PHOTOGRAMMETRY AND OUTCROP-SCALE MAPPING OF BRITTLE STRUCTURES IN THE ORENAUG BASALT, POMPERAUG BASIN, CONNECTICUT

The Pomperaug Basin is an early Mesozoic rift basin located in the western highlands of Connecticut. The basin is geographically located between the Hartford and Newark Basins. The magmatism within the basin is associated with Central Atlantic Magmatic Province and is represented by three basalt lava flows interbedded with sedimentary units. Within the basin, the Jurassic Orenaug Basalt is the primary ridge forming unit and is the equivalent of the Holyoke Basalt in the Hartford Basin and the Preakness Basalt in the Newark Basin. In 2006, the bedrock within the basin was mapped by the USGS. The igneous and sedimentary units within this half-graben basin dip to the east and are crosscut by intrabasinal faults and fractures.

Outcrop-scale maps of the Orenaug Basalt were developed from detailed panoramas using photogrammetry in combination with field observations. Structures mapped within the basalt include cooling fractures, such as columnar joints. In addition, faults and fractures crosscut the basalt. These faults and fractures are interpreted as tectonic in origin and occurred after the emplacement-related cooling of the basalt. Systematic fractures crosscut the Orenaug Basalt and range from steeply dipping N–S striking fractures to moderately dipping WNW–ESE fractures. Faults that crosscut the Orenaug Basalt display well-developed slickenlines and offset features. Well-developed slickenlines are also present on some of the cooling fractures suggesting reactivation as small-scale faults. The photogrammetry approach allowed for increased efficiency in data collection and interpretation of results. The outcrop scale maps, in combination with the detailed panoramas, serve as valuable tools for communication and distribution of observations and results.