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2. Mineral Associations and Geochemical Indicators in Upper Miocene to Pleistocene Sediments in the Alboran Basin1

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2. Mineral Associations and Geochemical Indicators in Upper Miocene to Pleistocene Sediments in the Alboran Basin1 Zahn, R., Comas, M.C., and Klaus, A. (Eds.), 1999 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 161 2. MINERAL ASSOCIATIONS AND GEOCHEMICAL INDICATORS IN UPPER MIOCENE TO PLEISTOCENE SEDIMENTS IN THE ALBORAN BASIN1 Francisca Martínez-Ruíz,2 Maria C. Comas,2 and Belén Alonso3 ABSTRACT Upper Miocene to Pleistocene hemipelagites and resedimented facies recovered at Holes 976B and 977A (Leg 161) in the Alboran Basin consist mainly of biogenic and detrital components, with a minor contribution of neoformed mineral phases. Diagenetic processes have not obliterated the primary deposition signal, and therefore detrital components (quartz, feldspar, detrital dolomite, rock fragments, and clays) provide information about source rocks and provenances. No major bulk or clay mineralogy differences were recognized between resedimented and hemipelagic facies; in fact, similar mineral assemblages in both types of facies suggest common source rocks. However, mineral abundance fluctuations can be related to climate varia- tions and tectonic factors, as the main controls of sediment fill of this basin. A marked increase in smectites in Messinian sedi- ments suggests an extensive development of soils during that time, probably favored by the alternation of wet and dry climate episodes and the relative aridification of the Mediterranean borderlands. A notable increase in detrital components suggests a sea-level fall and/or tectonic uplift during the late Pliocene. The significant increase in detrital dolomite in the uppermost Pliocene deposits suggests the uplift of dolomite-rich rocks as source areas. Mineral components in Pleistocene sediments indi- cate increasing tectonic stability, and clay-mineral fluctuations during the Pleistocene can be related not only to tectonic events, but also to alternating cooling and warming periods. INTRODUCTION 1996). ORLs, defined as sapropels in the eastern Mediterranean, ap- pear in deposits from the middle Miocene and younger (e.g., Hilgen, During Ocean Drilling Program Leg 161, four sites (Sites 976– 1991), although their origin remains controversial. 979) were drilled in the Alboran Sea basin (Fig. 1). Site 976 (1108 This paper analyzes mineral and geochemical compositions of meters below seafloor [mbsf]), in the West Alboran Basin, lies on top sediments recovered at Holes 976B and 977A to identify source rocks of a basement horst 60 km off the southern Spanish coast and 8 km and provenance of sediments, mineral origin and trends, and the in- northeast of Deep Sea Drilling Project Site 121. Site 977 (1984 mbsf) fluence of climatic and/or tectonic factors during sedimentary pro- is located in the East Alboran Basin, south of the Al-Mansour Sea- cesses in the Alboran basin since the Miocene. mount (Fig 1). These two sites provided information on the nature and ages of sediments located in the westernmost and easternmost re- MATERIALS AND METHODS gions of the Alboran Sea basin. Furthermore, drilling results shed light on paleoenvironmental behavior and the main events in sedi- mentary basin evolution from the Miocene to the present. Bulk and clay mineral data and bulk trace-element compositions Hole 976B in the West Alboran Basin cored a 670-m-thick, mid- were obtained from 400 samples from Holes 976B and 50 samples dle Miocene (Serravallian) to Pleistocene/Holocene sedimentary se- from Hole 977A. From Hole 976B, we analyzed samples from litho- − quence lying directly upon the metamorphic basement. Sediments stratigraphic Unit I (0 362.10 mbsf), consisting of nannofossil-rich − consist of nannofossil clay, nannofossil silty clay, sand, silt, calcare- clay, nannofossil clay, and nannofossil silty clay; Unit II (362.10 ous silty clay, and claystone. The sedimentary sequences at Site 976 518.30 mbsf), consisting of sand, silt, calcareous silty clay, and nan- − were divided into four lithostratigraphic units (Units I–IV) primarily nofossil clay; and Unit III (518.30 660.20 mbsf), comprising nanno- on the basis of downhole grain-size variations (Shipboard Scientific fossil-rich clay and claystone (Fig. 2). We also present data from − Party, 1996a). Hole 977A sampled 598.5 m of uppermost Miocene– lithostratigraphic Unit I from Hole 977A, from Subunits IA (0.0 − − Pleistocene/Holocene sediments consisting of nannofossil clay, and 417.4 mbsf), IB (417.4 490.6 mbsf), and IC (490.6 532.9 mbsf), calcareous and nannofossil silty clay to clay. Sediments recovered at made up of nannofossil clay and calcareous and nannofossil silty clay Site 977 were divided in two lithostratigraphic units (Units I and II) to clay (Fig. 3). on the basis of downhole changes in sedimentary structures and sed- iment grain size. Unit I was subdivided into three subunits (IA–IC; X-ray Diffraction Shipboard Scientific Party, 1996b). The discovery of organic-rich layers (ORLs) in the Alboran Basin was one of the major findings of A representative and homogeneous part of each sample was used Leg 161. At Site 976, ORLs were identified in the Pliocene deposits, for bulk mineralogy and clay mineral studies. Samples were homog- with total organic carbon (TOC) ranging from 0.95% to 1.3%. At Site enized by grinding and then splitting the powder. For bulk mineralo- 977, ORLs were identified in the upper Pliocene–Pleistocene se- gy, samples were air dried, ground in an agate mortar to <0.0053 µm, quence, with an average TOC of ~0.90% (Comas, Zahn, Klaus, et al., and packed in Al sample holders for X-ray diffraction (XRD). For clay mineral analyses, the carbonate fraction was removed using ace- tic acid. The reaction was started at a very low acid concentration (0.1 1Zahn, R., Comas, M.C., and Klaus, A. (Eds.), 1999. Proc. ODP, Sci. Results, 161: N), and the concentration was increased to 1 N, depending on the car- College Station, TX (Ocean Drilling Program). bonate content of each sample. Clay was deflocculated by successive 2Instituto Andaluz de Ciencias de la Tierra (CSIC-University of Granada), Campus washing with demineralized water after carbonate removal. The <2- Fuentenueva, 18002 Granada, Spain. [email protected] 3Instituto de Ciencias del Mar (CSIC), Paseo Joan de Borbo s/n 08039 Barcelona, µm fraction was separated by centrifugation at 9000 rpm for 1.3 min. Spain. The clay fraction was smeared onto glass slides for XRD. Separation 21 F. MARTÍNEZ-RUÍZ, M. COMAS, B. ALONSO 38°N IBERIAN FORELAND South Balearic Cartagena Betic Cordillera Sea Atlantic Alboran Sea Tell Ocean Rif SPAIN AFRICAN FORELAND 400 km External Zones Alboran Domain 37° Almería Málaga SBB 200 Site 976 Gibraltar DB Site 978 1000 ACH 2000 DSDP 121 MS Site 977 ° AI EAB 36 Ceuta SAB WAB AR Tetouan Site 979 Orán 1000 XB MOROCCO 200 ALGERIA Melilla 35° 6°W 5° 4° 3° 2° 1° 0 Figure 1. Bathymetric map of the Alboran Sea showing the location of Leg 161 sites. The inset map shows the location of the Alboran Sea between the Betic and Rif Cordilleras and the general tectonic subdivisions. Contour lines are in meters. EAB = East Alboran Basin, WAB = West Alboran Basin, SAB = South Alboran Basin, AR = Alboran Ridge, AI = Alboran Island, ACH = Alboran Channel, MS = Al-Mansour Seamount, XB = Xauen Bank, DB = Djibouti Bank. Clay DEPTH LITHO. Quartz Calcite Dolomite (mbsf) UNITS minerals SERIES 100 CORE STAGE 0 50 100 0 50 100 0 50 100 0 50 2H @@@@PPPPÀÀÀÀ 3H @PÀ@@PPÀÀ@PÀ 4H 5H @PÀ@@PPÀÀ@PÀ 40 6H @PÀ@@PPÀÀ@PÀ 7H 8H @PÀ@@PPÀÀ@PÀ 9H 80 10H @PÀ@@PPÀÀ@PÀ 11H 12H @PÀ@@PPÀÀ@PÀ 13H 120 14H @PÀ@@PPÀÀ@PÀ 15X @PÀ@@PPÀÀ@PÀ 16X 17X @PÀ@@PPÀÀ@PÀ 160 18X 19X @PÀUNIT@@PPÀÀ @PÀI 20X @PÀ@@PPÀÀ@PÀ 21X 200 22X @PÀ@@PPÀÀ@PÀ 23X 24X @PÀ@@PPÀÀ@PÀ 25X Pleistocene 240 26X @PÀ@@PPÀÀ@PÀ 27X @PÀ@@PPÀÀ@PÀ 28X @PÀ@@PPÀÀ@PÀ 29X 30X 280 31X @PÀ@@PPÀÀ@PÀ 32X @PÀ@@PPÀÀ@PÀ 33X 34X @PÀ@@PPÀÀ@PÀ 320 35X 36X @PÀ@@PPÀÀ@PÀ 37X @PÀ@@PPÀÀ@PÀ 38X 360 39X @@@@PPPPÀÀÀÀ 40X 41X @PÀ@@PPÀÀ@PÀ 42X 400 43X @PÀ@@PPÀÀ@PÀ 44X 45X @PÀ@@PPÀÀ@PÀ 46X @PÀ@@PPÀÀ@PÀ 440 47X UNIT II 48X @PÀ@@PPÀÀ@PÀ 49X 50X @PÀ@@PPÀÀ@PÀ Piacenzian 51X 480 @PÀ@@PPÀÀ@PÀ 52X upper Pliocene 53X @PÀ@@PPÀÀ@PÀ 54X @@@@PPPPÀÀÀÀQQQQ¢¢¢¢@@@@PPPPÀÀÀÀ 55X 520 56X 57X@@@@PPPPÀÀÀÀQQQQ¢¢¢¢@PÀ@@PPÀÀ@PÀ 58X @PÀ@@PPÀÀ@PÀ 59X 560 60X @PÀ@@PPÀÀ@PÀ Zanclean 61X lower Pliocene 62X@@@@PPPPÀÀÀÀQQQQ¢¢¢¢@PÀ@@PPÀÀ@PÀ 63X Mss UNIT III 64X @PÀ@@PPÀÀ@PÀ 600 65X 66X 67X @PÀ@@PPÀÀ@PÀ upper Miocene 69X@PÀQ¢@@@PPPÀÀÀQQQ¢¢¢@PÀ@@PPÀÀ@PÀ 640 70X Tortonian @PÀ@@PPÀÀ@PÀ @@PPÀÀQQ¢¢ Hiatus @@@@PPPPÀÀÀÀ @@PPÀÀQQ¢¢ Figure 2. Bulk mineralogy, Hole 976B. 22 MINERAL ASSOCIATIONS AND GEOCHEMICAL INDICATORS DEPTH LITHO. Clay Quartz Calcite Dolomite (mbsf) UNITS minerals 0 50 100 0 50 100 SERIES 0 50 100 CORE 0 50 100 1H 2H @@@PPPÀÀÀ 3H 4H @PÀ@PÀ@PÀ 5H @PÀ@PÀ@PÀ 40 6H 7H @PÀ@PÀ@PÀ 8H @PÀ@PÀ@PÀ 9H 10H 80 @PÀ@PÀ@PÀ 11H 12H @PÀ@PÀ@PÀ 13H @PÀ@PÀ@PÀ 14H 120 15H @PÀ@PÀ@PÀ 16H 17H @PÀ@PÀ@PÀ 18X @PÀ@PÀ@PÀ 160 19X Pleistocene 20X @PÀ@PÀ@PÀ 21X @PÀ@PÀ@PÀ 22X Subunit 23X @PÀ@PÀ@PÀ 200 IA 24X 25X @PÀ@PÀ@PÀ 26X @PÀ@PÀ@PÀ 240 27X 28X @PÀ@PÀ@PÀ 29X 30X @PÀ@PÀ@PÀ 31X 280 @PÀ@PÀ@PÀ 32X 33X @PÀ@PÀ@PÀ 34X @PÀ@PÀ@PÀ 320 35X 36X @PÀ@PÀ@PÀ 37X @PÀ@PÀ@PÀ 38X 39X 360 @PÀ@PÀ@PÀ 40X 41X @PÀ@PÀ@PÀ 42X 43X @PÀ@PÀ@PÀ 400 44X @PÀ@PÀ@PÀ 45X upper Pliocene 46X @PÀ@PÀ@PÀ 47X @PÀSubunit@PÀ@PÀ 440 48X IB 49X @PÀ@PÀ@PÀ 50X 51X @PÀ@PÀ@PÀ 52X @PÀ@PÀ@PÀ 480 53X @@PPÀÀQQ¢¢ 54X @PÀSubunit@PÀ@PÀ 55X IC @PÀ@PÀ@PÀ 500 56X lower Pliocene Hiatus @@@PPPÀÀÀ @@PPÀÀQQ¢¢ Figure 3.
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