We acquired a vertical seismic profile and high-resolution surface seismic data to investigate climate induced cyclostratigraphy in the Newark Triassic rift basin. Triassic lacustrine sediments deposited in basin record the cyclical rise and fall of lake depth. Changes in lake depth occur with a periodicity matching Milankovitch cycles and have been interpreted as a measure of climate change in response to an orbital forcing functions.
In this experiment, 2 VSP profiles were recorded in the Titusville well cored by Lamont-Doherty Earth Observatory as part of their drilling project investigating the relationship between cyclo-stratigraphy and paleoclimate in the Newark Rift Basin. A three component sonde recorded both P and S waves from a Bolt 60 cu. in. land air gun, at a 250 ms sample interval for 1.25 seconds. An offset VSP was used to image the lateral continuity of stratigraphy in the vicinity of the well bore and tie lithology from the well to a coincident high-resolution surface seismic profile, part of a larger 2-D grid tying two adjacent core holes. A second VSP using two sources positioned at a constant offset was used to produce a corridor stack and inverted to produce a pseudo-sonic log for comparison with sonic and density logs acquired in the well.
Spectral analyses of sonic velocity and density logs and the associated reflectivity series from the bore holes which sample the Triassic sediments show periodicities of 19k, 23k, 41k, 96k, 130k, and 413k years. The equatorial location and monsoonal climate of the Newark basin during the Triassic appear to have provided a setting in which changes in climate related to orbital forcing functions were recorded by changes in sedimentary facies within the basin as lake depth fluctuated in response to changing climate. The velocities and reflectivities recorded by the seismic surveys correlate with lake depth indices described from the core.
Sue McGeary: University of Deleware
John Louie: University of Nevada-Reno