27-1 Lateral continuity of facies in Jurassic ephemeral lake strata of the Hartford Basin: Implications for correlation and depositional environment interpretation

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

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Abstract:

Natural outcrops of sedimentary strata in the Hartford rift basin are typically small, and the best exposures for examining the vertical changes and lateral continuity of facies are widely scattered highway roadcuts. Strata in these exposures typically have structural dips of 10°-20°, however, limiting the ability to physically trace strata over distances greater than about 100m. The lacustrine strata of the Early Jurassic East Berlin and lower Portland Formations contain interbedded perennial lake and ephemeral lake facies that are arranged into 10-15m cycles, and it is often a challenge to correlate cycles from one exposure to the next. Facies representing perennial lake environments are widespread in the basin and can be correlated with reasonable confidence. Other facies, such as those representing ephemeral lake environments (such as poorly confined current flows, paleosols, and microbial mats) cannot be easily traced between exposures. Consequently, it is difficult to determine their lateral extent or vertical thickness variations with any confidence.

A set of cores drilled during revitalization construction in downtown Hartford (Adreian's Landing project) acquired a series of short (typically 1-4 m) cores with a 30-40 m spacing. Dip-oriented profiles do not have any stratigraphic overlap between adjacent cores due to the short core lengths and the local 15° structural dip. A strike-oriented core profile composed of 36 cores along Columbus Boulevard in Hartford, however, can be correlated bed-by-bed and provides the opportunity to assess lateral and vertical trends in ephemeral lake facies. Constraining the lateral continuity of these facies is important for improving our understanding of the depositional environments and refining their use as correlation tools. Facies attributed to microbial mats are laterally restricted, reflecting patchy mat development. Individual sandstone beds representing poorly confined flood events rarely occur in two adjacent cores, but intervals of stacked beds representing multiple events can be traced across two to three cores. Beds with pedogenic features such as carbonate nodules, sediment mixing and mudcracks, however, reflect more aerially widespread subaerial exposure processes and can be correlated across several cores (300+ meters). Thus, pedogenically altered horizons are the best ephemeral lake facies for correlation between scattered outcrops.

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

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