Facies analysis and seismic geomorphology of a fluvial-tidal depositional system from the miocene Malay Basin / Nurul Adilah Manshor

Nurul Adilah , Manshor (2021) Facies analysis and seismic geomorphology of a fluvial-tidal depositional system from the miocene Malay Basin / Nurul Adilah Manshor. PhD thesis, Universiti Malaya.

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Abstract

Various hierarchical classification schemes for channel architectural elements have been developed based on studies of modern and ancient alluvial and paralic systems. The datasets used by different schemes are varied and include seismic, well logs, core and/or outcrops. Most studies used outcrop datasets, which provide better views of higher resolution lateral and vertical relationships of bounding scour surfaces. However, recognizing these features in 3D seismic data and well data at depths ≥ 1.5 km in the subsurface is very challenging. This research presents an integrated facies analysis and seismic geomorphology study of a fluvio-tidal depositional system from the Lower to Middle Miocene (within Group I and H) of the Malay Basin. The targeted interval is >1000 m below sea bottom. An integrated dataset from a selected area in the central region of the Malay Basin was used for this study, which includes a high-quality 3D seismic cube (1563km2), 83.15 m of conventional core, and 3 well logs penetrating Group I and H. Facies analysis indicates that Group I and H strata in the study area are dominated by a mixture of fluvial and tidal facies. Identified facies associations represent paralic depositional elements such as prodelta mudstone, outer estuarine/abandoned channel deposits, and within a channel, tide-influenced barforms. The presence of a marine ichnofauna with varying degrees of diversity and bioturbation intensity is indicative of restricted marginal marine environments. Application of RMS (Root Means Square) attribute analysis and frequency decomposition in the seismic geomorphological analysis has enabled the imaging of a variety of architectural elements at different geometries, scales, and dimensions. Architectural elements of 120 channels are catalogued and evaluated. Three classes of channels are identified within the dataset, based on spatial and temporal channel geomorphology and other seismic signatures. Class-1 channel systems are the widest and characterised by high seismic amplitude, low to moderate sinuosity and are interpreted as bypass channels or estuaries. Class-2 channel systems are of high seismic amplitude, have low to moderate sinuosity, and are interpreted as fluvial/distributary channels. Class-3 channel systems contain the smallest channels with high sinuosity and are interpreted as tidal creeks and tidal channel networks. These channels show unique morphometric characteristics indicative of tidal influence, such as flaring mouths, cuspate meanders, high sinuosities, through-flow and dendritic networks. Quantitative morphometric elements have been compared to existing published datasets and modern-day tide-dominated channel systems. The characteristics of the widest channels in this study are not consistent with an incised valley interpretation and are most likely channel belts or amalgamated channel belts. The evolution of the depositional system and wide variation in channel geomorphologies is interpreted in relation to Miocene regressive-transgressive cycles and downstream autocyclic controls. A quantitative morphometric database for the Group I and H channels in the Malay Basin is presented in this project.

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