Waxy bitumen stranding in southern Australia: A geochemical study of multiple oil families and their likely origins

Remotely constraining the temporal evolution of offshore oil systems

“…Furthermore, comparison of the weathered exteriors (top 2 mm) of four asphaltites with their respective interiors all returned ratios within the range of analytical uncertainty (Table S2). Finally, the Re-Os characteristics of the asphaltites were compared to those of a waxy bitumen specimen (W13/007697) recovered from the same coastline and known to originate from one of several distant Cenozoic lacustrine petroleum systems in the Indonesian archipelago 3 . The waxy bitumen contained very low abundances of Re and Os (0.02 ppb and 1.34 ppt, respectively), with a 187 Re/ 188 Os ratio of 84.4 and 187 Os/ 188 Os ratio of 0.486.…”

“…The distance crude oils are transported by ocean currents may be short if the seepage site is near the coastline 5 . However, there is evidence of significantly longer transport, where bitumens are found on distant foreign coastlines 3 . The geochemistry of these crude oils can be used to characterise and identify their respective parent petroleum systems and potentially distinguish them from anthropogenic inputs of oil such as tanker spillage 6 .…”

“…Australia’s southern margin collects bitumens emitted from a variety of different petroleum systems 2,3,17,18 . One of the rarest, but most distinctive, types encountered is known as asphaltite 2,17 .…”

A second type of highly asphaltic crude oil seepage stranded on the South Australian coastline

“…Ocean beaches along Australia's southern margin are known to collect bitumen emitted from seafloor seeps associated with a variety of different petroleum systems (e.g. McKirdy et al, 1986McKirdy et al, , 1994Padley, 1995;Edwards et al, 1998Edwards et al, , 2016Edwards et al, , 2018. Reports of asphaltenerich coastal bitumen strandings (asphaltum, now referred to as asphaltite) in the region date back to the early 1800s and continue to the present (Trewartha, 1850;Tolmer, 1882;Sprigg and Woolley, 1963;Volkman et al, 1992;Edwards et al, 1998;Hall et al, 2014;Ross et al, 2017).…”

“…'waxy bitumens') which have been geochemically linked to Cenozoic petroleum systems in southeast Asia (Padley, 1995;Edwards et al, 2016Edwards et al, , 2018, the asphaltites are currently thought to originate from an undiscovered petroleum system in the offshore Bight Basin (Fig. 1A) located on Australia's southern margin (Boreham et al, 2001;Totterdell et al, 2008;Hall et al, 2014).…”