a sedimentological record of early miocene ice advance and retreat and 2a drill hole mcmurdo sound antarctica

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Early Jurassic palaeoenvironments in the Surat Basin, Australia - marine incursion into eastern Gondwana

Interpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two‐dimensional and three‐dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third‐order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub‐basins, with rivers flowing in different orientations in each sub‐basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas

Incised valley paleoenvironments interpreted by seismic stratigraphic approach in Patos Lagoon, Southern Brazil

<div><p>ABSTRACT: The Rio Grande do Sul (RS) coastal plain area (33,000 km 2 ) had its physiography modified several times through the Quaternary, responding to allogenic and autogenic forcings. The Patos Lagoon covers a significant area of RS coastal plain (10,000 km 2 ), where incised valleys were identified in previous works. About 1,000 km of high resolution (3.5 kHz) seismic profiles, radiocarbon datings, Standard Penetration Test (SPT) and gravity cores were analyzed to interpret the paleoenvironmental evolution as preserved in incised valley infills. Seismic facies were recognized by seismic parameters. The sediment cores were used to ground-truth the seismic interpretations and help in the paleoenvironmental identification. Key surfaces were established to detail the stratigraphical framework, and seismic facies were grouped into four seismic units, which one classified in respective system tracts within three depositional sequences. The oldest preserved deposits are predominantly fluvial and estuarine facies, representing the falling stage and lowstand system tracts. The Holocene transgressive records are dominated by muddy material, mainly represented by estuarine facies with local variations. The transgression culminated in Late Holocene deposits of Patos Lagoon, representing the highstand system tract. The depositional pattern of the vertical succession was controlled by eustatic variations, while the autogenic forcing (paleogeography and sediment supply) modulated the local facies variation.</p></div

A review of Cretaceous coal-bearing sequences in Australia

Coals of Cretaceous age are preserved within the fill of several Australian sedimentary basins. Presently, Cretaceous coal is mined in only one area, although numerous coalfields have been active over the past century. Cretaceous organic facies in the subsurface of the Gippsland Basin, offshore southeast Australia, are thought to have sourced the major oil and gas accumulations of that area. Cretaceous coal-bearing basins in Australia fall into four groups: 1. interior basins, notably the Eromanga Basin where the greatest occurrence of coal is in the Cenomanian Winton Formation; 2. east coast basins, including the Laura Basin (Late Jurassic to Early Cretaceous Battle Camp Formation), Styx Basin (Albiah to Cenomanian Styx Coal Measures), Stanwell Outlier (Albian Stanwell Coal Measures), and Maryborough Basin (Albian Burrum Coal Measures); 3. south coast basins, notably the Great Australian Bight, Otway Basin (Otway and Sherbrook Groups), Bass Basin, (Otway and Eastern View Groups), and Gippsland Basin (Strzelecki and Latrobe Groups), where coal is known from throughout the Cretaceous system; 4. west coast basins, notably the Perth Basin, which contains minor, Early Cretaceous coal. The major control on the formation and distribution of Cretaceous coal in Australia was the development of widespread, rapidly-subsiding lowland environments during passive margin breakup between Australia and Antarctica, and between Australia and Lord Howe Rise. The widespread stratigraphic distribution of coal resources suggests that fluctuating climate and evolving vegetational communities did not fundamentally affect coal development. The role of eustatic sea-level changes is difficult to assess at present. Within individual basins, structural regime and the distribution of depositional systems also played an active role in controlling coal distribution