Peter P. McLaughlin

Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States

We use backstripping to quantify the roles of variations in global sea level (eustasy), subsidence, and sediment supply on the development of the Miocene stratigraphic record of the mid-Atlantic continental margin of the United States (New Jersey, Delaware, and Maryland). Eustasy is a primary infl uence on sequence patterns, determining the global template of sequences (i.e., times when sequences can be preserved) and explaining similarities in Miocene sequence architecture on margins throughout the world. Sequences can be correlated throughout the mid-Atlantic region with Sr-isotopic chronology (±0.6 m.y. to ±1.2 m.y.). Eight Miocene sequences correlate regionally and can be correlated to global δ 18 O increases, indicating glacioeustatic control. This margin is dominated by passive subsidence with little evidence for active tectonic overprints, except possibly in Maryland during the early Miocene. However, early Miocene sequences in New Jersey and Delaware display a patchwork distribution that is attributable to minor (tens of meters) intervals of excess subsidence. Backstripping quantifi es that excess subsidence began in Delaware at ca. 21 Ma and continued until 12 Ma, with maximum rates from ca. 21‐ 16 Ma. We attribute this enhanced subsidence to local fl exural response to the progradation of thick sequences offshore and adjacent to this area. Removing this excess subsidence in Delaware yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude that sea-level rise and fall is a fi rstorder control on accommodation providing similar timing on all margins to the sequence record. Tectonic changes due to movement of the crust can overprint the record, resulting in large gaps in the stratigraphic record. Smaller differences in sequences can be attributed to local fl exural loading effects, particularly in regions experiencing largescale progradation.

Migration of Neogene marine environments, southwestern Dominican Republic

The Azua Basin contains a 4000-m-thick regressive Neogene sedimentary sequence that records the effects of neotectonic activity along the northern bounary of the Caribbean plate. Shifts of benthic foraminiferal depth zone boundaries between stratigraphic sections demonstrate a southeastward migration of paleoenvironments in the Miocene and early Pliocene which suggest that the Hispaniola restraining bend was activated near the beginning of the late Miocene. In the morthwestern part of the Azua basin, the boundary between the middle and upper bathyal biofacies is in the uppermost Miocene Globorotalia humerosa Zone; the bathyal-neritic boundary is near the top of the same zone. In contrast, toward the southeastern (i.e., seaward) end of the basin, the middle bathyal/upper bathyal boundary is just above the base of the lower Pliocene Globorotalia margaritae margaritae Subzone, and the bathyal-neritic transition falls within the upper part of the same zone or in the overlying Globorotalia margaritae evoluta Subzone. The diachroneity of biofacies boundaries spans a time interval of ca. 1 m.y. The foraminiferal trends are corroborated by the disposition of time-transgressive lithofacies.

JOSEPH A. CUSHMAN AWARD

Dr. Barun K. Sen Gupta received the Joseph A. Cushman Award for Excellence in Foraminiferal Research on October 18, 2005, during the Cushman Foundation reception at the annual meeting of the Geological Society of America in Salt Lake City, Utah. The award is in recognition of his many contributions to our understanding of modern and Cenozoic benthic foraminifera. Barun has enjoyed a long and distinguished career as a researcher and educator that extends over more than four decades. As Barun takes his rightful place in a pantheon of Cushman Award recipients that begins with Fred B Phleger and Ruth Todd (1980) and extends to Martin A. Buzas and Richard K. Olsson (2004), it is appropriate to consider the role his work has played in the development of our discipline. The field of foraminiferology has now left behind its earliest phase dominated by taxonomic description, and gone on to see the establishment of stratigraphic and distributional frameworks and their integration into ecological, biological, evolutionary and geochemical studies, with the result that Foraminifera now play a vital role in our understanding of oceanographic and climatic change—fields that are critical to mankind’s stewardship of the Earth. Barun has played a leading part in the research thrust that has so positioned our discipline, and it is appropriate that we honor him for this contribution. Barun was born in Jamshedpur, India and educated at the Calcutta University, Presidency College, receiving B.Sc. with honors in 1951 and an M.Sc. First Class in 1954. In 1960, he went to …