Stratigraphy Pelotas Basin

the basalts of serra geral formation exposed in fortaleza canyon of serra geral national park.

the sedimentary succession of pelotas basin underlain extremely deformed (highly stretched, thinned , faulted) continental crust, covered grabens can achieve thicknesses of more 20 kilometres (66,000 ft). nature of lower crust below pelotas basin remains uncertain, analogy namibian conjugate margin, may correspond high-density igneous crust-mantle interface intruded tristan da cunha plume. central onshore boundary of basin formed neoproterozoic pelotas batholith. stratigraphy of pelotas basin , punta del este basin south had different history due polônio paleohigh until late maastrichtian.

the basinal sequence starts imbituba formation, unit consisting of basaltic volcanic rocks. parts of these rocks have been dated @ ages between 125 ± 0.7 ma , 118 ± 1.9 ma, more recent flood basaltic serra geral formation of paraná , etendeka traps west in paraná basin. basalts exposed in serra geral national park 700 metres (2,300 ft) high cliff. volcanic deposits form seaward dipping reflectors (sdr) in seismic surveys of basin. conglomerates, siltstones , diamictites of cassino formation represent top of gondwana break-up unconformity, dates middle aptian. depositional environment has been interpreted fluvio-deltaic lacustrine. formation followed volcanics of curumim formation, dated @ 113 ± 0.1 ma, , small incursions in northern area of pelotas basin of ariri formation, evaporites form salt layer in santos basin north.

the rapid subsidence albian turonian created wide marine platform in north elevated areas due doming of curumim formation. on platform, marine limestones , siliciclastics of porto belo formation deposited. shales comprise outer marine deposition of stratigraphic unit, considered potential source rock. overlying porto belo formation proximal tramandaí , distal atlántida formations, composed of coarse-grained fluvial alluvial clastics, intercalated siltstones , shales. phase characteristic of large-scale prolonged transgression lasted until oligocene. in other areas of brazilian continental margin, late turonian marked regional unconformity.

the late cretaceous recent sequence subdivided proximal cidreira formation, related fluvial progradation of rio grande, , distal part known imbé formation, consisting of shales, intercalated sporadic siltstones , fine-grained sandstones. transgressive series interrupted presence of various paleogene hiatuses, appear in regressive miocene recent beds. unconformities have been analysed in detail using sr/sr ratios.