MIOCENE-PLIOCENE MARINE SEDIMENT PRESERVATION IN THE FALL ZONE: RESULTS FROM 1:24,000 SCALE MAPPING NEAR PETERSBURG, VIRGINIA
Data collected via power auger shows interfluves of stacked Miocene-Pliocene marine sediments that are laterally discontinuous and hidden, not outcropping at the surface, covered by younger Cold Harbor, Bacons Castle, or Pleistocene alloformations. The development of this patchwork of mapped sediments is attributed to either erosion/dissection via incision related to sea level drops or depositional environments that would prohibit their lateral extension. Detailed mapping at 1:24,000-scale shows the variable geometry and thickness of saprolite above the granite batholith creating depressions which we argue could be responsible for preserving Miocene-Pliocene marine units under younger fluvial-estuarine Coastal Plain units. The discovery of these hidden depressions through drilling and other borehole records indicates another possible cause for the laterally discontinuous nature of marine coastal plain sediments.