Thin Transgressive Systems Tract Research Articles

An extensive erosion surface of a strongly deformed limestone bed in the Gushan and Chaomidian formations (late Middle Cambrian to Furongian), Shandong Province, China: Sequence–stratigraphic implications

In order to understand sequence development and sea-level fluctuations during the late Middle Cambrian to early Furongian on the North China epeiric platform, the present study focuses on a unique, subtle erosion surface of an extensive (approx. 100 km), strongly deformed limestone bed in the uppermost part of the Gushan Formation, Shandong Province, China. The Gushan Formation and the overlying Chaomidian Formation consist mainly of shales and a variety of carbonates that were deposited in subtidal environments (e.g., deep subtidal, shallow subtidal, shoreface/shoal, subtidal microbial flat, and restricted platform interior). Three third-order depositional sequences (S1–3) are identified, each of which comprises a thin transgressive systems tract (TST) and a relatively thick highstand systems tract (HST). Each sequence is bounded by a drowning unconformity (SB1), a subaerial unconformity (SB2), or a surface of submarine erosion (SB3). The upper sequence boundary (SB2) of sequence 1 (S1) is represented by a subtle erosion surface of an extensive, deformed limestone bed with a wide variety of soft-sediment deformation structures (e.g., lime mudstone breccias, chaotic wacke-packstone laminae and fragments, homogenized oolites, and clastic dykes), and is overlain by small sporadic microbial buildups and an extensive bioclastic grainstone bed. The deformed limestone was formed during early diagenesis by differential deformation processes (brecciation, liquefaction/fluidization, and injection) which were most likely induced by pore-water overpressure during the period of rapid sea-level fall. Despite the lack of subaerial exposure features (e.g., paleokarst, paleosol, etc.), the characteristics of the erosion surface (cutting well-lithified sediment below), the missing of a significant geological record (the Prochuangia biozone), and the worldwide correlatable positive carbon isotope excursion collectively indicate that the erosion surface developed under conditions of subaerial exposure after contemporaneous marine cementation of the deformed sediment. The missing of the Prochuangia biozone is most likely due to non-deposition at a subaerial hiatal surface. The erosion surface was submerged as a result of subsequent rise in sea level, where sporadic microbial buildups formed under suitable conditions. Freshly deposited, winnowed, shell-dominated transgressive lag deposits (containing Chuangia trilobite fragments, brachiopod shells, and abundant glauconite grains) formed with continued rise in sea level, which became, in turn, overlain by shale-dominated facies. The unique combination of the subtle erosion surface ( sensu stricto a subaerial unconformity) and the underlying deformed limestone bed provides an important criterion for recognizing the subtle changes in relative sea level on shallow epeiric platforms.

Depositional sequences and palaeoceanographic change in the Ordovician of the Siberian craton

Nine major depositional sequences separated by regional unconformities are recognized in the Ordovician of the Siberian Craton. These sequences are typically characterized by an absence of lowstand systems tracts, relatively thin transgressive systems tracts and somewhat thicker shallowing upward highstand systems tracts. The most prominent unconformities, marking forced regressions are associated with the base of the Baykit depositional sequence (Early Darriwilian) and the top of the Ordovician. Across the former, the tropical-type carbonate factory was terminated and siliciclastic sediments (Baykit Sandstone) were deposited. These changes in lithology inferably correspond to tectonic events along the western margin of the Siberian continent. With major flooding events during the Volgino, Kirensk–Kudrino and Mangazeya depositional sequences phosphatization became much more widespread and carbonate rock compositions shift from tropical-type to temperate-type. This lithological shift is due to a combination of upwelling of cool water, increased nutrient influx and increased water turbidity. Major transgressions marked by widespread black shales and/or deep-water marine red bed facies occurred during the Volgino, Kirensk–Kudrino (Late Darriwilian), Mangazeya (Early Sandbian) and Kety (Middle Katian) depositional sequences. The Ordovician depositional sequences of the Siberian Craton can be tentatively correlated with those developed in the Baltica palaeocontinent, which suggests that most of them were controlled mainly by eustasy. The pattern of long-term lithological changes in the Ordovician of the Siberian Craton and our established sea-level curve demonstrate more similarities with North America than with Baltica.

The early Pliocene Titiokura Formation: Stratigraphy of a thick, mixed carbonate‐siliciclastic shelf succession in Hawke's Bay Basin, New Zealand

This paper presents a systematic stratigraphic description of the architecture of the early Pliocene Titiokura Formation (emended) in the Te Waka and Maungaharuru Ranges of western Hawke's Bay, and presents a facies, sequence stratigraphic, and paleoenvironmental analysis of the sedimentary succession. The Titiokura Formation is of early Pliocene (Opoitian‐Waipipian) age, and unconformably overlies Mokonui Formation, which is a regressive late Miocene and early Pliocene (Kapitean to early Opoitian) succession. In the Te Waka Range and the southern parts of the Maungaharuru Range, the Titiokura Formation comprises a single limestone sheet 20–50 m thick, with calcareous sandstone parts. In the vicinity of Taraponui Trig, and to the northeast, the results of 1:50 000 mapping show that the limestone gradually partitions into five members, which thicken markedly to the northeast to total thicknesses of c. 730 m, and concomitantly become dominated by siliciclastic sandstone. The members (all new) from lower to upper are: Naumai Member, Te Rangi Member, Taraponui Member, Bellbird Bush Member, and Opouahi Member. The lower four members are inferred to each comprise an obliquity‐controlled 41 000 yr 6th order sequence, and the Opouahi Member at least two such sequences. The sequences typically have the following architectural elements from bottom to top: disconformable sequence boundary that formed as a transgressive surface of erosion; thin transgressive systems tracts (TSTs) with onlap and backlap shellbeds, or alternatively, a single compound shellbed; downlap surface; and very thick (70–200 m) highstand (HST) and regressive systems tracts (RST) composed of fine sandstone. The sequences in the Opouahi Member have cryptic TSTs, sandy siltstone to silty sandstone HSTs, and cross‐bedded, differentially cemented, fine sandstone RSTs; a separate variant is an 11 m thick bioclastic limestone (grainstone and packstone) at the top of the member that crops out in the vicinity of Lake Opouahi. Lithostratigraphic correlations along the crest of the ranges suggest that the Titiokura Formation, and its correlatives to the south around Puketitiri, represent a shoreline‐to‐shelf linked depositional system. Carbonate production was focused around a rocky seascape as the system onlapped basement in the south, with dispersal and deposition of the comminuted carbonate on an inner shelf to the north, which was devoid of siliciclastic sediment input. The rates of both subsidence and siliciclastic sediment flux increased rapidly to the northeast of the carbonate “platform”, with active progradation and offlap of the depositional system into more axial parts of Hawke's Bay Basin.

Architecture and growth history of a Miocene carbonate platform from 3D seismic reflection data; Luconia province, offshore Sarawak, Malaysia

Using 3D seismic reflection data and wireline logs we reconstruct in detail the architecture and growth history of a Miocene carbonate platform in the Luconia province, offshore Sarawak, Malaysia. Platform growth started in the Late Oligocene to Early Miocene, by coalescence of isolated patch reefs. The growth history includes phases of progradation, backstepping and occasional collapsing of platform flanks, guided by syndepositional faulting. The most pronounced seismic reflections in the platform correspond to flooding events (thin transgressive systems tracts). Subaerial exposure preceding the flooding could be demonstrated in only one case. Platform growth was terminated by gradual submergence (drowning) indicated by smooth, concentric seismic reflectors forming a convex mound.

High-resolution architecture of late Holocene highstand prodeltaic deposits from southern Spain: the imprint of high-frequency climatic and relative sea-level changes

The stratigraphic architecture and recent evolution of two late Holocene prodeltas (Guadalquivir and Guadalhorce rivers) from the south of Spain are compared on the basis of a high-resolution seismic stratigraphic analysis. These sedimentary bodies display a similar internal architecture, being characterised by a thin transgressive systems tract at their bases and an overlying thick, wedge-shaped highstand systems tract (HST). The internal structure of the HST deposits shows the repetition of two progradational/aggradational cycles, whose generation seems to be related to the influence of high-frequency climatic changes during the last 6–7 ka. Those changes probably involved small amplitude (<3–4 m) sea-level oscillations and associated changes of sediment supply, conditioning the development of delta switching processes. Small differences in the distribution and characteristics of the seismic units in each area are attributed to local factors, such as physiography of the coastal plains, the wave climate and increased sediment supplies conditioned by anthropic actions.

Sequence stratigraphy with emphasis on platform-related parasequences of the Zechstein 2 carbonate (Ca2) – the northern platform margin of the Southern Permian Basin (NE Germany)

Facies analysis combined with sequence stratigraphic interpretation of the Upper Permian carbonate (Ca2) of NE Germany (i.e. northern basin margin of the Southern Permian Basin) confirm the existence of a rimmed platform with a steep and tectonically structured slope. The karstified A1 platform is overlain by deposits of a thin transgressive systems tract (TST) and a thick highstand systems tract (HST) which shows two larger-scale regressive shallowing-upwards cycles (4th order) with typical stacking patterns of small-scale cycles (5th order). The TST consists of bitumen-rich mudstones with reworked clasts of anhydrite and early cemented wacke- to grainstones, and it shows two, probably 5th-order, deepening-upwards cycles. The first larger-scale shallowing-up cycle on the Ca2 platform (4th-order) is dominated by aggradation of the bar and shoal deposits, whereas the second one is dominated by progradation. The tops of both cycles are characterised by erosional and exposure surfaces. Various types of small-scale shallowing-upwards cycles (5th-order) are observed in the bar, in the intertidal and in the algal-dominated supratidal environment, showing pronounced transgressive boundaries. On the slope and in the basin, equally thick TST and HST are observed. These incorporate carbonate turbidites which indicate "highstand shedding" from the platform. Various orders of relative sea-level variations are discussed. Controlling factors include tectonics, climate, and eustatic processes. A combined carbonate and evaporite sequence was found on the upper Ca2 slope, which may indicate a Ca2-lowstand systems wedge.

Sequence Stratigraphy, Facies, and Sea Level Change of the Hauterivian Productive Complex, Priobskoe Oil Field (West Siberia)

The productive complex of the Priobskoe field formed during the Hauterivian in the central part of the West Siberian basin as part of the Neocomian (Early Cretaceous) progradational complex. Its depositional setting was a shelf-break margin with well-developed clinoform units and a 1-2° slope gradient. Two depositional sequences have been identified and consist of distinct systems tracts. The lowstand systems tract of the lower sequence (AC12.2-4) formed as a result of rapid high-amplitude relative sea level fall, and is clearly differentiated into lowstand fan and lowstand prograding wedge deposits. Sea level fall of lower amplitude (and rate) led to deposition of a lowstand systems tract in the upper sequence (AC10.1-2) in which no lowstand fan unit was deposited. A thin transgressive systems tract of the lower sequence (AC11.0) formed during a short-term sea level rise. In contrast, prolonged high-amplitude sea level rise led to deposition of a thick transgressive deposit in the upper sequence (AC10.0-AC8). Deposition of the sandiest units is related to shelf (shoal-water) deltas and shelf-edge deltas on the shelf, and to submarine fans in basinal portions. Deposition of shelf-edge deltas was accompanied by abundant gravity-driven processes and formation of shingled turbidites, during which the basin margin significantly prograded and infilled accommodation space. In many cases, sediment supply into the deep-marine systems of Priobskoe was provided from multiple feeder entry points that led to coalescence of individual submarine fans into thick submarine ramps. Because it is based on copious drilling and seismic data, the sequence stratigraphic framework developed for the Priobskoe field may serve as a useful analog model for exploration and prospect generation in Hauterivian clinoforms, as well as in the entire West Siberian Neocomian. There is good correspondence between the relative sea level change interpreted for Priobskoe to the quantified eustatic curve (QEC) generated from Russian platform stratigraphy. This implies that eustasy played an important role in controlling sedimentation in the Priobskoe field. In addition, it supports the validity for the Hauterivian interval of the QEC.

The relationship between shellbed type and sequence architecture: examples from Japan and New Zealand

Examples of lithology, fossil content and taphonomic features of shellbeds and intervening less fossiliferous intervals are presented from four Plio–Pleistocene successions (Shimosa Group, Boso Peninsula, Omma Formation, Hokuriku area, Japan, and Okehu, Kai-iwi, and Shakespeare groups in Wanganui, and the Rangitikei Group along the Rangitikei River in New Zealand). As for pre-Pliocene 3rd- and 4th-order depositional sequences, Plio–Pleistocene 5th- to 7th-order depositional sequences contain a variety of shellbeds which are often associated with surfaces or intervals that are characterized by sedimentary condensation, omission or erosion (e.g. sequence boundaries, ravinement surfaces, downlap surfaces and condensed sections). Stratigraphic patterns of shellbed type tend to be similar and repetitive within a basin and a locality. This demonstrates that a specific palaeogeography played an important role in determining the nature of shellbeds. For example, shellbeds formed in the context of toplap are common only in the Shimosa Group, which was deposited in a moderately sheltered sea, the palaeo-Tokyo Bay. Toplap shellbeds are rare in other sequences formed in more open conditions. Despite the variability resulting from such basin characteristics, common styles of shellbeds can be recognized that formed under conditions of marine onlap, backlap, downlap and toplap. Each type of shellbed has a characteristic fossil composition and taphonomy. Onlap and toplap shellbeds contain low-diversity macrobenthic associations including Glycymeris, Mercenaria, Paphies or other bivalves having robust shells, which are often abraded or fragmented. Backlap shellbeds, which are equivalent to the condensed section formed at the maximum transgression, are characterized by dominance of epifaunal macrobenthos such as bryozoa, brachiopoda, pectinid and ostreid bivalves, preserved in a slightly cemented, glauconitic muddy matrix. In contrast to fossils in such condensed sections, the shell density and species diversity of downlap shellbed associations are rather low, and in a few examples the macrobenthic association was buried rapidly in a lower unit of the highstand systems tract (HST) stratigraphically located above the condensed sections. Variations in the stratigraphic distribution of shellbed types are reflected in symmetrical and asymmetrical sequence architectures. Symmetrical sequences have roughly the same thickness of transgressive systems tracts (TST) and highstand systems tracts (HST), and have well segregated shellbeds that were formed during marine onlap and backlap. Asymmetrical cycles have very thin TSTs and much thicker HSTs, and are characterized by the amalgamation of condensed onlap and backlap shellbeds. Such contrasting cycle architectures are interpreted to reflect inner (symmetrical) and outer (asymmetrical) shelf palaeodepositional settings. The amalgamated onlap/backlap shellbeds appear to be common in Plio–Pleistocene sequences. Owing to the short duration of glacio-eustatic sea-level changes with dominant frequencies of 20,000, 40,000 or 100,000 years, shellbeds in the Plio–Pleistocene are relatively simple and thin compared to those formed in ordinary third-order depositional sequences. Infauna-dominated benthic associations are generally more common than in third-order cycles, and epifaunal associations facilitated by taphonomic feedback on sediment-starved shell-gravel substrates occur only in the condensed section corresponding to maximum transgression in most Plio–Pleistocene sequences.

Sequence stratigraphy of the Upper Miocene Stage IVC in the Labuan-Paisley Syncline, northwest Sabah Basin

A sequence stratigraphic study of the Upper Miocene Stage IVe has been carried out in the Labuan-Paisley Syncline, Northwest Sabah Basin with the aim of identifying new hydrocarbon plays in the study area. Stage IVe contains up to 4,000 m thick, clastic sediments deposited in coastal plain to bathyal environments probably between 8.2 Ma and 10.5 Ma indicating an immense sedimentation rate of approximately 1,700 metreslMa. top and base of the Stage IVe are marked by the Shallow Regional and Upper Intermediate Unconformities respectively which are pronounced tectonic boundaries in the NW Sabah Basin. overall regressive Stage IVe sediments are characterised by oblique to shingled progradation towards the westerly-northwesterly directions as suggested by the mapping of the pronounced shelf­ edges. A generalised third-order sequence witlUn the Stage IVe includes very thin transgressive systems tract and very thick highstand and lowstand systems tracts. A Type-I, third order sequence boundary separates the Stage IVe into two third-order sequences. This sequence boundary is evidenced by the occurrence of a major erosional slump scar at the western part of the syncline. depositional model derived from this study includes thick shelf sands and basin floor/submarine fans interspersed by thinner sands of the levee-channel complexes at the shelf slopes. The Intra Stage IVe sequence boundary is thought likely to be caused by the fall in sea-level probably between 8.5 Ma and 9.0 Ma. This fall in.sea-Ievel is not represented in the global sea-level chart of Haq et al. (1987), suggesting that this fall in sea-level could be small and localised but it is evident in a basin with large sediment supply. This sequence stratigraphic study has resulted in the identification of various hydrocarbon plays. They comprise basin floor/submarine fans, slope fan/levee channel complex and shelf-edge/slump scar plays. 'basin floor /submarine fan play is considered the highest ranked but requires additional seismic coverage for detailed mapping.