TY - JOUR

T1 - Response of a proglacial delta to rapid high-amplitude lake-level change

T2 - An integration of outcrop data and high-resolution shear wave seismics

AU - Winsemann, Jutta

AU - Brandes, Christian

AU - Polom, Ulrich

PY - 2011/2

Y1 - 2011/2

N2 - In this paper, we will present the stratigraphic evolution, internal facies architecture and geomorphology of the Middle Pleistocene Emme delta, controlled by rapid high-amplitude lake-level change. The Emme delta was deposited on the northern margin of glacial Lake Weser, located in north-west Germany. Rates of lake-level rise were probably >50mmyear-1 and rates of lake-level fall 30-50m within a few days or weeks, due to the opening of lake outlets. We use digital elevation models, sedimentology and shear wave seismics to improve earlier reconstructions and investigate the influence of rapid base-level change on delta development. Shear wave seismic data resolve architectural elements in the range of metres and bridge the common gap between outcrop and conventional compression wave seismic data. The radial delta complex is about 2km long, 1.8km wide and up to 70m thick, overlying a concave, up to 13° steep dipping ramp surface. It consists of vertically and laterally stacked delta lobes, caused by lobe switching during base-level change. During the lake-level rise, vertically stacked (Gilbert-type) delta systems formed. The decrease in thickness and lateral extent indicates a rapid upslope shift of depocentres. A high rate and magnitude of lake-level fall (50m) promoted the development of a single incised valley and the deposition of forced regressive coarse-grained delta lobes in front of the valley. The incised valley was filled during decreasing rates of lake-level fall and low base-level, because the alluvial gradient was larger than the emergent lake profile. Attached sand-rich forced regressive aprons formed during lower magnitudes of lake-level falls in the range of 30-35m. Valley incision occurred, but was limited to the uppermost portion of the delta, controlled by the steep slope. The incised valley related to the final lake drainage is associated with long-wavelength (60-90m) bedforms at the downslope end, attributed to the formation of standing waves as a result of a hydraulic jump. Estimated palaeoflow depth during standing wave formation was ∼9-14m and flow velocity was 10-12ms-1. Because subsidence, waves or tides did not play a major role, the Emme delta can be used as an analogue-based predictive stratigraphical and sedimentological model for steep glacigenic deltas controlled by rapid base-level change and can help to understand better the facies distribution and three-dimensional geometry of these depositional systems.

AB - In this paper, we will present the stratigraphic evolution, internal facies architecture and geomorphology of the Middle Pleistocene Emme delta, controlled by rapid high-amplitude lake-level change. The Emme delta was deposited on the northern margin of glacial Lake Weser, located in north-west Germany. Rates of lake-level rise were probably >50mmyear-1 and rates of lake-level fall 30-50m within a few days or weeks, due to the opening of lake outlets. We use digital elevation models, sedimentology and shear wave seismics to improve earlier reconstructions and investigate the influence of rapid base-level change on delta development. Shear wave seismic data resolve architectural elements in the range of metres and bridge the common gap between outcrop and conventional compression wave seismic data. The radial delta complex is about 2km long, 1.8km wide and up to 70m thick, overlying a concave, up to 13° steep dipping ramp surface. It consists of vertically and laterally stacked delta lobes, caused by lobe switching during base-level change. During the lake-level rise, vertically stacked (Gilbert-type) delta systems formed. The decrease in thickness and lateral extent indicates a rapid upslope shift of depocentres. A high rate and magnitude of lake-level fall (50m) promoted the development of a single incised valley and the deposition of forced regressive coarse-grained delta lobes in front of the valley. The incised valley was filled during decreasing rates of lake-level fall and low base-level, because the alluvial gradient was larger than the emergent lake profile. Attached sand-rich forced regressive aprons formed during lower magnitudes of lake-level falls in the range of 30-35m. Valley incision occurred, but was limited to the uppermost portion of the delta, controlled by the steep slope. The incised valley related to the final lake drainage is associated with long-wavelength (60-90m) bedforms at the downslope end, attributed to the formation of standing waves as a result of a hydraulic jump. Estimated palaeoflow depth during standing wave formation was ∼9-14m and flow velocity was 10-12ms-1. Because subsidence, waves or tides did not play a major role, the Emme delta can be used as an analogue-based predictive stratigraphical and sedimentological model for steep glacigenic deltas controlled by rapid base-level change and can help to understand better the facies distribution and three-dimensional geometry of these depositional systems.

UR - http://www.scopus.com/inward/record.url?scp=78751538437&partnerID=8YFLogxK

U2 - 10.1111/j.1365-2117.2010.00465.x

DO - 10.1111/j.1365-2117.2010.00465.x

M3 - Article

AN - SCOPUS:78751538437

VL - 23

SP - 22

EP - 52

JO - Basin research

JF - Basin research

SN - 0950-091X

IS - 1

ER -