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Tectonic movements frequently expose marine organic-rich sediments on the continents for scientific study. These sediments may contain a wealth of clues to the paleoenvironments and paleoecology that led to the deposition and preservation of material that may prove favorable to hydrocarbon generation. An increasingly sophisticated tool-kit based on biomarker analysis and stable isotope determinations of individual organic compounds has been developed that now permits us to determine such important factors as the paleotemperatures and dominant phytoplankton production groups at the time these sediments formed. However, it is not clear how much alteration during uplift and exposure may affect these organic geochemical proxies, and hence, the reliability of paleoenvironmental reconstructions.

Our project focuses on obtaining long biomarker records from young (1.5-10 Ma) hemipelagic sediments exposed onland in central and southern Italy, and comparing results of specific biomarker analyses to those obtained from unaltered sediments of the same age recovered by ocean drilling in the Eastern Mediterranean. The juxtaposition of material of the same age, with very different burial and diagenetic histories, separated by distances of only few tens to hundred of kilometers, provides an unusual opportunity to ascertain how faithfully outcropping sequences preserve primary organic geochemical proxy information. In addition, the story of Mediterranean paleoenvironments has significance in its own right. Black, organic rich sapropels punctuate sedimentation in the basin (in particular, in the Eastern Mediterranean). The patterns of sapropel deposition, with their rhythmic alternations in response to orbitally-driven variations in climate, seem very similar to the much larger scale Òblack shaleÓ deposits of mid-Cretaceous age. The late Miocene-Pleistocene evolution of the Mediterranean also may shed light on one of the fundamental climate changes of the Cenozoic: the cooling of the northern hemisphere high latitudes and the concomitant drying of southern Europe and northern Africa toward the present.

We have conducted two seasons of field work, combined with laboratory analyses, that yielded important answers to some of the questions that prompted our study. We collected outcrop samples from 3 sections of early Pleistocene through mid-Pliocene (~1.5-3.5 Ma) at a temporal resolution of ~3 kyr. This sampling allowed us to reconstruct paleotemperatures time series that place sapropel deposition within a climatic context. Our reconstructions rely on the alkenone UkÕ37 organic proxy, which has been extensively validated in modern marine sediments. Having 3 sections that partially overlap also allowed us to assess how different burial and diagenetic histories affect the proxy. We also obtained samples covering the time interval ~1.5-2.1 Ma from Integrated Ocean Drilling Program Site 964, which allowed us to compare the alkenone-based results from the land sections to pristine material that has never been deeply buried and/or uplifted.

We published initial results from the first season of field work this year (Cleaveland and Herbert, 2009). This paper focuses on the comparison of outcrop results to the IODP section. We find that the patterns of temperature and sapropel deposition are extremely similar between the sediments exposed on land and cored below the sea. Sapropels are associated with warm intervals of climate, in agreements with models on the climatic control of sapropel deposition developed for the late Pleistocene. Our data suggest the possibility of a modest (order of 1oC) offset in the alkenone ÒpaleothermometerÓ to warmer temperatures in the land sections that could be the result of diagenesis and weathering. Further work will be needed to confirm that this is a systematic effect. We are now working on the climatic implications of a the entire 1.5-3.5 Ma time series that we have developed through laboratory work. Our major finding is that the amplitude of cyclic sea surface temperature changes increased very significantly at the Plio-Pleistocene boundary. This represents a new finding, and may imply that the region underwent a major step in climate at this time (our preliminary interpretation is that the size of the Fennoscandian ice sheets may have increased significantly during the early Pleistocene ice ages, leading to large regional coolings during ice ages). This material was developed by Brown undergraduate Gideon Ng in a senior Honors Thesis.

Our successful second field season will allow us to address new questions. We collected material from a core collected on land of the same age as our outcrop samples. This will allow us to investigate the diagenetic changes of biomarkers due to exposure in outcrop. We also extended our sampling into the Miocene, so that we can continue to investigate the relation of climatic change to organic-rich deposition under the altered climatic boundary conditions (no northern hemisphere glaciation, warmer climates) of the late Miocene. Approximately 500 samples of mid-Pliocene and late Miocene were obtained from rhythmically alternating strata outcropping near the central Italian port city of Ancona, and now await laboratory analysis.

Funding from the ACS has already contributed significantly to the professional development of the P.I., his graduate students, and an undergraduate. P.I. Herbert has led the application of the alkenone paleotemperature proxy in marine sediments, but the questions of biomarker preservation and interpretation in potentially altered sediments represents a new avenue of study for him. Ph.D. student Laura Cleaveland (now Assistant Professor at Luther College) included results from this project in her dissertation, and continues to work on the project in her current position. Brown graduate student Emily Pohlman and undergraduate Gideon Ng obtained valuable experience in the first field season; Ng produced marvelous results from his Honors Thesis that will make him a co-author on a manuscript in preparation.

At this point, we have concrete results to substantiate the most important hypotheses outline in our proposal to the PRF, and we anticipate addressing a number of important additional questions in the near future.