Changes In Accommodation Space Research Articles

Depositional model of clastic and carbonate rocks in a continental rift basin: a case study of the Paleogene Shahejie Formation in the Cangdong Depression, Bohai Bay Basin

The study of a clastic and carbonate rock depositional model in a continental rift basin is helpful to better understand the sedimentary processes active in continental rift basins. However, the spatiotemporal evolution characteristics and controlling factors of clastic and carbonate rocks in continental rift basins are still unclear. Therefore, the sedimentary characteristics of the clastic and carbonate rocks in the Paleogene Eocene Shahejie Formation (Es) are analysed via seismic, well log, core, thin section, and geochemistry data. Then, the impacts of tectonic movement, sediment supply and hydrologic conditions on sedimentary characteristics are discussed, and a depositional model is finally established. Five 3rd-order sequences, named SQ1–SQ5 from bottom to top, are identified in the Es. Fan delta, braided delta, meandering river delta, and lake sedimentary systems are identified in the Es; clastic rock sedimentary systems are identified in SQ1–SQ4, while concurrent clastic and carbonate rock sedimentary systems are identified in SQ5. During the SQ1–SQ4 period, the palaeogeomorphology formed by differential faulting activity or fault interactions and the inherited palaeogeomorphology resulted in different distributions of the sedimentary systems. The changes in accommodation space and sediment supply caused by tectonic movement led the delta to prograde or disappear. During the SQ5 period, the clastic rock sedimentary systems underwent a transition into clastic rock and carbonate rock sedimentary systems as a result of rift weakening, broad crustal thermal subsidence, sediment supply reduction and high-salinity lake water. This study provides a typical case for the evolution characteristics of the clastic rock and carbonate rock systems in continental rift basins, identifies changes in the tectonic, sediment supply, and hydrologic characteristics during their mutual transformations, and provides an important reference for hydrocarbon reservoir prediction.

Late Quaternary sedimentation and neotectonics in Liaodong Bay, northern Bohai Sea

The Bohai Sea is a typical shelf sea, with obvious sediment differences in different regions. Although Liaodong Bay is the largest bay in the Bohai Sea, there lacks boreholes with precise dating. In this paper, the core sediments taken from YKC-2 borehole in the northeastern of Liaodong Bay are dated with AMS14C and OSL, in addition to grain size analysis, foraminifera and pollen identification, lithological characteristics and other testing results. Correlation is made with the global sea level change curve, and upon the basis the evolution of paleoenvironment in the northeast of Liaodong Bay is reconstructed. It is speculated that the age of the bottom of borehole YKC-2 is 150 kyr B.P., and two transgressions have been recorded, similar to the situation in JXC-1, a borehole 46.7 km to the west. It can be found that the sedimentation rate of YKC-2 borehole is obviously higher than that of JXC-1. The authors’ research found that it is mainly controlled by two factors: the provenance difference and the differential movement of basin controlling faults. In the west, sediments are mainly transported by the Bohai Sea current, with insufficient sediment supply, and the basin-controlling faults are rather stable and very weak in activity. In the east, sediments are transported mainly by the surrounding rivers with sufficient sediment supply; and the changes in accommodation space are under the control of the Tan-Lu fault zone. Affected by the strong extensional dynamic environment of the Bohai Bay Basin, the accommodation space, where the borehole YKC-2 is located, continuously increased for deposition of near-source river sediments. This article is an endeavor to study the evolution of the Late Quaternary sedimentary environment and the influence of tectonic activity on Quaternary sedimentation in the Bohai Sea.

Allogenic and autogenic controls on facies and stratigraphic architecture of the Lower Jurassic Mashabba Formation, Gebel Al-Maghara, North Sinai, Egypt

The Lower Jurassic Mashabba Formation crops out in the core of the doubly plunging Al-Maghara anticline, North Sinai, Egypt. It represents a marine to terrestrial succession deposited within a rift basin associated with the opening of the Neotethys. Despite being one of the best and the only exposed Lower Jurassic strata in Egypt, its sedimentological and sequence stratigraphic framework has not been addressed yet. The formation is subdivided informally into a lower and upper member with different depositional settings and sequence stratigraphic framework. The sedimentary facies of the lower member include shallow-marine, fluvial, tidal flat and incised valley fill deposits. In contrast, the upper member consists of strata with limited lateral extension including fossiliferous lagoonal limestones alternating with burrowed deltaic sandstones. The lower member contains three incomplete sequences (SQ1-SQ3). The depositional framework shows transgressive middle shoreface to offshore transition deposits sharply overlain by forced regressive upper shoreface sandstones (SQ1), lowstand fluvial to transgressive tidal flat and shallow subtidal sandy limestones (SQ2), and lowstand to transgressive incised valley fills and shallow subtidal sandy limestones (SQ3). In contrast, the upper member consists of eight coarsening-up depositional cycles bounded by marine flooding surfaces. The cycles are classified as carbonate-dominated, siliciclastic-dominated, and mixed siliciclastic-carbonate. The strata record rapid changes in accommodation space. The unpredictable facies stacking pattern, the remarkable rapid facies changes, and chaotic stratigraphic architecture suggest an interplay between allogenic and autogenic processes. Particularly syndepositional tectonic pulses and occasional eustatic sea-level changes controlled the rate and trends of accommodation space, the shoreline morphology, the amount and direction of siliciclastic sediment input and rapid switching and abandonment of delta systems.

Middle Jurassic evolution of a northern Tethyan carbonate ramp (Alborz Mountains, Iran)

Here, we provide a detailed facies and depositional record from a NE-SW-directed, 250-km-long transect across a distally steepened, Middle Jurassic carbonate ramp in the northern Tethyan realm (Iran). Among the six main facies types described, two stand out because of their beyond-regional significance: (i) Middle Callovian microbial and microbial-skeletal mounds embedded in muddy intermound sediment and (ii) Upper Callovian conglomeratic debris-flow deposits truncating the mound unit. The mound features described here did not evolve into reefal structures and evidence for a framestone structure is lacking. They occur as low-relief, mud-dominated domical structures (a few metres wide). The development of the Middle Callovian mounds is perhaps best linked to a period of minimum sedimentation rates and sufficient accommodation space resulting from a long-term gradual sea-level rise commencing in the Late Bajocian. With respect to the Upper Callovian conglomeratic deposits overlying the mound interval, the absence of sedimentary structures such as grading, the nature of the sub-angular or rounded clasts and the very poor sorting are indicative of a catastrophic debris flow origin. Based on data compiled here, the conglomeratic deposits likely formed due to relative sea-level fall inducing the reworking of mound facies by the lowered wave base and currents, and basinward transport of reworked material to the distal outer ramp. Our findings are compared with coeval deposits from the western Tethyan domain and placed into a process-oriented context. The described northern Tethyan Late Bajocian to Middle Callovian deepening-upward trend, followed by relative sea-level fall in the Late Callovian near the Middle-Late Jurassic transition, is in agreement with observations from other coeval Tethyan basins/platforms. Data shown here have wider relevance for workers concerned with the Jurassic evolution of the Tethyan Ocean in general and shed light on the intricate relation of changes in accommodation space and ramp architecture.

A morphological investigation of marine transgression in estuaries

AbstractThe landscape setting of estuaries varies widely and is an important aspect of determining how they evolve. This paper focusses on alluvial estuaries in river valleys and how they respond to sea level rise. We examine the implications of marine transgression, as a response to sea level rise, where the estuary moves upwards and landwards to maintain its position in the tidal frame (so‐called stratigraphic rollover). Here we encapsulate such kinematic movement of the estuary morphology using a ‘morphokinematic’ model, to assess the potential response to sea level rise and sediment supply. The model of the estuary form includes a single convergent channel, intertidal and surrounding floodplains (the valley) and allows the relative importance of the space available for deposition of sediments, the accommodation space, to be investigated as a function of rates of sea level rise and sediment supply. The transgression of the system is determined using a sediment mass balance, taking account of any supply from the river and marine environment. Model results confirm that the transgression distance, measured as the distance the entity moves landward, varies in proportion to the change in accommodation space, which mainly depends on the floodplain area. As the size of the floodplain reduces, the transgression distance is less and the system becomes much more sensitive to changes in the rate of sea level rise or changes in sediment supply. The greater demand for sediment when a floodplain is present results in greater cannibalization of the estuary form (i.e. greater landward movement) to meet the sediment demand. When the floodplain is disconnected from the estuary, the synergistic relationship is lost and the accommodation space increases. The capacity for restoration will depend on the availability of sediment and the prevailing rate of sea level rise.

The evolution of a coastal wedge in response to Plio-Pleistocene climate change: The Northern Adriatic case

This work reconstructs the complex evolution of a coastal wedge in response to Pliocene tectonic activity and Pleistocene climate change recorded in the upper Neogene subsurface succession of the Friulian-Venetian Basin (FVB), since the latest Messinian sea-level drop event to the late Pleistocene. The FVB is the north-eastern portion of the wider Po Plain-Adriatic foreland basin (Northern Italy), which bounds to the east the whole Italian peninsula and is the place where most of the Italian hydrocarbon offshore fields presently occur. Also, the city of Venice and its surrounding lagoon is presently one of the sites most sensitive to land subsidence worldwide and even a few mm loss of ground elevations can significantly change the natural lagoon environments and threaten the city's survival. To this purpose, we have integrated seismics and well logs analysis with 1D-geohistory modelling on wells, using corrected paleobathymetric data, in order to extract decompacted sedimentation rates. The new age model is based on a complete chronostratigraphic revision of the continuously cored Venezia 1 well, correlated with other 12 hydrocarbon wells to form proper geological depth-calibrated profiles across the basin. Results suggest a major tectonic control on marine sedimentation and basin accommodation space changes during the entire Pliocene-early Pleistocene time, influenced by the Northern Apennines thrust fronts migration. On the contrary, the mid-upper Pleistocene deposition, characterized by a weak deformation, is mainly controlled by climate and basin geometry. During the early mid Pleistocene, an impressive progradational cycle (in the literature usually named “Sabbie di Asti group”) followed the deposition of deep-water turbidites; in this work, we subdivide the different clastic bodies the formation is made of. The uppermost part of the “Sabbie di Asti group” is dominated by shallow-water to continental deposits showing a prominent regressive-transgressive cyclicity, where unfortunately chronological ties are limited. Nevertheless, 6 main cycles driven by 100 kyr Milankovitch-type ciclicity were laterally correlated by means of the well electric logs and linked to marine ∂18O isotope and eustatic curves.

Facies and sequence stratigraphic architecture of the Mural Limestone (Albian), Arizona: Carbonate response to global and local factors and implications for reservoir characterization

AbstractThis study documents the detailed facies and sequence stratigraphic architecture of a multi‐cyclic patch‐reef and its associated ramp interior facies that formed during Oceanic Anoxic Event 1b in the Mural Limestone, Arizona, USA. Ramp interior facies are comprised of bedded wackestone/packstone, rudist build‐up and coral–algal patch‐reef facies located north of Bisbee, Arizona, at the Grassy Hill locality. The larger multi‐cyclic patch‐reef that developed coevally ca 5 km to the south of Grassy Hill consists of a high‐angle windward margin with a narrow ca 70 m long reef frame containing vertically zonated Microsolena, Actinastrea, diverse branching coral and rudist assemblages, and an 870 m long low‐angle leeward margin comprised of reef debris rudstone and grainstone shoal facies. Similar reef geomorphology and orientation is documented across the Gulf of Mexico and reflects the shelf‐wide north to north‐east‐trending prevailing wind and current energies. Controls affecting reef formation and growth patterns include changes in accommodation space associated with low‐amplitude global sea‐level rise and regional thermotectonic subsidence, local accommodation space and nutrient fluctuations associated with the inner shelf depositional setting within a humid and siliciclastic‐rich environment. Four aggradational to retrogradational high‐frequency sequences are documented in Arizona: High‐frequency sequences 1 and 2 represent the first pulse of patch‐reef development in an overall second‐order marine transgression over the Sonora/Bisbee Shelf. These sequences correlate to δ13C signatures associated with Oceanic Anoxic Event 1b across the Gulf of Mexico and suggest that carbonate reefs persisted on the ramp interior during this time. High‐frequency sequences 3 and 4 record a second brief transgression and backstepping of reef facies followed by the final regression of shallow shelf carbonates that correlates to more robust patch‐reef development in Sonora, Mexico. The patch‐reef at Paul Spur is an excellent outcrop analogue for productive patch‐reefs in the Maverick Basin (Comanche Shelf) of Texas. Detailed facies mapping of this outcrop analogue shows that the greatest reservoir potential is contained within the backreef grainstone shoals where primary porosity of up to 15% is observed.

The transition from meandering river delta to braided river delta: Depositional characteristics and controlling factors from the second member of Shanxi Formation to the eighth member of Lower Shihezi Formation in Southeastern Ordos Basin

The Ordos Basin, as one of the most petroliferous basins in China, hosts 12.9 billion tons of oil reserves and 15.2 trillion cubic meters of natural gas reserves. The extensive hydrocarbon exploration and production shows that the southeastern Ordos Basin contains considerable potential in the Shanxi Formation and Lower Shihezi Formation. In this study, cores, wireline logs, thin sections, and heavy minerals are employed to carry out research on classification of sequence stratigraphy, identification of sedimentary facies, reconstruction of palaeo‐geomorphology, analysis of sediment supply, palaeo‐climate, and accommodation space changes. The results indicate that palaeo‐geomorphology gradient tends to be steep, which results in increasing hydrodynamics and turns to be wide and flat which results in decreasing accommodation space. In addition, heavy mineral distribution reveals the direction of sediment supply which indicates provenance changes. The palaeo‐climate changes commonly cause differences in lithology associations, monsoon and vegetation properties. The differences in temperature and humidity result in different colours of lithology associations which indicate various sedimentary environments. The prevalence of monsoon assists in the preservation of fluvial delta by controlling lateral migration of rivers through affecting vegetation and lithology associations. The accommodation space variations control the development of fluvial delta and result in various depositional characteristics of fluvial delta. All these factors trigger the transition from meandering river delta to braided river delta. The reconstruction of the transition and analysis of controlling factors play an important role on understanding the sedimentary evolution of analogous reservoir successions.

Identification of sequence stratigraphy in the Dongying Formation of the Liaoxi low uplift, Bohai Bay Basin, China

A change in sea level (or lake level) causes a change in accommodation space and sediment compensation, which then controls the formation and evolution of sequences. A multidisciplinary approach based on the integration of clay minerals, major and trace elements, paleosalinity, and three-dimensional seismic data were applied to interpret the stratigraphic sequence of the Dongying Formation in the Liaoxi low uplift. The sequence surface indicates that multistage tectonic action, paleoclimate, paleosalinity, and lake level change jointly controlled the sequence stratigraphy. The illite and illite–smectite mixed layers indicate an arid to semi-arid climate, whereas kaolinite implies humid conditions. Based on this principle, it is clear that the stratigraphic sequence is closely related to paleoclimate. Interpretation of the continental or marine character of the sediments via paleosalinity is increasingly based on the concentration of some trace elements. Hence, the sequence surface can be better evaluated through paleosalinity data. Based on the Sr/Ba and boron content, paleosalinity was evaluated and the sequence boundary was identified. Analysis of the concentration of major and trace elements was used to identify the lithology of the sedimentary region and further discern the stratigraphic sequence. These sequences are composed of lowstand, transgressive, and highstand system tracts. The work herein aimed to understand the reasons for the changes in sequences under the paleoclimate. In addition, major and trace elements, studied together with paleosalinity and clay mineral content, result in the determination of implications for sequence stratigraphy in many other basins. This paper can provide a novel method for comprehensively discerning a sequence surface.

Holocene sedimentation in a blue hole surrounded by carbonate tidal flats in The Bahamas: Autogenic versus allogenic processes

The sediment in North Atlantic blue holes preserves paleoclimate records. However, accurate paleoclimate reconstructions require an improved understanding of allogenic versus autogenic processes controlling blue hole sedimentation. Here we provide a detailed case study of the Holocene stratigraphy within Freshwater River Blue Hole, which is currently surrounded by carbonate tidal flats in the northern Bahamas (Abaco Island). During the Holocene, concomitant coastal aquifer elevation and relative sea-level rise controlled internal blue hole depositional environments. The general Holocene facies succession observed is: (i) basal detrital and freshwater peat, (ii) palustrine to lacustrine marl, (iii) algal sapropel, and finally (iv) bedded carbonate mud. During the middle Holocene when groundwater levels were lower, small changes in accommodation space that were inherited from the bedrock surface below (<1 m) were able to promote significant lateral facies changes. Multiple cores are needed to characterize these lateral facies changes. Hydrographic characteristics of the coastal aquifer (e.g., vertical position, stratification, salinity) relative to the blue hole benthos exert a fundamental control on (a) benthic flora and meiofauna (e.g., charophytes, ostracodes, foraminifera, gastropods) and (b) organic matter production and preservation from pelagic productivity. Over the last 5000 years, water column stratification in Freshwater River Blue Hole was interrupted on millennial to sub-decadal timescales , which are potentially linked to changing aquifer recharge and rainfall. Lastly, historical intense hurricanes passing closely to the west of the site may have promoted deposition of coarse beds at the site. However, the lack of carbonate tidal flat microfaunal remains (foraminifera: Peneroplis) within these coarse intervals indicates that Freshwater River Blue Hole does not preserve a reliable record of hurricane-induced overwash deposition from the carbonate tidal flats during the last 2300 years.

Evolution of an ancient (Lower Cretaceous) marginal‐marine system from tide‐dominated to wave‐dominated deposition, McMurray Formation

AbstractRegionally extensive parasequences in the upper McMurray Formation, Grouse Paleovalley, north‐east Alberta, Canada, preserve a shift in depositional processes in a paralic environment from tide domination, with notable fluvial influence, through to wave domination. Three stacked parasequences form the upper McMurray Formation and are separated by allogenic flooding surfaces. Sediments within the three parasequences are grouped into three facies associations: wave‐dominated/storm‐dominated deltas, storm‐affected shorefaces to sheltered bay‐margin and fluvio‐tidal brackish‐water channels. The two oldest parasequences comprise dominantly tide‐dominated, wave‐influenced/fluvial‐influenced, shoreface to bay‐margin deposits bisected by penecontemporaneous brackish‐water channels. Brackish‐water channels trend approximately north‐west/south‐east, which is perpendicular to the interpreted shoreline trend; this implies that the basinward and progradational direction was towards the north‐west during deposition of the upper McMurray Formation in Grouse Paleovalley. The youngest parasequence is interpreted as amalgamated wave‐dominated/storm‐dominated delta lobes. The transition from tide‐dominated deposition in the oldest two parasequences to wave‐dominated deposition in the youngest is attributed mainly to drowning of carbonate highlands to the north and north‐west of the study area, and potentially to relative changes in accommodation space and deposition rate. The sedimentological, ichnological and regional distribution of the three facies associations within each parasequence are compared to modern and Holocene analogues that have experienced similar shifts in process dominance. Through this comparison it is possible to consider how shifts in depositional processes are expressed in the rock record. In particular, this study provides one of few ancient examples of preservation of depositional process shifts and showcases how topography impacts the character and architecture of marginal‐marine systems.

Sequence architecture and depositional evolution of the late Palaeogene in southwestern slope of Lufeng Depression, Pearl River Mouth Basin: Responses to tectonic processes and base‐level changes

The southwestern slope of Lufeng Depression, which is located in the central part of Zhu I Depression is a significant geomorphic unit due to its petroliferous discoveries and tectonic evolutions since early Palaeogene. Based on the comprehensive analysis of cores, wireline logs, seismic volumes, and other related geological and geophysical information, the sequence architecture and depositional evolution was analysed, and their responses to regional tectonic processes and base‐level changes were revealed. The results indicated that two second‐order sequences and six third‐order sequences defined by different types of sequence boundaries are recognized. The second‐order and third‐order sequences were bounded by regional erosional unconformities on the depression margin or slope and unconformities in the central depression with the assist of stacking patterns of wireline logs and depositional characteristics of cores. The second‐order sequence generally consists of two regional transgressive–regressive cycles which can be further subdivided into several local sub‐cycles equivalent to corresponding third‐order sequences which can be identified from wireline logs and cores. The palaeogeomorphology resulted from compound and complex tectonic events in the early Palaeogene plays an important and main role in controlling sequence architecture. In contrast, the base‐level changes largely controls the sequence architecture in the late Palaeogene. The depositional systems within the sequence stratigraphic framework are mainly composed of braided delta deposits and shore deposits, which respectively includes braided channel, subaqueous distributary channel, lacustrine shale, beach bar, maximum flooding surface, shoreface, and foreshore. The base‐level changes, which apparently originated from tectonic uplift and subsidence and sediment supply, controlled the regional transgressions and regressions in sedimentary facies distributions. The development of subsequence (what we call it sand units or sections) from 2,980 to 2,880 in Enping Formation in the Early Palaeogene is obviously influenced by a decrease in tectonic subsidence (rifting stage) and an increase in accommodation space (base‐level rising), while the case is opposite in subsequence 2,850 of Enping Formation. However, the subsequence in Zhuhai Formation in the late Palaeogene from 2,760 to 2,600 was formed in stable tectonic settings (transition stage), and thereby, it was mainly dominated by base‐level changes which were caused by sediment supply and accommodation space changes.

Depositional model and controlling factors of oolithic shoal: A case study of the Lower Triassic Feixianguan Formation in the northwestern Sichuan Basin, China

Lower Triassic Feixianguan oolithic shoal complexes are widely developed in the northwestern Sichuan Basin, southwest China, where they host large natural gas reserves. To understand their development and the factors that controlled their deposition, we have used observations and interpretations of outcrops, cores, thin sections, well-log data, and seismic data to characterize the geologic and geophysical properties of the oolithic shoals of the Lower Triassic Feixianguan Formation in the Jiange area, northwestern Sichuan Basin. The oolithic shoals of the Feixianguan Formation are composed of locally dolomitized oolithic grainstones or packstones deposited in a semirestricted platform environment. With a thickness of more than 50 m, oolithic shoals mainly occur in the Fei 2 Member within the southeastern Jiange area. The results indicate that the shoals mainly lie above tectonic uplifts (caused by the northwest-trending basement-involved faults) and surrounding microtopographic highs. Furthermore, the prograding clinoforms and changes in accommodation space caused by sea-level fall influence the thickness of oolithic shoal deposits, and constrain their development in highstand systems tracts, resulting in their migration coinciding with the trend of clinoform progradation. We concluded that the development of oolithic shoals in the Jiange area may be controlled by two major factors: (1) the influence of paleotopography governed by the syndepositional faults on the accumulation of oolithic shoals and (2) the role of sea-level change in the migration of oolithic shoals.

Object Pose Estimation in Accommodation Space using an Improved Fruit Fly Optimization Algorithm

The accommodation space changes as flexible products are packed into it. In order to improve the automatic loading of containers, it is necessary to solve the problem of object pose estimation in accommodation space. The goal of this study is to establish a method for pose estimation of a target object in the accommodation space. Firstly, the paper introduces basic algorithms and concepts, including the quick hull (Qhull) algorithm, oriented bounding box (OBB) algorithm, and fruit fly optimization algorithm (FOA). Secondly, the constraint conditions and the objective function of pose estimation are set up according to the pose variables in three-dimensional (3D) space, and a solution method for pose estimation is established using an improved FOA. Then, the algorithms with different population parameters are simulated, and the optimal parameters are obtained. The bounding box algorithm is used for system optimization, whereas a convex hull is used to simplify the target object significantly, reducing the corresponding running time. Finally, the hardware platform of the industrial robot is established, the initial and final poses of the end-effector are obtained using the proposed method, and tests are performed for different cases. The results show that the application of convex hull algorithm can significantly simplify a target object reducing the running time, and half individuals of the population guide the entire population to search for an optimal pose (6 degrees of freedom) in accommodation space.

The lacustrine microbial carbonate factory of the successive Lake Bonneville and Great Salt Lake, Utah, USA

AbstractThe Bonneville Basin is a continental lacustrine system accommodating extensive microbial carbonate deposits corresponding to two distinct phases: the deep Lake Bonneville (30 000 to 11 500 14C bp) and the shallow Great Salt Lake (since 11 500 14C bp). A characterization of these microbial deposits and their associated sediments provides insights into their spatio‐temporal distribution patterns. The Bonneville phase preferentially displays vertical distribution of the microbial deposits resulting from high‐amplitude lake level variations. Due to the basin physiography, the microbial deposits were restricted to a narrow shoreline belt following Bonneville lake level variations. Carbonate production was more efficient during intervals of relative lake level stability as recorded by the formation of successive terraces. In contrast, the Great Salt Lake microbial deposits showed a great lateral distribution, linked to the modern flat bottom configuration. A low vertical distribution of the microbial deposits was the result of the shallow water depth combined with a low amplitude of lake level fluctuations. These younger microbial deposits display a higher diversity of fabrics and sizes. They are distributed along an extensive ‘shore to lake’ transect on a flat platform in relation to local and progressive accommodation space changes. Microbial deposits are temporally discontinuous throughout the lake history showing longer hiatuses during the Bonneville phase. The main parameters controlling the rate of carbonate production are related to the interaction between physical (kinetics of the mineral precipitation, lake water temperature and runoff), chemical (Ca2+, Mg2+ and HCO3− concentrations, Mg/Ca ratio, dilution and depletion) and/or biological (trophic) factors. The contrast in evolution of Lake Bonneville and Great Salt Lake microbial deposits during their lacustrine history leads to discussions on major chemical and climatic changes during this interval as well as the role of physiography. Furthermore, it provides novel insights into the composition, structure and formation of microbialite‐rich carbonate deposits under freshwater and hypersaline conditions.

Sequence architecture and depositional evolution in Lufeng Depression, Pearl River Mouth Basin, South China Sea Part B: The shore deposits of Zhuhai Formation

The Zhuhai Formation in Lufeng Depression is mainly deposited during a depression stage. In this paper, we employ cores, wireline logs, and seismic reflections to reveal sequence architecture and depositional evolution in target intervals. The results indicated that one second‐order sequence and two third‐order sequences were identified and sequence stratigraphic framework was established. The second‐order sequence was developed in response to base‐level falling, while third‐order sequences were mainly formed during base‐level rising. In addition, each third‐order sequence did not change too much in thickness. Then the shore deposits (shoreface and foreshore) were delineated, and the depositional characteristics were described within the framework with the help of related data. The shoreface and foreshore deposits within the sequence stratigraphic framework varied significantly in stacking patterns of wireline logs and cores. Based on comprehensive analysis, it can be concluded that base‐level changes played an important role in controlling sequence architecture. And lacustrine fluctuations derived from accommodation space changes exerted an essential effect on depositional evolution. This study provides significant insights into revealing the sequence architecture and depositional evolution and discussing hydrocarbon potential in the transition stage in the Zhuhai Formation.

Depositional facies and cyclic patterns in a subtidal-dominated ramp during the Early-Middle Ordovician in the western Tarim Basin (NW China)

Due to a long-term transgression since the Early Cambrian, an extensive shallow-water carbonate platform was developed in the entire Tarim Basin (NW China). During the deposition of the Yingshan Formation (Early-Middle Ordovician), a carbonate ramp system was formed in the intrashelf basin in the Bachu-Keping area of the western basin. Four well-exposed outcrop sections were selected to investigate their depositional facies, cycles, and sequences, as well as the depositional evolution. Detailed facies analyses permit the recognition of three depositional facies associations, including peritidal, semi-restricted subtidal, and open-marine subtidal facies, and eleven types of lithofacies. These are vertically arranged into meter-scale, shallowing-upward peritidal, semi-restricted subtidal, and open-marine subtidal cycles, in the span of Milankovitch frequency bands, suggesting a dominant control of Earth’s orbital forcing on the cyclic sedimentation on the platform. On the basis of vertical facies (or lithofacies) and cycle stacking patterns, as well as accommodation changes illustrated graphically by Fischer plots at all studied sections, six third-order depositional sequences are recognized and consist of lower transgressive and upper regressive parts. In shallow depositional settings, the transgressive packages are dominated by thicker-than-average, shallow subtidal cycles, whereas the regressive parts are mainly represented by thinner-than-average, relatively shallow subtidal to peritidal cycles. In relatively deep environments, however, the transgressive and regressive successions display the opposite trends of cycle stacking patterns, i.e., thinner-than-average subtidal cycles of transgressive packages. Sequence boundaries are mainly characterized by laterally traceable, transitional zones without apparent subaerial exposure features. Good correlation of the long-term changes in accommodation space inferred from vertical facies and cycle stacking patterns with sea-level fluctuations elsewhere around the world suggests an overriding eustatic control on cycle origination, platform building-up and evolution during the Early-Middle Ordovician, although with localized influences of syndepositional faulting and depositional settings.

Depositional environments and cyclicity of the Early Ordovician carbonate ramp in the western Tarim Basin (NW China)

During the Early Ordovician, the Tarim Basin (NW China) was mainly occupied by an extensive shallow-water carbonate platform, on which a carbonate ramp system was developed in the Bachu-Keping area of the western part of the basin. Three well-exposed typical outcrop sections of the Lower Ordovician Penglaiba Formation were investigated in order to identify the depositional facies and to clarify origins of meter-scale cycles and depositional sequences, thereby the platform evolution. Thirteen lithofacies are identified and further grouped into three depositional facies (associations): peritidal, restricted and open-marine subtidal facies. These lithofacies are vertically stacked into meter-scale, shallowing-upward peritidal and subtidal cycles. The peritidal cycles are mainly distributed in the lower and uppermost parts of the Penglaiba Formation deposited in the inner-middle ramp, and commonly start with shallow subtidal to intertidal facies followed by inter- to supratidal facies. In contrast, the subtidal cycles occur throughout the formation mostly in the middle-outer ramp and are dominated by shallow to relatively deep (i.e., intermediate) subtidal facies. The dominance of asymmetrical and incomplete cycles suggests a dominant control of Earth’s orbital forcing on the cyclic deposition on the platform. On the basis of vertical facies and cycle stacking patterns, and accommodation changes illustrated by the Fischer plots from all studied sections, five third-order depositional sequences are recognized in the Penglaiba Formation. Individual sequences comprise a lower transgressive part and an upper regressive one. In shallow-water depositional environments, the transgressive packages are dominated by thicker-than-average subtidal cycles, indicating an increase in accommodation space, whereas regressive parts are mainly represented by thinner-than-average peritidal and subtidal cycles, denoting a decrease in accommodation space. In contrast, in intermediate to deep subtidal environments, transgressive and regressive packages display an opposite trend in accommodation space changes. Sequence boundaries (except the basal and top boundaries of the Penglaiba Formation) are usually represented by laterally traceable, transitional boundary zones without apparent subaerial exposure features. Good correlation of the long-term changes in accommodation space (or sea-level) inferred from vertical stacking patterns of facies and cycles suggests an overriding eustatic control on the formation of meter-scale cycles and third-order depositional sequences as well as platform evolution superimposed with local and/or regional tectonic influence during the Early Ordovician. This study would help understand the controls on the tempo-spatial facies distribution, stratal cyclicity and carbonate platform evolution in the western Tarim Basin during the Early Ordovician, facilitating prediction for favorable subsurface carbonate reservoirs and future hydrocarbon exploration and production in the Penglaiba Formation.

Facies analysis and depositional model of late Permian Raniganj formation: Study from Raniganj coal bed methane block

The Raniganj Formation (late Permian) forms the uppermost economic coal-bearing unit of the Gondwana succession. The dominant facies interpreted from analysis of cores from the Raniganj formation are classified as Sandstone dominated facies, Sandstone - shale heterolith facies, Shale facies and Coal facies. The natural Gamma response of Raniganj Formation shows predominance of repetitive fining upwards cycles. Integration of core analysis and geophysical log data of the Raniganj formation indicates meandering fluvial environment. The lower part of Raniganj Formation is channel dominated which corresponds to thick amalgamated sand bodies while the upper part represent overbank shows predominance of channel avulsion indicating a gradual change in accommodation space. Five major fining upward depositional sequences, bounded by sub-aerial unconformities (sequence boundaries) have been dentified in Raniganj formation, based on changes in depositional style that are correlated regionally. Each sequence comprises of Low accommodation system tract (LAST) at base and high accommodation system tract (HAST) at top. LAST is characterized by vertically stacked, multistory amalgamated channel sandstone dominated facies, while floodplain dominated facies characterize HAST. The coal seams deposited in LAST are thicker and relatively more continuous than the frequent thin seams of HAST. Such facies distribution study would be helpful for the development strategy for CBM blocks based on production priority.

New magnetostratigraphic dating of the Palaeogene syntectonic sediments of the west-central Pyrenees: tectonostratigraphic implications

AbstractNew magnetostratigraphic results from a 3300 m-thick section across the syntectonic fluvial sediments of the Campodarbe Formation (Upper Eocene–Oligocene) in the Ebro foreland basin (NE Spain) are presented. The new data allow the top of the Campodarbe Formation to be correlated to Chron 7r (Chattian), younger than previously stated (C10r), therefore shifting the age of significant palaeogeographical changes in the foreland basin. The deformation in the southern front produces the cannibalization in the piggyback basin of 1300 m of sediments spanning c. 3.7 Myr. Average accumulation rates are lower in the Ebro foreland basin than in the piggyback basin and decrease from 35 to 27 cm kyr−1 by the time the San Felices thrust sheet activity decelerates (at c. 28 Myr). Shifts of accumulation rates result from accommodation space changes, which occur locally and are linked to the activity of the San Felices thrust, while the sediment supply occurs at orogenic scale (source of sediments is c. 200 km to the NE). Finally, sequence boundaries previously considered isochronous in the continental record of the Cenozoic Pyrenean basins are revealed to be 1.8–1 Myr older in the piggyback basin than in the Ebro foreland basin.