Lake-level cycles. Lacustrine strata in the Newark basin, such as this part of the Metlars Member of the Passaic Formation from the NBCP Rutgers core, show cyclical changes in color and sediment fabrics. Core box 27 shows three 3-ft. sections of core. The left core consists of laminated black and white shale and somewhat more massive dark gray mudstone. The laminated black shales accumulated in deep-water lakes. The middle and right cores are mostly massive red mudstone, which accumulated in very shallow lakes or on playas (dry-lake beds). The individual segments from box 27 and those from boxes 26 and 28 were strung together to produce the composite section at left. The blue lake depth curve shows three cycles of rise and fall of lake depth. Note, however, that lake depth was deeper and the deep lake lasted longer in the lowest cycle, whereas lake depth was shallower and the "deep" lake lasted shorter in the uppermost cycle. Click on the image to see a larger version. Photos and photomosaic by Roy Schlische.
Wright-Rieman Laboratories