Late Cretaceous-early Tertiary floras of King George Island, West Antarctica: their stratigraphic distribution and palaeoclimatic significance

1989 ◽  
Vol 47 (1) ◽  
pp. 227-240 ◽  
Author(s):  
K. Birkenmajer ◽  
E. Zastawniak
1995 ◽  
Vol 7 (3) ◽  
pp. 265-276 ◽  
Author(s):  
C.J. Adams ◽  
D. Seward ◽  
S.D. Weaver

Rb-Sr ages of Swanson Formation on Edward VII Peninsula, West Antarctica, indicate a late Ordovician age, 421–432 Ma for regional metamorphism. K-Ar ages of 113–440 Ma, reflect a second thermal metamorphism during emplacement of widespread Cretaceous granites. Rb-Sr ages of five monzogranite/syenogranitic plutons of Byrd Coast Granite are in the range 95–105 Ma (initial 87Sr/86Sr ratios 0.710–0.715) and represent stages of crystallization of anorogenic granite (A subtype). These correlate with Byrd Coast Granite (100–110 Ma) farther east in Marie Byrd Land, and with Cretaceous granitoids on the Campbell Plateau and in southern New Zealand. K-Ar mica/hornblende and fission-track apatite/zircon ages indicate that regional cooling began c. 90–100 M.y. ago immediately after granite emplacement. Uplift continued throughout the peninsula during the period 55–100 Ma (late Cretaceous-early Tertiary), associated with regional uplift in the rift-drift stages of Gondwana break-up at the South-west Pacific spreading centre. Apatite fission track ages show that during late Cretaceous-early Tertiary time the peninsula behaved as two blocks. The Alexandra Mountains were exhumed 20 m.y. before the Rockefeller Mountains and are possibly separated by a fault active initially in the mid-Cretaceous or earlier, and later reactivated in the late Cretaceous-early Tertiary. An averaged uplift rate (50–100 Ma) of 0.025 mm yr−1 is characteristic of the inferred intraplate tectonic setting.


Zootaxa ◽  
2005 ◽  
Vol 932 (1) ◽  
pp. 1 ◽  
Author(s):  
HARRY M. SAVAGE ◽  
R. WILLS FLOWERS ◽  
WENDY PORRAS V.

A new genus, Tikuna, is described based on recent collections of adults and nymphs of Choroterpes atramentum Traver from western Costa Rica. All recent collections are from streams on or near the Nicoya Complex, the oldest geological formation in Lower Central America. Tikuna belongs to a lineage of South American Atalophlebiinae (Leptophlebiidae: Ephemeroptera) whose origin is hypothesized to have been in the late Cretaceous–early Tertiary. Some implications of the distribution of Tikuna for theories on the origin of Costa Rica’s biota are discussed.


2006 ◽  
Vol 368 (1) ◽  
pp. 236-247 ◽  
Author(s):  
Liguang Sun ◽  
Xuebin Yin ◽  
Xiaodong Liu ◽  
Renbin Zhu ◽  
Zhouqing Xie ◽  
...  

1991 ◽  
Vol 103 (10) ◽  
pp. 1297-1307 ◽  
Author(s):  
RALPH A. HAUGERUD ◽  
PETER VAN DER HEYDEN ◽  
ROWLAND W. TABOR ◽  
JOHN S. STACEY ◽  
ROBERT E. ZARTMAN

1986 ◽  
Vol 11 ◽  
pp. 1-46
Author(s):  
Ole Valdemar Vejbæk

The Lower Cretaceous sequence of the Danish Central Trough has been studied by the use of seismic stratigraphic analysis. The sequence has been subdivided into 6 seismic stratigraphic units named LCA, LCB, LCC, LCD, LCE and LCF. The studied area includes the Feda Graben, the Gertrud Graben (new name), the Tail End Graben, the Arne-Elin Graben (new name) and the Salt Dome Province, whereas the Grensen Nose and the Outer Rough Basin are not included. These basins are separated by the Inge High, the Mads High, the Gert Ridge (new name), the Manda! High, the Heno Plateau (new name) and the Pollerne Ridge (new name). The fault controlled subsidence of the Lower Cretaceous basins is claimed to have been governed by left lateral transtensional wrenching. This wrenching gradually ceased and gave way to regional subsidence with intermittent events of inversion resulting from right lateral transpressive wrenching in the Late Cretaceous and Early Tertiary. The first weak inversion is shown to have occurred in the Late Hauterivian. Sedimentation was influenced by a general gradual relative rise in sea-level starting with a low in the Volgian - Early Ryazanian times coeval with the deposition of the Farsund Formation and culminating in the Late Cretaceous. At the beginning of the Early Cretaceous gravity flow became an important depositional mechanism and resulted in preferred deposition in topographical lows, which were generated by simple tensional block-faulting or by wrench-induced, rapid local subsidence. As tectonic activity decreased and the elastic source areas became more remote and worn down, depocentres became less pronounced, especially with the last unit of the Lower Cretaceous.


2014 ◽  
Vol 26 (4) ◽  
pp. 400-412 ◽  
Author(s):  
Fernanda Quaglio ◽  
Lucas Veríssimo Warren ◽  
Luiz Eduardo Anelli ◽  
Paulo Roberto Dos Santos ◽  
Antonio Carlos Rocha-Campos ◽  
...  

AbstractShell bed levels in the Low Head Member of the early Oligocene Polonez Cove Formation at King George Island, West Antarctica, are re-interpreted based on sedimentological and taphonomic data. The highly fossiliferous Polonez Cove Formation is characterized by basal coastal marine sandstones, overlain by conglomerates and breccias deposited in fan-delta systems. The shell beds are mainly composed of pectinid bivalve shells of Leoclunipecten gazdzickii and occur in the basal portion of the Low Head Member. Three main episodes of bioclastic deposition are recorded. Although these shell beds were previously interpreted as shelly tempestites, we present an alternative explanation: the low fragmentation rates and low size sorting of the bioclasts resulted from winnowing due to tidal currents (background or diurnal condition) in the original bivalve habitat. The final deposition (episodic condition) was associated with subaqueous gravity driven flows. This new interpretation fits with the scenario of a prograding fan-delta front, which transported shell accumulations for short distances near the depositional site, possibly between fair-weather and storm wave bases. This work raises the notion that not every shell bed with similar sedimentological and taphonomic features (such as geometry, basal contact, degree of packing and shell orientation in the matrix) is made in the same way.


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