Stratigraphic evolution of the inner continental shelf in response to late Quaternary relative sea-level change, northwestern Gulf of Maine

Abstract

Research Article| May 01, 1997 Stratigraphic evolution of the inner continental shelf in response to late Quaternary relative sea-level change, northwestern Gulf of Maine Walter A. Barnhardt; Walter A. Barnhardt 1Department of Geological Sciences, University of Maine, Orono, Maine 04469-5711 Search for other works by this author on: GSW Google Scholar Daniel F. Belknap; Daniel F. Belknap 1Department of Geological Sciences, University of Maine, Orono, Maine 04469-5711 Search for other works by this author on: GSW Google Scholar Joseph T. Kelley Joseph T. Kelley 2Maine Geological Survey, 22 State House Station, Augusta, Maine 04333-0022 Search for other works by this author on: GSW Google Scholar Author and Article Information Walter A. Barnhardt 1Department of Geological Sciences, University of Maine, Orono, Maine 04469-5711 Daniel F. Belknap 1Department of Geological Sciences, University of Maine, Orono, Maine 04469-5711 Joseph T. Kelley 2Maine Geological Survey, 22 State House Station, Augusta, Maine 04333-0022 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1997) 109 (5): 612–630. https://doi.org/10.1130/0016-7606(1997)109<0612:SEOTIC>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Walter A. Barnhardt, Daniel F. Belknap, Joseph T. Kelley; Stratigraphic evolution of the inner continental shelf in response to late Quaternary relative sea-level change, northwestern Gulf of Maine. GSA Bulletin 1997;; 109 (5): 612–630. doi: https://doi.org/10.1130/0016-7606(1997)109<0612:SEOTIC>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Accumulations of deltaic and littoral sediments on the inner continental shelf of Maine, Gulf of Maine, preserve a record of postglacial sea-level changes and shoreline migrations. The depositional response of coastal environments to a cycle of regression, lowstand, and transgression was examined with seismic-reflection profiles, vibracores, and radiocarbon dates collected from sediments at the mouths of the Kennebec and Penobscot Rivers. Sequence-stratigraphic analysis of these data reveals two distinctly different successions of late Quaternary deposits that represent end members in an evolutionary model for this glaciated coast. Seaward of the Kennebec River, coarse-grained shorelines with foreset beds occur at depths of 20–60 m and outline the lobate margin of the Kennebec River paleodelta, a complex, rock-framed accumulation of glaciomarine and deltaic sediments capped by estuarine and marine deposits. Sand derived from this system today supports large barrier spits and extensive salt marshes. In contrast, the mouth of the Penobscot River is characterized by thick deposits of glaciomarine mud overlain by marine mud of Holocene age, including gas-charged zones that have locally evolved into fields of pockmarks. The distinct lack of sand and gravel seaward of the Penobscot River and its abundance seaward of the Kennebec River probably reflect differences in sediment sources and the physiography of the two watersheds. The contrasting stratigraphic framework of these systems demonstrates the importance of understanding local and regional differences in sediment supply, sea-level change, bedrock structure, and exposure to waves and tides in order to model river-mouth deposition on glaciated coasts.Evolution of shelf deposits was largely controlled by relative sea level, which locally fell from a highstand (+60 to +70 m at 14 ka) contemporary with deglaciation to a lowstand (−55 m at 10.8 ka). The sea-level lowering was accompanied by fluvial incision of older deposits, producing a regressive, basal unconformity. Major rivers deposited abundant sediment over this surface. Sea level then rose at varying rates, extensively reworking formerly emergent parts of the shelf and producing a shoreface ravinement surface in areas exposed to waves. A tidal ravinement surface has developed in sheltered embayments where erosion is due mainly to tidal currents. Incised valleys in both settings preserve transgressive estuarine deposits that contain lagoonal bivalves and salt-marsh foraminifera at depths of 15–30 m. These deposits accumulated ca. 9.2–7.3 ka, locally a period of relatively slow sea-level rise. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.