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Macroinvertebrate fossils from Mesozoic beds of Hole 511, Leg 71, were extracted and studied. Albian clays and marls of Sections 511-50-1 to 511-57-1 lack neritic belemnites but contain shelf-break foraminifers and numerous coquinas of Aucellina radiatostriata, which thrived in this environment because mud was intermittently removed by strong currents. Sections 511-57-2 to 511-58-3 contain late Aptian Epicheloniceras, Aconecerasi, and Australicerasl but lack belemnites and neritic pelecypods. Their mudstones are anoxic outermost neritic or upper bathyal deposits. Lower Aptian and ?uppermost Barremian fine-grained, calcareous sandstones of Sections 511-58-4 to 511-60-5 contain belemnites and numerous shallow-water pteriid pelecypods including the diagnostic Aucellina ex aff. radiatostriata. These well-aerated, inner neritic deposits indicate a brief regression. Planktonic foraminifers indicate a Barremian to ?basal Aptian age for Sections 511-60-5 to 511-62-5. These petroliferous, perhaps bathyal mudstones almost lack macroinvertebrates but are rich in fish remains. They overlie unconformably lower upper to ?mid-upper Tithonian ( = upper Kimmeridgian and perhaps slightly later) Sections 511-63-1 to 511-64-3. Uppermost Jurassic to Hauterivian rocks are absent, either because they were not deposited or perhaps because they were later eroded. Petroliferous mudstones of Sections 511-63-1 to 511-64-3, below this unconformity, are mid-neritic deposits containing oxytomid pelecypods, buchiids, ostreids, belemnites (Hibolithes and Hastitesl only), and ammonites. This fauna includes the diagnostic Virgatosphinctes ex aff. densistriatus-denseplicatus and Malayomaorica occidentalis n. sp. Sections 511 -64-4 to 511 -67-3 contain late early Tithonian (= mid-Kimmeridgian) Belemnopsis spp. ex gr. uhligi and M. occidentalis n.sp. The lower part of these beds is a complex interbedding of fossiliferous sandy mudstones with pelecypod coquinas replete with oysters. These innermost neritic, lagoonal and estuarine beds record a major shoaling and freshening event. The lowest Sections 511-67-4 to 511-70-5 contain early early Tithonian (= early Kimmeridgian) Jeletzkiella falklandensis and B. cf. keari, the presence of which apparently contradicts the Oxfordian age suggested by microfossils. These petroliferous mudstones are mid-neritic, partly anoxic deposits.

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Macroinvertebrate Paleontology, Biochronology, and Paleoenvironments of Lower Cretaceous and Upper Jurassic Rocks, Deep Sea Drilling Hole 511, Eastern Falkland Plateau