A NEW BEDROCK MAP AND QUADRANGLE REPORT (#42) FOR THE WALLINGFORD QUADRANGLE, CONNECTICUT

Bedrock mapping of the Wallingford 7.5 minute quadrangle was completed in 2019. The quadrangle is within the Mesozoic Hartford Basin and is underlain by typical Newark rift-basin sedimentary and volcanic rocks. The stratigraphic section exposed within the quadrangle includes the New Haven formation through the Holyoke basalt. In addition, two sets of diabase dikes and a lamprophyre dike intrude rocks of the New Haven formation. All except for the Holyoke basalt and the diabase dikes are poorly exposed.

The New Haven formation is intruded by two chemically distinct sets of diabase dikes which are inferred to be feeder dikes for the lower two lava flows in the basin. The West Rock diabase forms the numerous Fairhaven/Higganum dikes that are chemically correlated to the Talcott basalt¹. These dikes were formed by at least two pulses of intrusion: Where diabase from both pulses are in contact, the younger diabase is characteristically columnar jointed whereas the older diabase is not. Both younger diabase and older diabase are chemically and petrographically indistinguishable.

The New Haven formation is also intruded by the Buttress diabase forming the Buttress dikes in the northwest portion of the quadrangle. The Buttress diabase is chemically correlated with the Holyoke basalt¹.

A lamprophyre dike intrudes a segment of a West Rock diabase dike in the northeastern part of the quadrangle. It is Cretaceous in age² post-dating the rift basin sequence.

Because of poor exposure in the Wallingford quadrangle most of the faults are inferred from displacement of the Holyoke ridges in adjacent quadrangles. Faults that are recognizable from field evidence are minor. We find no evidence in the Wallingford quadrangle of either the Foxon fault or the related Gaillard graben interpreted by Sanders in the adjacent Branford quadrangle.

1. Philpotts and Martello, 1986.
2. Armstrong and Besancon, 1970; Armstrong and Stump, 1971.