SEQUENCE STRATIGRAPHY BACK TO BASICS: SEA-LEVEL AND CLIMATE INFLUENCES ON SEQUENCE ARCHITECTURE

Most sequence stratigraphic studies have tied interpretation of sequence and systems tracts to a relative sea-level curve. Here, we follow basic stratigraphic principles independent of sea-level curves and use seismic, log (downhole and core), sedimentary facies successions, chronostratigraphic data to recognize sequences, stratal surfaces, systems tracts, and parasequences. We use classic criteria to define seismic sequence boundaries and identify them in cores by surfaces of erosion associated with hiatuses. Systems tracts are identified by fining/deepening and coarsening/shallowing upward trends deciphered with lithologic, well log, and foraminiferal data. Maximum Flooding Surfaces are downlap surfaces and intervals of finest grain size and maximum water depth. We see little evidence of correlative conformities on this paleoshelf. Sequences embedded within Myr-scale composite sequences can be particularly challenging to interpret using seismic profiles alone. An excellent example of this is provided by seismic, core, and log analyses of lower Miocene Sequence m5.4 (17.7-16.1 Ma) on the New Jersey shallow shelf. Seismic stratigraphic interpretation reveals m5.4 to be a 1.2 Myr (long tilt cycle; “3rd order”) sequence with apparently thick LST, no TST, and strongly progradational HST. Closer examination reveals that m5.4 is a composite sequence consisting of three higher order sequences (m5.4-1, 17.7-17.6; m5.34, 17.6-17.7 Ma; m5.33, 16.7-16.6 Ma) as indicated by seismic terminations, facies stacking successions, benthic foraminifera-derived paleodepth trends, and chronostratigraphy. We compare the higher-order sequences with an independently derived eustatic estimate; m5.4-1 and m5.34 correlate with 100 kyr sea-level peaks within a 1.2 Myr low; sequence 5.33 is a 100 kyr peak within a 1.2 Myr high.