Paleogene and Cretaceous sediment cores from the Kilwa and Lindi areas of coastal Tanzania: Tanzania Drilling Project Sites 1–5

Abstract

Initial results of scientific drilling in southern coastal Tanzania are described. A total of five sites was drilled (mostly using continuous coring) by the Tanzania Drilling Project for paleoclimate studies. The sediments are predominantly clays and claystones deposited in a deep marine shelf environment and often contain excellently preserved microfossils suitable for geochemical analysis. The studies reported here include summaries of the lithostratigraphy, biostratigraphy (planktonic foraminifers, calcareous nannofossils, benthic foraminifers, and palynology), magnetostratigraphy, and organic geochemistry. TDP Site 1 was drilled near Kilwa Masoko airstrip (8°54.516 ′S, 39°30.397 ′E). It yielded 8.55 m of barren blue-grey clays that may be Miocene in age, followed by 1.2 m of greenish-black to dark greenish-grey clay probably of the same age. The remainder of the hole cored 62.35 m of lower Oligocene sediments (nannofossil Zone NP23), which are predominantly greenish-black to dark greenish-grey clays. Total penetration was 74.10 m. The coring represents the first report of a thick Oligocene clay formation in the area. TDP Site 2 was drilled near Kilwa Masoko prison (8°55.277 ′S, 39°30.219 ′E). It yielded 92.78 m of predominantly dark greenish-grey clay with occasional allochthonous limestone beds that consist mostly of redeposited larger foraminifers. The site encompasses lower to middle Eocene planktonic foraminifer Zones P8/9 to P11 and nannofossil Subzones NP14b to NP15c. It encompasses a rarely cored interval across the Ypresian–Lutetian transition. TDP Site 3 was drilled near Mpara in the Kilwa area (8°51.585 ′S, 39°27.655 ′E). It yielded 56.4 m of predominantly dark greenish-grey clays and claystones. The site is assigned to lower Eocene planktonic foraminifer Zone P6 and nannofossil Zone NP11. TDP Site 4 was drilled near Ras Tipuli on the northwest side of Lindi creek (9°56.999 ′S, 39°42.985 ′E). It yielded 19.8 m of predominantly dark greenish-grey clay with allochthonous limestone interbeds. The site encompasses middle Eocene planktonic foraminifer Zones P12–P14 and nannofossil Zone NP17. TDP Site 5 was drilled at Machole, near Lindi, south of Kitulo Hill (10°01.646 ′S, 39°41.375 ′E). It yielded 31.6 m of predominantly greenish-black to dark greenish-grey clay assigned to the upper Cretaceous Globotruncana falsostuarti planktonic foraminifer zone and nannofossil zones UC15e–UC17 (upper Campanian–lower Maastrichtian). Paleomagnetic analysis suggests that the site straddles two magnetic reversals, between Chrons C32r.2r and C32r.1n. Samples from TDP Sites 1–5 yielded dinocyst and miospore assemblages that are integrated with the calcareous stratigraphy. Organic geochemical analyses of samples from each of the cores revealed biomarkers of predominantly terrestrial origin and an unusually low degree of thermal maturity, suggesting shallow burial depths. X-ray diffraction studies suggest that much of the Paleogene clay may be reworked from eroded Mesozoic formations.