27-2 Re-evaluation of fluvial style in the Triassic-Jurassic Hartford Graben, Connecticut and Massachusetts

Session: Recent Work in Mesozoic East Coast Rift Basins: Structure, Sedimentology, Paleontology, Mapping, and More!

Presenting Author:

Christopher Fielding

Authors:

Fielding, Christopher¹, Drzewiecki, Peter², Wizevich, Michael C.³

(1) Department of Earth Sciences, University of Connecticut, Department of Earth Sciences, Storrs, , (2) Department of Earth & Environmental Sciences, Eastern Connecticut State University, Willimantic, , (3) Department of Earth & Space Sciences, Central Connecticut State University, Geological Sciences, New Britain, ,

Abstract:

The Triassic-Jurassic stratigraphy of the Hartford Graben has been investigated over more than a century, leading to evolving interpretations of nonmarine, mainly alluvial and lacustrine formative environments. Paleoclimate during this time has been interpreted as varying between humid and arid conditions, on different timescales, based on presence of dark, organic-rich mudrocks preserving rich vertebrate fossil faunas and floras, and presence of evaporite minerals and calcrete paleosols, respectively. Previous interpretations of fluvial style have fixated largely on variations in formative river planform (meandering, braiding, etc.), which is of questionable utility in elucidating paleoclimate or paleogeography. An alternative means of classifying alluvium is based on a statistical parameter derived from the analysis of flow variability in modern rivers, the coefficient of variance of annual peak discharge (CVQp). Deposits of rivers with low to moderate CVQp are internally dominated by dune-scale cross-bedding and preserve macroform architecture in full with limited lateral and vertical lithological variability, whereas increasing values of CVQp are associated with increasing abundance of flow transcritical structures, poor preservation of macroform architecture, increasing lithological variability, and increasing evidence of high magnitude/low frequency flow events that are often high-concentration flows. This alternative classification is independent of planform, and it provides information about the paleoclimatic regime under which preserved alluvial channel bodies were accumulated (Fielding et al., 2025, Sedimentology, 72, 275-329). With respect to the Hartford Graben stratigraphy, a survey of published literature supported by field observations and experience yields the following conclusions: 1. the lower New Haven Formation was formed under low CVQp conditions, which 2. increased into the upper New Haven Formation, 3. alternated through numerous arid-humid climatic cycles in the Shuttle Meadow and East Berlin Formations, 4. remained cyclic, but rose again through the lower Portland Formation, and 5. remained high to very high through the remainder of the Portland Formation. This interpretation is consistent with previous interpretations of paleoclimate change but adds new information about runoff patterns that were previously unknown. It may also help to better understand some of the more enigmatic fluvial (or possibly fluvial) deposits in the basin.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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