Whilst Albertine Rift marginal lacustrine and deltaic depositional environments each produce characteristic lithofacies which together can form a complex stratal architecture, ≥80% of the onshore area of these early continental rift basins is actually dominated by fluvial systems and their associated rift valley terrestrial environments. Albertine Rift rivers today can be classified as flank fan drainage, flank drainage rivers or long-axial systems. Dependent upon slope gradient and sinuosity, and reflecting the bed or suspended load transported, alluvial channels can cycle through four main stages before entering a delta distributary system at the lake shoreline. Higher energy flows closer to rift margins are dominated by gravel bed loads, transitioning to mixed and then suspended loads as gradients decrease out across the rift valley floor. Typical fluvial geomorphological features such as riffle–pool sequences, channel and side bars, meanders, point bars and oxbow lakes are accompanied by development of characteristic ichnofabrics and rhizofabrics in riparian sands and interfluve silts and clays. The four different fluvial stages can be recognized in onshore Pleistocene–Holocene sedimentary successions of both Lake Edward and Lake Albert, with well-sorted fluvial sandbodies, containing termite nests, correlating with petroleum reservoir intervals in the subsurface.
The Chukchi Borderland (ChB) is a prominent bathymetric structure located between the deep-water Chukchi Abyssal Plan and the Canada Basin in the Arctic Ocean. This region represents a block of extended continental crust that was tectonically connected to both Siberia and North America before the formation of the Canada Basin. The interior of the ChB is dissected by normal faults into high-standing blocks and troughs that define the first-order structural elements of the Chukchi Plateau, the Northwind Basin and the Northwind Ridge. The post-Hauterivian (Brookian) strata thin from 16 km in the North Chukchi Basin (south of the ChB) to 4–5 km in the Northwind Basin. The basin fill records a history of alternating periods of tectonic extension and quiescence, as reflected in distinct depositional cycles. In this chapter, we describe the ChB as a composite tectono-sedimentary element (CTSE) using original and published 2D multi-channel seismic reflection profiles, tied to the well-calibrated stratigraphy of the Chukchi Shelf and integrated with potential data. We also provide a brief summary of potential hydrocarbon plays based on analogies with the Arctic Alaska Basin.
One of the most obvious geomorphological features that can form at a coastline is a delta. In the Albertine Rift, at the long-axial shorelines of lakes away from rift-border faults at the basin flanks, and where there is a gentle, offshore topographic dip to the rift valley floor, then a long-axial delta system (LADS) can form. Low-level aerial photography demonstrates that these have a relatively high sediment discharge over a remarkably short period of time, prograding tens of metres in only a few years. This produces an elongate delta finger lobe, with associated characteristic geomorphological features, such as dextral and sinistral spits, barrier and mouth bars. Yet, no delta finger lobes are more than a few kilometres long, indicating that incremental movement along rift-bounding and intrabasinal faults change the dip of the rift valley floor and cause forced avulsion in rivers and rapid abandonment of a LADS. Together, these factors produce easily identifiable intervals within Pleistocene–Holocene rift-fill stratigraphy that display coarsening-up parasequence sets within an overall 3–5 m deltaic package. Typically, these will be stacked in the stratigraphy between recognizable marginal lacustrine sediments, such as sand berms and runnel lagoons.
Appendices A1–A3 and Acknowledgements for GSL Memoir 61, Sedimentary Dynamics in the Albertine Rift Valley, Equatorial East Africa .
Since early 1990s, the Arctic Ocean and surrounding seas have been witnessing a dramatic increase in geophysical and geological data acquisition related to the following major activities: (i) academia- and state-funded research; (ii) United Nations Convention on the Law of the Sea (UNCLOS) research; and (iii) industry-related hydrocarbon exploration programmes. The major advances have been related to the use of ice – capable research vessels assisted by icebreakers as research platforms, allowing use of a broad range of data-gathering tools to acquire a wealth of atmospheric, ice, ocean and sub-bottom data over relatively short periods of time. The data quality has increased greatly due to advances in the offboard towing equipment, GPS positioning, satellite communication and computing. In this chapter we provide a brief overview of geophysical data acquisition and geological sampling campaigns in the Arctic since 1990. Enclosure F is a part of this chapter, portraying locations of multichannel seismic reflection, wide-angle refraction profiles, sonobuoys, ocean-bottom seismometers and sampling sites including drilled wells. The corresponding metadata have been compiled in two tables in this chapter.
The tectonically active early continental Albertine Rift basins are dynamic entities, constantly evolving through time. Periods of crustal extension cause rift valley floor subsidence to create accommodation space and accumulate sediment in basinal depositional centres (‘depocentres’). Periods when stress fields change across a rift can move the maximum rupture along main rift-bounding faults to shift depocentre locations over time, often producing a series of synrift phases in basin development. In the Albertine Rift, the Lake Edward basin displays superb structural geomorphology that, in this study, could be mapped across the whole width of the rift valley. Often cited in the literature as a classic asymmetric half-graben, it is now clear that this basin is undergoing a change in rift phase, developing into an extremely asymmetric graben with a faulted eastern flexural arch. Tectonics does not operate alone, but forms a coupled dynamo with climate, that together drive and control the sedimentary fill of an early continental rift basin. The theoretical effects of this are modelled for Lake Edward to indicate basinal deposition when tectonics and climate are in, and out, of phase. Finally, the ‘sedimentary geodynamic elements’ which might be expected to characterize early continental rift basins are outlined.
Heat and groundwater flow through a rift basin are an integral part of its geodynamics, but predicting what is happening below the surface is often difficult due to a lack of direct information. Field observations on the occurrence, subaerial distribution, temperature and geochemistry of freshwater springs may help to form an idea of groundwater flow through the basin and what is, or has been, flowing through. Hot springs in the Albertine Rift are common and their occurrence is directly linked to deep-seated main rift-bounding faults, or major intrabasinal fault intersections. The majority of Lake Edward and Lake Albert active springs, or palaeosprings, are also associated with precipitation of localized tufa–travertine limestones. The cooler tufas may contain calcitized plant roots, leaf imprints and freshwater gastropods. Active scavenging of uranium (U) can be demonstrated in the algae and cyanobacteria that inhabit active spring mouths, and corresponding tufa–travertines are depleted in radioactive U, potassium (K) and thorium (Th) elements. The source for concentrated bicarbonate ions ( HCO 3 − ) in groundwater at depth – needed to precipitate limestones at the surface – remains problematic. However, rare earth element (REE) plus yttrium (Y) (REE + Y) geochemistry of the tufa–travertines suggest end-member sources of either carbonatites or marine limestones, indicating the possibility of a pre-Neogene rift sequence beneath the Albertine Rift.
The Albertine Rift of East Africa is a prime example of active early continental rifting in the world today. Geological field surveying of onshore modern-day sedimentary depositional environments here interprets older outcrop and constructs a chronostratigraphic framework based on global glacial–interglacial climatic cyclicity for the past 1.1 million years.
North Chukchi-Podvodnikov (NChP) and Zhokhov-Wrangel (ZhW) composite tectono-sedimentary elements (CTSEs) occupy the northern parts of East Siberian Sea, and Russia and United States Chukchi Sea, and adjacent part of the deep-water Podvodnikov and Toll basins of the Arctic Ocean. The NChP CTSE formed as a rift basin and includes one of the largest depocentres in the Arctic, the North Chukchi Basin. It contains a 23-km-thick succession of presumably Cretaceous and Cenozoic deposits, which may be underlain by either exhumed mantle or by incipient oceanic crust. Long-offset multichannel seismic profiles and seismic refraction data allow for many details of the basin's geology to be imaged. The ZhW CTSE is located in the front of Late Mesozoic New Siberian-Chukchi Fold-and-Thrust Belt. In Cretaceous and Cenozoic, it was dissected both by late contractional deformation and by succeeding extension probably related to the boundary between Eurasian and North American lithospheric plates. In this chapter we summarise geology of the North Chukchi – Podvodnikov and Zhokhov – Wrangel CTSEs and propose a stratigraphic model based on seismic data calibrated with the drilled stratigraphy of the US Chukchi Sea. We also briefly speculate on possible hydrocarbon plays and systems based on an analogy with Arctic Alaska.
The modern Arctic has been formed through a series of continent-continent collisions, accretion of terranes and phases of crustal extension. The Neoproterozoic Timanian, Paleozoic Caledonian and Uralian, and late Mesozoic Verkhoyansk-Kolyma, Chukotkan and Brookian orogenies formed several large fold-and-thrust belts (FTBs). The FTBs are exposed across vast areas of continents and continue offshore to form a complex tectonic basement for thick sedimentary basins, playing an important role in the history of accumulation and deformation of younger unmetamorphosed sedimentary successions that are the subject of this volume. Recognition of the importance of FTBs in the Arctic geological history and their role as a controlling factor of development of Arctic sedimentary basins resulted in this chapter, in which we review the current state-of-knowledge about Arctic FTBs and highlight questions that remain to be addressed. The Enclosure D, a Map showing boundaries of the FTB and their internal first-order structural fabric, is a part of the overview.
The glacial climatic cyclicity model (GCCM) for Albertine Rift onshore stratigraphy, constructed in Chapter 9, this volume, establishes the direct links between subsidence rate of the basin depocentre, increasing age of outcrop time slices away from it and, their height above modern-day base level (MDBL). In doing so, it potentially provides the mechanism for establishing chronostratigraphy in the Lake Edward or Lake Albert rift basins at an unprecedented high-resolution, kiloyear (ka) timescale. This chapter takes the GCCM model and applies it directly to field data from the Lake Edward and Lake Albert basins. By doing so, it confirms with field evidence the key assumptions made in the model concerning lithofacies deposition during glacial (G) or interglacial (IG) climatic cyclicity. The principal logged sedimentary sections from Lake Edward and Lake Albert have their absolute age dates calculated, and these results are then correlated with the numbered G and IG cycles of the global marine isotope stage curve. The data fit is remarkable and, therefore, not only does this G–IG (GIG) Limnostratigraphic method successfully resolve their rift-fill ages over the past 1.1 Ma, but also demonstrates how sedimentary dynamics in the Albertine Rift beat to the rhythm of global G–IG climatic oscillations.
The East Siberian Sea–Chukchi Sea Prograded Margin (ESCPM) and Makarov Oceanic Basin (MOB) include interconnected sedimentary accumulations with gradual facies transitions that occupy a significant part of the Amerasia Basin and the adjacent Siberian Arctic continental margin. The ESCPM contains a succession of Cenozoic clinothem featuring shelf-margin progradation caused by a rapid influx of siliciclastic material from NE Asia into the adjacent Amerasia Basin and represents a single tectono-sedimentary element (TSE) as per the volume's terminology. The MOB is a most distant and isolated from continental depositional systems part of the Arctic Ocean. It consists of two first-order sedimentary accumulations with distinct depositional styles and provenances. The lower, Passive margin TSE is composed of a fragment of the presumably Paleozoic-Mesozoic Barents and North Kara passive continental margin. The upper, Synoceanic TSE was formed following the separation of continental block of the Lomonosov Ridge from the Eurasian continental margin at ∼ 56 Ma and during the opening of the Eurasian Basin. It includes mostly Eocene to Holocene hemipelagic and pelagic deposits and ice-rafted sediments. Each of these accumulations is characterised as a TSE, and the MOB itself is considered as a composite TSE (CTSE). Assessments of petroleum potential in both elements rely on regional geological constraints, sedimentary architecture, and modelling. Direct hydrocarbon indicators have been detected in seismic profiles in both ESCPM and MOB. In the latter, petroleum generation likely began in the Jurassic or Late Cretaceous, peaking in the Paleocene and possibly extending into the Miocene. Reservoir rocks are inferred in Cretaceous and Cenozoic strata. In ESCPM TSE, Paleocene-middle Eocene sedimentary successions are considered to include potential source rocks, associated with main flooding surfaces and clinothem bottomset deposits.
Continental rifting is a fundamental geological process that has been responsible for breaking supercontinents apart and opening new ocean basins throughout Earth's history and the East African Rift System (EARS) is the best active example of this happening in the world today. The Albertine Rift lies at the northern end of the Western Arm of the EARS, consisting primarily of the Lake Albert and Lake Edward basins as they pass along the border between Uganda and the Democratic Republic of Congo. This Memoir describes the key geomorphological features found in the Albertine Rift Valley at the present day, identifying the sedimentary dynamic elements that dovetail together to characterize the dominant depositional environments in these early continental rift basins. These are then used to interpret the Pliocene–Holocene sedimentary sequences, documented during geological field surveys over an eight-year period, exposed around the onshore parts of the Lake Albert and Lake Edward rift valleys. Ultimately, the sedimentary dynamics of the Albertine Rift, and the stacking of its 3D stratigraphic architecture, is shown to beat to the rhythm of oscillating global glacial–interglacial climatic cyclicity and how this affects the Equatorial Tropics of Africa.
The present volume is rooted in a map of sedimentary successions of the Arctic Region by Grantz et al. (2011), and contains a brief, but comprehensive compilation of geological and geophysical data characterizing all significant sedimentary successions in the Arctic, which cover 57% of the polar area north of 64°N. Two main goals have been designated: (i) to provide, based on the present-day knowledge and data, a characterization of all Arctic sedimentary successions (or sedimentary accumulations), and (ii) to supply a snapshot of hydrocarbon-related exploration in the Arctic at the end of the second decade of this millennium. To achieve these goals, we represent sedimentary successions as consisting of one or several “Tectono-Sedimentary Elements” (TSE). This concept allows delineation, mapping, and characterization of 9 categories of TSEs based of main tectonic regimes that formed accommodation space.A TSE characterization template has been developed as an efficient method of organising and presenting the most important information about stratigraphy, structure, and petroleum geology of a TSE, including most significant exploration facts. This organizational architecture is the backbone of the volume and is a key feature that distinguishes it from other similar works about the sedimentary basins.
The geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.
A vast region of the Northeastern Siberia west of the Verkhoyansk Range includes two large sedimentary basins, Vilyui and Priverkhoyansk. Combined, these basins constitute the Lena-Vilyui Petroleum Province, which contains the largest gas reserves in the northeastern Asia. Both basins have a long and complex geological history that resulted in the accumulation of over 14 km-thick succession of Upper Proterozoic, Paleozoic, Mesozoic and Cenozoic sedimentary rocks. According to the volume's terminology, we subdivide this sedimentary body into two composite tectono-sedimentary elements (CTSE), the Vilyui and Priverkhoyansk (VI CTSE and PV CTSE), which closely correspond to the same-named basins. The CTSEs consist of ten distinct tectono-sedimentary elements (TSEs), each representing a distinct tectonic setting. This region has been studied very irregularly. In total, more than 400 deep wells have been drilled, mostly within the VI CTSE and only a few tens - in the PV CTSE. Eleven gas and gas condensate accumulations have been discovered in the VI CTSE. The PV CTSE remains poorly explored with only two commercial discoveries made as of the present-day.
Marginal lacustrine depositional environments in the Albertine Rift are highly sensitive to short-term, climatically controlled lake level fluctuations. As such, they act as one of the prime recorders of paleo-shoreline transgression or regression in rift-fill stratigraphy. In both Lakes Edward and Albert, modern day seasonal winds blow parallel with the long-axis of the rift basin, developing wave dominated shorelines at the end of a lake, but sheltered rift flanks display coastal features associated with longshore drift. The different types of shoreline around Albertine Rift lakes today produce characteristic geomorphological features and associated lithofacies, with key sedimentary structures and fauna/flora that can include hippopotamus, elephant, crocodile and fish remains. These can be identified in Pleistocene – Holocene onshore sedimentary successions around the Lake Edward and Lake Albert rift basins, providing a record of glacial – interglacial climatic cyclicity in the Equatorial Tropics of East Africa. Northern hemisphere interglacials result in a wet phase and lake level rise in the Albertine Rift, with marginal lacustrine shorelines back-stepping landward. Whereas, high latitude glacials cause corresponding periods of aridification and rift lake level fall, with paleo-shorelines prograding out towards the centre of the basin.
Maturation and accumulation of economic quantities of hydrocarbons are a common sedimentary component of continental rift basins around the world, both ancient and modern. Thus, groundwater is not the only fluid that may migrate along major rift faults away from basinal depocentres. De-risking petroleum exploration in rift basins requires demonstrating the presence of working petroleum play systems and the presence of leaking hydrocarbons to the surface is a primary way of demonstrating they are operating. Oil seeps have been known in Lake Albert since 1925 and the Kingfisher, Mputa-Waraga and Jobi-Rii petroleum play systems are due to go into full oil production. Lake Edward, however, has remained a virgin frontier exploration area. Tufa-travertine limestones along the eastern rift bounding fault of the Rwenzori Mountains have yielded organic residues which GCMS analyses indicate have a mature, oil-like distribution. Biomarkers suggest a marine shale source rock, the origin of which is at odds with both oils from Lake Albert and generation within the present EARS. A Lake Edward Slick Survey also sampled oil on the water surface that has the same biomarker signatures as the tufa-travertine-derived residues. Together they suggest maturation from a deeper pre-Neogene (?Mesozoic–Paleogene) rift sequence.
The Jan Mayen Micro-Continent (JMMC) is the result of two Cainozoic phases of continental breakup, and subsequent seafloor spreading. The first established a spreading ridge system consisting of the Reykjanes, Ægir, and Mohn spreading ridges between Norway and Greenland in early Eocene. The second phase established the Kolbeinsey Ridge in Oligocene/Miocene separating the JMMC form Greenland. Two major stratigraphic elements are established accordingly, the Jan Mayen Micro-Continent Composite Tectono-Sedimentary Element (JMMC CTSE) for the Middle Devonian to Miocene succession, and the Jan Mayen Prograded Margin Tectono-Sedimentary Element (JMPM TSE) for the Miocene to Holocene succession. OBS refraction data show that the JMMC is underlain by a generally thickened crust. Plate reconstructions show that this crust most likely is a remnant of continental crust rifted off East Greenland, and thereby, consist of rocks that correlates with the Late Palaeozoic and Mesozoic strata stratigraphy of the conjugate margins of East Greenland and Norway known to be hydrocarbon. The arrival of the Iceland hot spot and the breakup magmatism greatly influenced the historic and current heat flow. Published maturation models and play analysis, show that there is a potential for oil and gas in the Jan Mayen Ridge within the JMMC.
Abstract The Norwegian Sea oceanic basins and prograded margins have developed since NE Atlantic break-up in the earliest Eocene. Significant amounts of sediments were fed to the regionally subsiding and widening Norwegian Sea during the Cenozoic as a result of several phases of uplift and erosion of the bounding shelves and their hinterland. Despite an overall passive-margin evolution, the area experienced tectonic events and associated processes that interrupted the regional subsidence, causing contraction/inversion and tilting. The post-break-up depositional history of the mid-Norwegian margin comprises two main stages: (1) middle Eocene–Pliocene margin subsidence and relatively modest sedimentation during a period of climatic decline; and (2) latest Pliocene–Pleistocene full-scale northern hemisphere glaciations that resulted in deep erosion of shelves and hinterlands, and very high sedimentation rates and large-scale continental margin progradation. Slope failures within rapidly deposited glacial sediments affected both prograded margins, releasing large slides that travelled downslope into the oceanic Norway and Lofoten basins. Despite a long exploration history for hydrocarbon prospects in deeper waters and large amounts of data acquisition, no significant discovery has been made.
