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D4 - Con­struc­tio­nal im­pacts on bed­form dy­na­mics

2005 - 2009
Volkhard Spieß, Tobias Mörz
Ben­ja­min Schlue, Han­no Keil, Til­mann Schwenk

The aim of this pro­ject is the geo­phy­si­cal and geo­tech­ni­cal se­abed cha­rac­te­riza­t­i­on, with a spe­cial fo­cus on as­si­gned off­shore con­struc­tion sites (e.g. wind en­er­gy parks), the cor­re­la­ti­on of sur­vey in­for­ma­ti­on with soil strength data, and the stu­dy of lo­cal off­shore struc­tu­re-se­abed in­ter­ac­tions in a mor­pho­dy­na­mic and mi­cro­me­cha­ni­cal sen­se. A new shal­low-wa­ter mul­tichan­nel seis­mic sys­tem will be used to de­ri­ve vo­lu­me and re­flec­tor seis­mic pro­per­ties, which can be com­pa­red with in-situ geo­tech­ni­cal mea­su­re­ments and sam­ples to ge­ne­ra­te sta­tis­ti­cal­ly si­gni­fi­cant cor­re­la­ti­ons bet­ween geo­tech­ni­cal and geo­phy­si­cal data as pre­dic­tive tools for se­di­men­ta­ry site cha­rac­te­riza­t­i­on. New-pipe lay­ing tech­ni­ques in non-co­he­si­ve sub­stra­tes will be eva­lua­ted, de­si­gned and tested. The pro­ject spe­ci­fi­cal­ly ad­dres­ses how up­co­m­ing off­shore foun­da­ti­on ac­tivi­ties may af­fect the dy­na­mic strength of the Plei­sto­ce­ne and Ho­lo­ce­ne se­di­ment. Wi­t­hin the frame­work of re­se­arch area D, this pro­ject deals with an ac­cu­ra­te site cha­rac­te­riza­t­i­on by sur­veys, sam­pling and in-situ mea­su­re­ments, whi­le the com­pli­men­ta­ry pro­ject D1 fo­cu­ses on the en­vi­ron­men­tal im­pact of har­bors and con­struc­tions. Bey­ond the sci­en­ti­fic and me­tho­do­lo­gi­cal chal­len­ges in shal­low wa­ter re­se­arch, the pro­po­sed pro­ject in­tends to pro­vi­de re­le­vant me­thods and data for fu­ture tasks in ma­ri­ne off­shore con­struc­tion work, to keep clo­se con­tact with ad­mi­nis­tra­ti­on units (e.g. BSH, BGR) and sur­vey (e.g. OSAE) and con­struc­tion com­pa­nies, and to build up ex­per­ti­se for stu­dent edu­ca­ti­on in ap­p­lied geo­sci­en­ces.

Multifrequency Seismoacoustic Survey of a planned Wind Farm Area

The seis­mic data of a de­si­gna­ted wind farm area off Bor­kum re­veals that the wind farm area is lo­ca­ted above the eas­tern flank of an up­do­m­ing struc­tu­re, pro­bab­ly a salt dome. The flank is lo­ca­ted in depth of 170 to 280 me­ters. The near-sur­face struc­tu­re is qui­te he­te­ro­ge­neous and cha­rac­te­ri­zed by nu­merous fil­led chan­nels, of­ten cut into each other.

Pro­ject SD1: For­ma­ti­on and in­fill of bu­ried Plei­sto­ce­ne tun­nel-val­leys in the North Sea


T. Mörz, D. Hebbeln, H. Keil,
A. Bar­tho­lo­mä, J. Eh­lers, T. Ha­ne­buth, D. A. Hepp, T. Schwenk, V. Spieß

The re­lease of mel­twa­ter from the mar­gins of the Late Qua­tern­ary Fen­no­scan­dian ice sheets re­sul­ted in com­plex net­works of (now bu­ried) Plei­sto­ce­ne tun­nel-val­leys that ex­tend be­ne­ath lar­ge parts of the North Sea and the ad­ja­cent nort­hern Eu­ro­pean low­lands. De­eply in­cised (100-500 m) into most­ly Neo­ge­ne se­di­ment stra­ta, they form a do­mi­nant ar­chi­tec­tu­ral ele­ment of the North Sea se­di­men­ta­ry ba­sin and are a pri­ma­ry cau­se of small sca­le li­tho­lo­gi­cal he­te­ro­gen­ei­ties. Off­shore map­ping ba­sed on seis­mic sur­veys is far from com­ple­te, but has pro­vi­ded evi­dence of mul­ti­ple ge­ne­ra­ti­ons of bu­ried val­leys, in­fer­red to re­cord at least three suc­ces­si­ve cy­cles of con­ti­nen­tal gla­cia­ti­on and in­ter­gla­ci­al ma­ri­ne trans­gres­si­on. The lar­gest known bu­ried val­leys lie in and ad­ja­cent to the sou­thern North Sea and have been ten­ta­tive­ly cor­re­la­ted to the mid-Plei­sto­ce­ne Els­te­ri­an gla­cia­ti­on. The re­cent dis­co­very by MARUM sci­en­tists of a so far un­k­nown ma­jor E-W tren­ding bu­ried val­ley in the SE North Sea po­ses new mul­ti-di­sci­pli­na­ry ques­ti­ons with re­gard to the ages of cross-cut­ting fea­tures, their in­fill ar­chi­tec­tu­re and li­tho­lo­gy, the ori­en­ta­ti­ons and dy­na­mics of for­mer ice mar­gins, the num­ber and na­tu­re of in­ter­gla­ci­al ma­ri­ne trans­gres­si­ons and the miti­ga­ti­on of geo­tech­ni­cal risks. The lat­ter is of eco­no­mic im­port­an­ce as li­tho­lo­gi­cal he­te­ro­gen­ei­ties in shelf se­di­ments in­du­ced by such val­leys, com­mon fea­tures also in other for­mer­ly gla­cia­ted re­gi­ons, have re­cent­ly gai­ned at­ten­ti­on in off­shore wind park plan­ning as po­ten­ti­al geo­tech­ni­cal risks. 

To what extent are well-known N-S tren­ding bu­ried Plei­sto­ce­ne val­leys in the SE-North Sea cross-cut by youn­ger, but E-W tren­ding tun­nel-val­leys?

                       Deep (>100-500 m) Plei­sto­ce­ne tun­nel-val­leys be­ne­ath the nort­hern Eu­ro­pean low­lands (Den­mark, N-Ger­ma­ny, Nether­lands) and the SE North Sea com­mon­ly fol­low an over­all N-S trend and their in­fill is cap­ped by va­ry­ing thick­nes­ses of Late Els­te­ri­an Lau­en­burg Clay. Con­se­quent­ly, the for­ma­ti­on of the­se val­leys has been as­si­gned to the pre­ce­ding Els­te­ri­an gla­cia­ti­on. Si­mi­lar struc­tu­res for­med du­ring sub­se­quent gla­cia­ti­ons, alt­hough they are less ex­ten­si­ve and not so de­eply in­cised. The new­ly dis­co­ve­r­ed E-W tren­ding val­ley in the SE North Sea is more than 35 km long and ap­pa­r­ent­ly cross­cuts ol­der N-S tren­ding val­leys. Alt­hough ex­cep­tio­nal for the mo­ment, the pre­sence of ad­di­tio­nal such val­leys is very li­kely, ta­king into ac­count the poor map­ping sta­tus of the SE North Sea. As tun­nel-val­leys are thought to form by melt wa­ter drai­na­ge be­ne­ath and per­pen­di­cu­lar to ice sheet mar­gins, an E-W tren­ding post-Els­te­ri­an val­ley in the SE North Sea im­plies a N-S tren­ding ice mar­gin of Saa­li­an (?) age, which pre­vious­ly has not been pro­po­sed for the Ger­man North Sea sec­tor but would fit ob­ser­va­tions in the Dutch sec­tor. 2D/3D seis­mic in­ves­ti­ga­ti­ons of the extent, shape, in­fill ar­chi­tec­tu­re and cross­cut­ting re­la­ti­ons­hips of Plei­sto­ce­ne bu­ried val­leys will be an im­portant cont­ri­bu­ti­on to re­sol­ve the exis­ting in­con­sis­ten­cies in de­scri­bing past ice sheet dy­na­mics in this re­gi­on.

Figure 1. Seis­mic sec­tion through the re­cent­ly dis­co­ve­r­ed E-W tren­ding bu­ried val­ley in the Ger­man Bight.


Do dif­fe­rent in­fill suc­ces­si­ons of N-S and E-W tren­ding Plei­sto­ce­ne bu­ried val­leys in the SE-North Sea re­flect dif­fe­rent for­ma­ti­on and in­fill pro­ces­ses?

                       Ac­cor­ding to seis­mic in­ves­ti­ga­ti­ons and spar­se bo­re­ho­le in­for­ma­ti­on, most bu­ried val­leys in the North Sea and the ad­ja­cent nort­hern Eu­ro­pean low­lands are fil­led with a gla­ci­oflu­vi­al back­fill, de­po­si­ted clo­se to the re­trea­ting ice mar­gin. Their up­per parts of­ten con­tain also youn­ger well-laye­red mud­dy gla­cio­la­cus­tri­ne and/​or gla­cio­ma­ri­ne se­di­ments de­po­si­ted du­ring sub­se­quent in­ter­gla­ci­al trans­gres­si­ons and gla­ci­al ad­van­ces. Ta­king ad­van­ta­ge of ex­ten­si­ve (main­ly in­dus­tri­al) core ma­te­ri­al and in-situ log­ging data re­sul­ting from wind farm site sur­veys, the in­fill li­tho­lo­gies, and thus the in­fill his­to­ries, of N-S and E-W tren­ding val­leys will be ana­ly­zed. By de­ter­mi­na­ti­on of the ma­xi­mum pre-con­so­li­da­ti­on pres­su­re the in­fill ex­pe­ri­en­ced, the ice and se­di­ment loa­ding his­to­ry of the­se se­quen­ces can be as­ses­sed, thus al­lo­wing an esti­ma­ti­on of e.g. the ma­xi­mum thick­ness of Saa­li­an ice ad­van­ces ha­ving over­ridden the Els­te­ri­an and Hol­stei­ni­an val­ley fills. In con­trast, in­fills de­po­si­ted just af­ter the Saa­li­an gla­cia­ti­on should not show any over­com­pac­tion as the Weich­se­li­an gla­cia­ti­on did not reach the SE North Sea.                        


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