ANATOMY OF MIOCENE NEW JERSEY SEQUENCES ACROSS CLINOTHEMS: TESTING SEQUENCE STRATIGRAPHIC MODELS

Drilling in the onshore New Jersey coastal plain (ODP Legs 150X and 174AX) and offshore shallow shelf (IODP Expedition 313; Site M27-M29) provide unprecedented continuous coring of Miocene sequences across a transect of clinothems. This allows recognition of stratal surfaces and systems tracts in numerous settings and testing of sequence stratigraphic models. Fifteen Miocene (ca. 23-13 Ma) sequence boundaries have been imaged offshore using 3 generations of Multichannel Seismic (MCS) profiles and recognized using seismic criteria. Lower to middle Miocene sequences were sampled and dated across numerous clinothems on topset, foreset, and toeset locations. We recognize sequence boundaries (SB) in the cores and logs based on integrated study of key core surfaces, lithostratigraphy (grain size, mineralogy, facies, and paleoenvironments), facies successions, benthic foraminiferal biofacies, downhole logs, core gamma logs, and chronostratigraphic ages. Onshore Miocene sequences are truncated topset deposits with thin transgressive (TST) and thicker regressive highstand systems tracts (HST); merged transgressive surfaces (TS) and SB result in overstepping of delta front/nearshore facies by neritic (shelf) facies across unconformities. Landward of the clinoform rollover, offshore sequences also consist of coarsening upward shallow-water deposits below the merged TS/SB, with deeper-water, fining upward TST above. Offshore, drilling through the foresets yields thick lowstand systems tracts (LST) and HST, though TST are often thin to missing; the basal sequence boundaries of foreset deposits are recognizable, even though they stack LST on LST. Offshore toesets consist of downslope transported sedimentary facies deposited in 75-100 m water depths. Both highstand systems tracts (HST) and Lowstand Systems Tracts (LST) recognized seismically, show a regressive stacking pattern in the cores. Parasequence boundaries (flooding surfaces) are recognized in LST, TST, and HST. TS generally are recognized as erosional contacts at the top of the regressive LST. The correlative conformity is a chimera. Even in the foreset “thicks” where sequences are most complete, there is evidence of erosion and hiatuses associated with sequence boundaries.