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4. The Jameson Land basin

Jameson Land basin

Final­ly, the gra­ben sys­tems of the Old Red and New Red area had stop­ped sub­si­ding, and it was qui­te calm for a while. But soon, other, lar­ge are­as began to sub­si­de slow­ly. This time, sub­si­dence occu­red not along dis­tinct fault lines, but more as a wide-span­ned ben­ding of the crust, so the result is cal­led a ‘basin’ rather than a ‘gra­ben’. The sedi­ments depo­si­ted in the­se basins can be found in the who­le of Jame­son Land as well as in sou­the­as­tern Mil­ne Land.

Macknight Bjerg

Sedi­ment lay­ers (upper Tri­as­sic-lower Juras­sic) of the Jame­son Land basin fil­ling.
Mack­night Bje­rg (nort­hern Jame­son Land, Wes­tern side of Carls­berg Fjord)

Soon, shal­low sea star­ted to fill the­se basins. This sea was not extre­me­ly deep, a few hund­red metres maxi­mum or even less, so the coast­li­ne was not far away. They even fell com­ple­te­ly dry at times. Basin for­ma­ti­on star­ted in the youn­gest part of the Palaeo­zoic, the upper Permi­an, a bit more than 250 mil­li­on years ago. As a start, wide, low-lying plains for­med with desert-like land­s­capes, whe­re occa­sio­nal floo­ds left sand and gra­vel. First ingres­si­ons of the sea left lime­stone and, due to sub­se­quent eva­po­ra­ti­on of sea­wa­ter which was not repla­ced, gypsym. The­re are also some dark, fine-grai­ned mari­ne sedi­ments. The dark colour is due to a high con­tent of orga­nic mat­ter, which drew the atten­ti­on of the oil- and gas indus­try to the respec­ti­ve are­as in Liver­pool Land and Mil­ne Land, but spec­ta­cu­lar finds have not been publis­hed.

During fur­ther deve­lo­p­ment, the sea advan­ced and retrea­ted once again, lea­ving mari­ne siltstone (as sand­stone, but with some­what finer grains) cove­r­ed by dune sands and depo­sits of salt lakes, inclu­ding lay­ers of gypsym.

Final­ly, the sea advan­ced again and stay­ed for a long time. From now on, a qui­te nar­row but long basin in East Green­land, stret­ching from the Scores­by­sund area or even a bit fur­ther south far to the north, remai­ned fil­led with sea­wa­ter for more than 100 mil­li­on years.

Typi­cal sedi­ments were depo­si­ted in the­se rela­tively shal­low seas, most­ly sand­stone and clay­stone (as sand­stone depo­si­ted as sin­gle grains, which later stuck tog­e­ther and thus for­med a hard rock mass, but with invi­si­b­ly small sedi­ment grains). Also the inha­bi­tants of tho­se seas left their traces. At some loca­ti­ons, we can find lar­ge amounts of fos­sils such as ammo­ni­tes, shells etc. Espe­cial­ly the ammo­ni­tes are so abundant in some lay­ers and so well pre­ser­ved, that chan­ges in their phy­sio­lo­gy during the cour­se of evo­lu­ti­on are visi­ble. This enab­les geo­lo­gists to estab­lish a detail­ed chro­no­lo­gy of geo­lo­gi­cal events and the histo­ry of life in the area. The reso­lu­ti­on in time is almost razor-bla­de sharp, at least in geo­lo­gi­cal terms: a sin­gle stra­ti­gra­phic unit often cover just one mil­li­on years! The ammo­ni­te zone is 150-200 mil­li­on years old (Juras­sic).

Ammo­ni­te (Juras­sic)

Ammonite (Jurassic)

Uplift and sub­si­dence of dif­fe­rent parts of the basin led to chan­ges of water depths. When the sea beca­me very shal­low, the coast came near and coas­tal sedi­ments were depo­si­ted: san­dy beach depo­sits, but del­ta sedi­ments were often domi­nant: lar­ge volu­mes of sand depo­si­ted by rivers at the coast. The­se del­tas were some­ti­mes qui­te rich in vege­ta­ti­on, as is the Mis­sis­sip­pi Del­ta today. Some­ti­mes, the vege­ta­ti­on got buried under a new lay­er of sand. Then, it could sub­se­quent­ly be tur­ned into coal after a long time. The­re are inde­ed several coal seams in Jame­son Land and at other pla­ces fur­ther north, but of infe­riour qua­li­ty and quan­ti­ty. It has been used local­ly, though, for examp­le at Kap Hope near Itto­q­qor­toor­mi­it (Scores­by­sund), whe­re a small area of sedi­ments has sur­vi­ved ero­si­on at the sou­thwes­tern cor­ner of Liver­pool Land.

The depo­si­ti­on of sedi­ments in the basin las­ted throughout most of the Meso­zoic into the lower Cret­ace­ous, about 100 mil­li­on years ago. It pro­bab­ly las­ted even lon­ger, at least into the upper Cret­ace­ous (up to 65 mil­li­on years ago) or even bey­ond that. In the Scores­by­sund, all sedi­ments youn­ger than lower Cret­ace­ous, should they have exis­ted, have been remo­ved again by ero­si­on. The­re are some very small are­as of Ter­tia­ry sedi­ments south of the Scores­by­sund, at Kap Brews­ter and Kap Dal­ton at the outer coast.

Final­ly, basin sub­si­dence ended, and so did sub­se­quent­ly this chap­ter of Earth histo­ry in East Green­land.

The sedi­ments which slow­ly fil­led the basin can now be found ever­y­whe­re in Jame­son Land and at the sou­the­as­tern cor­ner of Mil­ne Land. The hori­zon­tal laye­ring is most­ly very obvious, for examp­le when you arri­ve at the litt­le air­port of Cons­ta­ble Point. Some of the har­der lay­ers have been dis­sec­ted by ero­si­on in such a way that they form very nice, regu­lar towers, which can remind one of a fort­ress or a Gothic church.

Sedimentary layers of the Jameson Land basin fill (here lower Jurassic) at Constable Point

Sedi­men­ta­ry lay­ers of the Jame­son Land basin fill (here lower Juras­sic) at Cons­ta­ble Point. The regu­lar towers were crea­ted by ero­si­on.

The basin sedi­ments are most­ly com­pa­ra­tively soft, at least com­pa­red to the gneis­ses and gra­ni­tes of the Pre­cam­bri­an Shield and the Cale­do­ni­an fold belt. Accord­in­gly, the­re are no high, poin­ted moun­tains, but rather open, rela­tively low hills which are often top­ped by mar­kant pla­teaus, fol­lowing the hori­zon­tal lay­ers.

Contrast between flat tundra in western Jameson Land and mountaineous Milne Land in the background

Con­trast bet­ween flat tun­dra in wes­tern Jame­son Land and moun­tai­ne­ous Mil­ne Land in the back­ground.

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last modification: 2013-10-12 · copyright: Rolf Stange
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