Northern Outcrop Research Articles

Depositional environments and thermal maturity of the hydrocarbon source rocks in the Devonian–Early carboniferous Ora Formation from palynological organic petrographic investigations in northern and western Iraq

The study investigates the palynofacies, organic matter character, and hydrocarbon generation potential of this rock unit, based on surface and subsurface samples from the Ora Formation type-section in extreme northern Iraq and the Akkas-3 well in western Iraq, respectively. Dark, mostly oxidized, gelified platy amorphous organic matter (AOM) dominates the palynological components in the surface section, in addition to a few rounded spores and structured phytoclasts. In contrast, palynomorphs, including Ambitisporites avitus, Aneurospora spp., Vallatisporites verrucosus, Acinosporites spp., Verrucosisporites nitidus and the algae Botryococcus, are predominant in studied samples from the Akkas-3 well. Statistical cluster analysis identified three palynofacies types in the surface section based on stratigraphic variations in the particulate organic matter. These vary from high amorphous organic matter (AOM), moderate phytoclast, and low palynomorph abundances that represent proximal suboxic–anoxic shelfal environments to moderate to good AOM and low to moderate palynomorph abundances that represent distal suboxic–anoxic or distal dysoxic–anoxic shelfal environments. The organic petrographic study of the outcrop section also revealed the strong effect of oxidation, where dispersed terrigenous and amorphous organic materials in the form of granular and gelified forms dominate and reflect a terrestrial origin of these components. In the subsurface section, a mixed terrestrial and less marine or lacustrine origin characterized the studied organic matter, where land plant spores (sporinite), in addition to vitrinite and inertinite, are dominant with a few scattered liptinite macerals. The difference in thermal maturity between the outcrop and subsurface samples is likely due to the higher tectonic burial of the outcrop samples that form part of the Northern Thrust Zone of Iraq. Nevertheless, higher abundances of AOM (oil-prone kerogen type II) accumulated in the northern outcrop type section. This might imply that the Ora Formation has a higher potential for hydrocarbon production north of the Akkas field.

Middle Pennsylvanian (Desmoinesian) Fusulinids of the Bug Scuffle Limestone Member of the Gobbler Formation, Sacramento Mountains, South-Central New Mexico

Analysis of fusulinids from the Bug Scuffle Limestone Member of the Gobbler Formation along the western escarpment of the Sacramento Mountains in south-central New Mexico demonstrates that all four Desmoinesian regional fusulinid zones documented in Midcontinent and Southwest North America are present in the stratigraphic unit. Earliest Desmoinesian (Df1 Zone) fusulinids from the basal Bug Scuffle limestone beds suggest that the carbonate unit transgressed northward on the Sacramento Shelf, with Beedeina insolita in basal beds of the southernmost canyon exposures, and the slightly more advanced B. hayensis and B. curta in basal limestone beds of more northern outcrops. Late early Desmoinesian (Df2 Zone) fusulinids are common and widespread throughout the escarpment outcrop belt indicating that it was the time period with the most widespread normal marine shelf paleoenvironmental conditions. The diverse assemblage of the Df2 Zone is characterized by Beedeina novamexicana, B. euryteines, B. leei, B. socorroensis, B. joyitaensis, Wedekindellina euthysepta, and W. excentrica. The microprobematical branching fossil Komia is also common in this zone. Wedekindellina and Komia do not range above the mid-Desmoinesian CSB1 composite sequence boundary. Above that sequence boundary, the early late Desmoinesian Df3 Zone is characterized by sparse Beedeina haworthi, and the closely related B. illinoisensis and B. tumida. The late late Desmoinesian Df4 Zone is represented by a diverse assemblage of fusulinids in the uppermost part of the Bug Scuffle Limestone Member in the southern canyon exposures, including Beedeina acme, B. megista, B. mysticensis, B. lonsdalenesis, B. bellatula, B. gordonensis, and B. vintonensis. No Beedeina identifiable to species were found in upper part of the Bug Scuffle Limestone Member in the northernmost canyon exposures, demonstrating that late Desmoinesian paleoenvironments became more restricted marine northward along the Sacramento Shelf. Above the CSB2 composite sequence boundary in the uppermost Bug Scuffle Limestone Member, the lower part of the uppermost depositional sequence continues to contain latest Desmoinesian Df4 Zone fusulinids in the southern canyon sections. Early Missourian conodonts have been reported in a limestone unit near the top of the Gobbler clastic detrital member in the north-central part of the outcrop belt(Wahlman and Barrick 2018; Lucas et al. 2021), but no early Missourian conodonts or fusulinids have been reported yet from the uppermost Bug Scuffle Limestone Member in the southern canyons.

Subantarctic Mode Water and its long-term change in CMIP6 models

AbstractThe Subantarctic Mode Water (SAMW) is a major water mass in the South Indian and Pacific oceans and plays an important role in the ocean uptake and anthropogenic heat and carbon. The characteristics, formation, and long-term evolution of the SAMW are investigated in the “historical” and “SSP245” scenario simulations of the sixth Coupled Models Intercomparison Project (CMIP6). Defined by the low potential vorticity, the simulated SAMW is consistently thinner, shallower, lighter, and warmer than in observations, due to biases in the winter mixed layer properties and spatial distribution. The biases are especially large in the South Pacific Ocean. The winter mixed layer bias can be attributed to unrealistic heat loss and stratification in the models. Nevertheless, the SAMW is presented better in the CMIP6 than CMIP5, regarding its volume, location, and physical characteristics. In warmer climate, the simulated SAMW in the South Indian Ocean consistently becomes lighter in density, with a reduced volume and a southward shift in the subduction region. The reduced heat loss, instead of the increased Ekman pumping induced by the poleward intensified westerly wind, dominates in the SAMW change. The winter mixed layer shoals in the northern outcrop region and the SAMW subduction shifts southward where the mixed layer remains deep. The projected reduction of the SAMW volume is likely to impact the heat and freshwater redistribution in the Southern Ocean.

Miocene Rocks Around the Marádah Oasis, Central Sirt Basin, Libya: Facies Development and Implication on Stratigraphy

The Miocene rocks of the Marádah Formation have been stratigraphically investigated from four stratigraphical sections around the Marádah Oasis in the Central Sirt Basin of Libya. The field investigations led to the identification of two members, the lower Qarat Jahannam Member and the upper Ar Ráhlah Member. Fourteen sedimentary facies at the outcrop-scale representing a gradual development of sedimentation from a continental clastic witness in the southwestern outcrops to transitional estuarine, lagoonal, and beaches to the proximal offshore in the northern outcrops, were recognized. The results indicates that the accumulation of the Marádah Formation is transgressive in nature and corresponding to two phases of deposition which have been mentioned in the earlier studies.
 
 The first phase is continental-dominated facies in which cross-bedded sandstones and calcareous sands comprise most of the depositional sequence of the lower Qarat Jahannam Member at the southwestern outcrops. This phase, however, is characterized by extremely bioturbated laminated-shale conquered by Skolithos ichnofacies in the lower part of the upper Ar Ráhlah Member at the northern outcrops. This phase is providing further evidence that the contact between the two members is diachronous everywhere in the study area. The clastic-phase has thought to be deposited in the Lower Miocene (Aquitanian-Burdigalian) since the lower Qarat Jahannam Member rests on an erosional surface of submarine origin in the southwestern outcrops above a 0.5 m. thick of a nummulitic unit of the Oligocene Bu Hashish Formation.
 
 The second phase is marine-dominated facies in which a bioclastic limestone unit rich in thick and disarticulated oysters, including Crassostrea gryphoides (Schlottheim), characterizes the sediments of the Ar Ráhlah Member at the southwestern outcrops. This phase also includes the upper part of the latter member at the northern outcrops in which a detrital limestone unit rich in turritelline gastropods is overlying by thick-bedded calcarenites rich in disarticulated oysters, gastropods, irregular echinoids (notably, Clypeaster and Echinolampas), bryozoans, and celestite corals. The upper part of the Ar Ráhlah Member at the northern outcrops, nevertheless, is terminated by a quite hard dolomitic limestone and by a pretty soft dolomitic marly limestone. Both lithologies, however, are combined with medium-sized oysters, including Ostrea digitalina Fuchs, and pectinid bivalves. The second phase, however, is interpreted to be deposited in the Middle Miocene (Langhian and Serravallian) based on the total-stratigraphic range of the larger benthic foraminifera Borelis melo melo (Fichtel & Moll), which recovered from the studied washed residues, and the associated microfacies.

Elucidating hydrological complexity and climate-influenced diagenesis during the early Carboniferous of South Wales

A revised age provided by conodonts from the Gilwern Oolite of the Clydach area of South Wales allows a clearer understanding of the palaeohydrology, palaeoclimatic history and diagenesis of previously correlated oolitic units. Earlier uncertainty over the apparent sub-regional differences in climate during the early Visean (Chadian—Arundian) lowstand is resolved. Previously a humid interval evidenced by prominent palaeo-epikarst capping the Gilwern Oolite along the northern outcrops of the South Wales synclinorium, was not recognized in what were regarded as correlative outcrops in the Chadian Gully Oolite in the southern part of the synclinorium. Conodont dating now shows that the Gilwern Oolite is much older (Courceyan) than the Chadian Gully Oolite, and during the prolonged exposure of the former there was an interval of weathering under a humid climate. This also explains the contrast between the diagenesis seen between the Gilwern and Gully oolites, which are no longer seen as correlatives.

Reassessment of a Historical Collection of Sauropod Dinosaurs from the Northern Morrison Formation of Wyoming, with Implications for Sauropod Biogeography

The Upper Jurassic Morrison Formation of the western United States preserves one of the best-known Mesozoic paleoecosystems worldwide. The formation crops out over an area from New Mexico and Oklahoma to Montana and Utah and encompasses a time span of approximately eight million years. Recent studies indicate a high diversity of gigantic, herbivorous sauropod dinosaurs, but the geographic and temporal distributions of species or even genera of these animals remain poorly understood. In particular, sauropod specimens from northern outcrops of the formation have rarely been studied in detail, and temporal relationships among sites are imprecise. Here, we reassess the taxonomic diversity of the sauropods from a historic Carnegie Museum locality in northern Wyoming. Previous referrals of material to the well-known diplodocid genera Apatosaurus and Diplodocus cannot be confidently confirmed; instead, all these specimens more likely represent elements from the recently recognized Galeamopus. Specimens previously assigned to Camarasaurus and Haplocanthosaurus could not be referred to these genera based on apomorphies, due to a lack of detailed knowledge concerning the genus- and species-level taxonomy of these sauropods. Our findings imply that many referrals of incomplete diplodocid skeletons to Apatosaurus and Diplodocus must be reassessed. These reassessments are particularly important with regard to specimens from northern localities of the Morrison Formation, as it is becoming increasingly evident that diplodocids from this area were distinct from better-known, more southerly taxa. This geographic segregation does not seem to apply to nondiplodocid sauropods; however, these taxa are also in need of systematic revision, which may reveal species-level patterns similar to those observed in Diplodocidae.

Sequence architecture of the cavi unit, Chasma Boreale, Mars

The principles of terrestrial sequence stratigraphy provide a proven approach for evaluating the cavi unit where it transitions into the north polar layered deposits (NPLD). Three cavi unit outcrops at the head of Chasma Boreale were examined using high resolution imagery and topography and interpreted in a sequence stratigraphic framework. Lithofacies present in the cavi unit were identified and consist of (1) dark lithic material, (2) dark material with icy foresets, (3) icy cavi, (4) isolated dunes, (5) dirty ice, and (6) layered ice. These lithofacies represent a progression in the dominance of aeolian to cryosphere processes and have analogs in the modern Chasma Boreale depositional environment. Parasequences were defined as aeolian units bounded by outcrop-scale unconformities, permafrost layers, and layered ice deposits. The northern outcrop is dominated by sandy lithofacies, with large bodies of sand also dominating the northern parts of the central and southern outcrops. In the central and southern outcrops, sandy lithofacies yield southward to icier accumulations. Concurrently, vertical trends in lithofacies distribution indicate an increasing prevalence of ice deposits through time. Considered across all three outcrops, the parasequences form a set that expresses the northward retreat of the cavi aeolian system coincident with transgression of an ice sheet originating in Gemini Lingula. This retrogradational stacking pattern of cavi aeolian parasequences with gradual transgression of the NPLD environment implies that the transitional cavi unit and NPLD form a single sequence that may correspond to allogenic forcing by orbital parameters. The dynamics between aeolian and cryosphere processes revealed at the parasequence scale indicate that preservation of the stratigraphic record is driven by the ice transgression, suggesting that during episodes of ice sheet collapse, the north polar sedimentary environment reverts to one dominated by aeolian erosion and reworking, as represented by the basal cavi unit.

Low Net: Gross Reservoirs of the Transgressive Shelf Systems in the Upper Mancos Shale, El Vado Sandstone, San Juan Basin, New Mexico

The El Vado (EV) Sandstone Member (upper Coniacian) of the Mancos Shale has been considered both a conventional and unconventional hydrocarbon resource target (Ridgley, 2001) in the San Juan Basin (SJB) of northwestern New Mexico. Sandstones of the EV were deposited on the marine intracontinental shelf along the west margin of the Cretaceous Seaway. The EV is part of a transgressive-regressive wedge of rock that overlies a large, older transgressive wedge that contains the Tocito Sandstone. The EV is examined in outcrops in the northeast and the southeast parts of the SJB. In northern outcrops, the EV consists of five parasequences of interbedded sands and shales of similar thickness (∼4 m each) separated by marine-shale units that become progressively sandier upward. To the south, the EV Sandstone transitions from a shelf-deposited into a lower-shoreface sandstone. Well logs and core are used to map the subsurface distribution of the EV Sandstone in the SJB. It is reflected in logs as a thick (∼36.6 m; 120 ft) interval of low gamma ray and high resistivity, associated with highly laminated sand to silt interbedded with shales. A total of 13 cross sections are correlated and used to construct total-interval isopach and parasequence-scale isopach maps for the EV. Regional net-sand and net:gross maps, determined from 104 digitized well logs, highlight the regional distribution of sand in the formation. Thicks are oriented north to south and show compensated deposition suggesting that individual parasequences are not in communication across the basin, but opportunity exists to penetrate stacked parasequences with single vertical wells.

The upper Palaeozoic Godar-e-Siah Complex of Jandaq: Evidence and significance of a North Palaeotethyan succession in Central Iran

The Upper Palaeozoic Godar-e-Siah Complex of Jandaq, Central Iran, comprises three isolated, fault-bounded outcrops exposing Palaeozoic fossiliferous carbonates, volcanics and siliciclastics, which are markedly distinct from the surrounding sedimentary successions. The three outcrops, that emerge below Cretaceous and younger sediments, are the Chah Rizab outcrop, the Godar-e-Siah northern outcrop, and the Godar-e-Siah central outcrop. Their sedimentary successions strongly differ from the typical passive margin successions of Gondwanan affinity that characterize the Yazd, Lut and Tabas blocks of Central Iran and the Alborz in North Iran. To understand the origin of these profound differences, we first calibrated the age of the Jandaq successions: U-Pb radiometric zircons ages, obtained from granitoid boulders in the conglomerates at Chah Rizab and in the Godar-e-Siah northern outcrop, gave a Late Devonian to Mississippian age. Biostratigraphic data from brachiopods and fusulinids from the Godar-e-Siah northern and central outcrops indicate a Pennsylvanian age. The age of the successions is thus post-Visean to Pennsylvanian. The petrographic composition of the siliciclastic deposits indicates the erosion of a magmatic arc. To understand where the Jandaq complex could have been located at that time, we have assessed the palaeobiogeographic affinity of the faunas. The collected brachiopods and fusulinids assemblages are mostly similar to coeval faunas from Spain, Donbass, Urals, and Yukon Territory (Canada) and have a North-Palaeotethyan affinity. The Godar-e-Siah Complex of Jandaq likely represents part of the southern active margin of Eurasia (northern margin of the Palaeotethys), in contrast to the surrounding Central and North Iran blocks, which were at that time located along the southern margin of the Neotethys.Our investigations confirm a complex palaeogeographic evolution for the studied outcrops, suggesting that they represent fragments of the southern Eurasian active margin - today preserved in NE Iran - displaced by crustal-scale wrench motions related to the opening and closure of the Sabzear Ocean and to the Cenozoic activity of the Great Kavir-Doruneh Fault and its possible precursors.

POST- ALPINE LATE PLIOCENE – MIDDLE PLEISTOCENE UPLIFTED MARINE SEQUENCES IN ZAKYNTHOS ISLAND

Post-orogenic marine sequences crop out in two areas of Zakynthos Island: a) In Gerakas peninsula at the southeastern edge of the island and b) Along the coastal zone of central northern Zakynthos from Alikanas in the west to Zakynthos town in the east. Detailed stratigraphic analysis of Gerakas area has shown the existence of three formations separated by two unconformities: 1) Gerakas Fm Q1 comprising marls of Late Pliocene–Early Pleistocene age (2.8 – 0.9 Ma). 2) Kalogeras Fm Q2 comprising littoral sandstones at the base (Q2a), alternations of sandstones and marls in the middle (Q2b) and marls (e.g. Porto Roma) in the upper part (Q2c). The age of this formation is middle Pleistocene (0,8 – 0,5 Ma). 3) Agios Nikolaos Fm Q3 comprising littoral sandstones. Stratigraphic correlations between the two aforementioned areas have been made and equivalent stratigraphic formations, slightly differentiated in the central northern Zakynthos, have been identified. The upper unconformity is well pronounced in the area of Cape Gaidaros whereas the lower unconformity is often masked by debris accumulated along the base of the cliffs produced by the compact sandstones of Q2a above the soft marls of the underlying Q1. A remarkable increase in the thickness of the middle member Q2b is observed in the northern part with respect to the equivalent Kalogeras Fm in Gerakas area. In contrast, the thickness of the upper member (Q2c) is highly reduced in the limited northern outcrops compared to those of the southeastern exposure. The Plio-Quaternary post-orogenic marine deposits in both regions represent the creation of the accommodation space formed by the westernmost extensional structure of the Hellenic arc. The two unconformities reflect sea-level changes during the Quaternary within an overall tectonic uplift of Zakynthos Island at the front of the Hellenic arc and trench system, while the entire post-orogenic sequence reflects the intense palaeoclimatic fluctuations of the Quaternary.

Paleobiogeographic distribution of Testudinata and neosuchian Crocodyliformes in the Morrison Formation (Upper Jurassic) of North America: Evidence of habitat zonation?

Nearly 150 occurrences of turtles and neosuchian crocodyliforms in the Upper Jurassic Morrison Formation indicate that, by number of localities and number of specimens, both are preferentially preserved off the Colorado Plateau in deposits in the eastern and northern parts of the Morrison basin, suggesting that these latter areas contained wetter paleoenvironments and either were more populated with these semi-aquatic taxa or more frequently preserved their remains, compared with areas to the south and west. Cursorial crocodylomorphs occur at more sites and in greater numbers on the Colorado Plateau than to the east and north, but this pattern is only significant by number of specimens. Previous suggestions of wetter paleoenvironmental conditions on floodplains distal to the southwestern source areas on the Colorado Plateau, or western source areas for northern outcrops, based on geological and microvertebrate data, seem to be borne out by these data from semi-aquatic mesovertebrates.

Prolonged isolation and persistence of a common endemic on granite outcrops in both mesic and semi‐arid environments in south‐western Australia

AbstractAimGranite outcrops may be able to act as refugia for species during adverse climate change, owing to their topographic complexity. We assessed this hypothesis by examining phylogeographical patterns in a common, geographically widespread granite endemic, Stypandra glauca (Hemerocallidaceae).LocationGranite outcrops of the Southwest Australian Floristic Region, Western Australia.MethodsTwenty‐four tetraploid individuals of the granite endemic Stypandra glauca were sampled from each of 12 granite outcrops: 7 from a mesic environment and 5 from the semi‐arid region. Phylogenetic reconstruction and divergence‐dating was achieved using Bayesian and parsimony analyses of chloroplast haplotypes from 90 individuals. Nuclear diversity and population differentiation were analysed across all individuals using 10 microsatellite loci.ResultsStypandra glauca exhibited high (chloroplast) or moderate (nuclear) levels of divergence among, and low diversity within, outcrops. Haplotype diversity was high in both sampling regions, and each haplotype was unique to one outcrop. There was little correlation between geographical and genetic distance. Both nuclear and chloroplast diversity were higher in southern (mesic) outcrops than in northern (semi‐arid) outcrops, although the level of chloroplast divergence among outcrops was similar for both climatic regions.Main conclusionsThe levels of divergence and low diversity revealed in S. glauca support a scenario of prolonged isolation and persistence on granite outcrops in both mesic and semi‐arid climatic regions, with no evidence of contraction–expansion dynamics across the outcrop network. The higher levels of diversity in the southern populations may result from the maintenance of a larger effective population size in southern regions, which retained more mesic climates during drier glacial periods. Although the climatic conditions differ between outcrops in this study, our results indicate that outcrops in both regions have harboured S. glauca throughout climatic changes, accentuating the value of these habitats to biodiversity conservation under future changing climate.

Age of ferroan A-type post-tectonic granitoids of the southern part of the Keimoes Suite, Northern Cape Province, South Africa

The granitoids of the Keimoes Suite represent part of a complex group of late Mesoproterozoic intrusions of granodioritic to potassic granite composition that occupy an outcrop belt striking approximately NW–SE to the immediate west of Upington, Northern Cape Province, South Africa. The intrusions are believed to mark the contact between the Kaapvaal Craton and the Namaqua Sector of the Namaqua-Natal Province. Published geological, geochemical and geochronological knowledge of the Keimoes Suite is poor in general, with most data restricted to the central portion of the outcrop belt. In this contribution new ages and geochemical data for three granitoids of the southeastern Keimoes Suite in the Putsonderwater – Van Wykspan area, the Klip Koppies, Gemsbokbult and a member of the Kleinbegin Subsuite, are presented. All three intrusions show petrological and geochemical characteristics that agree well with literature data for the central and northern outcrop portions of the Keimoes Suite. They are weakly foliated to unfoliated, medium- to coarse-grained ferroan, alkali-calcic late- to post-tectonic A-type biotite granitoids intruded within a collisional within-plate tectonic setting. Zircon U–Pb SHRIMP ages for the intrusion of the three granitoids are within error of one another at ca. 1100 Ma. Marked differences between the three granitoids include the abundance and age of inherited zircons and Sm–Nd isotope systematics. With an ε Nd(t) value of 1.83, the Gemsbokbult Granite is dominantly sourced from partial melting of material with a mantle derivation with a minor crustal component. The other two intrusions, on the other hand, show a strong crustal source component, as indicated by ε Nd(t) values of −2.03 for the Klip Koppies Granite and −8.46 for the Kleinbegin Granite. The Keimoes Suite granitoids provide important clues as to the timing and tectonic evolution of the western margin of the Kaapvaal Craton at its junction with the Proterozoic Namaqua Sector of the Namaqua-Natal Province. A contribution to these melts from the host rocks, the ∼1.24–1.30 Ga Areachap Group volcanic belt is traced through the presence of inherited zircon cores of this age that is particularly evident in the Klip Koppies Granite. Inheritance also reflects the major tectono-magmatic events which affected the western margin of the Kaapvaal Craton during Mesoproterozoic times, with the bulk of the inheritance in the zircon populations due to peak metamorphism and partial melting caused by continental collision between the Kaapvaal Craton and the Kakamas Terrane and Bushmanland Subprovince to the west at approximately 1.18–1.2 Ga. Post 1.1 Ga ages reflect isotopic disturbance due to a later collisional event to the west at ∼1.08 Ga and subsequent exhumation of the western margin of the Kaapvaal Craton.

Vent area and depositional mechanisms of the Upper Member of the Neapolitan Yellow Tuff (Campi Flegrei, Italy): new insights from directional fabric through image analysis

In order to provide new information about the source area and depositional mechanisms of the Upper Member of the Neapolitan Yellow Tuff (NYT), a prominent pyroclastic deposit of the Campi Flegrei Volcanic District (southern Italy), statistics on directional fabric, by means of computer-assisted image analysis on 32 rock samples, were compiled. Seventeen samples were collected along vertical direction on two selected exposures and fifteen were taken from outcrops widely distributed all around the Campi Flegrei Volcanic District. Fabric measurements within the investigated successions reveal a vertically homogeneous direction of the mean particle iso-orientation, with considerable variability in the strength of particle iso-orientation even at cm-scale. The existence of particle iso-orientation can be related to continuous sedimentation from a concentrated bedload region beneath suspension currents, producing massive or inversely graded beds by traction carpet sedimentation. The considerable vertical variability in the strength of iso-orientation is the result of very unstable flow regimes, up to the extreme condition of discrete depositional events, with a variable combination of traction carpet and/or direct suspension sedimentation. The vertical homogeneity in the mean orientation values, found in the investigated sections, may derive from the sequential deposition of laminae to thin beds, whose relatively flat upper surfaces were unable to significantly deflect the depositional system of the following currents. According to the observed homogeneous mean particle orientation values along the investigated vertical profiles, samples collected through areal distribution are considered representative of the local paleo-flow directions of the whole deposit. The mean directions of the samples collected areally show two different coherent patterns which point to the existence of two different source areas. The first, which includes all samples from the northern outcrops, appears to converge in a narrow area about 2 km NE of the town of Pozzuoli, largely in coincidence with the inferred area on the basis of the pumice fall distribution. The second, which includes samples from Capo Miseno and Posillipo areas, points to the central part of the Pozzuoli Bay, about 4 km offshore the town of Pozzuoli.

Stratigraphic architecture, palaeogeography and sea-level changes of a third order depositional sequence: The late Turonian–early Coniacian in the northern Iberian Ranges and Central System (Spain)

This paper reports a high-resolution stratal, palaeogeographical and quantitative analysis, of a late Turonian–early Coniacian carbonate ramp (the Northern Iberian Ranges) and its siliciclastic coastal margin (the Central System). The analyzed succession comprises a complete 3rd order depositional sequence with a shelf-margin wedge, a transgressive systems tract and a highstand systems tract. Based on the existence of a) subaerial exposure evidences and early diagenetic overprints; b) stratal relationships (onlap, offlap, toplap) regarding underlying and overlying sequences, and c) changes in the vertical facies evolution, the depositional sequence was bounded by two major sequence boundaries. These indicate that a major fall in relative sea level occurred in these boundaries. The comparative study of the internal stratal surfaces and the vertical facies succession allowed the identification of superimposed, higher-order depositional parasequences sets and parasequences (4th to 5th order), which record short-term changes in the relative sea level. Thus, when vertical facies trends in the parasequences are arranged in the framework of a parasequence set, a clearer palaeogeographic picture is obtained, and palaeogeographic maps can more clearly show the evolutionary trend of the basin. Each parasequence set was composed of a basal lowstand/transgressive systems tract in turn composed of fringing siliciclastic shoreface deposits and offshore muds. Older sequences were partially exposed further landwards. The sedimentation of these sands resulted in the progradation of the coastal systems during times of low relative sea level, during which the basal parasequence set boundary was also generated. Subsequent transgression remobilised underlying lowstand sands. The early highstand was composed of carbonate sediments in platform areas and mixed siliciclastic-carbonate sediments landwards, separated by a narrow fringe of muddy-marl offshore sediments. The late highstand showed a progressive shallowing trend, with carbonate littoral and tidal sediments covering broad areas of the basin, and lagoon facies were restricted to the northern outcrops. During late highstand, underlying transgressive systems tract and older highstand deposits were exposed landwards. Sea-level and accommodation curves have been obtained from paleogeographical, sedimentological and sequence stratigraphical data. The mean sea-level curve for the entire 3rd order sequence shows a rise of the sea-level and then an overall stillstand, but accommodation curve shows a positive trend along the sequence. The 3rd order sea-level cycle has a mean amplitude of 52 m and high-frequency cycles have amplitudes of 20–40 m (4th order) and about 1.5–4 m (5th order). The mean final rise in the sea-level (46.6 m) is quite similar to the total accommodation deduced from Fischer plot (45.75 m). The sea-level cycles are considered to be eustatic in origin and driven by orbital forcing in the Milankovitch band based on the estimated 4th order- (400 kyr) and 5th order-cycle lengths (80 kyr).

Stratigraphy and sedimentology of shoreface and fluvial conglomerates: insights from the Cardium Formation in NW Alberta and adjacent British Columbia

ABSTRACT In this paper we describe little-studied exposures of the Upper Cretaceous Cardium Formation in the northern Foothills and Peace River Plains, located north of Twp. 58. We correlate sixteen principal outcrop sections along the Foothills and across the northern escarpment of the Cardium as far east as the Smoky River. Correlations are based on tracing bounding erosion surfaces, initially observed in well logs and cores, and later extended into outcrop. The Kakwa Member is conglomeratic in many of these sections. The member displays a spectrum of conglomerate types, of both shallow marine and fluvial origin. Depositional environments are differentiated on the basis of stratigraphic context, conglomerate texture, sedimentary structures, stratification style and paleogeographic setting. We describe in detail four localities exemplifying the main paleoenvironments. At Bay Tree, a 12 m thick section consists primarily of clast-supported conglomerates representing a wave-dominated shoreface and beachface. This environment is dominated by broadly horizontal stratification with horizontal facies heterogeneity on a metre scale. At Cutbank Lake, swaley-stratified shoreface sandstones contain pebble-lined scours that show an upward increase in thickness and lateral continuity and represent rip current deposits. At Mount Niles, conglomerate forms a 2-6 m thick, >200 m wide, channelized body consisting of heterolithic matrix-supported conglomerates and pebbly sandstones capped by gravel wave ripples. Deposition may have been in a river-mouth setting. At 'Horseshoe Mountain', the upper part of the Kakwa Member consists of metre-scale crossbedded pebbly sandstone and matrix-supported conglomerate deposited in a pebbly fluvial system lacking marine influence. For the entire study area, paleocurrent observations indicate a strong NW to SE alongshore transport of gravel, with storm waves approaching from the NE. Fluvial crossbedding is directed towards the NE. Some of the outcrop facies can also be recognized in core from the adjacent subsurface. Our descriptions of conglomerate facies in outcrop facilitate interpretation of the depositional environment of comparable units in subsurface. Unfortunately, the limited extent of exposures does not allow us to determine with precision the geometry of conglomeratic units. However, a broad conglomerate-rich zone >90 km in dip extent and 10-20 km in strike extent can be traced across the northern outcrop belt and probably records the position of a major and long-lasting pebbly fluvial system. Subsurface analogs would be exploration fairways. At the reservoir scale, conglomerate bodies showing greater influence of wave reworking would tend to be more elongate, and have greater facies continuity/permeability, in a shore-parallel direction. The outcrops display lateral textural heterogeneity at scales of metres to 10s of metres. This heterogeneity would affect reservoir performance, but could not be captured (for reservoir modeling) using typical development well spacing. End_Page 437------------------------

Shallow to deep-water deposition in a Cratonic basin: an example from the Proterozoic Penganga Group, Pranhita–Godavari Valley, India

The unmetamorphosed Proterozoic succession dominated by deep-water lithographic limestone and shale in the western flank of the Pranhita–Godavari Valley is designated as the Penganga Group. The succession in different parts of the Valley includes the Pranhita Sandstone (25–400 m), the Chanda Limestone (300 m), and the Sat Nala Shale (>2000 m) in ascending order. The Pranhita Sandstone and the Chanda Limestone reveal considerable variations in the character of the stratal packages and depositional settings from Mancherial in the south to Adilabad in the north. The Sat Nala Shale in both southern and northern outcrop belts is completely devoid of sand. It is brown to purple in colour and resembles present-day deep-water mud deposits. In the Mancherial area, the Pranhita Sandstone consists of 25–400 m thick conglomerate, pebbly red arkose and quartzose sandstone succession of coastal alluvial fan to shallow shelf origin. The Chanda Limestone is micritic and locally includes interbedded lenses of cross-stratified quartzose sandstone in the lower part. The depositional milieu varies from shallow shelf to below wave base outer ramp carbonate platform. Around Adilabad, the Pranhita Sandstone (25 m) lacks the conglomerate–pebbly arkose association at the base and comprises only quartzose sandstone and shale of shoreface to muddy shelf settings. The Chanda Limestone is essentially micritic but, in contrast to the Mancherial area, includes several interbedded intervals of slope-related, autoclastic debris flow limestone conglomerates and calciturbidites, and represents deep, outer ramp to slope and basinal settings. A predominantly deep-water micritic limestone and deep-water shale succession suggests that the Penganga basin evolved to a vast, deep epicratonic sea connected to an open ocean. The absence of a coastal alluvial fan association at the lower part of the Pranhita Sandstone and presence of a slope to basinal association in the Chanda Limestone in the northern outcrop belts around Adilabad indicates a northward transition from coastal to deep shelf, slope and basinal conditions and a northerly paleoslope of the basin.

Comparison of Southern Appalachian high‐elevation outcrop plant communities with their Northern Appalachian counterparts

Abstract. Southern Appalachian high‐elevation outcrops harbour six regionally rare Northern Appalachian taxa usually considered relicts of a Pleistocene alpine flora. For five of the six taxa, minimum elevation in the south was 367–1113 m higher than in the north. While habitats compared between the two regions share only 9% of their total flora, individual plots had up to 70% of their species occurring in the opposite region. The northern affinity of southern outcrops increased with elevation, slope steepness, soil Cu, B and SO4 and decreased with potential solar radiation and soil Na. As a result, communities above 1600 m on felsic bedrock, and above 1350 m on mafic bedrock, were most northern in composition. Northern affinity of southern outcrops also increased with latitude, which may partly result from closer geographic proximity to past communities that provided progenitors for the current northern flora. Northern treeless habitats increased in southern affinity with increased slope steepness, perennial seepage, vegetation height, shade, soil pH, Al, Mn, Na and decreased elevation and organic matter. As a result, northern outcrop communities below treeline were most similar to those on southern outcrops. This suggests that southern outcrop vegetation may be more similar to Pleistocene outcrop vegetation than to Pleistocene alpine vegetation. Partial constrained ordination showed that while compositional differences between the Northern and Southern Appalachian habitats were largely explained by environmental differences, there was a significant component of residual variation explained by north or south position that was unrelated to environment. These residual compositional differences may result from historical influences on community structure involving stochastic extinction and colonization processes.

Mineralogy, origin and commercial value of the zeolite-rich tuffs in the Petrota-Pentalofos area, Evros County, Greece

The zeolite-rich tuffs of the Petrota-Pentalofos area were deposited in the Arrestees Basin during the Eocene. They are up to 100 m thick and extend more than 15 Km in a long axis. Most of the outcrops consist of frequent alternations of very fine grained tuff with pumice and lapel tuffs, the latter containing detrital fragments of the Mesozoic substrate of the basin. X-ray Diffraction, Scanning Electron Microscopy and light microscopy analysis on quarry and borehole samples has shown that the tuffs are composed mainly of clinoptilolite and minor cristobalite, with a small proportion of detrital constituents (quartz, mica-schist) and pyrogenic crystals (feldspars, quartz, biotite). Minor amounts of mordenite randomly occur in some of the northern outcrops, closer to the occurrences of lava. ICP-AES chemical analysis of the tuffs gives evidence that the original magmas were of quartz-latite composition. The tuffs rest on pre-Cenozoic metamorphic basement and pass gradationally upwards into sandstone and limestone. Evidence is given for deposition of the tuffs in a supra to infra-littoral environment. The zeolitic tuffs originated as epiclastic volcanic sediments, transported by water from the source of the eruption. The transformation of the volcanic glass of the tuffs to zeolite and cristobalite has taken place by meteoric waters in an open hydrological system existed during the Tertiary. The zeolitic rocks are currently being exploited as an animal feed supplement.

Lithostratigraphy, sedimentary evolution and sequence stratigraphy of the Upper Proterozoic Lyell Land Group (Eleonore Bay Supergroup) of East and North-East Greenland

The Late Proterozoic Lyell Land Group is an approximately 3 km thick succession of siliciclastic shelf deposits, within the upper part of the Eleonore Bay Supergroup. It is widely exposed in the region between Ardencaple Fjord in the north and Canning Land in the south. In this paper the seven formations named by Sønderholm & Tirsgaard (1993) are formally described. These are from base to top: the Kempe Fjord Formation (400-600 m thick), the Sandertop Formation (200-405 m thick), the Berzelius Bjerg Formation (250-450 m thick), the Kap Alfred Formation (500-640 m thick), the Vibeke Sø Formation (290-325 m thick), the Skjoldungebrae Formation (205-240 m thick) and the Teufelsschloss Formation (35-110 m thick).
 Five facies associations have been recognised. Outer shelf deposits dominated by dark green, brown to dark red mudstones with thin sandstone lenses are mainly found in the Sandertop, Kap Alfred and Skjoldungebræ Formations. Storm- and wave-dominated inner shelf deposits comprising fine-grained sandstones and dark heterolithic mudstones are common in the Sandertop, Kap Alfred, Vibeke Sø and Skjoldungebrae Formations and are also found in southern outcrops of the Teufelsschloss Formation. Tidally influenced shoreface deposits form stacks of laterally extensive sandstone bodies separated by heterolithic mudstones and are only found in the middle part of the Kap Alfred Formation. Storm- and wave-dominated shoreface deposits comprise highly mature, thick and laterally very extensive sandstone bodies of which a few may be traced for distances exceeding 150 km. This association is present in several intervals within all formations of the Lyell Land Group. Tidally dominated coastal plain deposits consist of stacked sandstone sheets forming laterally extensive, multistorey units separated by heterolithic mudstones and sandstones. These sediments form part of the Kempe Fjord and Berzelius Bjerg Formations and are also found in northern outcrops of the Teufelsschloss Formation. Evidence from palaeocurrent data combined with regional lithological variations suggest a consistent general N-S coastline with the basin deepening in an eastward direction. Deflection of geostrophic currents suggest a palaeolatitude on the southern hemisphere.
 The deposits of the Lyell Land Group are subdivided into four, large-scale sequences which overall show the same general sedimentary evolution through time reflecting large-scale, cyclic changes in relative sea-level. The sequences vary in thickness from 400-1000 m and are all readily traceable 300 km parallel and 100 km perpendicular to inferred palaeocoastline. The development of all sequences indicates that major regional translation of facies are related to large-scale forced regressions. Sequence stratigraphic considerations suggest that correlation of formations of the Lyell Land Group with units of the Petermann Bjerg Group some 75 km to the west may be very difficult to carry out.
 Citation: Tirsgaard, H. & Sønderholm, M. 1997: Lithostratigraphy, sedimentary evolution and sequence stratigraphy of the Upper Proterozoic Lyell Land Group (Eleonore Bay Supergroup) of East and North-East Greenland. Geology of Greenland Survey Bulletin 178, 60 pp.