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Deltas form where a river meets a standing body of water (e.g. ocean) and deposits its sediment load. They are sensitive recorders of the interplay of fluvial (river) processes, that deliver the sediment to the standing body of water, and wave and tidal processes that redistribute the delivered sediment. When basinal (waves/tides) processes cannot sufficiently redistribute the delivered sediments, river-dominated deltas prevail, which are fantastic recorders of autogenic (internal to the delta) processes that control its overall evolution and internal architecture. Allogenic (external to delta) processes, such as tectonics, can influence and modify the river produced architecture. Therefore, understanding these competing autogenic and allogenic processes is key to creating predictive evolutionary models of river-dominated deltas, and their depositional architecture in the subsurface. This project focuses on a spectacularly well-exposed Early Cretaceous fluvio-deltaic succession of the Maestrazgo Basin in central-eastern Spain. These were deposited in a semiisolated, tectonic rift sub-basin during a rifting cycle from the Upper Jurassic to Middle Cretaceous. The succession displays two regressive phases of shallow-water river-dominated deltas that prograded into a carbonate-dominated shelf during an overall longer term transgression. This project uses a combination of remote sensing and geological fieldwork techniques, and methods of sequence stratigraphy, and architectural element analysis in order to understand the possible autogenic and allogenic processes that controlled the stratigraphy and architecture of the fluvio-deltaic succession. The results show that at the scale of the delta, channel cannibalisation and re-channelisation of the mouth bar top (autogenic process) leads to the creation of mouth bars consisting of multiple smaller-scale sub-bars, which is the first to be reported in ancient river-dominated deltas. At the larger delta depositional scale, the overall evolution displays a combination of eustatic, tectonic, and sediment supply allogenic controls, influencing stacking patterns, internal architecture and overall evolution. This study advances our scientific understanding of these processes but has applied implications for subsurface reservoir architecture models used by the oil and gas industry.

The Paleogene strata of south-eastern Nigeria include the Imo Formation, Ameki Group and the Ogwashi Formation, which are collectively referred to as the outcropping Niger Delta succession and their ages range from Paleocene to Oligocene. This research involves the study of outcrops and borehole data for facies analysis, ichnology, palynology, clay mineralogy, petrology and heavy mineral analysis in order to reconstruct the paleogeography of the Paleogene period, develop new depositional models and re-interpret the depositional environments of the Paleogene strata. The results provide a new depositional environment for the lower Sandstone Member of the Imo Formation - tidal sandwave deposit and a new paleogeographic model for the Imo Formation. Improved facies and sequence stratigraphic models are developed for the deposits of the Ameki Group and these sedimentary deposits are re-interpreted as tide-dominated estuarine system. Novel depositional facies are produced for the Ogwashi Formation and the strata are also re-interpreted as tidally-influenced coastal plain deposit. Furthermore, the sand body geometries, their spatial distribution and continuity as well as the sandstone heterogeneities of representative outcrops of these formations are well documented in this research. Results from heavy mineral analysis suggest mixed provenance for the Paleogene sediments; the primary sources are polycyclic pre-existing sedimentary rocks, magmatic-gneiss complex and granitic rock of the Oban Massif and the magmatic-gneiss complex and the schist belt of the Western Nigerian Massif. This study proposed possible factors controlling the distribution of the heavy mineral suites in the Paleogene sediments to include river influx, tide and wave actions and hydraulic sorting. Four type-1 stratigraphic sequences, consisting of lowstand systems tracts and/or transgressive systems tracts and highstand systems tracts have been established for the depositional succession of the Paleogene strata. This detailed sedimentological research on the Niger Delta provides a new insight into the study of shallow marine environments.

Modern Delta systems commonly exhibit compound clinoforms that consist of two elements, a shoreline clinoform, and a separate subaqueous clinoform, both with a topset–foreset–bottomset morphology, with a wide low-gradient area called subaqueous platform (30-150 km wide) in between. Recent datasets on modern tidal Deltas suggest that a compound-clinoform model is characteristic for tide-dominated Deltas but there are few good examples from ancient deposits. The modern Colorado River Delta, in Baja California, Mexico, is tide-dominated and exhibits a compound clinoform. The 20 km-long outcrops of the Yuha and Camel Head members of the Deguynos Formation, located in Fish Creek-Vallecito Basin, California, are the ancient (mid-Pliocene) deposits of the paleo-Colorado Delta. These outcrops were measured, producing 4 stratigraphic sections through the Yuha and Camel Head members. From these measured sections 7 facies associations were recognized. These facies associations were assembled into 3 depositional environments: subaqueous foreset to bottomset, subaqueous topset, and platform, and shoreline clinoform, using as an analogy the modern Colorado Delta deposit. The Yuha and Camel Head Members exhibit multiple at least 22 high-frequency regressive-transgressive (R-T) cycles in which thickness changes laterally along the outcrops. R-T sequences, with an upward-coarsening lower part and a sandy to silty upward-fining upper part are interpreted as 5th order sequence related to autogenic changes within the environment, as suggested by variations in thickness and approximate time duration of each cycle. The 5th order R-T sequences are further organized in four sequences interpreted as 4th order sequence, mapped by vertical changes in thickness and environment along the outcrop, and probably controlled by eustatic processes. The exceptional setting of the basin (strongly dominated by tidal processes and the uncommonly high accommodation rate) probably was the key to the preservation of the compound clinoform morphology in the rock record of the Fish Creek-Vallecito basin. To better understand sediment dispersal in tidal influenced Deltas, 138 bathymetry maps near River mouth were examined, finding 54 compound clinoform morphologies. The annual sediment flux (Mt/y) appears to be the most important factor in the preservation of the compound clinoform morphology. All River mouths with an annual measured sediment flux higher than 100 Mt/yr have a compound clinoform. In contrast, in River mouths with less than 15 Mt/yr, the compound clinoforms are rare. The 39 systems were divided into tide-dominated, wave-dominated, and mixed, following the averages measured values of tidal ranges and wave height from public databases. In these systems, the subaqueous platform area has a direct relationship with the annual sediment influx

The Allensville Member of the Logan Formation (Late Tournaisian; 345 – 349 Ma) in south-central Ohio is an anomalously coarse-grained unit deposited in a shallow marine setting at a time when tectonic subsidence rates were low and after the onset of Late Paleozoic glaciations. The Allensville Member mainly consists of interbedded very fine- to very coarse-grained arenites with small amounts of laminated mudstone and coarse-grained laminations in finer-grained sandstones. Less common are well sorted and well rounded, granule to pebble conglomerates. Average grain size is 0.9 mm with a maximum clast size of 3.0 cm. Vertical grain size trends in the measured sections show similar trends of coarsening and fining upwards that can be correlated along strike for 30 km. Fossils within the member consist of crinoid columnal molds and rare brachiopod shell molds. Vertical burrows that are filled with coarse-grained sand and granules from overlying beds and which are present at the same stratigraphic position within each measured section are interpreted as the Glossifungites ichnofacies. The presence of the Glossifungites traces combined with the textures of the sandstones and conglomerates are interpreted to be the result of deposition as storm deposits and transgressive lags, respectively. Vertical changes in grain size, texture, and concentrations of fossils were used to subdivide the interval into systems tracts that represent two 4th order sequences in which deposition was controlled by high-frequency, high magnitude glacio-eustatic sea-level fluctuations.

The Upper Cretaceous Frontier Formation was studied along two strike-parallel cliff-lines in the Alkali Anticline region of the northeastern Bighorn Basin, Bighorn County, Wyoming. The unit comprises up to 145 m of mudrock, sandstone, conglomerate, and volcanic fallout sediments deposited along the western margin of the Cretaceous Western Interior Seaway (KWIS) in the mid- to late-Cenomanian. Eighteen facies, comprising six facies associations are identified from physical and biogenic sedimentary features. Sediments were deposited in open marine offshore to shoreface and subaqueous deltaic to delta platform environments. The observed trace fossil suites record departures from the archetypal ichnofacies. Such departures record environmental stresses associated with nearshore deltaic settings. Resolving the ichnological signature of these stressed nearshore settings was crucial to reconstructing the depositional environment. The Frontier Formation consists of multiple progradational and retrogradational sequences deposited during a low-frequency (high magnitude) lowstand characterized by lower-magnitude, higher- frequency fluctuations. This study reveals a complex succession of parasequences and deltaic coarsening upward successions deposited under low-accommodation conditions. Parasequence boundaries were the most useful for sub-regional correlation. Two sequence boundary candidates are identified in the Peay and Torchlight Members but they are not useful for correlating across the study area. This investigation provides new insights into the recognition and interpretation of the facies and stratigraphic architecture of nearshore sediments deposited in low accommodation settings, and provides a framework for future evaluations of similar deposits in the Western Interior Seaway.