Recent Abstracts

Characterization of the Eastern Border Fault in the Durham, CT, Vicinity

      The Connecticut Valley Eastern Border Fault marks the separation between late Triassic flood basalts and alluvial fan sediments filling the rift basin,  and the metamorphic rocks of the Eastern Highlands. The geomorphic expression of the EBT in the vicinity of Durham, CT, is a wide alluvial valley with several tributary offshoots.  Proximity to the fault from the west has always been inferred from the size of clasts in the Mesozoic-age fanglomerates at the margins of the graben. There is no consensus as to the exact position, number and nature of the fault(s) in this area. Previous literature has identified only one exposed fault cut along Route 77, which has so degraded over time that the contact is no longer discernible.  When the cut was fresh, exposures indicated a zone of fault gouge and a fault plane dip of approximately 55 degrees.  In the study area, from Lake Quonipaug 3.5 km north to the juncture of Routes 77 and 79, the fault is characterized by a 7m wide silicified zone in the Collins Hill schist on the fault’s upthrown side.  Here a series of quartz veins have two dominant orientations, demonstrating a northeasterly shift in the trace of the fault.  In the northern part of the study area, quartz veins, including a single vein 1.8m thick extending for 37m, show azimuths of 200 - 210 degrees, dipping 19 degrees SW; to the south, a second set oriented 185 degrees, dipping 24 degrees SW is present.  Further evidence of the fault(s) position lies to the south where a series of sag ponds and the linear N-S trending Lake Quonipaug are apparently established over the fault. 

      To delineate the actual trace of the fault(s) and to characterize the fault zone itself, cesium magnetometer surveys across the projected fault trace were run.  Pronounced differences in magnetic signatures between the Eastern Highland metamorphics and the Connecticut Valley redbeds allow us to more precisely map the position of the graben’s border fault.

Heavy Metal Contamination of a Restricted Tidal Marsh of the Sybil Creek Watershed, Branford, CT.

Sybil Creek is a tributary of the Branford River, which discharges into Long Island Sound approximately five miles east of New Haven, Ct. The watershed area of Sybil Creek, at its Route 146 tidegate, comprises 232 acres, most of which are glaciated uplands.  Degraded tidal wetlands consisting of three interconnected marshes, the Central Marsh (6.4 acres), the North Marsh (14.2 acres) and the East Marsh (52.6 acres) are the subject of a Connecticut Department of Environmental Protection project  to reestablish tidal circulation to the restricted marshes by replacing or augmenting the present tidegate. The intent is to generate a higher tidal prism with more invigorated flow to encourage a natural succession of preferred salt marsh plants and animals in areas currently overrun with the freshwater-tolerant species Phragmites australis.

            Lying within the North Marsh is an area identified as an old landfill. Thick oily sediment discharges have been observed by the DEP at the road crossing at the marsh’s southern boundary.  Fieldwork during the summer of 2000 was designed to sample these discharges and to test the water quality of tidal channels and pools up-gradient and down-gradient from the landfill site.  Samples were analyzed for heavy metals including zinc, manganese, chromium, iron, and copper.  Analyses were conducted using a Hach DRE 2010 Spectrophotometer.  Results show heavy metal contamination of surface waters elevated well-above pre-industrial background levels. Two sets of samples, totaling nineteen in number, were taken along the reaches of Sybil Creek at high and low tide.  Standing water close to the landfill was also sampled.  Samples were subjected to spectrophotometric analyses for select heavy metals using a HACH DRE 2010 Spectrophotometer.  Ranges for the indicator metals currently run are as follows (Concentrations in mg/L): Copper 0.02 - 1.61, Manganese  0.0 - 2.1, KMnO  0.0 -  6.0, MnO₄  0.0 - 4.5, Iron  0.0 - 3.26, Chromium (Cr⁶⁺)  0.01 - 0.14, NaCrO₄  0.02 -  0.45, CrO₄^2-  0.02 -  0.32. Concentrations of heavy metals are roughly equivalent along the reaches of Sybil Creek during low and high tides.  It is possible, however, that heavy metals are being contributed by the Branford River, equilibrating in the estuary, and are influencing the high tide values.  Exceptionally high concentrations also occur at standing pools on the west slope of the landfill and in the tidal marsh adjacent to the Branford River estuary.