An interglacial mudstone sequence from the Port Askaig Tillite Formation on Islay was analysed using an Olympus XRF detector. The resulting geochemical log was compared with an XRF dataset acquired from a Quaternary sedimentary core from the Lomonosov Ridge in the Arctic Ocean. Chemical proxies representing climatic and environmental changes were analysed in an effort to specifically identify evidence of orbital forcing in the Cryogenian Period. The studied non-glacial rock-section from the Port Askaig Formation was interpreted as being deposited in a shallow marine setting at semitropical latitudes during an episode of global warming at some stage of the Sturtian glaciation (ca 717 – 660 Ma). The transport mechanism of glaciogenic material was by ice rafting. High hematite content was interpreted as an oxygenation event in a peritidal zone when isostatic rebound caused a sea level regression. Increasing amount of muscovite is interpreted to indicate increased weathering. Underlaying sequence of dolostone and overlaying sequence of sandstone were consistent with these interpretations. One interglacial phase is thus observed, which possibly could be attributed to Milankovitch orbital forcing. The interpretation of the paleoclimatic setting of the studied interglacial mudstone did not provide support for the Snowball Earth hypothesis in its “hard” version. Neither did other observations such as evidence of repeating glacial-interglacial cycles and banded iron formations (BIF) appearing also within the Sturtian glaciation.

In the Grenville age basement rocks of Virginia and North Carolina, nearly thirty Cryogenian volcanic/plutonic complexes have been recognized. A-type granites and rhyolites dominate the igneous complexes within the Cryogenian Magmatic Province (CMP), but compositional variations range from gabbro through syenites. The mineralogy, chemical composition and field data including microstructural emphasis suggests emplacement of these igneous complexes in an extensional setting. In this study U/Pb zircon ages of several plutons were determined using secondary ion mass spectrometry. The ages suggest two episodes of magmatism. An older episode (739 to 745 Ma) of magmatism includes White Oak Creek, Suck Mountain, and Amisville plutons. The younger episode (613 to 694 Ma) includes Dillons Mill, Stewartsville, Mobley Mountain, Rockfish River, and Fine Creek Mills plutons. These two age groups also display differences in geochemistry. In contrast to the older group of plutons, the younger plutons are characteristically more metaluminous, lower in silica, higher in aluminum and phosphate, lower agpatic index, less REE enrichment, minimal K-feldspar and accessory mineral fractionation. The distribution of the older group of plutons over a distance of nearly 600km requires the development of a crustal scale zone of extension. A space-time analysis suggests that these plutons represent a continental plume track similar to the White Mountain Magma Series. Plume head arrival ages of 765 to 754 Ma in the southern part of the region are measurably older than 735 to 705 Ma observed in the north, and yield a plate motion rate of ~2 cm/year. / Master of Science