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  • 1
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    A major and long-term Pliocene intensification of the Mediterranean Outflow, 3.5-3.3 Ma ago (2009)
    GSA, Geological Society of America
    In:  Geology, 37 (9). pp. 811-814.
    Details
    Publication Date: 2017-05-24
    Description: Largely continuous millennial-scale records of benthic delta O-18, Mg/Ca-based temperature, and salinity variations in bottom waters were obtained from Deep Sea Drilling Project (DSDP) Site 548 (East Atlantic continental margin near Ireland, 1250 m water depth) for the period 3.7-3.0 Ma ago. High epsilon(Nd) values of -10.7 to -9 show that this site monitored changes in Mediterranean Outflow Water (MOW) throughout the mid-Pliocene. Bottom water variability at Ocean Drilling Progam (ODP) Site 978 (Alboran Sea, 1930 m water depth) provides a complementary record of MOW composition near its West Mediterranean source. Both sites show a singular and persistent rise in bottom water salinities by 0.7-1.4 psu, and in densities by similar to 1 kg m(-3) from 3.5 to 3.3 Ma ago, which is matched by an similar to 3 degrees C increase in bottom water temperature at Site 548. This event suggests the onset of strongly enhanced deep-water convection in the Mediterranean Sea and a related increase in MOW flow as a result of major aridification in the Mediterranean source region. In harmony with model suggestions, the enhanced MOW flow has possibly intensified Upper North Atlantic Deep Water formation.
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  • 2
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    Arctic Ocean evidence for late Quaternary initiation of northern Eurasian ice sheets (1997)
    GSA, Geological Society of America
    In:  Geology, 25 (9). pp. 783-786.
    Details
    Publication Date: 2017-04-10
    Description: A high-resolution multiparameter stratigraphy allows the identification of late Quaternary glacial and interglacial cycles in a central Arctic Ocean sediment core. Distinct sandy layers in the upper part of the otherwise fine-grained sediment core from the Lomonosov Ridge (lat 87.5°N) correlate to four major glacials since ca. 0.7 Ma. The composition of these ice-rafted terrigenous sediments points to a glaciated northern Siberia as the main source. In contrast, lithic carbonates derived from North America are also present in older sediments and indicate a northern North American glaciation since at least 2.8 Ma. We conclude that large-scale northern Siberian glaciation began much later than other Northern Hemisphere ice sheets.
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  • 3
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    Dolomite formation within the methanogenic zone induced by tectonically driven fluids in the Peru accretionary prism (2011)
    GSA, Geological Society of America
    In:  Geology, 39 (6). pp. 563-566.
    Details
    Publication Date: 2017-07-28
    Description: Early diagenetic dolomite formation in methanogenic marine sediments is enigmatic because acidifi cation by CO2, a by-product of methanogenesis, should lead to carbonate dissolution and not precipitation. However, petrographic relationships indicate that dolomite breccia layers with δ13C values of ~+15‰, recovered from the lower slope of the Peru continental margin (Ocean Drilling Program Site 1230), formed deep in the methanogenic zone during tectonic activity of a décollement. Based on radiogenic Sr isotope ratios (87Sr/86Sr 〉 0.711) and positive δ18O values (+6‰), we present evidence that the dolomite breccias mainly formed from fl uids originating from deep sedimentary units within the accretionary prism, where they interacted with continental crust and/or siliciclastic rocks of continental affi nity. Due to silicate alteration and dehydration, such fl uids are likely alkaline and thus have the potential to neutralize the acidifi cation imposed by the high dissolved CO2 concentrations. This scenario provides a potential mechanism by which dolomite formation can be induced deep in a highly active methanogenic zone.
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  • 4
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    Discovery of Miocene to early Pleistocene deposits on Mayaguana, Bahamas: Evidence for recent active tectonism on the North American margin (2011)
    GSA, Geological Society of America
    In:  Geology, 39 (6). pp. 523-526.
    Details
    Publication Date: 2017-05-18
    Description: We report here the discovery of Miocene, Pliocene, and early Pleistocene shallow-marine carbonates on Mayaguana Island (southeastern Bahamas) that have so far not been observed on any other Bahamian island. Spanning more than 17 m.y., but 〈12 m thick, this stratigraphic succession only occurs along the northern coast of the island, indicating that the Mayaguana Bank underwent minor subsidence throughout the late Cenozoic and was tilted toward the south during the Quaternary. In addition to considerably extending the stratigraphic record of the Bahamas Islands, our findings demonstrate that these carbonate banks were at different elevations and subsided at different rates during the Neogene. The young age of the tilting event detected on Mayaguana further shows that parts of the southeastern margin of North America have recently undergone tectonic activity a long way from its actual boundary with the Caribbean plate.
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  • 5
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    Nd and Pb isotopes in Atlantic and Pacific water masses before and after closure of the Panama Gateway (1999)
    GSA, Geological Society of America
    In:  Geology, 27 . pp. 1147-1150.
    Details
    Publication Date: 2017-09-26
    Description: Two Nd and Pb isotope time series of hydrogenous ferromanganese crusts, one from the Tehuantepec Ridge in the deep eastern equatorial Pacific and the other from Blake Plateau in the shallow northwestern Atlantic, which cover the past 7–8 m.y., show no variations coincident with the final closure of the Panama gateway, estimated as ca. 3.5 Ma. The record of the Atlantic crust located in the present-day Gulf Stream shows a shift in isotope composition from ca. 8 to 5 Ma that is explained by a diminishing supply of Pacific water. It is argued that the major restriction of water-mass exchange through the Panama gateway occurred before 5 Ma and thus cannot serve as a direct cause of the onset of Northern Hemisphere glaciation. The absence of a significant signature in the isotope records from the Pacific crust suggests that the volume of water exchanged with the Atlantic through shallow archipelagic straits of the gateway during the 3–4 m.y. prior to closure was too small to influence the radiogenic isotope composition of Pacific deep water.
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