Allen, Jonathan P.1, Robert A. Gastaldo2
(1) University of Nebraska-Lincoln, Lincoln, NE
(2) Colby College, Warterville, ME
ABSTRACT: A Sedimentologic And Plant Taphonomic Evaluation Of The Early Middle Devonian Trout Valley Formation, Maine
The Trout Valley Formation of Middle Devonian age is exposed in Baxter State Park of
North-Central Maine. These rocks were examined first in the late 1950s and early 1960s,
and the fossil plants preserved within this sequence have provided insights into the early
evolution of terrestrial ecosystems. However, no detailed, integrated sedimentologic or
taphonomic study of this formation had been conducted until the present.
The rocks of the formation consist of terrestrial, estuarine, and near-shore marine deposits. Massive, crudely bedded conglomerate represents deposits of proximal braided channels on an alluvial fan complex. Lithic sandstone bodies in channel-form geometries represent deposits of river channels draining the Acadian highlands whereas associated siltstones represent overbank deposits, intertidal flats, tidal channels, and a paleosol. Localized lenticular quartz arenites represent nearshore shelf bar deposits that were storm influenced.
The majority of plant assemblages preserved mainly in siltstone lithologies are allochthonous and parautochthonous, with only one autochthonous assemblage identified in the sequence. Plant remains are found in both fluvial and estuarine environments with trimerophytes (Psilophytons and Pertica quadrifaria), rhyniophytes (Taeniocrada) and lycopods (Drepanophycus and Kaulangiophyton) as the most common plants in estuarine environments near tidal channels. However, they are found also in fluvial settings. The presence of tidal influence in deposits where parautochthonous and autochthonous assemblages are preserved suggests that these plants may have been tolerant of brackish conditions. However, the role of this physical parameter on the growth and colonization of plants in the Middle Devonian is as yet unknown.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004