41-20 Varve Micromorphology and Intra-Seasonal Depositional Events; Pleistocene Lake Tight, Teays Valley, West Virginia

Session: Paleontology, Stratigraphy, Sediments, and Soils (Posters)

Presenting Author:

Authors:

Abstract:

Recognition and interpretation of intra-seasonal depositional events are an important component of efforts to fully utilize the natural archives that comprise annually laminated lake sediment. Newer techniques for acquiring proxy data, such as micro-XRF and SEM analyses, offer possible refinements for understanding environmental and depositional changes recorded by varves. Nonetheless, thin-section micro- morphology remains a fundamentally important technique for evaluating the depositional intricacies of thinly laminated varves preserved by both contemporary and ancient lakes. Thin-sections of archival core samples from Early Pleistocene Lake Tight reveal some of the depositional complexities recorded within the varves of this 300 kilometer-long, ice-dammed lake that once filled portions of the Teays River Valley. The coring location, in a functionally distal part of the lake, lies approximately 200 kilometers from the glacial ice front and at least 100 kilometers from where the Teays River entered the ancient lake when filled to its highest water level. Many of the varves examined are characteristically thin (1-3 mm). Nonetheless, both melt season (MS) and non-melt season (NMS) components are commonly complex internally. MS components of varve couplets include a variety of features such as: 1) a single massive lamination of fine or very fine silt that can contain single-grain layers of medium silt recording lake ice melting; 2) solitary, very fine, eolian sand grains dropped by rafted lake ice onto the lake floor at the start of the MS; 3) multiple normally graded laminations of very fine silt and clay interpreted as stream flooding pulses; and 4) a single normally graded lamination deposited by the largest flood of the season. NMS components of the varves include: 1) a massive, poorly-sorted layer of very fine silt and clay that splits the NMS lamination and records a rainfall event late in the MS; 2) an inversely graded silt layer splitting the NMS component deposited by a sub-ice density current in response to brief nival melting in a local catchment; and 3) massive clay layers with sharp or gradational contacts that record settling of suspended sediments following the last MS flood. Proximity of the drilling site to the lake margin suggests much of the micromorphological complexity observed within the seasonal laminations derives from rainfall and nival melting events in the catchment of a nearby tributary stream.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

doi: 10.1130/abs/2026SE-11572

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.