than 2 m, and channel sandstones thicker than 5 m for the UJ and CLJT and 3 m for the CCM at each borehole. Isopleth maps of the numbers of both coal plies and channel sandstones were generated across the basin for the three subdivisions. Results show that there is an upward stratigraphic trend from thick to thin, and then to thick stacked coal plies. This corresponds to a similar vertical thickness change in channel sandstones. The incidence of thick coal and thick sandstone is associated with rising base level within an early transgressive systems tract which was followed by a high stand prior to a regional erosive event above the UJ. Thick and stacked coal plies have a marked tendency to occur in belts adjacent to the thick channel thoroughfares in the basin.

Improving spatial predictability of petroleum resources within the Central Tertiary Basin, Spitsbergen: A geochemical and petrographic study of coals from the eastern and western coalfields

Central Tertiary Basin (CTB) coals from a variety of palaeogeographic conditions within the Longyear and Verkhnij seams, were sampled to assess the relationship between the petroleum present, the remaining generation potential and coal geochemistry in order to improve the spatial predictability of petroleum resources within the basin. Vitrinite reflectance (VR) values from the CTB coals have been shown to be suppressed (Marshall et al., 2015b). This study attempts to quantify and correct for this suppression effect by applying the Lo (1993) method (LoVR), which uses Hydrogen Index (HI) values to modify VR data, and the coal Rank(Sr) scale of Suggate (2000, 2002), a technique not affected by suppression. In addition, the oil generation and expulsion thresholds for the CTB coals were investigated, with discussions on oil potential versus marine influence upon the mires in which the coals formed.A pseudo-van Krevelen diagram shows that the majority of the coals plot on the Type II kerogen line, while the remainder plot between the Types II and III kerogen lines, with HI between 151 and 410mgHC/g TOC; however, maceral analysis shows that Type III kerogen predominates. This is attributed to the presence of abundant fluorescing (oil-prone) vitrinites. The LoVR, Tmax and Rank(Sr) parameters all show that maturity increases from basin margins towards basin centre (i.e. from Bassen to Lunckefjellet, to Breinosa and Colesdalen) and indicate that all the coals are within the oil generation window. The marginal samples at Bassen are within the early mature stage of the oil window (i.e. ~0.7% RO); meaning the threshold for oil generation in the basin could not be clearly defined. However, the observed maturation trend somewhat parallels the maturation pathway of the New Zealand Coal Band (NZ Coal Band) and the “envelope” of the Sykes and Snowdon (2002) NZ coal data-set; therefore, it is considered that the oil generation threshold for the CTB coals is likely at Rank(Sr) ~9–10, Tmax~420–430°C in line with the observed rise in Bitumen Index (BI). Some of the Lunckefjellet coals and all the Breinosa and Colesdalen coals have either reached or progressed beyond the threshold for oil expulsion as indicated by the peak in HI at Rank(Sr) ~11–12, LoVR ~0.75–0.85% RO, Tmax~430–440°C. The peak in BI at Rank(Sr) ~12.5–13.5 suggests that some of the Lunckefjellet and Breinosa coals, and all the Colesdalen coals have reached the “effective oil window”.Total sulphur (ST) contents range between 0.46 and 12.05% indicating non-marine to strong marine influence upon precursor peats, with ST contents of the Longyear seam appearing to record instances of coastal retreat associated with base level rise. Marine deposition seems to significantly control the distribution of oil-prone coals within seams and across the CTB. The levels of marine influence (as indicated by ST content) show clear positive relationships between BI and HI within the Bassen samples because they have not started expelling oil. Conversely, the levels of marine influence show clear negative relationships with BI and HI within the Colesdalen samples because they have commenced oil expulsion, and probably reached the “effective oil window”. The more marine influenced coals appear to have commenced petroleum generation relatively earlier, which is a plausible explanation why the coals from the Lunckefjellet locality appear to be at different stages within the oil window.

500 m of rapid base level rise along an inner passive margin – Seismic observations from the Pliocene Molo Formation, mid Norway

The positions of late Cenozoic coasts, related base level changes and tectonic events are still an enigma along large parts of the North Atlantic passive margin due to severe glacial erosion and inconclusive biostratigraphic ages. Periglacial paleo-coastlines are best preserved along the mid Norwegian margin from where we show the first 3D seismic images of a transgressive coastal delta (lower Molo Formation) that constrains the late Cenozoic geological history.Well data, 2D seismic sections and a 990 km2 3D survey, located above the Froan Basin and the Draugen oil field, are used to investigate the 60 km-wide and 600 km long coast-parallel Molo Formation. We interpret the Molo Formation to be younger (mainly Pliocene) than the Kai Formation (Mid and late Miocene) and propose a further subdivision of the Molo Formation into a lower, largely transgressive and an upper highstand regressive unit.A relative base level fall of several hundred meters is recorded at the onset of the Miocene compression phase (mid Miocene). Simultaneously, the Mid Miocene Unconformity (MMU) developed and the syntectonic and lowstand Kai Formation was deposited to the west of the study area. Upon termination of the Miocene compression phase a cumulative base level rise in the order of 500 m is interpreted. The lower Molo Formation is interpreted as a coastal delta sequence and characterized by a sand-rich parasequence set that exhibits a largely progradational motif. The deposits record a stepped landward migration of the paleo coastline during the initial transgression. Locally, the relative position of topset-foreset rollovers and trajectory analysis document 90 m of the base level rise. The upper Molo Formation is interpreted as a fluvial-dominated, wave-influenced progradational shelf-edge delta. Fluctuations in base level are interpreted to be largely tectonically driven.

The impact of avulsion on groundwater level and peat formation in delta floodbasins during the middle-Holocene transgression in the Rhine-Meuse delta, The Netherlands.

By redistributing water and sediment in delta plains, avulsions of river branches have major environmental impacts, notably in changing hydrological and peat-forming conditions in floodbasins. The central part of the Rhine-Meuse delta, with its extensive databases including detailed lithological data and high-resolution age control, offers a unique opportunity to study middle-Holocene avulsion impacts on floodbasin groundwater level and peat formation. Avulsion has caused local accelerations of rising groundwater tables to be superimposed on decelerating base-level rise. This is evident from comparing single-site groundwater rise for multiple floodbasins in the river-dominated part of the delta, with regionally averaged groundwater-rise reconstructions. Floodbasin type (lacustrine versus terrestrial wetland), size and openness, partly through effects on discharge dispersal, affect how strongly the floodbasin groundwater tables respond to avulsion-diverted discharge. Cross-sectional lithology repeatedly indicates a shift from high-organic wood peat to low-organic reed peat in the vicinity of the avulsed channel, resulting from changes in water-table regime and nutrient status. Avulsive impact on the floodbasin groundwater table was most pronounced during the transition from transgressive to high-stand stage (between ca. 6000 and 4000 years ago), owing to developing floodbasin compartmentalization (size reduction, confinement) resulting from repeated avulsion. By way of environmental impacts on groundwater tables and vegetation, avulsions thus affect the heterogeneity of floodbasin facies.

Dam-induced base-level rise effects on the gravel-bed channel planform

Little is known on the planform evolution of gravel-bed rivers in base-level raised backwater zones upstream from dam reservoirs. The general model of river channel response to base-level rise predicts a decrease in river sinuosity. However, the observations of channel adjustments in the reservoir backwater document a narrower and more sinuous channel developed as a result of fine sediment deposition and vegetation expansion. Here, the long-term aerial photo-based observations (1963–2015) of two gravel-bed rivers of different initial channel pattern (the Dunajec and its tributary, the Smolnik) located in the base-level raised zone of the Rożnów Reservoir in the Polish Carpathians were analyzed. The results show that the initially multi-thread river in backwater was significantly narrowed and its sinuosity increased (phase 1), which was followed by the stabilization of channel planform (phase 2). However, in the initially single-thread river only phase 2 occurred. The rate of channel narrowing observed on the initially multi-thread river was positively related to the initial channel width (R2=0.90, p<0.0001) and bar width (R2=0.81, p<0.0001). The increase in sinuosity was higher in the previously wider channel section and did not occur in the valley-confined zones of the single-thread river. The results are conceptualized in a two-phase conceptual model, which hypothesizes that the trajectories of the long-term planform adjustments of gravel-bed river in backwater are controlled by the initial river morphology which creates accommodation space for fine sediment deposition and associated vegetation expansion.