Dynamic Stratigraphy Research Articles

Topset-to-forest rollover trajectories as reliable predictors of sediment-volume partitioning into deep-lake areas

Topset-to-forest rollover trajectories and their relation to sediment- and sand-budget partitioning into deep-lake areas are far from being well understood, as compared with their marine counterparts of shelf edges. Two quantitatively distinctive topset-to-forest rollover trajectories and clinothem-stacking patterns were recognized in the Oligocene Qikou Sag of the Bohai Bay Basin and are quantified in terms of trajectory angles (Tse), topset thickness (Tt), forest thickness (Tf), bottomset thickness (Tb), and clinothem-set relief (Rc). Rising topset-to-forest trajectories have positive Tse of 0.15°–0.51° (averaging 0.35°). Ranges in Tt, Tf, Tb, and Rc of their associated progradational and aggradational clinothem sets are, respectively, 32.4–58.7 m (averaging 42.7 m), 76.9–176.2 m (averaging 148.3 m), 0 m, and 167.8–320.8 m (averaging 272.9 m). Falling topset-to-forest rollover trajectories, in contrast, have negative Tse of − 0.12° to − 0.02° (averaging − 0.06°). Ranges in Tt, Tf, Tb, and Rc of their associated progradational and downstepping clinothem sets are, respectively, 0 m, 266.0–395.7 m (averaging 333.4 m), 441.1–542.5 m (averaging 464.1), and 874.9–922.6 m (averaging 892.5 m). These two topset-to-forest rollover trajectories and clinothem-stacking patterns are closely linked to two distinctive patterns of sediment- and sand-volume partitioning into deep-lake areas, which are quantified in terms of Tt, Tb, and differential sediment aggradation of topset segments and forest-to-bottomset compartments (As/Ad). Rising topset-to-forest rollover trajectories and associated progradational and aggradational clinothem sets are characterized by aggradational topsets (reported as Tt of 32.4–58.7 m), a lack of time-equivalent bottomsets, and As/Ad of 0.22–0.87 (averaging 0.33), and are fronted by mud-dominated depositional deposits, with sporadic occurrence of thinner and regionally localized forest sands. They are, therefore, inefficient at delivering terrestrial sediments or sands into deep-lake settings. Falling topset-to-forest rollover trajectories and associated progradational and downstepping clinothem sets, in contrast, are characterized by toplap, erosional terminations but aggradational bottomsets (reported as Tb of 266.0–473.4 m), and As/Ad of 0, and are fronted by sand-rich depositional deposits, with widespread occurrence of thicker and regionally extensive time-equivalent deep-lake bottomset sands. They are, thus, efficient at delivering terrestrial sediments or sands into deep-lake settings. Topset-to-forest rollover trajectories and associated clinothem-stacking patterns are thus reliable predictors of sediment- and sand-volume partitioning into deep-lake areas, assisting greatly in developing a more dynamic stratigraphy.

Unfolding impacts of freaky tectonics on sedimentary sequences along passive margins: Pioneer findings from western Indian continental margin (Offshore Indus Basin)

The Western Passive Continental Margin of the Indian Plate (WCMI) serves as an elegant laboratory for understanding the syn-sedimentary rift-drift tectonics preserving a variety of episodic structural deformations and complex sedimentary infill. Here we present a multidisciplinary study on Offshore Indus Basin (OIB) that is less investigated compared to adjacent marginal basins along WCMI. Reflection seismic, gravity, borehole, and biostratigraphic data have been used to reconstruct the tectono-sedimentary history of the Meso-Cenozoic succession in OIB. Seismic based dynamic stratigraphy helped in mapping seven different depositional sequences grounded on morpho-tectonic considerations. The seismic expression of these sequences provided an idea of the depositional styles with different tectonic episodes since rifting in Jurassic to basin inversion in Miocene continued to present time. The OIB initially filled from the north with the sediments rapidly prograding southwards. In general, the basin deepens in the central and northwestern part where the formations achieve maximum depths. The analysis of 3D structural models revealed that the region experienced poly-phase deformation from the Late Cretaceous to recent times that include steeply dipping normal faults, horst, and graben, half-graben, half-graben with growth faulting, flower structures, anticline, syncline, and uplift with an angular unconformity. The most remarkable tectonic activity happened at the Early Miocene and resulted in the reactivation of extensional faults into strike-slip faults giving rise to a spectacular structural inversion due to transform movement between Indian and Arabian Plates that continues to present day. The most predominant faults are oriented in S20°-50°E with azimuth as 120°–160° and the maximum dip angles are >80° in the southwest flank of the basin. The main fault trend is S20°E-N20°W and dip angles ranging between 40° and 80° and above. A thick crust and the Ocean-Continent Transition (OCT) is imaged with massive felsic, mafic, and ultramafic intrusions by the help of forward gravity modeling. An initial onset of syn-rift tectonic subsidence between 90 and 68 Ma with a post-rift general increase between 68 and 54 Ma is comprehended while two uplift events at ~40 Ma and ~18 Ma are documented through backstripping analysis. It is inferred that the region is rapidly under complex structural inversion with growing folding, faulting, and flowering structures. This study could help in explaining the unanswered reasons of structural complexities, depositional styles, and basin inversion along worldwide passive margins.

Masuda, F. ed.: Dynamic Stratigraphy: Research for the “Chuseki-so”

Masuda, F. ed.: Dynamic Stratigraphy: Research for the “Chuseki-so”

Facies heterogeneity of a deep-sea depositional lobe complex: case study from the Słonne section of Skole Nappe, Polish Outer Carpathians

This article reports on the first detailed study of the Skole Nappe’s Ropianka Formation in the Slonne outcrop section along river San. Lithological and micropalaeontological similarities indicate that the sedimentary succession correlates with the formation’s Wiar Member of Campanian–late Maastrichtian age. The sedimentary succession, more than 140 m thick, is interpreted as a deep-marine complex of turbiditic depositional lobes and the study reveals its sedimentary anatomy. Six component facies of sediment gravity-flow deposits and their stratigraphic grouping into four facies associations are recognized, with these latter considered to represent deposits of the lobe axial zone, lateral flank zone and featheredge fringe zone, as well as an interlobe outer-fringe zone. Semi-quantitative characterization and comparison of facies associations gives insight into the succession’s sedimentary heterogeneity. Six depositional lobes superimposed upon one another are recognized in the stratigraphic succession, and their pattern of vertical stacking is interpreted in terms of dynamic stratigraphy on the basis of the upward succession of facies associations. The stratigraphic arrangement of facies associations is attributed to autogenic morphodynamic changes within the evolving depositional system, although it cannot be precluded that also eustatic and local tectonic forcing came into play. The case study sheds more light on the sedimentary environment, sediment sourcing system and spatial depositional pattern in the Late Cretaceous Skole Basin, where the aggrading seafloor apparently oscillated around the lysocline depth that could be mid-bathyal at that time.

Shelf-edge trajectories and stratal stacking patterns: Their sequence-stratigraphic significance and relation to styles of deep-water sedimentation and amount of deep-water sandstone

Using a seismic database from the Qiongdongnan Basin in the South China Sea, this study demonstrates that shelf-edge trajectories and stratal stacking patterns are reliable, but understated, predictors of deep-water sedimentation styles and volumes of deep-water sand deposits, assisting greatly in locating sand-rich environments and in developing a more predictive and dynamic stratigraphy. Three main types of shelf-edge trajectories and their associated stratal stacking patterns were recognized: (1) flat to slightly falling trajectories with negative trajectory angles () (−2° to 0°) and negative shelf-edge aggradation to progradation ratios () (−0.04 to 0) and associated progradational and downstepping stacking patterns with low clinoform relief () (150–550 m [492–1804 ft]) and negative differential sedimentation on the shelf and basin () (−0.6 to 0); (2) slightly rising trajectories with moderate (0°–2°) and medium (0–0.04), and associated progradational and aggradational stacking patterns with intermediate (250–400 m [820–1312 ft]) and intermediate (0–0.6); and (3) steeply rising trajectories with high (2°–6°) and high (0.04–0.10) and associated dominantly aggradational stacking patterns with high (350–650 m [1148–2132 ft]) and high (1–2). Each trajectory regime represents a specific stratal stacking patterns, providing new tools to define a model-independent methodology for sequence stratigraphy. Flat to slightly falling shelf-edge trajectories and progradational and downstepping stacking patterns are empirically related to large-scale, sand-rich gravity flows and associated bigger and thicker sand-rich submarine fan systems. Slightly rising shelf-edge trajectories and progradational and aggradational stacking patterns are associated with mixed sand/mud gravity flows and moderate-scale slope-sand deposits. Steeply rising shelf-edge trajectories and dominantly aggradational stacking patterns are fronted by large-scale mass-wasting processes and associated areally extensive mass-transport systems. Therefore, given a constant sediment supply, then , , , and are all proportional to intensity of mass-wasting processes and to amounts of mass-transport deposits, and are inversely proportional to the intensity of sand-rich gravity flows and to amounts of deep-water sandstone. These relationships can be employed to relate quantitative characteristics of shelf-edge trajectories and stratal stacking patterns to deep-water sedimentation styles.

Growth Styles of Shelf-Margin Clinoforms: Prediction of Sand- and Sediment-Budget Partitioning Into and Across The Shelf

Abstract Growth styles of shelf-margin clinoforms are reliable but understudied predictors of sand- and sediment-budget partitioning into and across the shelf. Three discrete clinoform-growth styles were recognized, including (1) strongly progradational shelf-margin clinoforms with low growth-trajectory angles (Gct,), low aggradation to progradation ratios (A/P), low clinoform heights (Hc), and long clinoform length (Lc); (2) mixed progradational and aggradational shelf-margin clinoforms with moderate Gct, moderate A/P, intermediate Hc, and moderate Lc; and (3) strongly aggradational clinoforms with high Gct, high A/P, high Hc, and short Lc. In the South China Sea dataset considered, strongly progradational shelf-margin clinoforms exhibit flat progradational and at times a mildly aggrading stacking patterns, whereas mixed progradational and aggradational clinoforms display stacking patterns with significant progradation and aggradation. Strongly aggradational shelf-margin clinoforms are dominated by aggradational stacking patterns. Each clinoform-growth style therefore represents a specific stratal stacking pattern, providing an important tool for approaching a model-independent methodology in sequence stratigraphy. In the study dataset, strongly progradational and strongly aggradational shelf-margin clinoforms are fronted by sand-prone submarine fan systems with high sand–shale ratios and mud-dominated mass-transport systems with low sand–shale ratios, respectively. Mixed progradational and aggradational clinoforms are associated with mixed sand–mud submarine canyon systems with moderate sand–shale ratios. Additionally, strongly progradational clinoforms partitioned great volumes of sediment into deep-water areas, as reflected by high rates of shelf-edge progradation and apparent toplap. Strongly aggradational clinoforms, in contrast, stored great volumes of sediment on the shelf itself, as indicated by high rates of shelf-edge aggradation and very thick clinoform topsets. Gct and Hc therefore increase linearly with sediment volumes partitioned into the shelf, but decrease linearly with sand- and sediment-budget partitioning into deep-water areas, given a constant sediment-supply condition. Growth styles of shelf-margin clinoforms are thus good predictors of source-to-sink sand- and sediment-volume partitioning into and across the shelf, assisting greatly in developing a more dynamic stratigraphy.

Dynamic stratigraphy of composite peripheral unconformity in a foredeep basin

AbstractThis study employs facies analysis and basic principles of sequence stratigraphy to correlate isolated outcrop sections and reveal the depositional history of the Chmielnik Formation – a prominent mid‐Serravalian clastic wedge formed on the basinward forebulge flank of the Polish Carpathian Foredeep. The coarse‐grained clastic wedge, up to 30 m thick and spanningca1·1 Ma within biozoneNN6, consists of fluvio‐deltaic, foreshore and shoreface deposits with a range of large littoral sand bars, all enveloped in muddy offshore‐transition deposits. Its dynamic stratigraphy indicates rapid shoreline shifts and environmental changes due to the interplay of forebulge tectonism, sediment supply and third‐order eustatic cycles. A similar interplay of tectonism and eustasy is recognizable in the whole middle Miocene sedimentary succession deposited on the forebulge flank, demonstrating an extreme case of an accommodation‐controlled shelf and indicating tectonic cycles of the forebulge uplift and subsidence spanningca800 to 900 ka. The episodes of forebulge uplift correlate with the main pulses of orogen thrusting. The resulting composite peripheral unconformity differs markedly from the idealized model of a ‘steady‐state’ stepwise onlap driven by forebulge continuous retreat. It is concluded that the foredeep peripheral unconformities, instead of being simplified in accordance with this idealized model, should rather be studied in detail because they bear a valuable high‐resolution record of regional events and give unique insights into the local role of tectonics, eustasy and sediment supply.

Dynamic stratigraphy of upper cretaceous in Northwest zogros (Kermanshah)-Iran

Kermanshah is part of the structural zone of autochtone Zagros in the boundary of Arabian and Iran plates. Stratigraphy sequence of upper cretaceous in two structural blocks of Kouh-e-Sefid in south and Kouh-e-Nesar in southwestern of Kermanshah up to Campanian stage was observed as similar sequence. There is a function of existing faults in area with distinct sedimentary condition in every block with each other, so that there is a reef sedimentary facies residue from collection of thick bed to massive limestone. While transitionally, in the block of Kouh-e-Sefid and Campanian, Marly limestone of Ilam formation changes to shalls of Gourpi formation in Kouh-e-Nesar. In Maestrischtian the block of Kermanshah's Kouh-e-Sefid suddenly forms Kermanshah reef which reaches detrical facies of sity shalls and siltstone and sandstones, which is equal with Amiran formation. Finally, Radiolarites sequence, located as a thrust on the Amiran formation, is observed as sedimentary sequence mentioned earlier; while in Kouh-e-Nesar's block, Gourpi formation is changed to Amiran formation by transitional boundary which in continuance this formation is finished by a disconfirmity to Kashkan's detrical formation that belongs to Eocene. Based on existing evidences, branchy function of Zagros thrust in the south of Kermanshah from Campanian causes sedimentary condition in two blocks which differ from each other. Key words: Dynamic stratigraphy, Zagros, structural block, microfacies.

A sequence stratigraphic approach to a Middle Triassic shelf-slope complex of the Ligurian Alps (Ligurian Briançonnais, Monte Carmo-Rialto unit, Italy)

The Mesozoic sedimentary cover belonging to the Monte Carmo-Rialto unit of the Ligurian Brianconnais domain is composed of Scythian clastics and Anisian to Carnian carbonate rocks over 300 m thick. This paper focuses on the stratigraphy of this carbonate complex, its environmental significance, and its evolution in light of dynamic stratigraphy. Our facies analysis of limestones and dolomites of the Triassic complex allowed us to reconstruct an environmental model. Data support a distally steepened carbonate ramp of Anisian age evolving to a more diversified Ladinian platform with an oolitic sand-bar belt separating the lagoon from the slope. The Monte Carmo-Rialto slope facies are the only witnesses of deep sedimentation in the Triassic terrains of the Ligurian Brianconnais domain, otherwise represented by shallow-water carbonate deposits. On the basis of facies succession, we have identified nine medium-scale cycles (third-order sequences) in the study area, comparable to those evidenced in the Brianconnais s.s. domain by the French authors. Small-scale cycles analysis evidenced mainly shallowing-upward trends in the examined sequences; although a few evidences of transgression-related deposits (deepening upward cycles) have been found at the base three sequences, they have been mostly obliterated by dolomitization and masked by local tectonics. For this reason, we can undoubtedly distinguish only the part of each sequence belonging to HST, while the TST, though present, still remains a partition that cannot be precisely characterized. In the same way, LSTs are not present in the Monte Carmo-Rialto unit, due to the original relative landward position of the examined area. Sequence stratigraphy analysis indicates different long-term dynamics for the two evolutionary stages of the Triassic Ligurian platform: a general landward backstepping to moderate progradation during the Early Anisian and true progradation during the latest Anisian and Ladinian. In addition, a good fit with the sequences proposed by the SEPM chart has been found, indicating a correspondence for the third-order sequences of the Middle Triassic.

Digitizing the Sedimentary Record: Efficient Data Structures for Dynamic Stratigraphy

As the surface of the Earth evolves over geologic time sediment is transported from high mountains to low lying sedimentary basins, accumulating stratigraphy which stores a sedimentary record of past environments. Understanding the structure of this stratigraphy is essential for exploiting sub-surface resources such as oil and water, and for deciphering the sedimentary record. Sophisticated computational models of Earth-surface dynamics can be used to predict formation of stratigraphy, but require stratigraphy in a discrete form. Here I present a discrete stratigraphic data structure which enables simulation of dynamic stratigraphic evolution. The data structure is robust and efficient, but can be easily coupled to existing Earth-surface dynamics models with minimal effort due to a simple interface. This represents a significant advance which will allow widespread use of dynamic models to predict and invert stratigraphy for application in a variety of fields.

Hierarchical dynamic stratigraphy in various Quaternary gravel deposits, Rhine glacier area (SW Germany): implications for hydrostratigraphy

The approach of ‘dynamic stratigraphy’ aims to understand genetic processes that form stratigraphic units in a hierarchy of spatial and temporal scales. This approach was used to investigate Quaternary gravel deposits in terms of their sedimentology and in order to characterize the various sedimentary units in terms of their hydrogeological properties. Facies analysis within 62 gravel pits, laboratory permeability measurements of field samples and geophysical surveys (3-D georadar, 2-D seismic reflection) led to the detection and classification of sedimentary heterogeneity according to the following six scales whereby each scale can be translated into defined hydrostratigraphic units. (1) Particles and pores (micro scale) that reflect depositional and diagenetic fluid dynamics as well as source material behaviour (e.g. grain-size, roundness, lithological composition). This was found to be important for the hydrogeochemistry of groundwater in gravel aquifers (e.g. higher sorption capacity of carbon-rich limestone particles for organic pollutants). (2) Strata (meso scale) contain the recognition of sorting, fabric, texture and stratinomic features, which can give an indication of transport and depositional dynamics. Five major lithofacies groups, for example, were distinguished within fluvial gravel-bed deposits. Their variable hydraulic properties led to their subdivision into 12 hydrofacies types. They form the smallest mappable hydrostratigraphic units, which may result in either preferred pathways for fluid flow or flow barriers. (3) Depositional elements (macro scale) enable reconstruction of sedimentary/geomorphic elements and their dynamics within a depositional system (e.g. gravel-bed braided river systems are dominated by gravel sheet, gravel dunes and scour pool depositional elements). Hydrostratigraphically, the architecture of depositional elements influences the hydraulic connectivity and local permeability structure/distribution within an aquifer body. Five types of depositional elements in fluvial gravel-bed deposits were distinguished and their geometries/dimensions quantified. (4) Facies bodies (mega scale) composed of a stack of depositional elements and strata recording distinct environmental systems and their dynamics (e.g. a coarse-grained prograding delta system). Hydrostratigraphically, facies bodies represent major compartments of an aquifer. Six major types of meltwater-controlled facies bodies were identified in the study area. (5) Genetic sequences (mega scale) reflect the shifts of depositional environments caused by allocyclic changes (e.g. glacial advance recorded by a coarsening upward sequence) or autocyclic changes of landscape shaping events. These sequences may form separate hydrostratigraphic units or aquifer storeys. (6) Basin fill (giga scale) comprising the lateral and vertical stacking of facies bodies and genetic sequences controlled by either long-term glacier dynamics or short term flood events. The regional distribution of permeable gravel units and, for example, less permeable diamicts builds the larger scale hydrostratigraphy.

Dynamic stratigraphy as a tool in economic mineral exploration: ultra-pure limestones (Upper Jurassic, SW Germany)

Ultra-pure limestones form valuable economic minerals used in the glass, paper, pharmaceutical, chemical and building industries. Both exploration and exploitation of economic materials require predictions of the subsurface stratigraphy. Such predictions are most reliable when the depositional processes creating these deposits are well understood. We present a simple, process-based methology (‘Dynamic Stratigraphy’) to break down stratigraphic packages into a hierarchy of easily recognisable genetically defined units of various scales. Each scale of analysis at the same time provides critical data on the composition, quality, volumes and preferred occurrence of economic minerals. In this study, Upper Jurassic carbonates of SW-Germany, deposited on a deeper epicontinental ramp, have been re-evaluated, based on newly available borehole data of an exploration programme for industrial minerals, especially for ultra-pure limestones, carried out by the Geological Survey of Baden-Württemberg. About 2.5 km of core were slabbed and continuously studied for micro- and macrofacies, geochemistry, colourimetry (‘whiteness index’) and calibrated to the gamma-ray signatures. In a number of key outcrops stratal and facies patterns as well as sedimentary geometries were mapped. The carbonate buildups form the most promising rock bodies hosting ultra-pure limestones. Gamma-ray signatures correlate both with major facies types and their bulk chemical composition and are thus useful for an initial evaluation of raw materials properties. In both major facies associations, (1) the bedded and (2) the massive microbial/sponge buildup facies, distinct sedimentary cycles were recognised, building systematic stacking patterns and a cycle hierarchy. Within the buildup facies, this cyclicity mirrors the ‘whiteness’ and ‘pureness’ of limestones. The cycles are used to carry out regional correlations between and across extensive buildup complexes, which are generally regarded as completely massive and homogenous. Based on this, the occurrence and distribution of economically valuable ultra-pure limestone bodies can be understood, and used to develop predictive genetic models. Dynamic or genetic stratigraphy integrated with petrophysical measurements (colourimetry, gamma-ray logs) leads to more cost-effective techniques of exploration and exploitation. While similar sedimentological concepts are commonly used in the petroleum industry, this study documents their usefulness also in the economic minerals industry.

Sedimentary Architecture and Dynamic Stratigraphy of a Marine Ice-Contact System

ABSTRACT The Mona moraine in southern Norway is a sedimentary ridge, 3.5 km long, formed at the mouth of a shelf trough during a late Younger Dryas readvance of the Scandinavian ice sheet. The moraine architecture, sedimentation processes, and record of ice-front behavior have been reconstructed in a high-resolution allostratigraphic framework on the basis of ground-penetrating radar profiles and sedimentologic analysis of outcrop sections. The shelf trough was draining ice from adjacent platforms, which resulted in ice-front protrusion with a moraine offset relative to the coeval swarm of small moraines formed in the shallow-water zone. The grounding-line system at Mona commenced its development as an ice-contact submarine fan, while the glacier front was thinning and grinding to a halt on a bedrock threshold. The ice flux declined, but fluctuated, and the subglacial sediment supply by meltwater prevailed. The ice-front stillstand allowed the submarine fan to aggrade to the sea level and turn into a Gilbert-type delta with a short (160 m) distributary plain. The delta foreset, 50-60 m thick, consists of gravelly massflow deposits, and its sandy turbiditic toe has been extended on the threshold's steep lee slope to a distance of at least 2 km. The delta was abandoned by rapid calving of the ice front, and the ice-contact slope was covered with marine mud and resedimentation products. A radiocarbon date from the base of this thin cover indicates ice retreat at around 10,100 yr BP. The moraine was surrounded by the sea and subject to reworking by waves, tides, and longshore currents. A thick package of regressive foreshore deposits with downstepping wave-cut terraces on the moraine slopes reflects gradual emergence due to regional glacioisostatic uplift. The study demonstrates that the facies architecture of marine moraines bears an important record of glacier dynamics and ice-front behavior.

Dynamics of marine glacier termini read from moraine architecture

Research Article| March 01, 2001 Dynamics of marine glacier termini read from moraine architecture Ida Lønne Ida Lønne 1The University Courses on Svalbard (UNIS), P.O. Box 156, N-9171 Longyearbyen, Norway Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (3): 199–202. https://doi.org/10.1130/0091-7613(2001)029<0199:DOMGTR>2.0.CO;2 Article history received: 07 Aug 2000 rev-recd: 20 Nov 2000 accepted: 01 Dec 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ida Lønne; Dynamics of marine glacier termini read from moraine architecture. Geology 2001;; 29 (3): 199–202. doi: https://doi.org/10.1130/0091-7613(2001)029<0199:DOMGTR>2.0.CO;2 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 SocietyGeology Search Advanced Search Abstract Allostratigraphic mapping of the internal facies architecture of marine moraines reveals the development history of ice-contact sedimentary systems. The new method for a high-resolution analysis of the dynamic stratigraphy of moraines provides important information on the ice-front behavior, glacier dynamics, and regional climatic conditions. Based on a series of case studies of the moraines of temperate glaciers in Norway, an allostratigraphic model is suggested as a conceptual guide for the field analysis of ice-contact deposits based on outcrop sections as well as seismic or ground-penetrating radar profiles. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Early Cretaceous drowning unconformities of the Apulia carbonate platform (Gargano Promontory, southern Italy): local fingerprints of global palaeoceanographic events.

Drowning successions which cap carbonate platforms and flanks bear palaeoenvironmental information which is useful for genetic stratigraphy; they constitute predictive key‐markers in regional to global correlations. An Early Cretaceous platform‐to‐basin transition has been investigated in Apulia (southern Italy) and two drowning unconformities, dated as early Valanginian and late early Aptian, have been documented. They occur at the base of thick pelagic tongues wedging toward the platform and mark the base of two depositional sequences showing distinct transgressive–regressive cycles. Timing of drowning processes, based on biostratigraphy and dynamic stratigraphy, allows the correlation of unconformities with global‐scale palae‐ oceanographic events marked, among others, by positive spikes of well‐established δ13C curves. Drowning signatures in the Apulia carbonates fit the stratigraphic, palaeoecological and possibly geochemical evidence found in global records at the same stratigraphic levels. Moreover, it is proposed that the observed drowning events were caused by palaeoceanographic crises affecting factory productivity.

高密度で測定された｀１４´Ｃ年代測定値による完新統のダイナミック地層学

高密度で測定された｀１４´Ｃ年代測定値による完新統のダイナミック地層学

Whither stratigraphy?

There have been three revolutions in sedimentary geology. The first two began in the 1960s, consisting of the development of process-response sedimentary models and the application of plate-tectonic concepts to large-scale aspects of basin analysis. The third revolution, that of sequence stratigraphy, began in the late 1970s and helped to draw together the main results of the first two: the knowledge of autogenic processes learned through facies analysis, and the understanding of tectonism implicit in the unravelling of regional plate kinematics. Developments in the use of seismic-reflection data and the evaluation of a hypothesis of global eustasy provided considerable stimulation for stratigraphic research. Current developments in the field of sequence stratigraphy are focusing on three areas. (1) Elaboration of the sequence-architecture models for various configurations of depositional environment and sea-level history. (2) Exploration of various mechanisms for sequence generation, especially tectonism and orbital forcing. (3) Attempts to improve the level of precision in stratigraphic correlation and to refine the geological time scale, as a means to test the model of global eustasy. The growth in the power of computers and our knowledge of physical and chemical processes has led to the evolution of an entirely new way of evaluating earth history, termed quantitative dynamic stratigraphy. Mathematical modelling and numerical simulation of complex earth processes are now possible, and require the collection and integration of a wide array of quantitative and qualitative data sets. Applications include the study of the geodynamic evolution of sedimentary basins, modelling of stratigraphic sequences and global climates, studies of Milankovitch cycles (cyclostratigraphy) and simulation of fluid flow through porous media. The Global Sedimentary Geology Program has brought many of these areas of study together in multidisciplinary, global-scale studies of the sedimentary history of the earth. The results of these studies have wide application to many problems of importance to the human condition, including the past history of global climate change and other environmental concerns. The study of stratigraphy is at the centre of the new view of the earth, termed earth-systems science, which views earth as an ‘organic’ interaction between the lithosphere, biosphere, hydrosphere, and atmosphere.

Dynamic stratigraphy of the Triassic and Jurassic of the Hebrides Basin, NW Scotland

Abstract The evolution of the Hebrides Basin during the late Triassic and Jurassic has been established by integrating analyses of subsidence history, sequence stratigraphy and stratigraphical architecture. Two episodes of three-phase evolution occurred from extension-related variable sequences (1A, late Triassic to early Sinemurian; 2A, latest Toarcian to late Bajocian), through sag-related laterally more uniform sequences (1B, mid-Sinemurian to earliest Toarcian; 2B, late Bajocian to late Bathonian), to stabilization—related condensed sequences (1C, Toarcian; 2C, late Bathonian to Callovian). A final third episode of subsidence in Oxfordian to early Kimmeridgian was followed by partial basin inversion in latest Jurasic or early Cretaceous, which caused faulting, tilting and uplift of basement ridges. These structures are unconformably overlain by Upper Cretaceous sediments and Palaeocene volcanics. There was a single Hebrides Basin during the late Triassic and Jurassic subsiding as a half-graben bounded on the west by the Minch Fault. The intrabasinal Camasunary and related faults are demonstrated not to have been significant tectonic features during the Jurassic. Occasionally they were slightly active but they did not divide the area into two sub-basins. They are largely post-Jurassic. There is evidence of a less strongly subsiding central Skye block, apparently in the area of the later Palaeocene plutonic centre.

Quantitative Dynamic Stratigraphy. Timothy A. Cross

Previous articleNext article No AccessReviewsQuantitative Dynamic Stratigraphy. Timothy A. Cross Steven M. HollandSteven M. Holland Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 99, Number 5Sep., 1991 Article DOIhttps://doi.org/10.1086/629545 Copyright 1991 The University of ChicagoPDF download Crossref reports no articles citing this article.

Orbital forcing of low‐frequency glacioeustasy

The role of orbital forcing in glacioeustasy has long presented a major problem regarding the reconciliation of data‐oriented seismic sequence stratigraphy with process‐oriented dynamic stratigraphy. Dynamic stratigraphy commonly cites orbital forcing periods of approximately 20,000 years (precession), 40,000 years (tilt), and 100,000 years (eccentricity) which are too fine scale to be resolved consistently by seismic sequence stratigraphy. Seismic sequence stratigraphy consistently identifies seemingly eustatic events on a scale of millions of years which have no heretofore easily identifiable causal mechanisms. In this paper, we propose a geologic mechanism and realistic quantitative construct to explain how Antarctic ice volume varies as a function of orbital forcing in the Tertiary. We demonstrate that this mechanism, which has a nonlinear response to long‐period modulation of the orbital forcing time series, can produce major glacioeustatic events with quasi‐periodicities of the order of 2 m.y. We use a FORTRAN program, STRATA‐various, to construct a two‐dimensional forward model demonstrating that this proposed mechanism can produce a synthetic sequence stratigraphy which bears strong resemblance to the generalizations of seismic sequence stratigraphy. We acknowledge important achievements of seismic sequence stratigraphy. Nevertheless, we propose that the seismic sequence stratigraphy concepts of long‐term and short‐term eustatic curves be replaced by independent estimates of tectonoeustasy and glacioeustasy based upon data sets which are, wherever possible, independent of seismic sequence stratigraphy. Likewise, we propose that qualitative generalizations be replaced with explicit forward models as the targets for model/data convergence.