Thesis advisor: Douglas Edmonds / Due to their low-lying position near the shoreline, river deltas are vulnerable to fluctuations in relative sea-level (RSL). Moreover, relatively little is known about fluvio-deltaic dynamics during RSL fall because the resulting deposits have low preservation potential. In this paper, I present a field-based study of the Goose River delta, coupled with numerical model simulations, that investigates the fluvio-deltaic response to RSL fall. The Goose River delta is a sandy fjord delta at the mouth of the Goose River located at the western end of Lake Melville, an inlet of the Labrador Sea, Canada and has experienced a RSL fall of 3 to 6 mm/yr in the past 5000 years due to post-glacial isostatic rebound. Aerial images show three abandoned delta lobes and one active lobe, suggesting that avulsions and lobe-switching occurred during RSL fall. Elevation analysis using Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data and optically-stimulated luminescence (OSL) dating suggest that a series of downstepping terraced delta lobes formed at the mouth of the Goose River during a period of RSL fall. Similarly, Delft3D model runs show continued avulsions and formation of multiple terraced delta lobes deposited at progressively lower elevations. I show computationally that by decreasing delta lobe widths, deltas may remain aggradational during RSL fall, creating conditions favorable for lobe-switching during RSL fall. Observations from the field and model runs provide a critical link in understanding the geomorphic processes occurring during RSL fall, and in particular show that 1) incision and sediment bypass is not a necessary response to RSL fall and 2) lateral migration of a delta via avulsion can continue to occur with falling sea-level. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Upper to lower delta plain fluvial sand bodies, sealed by delta plain mudstones, form important hydrocarbon reservoir targets. Modelling complex geobodies in the subsurface is challenging, with a significant degree of uncertainty on dimensions, distribution and connectivity. Studies of modern and ancient paralic systems have produced a myriad of nomenclature and hierarchy schemes for classifying fluvial architectural elements; often lacking clearly-defined terminology. These are largely based on outcrop data where lateral and vertical relationships of bounding scour surfaces can be assessed in detail. Many of these key defining criteria are difficult to recognise or cannot be obtained from typical 3D seismic reflection data at reservoir depths greater than or equal to 2 km subsurface. This research provides a detailed statistical analysis of the Triassic fluvio-deltaic Mungaroo Formation on the North West Shelf of Australia, which is one of the most important gas plays in the world. A multidisciplinary approach addresses the challenge of characterising the reservoir by utilising an integrated dataset of 830 m of conventional core, wireline logs from 21 wells (penetrating up to 1.4 km of the upper Mungaroo Fm) and a 3D seismic volume covering approximately 10,000 km2. Using seismic attribute analysis and frequency decomposition, constrained by well and core data, the planform geobody geometries and dimensions of a variety of architectural elements at different scales of observation are extracted. The results produce a statistically significant geobody database comprising over 27,000 measurements made from more than 6,000 sample points. Three classes of geobodies are identified and interpreted to represent fluvial channel belts and channel belt complexes of varying scales. Fluvial geobody dimensions and geomorphology vary spatially and temporally and the inferred controls on reservoir distribution and architecture are discussed. Results document periods of regression and transgression, interpreted in relation to potential allocyclic and autocyclic controls on the evolution of the depositional system. Statistical analysis of width-to-thickness dimensions and key metrics, such as sinuosity, provided a well-constrained and valuable dataset that augments, and has been compared to, existing published datasets. Uncertainty in interpretation caused by data resolution is addressed; something recognised in many other studies of paralic systems. Given the data distribution, type and resolution, geobodies have possible interpretations as either incised valleys or amalgamated channel belts, with implications for developing predictive models of the system. This study offers the first published, statistically significant dataset for the Mungaroo Formation. It builds upon previous regional work, offering a detailed analysis of this continental scale paralic system and provides insight into the controls and mechanisms that influenced its spatial and temporal evolution. Focusing on improved understanding of geobody distribution and origin, the statistical parameters generated provide a robust dataset that can be used for 3D static reservoir models of analogue systems. Thus, helping to constrain potential geobody dimensions and reduce the uncertainties associated with modelling.