Geology topics

T.C. Moore

Publications and source records attributed to T.C. Moore.

5 recordsLinked to original sources

USGS2006

Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

The Palaeocene/Eocene thermal maximum, ???55 million years ago, was a brief period of widespread, extreme climatic warming, that was associated with massive atmospheric greenhouse gas input. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition. We show that sea surface temperatures near the North Pole increased from ???18??C to over 23??C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations, but the absolute polar temperatures that we derive before, during and after the event are more than 10??C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms-perhaps polar stratospheric clouds or hurricane-induced ocean mixing-to amplify early Palaeogene polar temperatures. ?? 2006 Nature Publishing Group.

Nature↗

USGS2006

The Cenozoic palaeoenvironment of the Arctic Ocean

The history of the Arctic Ocean during the Cenozoic era (0–65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm ‘greenhouse’ world, during the late Palaeocene and early Eocene epochs, to a colder ‘icehouse’ world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ∼ 14 Myr, we find sedimentation rates of 1–2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice ( ∼ 3.2 Myr ago) and East Antarctic ice ( ∼ 14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch ( ∼ 45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ∼ 49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum ( ∼ 55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

Nature↗

USGS2000

Younger Dryas interval and outflow from the Laurentide ice sheet

A boxmodel of the Great Lakes is used to estimate meltwater flow into the North Atlantic between 8000 and 14,000 calendar years B.P. Controls on the model include the oxygen isotopic composition of meltwaters and lake waters as measured in the shells of ostracodes. Outflow rates are highest when oxygen isotopic values of the lake waters are most negative, denoting a maximum glacial meltwater component. Flow rates reach maximum values before the onset of the Younger Dryas and after it ends. These maxima appear to be correlative with the major meltwater pulses MWP 1A and 1B. Although the resumption of North Atlantic Deep Water formation may be tied to the reduction in ice sheet melting, neither the onset nor the end of the Younger Dryas, as recorded in the Greenland Ice Sheet Project (GISP2) records, appear tied to maxima in meltwater outflow from the Laurentide ice sheet.

Great Lakes↗

USGS1998

Comparative sequence stratigraphy of low-latitude versus high-latitude lacustrine rift basins: Seismic data examples from the East African and Baikal rifts

Lakes Baikal, Malawi and Tanganyika are the world's three largest rift valley lakes and are the classic modem examples of lacustrine rift basins. All the rift lakes are segmented into half-graben basins, and seismic reflection datasets reveal how this segmentation controls the filling of the rift basins through time. In the early stages of rifting, basins are fed primarily by flexural margin and axial margin drainage systems. At the climax of syn-rift sedimentation, however, when the basins are deeply subsided, almost all the margins are walled off by rift shoulder uplifts, and sediment flux into the basins is concentrated at accommodation zone and axial margin river deltas. Flexural margin unconformities are commonplace in the tropical lakes but less so in high-latitude Lake Baikal. Lake levels are extremely dynamic in the tropical lakes and in low-latitude systems in general because of the predominance of evaporation in the hydrologic cycle in those systems. Evaporation is minimized in relation to inflow in the high-latitude Lake Baikal and in most high-latitude systems, and consequently, major sequence boundaries tend to be tectonically controlled in that type of system. The acoustic stratigraphies of the tropical lakes are dominated by high-frequency and high-amplitude lake level shifts, whereas in high-latitude Lake Baikal, stratigraphic cycles are dominated by tectonism and sediment-supply variations.

Conference Paper↗

USGS1992

Depositional and tectonic framework of the rift basins of Lake Baikal from multichannel seismic data

Recent multichannel seismic reflection data from Lake Baikal, located in a large, active, continental rift in central Asia, image three major stratigraphic units totalling 3.5 to 7.5 km thick in four subbasins. A major change in rift deposition and faulting between the oldest and middle-rift units probably corresponds to the change from slow to fast rifting. A brief comparison of the basins of Lake Baikal with those of the East African rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks. -from Authors

Lake Baikal↗