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Geomagnetic excursions, brief deviations in geomagnetic field behaviour from that expected during 'normal' secular variation, remain some of the most enigmatic features of geomagnetic field behaviour. This thesis presents high-resolution records of geomagnetic excursions recorded at the Blake-Bahama Outer Ridge in the Western North Atlantic. The highest resolution record yet of the Blake geomagnetic excursion (~125 ka) is measured in three cores from Ocean Drilling Program Site 1062 (ODP Leg 172). These cores have sufficiently high sedimentation rates (>10 cm ka^-1) to allow detailed reconstruction of the field behaviour at these sites during the excursions. Previous reconstructions of geomagnetic field behaviour during excursions from marine cores have been limited by low-resolution age models. This thesis discusses a new approach, whereby measurements of excess ²³⁰Th (²³⁰Th_xs) are used to constrain relative variations in sedimentation rate. Modifications are suggested to the methods previously used to calculate the concentration of ²³⁰Th_xs and a new MATLAB® program is developed and described that allows rapid and flexible calculation of ²³⁰Th_xs. Using this new approach, the duration (6.5±1.3 kyr) and age (129-122 ka) of the Blake excursion are accurately constrained. A palaeomagnetic study is also conducted on two ODP Sites, 1061 and 1062 on the Blake-Bahama Outer Ridge to obtain a high-resolution record of the Laschamp geomagnetic excursion (~41 ka). The Blake excursion is found to be of 'long' duration (6.5±1.3 kyr) whilst the Laschamp excursion is relatively short (<400 years) showing that excursions do not have a characteristic duration, linked to the conductivity of the inner core, but instead occupy a continuous range of durations. The records of both the Blake excursion and the Laschamp excursion from the Blake-Bahama Ridge sites also show rapid transitions to excursional geomagnetic pole positions (less than 500 years), much faster than often quoted for full geomagnetic reversals. Based on current estimates for reversal durations, this would imply that excursions and reversals are controlled by different processes.

Little is known about the paleo-precipitation of the Florida Peninsula. In order to better understand Floridas late Holocene climate variability (last 4,200 years), the isotopic composition was analyzed of four speleothems from two caves, in West-Central Florida. Two speleothems were collected from BRC Cave in Hernando County, and two others from Briar Cave in Marion County. This study represents the first speleothem-based paleoclimate records for Florida. Uranium-series disequilibrium analyses were determined by using thermal ionization mass spectrometry (TIMS) to provide accurate determination of chronology of the deposition of the speleothems. Stable isotopic analyses of oxygen and carbon were performed using stable isotope mass spectrometry, which provided information regarding changing amounts of precipitation (increase in precipitation, decrease in the δ18Oc) and types of vegetation above the cave (increased forest density, decrease in the δ13Cc). Variations in the speleothems δ18O composition reveal abrupt changes in precipitation amount, fluctuations that appear both regional and hemispheric in nature. Strong similarities between the speleothem δ18O, Lake TulaneδD record (Cross et al. 2003; 2004) and the SE US tree-ring record (surrogate for spring precipitation - Stahle and Cleaveland 1992) suggests a regional atmospheric influence on Floridas precipitation. The major causes of changes in precipitation are proposed to be Atlantic Multi-decadal Oscillation (AMO), El Nino and changes in the relative positions of the Intertropical Convergence Zone (ITCZ)-North Atlantic High (NAH). Comparison between the δ18Oc and surrogates of these influences, show all three have some effect. AMO and El Nino have short-term (decadal) influence and ITCZ-NAH has a long term (centennial) influence. The contributions of these climatic effects have implications for teleconnections involving Floridas climate; the AMO correlation shows higher latitude influence, while El Nino and the ITCZ show tropical influence on subtropical Florida.

Coral terrace surveys and U-series ages of coral and mollusk shells yield a surface uplift rate of ~0.6 m/ka for Kisar Island. The small island is located NE of Timor in the active Banda Arc of Indonesia. Based on this rate, Kisar first emerged from the ocean as recently as ~450 ka. Terrace surveys show warping that follows a pattern of east-west striking folds, which are along strike of thrust-related folds of similar wavelength imaged by a seismic reflection profile just offshore. This deformation shows that the emergence of Kisar can be attributed to forearc closure along the south-dipping Kisar Thrust. Terrace morphology and coral ages are best explained by recognizing major terraces as mostly growth terraces and minor terraces as mostly erosional into older growth terraces. All reliable and referable coral U-series ages are marine isotope stage (MIS) 5e (118-128 ka), which encrusted the coast up to 60 m elevation. All coral samples are found below 6 m elevation, but a tridacna (giant clam) shell in growth position at 95 m elevation yields an age of 195 +/- 31 ka, which corresponds to MIS Stage 7. Loose deposits of coral fragments found on top of low terraces between 8 and 20 m elevation yield ages of < 100 years and may represent paleotsunami deposits from previously undocumented seismic activity in the region. The metamorphic rocks of Kisar, Indonesia, which correlate with the Aileu Metamorphic Complex of East Timor, record the breakup of a supercontinent with associated rifting, metamorphism from arc-continent collision, and the growth and exhumation of a new orogenic belt. The protoliths of these rocks are mostly psammitic with minor basaltic and felsic igneous rocks. Geochemical analyses of mafic meta-igneous rocks show rift affinities that are likely related to rifting of Gondwana and later breakup in the Jurassic Period. The Aileu Complex is overlain by younger sedimentary rocks deposited on the northern passive margin of Australia, which collided with the Banda Arc in latest Miocene time. This collision caused metamorphism of the distal edge of the continental margin rocks at conditions of 600-700°C at 6-8 kbar and up to 700-850°C at 8-9 kbar locally, corresponding to depths from 25 to 30 km. These rocks were then rapidly uplifted and exhumed. U-Pb analysis of detrital zircons indicates a Permian to Late Jurassic age of the sedimentary sources and confirm an Australian provenance. The timing of metamorphism of the Aileu Complex is poorly constrained by previous studies, of which only a white mica cooling age of 5.36 +/- 0.05 Ma proved reliable. Prior apatite fission track studies show that all tracks are partially to completely annealed suggesting recent rapid cooling. A domal geometry of the island above the sea floor is expressed in the pinnacle shape. Foliations on Kisar Island generally strike parallel to the coastline, which is may be suggestive of doming. The Kisar Thrust, which is imaged in offshore seismic reflection data, may indicate that the doming corresponds to diapirism into the hinge of an active thrust-related anticline or diapirism of buoyant continental material along the thrust itself.