Clinoform Stacking Patterns, Clinothem Depositional Architecture, and the Process Link between Shallow-Marine and Deep-Marine Deposits: Key Initial Findings from IODP Expedition 313
A dip direction transect of three research boreholes collected during IODP Expedition 313 were located to intersect seismically imaged Miocene clinoforms on the New Jersey margin. The clinoforms are 100-300 m deep with maximum slope gradients of 1-4°, and prograded across the continental shelf. The seismic architecture indicates a clinoform rollover trajectory from low angle (flat) through high angle (rising) to falling, allowing the succession to be divided into different clinoform sets. The extensive core and well log dataset is tied to key seismic surfaces, which permits analysis of the sequence stratigraphic relationship between current-driven processes in top-set deposits, and gravity-driven processes in toe-set deposits.
The depositional architecture from core analysis reveals two clinothem types. Type I clinothems have thick top-set (where preserved) and foreset deposits, but thin toe-set deposits. The foreset deposits comprise thick (~100m) coarsening-upward successions that preserve shallowing-upward from silt-prone offshore to clean quartz sands in shoreface settings. The toe-set deposits are thin and silt-prone suggesting limited down-slope sediment supply. In contrast, Type II clinothems have thin top-set deposits, variable foreset deposits, and thick toe-set deposits. The top-set deposits are poorly sorted glauconitic coarse-grained deposits that overlie erosion surfaces, suggesting degradation of clinoform top-sets by fluvial processes. Toe-sets deposits of Type II clinothems are coarse-grained, and are dominated by poorly-sorted glauconitic deposits with complete macrofauna, interpreted as debrites, which are intercalated with normally graded beds interpreted as turbidites. The toe-set deposits are interpreted to have formed coalesced base-of-slope apron supplied by gullies. Commonly, the basal surface of Type II toe-set deposits is sharp and deeply bioturbated suggesting an unconformity.
Type I clinothems are found in rising clinoform sets, whereas Type II clinothems are found in flat clinoform sets, which together with the sedimentary facies, supports that the Type I clinothems formed during relative sea-level rise, and Type II formed during relative sea-level fall. However, a 2D grid of seismic lines suggests that clinothems may transition laterally from one type to another. Ongoing research aims to chronostratigraphically tie the succession into eustatic sea-level changes in order to refine sequence stratigraphic models of clinothems.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California