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Lake Simcoe is a large lake 45 km across and in places over 30 m deep, located between Lake Huron and Lake Ontario, in the
glaciated terrain of southern Ontario, Canada. Seismostratigraphic analysis of high-resolution seismic reflection profiles,
together with lakebed sediment sampling and pollen study, revealed distinctive sequences in the sediments beneath Lake Simcoe,
Ontario. A surface unit (Blue Sequence) of soft Holocene mud (low-amplitude surface reflection, discontinuous parallel internal
reflections) lies in the deeper basins of the lake. The underlying unit (Green Sequence) is characterized by high-amplitude
parallel internal reflections; basal sediments of this sequence consist of clay rhythmites with dropstones. The Green Sequence
was deposited by lacustrine sedimentation in proglacial Lake Algonquin; sedimentation persisted until the basin was isolated
from other glacial lakes at about 10 14C ka at the Penetang post-Algonquin phase. Subsequent erosion of the uppermost portion of the Green Sequence is attributed
to wave action in a low-level early Holocene lake, possibly closed hydrologically and coeval with closed lowstands in the
Huron and Georgian Bay basins. Two sequences with high-amplitude surface reflections and chaotic internal reflections (Purple
and Red Sequences) lie below the Green Sequence. Northeast-southwest trending ridges, tens of metres in height, on the Red
Sequence (the lowermost of these two units) are interpreted to be drumlins. An erosion surface descends into narrow valleys
50–80 m deep beneath the lake in bays to the west and south of the main lake basin. These depressions are interpreted as subglacial
tunnel channels cut by rapid flows of meltwater. The sediments of Purple Sequence are interpreted as channel-fill sediments
rapidly deposited during waning stages of the meltwater drainage. The Red Sequence is correlated with the Newmarket Till of
the last glacial maximum identified beneath the Oak Ridges Moraine to the south. 相似文献
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Darío Andrés Giagante Salvador Aliotta Silvia Susana Ginsberg Laura Gabriela Vecchi Jorge Osvaldo Spagnuolo 《Quaternary Research》2011,75(3):614-623
The purpose of this research is to analyze the seismostratigraphic and paleoenvironmental features of an ancient fluvial deposit characterized by the presence of paleochannels and sedimentary structures in Bahía Blanca estuary, Argentina. To this end, high-resolution seismic methods were used. Paleochannels exhibiting v-shaped cuts were found at different topographic positions at the base of this deposit. It was observed that channel silting is indicative of the relative change of river base level and the consequent migration of fluvial tributaries. This alluvial deposit is composed of low compacted fine sand and its middle–upper facies is characterized by the presence of horizontal and discontinuous wavy reflectors. The upper boundary of this deposit is an erosive discontinuity resulting from Holocene sea-level rise during which the mouth of old fluvial courses underwent changes. The deposit was subsequently buried by sandy and clayey silt sediments. The paleodrainage at subbottom indicates that this deposit is associated with an ancient river mouth. Based on the seismostratigraphic and lithological characteristics and the paleochannel structures found in the study area, it can be concluded that the deposit analyzed is an alluvial sequence formed in the period from the Middle-Late Pleistocene to Holocene marine transgression. 相似文献
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A seismostratigraphic approach constrained by well data is used for the interpretation of the deformation style along the central Elbe Fault System (EFS) within the sedimentary succession. Structural analysis allows to qualify, to quantify, and to date tectonic events. The stratigraphic interpretation is complicated by the mobilized Upper Permian Zechstein salt and by erosional events. A first-order quantification of the inversion-related uplift is estimated from vertical fault offsets that reach up to 4 km. The main uplift occurred during the Maastrichtian/Paleocene. Amounts of erosion inferred from comparing the strata thickness on top of the Flechtingen High with the surrounding basinal areas range from 3 to 4 km. The data indicate a changing deformation style: Thick-skinned deformation with southwest-dipping thrusts that vertically offset the pre-Permian basement is observed along the Flechtingen High in the central part of the EFS. Thin-skinned deformation occurs in the North German Basin where salt detaches the post-Permian cover from the barely faulted basement. It is concluded that during the Late Cretaceous/Early Tertiary inversion, the EFS responded to regional compression with uplift and formation of an internal high, the Flechtingen High. A stress-sensitive crustal weak zone beneath the EFS could be the reason for the repeated strain localization in the area. 相似文献
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