Non-marine Successions Research Articles

Radiometric Zircon Ages of a Tuff Sample from the Baishantou Member of Wuyun Formation, Jiayin: A Contribution to the Search for the K‐T Boundary in Heilongjian River Area, China

Abstract:The existence of the Cretaceous‐Tertiary (K/T) boundary in the non‐marine succession is expected at Jiayin in the Heilongjiang River area, China. Zircons from a tuff sample from the Baishantou Member of Wuyun Formation in Jiayin were analyzed by the laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) U‐Pb dating and fission‐track dating methods. Ages of 64.1±0.7 Ma (U‐Pb) and 61.7±1.8 Ma (fission‐track dating) were obtained, which allow re‐evaluation of a previously reported late Maastrichian age for the tuff layer that was in conflict with the paleontological evidence. These results confirm the Danian age of the section in agreement with the paleontological evidence.

Late Maastrichtian paleovalley systems in west-central Alberta: Mapping the Battle Formation in the subsurface

Abstract The Maastrichtian Battle Formation forms an important stratigraphic marker in the nonmarine Upper Cretaceous succession across a wide area of west-central Alberta. This mudstone-dominated unit, with a maximum thickness of 18.0 m, is distinctive both at outcrop and in down-hole geophysical well logs. New stratigraphic picks for the top and base of the Battle Formation in 8935 wells, together with data-points from a further 608 wells in which the Battle Formation is absent, were used to generate a regional isopach map. In combination with closely spaced well-log cross-sections, the isopach map allows delineation of a series of paleovalley systems incised into the Battle Formation and filled by sandy fluvial deposits of the overlying Scollard Formation. Across wide areas within the paleovalleys, the Battle Formation has been completely removed and Scollard Formation strata rest directly on the underlying Horseshoe Canyon or Wapiti formations. Paleovalley trends appear to have been broadly similar to those of major present-day river systems in the region. A paleo-Athabasca River system with a main trunk valley up to 30 km across trends southwest to northeast in the area between Edson and Whitecourt. Farther south, a well-defined paleovalley system with a main valley up to 10 km wide trending northwest to southeast in the area between Red Deer and Drumheller can be considered as a precursor to the present Red Deer River drainage system. A less well-defined paleovalley trends northwest to southeast in the area of the present Bow River to the east of Calgary.

CARBONIFEROUS NON‐MARINE SOURCE ROCKS FROM SPITSBERGEN AND BJØRNØYA: COMPARISON WITH THE WESTERN ARCTIC

In this paper, we demonstrate that Carboniferous coaly and lacustrine strata have significant liquid hydrocarbon potential in an area extending from the Norwegian Barents Sea in the east to the Canadian Arctic in the west. Organic geochemical analyses were conducted on seven coals and coaly shales from the islands of Spitsbergen (Svalbard archipelago) and Bjørnøya (Norwegian Barents Sea). The results were interpreted in the context of published data from the two areas, and of time‐equivalent non‐marine successions on the Finnmark Platform (Norwegian Barents Sea), East Greenland, and the Sverdrup Basin (Canadian Arctic). In each of these areas, a warm and humid climate, together with the onset of rifting on the northern Pangea margin, facilitated the deposition and preservation of organic‐rich non‐marine sediments on a regional scale. All of the sediments have an elevated content of liptinitic macerals, dominated by alginite or sporinite. In the studied areas, the prolific younger source rocks which may be common in adjacent regions are often immature or absent. The identification of Carboniferous terrestrial strata with source rock potential may therefore enhance the petroleum potential of the studied regions.

The geomagnetic polarity timescale for the Triassic: linkage to stage boundary definitions

Abstract Studies of Triassic magnetostratigraphy began in the 1960s, with focus on poorly fossilferous nonmarine red-beds. Construction of the Triassic geomagnetic polarity timescale was not consolidated until the 1990s, when access to magnetometers of sufficient sensitivity became widely available to measure specimens from marine successions. The biostratigraphically-calibrated magnetostratigraphy for the Lower Triassic is currently largely based on ammonoid zonations from Boreal successions. Exceptions are the Permian–Triassic and Olenekian–Anisian boundaries, which have more extensive magnetostratigraphic studies calibrated by conodont zonations. Extensive magnetostratigraphic studies of nonmarine Lower Triassic successions allow a validation and cross-calibration of the marine-based ages into some nonmarine successions. The Middle Triassic magnetostratigraphic timescale is strongly age-constrained by conodont and ammonoid zonations from multiple Tethyan carbonate successions, the conclusions of which are supported by detailed work on several nonmarine Anisian successions. The mid Carnian is the only extensive interval in the Triassic in which biostratigraphic-based age calibration of the magnetostratigraphy is not well resolved. Problems remain with the Norian and early Rhaetian in properly constraining the magnetostratigraphic correlation between the well-validated nonmarine successions, such as the Newark Supergroup, and the marine-section-based polarity timescale. The highest time-resolution available from magnetozone correlations should be about 20–30 ka, with an average magnetozone duration of c . 240 ka, for the Lower and Middle Triassic, and about twice this for the Upper Triassic.

Upper Triassic–lowermost Jurassic palynology and palynostratigraphy: a review

Abstract This review advances understanding of the palynostratigraphy of the Late Triassic–Early Jurassic by correlating the established palynozonations for the northern and southern hemispheres. Previous palynological studies have contributed greatly to our understanding of the biostratigraphy, paleoclimatology and paleogeography of the Upper Triassic. In general, palynology is a good tool for interregional cross-correlation of marine and non-marine successions because palynomorphs, unlike most of other fossils, commonly are present in continental and marine environments. Currently, however, biostratigraphical resolution based on Upper Triassic palynomorph assemblages is rather low, primarily because of the rarity of successions that are independently dated (i.e. via ammonoids, conodonts, isotopes, paleomagnetism) to correlate the palynomorph assemblages, but also for other reasons, such as microfloristic provincialism, palaeoenvironmental conditions and differential preservation of palynomorph assemblages. During the last few decades many palynological studies have attempted to integrate and improve the biostratigraphical correlations and paleoclimatologic reconstructions across the Triassic–Jurassic boundary. Several authors have recognized specific microfloral assemblages with well-defined and recognizable suites of palynomorphs that enhance the importance of palynomorphs in the definition of Triassic–Jurassic stages. Comparison of the palynomorph assemblages from different biostratigraphical stages demonstrates that a change occurred in the palynofloral composition of the Tethyan domain between the Carnian and the earliest Hettangian that was gradual and without abrupt changes.

Predictive diagenetic clay-mineral distribution in siliciclastic rocks as a tool for identifying sequence boundaries in non-marine successions: the Coalspur Formation, west-central Alberta

Predictive diagenetic clay-mineral distribution in siliciclastic rocks as a tool for identifying sequence boundaries in non-marine successions: the Coalspur Formation, west-central AlbertaThe study of upper Cretaceous-lower Tertiary fluvial deposits of the Coalspur Formation in the Foothills region of west-central Alberta reveals that the distribution of early authigenic kaolinite has a well-defined relation to the sequence stratigraphic framework. In this context, it has been observed that the kaolin mineral content increases in sandstones lying below subaerial unconformities, which mark the most significant stratigraphic hiatuses and hence the sequence boundaries in fully fluvial successions. The increased abundance of authigenic kaolinite immediately below sequence boundaries may have been caused by the infiltration of meteoric water during times of subaerial erosion, resulting in the dissolution of unstable minerals (e.g., micas and feldspar) and the formation of kaolinite and secondary porosity. It is therefore suggested that the change in clay mineral assemblages in the stratigraphic section depends in part on the position of the analyzed sandstone samples relative to the sequence boundaries. In a larger context, the method of using authigenic clays to delineate depositional sequences in non-marine successions needs to be evaluated on a case-by-case basis, as the diagnostic early diagenetic minerals underlying the sequence boundary may change as a function of palaeoclimate and also as a function of late diagenetic processes.

Structural development and tectonic evolution of Gunsan Basin (Cretaceous–Tertiary) in the central Yellow Sea

This study analyzes the structural development of the Gunsan Basin in the central Yellow Sea, based on multi-channel seismic reflection profiles and exploratory well data. The basin comprises three depressions (the western, central, and eastern subbasins) filled with a thick (ca. 6000 m) Cretaceous to Paleogene nonmarine succession. It was initiated in the early Cretaceous due to intracontinental extension caused by oblique subduction of the Izanagi plate under the Eurasian plate and sinistral movement of the Tan-Lu fault. The basin appears to have undergone transtension in the late Cretaceous–Eocene, caused by dextral movement of the Tan-Lu and its branching faults. The transtension was accommodated by oblique intra-basinal normal faults and strike-slip (or oblique-slip) movement of a NE-trending bounding fault in the northern margin of the central subbasin. The entire basin was deformed (NE–SW contraction) in the Oligocene when tectonic inversion occurred, possibly due to the changes in strike-slip motion, from right- to left-lateral, of the Tan-Lu fault. During the early Miocene, extension resumed by reactivation of the pre-existing normal and transpressional faults. A combination of extension, uplift, and erosion resulted in differential preservation of the early Miocene succession. At the end of the early Miocene, extension ceased with mild contraction and then the basin thermally subsided with ensued rise in sea level.

Jurassic synorogenic basin filling in western Korea: sedimentary response to inception of the western Circum‐Pacific orogeny

ABSTRACTThis is the first sedimentologic and stratigraphic attempt to demonstrate Jurassic subduction‐induced basin‐filling processes in the early stage of the western Circum‐Pacific orogeny. The Chungnam Basin in western Korea was filled with a Lower to Middle Jurassic nonmarine succession, the Nampo Group, whose deposition postdated the Triassic final assembly of Chinese continental blocks. The Nampo Group consists of two repeated, fining‐ to coarsening‐upward alluvio‐lacustrine sequences, separated by an interval of thick breccia–gravel progradation deposits and its related strong proximal unconformities. No temporal variation in the degree of chemical weathering, along with the predominance of coals and a tropic to subtropic paleoflora, reveals little or no climate fluctuations during deposition of the Nampo Group. The observed relationships provide a record of sedimentation most likely controlled by temporal variations of tectonically driven sediment flux. Such syntectonic sedimentation of the Chungnam Basin occurred at a convergent margin of continental‐arc setting during the Daebo orogeny, synchronous with the early subduction of the western paleo‐Pacific ocean that resulted in formation of an accretionary complex along the East Asian continental margin during Jurassic time. Hence, synorogenic deposition in the Chungnam Basin is interpreted as sedimentary response to subduction–accretion of the western paleo‐Pacific plate.

Bentonite chemical features as proxy of late Cretaceous provenance changes: A case study from the Western Interior Basin of Canada

Bentonite beds are fairly common in both marine and terrestrial Upper Cretaceous (Campanian–Maastrichtian) deposits of the Western Interior Basin of western Canada and northwestern United States. A detailed stratigraphic, sedimentologic, geochemical (X-ray fluorescence), and mineralogical (X-ray diffraction) study of twenty-one bentonites from the Puskwaskau and Wapiti formations in the Grande Prairie area (west-central Alberta, Canada) is here presented. Major and trace-element concentrations from altered volcanic ashes document the presence in the study area of predominantly trachyandesitic and rhyolitic volcanogenic products, resulted from intense volcanic arc to within-plate pyroclastic activity. Concentration values of high field strength elements (HFSE) and selected large ion lithophile elements (LILE) (e.g. Nb, Zr, Th, and Y) obtained by X-ray fluorescence spectroscopy strongly support the presence of multiple volcanic sources. Integrated paleoenvironmental and geochemical criteria for provenance determination indicate a bimodal occurrence of basic and acid volcanic products interpreted as reflection of source areas characterized by different tectonic setting and magmatic composition. A comparative analysis of geochemical compositions between Grande Prairie bentonites and 30 known volcanic beds from central and southern Alberta, Manitoba and Montana 1. documents a trend toward more acidic and alkali-depleted volcanic products during the late Campanian–early Maastrichtian interval, and 2. suggests a well constrained stratigraphic and geographic subdivision of the non-marine successions of the foreland basin on the basis of geochemical characteristic of volcanic ash beds. Furthermore, geochemical “fingerprints” of several decimeter to meter thick bentonite beds have been coupled with volcanic ash subsurface signature in order to investigate their role as marker beds. This multiple-approach provides a reliable tool for basin-scale identification and correlation of non-marine sedimentary successions.

Depositional facies, architecture and environments of the Sihwa Formation (Lower Cretaceous), mid-west Korea with special reference to dinosaur eggs

This paper presents detailed facies and architectural analyses and palaeoenvironmental reconstruction of the Sihwa Formation (Lower Cretaceous), mid-west Korea, which comprises an about 3-km-thick non-marine succession containing abundant dinosaur eggshells. Based on constituent facies, bedset geometry, stacking pattern, and bounding surface characteristics, the entire succession can be classified into three architectural elements. Element I occurs along the basin margin and shows a monotonous stacking of tabular or crudely stratified conglomeratic units. It represents alluvial-fan deposits of debris-flow-dominated fan and sheetflood-dominated fan. Element II is characterized by multi-storey, sheet or upward-widening, conglomeratic channel-fills whose maximum thickness exceeds 1.5 m. Each channel-fill unit is encased within red–brown silty sandstones of Element III with sharp erosional bases but diffuse gradational upper boundaries. It consists generally of (1) cut-and-fill deposit (trough cross-stratified or openwork conglomerate) in the lower part and (2) composite low-relief bar deposit (lenticular conglomerate and stratified gravelly sandstone) in the upper part. Shallowness of each cut-and-fill unit, absence of fining-upward lateral accretion package and the predominance of simple-bar deposit collectively suggest deposition from ephemeral braided streams. Element III typically shows a fining-upward stacking of (1) single- or multi-storey small-scale (<1.5 m thick) channel fills with limited lateral extent of less than 15 m, (2) poorly sorted, graded and diffusely bounded silty conglomerates or gravelly siltstones with discontinuous gravel sheets and pockets and (3) homogeneous or graded, red–brown fine-grained deposits with calcretes and burrows in ascending order. Element III is interpreted as channel-margin to floodplain, including crevasse channel fill, crevasse splay and floodplain fines. The entire sequence of the Sihwa Formation can be divided into the alluvial-fan and terminal-fan successions. The alluvial-fan succession displays a progradational stacking pattern and indicates a low rate of basin subsidence in the initial phase of rifting. The upper terminal-fan succession consists of proximal braided stream and distal floodplain deposits in the western and central parts of the basin and is characterized by an axial dispersal pattern and an aggradational stacking. It suggests rapid subsidence of the basin floor during the main phase of rifting. The asymmetrical cross-basin distribution of each architectural element reflects a half-graben structure of the basin with steep-gradient fault-bounded eastern margin (footwall block) and gently sloped, flexural western margin (hangingwall block). The predominance of ephemeral braided-stream deposits along with red–brown fine-grained floodplain deposits with common calcretes indicates arid to semi-arid palaeoclimates. Approximately 140 dinosaur eggs (Faveoloolithidae and Dendroolithidae) were identified mainly from the (gravelly) siltstones and small-scale channel fills of Element III deposits and partly from the cut-and-fill conglomerates of Element II deposits. The eggs commonly retain their original oval shape but are invariably breached and stuffed with the substrate of gravels and silt. They are either isolated or clustered, forming a circular concentration in plan view. The abundant yield of eggs, more than 20 eggs in 5 separate nests from a single depositional unit, suggests a dense population of the parental dinosaurs. The repetitive occurrence in many stratigraphic horizons reflects site preference as a nesting habitat of the near-channel or abandoned channel areas.

UPPER CRETACEOUS TO NEOGENE PALYNOLOGY OF THE MELUT BASIN, SOUTHEAST SUDAN

Abstract The palynology of the Upper Cretaceous to Neogene non-marine succession in the Melut Basin, southeast Sudan was investigated. The palynomorphs are overwhelmingly of terrestrial origin, but rare brackish water dinoflagellate cysts and scolecodonts were encountered from the Lower Miocene and Oligocene-Miocene. Mangrove pollen, which is common in coeval West African coastal basins, is rare and inconsistent. Examples are Spinizonocolpites (Nypa) from the Campanian-Maastrichtian to Eocene and Rhizophoraceae (Zonocostites ramonae) from the Neogene. Based on the stratigraphic distribution of selected pollen and spores from four exploration wells, eight informal palynozones from the Campanian to the Neogene are proposed. The zones, in stratigraphically ascending order, are as follows: Assemblage Zone I, Campanian (lower Melut Formation); Assemblage Zone II, Campanian-Maastrichtian (middle Melut Formation); Assemblage Zone III, Maastrichtian (upper Melut Formation); Assemblage Zone IV, Paleocene (Yale For...

Lithofacies associations and structural evolution of the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil: A review of the setting of gold deposits

The Rio das Velhas greenstone belt is located in the Quadrilátero Ferrífero region, in the southern extremity of the São Francisco Craton, central-southern part of the State of Minas Gerais, SE Brazil. The metavolcano–sedimentary rocks of the Rio das Velhas Supergroup in this region are subdivided into the Nova Lima and Maquiné Groups. The former occurs at the base of the sequence, and contains the major Au deposits of the region. New geochronological data, along with a review of geochemical data for volcanic and sedimentary rocks, suggest at least two generations of greenstone belts, dated at 2900 and 2780 Ma. Seven lithofacies associations are identified, from bottom to top, encompassing (1) mafic–ultramafic volcanic; (2) volcano–chemical–sedimentary; (3) clastic–chemical–sedimentary, (4) volcaniclastic association with four lithofacies: monomictic and polymictic breccias, conglomerate–graywacke, graywacke–sandstone, graywacke–argillite; (5) resedimented association, including three sequences of graywacke–argillite, in the north and eastern, at greenschist facies and in the south, at amphibolite metamorphic facies; (6) coastal association with four lithofacies: sandstone with medium- to large-scale cross-bedding, sandstone with ripple marks, sandstone with herringbone cross-bedding, sandstone–siltstone; (7) non-marine association with the lithofacies: conglomerate–sandstone, coarse-grained sandstone, fine- to medium-grained sandstone. Four generations of structures are recognized: the first and second are Archean and compressional, driven from NNE to SSW; the third is extensional and attributed to the Paleoproterozoic Transamazonian Orogenic Cycle; and the fourth is compressional, driven from E to W, is related to the Neoproterozoic Brasiliano Orogenic Cycle. Gold deposits in the Rio das Velhas greenstone belt are structurally controlled and occur associated with hydrothermal alterations along Archean thrust shear zones of the second generation of structures. Sedimentation occurred during four episodes. Cycle 1 is interpreted to have occurred between 2800 and 2780 Ma, based on the ages of the mafic and felsic volcanism, and comprises predominantly chemical sedimentary rocks intercalated with mafic–ultramafic volcanic flows. It includes the volcano–chemical–sedimentary lithofacies association and part of the mafic–ultramafic volcanic association. The cycle is related to the initial extensional stage of the greenstone belt formation, with the deposition of sediments contemporaneous with volcanic flows that formed the submarine mafic plains. Cycle 2 encompasses the clastic–chemical–sedimentary association and distal turbidites of the resedimented association, in the eastern sector of the Quadrilátero Ferrífero. It was deposited in the initial stages of the felsic volcanism. Cycle 2 includes the coastal and resedimented associations in the southern sector, in advanced stages of subduction. In this southern sedimentary cycle it is also possible to recognize a stable shelf environment. Following the felsic volcanism, Cycle 3 comprises sedimentary rocks of the volcaniclastic and resedimented lithofacies associations, largely in the northern sector of the area. The characteristics of both associations indicate a submarine fan environment transitional to non-marine successions related to felsic volcanic edifices and related to the formation of island arcs. Cycle 4 is made up of clastic sedimentary rocks belonging to the non-marine lithofacies association. They are interpreted as braided plain and alluvial fan deposits in a retroarc foreland basin with the supply of debris from the previous cycles.

How do we identify big rivers? And how big is big?

“Big rivers” are the trunk rivers that carry the water and sediment load from major orogens, or that drain large areas of a continent. Identifying such rivers in the ancient record is a challenge. Some guidance may be provided by tectonic setting and sedimentological evidence, including the scale of architectural elements, and clues from provenance studies, but such data are not infallible guides to river magnitude. The scale of depositional elements is the most obvious clue to channel size, but evidence is typically sparse and inadequate, and may be misleading. For example, thick fining-upward successions may be tectonic cyclothems. Two examples of the analysis of large ancient river systems are discussed here in order to highlight problems of methodology and interpretation. The Hawkesbury Sandstone (Triassic) of the Sydney Basin, Australia, is commonly cited as the deposit of a large river, on the basis of abundant very large-scale crossbedding. An examination of very large outcrops of this unit, including a coastal cliff section 6 km long near Sydney, showed that even with 100% exposure there are ambiguities in the determination of channel scale. It was concluded in this case that the channel dimensions of the Hawkesbury rivers were about half the size of the modern Brahmaputra River. The tectonic setting of a major ancient fluvial system is commonly not a useful clue to river scale. The Hawkesbury Sandstone is a system draining transversely from a cratonic source into a foreland basin, whereas most large rivers in foreland basins flow axially and are derived mainly from the orogenic uplifts (e.g., the large tidally influenced rivers of the Athabasca Oil Sands, Alberta). Epeirogenic tilting of a continent by the dynamic topography process may generate drainages in unexpected directions. For example, analyses of detrital zircons in Upper Paleozoic–Mesozoic nonmarine successions in the SW United States suggests significant derivation from the Appalachian orogen. Many large rivers in SE Asia flow along structural trends generated during the Himalayan orogeny (e.g., Brahmaputra/Jamuna, Irrawaddy, Mekong, Red), but evidence for large channel systems is not always present where it might be expected. For example, in the Gulf of Thailand, up to 8 km of Cenozoic nonmarine sediments have been recorded in fault-bounded basins, but seismic time-slice images of the Pliocene–Holocene section indicate rivers of modest dimensions. The existing major trunk river, the Chao Phraya, which empties into the gulf at Bangkok, may be but a remnant of the Mekong, which was tectonically diverted to its present course at some point during the late Cenozoic.

Non-marine successions in the northwestern part of Kyongsang Basin (Early Cretaceous): Fluvial styles and stratigraphic architecture

Non-marine successions in the northwestern part of Kyongsang Basin (Early Cretaceous) are divided into successive stratigraphic units based on facies assemblages and architecture of sandstone bodies. In the present study, two stratigraphic units (Sinpyong-Anpyong and Jotap units) are documented in detail in terms of fluvial architecture. The Sinpyong-Anpyong unit is divided into thick sandstone, thin sandstone, and mudstone-dominated bodies, representing major channels, sand splays, and floodplains, respectively. The channel sandstone bodies are characterized by superposition of numerous bars and channels deposits formed in braided rivers. The mudstone-dominated bodies largely consist of purple siltstone in the northern (proximal) part and gray mudstone in the southern (distal) part, reflecting well-drained floodplains and poorly drained floodplains with local shallow lakes, respectively. The Jotap unit is divided into thick sandstone, interbedded sandstone/siltstone, and siltstone-dominated bodies, respresenting major channels, proximal floodplains, and distal floodplains, respectively. The thick sandstone bodies consist of trough cross-stratified sets and horizontally stratified sets with common internal scour surfaces and lenticular beds of purple siltstone, indicative of ephemeral channels dominated by small-scale bedforms. The siltstone-dominated bodies consist of purple siltstone and suggest well-drained floodplains. Along with the marked change in fluvial styles, the successions show systematic variations in the stacking patterns of channel bodies and the distribution of floodplain/lake facies. The basal and uppermost parts of the Sinpyong-Anpyong unit are characterized by sourceward expansion of distal, poorly drained floodplain/shallow lake facies and the low proportion and connectedness of channel bodies. Overlying these gray mudstone-dominated sequences, the middle part of Sinpyong-Anpyong unit and Jotap unit show increases in the proportion, connectedness, and grain size of channel bodies and basinward progradation of proximal, well-drained floodplain facies. Such a stratigraphic architecture can be attributed to the fluctuations in the ratio of accommodation space/sediment supply, regulated by repeated basin subsidence.

Depositional environments, architecture, and controls of Early Cretaceous non-marine successions in the northwestern part of Kyongsang Basin, Korea

In the northwestern part of Kyongsang Basin, southeast Korea, non-marine successions of interbedded sandstone and mudstone are divided into successive stratigraphic units on the basis of facies assemblages and sandstone architecture. Parts of the successions (Sinpyong–Anpyong and Jotap units), formed in southward- or southeastward-draining fluvial systems, are documented in detail in terms of macroform-scale to stratigraphic-level architecture for the assessment of fluvial styles and evolution of non-marine depositional environments. The Sinpyong–Anpyong unit consists of thick sandstone bodies (2–47 m thick), thin sandstone bodies (generally <2 m thick), and mudstone-dominated bodies. The thick sandstone bodies are characterized by superposition of numerous bars and channels, indicative of braided-channel systems. The channels are estimated at a few to 10 m deep and 9 m to tens of meters wide. The thin sandstone bodies comprise planar beds of massive, horizontally stratified, and trough cross-stratified sandstones, interpreted as sand sheets and splays. The mudstone-dominated bodies largely consist of purple siltstone in the northern (proximal) part and gray mudstone in the southern (distal) part, representing well-drained floodplains and poorly drained floodplains with local shallow lakes, respectively. In the basal and uppermost parts of Sinpyong–Anpyong unit, the distal poorly drained facies (gray mudstone) expands to the northern basin margin. The Jotap unit, overlying the Sinpyong–Anpyong unit, comprises thick sandstone bodies (2–10 m thick), interbedded sandstone/siltstone bodies, and siltstone-dominated bodies. The thick sandstone bodies are dominated by the deposits of small bars and dunes with common lenticular beds of purple siltstone and internal scour surfaces, suggestive of bedform-dominated channels with ephemeral discharges. The channels are estimated at generally a few meters in depth and a few tens to hundreds of meters in width. The interbedded sandstone/siltstone bodies comprise thin, sheet-like and lenticular sandstone beds (<2 m thick) interbedded with purple siltstone, interpreted as channel-proximal floodplains where sand was frequently deposited as sand sheets and splays, levees, and crevasse-channel fills. The siltstone-dominated bodies consist mostly of purple siltstone with subordinate thin sandstone beds, representing channel-distal, well-drained floodplains. Along with the marked change in fluvial styles, the successions show systematic variations in the proportion and connectedness of channel sandstone bodies and the distribution of floodplain/lake facies. The basal and uppermost parts of the Sinpyong–Anpyong unit are characterized by the sourceward expansion of distal, poorly drained floodplain/shallow lake facies and the low proportion and connectedness of channel bodies. Following these gray mudstone-dominated sequences, the middle part of Sinpyong–Anpyong unit and Jotap unit show increases in the proportion, connectedness, and grain size of channel bodies and basinward expansion of proximal, well-drained floodplain facies. Such a stratigraphic architecture can be attributed to the fluctuations in the ratio of accommodation space/sediment supply, regulated by repeated basin subsidence.

The middle Pleistocene Merced-2 and -3 sequences from Ocean Beach, San Francisco

The Merced Formation comprises a 2-km-thick shallow marine and non-marine succession that was deposited in a small transtensional basin along the San Andreas Fault during the late Pliocene to middle Pleistocene. The sediments dip between 10° and 80° to the northeast, and are locally disrupted by small faults. During tilting, the beds have been rotated into subparallelism with the San Andreas Fault zone, splays of which bound the outcrop belt of Merced sediments to both the southwest and northeast. The Merced Formation contains more than 20 transgressive–regressive sedimentary rhythms (cyclothems, or sequences) that are generally between 40 and 120 m thick, and which were deposited mostly during interglacial time, under the influence of rising, highstand and early falling sea levels. Sequences Merced-2 [units M1–N of Soc. Econ. Paleontol. Mineral., Field Guidebook 3 (1984) 1] and Merced-3 (units O–P), though in fault contact, comprise typical Plio-Pleistocene shallow water cyclothems. The Merced-2 Sequence is 22+ m thick, and comprises a sandy and shelly transgressive systems tract, including a basal Type A shellbed, an in situ Type B mid-cycle shellbed, and a highstand systems tract of massive siltstone. The Merced-3 Sequence is 47 m thick, and comprises a basal compound shellbed, a thin highstand systems tract siltstone, and a sand-rich regressive systems tract. The RST comprises distal shoreface sands with an abundant in situ molluscan fauna, and upper shoreface and back-beach trough cross-bedded sands and pebbly sands. The top of the Merced-3 cycle comprises a beach sand capped by a palaeosol and lignite (the “Beetle Bed”), which together mark the subaerial exposure of the site during the ensuing glacial sea-level lowstand. Analysis of 10Be across the Merced-3 Sequence shows major peaks, indicative of sedimentation starvation, in the basal transgressive systems tract shellbed and in the capping lignite of the Beetle Bed. Smaller 10Be peaks are associated with a shellbed that is inferred to represent winnowing at the foot of the shoreface, and with a minor exposure surface that delimits a small paracycle in the top of the sequence. Otherwise, 10Be abundances decline regularly across the Merced-3 Sequence, consistent with an increasing sedimentation rate as shoreface progradation, and regression, progressed. The character of cycles Merced-2 and Merced-3 respectively resembles the Seafield and Rangitikei sequence motifs described from similar Plio-Pleistocene sediments in New Zealand. The cycles are of mid-Pleistocene age, and were probably deposited during interglacial oxygen isotope stages 21 and 19, respectively.

Stratigraphic response to sedimentation in a net-accommodation-limited setting, Lower Cretaceous Basal Quartz, south-central Alberta

Research Article| March 01, 2002 Stratigraphic response to sedimentation in a net-accommodation-limited setting, Lower Cretaceous Basal Quartz, south-central Alberta R.W.C. Arnott; R.W.C. Arnott Department of Earth Sciences and Ottawa-Carleton Geosciences Centre, University of Ottawa, Ottawa, ON KIN 6N5 Search for other works by this author on: GSW Google Scholar B.A. Zaitlin; B.A. Zaitlin EnCana Corporation, 150-9 Avenue SW, Calgary, AB T2P 2S5 Search for other works by this author on: GSW Google Scholar D.J. Potocki D.J. Potocki EnCana Corporation, 150-9 Avenue SW, Calgary, AB T2P 2S5 Search for other works by this author on: GSW Google Scholar Author and Article Information R.W.C. Arnott Department of Earth Sciences and Ottawa-Carleton Geosciences Centre, University of Ottawa, Ottawa, ON KIN 6N5 B.A. Zaitlin EnCana Corporation, 150-9 Avenue SW, Calgary, AB T2P 2S5 D.J. Potocki EnCana Corporation, 150-9 Avenue SW, Calgary, AB T2P 2S5 Publisher: Canadian Society of Petroleum Geologists Received: 19 Apr 2001 Revision Received: 15 Sep 2001 First Online: 02 Mar 2017 Online ISSN: 2368-0261 Print ISSN: 0007-4802 © The Society of Canadian Petroleum Geologists Bulletin of Canadian Petroleum Geology (2002) 50 (1): 92–104. https://doi.org/10.2113/50.1.92 Article history Received: 19 Apr 2001 Revision Received: 15 Sep 2001 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R.W.C. Arnott, B.A. Zaitlin, D.J. Potocki; Stratigraphic response to sedimentation in a net-accommodation-limited setting, Lower Cretaceous Basal Quartz, south-central Alberta. Bulletin of Canadian Petroleum Geology 2002;; 50 (1): 92–104. doi: https://doi.org/10.2113/50.1.92 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Based on differences in mineralogy, paleovalley morphology, hydrocarbon production history and crosscutting Stratigraphic relationships, the subsurface Basal Quartz in the study area is interpreted to comprise four paleovalley fills consisting of braided-fluvial strata overlain abruptly by meandering fluvial strata. Significantly these strata accumulated in an accommodation-limited part of the basin where net sedimentation rate was only about 1 m/m.y. Accordingly, stratal characteristics contrast markedly with those in more extensively studied nonmarine successions that accumulated in high net-accommodation basins, and include (1) each unconformity bounded sequence is significantly thinner, (2) the upward change from braided-fluvial to meandering-fluvial or tidal strata occurs abruptly, and (3) a general lack of finegrained floodplain mudstone, which improves significantly the lateral connectivity of reservoir sandstones. A long-term effect of limited net accommodation, and the consequent slow aggradation of the sedimentary pile, is the repeated cannibalization of older valley-fill deposits by younger paleovalleys. This creates a stratigraphy consisting of laterally and vertically consistent stratal assemblage dominated by a single, typically the youngest, paleovalley fill. In places, however, parts of older paleovalley fills are preserved as localized remnants surrounded on most sides by younger strata. On a local scale, this results in the development of a significantly more complicated stratigraphy marked by rapid lithological changes, and similarly reservoir quality, even over short horizontal distances. On a more regional scale, the complex crosscutting of different-aged paleovalley fills, in addition to the tendency for each paleovalley to incise from a similar Stratigraphic level, makes Stratigraphic correlation difficult. Together, these characteristics can have significant Stratigraphic and economic ramifications. This content is PDF only. Please click on the PDF icon to access. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Architectural analysis of fluvial sequences in the northwestern part of Kyongsang Basin (Early Cretaceous), SE Korea

Abstract The northwestern part of Kyongsang Basin (Early Cretaceous) largely comprises interbedded sandstones and mudstones of fluvial depositional environments with local basin-margin conglomeratic deposits of alluvial fan systems. These non-marine successions are divided into 5 successive stratigraphic units, each of which is unique in facies assemblages and architecture of sandstone bodies. One stratigraphic unit (Sinpyong–Anpyong unit) is documented in this paper with detailed architectural analysis of sandstone bodies. The deposits of the Sinpyong–Anpyong unit are divided into three major components: thick sandstone, thin sandstone, and mudstone-dominated bodies. The thick sandstone bodies (2–47 m thick) comprise stacked element groups bounded by laterally persistent erosional surfaces, probably representing superposition of channel belts. Within individual element groups, elements are laterally superposed, indicating growth and superposition of bars and movement of associated channels. The thickness of bar deposits and dip angles of laterally inclined strata suggest that channels were a few to 10 m in depth and 9 m to several tens of meters in width. Paleocurrent data indicate southward- or southeastward-draining channel systems. The thin sandstone bodies (generally The thick sandstone bodies, formed in major channels and channel belts, are characterized by lateral superposition of numerous bar and channel deposits, limited extent of individual lateral-accretion sets, and the presence of mid-channel bar deposits, suggesting deposition in braided rivers. Detailed reconstruction of bars and channels reveals a range of processes including growth, coalescence, and erosion of bars and migration, switching, and filling of channels. Lateral accretion of bars and the associated channel migration might have been principal processes in the Sinpyong–Anpyong river systems. Bars were commonly coalesced by lateral superposition, forming large bar complexes.

THE APPLICATION OF SEQUENCE STRATIGRAPHY TO EXPLORATION AND RESERVOIR DEVELOPMENT IN THE COOPER-EROMANGA-BOWEN-SURAT BASIN SYSTEM

The application of sequence stratigraphy to non-marine strata in intracratonic basins is still in its infancy, however, the predominantly non-marine Cooper- Eromanga-Surat-Bowen basin system of Eastern Australia provides an excellent opportunity to demonstrate how sequence stratigraphic concepts can be applied to non-marine successions to assist with exploration and reservoir development. The key to applying sequence stratigraphic concepts in non-marine basins lies in understanding the role of alluvial sediment accommodation relative to sediment supply. Accommodation is created by a combination of tectonic subsidence, compaction and changing water tables in floodplain lakes, marshlands and peat mires. If the alluvial basin is directly connected to the marine system then eustacy may influence accommodation in the lower reaches of the alluvial network, but its effect will significantly diminish upstream depending on the slope. Climate change will, however, have an impact on fluvial discharge, rising water tables, floodplain lake levels, and sediment flux. For sediments to accumulate, accommodation must be positive, whereas negative accommodation leads to erosion. Fluvial accommodation is, therefore, comparable with the concept of base-level. During an episode of basin-wide tectonic uplift or tilting, falling base-level (negative accommodation) leads to widespread erosion on the basin margins or over intra-basinal highs, and an unconformity equivalent to a sequence boundary develops. If followed by a period of low accommodation, rivers rework much of their floodplain, resulting in a sheetlike, amalgamated succession of predominantly sandy bedload deposits of high nett to gross, equivalent to an alluvial lowstand. Further downstream, lowstand deltas may form in the lakes.

Unusual features of sediment supply-dominated, transgressive–regressive sequences: Paleogene clastic wedges, SE Pyrenean foreland basin, Spain

Abstract The Paleogene marine to nonmarine succession in the southeastern Pyrenean foreland basin consists of a series of 3rd-order (3–5 m.y.) transgressive-to-regressive sequences that can be related directly to the stacking and southward displacement of successive basement-cover thrust sheets. The regressive limbs of the 3rd-order clastic wedges are coeval with thrust movement, with maximum subsidence developing towards peak regression. This relationship between sedimentation and tectonics is sediment supply-driven. One of these 3rd-order wedges, which was produced by the Montserrat and Sant Llorenc del Munt fan-delta systems, demonstrates how such steep-sloped, coarse-grained, high sediment supply systems generate a hierarchy of transgressive–regressive architectures. Striking features of this rapidly subsiding, supply-dominated basin margin, in addition to the tectonics/wedge architecture relationship, include: • the nonperiodic character of the contained high-frequency sequences; • the unusual thickness and landward-thickening geometry of transgressive systems tracts; • a tendency for “misfit” between alluvial fan and shorezone sectors of sequences; • a lack of marked incision associated with the tops of coarse-grained, regressive phases of sequences. Most of the features are symptomatic of high subsidence rates and very high sediment-supply. The last feature, suggestive of few major relative falls of sea level, is also consistent with continuous rapid subsidence. However, it should be remembered that lack of incision may be a poor indicator for lack of base-level fall in a setting where the steepness of alluvial slopes exceeds the slope of the coeval shelf.