1 3 Facies (2017) 63:14 DOI 10.1007/s10347-017-0495-y ORIGINAL PAPER Growth of the Ballena fan delta on the Gulf of California (Mexico) at the close of the Pliocene Warm Period Markes E. Johnson 1 · David H. Backus 2 · Jorge Ledesma-Vázquez 3 Received: 28 November 2016 / Accepted: 1 April 2017 © Springer-Verlag Berlin Heidelberg 2017 the close of the Pliocene Warm Period, during which a per- sistent El Niño climate brought tropical storms and exces- sive rainfall to the upper Gulf of California. Comparisons with other Pliocene deltas throughout the Gulf of Califor- nia underscore the unique status of the complex named the Ballena fan delta. Keywords Basin outwash · Coastal processes · Fan delta · El Niño climate · Pliocene Warm Period · Sand dollars (Echinodermata) · Surface weathering Introduction Surges in hurricane activity and the exposure of coastal zones to intense rainfall where storms make landfall are associated with patterns in El Niño Southern Oscillation (ENSO). After landfall, storms remain destructive due to flood erosion, especially where vegetation is sparse in places such as Mexico’s Baja California on the Pacific Ocean. Research on global warming suggests that the rate of hurricane incidence and level of severity across the Pacific Basin has increased during the last six decades over which reliable data are available (Mei et al. 2015). Inter- est in the topic also promotes research in paleoclimatol- ogy with the expectation that windows on the past help to better appraise future climate change. Global modeling by Brierley et al. (2009) on Pliocene climate between 5 and 3 Ma provides a strong analog to conditions under which contemporary global warming occurs. In theory, warmer water over larger equatorial areas across both the Pacific and Atlantic oceans during the Pliocene Warm Period weakened day-to-day patterns of atmospheric circulation regulated by Hadley cells while also boosting storm activ- ity. Historically, the run up toward elevated global average Abstract Tectonic uplift on the shores of Bahía San Rafael in Mexico’s upper Gulf of California exposed a Pliocene delta system that covers a map area of 4 km 2 . Subaerial dissection by arroyos entrenched during Pleistocene and post-Pleistocene time carved cross-sectional slices through the delta, showing its dominant construction resulting from massive transfers of siliciclastic sand derived from the breakdown of igneous rocks (tonolite) in a well-defined ter- restrial basin. Restoration of the sedimentary structure by elimination of Pleistocene arroyos and linkage of former topographic lines reveals a triangular shape recognizable as a classic fan delta. The complex includes an alluvial fan that emerges from a small opening in the landscape con- nected to a semi-circular, high-walled basin with a map area of 2.6 km 2 . Through a strictly longitudinal sequence, estimates of the excavated basin’s volume and the delta’s sedimentary volume were conducted as a mass-balance exercise that yielded a strong match. The lower central part of the delta features dense concentrations of sand dollars (Dendraster granti) that form a distinct limestone coquina not previously recognized elsewhere in Baja California. Through the regional biostratigraphy of concurrent range zones supplemented by absolute age dates from inter-bed- ded volcanics in other places, a later Pliocene age around 3–2 Ma is suggested for the sand dollars and the delta com- plex in which they are buried. Such timing corresponds to * Markes E. Johnson mjohnson@williams.edu 1 Department of Geosciences, Williams College, Williamstown, MA 01267, USA 2 Environmental Studies Department, Davidson College, Davidson, NC 28035, USA 3 Facultad de Ciencias Marinas, 22800 Ensenada, BC, Mexico