Shallow-marine Siliciclastics Research Articles

The Upper Neoproterozoic lacustrine–fan delta depositional systems associated with braided alluvial fans in the Nubian Shield, Egypt

The present paper affords new data and results that enhance and refine the lacustrine and alluvial fan depositional models in the Precambrian. Well-exposed siliciclastic profiles along the intermontane Kareim Basin in the Nubian Shield signify an excellent occurrence of the Late Neoproterozoic lacustrine/fan delta and alluvial fan settings. Detailed sedimentologic data are integrated to define thirteen depositional facies that belong to six main facies associations (FA1 to FA6). Incorporation of facies architectures, physical sedimentary structures, stratigraphic relations and depositional patterns is used to suggest depositional models that comprise three interrelated depositional phases. The subaerial humid to semi-arid depositional phase of the braided alluvial fan has been suggested to interpret the sedimentological pattern and facies architecture of the conglomerate and sandstone deposits (FA1 to FA3) which are attributed to debris flow, sheet flood and copious braided stream processes. The depositional pattern of the transitional phase is represented by distributary channels and mouth bar strata (FA4) of a shoal-water fan delta that has indistinctive prodelta deposits and a non-vegetated delta plain of the fringing alluvial fan. The subaqueous phase demonstrates accumulations of sandstone and mudstone-dominated deposits (FA5–6) in wave-dominated lacustrine nearshore and offshore, under humid to semi-arid climates and recurrent short-aridity periods. This Neoproterozoic lake was characterized by relatively large extent, shallow depths, an insignificant profound zone and remarkable starvation of stromatolites, evaporites and carbonate sediments. Allogenic factors such as differential uplift and subsidence, climatic fluctuations and varied sediment supply control and modulate the depositional patterns and facies models. Outcome datasets and results can be applied in distinguishing lacustrine from shallow-marine siliciclastics, and may be of further help in discrimination of humid/semi-arid lakes from arid lakes and playas in the Precambrian non-vegetated and unfossiliferous successions.

The early middle Eocene transition at the Esera valley

An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulitesand Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12.

Macroinvertebrate fauna and depositional environment of the lower Upper Cenomanian Oberhäslich Formation in the Saxonian Cretaceous Basin (Germany)

In Saxony (southeast Germany), the global early Late Cretaceous transgression is reflected by the onlap of shallow-marine siliciclastics of the lower Upper Cenomanian Oberhäslich Formation (Calycoceras naviculare Zone) onto the eastern Erzgebirge, the central part of the emergent Mid-European Island. Based on detailed logging of sections south of Dresden and the study of extensive collection material, the depositional environment and macroinvertebrate assemblages of the Oberhäslich Formation have been reconstructed. This unit, with a mean thickness of 10–15m, usually shows a fining-upward trend that may become reversed towards the top, was laid down in a single 3rd-order sea-level cycle and is capped by an unconformity at the base of the overlying upper Upper Cenomanian Dölzschen Formation (sequence boundary Cenomanian 5; junction of the Calycoceras naviculare and Metoicoceras geslinianum zones). The macroinvertebrate assemblage of the Oberhäslich Formation, collected mainly from bioturbated, fine- or rarely medium-grained, quartz-rich sandstones, is fairly diverse, comprising nearly 50 taxa, predominantly bivalves (94.3%). Most conspicuous and abundant are relatively large forms such as Rhynchostreon (R.) suborbiculatum (25%) and Inoceramus pictus spp. (21%), eponymous taxa of the Rhynchostreon suborbiculatum/Inoceramus pictus assemblage. Non-bivalve benthic invertebrates are rare and represented by rather poorly preserved irregular and regular echinoids, siliceous sponges, a few gastropods, crustacean remains and a single starfish. Common Thalassinoides and Ophiomorpha burrows indicate that crustaceans were an important part of the infauna. Pervasive bioturbation resulted in a post-depositional homogenization of the sediments while all body fossils are preserved as (composite) internal moulds. The guild structure of the Rhynchostreon suborbiculatum/Inoceramus pictus assemblage shows a predominance of epifaunal and semi-infaunal suspension feeders (95.3%), suggesting eutrophic and unstable “green-water conditions” of an inner-shelf setting. Deposit-feeding biota are rare. The common occurrence of articulated bivalves and storm-induced shell beds indicate episodic rapid burial, most probably by tempestites. A current-influenced, well-oxygenated and nutrient-rich environment slightly below fair-weather base is inferred for the fine-grained sandy, fossiliferous sediments of the Oberhäslich Formation.

THE PERMIAN -TRIASSIC BOUNDARY, DEAD SEA, JORDAN: TRANSITIONAL ALLUVIAL TO MARINE DEPOSITIONAL SEQUENCES AND BIOSTRATIGRAPHY

The Permian to Triassic transition in Jordan is characterised by a sequence boundary underlain by red-bed, alluvial lithofacies deposited in a humid-tropical climate by low-sinuosity rivers, and overlain by shallow marine siliciclastics with thin carbonates. The low-gradient alluvial floodplain was repeatedly subjected to the development of ferralitic and pisolitic paleosols on the interfluves. In contrast, dysaerobic environments in the fluvial channels and abandoned lakes resulted in the preservation of a prolific flora of macro-plants and palynomorphs that indicate a probable range from Mid- to Late Permian age, though the abundant presence of the distinctive pollen Pretricolpipollenites bharadwajii indicates the youngest part of that range. Above the sequence boundary, reddened shallow-marine beds characterised by ripple cross-laminated, siltstones/sandstone with desiccation cracks and sparse surface burrows mark the initial Triassic marine transgression in the region (Arabian Plate Tr 10). These are followed by two thin limestone (packstone) beds with shallow scours and bivalve shell lags, that have yielded a low diversity assemblage of conodonts (e.g. Hadrodontina aequabilis ) and foraminifera (“ Cornuspira ” mahajeri ) that are interpreted as euryhaline taxa characterising the early Induan (Early Triassic). Thus the absence of body fossils and vertical infaunal burrows in the lowest marine beds may reflect low-diversity ecosystems following the Permian-Triassic extinction event, or be a result of stressed shallow marine environments. A gradational upward increase in grey, green and yellow siltstones beds accompanied by a concomitant increase in bioturbation (and infaunal vertical burrows) and thin-shelled bivalves about 15 m above the boundary indicates colonisation of the substrate under more normal shallow marine conditions perhaps indicating recovery phase following the extinction event.

Ediacaran Araba Complex of Jordan

ABSTRACTThe Ediacaran Araba Complex in Jordan is defined and described for the first time in lexicon style, with an emphasis on the sedimentary, volcanic and volcaniclastic units outcropping adjacent to Wadi Araba, and from seismic and deep exploration well data. The Araba Complex ranges in age from ca. 605 to 550 Ma and comprises a major cycle of sedimentary, volcanic and volcaniclastic, and igneous rocks emplaced in an overall extensional tectonic regime that followed intrusion and amalgamation of the granitoid and metamorphic Aqaba Complex, a part of the Gondwanan Arabian-Nubian Shield (ANS; ca. 900 to 610 Ma).The Araba Complex is bounded by two major erosional unconformities, the newly defined Ediacaran Araba Unconformity (ca. 605 Ma) at its base, underlain by the Aqaba Complex, and the post-extensional, regional lower Cambrian Ram Unconformity (ca. 530 Ma) that is marked by the widespread deposition of thick alluvial and marginal-marine siliciclastics (Ram Group).Two sub-cycles can be recognised in the Araba Complex mega-cycle. The earliest (Safi Group) followed suturing and extensional rifting of the Aqaba Complex that resulted in rapid basinal subsidence and the deposition of coarse-grained, polymict conglomerates (Saramuj Formation) in predominantly proximal, but evolving to more distal, alluvial fan settings. The early extensional basin appears to have been orientated approximately north-south (depocentre to the west) and can be traced from north Sinai to Lebanon, approximately parallel to the present-day Dead Sea Transform. Rounded clasts, up to boulder-size, include a variety of local to regionally-derived basement lithologies, including granites, diorites, metamorphic rocks; doleritic and rhyolitic dyke rocks. Rapid isostatic uplift and weathering of the granitoid basement resulted in high sediment flux that kept pace with rapid basin subsidence; this, in turn, led to erosion and partial peneplanation of the hinterland ANS. Regional detrital zircon ages from the conglomerate clasts and matrix indicate age ranges from ca. 650 to 600 Ma with a minor cluster between 750 to 700 Ma, indicating mostly a local or, at least, near-field provenance. Subsequent to this early, rapid basin-fill, continued crustal extension resulted in tapping of rhyolitic and basaltic effusive volcanics and volcaniclastics (Haiyala Volcaniclastics and Museimir Effusives, ca. 598–595 Ma), including flow-banded rhyolitic lavas and air-fall tuffs, the latter deposited in a lacustrine or shallow-water environments.The second Araba sub-cycle (595–586 Ma) is characterised by renewed basinal subsidence, very low burial metamorphism to about 6 km depth, and associated stock-like intrusion of the Qunaia Monzogabbro (595 ± 2 Ma) that resulted in thermal contact metamorphism of the Saramuj conglomerate, as well as granite plutons (e.g. Feinan-Humrat intrusions) and dolerite dykes. The second cycle is characterised by renewed extension, rifting and the deposition of volcanic rocks, agglomerates (Aheimir Volcanics) and monomict conglomerates (Umm Ghaddah Formation) that were sourced, locally, from volcanic rocks on the rift margins.To the east, in the sub-surface of south-central Jordan, the early Safi sub-cycle is absent. Deep exploration wells and seismic data in the Jafr area demonstrate that the Araba Complex comprises terrestrial lavas (Ma’an Formation) with weathered soil horizons, unconformably overlying weathered Aqaba Complex granitic basement (Araba Unconformity). Seismic data in the Jafr region records the eruption of lavas in north-south trending graben and half-graben settings, and possible northwest-trending bounding faults similar to the Najd basins in Saudi Arabia. Again, in contrast to the outcrop areas to the west, the upper part of the Araba Complex, hereabouts, consists of fine-grained, in part carbonate-cemented sandstone and claystone, together with anhydrite (Jafr Formation) suggesting a shallow-marine or coastal sabkha setting, and a possible link to similar shallow-marine extensional basin-fills that developed widely within NW-trending Najd basins across the ANS in Saudi Arabia (e.g. Jibalah and Antaq basins). To date, no Ediacaran biotas have been described from the Araba Complex, but the Jafr Formation, which post-dates the appearance of soft-bodied faunas around 579 Ma, and which was probably deposited in marginal-marine environments, is a potential candidate for these enigmatic fossils.Subsequent to the final Araba extensional rifting phase, renewed regional uplift, far to the south, of the ANS hinterland during the early Cambrian, led to widespread deposition of alluvial and shallow-marine siliciclastics as a progradational ‘sand-sea’ (Ram Group) that blanketed the now peneplained Aqaba Complex in south Jordan and surrounding countries (Ram Unconformity). However, the younger Ediacaran Araba Complex outcrops adjacent to Wadi Araba remained, in places, as a relatively immature palaeotopography. It was not until early mid-Cambrian times (ca. 509 Ma), during the Burj marine transgression that this late Ediacaran palaeotopography was finally buried.The Araba Complex in Jordan with its multi-cycle development provides an insight to the regional development of Ediacaran extensional basins in the Arabian-Nubian Shield, an important phase in the evolution and transition from Neoproterozoic to Phanerozoic crustal tectonics and associated basin-fill.

Micropalaeontology and palaeoenvironments of the Miocene Wadi Waqb carbonate of the northern Saudi Arabian Red Sea

ABSTRACTThe Saudi Arabian Red Sea stratigraphy consists of a variety of lithologies that range from evaporites, deep- and shallow-marine siliciclastics and carbonates, biostratigraphically constrained to range from the Late Cretaceous, Campanian, to Late Pliocene. The succession consists of pre-rift Mesozoic and Palaeogene sediments, and syn-rift and post-rift late Palaeogene and Neogene sediments. Three main episodes of shallow-marine carbonate deposition can be determined, including those of the earliest Early Miocene Musayr Formation of the Tayran Group later Early Miocene Wadi Waqb Member of the Jabal Kibrit Formation and of the Pliocene Badr Formation of the Lisan Group. The Midyan area of the northern Red Sea offers a unique window into the Cretaceous and Miocene succession that is otherwise only present in the deep subsurface. The sediments are of hydrocarbon interest because of the presence of source rocks, siliciclastic and carbonate reservoirs. The Wadi Waqb reservoir is hosted within the Wadi Waqb Member of the Jabal Kibrit Formation, and is of latest Early Miocene to possibly earliest Middle Miocene age. It is considered to have formed a fringing reef complex that formed a steep, fault-influenced margin to a narrow platform, similar to Recent coralgal reefs of the Red Sea.The Wadi Waqb Member is exposed on the east and west flanks of the Ifal Plain. The bioclasts are considered to have traveled as a submarine carbonate debris flow 25 km from their presumed source to the east and possibly the west, and consist mostly of rhodoliths, echinoid and coral fragments together with the benthonic larger foraminifera Operculinella venosa, Operculina complanata, Heterostegina depressa and Borelis melo. The planktonic foraminifera include species of Globigerina, Globigerinoides and Praeorbulina; no specimens of the Middle Miocene planktonic foraminiferal genus Orbulina have yet been encountered in the thin sections. The presence of Borelis melo melo, and of B. melo curdica within the region, indicates a latest Early Miocene age. No specimens of the age-equivalent larger benthonic foraminiferal genera Miogypsina or Lepidocyclina have been observed, and this is consistent with evidence from the Wadi Waqb equivalent carbonates elsewhere in the Red Sea and Gulf of Suez.In the east, the Wadi Waqb is represented by discontinuous fringing rhodolith and coral reefs that are welded to steep cliffs of granitic basement. In Wadi Waqb, located in hills that form the western margin to the Ifal Plain, the Wadi Waqb carbonates consist of packstones containing autochthonous planktonic foraminifera and abundant shallow-marine microfossils that are considered to have been derived from the basement-founded rhodolith and coral reefs in the east. The Wadi Waqb reservoir is located beneath the central part of the Ifal Plain, approximately midway down a ramp between the in situ rhodolith-coral reefs and the mixed allochthonous and autochthonous facies at Wadi Waqb. The reservoir contains biofacies similar to those exposed in Wadi Waqb, and indicative of a deep-marine environment, in excess of 50 m water depth. The Wadi Waqb carbonates display sedimentological and petrographic features that closely resemble those described from stratigraphically equivalent carbonates from the localities along the west coast of the Gulf of Suez, including Abu Shaar, where three depositional facies have been defined. It is apparent that these shallow-marine carbonates were established along the west and east rift margins of the Red Sea-Gulf of Suez rift complex prior to their dislocation during the Late Miocene and Pliocene by the left-lateral Aqaba faulting.

Cambrian stratigraphy of Jordan

ABSTRACTThe lower and middle Cambrian succession (Ram Group) in Jordan is described in lexicon-style format to document an important phase of Earth history following the uplift and erosion of the Arabian-Nubian Shield (Aqaba Complex) during the late Neoproterozoic, and younger, but more localised, intrusive and volcanic/volcaniclastic activity that formed the Araba Complex. The early Cambrian Ram Unconformity (ca. 530 Ma) marks the base of a predominantly fluvial siliciclastic succession derived from rapidly eroding Neoproterozoic (including Ediacaran) basement rocks, but includes a brief, but biostratigraphically significant, sequence of marine siliciclastics and carbonates, the early mid-Cambrian Burj Formation.Rapid uplift and erosion of the granitoid basement (Arabian-Nubian Shield or ANS) resulted in a peneplanation of the Aqaba Complex over millions of years duration (latest Neoproterozoic to Cambrian) in the Southern Desert of Jordan. Early Cambrian pebbly sandstones and locally derived conglomerates (Salib Formation) were deposited on an alluvial plain by high velocity-high discharge, northward flowing (NNE to NNW) braided rivers, characterised by trough cross-bedding and erosive tabular sets. Brief, and rare, marine influence is represented, locally, by thin Skolithos-burrowed sandstones.A regional sea-level rise in the early mid-Cambrian marks a major marine transgressive-regressive cycle and southward thinning carbonate-siliciclastic wedge (Burj Formation) widely present in the subsurface across the Arabian Platform. During deposition of this transgressive marine sequence the palaeoshoreline was oriented WNW-ESE in southern Jordan. The transgressive phase (TST) is represented by tidal-dominated siltstones and fine-grained sandstones (Tayan Member) containing a diverse Cruziana/Rusophycus ichnofaunal assemblage. The overlying carbonate unit (Numayri Member) represents the highstand (HST) and maximum marine flooding surface (MFS), and comprises a carbonate ramp sequence of shelly wackestone, packstone and grainstone with ooids and oncolites, and a diverse shelly fauna including trilobites, brachiopods and hyolithids. A return to regressive tidal-influenced sandstone and siltstone (along with thin carbonates in central Jordan) (Hanneh Member) represents a regressive wedge (RST) deposited in response to renewed uplift of the ANS. Trilobites, represented by the Kingaspis campbelli and Redlichops faunules, suggest a biostratigraphical age of early mid-Cambrian for the carbonate MFS, which equates approximately to the base of the Cambrian Series 3 (Stage 5). This event probably represents the Cambrian marine flooding surface Cm20 (approximate geochronological age of 509 to 505 Ma). South of Feinan, in the Wadi Araba, the carbonates pass laterally to marine sandstone (Abu Khusheiba Sandstone) with extensive Skolithos burrows and Cruziana/Rusophycus traces. Traced southwards (palaeohinterland) the marine influence diminishes, so that the Burj/Abu Khusheiba units are absent in the Southern Desert.Ediacaran intrusives, together with extrusive volcanic and volcaniclastic rocks (Araba Complex) are associated with rifting and half-graben formation in the Feinan-Petra area. This later tectonic activity produced a younger (Ediacaran to early Cambrian), immature palaeotopography, in marked contrast to the Neoproterozoic Aqaba Complex peneplain in the Southern Desert. Consequently, early and mid-Cambrian fluvial and shallow-marine siliciclastics (Salib and Abu Khusheiba formations) onlap progressively onto this immature palaeotopography that was subsequently buried by mid-Cambrian time. Increased basinal subsidence to the north of the Araba Complex ‘high’ provided increased accommodation space that resulted in the deposition of a thick sandstone succession in north Jordan. The Feinan-Petra region seems to have acted as an east-west hinge-line with greater subsidence of the Arabian Platform to the north; similar thickness trends are seen in the Burj and Umm Ishrin formations.Renewed uplift and erosion of the ANS to the south led to deposition of a thick succession of fluvial-dominated sands, again deposited by large-scale braided rivers (Umm Ishrin Formation). Fluvial sedimentation continued through mid to late Cambrian times and also the Ordovician (Disi and Umm Sahm formations), but episodic shallow-marine or estuarine flooding of the low-gradient alluvial plain resulted in colonisation, locally, by arthropods and annelid worms that produced a diverse and abundant Cruziana/Rusophycus/Planolites assemblage of tentative Floian (Arenig) age (upper Disi Formation).Overall the Cambrian to Ordovician Ram Group siliciclastics (Salib-Umm Ishrin-Disi-Umm Sahm formations) show an upward increase in sand maturity from arkose (Salib) to orthoquartzite (Disi); heavy-mineral signatures (ZTR), specifically datable zircons, indicate provenance from a predominantly distant Neoproterozoic granitoid source rock area located to the south (ANS) that was undergoing intensive weathering. However, a small zircon component was derived from older pre-Neoproterozoic rocks, consistent with the general trend in the Levant.The highly permeable Cambrian siliciclastics of Jordan and surrounding countries provide an important regional aquifer, the Ram (formerly Disi) Aquifer. In a suitable setting these reservoir rocks might have potential for hydrocarbon exploration where source rocks of Neoproterozoic, Silurian or Permian age are faulted and in proximity, at depth, in the central Arabian Platform.

Tectonostratigraphy of the Chazyan (Late Middle-Early Late Ordovician) Mixed Siliciclastic-Carbonate Platform, Quebec Embayment

Abstract The Middle to lower Upper Ordovician (Chazyan) platform succession of eastern North America extends landward of the ancient Quebec Embayment along the Laurentian margin, part of a foreland basin peripheral to an arc-collisional plate boundary. The platform grades from seaward reefal carbonate (Chazy Group, Champlain Valley) into platform- and foreland-interior tide- and wave-dominated siliciclastics (Rockcliffe Formation) and restricted peritidal muddy carbonate (Hog's Back Formation). The latter two formations occur in the sedimentary Ottawa Embayment, which overlies the trace of a Neoproterozoic rift. Prominent tectonostratigraphic surfaces bound and subdivide the Chazyan platform-interior succession, and are characterized by abrupt marine transgressions, local synsedimentary faults, and seismogenic beds. The depositional history includes: (1) accumulation of shallow-marine siliciclastics (Rockcliffe Fm) across a differentially faulted paleoplatform; (2) abrupt regional retrogradation (∼ 100 km) of this siliciclastic system, replaced by an intraplatform shale basin (lower Hog's Back Formation); (3) basin fill and development of a low-energy muddy carbonate platform interior (upper Hog's Back Formation) coincident with regional fall in sea level and change in subsidence along the Laurentian margin; and (4) abrupt high-frequency base-level changes preceding regional onlap of Mohawkian (Turinian) shale contemporary with local synsedimentary deformation and rapid subsidence along the distal arc-collisional plate boundary. Structurally controlled sedimentation patterns in the platform (and foreland) interior document episodic tectonism coincident with relatively sustained deposition along the outer platform (the Chazy Group). This difference is interpreted to be a response to foreland-interior flexuring, modified by local reactivation of the Precambrian rift, that was coincident with preferential subsidence at seaward sites more proximal to structural loading along the arc-collision plate boundary.

Terpenoids in extracts of Lower Cretaceous ambers from the Basque-Cantabrian Basin (El Soplao, Cantabria, Spain): Paleochemotaxonomic aspects

The composition of terpenoids from well preserved Cretaceous fossil resins and plant tissues from the amber bearing deposits of El Soplao and Reocín in Cantabria (northern Spain) have been analyzed using gas chromatography–mass spectrometry and the results are discussed using the terpenoid composition of extant conifers as a reference. Amber is present at many horizons within two units of coastal to shallow marine siliciclastics of Albian and Cenomanian age. The fossil resins are associated with black amber (jet) and abundant, well preserved plant cuticle compressions, especially those of the extinct conifer genus Frenelopsis (Cheirolepidiaceae). We report the molecular characterization of two types of amber with different botanical origins. One of them is characterized by the significant presence of phenolic terpenoids (ferruginol, totarol and hinokiol) and pimaric/isopimaric acids, as well as their diagenetic products. The presence of phenolic diterpenoids together with the lack of abietic and dehydroabietic acids excludes both Pinaceae and Araucariaceae as sources for this type of amber. The biological diterpenoid composition is similar to that observed for extant Cupressaceae. The second type of amber is characterized by the absence of phenolic terpenoids and other specific biomarkers. Some terpenoids with uncertain structure were detected, as well as the azulene derivative guaiazulene. Our results suggest that the amber from Cantabria could be fossilized resin from Frenelopsis and other undetermined botanical sources. The biological terpenoid assemblage confirms a chemosystematic relationship between Frenelopsis and modern Cupressaceae.

The Mesozoic continental rifting in the Mediterranean area: insights from the Verrucano tectofacies of southern Tuscany (Northern Apennines, Italy)

In the Alpine-Mediterranean region, the continental redbeds and shallow-marine siliciclastics related to the early depositional phases of the Late Permian-Mesozoic continental rifting are referred to as the most common representative of the “Verrucano tectofacies”. The Verrucano-type successions exposed in southern Tuscany are diachronous, spanning from Triassic to earliest Jurassic in age, and accumulated within the Tuscan domain, a paleogeographic region of continental crust that due to the opening of the Piedmont–Ligurian ocean formed part of the Adria passive-margin. They belong to the metamorphic Verrucano Group and the non-metamorphic Pseudoverrucano fm. Viewed overall, these Verrucano-type successions appear to manifest five episodes or pulses of an ongoing continental rifting. With the exception of the first episode that developed entirely within a terrestrial setting, each one is represented by basal Verrucano-type continental siliciclastics overlain by compositionally mixed marine deposits, which resulted from four diachronous, post-Middle Triassic transgressions. This suite of tectonic pulses produced the progressive westward widening (backstepping) of the Tuscan domain in the rifting south-Tuscany area.

Stratigraphic evolution of Oligocene–Miocene carbonates and siliciclastics, East Java basin, Indonesia

The Oligocene–Miocene of East Java is characterized by multiple stages of isolated carbonate mound growth surrounded by deeper marine off-mound sediments or by shallow-marine siliciclastics. Three stratigraphic intervals are recognized: Kujung (carbonate mound and off-mound), Tuban (mixed carbonate-siliciclastic), and Ngrayong (siliciclastic). Exposures of the Kujung unit (28–22 Ma) are limited to a few isolated outcrops. At the base, the Kujung is represented by a high-energy, extensive, shallow-marine carbonate facies that grades laterally into deep-marine off-mound sediments of calcareous mudstone and chalk (lower Kujung). In other locations, shallow-water carbonate deposition was restricted to faulted topographic highs in the middle–upper Kujung. The shallow-marine sediments of the lower Kujung were covered by thick chalk and marl sediments of the middle–upper Kujung. The Tuban unit (22–15 Ma) consists of widely exposed shallow-marine mixed carbonate and siliciclastic and poorly exposed open-marine shale and chalk facies. The Tuban consists of at least six stacked cycles that reflect deltaic deposition with episodes of shallow-marine carbonate mound growth. The Ngrayong unit (15–12 Ma) represents a period of regional siliciclastic influx and progradation of tidally influenced deltas and grades into turbidites, basinal shale, mudstone, and chalk. Ngrayong beds are truncated by Bulu carbonates (Serravallian–Tortonian). This is consistent with the tectonic evolution of the region.

Evolution of geochemistry and depositional settings of Early Palaeozoic siliciclastics of the Barrandian (Teplá-Barrandian Unit, Bohemian Massif, Czech Republic)

Cambrian and Ordovician-Middle Devonian sequences of two successive Early Palaeozoic basins of the Barrandian unconformably overlie Cadomian basement in the Bohemian Massif NW interior (Tepla-Barrandian unit) which is the easternmost peri-Gondwanan remnant within the Variscides. Correlation of stratigraphy and geochemistry of the Early Palaeozoic siliciclastic rocks elucidated sediment provenances. Sandstones of the Middle Cambrian Přibram-Jince Basin were derived from a Cadomian Neoproterozoic island arc. The source area of the Ordovician shallow-marine siliciclastics of the successor Prague Basin is a dissected Cadomian orogen. Late Cambrian acid volcanics of the Barrandian and Cambrian (meta)granitoids emplaced in the W part of the Tepla-Barrandian Cadomian basement are also discernible in these sediments. Old sedimentary component increased during the Ordovician. Early Llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of Silurian transgression. Emsian siliciclastics (intercalated in the Late Silurian to Early Devonian limestone suite) presumably comprise an addition of coeval basic/ultrabasic volcaniclastics. Middle Devonian flysch-like siliciclastics indicate reappearance of Cadomian source near the Barrandian during early Variscan convergences of Armorican microplates that preceeded accretion of the Tepla-Barrandian unit within the Bohemian Massif terrane mosaic.

Development of early Palaeozoic ichnofabrics: evidence from shallow marine siliciclastics

Abstract Earliest Cambrian fine-grained sediments appear to have been firm close to the sediment-water interface. As a result there was a high preservational potential of shallow tiers. There is limited evidence for a mixed layer at this time; rather, most of the preserved trace fossils were open burrows. Later in the Cambrian, depth of sediment mixing increased but firmground conditions are still found relatively close to the sediment-water interface. The development of the mixed layer and properties of Cambrian muddy sediments have numerous stratigraphic and ichnological consequences. These include secular trends in the preservation of event beds and shallow-tier trace fossils including Rusophycus and Cruziana .

THE PETROLEUM POTENTIAL OF EAST TIMOR

The hydrocarbon prospectivity of East Timor is widely considered to be only moderate due to Timor island’s well-known tectonic complexity, but in the present study a much higher potential is interpreted, with structures capable of hosting giant hydrocarbon accumulations. High quality source rocks are found in restricted marine sequences of Upper Triassic-Jurassic age. The most likely reservoir target is shallow marine siliciclastics of Upper Triassic-Middle Jurassic age encountered in the Banli–1 well in West Timor, comparable to the Malita and Plover Formations of the northern Bonaparte Basin, and sealed by Middle Jurassic shales of the Wai Luli Formation. The Wai Luli Formation also forms a major structural décollement level which detaches shallow level structural complexity from a simpler structural régime beneath.The principal exploration targets are large, structurally simple inversion anticlines developed beneath the complex shallow-level fold and thrust/mélange terrain. Eroded-out examples of inversion anticlines, such as the Cribas, Aitutu and Bazol anticlines, are typically several tens of kilometres long and up to 10 km broad. Comparable structures in the subsurface of southern East Timor are interpreted north of Betano, and probably also near Suai, Beaco, Aliambata and Iliomar. Other potential targets include a possible non-inverted rollover anticline at Pualaca, stratigraphic and structural traps in the south coast syn/postorogenic basins, and possibly large structural domes beneath extensive Quaternary reef plateaux in the extreme east of the island.

Distribution and facies patterns of Lower Cretaceous sediments in northern Germany: a review

Marine sediments of Early Cretaceous age (Berriasian–Albian) have a widespread distribution in the Lower Saxony Basin of northern Germany. This basin, which is about 400km long and 100km wide, formed the southernmost extension of the North Sea Basin. Sediments attaining a maximum thickness of up to several hundred metres are represented by shallow marine siliciclastics in the west, south and easternmost part of the basin. These interfinger with the basin facies represented by dark mudstones up to 2000m thick. The distribution and facies patterns of the sediments as well as thicknesses are related to three factors: differential subsidence, local tectonics and sea-level changes. For various parts of the basin and certain stratigraphic intervals it is possible to distinguish between these causes. Sedimentary thicknesses are clearly a result of differential subsidence from Kimmeridgian to Albian times onwards, being controlled by tectonic movements along northwest–southeast trending faults. These result in an asymmetric trough, bound to the north and south by synsedimentary faults with sedimentation rates highest in the north. Local tectonics are clearly caused by salt diapirs mainly in the eastern part of the basin and along the western, southern and eastern margins. These areas in particular include parts of the western Emsland and the Salzgitter area. Sedimentary patterns vary considerably over less than a kilometre, showing an extreme range of different lithologies. This is ideally observed in the Salzgitter area. Sea-level changes finally are reflected by widespread facies patterns and particularly by fossils of different provenance. The following sea-level-related events can be followed throughout the basin: the Wealden regressive phase, the Early Valanginian transgression, the early Late Valanginian transgression, the mid Hauterivian transgression, the Barremian regression, deposition of the Early Aptian anoxic sediments, and accumulation of the mid Albian hemipelagic marls.

Structure and sedimentation of Permo-Triassic and Triassic rocks exposed in small-scale horsts and grabens of pre-Cretaceous age: Dead Sea margin, Jordan

Small-scale horsts and grabens, formed prior to the deposition of the Lower Cretaceous Kurnub Sandstone, are described for the first time from remote exposures near the eastern shore of the Dead Sea, Jordan. The grabens preserve a sequence of Permo-Triassic and Triassic rocks (Umm Irna and Ma'in Formations), flanked by horsts of Cambrian sandstone (Umm Ishrin Formation). The pre-Cretaceous faults are mostly orientated NNE or ENE, with a maximum vertical displacement of 130 m. Rotation of a joint system, formed during the late Palaeozoic, in the Cambrian sandstone indicates that the horst blocks were rotated anti-clockwise during block faulting. Local and regional stratigraphical evidence suggest that faulting occurred during an extensional tectonic regime in late Jurassic to early Cretaceous times. The horsts and grabens did not affect sedimentation of the basal Kurnub Sandstone and they are preserved without relief below the unconformity, suggesting a period of erosional peneplanation prior to deposition of the fluvial Kurnub Sandstone. The structures probably represent an extension of the Central Naqab-Sinai fault zone which was displaced by sinistral shear along the Dead Sea-Gulf of Aqaba Rift in Tertiary (Neogene) times. Lithofacies sequences in the Umm Irna Formation exposed in the grabens comprise, in ascending sequence, braided to low-sinuosity or meandering fluvial siliciclastic facies, derived from the Arabo-Nubian Shield to the south and south-east. Lithological characteristics, bedforms and pedogenic features suggest a fluctuating, seasonal, semi-arid climate. Transgression of the Tethys Ocean in early Triassic times resulted in deposition of shallow-marine siliciclastics and carbonates (Ma'in Formation) in subtidal to intertidal environments.

Tectonic affinity of the Mathinna Group in the Lachlan Fold Belt

Pre-Carboniferous rocks of Tasmania comprise two disparate terranes which were brought together during the middle Palaeozoic. The Eastern Tasmania Terrane consists of middle Palaeozoic granitoids and the Mathinna Group, a turbidite succession of Ordovician to Early Devonian age. The older part of the adjacent Western Tasmania Terrane, the only part of the southern Tasmanides with exposed Precambrian basement, is related to the Kanmantoo Fold Belt and older tectonic provinces located northwest of Tasmania. The younger part of the Western Tasmania Terrane comprises Upper Cambrian to Lower Devonian terrestrial to shallow-marine siliciclastics and carbonates—a marked contrast to the coeval deep-water deposits of the Mathinna Group. The contact between the two terranes is concealed by the Tamar Valley in northern Tasmania. The main folds in the Eastern Tasmania Terrane verge to the northeast, whereas structures in the adjacent Western Tasmania Terrane indicate tectonic transport to the southwest, with the break in structural facing coinciding with the Tamar Valley. Reinvestigation of the structure of the westernmost Eastern Tasmania Terrane, where there is a large recumbent F 1-fold (> 10 km extent in profile view), raises the possibility that a second generation of structures, previously regarded as of only local importance, could have caused rotation of the upright to steeply west-dipping axial surfaces of F 1-folds to recumbent attitudes during southwesterly-directed thrusting. In this interpretation, recumbent or near-recumbent zones could reflect ramps in a sole thrust, and the mid-Devonian imbricate thrust zone near Beaconsfield on the west bank of the Tamar River would be either the frontal thrust system or a splay off the sole thrust which continues westward beneath the exposed ?Precambrian Badger Head Block. The implications of this new interpretation are that docking of the Eastern and Western Tasmania terranes must have occurred after the Ordovician but before the Middle Devonian. During the consolidation phase there were two deformations of the Mathinna Group. The first, which occurred in the Early Devonian prior to emplacement of the St Marys Porphyrite (388 ± 1 Ma), produced upright to locally overturned folds verging to the northeast. The second, which took place during the early Middle Devonian before deposition of Givetian cave deposits, resulted in the Mathinna Group being thrust southwestward. This sense of thrusting is opposite to the direction of thrusting at the same time in the Melbourne zone of Victoria, where the fold-and-thrust belt verges eastward away from the craton. A concealed Devonian transfer fault zone in Bass Strait could account for this change of polarity.