Changing provenance and stratigraphic signatures across the Triassic–Jurassic boundary in eastern Spitsbergen and the subsurface Barents Sea

A change to more sandstone dominated deposits and increasing condensation across the Triassic–Jurassic boundary is generally associated with improved reservoir quality in the Barents Sea. However, spatial and temporal changes in reservoir quality in this interval shows that the composition of the sediment source, immature sedimentary rocks supplied from the east or recycled in the basin in contrast to mature arenites to the south and west, affect the reservoir quality. The regional distribution of the different sources is best constrained in the southwestern part of the Barents Sea, and hitherto there has been no direct comparison between the zircon signature in outcrop analogues and their subsurface equivalents. In this study we evaluate the stratigraphic development of formations across the Triassic–Jurassic boundary in the Barents Sea and eastern Spitsbergen to compare their provenance signatures. By coupling outcrop and core data, we tie together the regional tectono-stratigraphic evolution of this important reservoir interval and relate the variable degree of sediment reworking with the relative distribution of immature Triassic sedimentary rocks across the basin. Results show higher degrees of erosion and reworking in Spitsbergen compared to the Barents Sea, consistent with local variations in the forebulge province of Novaya Zemlya observed in the subsurface. Provenance samples from Spitsbergen also record the same change in signature as in the subsurface Barents Sea. However, mature sediments are mixed with immature sediments later in Spitsbergen, indicating a latency in progradation from mature source areas which favour southern provenance areas in Fennoscandia as opposed to Greenland. Presence of young detrital zircon grains with similar Norian ages are recorded in the Upper Triassic strata both in the southernmost Barents Sea and on Spitsbergen, suggesting that a sediment source was active east of the basin and supplied sediment uniformly to the entire basin during the late Triassic.publishedVersio

Geological control on dinosaurs’ rise to dominance: Late Triassic ecosystem stress by relative sea level change

The Late Triassic is enigmatic in terms of how terrestrial life evolved: it was the time when new groups arose, such as dinosaurs, lizards, crocodiles and mammals. Also, it witnessed a prolonged period of extinctions, distinguishing it from other great mass extinction events, while the gradual rise of the dinosaurs during the Carnian to Norian remains unexplained. Here we show that key extinctions during the early Norian might have been triggered by major sea-level changes across the largest delta plain in Earth's history situated in the Triassic Boreal Ocean, northern Pangea. Fossil and rock records display extensive marine inundations with floral turnover, demonstrating how susceptible widespread low-gradient delta plains were to transgressions. Landward shoreline translocation implies decrease in important coastal regions and ecological stress on the dominant Archosauria, thriving in these habitats, and we argue that these unique geological factors played an important role in dinosaurs gradual rise to dominance.publishedVersio

Linking an Early Triassic delta to antecedent topography: Source-to-sink study of the southwestern Barents Sea margin

Present-day catchments adjacent to sedimentary basins may preserve geomorphic elements that have been active through long intervals of time. Relicts of ancient catchments in present-day landscapes may be investigated using mass-balance models and can give important information about upland landscape evolution and reservoir distribution in adjacent basins. However, such methods are in their infancy and are often difficult to apply in deep-time settings due to later landscape modification. The southern Barents Sea margin of N Norway and NW Russia is ideal for investigating source-to-sink models, because it has been subject to minor tectonic activity since the Carboniferous, and large parts have eluded significant Quaternary glacial erosion. A zone close to the present-day coast has likely acted as the boundary between basin and catchments since the Carboniferous. Around the Permian-Triassic transition, a large delta system started to prograde from the same area as the present-day largest river in the area, the Tana River, which has long been interpreted to show features indicating that it was developed prior to present-day topography. We performed a source-to-sink study of this ancient system in order to investigate potential linkages between present-day geomorphology and ancient deposits. We investigated the sediment load of the ancient delta using well, core, two-dimensional and three-dimensional seismic data, and digital elevation models to investigate the geomorphology of the onshore catchment and surrounding areas. Our results imply that the present-day Tana catchment was formed close to the Permian-Triassic transition, and that the Triassic delta system has much better reservoir properties compared to the rest of Triassic basin infill. This implies that landscapes may indeed preserve catchment geometries for extended periods of time, and it demonstrates that source-to-sink techniques can be instrumental in predicting the extent and quality of subsurface reservoirs.publishedVersio

Linking sediment supply variations and tectonic evolution in deep time, source-to-sink systems—The Triassic Greater Barents Sea Basin

Triassic strata in the Greater Barents Sea Basin are important records of geodynamic activity in the surrounding catchments and sediment transport in the Arctic basins. This study is the first attempt to investigate the evolution of these source areas through time. Our analysis of sediment budgets from subsurface data in the Greater Barents Sea Basin and application of the BQART approach to estimate catchment properties shows that (1) during the Lower Triassic, sediment supply was at its peak in the basin and comparable to that of the biggest modern-day river systems, which are supplied by tectonically active orogens; (2) the Middle Triassic sediment load was significantly lower but still comparable to that of the top 10 largest modern rivers; (3) during the Upper Triassic, sediment load increased again in the Carnian; and (4) there is a large mismatch (70%) between the modeled and estimated sediment load of the Carnian. These results are consistent with the Triassic Greater Barents Sea Basin succession being deposited under the influence of the largest volcanic event ever at the Permian-Triassic boundary (Siberian Traps) and concurrent with the climatic changes of the Carnian Pluvial Event and the final stages of the Northern Ural orogeny. They also provide a better understanding of geodynamic impacts on sedimentary systems and improve our knowledge of continental-scale sediment transport. Finally, the study demonstrates bypass of sediment from the Ural Mountains and West Siberia into the adjacent Arctic Sverdrup, Chukotka, and Alaska Basins in Late Carnian and Late Norian time.publishedVersio

Linking regional unconformities in the Barents Sea to compression-induced forebulge uplift at the Triassic-Jurassic transition

The Triassic-Jurassic transition marks an important change in the basin configuration of the Greater Barents Sea. A contiguous basin with km-thick sedimentary successions changed into a partitioned basin with uplift in the west and foreland basins in the east with significant implication for the basin infill history. Our study employs a range of different high-resolution datasets from a distal part of the basin which unravels the complex pattern of differential uplift and erosion in the basin during this period. We record for the first time distinct angular unconformities between Upper Triassic strata and overlying Lower Jurassic strata within the basin, showing that large parts of it formed topographic highs. Our study links these angular unconformities to compression induced by the Novaya Zemlya Fold and Thrust Belt. A heterolithic basement below a thick sedimentary succession where the fold belt developed created a complex uplift pattern in the basin, at the same time similar to but different from typical forebulge areas. Compression caused inversion of older basement rooted faults defining platforms and graben systems throughout western parts of the Barents Sea basin, in addition to salt remobilization that resulted in differential uplift and erosion. These local zones of uplift controlled the sediment distribution pattern to the basin at a time when the most important reservoir units in the basin were deposited. This new understanding of the basin development explains hitherto enigmatic sequence boundaries that has inspired complex paleogeographic models in the past.publishedVersio

Tectonostratigraphic development of the Upper Triassic to Middle Jurassic in the Hoop Area, Barents Sea: Implications for understanding ultra-condensed reservoir units

The most prolific reservoir intervals in the Barents Sea are found in the Upper Triassic to Middle Jurassic Realgrunnen Subgroup, deposited during a major change in the structural evolution of the basin which greatly influenced its development and distribution. The effects are evident in one of the petroleum provinces in the SW Barents Sea, the Hoop Area. Due to the condensed nature of the succession, the tectonostratigraphic evolution has been enigmatic. We use a range of different methods and dataset, including high-resolution P-Cable seismic to determine the tectono-stratigraphic evolution of the succession. Results are important for exploration and production in the Hoop Area and beyond, but also for a broader understanding of how ultra-condensed successions might evolve during long periods of non-deposition and short bursts of deposition. Seven major phases of deposition and non-deposition/erosion are defined. Stage 1 represents fluvio-deltaic deposition in the Fruholmen Formation (Norian), followed by Stage 2 with significant truncation and non-deposition, lasting up to 35 million years. Deposition resumed with the shallow marine to fluvial Nordmela and Stø formations (Pliensbachian to Bajocian), which both encapsule long periods of erosion and non-deposition (stage 3–6). Stage 7 is represented by transgression and shelf deposition in the Fuglen Formation (Bathonian). The change from a high-accommodation setting with continuous and relatively high rate of accumulation in the Triassic, to a low-accommodation setting with episodic deposition and extensive sediment cannibalization in the Jurassic, resulted in cleaner sandstones with better reservoir properties. The low-accommodation setting also enabled coarse-graded detritus from hinterlands in Fennoscandia to prograde into distal part of the basin and more amalgamation of the sands during the Jurassic. Adversely, the low accommodation setting also caused a fragmented pattern of deposition and preservation that needs to be carefully considered in subsurface datasets, often with limited resolution.publishedVersio

Sedimentology and seuence stratigraphy of the late cretaceous lowe Ferron Sandstone: Application of 3-D geocellular modelling to the drunkards wash CBM-field in central Utha, USA

Deposition of the Ferron Sandstone Member occurred during a widespread regression of the Western Interior Seaway during the Turonian. The Ferron is informally subdivided into two units. The Upper Ferron, ferronensis sequence is well exposed as a shallow marine and coastal plain clastic wedge along the edge of the Wasatch Plateau in central Utah. In contrast the Lower Ferron, hyatti sequence, has previously only been documented in the outcrop and as a basal sandstone in the subsurface Drunkards Wash, Buzzard Bench and Helper fields around the town of Price, where the Upper Ferron is interpreted to form a major coal bed methane accumulation in non-marine deposits overlying the Lower Ferron sandstone. The aim of this study is to improve the current understanding of the stratigraphy and sedimentology of the Lower Ferron unit. Correlation of 55 borehole logs coupled with outcrop studies have resulted in a new depositional model for the system. The correlations suggest that the Lower Ferron is comprised of a series of progradational to aggradational shoreface parasequences which prograded in an east to south-easterly direction. Modelling also suggests that a series of outcrops, previously interpreted as long shore bars, are in fact the downdip expression of these shorefaces. This model is supported by extrapolation of the facies tracts mapped in the subsurface, geometric reconstruction of the large scale structures and correlation of bentonite horizons. The final model suggests a more prominent Lower Ferron depositional system than previous studies and suggests a dynamic transition between the informally named Upper and Lower Ferron Sandstone

Geological Deposition

We propose a method for modelling and visualizing geological scenarios by sequentially disposing stratigraphy layers. Evolution of rivers and deltas is important for geologists when interpreting the stratigraphy of the subsurface, in particular for hydrocarbon exploration. We illustratively visualize rivers and deltas, and how they change the morphology of a terrain during their evolution. We present a compact representation of the model and a novel rendering algorithm that allows us to obtain an interactive and illustrative layer-cake visualization. We use a data structure consisting of a stack of layers, where each layer represents a unique erosion or deposition event.

Geological control on dinosaurs’ rise to dominance: Late Triassic ecosystem stress by relative sea level change

The Late Triassic is enigmatic in terms of how terrestrial life evolved: it was the time when new groups arose, such as dinosaurs, lizards, crocodiles and mammals. Also, it witnessed a prolonged period of extinctions, distinguishing it from other great mass extinction events, while the gradual rise of the dinosaurs during the Carnian to Norian remains unexplained. Here we show that key extinctions during the early Norian might have been triggered by major sea-level changes across the largest delta plain in Earth's history situated in the Triassic Boreal Ocean, northern Pangea. Fossil and rock records display extensive marine inundations with floral turnover, demonstrating how susceptible widespread low-gradient delta plains were to transgressions. Landward shoreline translocation implies decrease in important coastal regions and ecological stress on the dominant Archosauria, thriving in these habitats, and we argue that these unique geological factors played an important role in dinosaurs gradual rise to dominance