Marl Deposits Research Articles

Changes in sedimentary patterns of coastal and deep-sea successions from the North Atlantic (Portugal) linked to Early Cretaceous environmental change

Coastal mixed carbonate-siliciclastic and carbonate deposits of Late Barremian to Early Aptian age from the Lusitanian Basin (Portugal) are compared with a deep-sea succession (ODP 641) off the coast of Portugal. The coastal deposits show an abrupt cessation of rudist-dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid-rich marls during the Early Aptian. The subsequent development of the carbonate platform during the Late Aptian is masked by a hiatus. For this time interval shallow-water debris deposits of the deep-sea succession ODP 641 indicate that carbonate production in shallow-water areas resume in the early Late Aptian. Carbon-isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the Portuguese with shallow-water successions from Switzerland, France, Oman and the Pacific. The correlation reveals that during the Early Aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon-isotope values associated with the global deposition of organic rich black shales in the deep sea (OAE 1a). In all compared sections rudist-dominated carbonate deposition is stopped and followed either by orbitolinid-rich deposits, the deposition of microbial carbonates or by the drowning of the carbonate platform. The comparison shows that the deterioration for carbonate platform growth conditions during the Early Aptian occurred essentially simultaneously at the various localities. During this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms. Sea level change combined with local effects like elevated nutrient levels and higher temperatures, were probably determining the nature of sedimentary change in shallow-water environments during the carbonate crisis. In the sections studied in Portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late Early Aptian.

Diagnosis of the Upper Cretaceous palaeokarst and turbidite systems from the Iranian Persian Gulf using volume-based multiple seismic attribute analysis and pattern recognition

Depositional facies variability with a secondary overprint of Turonian palaeokarst controls the quality of the Cenomanian Mishrif reservoir, the main oil producer in the southeastern Persian Gulf. Subsequent drowning of the prominent area and successive deepening of the basin during the Coniacian and Santonian enabled the deposition of pelagic marls of the Coniacian Laffan Formation and the development of a carbonate turbidite system within the overlying Santonian Ilam Formation. The Ilam Formation occurs within slope and pelagic carbonates and consists of oil-bearing channel-reworked limestone facies. Although high-quality 3D seismic data exist over the Sirri C/D oil fields studied in this paper, it is a real challenge to map the palaeokarst and turbidite deposits in 3D space using conventional seismic interpretation procedures. This work describes a procedure using Paradigm's Seisfacies software for seismic facies classification and uses this to develop a volume-based interpretation of palaeokarst geobodies and sedimentary patterns of the carbonate turbidite. A hierarchical facies classification technique combined with principal component analysis (PCA) is used to analyse a set of seismic attribute volumes that capture the seismic stratigraphic patterns inherent in the data. PCA as a data reduction algorithm greatly optimized the analysis of the attribute volumes while preserving the essential features of seismic character. A hierarchical facies classifier recognized enough variability within the seismic data to reveal details of the associated geological features. This classification method uses multiple 3D volume attributes as input and generates a single 3D seismic facies volume (a synthesis of different attributes). Using this method, interpretative work can focus directly on geological features in 3D space. This study gives new insights into the internal variability of palaeokarst and carbonate turbidite systems in the Sirri C/D oil fields (SE Persian Gulf) that are essential for the estimation of reservoir volume, connectivity and variability.

Primary carbonates and Ca-chloride brines as monitors of a paleo-hydrological regime in the Dead Sea basin

Lakes Samra, Lisan and the Dead Sea occupied the Dead Sea basin during the Last Interglacial (∼140–75 ka BP), last glacial (∼70–14 ka BP) and Holocene periods, respectively. The age of Lake Lisan and Samra was determined by U–Th dating of primary aragonites comprising parts of the lacustrine sedimentary sequences. The lakes have periodically deposited sequences of layered calcitic marls (Lake Samra) or laminated primary aragonite (Lake Lisan). The deposition of aragonite as the primary carbonate phase reflects the contribution of the incoming freshwater (loaded with bi-carbonate) and high Mg-, Ca-chloride brine that originated from the subsurface vicinity of the Dead Sea basin. Deposition of calcitic marls suggests a minor effect of the brines. The Ca-chloride subsurface brine has been migrating in and out of the wall rocks of the Dead Sea basin, reflecting the regional hydrological conditions. During most of the last glacial period and during the late Holocene, sufficient precipitation above the Judea Mountains pushed the subsurface Ca-chloride brines into the lakes causing the deposition of aragonite. During the Last Interglacial period the rain that precipitated above the Judea Mountains was insufficient to induce brine flow toward Lake Samra. It appears that sporadic floods provided calcium, bicarbonate and detritus to produce the Samra calcitic marls. Travertines deposited at the Samra–Lisan boundary indicate the early stage in the resumption of groundwater (springs) activity that led to the resurgence of Ca-chloride brine and rise of Lake Lisan. Similar variations in the regional rain precipitation and hydrological activity probably characterized the long-term geochemical evolution of Pleistocene lacustrine water-bodies in the Dead Sea basin, enabling the use of the carbonates as paleo-hydrological monitors.

Geology of the Severnaya Zemlya Archipelago and the North Kara Terrane in the Russian high Arctic

The Severnaya Zemlya Archipelago is located at 80°N near the continental shelf break, between the Kara and Laptev seas. Sedimentary successions of Neoproterozoic and Palaeozoic age dominate the bedrock geology. Together with Northern Tajmyr, Severnaya Zemlya constitutes the main land areas of the North Kara Terrane (NKT), which is inferred here to have been a part of the Timanide margin of Baltica, i.e. an integral part of Baltica at least since the Vendian. Vendian turbidites derived from the Timanide Orogen are inferred to have been deposited on Neoproterozoic greenschist facies, granite-intruded basement. Shallow-water siliclastic deposition in the Early to Mid-Cambrian was followed by highly organic-rich shales in the Late Cambrian and influx of more turbidites. An episode of folding, the Kan’on River deformation, separates these formations from the overlying Tremadocian conglomerates and sandstones. In the Early Ordovician, rift-related magmatic rocks accompanied the deposition of variegated marls, sandstones, carbonates and evaporites. Dark shales and gypsiferous limestones characterise the Mid-Ordovician. Late Ordovician quartz-sandstones mark a hiatus, followed by carbonate rocks that extend up into and through most of the Silurian. The latter give way upwards into Old Red Sandstones, which are inferred to have been deposited in a Caledonian foreland basin. Deformation, reaching the area in the latest Devonian or earliest Carboniferous and referred to as the Severnaya Zemlya episode, is thought to be Caledonian-related. The dominating E-vergent structure was controlled by decollement zones in Ordovician evaporite-bearing strata; detachment folds and thrusts developed in the west and were apparently impeded by a barrier of Ordovician igneous rocks in the east. Below the decollement zones, the Neoproterozoic to Early Ordovician succession was deformed into open to close folds. The exposed strata in the lower structural level have been juxtaposed with those in the upper structural level along the major N-trending Fiordovoe Lake Fault Zone, which involved several kilometres of dextral strike-slip movement and downthrow to the west. A major Early Carboniferous unconformity separates the folded Mid-Palaeozoic and older rocks from overlying Carboniferous formations, as on Franz Joseph Land and Svalbard. Subsequent latest Palaeozoic to Early Mesozoic orogeny, as on Taimyr, apparently had little influence on the Severnaya Zemlya successions.

PTB mass extinction and earliest Triassic recovery overlooked? New evidence for a marine origin of Lower Triassic mixed carbonate–siliciclastic sediments (Rogenstein Member), Germany

The Central European Permo-Triassic basin was land-locked with occasional connections to the North Pangaea shelf and Tethys. A thick sequence of siliciclastic fluvial and floodplain sediments separates the Late Permian marine carbonate–evaporite cycles of the Zechstein Basin from marine Middle Triassic marls and carbonates of the Germanic Basin. Within this Latest Permian–Middle Triassic siliciclastic interval, the location of the Permian–Triassic Boundary (PTB) is difficult to recognize. The first limestones after the PTB are Induan mixed carbonate–siliciclastic oolites and microbialites of the Bernburg and Calvörde Formations (Untere Buntsandstein Group). Consensus emerged after a long-lasting controversy that the carbonates of the so-called Rogensteine are the relics of an alkaline playa lake. The idea of the marine genesis was finally rejected, because of the obvious lack of calcified metazoans. The existing depositional playa lake-model will be tested using previously unconsidered data, such as currently discussed Early Triassic recovery scenarios of marine benthic communities after the Permian–Triassic mass extinction, global patterns of Early Triassic carbonate production, Permian–Triassic tectono-sedimentary evolution of northern Pangaea and stable oxygen and carbon isotope data. The Rogenstein is interpreted as marine carbonate, showing the characteristic features of marine carbonates of the Early Triassic recovery period: – Calcified invertebrates are rare in many marine settings during the aftermath of the Permian–Triassic mass extinction. Thin shells of the oolites resemble opportunistic bivalves flourishing in marine Early Triassic oceans. – The oolites and microbialites are the product of abiotic and biotically-induced carbonate precipitation following the Permian–Triassic mass extinction while biomineralisation is insignificant; Rogenstein microbialites look like marine Early Triassic microbial reefs. – The extraordinary size of the Rogenstein ooids resembles marine Neoproterozoic ooids. The term “anachronistic” has been used in the literature to describe the similarities in the fabric and composition of Early Triassic and Early Palaeozoic/Neoproterozoic marine carbonates. – Stable carbon isotopes of least altered Rogenstein ooids and stromatolites exhibit trends similar to the composition of Triassic seawater. – The presence of flat pebble conglomerates and sediment structures similar to herring-bone cross stratification confirm the marine genesis. I propose that cool seawater transgressed during a global rise of Late Permian–Early Triassic base-level from the Barents shelf southward along reactivated extensional graben structures and flooded the Central European Permo-Triassic basin. There, the extremely hot and arid climate of the megacontinent Pangaea caused increased evaporation of seawater and subsequent supersaturation with respect to calcium carbonate. Insignificant biomineralisation and high water energy in the shallow sea give rise to largely abiotic and biotically-induced carbonate precipitation which resembles lake sediments at first sight. Benthic tropical carbonate production started with the next transgression during the Röt Formation, leading to the sedimentation of marls and limestones during the Spathian (late Olenekian).

Sedimentation and palaeogeography of the eastern part of the Paris Basin (France) at the Middle–Upper Jurassic boundary

The Middle–Upper Jurassic boundary corresponds to a period of far-reaching changes in sedimentation patterns related to alterations in the palaeoclimate and in the global carbon cycle. Marl deposits were laid down in the east of the Paris Basin at this time and ANDRA has selected these lithological units as the site for an underground study laboratory. The build-up of these marls is the result, among other things, of the area long having been a shelf and of more rapid subsidence from the Early Callovian to the Early Oxfordian. Changes are detected between areas on either side of the Vittel Fault from the onset of the mid-Oxfordian onwards. To cite this article: P.-Y. Collin, P. Courville, C. R. Geoscience ••• (••••).

Bivalve Wood Borings of the Ichnogenus Teredolites Leymerie from the Bohemian Cretaceous Basin (Upper Cretaceous, Czech Republic)

Finds of fossil wood with bivalve wood borings (Teredolites clavatus and T. longissimus) occur in various facies and presumed sedimentary settings of the platform, shallow-marine Bohemian Crectaceous Basin. The basin comprises areas with sandy-dominated sediments, with marl and clay-dominated sediments, areas with predominat sandy-marly rocks, and finally areas dominated by calcareous nearshore sediments. Teredolites clavatus is common in fossil wood of sandstones, originating in beach or deltaic settings; marl and clay-dominated rock frequently bear wood fragments densely bored by Teredolites longissimus. When accompanied by evidence of marine environments as body fossils, glauconite or typical trace fossils, most of the wood fragments are bored. The presence/absence of borings in wood fragments can be considered the most reliable and easily useable criterion of distinction of marine settings in sandy sediments of the margin of the Bohemian Cretaceous Basin.

A 14,000-year environmental change history revealed by mineral magnetic data from White Lake, New Jersey, USA

The increasing use of magnetic parameters as a proxy for environmental change necessitates the understanding of processes that link magnetic properties of sediments, especially organic-rich lake sediments, and environmental change. To explore the magnetic mineral-paleoenvironment link, we have recovered a 14,000 yr mineral-magnetic record from White Lake, a hardwater lake containing organic-rich sediments in northwestern New Jersey, USA. Pre-14 ka (1 ka = 1000 cal yr BP) sediments are dominated by clays, and the magnetic variations of the clays recorded the deglaciation process, the initial development of the lake, and the stabilization of the watershed. The rapid increase in organic matter and carbonate around 14 ka likely marks the Bølling warming event. The marl sediments were deposited from 14 to 11 ka and displayed a continued decline in magnetic mineral concentration, which indicates increasing marl precipitation in the lake and stabilization of the watershed by vegetation growth. The Holocene gyttja-dominated sediments generally have weak magnetizations. However, yellowish marl layers in the Holocene sediments display strong magnetizations. The strong magnetization of marl layers at ∼ 1.3, 3.0, 4.4, and 6.1 ka probably resulted from oxidation of the precipitated marl sediments near to shore, which were then eroded, transported, and redeposited during periods of low lake levels. This study demonstrates that multiple magnetic parameters can provide a more detailed and robust interpretation of environmental change than lithologic data alone.

Abundant Sr-rich aragonite in eastern Mediterranean sapropel S1: Diagenetic vs. detrital/biogenic origin

CaCO 3 contents in eastern Mediterranean sapropels are generally lower than in the enclosing marl sediments. In sediments of a transect from ∼ 650 to 2100 m water depth at the Sirte continental slope, the opposite feature was observed. Although the increased Sr/Ca ratios observed in these sediments agree with such feature observed in other eastern Mediterranean S1 sediments, their absolute magnitude is much higher. The enhanced Sr/Ca ratio in these sediments is associated with their aragonite content, which for the Sirte transect reaches levels of up to ∼ 40 wt.%. The aragonite content and Sr/Ca ratios in the S1 sediments of this transect decrease with increasing water depth and decrease with distance to the African coast for all eastern Mediterranean cores. In view of the lack of a coherent relationship with sedimentary reduced sulphur contents and porosity, and considering the major amount of aragonite found specifically in the sediments of the Sirte transect, authigenic precipitation can contribute only a limited fraction at most. SEM observation and electron-microprobe analyses showed that the needles and needle clusters are morphologically aragonite, contain the highest Sr/Ca ratio, and are similar to skeleton fragments of the green alga Halimeda. Consequently, a detrital/biogenic source is the likely mechanism for the major part of the aragonite enrichments found in S1 sediments. Possibly, offshore-directed surface water flows related to wind stress and/or enhanced run-off (consistent with enhanced precipitation during sapropel S1) may have assisted in the transport of near-coastal aragonitic organisms to more coast-remote areas.

Facies, outcrop gamma ray and C–O isotopic signature of exposed Miocene subtropical continental shelf carbonates, North West Cape, Western Australia

Exposed, uplifted Miocene carbonate sequences of the Cape Range, North West Cape, Western Australia, provide outcrop analogues of seismic sequences from offshore parts of the shelf. Facies include deep shelf marls (very fine and fine packstone), larger foram wackestone, floatstone and muddy rudstone, foram-coralline algal skeletal fragment packstone–wackestone (shallow seagrass facies), lagoonal wackestone–mudstone with scattered corals, and tidal flat laminites. The exposed Early Miocene units include the Mandu highstand, a sequence in the Tulki and one in the Middle Miocene Trealla Limestone. Sequences contain decameter scale (5–20 m thick), 4th-order parasequences evident on gamma ray logs and by facies stacking, that shallow and coarsen up; they appear to be due to eccentricity driven sea-level changes which may have been up to 50 m. Higher frequency meter-scale parasequences of deep water marl up into larger foram rudstone/floatstone (perhaps precession/obliquity) are evident at the base of the exposed Mandu section. These parasequences are not merely random storm deposits. This is indicated by the covariance of C and O isotopes, with the lighter values associated with deepening and deposition of deep shelf marls, and the heavier values being associated with shallowing and deposition of larger foram facies. The uplifted Miocene continental shelf sediments of the North West Cape preserve a record of eustasy, paleoclimate and paleoceanography and thus provide a window into factors affecting the shelf, that can be compared with coeval, better studied deep sea cores.

Mass-Transport Complexes (MTCs) and Tectonic Control on Basin-Floor Submarine Fans, Middle Eocene, South Spanish Pyrenees

In many deep-marine clastic systems, mass-transport complexes (MTCs) constitute a major component of the stratigraphy and represent an integral part of the evolution and depositional style. In tectonically active basins, as is the case in our study of the syntectonic deep-marine Ainsa submarine fans (Eocene of the Ainsa basin, Spanish Pyrenees), organized, predictable vertical sedimentary sequences provide a testable generic model for submarine fan development in other basins where tectonic processes provide a first-order driver on fan growth. In the Ainsa basin, the linear submarine fans were confined by lateral thrust ramps and influenced by intra-basinal growth anticlines. This study represents an integration of outcrop data from sedimentary logs and mapping, with core data from eight wells and micropaleontological and palynomorph analyses. Mapping shows the lateral stepwise migration of sandy channelized submarine fans, as a foreland-propagating clastic wedge. The stepwise foreland migration of each fan (away from the deformation front), and also the time scales involved (many hundreds of thousands of years for each fan), are interpreted within the context of a primary tectonic control. Three distinct types of MTC are recognized, each of which appears to be characteristic of stratigraphic position in relation to the evolution of individual fans. The deep-marine expression of the inferred tectonic pulses began with the large-scale basin-slope collapse as sediment slides and debris flows (type I MTCs) that formed much of the seafloor topography for each fan and contributed to their lateral confinement. The uppermost slope and any shelf edge, including the narrow shelf, then collapsed, redepositing unconsolidated sands and gravels into deep water (type II MTCs). The basal coarse clastics are overlain by an interval of mainly channelized and amalgamated sandy deposits, with major erosional events, including reincision processes associated with channel development, being characterized by pebbly mudstones and sandstones rich in angular, locally derived intraclasts (type III MTCs). The channelized sands pass up into several tens of meters of less confined, non-amalgamated, medium- and thin-bedded, fine-grained sands and marls. These deposits represent the phase of most active fan growth, initially by erosional channel development, sediment bypass, and backfill (in several cycles), giving way to nonchannelized, fine-grained sandy deposition, interpreted as a response to the flushing out of the coarser clastics from the coastal and near-coastal fluvial systems. During this latter stage in active fan growth and when sediment accumulation rates probably remained high, the degraded submarine slope was regraded and healed by fine-grained depositional events. The high amount of woody material and the high nonmarine palynomorph signal in these sandy deposits suggest direct river input as both turbidity currents and hyperpycnal flows for the silty marls. In the upper few meters, a thinning and fining-upward sequence shows a return to background marl deposition, representing fan abandonment. Many sequences are overlain by intraformational sediment slides (typically type I MTCs but, rarely type II MTCs) that attest to the increasing seafloor gradients associated with the regrading and healing stage in slope development. Our explanation for these vertical sequences provides a readily testable depositional model for other deep-marine clastic systems associated with a tectonically active hinterland and basin slopes.

Depositional environments and iron ooid formation in condensed sections (Callovian–Oxfordian, south‐eastern Paris basin, France)

AbstractCarbonate platforms across Western Europe were superseded at the Middle–Upper Jurassic (Callovian–Oxfordian) boundary either by alternating marl–limestone and widespread marl deposits or by condensed sections containing iron ooids. The characteristics of marine condensed sections in the south‐eastern part of the Paris Basin (France) and their distribution pattern are examined here, and a model of iron ooid formation is developed. Iron ooids are found from the shoreface to the offshore zone. They are most abundant in the median‐to‐distal offshore transition zone, where they originally formed. They also occur commonly, albeit often as reworked grains, in the proximal offshore zone, to which they were transported. The contemporaneous, thick, predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings (distal offshore zone). The iron ooids are composed of goethite. Typically, they have a nucleus made up of a clump of goethite crystals and a laminated cortex. Three distinctive nanostructures are identified in the cortex laminae: (i) a nanograined crystalline structure typical of primary goethite; (ii) a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals; and (iii) a coalesced structure acquired by subsequent diagenetic recrystallization. The iron ooids formed successively (i) by lamina growth when goethite precipitated in the surface layer of the sediment (nanograined structure) and (ii) by interruption of growth when the ooids were remobilized by hydrodynamic agents, as reflected by the flaked nanostructure; (iii) these two nanostructures were sometimes transformed into a coalesced structure by recrystallization when ooids were buried.

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.

Upper Cretaceous oceanic red beds (CORB) in the Northern Calcareous Alps (Nierental Formation, Austria): slope topography and clastic input as primary controlling factors

In the Northern Calcareous Alps, Upper Cretaceous oceanic red beds are composed of the Nierental Formation, deposited in bathyal slope basins along the active margin of the Austroalpine microplate. The sedimentation of red shales and marls was highly diachronous, starting in the Late Santonian. Carbonate contents vary between 50 and 90%. Siliciclastic and carbonate-dominated turbidite and mass-flow and slump deposits are common. Planktic foraminifera dominate the foraminiferal assemblages. Sedimentation rates for red (hemi)pelagic intervals are generally in the order of a few mm/ka up to 26 mm/ka. Within the Gosau valley area red (hemi)pelagic intervals a few tens of metres thick are diachronous. This case study suggests that Late Cretaceous oceanic red-bed deposition was not a single event but distributed over a longer time span and can, therefore, be regarded as the normal background sedimentation in deep-sea settings with relatively low sedimentation rates. However, the colour and thus the oxidation state of the (hemi)pelagic as well as turbiditic sediments was controlled by various regional and local factors. Within the morphologically complex orogenic-wedge setting of the slope basins of the Gosau Group, basin topography and local clastic input strongly influenced the occurrence and facies of the oceanic red beds.

Mass transport complexes and tectonic control on confined basin-floor submarine fans, Middle Eocene, south Spanish Pyrenees

Abstract The syn-tectonic deep-marine Ainsa fans (Eocene of the Ainsa basin, Spanish Pyrenees) were confined by lateral thrust ramps and influenced by intra-basinal growth anticlines. Mass transport complexes (MTCs) constitute a major component of the stratigraphy and represent an integral part of the evolution and depositional style of the deep-marine clastics. Using an integrated study of outcrop data from sedimentary logs and mapping, with core data from eight wells and micropalaeontological and palynomorph analyses, we demonstrate the lateral step-wise migration of sandy channelized submarine fans, as a foreland-propagating clastic wedge on a time-scale of hundreds of thousands of years. The deep-marine expression of the inferred tectonic pulses began with the large-scale basin-slope collapse as sediment slides and debris flows that formed much of the seafloor topography for each fan and contributed to their lateral confinement. The uppermost slope and any shelf-edge, including the narrow shelf, then collapsed, redepositing unconsolidated sands and gravels into deep water. This is overlain by an interval of mainly channelized and amalgamated sandy deposits, passing up into several tens of metres of less confined, non-amalgamated, medium- and thin-bedded, finer grained sands and marls. These deposits represent the phase of most active fan growth, initially by erosional channel development, sediment bypass and backfill (in several cycles), giving way to non-channelized, finer grained sandy deposition, interpreted as a response to the flushing out of the coarser clastics from the coastal and near coastal fluvial systems. During this latter stage in active fan growth and when sediment accumulation rates probably remained high, the degraded submarine slope was regraded and healed by finer grained depositional events. The high amount of woody material and the high non-marine palynomorph signal in these sandy deposits suggest direct river input as both turbidity currents and hyperpycnal flows for the silty marls. In the upper few metres, a thinning-and-fining-upward sequence shows a return to background marl deposition, representing fan abandonment. Many sequences are overlain by intraformational sediment slides that attest to the increasing seafloor gradients associated with the regrading and healing stage in slope development. These organized, predictable vertical sedimentary sequences provide a testable generic model for submarine fan development where fan growth is strongly influenced by tectonic processes.

FORAMINIFERAL BIOFACIES OF THE MIOCENE WARM TO COOL CLIMATIC TRANSITION IN THE PORT PHILLIP BASIN, SOUTHEASTERN AUSTRALIA

The Miocene marine sediments of the Torquay Group in the Port Phillip Basin of southeast Australia were deposited at a paleolatitude of at least 45S. Nevertheless, the presence of subtropical larger foraminifers, plankton of the ‘‘Orbulina’’ bioseries and other biofacies signals testify to a time of global warmth and correspond to the ‘‘Miocene Climatic Optimum’’. Throughout the Early Miocene to early Middle Miocene, bioclastic calcarenite of the Batesford Limestone was deposited in warm, subtropical and oligotrophic marine conditions in a highenergy inner-shelf (70 m depth) environment. During the early Middle Miocene, a distinct change in foraminiferal assemblage accompanied the transition to deposition of finer-grained marl and silty clay of the Fyansford Formation. At this level, a significant increase in the abundance of infaunal and planktonic taxa indicates a shift to a low-energy, middle- to outer-shelf environment (50–100 m depth). The disappearance of the larger subtropical foraminifera and the shift to a foraminiferal assemblage dominated by cool-water upwelling indices later in the Middle Miocene, signal the onset of oceanic upwelling and climatic cooling as identified in other southern Australian Tertiary basins. This event can be correlated to a period of global climatic cooling and intensified oceanic circulation that occurred in response to expansion of the East and West Antarctic ice sheets during the Middle to Late Miocene.

Palaeoenvironmental control on sponge-microbialite reefs and contemporaneous deep-shelf marl-limestone deposition (Late Oxfordian, southern Germany)

The Late Oxfordian (Bimammatum Zone) deep-shelf deposits of southern Germany are characterised by abundant reefs that laterally pass into marl-limestone alternations. The bioconstructions are made from three main components, sponges, microbialites and allochthonous sediment. A detailed morphological analysis of sponge-microbialite reefs in the Plettenberg section (Swabian Alb, southern Germany) is combined with investigation of calcareous nannofossil assemblages in laterally correspondent marl-limestone alternations in order to trace the evolution of palaeoenvironmental conditions during reef development. Fluctuations of CaCO3 content in deep-shelf deposits provides evidence of a succession of small-scale lithological units, generally formed by five to six marl-limestone couplets. Within a small-scale lithological unit, a close link is observed between growth patterns of sponge-microbialite reefs and the changes in the nannofossil assemblage composition. Phases of expansion of the build-ups correspond to carbonate deposits, characterised by a relative dominance of large, oligotrophic nannoplankton species (large Watznaueria britannica, Watznaueria manivitiae and Schizosphaerella spp.). Marly intervals reveal a high relative abundance of small-sized taxa (mainly Lotharingius hauffii, small W. britannica and subordinated Biscutum dorsetensis), and bioconstructions show a net reduction in size, or a total demise. This suggests that the same palaeoenvironmental parameters controlled, at the same time, marl versus limestone deposition, reef growth-phases, and calcareous nannofossil assemblage composition. Successive reef growth-phases recognized within a bioherm are correlated to the limestone hemi-couplets. Each reef growth-phase is composed of several stacked elementary sequences, comprising the following succession: (i) sponge, (ii) microbialites and (iii) carbonate mud. In turn, the microbialitic crust is formed of three successive microbial layers: (1) a fine crust of dense to clotted micrite; (2) a centimetre-scale to multicentimetric columnar layer of clotted to peloidal micrite; (3) a centimetre-scale stromatolitic crust. The passage from an initial dense microbial layer, with numerous microencrusters, to a final stromatolitic crust is interpreted as resulting from an increase of the microbial growth-rate, mainly driven by changes in the accumulation rate. Deep-shelf deposits resulted from changes in platform carbonate production and export basinwards controlled both by sea-level and climate changes. Climate controlled the intensity of carbonate production in shallow-platform environments and export towards the deep-shelf, as well as the trophic conditions of the deep-shelf marine-waters. Low trophic conditions favoured platform carbonate production and export basinwards, and a large development of the sponge-microbialite reefs in the deep-shelf. However, a high carbonate accumulation rate in the deep-shelf was also commonly responsible for the demise of sponge-microbialite reefs. During unfavourable and higher trophic conditions (during marl deposition), reduced development and frequent demise of the sponge-microbialite reefs is observed.

Palaeoenvironmental control on sponge-microbialite reefs and contemporaneous deep-shelf marl-limestone deposition (Late Oxfordian, southern Germany)

The Late Oxfordian (Bimammatum Zone) deep-shelf deposits of southern Germany are characterised by abundant reefs that laterally pass into marl-limestone alternations. The bioconstructions are made from three main components, sponges, microbialites and allochthonous sediment. A detailed morphological analysis of sponge-microbialite reefs in the Plettenberg section (Swabian Alb, southern Germany) is combined with investigation of calcareous nannofossil assemblages in laterally correspondent marl-limestone alternations in order to trace the evolution of palaeoenvironmental conditions during reef development. Fluctuations of CaCO 3 content in deep-shelf deposits provides evidence of a succession of small-scale lithological units, generally formed by five to six marl-limestone couplets. Within a small-scale lithological unit, a close link is observed between growth patterns of sponge-microbialite reefs and the changes in the nannofossil assemblage composition. Phases of expansion of the build-ups correspond to carbonate deposits, characterised by a relative dominance of large, oligotrophic nannoplankton species (large Watznaueria britannica, Watznaueria manivitiae and Schizosphaerella spp.). Marly intervals reveal a high relative abundance of small-sized taxa (mainly Lotharingius hauffii, small W. britannica and subordinated Biscutum dorsetensis), and bioconstructions show a net reduction in size, or a total demise. This suggests that the same palaeoenvironmental parameters controlled, at the same time, marl versus limestone deposition, reef growth-phases, and calcareous nannofossil assemblage composition. Successive reef growth-phases recognized within a bioherm are correlated to the limestone hemi-couplets. Each reef growth-phase is composed of several stacked elementary sequences, comprising the following succession: (i) sponge, (ii) microbialites and (iii) carbonate mud. In turn, the microbialitic crust is formed of three successive microbial layers: (1) a fine crust of dense to clotted micrite; (2) a centimetre-scale to multicentimetric columnar layer of clotted to peloidal micrite; (3) a centimetre-scale stromatolitic crust. The passage from an initial dense microbial layer, with numerous microencrusters, to a final stromatolitic crust is interpreted as resulting from an increase of the microbial growth-rate, mainly driven by changes in the accumulation rate. Deep-shelf deposits resulted from changes in platform carbonate production and export basinwards controlled both by sea-level and climate changes. Climate controlled the intensity of carbonate production in shallow-platform environments and export towards the deep-shelf, as well as the trophic conditions of the deep-shelf marine-waters. Low trophic conditions favoured platform carbonate production and export basinwards, and a large development of the sponge-microbialite reefs in the deep-shelf. However, a high carbonate accumulation rate in the deep-shelf was also commonly responsible for the demise of sponge-microbialite reefs. During unfavourable and higher trophic conditions (during marl deposition), reduced development and frequent demise of the sponge-microbialite reefs is observed.

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.

Mixed carbonate–siliciclastic sequence stratigraphy of a Paleogene transition zone continental shelf, southeastern USA

The sequence stratigraphy and facies of the Paleogene in the subsurface of the Albemarle Basin, North Carolina was defined using 1600 thin sections of plastic impregnated well cuttings from 24 wells, wireline logs, biostratigraphic data, and seismic data. The facies formed in the transition zone between warm subtropical and temperate conditions on a swell-wave dominated, open shelf exposed to major boundary current activity. The shelf has a distinctive seismic profile consisting of a shallow inner shelf, inner-shelf break, deep shelf (depths in excess of 200 m), and the continental slope. The inner shelf was characterized by distinctive quartz sand and sandy mollusk facies inshore, passing seaward into a broad, wave-swept abrasional shelf, and then into storm-influenced bryozoan–echinoderm limestones to depths of several tens of meters. Argillaceous lime mud (marl) deposition was widespread across the deep shelf, extending onto the inner-shelf during major highstands. Sediment thickness trends were controlled by greater differential subsidence of crustal blocks within the Albemarle Basin, which considerably modified but did not obliterate the effects of eustatic sea level changes in this passive margin setting. Five supersequences were identified on seismic and in wells, each consisting of multiple regionally identifiable sequences. The Paleocene supersequence is dominated by widespread marl deposition, reflecting shelf flooding into the Late Paleocene thermal maximum. This warming corresponds with widespread inner-shelf skeletal carbonate deposition from the Late Paleocene through the Middle Eocene. The two Eocene supersequences identified are dominated by bryozoan–echinoderm-rich carbonates that formed a seismically definable sediment buildup 50 km wide by 100 m thick across the deepest inner-shelf during the Lower to early Middle Eocene. Middle to Upper Eocene supersequence highstand sequences indicate increased progradation and greater mixing of shelf carbonates with nearshore siliciclastics, likely in response to lowering sea-levels and cooling climate. The two Oligocene supersequences identified are dominated by coarse siliciclastic sand that is heavily admixed with mollusk-foraminifer-dominated carbonates. Rapid flooding, followed by extensive progradation of shallow shelf sediments in Oligocene sequences reflects continued eustatic lowering driven by the onset of icehouse climatic conditions. Increased incision and reworking of deep shelf sediments during Oligocene supersequence highstands resulted from increased ancestral Gulf Stream boundary current activity during icehouse times. Key elements controlling facies distribution through time include significant wave energy, which controls the width and distribution of inner-shelf facies belts through the degree of water bottom abrasion and winnowing. Boundary currents also are capable of large-scale reworking of deep shelf sediment; they also provide a mechanism for widespread inner-shelf hardground development during major transgressions. In addition, boundary currents play a major role in stabilizing local climate by buffering seasonal temperature variations, directly influencing which carbonate grain producers can thrive in this transition zone setting.