In this volume John Murray investigates the ecological processes that control the distribution, abundance, and species diversity of benthic foraminifera in environments ranging from marsh to the deepest ocean. To interpret the fossil record it is necessary to have an understanding of the ecology of modern foraminifera and the processes operating after death leading to burial and fossilisation. This book presents the ecological background required to explain how fossil forms are used in dating rocks and reconstructing past environmental features including changes of sea level. It demonstrates how living foraminifera can be used to monitor modern-day environmental change. Ecology and Applications of Benthic Foraminifera presents a comprehensive and global coverage of the subject using all the available literature. It is supported by a website hosting a large database of additional ecological information (www.cambridge.org/0521828392) and will form an important reference for academic researchers and graduate students in Earth and Environmental Sciences.

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Ecology and Applications of Benthic Foraminifera

The subterranean estuary: a reaction zone of ground water and sea water

Present-day production of CaCO3 in tne world ocean is calculated to be about 5 billion tons (bt) per year, of which about 3 bt accumulate in sediments; the other 40% is dissolved. Nearly half of the carbonate sediment accumulates on reefs, banks, and tropical shelves, and consists largely of metastable aragonite and magnesian calcite. Deep-sea carbonates, predominantly calcitic coccoliths and planktonic foraminifera, have orders of magnitude lower productivity and accumulation rates than shallow-water carbonates, but they cover orders of magnitude larger basin area. Twice as much calcium is removed from the oceans by present-day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity (1.6 bt), suggesting that outputs have been overestimated or inputs underestimated, that one or more other inputs have not been identified, and/or that the oceans are not presently in steady state. One “missing” calcium source might be groundwater, although its present-day input is probably much smaller than that of rivers. If, as seems likely, CaCO3 accumulation presently exceeds terrestial and hydrothermal input, this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level: shallow-water accumulation decreases by an order of magnitude with a 100 m drop in sea level, while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow-water carbonates.

Production and accumulation of calcium carbonate in the ocean: Budget of a nonsteady state

The exchange of groundwater between land and sea is a major component of the hydrological cycle. This exchange, called submarine groundwater discharge (SGD), is comprised of terrestrial water mixed with sea water that has infiltrated coastal aquifers. The composition of SGD differs from that predicted by simple mixing because biogeochemical reactions in the aquifer modify its chemistry. To emphasize the importance of mixing and chemical reaction, these coastal aquifers are called subterranean estuaries. Geologists recognize this mixing zone as a site of carbonate diagenesis and dolomite formation. Biologists have recognized that terrestrial inputs of nutrients to the coastal ocean may occur through subterranean processes. Further evidence of SGD comes from the distribution of chemical tracers in the coastal ocean. These tracers originate within coastal aquifers and reach the ocean through SGD. Tracer studies reveal that SGD provides globally important fluxes of nutrients, carbon, and metals to coastal waters.

https://moritz.botany.ut.ee/~olli/eutrsem/Moore_2010.pdf

The Effect of Submarine Groundwater Discharge on the Ocean

Discharge of groundwater into the sea is widespread. Overlooking it may lead to serious misinterpretations of ecological data in studies of coastal pollution, of benthic zonation and productivity, and of the flux of dissolved substances within and between bottom sediments and over ly~ng water. Data are presented indicating that in the Perth region of Western Australia, submarine groundwater discharge delivers several times as much nltrate to coastal waters a s does river runoff.

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The Ecological Significance of the Submarine Discharge of Groundwater

The first broad program of scientific shallow drilling on the U.S. Atlantic continental shelf has delineated rocks of Pleistocene to Late Cretaceous age, including phosphoritic Miocene strata, widespread Eocene carbonate deposits that serve as reflective seismic markers, and several regional unconformities. Two sites, off Maryland and New Jersey, showed light hydrocarbon gases having affinity to mature petroleum. Pore fluid studies showed that relatively fresh to brackish water occurs beneath much of the Atlantic continental shelf, whereas increases in salinity off Georgla and beneath the Florida-Hatteras slope suggest buried evaporitic strata. The sediment cores showed engineering properties that range from good foundation strength to a potential for severe loss of strength through interaction between sediments and man-made structures.

U.s. Geological survey core drilling on the atlantic shelf.

Sediment thickness, paleobathymetry, and chronostratigraphy from COST wells offshore from Georgia and New Jersey indicate periods of rapid subsidence superimposed on the slower thermal subsidence of the continental margin. Rapid subsidence occurred during the Coniacian-Santonian, the Eocene and, in the COST wells off New Jersey, since the end of early Miocene. Once the maximum effects of water and sediment loading, compaction, and thermal cooling are removed, the residual vertical movements caused by tectonic and sea-level fluctuations can be analyzed. Because no global sea-level change can account for all residual movements, we propose that tectonism, variously amplified by loading, is responsible for the observed episodes of rapid subsidence. Synchroneity of subsidence with sea-floor–spreading changes in the North Atlantic suggests a unified cause for these events. Recognition of episodic subsidence may have implications for fault timing, petroleum potential, and global sea-level effects on passive margins.

Episodic post-rift subsidence of the United States Atlantic continental margin

Mesozoic and Cenozoic stratigraphy of the United States Atlantic continental shelf and slope

/pdf/late-cretaceous-and-cenozoic-evolution-of-the-new-jersey-354nhm41rc.pdf

Late Cretaceous and Cenozoic evolution of the New Jersey continental slope and upper rise: an integration of borehole data with seismic reflection profiles: Chapter 30 in Initial reports of the Deep Sea Drilling Project

Three ancient impact craters (Chesapeake Bay—35.7 Ma; Toms Canyon—35.7 Ma; Montagnais—51 Ma) and one multiring impact basin (Chicxulub—65 Ma) are currently known to be buried beneath modern continental shelves. All occur on the passive Atlantic margin of North America in regions extensively explored by seismic reflection surveys in the search for oil and gas reserves. We limit our discussion herein to the three youngest structures. These craters were created by submarine impacts, which produced many structural and morphological features similar in construction, composition, and variability to those documented in well-preserved subaerial and planetary impact craters. The subcircular Chesapeake Bay (diameter 85 km) and ovate Montagnais (diameter 45–50 km) structures display outer-rim scarps, annular troughs, peak rings, inner basins, and central peaks similar to those incorporated in the widely cited conceptual model of complex impact craters. These craters differ in several respects from the model, however. For example, the Montagnais crater lacks a raised lip on the outer rim, the Chesapeake Bay crater displays only small remnants of a raised lip, and both craters contain an unusually thick body of impact breccia. The subtriangular Toms Canyon crater (diameter 20–22 km), on the other hand, contains none of the internal features of a complex crater, nor is it typical of a simple crater. It displays a prominent raised lip on the outer rim, but the lip is present only on the western side of the crater. In addition, each of these craters contains some distinct features, which are not present in one or both of the others. For example, the central peak at Montagnais rises well above the elevation of the outer rim, whereas at Chesapeake Bay, the outer rim is higher than the central peak. The floor of the Toms Canyon crater is marked by parallel deep troughs and linear ridges formed of sedimentary rocks, whereas at Chesapeake Bay, the crater floor contains concentric faults and compression ridges formed in rocks of the crystalline basement. The Chesapeake Bay crater is distinguished further by its cluster of at least 23 adjacent secondary craters. The North American tektite strewn field, a widespread deposit of distal ejecta, is thought to be derived from the Chesapeake Bay impact, perhaps with a small contribution from the Toms Canyon impact. No ejecta field is known to be associated with the Montagnais impact. No immediate major extinction event is directly linked to any of these three impacts. There is evidence, however, that the Chesapeake Bay and Toms Canyon impacts helped initiate a long-term pulse of warm global climate, whose eventual dissipation coincided with an early Oligocene mass extinction event, 2 Ma after the impacts.

C. Wylie Poag

Papers

U.s. Geological survey core drilling on the atlantic shelf.

Episodic post-rift subsidence of the United States Atlantic continental margin

Mesozoic and Cenozoic stratigraphy of the United States Atlantic continental shelf and slope

Late Cretaceous and Cenozoic evolution of the New Jersey continental slope and upper rise: an integration of borehole data with seismic reflection profiles: Chapter 30 in Initial reports of the Deep Sea Drilling Project

Ancient impact structures on modern continental shelves: The Chesapeake Bay, Montagnais, and Toms Canyon craters, Atlantic margin of North America