27-5 Syndepositional Faulting in the Hanging Hills and Watchungs, Hartford and Newark Basins, Associated with the Initial Pulse of the Central Atlantic Magmatic Province (CAMP)

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

Presenting Author:

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Abstract:

Marked thickness variations within lacustrine strata of the Shuttle Meadow Formation, between the first (Talcott) and second (Holyoke) CAMP lavas of the Hartford Basin, provide evidence for syndepositional activity and tilting along internal basin faults during early CAMP magmatism and onset of lacustrine deposition. Coring and outcrops of deep-water marker beds and overlying strata document thickness changes arising from onlap into hanging walls of small half graben as well as up‑dip thinning, producing dramatic variations over only a few kilometers across adjacent fault blocks.

Lacustrine cycles and map patterns demarcate lens‑shaped Shuttle Meadow lithosomes with depocenters aligned along normal faults at roughly 10 km length scales in the central Hartford Basin. The resulting sub‑basins had topographic relief of about 100 m on the Talcott surface that required fault‑controlled subsidence on the order of 1 m/kyr to accumulate thick lacustrine deposits in the lows while maintaining a nearly flat lake floor. Talcott lavas, representing a near instant in geological time, also thin along strike, but much less than the Shuttle Meadow, indicating the basin floor was nearly flat at the time of the eruptions. Comparable variability is absent in the overlying East Berlin, Holyoke, and Portland formations, implying internal faults had largely stabilized during the later Early Jurassic when subsidence was accommodated along major eastern border faults. Subsequently, the internal faults were reactivated resulting the present Hanging Hills structure.

The absence of lower Shuttle Meadow strata on structural highs plausibly reflects a combination of low lake stand erosion and high stand nondeposition and bypassing. At least some highs were submerged, yet above wave base, as suggested by non‑laminated black sediment locally onlapping upper Talcott rubble.

Reflecting a more regional pattern, thickness variations in coeval lacustrine cycles of the Feltville Formation in the Newark Basin Watchung syncline likewise record syndepositional formation of that structure, whereas the underlying pre‑CAMP Passaic Formation lacks this pattern, placing localized subsidence at initial CAMP and Feltville time. The inferred depositional geometry, onlapping lacustrine strata across fault‑bounded highs with sediment focusing in lows, is similar to internal structures in modern rift such as in Lakes Tanganyika and Malawi, but in eastern North America this smaller‑scale synsedimentary structuring was restricted to the earliest 300-kyr-local-pulse of CAMP eruptions.

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

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