Eight 4th-order (~400 k.y.) disconformity-bounded mixed carbonate-siliciclastic sequences were deposited in the tectonically-active, tide-dominated Illinois basin during the Late Mississippian greenhouse to icehouse transition. Detailed, lithologic cross-sections were constructed through the Chesterian Ste. Genevieve through Glen Dean interval which show an upward change in character from carbonate-dominated sequences bounded by caliche and breccia paleosols to mixed-carbonate siliciclastic sequences bounded by red, slickensided mudrock paleosols and incised valleys. The 4th-order sequences are composed of 5th-order parasequences that can be correlated basin-wide. Parasequences in the basal, dominantly carbonate sequences are composed of patchy ooid grainstone tidal ridge reservoir facies which interfinger with skeletal limestone and are capped by laterally extensive muddy carbonate units. Parasequences in the overlying mixed carbonate siliciclastic interval commonly have basal quartz sandstone valley fill and tidal sand ridge reservoir facies overlain by skeletal limestone and shale-dominated siliciclastics. The sequences can be bundled into sequence pairs and composite sequences. Composite sequences are composed of 4 sequences and are bounded by better developed disconformities that commonly coincide with biostratigraphic zone boundaries. High energy reservoir facies are widespread in transgressive sequence tracts and late highstand sequence tract (where present) and confined to updip areas in the early highstand sequence tracts. Increasing amplitude 4th-order glacio-eustasy produced the sequences and caused the upward increase in incised valleys and deeper water carbonate deposition. Parasequences were produced by 5th-order glacio-eustatic sea-level fluctuations (20-100 k.y.). Sequence pairs and composite sequences were produced by 3rd-order sea-level fluctuations possibly in combination with local tectonics. Spatial and temporal variations in differential subsidence between the eastern and western shelves and the more rapidly subsiding basin interior caused variations in onlap/offlap geometries of sequences and parasequences. Increasingly wetter wet-dry seasonality caused an upward increase in siliciclastic influx and concurrent decrease in ooid deposition. The increasing-amplitude eustasy and progressively more humid climate were caused by the onset of continental glaciation on Gondwana. / Ph. D.

The Miocene of the Lidam area, Eastern Province, Saudi Arabia, was studied to examine the interaction of glacio-esustasy during moderate Antarctic glaciation, within a small back bulge basin on the slowly subsiding distal Arabian foreland, distal from the active Zagros fold-thrust belt. Low subsidence rates of 1 to 4 cm/k.y generated the long-term accommodation, which were considerable slower than those in the proximal foredeep in Iran. Deposition of the siliciclastics was driven by lowered sea levels, and moderately humid to arid climate. Rising sea levels pushed the siliciclastics updip allowing mixed siliciclastics and carbonates to form downdip, under semi-arid climate and locally hypersaline conditions. Maximum transgression slightly predated the Middle Miocene climatic optimum when prograding siliciclastics migrated across the platform. Falling triggered siliciclastic deposition under semi-arid climate. Sequences appear to relate to long-term obliquity (~1.2 m.y. cycles) and long-term eccentricity (400 k.y.) cycles. The succession contains numerous missing beats reflecting the updip position of the study area, and sea level changes of tens of meters that frequently exposed the platform. Siliciclastic units commonly are incised into muddy sediments beneath sequence boundaries. Multiple exposure surfaces occur within Hadrukh brecciated palustrine carbonates. Within Dam carbonates, parasequence boundaries commonly are capped by tidal flat laminites (some of which are incipiently brecciated). High frequency negative excursions of ∂¹³C within the succession appear to relate to near-surface diagenesis by soil gas depleted in ∂¹³C beneath sequence boundaries. Positive C isotope excursions in the Lidam Miocene section can be tied to similar excursions in Qatar and UAE, where Sr isotope dates constrain the ages of the units. The overall C isotope profile at Lidam shows depleted values early in the Miocene to heavy values in the Middle Miocene, becoming lighter again in the late Miocene. The profile appears to follow the long-term global ∂¹³C curve. Incursion of meteoric groundwaters into the study area was driven by the long-term global sea level changes. Oxygen isotopes are surprisingly light, extending down to -12.5 ‰VPDB. The very light δ¹⁸O values of the meteoric waters may be explained by rainfall associated with enhanced Miocene Indian monsoons, and with far travelled air mass trajectories migrating across north Africa and from the polar region. / Ph. D.