Planktonic foraminiferal assemblage of the Yorktown Formation, Virginia, USA

摘要: Planktonic foraminifers from Coastal Plain deposits in southeastern Virginia provide biochronologic control and paleoceanographic information for the lectostratotype of Yorktown Formation type localities its four members. Faunas recovered six are consistent with faunas reported North Carolina correlatives (Duplin Raysor Formations) Georgia to support an age assignment between 3.0 4.0 Ma. Quantitative estimates surface temperature based upon planktonic foraminifer assemblages indicate winter conditions 3? 5?C warmer than today summer essentially equivalent during deposition. PURPOSE AND SCOPE The is unconformity bounded package fine grained sandy clays shell marls exposed along Atlantic Carolina. Originally thought be Late Miocene age, now referred as were placed Chesapeake Group all other rocks Bay area Florida by Dall Harris (1892). was originally described Clark Miller (1906). As redefined Ward Blackwelder (1980), consists members: a basal Sunken Meadows Member, overlain Rushmere, Morgarts Beach Moore House Members. geographic distribution these members mid-Atlantic suggests three transgressive pulses. first pulse represented second Rushmere Members, third Member (Ward Strickland 1985). Beach-Rushmere transgression most extensive pulses deposited marine sediments directly on crystalline over 130km inland present shoreline (Gibson 1983; Recent biostratigraphic studies focusing ostracodes, calcareous nannofossils have firmly Pliocene (Akers 1972; Hazel Gibson Snyder et al. Cronin 1984). Most this work has been done at Lee Creek Mine, Carolina, or correlative units south. Relatively little published foraminiferal found where Virginia. This study undertaken northern outcrop assess paleoceanographic/paleoclimatic significance region. We analyzed series samples outcrops Yorktown, including House, Beach, Members (text-figs. 1, 2). Semi-quantitative quantitative analyses reveal important paleoclimatic well documentation taxa that exist MATERIALS METHODS Twenty collected Approximately 500 grams each sample washed through >850gim >63gm sieves. 850gm portion discarded. remaining 63gm fraction transferred filter TEXT-FIGURE 1 Map showing location investigated foraminifers. micropaleontology, vol. 38, no. pp. 75-86, pls. 1-3, text-figs. 1-6, table 1992 75 content downloaded 157.55.39.127 Sun, 26 Jun 2016 07:12:50 UTC All use subject http://about.jstor.org/terms H. J. Dowsett L B. Wiggs: Planktonicforaminiferal assemblage Formation, Virginia, USA