Thickening-upward Cycles Research Articles

Architecture of deepwater turbidite lobes: A case study of Carboniferous turbidite outcrop in the Clare Basin, Ireland

Abstract Through lithofacies analysis and architecture anatomy of the Carboniferous Ross Sandstone turbidites outcropped at western Ireland, the depositional model of deepwater turbidite lobes is established. Seven types of lithofacies are recognized including goniatites-rich shale, laminated shale, laminated siltstone, massive sandstone, fine-medium sandstone with mud-clast, basal gravel, and chaotic mudstone, which can be subdivided into units of three origins, turbidite lobe, turbidite channel, and slide-slump; and four hierarchical levels, lobe complex, lobe, lobe element and single sandstone layer. The lobes show apparent compensational stacking pattern, lobe elements display typical thickening-upward cycles on vertical profile, and the higher the hierarchical level, the better the preservation of the hierarchical boundary is. In general, turbidite lobe deposits appear as tabular, parallel/sub-parallel sandstone and mudstone interbeds, and change from thick, massive sandstone in the proximal end to thinner sandstone and mudstone interbeds from axis to fringe, with the sand-shale ratio and degree of sandstone amalgamation decreasing.

Thickening-upward cycles in deep-marine and deep-lacustrine turbidite lobes: examples from the Clare Basin and the Ordos Basin

Deep-marine and deep-lacustrine reservoirs have been targets for conventional and unconventional oil and gas exploration and development for decades. Thickening-upward cycles in the deep-marine Carboniferous Ross Sandstone Formation outcrops in western Ireland and the deep-lacustrine Triassic Yanchang Formation outcrops in southeast Ordos Basin have been investigated and correlated in this study. Typical thickening-upward cycles consisting of, from bottom to top: (1) laminated shales/shales with interbedded siltstone beds; (2) interbedded sandstones/siltstones and mudstones; (3) structureless massive sandstones, are well recognized in these outcrops and are interpreted as turbidite lobes. A continuously prograding lobe-element model is proposed to explain the repeated stacking of thickening-upward cycles. Thickening-upward cycles developed within deep-marine and deep-lacustrine environments are highly comparable in many aspects, such as sedimentary structures, sheet-like geometries and amalgamation features. A frequent and strong degree of amalgamation is developed within the massive sandstone at the top of each thickening-upward cycle, suggesting a layer-by-layer depositional manner. Field observations and comparison with deep-marine counterparts support the occurrence of turbidity flows in the Yanchang Formation, Ordos Basin.

Famennian glaciation in the eastern side of Parnaíba Basin, Brazil: evidence of advance and retreat of glacier in Cabeças Formation

ABSTRACTGlaciotectonic features studied in the siliciclastic deposits of Cabeças Formation, Upper Devonian, represent the first evidence of Famennian glaciation in Southeastern Parnaíba Basin, Brazil. Outcrop-based stratigraphic and facies analyses combined with geometric-structural studies of these deposits allowed defining three facies association (FA). They represent the advance-retreat cycle of a glacier. There are: delta front facies association (FA1) composed of massive mudstone, sigmoidal, medium-grained sandstone with cross-bedding and massive conglomerate organized in coarsening- and thickening-upward cycles; subglacial facies association (FA2) with massive, pebbly diamictite (sandstone, mudstone and volcanic pebbles) and deformational features, such as intraformational breccia, clastic dikes and sills of diamictite, folds, thrust and normal faults, sandstone pods and detachment surface; and melt-out delta front facies associations (FA3), which include massive or bedded (sigmoidal cross-bedding or parallel bedding) sandstones. Three depositional phases can be indicated to Cabeças Formation: installation of a delta system (FA1) supplied by uplifted areas in the Southeastern border of the basin; coastal glacier advance causing tangential substrate shearing and erosion (FA1) in the subglacial zone (FA2), thus developing detachment surface, disruption and rotation of sand beds or pods immersed in a diamicton; and retreat of glaciers accompanied by relative sea level-rise, installation of a high-energy melt-out delta (FA3) and unloading due to ice retreat that generates normal faults, mass landslide, folding and injection dykes and sills. The continuous sea-level rise led to the deposition of fine-grained strata of Longá Formation in the offshore/shoreface transition in the Early Carboniferous.

Permian Cyclothem Development within the Onshore Canning Basin, Western Australia

Earth's climate during the latter part of the Permian has long been the subject of speculation and debate. Some studies suggest that Permo-Carboniferous glaciation persisted on parts of Gondwana up to at least the Permo-Triassic boundary. Other studies argue that deglaciation occurred as early as the late Sakmarian (lower Early Permian). Many such investigations have been based upon the sometimes ambiguous occurrence of direct glacial deposits (e.g. striated clasts, tillites). In contrast, this study evaluates the likelihood of post-Sakmarian glaciation by testing high-frequency, sedimentary cycles for a glacio-eustatic driving mechanism. The focus of this thesis is the Artinskian (upper Early Permian) Tuckfield Member of the Poole Sandstone. The Tuckfield Member is exposed around the periphery of the St George, Poole, and Grant Ranges of the Fitzroy Trough (onshore Canning Basin, Western Australia). In the St George and Poole Ranges, the Tuckfield Member outcrops as a 50 to 100 m thick package of vertically stacked, laterally continuous, coarsening- and thickening-upward cycles. In contrast, the Tuckfield Member outcrops in the Grant Range as a less than 50 m thick package of vertically stacked, laterally discontinuous, fining- and thinning-upward cycles. Primary sedimentary structures, trace fossils, and the vertical succession of facies suggest that the Tuckfield Member records shallow-marine, shorezone deposition in the St. George and Poole Ranges and non-marine, coastal plain deposition in the Grant Range. Gamma-ray and grainsize data, collected from 17 measured outcrops (11 in the St George Ranges; 4 in the Poole Range; 2 in the Grant Range), were analyzed for cyclicity. Spectral analyses identified several orders of meter- to decameter-scale cycles in both the shallow-marine and non-marine facies. The average periodicities of the identified cycles occur in the ratio of ~36:10:4:2 m. This ratio correlates strongly with the known mid-Permian orbital periodicities of elongated eccentricity, eccentricity, obliquity, and precession (~410:100:40:20 thousand years). Additionally, the Tuckfield Member is herein traced throughout the northern Fitzroy Trough and onto the adjacent Lennard Shelf via sub-surface data. Similar to outcrop, subsurface gamma-ray logs display several orders of meter- to decameter-scale cycles that correlate strongly with the orbital periodicities. This cyclicity is manifested by the systematic bundling of smaller-scale cycles into larger-scale cycles that can be traced laterally for more than 200 km. For comparison, correlative shallow-marine cycles from the Artinskian to Ufimian Pebbley Beach Formation (Sydney Basin, New South Wales) were also studied. Four outcrop sections were measured and correlated, giving a total stratigraphic column of approximately 45 m. Spectral analysis of gamma-ray data identified several orders of meter- to decameter-scale cycles. These cycles correlate strongly with the mid-Permian orbital periodicities and the identified Tuckfield Member cycles. The favorable comparison between the Tuckfield Member cycles and the orbital parameters indicates that Milankovitch-forcing of climate influenced the formation of depositional cyclicity. Furthermore, it is highly probable that these cycles are glacioeustatic in origin due to their laterally extensive nature and positive correlation with identified cyclicity in New South Wales. This suggests that Permo-Carboniferous glaciation must have persisted into at least the Ufimian stage of the Late Permian.

Sedimentology of the Madumabisa Mudstone Formation (Late Permian), Lower Karoo Group, mid-Zambezi Valley Basin, southern Zambia

Sediments of the Upper Carboniferous to Lower Jurassic Karoo Supergroup (∼ 4.5 km thick) were deposited in the mid-Zambezi Valley Basin, southern Zambia. The Upper Palæozoic Lower Karoo Group in this area ends with a Late Permian sedimentary unit called the Madumabisa Mudstone Formation. The formation is 700 m thick and comprises four lithofacies grouped into two facies assemblages, collectively interpreted as lacustrine deposits. Sediments of a massive mudrock facies assemblage were deposited from suspension, probably from sediment-laden rivers entering a lake. Concretionary calcilutite beds probably mark the positions of palæosediment-water interfaces where calcite was precipitated. A laminated mudrock facies assemblage is attributed to lacustrine deposition from inflowing rivers at the lake margins and shallow parts of the lake. Repeated thickening-upward cycles are evidence of upward shallowing, interrupted by events of more abrupt deepening. Sandstone interbeds are interpreted as fluvial deposits laid down during low lake stands, with cross-lamination and asymmetrical ripples indicating current rather than wave deposition. A fossil assemblage of ostracods, bivalves, gastropods, fish scales, the alga Botryococcus sp. and fossil burrows is consistent with a lacustrine origin for the formation.

Variation in bed thickness in a turbidite succession, Dezadeash Formation (Jurassic-Cretaceous), Yukon, Canada: evidence of thinning-upward and thickening-upward cycles

Analysis of the vertical variation in thickness of turbidites in an 883 in thick stratigraphic section of the Dezadeash Formation (Jurassic-Cretaceous), Yukon, Canada, indicates that the turbidites are comprised of alternating sequences of thick beds and thin beds. Visual inspection reveals that 40 thick-bedded cycles, or megasequences, are present. Fourier analysis indicates 38 cycles. Five different methods (i.e., freehand, signs-of-differences test, correlation analysis, least squares, and moving averages) used to determine the trend in bed thickness of the megasequences, demonstrate that asymmetric cycles are present, and most of these methods show that thickening-upward trends are more common than thinning-upward trends. The best objective method for determining the asymmetry of megasequences appears to be correlation analysis (viz., Pearson's, Spearman's and Kendall's correlation coefficients) and possibly the least squares method. This particular section of the Dezadeash Formation is characterized by asymmetric cycles that are both common and statistically convincing, and thickening-upward sequences are more plentiful, than thinning-upward sequences.

Lateral Correlation Trends in Bedded and Massive Turbidites, with an Example From De Gray Lake, Arkansas

Lateral Correlation Trends in Bedded and Massive Turbidites, with an Example From De Gray Lake, Arkansas

Correlation Trends in Thin-Bedded Turbidites, Jackfork Sandstone, DeGray Lake, Arkansas

Michael B. De Vries and Arnold H. Bouma The methods of data collection for modern and ancient turbidite systems are necessarily different. Therefor, the integration of data sets from modern and ancient turbidite systems is desirable if lithofacies and surface morphological models are to be linked. To achieve this, two activities have to be dealt with: 1) Modern and subsurface turbidite systems must be extensively cored and described, and 2) outcrops in ancient turbidite systems must be correlated laterally in sufficient detail to establish a framework to facilitate the interpretation of subenvironments which build the turbidite system. The latter approach can be accomplished only in a few turbidite systems that are relatively well exposed, with outcrops exposing thick sections of turbidites which have an equally thick correlative. One ancient turbidite system meeting the above criteria is the Pennsylvanian Jackfork Group exposed around DeGray Lake, Arkansas. Two correlatable outcrops form the east and west wall of the Spillway, 214 feet (65 m) apart, while the third outcrop is 5500 feet (1675 m) to the west near the intake for the power-generating dam. Each outcrop was divided into lithofacies-based units and each unit was described in general terms and individual beds in each unit were measured. The lithofacies-based units established a rough correlation between large segments of each outcrop using changes in character. A more detailed assessment and quantification of these changes is then produced when dividing the units into smaller subunits. Stratigraphically thick sections of individual beds can often be correlated between Spillway walls. It is difficult to accomplish this using lithologic logs derived from measured sections. It is easier to plot the sandstone bed thickness values on a graph such as shown in Figure 1. Each successive bed is weighted the same on the vertical scale with the horizontal scale representing bed thickness. The thinner beds, represented by the left-deflecting spikes, show no characteristic pattern and do not necessarily follow the same trend as the thicker beds, represented by the right-deflecting spikes. The thicker beds can be divided into thickening-upward, thinning-upward and symmetrical successions of beds which may be called cycles. These cycles form distinctive patterns for each outcrop and unit. Pattern recognition can be used to correlate cycles from each outcrop similar to the correlation of subsurface well-logs. Individual beds which make up each cycle can then be correlated across the Spillway. This method allows for important lithofacies changes and thinning trends to be recognized. The lower one-third (approx. 140 feet [42 m] thick) of the Spillway section overlies massive channel deposits. The thinningand fining-upward nature of these beds and their position over channel deposits make these interpretable as a channel-levee-overbank succession. Paleocurrent direction for the channels in this part of the Jackfork Group is westerly. Detailed correlation of individual beds, using a plot similar to Figure 1, reveals an increasing degree of correlatability upward, from 40% in the lower part to over 80% in the upper part of the section. This increase may reflect more laterally extensive, sheet-type flow deposition. The second section is relatively thick-bedded and is sandwiched between very thin-bedded distal overbank deposits. This section is interpreted as a depositional lobe deposit. Mostly thickening-upward cycles can be recognized and used for correlation between Spillway walls. Individual bed and cycle thicknesses for each cycle show thinning trends across the Spillway which switch back and forth in direction, compatible to compensation cycles. A correlative section of turbidites, which were measured at the Intake, also shows thickening-upward trends. The overall thickness of this section is about 51 feet (16 m) thick while the Spillway sections are much thicker at about 80 feet (42 m) thick. Paleocurrent directions measured from sole markings show that this section is slightly oblique to directly down-current of the Spillway. Figure 1 shows good overall correlation between Spillway sections and the Intake section, but relatively poor bed-to-bed correlatability. The third section is 14 feet (4 m) thick and comprises thicker-bedded turbidites which are thinning-upward and are sandwiched between very thin-bedded basin plain or distal overbank deposits. This section is interpreted as a small channel deposit. The thicker beds typically split into several low angle amalgamations. A correlative section at the Intake is slightly thicker, but is thinner-bedded and shalier. As in all sections, the original correlation was based upon lithofacies. The thickness plot for this section shows that the beds included in the overbank deposits at the Spillway can be correlated with Louisiana State University, Department of Geology and Geophysics, Baton Rouge, Louisiana 70803

Depositional Environments and Controls of Juncal Formation, Southern San Rafael Mountains, California: ABSTRACT

The lower to middle Eocene Juncal Formation, north of the Santa Ynez fault in easternmost Santa Barbara County, represents the onset of marine sedimentation following an approximately 20-m.y. hiatus. The Juncal paraconformably overlies the upper Campanian Unnamed sandstone and is gradationally overlain by the middle Eocene Matilija Formation. Access to the Juncal exposures of this area was considerably enhanced by the Wheeler fire of July 1985. Facies analysis of both the vertical and lateral exposures of the Juncal Formation (approx. 1400 m thick) indicate that the Juncal represents coalescing outer-fan depositional lobes. This interpretation is based on the lateral continuity of sandstone beds, presence of thickening-upward cycles, and high-concentration sediment gravity flows, bathyal fauna, and regional associations. Local channelization (to 10 m deep) represents the extension of a mid-fan channel over its associated depositional lobe. Outcrops are subparallel to depositional strike in the eastern part of the study area and form a broad syncline in the western part. Together, these exposures allow documentation of the depositional lobes vertically, laterally, and longitudinally. Outer-fan deposits of the Juncal Formation are part of a progradational basin-filling episode. The Juncal grades upward into the outer- to mid-fan depositions of the lower Matilija Formation. Themore » upper Matilija Formation shoals upward into deltaic facies. This regressive sedimentary sequence was probably initiated by the major sea level fall which occurred near the early/middle Eocene boundary and coincides with the onset of fan sedimentation elsewhere along the California margin. Within the study area, depositional lobe activity was probably governed by either minor fluctuations in relative sea level or channel switching up-system.« less

Early neogene continental sedimentation in the vallecito and fish creek mountains, Western Salton Trough, California

Lower Neogene sedimentary rocks in the Vallecito and the Fish Creek Mountains, along with locally intercalated basalts, were deposited in a half-graben Basin-and-Range setting. Three depositional environments are recognized: (1) braided stream; (2) alluvial fan; and (3) landslide. A Platte-type braided stream system, with local accumulation of seif dunes, drained a westward-tilted pediment surface. Coarse sand was deposited as transverse and linguoid bars, sand dunes and flat beds, and gravel was deposited as longitudinal bars, modified by tractive flow, in broad, shallow channels. This system joined a Donjek-type northward-flowing axial drainage characterized by channels with marked topographic relief. Deep channel reaches were infilled with longitudinal gravel bars and massive granular, very coarse sand from concentrated dispersions. Giant sand waves were rarely present in deeper channel reaches. In shallower channel tracts, coarse sand was deposited as transverse bars, sand dunes and flat beds, and gravel was deposited as small longitudinal bars. The alluvial fan deposits accumulated along the faulted western margin of the basin and prograded eastward over the axial drainage. They consist of debris flow, sheetflood and Donjek-type channel-fill deposits. Subenvironments are defined by the distribution of these deposits and their bedding geometries. The upper fan (above the intersection point) is characterized by debris flow and channel-fill deposits with numerous internal erosional contacts and laterally discontinuous beds. The middle fan (below the intersection point) is marked by crudely developed thickening-upward cycles of laterally continuous, repetitively interbedded, very thick debris flow and thinner bedded sheetflood deposits. The lower fan is represented by interbedded debris flow and sheetflood deposits that are thinner bedded and less organized than the middle fan subfacies. The landslide deposits locally top the sequence. They are massive, laterally continuous sedimentary megabreccias containing clasts that are up to 5 m in diameter and display a distinctive jigsaw-puzzle texture. These breccias formed as two cataclysmically emplaced, air-cushioned landslides. One was dislodged from the Vallecito Mountains and traveled eastward, while the other was released from the Fish Creek Mountains and traveled westward.

Deep-Sea Fan Deposits in the Macigno Formation (Middle-Upper Oligocene) of the Gordana Valley, Northern Apennines, Italy

ABSTRACT Facies characteristics are described for a 2300 m thick turbidite succession of the Macigno Formation (middle-upper Oligocene), which crops out as a continuously exposed section in the Gordana Valley (northern Apennines). In the study area the Macigno Formation consists of two sandy members separated by a shaly member. The sandy members contain lithic associations characteristic of submarine fan deposits and form distinct fan complexes. The middle shaly member represents a period of basin starvation. Three main facies associations are recognized in the Macigno fan deposits, fan-fringe, outer-fan lobe, and braided midfan facies associations. The fan-fringe deposits consist of monotonous or small-scale cyclically arranged thin-bedded turbidites. The outer-fan lobe deposits are composed of medium-to very thick-bedded classical turbidites internally organized in thickening-upward cycles with minor intercalations of thin-bedded sandstone beds. Two distinct types of outer-fan lobe deposits, distal and proximal, are recognized on the basis of rock-type, internal organization, and vertical facies relationships. The midfan deposits consist of amalgamated massive sandstone and pebbly sandstone which display repeated thinning-upward cycles. The three main facies associations are superposed t define major thickening and coarsening-upward cycles reflecting distinct episodes of fan progradation. The relationships between the facies associations of the Macigno deposits and the existing models of submarine fan sedimentation are discussed. After the deposition of the fan complexes, fan sedimentation in this part of the basin was replaced by movements of allochthonous units heralded by large olistostromes.

Paleogene Depositional Systems, Western Transverse Ranges, Southern California: ABSTRACT

Paleogene strata of the western Transverse Ranges include varied clastic facies that prograded southwestward from arkosic sediment sources in granitic and metamorphic terranes of the Salinian and Mojave blocks. Deposition occurred within a complex fore-arc basin whose bathymetry was modified by pronounced uplift of a structural high along the trench slope break, and by internal deformation associated with oblique subduction during shallow plate descent beneath the Laramide cordillera. Integrated depositional systems produced intertonguing deep-marine, shallow-marine, marginal-marine, and nonmarine deposits. Exposed transitions between basinal turbidite successions, deltaic strandline complexes, and alluvial-plain sequences are common at several horizons. Mappable formatio s and local members are distinguished chiefly by their shaly, sandy and conglomeratic, or mixed lithologic character. Each such stratigraphic unit typically includes several facies associations. Shale-rich facies were deposited on terrestrial flood plains, prodelta and basin-flank slopes, overbank surfaces of subsea fans, and distal basin plains. Sand-rich intervals include thickening-upward cycles of sheet-flow depositional lobes on subsea fans, thinning-upward cycles of turbidite channels on subsea fans, coarsening-upward cycles of prograding shelf breaks, fining-upward cycles of migratory shelf and shoal-water bars, coarsening-upward cycles of distributary-mouth bars, and fining-upward cycles of fluviodeltaic End_Page 698------------------------------ channels. Conglomeratic strata occur both as piedmont-fan deposits and within proximal turbidite channel complexes. Sparse nonclastic facies include local algal carbonate platforms built on isolated submarine banks formed by tectonic uplift, and minor lagoonal beds of algal carbonate rocks and gypsiferous evaporites associated with delta platforms. End_of_Article - Last_Page 699------------

Rhythms in Deep-Marine Turbiditic Shales and Fine-Grained Debris Flow: ABSTRACT

Rhythms in fine-grained sediments have not been studied previously because of their complex depositional cycles and diagenetic changes. Examination of nearly 9,000 layers in outcrops, polished slab samples, and thin sections has led to recognition of rhythms in the Middle Ordovician Whitesburg, Blockhouse, and Sevier formations in eastern Tennessee. Rhythms have been described in four orders, based on their magnitude. First-order cycles (basin-fill sequences, hundreds of meters thick) are composed of thinning-upward debris-flow sequences and thickening-upward turbiditic shale sequences. Second-order cycles (multiple-sedimentation units, tens of centimeters thick) constitute six types: (1) thinning-upward cycles, (2) symmetrical cycles, (3) thickening-upward cycles, (4) minor multiple cycles, (5) uniform cycles, and (6) dubious cycles. Third-order cycles (single-sedimentation unit, tens of millimeters thick) have thinning-upward and asymmetric types. Fourth-order cycles show the grain-size variations within a single silt layer of the third order. First-order rhythms were controlled by tectonism, progradation of a deep-sea-fan system, and debris flow. Second- and third-order rhythms were controlled by depositional processes, bottom topography, and sediment source. In the fourth-order rhythms, depositional processes, sediment source, and bioturbation were the dominant controlling factors. Rhythm analyses of fine-grained sediments are significant in understanding (1) major events related to tectonism, End_Page 525------------------------------ (2) deep-sea environments, and (3) frequency and dynamics of depositional events. End_of_Article - Last_Page 526------------

Submarine fan facies of the Upper Cretaceous Great Valley sequence, northern and central California

The Upper Cretaceous part of the Great Valley Sequence provides a unique opportunity to study deep-marine sedimentation within an arc-trench gap. Facies analysis delineates submarine fan facies similar to those described from other ancient basins. Fan models and facies of Mutti and Ricci-Lucchi allow reconstruction of the following depositional environments: basin plain, outer fan, midfan, inner fan, and slope. Basin plain deposits are characterized by hemipelagic mudstone with randomly interbedded thin sandstone beds exhibiting distal turbidite characteristics. Outer fan deposits are characterized by regularly interbedded sandstone and mudstone, and commonly exhibit thickening-upward (negative) cycles that constitute depositional lobes. The sandstone occurs as proximal to distal turbidites without channeling. Midfan deposits are characterized by the predominance of coarse-grained, thick, channelized sandstone beds that commonly are amalgamated. Thinning-upward (positive) cycles and braided channelization also are common. Inner fan deposits are characterized by major channel-fill complexes (conglomerate, pebbly sandstone, and pebbly mudstone) enclosed in mudstone and siltstone. Positive cycles occur within these channel-fill complexes. Much of the fine-grained material consists of levee (overbank) deposits that are characterized by rhythmically interbedded thin mudstone and irregular sandstone beds with climbing and starved ripples. Slope deposits are characterized by mudstone with little interbedded sandstone; slumping and contortion of bedding is common. Progressions of fan facies associations can be described as retrogradational and progradational suites that correspond, respectively, to onlapping and offlapping relations in the basin. The paleoenvironments, fan facies associations, and tectonic setting of the Late Cretaceous fore-arc basin are similar to those of modern arc—trench systems.