Isotopic ages and stratigraphy of Cenozoic rocks of the Marysvale volcanic field and adjacent areas, west-central Utah /

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Early-Middle Jurassic stratigraphy of the Fortrose-Chaslands region, southernmost South Island, New Zealand

The 40 km of coastline from Fortrose to Chaslands Mistake (southeastern South Island, New Zealand) comprises sediments that are part of the Early-Middle Jurassic of the Murihiku Terrane. The sediments are dominantly fluvial with some marine beds and alluvial fan deposition, and display an evolution of fluvial style which progresses from perennial flow to seasonal flow. The McPhee Cove Conglomerate is a prominent unit to the north. It has been used to separate two formations which would otherwise, on inherent lithological grounds, be difficult to distinguish. This paper discusses several similar conglomerates which occur in the south, but which are separated from the type area of the McPhee Conglomerate by major tectonic disruption. Hence, the existing lithostratigraphic nomenclature to the north, including the McPhee Cove Conglomerate, cannot be simply extended southwards. The Fortrose-Chaslands area appears to consist of two tectonic blocks, the Slope Point Block and the Brothers Block, which are separated from each other and from the adjacent Papatowai Block by major strike faults (or fault zones). A change is proposed to the existing stratigraphy which involves recognising all terrestrial sediments as part of the False Island Formation. Four prominent clast-supported conglomerate horizons are named as members of the False Islet Formation: the White Head Conglomerate, Black Bluff Conglomerate. Hoiho Conglomerate, and Slope Point Conglomerate Members. The latter contains five named conglomerate beds.

Triassic stratigraphy and sedimentology in central England

The Triassic rocks of Central England consist of three major stratigraphic units: Sherwood Sandstone Group, Mercia Mudstone Group, and Penarth Group. The lower part of the Sherwood Sandstone Group represented by the Kidderminster, Cannock Chase, and Polesworth Formations represents pebbly braided river deposits carried by a major fluvial system flowing to the North-Northwest. The upper part of the Sherwood Sandstone Group includes the Wildmoor and Bromsgrove Sandstone Formations, the deposits of a sandy alluvial system. The Mercia Mudstone Group represents quiet-water deposits of marginal palya type which were subjected to occasional marine flooding. The overlying Penarth Group represent shallow marine and lagoonal environment associated with the Rhaetian marine transgression. The mineralogy of the Triassic sandstones indicates that the main source was from medium to low rank metamorphic rocks with additional supplies from igneous and metamorphic rocks. The study of size-composition trends shows that the climate was semiarid in early Triassic time and became more humid later. The Triassic sandstones show a variety of diagenetic features typical of continental red beds; these include: 1. the dissolution of unstable ferromagnesian silicates, 2. the replacement of detrital grains by clay, 3. the pseudomorphism of biotite by haematite, and 4. the formation of a suite of authigenic minerals including quartz, illite, mixed-layer illite-montmorillonite, kaolinite, k-feldspar, haematite, titanium oxide and later carbonate cement. Palaeomagnetic studies of selected samples show that the magnetization is muticomponent with the various components being carried by different textural phases of haematite.

The stratigraphy of the Fishguard volcanic complex and associated sediments, SW Dyfed, Wales

This thesis describes the geology of a Lower Palaeozoic terrain, situated west of the town of Fishguard, SW Dyfed, Wales. The area is dominated by the Fishguard Volcanic Complex (Upper Llanvirn), and sediments that range in age from the Middle Cambrian to the Lower Llandeilo. The successions represent an insight into sedimentation and volcanism for c. 100 Ma. along the south-western margin of the Lower Palaeozoic Welsh Basin. The stratigraphy of the sedimentary sequence has been completely revised and the existing volcanostratigraphy modified. The observed complexity of the stratigraphy is primarily the consequence of Caldedonide deformation which resulted in large scale repetition. Fold-thrust tectonics dominates the structural style of the area. Caledonide trending (NE-SW) cross-faults complicate preexisting structures. Middle Cambrian (?) sedimentation is documented by shallow marine clastics and red shales deposited within tidal - subtidal environments. Upper Cambrian sedimentation was dominated by shallow marine `storm' and `fair weather' sedimentation within a muddy shelf environment. Shallow marine conglomerates and heterolithic intertidal siliciclastics mark the onset of Ordovician sedimentation during the lower Arenig transgression. Mid-Arenig sediments reflect deposits influenced by storm, fair-weather and wave related processes in various shallow marine environments, including; shoreface, inner shelf, shoaling bar, and deltaic. Graptolitic marine shales were deposited from the upper mid-Arenig through to the lower Llandeilo; during which time sediments accumulated by pelagic processes and fine grained turbidites. The varied nature of sedimentation reflects both localised change within the depositional system and the influence of larger regional eustatic events. Ordovician subaqueous volcanic activity produced thick accumulations of lavas, pyroclastics, hydroclastics, and hyaloclastics. The majority of volcanism was effusive in nature, erupted below the Pressure Compensation Level. Basaltic volcanism was characterised by pillowed lavas and tube networks, whilst sheet-flow lavas, pillow breccias and minor hyaloclastites developed locally. Silicic volcanism was dominated by rhyolitic clastics of various affinities, although coherent silicic obsidian lavas, sheet-flow lavas and pyroclastics developed. Hypabyssal intrusives of variable composition and habit occur throughout the volcanic successions. Low-grade regional metamorphism has variably affected the area, conditions of the prehnite-pumpellyite and greenschist facies having been attained. Numerous secondary phases developed in response to the conditions imposed, which collectively indicate that P-T conditions were of low-pressure facies series in the range P= 1.2-2.0 kbars and T= 230-350oC, under an elevated geothermal gradient of 40-45oC km-1. Polymineralic cataclastites associated with Caledonide deformation indicate that tectonism and metamorphism were in part contemporaneous.

Oxygen isotope stratigraphy Ojplus03 for the last 838,000 years

Global warming is real and has been with us for at least two decades. Questions arise regarding the response of the ocean to greenhouse forcing, including expectations for changes in ocean circulation, in uptake of excess carbon dioxide, and in upwelling activity. The large climate variations of the ice ages, within the last million years, offer the opportunity to study responses of the ocean to climate change. A histogram of sealevel positions for the last 700,000 years (based on a new d/sup 18/O stratigraphy here compiled) shows that the present is near the margin of the range of fluctuations, with only 6 percent of positions indicating a warmer climate. Thus, the future will be largely outside of experience with regard to fluctuations of the recent geologic past. The same is true for greenhouse forcing. Our inability to explain sudden climate change in the past, including the rapid rise of carbon dioxide during deglaciation, and differences in ocean productivity between glacial and interglacial conditions, demonstrates a lack of understanding that makes predictions suspect. This is the lesson from ice age studies.

Sequence stratigraphy and sea-level history of Kangan formation in south pars field

Dehram group includes Faraghan, Dalan and Kangan formations. Kangan formation ages lower terias. That is one of the important reservoir rocks of southern Iran and Persian Gulf. In this research Kangan formation is studied in two A and B wells. Based on 75 studies on thin section, four carbonate litho acies association A, B, C, D with 12 subfacies are identified. A lithofacies association includes 4 subfacies: A1, A2, A3 and A4. B lithofacies association consists of 3 subfacies: B1, B2 and B3. C lithofacies association consists of 3 subfacies: C1, C2, C3 and D lithofacies association includes 2 subfacies: D1 and D2. On the base of studies lithofacies association of Kangan formations are formed in 3 environments of: Tidal Flat, Lagoon and Barrier Shore Complex in a Carbonated Platform Ramp type. Diagenetic processes have effected this formation. The most important Diagenetic processes are: Cementation, Anhydritization, Micrization, Neomorphism, Bioturbation, Dissolution, Compaction, Dolomitization and Porosity. Sequence staratigraphy studies were performed base on the vertical and horizontal relationship of lithofacies association and well logging in gamma ray and sonic type that causes the identification of two sedimentary sequences: First sedimentary sequence includes: Transgressive System Tract (TST) and High Stand System Tract (HST). The lower boundary of this sequence is in Sequence Boundary 1 (SB1) which shows unconformities of Dalan and Kangan that are Permian-terias unconformities. The upper boundary is in Sequence Boundary 2 (SB2) type that is identified by carbonate facies associated by anhydrite nodular. Second sedimentary sequence includes: TST and HST. Lower and upper boundaries of these sequences are both in SB2 type. The lower and upper boundary is made of carbonate facies with anhydrite nodular.

Lower Aptian Comparative Stratigraphy of the Basco-Cantabrian Region (Spain) and Eastern Cordillera (Colombia): implications for local factors in the depositional record of Oceanic Anoxic Event 1a (OAE-1a)

An important episode of carbon sequestration, Oceanic Anoxic Event 1a (OAE-1a), characterizes the Lower Aptian worldwide, and is mostly known from deeper-water settings. The present work of two Lower Aptian deposits, Madotz (N Spain) and Curití Quarry (Colombia), is a multiproxy study that includes fossil assemblages, microfacies, X-ray diffraction bulk and clay mineralogy, elemental analyses (major, minor, trace elements), Rock-Eval pyrolysis, biomarkers, inorganic and organic carbon content, and stable carbon isotopes. The results provide baseline evidence of the local and global controlling environmental factors influencing OAE-1a in shallow-water settings. The data also improve our general understanding of the conditions under which organic-carbon-rich deposits accumulate. The sequence at Madotz includes four intervals (Unit 1; Subunits 2a, 2b and 2c) that overlap the times prior to, during and after the occurrence of OAE-1a. The Lower Unit 1(3m thick) is essentially siliciclastic, and Subunit 2a (20m) contains Urgonian carbonate facies that document abruptly changing platform conditions prior to OAE-1a. Subunit 2b (24.4 m) is a mixed carbonate-siliciclastic facies with orbitolinid-rich levels that coincides with OAE-1a δ13C stages C4-C6, and is coeval with the upper part of the Deshayesites forbesi ammonite zone. Levels with pyrite and the highest TOC values (0.4-0.97%), interpreted as accumulating under suboxic conditions, and are restricted to δ13C stages C4 and C5. The best development of the suboxic facies is at the level representing the peak of the transgression. Subunit 2c, within δ13C stage C7, shows a return of the Urgonian facies. The 23.35-m section at Curití includes a 6.3-m interval at the base of the Paja Formation dominated by organic-rich marlstones and shales lacking benthic fossils and bioturbation, with TOC values as high as 8.84%. The interval overlies a level containing reworked and phosphatized assemblages of middle Barremian to lowest Aptian ammonites. The range of values and the overall pattern of the δ13Corg (-22.05‰ to -20.47‰) in the 6.3m-interval is comparable with Lower Aptian δ13C stage C7. Thus, conditions of oxygen depletion at this site also occurred after Oceanic Anoxic Event-1a, which developed between carbon isotope stages C3 and C6. Both sites, Madotz and Curití, attest to the importance of terrigenous and nutrient fluxes in increasing OM productivity that led to episodic oxygen deficiency.