Cretaceous Ferron Sandstone Research Articles

A new fossil assemblage shows that large angiosperm trees grew in North America by the Turonian (Late Cretaceous).

The diversification of flowering plants and marked turnover in vertebrate faunas during the mid-Cretaceous transformed terrestrial communities, but the transition is obscured by reduced terrestrial deposition attributable to high sea levels. We report a new fossil assemblage from multiple localities in the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah. The fossils date to the Turonian, a severely underrepresented interval in the terrestrial fossil record of North America. A large silicified log (maximum preserved diameter, 1.8 m; estimated height, ca. 50 m) is assigned to the genus Paraphyllanthoxylon; it is the largest known pre-Campanian angiosperm and the earliest documented occurrence of an angiosperm tree more than 1.0 m in diameter. Foliage and palynomorphs of ferns, conifers, and angiosperms confirm the presence of mixed forest or woodland vegetation. Previously known terrestrial vertebrate remains from the Ferron Sandstone Member include fish teeth, two short dinosaur trackways, and a pterosaur; we report the first turtle and crocodilian remains and an ornithopod sacrum. Previous studies indicate that angiosperm trees were present by the Cenomanian, but this discovery demonstrates that angiosperm trees approaching 2 m in diameter were part of the forest canopies across southern North America by the Turonian (~92 million years ago), nearly 15 million years earlier than previously thought.

Re-evaluating the Paleogeography of the River-dominated and Wave-influenced Ferron Notom Delta, Southern Central Utah: an Integration of Detailed Facies-architecture and Paleocurrent Analysis

Abstract This study re-evaluates the paleogeography of a river-dominated and wave-influenced deltaic system in a single parasequence (6a) of the Cretaceous Ferron Sandstone, south-central Utah, which was previously interpreted as a typical asymmetric delta. The conceptual asymmetric-delta model of Bhattacharya and Giosan (2003) has been widely applied to interpret ancient deltaic systems. However, reconstructed paleogeographies relying on this conceptual model are commonly not scaled to the architectural elements, which could possibly lead to inaccurate interpretations, especially when data are relatively sparse. The extensively exposed Ferron Sandstone outcrops provide an opportunity to demonstrate how detailed facies-architecture work can be integrated with regional facies relationships to elucidate a properly scaled paleogeography. Seven facies associations (FA) are identified in parasequence 6a and are arranged into two distinctively different successions. The river-dominated succession consists of prodelta, distal delta-front, proximal delta-front, and terminal-distributary-channel FA, while the wave- and storm-dominated succession comprises offshore-shelf, lower-shoreface, and upper-shoreface FA. The river-dominated succession is muddier and less bioturbated than the wave- and storm-dominated succession. Facies-architecture analysis shows that the river-dominated proximal delta-front facies consists of mouth-bar and terminal distributary-channel elements that are not seen in the wave- and storm-dominated facies. The scales of mouth bars and terminal distributary channels suggest that they are rather small features compared with the river-dominated delta lobe, which is incompatible with the simple bar-elongation asymmetric-delta model presented by Li et al. (2011). Instead, parasequence 6a is interpreted to be a valley-fed, river-dominated symmetric delta protected from waves by an updrift barrier system, which is analogous to the modern Mongky river delta on the west coast of Madagascar. The progressive change in orientation of west-directed mouth bars, to north-directed and east-directed lobes around the periphery of the river-dominated delta, indicates a highly radial Lafourche-type delta. Moving away from the protection of the barrier system, there is a gradual change from highly river-dominated facies to increasingly wave- and storm-influenced facies toward the southeast. Due to the entrenched nature of the feeder river associated with an incised-valley system, the parasequence 6a delta was bifurcation-dominated rather than avulsion-dominated. This study shows that it is critical to integrate detailed facies-architecture analysis in order to reconstruct properly scaled paleogeographies and hypothesizes that stable bifurcation-dominated deltas should be more common than avulsion-dominated deltas in a lowstand delta system due to the entrenched nature of the feeding trunk river, which inhibits avulsion.

Facies, Backwater Limits, and Paleohydraulic Analysis of Rivers in a Forced-regressive, Compound Incised Valley, Cretaceous Ferron Sandstone, Utah, U.s.a.

Abstract We analyze a compound, piedmont-linked, coastal-plain incised-valley system from the Turonian Ferron sandstone, Utah, to evaluate valley-fill facies models in the context of bayline and backwater effects, as well as presenting quantitative estimates of paleohydraulic parameters, such as slope and discharge. Three photomosaics and eight measured sections along variably oriented cliffs show three terraces formed by a single-thread meandering trunk river that was about 7 m deep, forming a compound valley with up to 28 m of erosional relief. Channel fills in some of the terrace deposits show double mudstone drapes, tidal reworking, and brackish-water to marine trace fossils, suggesting deposition in both the tidal backwater and bayline regions. Paleoslope estimates are on the order of 2.6 to 5.3 × 10–4, and corresponding backwater lengths are estimated to range from 3 to 25 km. Assuming microtidal conditions, the bayline limit was likely less than 7 km and the shoreline was likely positioned within 20 km of the study area. Each successive valley-fill terrace is punctuated by a transgressive then regressive episode of cut and fill thus forming stepped forced-regressive fluvially dominated, tidally affected valley fills. There is a lack of extensive transgressive marine or estuarine fill, consistent with an ever-wet tropical climate and a steep gradient that resulted in a high-sediment supply system, rather different from the transgressive, estuarine to marine simple valley-fill facies models that dominate much of the literature. Width-to-thickness ratios are 10:1, < 100:1, and about 1000:1 for channels, channel belts, and valleys respectively. These are consistent with ratios from modern systems, and the lower channel-belt widths are also consistent with deposition in the lower backwater, which favors aggradation versus lateral migration of channels.

Quantitative characterization of shales within tidally influenced fluvial valley fill deposits of the Ferron Sandstone, eastern Utah: Implications for hydrocarbon exploration

This study evaluates the proportion, length, and effective properties of thin (0.003 - 0.7 m [0.01 – 2.3 ft.]) shale beds and drapes in tidally-influenced channels within a compound valley fill with a focus on estimating geologically-based effective rock properties. The Cretaceous Ferron Sandstone is an outcrop analog for fluvial-tidal systems with primary reservoirs being deposited as tidally-influenced valley filling point bars. The study outcrops expose three valley systems in Neilson Wash of Utah. Light detection and ranging derived digital outcrop models have been used to characterize shale length, width, thickness and frequency of each valley fill succession. Long, uncommon, and anisotropic shales in Valley-1 (V1) were deposited in a braided setting with little tidal influence. In contrast, shales in Valley-2 (V2) were abundant, short, common, and equidimensional suggesting deposition by more tidally-influenced meandering rivers. Short, frequent, and equidimensional shales in Valley-3 (V3) were deposited in single-thread meandering rivers with less tidal influence. A sandstone-shale model was utilized to estimate the effects of shales on vertical to horizontal permeability ratio (kv/kh). The unique character of each depositional unit was reflected in resultant kv/kh distributions. The valley fill deposits, V1, V2, and V3 had an average kv/kh ratio of 0.11, 0.09 and 0.17, respectively. More tidally-influenced reservoirs such as the studied V2 had short, but frequent shales which resulted in low kv/kh estimates. Estimates of kv/kh for valleys that predominantly contained fluvial point bar deposits with lesser tidal influence (V1 and V3) were higher. The results of this study highlight the link between shale heterogeneity, reservoir architecture, and inferred flow parameters.

Source-To-Sink Sediment Budget Analysis of the Cretaceous Ferron Sandstone, Utah, U.S.A., Using the Fulcrum Approach

Abstract: This paper matches sediment fluxes, estimated to have passed through an ancient river system, with mapped downstream sediment volumes in a deltaic sink, providing a test of the recently developed fulcrum approach to source-to-sink analysis. This paper uses field measurements (such as channel depth, width, and grain size) to estimate paleodischarge in an ancient trunk channel of the Cretaceous Ferron Sandstone in central Utah. The estimates of instantaneous discharge are then integrated over the geological duration of the river to estimate the total sediment volume delivered to downstream deltaic sinks in an attempt to balance the estimated sediment flux with the mapped deltaic deposits in the sink. The bankfull channel depths, calculated using the scaling relationship between the flow depth and the mean dune height, vary from 3.3 to 5.5 m with an average depth of 4.4 m. The corresponding bankfull channel width estimates vary from 50 to 80 m, with an average value of 65 m, calculated using scaling relationship between channel width and the width of accretion surfaces. Water discharge calculated for these bankfull dimensions vary from 2.7 × 10 2 m 3 /s to 8.6 × 10 2 m 3 /s, also indicating that these rivers were routinely capable of generating hyperpycnal flows. The instantaneous sediment discharge reaching the fulcrum was calculated using established sediment transport equations. These instantaneous discharge values were first converted to mean annual sediment volume using the bankfull event durations, recurrence intervals, and a factor for the proportion of the total annual sediment load transported during the bankfull period, based on empirical relationships from modern climate analogs, and then projected over the average time duration of individual parasequences in the Ferron Notom clastic wedge, which is approximately 14 kyr. The mass balance across the fulcrum reveals that the average bedload sediment volume derived from the source (about 3 km 3 ) matches with that deposited in the sink within a factor of two. However, underestimation of the bedload volume in the sink suggests sediment escape beyond the limits of currently mapped sink area. Previous models for the Ferron indicate significant SE deflection of sediment due to wave reworking, which may account for the missing sandy sediment. It is also possible that there is an overestimation of time duration for individual valleys, resulting in higher sink-volume estimation and larger source-to-sink mass imbalance. Monte Carlo simulations, based on probabilistic estimation, were used to test the sensitivity of key parameters used in converting bankfull discharge to mean annual discharge. The P10, P50 (median), and P90 values for the average annual bedload volume ( Q mas ) are 9.1 × 10 4 m 3 , 1.7 × 10 5 m 3 , and 3.7 × 10 5 m 3 , respectively. A Q mas value between P50 and P90 yields a source-to-sink balance for bedload volume. The current study establishes a mass balance across the fulcrum with a reduced range of uncertainty for the various parameters used. Uncertainty associated with bankfull channel dimensions has been reduced through inclusion of detailed outcrop data. The uncertainty in estimating average annual sediment volume ( Q mas ) from bankfull events is less than a factor of three. This uncertainty can be further reduced by incorporating a more robust global-discharge dataset from modern analog river systems. Despite many assumptions and uncertainties, our study shows that the fulcrum method appears to be capable of balancing sediment budgets to within at least an order of magnitude in deep-time sedimentary systems.

A large pterodactyloid pterosaur from the Late Cretaceous Ferron Sandstone of Utah

Abstract Three associated incomplete wing bones of a large pterodactyloid pterosaur from the Ferron Sandstone Member of the Mancos Shale Formation of Utah are described. Based on the morphology of the bones’ articular ends, the specimen is referred to the Pteranodontoidea. Associated ammonites indicate that the specimen's age is Middle Turonian, so it adds to the sparse worldwide record of Turonian pterosaurs. The record of pteranodontoid pterosaurs in the Western Interior Seaway of North America is reviewed, and it is suggested that pteranodontoids were not diverse.

Plan-view Paleochannel Reconstruction of Amalgamated Meander Belts, Cretaceous Ferron Sandstone, Notom Delta, South-central Utah, U.s.a.

Abstract Few studies reconstruct paleohydraulic parameters, such as meander amplitude and sinuosity, of ancient rivers based on plan-view outcrop exposures, but rather rely on interpolation from cliff exposures. In this study, extensive plan-view exposures of amalgamated ancient meander belts in the Cretaceous Ferron Sandstone Member of the Mancos Shale Formation, Utah, USA, allow paleohydraulic reconstruction, evaluation of grain-size variability in meander belts, and their component unit and compound bars by incorporating the variability of paleocurrents, facies architectural-element analysis, and bar migration patterns. Three channel belts were identified, marked by scour surfaces, an increase in grain size, and abrupt changes in paleocurrent orientations. The youngest channel was about 2.1 m deep and 118 m wide, and had a meander wavelength of 1 km and a sinuosity of 1.1–2.9. The middle channel was about 3.4 m deep, with a meander wavelength of 2.6 km, and a sinuosity of 1.2. The oldest channel was insufficiently exposed to document its plan-view style. Grain-size trends showed systematic upwards fining in each channel story. In plan view, coarsening occurs towards the bend apex along the bend axis, and fining occurs downstream within some meander scrolls. Plan-form grain-size trends were not obvious, partially due to grain-size variation within unit bars, perhaps also reflecting the fact that the exposures capture variable vertical position in each channel belt. Paleocurrents showed systematically varying trends within individual channel belts (from NE, to SW, to E), and abrupt changes between belts. Grain size and vertical facies associations vary as a function of the style of bar migration, as well as position within a bar (upstream vs. downstream). The outcrop shows a dominance of a meandering-river style, with significant lateral amalgamation of successive point bars within each belt. Compound braid bars, built by overlapping unit bars, constitute the youngest channel deposits, and are probably associated with channel abandonment. Independent measurements of meander wavelength, based on plan-view exposures, match results estimated from empirical equations. The Ferron rivers are small to medium in scale according to calculated paleohydraulic parameters (Qw = 1.6 ∼ 2.8 × 102 m3/s). Architectural-element analysis shows that the last stage, and the most sinuous channel belt (A1), filled largely with downstream accreting unit and compound braid bars, similar to those seen in high-sinuosity meander loops of the modern Red River at the Texas–Oklahoma border. This suggests that both braid bars and point bars may occur within a single meander channel and that braid bars may evolve into compound point bars as they migrate and attach to a channel margin.

Formation of point bars through rising and falling flood stages: Evidence from bar morphology, sediment transport and bed shear stress

ABSTRACTFlow processes and sediment transport in a channel bend and associated point bar have been studied in modern rivers, theoretical models and physical experiments: however, the relationship between flow process and point‐bar morphology has rarely been explained due to the complex nature of open channel flow. Plan‐view exposures of an ancient point‐bar complex, exposed at the top of the Cretaceous Ferron Sandstone Member of the Mancos Shale Formation, south‐central Utah, allowed reconstruction of bar morphology, sediment transport and bed shear stress, which were used to extrapolate flow processes. Studies of these outcrops show that compound point bars and scroll bars were probably formed during falling and rising flood stages, respectively. A simulation model of plan‐view channel form shows that channel dimensions, such as radius of curvature and sinuosity of the point‐bar complex, range between 205 m and 351 m and 1·04 and 1·22, respectively, throughout the evolution of the channel bend. Variations in strength of the helical flow were interpreted as the main control on facies architecture and bar morphology. Strong helical flow was related to the deposition of the scroll bars, while strength of helical flow is decreased for compound bars. The use of cross‐beds as a common palaeocurrent indicator was found to be inconsistent with mean flow directions and channel margin orientation.

Palynology of the Upper Cretaceous (Turonian) Ferron Sandstone Member, Utah, USA: identification of marine flooding surfaces and Milankovitch cycles in subtropical, ever-wet, paralic to non-marine palaeoenvironments

The Upper Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah includes coal and gas deposits and is an important outcrop analogue to study reservoir characterisation of fluvial–deltaic petroleum systems. Numerous sedimentological and sequence stratigraphic studies of the Notom fluvial–deltaic wedge have been conducted recently; however, palynological analyses had not previously been undertaken. Here, we present palynological data from 128 samples collected in the Notom wedge of the Ferron Sandstone Member outcropping in south-central Utah. The purpose of this study is to use palynological analysis to refine the broader depositional environments, evaluate the climatic setting, and to build a biostratigraphic palynological framework. The dominance of terrestrial palynomorphs, especially the high yield of moisture-loving cryptogam spores, indicates a primarily ever-wet depositional environment characteristic of hydromorphic floodplain palaeosols formed in subtropical to tropical climates. Although dinoflagellates are rare, four intervals with occurrences of marine cysts indicate periods of increased marine/tidal influence associated with previously identified flooding surfaces within Milankovitch-scale parasequences of the largely non-marine stratal succession. These flooding surfaces confirm correlations from regional high-resolution sequence stratigraphic studies and allow correlative marine parasequences and systems tracts to be extended within floodplain-dominated stratal successions. The presence of Nyssapollenites albertensis pollen places the interval studied within the Nyssapollenites albertensis Interval Zone (Nichols 1994), constraining the age of the Ferron Sandstone Member to the latter part of the Cenomanian and the early Coniacian. This largely agrees with the bentonite- and ammonite-derived Turonian age proposed in previous studies.

Three-dimensional modeling of clinoforms in shallow-marine reservoirs: Part 1. Concepts and application

Clinoform surfaces control aspects of facies architecture within shallow-marine parasequences and can also act as barriers or baffles to flow where they are lined by low-permeability lithologies, such as cements or mudstones. Current reservoir modeling techniques are not well suited to capturing clinoforms, particularly if they are numerous, below seismic resolution, and/or difficult to correlate between wells. At present, there are no modeling tools available to automate the generation of multiple three-dimensional clinoform surfaces using a small number of input parameters. Consequently, clinoforms are rarely incorporated in models of shallow-marine reservoirs, even when their potential impact on fluid flow is recognized. A numerical algorithm that generates multiple clinoforms within a volume defined by two bounding surfaces, such as a delta-lobe deposit or shoreface parasequence, is developed. A geometric approach is taken to construct the shape of a clinoform, combining its height relative to the bounding surfaces with a mathematical function that describes clinoform geometry. The method is flexible, allowing the user to define the progradation direction and the parameters that control the geometry and distribution of individual clinoforms. The algorithm is validated via construction of surface-based three-dimensional reservoir models of (1) fluvial-dominated delta-lobe deposits exposed at the outcrop (Cretaceous Ferron Sandstone Member, Utah), and (2) a sparse subsurface data set from a deltaic reservoir (Jurassic Sognefjord Formation, Troll Field, Norwegian North Sea). Resulting flow simulation results demonstrate the value of including algorithm-generated clinoforms in reservoir models, because they may significantly impact hydrocarbon recovery when associated with areally extensive barriers to flow.

Three-dimensional modeling of clinoforms in shallow-marine reservoirs: Part 2. Impact on fluid flow and hydrocarbon recovery in fluvial-dominated deltaic reservoirs

Permeability contrasts associated with clinoforms have been identified as an important control on fluid flow and hydrocarbon recovery in fluvial-dominated deltaic parasequences. However, they are typically neglected in subsurface reservoir models or considered in isolation in reservoir simulation experiments because clinoforms are difficult to capture using current modeling tools. A suite of three-dimensional reservoir models constructed with a novel, stochastic, surface-based clinoform-modeling algorithm and outcrop analog data (Upper Cretaceous Ferron Sandstone Member, Utah) have been used here to quantify the impact of clinoforms on fluid flow in the context of (1) uncertainties in reservoir characterization, such as the presence of channelized fluvial sandbodies and the impact of bed-scale heterogeneity on vertical permeability, and (2) reservoir engineering decisions, including oil production rate. The proportion and distribution of barriers to flow along clinoforms exert the greatest influence on hydrocarbon recovery; equivalent models that neglect these barriers overpredict recovery by up to 35%. Continuity of channelized sandbodies that cut across clinoform tops and vertical permeability within distal delta-front facies influence sweep within clinothems bounded by barriers. Sweep efficiency is reduced when producing at higher rates over shorter periods, because oil is bypassed at the toe of each clinothem. Clinoforms are difficult to detect using production data, but our results indicate that they significantly influence hydrocarbon recovery and their impact is typically larger than that of other geologic heterogeneities regardless of reservoir engineering decisions. Clinoforms should therefore be included in models of fluvial-dominated deltaic reservoirs to accurately predict hydrocarbon recovery and drainage patterns.

Paleo-channel reconstruction and grain size variability in fluvial deposits, Ferron Sandstone, Notom Delta, Hanksville, Utah

Planform meanderbelt exposures display the evolution of the channel which leads to better understanding of three dimensional architecture of the fluvial deposit. Due to the paucity of extensive plan-view exposures in rock record, reconstruction of paleo channels from plan form exposures has been hardly studied. This study combines closely spaced paleocurrent and grain size data from plan-view exposures of point bar deposits in the delta plain deposits of the Cretaceous Ferron Sandstone near Hanksville, Utah, USA. Airborne Light Detection and Ranging (LiDAR) was used to create hillshade images in which numerous crescent shaped sandstone ridges were identified. These are dominated by unidirectional paleocurrent and thus they are interpreted as scroll bars associated with four distinct meander loops. The loops show a combination of growth by lateral expansion and downstream translation. Cross-cutting relationships allow us to decipher the order of loop formation. Paleocurrent directions closely follow the shape of individual scroll bars. Plan-view grain size distributions show a coarsening trend toward the bend apex on individual scroll bars. However, at the scale of an entire meander loop, this trend is less prominent. Paleohydraulic estimates show that these channels have low sinuosity (1.3–1.7) and have an average discharge ranging from 42.1 to 66.4m3/s. Comparison with larger sandbodies in underlying valley systems suggests that the studied channels represent the upper delta plain distributary channels and indicate an overall backstep with respect to channels in the immediately underlying incised valley.

Anatomy of falling‐stage deltas in the Turonian Ferron Sandstone of the western Henry Mountains Syncline, Utah: Growth faults, slope failures and mass transport complexes

AbstractFalling‐stage deltas are predicted by sequence stratigraphic models, yet few reliable criteria are available to diagnose falling‐stage deltaic systems in surface exposures. Recent work on the Upper Cretaceous (Turonian) Ferron Sandstone in the western Henry Mountains Syncline of south‐central Utah has established its environment of deposition as a series of modest‐sized (5 to 20 km wide), probably asymmetrical, mixed‐influence deltas (‘Ferron Notom Delta’) that dispersed sediment eastwards from the rising Sevier orogenic hinterland into the Western Cordilleran Foreland Basin. Analysis of sandstone body stacking patterns in a 67 km long, depositional strike‐parallel (north–south) transect indicates that the growth of successive deltas was strongly forced by synsedimentary growth of a long wavelength (ca 100 km), 50 m amplitude fold structure. Herein, two discrete areas within this transect, superbly exposed in three dimensions, are documented in order to determine the details of stratal stacking patterns in the depositional dip direction, and thereby to assess the stratigraphic context of the Ferron Notom Delta. In the two study areas, dip transects expose facies representing river mouth bar to distal delta front environments over distances of 2 to 4 km. Key stratal packages are clinothems that offlap, downlap, and describe descending regressive trajectories with respective to basal and top datums; they are interpreted as the product of relative sea‐level fall. The vertical extent of clinoforms suggests that deltas prograded into &lt;30 m of water. Furthermore, these deltaic successions preserve abundant evidence of delta front slope failure, growth faulting, and incision and filling of deep (&lt;15 m) slope gullies. Gully fills are composed of chaotic intraformational breccia and/or massive sandstone, and constitute linear, ‘shoestring’ sandbodies in the distal portions of individual palaeodelta systems. They are interpreted to have been cut and filled during the late falling‐stage and lowstand of relative sea‐level cycles. The north–south distribution of the stratal style described above seems to be focused on the flanks of the growth anticline, and so the numerous falling‐stage systems tracts preserved within the Ferron Notom Delta probably owe their origin to synsedimentary structural growth, and the unstable fluid pressure regime that this growth imposed on the sea floor and shallow subsurface.

Facies architecture of asymmetrical branching distributary channels: Cretaceous Ferron Sandstone, Utah, USA

AbstractDistributary channel systems are an important component of deltaic systems, but details of their branching pattern, stream‐order, internal variability and relation with adjacent levée, bay and bayhead delta are rather poorly documented in ancient examples. Photomosaic and measured sections collected along a gooseneck‐shaped canyon in southern Utah allow direct mapping of the branching pattern of an ancient distributary system. The main channel belt is ca 250 m wide and narrows to ca 200 m downstream of the branching point. A subordinate channel belt, ca 80 m wide, branches off of the main channel, forming a distinctly asymmetrical branching pattern. Water discharge in the main channel is estimated to be 85 to 170 m3 sec−1. Comparison with palaeodischarge estimates of trunk rivers mapped in previous studies suggests that the branching documented in this study probably is a fourth‐order split. The distributary channels are characterized by a U‐shaped geometry filled with medium‐grained, cross‐bedded sandstone, and are dominated by lateral accretion, suggesting limited lateral migration and moderate sinuosity. Tidally influenced facies and limited trace fossils indicate direct marine influence. The distributary channels erode into adjacent levée and underlying heterolithic bay‐fill deposits, and the marine influence suggests that they were deposited on a lower delta plain, rather than on a non‐marine floodplain. The subordinate channel fed a bayhead delta, suggesting that it was formed by a partial avulsion, rather than bifurcation around a mouth bar, as is more characteristic of terminal distributary channels. Channel‐floor drapes, bar‐accretion drapes and abandoned channel fills within the sandstone channel belts represent the most important heterogeneity from the perspective of reservoir characterization.

Characterization of stratigraphic architecture and its impact on fluid flow in a fluvial-dominated deltaic reservoir analog: Upper Cretaceous Ferron Sandstone Member, Utah

Fluviodeltaic stratigraphic architecture and its impact on fluid flow have been characterized using a high-resolution, three-dimensional, reservoir-scale model of an outcrop analog from the Upper Cretaceous Ferron Sandstone Member of central Utah. The model contains two parasequence sets (delta complexes), each with five or six parasequences, separated by an interval of coastal plain strata. Each parasequence contains one or two laterally offset teardrop-shaped delta lobes that are 6 to 12 km (4–7 mi) long, 3 to 9 km (2–6 mi) wide, 5 to 29 m (16–95 ft) thick, and have aspect ratios (width/length) of 0.4 to 0.8. Delta lobes have a wide range of azimuthal orientations (120) around an overall east-northeastward progradation direction. In plan view, delta lobes in successive parasequences exhibit large (as much as 91) clockwise and counterclockwise rotations in progradation direction, which are attributed to autogenic lobe switching. In cross-sectional view, parasequence stacking is strongly progradational, but a small component of aggradation or downstepping between parasequences reflects relative sea level fluctuations. We use flow simulations to characterize the impact of this heterogeneity on production in terms of the sweep efficiency, which is controlled by (1) the continuity, orientation, and permeability of channel-fill sand bodies; (2) the vertical permeability of distal delta-front heteroliths; (3) the direction of sweep relative to the orientation of channel-fill and delta-lobe sand bodies; and (4) well spacing. Distributary channel-fill sand bodies terminate at the apex of genetically related delta lobes and provide limited sand body connectivity. In contrast, fluvial channel-fill sand bodies cut into, and connect, multiple delta-lobe sand bodies. Low, but non-zero, vertical permeability within distal delta-front heteroliths also provides connectivity between successive delta-lobe sand bodies.

Evaluating delta asymmetry using three‐dimensional facies architecture and ichnological analysis, Ferron ‘Notom Delta’, Capital Reef, Utah, USA

AbstractDelta asymmetry occurs where there is strong wave influence and net longshore transport. Differences in the morphology and facies architecture between updrift and downdrift sides of asymmetric deltas are potentially significant for exploration and exploitation of resources in this class of reservoirs. Although delta asymmetry has been recognized widely from modern wave‐influenced deltaic shorelines, there are few documented examples in the ancient record. Based on an integrated sedimentological and ichnological study, the along‐strike variability and delta asymmetry within a single parasequence (Ps 6) is documented in continuously exposed outcrops of the Cretaceous Ferron Sandstone Member of the Mancos Shale Formation near Hanksville in southern Utah. Two intra‐parasequence discontinuity surfaces are recognized which allow subdivision of the parasequence into three bedsets, marked as Ps 6‐1 to Ps 6‐3. Four facies successions are recognized: (i) wave/storm‐dominated shoreface; (ii) river‐dominated delta front; (iii) wave/storm‐reworked delta front; and (iv) distributary channel and mouth bar. Dips of cross‐strata within distributary‐mouth bars and shorefaces show a strong downdrift (southward) component. Ps 6‐3 predominantly consists of river‐dominated delta‐front deposits, whereas Ps 6‐1 and Ps 6‐2 show an along‐strike facies change with shoreface deposits in the north, passing into heterolithic, river‐dominated delta‐front successions south to south‐eastward, and wave/storm‐reworked delta‐front deposits further to the south‐east. Trace fossil suites correspondingly show distinct along‐strike changes from robust and diverse expressions of the archetypal Cruziana Ichnofacies and Skolithos Ichnofacies, into suites characterized by horizontal, morphologically simple, facies‐crossing ichnogenera, reflecting a more stressed, river‐dominated environment. Further south‐eastward, trace fossil abundance and diversity increase, reflecting a return to archetypal ichnofacies. The overall facies integrated with palaeocurrent data indicate delta asymmetry. The asymmetric delta consists of sandier shoreface deposits on the updrift side and mixed riverine and wave/storm‐reworked deposits on the downdrift side, similar to that observed in the modern examples. However, in contrast to the recent delta asymmetry models, significant paralic, lagoonal and bay‐fill facies are not documented in the downdrift regions of the asymmetric delta. This observation is attributed to a negative palaeoshoreline trajectory during delta progradation and subsequent transgressive erosion. The asymmetric delta was induced by net longshore transport from north to south. The forced regressive nature of the delta precludes significant preservation of topset mud.

Temporal Evolution of Fluvial Style in a Compound Incised-Valley Fill, Ferron "Notom Delta", Henry Mountains Region, Utah (U.S.A.)

Abstract Nonmarine sequence stratigraphic models hypothesize systematic changes in fluvial style within individual sequences and across sequence boundaries, based largely on mudstone–sandstone ratios. The main purpose of the paper is to evaluate the validity of these models by documenting facies relationships and detailed bedding architecture of bar and channel deposits as well as mudstone–sandstone ratio within a compound incised-valley fill at the top of the Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in the Henry Mountains region, Utah, U.S.A. Field photomosaics, walking out of beds, and 42 measured sections document the stratal and facies organization in the incised-valley fill. Two erosional surfaces with erosional relief up to 17 m are traced continuously for up to 7 km. These erosional surfaces are defined by onlap and truncation and show a marked basinward shift in facies, with pebbly coarse-grained and conglomeratic fluvial sandstones overlying highly burrowed marine mudstones and sandstones. These major erosional surfaces partition the valley fill into two sequences, marked as V2 and V1 in ascending order. Each sequence comprises a multistory fill that reaches a maximum thickness of about 30 m. Within each sequence there is a vertical transition in facies from fluvial, to tidal, and finally back into fluvial facies. In the younger V1, there is a systematic vertical evolution of fluvial style from braided, to single-thread meandering, and finally to a low-sinuosity river system. In contrast, formative rivers in the older V2 were always meandering and show more marine and tidal influence. A major change in valley sedimentology is recognized from V2 to V1, as shown by a 30° eastward shift in main flow direction, overall increase in grain size and river discharge, and a clear change in fluvial style from meandering into braided streams. This is also shown by the increase in preserved dune height in fluvial bar and channel deposits across the boundary, which suggests that deeper rivers cut the younger V1 valley. The change in river style from braided to meandering in V1 is interpreted to reflect a gradual decrease in slope and discharge as the valley was filled. The change in fluvial style across the sequence boundary reflects an increase in grain size and discharge, probably driven by a high-frequency climate change, as well as local increase in valley slope.

Planform and Facies Variability in Asymmetric Deltas: Facies Analysis and Depositional Architecture of the Turonian Ferron Sandstone in the Western Henry Mountains, South-Central Utah, U.S.A.

Abstract Facies analysis of the Upper Cretaceous (Turonian) Ferron Sandstone in the western Henry Mountains of south-central Utah, U.S.A., indicates sediment accumulation in a series of flood-dominated, marine current- and wave-influenced, deltas. Twelve lithofacies are recognized: 1. erosionally based, thick cross-bedded sandstone bodies (Distributary Channels), 2. similar though thinner bodies containing common bioturbation (Marine-Influenced Distributary Channels), 3. root-penetrated, plant fossil bearing siltstone with minor sandstone (Coastal Floodplain and Floodbasin), 4. coal and carbonaceous shale (Coastal Mire), 5. thin-bedded, carbonaceous and bioturbated sandstone–siltstone (Coastal Lagoon), 6. erosionally based sandstone with large- and small-scale cross-bedding and bioturbation (Mouth-Bar Complex), 7. sharply based sandstone bodies internally dominated by hummocky cross-stratification, soft-sediment deformation, or lacking structure (Proximal Delta Front), 8. sharply bounded, calcareous, fossiliferous and bioturbated sandstone sheets (Abandoned Delta Lobe), 9. thickly interbedded sandstone, coarse- and fine-grained siltstone (Medial Delta Front), 10. thinly interbedded sandstone, coarse- and fine-grained siltstone (Distal Delta Front), 11. mainly siltstone with minor thin-bedded sandstone (Prodelta) and 12. fine-grained siltstone with bentonite beds (Offshore). Deltas prograded into shallow water, forming sharp-based mouth-bar sand bodies. The upper delta front was evidently fluidal and prone to failure, leading to the development of rotational slope failures, debris–flow filled gullies, and, in places, growth faults. Paleocurrent data indicate that the regional sediment dispersal direction was eastward. Data from delta-front facies, however, suggest that outflow plumes and associated bottom currents were deflected towards the southeast, giving rise to an asymmetric delta planform. The Holocene and modern Burdekin River Delta of NE Australia is considered a close planform, process, and facies analog for the Ferron Notom deltas. The Burdekin Delta facies assemblage is vertically and laterally heterogeneous, despite being the product of a consistent array of environmental controls. Adopting a model that incorporates such a degree of heterogeneity negates the need for multiple depositional models for complex stratigraphic intervals such as the Ferron Sandstone. The facies model also suggests that asymmetric deltas may be produced by directional growth of delta lobes, rather than by deflection of beach ridges. Stratigraphic stacking patterns strongly suggest that sediment accumulation in the Ferron Sandstone of the western Henry Mountains was forced by a regime of progressively more limited accommodation through time.

A 3-D ground-penetrating radar and wavelet transform analysis of the morphology of shoreface deposits in the Upper Cretaceous Ferron Sandstone Member, Utah

Wavelengths of hummocky cross-stratified (HCS) beds (a common sedimentary feature of storm-dominated shorefaces) are documented for the first time using measurements in three-dimensional (3-D) ground-penetrating radar (GPR) data for a well-developed Upper Cretaceous lower-shoreface succession at Dry Wash in the Ferron Sandstone Member, Utah. The shallow-marine sequence consists of upward-thickening HCS sand beds alternating with interstorm deposits. The thickness variation of the storm beds indicates locally steadily growing storm intensity with at least four cycles. Weakly coarsening-upward (mud to very fine-grained sand) fair-weather background deposits suggest a slow progradation of deposition with no significant change in environment. The GPR interpretation mapped three conformable, high-continuity, high-amplitude reflections throughout the 3-D GPR data volume. The interpreted radar surfaces (RSs) are well correlated with tops of HCS sand beds (and thus paleotopographic surfaces); the associated radar units (RUs) have a uniform thickness (on average 0.8 m [2.6 ft]). The RUs and the adjacent outcrop observations suggest that the shoreface sandstone at the Dry Wash site has a simple layered internal architecture. The hummocky-swaley surfaces generally dip westerly, as a product of postdepositional structural alterations that are mostly in the shoreline direction, and contain variable-size, structurally undulating rounded features. A 2-D continuous wavelet transform analysis is applied to the detrended RSs, producing a multiresolution image decomposition of the GPR surfaces. Surface features with a wavelength range of 1–7 m (3–23 ft) are in good agreement with the observations on modern hummocky shallow-marine seabeds. Quantitative measurements indicate that the hummocky surfaces at the Dry Wash site are dominated by uniformly distributed circular to elongate bed forms with maximum correlation at 1.5–3.5-m (4.9–11.4 ft) wavelength and that the deltaic sedimentary layers were simultaneously deformed by the middle Campanian compressional stress of the Sevier orogeny transmitted from the northwest. Quantitative information on the subseismic-scale surface geometry of the HCS beds is expected to result in more refined reservoir models. In addition, the connectivity of units indicated by the scale of the morphology can be an indirect indicator of unit correlation and permeability paths.

Interpreting shoreline sands using borehole images: A case study of the Cretaceous Ferron Sandstone Member in Utah

To establish borehole image interpretation guidelines in a siliciclastic shoreline environment, this study used unique data from the Ferron Sandstone Member in Utah, where several core holes were drilled next to the outcrop cliff and logged with electrical borehole images. The guidelines include three main components: (1) differentiating depositional elements based on borehole image textures, (2) multiwell stratigraphic correlation and depositional architectures, and (3) ambiguity and data limitations. The stratigraphic interpretation of the image logs is closely correlated with the cores and the outcrops to evaluate the interpretation methodology. The sandstones of upper shoreface, middle shoreface, and channels are differentiated in each well based on a list of depositional textures and sequence characteristics revealed by the images and open-hole logs. The coals, carbonaceous shales, bay fill, and transgression lag deposits are identified as important elements in building the stratigraphic framework. Channels eroding into the shoreface and shoreface pinch-out into delta plains are recognized based on the facies classification and stratigraphic framework. The shoreface progradation directions are drawn through multiwell sequence correlation, paleoflow, and seaward facies transition analysis. In the Muddy Canyon area, the progradation directions of the shoreface parasequences vary from north to east with dominance to the northeast. The complex channel systems with diverse flow directions amalgamated in the delta plains and eroded into the strand-plain shoreface sandstones in most of the regression cycles. In the northern study area, the latest borehole image data revealed the south- or southeastward-prograding Ferron shorelines and the cyclic Blue Gate Member shoreline sequences. The integrated study supports the regional V-shaped Ferron shoreline with oblique delta progradations within the regional eastward transportation into the Mancos Sea.