CURRENT AND PROPOSED POCKMARK RESEARCH IN COASTAL MAINE: LIFE CYCLES AND FLUID ORIGINS

King and MacLean (1970) recognized and described the first pockmarks on the Scotian Shelf. Researchers then found pockmarks in varied subaqueous environments (e.g., Hovland and Judd, 1988) including coastal Maine. Scanlon and Knebel (1985) found pockmarks within Penobscot Bay; Barnhardt et al. (1995) recognized them in Blue Hill Bay; and Fader (1990) noted pockmarks in Passamaquoddy Bay. Nearly every muddy bay in Maine shows evidence of pockmarks or gassy sediments. This has led us to question the origin of the gas and why pockmarks do not exist in all of Maine's muddy bays. Our current and proposed research seeks to decipher the estuarine pockmark. Previous work focused on mapping pockmark locations and determining pockmark activity levels (e.g., Kelley, et al., 1994; Rogers, 1999). The time has come to compare the well-mapped Penobscot Bay to other known pockmarked bays (e.g., Blue Hill and Passamaquoddy Bays), muddy bays hosting gassy sediments and no pockmarks, and muddy bays that lack both pockmarks and gassy sediments in Maine. This comparison has driven the formulation of our hypotheses. Working hypotheses for current research are: 1) Biogenic methane is the fluid for pockmark formation; 2) Anoxic decay of organic-rich sediments from paleo-lakes and wetlands provides the source for biogenic methane; 3) Individual pockmarks and pockmark fields follow a life cycle dependent on local conditions; 4) Pockmark occurrences in Penobscot, Blue Hill, and Passamaquoddy bays are similar in 4a) source material, 4b) mechanisms of formation, and/or 4c) life cycle; 5) Paleo-lakes and wetlands occurred during a slow-stand of sea level; 6) Areas of gassy sediments without pockmarks and areas of gassy sediments with pockmarks differ in 6a) origin of fluid, 6b) evolutionary history, 6c) stratigraphy, 6d) sedimentology, 6e) physical oceanography, and/or 6f) age of fluid-producing deposits; and 7) Sea-level changes play a major role in pockmark evolution. Proposed research to validate these hypotheses includes: vibracoring; dating organics recovered from cores; stratigraphic analysis of cores; construction of paleogeographic reconstructions based on cores and seismic stratigraphy; and data collection using high-resolution geophysics. Additional work will focus on validation of the Gontz et al. (2001) evolutionary model.