Postilla Published by the PEABODY MUSEUM OF NATURAL HISTORY YALE UNIVERSITY New Haven, CT_Qé6 Number 225 8 January 2001 JAN 17 2uuz * ) 10 MATRS& 23 Los 182 4 Source: Visher 1954. b Mean annual temperature in °C. © Mean annual temperature range in °C. d Length of growing season in days. external ligament preserved (Figure 2C). Neither of the common infaunal bivalve species is preserved in life position. The Laevicardium and Mercenaria specimens that have both valves attached do not have their long axes parallel to one another in the same concretion. The two concretions with the most (combined total of 59) double-valved Argopecten (Figure 2D; Waage 1962:28, top figure, YPM 39360) have shells that range in height from 17 to 28 mm and 16 to 25 mm, respectively. Only one shell, 40 mm high, is larger. All of these individuals, with the one excep- tion, died about half way through their first year of life, perhaps in the same storm. An additional indication of rapid burial is the presence of many articulated crustacean shells (Figure 4). The lateral extent of bedding and thin peat layers preserved in the mud clasts is indicative of these sediments having been deposited in an area on the sea floor that was very shallow and protected from strong wave action, perhaps behind a sand bar. If, as seems likely, the mud clasts came from above the concretion layer, Past jae 2 24+2 155-= 25 and given that sea level rose continuously during the time from 5000 BP to the present, it would not have been possible for the mud clast layer to have been deposited in deep water below wave base, currently about 12 m in Long Island Sound. In addition, if the sediments had accumulated in deep water one would expect to find taxa representative of that environment, such as Yoldia. Conclusion Fossils in calcareous concretions and noncalcareous mud clasts from an offshore borrow area at Prospect Beach, West Haven, Connecticut, were brought onshore by dredging as an unintended consequence of adding sand to a public beach. The concretions are from an inferred depth of 7.4 to 8 m (25 to 27 ft) below MLW; they contain a fauna of 53 identified taxa dominated by Argopecten irradians and Anomia simplex, and a small but significant flora of eight identified taxa. The invertebrates lived in a muddy bottom, shallow water, subtidal environ- 22 Postilla 225 East Haven Branford Mm Figure 6 Post-glacial fossils from Long Island Sound off West Haven, Connecticut Concretion from East Haven, Connecticut. A, locality map, based on Oyster Grounds lease map (Connecticut 1998). Contour interval of 1 ft based on depths (feet below MLW) given on that map and reproduced here. EI, East Indies Rocks; FR, Farm River estuary; ME, Marc Even lease no. 538 of the Oyster Grounds lease map; MP, Mansfield Point; SI, Stony Island. B,C, Squilla empusa, YPM 200984. Bar scale 1 cm. B, carapace, six abdominal segments, telson, dorsal; C, propodi, ventral, and Recent Balanus bases on concretion surface. ment, disturbed from time to time by storm waves and ebb and flow tidal currents, and were buried quickly in shell lag deposits. The concretion fauna is composed entirely of species found living in the area today. Only one species, Nassarius vibex, stands out by being common in the fauna. Today this gastropod is abundant in the southern United States and rare in New England. The sparse terrestrial flora suggests a somewhat cooler, less equable climate with a slightly shorter growing season than at present. The common occurrence of Nassarius vibex by itself does not provide enough invertebrate evidence to contradict the climatic conditions derived from the terrestrial plants. During dredging, the noncalcareous mud clasts were torn from what was a Post-glacial fossils from Long Island Sound off West Haven, Connecticut Postilla 225 23 continuous sedimentary layer and deposited on the beach with the concre- tions. Their limited molluscan fauna probably lived and accumulated in a quiet lagoonal environment. One gastropod, Littorina irrorata, not found in Long Island Sound today (except by introduc- tion) is present in the fauna. Several lines of evidence point to the likelihood of a stratigraphic succession of post-glacial faunas and floras in this area. First there is the roughly 750-year gap in the radiocarbon dates between the older (5330 BP) and younger (4530 BP) of the blue-gray concretions and their contents. Then, there is the difference in appearance among the calcareous concretions and the shells associated with them. And finally there are the mud clasts, which, although probably much younger than the concre- tions, remain undated. The unexpected find of such rich faunas and floras calls attention to the potential of the nearshore sedimentary record to supply valuable data on the marine and coastal environment during the middle and late Holocene that is available nowhere else in the region. Efforts should be made to visit all such dredging projects in the future. The West Haven site itself would be worth further investigation by collecting from a measured section either after exhuming the old borrow area and collecting by divers or by sinking a large-diameter pipe while hydraulically bringing up material from known depths. Even without the desired stratigraphic controls, the value of this deposit to the scientific community far exceeds its value to the local West Haven commu- nity as beach fill—that sand having been washed away long ago. Acknowledgments We are indebted to several colleagues in the Yale University Department of Geology and Geophysics from 1968 for special assistance: Minze Stuiver, of Yale’s former Radiocarbon Laboratory, for radiometric tests; Giorgio Pannella for information on the fossil pollen, spores and diatoms; and Robert Berner for X-ray analysis of the cement. Ian Speden, when a graduate student at Yale, contributed to collecting and microscopic examination of the concretions; Solene Roming Morris assisted in preparation of microfossils and fossil counts; the photography was done by Al Coleman (Figures 2A,B,D) and William K. Sacco (Figures 2C,E-I, 3 and 4). From the Peabody Museum, Eric Lazo- Wasem helped identify the arthropods; Willard Hartman identified the sponges and serpulids; Ray Pupedis identified the insects; and Lucinda McWeeney helped identify the plants. Ellen Thomas (Department of Earth and Environmental Sciences, Wesleyan University) identified the foraminifera. Stephen Hasiotis (Department of Geology, Indiana State University) identified the polychaete worm burrows. Jon Moore (Honors College, Florida Atlantic University) iden- tified the fish. Donald Rhoads (formerly of the Woods Hole Oceanographic Insti- tution) gave guidance to critical literature and possible sources of pectens on Cape Cod. Sheila Stiles and Joseph Choro- manski (Milford Laboratory, National Marine Fisheries Service) provided speci- 24 Postilla 225 Post-glacial fossils from Long Island Sound off West Haven, Connecticut mens and valuable information on pectens, and Peter Fisher and Barry Wassel kindly donated pecten shells from Buzzards Bay. Laura Skorina typed the manuscript and provided computer support. Addendum: East Haven Concretion After this manuscript was submitted for publication, we obtained a concretion similar to those from West Haven, but from some 9 km to the east, offshore of East Haven. The concretion was collected about 1995 by Marc Even of West Haven, Connecticut, while dredging for clams at his lease site in East Haven along the Branford town line. The site, Connecticut Department of Agriculture (Aquaculture Division) Lease No. 538, is a rectangle 300 m (N-S) by 250 m (E-W) centered around a point 1150 m SO5E of the south- ernmost tip of Mansfield Point (Figure 6A). The concretion is a dark bluish-gray limestone containing very little silt and sand, and has a 0.5-mm-thick weathered rind. It contains a well preserved, nearly complete specimen of Squilla empusa (Figure 6B,C). Living barnacles (Figure 6C) and bryozoa on the concretion indi- cate that it had been loose on the bottom surface for about a year before collecting, probably brought to the bottom surface during a previous dredging. The bottom at the site slopes from a depth below MLW of 6.5 m (22 ft) in the northwest corner to 7.4 m (25 ft) in the southeast. Given that the hydraulic power dredge used in the operation penetrated to a maximum depth of about 0.37 m (15 in) below the surface, this would place the stratigraphic level of the concretion’s source beds over much of the site within the 7.4 to 8 m (25 to 27 ft) depth range below MLW inferred for the West Haven concretions. Thus this find strongly suggests that the West Haven concretion zone has an eastward lateral extent of at least 9 km, and is possibly part of a much more extensive stratigraphic unit along this section of the Connecticut coastline. We thank Marc Even for bringing the specimen to our attention and for gener- ously donating it to the Peabody Museum. Robert Granfield, the present owner of the lease, kindly loaned us the original map on which the Even lease was plotted. Post-glacial fossils from Long Island Postilla 225 25 Sound off West Haven, Connecticut Literature Cited Bloom, A. L. and M. Stuiver. 1963. Submergence of the Connecticut coast. Science 139:332-334. Brown, R. W. 1930. Section at Stiles (North Haven Brick Co.) clay pit, opposite Montowese. In: Flint, R. F., ed. The glacial geology of Connecticut. Bull. Conn. Geol. Nat. Hist. Surv. 47:263—266. Brumbach, J. J. 1965. The climate of Connecticut. Bull. Conn. Geol. Nat. Hist. Surv. 99. 215 pp. Connecticut. 1964. New Haven Harbor, U.S. Coast and Geodetic Survey Chart 218 [nautical chart]. Washington, DC: U.S. Department of Commerce, U.S. Coast and Geodetic Survey. 1 sheet. Scale 1:20,000. Connecticut. 1998. 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