Major Transgressive-regressive Cycles Research Articles

Middle Eocene–early Miocene planktonic foraminiferal biostratigraphy, chronostratigraphy, sea‐level reconstruction and sequence biostratigraphy at N. ElFaras‐1Xwell, Qattara Depression, Western Desert, Egypt

The planktonic foraminiferal assemblages are tracked in the middle Eocene–early Miocene succession within N. El Faras‐1X Well, Qattara Depression, Egypt. This succession is composed mainly of three lithostratigraphic units the upper part of the Apollonia Formation (middle to late Eocene), Dabaa Formation (late Eocene and Oligocene) and the lower part of the Moghra Formation (early Miocene). Biostratigraphically, the recorded 77 planktonic foraminiferal species enabled the recognition of 12 planktonic foraminiferal biozones; 4 biozones belong to middle to late Eocene, 7 biozones belong to the Oligocene and 1 belongs to the early Miocene. The proposed biozones were compared with their equivalents in other Egyptian regions and other schemes. Eleven Lowest Occurrence and two Highest Occurrence planktonic foraminiferal bioevents were also recognized and correlated all over the world. The chronostratigraphy and the stage boundaries were mainly delineated according to the diagnostic planktonic foraminifera. The middle–late Eocene boundary (Bartonian–Priabonian boundary), The Eocene–Oligocene boundary (Priabonian–Rupelian boundary), the early Oligocene–late Oligocene boundary (Rupelian–Chattian boundary) and the Oligocene–Miocene boundary (Chattian–Aquitanian boundary) were accurately determined. Based on the % P, the palaeobathymetry was estimated and hence the sea‐level fluctuation. The reconstructed sea‐level curve revealed two major transgressive–regressive cycles with minor oscillation within them. These events were globally correlated and match in most parts with that of the worldwide sea‐level curves. The sequence stratigraphy framework consists mainly of two transgressive–regressive (T–R) depositional sequences (DS1 and DS2). The DS1 includes the TST1 below which is capped by mfs1 and the HST1 above. The DS2 involves the TST2 below that was capped by mfs2 and the HST2 above.

Relative sea-level change in western New Guinea recorded by regional biostratigraphic data

We present new biostratigraphic analyses of approximately 200 outcrop samples and review biostratigraphic data from 136 public domain exploration wells across western New Guinea. Biostratigraphic ages and palaeodepositional environments were interpreted from occurrences of planktonic and larger benthic foraminifera, together with other fossils and environmental indicators where possible. These data were compared with existing geological maps and exploration well data to reconstruct the palaeogeography of western New Guinea from the Carboniferous to present day. In addition, we used the known bathyal preferences of fossils to generate a regional sea-level curve and compared this with global records of sea-level change over the same period. Our analyses of the biostratigraphic data identified two major transgressive-regressive cycles in regional relative sea-level, with the highest sea levels recorded during the Late Cretaceous and Late Miocene and terrestrial deposition prevalent across much of western New Guinea during the Late Paleozoic and Early Mesozoic. An increase in the abundance of carinate planktonic foraminifera indicates a subsequent phase of relative sea-level rise during a regional transgressive event between the Late Jurassic and Late Cretaceous. However, sea-levels dropped once more during a regressive event between the Late Cretaceous and the Paleogene. This resulted in widespread shallow water carbonate platform development in the Middle to Late Eocene. A minor transgressive event occurred during the Oligocene, but this ceased in the Early Miocene, likely due to the collision of the Australian continent with intra-Pacific island arcs. This Miocene collision event resulted in widespread uplift that is marked by a regional unconformity. Carbonate deposition continued in platforms that developed in shallow marine settings until these were drowned during another transgressive event in the Middle Miocene. This transgression reached its peak in the Late Miocene and was followed by a further regression culminating in the present day topographic expression of western New Guinea.

Tectonically controlled sedimentation: impact on sediment supply and basin evolution of the Kashafrud Formation (Middle Jurassic, Kopeh-Dagh Basin, northeast Iran)

The Kashafrud Formation was deposited in the extensional Kopeh-Dagh Basin during the Late Bajocian to Bathonian (Middle Jurassic) and is potentially the most important siliciclastic unit from NE Iran for petroleum geology. This extensional setting allowed the accumulation of about 1,700 m of siliciclastic sediments during a limited period of time (Upper Bajocian–Bathonian). Here, we present a detailed facies analysis combined with magnetic susceptibility (MS) results focusing on the exceptional record of the Pol-e-Gazi section in the southeastern part of the basin. MS is classically interpreted as related to the amount of detrital input. The amount of these detrital inputs and then the MS being classically influenced by sea-level changes, climate changes and tectonic activity. Facies analysis reveals that the studied rocks were deposited in shallow marine, slope to pro-delta settings. A major transgressive–regressive cycle is recorded in this formation, including fluvial-dominated delta to turbiditic pro-delta settings (transgressive phase), followed by siliciclastic to mixed siliciclastic and carbonate shoreface rocks (regressive phase). During the transgressive phase, hyperpycnal currents were feeding the basin. These hyperpycnal currents are interpreted as related to important tectonic variations, in relation to significant uplift of the hinterland during opening of the basin. This tectonic activity was responsible for stronger erosion, providing a higher amount of siliciclastic input into the basin, leading to a high MS signal. During the regressive phase, the tectonic activity strongly decreased. Furthermore, the depositional setting changed to a wave- to tide-dominated, mixed carbonate–siliciclastic setting. Because of the absence of strong tectonic variations, bulk MS was controlled by other factors such as sea-level and climatic changes. Fluctuations in carbonate production, possibly related to sea-level variations, influenced the MS of the siliciclastic/carbonate cycles. Carbonate intervals are characterized by a strong decrease of MS values indicates a gradual reduction of detrital influx. Therefore, the intensity of tectonic movement is thought to be the dominant factor in controlling sediment supply, changes in accommodation space and modes of deposition throughout the Middle Jurassic sedimentary succession in the Pol-e-Gazi section and possibly in the Kopeh-Dagh Basin in general.

Relative sea-level change, climate, and sequence boundaries: insights from the Kimmeridgian to Berriasian platform carbonates of Mount Salève (E France)

The present study analyses the stratal architecture of the Late Jurassic (Kimmeridgian) to Early Cretaceous (Berriasian) sedimentary succession of Mount Saleve (E France), and four Berriasian stratigraphic intervals containing four sequence-boundary zones reflecting lowering trends of the relative sea-level evolution. Massive Kimmeridgian limestones characterized by the presence of colonial corals appear to be stacked in an aggrading pattern. These non-bedded thick deposits, which are interpreted to have formed in balance between relative sea-level rise and carbonate accumulation, suggest a keep-up transgressive system. Above, well-bedded Tithonian-to-Berriasian peritidal carbonates reflect a general loss of accommodation. These strata are interpreted as a highstand normal-regressive unit. During the early phase of this major normal regression, the vertical repetition of upper intertidal/lower supratidal lithofacies indicates an aggrading depositional system. This is in agreement with an early stage of a highstand phase of relative sea level. The Berriasian sequence-boundary zones investigated (up to 4 m thick) developed under different climatic conditions and correspond to higher-frequency, forced- and normal-regressive stages of relative sea-level changes. According to the classical sequence-stratigraphic principles, these sequence-boundary zones comprise more than one candidate surface for a sequence boundary. Three sequence-boundary zones studied in Early Berriasian rocks lack coarse siliciclastic grains, contain a calcrete crust, as well as marly levels with higher abundances of illite with respect to kaolinite, and exhibit fossilized algal-microbial laminites with desiccation polygons. These sedimentary features are consistent with more arid conditions. A sequence-boundary zone interpreted for the Late Berriasian corresponds to a coal horizon. The strata above and below this coal contain abundant quartz and marly intervals with a higher kaolinite content when compared to the illite content. Accordingly, this Late Berriasian sequence-boundary zone was formed under a more humid climate. The major transgressive–regressive cycle of relative sea level identified and the climate change from more arid to more humid conditions recognized during the Late Berriasian have been reported also from other European basins. Therefore, the Kimmeridgian to Berriasian carbonate succession of Mount Saleve reflects major oceanographic and climatic changes affecting the northern margin of the Alpine Tethys ocean and thus constitutes a reliable comparative example for the analysis of other coeval sedimentary records. In addition, the stratigraphic intervals including sequence-boundary zones characterized in this study constitute potential outcrop analogues for sequence-boundary reflectors mapped on seismic profiles of subsurface peritidal carbonate successions. The detailed sedimentological analyses provided here highlight that on occasions the classical principles of sequence stratigraphy developed on seismic data are difficult to apply in outcrop. A sequence-boundary reflector when seen in outcrop may present successive subaerial exposure surfaces, which formed due to high-frequency sea-level changes that were superimposed on the longer-term trend of relative sea-level fall.

Middle-Miocene (Serravallian) temperate carbonates in a seaway connecting the Atlantic Ocean and the Mediterranean Sea (North Betic Strait, S Spain)

Miocene deposits in the contact area between the Prebetic and Subbetic domains (Betic Cordillera, S Spain) record the last stages of marine deposition on the southern Iberian margin and the final closure of the North Betic Strait in the early Tortonian (Late Miocene). Serravallian (Middle Miocene) shallow-water carbonates and mixed carbonate–siliciclastics formed on a platform at the southern margin of the North Betic Strait. These shallow-water deposits, informally termed the La Escalera Formation, onlap an erosion surface carved into underlying Miocene and older rocks. Carbonate components are mainly bryozoans, coralline red algae, molluscs, and benthic and planktonic foraminifers, typical of heterozoan lithofacies. Several facies types can be distinguished based on different grain sizes and sedimentary structures. Large-scale geometries and stratigraphic facies relationships indicate that the La Escalera Formation was deposited on a homoclinal ramp attached to a deeply eroded, emergent relief to the south. A beach system developed at the southern margin, with backshore lagoons and local incursions of coarse terrigenous sediments. Seawards of the beach system was a submarine-dune belt that extended over several square kilometres at the northeastern end of the La Escalera Formation. Longshore currents shifted submarine dunes to the northeast. Maximum production of carbonate skeletons took place seawards of the dune field. From this factory area, skeletal debris was moved landwards and incorporated into the dunes and beaches, whereas other skeletal particles were transported downslope by storms and fed a facies belt with hummocky and swaley cross-stratified sediments. The finest-grained particles accumulated below a storm-wave base, along with significant planktic debris. Carbonate deposits change laterally westwards to terrigenous sediments formed in similar facies belts. Terrigenous influx limited carbonate production on the western part of the ramp by disturbing the growth of coralline algae and bryozoans. Vertical variations of facies within the formation depict a major transgressive–regressive cycle, modulated by up to 10 higher-frequency cycles. Despite its location in an Atlantic-linked basin, the sedimentary model of the La Escalera Formation shows similarities to the models proposed for Neogene Mediterranean temperate carbonates, which imply a relatively low-energy regime on the ramp in comparison with the open-ocean platforms. This relatively low-energy regime can be explained by the position of the North Betic Strait at the eastern end of the Guadalquivir Basin. However, hummocky and swaley cross-stratified deposits are significantly more developed in La Escalera deposits than in known examples of Neogene Mediterranean carbonates.

Jurassic transgressions and regressions in the Caucasus (northern Neotethys Ocean) and their influences on the marine biodiversity

In the Jurassic, the Caucasus, presently located in the southwest of Russia, Georgia, Armenia and Azerbaijan, was located on the northern active margin of the Neotethys Ocean. Facies interpretation in all 62 areas, distinguished by differences in facies, allows to semi-quantitatively evaluate Jurassic regional transgressions and regressions for this region. Major transgressive regressive cycles took place in the Hettangian–Aalenian, Bajocian–Bathonian and Callovian–Tithonian. Each transgression was more extensive than the previous. The same cycles are established in the Greater Caucasus Basin. Deep-marine environments were common in the Pliensbachian, late Aalenian and late Bathonian, whereas they were very restricted in the Late Jurassic. The Jurassic transgressions and regressions in the Caucasus coincided with the proposed global eustatic changes. However, some differences were caused by the regional tectonic activity. Although transgressions and regressions cause some changes in marine biodiversity, it seems that only ammonites might have been directly influenced by them. Diversity of bivalves, brachiopods and belemnites was driven by other factors. However, global changes in marine biodiversity were more closely related to the eustatic fluctuations than it was documented on a regional scale.

Sea‐level changes, river activity, soil development and glaciation around the western margins of the southern North Sea Basin during the Early and early Middle Pleistocene: evidence from Pakefield, Suffolk, UK

AbstractThis paper outlines evidence from Pakefield (northern Suffolk), eastern England, for sea‐level changes, river activity, soil development and glaciation during the late Early and early Middle Pleistocene (MIS 20–12) within the western margins of the southern North Sea Basin. During this time period, the area consisted of a low‐lying coastal plain and a shallow offshore shelf. The area was drained by major river systems including the Thames and Bytham. Changes in sea‐level caused several major transgressive–regressive cycles across this low‐relief region, and these changes are identified by the stratigraphic relationship between shallow marine (Wroxham Crag Formation), fluvial (Cromer Forest‐bed and Bytham formations) and glacial (Happisburgh and Lowestoft formations) sediments. Two separate glaciations are recognised—the Happisburgh (MIS 16) and Anglian (MIS 12) glaciations, and these are separated by a high sea level represented by a new member of the Wroxham Crag Formation, and several phases of river aggradation and incision. The principal driving mechanism behind sea‐level changes and river terrace development within the region during this time period is solar insolation operating over 100‐kyr eccentricity cycles. This effect is achieved by the impact of cold climate processes upon coastal, river and glacial systems and these climatically forced processes obscure the neotectonic drivers that operated over this period of time. © British Geological Survey/Natural Environment Research Council copyright 2005. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.

Depositional architecture and transgressive–regressive cycles within Liassic backstepping carbonate ramps in the Basque–Cantabrian basin, northern Spain

An integrated stratigraphical, sedimentological, geochemical and sequential analysis has been carried out on the Liassic rocks of the Basque–Cantabrian basin in northern Spain using outcrop and subsurface data. The study documents the progressive drowning and backstepping of an epeiric carbonate ramp that originated during the worldwide late Triassic–early Jurassic transgression. Two major carbonate depositional systems have been recognized within the drowning succession: (1) a late Triassic–early Sinemurian shallow-marine ramp, which reflects a progressive marine transgression over Triassic continental deposits; (2) a late Sinemurian–Toarcian set of hemipelagic ramps, which recorded the progressive drowning and backstepping of the ramp system during a second major event of marine flooding. Sequence stratigraphic analysis of the Liassic succession has revealed that transgressive–regressive trends constitute the most evident cyclicity. A major transgressive–regressive cycle and six subsidiary transgressive–regressive facies cycles have been defined in the basin and compared with those defined in other European basins. Although a good correlation exists for the major transgressive–regressive cycle, significant discrepancies have been found for the number, limits and extent of the transgressive–regressive facies cycles reflecting the effects of local tectonics. The overall backstepping within the Basque–Cantabrian basin resulted in a dominance of transgressive episodes across a range of different scales. Accordingly, regressive intervals are less well developed except during limited periods of active tectonics as occurred in the mid-Sinemurian. These progressively longer and deeper marine flooding intervals, followed by relative stillstand or minor sea-level falls, are interpreted to reflect high thermal subsidence rates coupled with a Liassic eustatic transgression.

New algae and problematica of algal affinity from the permian of the Aseelah Unit of the batain plain (East Oman)

Permian microfloras occur in limestone boulders of the Aseelah Unit at the lower part of the Batain Group (NE Oman). The boulders are composed of bioclastic limestones deposited during the Permian on a shallow marine warm shelf environment. They yield several rich associations of Dasycladales, tubiphytids and Archaeolithophyllaceae indicating a Yakhtashian to Dzhulfian age (dated by fusulinids). The algal-bearing Aseelah Unit overlies conformably the Permian Qarari Unit deposited on the distal slope of the Arabian carbonate platform. The conglomerate and sandstone sheddings of the Aseelah Unit indicate the end of a major transgressive-regressive cycle at the Permian/Triassic boundary. The oldest age of the depositional event is given by the Dzhulfian age of the youngest reworked boulders. The age of the sandstones and sandy matrix is not well established; it is post-Dzhulfian, probably Triassic on the basis of some palynological indications. Several new taxa are described: Aphralysiaceae nov. fam., Sparaphralysia orientalis nov. sp., Mellporellopsis corpulenta nov. gen. nov. sp., Aseelahella granieri nov. gen. nov. sp., Claracrustinae nov. subfam., Claracrusta ungdarelloidea nov. sp. and Sphairionia galinae nov. sp.

Palynology and sequence stratigraphy of the Cretaceous of eastern Venezuela

From Jurassic to Tertiary times, northeastern Venezuela represented the continental shelf of a tectonically passive margin. A dominantly marine Cretaceous sedimentary section, within an overthrusted allochthonous block and with a maximum thickness of 3658 m, is found in the subsurface in this area. Palynomorph recovery from these strata, together with planktonic foraminifera and calcareous nannofossils, indicate an age-range from at least Aptian to Maastrichtian. The palynological assemblages observed exhibit changes with time and environments, which are here related to the sedimentary evolution. Integrated analyses of palynology, lithology, and well logs are the basis for the reconstruction of the sedimentary evolution in the area. The oldest marine sediments in this section correspond to the uppermost part of the Lower Zuni Megacycle and contain a maximum flooding surface correlative with that dated at 111Ma. The rest of the sequence represents a major transgressive-regressive cycle (Upper Zuni) and contains seven sequences correlative with global eustatic cycles. The Turonian transgression dated at 91.5Ma is the most important marine transgression in the entire section and is recognizable in all sections studied, while the Maastrichtian-Paleocene boundary dated at 68Ma is not always clearly recognizable.

EVIDENCE OF A GUADALUPIAN AGE FOR THE KHUFF FORMATION OF SOUTHEASTERN OMAN: PRELIMINARY REPORT

The Guadalupian succession of the Huqf area (Sultanate of Oman) represents a mega-sequence comprising the fluvial terrigenous Gharif Formation and the overlying marine Khuff Formation. The Khuff Fm. is subdivided into four members and is composed of marls and bioclastic limestones. The Khuff Fm. yields a rich fauna of brachiopods, conodonts, foraminifers, bivalves, gastropods, ostracods and cephalopods. The brachiopod fauna of the Khuff Fm. includes strophomenids, productids, orthids and terebratulids. The associated conodont fauna includes Hindeodus excavatus Behnken, Merrilina sp., M. praedivergens Kozur & Mostler, and Sweetina n. sp. (systematic descriptions of conodonts are given in the Paleontological Appendix). Foraminifers are represented by species of Miliolina and Rotaliina. The Khuff Fm. is given a Wordian age, based on brachiopods and conodonts. The depositional environment of the Khuff Fm. of southeastern Oman corresponds to the outer shelf of a large carbonate platform covering most of the Arabian Platform. The Khuff Fm. is interpreted as a major transgressive-regressive cycle related to differential subsidence.

Stratigraphy of the Lower Paleozoic Haima Supergroup of Oman

ABSTRACT Following the discovery of significant gas/condensate reserves in Lower Paleozoic clastics in Central Oman a regional geological review using all available well data and a set of regional seismic lines was carried out by Petroleum Development Oman. The objective of this study was to support further appraisal and exploration activities. A chronostratigraphic framework of regional correlatable major flooding surfaces improved the understanding of the stratigraphic relationship between the different units and the regional distribution of the reservoir seal pairs. The interval of interest, the Cambrian to Lower Silurian Haima Supergroup, is a late syn- to post-rift siliciclastic infill of an extensive graben system. The depositional setting was initially continental but higher in the sequence of marine deltaic setting prevailed. The sequence is characterised by the occurrence of laterally extensive sand sheets typical of pre-vegetational times but difficult to interpret sedimentologically. At least six major transgressive regressive cycles can be recognised which can be regionally correlated. Marine intercalations are limited to Central and North Oman. The clastic influx into the grabens was initially of local origin but as the grabens filled up the sediments were predominantly derived from a southern source.

Stratigraphic record of the structural evolution of the western extensional margin of the Subalpine Basin during the Triassic and Jurassic, Ardeche, France

The nature and the geometry of Mesozoic deposits in the Ardeche region reflect the different stages of structural evolution of the western extensional margin of the Subalpine Basin. Through stratigraphic analysis of a broad transect passing from the Uzer block, through the GPF (“Géologie Profonde de la France”) borehole Balazuc 1 and two petroleum exploration wells on the different blocks of the margin, it has been possible to integrate data from borehole BAI in a sequential stratigraphic and regional dynamic framework, and to attempt to specify the modes of tectonic control on the organization of the deposits along a profile of this extensional palaeomargin. The Triassic and Jurassic deposits are composed of six major transgressive-regressive cycles for which the geometric and stratigraphic characteristics indicate that they were controlled by the tectonic evolution of the basin, and more specifically by variations in the type and rate of subsidence. The first two cycles, Anisian-early Sinemurian in age, correspond to the initial structural creation of the margin with a west-east sedimentary polarity. Extensional tectonism, which affected the Palaeozoic basement, in part controlled the duration and intensity of the transgressive phases, with the regressive phases reflecting a decrease in regional subsidence. The third and fourth cycles, early Sinemurian-middle Bathonian in age, were contemporaneous with the Tethyan rifting. In particular, they record evidence of decreasing regional subsidence, and even uplift, associated with block faulting. This caused strong tectonic decoupling and highly variable subsidence along the margin profile; episodes that are represented by that part of each sedimentary cycles deposited around the maximum regression, i.e. end of the regressive phase and beginning of the transgressive phase (Sinemurian and Aalenian). A regional phase of subsidence followed which allowed maximum expansion of the transgression (Toarcian and Bajocian transgressive peaks). The fifth and sixth cycles, middle Bath on ian-Kimmeridgian in age, were deposited during a period of widespread subsidence of the margin that was synchronous with the onset of Tethyain oceanic spreading. They preferentially record episodes of accelerated subsidence giving rise to transgressive phases generally associated with a synsedimentary tectonic activity that incurred relatively heterogeneous subsidence across the entire palaeomargin (late Bathonian and early Oxfordian). The regressive phases are subsequently marked by a decreased, but uniform subsidence with no evidence of uplift. The sediments of these last two cycles were deposited in a post-rift context and are liable to record effects of geodynamic events outside the basin. Characterization of the different stages in the evolution of the Ardeche palaeomargin by their stratigraphic expression provides geological constraints for modelling fluid migration throughout this extensional margin, the objective of the 'GPF Ardeche' project.

Facies variation, depositional setting and hydrocarbon potential of the Upper Cretaceous rocks in the United Arab Emirates

The Upper Cretaceous (Aruma Group) of the United Arab Emirates (UAE) was deposited over nearly 23 Ma. This was after a period of major erosional emergence in the Turonian. The variable thicknesses and lithofacies of the sediments of this group were controlled by regional subsidence induced by plate collision and partial subduction, eustatic sea-level fluctuations and differential sedimentation rates. The Upper Cretaceous in the southern UAE (Abu Dhabi region) consists of two major transgressive-regressive cycles involving the sediments of four formations, the Laffan, Halul, Fiqa and Simsima. In the central UAE (Dubai region) the group consists of the Laffan, Ilam, and Fiqa Formations, while in the northern UAE it consists of the Muti, Juweiza, Qahlah and Simsima Formations. The earliest Late Cretaceous sedimentation accompanied a marine transgression that probably began in the late Turonian, with the sea spreading to cover most of the UAE by Coniacian times. This marine event was marked by the deposition of basinal muds (not shales) and neritic marls. Later, during Santonian, neritic shelf carbonates were deposited. Subsequent subsidence in the early Campanian resulted in the accumulation of deep-water marls, argillaceous limestones and muds (shales). During the Maastrichtian, a widespread regression occurred, and neritic shelf bioclastic limestones and dolomites containing rudists and orbitoids were deposited on the shelf margin. Toward the centre of the basin, in the northern UAE, thicker, basinal, slope and shelf edge sediments were deposited resulting in a succession that consists mostly of marls, argillaceous limestones, cherts, conglomerates, sandstones and shales. Commercial hydrocarbons in the Upper Cretaceous are confined to the Simsima and Ilam Formations, which are the best potential exploration targets, particularly in the offshore of the northeastern Emirates in a belt parallel to the Oman Mountains. The basal part of the Upper Cretaceous is a major seal over middle Cretaceous reservoirs of the UAE.

Sequence Stratigraphy and Depositional Environments on a Palaeozoic Clastic Ramp Margin, Ahnet-Timimoun Basin, Algeria: ABSTRACT

A wide, ramp margin was developed during the Devonian/Carboniferous in the Ahnet-Timimoun Basin, Algerian Sahara. Variations in relative sea level resulted in rapid, long distance (>500km) lateral translations of the clastic facies belts; this was the main influence on the locations of sand depocentres. The geometry and distribution of both Gedinnian and Emsian shallow marine sandstones is complex. Understanding the influence of relative sea level, shelf processes and local tectonics is essential to predicting the distribution of potential reservoir units. The Silurian to Carboniferous succession preserved in the Ahnet-Timimoun Basin can be divided into two major Transgressive-Regressive cycles, each of approximately 45 million years duration (Ashigill to Siegenian; Siegenian to Tournaisian). The T-R cycles several sequences of approximately 10 million years duration. Major source the basin were deposited in the Early Silurian (Llandovery) and Late Devonian (Frasnian) around the transgressive maximum of the T-R cycles. In the Ahnet-Timimoun Basin, marine sedimentation prevailed across much of the ramp margin. During Gedinnian times (early Devonian), progradational events associated with each sequence deposited a succession of extensive, shallow marine, coarsening-up sandstones. The sequence boundary marking the regressive maximum. Of the first T-R cycle (Siegenian) resulted in a rapid transition from an inner shelfmore » environment to braided rivers which deposited a regional, high N/G sandstone. Sequence boundaries, although marked by rapid basinward shifts in facies belts, are without significant fluvial incision. The transgressive sequence set in the overlying T/R cycle, is marked initially by rapid southwards directed trangression and an extensive ravinement surface of early Emsian age.« less

INFLUENCE OF PLATE TECTONIC RE-ORGANISATIONS AND TECTONIC SUBSIDENCE ON THE MESOZOIC STRATIGRAPHY OF NORTHWESTERN AND SOUTHEASTERN AUSTRALIA: IMPLICATIONS FOR SEQUENCE STRATIGRAPHIC ANALYSIS

Determining and predicting the interplay of plate tectonic events, subsidence, flexure and depositional systems is important in frontier exploration, play concept development, and maturation modelling. A circum-Australian plate tectonic model is here tied to an internally consistent global plate tectonic model to determine the timing and orientation of changes in the lithospheric stress regime induced by plate tectonic changes. One-and three-dimensional geohistory results for the Otway Basin and North West Shelf/Exmouth Plateau are presented, based on an integrated sequence stratigraphic framework. These geohistory results compare the timing and types of changes in subsidence rate to the changes in lithospheric stress due to plate tectonic changes. Changes in tectonic subsidence rate appear to be discrete events related to plate tectonic changes; subsidence events bound major transgressive-regressive facies cycle packages ('supersequences') in a basin. The recognition of sequence system tracts and especially system tract boundaries within a 'supersequence' is enhanced or diminished by processes occurring only during certain phases of the supersequences. Recognition of lowstand systems tracts and sequence boundaries is improved due to erosion during the regressive phase of the supersequence. Conversely, during the transgressive phase of the supersequence, transgressive and highstand system tracts are emphasised and recognition of flooding surfaces improved. Good reservoir sands form during enhanced lowstands, while good source and sealing shales form during enhanced transgressions.In the southeastern Australian Otway Basin, every perturbation of the tectonic subsidence rate during the Late Cretaceous can be correlated directly to a local and/or global plate tectonic event, and each supersequence is bounded by tectonic events. In the North West Shelf/Exmouth Plateau region of Western Australia, the situation is complicated during the Berriasian by uncompensated f lexural load effects related to the rapid formation and filling of multiple Barrow Delta depocentres. Two supersequences correlate to tectonic events, while one supersequence is bounded by a f lexural subsidence event unrelated to regional or global plate tectonic events. Hence not all perturbations of the tectonic subsidence curve are related to tectonic events, and not all supersequences are bound by tectonic events. Without three-dimensional geohistory techniques, it is impossible to isolate the flexural load effects from the effects of plate tectonic events.

Late Cretaceous stratigraphy of the Upper Magdalena Basin in the Payandé-Chaparral segment (western Girardot Sub-Basin), Colombia

The Cretaceous section on the western margin of the Girardot Sub-Basin, Upper Magdalena Valley, is composed of the Lower Sandstone (Hauterivian-Barremian?), Tetuán Limestone (pre-Aptian?), and Bambuca Shale (pre-Aptian?), and the following formations: Caballos (Aptian-Albian), Villeta (Albian-Campanian), Monserrate (Campanian-Maastrichtian), and Guaduas (Maastrichtian-Paleocene). The Lower Sandstone is composed of quartz arenites with abundant calcareous cement; the Tetuúan Limestone is a succession of fossiliferous limestones and calcareous shales; the the Bambuca Shale is composed of black shales that grade upward to micritic limestones and calcarenites. The Caballos Formation comprises three members: a lower member of quartz arenites, a middle member of black shales and limestones, and an upper member of crossbedded, coarsening-upward quartz arenites. The Villeta Formation is a sequence of shales intercalated with micritic limestones and calcarenites. Two levels of chert (Upper and Lower Chert) are differentiated within the Villeta Formation throughout the study area, with a sandstone unit (El Cobre Sandstone) to the north. The Monserrate Formation is composed of quartz arenites, with abundant crossbedding, and locally of limestone breccias and coarse-grained fossiliferous packstones. The Guaduas Formation is a monotonous succession of red shales and lithic sandstones. Our data suggest three major transgressive-regressive cycles in the Girardot Sub-Basin. The first cycle (Hauterivian?-lower Aptian) is represented by the Lower Sandstone-Tetuán-Bambuca-lower Caballos succession, the second cycle (Aptian-Albian) by the middle-upper Caballos members, and the third cycle (Albian-Paleocene) by the lower Villeta-Monserrate-Guaduas succession. Previous studies proposed a eustatic control during deposition of the Upper Cretaceous in the Upper Magdalena Valley. The lowermost transgressive-regressive cycle was not previously differentiated in the study area, and this implies a transition between the thick Bogotá depocenter to the north and the thinner Magdalena basin fill to the south.

Depositional Environments, Lithofacies Types, and Reservoir Development of the Permian Khuff Formation in Eastern Saudi Arabia.

The Later Permian carbonates and evaporites of the Khuff Formation contain considerable amounts of gas in Ghawar field, eastern Saudi Arabia. Sedimentary structures, textures, and grain types were used to interpret the depositional environments and to define the different lithofacies types which determine the original reservoir face is distribution within this 1,500-ft-thick formation. There are three major depositional environments: subtidal, intertidal, and sabkha. Locally, these include shoals, belts, bars, bays, lagoons, ponds, tidal channels, sabkha. Locally, these include shoals, belts, bars, bays, lagoons, ponds, tidal channels, sabkha islands, and sabkha pans. Tidal flooding and storms are represented. These environments represent four major transgressive-regressive cycles, which conform to four Khuff units: Khuff A, B, C and D (from youngest to oldest). Transgressive phases (subtidal), with lithofacies of grainstones and horizontally burrowed mudstones usually comprise the reservoir facies. The regressive phases (intertidal and sabkha) with lithofacies of anhydritic mudstones and anhydrites, usually seal the Khuff reservoirs. Later disappearance of reservoir facies are due to deposition or diagenesis. Depositionally, the lateral change in facies may occur, for example, from a non-reservoir anhydrite and mudstone facies to a reservoir grainstone facies, or from a non-reservoir anhydritic mudstones to a reservoir burrowed-mudstone facies. Diagenetically, ooidmore » grainstones may be greatly cemented by anhydrite. A combination of dolomitization and leaching may create intercrystalline porosity in mudstone. Leaching creates poorly connected moldic porosity in grainstones because the resulting calcite cement plugs the interparticle porosity.« less

Relative Sea Level Changes During the Cretaceous in Israel

Detailed lithologic, microfaunal, and biometric investigations, using relative abundances, diversity indexes, and duration charts of ostracods and foraminifera, allowed the recognition of sea level changes during the Cretaceous of Israel. Three major transgressive-regressive sedimentation cycles occur on the northwest margins of the Arabian craton. These cycles are the Neocomian-Aptian, which is mostly terrigenous sediments; the Albian-Turonian, which is basin marls and platform carbonates; and the Senonian, which is uniform marly chalks. The cycles are separated by two major regional unconformities, the Aptian-Albian and Turonian-Coniacian boundaries. The sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes. The paleodepth curve il ustrates the gradual sea level rise, reaching its maximum during the Late Cretaceous, with conspicuous advances during the late Aptian, late Albian-Cenomanian, early Turonian, early Santonian, and early Campanian. Major lowstands occur at the Aptian-Albian, Cenomanian-Turonian, Turonian-Coniacian, and Campanian-Maastrichtian boundaries. This model for Israel agrees well with other regional and global sea level fluctuations. Four anoxic events (black shales) accompanying transgressions correspond to the Cretaceous oceanic record. We hypothesize the presence of mature oil shales in the present-day eastern Mediterranean basin close to allochthonous reef blocks detached from the Cretaceous platform.

Seismic Stratigraphy and Cenozoic Evolution of West Sumatra Forearc Basin

Late Tertiary (Neogene) sediments deposited in the Sunda forearc reveal the stratigraphic and structural evolution of this active plate margin. A dense grid of multichannel seismic reflection data and information from 17 exploratory wells were used to establish a detailed seismic-stratigraphic framework of the forearc region from 0° to 6°N. Several important tectonic cycles are recognized: Paleogene orogeny, Neogene subsidence, and late Tertiary tectonism. Superimposed on these regional tectonic events are three major transgressive-regressive cycles of sedimentation related to changes in sea level and provenance. Paleogene and older metasedimentary and metamorphic rocks comprise basement beneath the landward (inner) margin of the forearc basin. Both basement rocks and lower Tertiary sedimentary rocks were deformed and eroded approximately 25 to 30 Ma. The continental shelf was exposed to subaerial erosion, and basin deposits were restricted offshore, coincident with a worldwide lowstand of sea level in the Oligocene. The Paleogene orogeny probably occurred prior to the erosional event that cut the prominent angular unconformity on the shelf. The Neogene history of forearc basin development is characterized by subsidence and nearly continuous sedimentation. A basal transgression began in latest Oligocene time and culminated in the middle Miocene. Alternating sequences of limestone and shale comprise two second-order cycles of sedimentation that are superimposed on an overall transgressive event. A major regressive sequence followed in the Pliocene, owing to an influx of siliciclastic clay, silt, and sand derived from Sumatra. Sedimentation rates were high, and large volumes of terrigenous material were deposited in deltaic systems on the shelf. The shelf-slope break prograded basinward nearly 10 km (6 mi) through lateral accretion and aggradation during a relative highstand or stillstand of sea level.