Long-term Transgression Research Articles

Cretaceous sequence stratigraphy of the northern Baltimore Canyon Trough: Implications for basin evolution and carbon storage

Abstract We evaluate the Cretaceous stratigraphy and carbon sequestration potential of the northern Baltimore Canyon Trough (NBCT) using >10,000 km of multi-channel seismic profiles integrated with geophysical logs, biostratigraphy, and lithology from 29 offshore wells. We identify and map six sequences resolved primarily at the stage level. Accommodation was dominated by thermal and non-thermal subsidence, though sequence boundaries correlate with regional and global sea-level changes, and the record is modified by igneous intrusion, active faulting, and changes in sediment supply and sources. Our stratigraphic maps illustrate a primary southern (central Appalachian) Early Cretaceous source that migrated northward during the Aptian and Albian. During the Cenomanian, sedimentation rates in the NBCT increased and depocenters shifted northward and landward. We show that deposition occurred in three phases: (1) earlier Cretaceous paleoenvironments were primarily terrestrial indicated by variable amplitude, chaotic seismic facies, serrated gamma logs, and heterolithic sandstones and mudstones with terrestrial microfossils; (2) the Albian to Cenomanian was dominated by deltaic paleoenvironments indicated by blocky, funnel-shaped, gamma-ray logs and clinoforms characterized by continuous high-amplitude seismic reflections with well-defined terminations; and (3) the Cenomanian and younger was marine shelf, inferred from mudstoneprone lithologies, peak gamma-ray values in well logs, and foraminiferal evidence. Long-term transgression and maximum water depths at the Cenomanian/Turonian boundary correlative with Ocean Anoxic Event 2 were followed by a regression and relative sea-level fall. We show that porous and permeable sandstones of three Aptian to Cenomanian highstand systems tracts are high-volume reservoirs for supercritical CO2 storage that are confined by overlying deep water mudstones.

Progressive opening of a shallow-marine bay (Oliete Subbasin, Spain) and the record of possible eustatic fall events near the Barremian-Aptian boundary

In this paper, we analyse the upper Barremian-lowermost Aptian Alacón Formation (Oliete subbasin, Maestrazgo Basin) of Spain to understand the progressive opening of a shallow-marine bay found on the northeastern margin of Iberia. The succession consists of four transgressive-regressive sequences (S1S4) bounded by widespread unconformities caused by rapid base-level fall. The transgressive interval of each sequence is characterized by relatively high detrital input and fresh-water inflow that caused the demise of shallow-marine benthic communities. The regressive interval of each sequence triggered progressive regeneration of the benthic carbonate producers. Sequences 1 and 2 consist of lacustrine to restricted shallow-marine facies, followed by accumulations of the gryphaeid oyster Ceratostreon , with progressive colonization of the bay by marine benthic communities subjected to frequent salinity oscillations. Sequences 3 and 4 represent the stabilization of open-marine conditions in the bay with widespread development of high-energy bioclastic tidal dunes. The long-term transgression around the Barremian-Aptian boundary, which gave rise to the progressive flooding of the Oliete bay, was episodically interrupted by shorter-term episodes of abrupt base-level fall, with the eventual subaerial exposure of the entire bay at the end of the deposition of the Alacón Formation. Our data suggest that the observed sequence architecture was mostly controlled by climatic and eustatic sea-level oscillations, with local synsedimentary tectonics having a minor impact. Two major sea-level fall events responsible for the discontinuities found on top of sequences 3 and 4 are possibly correlated to the cooling episodes close to the Barremian-Aptian boundary and during the earliest Aptian (predating the OAE 1a) described in many other worldwide basins. • The progressive opening of a shallow marine bay in Iberia (W Tethys) is documented. • Four sequences register progressive paleogeographical and paleoecological changes. • Sequence boundaries are tentatively linked to major cooling events KBa5 and KAp1.

Low-accommodation foreland basin response to long-term transgression: A record of change from continental-fluvial and marginal-marine to open-marine sequences over 60,000 km2 in the western Canada foreland basin

Low-accommodation foreland basins have been of recent interest because their stratigraphic architectures provide insight into the interaction of tectonic subsidence and eustasy. Aptian-aged strata in Alberta, Canada (McMurray Formation and Wabiskaw Member) were deposited under the influence of a continental-scale river that longitudinally transported and debouched sediment into the southward-transgressing Boreal Sea in the distal, low-accommodation Western Canada Foreland Basin (WCFB). In this study, we present a high-resolution stratigraphic framework for the McMurray-Wabiskaw interval, which was deposited during a long-term transgression. Using wireline logs from >20,000 wells and more than 500 cores, regional mapping focused on resolving stratigraphic relationships and the distribution of depositional environments across approximately 60,000 km2 in the Athabasca Oil Sands Region of northeastern Alberta. The studied stratigraphic interval is part of a third-order sequence: the McMurray Formation developed during a period of relative sea-level fall, lowstand, and early transgression, while the overlying Wabiskaw Member was deposited during late transgression. Within the McMurray Formation, superimposed fourth-order sea-level fluctuations in this low accommodation setting created a complex amalgam of deltaic strata vertically and laterally juxtaposed with valley-fill deposits. Relative sea-level rises resulted in rapid transgressions in which the shorelines migrated >400 km landward. Thin (5–15 m thick), widespread deltaic parasequence sets were deposited during subsequent sea-level highstands. During relative sea-level falls, fluvial meandering channel belts developed in downcutting valleys, with associated shorelines dramatically prograding basinward. In the Wabiskaw Member, continued sea-level rise coupled with potentially decreasing sediment supply resulted in the development of tide-influenced/dominated channels and bars in estuaries. The final phase of the third-order transgression was marked by a regional transgressive ravinement event and several southwestward backstepping wave-dominated shorefaces/strandplains. This low-accommodation foreland basin succession demonstrates a transition from deposition in continental fluvial and marginal-marine settings subject to high-frequency eustatic changes, to open-marine conditions over a long-term transgression.

Permian-Triassic biofacies of the Teočak section, Bosnia and Herzegovina

The Teočak section in Bosnia and Herzegovina (Sava-Vardar Zone) composed of the Upper Permian Bellerophon Formation and the Lower Triassic “Werfen Formation” was studied sedimentologically and micropaleontologically by using foraminifers and conodonts. The Bellerophon Formation was deposited in a shallow subtidal lagoon rich in biota characterized by typical Changsingian foraminiferal species. Deposition on a shallow epicontinental ramp with pronounced long-term transgression is proposed for the Lower Triassic strata. The recovered conodont faunas are assigned to the Late Permian praeparvus (Changhsingian) and to the Early Triassic isarcica-staeschei (Griesbachian), costatus (? latest Dienerian-early Smithian) and hungaricus (early Spathian) Zones. The studied strata include the Permian-Triassic Boundary as well as the Induan-Olenekian Boundary. The introduced conodont biozonation in the Teočak section is for the first time proposed for the region and is an important contribution for paleobiogeographic correlation of Western Tethys. • Uppermost Permian and Lower Triassic strata of the Teočak section were studied. • The section is composed of the Bellerophon Formation and the “Werfen Formation”. • The recovered conodont faunas enabled identification of four conodont zones. • Foraminifers of the Bellerophon Formation are marked by typical Changhsingian taxa. • A deposition on a shallow epicontinental ramp is proposed for the Triassic strata.

Sedimentology and carbon isotope stratigraphy of the Rhaetian Hochalm section (Late Triassic, Austria)

The Rhaetian (~201–209 Ma, the latest stage of the Triassic) is an important time-interval for the study of environmental changes preceding the End-Triassic Mass extinction. A detailed sedimentological and chemostratigraphic study was conducted in the lower Kössen Formation at Hochalm (Austria), the type-section of the Hochalm Member (Mb). This section exposes mid-Rhaetian sediments deposited in an intraplatform shallow marine basin on the north-western margin of the Tethys. The study highlights eight apparent shallowing-upward sequences from the middle of Unit 2 to Unit 4 of the Hochalm Mb stacked within the long-term transgression that characterizes the Kössen Formation. Both the bulk carbonate and the bulk organic matter δ 13 C records indicate the presence of a distinct increase in carbon isotope values in the lower part of the lower Hochalm Mb. This excursion might represent a new chemostratigraphic marker that could be used for refining the Rhaetian stratigraphy and represents another important Late Triassic carbon-cycle perturbation prior to the major disturbance associated with the End Triassic biotic crisis. • Detailed paleoenvironmental model of the Hochalm Mb. • Shallowing-deepening sequences related to sea-level changes. • Carbon isotope stratigraphy in mid-Rhaetian Hochalm Mb. • Distinct increase in carbon isotopes in the lower Hochalm Mb.

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.

Anatomy And Sequence Architecture of the Early Post-Rift In the Neuquen Basin (Argentina): A Response To Physiography and Relative Sea-Level Changes

Abstract A detailed architectural and sequence stratigraphic analysis was carried out in the early-post-rift succession of central Neuquen Basin (Middle Jurassic Cuyo Group), integrating outcrop and subsurface information from a 3,000 km2 area. Sedimentary facies analysis allowed the definition of six marine facies associations, which are grouped in two main depositional systems. During the late Toarcian to early Bathonian a storm- and wave-dominated shoreface to offshore system was developed. This is overlain by a late Bathonian–early Callovian fluvio-deltaic depositional system. The sequence stratigraphic analysis of this succession identified parasequences limited by marine flooding surfaces with little evidence of erosion. Parasequences could be grouped into four parasequence sets that show the evolution of the depositional systems and can be interpreted in terms of shoreline trajectories. In this sense, a log-term transgressive event defined by a complicated retrogradational stacking pattern and spanning for almost 10 My is identified for the older deposits. This succession is eventually replaced by a progradational unit that represents highstand conditions. The Cuyo succession identified in this part of the basin is completed by the development of a regressive surface and the onset of a deltaic depositional system with no parasequence development but indicating an abrupt basinward facies shift. The long-term transgression that dominates the early post-rift succession in this part of the basin is interpreted to represent a period of sustained accommodation creation produced by the combination of thermal subsidence, differential compaction of syn-rift deposits, and eustatic rise under a relatively low sediment supply. Changes in the stacking pattern of retrogradational parasequence sets are thought to be produced by changes in the bathymetry of the topography being flooded, which is a relic of a complex array of footwalls and shoulders generated during the syn-rift stage. Regional changes in thickness and timing for the early post-rift succession could be therefore the result of the relatively passive infill of an inherited topography of the syn-rift, suggesting that most of the accommodation was already created before the onset of the long-term transgressive trend that characterizes the post-rift succession in this part of the basin. The Cuyo Group succession reported here reflects the complexity in terms of depositional styles, sequence stratigraphic patterns, and controls that can be expected during the early-post rift infill of syn-rift structural depressions. Therefore, the results of this study can provide useful lessons for post-rift systems having prolific hydrocarbon production worldwide (e.g., in the Northern North Sea, Norwegian Sea, Thailand, and Argentina and Chile).

Sequence stratigraphy and formalization of the Middle Uinta Mountain Group (Neoproterozoic), central Uinta Mountains, Utah: A closer look at the western Laurentian Seaway at ca. 750 Ma

The mid-Neoproterozoic (ca. 750Ma) Uinta Mountain Group (UMG), northeast Utah, USA, records transgressions of an epicontinental sea at least 150 million years before inception of the Laurentian western passive margin. This work refines middle UMG stratigraphy by formalizing three lithostratigraphic formations and interpreting a sequence stratigraphic framework in the central part of the Uinta Mountains. Middle UMG marine and fluvial-deltaic facies associations comprise eight depositional sequences within a kilometer-thick upward-fining composite sequence. These depositional sequences form one progradational–aggradational (“lowstand”) sequence set (PASS) and one aggradational–progradational (“highstand”) sequence set (APSS). Depositional sequences were deposited within a tide- and wave-affected epicontinental seaway that received sediment from a south-flowing fluvial system proximally sourced in the Neoarchean southern Wyoming Province to the north and from a separate system of major, west-flowing trans-Laurentian rivers distally sourced in the Grenville orogen, the mid-continent granite province, and the Yavapai and Mazatzal provinces to the south and east.Middle UMG fluvial-marine paleogeography strengthens the genetic link with the coeval Big Cottonwood and Little Willow formations (Utah), the Chuar Group (Arizona), and upper Pahrump Supergroup (California), which collectively indicate a ca. 770–740Ma epicontinental seaway existed across much of western Laurentia before 700Ma rifting and 600Ma formation of the Cordilleran passive margin. Long-term marine transgression onto continental Laurentia was likely caused by supercontinent breakup, particularly rifting of the Tarim and South China blocks from the remainder of Rodinia. Poorly constrained autocyclic drivers (delta lobe switching, channel avulsion) and allocyclic drivers (climatic fluctuations, local tectonism) controlled higher frequency depositional cycles superimposed on this long-term transgression. Western Laurentia thus records prolonged (750–600Ma) episodic basin formation, mafic volcanism, and faulting before establishment of a continental terrace after 600Ma. The Neoproterozoic western Laurentian epicontinental seaway can be used as a tie-point with other continents to help constrain the original continental configuration of Rodinia.

Allostratigraphy of the Upper Cretaceous Cardium Formation in subsurface and outcrop in southern Alberta, and correlation to equivalent strata in northwestern Montana

Abstract The Cardium Formation is a shallow marine clastic unit of upper Middle Turonian to Lower Coniacian age that was deposited in a ramp setting on the western side of the Western Canada foreland basin. The regional subsurface and outcrop stratigraphy of the Cardium is well-known in northern and central Alberta, but is poorly-known in southern Alberta. A correlation grid of >1200 well logs allowed allomember-bounding erosion surfaces E1 to E7 of the Cardium Formation to be traced across southern Alberta and into northern Montana. Twenty-five outcrop sections in Alberta and Montana were correlated to this stratigraphic framework. Two new bounding unconformities, designated E5.2 and E5.5 were recognized. Both surfaces onlap onto surface E5 towards the NW, showing that the original E5 surface is a composite of three unconformities. The lower Raven River allomember below E5 contains the most basinally-extensive sandstone and is composed of eastward-inclined clinothems indicative of long-term regression. The lower Raven River contains ammonites representative of four Upper Turonian Zones. The overlying upper Raven River and lower and upper Dismal Rat allomembers become progressively muddier upward and form a retrogradational stacking pattern, indicative of long-term transgression. Ammonites and bivalves locate the Turonian-Coniacian boundary just above the E5.5 surface. The E6.5 surface, originally recognized in the Willesden Green area, has been traced over the entire study area, confirming its importance as a major bounding discontinuity. The E7 surface has major erosional relief (>35 m in places) across southern Alberta. Overall, Cardium allomembers between E1 and E5 have a progradational stacking pattern. Allomembers between E5 and E6 are retrogradational whereas those between E6 and E7 are again progradational. Correlation of the Cardium in well logs from Alberta to outcrop of coeval rocks of the Marias River Formation at Ferdig and Deer Creek in Montana, supplemented by biostratigraphic information, suggests that the upper 8–16 m of the Ferdig Member is of Early Coniacian age. The new correlations imply that the top of the Carlile Formation, defined in subsurface, is not the Turonian-Coniacian boundary, as indicated by previous authors, but instead is equivalent to the E7 surface, which defines the top of the Cardium alloformation, and is of Early Coniacian age.

Community replacement of neritic carbonate organisms during the late Valanginian platform demise: A new record from the Provence Platform

The Valanginian is marked by a major platform demise inducing a hiatus in the northern Tethyan neritic carbonate record from the top of the lower Valanginian to the lower Hauterivian. New biostratigraphic and chemostratigraphic data from the Ollioules section (Provence Platform, southern France) are presented here, demonstrating that a large part of the upper Valanginian is preserved in an inner platform environment. The thick, upper Valanginian, aggrading carbonate succession is observed in an aborted rift domain, implying relatively low subsidence. In this context, a relatively long-term sea-level rise was required to sustain a keep-up style of carbonate production. Like the Apulian Platform, the remarkable preservation of the Provence Platform may have been favored by its remoteness from terrigenous source areas, as suggested by the low clastic inputs and low P-accumulation rates. Two main biotic community replacements are observed in Ollioules. The first saw the development of abundant microbialites and algae at the onset of the late Valanginian. A Tubiphytes concentration occurred during the coolest climatic conditions and the transition towards arid conditions, whereas the subsequent Lithocodium–Bacinella and orbitolinids assemblages developed under low nutrient conditions during a warmer interval. Both assemblages may have been triggered by increased alkalinity. The second community replacement saw the installation of coral- and rudist-dominated communities during the latest Valanginian to early Hauterivian. They indicate a change to oligotrophic, open marine conditions. Six medium-scale sequences have been defined in Ollioules, indicating short-term transgressive–regressive trends superimposed on a long-term transgression. Low nutrient inputs and relatively low subsidence in an aggradational context may explain the survival of the isolated Provence Carbonate Platform during a time of widespread drowning episodes and platform demise in the northern Tethyan domain.

The transgressive infill of an inherited-valley system: The Springhill Formation (lower Cretaceous) in southern Austral Basin, Argentina

The Berriasian–Valanginian Springhill Formation of the Austral Basin of southern South America comprises fluvial to marine deposits. In order to interpret depositional systems and unravel the stratigraphic architecture of this unit in the southern region of the basin (Tierra del Fuego Province, Argentina), 500 m of cores combined with well-log data from 41 wells were studied. Facies associations corresponding to fluvial (A1–A6), estuarine (B1–B5) and open-marine (C1–C4) depositional environments were identified. These facies associations succeed each other vertically across the entire study area (6800 km 2) forming a ∼120-m-thick transgressive succession. This unit filled a north-south-oriented valley system, developed in the underlying Jurassic volcanic complex. Lowstand fluvial deposits of the first stage of the valley-system fill occur in downdip segments of the system above a sequence boundary (SB). These fluvial deposits are overlain by coastal-plain and tide-dominated estuarine strata across an initial transgressive surface (ITS). In the northern sector the earliest valley infill is characterized by a transgressive fluvial succession, overlying a merged SB/ITS that is probably time-equivalent of marginal-marine deposits of the southern sector. The fluvial strata in the north are overlain by wave-dominated estuarine deposits. A drastic change to open-marine conditions is marked by a marine flooding surface, with local evidence of marine erosion (FS-RS). Open-marine strata are thin (<10 m) and dominated by lower-shoreface and offshore-transition deposits. They are capped by a younger flooding surface (FS), which represents the onset to offshore conditions across the study area due to a continuous long-term transgression that persisted until the Barremian. Although the interpreted depositional systems and stratigraphic architecture of the Springhill Formation resemble transgressive incised-valley-fill successions, the greater thickness and larger size of the Springhill valleys suggest inherited rift topography rather than valley development during a relative sea-level fall.

Sedimentary evolution of an Upper Jurassic epeiric carbonate ramp, Iberian Basin, NE Spain

Abstract A synthesis of the sedimentary evolution of the Upper Jurassic carbonate epeiric ramps that developed in the northern part of the Iberian Basin (NE Spain) is presented. The facies distributions reconstructed from the analysis of a 200 km-long transect, show a transition from shallow to relatively deep sedimentation sites. The studied carbonate ramps record major long-term transgression, from mid-Oxfordian to mid-Kimmeridgian followed by progressive basinwards coastal shift until the major regressive event around the mid-Berriasian. Subsidence was relatively homogeneous across the northern Iberian Basin during most of the studied interval. Major episodes of differential subsidence occurred around the Oxfordian–Kimmeridgian transition and onwards from the mid-Tithonian. The sedimentary evolution and particular facies types of the successive Iberian carbonate ramps is described, considering five depositional sequences that have a long-term transgressive-regressive evolution. The Oxfordian sequence shows a sharp transition from shallow to deep ramp areas: from mixed siliciclastic-carbonate (ooidal, skeletal, peloidal) facies to condensed (i.e. spongiolithic, peloidal, glauconitic) facies in the open platform domain. In the two Kimmeridgian sequences (Kim1 and Kim2), the transition between shallow and deep areas is more gradual and thickness distribution across the ramp is more homogeneous. Coral-microbial reefs and oolitic-peloidal-skeletal shoals characterized the shallow areas. Towards the offshore domain, these facies grade rapidly to a tempestite-dominated lithofacies and then into thick lime mudstone successions (i.e. rhythmic marls-mudstone alternations). Shallow oncolitic-peloidal and skeletal facies covered wide areas of the carbonate ramp during the early Tithonian (Ti1 sequence) and graded basinwards to thick successions of well-bedded micrites. The middle Tithonian to lower Berriasian platform (Ti2 sequence) is only partly exposed and formed during a stage of more heterogeneous subsidence. It is characterized by a thick succession with metre-scale shallowing-upward sequences with local development of peritidal, algal-laminated caps. The factors that controlled the sedimentary evolution and major facies changes across the successive epeiric carbonate ramps are discussed by comparison to other Upper Jurassic platforms developed in the western Tethyan realm.

Controls and evolution of facies patterns in the Upper Barremian–Albian Levant Platform in North Sinai and North Israel

Abstract The Upper Barremian–Albian Levant Platform was studied in North Sinai and Israel (Galilee and Golan Heights) by bio- and lithostratigraphy, facies analyses, and sequence stratigraphy. Integrating shallow-marine benthic foraminifera (mainly orbitolines), ammonite, and stable isotope data resulted in a detailed stratigraphic chart. Transects across the shallow shelf in both regions are based on facies analysis and form the basis for depositional models. In both transects five platform stages (PS I–V) were identified, which differ significantly in their stratigraphic architecture, mainly controlled by local tectonics, climate and second-order sea-level changes. In North Sinai, a transition from a shallow-shelf that is structured by sub-basins through a homoclinal ramp into a flat toped platform is recognized, while the sections in North Israel show a transition from a homoclinal ramp into a fringing platform. Local normal faults influenced the depositional architecture of the Upper Barremian–Lower Aptian strata in North Sinai and were attributed to syn-rift extensional tectonics. Four second-order sequence boundaries were identified, bounding Mid-Cretaceous Levant depositional sequences. These well-dated second-order sequence boundaries are MCL-1 (Late Barremian), MCL-2 (earliest Late Aptian), MCL-3 (Lower Albian), and MCL-4 (Late Albian). The sea-level history of the Levant Platform reflects the Late Aptian–Albian global long-term transgression, while the second-order sea-level changes show good correlation with those described from the Arabian plate.

Architectural Characterization and Three-Dimensional Modeling of a Carbonate Channel Levee Complex: Permian San Andres Formation, Last Chance Canyon, New Mexico, U.S.A.

Abstract Complete understanding of outcrop-scale stratal architectures requires extrapolation of two-dimensional depositional cross sections into three dimensions. This study integrates a high-resolution digital outcrop model with outcrop observations to create a three-dimensional geologic model of distal outer-ramp carbonate stratigraphy. Data were taken from sinuous canyon-wall exposures of the Permian San Andres Formation of Last Chance Canyon, New Mexico. A series of laterally extensive carbonate benches previously interpreted as constructional sponge mud mounds are here modeled as a channel–levee complex that is characterized by an alternating history of aggradation punctuated by erosional sediment bypass. Levee mudstones have an erosional base, contain dolomitized peloidal thin beds, and have limited faunal constituents. Primary levees were initiated as a carbonate apron and transformed into a low-relief channel–levee system as a result of deposition by dilute turbidity currents. Subsequent sediment bypass incised through the pre-established channels and into the underlying facies. The fill consists of skeletal packstone lags and fine peloidal packstones, which are correlated to coral- and sponge-bearing secondary levee deposits that drape the primary levees. Debrites, also found within some channelized areas, are thought to represent channel-margin oversteepening and slumping. Channel widths range from approximately 300 to 800 m, and channel-to-levee relief reaches up to 40 m. Three-dimensional surface models representing architectural elements of the channel–levee complex confirm outcrop observations. Surfaces that were modeled as a best fit to the three-dimensional outcrop tracings reveal development of low-sinuosity channels in previously established bathymetric lows created by earlier phases of sediment bypass and erosion. Sequence stratigraphic interpretations suggest that the channel–levee complex developed during the highstand part of a long-term transgression. The overall transgressive setting led to generation of substantial quantities of carbonate mud in more proximal areas of the ramp. Accumulated mud in the source region was transported down depositional dip during highstand parts of high-frequency cycles and resulted in growth of the levees. Carbonate channel–levee complexes are not likely to form during highstand sequences in which the source sediment is grain-dominated. Leveed channels are a viable component of deep-water carbonate settings and may be more common than has been previously recognized. Complex stratal architectures found in this channel–levee complex could be analogous to apparently gullied slopes of muddy carbonate ramps, especially those developed in transgressive sequences.

Relative Sea-Level Changes Recorded on an Isolated Carbonate Platform: Tithonian to Cenomanian Succession, Southern Croatia

Abstract Superb sections of Tithonian to Cenomanian carbonates of the Adriatic (Dinaric) platform are exposed on the islands of southern Croatia. A succession approximately 1,800 m thick consists exclusively of shallow-water marine carbonates (limestone, dolomitized limestone, dolomite, and intraformational breccia), formed in a protected and tectonically stable part of the platform interior. Several phases of exposure and incipient drowning are recorded in the platform interior. Four are crucial for understanding the Late Jurassic to mid-Cretaceous evolution of the wider peri-Adriatic area: (1) latest Jurassic–earliest Cretaceous sea-level fall, (2) Aptian drowning, followed by (3) Late Aptian platform exposure, and (4) Late Albian–Early Cenomanian sea-level fall. Deciphering these complex events from the vertical and lateral facies distribution has led to an evaluation of facies dynamics and construction of a relative sea-level curve for the study area. This curve shows that long-term transgression during the Early Tithonian, Hauterivian, Early Aptian, and Early Albian, resulted in generally thicker beds deposited in subtidal environments of lagoons or shoals. Regression was characterized by shallowing-upward peritidal parasequences, with well-developed tidal-flat laminites commonly capped by emersion breccia and/or residual clay sheets (Early Berriasian, Barremian, Late Aptian, Late Albian). The southern part of the Dinarides was tectonically quiet during the Tithonian through Aptian; sea-level oscillations appear to have been the primary control on facies stacking. Some correlation exists between local sea-level fluctuations and the published global eustasy charts for the Tithonian through Aptian. A significant departure is recognized at the Albian–Cenomanian transition, suggesting that it was influenced by tectonics associated with the disintegration of the Adriatic (Dinaric) platform.

Spatial and temporal distribution of calcareous nannofossils along a proximal–distal transect in the Lower Jurassic of the Umbria–Marche Basin (central Italy)

Three Upper Pliensbachian/Lower Toarcian successions of the Umbria–Marche Basin were analysed for sedimentology and calcareous nannofossil content across a 120-km-long transect from proximal to distal areas with respect to the shallow Latium–Abruzzi Platform. The uppermost part of the Corniola Unit (Uppermost Pliensbachian) and the Marne di Monte Serrone Formation (p.p., Lower Toarcian; Polymorphum to Levisoni Ammonite Zones) that contains organic matter-rich levels were studied in the three localities. The analysis of the sedimentary structures in the studied successions indicates that the basin was a shallow-water system, above storm-wave base, during the Late Pliensbachian/Early Toarcian. The stratigraphic evolution of the sedimentary structures recorded in the studied localities shows that the Upper Pliensbachian corresponded to a regressive sedimentary interval, whereas a complete transgressive–regressive relative sea-level cycle occurred during the Lower Toarcian Polymorphum Zone. A further transgression occurred in the lowermost Levisoni Zone (Lower Toarcian). Changes from carbonate-dominated to marl-dominated sediments form decimetre- to metre-scale lithological units, that can be correlated from succession to succession, and may have resulted from short-term sea-level and/or palaeoenvironmental variations. The mean duration of these lithological units suggests that they formed in tune with the first orbital eccentricity cycle (100 ka). The analysis of calcareous nannofossil quantities (abundance per mm 2 of the smear slide, percentage, mean abundance) shows both spatial and temporal changes in the community structure. Schizosphaerella spp. and Crepidolithus crassus were more abundant in proximity to the shallow Latium–Abruzzi Platform. These two taxa were likely affiliated to oligotrophic conditions in marine surface waters, explaining why they were generally more abundant in carbonate-rich intervals than in marls. Mitrolithus jansae is interpreted as being a deep-dwelling species, which was more abundant during rising sea level in the earliest Toarcian. Species of the genera Lotharingius, Biscutum and Calyculus were more abundant when higher trophic conditions occurred, and were thus more common during periods of marl deposition. The stratigraphic distribution of calcareous nannoplankton and its interpretation in terms of palaeoecological affinities allow three main phases in the environmental evolution during the Early Toarcian anoxic event to be recognised. The first phase corresponds to a long-term transgression, and high-nannoplankton abundance in distal areas (mainly Lotharingius, Biscutum and Calyculus species) suggests high productivity that may have resulted from upwelling. The beginning of accumulation and preservation of organic matter in the sediments occurred during this phase. The scarcity of nannoplankton during the second phase may indicate oligotrophic conditions in surface waters, possibly due to water stratification during the highest sea-level stand. A high abundance of Schizosphaerella spp. and C. crassus is recorded in proximal areas, probably resulting from sporadic nutrient input from continental or shallow-platform areas. The maximum of organic matter preservation is recorded during this phase. During the third phase, relative sea-level fall and efficient water mixing by frequent storm events led to enhanced nannoplankton productivity in proximal and distal areas and to a decrease in organic matter accumulation in the Umbria–Marche Basin.

Sequence stratigraphy and sedimentary history of the Humber Group (Late Jurassic-Ryazanian) in the Outer Moray Firth (UKCS, North Sea)

The Humber Group in the Outer Moray Firth is an onlapping sedimentary succession of Late Oxfordian to Ryazanian age, recording a trend of continuously rising relative sea-level. Nineteen subordinate transgressive–regressive cycles (‘sequences’) have been identified in the numerous wells in the area. The identification of these sedimentary units throughout the study area is indispensable for the interpretation of its sedimentary history, and hence for the ability to predict the possibility of subtle stratigraphic traps. Transgression began during the Late Oxfordian in the North Buchan Graben and culminated in the Early Ryazanian, when only parts of the Halibut Horst and the Fladen Ground Spur remained exposed. Mapping of the onlap reveals the drowning from the south of a significant topographic relief, which was further enhanced by syndepositional rifting. Three structural grains affected sedimentation: (1) E–W (possibly a repeated reactivation of pre-Late Jurassic faults, e.g. North Halibut Graben: pre-Late Oxfordian to Middle Volgian); (2) NE–SW (e.g. Theta Graben: Late Oxfordian to Early Kimmeridgian; Highlander–Piper Ridge: Kimmeridgian to Mid-Volgian); (3) NW–SE (e.g. Witch Ground Graben: Early Volgian to Ryazanian). Sedimentation was initially dominated by coastal plain and shoreface facies of marine-dominated deltas and estuaries (Piper Formation s.l. ), sourced mainly from the Fladen Ground Spur. From deposition of the upper Piper Formation onwards, intra-rift horsts, particularly the Halibut Horst, were also important sand sources. Deltaic systems back-stepped toward the basin flanks when accommodation space generation began to exceed sediment supply. Increased rifting in Early Volgian times triggered large-scale mass flow deposition from the Halibut Horst and from the East Piper High. Back-stepping shoreface systems continued their progressive onlap of the basin margins. Lowstand systems tracts in the individual sequences were muted by the overpowering long-term transgression, and significant mass flow deposits were not primarily controlled by the collapse of constructional highstand shelf margins. Instead, long-term tectonic uplift of specific areas sourced basin-margin submarine fan systems, typically confined to half graben on the flanks of the basin (e.g. Claymore sands), and basin-floor submarine channel systems in the core of the Witch Ground Graben (e.g. Galley sands). The potential for subtle stratigraphic traps is greatest in these turbiditic sandbodies where their boundaries are abrupt, as a result of channeling in self-constructed levees, or confinement by fault-induced seafloor topography.

Sequential Evolution of Lower Cretaceous Carbonate Platforms in the Maracaibo Basin, Venezuela

The sequence stratigraphic framework of the Upper Barremian to the Upper Cenomanian series was carried out in detail on cored material and well logs from Perija region and central part of Lake Maracaibo. Sediments are predominantly shallow marine carbonates (muddy lagoons, grainstone bars, pelecypod biostroms, intrabars), with an occasional siliciclastic input (nearshore sand bars, mixed tidal flats). Three second order cycles representing various stages of the evolution of the Cogollo platform have been identified. Cycle I (Upper Barremian-Lower Aptian) is a time transgressive unit, bounded at the base by backstepping sandstones (Rio Negro Formation) and at the top by a drowning unconformity (Machiques Member). Cycle II (Upper Aptian-Middle Albian) is a complete second-order cycle with a regressive phase followed by a long-term transgression. It corresponds mainly to the Apon Formation, and it is limited by two drowning unconformities: the Machiques at the base and the basal Lisure at the top. It is made up of 7 depositional sequences. They are slightly prograding during the regressive phase, aggrading and then backstepping during the transgression. Cycle III (Upper Albian-Upper Cenomanian) is another complete second-order cycle covering the Lisure, Maraca and La Luna Formations. The drowning unconformity at the top of the Maracamore » Formation is not the peak transgression, this one is at the top of La Luna Formation at the Cenomanian/Turonian boundary. Cycle III is made up of 15 depositional sequences. This sequence stratigraphic framework reveals that carbonate reservoirs of the Cogollo group are best developed at the top of highstand systems tracts.« less

On the model experiment of tsunami in Kesennuma Bay : Iwasaki, Toshio and Akira Miura, 1962. Coast. Engng Jap., 5: 49–57

The Valanginian is marked by a major platform demise inducing a hiatus in the northern Tethyan neritic carbonate record from the top of the lower Valanginian to the lower Hauterivian. New biostratigraphic and chemostratigraphic data from the Ollioules section (Provence Platform, southern France) are presented here, demonstrating that a large part of the upper Valanginian is preserved in an inner platform environment. The thick, upper Valanginian, aggrading carbonate succession is observed in an aborted rift domain, implying relatively low subsidence. In this context, a relatively long-term sea-level rise was required to sustain a keep-up style of carbonate production. Like the Apulian Platform, the remarkable preservation of the Provence Platform may have been favored by its remoteness from terrigenous source areas, as suggested by the low clastic inputs and low P-accumulation rates. Two main biotic community replacements are observed in Ollioules. The first saw the development of abundant microbialites and algae at the onset of the late Valanginian. A Tubiphytes concentration occurred during the coolest climatic conditions and the transition towards arid conditions, whereas the subsequent Lithocodium–Bacinella and orbitolinids assemblages developed under low nutrient conditions during a warmer interval. Both assemblages may have been triggered by increased alkalinity. The second community replacement saw the installation of coral- and rudist-dominated communities during the latest Valanginian to early Hauterivian. They indicate a change to oligotrophic, open marine conditions. Six medium-scale sequences have been defined in Ollioules, indicating short-term transgressive–regressive trends superimposed on a long-term transgression. Low nutrient inputs and relatively low subsidence in an aggradational context may explain the survival of the isolated Provence Carbonate Platform during a time of widespread drowning episodes and platform demise in the northern Tethyan domain.