Narrow Stratigraphic Interval Research Articles

Hydrous pyrolysis: a tool for the study of organic acid synthesis

Hydrous pyrolysis, commonly used for the simulation of liquid hydrocarbon generation, is a potentially useful technique for the study of dissolved organic acid synthesis if modifications to conventional methods are made. Simple experiments demonstrate the thermal origin of formic, acetic, proprionic, and butyric acids. The use of stainless steel reactors at high temperatures ( ca. 300°C), however, results in short chain aliphatic acid yields and distributions that are a function of experimental conditions. Once generated, propionate is destroyed more rapidly than acetate during the experiments. Experimental artifacts can be reduced by using lower temperatures and less catalytically active reactor materials. With present methodology, hydrous pyrolysis provides a useful semi-quantitative method for assessing the organic acid generating capacities of different rocks and organic matter types. As much as 1.2 wt% of the organic C in low thermal rank kerogen can be converted to short chain aliphatic acids. However, carbon dioxide is the dominant oxygen-containing product, exceeding organic acid yields by roughly 10 times. Relative organic acid generating capacities can vary by a factor of two or more in narrow stratigraphic intervals (<3 m). Bulk geochemical parameters, like oxygen indices, and gross organic petrography (organic matter type) only partly explain the observed variations in organic acid yields between samples.

Stoveracysta, a new gonyaulacacean dinoflagellate genus from the upper Eocene and lower Oligocene of New Zealand

Abstract A new dinoflagellate cyst genus, Stoveracysta, is proposed to accommodate forms superficially resembling Alisocysta but differing in having a sexiform rather than a quinqueform hypocystal plate topology. The type species, Stoveracysta kakanuiensis sp. nov., is described from the upper Eocene/lower Oligocene boundary sequence exposed at Kakanui River mouth, south of Oamaru, New Zealand. The new combination S. (formerly Eisenackia and Alisocysta) ornata (Cookson & Eisenack 1965) is proposed. Both species may occur widely throughout the southern hemisphere but appear to be confined to a narrow stratigraphic interval, close to the Eocene/Oligocene boundary.

Stratiform and stratabound tungsten mineralisation in the Broken Hill Block, N.S.W.

Abstract The Early‐Middle Proterozoic Broken Hill Block contains three types of W occurrences, which show close stratigraphic control. All three types occur within a relatively narrow stratigraphic interval (the ‘Mine Sequence’ Suite of Stevens et al., 1980) comprising a highly variable group of metamorphosed silicic and mafic volcanics, clastic sediments, and exhalative and chemical sediments containing base metals. The first type includes occurrences of W and base metals in bedded calc‐silicate rocks. In the second type, W occurs in layered to non‐layered calcsilicate rocks associated with amphibolite; these are intimately associated in a narrow stratigraphic interval containing abundant, small, Broken Hill type deposits. The third type comprises stratabound, W‐bearing pegmatites, which have been remobilised from quartz‐feldspar‐biotite gneiss and bedded quartz‐tourmaline rocks. Tungsten has been mined only from the third type and only in small quantities. The three types of tungsten deposits show a close spatial relationship with stratiform and stratabound Pb‐Zn mineralisation, including the Broken Hill type. The Pb‐Zn and W deposits are inferred to be genetically related.

Tomstown Dolomite (Lower Cambrian), central Appalachian Mountains, and the habitat of Salterella conulata

Measured sections in the Tomstown Dolomite, Washington County, Maryland, indicate a considerably thinner section of carbonate rocks than in Virginia. Salterella conulata Clark, found at three previously undescribed localities, is confined to a narrow stratigraphic interval and may have biostratigraphic value. S. conulata is a faunal component in the lagoon-bay portion of an Early Cambrian tidal flat complex.